21September2020

Nano-Micro Letters

A Review on Nano-/Microstructured Materials Constructed by Electrochemical Technologies for Supercapacitors

View ResearcherID and ORCID

Huizhen Lv1, a, Qing Pan1, a, Yu Song1, *, Xiao-Xia Liu1, Tianyu Liu2, *

Abstract
icon-htmlFull Text Html
icon-pdf-smPDF w/ Links
icon-citExport Citation
Figures
+Show more

Nano-Micro Lett. (2020) 12: 118

First Online: 30 May 2020 (Review)

DOI:10.1007/s40820-020-00451-z

*Corresponding author. E-mail: songyu@mail.neu.edu.cn (Yu Song); tliu23@vt.edu (Tianyu Liu)

 

Abstract

 


Toc

The article reviews the recent progress of electrochemical techniques on synthesizing nano/microstructures as supercapacitor electrodes. With a history of more than a century, electrochemical techniques have evolved from metal plating since their inception to versatile synthesis tools for electrochemically active materials of diverse morphologies, compositions, and functions. The review begins with tutorials on the operating mechanisms of five commonly used electrochemical techniques, including cyclic voltammetry, potentiostatic deposition, galvanostatic deposition, pulse deposition, and electrophoretic deposition, followed by thorough surveys of the nano/microstructured materials synthesized electrochemically. Specifically, representative synthesis mechanisms and the state-of-the-art electrochemical performances of exfoliated graphene, conducting polymers, metal oxides, metal sulfides, and their composites are surveyed. The article concludes with summaries of the unique merits, potential challenges, and associated opportunities of electrochemical synthesis techniques for electrode materials in supercapacitors.


 

Keywords

Nanostructure, Microstructure, Electrochemical, Synthesis, Supercapacitor

 

Full Text Html

1 Introduction

    The rapidly expanding markets of mobile electronics, electrified transportation, wireless networks (e.g., the Internet of Things), and sustainable energy utilization have substantially fueled the development of electrochemical energy storage systems [1-4]. Supercapacitors, including electrochemical capacitors and pseudocapacitors, stand out among diverse arrays of energy storage devices due to their ultrahigh power density and ultralong lifespans [5-9]. Since the first introduction in 1957 by Howard Becker of American General Electric [10], supercapacitors have pervaded in applications demanding energy input and output with high power, e.g., the power source to the emergency doors of Airbus A380 aircraft [11, 12]. Therefore, elevating the capacitance and energy density of supercapacitors at ultrafast charging rates has remained a central topic [13-16]. Extensive research efforts have been devoted to developing high-performance electrode materials [13, 15-17], since electrodes primarily determine the capacitance, energy density, and power density of supercapacitors.
    Supercapacitors are classified into two categories: electric double-layer capacitors (EDLCs) and pseudocapacitors. EDLCs store charges through adsorption and desorption of ions in electrolytes at the electrolyte/electrode interfaces. Carbon materials are conventional electrode materials in EDLCs. Pseudocapacitors store charges through kinetically fast faradaic reactions. Surface redox pseudocapacitance, intercalation pseudocapacitance, and underpotential deposition are examples of pseudocapacitance [13]. Redox pseudocapacitance occurs when electrolyte ions adsorbed on or near the electrode surfaces and involves interfacial charge transfer. Intercalation pseudocapacitance comes from reversible insertion and desertion of electrolyte ions in layered or tunneled electrode materials without phase transitions. Underpotential deposition will be elaborated in Section 2.2, but it is not used for charge storage due to its limited capacity. Pseudocapacitance has its electrochemical features, such as quasi-rectangular cyclic voltammetry curves, linear galvanostatic charge/discharge profiles, as well as a near-linear response between current and scan rate in cyclic voltammograms. These characteristics must be clearly distinguished from battery-type behaviors (Section 5.6).
    Electrochemical techniques are a group of synthesis methods of versatile active materials in supercapacitors. These methods have a history of more than 150 years [18], and their first application is to plate metals for jewelry decoration, surface protection, and electronic-circuit manufacturing [19]. Along with the boom of electrochemical energy storage, the role of electrochemical techniques has been enriched by synthesizing nano/microstructured materials for electrochemical energy storage [2, 20]. The syntheses involve electrochemical processes including reduction, oxidation, gas evolution, ion intercalation, and combinations of these methods thereof. Chemical reactions, such as the electrolysis of electrolytes (e.g., H2 and O2 evolution in aqueous electrolytes), redox reactions of electrolyte ions, as well as modifications of the structures and compositions of electrode materials, are typically accompanying phenomena.
   Compared to other synthesis strategies, electrochemical techniques have their unique advantages. First, they are facile and mild. Room temperature, ambient pressure, and aqueous solutions are sufficient for performing electrochemical techniques. Second, the experimental setups, such as electrolytic cells and electrochemical workstations, are often readily available in electrochemistry laboratories. This availability allows electrochemists to prepare active materials without delicate instruments and sophisticated protocols. Perhaps the most striking feature of electrochemical techniques is their high tunability towards the structure, composition, property, and morphology of products [2, 20]. Magnitudes of applied current or voltage, types and concentrations of salts in electrolytes, reaction durations, solution temperatures, as well as substrate morphologies are all tunable parameters that result in versatile materials. Benefited from these merits, electrochemical techniques have been extensively studied and rapidly developed in the past decades. The materials that have been prepared electrochemically include exfoliated graphene [21], metal oxides [22-24], conducting polymers [25, 26], and their composites [27-29].
    This review article presents a thorough survey of electrochemically synthesized nano/microstructured materials for supercapacitors. It starts with introduction of the operating mechanisms, characteristics of input and output signals, strengths, and weaknesses of cyclic voltammetry, potentiostatic (constant voltage) and galvanostatic (constant current) depositions, pulse electrodeposition, and electrophoretic deposition. Afterward, the article reviews the recent progress of the active materials synthesized by electrochemical techniques. This part is segmented based on the compositions of materials, including carbon-based materials, metal oxides, conducting polymers, composites, and other materials. Each subsection starts with typical synthesis mechanisms and is exemplified with one or more representative examples in the literature. At last, the article comments on the merits, challenges, and opportunities of electrochemical technologies in terms of synthesizing nano/microstructured materials for electrochemical energy storage.

2 Fundamentals of Electrochemical Synthesis Techniques

    Cyclic voltammetry, galvanostatic deposition, potentiostatic deposition, pulse deposition, and electrophoretic deposition constitute the most widely and extensively investigated and practiced electrochemical synthesis techniques for nano/microstructured materials as supercapacitor electrodes. These processes are typically carried out in electrolytic cells powered by electrochemical workstations. Based on the number of electrodes involved, the set-up for electrochemical synthesis is categorized into two types: two-electrode (Fig. 1a) and three-electrode (Fig. 1b) configurations [30]. The two-electrode configuration contains a positive electrode and a negative electrode that are both immersed in electrolytes. An electrochemical workstation or power source provides voltage across the two electrodes. Therefore, the measured voltage in this scenario is the overall cell voltage. The three-electrode system comprises a working electrode (WE), a counter electrode (CE), and a reference electrode (RE). Ideally, current flows only between WE and CE, and the voltage of WE is referenced to that of RE. Saturated calomel electrode (SCE), Ag/AgCl, and Hg/HgO electrodes with their nearly constant half-reaction potentials are common REs. REs are placed in vicinity to WEs to minimize iR drop and voltage fluctuation due to electrolyte resistance [31]. The measured voltage in three-electrode configurations is the real-time potential of WEs.

Fig. 1 Schemes illustrating the experimental setups of a two-electrode and b three-electrode electrolytic cells for electrochemical syntheses

Fig. 1 Schemes illustrating the experimental setups of a two-electrode and b three-electrode electrolytic cells for electrochemical syntheses

2.1 Cyclic Voltammetry (CV)
   Besides a conventional electrochemical technique for probing electrochemically redox activities [32], CV serves as a synthetic tool. It linearly scans potential within a range, termed potential window, and simultaneously records current as a response [33]. Increasing the applied potential, the forward scan oxidizes species in electrolytes or on electrodes and produces anodic current. Conversely, the backward scan decreases the applied potential, reduces active components, and generates a cathodic current.
   CV has three main advantages as a synthetic approach. First, it allows for determining the onset potential of an electrodeposition reaction. Oxidation or reduction reactions involving charge transfer across the electrolyte-electrode interfaces will display sharp increases or well-defined peaks in the current. Since the onset potential is the minimum voltage needed to initiate electrodeposition reactions, CV is useful for developing experimental protocols. Second, the potential linear scan of CV is beneficial for growing uniform and conformal films. This characteristic provides a gradient driving force for deposition: Deposition will only begin until the potential is scanned above the onset potential, and the driving force of deposition scales linearly with the potential gradually elevated away from the onset. This gradient driving force of CV adjusts the deposition rate and avoids consistently high deposition voltages that can lead to overgrowth of materials, rapid clogging of pores, and/or uneven deposition of films. Third, CV is suitable for synthesizing materials with multiple valence states, e.g., transition metal oxides. For example, deposited by CV within a potential range between -1.5 and 1.5 V vs. SCE in a 0.1 M VOSO4 aqueous electrolyte, vanadium oxide nanorods contained ~50% V5O12 (a mixture of V5+ and V4+) and ~50% VO2 [34]. The high valence state, V5+, formed during the anodic or forward scan, while the as-deposited V5O12 was partially reduced to VO2 in the subsequent cathodic or backward scan. These redox processes were documented by the broad peaks in the corresponding CV curve (Fig. 2). Compounds with multi-valent species reportedly possess augmented capacitance [35], improved rate capability [34, 36], as well as enhanced cycling stability [37, 38] compared to their monovalent counterparts.

Fig. 2 CV curves of the deposition of mixed-valence vanadium oxide nanorods

Fig. 2 CV curves of the deposition of mixed-valence vanadium oxide nanorods

2.2 Potentiostatic (Constant-Voltage) Deposition
    Potentiostatic deposition synthesizes materials by applying a constant potential across the positive and negative electrodes (two-electrode system) or between the working and counter electrodes (three-electrode system). The deposition potential is maintained constant by an electrochemical workstation (Fig. 3a), and the current is recorded as a function of time (Fig. 3b) [39]. Based on the difference between applied and thermodynamic equilibrium potentials, potentiostatic deposition is categorized into underpotential deposition (UPD) and overpotential deposition (POD) [40, 41].

Fig. 3 a Constant potential applied in potentiostatic deposition; E0 and E are the open circuit potential and the applied potential; t0 marks the starting time of deposition. b Corresponding current as a function of time

Fig. 3 a Constant potential applied in potentiostatic deposition; E0 and E are the open circuit potential and the applied potential; t0 marks the starting time of deposition. b Corresponding current as a function of time

    UPD happens at potentials below thermodynamic equilibrium potentials. For example, metal deposition can initiate at potentials smaller than the corresponding equilibrium reduction potentials, due to the lower work function of the deposited metal than that of the substrate metal, as described by the Kolb-Gerischer equation [42]:

12 118 gs1

where  is the downshift of deposition potential (in V) and  is the difference in the work functions between the deposited and substrate metals (in eV). The coefficient 0.5 (in V eV-1) comes from a linear fitting involving 21 metal-metal couples [42]. UPD involves adsorption, nucleation, and growth processes determined by surface characteristics of substrates (e.g., chemical composition, crystal structure, morphology, and electrolyte wettability) and ion-substrate interactions. Besides, the types of cations in electrolytes and anions strongly influence the structure and properties of the deposited materials, as well as deposition kinetics [43-45]. One example is the UPD of Cu on Au (111) facets in aqueous sulfuric acid solutions [46]. The deposition was much slower under pH = 2 than pH = 4. This discrepancy in the deposition rate was correlated to the different anions under different pH values. Increasing the solution acidity converted bisulfate ions to sulfate ions. The latter adsorbed much more strongly than the former on the gold substrate, which blocked some active sites for deposition and hence, decelerated the UPD.
    OPD occurs in potentials above thermodynamic equilibrium potentials [39, 47]. The structure and properties of the OPD deposits highly depend on various factors, including overpotential (the difference between applied and equilibrium potentials), electrolyte concentration, growth mechanism, deposit-substrate interactions [41]. Notably, diffusion-controlled nucleation is often the rate-determining step of OPD, while that of UPD is the deposit lattice incorporation into substrate [46].
2.3 Galvanostatic (Constant-Current) Deposition
    Galvanostatic deposition refers to electrodeposition with constant currents between the positive and negative electrodes in a two-electrode system, or between the working electrode and counter electrode in a three-electrode set-up (Fig. 4a) [39]. The recorded response is the time-dependent potential of the cell (two-electrode) or the working electrode (three-electrode). The V-t curves (Fig. 4b) sometimes are called polarization curves. Unlike potentiostatic deposition that can start the moment when potentials are applied, galvanostatic deposition needs a short period to start [48, 49]. It is because that some applied current needs first to charge electrical double layers (EDLs). After potential reaches certain thresholds (usually equilibrium potentials plus overpotentials), electrochemical reactions occur. Therefore, the applied constant current (I) is contributed from two components:

12 118 gs2

where IDL is capacitive current for charging EDLs, and Ict is charge transfer current for electrodeposition. IDL rapidly approaches zero when electrodeposition starts.

Fig. 4 a Constant current applied during a galvanostatic deposition; t0 represents the moment when current is applied. b Potential response as a function of time in a galvanostatic deposition; E0 and Ei are the equilibrium potential and maximal potential of a working electrode during galvanostatic deposition, respectively; c Double-layer charging current (IDL) decays exponentially with time. d Time evolutions of the potential during galvanostatic depositions of MnO2 at temperatures of 25 °C (orange) and 60 °C (red)

Fig. 4 a Constant current applied during a galvanostatic deposition; t0 represents the moment when current is applied. b Potential response as a function of time in a galvanostatic deposition; E0 and Ei are the equilibrium potential and maximal potential of a working electrode during galvanostatic deposition, respectively; c Double-layer charging current (IDL) decays exponentially with time. d Time evolutions of the potential during galvanostatic depositions of MnO2 at temperatures of 25 °C (orange) and 60 °C (red)

    V-t curves of galvanostatic deposition contain essential information on electrodeposition chemistries. Since EDL charging time is on the order of milliseconds, V-t curves collected on the time scale of minutes or hours are almost contributed from electrodeposition. For example, the V-t curves of manganese dioxide (MnO2) deposition processes at different temperatures qualitatively elucidate the nucleation kinetics (Fig. 4d) [50]. The increased potentials at the beginning of the electrodeposition corresponded to the nucleation of MnO2 as nucleation demanded more energy than its growth to surmount the activation energy barrier. Increasing temperature from 25 to 60 °C offered the additional electrodeposition energy to enable the MnO2 deposition at the reduced deposition potentials. The prolonged nucleation process at 25 °C results in dense manganese oxide nanosheets.
2.4 Pulse Electrodeposition
    Pulse electrodeposition technique deposits materials by applying pulses of potential or current, i.e., a series of pulses with equal polarization, amplitude, and duration, separated by periodic zero current or open circuit potentials (Fig. 5) [39, 51]. Each pulse has "on" periods when the current or potential is applied, and "off" periods with no current or potential (Fig. 5) [52-54]. During the "off" periods, ions in electrolytes diffuse into electric double layers along the surfaces of the deposition substrates, which is beneficial to obtain the uniform deposition of fine-grained deposits during “on” periods [55-57].

Fig. 5 Current or potential signals applied in pulse electrodeposition

Fig. 5 Current or potential signals applied in pulse electrodeposition

    Using pulsed electrodeposition, Yu et al. synthesized flexible graphene/polypyrrole composite films as pseudocapacitor electrodes [57]. The "off" period allowed pyrrole monomers to diffuse into the inter-sheet spaces of graphene, and then electropolymerized into uniform polypyrrole coatings over the "on" periods. By contrast, the continuous, un-pulsed electrodeposition triggered the fast polymerization of pyrrole near the graphene sheets. Since there are no "off" periods to replenish pyrrole monomers near graphene surfaces, the lowered reactant concentration led to scattered polypyrrole particles on the graphene surface. This work highlights the suitability of pulse electrodeposition in coating uniform films onto irregularly shaped substrates. 
2.5 Electrophoretic Deposition
    Electrophoretic deposition (EPD) differs from all the above-discussed techniques. First, the charge carriers in EPD are suspending, charged colloidal particles, not ions. Second, EPD involves electrostatic attractions between the particles and substrates but no charge transfer. Third, unlike electrodeposition that demands electrolytes to conduct ions, EPD can perform in poorly conductive media, e.g., water [58, 59].
    Depending on charges carried by the colloidal particles, EPD is classified into cathodic and anodic EPD. The cathodic EPD refers to the deposition of positively charged particles onto negatively charged substrates (Fig. 6a), whereas anodic EPD proceeds in a reverse manner (Fig. 6b) [58]. The structures of the deposits are tailorable by varying parameters of applied potential, particle concentration, and deposition duration [60-65]. Notably, the stoichiometry of the electrosorbed particles directly determines the stoichiometry of the deposit [59].

Fig. 6 Schematic illustrations of a cathodic and b anodic electrophoretic deposition. Only ions of interest are shown for brevity

Fig. 6 Schematic illustrations of a cathodic and b anodic electrophoretic deposition. Only ions of interest are shown for brevity

3 Electrochemically Synthesized Carbon Materials

    Carbon materials, including activated carbon, carbon fibers, carbon aerogels, carbon nanotubes, and graphene, are conventional materials in electrical double-layer capacitors [17]. Their high electrical conductivity, large surface areas, cost-effectiveness, chemical inertness, and tailorable porous structures make them suitable electrode candidates [66, 67]. The two outstanding advantages of carbon electrodes are their exceptional rate capability and ultralong lifetimes. Electrochemical approaches have been widely used to produce carbon materials [68-70]. The following sections first present the recent progress in syntheses of graphene (Section 3.1) and 3D carbons (Section 3.2), the two carbon materials that have been prepared by electrochemical technologies. Their applications in supercapacitors are highlighted separately in Section 3.3.
3.1 Graphene
   Electrochemical exfoliation is a facile method for synthesizing graphene. Compared with chemical exfoliation, electrochemical exfoliation avoids chemical treatments that can introduce unwanted species, simplifying product purification [66, 71]. Electrochemically exfoliated graphene often maintains more sp2-hybridized carbon networks than that made by chemical oxidation. Additionally, the graphene surface functionalization often accompanies with exfoliation [72, 73], and the heteroatom doping level is highly controllable. Another strength of electrochemical exfoliation is its high efficiency. It only needs minutes or hours, depending on applied potentials, electrolyte compositions, and graphite sources, to produce grams of graphene sheets in laboratories [74, 75].
    According to the potential polarity, electrochemical exfoliation is classified into (1) anodic exfoliations performed in aqueous electrolytes containing inorganic salts [76], mineral acids [77, 78], ionic liquids [79], or their mixtures [67, 80]; and (2) cathodic exfoliations in organic electrolytes having lithium or alkylammonium salts [21, 67, 81-83].
3.1.1 Anodic Exfoliation
    Anodic exfoliation separates graphite into graphene by anion intercalation [73, 76]. It is the most used electrochemical approach for graphene production due to its high exfoliation efficiency. With inorganic acids (e.g., H2SO4 [78, 84], HNO3 [85, 86], and H3PO4 [87]) or salts (e.g., KNO3 [88] and (NH4)2SO4 [89]] as supporting electrolytes, a high exfoliation potential (e.g., 3-10 V) can generate single-layer or multi-layer graphene sheets from graphite. For example, Parvez et al. exfoliated graphite foils in sulphuric acid aqueous solutions with concentrations of 0.1, 1, and 5 M [84]. The synthesis procedures involved multiple steps (Fig. 7a). First, a high potential of 10 V was applied across a graphite positive electrode and a Pt negative electrode (Fig. 7b), splitting water into hydroxyl (OH∙) and oxygen radicals (O∙). These radicals preferentially oxidized the boundaries and defects of graphite, opening its edges. Second, driven by the applied electrical field, sulfate ions (SO42-), together with water molecules, intercalated into graphite layers through the open edges and expanded graphite layers. Meanwhile, oxygen gas evolution in between graphite layers further torn apart graphite sheets and dispersed exfoliated graphene layers into electrolytes (Figs. 7c-e). Water in the electrolytes was critical for electrochemically exfoliation, as it both generated OH∙ and O∙ (the exfoliation initiators) and served as an intercalant. The exfoliation efficiency in the 0.1 M H2SO4 electrolyte reached the highest, since the 5 M H2SO4 electrolyte over-exfoliated graphite into graphitic particles while the 0.1 M H2SO4 electrolyte led to incomplete exfoliation due to insufficient sulfate ions. The obtained graphene sheets in 0.1 M H2SO4 had a high yield of >80%, less than three layers, a high C/O ration of 12.3, and good electrical conductivity (sheet resistance of ~4.8 ), all of which are comparable to those of high-quality graphene sheets synthesized by chemical vapor deposition.

Fig. 7 a Schemes of the microscopic processes of graphite exfoliation in H2SO4 aqueous electrolytes. Step 1: edge opening by water-borne radicals; Step 2: SO42- intercalation and exfoliation. b Experimental setup for the graphite exfoliation. c Photographs of the exfoliated electrodes before and after exfoliation. d Exfoliated graphene floating on an electrolyte. e Dispersed graphene sheets in dimethylformamide solution. Adapted from Ref. [84] with permission

Fig. 7 a Schemes of the microscopic processes of graphite exfoliation in H2SO4 aqueous electrolytes. Step 1: edge opening by water-borne radicals; Step 2: SO42- intercalation and exfoliation. b Experimental setup for the graphite exfoliation. c Photographs of the exfoliated electrodes before and after exfoliation. d Exfoliated graphene floating on an electrolyte. e Dispersed graphene sheets in dimethylformamide solution. 

    Changing the water content of non-aqueous electrolytes can yield graphene-based materials with different surface areas and morphologies. Specifically, Lu et al. found that the morphologies of the exfoliation products in 1-methyl-3-butylimidazolium tetrafluoroborate, an ionic liquid (IL), depended on the water to IL ratio [79]. Identical to electrochemical exfoliations in aqueous solutions, water in the IL produced OH∙ and O∙ to drive the exfoliation process, while subsequent intercalation of BF4- promoted complete exfoliation. Decreasing the water/IL ratio favored BF4- intercalation that significantly expanded graphite into graphene nanoribbons. Increasing the water/IL ratio increased the populations of OH∙ and O∙, which substantially oxidized and broke graphite into hydroxylated carbon particles. In this case, the oxygen-containing radicals acted as electrochemical “scissors” that cut the graphite plates into nanoribbons or nanoparticles.
    Graphite exfoliation in aqueous solutions often yields oxygenated graphene with reduced electrical conductivity, a property unfavorable for rapid charge storage [36, 80, 90-94]. To circumvent this shortcoming, a variety of additives, including reducing agents [95] and oxygen-radical scavengers [76], have been introduced into electrolytes to prevent over-oxidation of exfoliated graphene. For example, Yang et al. demonstrated that (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), ascorbic acid, and sodium borohydride could consume radicals. This characteristic kept oxygen content at low levels (3.8 atom% O of TEMPO-added exfoliated graphene vs. 11 atom% O of TEMPO-free exfoliated graphene) [95]. Besides, Ejigu et al. reported that transition metal ions (e.g., Co2+, Ni2+, Fe3+, Mn2+, Ru3+, Ir3+, and V3+) as electrolyte additives were conducive to acquiring high-quality graphene because they scavenged oxygen radicals [76]. Among all these ions, Co2+ was the most promising one because it converted to an oxygen evolution reaction catalyst. During anodic exfoliation, Co2+ was first oxidized to Co4+, an active species for oxygen evolution. The Co4+ adsorbed on graphite facilitated oxygen evolution from water, bypassing the formation of oxygen radicals that oxidized exfoliated graphene. The lowest oxygen content was 2.6%.
3.1.2 Cathodic Exfoliation
    Cathodic exfoliation, which produces graphene by applying negative biases to graphite, is a method free of oxidation concerns. Though this technique is not as developed as anodic exfoliation, it has successes in graphite exfoliation in organic-based electrolytes [21, 67, 81, 83] and molten salts [82]. For example, Wang et al. deployed a cathodic exfoliation method that acquired highly conductive, less than five layers of graphene nanosheets from graphite with yields of >70% [21]. At a high cathodic potential of -15±5 V, Li+-propylene carbonate (PC, a solvent) complexes intercalated into graphite and expanded graphite layers. Subsequently, the reduction of PC molecules liberated gas bubbles in between graphite layers, eventually exfoliating graphite into graphene sheets (Figs. 8a-c). Because the exfoliation involved no oxidation, the resultant graphene contained little defects, as evidenced by the small ID/IG ratio of 0.1 revealed by Raman spectroscopy (Fig. 8d).

Fig. 8 a Schematic illustration of cathodic exfoliation of graphite by intercalation of Li+ complexes. b, c SEM images of the cathodically exfoliated graphene plates. d Raman spectra of the cathodically exfoliated graphene with bilayers and trilayers, in comparison with that of pristine graphite

Fig. 8 a Schematic illustration of cathodic exfoliation of graphite by intercalation of Li+ complexes. b, c SEM images of the cathodically exfoliated graphene plates. d Raman spectra of the cathodically exfoliated graphene with bilayers and trilayers, in comparison with that of pristine graphite

    In addition to liquid electrolytes, quasi-solid molten salts were potent electrolytes for graphite exfoliation. For instance, Huang et al. successfully exfoliated graphite in molten LiOH with a high cathodic current of 15 A [82]. This process was based on intercalation, expansion, and micro-explosion. First, Li+ ions in the molten LiOH intercalated into graphite layers and widened the interlayer gap of graphite, forming graphite intercalation compound (LixCy). Afterward, the Li+-intercalated graphite was soaked in water. LixCy and metallic Li reacted violently with water (micro-explosion), creating hydrogen gas bubbles that further exfoliated graphite into graphene. The conversion efficiency was ~80%.
3.2 Three-Dimensional Carbons
    As supercapacitor electrodes, three-dimensional (3D) carbon materials have advantages over other conventional carbon powders (e.g., activated carbon) and graphene. First, their self-standing nature requires no binder blending for preparing electrodes, which eases fabrication and reduces the negative impact of the binders on electron transport. Second, their tailorable structures offer opportunities to achieve both high surface areas and hierarchical porous networks known to facilitate ion diffusion [4, 96-102].
    Electrochemical partial exfoliation of graphitic materials is the most common synthesis method of electrochemically synthesizing 3D carbon materials. As indicated by its name, electrochemical partial exfoliation only partially exfoliates graphitic precursors, e.g., carbon fibers [37, 85, 97, 99], graphene aerogels [99], and graphite foils [88, 103, 104], leading to graphene sheets anchored on the exposed surfaces. For example, Song et al. demonstrated a two-step electrochemical partial exfoliation method to prepare oxygen-functionalized, partially exfoliated graphite foils (Fig. 9a) [88]. The authors first scanned a piece of graphite foil (EG in Fig. 9b) in aqueous K2CO3 electrolytes by cyclic voltammetry. This step partially exfoliated the graphite layers on and near the outer surface of EG through vigorous gas evolution from water splitting (Fig. 9c). The secondary exfoliation process intercalated NO3- into EG through the open edges and defects formed during the first step, forming graphite intercalation compounds (C-NO3). These compounds, when placed in water, hydrolyzed and released oxygen gas. The gas evolution further exfoliated and oxygenated the top layers of EG (Fig. 9d). The introduced oxygen-functionalities rendered the foil super hydrophilicity as reflected from the zero contact angle (Fig. 9d inset). The potential applied in the second step controlled the degrees of the exfoliation and oxygenation. The functionalized, exfoliated EG possessed a 3D network consisting of oxygenated graphene sheets integrated onto graphite foil. The seamless integration between the top layer and the graphite bottom ensured fast electron conduction pathways. Besides improving electrolyte wettability, the oxygen moieties served as anchoring sites for depositing guest materials for polyaniline [27], polypyrrole [105], manganese oxides [86], vanadium oxides [37], iron oxides [35, 106], nickel-cobalt double hydroxides [106], and molybdenum-based materials [28].

Fig. 9 a Schemes of the two-step partial exfoliation of graphite foil. b-d SEM images and contact angles of b graphite foil, c graphite foil after primary exfoliation, and d graphite foil after secondary exfoliation. Insets: photographs of graphite foil at different treatment stages. e SEM image and EDS element mappings (C and O) of the cross-sections of exfoliated carbon cloth fibers. f XPS C 1s spectra of pristine carbon cloth (CC) and exfoliated carbon cloth (ECC). g CV curves of CC and ECC

Fig. 9 a Schemes of the two-step partial exfoliation of graphite foil. b-d SEM images and contact angles of b graphite foil, c graphite foil after primary exfoliation, and d graphite foil after secondary exfoliation. Insets: photographs of graphite foil at different treatment stages. e SEM image and EDS element mappings (C and O) of the cross-sections of exfoliated carbon cloth fibers. f XPS C 1s spectra of pristine carbon cloth (CC) and exfoliated carbon cloth (ECC). g CV curves of CC and ECC

    In addition to graphite, carbon fibers can also be partially electro-exfoliated. For example, Wang et al. synthesized electrochemically activated carbon fiber cloth electrodes by applying a voltage of 3 V in HNO3/H2SO4 mixed aqueous electrolytes [85]. The high voltage, together with the highly oxidative and corrosive acids, roughened the carbon fiber surfaces and introduced functionalities of C—OH, —C=O and —COOH. This activated carbon cloth electrode exhibited a high areal capacitance of 756 mF cm-2 at 6 mA cm-2. Song et al. demonstrated an acid-free method to exfoliate carbon fiber cloth partially [37]. First, NO3- anions intercalated into carbon fibers, exfoliating and oxidizing the outer surface (Fig. 9e). To recover the electrical conductivity of carbon fibers, the researchers immersed the oxidized carbon cloth in a 0.1% hydrazine hydrate aqueous solution to reduce the oxygen content. This reduction process removed most of the oxygen functionalities (Fig. 9f) and resulted in enhanced capacitive performance (Fig. 9g). The partially exfoliated carbon cloth electrode exhibited a high areal capacitance of ~500 mF cm-2 at 20 mA cm-2.
3.3 Application for Supercapacitors
    Owing to the enhanced surface areas and high electrical conductivity, electrochemically exfoliated graphene-based materials or activated carbon fibers have functioned either as electrode materials or current collectors in supercapacitors. Liu et al. fabricated an in-plane micro-supercapacitor through directly printing electrochemically exfoliated graphene on patterned microelectrodes. This micro-supercapacitor delivered an areal capacitance of 800 μF cm-2 at 1 mV s-1 [107]. Wu et al. used electrochemically exfoliated graphene to prepare graphene paper and 3D graphene foams as supercapacitor electrodes [75]. The specific capacitance of the 3D graphene electrode reached 113.2 F g-1 and 58.9 F g-1 at 0.5 A g-1 in 6 M KOH aqueous and 1 M triethylmethylammonium tetrafluoroborate acetonitrile (TEMABF4/AN), respectively.
    Besides reporting the outstanding electrochemical performance, some researchers devoted to revealing the interplays between exfoliation conditions and electrochemical properties. Ambrosi et al. compared the capacitive performances of electrochemically exfoliated graphene synthesized in different aqueous electrolytes, i.e., 0.5 M H2SO4, Na2SO4, and LiClO4 [71]. The results showed that the graphene prepared in H2SO4 and Na2SO4 exhibited relatively high specific capacitance of 78 and 106 F g-1, respectively. LiClO4 introduced a large amount of oxygen functional groups on the exfoliated graphene, which could be anchoring sites for growing other materials to form graphene-based composites. Notably, the specific capacitances of the electrochemically exfoliated graphene often fall in the range of 50~100 F g-1, which were slightly lower than those of graphene obtained through chemical oxidation. The underlying reason was revealed by Xia et al., who studied the different graphite exfoliation routes via chemical oxidation and electrochemical exfoliation [66]. The authors discovered that the surface area of the electrochemically exfoliated graphite was only 6.6 m2 g-1, which was three orders of magnitude lower than that of the theoretical value (2600 m2 g-1) of a graphene monolayer achieved by chemical exfoliation. Therefore, electrochemical exfoliation is challenging to fully separate graphite into monolayer graphene, resulting in the relatively low gravimetric capacitance due to the small surface area (Table 1). This limitation has motivated the introduction of pseudocapacitive functional groups to boost capacitance [85, 99, 101].

Table 1 Synthesis conditions and specific capacitance of electrochemically exfoliated graphene-based electrodes

12 118 table1

    Compared with fully exfoliated graphene sheets, partial exfoliated graphite and carbon electrodes have the main advantage that the whole electrodes remain structurally and electrically connected, enabling them to function as current collectors for loading pseudocapacitive materials. The resultant composite materials possess both high capacitance from the incorporated pseudocapacitive materials and the excellent rate capability characteristic of carbon-based materials. In this regard, the mass loadings of the pseudocapacitive materials must be meticulously tuned to ensure the highest specific capacitance without significantly compromising the rate capability.

4 Conducting Polymers

    Conducting polymers, or conjugated polymers, are organic polymers that conduct electricity in their electron conjugated networks in the polymer backbones [116-118]. Polyaniline (PANI) [119-122], polypyrrole (PPy) [105, 123], polythiophene (PTh) [124, 125], and poly(3,4-ethylene dioxythiophene) (PEDOT) [126-129] are common supercapacitor electrode materials. In terms of electrochemical synthesis, electrochemical polymerization of monomers is typical to prepare these conducting polymers. It grows conducting polymers onto electrically conductive substrates (current collectors), eliminating the need for blending powdered materials with binders and conductive additives when preparing electrodes. Potentiostatic deposition [130], galvanostatic deposition [131, 132], and cyclic voltammetry [105] are synthesis techniques of conducting polymers. The thicknesses and mass loadings of conducting polymers are controllable by tuning deposition duration. The compositions of electrolytes mainly influence their electrical conductivity. This section summarizes the mechanisms of electrochemical polymerization, recent progress of the electrochemically synthesized conducting polymers, and their electrochemical performance as supercapacitor electrodes. 
4.1 Mechanism of Electrochemical Polymerization of Conducting Polymer Materials
    Electrochemical technologies are time- and cost-efficient in preparing conducting polymers. Electrochemical polymerization begins with oxidizing monomers possessing five-membered aromatic heterocycles (e.g., pyrrole or thiophene) [133, 134] or cyclic aromatic amines (e.g., aniline) [116]. The oxidation involves generating and dimerizing radical cations, followed by polymer chain growth. Electrochemical polymerization initiates polymer growth on the surfaces of conductive substrates.
    Diaz proposed the widely accepted electrochemical polymerization mechanism of five-membered aromatic monomers in 1983 (Fig. 10a) [133]. Taking polypyrrole (PPy) as an example, pyrrole (Py) monomers are first oxidized to radical cations under an anodic potential. Subsequently, the radical cations dimerize through radical-radical coupling reactions at α-positions and deprotonated into neutral dimers. The as-formed dimers further combine and eventually extend to PPy.

Fig. 10 a Electrochemical polymerization mechanism of pyrrole. b Electrochemical polymerization mechanism of polyaniline.

Fig. 10 a Electrochemical polymerization mechanism of pyrrole. b Electrochemical polymerization mechanism of polyaniline.

    The polymerization of another conducting polymer, polyaniline, follows a similar path as that of PPy (Fig. 10b) [135]. Its monomers are first oxidized to radical cations, then coupled and deprotonated to dimers. Unlike PPy, whose chain propagation is driven by continuous dimer combination, aniline dimers undergo further oxidation and couple with one aniline radical cation at a time. The coupling extends to polyaniline. For both cases, anions (or counterions in general) will dope into the as-formed conducting polymers to balance the charges carried by the positively charged sites on the polymer backbones. Note that the concept of doping in the context of conducting polymers is fundamentally different from that in conventional solid-state semiconductors. Doping semiconductors means to incorporate dopants into the crystal lattices of the host materials [136].
    This counter-ion doping process maintains the electroneutrality of conducting polymer and affects the electrical conductivity of conducting polymers [137]:

12 118 gs3

where Pol* is the positively charged sites in a conducting polymer, A- stands for counter-ion, and S represents a solvent molecule. When electrons enter in conducting polymers, doping of A- and concurrently, co-insertion of solvent molecules, lead to volumetric expansion of the host polymers. Conversely, electron extraction causes de-doping of A- and de-solvation of conducting polymers, resulting in volumetric contraction. The irreversible volumetric deformation is a typical culprit for the structural instability that causes unsatisfactory cycling stability of conducting polymers [138, 139].
4.2 Electrochemically Synthesized Conducting Polymers for Supercapacitors
4.2.1 Films
    Conformal films are the most common morphologies of electrochemically polymerized conducting polymer electrodes [97, 140, 141]. Parameters associated with electro-polymerization have profound influences on the chemical compositions, morphologies, and electrochemical properties of the deposited polymer films [130, 142].
   The surface properties of the substrates influence the adhesion strength and chemical compositions of the polymer films. For example, Feng et al. electrochemically deposited a thin PPy layer on oxygen functionalized carbon cloth (FCC) [97]. Comparing with PPy deposited on pristine carbon cloth (CC), PPy/FCC exhibited enhanced dopant concentrations and electrical conductivity, because the oxygen functional groups on FCC could dope into PPy and reinforced the adhesion of PPy onto FCC. Consequently, PPy/FCC displayed an areal capacitance of 341 mF cm-2 at 1 mA cm-2, about 40 mF cm-2 higher than that of PPy/CC at the same current density.
    Electrochemically polymerized conducting polymer films have different molecular structures from those prepared by chemical polymerization. Huang et al. reported that PPy film deposited via galvanostatic electro-deposition exhibited higher molecular order than that made by chemical oxidation (Fig. 11a) [143]. During electrochemical polymerization, the α-α coupled PPy chains stacked layer-by-layer with an interlayer spacing of 3.45 Å, as evident from the pronounced X-ray diffraction peak (Figs. 11b, c). This layered molecular structure facilitated ion transport within the electrode and induced a homogeneous stress distribution in the polymer films, both of which improved the cycling stability of PPy.

Fig. 11 a SEM image of electrodeposited PPy film on an oxygen-functionalized carbon fiber. b XRD patterns of electrochemically and chemically deposited PPy. c Models proposing possible molecular structure of electrodeposited PPy. d PPy film electrochemically deposited on a flexible stainless-steel mesh. e Schematic illustration of the stretched mesh structure. f Cauliflower-like PPy film

Fig. 11 a SEM image of electrodeposited PPy film on an oxygen-functionalized carbon fiber. b XRD patterns of electrochemically and chemically deposited PPy. c Models proposing possible molecular structure of electrodeposited PPy. d PPy film electrochemically deposited on a flexible stainless-steel mesh. e Schematic illustration of the stretched mesh structure. f Cauliflower-like PPy film

   Coating conducting polymer films onto flexible substrates is a strategy of making flexible electrodes for wearable supercapacitors. Huang et al. demonstrated a stretchable stainless-steel mesh as an electrically conductive substrate to endow the deposited PPy film excellent stretchability (Fig. 11d) [132]. The PPy-coated stainless-steel mesh delivered a specific capacitance of 170 F g-1 at 0.5 A g-1, and the capacitance augmented to 214 F g-1 when the electrode was applied a 20% strain. The strain improved the contact between PPy and stainless steel and reduced the contact resistance, which augmented the specific capacitance (Fig. 11e).
    It should be noted that thin films are usually obtained at the early stage of electrode-polymerization, and prolonging deposition time may modify the film morphology due to overgrowth. For instance, Song et al. observed that instead of thin films, PPy cauliflowers formed (Fig. 11f) after 10 cycles scanning from 0 to 0.8 V vs. SCE at 50 mV s-1 [105].
    Soft templates (e.g., surfactant) can introduce porosity in electro-deposited conducting polymer films. Kurra et al. used a potentiostatic method to deposit a thin layer of PEDOT on an Au-coated, interdigitated electrode (Fig. 12a, b) [144]. Sodium dodecyl sulfate, an anionic surfactant, was used to increase the solubility of 3,4-ethylenedioxythiophene (EDOT) in water, and thus, decreased the polymerization potential of EDOT. The surfactant molecules also served as soft templates that created cracks in the PEDOT film (Figs. 12c, d). These cracks provided electrolyte ions percolation pathways and benefited rate capability at high frequencies. A symmetric micro-supercapacitor consisting of two identical interdigitated electrodes displayed a typical capacitive behavior as reflected from the plateau-free galvanostatic charge-discharge profiles (Fig. 12e). This micro-supercapacitor exhibited a positive trend between its areal capacitance and the electro-polymerization time, but the volumetric capacitance peaked after 15 min polymerization (Fig. 12f). The drop in the volumetric capacitance was attributed to the increased PEDOT thickness that impeded ion diffusion.

Fig. 12 a Photograph and b SEM image of PEDOT-coated interdigitated electrode. c Magnified-view SEM image of the electrodeposited PEDOT film. The red circles highlight the cracks formed by soft templates. d Scheme illustrating the surfactant-induced crack formation. e Galvanostatic charge-discharge profiles of a symmetric micro-supercapacitor consisting of two PEDOT-coated interdigitated electrodes. Electrolyte: 1 M H2SO4 aqueous solutions. f Areal and volumetric capacitances of the symmetric micro-supercapacitor as a function of polymer deposition time

Fig. 12 a Photograph and b SEM image of PEDOT-coated interdigitated electrode. c Magnified-view SEM image of the electrodeposited PEDOT film. The red circles highlight the cracks formed by soft templates. d Scheme illustrating the surfactant-induced crack formation. e Galvanostatic charge-discharge profiles of a symmetric micro-supercapacitor consisting of two PEDOT-coated interdigitated electrodes. Electrolyte: 1 M H2SO4 aqueous solutions. f Areal and volumetric capacitances of the symmetric micro-supercapacitor as a function of polymer deposition time

4.2.2 Nanowires and Nanorods
    One-dimensional (1D) conducting polymers, such as polyaniline nanofibers [145-147], polypyrrole nanorods [148-150], are popular morphologies of pseudocapacitor electrodes. Their merits include the wide-open inter-fiber space that facilitates electrolyte infiltration and diffusion and minimizes dead volumes (materials that are unusable for charge storage).
   In the absence of any structure-directing agents, polyaniline preferentially forms randomly intertwined nanofibers [151]. Liu et al. electrodeposited polyaniline (PANI) nanowires on carbon cloth using cyclic voltammetry within a potential window between -0.2 to 0.8 V in aqueous electrolytes containing 0.1 M aniline and 1 M H2SO4 [25]. PANI nanowires were uniformly grown on carbon cloth fibers (Fig. 13a). To address the intrinsic cycling instability of PANI, the researchers conformally coated the deposited PANI nanowires with 5-nm-thick carbonaceous shells by hydrothermally decomposing glucose. The coated PANI electrode exhibited a high theoretical areal capacitance of 787.4 mF cm-2 (estimated by the Trasatti method) and excellent cycling stability of ~95% after 10000 charge-discharge cycles. SEM revealed that the carbonaceous shell mitigated the volumetric-deformation-induced structural pulverization of PANI.

Fig. 13 Electrochemically deposited 1D polymer structures. a PANI nanofibers on carbon cloth; b PANI nanorod arrays on Au plates; c PANI nanorod arrays on carbon-nanotube paper; d PPy nanorod arrays on carbon cloth

Fig. 13 Electrochemically deposited 1D polymer structures. a PANI nanofibers on carbon cloth; b PANI nanorod arrays on Au plates; c PANI nanorod arrays on carbon-nanotube paper; d PPy nanorod arrays on carbon cloth

    Confining the growth of conducting polymers from current collector surfaces is a prerequisite to obtaining binder-free supercapacitor electrodes. To suppress electro-polymerization of monomers in bulk electrolytes, small current, low potential, and dilute monomer solutions are preferred. Once polymer nucleate on substrate surfaces, they minimize the energy barrier for the subsequent growth of conducting polymer nanostructures [152, 153]. For example, PANI nanorod arrays were grown on an Au plate using a galvanostatic method with a small current density of 0.01 mA cm-2 (Fig. 13b) [153]. The formation mechanism followed the nucleation-initiated growth process. The electrodeposited PANI nanorod array electrode exhibited a high specific capacitance of 950 F g-1 at 1 A g-1. Following the same protocol, PANI nanorod arrays were grown on other conductive substrates, such as carbon nanotubes (Fig. 13c) [145], exfoliated graphene sheets [154], as well as graphene papers [155, 156]. The generality of substrates indicated that the nucleation-growth process is independent of substrate properties.
    In addition to PANI, electrochemical technology also produces polypyrrole (PPy) nanorod arrays on conductive substrates. Huang et al. fabricated PPy nanorod arrays via a one-step galvanostatic deposition at 1 mA cm-2 with p-toluenesulfonate acid (TsOH) as a soft template (Fig. 13d) [149]. The TsOH anions prevented the as-formed PPy oligomers from growing in random directions, promoting the growth of PPy nanorods on carbon cloth. Significantly, the PPy nanorods exhibited capacitance of 699 F g-1 at 1 A g-1. When the current density increased from 1 to 20 A g-1, 81.5% capacitance retained, indicating its excellent rate capability.
    The use of hard templates enables the growth of sophisticated 1D nanostructures, such as nanotubes. Using nickel nanotube arrays (NiNTAs) hard templates, Chen et al. made perchlorate-doped PPy nanotubes (Fig. 14) [157]. First, Ni nanoparticles were dispersed on ZnO nanorod arrays to form ZnO@NiNRAs, followed by dissolving the ZnO templates to produce NiNTAs. Second, the electro-polymerization of PPy on NiNTAs generated NiNTAs@PPy (Figs. 14a, b). High-resolution TEM showed abundant mesopores throughout the PPy layer (Figs. 14c, d). Possibly, the mesopores formed during the polymerization process when the anions were inserted into PPy, and the cations were extracted. The highly porous hollow nanotube arrays in NiNTAs@PPy acted as ion reservoirs that shortened ion diffusion distance. Therefore, NiNTAs@PPy-electrode displayed a high specific capacitance of 474.4 F g-1 at 5 mV s-1. The PPy nanotubes also had excellent electrochemical stability with 75.3% capacitance retention after 10,000 charge-discharge cycles. The nanotube morphology and many pores and voids in PPy buffered the volumetric change of PPy and facilitated ion diffusion (Fig. 14e), which ensured excellent cycling stability.

Fig. 14 a, b SEM and c, d TEM images of NiNTAs@PPy. The black dotted circles in d highlight micropores in PPy. e Schemes showing the charge storage mechanism of NiNTAs@PPy in supercapacitors during (top) charging and (bottom) discharging

Fig. 14 a, b SEM and c, d TEM images of NiNTAs@PPy. The black dotted circles in d highlight micropores in PPy. e Schemes showing the charge storage mechanism of NiNTAs@PPy in supercapacitors during (top) charging and (bottom) discharging

4.2.3 Nanoplates
    Electrochemically synthesized two-dimensional (2D) conducting polymers are rare because conducting polymers intrinsically prefer to grow into fibers or films. One typical example of 2D conducting polymer made by electro-polymerization is pyrene nanosheets (Fig. 15a). They were grown in a mixed electrolyte containing boron trifluoride diethyl etherate (BFEE), trifluoroacetic acid (TFA), and polyethylene glycol (PEG), using a potentiostatic technique (1.2 V vs.SCE) [158]. Spectroscopy revealed that the formation of nanosheets was due to oligomer growth via α-α coupling of pyrene rings. Besides pyrene, PPy nanosheets (Fig. 15b) were synthesized using cyclic voltammetry at a high scan rate of 200 mV s-1 in an aqueous electrolyte containing 0.05 M pyrrole and 0.1 M KNO3 [159]. These PPy nanosheets interconnected with each other and assembled into a macroporous structure. It had a specific surface area of 37.1 m2 g-1 and a specific capacitance of 584 F g-1 at 5 mA cm-2.

Fig. 15 Electrodeposited two-dimensional conducting polymers. a oligopyrene nanosheets; b PPy nanosheets; c PANI nanosheets on graphene sheets; d PEDOT thin films on CoAl layered double hydroxide nanoplates

Fig. 15 Electrodeposited two-dimensional conducting polymers. a oligopyrene nanosheets; b PPy nanosheets; c PANI nanosheets on graphene sheets; d PEDOT thin films on CoAl layered double hydroxide nanoplates

    Hard template methods can also synthesize 2D polymer materials (Figs. 15c, d). These 2D templates (e.g., graphene sheets [160] and layered double hydroxides [161]) are structural scaffolds to direct the growth of conducting polymers in 2D fashion, endowing fast ion diffusion pathways in the electrode materials that results in excellent rate capability.
4.2.4 3D Networks
    Three-dimensional (3D) conductive structures provide large ion-accessible surface areas and abundant pores compared to 2D architectures, and thus, are increasingly popular morphologies of electrochemically deposited conducting polymers. High surface area can effectively reduce the local current density and polarization in bulk electrodes, and thus improve the electrodes' charge-storage kinetics. Unfortunately, ideal 3D structures composed merely of conducting polymers are challenging to acquire, due to their preferably random growth into films or fibers during electro-polymerizations.
    To circumvent this challenge, researchers adopt templates to construct 3D conducting polymers. Demonstrated templates include carbon nanotube foam [163] (Fig. 16a, b), graphene foam [164] (Fig. 18c), partial exfoliated graphite [26] (Fig. 16d), as well as Ni foam [165] (Fig. 16e-g), have been used to construct 3D polymer-based electrodes. For example, Park et al. deposited a PPy film on graphene foam (Fig. 16c) [164]. The high surface area of graphene foam and the pseudocapacitance of PPy synergistically improved the performance of the electrode. Wang et al. reported a PPy foam using a sacrificial Ni foam template (Fig. 16e) [165]. PPy was first electrodeposited on a Ni foam (Fig. 16f), and subsequently, the Ni foam was etched away, leaving a free-standing 3D PPy foam (Fig. 16g). This as-prepared 3D PPy foam was mechanically strong and highly flexible, making it a multifunctional 3D material in sensors, supercapacitors, and supports for graphene. Moreover, the free-standing 3D PPy exhibited a capacitance of 316.2 F g-1 at 2 mV s-1, and the graphene-coated 3D PPy achieved a higher capacitance of 702.9 F g-1 at the same scan rate. The incorporation of graphene created highly conductive surface coatings as well as increasing specific surface area from 72 m2 g-1 to 113.4 m2 g-1.

Fig. 16 a Photographs and b SEM and TEM (inset) images of a compressible, PEDOT-coated carbon nanotube sponge. c SEM image of PPy-coated graphene (top) and bare graphene (bottom) foams. d PPy film deposited on electrochemically exfoliated graphite foil. e Scheme of the fabrication process of 3D PPy foam. f, g SEM images of 3D PPy foam at different magnifications

Fig. 16 a Photographs and b SEM and TEM (inset) images of a compressible, PEDOT-coated carbon nanotube sponge. c SEM image of PPy-coated graphene (top) and bare graphene (bottom) foams. d PPy film deposited on electrochemically exfoliated graphite foil. e Scheme of the fabrication process of 3D PPy foam. f, g SEM images of 3D PPy foam at different magnifications

5 Metal Oxides and Hydroxides

5.1 Manganese Oxides
    Manganese oxides, particularly manganese dioxide (MnO2), have attracted immense interest as one of the most commercially promising pseudocapacitive materials, due to its high theoretical capacitance (~1000 F g-1), cost efficiency, source abundance, and environmental friendliness [166, 167]. A variety of chemical and electrochemical techniques have synthesized manganese oxides. Among them, anodic electrodeposition is the most time-efficient. This technique deposited MnOx by consecutive oxidation of Mn2+, as illustrated in the following equations [168, 169]:

12 118 gs456

    The nanostructures of electro-deposited MnOx are tunable by varying the electrolyte composition, temperature, potential, and current density. For example, Feng et al. demonstrated that complexing agents such as CH3COO- and NH4+ significantly reduced the charge-transfer resistance of the electrooxidation of Mn2+ [166], changing the morphology of MnOx from 2D nanosheets to 1D nanoneedles. These observations indicate that diminishing charge-transfer resistance of MnOx electro-deposition impedes its lateral growth.
    Wei et al. proposed a theory of the supersaturation ratio of Mn2+ to rationalize the diverse morphologies of anodically electrodeposited MnOx (Fig. 17a) [170]. Super-saturation ratio is defined as the ratio of the actual concentrations (or more vigorously speaking, activities) of all the ions associated with electrodeposition to the equilibrium concentrations of the same set of ions. The authors observed that high concentrations of Mn(NO3)2 and large current densities induced high super-saturation ratios that led to uniform coatings. In contrast, low concentrations of Mn(NO3)2 and small current densities favored epitaxial growth into interconnected nanosheets (Fig. 17b-f). These different morphologies were associated with the number of nucleates formed at the beginning of electrodeposition. High super-saturation ratios yielded abundant nucleation sites that suppressed epitaxial growth. Parameters that lowered the super-saturation ratio decreased the number of nucleation sites and favored the formation of nanostructures.

Fig. 17 a Schemes of the morphological evolution of MnOx across different electrodeposition supersaturation ratios. b-d Top-view SEM images of MnOx electrodeposited in 0.1 M Mn(NO3)2 aqueous solutions at various current densities: b 20 mA cm-2, c 1 mA cm-2, and d 0.1 mA cm-2. e-f SEM images of MnOx prepared in 0.0025 M Mn(NO3)2 at e 0.1 mA cm-2 and f 0.05 mA cm-2

Fig. 17 a Schemes of the morphological evolution of MnOx across different electrodeposition supersaturation ratios. b-d Top-view SEM images of MnOx electrodeposited in 0.1 M Mn(NO3)2 aqueous solutions at various current densities: b 20 mA cm-2, c 1 mA cm-2, and d 0.1 mA cm-2. e-f SEM images of MnOx prepared in 0.0025 M Mn(NO3)2 at e 0.1 mA cm-2 and f 0.05 mA cm-2

5.1.1 Nanorods and Nanotubes
    Templating is a typical strategy to prepare 1D MnOx nanostructures [171, 172]. ZnO nanorods [173], anodized alumina [174, 175], hydrogenated TiO2 nanorods [176], and silicon square pillars [177] are reported templates for electrodepositing MnOx nanorod or nanotube arrays. For example, Li and coworkers synthesized double-walled carbon/MnO2 nanotube arrays using ZnO nanorods as sacrificial templates [173] (Fig. 18a). First, ZnO nanorod arrays were grown on Ti plates via electrodeposition, and thin layers of carbon were coated on the nanorods to render the ZnO nanorods electrically conductive. Afterward, a uniform MnO2 film was electrodeposited on the carbon-coated ZnO nanorod arrays (Fig. 18b). Finally, dissolving the ZnO nanorod arrays using 0.5 M NaOH solution generated the double-walled carbon/MnO2 nanotube arrays (Fig. 18c). These double-walled nanotubes displayed a high specific capacitance of 793 F g-1 at 1.5 A g-1, and a rate capability of 83% when the scan rate increased from 5 to 50 mV s-1. The excellent electrochemical performances were ascribed to factors including: (1) The hollow structure of the nanotube arrays exposed plentiful active sites of MnO2 and provided ions fast diffusion pathways; (2) The conformal carbon coating served as electron transport expressways, minimizing capacitance loss at elevated scan rates; (3) the high weight fraction of MnO2 (~98.94 wt%) in the electrodes was beneficial to achieve high specific capacitance and energy density.

Fig. 18 a Schemes of the synthesis procedures of double-walled MnO2 nanotube arrays on carbon cloth. b SEM image of ZnO/C/MnO2 nanorod arrays. Inset: Magnified view of a single nanorod. c SEM image of C-coated MnO2 double-walled nanotubes. Inset: Magnified view showing a C-coated MnO2 nanotube. d, e SEM images of MnOx d nanorods and e herringbones. f, g Schemes of the charge transfer pathways in f MnOx nanorod arrays and g MnOx herringbones

Fig. 18 a Schemes of the synthesis procedures of double-walled MnO2 nanotube arrays on carbon cloth. b SEM image of ZnO/C/MnO2 nanorod arrays. Inset: Magnified view of a single nanorod. c SEM image of C-coated MnO2 double-walled nanotubes. Inset: Magnified view showing a C-coated MnO2 nanotube. d, e SEM images of MnOx d nanorods and e herringbones. f, g Schemes of the charge transfer pathways in f MnOx nanorod arrays and g MnOx herringbones

    Besides templating, template-free methods could also synthesize 1D nanostructured MnOx. These methods are time-efficient and can synthesize products of high purity because they lift the needs for template incorporation and removal [178, 179]. For example, Lu and coworkers demonstrated that adding dimethyl sulfoxide (DMSO) in the deposition solution of MnO2 led to MnO2 nanorod arrays without any templates [180]. They applied a constant anodic current of 0.2 mA cm-2 at 70 °C and used aqueous electrolytes containing 0.01 M manganese(II) acetate, 0.02 M ammonium acetate, and 10 wt% DMSO. The resultant MnO2 nanorods had diameters between 70 and 100 nm, and lengths up to ~1.5 μm (Fig. 18d). Electrodeposition without DMSO only yielded MnO2 herringbones (Fig. 18e). Though the authors did not justify how DMSO changed the deposit morphology, we hypothesized that the addition of DMSO reduced the supersaturation ratio of Mn2+ and thus, promoted epitaxial growth of MnO2 into nanorods. The specific capacitance of the MnO2 nanorod array was 660.7 F g-1 at 10 mV s-1, which was ~100 F g-1 higher than that of the herringbone structured MnO2 (564.3 F g-1). This capacitance discrepancy was associated with the morphology: The ordered vertically aligned nanorods, compared with the herringbones, reduced the tortuosity and distances for electron transport, which boosted capacitance (Figs. 18f, g).
5.1.2 Nanosheets and Nanoplates
    Ultrathin 2D MnOx nanosheets were another common morphologies of electrodeposited MnOx [181-185]. Anodic deposition is widely demonstrated to prepare MnOx nanosheets [186-195]. For example, Yao et al. deposited MnO2 nanosheets onto 3D printed graphene aerogel lattices through an anodic galvanostatic deposition at 10 mA cm-2 (Fig. 19a) [196]. The outstanding property of these 3D printed MnO2/graphene composite electrodes was their uncompromised electrochemical performance at MnO2 mass loadings as high as 182.2 mg cm-2. The areal capacitance scaled linearly with the thickness of the electrode, reaching 44.13 F cm-2 at 0.5 mA cm-2 in 3 M LiCl aqueous electrolytes at a thickness of 4.0 mm (MnO2 mass loading: 182.2 mg cm-2). This linear relationship indicated that the charge storage process of the electrode was not under diffusion control or limited by ion-percolation even at ultrahigh mass loadings and thicknesses. This merit was attributed to the 3D-printed graphene lattices with macropores of 5–50 μm pores (Fig. 19b, c), which promoted the uniform deposition of MnO2 and opened up wide ion diffusion pathways throughout the entire electrodes.

Fig. 19 a Schemes of the synthesis procedures of MnO2 nanosheets deposited on 3D printed graphene aerogel lattices. b A top-view SEM image of MnO2-coated 3D printed graphene aerogel. c, d SEM images of the deposited MnO2 nanosheets at two magnifications

Fig. 19 a Schemes of the synthesis procedures of MnO2 nanosheets deposited on 3D printed graphene aerogel lattices. b A top-view SEM image of MnO2-coated 3D printed graphene aerogel. c, d SEM images of the deposited MnO2 nanosheets at two magnifications

    In addition to anodic electrodeposition, cathodic electrodeposition also synthesizes 2D MnOx nanosheets. For example, Beyazay et al. used a chronoamperometry technique to deposit Mn3O4 hexagonal nanosheets on graphene paper. This electrode delivered a maximal specific capacitance of 546 F g-1 at 0.5 A g-1. Interestingly, the capacitance increased about 1.5 times after being charged and discharged for 10,000 times. XPS analysis after the stability test found that the average valence of Mn raised from 2.7 to 3.2, indicating that part of Mn3O4 was oxidized to MnO2. Besides the valence change, some hexagonal nanosheets transformed into particles and needles. These results suggested that the hexagonal Mn3O4 nanosheets were both chemically and structurally unstable during long-term cycling tests.
5.1.3 Hierarchical Structures
    Hierarchical MnOx integrates nanostructures of different dimensions, e.g., 1D nanorod, 2D nanosheet, and 2D nanoplate. Electrodepositing hierarchical structures often begins with one specific structure. For example, Jabeen et al. synthesized Mn3O4 nanosheet-on-nanowall arrays via a cathodic potentiostatic method (-1.8 V vs. Ag/AgCl) in an aqueous solution containing 0.1 M manganese acetate and 0.1 M sodium sulfate. High resolution scanning electron microscopy revealed that these nanowalls were composed of interconnected nanoparticles (Fig. 20a) [14]. After 500 cycles of electrochemical oxidation in 10 M sodium sulfate aqueous solutions, the nanoparticles disappeared, and nanosheets appeared on the surface of the nanowalls, assembling the nanosheet-on-nanowall hierarchical structure (Figs. 20b, c). Meanwhile, the composition of the electrode changed from Mn3O4 to Na0.5MnO2. The hierarchically structured Na0.5MnO2 exhibited a specific capacitance of 366 F g-1 at 1 A g-1. Besides, the redox peak of Na0.5MnO2 at ~0.96 V vs. Ag/AgCl extended the upper limit potential to approximately 1.3 V vs. Ag/AgCl, enabling the development of aqueous-based supercapacitors with high voltages and energy densities.

Fig. 20 a-c SEM image of a Mn3O4 nanowall arrays, b intermediates during electrochemical oxidation, and c hierarchical Na0.5MnO2 nanowall arrays. d, e SEM images of d as-deposited and e hydrothermally treated MnOx thick layer on carbon fiber. f TEM image of hydrothermally treated MnOx. g-i SEM images of MnO2 deposited at g 25 °C, h 40 °C, and i 60 °C

Fig. 20 a-c SEM image of a Mn3O4 nanowall arrays, b intermediates during electrochemical oxidation, and c hierarchical Na0.5MnO2 nanowall arrays. d, e SEM images of d as-deposited and e hydrothermally treated MnOx thick layer on carbon fiber. f TEM image of hydrothermally treated MnOx. g-i SEM images of MnO2 deposited at g 25 °C, h 40 °C, and i 60 °C

    The most significant characteristic of hierarchical structures is their capability to maintain excellent electrochemical performance at MnOx mass loadings exceeding 10 mg cm-2. Increasing the mass loadings of MnOx (and other pseudocapacitive materials) becomes a trend in recent years, due to the consideration of practicality. Unfortunately, the capacitances of poorly conductive pseudocapacitive materials, including MnOx, are greatly compromised when enhancing their mass loadings, particularly under fast charge and discharge rates. Hierarchical structures could resolve this challenge. For example, Song et al. developed an Ostwald ripening strategy that improved the rate capability of electrodeposited MnOx thick films with a high mass loading of ~10 mg cm-2 (Figs. 20d-f) [197]. The authors first coated carbon fibers with MnOx films of ~4.5 µm thick using a constant current of 10 mA cm-2 in 0.1 M manganese acetate aqueous solutions (Fig. 20d). They then hydrothermally treated the electrodeposited MnOx at 90 °C, which appreciably altered the morphology of the MnOx films. First, many crystalline MnOx nanosheets formed on the surface. Second, the porosity of the MnOx core increased (Figs. 20e, f). The porous MnOx core and oxide shell together constituted a core-shell hierarchical structure. The crystalline surface ensured good electrical conductivity, and the porous MnOx core sped up ion diffusion. Therefore, the electrode exhibited improved rate performance even at a high mass loading of 10 mg cm-2. Recently, Huang et al. demonstrated a facile electrochemical technology that synthesized a nanorod-on-sheet hierarchical structure. The structure consisted of primary two-dimensional ε-MnO2 nanosheets and secondary one-dimensional α-MnO2 nanorod arrays (Fig. 20g-i) [50]. Morphology studies indicated that elevating the deposition temperature to 60 °C and 80 °C added nucleation sites on the as-formed nanorods, which favored the secondary growth of nanorods. This hierarchical electrode had a high MnO2 mass loading of 10 mg cm-2 and delivered a high areal capacitance of 3.04 F cm-2 at 3 mA cm-2. Significantly, the areal capacitance maintained at 1.9 F cm-2 at 30 mA cm-2. The authors ascribed this excellent rate capability performance to two factors: First, the multiple connections between the nanorods and nanosheets created fast avenues for electron transport. Second, the voids among the nanorods and nanosheets throughout the hierarchical structure facilitated electrolyte ion percolation and ion diffusion kinetics.
5.2 Vanadium Oxides
    Vanadium oxides (VOx), mainly vanadium pentoxide (V2O5), have the advantages of high specific capacitance (multiple electron reaction, e.g., from +3 to +5), low cost, ease of fabrication, as well as wide potential windows [37, 198-202]. Electrochemical technologies are particularly suitable for synthesizing VOx of diverse morphologies, crystal structures, and valence states [203-209]. In aqueous electrolytes, vanadium oxide is typically synthesized from the oxidation of vanadium-containing ions with the aid of water molecules. For example, oxovanadium(IV) cations, VO2+, are electro-oxidized to high-valence vanadium oxides (e.g., V2O5) through the following equation [208]:

12 118 gs7

    For example, Xie et al. demonstrated that the pH value and composition of acetate salts (CH3COONa, CH3COOLi, CH3COOK) were critical in tuning the deposition rate, crystal structure, and morphology of VOx [209]. Drosos et al. studied the effects of the deposition current density on the morphology and electrochemical performance of V2O5 coatings on indium-doped tin oxide glass substrates in 1 M LiClO4 polypropylene carbonate electrolytes. The V2O5 film deposited at 1 mA cm-2 exhibited the highest capacitance owing to its roughest surface [210].
    Electrodeposited VOx with mixed V valences are platforms for studying the interplays between V valence and cycling stability. Recent studies indicated that the performance degradation was linked to dissolution, structural pulverization, and irreversible phase transition of VOx [34, 37, 199]. Investigating the cycling behavior of electrodeposited VOx electrodes in various aqueous environments, Engstrom and Doyle concluded that the formation of water-soluble V-containing species, including H2VO4-, HVO42-, HV2O5-, VO2+, HVO2+, and VO+ (Fig. 21a) was the primary cause of capacitive decay of VOx during extensive cycling tests [199]. Though chemical strategies such as surface coating [211, 212] and electrolyte pH value tuning [199] minimized dissolution of VOx, the altered electrode kinetics usually compromised capacitance. To circumvent these limitations, Song et al. utilized a potentiostatic electrochemical method to tune the V valence in VOx and achieved record-high cycling stability without capacitive decay over 100 000 cycles (Figs. 21b-d) [37]. VOx nanorods were first electrodeposited on electrochemically exfoliated carbon cloth fibers using cyclic voltammetry between -1.5 and 1.4 V vs. SCE (Fig. 21c). The authors then reduced the as-deposited VOx at a constant potential of -1.5 V vs. SCE for 1 min. This reduction raised the V4+/V5+ ratio from 0.4 to an optimal value of around 0.5. The optimized V4+/V5+ ratio in VOx effectively suppressed the chemical dissolution of VOx. Meanwhile, the firm anchoring of the reduced VOx nanorods on oxygenated, exfoliated carbon cloth fibers via C-O-V bonds retained the structural integrity of VOx. Both factors contributed to the excellent cycling stability (ECC/RVOx in Fig. 21d).

Fig. 21 a E-pH diagram of vanadium oxide-water system with various V based species at activities (the letter a in the figure) of 0.01, 1 and 100. b Schemes of the synthesis steps, c SEM image, and d cycling stability of amorphous, mixed-valence vanadium oxide (RVOx) deposited on exfoliated carbon cloth fibers.

Fig. 21 a E-pH diagram of vanadium oxide-water system with various V based species at activities (the letter a in the figure) of 0.01, 1 and 100. b Schemes of the synthesis steps, c SEM image, and d cycling stability of amorphous, mixed-valence vanadium oxide (RVOx) deposited on exfoliated carbon cloth fibers.

    The easy valence tuning of VOx by electrochemical techniques allowed the synthesis of heterojunctions between VOx of two valences. These configurations help facilitate electron transfer within VOx electrodes having large thicknesses or high mass loadings [34]. For instance, Dong et al. performed a density functional theory (DFT) calculation and discovered that a built-in electric field formed at the V5O12/VO2 heterojunction. The charge redistribution between the two oxides led to an electric field pointing from VO2 to V5O12 (Fig. 22a) [34]. This built-in electrical filed facilitated electron transfer and modulated ion absorption during charge-storage processes, which improved electrochemical performance. Inspired by this calculation result, the authors adopted cyclic voltammetry (-1.5 to 1.5 V vs. SCE) to electrodeposit V5O12/VO2 nanorods on an exfoliated graphite substrate. V5O12 first formed during the positive scan, and it was partially reduced to VO2 in the subsequent negative scan (Fig. 22b). V5O12/VO2 with a high mass loading of about 10.8 mg cm-2 delivered a high areal capacitance of 5.03 F cm-2 (465 F g-1) at 1 mA cm-2, outperforming pure V5O12 and VO2 (Fig. 22c). Significantly, V5O12/VO2 also exhibited enhanced cycling stability compared to V5O12 and VO2 alone (Fig. 22d). Two reasons could account for this stability enhancement. First, EIS indicated that V5O12/VO2 exhibited reduced charge-transfer resistance due to the heterojunction (Fig. 22e). Second, ex-situ XRD confirmed that V5O12/VO2 underwent no phase transitions after charging and discharging, while the phases of V5O12 and VO2 changed dramatically (Figs. 22f-h). The reduced resistance and suppressed phase change of V5O12/VO2 both enhanced cycling stability.

Fig. 22 a Charge density distribution along the interface of V5O12/VO2. b TEM image of V5O12/VO2 junction. c Areal capacitance of V5O12/VO2, V5O12, and VO2 as a function of current density. d Cycling stability of V5O12/VO2, V5O12, and VO2 electrodes in 3 M LiCl aqueous electrolyte. e Nyquist plots of V5O12/VO2, V5O12, and VO2. f-h Ex-situ XRD patterns of f V5O12, e VO2 and h V5O12/VO2 without charging (pristine), charged (-1 V), and discharged (0 V)

Fig. 22 a Charge density distribution along the interface of V5O12/VO2. b TEM image of V5O12/VO2 junction. c Areal capacitance of V5O12/VO2, V5O12, and VO2 as a function of current density. d Cycling stability of V5O12/VO2, V5O12, and VO2 electrodes in 3 M LiCl aqueous electrolyte. e Nyquist plots of V5O12/VO2, V5O12, and VO2. f-h Ex-situ XRD patterns of f V5O12, e VO2 and h V5O12/VO2 without charging (pristine), charged (-1 V), and discharged (0 V)

5.3 Molybdenum Oxides
    Molybdenum oxides (MoOx) are another group of electrodeposited pseudocapacitive materials [213-215]. Unlike MnOx discussed in the previous sections, MoOx is acid-resistant and thus can work in acidic electrolytes [216]. Besides surface redox reactions, some MoOx, e.g., α-MoO3, possess layered structures that allow ion insertion and de-insertion that contribute intercalative pseudocapacitance [217]. Specifically, α-MoO3 can accommodate up to 1.5 Li per Mo, having a high theoretical capacity of 1117 mAh g-1 [218].
   MoOx is usually deposited by cathodic electrodeposition in aqueous electrolytes containing molybdates (e.g., sodium molybdate and ammonium molybdate) [38], iso-/peroxo-polymolybdates [213], and ammonium paramolybdates [219]. Electrodeposited MoOx are typically quasi-amorphous, nonstoichiometric oxide films [38, 220-222]. Its composition, structure, and electrochemical performance of the deposited MoOx materials highly depend on electrolyte composition, pH value, and magnitudes of the applied current density and voltage [223-225].
    Nanostructured substrates with large ion-accessible surface areas are preferred electrodeposition scaffolds for MoOx. For example, a ~18-nm-thick layer of MoOx (3 mg cm-2) was deposited on tungsten oxide nanowires, forming a WO3–x/MoO3–x core/shell structure (Figs. 23a-d) [226]. This core/shell electrode delivered an areal capacitance of 500 mF cm-2. Li et al. electrodeposited a 40 nm-thick MoO3 layer (2.43 mg cm-2) on ZnO nanorod arrays (Figs. 23e, f). The ZnO-supported MoO3 displayed a specific capacitance of 241 F g-1 at 5 mV s-1 and 198 F g-1 at 100 mV s-1 [227]. Liu et al. demonstrated that functionalized, partially exfoliated graphite foil substrates could support MoOx films with high mass loadings (18.4 mg cm-2) (Fig. 23g) [228]. The exfoliated graphene sheets and the laminar structure of the graphite base addressed the negative impact of the poor electrical conductivity of the atop MoOx. This highly conductive carbon-based structure permitted efficient ion diffusion and fast electron transport. Besides, the O-functional groups on the exfoliated graphite foil formed covalent C-O-Mo bonds with MoO3, which served as bridges that permitted fast charge transport from MoOx to the substrate. All the above factors led to excellent rate capability: The optimized electrode with a high MoOx mass loading of 15.4 mg cm-2 delivered an areal capacitance of 4.34 F cm-2 at 1 mA cm-2 and retained 67.8% of the initial capacitance at 20 mA cm-2.

Fig. 23 a-c TEM images of a MoO3-x-coated WO3-x nanowire: a, b bright and c dark fields. d High-resolution TEM image of a MoO3-x-coated WO3-x nanowire. Inset: Selected electron diffraction pattern of WO3-x. e An SEM and f TEM images of ZnO@MoO3 core-shell structure. g A SEM image of MoO3-x film deposited on an exfoliated graphite substrate. h, i SEM images of the helical porous MoO2 with different magnifications

Fig. 23 a-c TEM images of a MoO3-x-coated WO3-x nanowire: a, b bright and c dark fields. d High-resolution TEM image of a MoO3-x-coated WO3-x nanowire. Inset: Selected electron diffraction pattern of WO3-x. e An SEM and f TEM images of ZnO@MoO3 core-shell structure. g A SEM image of MoO3-x film deposited on an exfoliated graphite substrate. h, i SEM images of the helical porous MoO2 with different magnifications

    Films deposited onto fibers can develop unique morphologies, such as helical cracks demonstrated by Lu et al. They utilized a combined electrochemistry-annealing strategy and deposited hierarchical porous MoO2 films composed of mesoporous nanoparticles on carbon cloth fibers (Figs. 23h, i) [229]. First, mixed-valence MoOx was electrochemically deposited on carbon cloth by reducing Mo7O246-:

12 118 gs8

     Subsequently, the as-formed MoOx was annealed in NH3 at 700 °C to obtain MoO2 films. Scanning electron microscopy revealed that the MoO2 films exhibited helical cracks of ~100-200 nm wide. Owing to the helical openings that reduced the dead volume of MoO2, the electrode delivered a high areal capacitance of 175 mF cm-2 at 1.43 mA cm-2 in Na2SO4 aqueous electrolytes. The formation mechanism of the helical cracks remained unclear, but we hypothesized that it might be associated with dehydration of the electro-deposited films during the thermal treatment in NH3. The cracks were initiated by volume shrinkage during annealing and propagated around carbon fibers following a helical path.
    Like other pseudocapacitive materials, electrodeposited MoOx exhibits high capacitance but unsatisfactory cycling instability. To extend the lifespan of electrodeposited MoOx, Cai et al. reported a potential-window-tuning strategy for MoOx [38]. They discovered that the potential window within -1 to -0.4 V vs. SCE permitted the redox reaction associated with Mo4+ and Mo5+ and prevented the formation of Mo6+. This feature resulted in no capacitance decay in 30,000 cycles. In contrast, the same electrode scanned between -1.0 and 0 V vs. SCE irreversibly generated Mo6+ and its capacitance decayed by more than 25% within 500 charge-discharge cycles. Electrochemical impedance spectroscopy revealed that the accumulation of Mo6+ increased the combined series resistance of MoOx, which made the electrode electrically insulating. Besides, optimizing the composition of electrodeposited MoOx materials via electrochemical technologies could provide new opportunities for enhancing their durability, as already proved to be successful in stabilizing VOx [34].
5.4 Tungsten Oxides
    Another transition metal oxide is tungsten oxides (WOx) [230-233]. WOx is usually deposited by cathodic deposition (e.g., applying a CV scan of -0.5 - 0 V vs. SCE [234]) in aqueous electrolytes containing peroxy-tungstate species (e.g., ) [235-237]:

12 118 gs910

    Most as-deposited WOx materials are amorphous with stacked, hydrated nanoparticles, WOx·nH2O [234, 238, 239]. Thermal annealing of WOx·nH2O at temperatures above 400 °C in air dehydrates and converts the nanoparticles to crystalline WOx [239, 240]. However, the annealing treatment usually triggers particle coalescence that decreases surface area. To circumvent this problem, Sun et al. developed an electrochemical post-crystallization process to convert electro-deposited amorphous, mixed-valence WOx into crystalline tungsten bronze HxWO3 (Figs. 24a-c) [234]. The electrochemical crystallization process turned the non-porous film into highly porous nanosheets, enhancing specific surface area (Fig. 24d).

Fig. 24 a, b SEM images of a electrodeposited tungsten oxide and b tungsten bronze films d on carbon cloth. c XRD patterns of tungsten oxide, tungsten bronze, and carbon cloth. d N2 adsorption-desorption isotherms of tungsten oxide and tungsten bronze. Inset: pore size distributions. e, f Cycling stability of tungsten bronze in e 1 M Na2SO4 and f Na2SO4/H2SO4 (1 M/0.01 M) mixed aqueous electrolytes. g XRD patterns of tungsten bronze after cycled in Na2SO4 and Na2SO4/H2SO4. h CV curves of tungsten bronze in Na2SO4 (green), Na2SO4/H2SO4 (red), and H2SO4 (blue) aqueous electrolytes. i Rate capability of tungsten bronze in Na2SO4/H2SO4

Fig. 24 a, b SEM images of a electrodeposited tungsten oxide and b tungsten bronze films d on carbon cloth. c XRD patterns of tungsten oxide, tungsten bronze, and carbon cloth. d N2 adsorption-desorption isotherms of tungsten oxide and tungsten bronze. Inset: pore size distributions. e, f Cycling stability of tungsten bronze in e 1 M Na2SO4 and f Na2SO4/H2SO4 (1 M/0.01 M) mixed aqueous electrolytes. g XRD patterns of tungsten bronze after cycled in Na2SO4 and Na2SO4/H2SO4. h CV curves of tungsten bronze in Na2SO4 (green), Na2SO4/H2SO4 (red), and H2SO4 (blue) aqueous electrolytes. i Rate capability of tungsten bronze in Na2SO4/H2SO4

    Changing electrolyte composition to extend the lower potential limit of WOx electrodes is necessary to increase the capacitance and energy density of WOx-based supercapacitors. As a hydrogen evolution reaction (HER) catalyst, WOx has a low potential of around -0.5 V vs. SCE [233]. Reducing pH values of electrolytes could push this limit to -1 V vs. SCE but at the cost of cycling stability (Fig. 24e) [234, 241]. Sun et al. achieved both a low cutoff potential to -0.9 V vs. SCE and good cycling stability with 98% capacitive retained after 30000 charge-discharge cycles by testing HxWO3 in a mixed electrolyte containing 1 M Na2SO4 and 0.01 M H2SO4 (Fig. 24f) [234]. XRD indicated that a new crystal phase (Na6WO6) formed after cycling in the Na2SO4 electrolyte (Fig. 24g), creating internal stress and detaching the active material from the current collector (carbon cloth fibers). While cycled in the mixed electrolyte, the structure of HxWO3 was well maintained. It was because, in proton-rich electrolytes, H+ insertion and de-insertion became the dominant charge storage mechanism, which was less destructive for the structure of HxWO3. Moreover, the mixed electrolyte enhanced the capacitance of HxWO3, as illustrated by the expanded area enclosed by the CV curve (Fig. 24h). Specifically, when tested in the mixed electrolyte, the electrode exhibited a high areal capacitance of 860 mF cm-2, corresponding to 143 F g-1, at 5 mV s-1 (Fig. 24i). The rational design of electrolyte composition enabled electrodeposited WOx electrodes with mutually high capacitance and excellent cycling stability.
5.5 Iron Oxides and Hydroxides
    Iron oxides and hydroxides are one of the most attractive, low-cost negative electrode active materials for supercapacitors [242-244]. Electrodeposition is a simple strategy to prepare nanostructured iron oxide and hydroxide [245]. Typically, Fe2+ (e.g., Fe(NH4)2(SO4)2·6H2O) is the iron source [35, 36, 246, 247]. During electrodeposition, Fe2+ is first oxidized to Fe3+ on positive electrodes, which then combines with OH- that was present in weakly alkaline electrolytes (pH ~8) or dissociated from water reduction to form Fe(OH)3 deposits. The as-deposited Fe(OH)3 further dehydrates to FeOOH in air. The associated chemical reactions are [248]:

12 118 gs1123

    To date, iron oxide of different dimensionalities, including 0D nanoparticles (Fig. 25a) [249], 1D nanorods (Fig. 25b) [250], 2D nanosheets (Fig. 25c) [251], and 3D hierarchical structures (Fig. 25d) [35], have been synthesized electrochemically. For example, Mai et al. reported a cyclic voltammetry method that transformed highly crystalline Fe2O3 nanoparticles into low-crystalline FeOOH nanoparticles (Fig. 25a) [249]. The resultant FeOOH electrode, with a high mass loading of 9.1 mg cm-2, exhibited an outstanding specific capacitance of 716 F g-1 at 1 A g-1 in 2 M KOH electrolyte. The specific capacitance was attributed to the facilitated ion diffusion kinetics in the FeOOH electrode, but further studies were needed to unveil the mechanism fully.

Fig. 25 a, b TEM images of a electro-deposited FeOOH nanoparticles and b Fe2O3 nanorods. c, d SEM images of electro-deposited FeOOH nanosheets and d chemically converted Fe3O4/Fe2O3 nanosheets. Inset: Magnified view of a nanosheet

Fig. 25 a, b TEM images of a electro-deposited FeOOH nanoparticles and b Fe2O3 nanorods. c, d SEM images of electro-deposited FeOOH nanosheets and d chemically converted Fe3O4/Fe2O3 nanosheets. Inset: Magnified view of a nanosheet

    As electrodeposited iron species are typically Fe(OH)3 and FeOOH, thermal conversion to Fe2O3 with enhanced electrochemical activity is usually performed for processing supercapacitor electrodes [252]. For example, FeOOH nanoneedles were first deposited on Ni-plated ZnO nanorods using a constant potential of 1.5 V vs. Ag/AgCl [253]. During the electrodeposition, the acidic environment created by Fe3+ hydrolysis corroded the ZnO nanorods, forming Ni@FeOOH. Subsequent annealing Ni@FeOOH in Ar at 450 °C dehydrated FeOOH to Ni@Fe2O3 nanoneedles. The Ni nanotubes swiftly conducted electrons between Fe2O3 and the substrate, while the ultrathin thickness of Fe2O3 nanosheets endowed fast charge transfer kinetics. Benefiting from these merits, Ni@Fe2O3 achieved a high specific capacitance of 418 F g-1 at 10 mV s-1 in the potential window from -0.8 to 0 V vs. Ag/AgCl, excellent rate capability (215 F g-1 at 64 A g-1), and cycling stability (93% capacitance retention after 5000 charge-discharge cycles).
   In addition to thermal annealing, chemical conversion in hot alkaline solutions represents another means to convert electrodeposited iron oxy-hydroxides into iron oxides. Chemical conversion avoids high-temperature annealing that may trigger structural deformation and particle agglomeration. One excellent example was demonstrated by Sun et al. [35]. They utilized a post chemical transition method to obtain composite mesoporous iron oxides (Fe3O4 and Fe2O3) from electro-deposited FeOOH nanosheets on a 3D exfoliated graphite substrate (EG). First, iron oxy-hydroxide nanosheets were deposited on EG using a potentiostatic method (-0.5 V vs. SCE for 80 mins in an aqueous electrolyte containing 0.05 M Fe(NH4)2(SO4)2 and 0.05 M (NH4)2SO4). Afterward, the as-deposited nanosheets were immersed in a 1 M NaOH aqueous solution for 1 h at 70 °C to convert iron oxy-hydroxides to iron oxide (containing Fe2O3 and Fe3O4) nanosheets interconnected into a honeycomb-like structure (Fig. 25d). The conversion mechanism is unclear, but we hypothesize that it is associated with dehydration of iron oxy-hydroxides during the treatment. High-resolution SEM image presented that each oxide nanosheet was composed of nanoparticles (Fig. 25d inset). The EG@Fe3O4/Fe2O3 electrode delivered an ultrahigh areal capacitance of 1.57 F cm-2 at 5 mA cm-2, corresponding to 165 F g-1 based on the total mass of the electrode. The excellent capacitive performance of the EG@Fe3O4/Fe2O3 electrode was ascribed to several factors. First, the hierarchically porous structure with mesopores and macropores in the electrode shortened ion diffusion distance. Second, the heterojunction between Fe3O4/Fe2O3 introduced a built-in electric field that facilitated charge transfer between different oxide particles. Third, the interconnected graphene sheets on EG constructed highly conductive electron transport networks that minimized capacitance loss at fast discharging rates.
5.6 Nickel/Cobalt Oxides and Hydroxides
    A critical issue that we would like to highlight first in this section is the concepts of intrinsic and extrinsic pseudocapacitive materials. Intrinsic pseudocapacitive materials refer to materials that always show pseudocapacitive characteristics (CV curves with broad or no redox peaks and plateau-free charge-discharge profiles) irrespective of size. Extrinsic pseudocapacitive materials exhibit pseudocapacitive signatures only at nanoscales. This transition of the electrochemical behaviors of extrinsic pseudocapacitive materials was due to the reduced ion diffusion distance that accelerated charge-storage kinetics, and in some cases, suppressed phase transformations [13].
    Nickel and cobalt oxides and hydroxides are extrinsic pseudocapacitive materials [254]. Charge storage in their bulk forms involves phase transitions, resulting in apparent redox peaks in CV curves (Fig. 26a) and plateaus in galvanostatic charge-discharge profiles (Fig. 26b) [255]. Therefore, these battery-like materials have been used as electrodes in aqueous batteries [256-258] or battery-type electrodes in hybrid supercapacitors [267], but cannot be studied in the context of pseudocapacitors. However, once their size shrinks to nanoscales, their pseudocapacitive features will emerge [262-266], as indicated by the broad redox peaks in CV curves (Fig. 26c) and sloping charge-discharge profiles (Fig. 26d) [267].

Fig. 26 a CV curves and b galvanostatic charge-discharge profiles of Co(OH)2 (blue) and Ni(OH)2 (red). c CV curves and d galvanostatic charge-discharge profiles of Co3O4/Co(OH)2 core/shell nanowire arrays

Fig. 26 a CV curves and b galvanostatic charge-discharge profiles of Co(OH)2 (blue) and Ni(OH)2 (red). c CV curves and d galvanostatic charge-discharge profiles of Co3O4/Co(OH)2 core/shell nanowire arrays

    Nickel and cobalt (hydro)oxides are electrochemically synthesized via cathodic deposition in aqueous solutions. Ni2+ or Co2+ combine with OH- produced from water or anions in electrolytes. Taking Co(OH)2 as an example, one reported electrodeposition mechanism in Co(NO3)2 aqueous solutions is [268]:

12 118 gs145

    Guo et al. recently demonstrated a converse voltage strategy to activate electrodeposited Co(OH)2 nanosheets on carbon fibers (Fig. 27a) [268]. First, Co(OH)2 nanosheets were electrodeposited with a constant potential of -1.5 V vs. SCE (Fig. 27b). The voltage then reversed (1.5 V vs. SCE) (Fig. 27c), triggering a phase transition from Co(OH)2 to low crystalline CoOOH (denoted as EA-CoOOH) containing abundant structural defects (oxygen vacancies, lattice disorders, and interconnected mesopores) (Fig. 27d). Quantitative analyses on the electrode kinetics revealed that the capacitance of EA-CoOOH contributing from kinetically fast, surface-controlled processes occupied 93% at 5 mV s-1, and further increased to 99% at 100 mV s-1. The nanosheets and defects altered the intrinsic battery-type behavior of CoOOH to pseudocapacitive characteristics. Outstandingly, EA-CoOOH electrode exhibited substantially enhanced capacitance than Co(OH)2 and deeply oxidized O-CoOOH electrode (Fig. 27e), delivering a high specific capacitance of 832 F g-1 at 1 A g-1 and retained 78% of the capacitance (649 F g-1) at 200 A g-1 (Fig. 27f).

Fig. 27 a Schemes of the synthesis steps of EA-CoOOH by a converse voltage method and the molecular structure of Co2+- and defect-rich EA-CoOOH. b Schemes showing the ion concentration gradients during constant voltage for electrodeposition (left) and converse voltage for oxidization (right). c Voltage profiles of electrodeposition and converse voltage stages. d TEM image of EA-CoOOH. e CV curves and g rate capability of EA-CoOOH in comparison with other electrodes

Fig. 27 a Schemes of the synthesis steps of EA-CoOOH by a converse voltage method and the molecular structure of Co2+- and defect-rich EA-CoOOH. b Schemes showing the ion concentration gradients during constant voltage for electrodeposition (left) and converse voltage for oxidization (right). c Voltage profiles of electrodeposition and converse voltage stages. d TEM image of EA-CoOOH. e CV curves and g rate capability of EA-CoOOH in comparison with other electrodes

    Introducing a secondary cation, such as Fe3+ and Al3+, in Ni/Co hydroxides to form double hydroxides have been proven to enhance capacitive performance due to charge hopping or valence interchange between different cations [96, 266, 269, 270]. Double hydroxides usually possess layered structures with large interlayer spacings (e.g., ~1 nm), which resulted in their high specific capacitance (e.g., > 2000 F g-1) [96, 106, 271]. Unfortunately, their limited potential windows in alkaline electrolytes (~0.5 V) and poor rate performance still hinder their large-scale applications in aqueous batteries and supercapacitors. Neutral aqueous electrolytes can suppress appreciable oxygen evolution in alkaline solutions and thus, extend the potential window of layered double hydroxides (LDHs) to ~1 V.
    Since anions residing between the interlayer space and the electrostatic repulsion from positively charge LDH laminate, cation intercalation into LDHs in neutral electrolytes remains thermodynamically unfavorable, resulting in unsatisfactory electrochemical performance. Recently, Li et al. demonstrated an electrochemical strategy to ease the cation intercalation into LDHs in neutral electrolytes [272]. Co-Fe LDH nanoplates were first electrodeposited on Ni foam using a cathodic electrodeposition method (Fig. 28a). Subsequently, electrochemical activation (EA) of the Co-Fe LDH nanosheets was conducted by CV between 0 – 0.6 V vs. SCE in KOH or NaOH electrolyte (denoted as EA-Co-Fe LDH). The obtained electrode exhibited pronounced electrochemical activity in various aqueous electrolytes, including NaNO3, KNO3, Ca(NO3)2, Mg(NO3)2, Zn(NO3)2 between 0 and 1 V vs. SCE (Figs. 28b, c). The specific capacitance of EA-Co-Fe LDH in NaNO3 reached 417 F g-1, which was 27 times higher than that of as-deposited Co-Fe LDH nanoplates. XRD, XPS, FT-IR, and X-ray absorption near-edge structure (XANES) all indicated that during the electrochemical activation, Co(OH)2 in CoFe-LDH was oxidized to CoOOH, resulting in hydrogen vacancies and removal of carbonate anions residing within the interlayer space of CoFe-LDH (Fig. 28d). Density functional theory calculations elucidated the adsorption sites of metal ions in LDH and EA-LDH materials (Fig. 28e). The results suggested that the adsorption of metal ions (Li+, Na+, K+, Ca2+, Mg2+, and Zn2+) on terminal H was unfavorable, whereas adsorptions of the same set of ions on O termination were thermodynamically stable, as reflected from the negative adsorption energy (Fig. 28e, blue bars). The enhanced adsorption tendency with O terminals was ascribed to the H vacancies formed during the activation step. Taking together, the formation of H vacancies and extraction of interlayer anions after the electrochemical activation together imparted the ion-intercalation capability of CoFe-LDH in neutral electrolytes.

Fig. 28 a SEM image of CoFe layered double hydroxide (LDH) nanoplates. b CV curves and c galvanostatic charge-discharge profiles of CoFe-LDH in different aqueous solutions. d Evolution of the crystal structure and composition of CoFe-LDH before and after electrochemical activation. e Adsorption energies of various metal ions over H-terminated (magenta) and O-terminated (blue) LDH laminates

Fig. 28 a SEM image of CoFe layered double hydroxide (LDH) nanoplates. b CV curves and c galvanostatic charge-discharge profiles of CoFe-LDH in different aqueous solutions. d Evolution of the crystal structure and composition of CoFe-LDH before and after electrochemical activation. e Adsorption energies of various metal ions over H-terminated (magenta) and O-terminated (blue) LDH laminates

6 Composites

    Composites that combine the merits of two or more materials are versatile electrode candidates for supercapacitor electrodes. These composites are typically electrodeposited through a one-step co-electrodeposition. The reported electrodeposited composites are classified according to their constituent species, including composites having the same group of materials, such as oxide/oxide (manganese oxide/molybdenum oxide [273, 274], nickel-manganese oxide [275], molybdenum oxide/tungsten oxide [276]), and composites with different types of materials, including oxide/conducting polymer (polypyrrole/manganese oxide [277, 278], manganese oxide/polyaniline [279, 280], manganese oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) [281, 282], polyaniline/vanadium oxide [27], polypyrrole/vanadium oxide [283, 284], polypyrrole/molybdenum oxide [285], polyaniline/tungsten oxide [286]) and oxide/hydroxide (NiAl-layered double hydroxide/manganese oxide [287] and manganese oxide/nickel hydroxide [288]). Their capacitance and corresponding synthesis methods are summarized in Table 2. Electrodeposited composites usually exhibit advantages of synergies and strong interactions among the incorporated materials that exhibit superior capacitive performance to the corresponding single-component counterparts.

Table 2 Different types of composites synthesized via electrochemical methods

12 118 table2

    Not all the active materials are co-electrodepositable in one step. One prerequisite is that the materials to be compounded must be synthesizable under similar electrochemical conditions, including pH value, polarization potential, current density, and temperature. For example, Zou et al. electrodeposited a tungsten oxide and polyaniline composite via one-step cyclic voltammetry in a mixed acidic electrolyte containing tungstic acid and aniline monomers [289]. The success of the co-deposition was owing to the acidic environment needed for both tungsten oxide and polyaniline. In contrast to the densely stacked tungsten oxide particles, the composite possessed widened pores and interconnected particles. This difference in the morphology was ascribed to the incorporated polyaniline, which acted as a structural scaffold that prevented the aggregation of tungsten oxide particles. The composite electrode exhibited enhanced pseudocapacitive performance over a wide potential window from -0.5 to 0.7 vs. SCE, which combined the potential windows of polyaniline (-0.1 – 0.7 V vs. SCE) and tungsten oxide (-0.5 – 0.3 V vs. SCE). The synergistic effects between polyaniline and tungsten oxide improved the capacitive performance of the composite. Tungsten oxide offered high pseudocapacitance; Polyaniline created inter-particle pores that increased surface area and conducted electrons to maintain superior rate capability to those of bare tungsten oxide or polyaniline.     
    Another example is a series of molybdenum-tungsten mixed oxide composites co-electrodeposited into titanium dioxide nanotube arrays using a one-step galvanostatic plating [276]. The plating electrolyte was an aqueous mixture of different concentrations of sodium molybdate dihydrate, sodium tungstate dihydrate, ethylenediamine tetra-acetic acid disodium, and ammonium acetate. The as-electrodeposited amorphous Mo-W mixed oxide film was thermally annealed at 450 °C in air to improve its crystallinity. The similarities in the valence state, ionic radius, and electronegativity of W6+ and Mo6+, were the keys to the successful co-deposition. XRD and Raman spectroscopy indicated that the fabricated Mo-W mixed oxides were monoclinic, and the crystal structure transited from m-WO3-like to β-MoO3-like when increasing the Mo/W ratio (Fig. 29a). Though pure MoO3 exhibited higher capacitance than the composite electrodes at 20 mV s-1 (Fig. 29b), its rate capability (Fig. 29c) and cycling stability (Fig. 29d) were inferior to those of the composites. Among all the synthesized Mo-W mixed oxides, 0.5MoW with a Mo/W ratio of 1 achieved the best electrochemical performance: high specific capacitance of 517.4 F g-1 at 1 A g-1 and good capacitance retention of 89.3% at 10 A g-1. The enhanced rate capability of the composites over that of MoO3 was attributed to two factors. First, the long-range ordered structure of pure oxides was disrupted in the mixed oxides, which decreased crystal size, increased surface area, and facilitated ion diffusion. Second, the disordered monoclinic crystal structure of the mixed oxides yielded a larger lattice space than those of WO3 and MoO3 alone, resulting in decreased ion diffusion resistance.

Fig. 29 a Schemes of the formation mechanism and crystal structure of Mo-W mixed oxides. b CV curves, c capacitance contributions (capacitive vs. diffusion-controlled processes), d cycling stability, and e ion transport patterns of different Mo-W mixed oxides

Fig. 29 a Schemes of the formation mechanism and crystal structure of Mo-W mixed oxides. b CV curves, c capacitance contributions (capacitive vs. diffusion-controlled processes), d cycling stability, and e ion transport patterns of different Mo-W mixed oxides

    Recently, Zhang et al. demonstrated a facile cyclic voltammetry method capable of depositing coupled strongly, layer-by-layer PPy/MoOx composite films on 3D exfoliated graphite substrates (Fig. 30a) [285]. MoOx layer was first deposited on graphite foil during the cathodic scan, while the PPy layer was subsequently grown on MoOx in the following anodic scan. Therefore, a layer-by-layer PPy/MoOx structure was obtained after multiple depositions (Figs. 30b-d). In addition, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy detected that the reduction in Mo valence and the enhancement of protonation level of PPy, both of which resulted from the strong coupling between PPy and MoOx (Fig. 30h) that are beneficial for enhancing the electrochemical performance. The composite electrode exhibited a specific capacitance of 398 F g-1 at 1 A g-1, higher than those of PPy (160 F g-1) and MoOx (320 F g-1) at identical current density (Figs. 30i-k).

Fig. 30 a Schemes of the synthesis steps, b SEM image, c TEM image, and d-g elemental mappings of layer-by-layer PPy/MoOx electrode. h Interactions between PPy and MoOx layers. i CV curves of PPy, MoOx, and PPy/MoOx. j CV curves of PPy/MoOx at different scan rates. k Rate capability of PPy, MoOx, and PPy/MoOx electrodes

Fig. 30 a Schemes of the synthesis steps, b SEM image, c TEM image, and d-g elemental mappings of layer-by-layer PPy/MoOx electrode. h Interactions between PPy and MoOx layers. i CV curves of PPy, MoOx, and PPy/MoOx. j CV curves of PPy/MoOx at different scan rates. k Rate capability of PPy, MoOx, and PPy/MoOx electrodes

    Besides one-step co-electrodeposition, composites have been prepared using multi-step electrodeposition methods [290-294]. For example, Wang and Cai et al. synthesized a VOx@MoO3 composite through a two-step electrochemical deposition. VOx nanorods were first grown on carbon cloth by cyclic voltammetry (Fig. 31a) [295]. Subsequently, a thin layer of MoO3 was coated on the VOx nanorods by a constant-current deposition for 9 seconds (Figs. 31b, c). The composite electrode VOx@MoO3 displayed an areal capacitance of 1980 mF cm-2 at 2 mA cm-2, against 1309 mF cm-2 of VOx and 233 mF cm-2 of MoO3 under identical testing conditions. Fourier-transform infrared spectroscopy revealed that the V—O—V peaks of VOx@MoO3 blue-shifted in comparison to that of VOx (Fig. 31d). The V 2p3/2 XPS spectrum showed that the binding energies of both V5+ and V4+ of VOx@MoO3 downshifted by 0.2 eV. Both results indicated that the electronic structure and chemical environment of VOx in VOx@MoO3 were modified by the strong interaction between VOx and MoO3, accounting for the improved capacitive performance. Specifically, VOx@MoO3 reached a high areal capacitance of 1980 mF cm-2 at 2 mA cm-2, exceeding 1309 mF cm-2 of VOx (Fig. 31f). Strong interaction among the incorporated materials is indispensable in realizing the synergy of the composite electrodes. Poor interactions will not only interrupt electron transport but also induce structural instability of composite [296].

Fig. 31 a, b SEM images of a VOx and b VOx@MoO3. c Elemental mappings of VOx@MoO3. d FTIR spectra of VOx and VOx@MoO3. e V 2p3/2 XPS spectra of VOx and VOx@MoO3. f Areal capacitances of VOx and VOx@MoO3 as a function of current density

Fig. 31 a, b SEM images of a VOx and b VOx@MoO3. c Elemental mappings of VOx@MoO3. d FTIR spectra of VOx and VOx@MoO3. e V 2p3/2 XPS spectra of VOx and VOx@MoO3. f Areal capacitances of VOx and VOx@MoO3 as a function of current density

7 Other Materials

    Electrodeposition has occasionally been used to synthesize nano/microstructured sulfides [297-300], polyanionic compounds [28], and selenides [301]. These materials typically exhibit higher capacitance than their corresponding oxides due to the different chemical environments created by substituting oxygen near the redox sites, which enhanced electrical conductivity or led to crystal structures favorable for fast ion diffusion, e.g., channels, slits, and pores [28, 297, 302, 303]. Electrochemical syntheses of these materials usually proceed in electrolytes containing precursors of sulfide, phosphate, or selenide.
   Using a one-step electrochemical co-deposition method, Chen et al. electrodeposited ternary nickel-cobalt sulfide nanosheets on carbon cloth [302]. The electrodeposition was conducted in a three-electrode electrolytic cell containing 5 mM CoCl2 with different concentrations of NiCl2 (1, 2.5, 5, 7.5, and 10 mM) and 0.75 M thiourea. The deposition technique was cyclic voltammetry within a potential range between -1.2 and 0.2 V vs. Ag/AgCl at 5 mV s-1 for 15 cycles. SEM displayed that the electrodeposited materials formed a dense array of highly porous nanosheets. High-angel annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) confirmed the uniform distributions of Co, Ni, and S in the deposited nanosheets. The as-deposited sulfide exhibited extrinsic pseudocapacitive characteristics of symmetric and plateau-free charge-discharge profiles. The sulfide with an optimal Ni to Co ratio (Ni-Co-S-4) showed the highest specific capacitance of 1418 F g-1 at 5 A g-1 among all Ni-Co-S compounds. It retained 90.6% of its initial capacitance when the current density increased to 100 A g-1. Falola et al. synthesized MoS2 film on a glass carbon electrode using an electrochemical deposition coupled with thermal annealing [300]. The electrochemical deposition was conducted via a CV scan from -1.2 to 1 V vs. Ag/AgCl in an aqueous electrolyte containing 10 mM (NH4)2MoS4 and 0.2 M KCl at pH=6.8, following the reaction [304]:

12 118 gs16

    The as-deposited MoS2 was thermally annealed under Ar at 600 °C to increase its crystallinity. The resultant MoS2 film exhibited a gravimetric capacitance of ~500 F g-1 at 0.75 A g-1. Increasing the film thickness from 50 to 200 nm decreased the capacitance to ~100 F g-1, which could be due to the sluggish ion diffusion kinetics throughout the thick films.
    Molybdenophosphate (A-Mo-O-P, A = Na, K, etc.) materials are a family of polyanionic phosphate compounds with open frameworks, which have recently aroused great interest in rechargeable batteries [305-308]. Similar promising performance is also expected in capacitive applications, albeit seldomly reported. Recently, Song et al. electro-synthesized a polyanionic molybdenophosphate film on a 3D exfoliated graphite substrate (EG) using a galvanostatic method [28]. The deposition electrolyte was 0.025 M ammonium molybdate mixed with 0.2 M phosphate buffer. The polyanion PO43- in the electrolyte were incorporated into the mixed-valence Mo oxide lattice (containing Mo5+ and Mo6+), replacing O atoms and forming Mo-O-P bonds (denoted as MoPO/EG). MoPO/EG was in-situ electrochemically activated in 3 M KCl using cyclic voltammetry for 10,000 cycles at a scan rate of 200 mV s-1 (denoted as A-MoPO/EG). This process allowed repeated K+ intercalation and de-intercalation. A-MoPO/EG exhibited a film morphology with an average thickness of 100 nm (Fig. 32a). EDS indicated the even contributions of Mo, O, P, and K elements in A-MoPO/EG (Figs. 32b-e). The stable P signal after the activation indicated the electrochemical stability of Mo-O-P bonds. Inductively coupled plasma mass spectroscopy (ICP-OES) suggested the chemical formulae of MoPO and A-MoPO were K0.7Na0.35Mo2O4.5PO4 and K1.55Mo2O4.2PO4, respectively. Due to the incorporation of Mo4+ after the activation, the average valence state of Mo in MoPO/EG was reduced from +5.38 to +4.84 (Figs. 32f, g). Meanwhile, the content of O vacancy increased, as indicated by the enhanced intensity in the electron spin resonance (EPR) spectra (Fig. 32h). Additionally, all Na+ in MoPO/EG was fully exchanged by K+ and additional K+ incorporated, both expanding the lattice spacing of molybdophosphate. Benefiting from the widened layers, as well as the enhanced electrical conductivity brought by the O vacancy, A-MoPO/EG showed better charge transfer kinetics than MoPO/EG (Fig. 32i). A-MoPO/EG exhibited quasi-rectangular CV curves, even at scan rates up to 200 mV s-1 (Fig. 32j). CV (Fig. 32k), XPS, and inductively coupled plasma mass spectroscopy (ICP-MS) both indicated that cation (e.g., Li+, Na+, and K+) intercalation was the primary charge storage mechanism of A-MoPO/EG. This polyanionic negative electrode exhibited a high specific capacitance of 556 F g-1 at 4.5 A g-1, a low cutoff potential window limit of -1.5 V vs. SCE, as well as high electrochemical durability without capacitance decay after 100,000 charge-discharge cycles (Fig. 32l). The authors speculated that the stable potential window of A-MoPO/EG down to -1.5 V vs. SCE could be due to the reversible K+-intercalation (around -1.4 V vs. SCE) near the water splitting potential, which suppressed hydrogen gas evolution [309].

Fig. 32 a SEM image of activated polyanionic molybdenophosphate (A-MoPO/EG) on electrochemically exfoliated graphite foil. Inset: Magnified view showing the thickness of A-MoPO. b-e EDS elemental mappings of Mo, O, P, and K in A-MoPO/EG. f, g Mo 3d XPS spectra of f MoOP/EG and g A-MoPO/EG. h EPR spectra of oxygen deficiency signals of MoOP/EG and A-MoOP/EG. i Nyquist plots of A-MoPO/EG, MoPO/EG, and MoPO/non-exfoliated graphite foil electrodes. j CV curves of A-MoPO/EG at different scan rates in 3 M aqueous KCl electrolyte. k CV curves of MoPO/EG recorded in various aqueous electrolytes. i Cycling stability of A-MoPO/EG in 100000 charge-discharge cycles

Fig. 32 a SEM image of activated polyanionic molybdenophosphate (A-MoPO/EG) on electrochemically exfoliated graphite foil. Inset: Magnified view showing the thickness of A-MoPO. b-e EDS elemental mappings of Mo, O, P, and K in A-MoPO/EG. f, g Mo 3d XPS spectra of f MoOP/EG and g A-MoPO/EG. h EPR spectra of oxygen deficiency signals of MoOP/EG and A-MoOP/EG. i Nyquist plots of A-MoPO/EG, MoPO/EG, and MoPO/non-exfoliated graphite foil electrodes. j CV curves of A-MoPO/EG at different scan rates in 3 M aqueous KCl electrolyte. k CV curves of MoPO/EG recorded in various aqueous electrolytes. i Cycling stability of A-MoPO/EG in 100000 charge-discharge cycles

    Besides electrodeposition, electrochemical exfoliation is applicable to synthesize high-quality two-dimensional (2D) nanomaterials, e.g., MoS2, boron nitride, and MXene, from their corresponding bulk materials [310]. One example is 2D titanium carbide, Ti3C2Tx (T=O and OH), belonging to the MXene family [311]. Yang et al. applied a constant potential of 5 V for 5 hours that delaminated bulk TiAlC2 into Ti3C2Tx. The experimental set-up was a two-electrode system with the first exfoliation step in an aqueous electrolyte composed of 1.0 M ammonium chloride (NH4Cl) and 0.2 M tetramethylammonium hydroxide (TMA·OH). The subsequent delamination in 25 wt% TMA·OH yielded single or double-layered Ti3C2Tx flakes with sizes up to 18.6 μm. During the electrochemical etching, Cl- ions etched Al and broke the Ti-Al bonds. The intercalation of ammonium hydroxide subsequently opened the edges of the etched materials and triggered the etching. This fluoride-free electrochemical exfoliation process provided a safe and scalable way to synthesize MXenes. As a supercapacitor electrode, the Ti3C2Tx film exhibited an areal capacitance of 220 mF cm-2 (volumetric capacitance: 439 F cm-3) at 10 mV s-1, comparable or even superior to those made from traditional wet chemical etching methods.

8 Summary and Outlook

    Electrochemical methods constitute a family of facile, economic, and versatile synthesis technology for a plethora of nano/microstructured materials as active materials in supercapacitors. In this review article, we have demonstrated that electrodeposition strategies can synthesize active materials consisting of zero-dimensional, one-dimensional, two-dimensional, and three-dimensional nano/micromaterials, including particles, rods, tubes, wires, plates, sheets, and hierarchical structures.

Fig. 33 The advantages, challenges, and future opportunities of electrochemical synthesis for supercapacitors

Fig. 33 The advantages, challenges, and future opportunities of electrochemical synthesis for supercapacitors

    To sum up, we have listed below the advantages of electrochemical technologies in preparing nano/microstructured materials for supercapacitors, or broadly speaking, electrochemical energy storage devices.
    (1) Their synthesis conditions are often mild (e.g., under room temperature) without elevated temperatures or ultrahigh pressures that might damage the structural integrity or alter the composition of the deposits and substrates. Additionally, electrochemical synthesis requires no advanced instruments and sophisticated operations, making it highly attainable and readily achievable.
    (2) Electrodeposition directly and seamlessly incorporates active materials onto current collectors, a feature eliminating the need for polymer binders and conductive additives and easing electrode preparations.
   (3) Electrodeposition offers facile tunability over the composition, crystal phase, and morphology of the deposited materials via changing depositing conditions, electrolyte compositions, current, voltage, and temperature.
  (4) Electrodeposition is possible to direct the growth of active components onto user-designed patterns, as it only deposits materials in electrically conductive regions. This deposition selectivity makes electrodeposition particularly suitable to coat active materials on supercapacitors with delicate electrode architectures, such as micro-supercapacitors with interdigitated electrodes [196, 312, 313]. Additionally, the preferred deposition at ion-accessible locations ensures the high utilization efficiency of the active materials.
    (5) Electrochemically synthesized materials are usually poorly crystalline or completely amorphous. The amorphous nature and abundant defects sometimes are beneficial for enhancing capacitance.
    Despite the above strengths, electrochemical techniques are facing many challenges and difficulties, including:
   (1) Post-treatments after electrodeposition, which are usually needed to improve the crystallinities of deposits, might alter the mechanical strength, functionality concentrations, crystal structures, or porous structure. For example, electrochemically exfoliated graphene sheets are usually stacks of 2 - 20 nm thick, instead of few- or single-layered graphene. Therefore, ultrasonication is needed to delaminate the exfoliated graphene into few-layer graphene sheets. This process, however, will inevitably break the resultant graphene sheets into pieces that will increase sheet-to-sheet contact resistance.
  (2) As discussed in Section 7, some active materials, e.g., metal sulfides, have not been extensively synthesized directly by electrodeposition. Converting metal oxides into the corresponding sulfides through sulfurization is one possible way. Still, this post-conversion usually involves high temperatures that might encounter problems with thermally unstable compounds or loss of structural water that are critical for charge transport [314].
   (3) Controlling the uniformity of deposits remains a grand hurdle for electrodeposition, as edges of the deposition substrates are usually deposited first due to the strong local electrical field.
    Projecting forward, we believe the following issues, if adequately addressed, could considerably enhance the electrochemical performance of electrodeposited materials and the practicality of electrodeposition.
   (1) Rational design and realization of hierarchical structures with one-step electrodepositions is highly attractive to make high-performance supercapacitor electrodes with high mass loadings. Alternatively, combining electrodeposition strategies with other established materials synthesis methods (e.g., hydrothermal reactions to induce Ostwald ripening [197]) could also be explored to achieve hierarchical structures.
    (2) Developing substrates with mutually high surface areas and excellent electrical conductivity is preferred to improve the ion diffusion kinetics in supercapacitors, but one must be meticulous about the deposition time and rate to avoid pore-clogging. In this respect, self-limiting electrodeposition to control the deposit thickness is necessary [315].
    (3) Diversifying the materials synthesized by electrodeposition. For example, metal sulfides have gained increasing attention as a new generation of electrochemical energy storage materials [316-318], but it is a pity that electrochemical methods can hardly synthesize them without post-treatments. Besides metal sulfides, can electrodeposition grow electrochemically active, 2D materials beyond graphene (e.g., layered metal oxides/hydroxides, boron nitride, and g-C3N4) [319], porous polymers and organic compounds, or pseudocapacitive materials compatible with non-aqueous electrolytes. The room for the development of electrochemical synthesis technologies is undoubtedly immense.
   (4) The purity of electrodeposited materials is often subpar to those made by vapor phase depositions. The multivalence could benefit charge storage but might pose challenges for studies on charge-storage mechanisms because differentiating outcomes resulting from collective behaviors of all the active components is nontrivial.
    (5) Deepening the understandings of the electrodepositions mechanism, including electrochemical nucleation and growth processes, will be highly rewarding to propel the development of electrochemical synthesis. For example, understanding the microscopic, complicated, and transient nucleation processes is imperative for controlling the morphology and uniformity of deposits. Mechanistic studies of electrodeposition, especially those developed recently, are limited. With the aid of in-situ imaging technologies practiced in battery communities, the gain of insights into the early stages of electrodeposition will accumulate steadily.
    Finally, we would like to stress that electrochemical synthesis technologies by no means can replace any existing materials synthesis methods. On the contrary, electrochemical strategies need to cooperate with other techniques to facilitate the explorations and development of high-performance electrodes in supercapacitors. Considering that electrodes play a central role in the charge-storage performances, we envision that the advancement and diversification of electrochemical synthesis technologies will directly push the development of electrochemical energy storage devices within and beyond electrochemical energy storage fields.

Acknowledgments

    Y.S. acknowledges the financial support from the National Natural Science Foundation of China (51804066) and the China Postdoctoral Science Foundation (2019T120214). X.-X.L. acknowledges the financial support from the National Natural Science Foundation of China (21673035).

 

References

[1] C. Choi, D.S. Ashby, D.M. Butts, R.H. DeBlock, Q. Wei, J. Lau, B. Dunn, Achieving high energy density and high power density with pseudocapacitive materials. Nat. Rev. Mater. 5, 5-19 (2019). https://doi.org/10.1038/s41578-019-0142-z
[2] J. Pu, Z. Shen, C. Zhong, Q. Zhou, J. Liu, J. Zhu, H. Zhang, Electrodeposition technologies for Li-based batteries: New frontiers of energy storage. Adv. Mater. 1903808 (2019). https://doi.org/10.1002/adma.201903808
[3] P. Simon, Y. Gogotsi, B. Dunn, Materials science. Where do batteries end and supercapacitors begin? Science 343, 1210-1211 (2014). https://doi.org/10.1126/science.1249625
[4] T. Liu, F. Zhang, Y. Song, Y. Li, Revitalizing carbon supercapacitor electrodes with hierarchical porous structures. J. Mater. Chem. A 5, 17705-17733 (2017). https://doi.org/10.1039/c7ta05646j
[5] B.E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications (Springer US; 2013), pp. 11-31.
[6] Y. Jiang, J. Liu, Definitions of pseudocapacitive materials: A brief review. Energ. Environ. Mater. 2, 30-37 (2019). https://doi.org/10.1002/eem2.12028
[7] J. Miller, Introduction to electrochemical capacitor technology. IEEE. Electr. Insul. M. 26, 40-47 (2010). https://doi.org/10.1109/mei.2010.5511188
[8] Y. Huang, Z. Tang, Z. Liu, J. Wei, H. Hu, C. Zhi, Toward enhancing wearability and fashion of wearable supercapacitor with modified polyurethane artificial leather electrolyte. Nano-Micro Lett. 10, 38 (2018). https://doi.org/10.1007/s40820-018-0191-7
[9] Z. Bo, C. Li, H. Yang, K. Ostrikov, J. Yan, K. Cen, Design of supercapacitor electrodes using molecular dynamics simulations. Nano-Micro Lett. 10, 33 (2018). https://doi.org/10.1007/s40820-018-0188-2
[10] Y. Liu, B. Soucaze-Guillous, P.-L. Taberna, P. Simon, Understanding of carbon-based supercapacitors ageing mechanisms by electrochemical and analytical methods. J. Power Sources 366, 123-130 (2017). https://doi.org/10.1016/j.jpowsour.2017.08.104
[11] J.R. Miller, P. Simon, Materials science. Electrochemical capacitors for energy management. Science 321, 651-652 (2008). https://doi.org/10.1126/science.1158736
[12] P. Simon, Y. Gogotsi. Materials for electrochemical capacitors. Nat. Mater. 7, 845-854 (2008). https://doi.org/10.1038/nmat2297
[13] V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate electrochemical energy storage. Energy Environ. Sci. 7, 1597-1614 (2014). https://doi.org/10.1039/c3ee44164d
[14] N. Jabeen, A. Hussain, Q. Xia, S. Sun, J. Zhu, H. Xia, High-performance 2.6 V aqueous asymmetric supercapacitors based on in situ formed Na0.5MnO2 nanosheet assembled nanowall arrays. Adv. Mater. 29, 1700804 (2017). https://doi.org/10.1002/adma.201700804
[15] W. Wei, X. Cui, W. Chen, D.G. Ivey, Manganese oxide-based materials as electrochemical supercapacitor electrodes. Chem. Soc. Rev. 40, 1697-1721 (2011). https://doi.org/10.1039/c0cs00127a
[16] Y. Wu, Y. Yang, X. Zhao, Y. Tan, Y. Liu, Z. Wang, F. Ran, A novel hierarchical porous 3D structured vanadium nitride/carbon membranes for high-performance supercapacitor negative electrodes. Nano-Micro Lett. 10, 63 (2018). https://doi.org/10.1007/s40820-018-0217-1
[17] L.L. Zhang, X. S. Zhao, Carbon-based materials as supercapacitor electrodes. Chem. Soc. Rev. 38, 2520-2531 (2009). https://doi.org/10.1039/b813846j
[18] D. Landolt, Electrodeposition science and technology in the last quarter of the twentieth century. J. Electrochem. Soc. 149, S9 (2002). https://doi.org/10.1149/1.1469028
[19] I.M. Dharmadasa, J. Haigh, Strengths and advantages of electrodeposition as a semiconductor growth technique for applications in macroelectronic devices. J. Electrochem. Soc. 153, G47-G52 (2006). https://doi.org/10.1149/1.2128120
[20] M.F. Montemor, S. Eugénio, N. Tuyen, R.P. Silva, T.M. Silva, M.J. Carmezim, Nanostructured Transition Metal Oxides Produced by Electrodeposition for Application as Redox Electrodes for Supercapacitors (Springer International Publishing, 2016), pp. 681-714. https://doi.org/10.1007/978-3-319-15266-0_14
[21] J. Wang, K.K. Manga, Q. Bao, K.P. Loh, High-yield synthesis of few-layer graphene flakes through electrochemical expansion of graphite in propylene carbonate electrolyte. J. Am. Chem. Soc. 133, 8888-8891 (2011). https://doi.org/10.1021/ja203725d
[22] W. Chen, R.B. Rakhi, L. Hu, X. Xie, Y. Cui, H.N. Alshareef, High-performance nanostructured supercapacitors on a sponge. Nano Lett. 11, 5165-5172 (2011). https://doi.org/10.1021/nl2023433
[23] X. Lang, A. Hirata, T. Fujita, M. Chen, Nanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors. Nat. Nanotechnol. 6, 232-236 (2011). https://doi.org/10.1038/nnano.2011.13
[24] T. Liu, Y. Ling, Y. Yang, L. Finn, E. Collazo, T. Zhai, Y. Tong, Y. Li, Investigation of hematite nanorod–nanoflake morphological transformation and the application of ultrathin nanoflakes for electrochemical devices. Nano Energy 12, 169-177 (2015). https://doi.org/10.1016/j.nanoen.2014.12.023
[25] T. Liu, L. Finn, M. Yu, H. Wang, T. Zhai, X. Lu, Y. Tong, Y. Li, Polyaniline and polypyrrole pseudocapacitor electrodes with excellent cycling stability. Nano Lett. 14, 2522-2527 (2014). https://doi.org/10.1021/nl500255v
[26] Y. Song, T.-Y. Liu, X.-X. Xu, D.-Y. Feng, Y. Li, X.-X. Liu, Pushing the cycling stability limit of polypyrrole for supercapacitors. Adv. Funct. Mater. 25, 4626-4632 (2015). https://doi.org/10.1002/adfm.201501709
[27] M.-H. Bai, T.-Y. Liu, F. Luan, Y. Li, X.-X. Liu, Electrodeposition of vanadium oxide–polyaniline composite nanowire electrodes for high energy density supercapacitors. J. Mater. Chem. A 2, 10882-10888 (2014). https://doi.org/10.1039/c3ta15391f
[28] Y. Song, P. Deng, Z. Qin, D. Feng, D. Guo, X. Sun, X.-X. Liu, A polyanionic molybdenophosphate anode for a 2.7 V aqueous pseudocapacitor. Nano Energy 65, 104010 (2019). https://doi.org/10.1016/j.nanoen.2019.104010
[29]  F. Liu, Z. Chen, G. Fang, Z. Wang, Y. Cai, B. Tang, J. Zhou, V2O5 Nanospheres with mixed vanadium valences as high electrochemically active aqueous zinc-ion battery cathode. Nano-Micro Lett. 11, 25 (2019). https://doi.org/10.1007/s40820-019-0256-2
[30] R.G. Kelly, J.R. Scully, D. Shoesmith, R.G. Buchheit, Electrochemical Techniques in Corrosion Science and Engineering (CRC Press; 2002). https://doi.org/10.1201/9780203909133
[31] A.J. Bard, L.R. Faulkner, J. Leddy, C.G. Zoski, Electrochemical Methods: Fundamentals and Applications (Wiley New York; 1980). 
[32] N. Elgrishi, K.J. Rountree, B.D. McCarthy, E.S. Rountree, T.T. Eisenhart, J.L. Dempsey, A practical beginner’s guide to cyclic voltammetry. J. Chem. Educ. 95, 197-206 (2017). https://doi.org/10.1021/acs.jchemed.7b00361
[33] D.K. Gosser. Cyclic Voltammetry: Simulation and Analysis of Reaction Mechanisms (VCH New York; 1993). 
[34] R. Dong, Y. Song, D. Yang, H.-Y. Shi, Z. Qin et al., Electrochemical in situ construction of vanadium oxide heterostructures with boosted pseudocapacitive charge storage. J. Mater. Chem. A 8, 1176-1183 (2020). https://doi.org/10.1039/c9ta12097a
[35] Z. Sun, X. Cai, D.-Y. Feng, Z.-H. Huang, Y. Song, X.-X. Liu, Hybrid iron oxide on three-dimensional exfoliated graphite electrode with ultrahigh capacitance for energy storage applications. ChemElectroChem 5, 1501-1508 (2018). https://doi.org/10.1002/celc.201800143
[36] Z. Sun, X. Cai, Y. Song, X.-X. Liu, Electrochemical deposition of honeycomb magnetite on partially exfoliated graphite as anode for capacitive applications. J. Power Sources 359, 57-63 (2017). https://doi.org/10.1016/j.jpowsour.2017.05.055
[37] Y. Song, T.Y. Liu, B. Yao, T.Y. Kou, D.Y. Feng, X.X. Liu, Y. Li, Amorphous mixed-valence vanadium oxide/exfoliated carbon cloth structure shows a record high cycling stability. Small 13, 1700067 (2017). https://doi.org/10.1002/smll.201700067
[38] X. Cai, Y. Song, S.-Q. Wang, X. Sun, X.-X. Liu, Extending the cycle life of high mass loading MoOx electrode for supercapacitor applications. Electrochim. Acta 325, 134877 (2019). https://doi.org/10.1016/j.electacta.2019.134877
[39] M. Paunovic, Electrochemical Deposition. Encyclopedia of Electrochemistry: Online (2007). https://doi.org/10.1002/9783527610426.bard050003
[40] D. Lincot, Electrodeposition of semiconductors. Thin Solid Films 487, 40-48 (2005). https://doi.org/10.1016/j.tsf.2005.01.032
[41] M. Paunovic, M. Schlesinger, Fundamentals of Electrochemical Deposition (New York, 1998). 
[42] D.M. Kolb, M. Przasnyski, H. Gerischer, Underpotential deposition of metals and work function differences. J. Electroanal. Chem. 54, 25-38 (1974). https://doi.org/10.1016/s0022-0728(74)80377-3
[43] E. Herrero, L.J. Buller, H.D. Abruna, Underpotential deposition at single crystal surfaces of Au, Pt, Ag and other materials. Chem. Rev. 101, 1897-1930 (2001). https://doi.org/10.1021/cr9600363
[44] Z. Shi, S. Wu, J. Lipkowski. Investigations of Cl adsorption at the Au(111) electrode in the presence of underpotentially deposited copper atoms. J. Electroanal. Chem. 384, 171-177 (1995). https://doi.org/10.1016/0022-0728(94)03747-q
[45] J.C. Ballesteros, E. Chaînet, P. Ozil, G. Trejo, Y. Meas, Electrochemical studies of Zn underpotential/overpotential deposition on a nickel electrode from non-cyanide alkaline solution containing glycine. Electrochim. Acta 56, 5443-5451 (2011). https://doi.org/10.1016/j.electacta.2011.02.106
[46] M. Palomar-Pardavé, I. González, N. Batina, New insights into evaluation of kinetic parameters for potentiostatic metal deposition with underpotential and overpotential deposition processes. J. Phys. Chem. B 104, 3545-3555 (2000). https://doi.org/10.1021/jp9931861
[47] R.E. Rettew, J.W. Guthrie, F.M. Alamgir, Layer-by-layer Pt growth on polycrystalline Au: Surface-limited redox replacement of overpotentially deposited Ni monolayers. J. Electrochem. Soc. 156, D513-D516 (2009). https://doi.org/10.1149/1.3224113
[48] M.G. Pavlović, L.J. Pavlović, N.D. Nikolić, K.I. Popov, The effect of some parameters of electrolysis on apparent density of electrolytic copper powder in galvanostatic deposition. Mater. Sci. Forum 352, 65-72 (2000). https://doi.org/10.4028/www.scientific.net/MSF.352.65
[49] R. Salazar, C. Lévy-Clément, V. Ivanova, Galvanostatic deposition of ZnO thin films. Electrochim. Acta 78, 547-556 (2012). https://doi.org/10.1016/j.electacta.2012.06.070
[50] Z.H. Huang, Y. Song, D.Y. Feng, Z. Sun, X. Sun, X.X. Liu, High mass loading MnO2 with hierarchical nanostructures for supercapacitors. ACS Nano 12, 3557-3567 (2018). https://doi.org/10.1021/acsnano.8b00621
[51] E.J. Podlaha, Selective electrodeposition of nanoparticulates into metal matrices. Nano Lett. 1, 413-416 (2001). https://doi.org/10.1021/nl015508u
[52] G. Zhu, C. Pan, W. Guo, C.Y. Chen, Y. Zhou, R. Yu, Z.L. Wang, Triboelectric-generator-driven pulse electrodeposition for micropatterning. Nano Lett. 12, 4960-4965 (2012). https://doi.org/10.1021/nl302560k
[53] Y. Su, I. Zhitomirsky, Pulse electrosynthesis of MnO2 electrodes for supercapacitors. Adv. Eng. Mater. 16, 760-766 (2014). https://doi.org/10.1002/adem.201400077
[54] M. Ghaemi, Effects of direct and pulse current on electrodeposition of manganese dioxide. J. Power Sources 111, 248-254 (2002). https://doi.org/10.1016/s0378-7753(02)00309-9
[55] H. Cheh, Electrodeposition of gold by pulsed current. J. Electrochem. Soc. 118, 551 (1971). https://doi.org/10.1149/1.2408110
[56] H.M.M.N. Hennayaka, H.S. Lee, Structural and optical properties of Zns thin film grown by pulsed electrodeposition. Thin Solid Films 548, 86-90 (2013). https://doi.org/10.1016/j.tsf.2013.09.011
[57] A. Davies, P. Audette, B. Farrow, F. Hassan, Z. Chen, J.-Y. Choi, A. Yu, Graphene-based flexible supercapacitors: Pulse-electropolymerization of polypyrrole on free-standing graphene films. J. Phys. Chem. C 115, 17612-17620 (2011). https://doi.org/10.1021/jp205568v
[58] L. Besra, M. Liu, A review on fundamentals and applications of electrophoretic deposition (EPD). Prog. Mater. Sci. 52, 1-61 (2007). https://doi.org/10.1016/j.pmatsci.2006.07.001
[59] P. Sarkar, P.S. Nicholson, Electrophoretic deposition (EPD): Mechanisms, kinetics, and application to ceramics. J. Am. Ceram. Soc. 79, 1987-2002 (1996). https://doi.org/10.1111/j.1151-2916.1996.tb08929.x
[60] C. Du, N. Pan, Supercapacitors using carbon nanotubes films by electrophoretic deposition. J. Power Sources 160, 1487-1494 (2006). https://doi.org/10.1016/j.jpowsour.2006.02.092
[61] C. Du, N. Pan, High power density supercapacitor electrodes of carbon nanotube films by electrophoretic deposition. Nanotechnology 17, 5314-5318 (2006). https://doi.org/10.1088/0957-4484/17/21/005
[62] D. Pech, M. Brunet, H. Durou, P. Huang, V. Mochalin, Y. Gogotsi, P.L. Taberna, P. Simon, Ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon. Nat. Nanotechnol. 5, 651-654 (2010). https://doi.org/10.1038/nnano.2010.162
[63] Y. Su, I. Zhitomirsky, Electrophoretic nanotechnology of composite electrodes for electrochemical supercapacitors. J. Phys. Chem. B 117, 1563-1570 (2013). https://doi.org/10.1021/jp304358q
[64] Y. Wang, I. Zhitomirsky. Electrophoretic deposition of manganese dioxide-multiwalled carbon nanotube composites for electrochemical supercapacitors. Langmuir 25, 9684-9689 (2009). https://doi.org/10.1021/la900937e
[65] H. Zhang, X. Zhang, D. Zhang, X. Sun, H. Lin, C. Wang, Y. Ma, One-step electrophoretic deposition of reduced graphene oxide and Ni(OH)2 composite films for controlled syntheses supercapacitor electrodes. J. Phys. Chem. B 117, 1616-1627 (2013). https://doi.org/10.1021/jp305198j
[66] Z.Y. Xia, S. Pezzini, E. Treossi, G. Giambastiani, F. Corticelli et al., The exfoliation of graphene in liquids by electrochemical, chemical, and sonication-assisted techniques: A nanoscale study. Adv. Funct. Mater. 23, 4684-4693 (2013). https://doi.org/10.1002/adfm.201203686
[67] A.M. Abdelkader, I.A. Kinloch, R.A. Dryfe, Continuous electrochemical exfoliation of micrometer-sized graphene using synergistic ion intercalations and organic solvents. ACS Appl. Mater. Interfaces 6, 1632-1639 (2014). https://doi.org/10.1021/am404497n
[68] A.M. Abdelkader, A.J. Cooper, R.A. Dryfe, I.A. Kinloch, How to get between the sheets: A review of recent works on the electrochemical exfoliation of graphene materials from bulk graphite. Nanoscale 7, 6944-6956 (2015). https://doi.org/10.1039/c4nr06942k
[69] A. Ambrosi, M. Pumera. Exfoliation of layered materials using electrochemistry. Chem. Soc. Rev. 47, 7213-7224 (2018). https://doi.org/10.1039/c7cs00811b
[70] R. Kumar, S. Sahoo, E. Joanni, R.K. Singh, W.K. Tan, K.K. Kar, A. Matsuda, Recent progress in the synthesis of graphene and derived materials for next generation electrodes of high performance lithium ion batteries. Prog. Energ. Combust. 75, 100786 (2019). https://doi.org/10.1016/j.pecs.2019.100786
[71] A. Ambrosi, M. Pumera, Electrochemically exfoliated graphene and graphene oxide for energy storage and electrochemistry applications. Chem 22, 153-159 (2016). https://doi.org/10.1002/chem.201503110
[72] P. Yu, S.E. Lowe, G.P. Simon, Y.L. Zhong, Electrochemical exfoliation of graphite and production of functional graphene. Curr. Opin. Colloid. Interface Sci. 20, 329-338 (2015). https://doi.org/10.1016/j.cocis.2015.10.007
[73] S. Yang, M.R. Lohe, K. Mullen, X. Feng, New-generation graphene from electrochemical approaches: Production and applications. Adv. Mater. 28, 6213-6221 (2016). https://doi.org/10.1002/adma.201505326
[74] W. Wei, G. Wang, S. Yang, X. Feng, K. Mullen, Efficient coupling of nanoparticles to electrochemically exfoliated graphene. J. Am. Chem. Soc. 137, 5576-5581 (2015). https://doi.org/10.1021/jacs.5b02284
[75] L. Wu, W. Li, P. Li, S. Liao, S. Qiu et al., Powder, paper and foam of few-layer graphene prepared in high yield by electrochemical intercalation exfoliation of expanded graphite. Small 10, 1421-1429 (2014). https://doi.org/10.1002/smll.201302730
[76] A. Ejigu, K. Fujisawa, B.F. Spencer, B. Wang, M. Terrones, I.A. Kinloch, R.A.W. Dryfe, On the role of transition metal salts during electrochemical exfoliation of graphite: Antioxidants or metal oxide decorators for energy storage applications. Adv. Funct. Mater. 28, 1804357 (2018). https://doi.org/10.1002/adfm.201804357
[77] K.S. Rao, J. Sentilnathan, H.-W. Cho, J.-J. Wu, M. Yoshimura, Soft processing of graphene nanosheets by glycine-bisulfate ionic-complex-assisted electrochemical exfoliation of graphite for reduction catalysis. Adv. Funct. Mater. 25, 298-305 (2015). https://doi.org/10.1002/adfm.201402621
[78] C.Y. Su, A.Y. Lu, Y. Xu, F.R. Chen, A.N. Khlobystov, L.J. Li, High-quality thin graphene films from fast electrochemical exfoliation. ACS Nano 5, 2332-2339 (2011). https://doi.org/10.1021/nn200025p
[79] J. Lu, J.X. Yang, J. Wang, A. Lim, S. Wang, K.P. Loh, One-pot synthesis of fluorescent carbon nanoribbons, nanoparticles, and graphene by the exfoliation of graphite in ionic liquids. ACS Nano 3, 2367-2375 (2009). https://doi.org/10.1021/nn900546b
[80] W. Cai, X. Feng, W. Hu, Y. Pan, Y. Hu, X. Gong, Functionalized graphene from electrochemical exfoliation for thermoplastic polyurethane: Thermal stability, mechanical properties, and flame retardancy. Ind. Eng. Chem. Res. 55, 10681-10689 (2016). https://doi.org/10.1021/acs.iecr.6b02579
[81] M. Mao, M. Wang, J. Hu, G. Lei, S. Chen, H. Liu, Simultaneous electrochemical synthesis of few-layer graphene flakes on both electrodes in protic ionic liquids. Chem. Commun. 49, 5301-5303 (2013). https://doi.org/10.1039/c3cc41909f
[82] H. Huang, Y. Xia, X. Tao, J. Du, J. Fang, Y. Gan, W. Zhang, Highly efficient electrolytic exfoliation of graphite into graphene sheets based on Li ions intercalation–expansion–microexplosion mechanism. J. Mater. Chem. 22, 10452-10456 (2012). https://doi.org/10.1039/c2jm00092j
[83] Y. Yang, F. Lu, Z. Zhou, W. Song, Q. Chen, X. Ji, Electrochemically cathodic exfoliation of graphene sheets in room temperature ionic liquids N-butyl, methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and their electrochemical properties. Electrochim. Acta 113, 9-16 (2013). https://doi.org/10.1016/j.electacta.2013.09.031
[84] K. Parvez, R. Li, S. R. Puniredd, Y. Hernandez, F. Hinkel, S. Wang, X. Feng, K. Mullen, Electrochemically exfoliated graphene as solution-processable, highly conductive electrodes for organic electronics. ACS Nano 7, 3598-3606 (2013). https://doi.org/10.1021/nn400576v
[85] W. Wang, W. Liu, Y. Zeng, Y. Han, M. Yu, X. Lu, Y. Tong, A novel exfoliation strategy to significantly boost the energy storage capability of commercial carbon cloth. Adv. Mater. 27, 3572-3578 (2015). https://doi.org/10.1002/adma.201500707
[86] Y. Song, S. Duan, D. Yang, R. Dong, D. Guo, X. Sun, X.-X. Liu, 3D exfoliated carbon paper toward highly loaded aqueous energy storage applications. Energy Technol. 7, 1900892 (2019). https://doi.org/10.1002/ente.201900892
[87] F. Zeng, Z. Sun, X. Sang, D. Diamond, K.T. Lau, X. Liu, D.S. Su, In situ one-step electrochemical preparation of graphene oxide nanosheet-modified electrodes for biosensors. ChemSusChem 4, 1587-1591 (2011). https://doi.org/10.1002/cssc.201100319
[88] Y. Song, D.Y. Feng, T.Y. Liu, Y. Li, X.X. Liu, Controlled partial-exfoliation of graphite foil and integration with MnO2 nanosheets for electrochemical capacitors. Nanoscale 7, 3581-3587 (2015). https://doi.org/10.1039/c4nr06559j
[89] K. Parvez, Z.S. Wu, R. Li, X. Liu, R. Graf, X. Feng, K. Mullen, Exfoliation of graphite into graphene in aqueous solutions of inorganic salts. J. Am. Chem. Soc. 136, 6083-6091 (2014). https://doi.org/10.1021/ja5017156
[90] M. Alanyalıoğlu, J.J. Segura, J. Oró-Solè, N. Casañ-Pastor, The synthesis of graphene sheets with controlled thickness and order using surfactant-assisted electrochemical processes. Carbon 50, 142-152 (2012). https://doi.org/10.1016/j.carbon.2011.07.064
[91] C.-H. Chen, S.-W. Yang, M.-C. Chuang, W.-Y. Woon, C.-Y. Su, Towards the continuous production of high crystallinity graphene via electrochemical exfoliation with molecular in situ encapsulation. Nanoscale 7, 15362-15373 (2015). https://doi.org/10.1039/c5nr03669k [92] K. Chen, D. Xue, Preparation of colloidal graphene in quantity by electrochemical exfoliation. J. Colloid Interf. Sci. 436, 41-46 (2014). https://doi.org/10.1016/j.jcis.2014.08.057
[93] A.J. Cooper, N.R. Wilson, I.A. Kinloch, R.A.W. Dryfe, Single stage electrochemical exfoliation method for the production of few-layer graphene via intercalation of tetraalkylammonium cations. Carbon 66, 340-350 (2014). https://doi.org/10.1016/j.carbon.2013.09.009
[94] A. Ejigu, I.A. Kinloch, R.A. Dryfe, Single stage simultaneous electrochemical exfoliation and functionalization of graphene. ACS Appl. Mater. Interfaces 9, 710-721 (2017). https://doi.org/10.1021/acsami.6b12868
[95] S. Yang, S. Bruller, Z.S. Wu, Z. Liu, K. Parvez et al., Organic radical-assisted electrochemical exfoliation for the scalable production of high-quality graphene. J. Am. Chem. Soc. 137, 13927-13932 (2015). https://doi.org/10.1021/jacs.5b09000
[96] X. Cai, Y. Song, Z. Sun, D. Guo, X.-X. Liu, Rate capability improvement of Co−Ni double hydroxides integrated in cathodically partially exfoliated graphite. J. Power Sources 365, 126-133 (2017). https://doi.org/10.1016/j.jpowsour.2017.08.039
[97] D.-Y. Feng, Y. Song, Z.-H. Huang, X.-X. Xu, X.-X. Liu, Rate capability improvement of polypyrrole via integration with functionalized commercial carbon cloth for pseudocapacitor. J. Power Sources 324, 788-797 (2016). https://doi.org/10.1016/j.jpowsour.2016.05.112
[98] L. Hu, X. Peng, Y. Li, L. Wang, K. Huo, L.Y. S. Lee, K.Y. Wong, P.K. Chu, Direct anodic exfoliation of graphite onto high-density aligned graphene for large capacity supercapacitors. Nano Energy 34, 515-523 (2017). https://doi.org/10.1016/j.nanoen.2017.03.007
[99] T. Liu, C. Zhu, T. Kou, M.A. Worsley, F. Qian, C. Condes, E.B. Duoss, C.M. Spadaccini, Y. Li, Ion intercalation induced capacitance improvement for graphene-based supercapacitor electrodes. ChemNanoMat 2, 635-641 (2016). https://doi.org/10.1002/cnma.201600107
[100] Y. Song, T. Liu, F. Qian, C. Zhu, B. Yao, E. Duoss, C. Spadaccini, M. Worsley, Y. Li, Three-dimensional carbon architectures for electrochemical capacitors. J. Colloid Interf. Sci. 509, 529-545 (2018). https://doi.org/10.1016/j.jcis.2017.07.081
[101] Y. Song, T.-Y. Liu, G.-L. Xu, D.-Y. Feng, B. Yao, T.-Y. Kou, X.-X. Liu, Y. Li, Tri-layered graphite foil for electrochemical capacitors. J. Mater. Chem. A 4, 7683-7688 (2016). https://doi.org/10.1039/c6ta02075e
[102] Y. Zou, S. Wang, Interconnecting carbon fibers with the in-situ electrochemically exfoliated graphene as advanced binder-free electrode materials for flexible supercapacitor. Sci. Rep. 5, 11792 (2015). https://doi.org/10.1038/srep11792
[103] S.-H. Lee, S.-D. Seo, Y.-H. Jin, H.-W. Shim, D.-W. Kim, A graphite foil electrode covered with electrochemically exfoliated graphene nanosheets. Electrochem. Commun. 12, 1419-1422 (2010). https://doi.org/10.1016/j.elecom.2010.07.036
[104] R.M. Tamgadge, A. Shukla, A PH-dependent partial electrochemical exfoliation of highly oriented pyrolytic graphite for high areal capacitance electric double layer capacitor electrode. Electrochim. Acta 325, 134933 (2019). https://doi.org/10.1016/j.electacta.2019.134933
[105] Y. Song, J.-L. Xu, X.-X. Liu, Electrochemical anchoring of dual doping polypyrrole on graphene sheets partially exfoliated from graphite foil for high-performance supercapacitor electrode. J. Power Sources 249, 48-58 (2014). https://doi.org/10.1016/j.jpowsour.2013.10.102
[106] Y. Song, X. Cai, X. Xu, X.-X. Liu, Integration of nickel–cobalt double hydroxide nanosheets and polypyrrole films with functionalized partially exfoliated graphite for asymmetric supercapacitors with improved rate capability. J. Mater. Chem. A 3, 14712-14720 (2015). https://doi.org/10.1039/c5ta02810h
[107] Z. Liu, Z.S. Wu, S. Yang, R. Dong, X. Feng, K. Mullen, Ultraflexible in-plane micro-supercapacitors by direct printing of solution-processable electrochemically exfoliated graphene. Adv. Mater. 28, 2217-2222 (2016). https://doi.org/10.1002/adma.201505304
[108] J.M. Munuera, J.I. Paredes, M. Enterria, A. Pagan, S. Villar-Rodil, M.F.R. Pereira et al., Electrochemical exfoliation of graphite in aqueous sodium halide electrolytes toward low oxygen content graphene for energy and environmental applications. ACS Appl. Mater. Interfaces 9, 24085-24099 (2017). https://doi.org/10.1021/acsami.7b04802
[109] N. Parveen, M.O. Ansari, S.A. Ansari, M.H. Cho, Simultaneous sulfur doping and exfoliation of graphene from graphite using an electrochemical method for supercapacitor electrode materials. J. Mater. Chem. A 4, 233-240 (2016). https://doi.org/10.1039/c5ta07963b
[110] J. Liu, M. Notarianni, G. Will, V.T. Tiong, H. Wang, N. Motta, Electrochemically exfoliated graphene for electrode films: Effect of graphene flake thickness on the sheet resistance and capacitive properties. Langmuir 29, 13307-13314 (2013). https://doi.org/10.1021/la403159n
[111] S.M. Jung, D.L. Mafra, C.T. Lin, H.Y. Jung, J. Kong, Controlled porous structures of graphene aerogels and their effect on supercapacitor performance. Nanoscale 7, 4386-4393 (2015). https://doi.org/10.1039/c4nr07564a
[112] X. Xiao, Y. Zeng, H. Feng, K. Xu, G. Zhong et al., Three-dimensional nitrogen-doped graphene frameworks from electrochemical exfoliation of graphite as efficient supercapacitor electrodes. ChemNanoMat 5, 152-157 (2019). https://doi.org/10.1002/cnma.201800452
[113] P. Khanra, T. Kuila, S.H. Bae, N.H. Kim, J.H. Lee, Electrochemically exfoliated graphene using 9-anthracene carboxylic acid for supercapacitor application. J. Mater. Chem. 22, 24403-24410 (2012). https://doi.org/10.1039/c2jm34838a
[114] S. Liu, J. Ou, J. Wang, X. Liu, S. Yang, A simple two-step electrochemical synthesis of graphene sheets film on the ITO electrode as supercapacitors. J. Appl. Electrochem. 41, 881-884 (2011). https://doi.org/10.1007/s10800-011-0304-1
[115] V. Thirumal, A. Pandurangan, R. Jayavel, K.S. Venkatesh, N.S. Palani, R. Ragavan, R. Ilangovan. Single pot electrochemical synthesis of functionalized and phosphorus doped graphene nanosheets for supercapacitor applications. J. Mater. Sci.-Mater. El. 26, 6319-6328 (2015). https://doi.org/10.1007/s10854-015-3219-5
[116] C. Li, H. Bai, G. Shi, Conducting polymer nanomaterials: Electrosynthesis and applications. Chem. Soc. Rev. 38, 2397-2409 (2009). https://doi.org/10.1039/b816681c
[117] G.A. Snook, P. Kao, A.S. Best, Conducting-polymer-based supercapacitor devices and electrodes. J. Power Sources 196, 1-12 (2011). https://doi.org/10.1016/j.jpowsour.2010.06.084
[118] R. Gangopadhyay, A. De. Conducting polymer nanocomposites: A brief overview. Chem. Mater. 12, 608-622 (2000). https://doi.org/10.1021/cm990537f
[119] Z. Cai, L. Li, J. Ren, L. Qiu, H. Lin, H. Peng, Flexible, weavable and efficient microsupercapacitor wires based on polyaniline composite fibers incorporated with aligned carbon nanotubes. J. Mater. Chem. A 1, 258-261 (2013). https://doi.org/10.1039/c2ta00274d
[120] K.M. Kim, Y.-G. Lee, D.O. Shin, J.M. Ko, Supercapacitive properties of layered electrodes composed of electrodeposited RuO2 and polyaniline. Electrochim. Acta 196, 309-315 (2016). https://doi.org/10.1016/j.electacta.2016.02.194
[121] H. Li, J. Song, L. Wang, X. Feng, R. Liu, W. Zeng, Z. Huang, Y. Ma, L. Wang, Flexible all-solid-state supercapacitors based on polyaniline orderly nanotubes array. Nanoscale 9, 193-200 (2017). https://doi.org/10.1039/c6nr07921k
[122] C. Tran, R. Singhal, D. Lawrence, V. Kalra, Polyaniline-coated freestanding porous carbon nanofibers as efficient hybrid electrodes for supercapacitors. J. Power Sources 293, 373-379 (2015). https://doi.org/10.1016/j.jpowsour.2015.05.054
[123] Y. Xie, D. Wang, J. Ji, Preparation and supercapacitor performance of freestanding polypyrrole/polyaniline coaxial nanoarrays. Energy Technol. 4, 714-721 (2016). https://doi.org/10.1002/ente.201500460
[124] C. Fu, H. Zhou, R. Liu, Z. Huang, J. Chen, Y. Kuang, Supercapacitor based on electropolymerized polythiophene and multi-walled carbon nanotubes composites. Mater. Chem. Phys. 132, 596-600 (2012). https://doi.org/10.1016/j.matchemphys.2011.11.074
[125] A. Laforgue, P. Simon, C. Sarrazin, J.-F. Fauvarque, Polythiophene-based supercapacitors. J. Power Sources 80, 142-148 (1999). https://doi.org/10.1016/s0378-7753(98)00258-4
[126] F.N. Ajjan, N. Casado, T. Rębiś, A. Elfwing, N. Solin, D. Mecerreyes, O. Inganäs. High performance PEDOT/lignin biopolymer composites for electrochemical supercapacitors. J. Mater. Chem. A 4, 1838-1847 (2016). https://doi.org/10.1039/c5ta10096h
[127] A.M. Osterholm, D.E. Shen, A.L. Dyer, J.R. Reynolds, Optimization of PEDOT films in ionic liquid supercapacitors: Demonstration as a power source for polymer electrochromic devices. ACS Appl. Mater. Interfaces 5, 13432-13440 (2013). https://doi.org/10.1021/am4043454
[128] J. Xu, Z. Ku, Y. Zhang, D. Chao, H. J. Fan, Integrated photo-supercapacitor based on PEDOT modified printable perovskite solar cell. Adv. Mater. Technol. 1, 1600074 (2016) https://doi.org/10.1002/admt.201600074
[129] S.-B. Yoon, K.-B. Kim, Effect of poly(3,4-ethylenedioxythiophene) (PEDOT) on the pseudocapacitive properties of manganese oxide (MnO2) in the PEDOT/MnO2/multiwall carbon nanotube (MWNT) composite. Electrochim. Acta 106, 135-142 (2013). https://doi.org/10.1016/j.electacta.2013.05.058
[130] G. Cai, P. Darmawan, M. Cui, J. Wang, J. Chen, S. Magdassi, P.S. Lee, Highly stable transparent conductive silver grid/PEDOT:PSS electrodes for integrated bifunctional flexible electrochromic supercapacitors. Adv. Energy Mater. 6, 1501882 (2016). https://doi.org/10.1002/aenm.201501882
[131] D. Yang, Y. Song, Y.-J. Ye, M. Zhang, X. Sun, X.-X. Liu, Boosting the pseudocapacitance of nitrogen-rich carbon nanorod arrays for electrochemical capacitors. J. Mater. Chem. A 7, 12086-12094 (2019). https://doi.org/10.1039/c9ta01973a
[132] Y. Huang, J. Tao, W. Meng, M. Zhu, Y. Huang, Y. Fu, Y. Gao, C. Zhi, Super-high rate stretchable polypyrrole-based supercapacitors with excellent cycling stability. Nano Energy 11, 518-525 (2015). https://doi.org/10.1016/j.nanoen.2014.10.031
[133] J.G. Ibanez, M.E. Rincon, S. Gutierrez-Granados, M. Chahma, O.A. Jaramillo-Quintero, B.A. Frontana-Uribe, Conducting polymers in the fields of energy, environmental remediation, and chemical-chiral sensors. Chem. Rev. 118, 4731-4816 (2018). https://doi.org/10.1021/acs.chemrev.7b00482
[134] G. Sabouraud, S. Sadki, N. Brodie, The mechanisms of pyrrole electropolymerization. Chem. Soc. Rev. 29, 283-293 (2000). https://doi.org/10.1039/a807124a
[135] J. Jang, Conducting Polymer Nanomaterials and Their Applications (Springer, Berlin, 2006), pp. 189-260.
[136] S.C. Erwin, L. Zu, M.I. Haftel, A.L. Efros, T.A. Kennedy, D.J. Norris, Doping semiconductor nanocrystals. Nature 436, 91-94 (2005). https://doi.org/10.1038/nature03832
[137] T.F. Otero, J.G. Martinez, Structural and biomimetic chemical kinetics: Kinetic magnitudes include structural information. Adv. Funct. Mater. 23, 404-416 (2013). https://doi.org/10.1002/adfm.201200719
[138] T. Liu, Y. Li, Addressing the achilles' heel of pseudocapacitive materials: Long‐term stability. InfoMat (2020). https://doi.org/10.1002/inf2.12105
[139] Y. Shi, L. Peng, Y. Ding, Y. Zhao, G. Yu, Nanostructured conductive polymers for advanced energy storage. Chem. Soc. Rev. 44, 6684-6696 (2015). https://doi.org/10.1039/c5cs00362h
[140] B. Anothumakkool, A.T.A. Torris, S.N. Bhange, M.V. Badiger, S. Kurungot, Electrodeposited polyethylenedioxythiophene with infiltrated gel electrolyte interface: A close contest of an all-solid-state supercapacitor with its liquid-state counterpart. Nanoscale 6, 5944-5952 (2014). https://doi.org/10.1039/c4nr00659c
[141] Y. Xie, Y. Liu, Y. Zhao, Y.H. Tsang, S.P. Lau, H. Huang, Y. Chai, Stretchable all-solid-state supercapacitor with wavy shaped polyaniline/graphene electrode. J. Mater. Chem. A 2, 9142-9149 (2014). https://doi.org/10.1039/c4ta00734d
[142] S. Lehtimaki, M. Suominen, P. Damlin, S. Tuukkanen, C. Kvarnstrom, D. Lupo. Preparation of supercapacitors on flexible substrates with electrodeposited PEDOT/graphene composites. ACS Appl. Mater. Interfaces 7, 22137-22147 (2015). https://doi.org/10.1021/acsami.5b05937
[143] Y. Huang, M. Zhu, Z. Pei, Y. Huang, H. Geng, C. Zhi, Extremely stable polypyrrole achieved via molecular ordering for highly flexible supercapacitors. ACS Appl. Mater. Interfaces 8, 2435-2440 (2016). https://doi.org/10.1021/acsami.5b11815
[144] N. Kurra, M.K. Hota, H.N. Alshareef, Conducting polymer micro-supercapacitors for flexible energy storage and Ac line-filtering. Nano Energy 13, 500-508 (2015). https://doi.org/10.1016/j.nanoen.2015.03.018
[145] N. Hui, F. Chai, P. Lin, Z. Song, X. Sun, Y. Li, S. Niu, X. Luo, Electrodeposited conducting polyaniline nanowire arrays aligned on carbon nanotubes network for high performance supercapacitors and sensors. Electrochim. Acta 199, 234-241 (2016). https://doi.org/10.1016/j.electacta.2016.03.115
[146] X.-Y. Peng, F. Luan, X.-X. Liu, D. Diamond, K.-T. Lau. pH-controlled morphological structure of polyaniline during electrochemical deposition. Electrochim. Acta 54, 6172-6177 (2009). https://doi.org/10.1016/j.electacta.2009.05.075
[147] B. Yao, L. Yuan, X. Xiao, J. Zhang, Y. Qi et al., Paper-based solid-state supercapacitors with pencil-drawing graphite/polyaniline networks hybrid electrodes. Nano Energy 2, 1071-1078 (2013). https://doi.org/10.1016/j.nanoen.2013.09.002
[148] Y. Wang, Y. Shi, L. Pan, Y. Ding, Y. Zhao, Y. Li, Y. Shi, G. Yu, Dopant-enabled supramolecular approach for controlled synthesis of nanostructured conductive polymer hydrogels. Nano Lett. 15, 7736-7741 (2015). https://doi.org/10.1021/acs.nanolett.5b03891
[149] Z. H. Huang, Y. Song, X.X. Xu, X.X. Liu, Ordered polypyrrole nanowire arrays grown on a carbon cloth substrate for a high-performance pseudocapacitor electrode. ACS Appl. Mater. Interfaces 7, 25506-25513 (2015). https://doi.org/10.1021/acsami.5b08830
[150] S. Huang, Y. Han, S. Lyu, W. Lin, P. Chen, S. Fang, A facile one-step approach for the fabrication of polypyrrole nanowire/carbon fiber hybrid electrodes for flexible high performance solid-state supercapacitors. Nanotechnology 28, 435204 (2017). https://doi.org/10.1088/1361-6528/aa84cb
[151] J. Huang, R.B. Kaner. Nanofiber formation in the chemical polymerization of aniline: A mechanistic study. Angew. Chem. Int. Ed. 43, 5817-5821 (2004). https://doi.org/10.1002/anie.200460616
[152] N.R. Chiou, C. Lu, J. Guan, L.J. Lee, A.J. Epstein, Growth and alignment of polyaniline nanofibres with superhydrophobic, superhydrophilic and other properties. Nat. Nanotechnol. 2, 354-357 (2007). https://doi.org/10.1038/nnano.2007.147
[153] K. Wang, J. Huang, Z. Wei, Conducting polyaniline nanowire arrays for high performance supercapacitors. J. Phys. Chem. C 114, 8062-8067 (2010). https://doi.org/10.1021/jp9113255
[154] Y.-J. Ye, Z.-H. Huang, Y. Song, J.-W. Geng, X.-X. Xu, X.-X. Liu, Electrochemical growth of polyaniline nanowire arrays on graphene sheets in partially exfoliated graphite foil for high-performance supercapacitive materials. Electrochim. Acta 240, 72-79 (2017). https://doi.org/10.1016/j.electacta.2017.04.025
[155] H.-P. Cong, X.-C. Ren, P. Wang, S.-H. Yu, Flexible graphene–polyaniline composite paper for high-performance supercapacitor. Energy Environ. Sci. 6, 1185-1191 (2013). https://doi.org/10.1039/c2ee24203f
[156] M. Yu, Y. Ma, J. Liu, S. Li, Polyaniline nanocone arrays synthesized on three-dimensional graphene network by electrodeposition for supercapacitor electrodes. Carbon 87, 98-105 (2015). https://doi.org/10.1016/j.carbon.2015.02.017
[157] G.F. Chen, X.X. Li, L.Y. Zhang, N. Li, T.Y. Ma, Z.Q. Liu, A porous perchlorate-doped polypyrrole nanocoating on nickel nanotube arrays for stable wide-potential-window supercapacitors. Adv. Mater. 28, 7680-7687 (2016). https://doi.org/10.1002/adma.201601781
[158] G. Lu, G. Shi, Electrochemical polymerization of pyrene in the electrolyte of boron trifluoride diethyl etherate containing trifluoroacetic acid and polyethylene glycol oligomer. J. Electroanal. Chem. 586, 154-160 (2006). https://doi.org/10.1016/j.jelechem.2005.10.020
[159] D.P. Dubal, S.H. Lee, J.G. Kim, W.B. Kim, C.D. Lokhande, Porous polypyrrole clusters prepared by electropolymerization for a high performance supercapacitor. J. Mater. Chem. 22, 3044-3052 (2012). https://doi.org/10.1039/c2jm14470k
[160] D.W. Wang, F. Li, J. Zhao, W. Ren, Z.G. Chen et al., Fabrication of graphene/polyaniline composite paper via in situ anodic electropolymerization for high-performance flexible electrode. ACS Nano 3, 1745-1752 (2009). https://doi.org/10.1021/nn900297m
[161] J. Han, Y. Dou, J. Zhao, M. Wei, D.G. Evans, X. Duan, Flexible CoAl LDH@PEDOT core/shell nanoplatelet array for high-performance energy storage. Small 9, 98-106 (2013). https://doi.org/10.1002/smll.201201336
[162] G. Lu, L. Qu, G. Shi, Electrochemical fabrication of neuron-type networks based on crystalline oligopyrene nanosheets. Electrochim. Acta 51, 340-346 (2005). https://doi.org/10.1016/j.electacta.2005.04.043
[163] X. He, W. Yang, X. Mao, L. Xu, Y. Zhou et al., All-solid state symmetric supercapacitors based on compressible and flexible free-standing 3D carbon nanotubes (CNTs)/poly(3,4-ethylenedioxythiophene) (PEDOT) sponge electrodes. J. Power Sources 376, 138-146 (2018). https://doi.org/10.1016/j.jpowsour.2017.09.084
[164] H. Park, J.W. Kim, S.Y. Hong, G. Lee, D.S. Kim, J.h. Oh et al., Microporous polypyrrole-coated graphene foam for high-performance multifunctional sensors and flexible supercapacitors. Adv. Funct. Mater. 28, 1707013 (2018). https://doi.org/10.1002/adfm.201707013
[165] C. Wang, Y. Ding, Y. Yuan, A. Cao, X. He, Q. Peng, Y. Li, Multifunctional, highly flexible, free-standing 3D polypyrrole foam. Small 12, 4070-4076 (2016). https://doi.org/10.1002/smll.201601905
[166] D.-Y. Feng, Z. Sun, Z.-H. Huang, X. Cai, Y. Song, X.-X. Liu, Highly loaded manganese oxide with high rate capability for capacitive applications. J. Power Sources 396, 238-245 (2018). https://doi.org/10.1016/j.jpowsour.2018.06.026
[167] T. Zhai, S. Xie, M. Yu, P. Fang, C. Liang, X. Lu, Y. Tong, Oxygen vacancies enhancing capacitive properties of MnO2 nanorods for wearable asymmetric supercapacitors. Nano Energy 8, 255-263 (2014). https://doi.org/10.1016/j.nanoen.2014.06.013
[168] Z. Sun, S. Firdoz, E. Y. Yap, L. Li, X. Lu, Hierarchically structured MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors. Nanoscale 5, 4379-4387 (2013). https://doi.org/10.1039/c3nr00209h
[169] W. Wei, X. Cui, W. Chen, D.G. Ivey, Phase-controlled synthesis of MnO2 nanocrystals by anodic electrodeposition: Implications for high-rate capability electrochemical supercapacitors. J. Phys. Chem. C 112, 15075-15083 (2008). https://doi.org/10.1021/jp804044s
[170] W. Wei, X. Cui, X. Mao, W. Chen, D.G. Ivey, Morphology evolution in anodically electrodeposited manganese oxide nanostructures for electrochemical supercapacitor applications—effect of supersaturation ratio. Electrochim. Acta 56, 1619-1628 (2011). https://doi.org/10.1016/j.electacta.2010.10.044
[171] F. Grote, Y. Lei, A complete three-dimensionally nanostructured asymmetric supercapacitor with high operating voltage window based on PPy and MnO2. Nano Energy 10, 63-70 (2014). https://doi.org/10.1016/j.nanoen.2014.08.019
[172] S.B. Singh, T.I. Singh, N.H. Kim, J.H. Lee, A core–shell MnO2@Au nanofiber network as a high-performance flexible transparent supercapacitor electrode. J. Mater. Chem. A 7, 10672-10683 (2019). https://doi.org/10.1039/c9ta00778d
[173] Q. Li, X.F. Lu, H. Xu, Y.X. Tong, G.R. Li, Carbon/MnO2 double-walled nanotube arrays with fast ion and electron transmission for high-performance supercapacitors. ACS Appl. Mater. Interfaces 6, 2726-2733 (2014). https://doi.org/10.1021/am405271q
[174] H. Xia, J. Feng, H. Wang, M.O. Lai, L. Lu, MnO2 nanotube and nanowire arrays by electrochemical deposition for supercapacitors. J. Power Sources 195, 4410-4413 (2010). https://doi.org/10.1016/j.jpowsour.2010.01.075
[175] J. Duay, S.A. Sherrill, Z. Gui, E. Gillette, S.B. Lee, Self-limiting electrodeposition of hierarchical MnO2 and Mn(OH)2/MnO2 nanofibril/nanowires: Mechanism and supercapacitor properties. ACS Nano 7, 1200-1214 (2013). https://doi.org/10.1021/nn3056077
[176] X. Lu, M. Yu, G. Wang, T. Zhai, S. Xie, Y. Ling, Y. Tong, Y. Li, H-TiO2@MnO2//H-TiO2@C core-shell nanowires for high performance and flexible asymmetric supercapacitors. Adv. Mater. 25, 267-272 (2013). https://doi.org/10.1002/adma.201203410 [177] E. Eustache, C. Douard, R. Retoux, C. Lethien, T. Brousse, MnO2 thin films on 3D scaffold: Microsupercapacitor electrodes competing with “bulk” carbon electrodes. Adv. Energy Mater. 5, 1500680 (2015). https://doi.org/10.1002/aenm.201500680
[178] L. Yuan, X.H. Lu, X. Xiao, T. Zhai, J. Dai et al., Flexible solid-state supercapacitors based on carbon nanoparticles/MnO2 nanorods hybrid structure. ACS Nano 6, 656-661 (2012). https://doi.org/10.1021/nn2041279
[179] S.H. Lee, H. Lee, M.S. Cho, J.-D. Nam, Y. Lee, Morphology and composition control of manganese oxide by the pulse reverse electrodeposition technique for high performance supercapacitors. J. Mater. Chem. A 1, 14606-14611 (2013). https://doi.org/10.1039/c3ta12828h
[180] X. Lu, D. Zheng, T. Zhai, Z. Liu, Y. Huang, S. Xie, Y. Tong, Facile synthesis of large-area manganese oxide nanorod arrays as a high-performance electrochemical supercapacitor. Energy Environ. Sci. 4, 2915-2921 (2011). https://doi.org/10.1039/c1ee01338f
[181] T. Beyazay, F. Eylul Sarac Oztuna, U. Unal, Self-standing reduced graphene oxide papers electrodeposited with manganese oxide nanostructures as electrodes for electrochemical capacitors. Electrochim. Acta 296, 916-924 (2019). https://doi.org/10.1016/j.electacta.2018.11.033
[182] Q. Chen, Y. Meng, C. Hu, Y. Zhao, H. Shao, N. Chen, L. Qu, MnO2-modified hierarchical graphene fiber electrochemical supercapacitor. J. Power Sources 247, 32-39 (2014). https://doi.org/10.1016/j.jpowsour.2013.08.045
[183] H. Gao, F. Xiao, C.B. Ching, H. Duan, High-performance asymmetric supercapacitor based on graphene hydrogel and nanostructured MnO2. ACS Appl. Mater. Interfaces 4, 2801-2810 (2012). https://doi.org/10.1021/am300455d
[184] S.H. Kazemi, M.A. Kiani, M. Ghaemmaghami, H. Kazemi, Nano-architectured MnO2 electrodeposited on the Cu-decorated nickel foam substrate as supercapacitor electrode with excellent areal capacitance. Electrochim. Acta 197, 107-116 (2016). https://doi.org/10.1016/j.electacta.2016.03.063
[185] M. Kundu, L. Liu, Direct growth of mesoporous MnO2 nanosheet arrays on nickel foam current collectors for high-performance pseudocapacitors. J. Power Sources 243, 676-681 (2013). https://doi.org/10.1016/j.jpowsour.2013.06.059
[186] L. Li, X. Zhang, G. Wu, X. Peng, K. Huo, P.K. Chu, Supercapacitor electrodes based on hierarchical mesoporous MnOx/nitrided TiO2 nanorod arrays on carbon fiber paper. Adv. Mater. Interfaces 2, 1400446 (2015). https://doi.org/10.1002/admi.201400446
[187] S.-M. Li, Y.-S. Wang, S.-Y. Yang, C.-H. Liu, K.-H. Chang et al., Electrochemical deposition of nanostructured manganese oxide on hierarchically porous graphene–carbon nanotube structure for ultrahigh-performance electrochemical capacitors. J. Power Sources 225, 347-355 (2013). https://doi.org/10.1016/j.jpowsour.2012.10.037
[188] W. Li, K. Xu, B. Li, J. Sun, F. Jiang et al., MnO2 nanoflower arrays with high rate capability for flexible supercapacitors. ChemElectroChem 1, 1003-1008 (2014). https://doi.org/10.1002/celc.201400006
[189] Y.-H. Lin, T.-Y. Wei, H.-C. Chien, S.-Y. Lu, Manganese oxide/carbon aerogel composite: An outstanding supercapacitor electrode material. Adv. Energy Mater. 1, 901-907 (2011). https://doi.org/10.1002/aenm.201100256
[190] Z. Pan, Y. Qiu, J. Yang, F. Ye, Y. Xu, X. Zhang, M. Liu, Y. Zhang, Ultra-endurance flexible all-solid-state asymmetric supercapacitors based on three-dimensionally coated MnOx nanosheets on nanoporous current collectors. Nano Energy 26, 610-619 (2016). https://doi.org/10.1016/j.nanoen.2016.05.053
[191] Z. Qi, A. Younis, D. Chu, S. Li, A facile and template-free one-pot synthesis of Mn3O4 nanostructures as electrochemical supercapacitors. Nano-Micro Lett. 8, 165-173 (2016). https://doi.org/10.1007/s40820-015-0074-0
[192] A. Rafique, A. Massa, M. Fontana, S. Bianco, A. Chiodoni, C.F. Pirri, S. Hernandez, A. Lamberti, Highly uniform anodically deposited film of MnO2 nanoflakes on carbon fibers for flexible and wearable fiber-shaped supercapacitors. ACS Appl. Mater. Interfaces 9, 28386-28393 (2017). https://doi.org/10.1021/acsami.7b06311
[193] W. Wei, X. Cui, W. Chen, D.G. Ivey, Electrochemical cyclability mechanism for MnO2 electrodes utilized as electrochemical supercapacitors. J. Power Sources 186, 543-550 (2009). https://doi.org/10.1016/j.jpowsour.2008.10.058
[194] Z. Ye, T. Li, G. Ma, X. Peng, J. Zhao, Morphology controlled MnO2 electrodeposited on carbon fiber paper for high-performance supercapacitors. J. Power Sources 351, 51-57 (2017). https://doi.org/10.1016/j.jpowsour.2017.03.104
[195] Y. Zheng, W. Pann, D. Zhengn, C. Sun, Fabrication of functionalized graphene-based MnO2 nanoflower through electrodeposition for high-performance supercapacitor electrodes. J. Electrochem. Soc. 163, D230-D238 (2016). https://doi.org/10.1149/2.0341606jes
[196] B. Yao, S. Chandrasekaran, J. Zhang, W. Xiao, F. Qian, C. Zhu, E.B. Duoss, C.M. Spadaccini, M.A. Worsley, Y. Li, Efficient 3D printed pseudocapacitive electrodes with ultrahigh MnO2 loading. Joule 3, 459-470 (2019). https://doi.org/10.1016/j.joule.2018.09.020
[197] Y. Song, T. Liu, B. Yao, M. Li, T. Kou et al., Ostwald ripening improves rate capability of high mass loading manganese oxide for supercapacitors. ACS Energy Lett. 2, 1752-1759 (2017). https://doi.org/10.1021/acsenergylett.7b00405
[198] Z.-H. Huang, Y. Song, X.-X. Liu, Boosting operating voltage of vanadium oxide-based symmetric aqueous supercapacitor to 2V. Chem. Eng. J. 358, 1529-1538 (2019). https://doi.org/10.1016/j.cej.2018.10.136
[199] A.M. Engstrom, F.M. Doyle, Exploring the cycle behavior of electrodeposited vanadium oxide electrochemical capacitor electrodes in various aqueous environments. J. Power Sources 228, 120-131 (2013). https://doi.org/10.1016/j.jpowsour.2012.11.075
[200] A. Ghosh, E.J. Ra, M. Jin, H.-K. Jeong, T.H. Kim, C. Biswas, Y.H. Lee, High pseudocapacitance from ultrathin V2O5 films electrodeposited on self-standing carbon-nanofiber paper. Adv. Funct. Mater. 21, 2541-2547 (2011). https://doi.org/10.1002/adfm.201002603
[201] R.S. Ingole, B.J. Lokhande, Electrochemically synthesized mesoporous architecture of vanadium oxide on flexible stainless steel for high performance supercapacitor. J. Mater. Sci.-Mater. Electron. 28, 10951-10957 (2017). https://doi.org/10.1007/s10854-017-6875-9
[202] C.-H. Lai, C.-K. Lin, S.-W. Lee, H.-Y. Li, J.-K. Chang, M.-J. Deng, Nanostructured Na-doped vanadium oxide synthesized using an anodic deposition technique for supercapacitor applications. J. Alloy Compd. 536, S428-S431 (2012). https://doi.org/10.1016/j.jallcom.2011.12.038
[203] E. Armstrong, M. O'Sullivan, J. O'Connell, J.D. Holmes, C. O'Dwyer, 3D vanadium oxide inverse opal growth by electrodeposition. J. Electrochem. Soc. 162, D605-D612 (2015). https://doi.org/10.1149/2.0541514jes
[204] D.L. da Silva, R.G. Delatorre, G. Pattanaik, G. Zangari, W. Figueiredo, R.-P. Blum, H. Niehus, A.A. Pasa, Electrochemical synthesis of vanadium oxide nanofibers. J. Electrochem. Soc. 155, E14 (2008). https://doi.org/10.1149/1.2804856
[205] Y.R. Lu, T.Z. Wu, C.L. Chen, D.H. Wei, J.L. Chen, W.C. Chou, C.L. Dong, Mechanism of electrochemical deposition and coloration of electrochromic V2O5 nano thin films: An in situ X-ray spectroscopy study. Nanoscale Res. Lett. 10, 387 (2015). https://doi.org/10.1186/s11671-015-1095-9
[206] D. Rehnlund, M. Valvo, K. Edström, L. Nyholm, Electrodeposition of vanadium oxide/manganese oxide hybrid thin films on nanostructured aluminum substrates. J. Electrochem. Soc. 161, D515-D521 (2014). https://doi.org/10.1149/2.0511410jes
[207] K. Takahashi, S.J. Limmer, Y. Wang, G. Cao, Synthesis and electrochemical properties of single-crystal V2Onanorod arrays by template-based electrodeposition. J. Phys. Chem. B 108, 9795-9800 (2004). https://doi.org/10.1021/jp0491820
[208] Y. Wang, K. Takahashi, H. Shang, G. Cao, Synthesis and electrochemical properties of vanadium pentoxide nanotube arrays. J. Phys. Chem. B 109, 3085-3088 (2005). https://doi.org/10.1021/jp044286w
[209] J.-D. Xie, H.-Y. Li, T.-Y. Wu, J.-K. Chang, Y.A. Gandomi, Electrochemical energy storage of nanocrystalline vanadium oxide thin films prepared from various plating solutions for supercapacitors. Electrochim. Acta 273, 257-263 (2018). https://doi.org/10.1016/j.electacta.2018.04.007
[210] H. Drosos, A. Sapountzis, E. Koudoumas, N. Katsarakis, D. Vernardou. Effect of deposition current density on electrodeposited vanadium oxide coatings. J. Mater. Chem. 159, E145-E147 (2012). https://doi.org/10.1149/2.017208jes
[211] Q. Qu, Y. Zhu, X. Gao, Y. Wu, Core-shell structure of polypyrrole grown on V2O5 nanoribbon as high performance anode material for supercapacitors. Adv. Energy Mater. 2, 950-955 (2012). https://doi.org/10.1002/aenm.201200088
[212] J.G. Wang, H. Liu, H. Liu, W. Hua, M. Shao, Interfacial constructing flexible V2O5@polypyrrole core-shell nanowire membrane with superior supercapacitive performance. ACS Appl. Mater. Interfaces 10, 18816-18823 (2018). https://doi.org/10.1021/acsami.8b05660
[213] T.M. McEvoy, K.J. Stevenson, Elucidation of the electrodeposition mechanism of molybdenum oxide from iso- and peroxo-polymolybdate solutions. J. Mater. Res. 19, 429-438 (2011). https://doi.org/10.1557/jmr.2004.19.2.429
[214] V.S. Saji, C.W. Lee, Molybdenum, molybdenum oxides, and their electrochemistry. ChemSusChem 5, 1146-1161 (2012). https://doi.org/10.1002/cssc.201100660
[215] W. Zhang, H. Li, C.J. Firby, M. Al-Hussein, A.Y. Elezzabi, Oxygen-vacancy-tunable electrochemical properties of electrodeposited molybdenum oxide films. ACS Appl. Mater. Interfaces 11, 20378-20385 (2019). https://doi.org/10.1021/acsami.9b04386
[216] H. Farsi, F. Gobal, H. Raissi, S. Moghiminia, The pH effects on the capacitive behavior of nanostructured molybdenum oxide. J. Solid State Electrochem. 14, 681-686 (2009). https://doi.org/10.1007/s10008-009-0828-z
[217] H. Farsi, F. Gobal, H. Raissi, S. Moghiminia, On the pseudocapacitive behavior of nanostructured molybdenum oxide. J. Solid State Electrochem. 14, 643-650 (2009). https://doi.org/10.1007/s10008-009-0830-5
[218] T. Tsumura, Lithium insertion/extraction reaction on crystalline MoO3. Solid State Ionics 104, 183-189 (1997). https://doi.org/10.1016/s0167-2738(97)00418-9
[219] C.R. Clayton, Y.C. Lu, Electrochemical and XPS evidence of the aqueous formation of Mo2O5. Surf. Inter. Anal. 14, 66-70 (1989). https://doi.org/10.1002/sia.740140114
[220] C. Liu, Z. Xie, W. Wang, Z. Li, Z. Zhang, The Ti@MoO>x nanorod array as a threedimensional film electrode for micro-supercapacitors. Electrochem. Commun. 44, 23-26 (2014). https://doi.org/10.1016/j.elecom.2014.04.007
[221] C. Liu, Z. Xie, W. Wang, Z. Li, Z. Zhang, Fabrication of MoOfilm as a conductive anode material for micro-supercapacitors by electrodeposition and annealing. J. Electrochem. Soc. 161, A1051-A1057 (2014). https://doi.org/10.1149/2.081406jes
[222] K.K. Upadhyay, T. Nguyen, T.M. Silva, M.J. Carmezim, M.F. Montemor, Electrodeposited MoOx films as negative electrode materials for redox supercapacitors. Electrochim. Acta 225, 19-28 (2017). https://doi.org/10.1016/j.electacta.2016.12.106
[223] D.D. Yao, J.Z. Ou, K. Latham, S. Zhuiykov, A.P. O’Mullane, K. Kalantar-zadeh, Electrodeposited α- and β-phase MoO3 films and investigation of their gasochromic properties. Cryst. Growth Des. 12, 1865-1870 (2012). https://doi.org/10.1021/cg201500b
[224] F. Wang, Z. Liu, X. Wang, X. Yuan, X. Wu, Y. Zhu, L. Fu, Y. Wu, A conductive polymer coated MoOanode enables an Al-ion capacitor with high performance. J. Mater. Chem. A 4, 5115-5123 (2016). https://doi.org/10.1039/c6ta01398h
[225] S. Sun, X. Liao, Y. Sun, G. Yin, Y. Yao, Z. Huang, X. Pu, Facile synthesis of a α-MoO3 nanoplate/TiO2 nanotube composite for high electrochemical performance. RSC Adv. 7, 22983-22989 (2017). https://doi.org/10.1039/c7ra01164d
[226] X. Xiao, T. Ding, L. Yuan, Y. Shen, Q. Zhong et al., WO3x/MoO3core/shell nanowires on carbon fabric as an anode for all-solid-state asymmetric supercapacitors. Adv. Energy Mater. 2, 1328-1332 (2012). https://doi.org/10.1002/aenm.201200380
[227] G.-R. Li, Z.-L. Wang, F.-L. Zheng, Y.-N. Ou, Y.-X. Tong, ZnO@MoO3 core/shell nanocables: Facile electrochemical synthesis and enhanced supercapacitor performances. J. Mater. Chem. 21, 4217-4221 (2011). https://doi.org/10.1039/c0jm03500a
[228] J.-C. Liu, H. Li, M. Batmunkh, X. Xiao, Y. Sun et al., Structural engineering to maintain the superior capacitance of molybdenum oxides at ultrahigh mass loadings. J. Mater. Chem. A 7, 23941-23948 (2019). https://doi.org/10.1039/c9ta04835a
[229] X.F. Lu, Z.X. Huang, Y.X. Tong, G.R. Li, Asymmetric supercapacitors with high energy density based on helical hierarchical porous NaxMnO2 and MoO2. Chem. Sci. 7, 510-517 (2016). https://doi.org/10.1039/c5sc03326h
[230] H. Zheng, J.Z. Ou, M.S. Strano, R.B. Kaner, A. Mitchell, K. Kalantar-zadeh, Nanostructured tungsten oxide-properties, synthesis, and applications. Adv. Funct. Mater. 21, 2175-2196 (2011). https://doi.org/10.1002/adfm.201002477
[231] B. Yang, H. Li, M. Blackford, V. Luca, Novel low density mesoporous WO3 films prepared by electrodeposition. Curr. Appl. Phys. 6, 436-439 (2006). https://doi.org/10.1016/j.cap.2005.11.035
[232] S. Wang, X. Feng, J. Yao, L. Jiang, Controlling wettability and photochromism in a dual-responsive tungsten oxide film. Angew. Chem. Int. Ed. 45, 1264-1267 (2006). https://doi.org/10.1002/anie.200502061
[233] P. Shen, N. Chi, K.-Y. Chan, Morphology of electrodeposited WO3 studied by atomic force microscopy. J. Mater. Chem. 10, 697-700 (2000). https://doi.org/10.1039/a908348k
[234] Z. Sun, X.G. Sang, Y. Song, D. Guo, D.Y. Feng, X. Sun, X.X. Liu, A high performance tungsten bronze electrode in a mixed electrolyte and applications in supercapacitors. Chem. Commun. 55, 14323-14326 (2019). https://doi.org/10.1039/c9cc06845g
[235] G. Yang, X.-X. Liu, Electrochemical fabrication of interconnected tungsten bronze nanosheets for high performance supercapacitor. J. Power Sources 383, 17-23 (2018). https://doi.org/10.1016/j.jpowsour.2018.02.035
[236] T. Pauporté, A simplified method for WO3 electrodeposition. J. Electrochem. Soc. 149, C539-C545 (2002). https://doi.org/10.1088/2053-1583/ab1e0a
[237] S.H. Baeck, K.S. Choi, T.F. Jaramillo, G.D. Stucky, E.W. McFarland, Enhancement of photocatalytic and electrochromic properties of electrochemically fabricated mesoporous WO3 thin films. Adv. Mater. 15, 1269-1273 (2003). https://doi.org/10.1002/adma.200304669
[238] A.K. Srivastava, M. Deepa, S. Singh, R. Kishore, S.A. Agnihotry, Microstructural and electrochromic characteristics of electrodeposited and annealed WO3 films. Solid State Ionics 176, 1161-1168 (2005). https://doi.org/10.1016/j.ssi.2004.10.006
[239] M. Deepa, A.K. Srivastava, T.K. Saxena, S.A. Agnihotry, Annealing induced microstructural evolution of electrodeposited electrochromic tungsten oxide films. Appl. Surf. Sci. 252, 1568-1580 (2005). https://doi.org/10.1016/j.apsusc.2005.02.123
[240] M. Deepa, M. Kar, S.A. Agnihotry, Electrodeposited tungsten oxide films: Annealing effects on structure and electrochromic performance. Thin Solid Films 468, 32-42 (2004). https://doi.org/10.1016/j.tsf.2004.04.056
[241] C. Yao, B. Wei, H. Li, G. Wang, Q. Han, H. Ma, Q. Gong, Carbon-encapsulated tungsten oxide nanowires as a stable and high-rate anode material for flexible asymmetric supercapacitors. J. Mater. Chem. A 5, 56-61 (2017). https://doi.org/10.1039/c6ta08274b
[242] Y. Zeng, M. Yu, Y. Meng, P. Fang, X. Lu, Y. Tong, Iron-based supercapacitor electrodes: Advances and challenges. Adv. Energy Mater. 6, 1601053 (2016). https://doi.org/10.1002/aenm.201601053
[243] Q. Xia, M. Xu, H. Xia, J. Xie, Nanostructured iron oxide/hydroxide-based electrode materials for supercapacitors. ChemNanoMat 2, 588-600 (2016). https://doi.org/10.1002/cnma.201600110
[244] J. Chen, J. Xu, S. Zhou, N. Zhao, C.-P. Wong, Amorphous nanostructured FeOOH and Co–Ni double hydroxides for high-performance aqueous asymmetric supercapacitors. Nano Energy 21 145-153 (2016). https://doi.org/10.1016/j.nanoen.2015.12.029
[245] X.-F. Lu, X.-Y. Chen, W. Zhou, Y.-X. Tong, G.-R. Li, α-Fe2O3@PANI core–shell nanowire arrays as negative electrodes for asymmetric supercapacitors. ACS Appl. Mater. Interfaces 7, 14843-14850 (2015). https://doi.org/10.1021/acsami.5b03126
[246] J. Liu, M. Zheng, X. Shi, H. Zeng, H. Xia, Amorphous FeOOH quantum dots assembled mesoporous film anchored on graphene nanosheets with superior electrochemical performance for supercapacitors. Adv. Funct. Mater. 26, 919-930 (2016). https://doi.org/10.1002/adfm.201504019
[247] J. Sun, Y. Huang, C. Fu, Y. Huang, M. Zhu, X. Tao, C. Zhi, H. Hu, A high performance fiber-shaped PEDOT@MnO2//C@Fe3Oasymmetric supercapacitor for wearable electronics. J. Mater. Chem. A 4, 14877-14883 (2016). https://doi.org/10.1039/c6ta05898a
[248] M.-S. Wu, R.-H. Lee, Electrochemical growth of iron oxide thin films with nanorods and nanosheets for capacitors. J. Electrochem. Soc. 156, A737-A743 (2009). https://doi.org/10.1149/1.3160547
[249] K.A. Owusu, L. Qu, J. Li, Z. Wang, K. Zhao et al., Low-crystalline iron oxide hydroxide nanoparticle anode for high-performance supercapacitors. Nat. Commun. 8 14264 (2017). https://doi.org/10.1038/ncomms14264
[250] W. Fu, E. Zhao, X. Ren, A. Magasinski, G. Yushin, Hierarchical fabric decorated with carbon nanowire/metal oxide nanocomposites for 1.6V wearable aqueous supercapacitors. Adv. Energy Mater. 8, 1703454, (2018). https://doi.org/10.1002/aenm.201703454
[251] Y.C. Chen, Y.G. Lin, Y.K. Hsu, S.C. Yen, K.H. Chen, L.C. Chen, Novel iron oxyhydroxide lepidocrocite nanosheet as ultrahigh power density anode material for asymmetric supercapacitors. Small 10, 3803-3810 (2014). https://doi.org/10.1002/smll.201400597
[252] X. Tang, R. Jia, T. Zhai, H. Xia, Hierarchical Fe3O4@Fe2O3 core-shell nanorod arrays as high-performance anodes for asymmetric supercapacitors. ACS Appl. Mater. Interfaces 7, 27518-27525 (2015). https://doi.org/10.1021/acsami.5b09766
[253] Y. Li, J. Xu, T. Feng, Q. Yao, J. Xie, H. Xia, Fe2O3 nanoneedles on ultrafine nickel nanotube arrays as efficient anode for high-performance asymmetric supercapacitors. Adv. Funct. Mater. 27, 1606728 (2017). https://doi.org/10.1002/adfm.201606728
[254] T. Deng, W. Zhang, O. Arcelus, J.G. Kim, J. Carrasco et al., Atomic-level energy storage mechanism of cobalt hydroxide electrode for pseudocapacitors. Nat. Commun. 8, 15194 (2017). https://doi.org/10.1038/ncomms15194
[255] V. Gupta, S. Gupta, N. Miura, Potentiostatically deposited nanostructured CoxNi1layered double hydroxides as electrode materials for redox-supercapacitors. J. Power Sources 175, 680-685 (2008). https://doi.org/10.1016/j.jpowsour.2007.09.004
[256] Y. Zeng, Z. Lai, Y. Han, H. Zhang, S. Xie, X. Lu, Oxygen-vacancy and surface modulation of ultrathin nickel cobaltite nanosheets as a high-energy cathode for advanced Zn-ion batteries. Adv. Mater. 30, 1802396 (2018). https://doi.org/10.1002/adma.201802396
[257] Y. Zeng, Y. Meng, Z. Lai, X. Zhang, M. Yu et al., An ultrastable and high-performance flexible fiber-shaped Ni-Zn battery based on a Ni-NiO heterostructured nanosheet cathode. Adv. Mater. 29, 1702698 (2017). https://doi.org/10.1002/adma.201702698
[258] M. Huang, M. Li, C. Niu, Q. Li, L. Mai, Recent advances in rational electrode designs for high-performance alkaline rechargeable batteries. Adv. Funct. Mater. 29, 1807847 (2019). https://doi.org/10.1002/adfm.201807847
[259] Y. Liu, N. Fu, G. Zhang, M. Xu, W. Lu, L. Zhou, H. Huang, Design of hierarchical Ni-Co@Ni-Co layered double hydroxide core-shell structured nanotube array for high-performance flexible all-solid-state battery-type supercapacitors. Adv. Funct. Mater. 27, 1605307 (2017). https://doi.org/10.1002/adfm.201605307
[260] G. Nagaraju, S. Chandra Sekhar, L. Krishna Bharat, J.S. Yu, Wearable fabrics with self-branched bimetallic layered double hydroxide coaxial nanostructures for hybrid supercapacitors. ACS Nano 11, 10860-10874 (2017). https://doi.org/10.1021/acsnano.7b04368 [261] T. Wang, B. Zhao, H. Jiang, H.-P. Yang, K. Zhang et al., Electro-deposition of CoNi2S4 flower-like nanosheets on 3D hierarchically porous nickel skeletons with high electrochemical capacitive performance. J. Mater. Chem. A 3, 23035-23041 (2015). https://doi.org/10.1039/c5ta04705f
[262] H. Xu, C. Zhang, W. Zhou, G.R. Li, Co(OH)2/RGO/NiO sandwich-structured nanotube arrays with special surface and synergistic effects as high-performance positive electrodes for asymmetric supercapacitors. Nanoscale 7, 16932-16942 (2015). https://doi.org/10.1039/c5nr04449a
[263] G. Xiong, P. He, D. Wang, Q. Zhang, T. Chen, T.S. Fisher, Hierarchical Ni-Co hydroxide petals on mechanically robust graphene petal foam for high-energy asymmetric supercapacitors. Adv. Funct. Mater. 26, 5460-5470 (2016). https://doi.org/10.1002/adfm.201600879
[264] Hierarchical multicomponent electrode with interlaced Ni(OH)2 nanoflakes wrapped zinc cobalt sulfide nanotube arrays for sustainable high-performance supercapacitors. Adv. Energy Mater. 7, 1701228 (2017). https://doi.org/10.1002/aenm.201701228
[265] X. Lu, X. Huang, S. Xie, T. Zhai, C. Wang et al., Controllable synthesis of porous nickel–cobalt oxide nanosheets for supercapacitors. J. Mater. Chem. 22, 13357-13364 (2012). https://doi.org/10.1039/c2jm30927k
[266] H. Li, Y. Gao, C. Wang, G. Yang, A simple electrochemical route to access amorphous mixed-metal hydroxides for supercapacitor electrode materials. Adv. Energy Mater. 5, 1401767 (2015). https://doi.org/10.1002/aenm.201401767
[267] X. Xia, J. Tu, Y. Zhang, J. Chen, X. Wang, C. Gu, C. Guan, J. Luo, H.J. Fan, Porous hydroxide nanosheets on preformed nanowires by electrodeposition: Branched nanoarrays for electrochemical energy storage. Chem. Mater. 24, 3793-3799 (2012). https://doi.org/10.1021/cm302416d
[268] W. Guo, C. Yu, S. Li, X. Song, H. Huang et al., A universal converse voltage process for triggering transition metal hybrids in situ phase restruction toward ultrahigh-rate supercapacitors. Adv. Mater. 31, 1901241 (2019). https://doi.org/10.1002/adma.201901241
[269] J.C. Chen, C.-T.Hsu, C.-C. Hu, Superior capacitive performances of binary nickel–cobalt hydroxide nanonetwork prepared by cathodic deposition. J. Power Sources 253, 205-213 (2014). https://doi.org/10.1016/j.jpowsour.2013.12.073
[270] R. Li, S. Wang, Z. Huang, F. Lu, T. He, NiCo2S4@Co(OH)2 core-shell nanotube arrays in situ grown on Ni foam for high performances asymmetric supercapacitors. J. Power Sources 312, 156-164 (2016). https://doi.org/10.1016/j.jpowsour.2016.02.047
[271] H. Pourfarzad, M. Shabani-Nooshabadi, M. R. Ganjali, H. Kashani, Synthesis of Ni–Co-Fe layered double hydroxide and Fe2O3/graphene nanocomposites as actively materials for high electrochemical performance supercapacitors. Electrochim. Acta 317, 83-92 (2019). https://doi.org/10.1016/j.electacta.2019.05.122
[272] Z. Li, H. Duan, M. Shao, J. Li, D. O'Hare, M. Wei, Z.L. Wang, Ordered-vacancy-induced cation intercalation into layered double hydroxides: A general approach for high-performance supercapacitors. Chem 4, 2168-2179 (2018). https://doi.org/10.1016/j.chempr.2018.06.007
[273] G. Lee, J.W. Kim, H. Park, J.Y. Lee, H. Lee et al., dynamically stretchable, planar supercapacitors with buckled carbon nanotube/Mn-Mo mixed oxide electrodes and air-stable organic electrolyte. ACS Nano 13, 855-866 (2019). https://doi.org/10.1021/acsnano.8b08645
[274] K. Okamura, R. Inoue, T. Sebille, K. Tomono, M. Nakayama, An approach to optimize the composition of supercapacitor electrodes consisting of manganese-molybdenum mixed oxide and carbon nanotubes. J. Electrochem. Soc. 158, A711 (2011). https://doi.org/10.1149/1.3578039
[275] Y.-H. Li, Q.-Y. Li, H.-Q. Wang, Y.-G. Huang, X.-H. Zhang et al., Synthesis and electrochemical properties of nickel–manganese oxide on MWCNTs/CFP substrate as a supercapacitor electrode. Appl. Energy 153, 78-86 (2015). https://doi.org/10.1016/j.apenergy.2014.09.055
[276] H. Zhou, X. Zou, K. Zhang, P. Sun, M.S. Islam, J. Gong, Y. Zhang, J. Yang, Molybdenum-tungsten mixed oxide deposited into titanium dioxide nanotube arrays for ultrahigh rate supercapacitors. ACS Appl. Mater. Interfaces 9, 18699-18709 (2017). https://doi.org/10.1021/acsami.7b01871
[277] E. Karaca, D. Gökcen, N.Ö. Pekmez, K. Pekmez, Electrochemical synthesis of PPy composites with nanostructured MnOx, CoOx, NiOx, and FeOx in acetonitrile for supercapacitor applications. Electrochim. Acta 305, 502-513 (2019). https://doi.org/10.1016/j.electacta.2019.03.060
[278] C.H. Ng, H.N. Lim, Y.S. Lim, W.K. Chee, N.M. Huang, Fabrication of flexible polypyrrole/graphene oxide/manganese oxide supercapacitor. Int. J. Energy Res. 39, 344-355 (2015). https://doi.org/10.1002/er.3247
[279] L. Chen, L.-J. Sun, F. Luan, Y. Liang, Y. Li, X.-X. Liu, Synthesis and pseudocapacitive studies of composite films of polyaniline and manganese oxide nanoparticles. J. Power Sources 195, 3742-3747 (2010). https://doi.org/10.1016/j.jpowsour.2009.12.036
[280] J. Kim, H. Ju, A.I. Inamdar, Y. Jo, J. Han, H. Kim, H. Im, Synthesis and enhanced electrochemical supercapacitor properties of Ag–MnO2–polyaniline nanocomposite electrodes. Energy 70, 473-477 (2014). https://doi.org/10.1016/j.energy.2014.04.018
[281] Z. Su, C. Yang, C. Xu, H. Wu, Z. Zhang et al., Co-electro-deposition of the MnO2–PEDOT:PSS nanostructured composite for high areal mass, flexible asymmetric supercapacitor devices. J. Mater. Chem. A 1, 12432 (2013). https://doi.org/10.1039/c3ta13148c
[282] Z. Wang, J. Du, M. Zhang, J. Yu, H. Liu et al., Continuous preparation of high performance flexible asymmetric supercapacitor with a very fast, low-cost, simple and scalable electrochemical co-deposition method. J. Power Sources 437, 226827 (2019). https://doi.org/10.1016/j.jpowsour.2019.226827
[283] P. Asen, S. Shahrokhian, A. Iraji zad, One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor. Int. J. Hydrog. Energy 42, 21073-21085 (2017). https://doi.org/10.1016/j.ijhydene.2017.07.008
[284] M.H. Bai, L.J. Bian, Y. Song, X.X. Liu, Electrochemical codeposition of vanadium oxide and polypyrrole for high-performance supercapacitor with high working voltage. ACS Appl. Mater. Interfaces 6, 12656-12664 (2014). https://doi.org/10.1021/am502630g
[285] M.-Y. Zhang, Y. Song, D. Guo, D. Yang, X. Sun et al., Strongly coupled polypyrrole/molybdenum oxide hybrid films via electrochemical layer-by-layer assembly for pseudocapacitors. J. Mater. Chem. A 7, 9815-9821 (2019). https://doi.org/10.1039/c9ta00705a
[286] J.-W. Geng, Y.-J. Ye, D. Guo, X.-X. Liu, Concurrent electropolymerization of aniline and electrochemical deposition of tungsten oxide for supercapacitor. J. Power Sources 342, 980-989 (2017). https://doi.org/10.1016/j.jpowsour.2017.01.029
[287] Y. Wang, S. Dong, X. Wu, M. Li, One-step electrodeposition of MnO2@NiAl layered double hydroxide nanostructures on the nickel foam for high-performance supercapacitors. J. Electrochem. Soc. 164, H56-H62 (2016). https://doi.org/10.1149/2.0861702jes
[288] Z. Zeng, P. Sun, J. Zhu, X. Zhu, Porous petal-like Ni(OH)2−MnOx nanosheet electrodes grown on carbon fiber paper for supercapacitors. Surf. Inter. 8, 73-82 (2017). https://doi.org/10.1016/j.surfin.2017.04.011
[289] B.-X. Zou, Y. Liang, X.-X. Liu, D. Diamond, K.-T. Lau, Electrodeposition and pseudocapacitive properties of tungsten oxide/polyaniline composite. J. Power Sources 196, 4842-4848 (2011). https://doi.org/10.1016/j.jpowsour.2011.01.073
[290] X. Fan, X. Wang, G. Li, A. Yu, Z. Chen, High-performance flexible electrode based on electrodeposition of polypyrrole/MnO2 on carbon cloth for supercapacitors. J. Power Sources 326, 357-364 (2016). https://doi.org/10.1016/j.jpowsour.2016.05.047
[291] C.-C. Hu, C.-Y. Hung, K.-H. Chang, Y.-L. Yang, A hierarchical nanostructure consisting of amorphous MnO2, Mn3O4 nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors. J. Power Sources 196, 847-850 (2011). https://doi.org/10.1016/j.jpowsour.2010.08.001
[292] P. Tang, L. Han, L. Zhang, Facile synthesis of graphite/PEDOT/MnO2 composites on commercial supercapacitor separator membranes as flexible and high-performance supercapacitor electrodes. ACS Appl. Mater. Interfaces 6, 10506-10515 (2014). https://doi.org/10.1021/am5021028
[293] N. Zhao, H. Fan, M. Zhang, C. Wang, X. Ren et al., Preparation of partially-cladding NiCo-LDH/Mn3O4 composite by electrodeposition route and its excellent supercapacitor performance. J. Alloy. Compd. 796, 111-119 (2019). https://doi.org/10.1016/j.jallcom.2019.05.023
[294] D.V. Zhuzhelskii, E.G. Tolstopjatova, S.N. Eliseeva, A.V. Ivanov, S. Miao, V.V. Kondratiev, Electrochemical properties of PEDOT/WO3 composite films for high performance supercapacitor application. Electrochim. Acta 299, 182-190 (2019). https://doi.org/10.1016/j.electacta.2019.01.007
[295] S.-Q. Wang, X. Cai, Y. Song, X. Sun, X.-X. Liu, VOx@MoOnanorod composite for high-performance supercapacitors. Adv. Funct. Mater. 28, 1803901 (2018). https://doi.org/10.1002/adfm.201803901
[296] G.-F. Chen, Z.-Q. Liu, J.-M. Lin, N. Li, Y.-Z. Su, Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors. J. Power Sources 283, 484-493 (2015). https://doi.org/10.1016/j.jpowsour.2015.02.103
[297] J. Yang, C. Yu, X. Fan, S. Liang, S. Li, H. Huang, Z. Ling, C. Hao, J. Qiu, Electroactive edge site-enriched nickel–cobalt sulfide into graphene frameworks for high-performance asymmetric supercapacitors. Energy Environ. Sci. 9, 1299-1307 (2016). https://doi.org/10.1039/c5ee03633j
[298] J. Zeng, J. Liu, S.S. Siwal, W. Yang, X. Fu, Q. Zhang, Morphological and electronic modification of 3D porous nickel microsphere arrays by cobalt and sulfur dual synergistic modulation for overall water splitting electrolysis and supercapacitors. Appl. Surf. Sci. 491, 570-578 (2019). https://doi.org/10.1016/j.apsusc.2019.06.182
[299] B.D. Falola, L. Fan, T. Wiltowski, I.I. Suni, Electrodeposition of Cu-doped MoS2 for charge storage in electrochemical supercapacitors. J. Electrochem. Soc. 164, D674-D679 (2017). https://doi.org/10.1149/2.0421712jes
[300] B.D. Falola, T. Wiltowski, I.I. Suni, Electrodeposition of MoS2 for charge storage in electrochemical supercapacitors. J. Electrochem. Soc. 163, D568-D574 (2016). https://doi.org/10.1149/2.0011610jes
[301] X. Zhang, J. Gong, K. Zhang, W. Zhu, J.-C. Li, Q. Ding, All-solid-state asymmetric supercapacitor based on porous cobalt selenide thin films. J. Alloys Compd. 772, 25-32 (2019). https://doi.org/10.1016/j.jallcom.2018.09.023
[302] W. Chen, C. Xia, H.N. Alshareef, One-step electrodeposited nickel cobalt sulfide nanosheet arrays for high-performance asymmetric supercapacitors. ACS Nano 8, 9531-9541 (2014). https://doi.org/10.1021/nn503814y
[303] K.R. Prasad, K. Koga, N. Miura, Electrochemical deposition of nanostructured indium oxide:  High-performance electrode material for redox supercapacitors. Chem. Mater. 16, 1845-1847 (2004). https://doi.org/10.1021/cm0497576
[304] A. Albu-Yaron, C. Lévy-Clément, A. Katty, S. Bastide, R. Tenne, Influence of the electrochemical deposition parameters on the microstructure of MoS2 thin films. Thin Solid Films 361-362, 223-228 (2000). https://doi.org/10.1016/s0040-6090(99)00838-x
[305] W. Deng, X. Feng, Y. Xiao, C. Li, Layered molybdenum (oxy) pyrophosphate (MoO2)2P2O7 as a cathode material for sodium-ion batteries. ChemElectroChem 5, 1032-1036 (2018). https://doi.org/10.1002/celc.201800005
[306] B. Wen, N.A. Chernova, R. Zhang, Q. Wang, F. Omenya, J. Fang, M.S. Whittingham, Layered molybdenum (oxy)pyrophosphate as cathode for lithium-ion batteries. Chem. Mat. 25, 3513-3521 (2013). https://doi.org/10.1021/cm401946h
[307] C. Masquelier, L. Croguennec, Polyanionic (phosphates, silicates, sulfates) frameworks as electrode materials for rechargeable Li (or Na) batteries. Chem. Rev. 113, 6552-6591 (2013). https://doi.org/10.1021/cr3001862
[308] R. Murugavel, A. Choudhury, M.G. Walawalkar, R. Pothiraja, C.N. Rao, Metal complexes of organophosphate esters and open-framework metal phosphates: Synthesis, structure, transformations, and applications. Chem. Rev. 108, 3549-3655 (2008). https://doi.org/10.1021/cr000119q
[309] R. Sahoo, D.T. Pham, T.H. Lee, T.H.T. Luu, J. Seok, Y.H. Lee, Redox-driven route for widening voltage window in asymmetric supercapacitor. ACS Nano 12, 8494-8505 (2018). https://doi.org/10.1021/acsnano.8b04040
[310] Y. Yang, H. Hou, G. Zou, W. Shi, H. Shuai, J. Li, X. Ji, Electrochemical exfoliation of graphene-like two-dimensional nanomaterials. Nanoscale 11, 16-33 (2018). https://doi.org/10.1039/c8nr08227h
[311] S. Yang, P. Zhang, F. Wang, A.G. Ricciardulli, M.R. Lohe, P.W.M. Blom, X. Feng, Fluoride-free synthesis of two-dimensional titanium carbide (MXene) using a binary aqueous system. Angew. Chem. Int. Ed. 57, 15491-15495 (2018). https://doi.org/10.1002/anie.201809662
[312] M. Le Thai, G.T. Chandran, R.K. Dutta, X. Li, R.M. Penner, 100k cycles and beyond: Extraordinary cycle stability for MnOnanowires imparted by a gel electrolyte. ACS Energy Lett. 1, 57-63 (2016). https://doi.org/10.1021/acsenergylett.6b00029
[313] P. Zhang, F. Wang, S. Yang, G. Wang, M. Yu, X. Feng, Flexible in-plane micro-supercapacitors: Progresses and challenges in fabrication and applications. Energy Storage Mater. 28, 160-187 (2020). https://doi.org/10.1016/j.ensm.2020.02.029
[314] A. Emrani, P. Vasekar, C.R. Westgate, Effects of sulfurization temperature on CZTS thin film solar cell performances. Sol. Energy 98, 335-340 (2013). https://doi.org/10.1016/j.solener.2013.09.020
[315] J.G. Werner, G.G. Rodríguez-Calero, H.D. Abruña, U. Wiesner, Block copolymer derived 3-D interpenetrating multifunctional gyroidal nanohybrids for electrical energy storage. Energy Environ. Sci. 11, 1261-1270 (2018). https://doi.org/10.1039/c7ee03571c
[316] T. Liu, F. Yang, G. Cheng, W. Luo, Reduced graphene oxide-wrapped Co9-xFexS8 /Co,Fe-N-C composite as bifunctional electrocatalyst for oxygen reduction and evolution. Small 14, 1703748 (2018). https://doi.org/10.1002/smll.201703748
[317] H. Niu, Y. Zhang, Y. Liu, B. Luo, N. Xin, W. Shi, MOFs-derived Co9S8-embedded graphene/hollow carbon spheres film with macroporous frameworks for hybrid supercapacitors with superior volumetric energy density. J. Mater. Chem. A 7, 8503-8509 (2019). https://doi.org/10.1039/c8ta11983j
[318] X.M. Lin, J.H. Chen, J.J. Fan, Y. Ma, P. Radjenovic et al., Synthesis and operando sodiation mechanistic study of nitrogen-doped porous carbon coated bimetallic sulfide hollow nanocubes as advanced sodium ion battery anode. Adv. Energy Mater. 9, 1902312 (2019). https://doi.org/10.1002/aenm.201902312
[319] R. Kumar, S. Sahoo, E. Joanni, R.K. Singh, R.M. Yadav et al., A review on synthesis of graphene, h-BN and MoS2 for energy storage applications: Recent progress and perspectives. Nano Res. 12, 2655-2694 (2019). https://doi.org/10.1007/s12274-019-2467-8

References

[1] C. Choi, D.S. Ashby, D.M. Butts, R.H. DeBlock, Q. Wei, J. Lau, B. Dunn, Achieving high energy density and high power density with pseudocapacitive materials. Nat. Rev. Mater. 5, 5-19 (2019). https://doi.org/10.1038/s41578-019-0142-z
[2] J. Pu, Z. Shen, C. Zhong, Q. Zhou, J. Liu, J. Zhu, H. Zhang, Electrodeposition technologies for Li-based batteries: New frontiers of energy storage. Adv. Mater. 1903808 (2019). https://doi.org/10.1002/adma.201903808
[3] P. Simon, Y. Gogotsi, B. Dunn, Materials science. Where do batteries end and supercapacitors begin? Science 343, 1210-1211 (2014). https://doi.org/10.1126/science.1249625
[4] T. Liu, F. Zhang, Y. Song, Y. Li, Revitalizing carbon supercapacitor electrodes with hierarchical porous structures. J. Mater. Chem. A 5, 17705-17733 (2017). https://doi.org/10.1039/c7ta05646j
[5] B.E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications (Springer US; 2013), pp. 11-31.
[6] Y. Jiang, J. Liu, Definitions of pseudocapacitive materials: A brief review. Energ. Environ. Mater. 2, 30-37 (2019). https://doi.org/10.1002/eem2.12028
[7] J. Miller, Introduction to electrochemical capacitor technology. IEEE. Electr. Insul. M. 26, 40-47 (2010). https://doi.org/10.1109/mei.2010.5511188
[8] Y. Huang, Z. Tang, Z. Liu, J. Wei, H. Hu, C. Zhi, Toward enhancing wearability and fashion of wearable supercapacitor with modified polyurethane artificial leather electrolyte. Nano-Micro Lett. 10, 38 (2018). https://doi.org/10.1007/s40820-018-0191-7
[9] Z. Bo, C. Li, H. Yang, K. Ostrikov, J. Yan, K. Cen, Design of supercapacitor electrodes using molecular dynamics simulations. Nano-Micro Lett. 10, 33 (2018). https://doi.org/10.1007/s40820-018-0188-2
[10] Y. Liu, B. Soucaze-Guillous, P.-L. Taberna, P. Simon, Understanding of carbon-based supercapacitors ageing mechanisms by electrochemical and analytical methods. J. Power Sources 366, 123-130 (2017). https://doi.org/10.1016/j.jpowsour.2017.08.104
[11] J.R. Miller, P. Simon, Materials science. Electrochemical capacitors for energy management. Science 321, 651-652 (2008). https://doi.org/10.1126/science.1158736
[12] P. Simon, Y. Gogotsi. Materials for electrochemical capacitors. Nat. Mater. 7, 845-854 (2008). https://doi.org/10.1038/nmat2297
[13] V. Augustyn, P. Simon, B. Dunn, Pseudocapacitive oxide materials for high-rate electrochemical energy storage. Energy Environ. Sci. 7, 1597-1614 (2014). https://doi.org/10.1039/c3ee44164d
[14] N. Jabeen, A. Hussain, Q. Xia, S. Sun, J. Zhu, H. Xia, High-performance 2.6 V aqueous asymmetric supercapacitors based on in situ formed Na0.5MnO2 nanosheet assembled nanowall arrays. Adv. Mater. 29, 1700804 (2017). https://doi.org/10.1002/adma.201700804
[15] W. Wei, X. Cui, W. Chen, D.G. Ivey, Manganese oxide-based materials as electrochemical supercapacitor electrodes. Chem. Soc. Rev. 40, 1697-1721 (2011). https://doi.org/10.1039/c0cs00127a
[16] Y. Wu, Y. Yang, X. Zhao, Y. Tan, Y. Liu, Z. Wang, F. Ran, A novel hierarchical porous 3D structured vanadium nitride/carbon membranes for high-performance supercapacitor negative electrodes. Nano-Micro Lett. 10, 63 (2018). https://doi.org/10.1007/s40820-018-0217-1
[17] L.L. Zhang, X. S. Zhao, Carbon-based materials as supercapacitor electrodes. Chem. Soc. Rev. 38, 2520-2531 (2009). https://doi.org/10.1039/b813846j
[18] D. Landolt, Electrodeposition science and technology in the last quarter of the twentieth century. J. Electrochem. Soc. 149, S9 (2002). https://doi.org/10.1149/1.1469028
[19] I.M. Dharmadasa, J. Haigh, Strengths and advantages of electrodeposition as a semiconductor growth technique for applications in macroelectronic devices. J. Electrochem. Soc. 153, G47-G52 (2006). https://doi.org/10.1149/1.2128120
[20] M.F. Montemor, S. Eugénio, N. Tuyen, R.P. Silva, T.M. Silva, M.J. Carmezim, Nanostructured Transition Metal Oxides Produced by Electrodeposition for Application as Redox Electrodes for Supercapacitors (Springer International Publishing, 2016), pp. 681-714. https://doi.org/10.1007/978-3-319-15266-0_14
[21] J. Wang, K.K. Manga, Q. Bao, K.P. Loh, High-yield synthesis of few-layer graphene flakes through electrochemical expansion of graphite in propylene carbonate electrolyte. J. Am. Chem. Soc. 133, 8888-8891 (2011). https://doi.org/10.1021/ja203725d
[22] W. Chen, R.B. Rakhi, L. Hu, X. Xie, Y. Cui, H.N. Alshareef, High-performance nanostructured supercapacitors on a sponge. Nano Lett. 11, 5165-5172 (2011). https://doi.org/10.1021/nl2023433
[23] X. Lang, A. Hirata, T. Fujita, M. Chen, Nanoporous metal/oxide hybrid electrodes for electrochemical supercapacitors. Nat. Nanotechnol. 6, 232-236 (2011). https://doi.org/10.1038/nnano.2011.13
[24] T. Liu, Y. Ling, Y. Yang, L. Finn, E. Collazo, T. Zhai, Y. Tong, Y. Li, Investigation of hematite nanorod–nanoflake morphological transformation and the application of ultrathin nanoflakes for electrochemical devices. Nano Energy 12, 169-177 (2015). https://doi.org/10.1016/j.nanoen.2014.12.023
[25] T. Liu, L. Finn, M. Yu, H. Wang, T. Zhai, X. Lu, Y. Tong, Y. Li, Polyaniline and polypyrrole pseudocapacitor electrodes with excellent cycling stability. Nano Lett. 14, 2522-2527 (2014). https://doi.org/10.1021/nl500255v
[26] Y. Song, T.-Y. Liu, X.-X. Xu, D.-Y. Feng, Y. Li, X.-X. Liu, Pushing the cycling stability limit of polypyrrole for supercapacitors. Adv. Funct. Mater. 25, 4626-4632 (2015). https://doi.org/10.1002/adfm.201501709
[27] M.-H. Bai, T.-Y. Liu, F. Luan, Y. Li, X.-X. Liu, Electrodeposition of vanadium oxide–polyaniline composite nanowire electrodes for high energy density supercapacitors. J. Mater. Chem. A 2, 10882-10888 (2014). https://doi.org/10.1039/c3ta15391f
[28] Y. Song, P. Deng, Z. Qin, D. Feng, D. Guo, X. Sun, X.-X. Liu, A polyanionic molybdenophosphate anode for a 2.7 V aqueous pseudocapacitor. Nano Energy 65, 104010 (2019). https://doi.org/10.1016/j.nanoen.2019.104010
[29]  F. Liu, Z. Chen, G. Fang, Z. Wang, Y. Cai, B. Tang, J. Zhou, V2O5 Nanospheres with mixed vanadium valences as high electrochemically active aqueous zinc-ion battery cathode. Nano-Micro Lett. 11, 25 (2019). https://doi.org/10.1007/s40820-019-0256-2
[30] R.G. Kelly, J.R. Scully, D. Shoesmith, R.G. Buchheit, Electrochemical Techniques in Corrosion Science and Engineering (CRC Press; 2002). https://doi.org/10.1201/9780203909133
[31] A.J. Bard, L.R. Faulkner, J. Leddy, C.G. Zoski, Electrochemical Methods: Fundamentals and Applications (Wiley New York; 1980).
[32] N. Elgrishi, K.J. Rountree, B.D. McCarthy, E.S. Rountree, T.T. Eisenhart, J.L. Dempsey, A practical beginner’s guide to cyclic voltammetry. J. Chem. Educ. 95, 197-206 (2017). https://doi.org/10.1021/acs.jchemed.7b00361
[33] D.K. Gosser. Cyclic Voltammetry: Simulation and Analysis of Reaction Mechanisms (VCH New York; 1993).
[34] R. Dong, Y. Song, D. Yang, H.-Y. Shi, Z. Qin et al., Electrochemical in situ construction of vanadium oxide heterostructures with boosted pseudocapacitive charge storage. J. Mater. Chem. A 8, 1176-1183 (2020). https://doi.org/10.1039/c9ta12097a
[35] Z. Sun, X. Cai, D.-Y. Feng, Z.-H. Huang, Y. Song, X.-X. Liu, Hybrid iron oxide on three-dimensional exfoliated graphite electrode with ultrahigh capacitance for energy storage applications. ChemElectroChem 5, 1501-1508 (2018). https://doi.org/10.1002/celc.201800143
[36] Z. Sun, X. Cai, Y. Song, X.-X. Liu, Electrochemical deposition of honeycomb magnetite on partially exfoliated graphite as anode for capacitive applications. J. Power Sources 359, 57-63 (2017). https://doi.org/10.1016/j.jpowsour.2017.05.055
[37] Y. Song, T.Y. Liu, B. Yao, T.Y. Kou, D.Y. Feng, X.X. Liu, Y. Li, Amorphous mixed-valence vanadium oxide/exfoliated carbon cloth structure shows a record high cycling stability. Small 13, 1700067 (2017). https://doi.org/10.1002/smll.201700067
[38] X. Cai, Y. Song, S.-Q. Wang, X. Sun, X.-X. Liu, Extending the cycle life of high mass loading MoOx electrode for supercapacitor applications. Electrochim. Acta 325, 134877 (2019). https://doi.org/10.1016/j.electacta.2019.134877
[39] M. Paunovic, Electrochemical Deposition. Encyclopedia of Electrochemistry: Online (2007). https://doi.org/10.1002/9783527610426.bard050003
[40] D. Lincot, Electrodeposition of semiconductors. Thin Solid Films 487, 40-48 (2005). https://doi.org/10.1016/j.tsf.2005.01.032
[41] M. Paunovic, M. Schlesinger, Fundamentals of Electrochemical Deposition (New York, 1998).
[42] D.M. Kolb, M. Przasnyski, H. Gerischer, Underpotential deposition of metals and work function differences. J. Electroanal. Chem. 54, 25-38 (1974). https://doi.org/10.1016/s0022-0728(74)80377-3
[43] E. Herrero, L.J. Buller, H.D. Abruna, Underpotential deposition at single crystal surfaces of Au, Pt, Ag and other materials. Chem. Rev. 101, 1897-1930 (2001). https://doi.org/10.1021/cr9600363
[44] Z. Shi, S. Wu, J. Lipkowski. Investigations of Cl adsorption at the Au(111) electrode in the presence of underpotentially deposited copper atoms. J. Electroanal. Chem. 384, 171-177 (1995). https://doi.org/10.1016/0022-0728(94)03747-q
[45] J.C. Ballesteros, E. Chaînet, P. Ozil, G. Trejo, Y. Meas, Electrochemical studies of Zn underpotential/overpotential deposition on a nickel electrode from non-cyanide alkaline solution containing glycine. Electrochim. Acta 56, 5443-5451 (2011). https://doi.org/10.1016/j.electacta.2011.02.106
[46] M. Palomar-Pardavé, I. González, N. Batina, New insights into evaluation of kinetic parameters for potentiostatic metal deposition with underpotential and overpotential deposition processes. J. Phys. Chem. B 104, 3545-3555 (2000). https://doi.org/10.1021/jp9931861
[47] R.E. Rettew, J.W. Guthrie, F.M. Alamgir, Layer-by-layer Pt growth on polycrystalline Au: Surface-limited redox replacement of overpotentially deposited Ni monolayers. J. Electrochem. Soc. 156, D513-D516 (2009). https://doi.org/10.1149/1.3224113
[48] M.G. Pavlović, L.J. Pavlović, N.D. Nikolić, K.I. Popov, The effect of some parameters of electrolysis on apparent density of electrolytic copper powder in galvanostatic deposition. Mater. Sci. Forum 352, 65-72 (2000). https://doi.org/10.4028/www.scientific.net/MSF.352.65
[49] R. Salazar, C. Lévy-Clément, V. Ivanova, Galvanostatic deposition of ZnO thin films. Electrochim. Acta 78, 547-556 (2012). https://doi.org/10.1016/j.electacta.2012.06.070
[50] Z.H. Huang, Y. Song, D.Y. Feng, Z. Sun, X. Sun, X.X. Liu, High mass loading MnO2 with hierarchical nanostructures for supercapacitors. ACS Nano 12, 3557-3567 (2018). https://doi.org/10.1021/acsnano.8b00621
[51] E.J. Podlaha, Selective electrodeposition of nanoparticulates into metal matrices. Nano Lett. 1, 413-416 (2001). https://doi.org/10.1021/nl015508u
[52] G. Zhu, C. Pan, W. Guo, C.Y. Chen, Y. Zhou, R. Yu, Z.L. Wang, Triboelectric-generator-driven pulse electrodeposition for micropatterning. Nano Lett. 12, 4960-4965 (2012). https://doi.org/10.1021/nl302560k
[53] Y. Su, I. Zhitomirsky, Pulse electrosynthesis of MnO2 electrodes for supercapacitors. Adv. Eng. Mater. 16, 760-766 (2014). https://doi.org/10.1002/adem.201400077
[54] M. Ghaemi, Effects of direct and pulse current on electrodeposition of manganese dioxide. J. Power Sources 111, 248-254 (2002). https://doi.org/10.1016/s0378-7753(02)00309-9
[55] H. Cheh, Electrodeposition of gold by pulsed current. J. Electrochem. Soc. 118, 551 (1971). https://doi.org/10.1149/1.2408110
[56] H.M.M.N. Hennayaka, H.S. Lee, Structural and optical properties of Zns thin film grown by pulsed electrodeposition. Thin Solid Films 548, 86-90 (2013). https://doi.org/10.1016/j.tsf.2013.09.011
[57] A. Davies, P. Audette, B. Farrow, F. Hassan, Z. Chen, J.-Y. Choi, A. Yu, Graphene-based flexible supercapacitors: Pulse-electropolymerization of polypyrrole on free-standing graphene films. J. Phys. Chem. C 115, 17612-17620 (2011). https://doi.org/10.1021/jp205568v
[58] L. Besra, M. Liu, A review on fundamentals and applications of electrophoretic deposition (EPD). Prog. Mater. Sci. 52, 1-61 (2007). https://doi.org/10.1016/j.pmatsci.2006.07.001
[59] P. Sarkar, P.S. Nicholson, Electrophoretic deposition (EPD): Mechanisms, kinetics, and application to ceramics. J. Am. Ceram. Soc. 79, 1987-2002 (1996). https://doi.org/10.1111/j.1151-2916.1996.tb08929.x
[60] C. Du, N. Pan, Supercapacitors using carbon nanotubes films by electrophoretic deposition. J. Power Sources 160, 1487-1494 (2006). https://doi.org/10.1016/j.jpowsour.2006.02.092
[61] C. Du, N. Pan, High power density supercapacitor electrodes of carbon nanotube films by electrophoretic deposition. Nanotechnology 17, 5314-5318 (2006). https://doi.org/10.1088/0957-4484/17/21/005
[62] D. Pech, M. Brunet, H. Durou, P. Huang, V. Mochalin, Y. Gogotsi, P.L. Taberna, P. Simon, Ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon. Nat. Nanotechnol. 5, 651-654 (2010). https://doi.org/10.1038/nnano.2010.162
[63] Y. Su, I. Zhitomirsky, Electrophoretic nanotechnology of composite electrodes for electrochemical supercapacitors. J. Phys. Chem. B 117, 1563-1570 (2013). https://doi.org/10.1021/jp304358q
[64] Y. Wang, I. Zhitomirsky. Electrophoretic deposition of manganese dioxide-multiwalled carbon nanotube composites for electrochemical supercapacitors. Langmuir 25, 9684-9689 (2009). https://doi.org/10.1021/la900937e
[65] H. Zhang, X. Zhang, D. Zhang, X. Sun, H. Lin, C. Wang, Y. Ma, One-step electrophoretic deposition of reduced graphene oxide and Ni(OH)2 composite films for controlled syntheses supercapacitor electrodes. J. Phys. Chem. B 117, 1616-1627 (2013). https://doi.org/10.1021/jp305198j
[66] Z.Y. Xia, S. Pezzini, E. Treossi, G. Giambastiani, F. Corticelli et al., The exfoliation of graphene in liquids by electrochemical, chemical, and sonication-assisted techniques: A nanoscale study. Adv. Funct. Mater. 23, 4684-4693 (2013). https://doi.org/10.1002/adfm.201203686
[67] A.M. Abdelkader, I.A. Kinloch, R.A. Dryfe, Continuous electrochemical exfoliation of micrometer-sized graphene using synergistic ion intercalations and organic solvents. ACS Appl. Mater. Interfaces 6, 1632-1639 (2014). https://doi.org/10.1021/am404497n
[68] A.M. Abdelkader, A.J. Cooper, R.A. Dryfe, I.A. Kinloch, How to get between the sheets: A review of recent works on the electrochemical exfoliation of graphene materials from bulk graphite. Nanoscale 7, 6944-6956 (2015). https://doi.org/10.1039/c4nr06942k
[69] A. Ambrosi, M. Pumera. Exfoliation of layered materials using electrochemistry. Chem. Soc. Rev. 47, 7213-7224 (2018). https://doi.org/10.1039/c7cs00811b
[70] R. Kumar, S. Sahoo, E. Joanni, R.K. Singh, W.K. Tan, K.K. Kar, A. Matsuda, Recent progress in the synthesis of graphene and derived materials for next generation electrodes of high performance lithium ion batteries. Prog. Energ. Combust. 75, 100786 (2019). https://doi.org/10.1016/j.pecs.2019.100786
[71] A. Ambrosi, M. Pumera, Electrochemically exfoliated graphene and graphene oxide for energy storage and electrochemistry applications. Chem 22, 153-159 (2016). https://doi.org/10.1002/chem.201503110
[72] P. Yu, S.E. Lowe, G.P. Simon, Y.L. Zhong, Electrochemical exfoliation of graphite and production of functional graphene. Curr. Opin. Colloid. Interface Sci. 20, 329-338 (2015). https://doi.org/10.1016/j.cocis.2015.10.007
[73] S. Yang, M.R. Lohe, K. Mullen, X. Feng, New-generation graphene from electrochemical approaches: Production and applications. Adv. Mater. 28, 6213-6221 (2016). https://doi.org/10.1002/adma.201505326
[74] W. Wei, G. Wang, S. Yang, X. Feng, K. Mullen, Efficient coupling of nanoparticles to electrochemically exfoliated graphene. J. Am. Chem. Soc. 137, 5576-5581 (2015). https://doi.org/10.1021/jacs.5b02284
[75] L. Wu, W. Li, P. Li, S. Liao, S. Qiu et al., Powder, paper and foam of few-layer graphene prepared in high yield by electrochemical intercalation exfoliation of expanded graphite. Small 10, 1421-1429 (2014). https://doi.org/10.1002/smll.201302730
[76] A. Ejigu, K. Fujisawa, B.F. Spencer, B. Wang, M. Terrones, I.A. Kinloch, R.A.W. Dryfe, On the role of transition metal salts during electrochemical exfoliation of graphite: Antioxidants or metal oxide decorators for energy storage applications. Adv. Funct. Mater. 28, 1804357 (2018). https://doi.org/10.1002/adfm.201804357
[77] K.S. Rao, J. Sentilnathan, H.-W. Cho, J.-J. Wu, M. Yoshimura, Soft processing of graphene nanosheets by glycine-bisulfate ionic-complex-assisted electrochemical exfoliation of graphite for reduction catalysis. Adv. Funct. Mater. 25, 298-305 (2015). https://doi.org/10.1002/adfm.201402621
[78] C.Y. Su, A.Y. Lu, Y. Xu, F.R. Chen, A.N. Khlobystov, L.J. Li, High-quality thin graphene films from fast electrochemical exfoliation. ACS Nano 5, 2332-2339 (2011). https://doi.org/10.1021/nn200025p
[79] J. Lu, J.X. Yang, J. Wang, A. Lim, S. Wang, K.P. Loh, One-pot synthesis of fluorescent carbon nanoribbons, nanoparticles, and graphene by the exfoliation of graphite in ionic liquids. ACS Nano 3, 2367-2375 (2009). https://doi.org/10.1021/nn900546b
[80] W. Cai, X. Feng, W. Hu, Y. Pan, Y. Hu, X. Gong, Functionalized graphene from electrochemical exfoliation for thermoplastic polyurethane: Thermal stability, mechanical properties, and flame retardancy. Ind. Eng. Chem. Res. 55, 10681-10689 (2016). https://doi.org/10.1021/acs.iecr.6b02579
[81] M. Mao, M. Wang, J. Hu, G. Lei, S. Chen, H. Liu, Simultaneous electrochemical synthesis of few-layer graphene flakes on both electrodes in protic ionic liquids. Chem. Commun. 49, 5301-5303 (2013). https://doi.org/10.1039/c3cc41909f
[82] H. Huang, Y. Xia, X. Tao, J. Du, J. Fang, Y. Gan, W. Zhang, Highly efficient electrolytic exfoliation of graphite into graphene sheets based on Li ions intercalation–expansion–microexplosion mechanism. J. Mater. Chem. 22, 10452-10456 (2012). https://doi.org/10.1039/c2jm00092j
[83] Y. Yang, F. Lu, Z. Zhou, W. Song, Q. Chen, X. Ji, Electrochemically cathodic exfoliation of graphene sheets in room temperature ionic liquids N-butyl, methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and their electrochemical properties. Electrochim. Acta 113, 9-16 (2013). https://doi.org/10.1016/j.electacta.2013.09.031
[84] K. Parvez, R. Li, S. R. Puniredd, Y. Hernandez, F. Hinkel, S. Wang, X. Feng, K. Mullen, Electrochemically exfoliated graphene as solution-processable, highly conductive electrodes for organic electronics. ACS Nano 7, 3598-3606 (2013). https://doi.org/10.1021/nn400576v
[85] W. Wang, W. Liu, Y. Zeng, Y. Han, M. Yu, X. Lu, Y. Tong, A novel exfoliation strategy to significantly boost the energy storage capability of commercial carbon cloth. Adv. Mater. 27, 3572-3578 (2015). https://doi.org/10.1002/adma.201500707
[86] Y. Song, S. Duan, D. Yang, R. Dong, D. Guo, X. Sun, X.-X. Liu, 3D exfoliated carbon paper toward highly loaded aqueous energy storage applications. Energy Technol. 7, 1900892 (2019). https://doi.org/10.1002/ente.201900892
[87] F. Zeng, Z. Sun, X. Sang, D. Diamond, K.T. Lau, X. Liu, D.S. Su, In situ one-step electrochemical preparation of graphene oxide nanosheet-modified electrodes for biosensors. ChemSusChem 4, 1587-1591 (2011). https://doi.org/10.1002/cssc.201100319
[88] Y. Song, D.Y. Feng, T.Y. Liu, Y. Li, X.X. Liu, Controlled partial-exfoliation of graphite foil and integration with MnO2 nanosheets for electrochemical capacitors. Nanoscale 7, 3581-3587 (2015). https://doi.org/10.1039/c4nr06559j
[89] K. Parvez, Z.S. Wu, R. Li, X. Liu, R. Graf, X. Feng, K. Mullen, Exfoliation of graphite into graphene in aqueous solutions of inorganic salts. J. Am. Chem. Soc. 136, 6083-6091 (2014). https://doi.org/10.1021/ja5017156
[90] M. Alanyalıoğlu, J.J. Segura, J. Oró-Solè, N. Casañ-Pastor, The synthesis of graphene sheets with controlled thickness and order using surfactant-assisted electrochemical processes. Carbon 50, 142-152 (2012). https://doi.org/10.1016/j.carbon.2011.07.064
[91] C.-H. Chen, S.-W. Yang, M.-C. Chuang, W.-Y. Woon, C.-Y. Su, Towards the continuous production of high crystallinity graphene via electrochemical exfoliation with molecular in situ encapsulation. Nanoscale 7, 15362-15373 (2015). https://doi.org/10.1039/c5nr03669k
[92] K. Chen, D. Xue, Preparation of colloidal graphene in quantity by electrochemical exfoliation. J. Colloid Interf. Sci. 436, 41-46 (2014). https://doi.org/10.1016/j.jcis.2014.08.057
[93] A.J. Cooper, N.R. Wilson, I.A. Kinloch, R.A.W. Dryfe, Single stage electrochemical exfoliation method for the production of few-layer graphene via intercalation of tetraalkylammonium cations. Carbon 66, 340-350 (2014). https://doi.org/10.1016/j.carbon.2013.09.009
[94] A. Ejigu, I.A. Kinloch, R.A. Dryfe, Single stage simultaneous electrochemical exfoliation and functionalization of graphene. ACS Appl. Mater. Interfaces 9, 710-721 (2017). https://doi.org/10.1021/acsami.6b12868
[95] S. Yang, S. Bruller, Z.S. Wu, Z. Liu, K. Parvez et al., Organic radical-assisted electrochemical exfoliation for the scalable production of high-quality graphene. J. Am. Chem. Soc. 137, 13927-13932 (2015). https://doi.org/10.1021/jacs.5b09000
[96] X. Cai, Y. Song, Z. Sun, D. Guo, X.-X. Liu, Rate capability improvement of Co−Ni double hydroxides integrated in cathodically partially exfoliated graphite. J. Power Sources 365, 126-133 (2017). https://doi.org/10.1016/j.jpowsour.2017.08.039 [97] D.-Y. Feng, Y. Song, Z.-H. Huang, X.-X. Xu, X.-X. Liu, Rate capability improvement of polypyrrole via integration with functionalized commercial carbon cloth for pseudocapacitor. J. Power Sources 324, 788-797 (2016). https://doi.org/10.1016/j.jpowsour.2016.05.112
[98] L. Hu, X. Peng, Y. Li, L. Wang, K. Huo, L.Y. S. Lee, K.Y. Wong, P.K. Chu, Direct anodic exfoliation of graphite onto high-density aligned graphene for large capacity supercapacitors. Nano Energy 34, 515-523 (2017). https://doi.org/10.1016/j.nanoen.2017.03.007
[99] T. Liu, C. Zhu, T. Kou, M.A. Worsley, F. Qian, C. Condes, E.B. Duoss, C.M. Spadaccini, Y. Li, Ion intercalation induced capacitance improvement for graphene-based supercapacitor electrodes. ChemNanoMat 2, 635-641 (2016). https://doi.org/10.1002/cnma.201600107
[100] Y. Song, T. Liu, F. Qian, C. Zhu, B. Yao, E. Duoss, C. Spadaccini, M. Worsley, Y. Li, Three-dimensional carbon architectures for electrochemical capacitors. J. Colloid Interf. Sci. 509, 529-545 (2018). https://doi.org/10.1016/j.jcis.2017.07.081
[101] Y. Song, T.-Y. Liu, G.-L. Xu, D.-Y. Feng, B. Yao, T.-Y. Kou, X.-X. Liu, Y. Li, Tri-layered graphite foil for electrochemical capacitors. J. Mater. Chem. A 4, 7683-7688 (2016). https://doi.org/10.1039/c6ta02075e
[102] Y. Zou, S. Wang, Interconnecting carbon fibers with the in-situ electrochemically exfoliated graphene as advanced binder-free electrode materials for flexible supercapacitor. Sci. Rep. 5, 11792 (2015). https://doi.org/10.1038/srep11792
[103] S.-H. Lee, S.-D. Seo, Y.-H. Jin, H.-W. Shim, D.-W. Kim, A graphite foil electrode covered with electrochemically exfoliated graphene nanosheets. Electrochem. Commun. 12, 1419-1422 (2010). https://doi.org/10.1016/j.elecom.2010.07.036
[104] R.M. Tamgadge, A. Shukla, A PH-dependent partial electrochemical exfoliation of highly oriented pyrolytic graphite for high areal capacitance electric double layer capacitor electrode. Electrochim. Acta 325, 134933 (2019). https://doi.org/10.1016/j.electacta.2019.134933
[105] Y. Song, J.-L. Xu, X.-X. Liu, Electrochemical anchoring of dual doping polypyrrole on graphene sheets partially exfoliated from graphite foil for high-performance supercapacitor electrode. J. Power Sources 249, 48-58 (2014). https://doi.org/10.1016/j.jpowsour.2013.10.102
[106] Y. Song, X. Cai, X. Xu, X.-X. Liu, Integration of nickel–cobalt double hydroxide nanosheets and polypyrrole films with functionalized partially exfoliated graphite for asymmetric supercapacitors with improved rate capability. J. Mater. Chem. A 3, 14712-14720 (2015). https://doi.org/10.1039/c5ta02810h
[107] Z. Liu, Z.S. Wu, S. Yang, R. Dong, X. Feng, K. Mullen, Ultraflexible in-plane micro-supercapacitors by direct printing of solution-processable electrochemically exfoliated graphene. Adv. Mater. 28, 2217-2222 (2016). https://doi.org/10.1002/adma.201505304
[108] J.M. Munuera, J.I. Paredes, M. Enterria, A. Pagan, S. Villar-Rodil, M.F.R. Pereira et al., Electrochemical exfoliation of graphite in aqueous sodium halide electrolytes toward low oxygen content graphene for energy and environmental applications. ACS Appl. Mater. Interfaces 9, 24085-24099 (2017). https://doi.org/10.1021/acsami.7b04802
[109] N. Parveen, M.O. Ansari, S.A. Ansari, M.H. Cho, Simultaneous sulfur doping and exfoliation of graphene from graphite using an electrochemical method for supercapacitor electrode materials. J. Mater. Chem. A 4, 233-240 (2016). https://doi.org/10.1039/c5ta07963b
[110] J. Liu, M. Notarianni, G. Will, V.T. Tiong, H. Wang, N. Motta, Electrochemically exfoliated graphene for electrode films: Effect of graphene flake thickness on the sheet resistance and capacitive properties. Langmuir 29, 13307-13314 (2013). https://doi.org/10.1021/la403159n
[111] S.M. Jung, D.L. Mafra, C.T. Lin, H.Y. Jung, J. Kong, Controlled porous structures of graphene aerogels and their effect on supercapacitor performance. Nanoscale 7, 4386-4393 (2015). https://doi.org/10.1039/c4nr07564a
[112] X. Xiao, Y. Zeng, H. Feng, K. Xu, G. Zhong et al., Three-dimensional nitrogen-doped graphene frameworks from electrochemical exfoliation of graphite as efficient supercapacitor electrodes. ChemNanoMat 5, 152-157 (2019). https://doi.org/10.1002/cnma.201800452
[113] P. Khanra, T. Kuila, S.H. Bae, N.H. Kim, J.H. Lee, Electrochemically exfoliated graphene using 9-anthracene carboxylic acid for supercapacitor application. J. Mater. Chem. 22, 24403-24410 (2012). https://doi.org/10.1039/c2jm34838a
[114] S. Liu, J. Ou, J. Wang, X. Liu, S. Yang, A simple two-step electrochemical synthesis of graphene sheets film on the ITO electrode as supercapacitors. J. Appl. Electrochem. 41, 881-884 (2011). https://doi.org/10.1007/s10800-011-0304-1
[115] V. Thirumal, A. Pandurangan, R. Jayavel, K.S. Venkatesh, N.S. Palani, R. Ragavan, R. Ilangovan. Single pot electrochemical synthesis of functionalized and phosphorus doped graphene nanosheets for supercapacitor applications. J. Mater. Sci.-Mater. El. 26, 6319-6328 (2015). https://doi.org/10.1007/s10854-015-3219-5
[116] C. Li, H. Bai, G. Shi, Conducting polymer nanomaterials: Electrosynthesis and applications. Chem. Soc. Rev. 38, 2397-2409 (2009). https://doi.org/10.1039/b816681c
[117] G.A. Snook, P. Kao, A.S. Best, Conducting-polymer-based supercapacitor devices and electrodes. J. Power Sources 196, 1-12 (2011). https://doi.org/10.1016/j.jpowsour.2010.06.084
[118] R. Gangopadhyay, A. De. Conducting polymer nanocomposites: A brief overview. Chem. Mater. 12, 608-622 (2000). https://doi.org/10.1021/cm990537f
[119] Z. Cai, L. Li, J. Ren, L. Qiu, H. Lin, H. Peng, Flexible, weavable and efficient microsupercapacitor wires based on polyaniline composite fibers incorporated with aligned carbon nanotubes. J. Mater. Chem. A 1, 258-261 (2013). https://doi.org/10.1039/c2ta00274d
[120] K.M. Kim, Y.-G. Lee, D.O. Shin, J.M. Ko, Supercapacitive properties of layered electrodes composed of electrodeposited RuO2 and polyaniline. Electrochim. Acta 196, 309-315 (2016). https://doi.org/10.1016/j.electacta.2016.02.194
[121] H. Li, J. Song, L. Wang, X. Feng, R. Liu, W. Zeng, Z. Huang, Y. Ma, L. Wang, Flexible all-solid-state supercapacitors based on polyaniline orderly nanotubes array. Nanoscale 9, 193-200 (2017). https://doi.org/10.1039/c6nr07921k
[122] C. Tran, R. Singhal, D. Lawrence, V. Kalra, Polyaniline-coated freestanding porous carbon nanofibers as efficient hybrid electrodes for supercapacitors. J. Power Sources 293, 373-379 (2015). https://doi.org/10.1016/j.jpowsour.2015.05.054
[123] Y. Xie, D. Wang, J. Ji, Preparation and supercapacitor performance of freestanding polypyrrole/polyaniline coaxial nanoarrays. Energy Technol. 4, 714-721 (2016). https://doi.org/10.1002/ente.201500460
[124] C. Fu, H. Zhou, R. Liu, Z. Huang, J. Chen, Y. Kuang, Supercapacitor based on electropolymerized polythiophene and multi-walled carbon nanotubes composites. Mater. Chem. Phys. 132, 596-600 (2012). https://doi.org/10.1016/j.matchemphys.2011.11.074
[125] A. Laforgue, P. Simon, C. Sarrazin, J.-F. Fauvarque, Polythiophene-based supercapacitors. J. Power Sources 80, 142-148 (1999). https://doi.org/10.1016/s0378-7753(98)00258-4
[126] F.N. Ajjan, N. Casado, T. Rębiś, A. Elfwing, N. Solin, D. Mecerreyes, O. Inganäs. High performance PEDOT/lignin biopolymer composites for electrochemical supercapacitors. J. Mater. Chem. A 4, 1838-1847 (2016). https://doi.org/10.1039/c5ta10096h
[127] A.M. Osterholm, D.E. Shen, A.L. Dyer, J.R. Reynolds, Optimization of PEDOT films in ionic liquid supercapacitors: Demonstration as a power source for polymer electrochromic devices. ACS Appl. Mater. Interfaces 5, 13432-13440 (2013). https://doi.org/10.1021/am4043454
[128] J. Xu, Z. Ku, Y. Zhang, D. Chao, H. J. Fan, Integrated photo-supercapacitor based on PEDOT modified printable perovskite solar cell. Adv. Mater. Technol. 1, 1600074 (2016) https://doi.org/10.1002/admt.201600074
[129] S.-B. Yoon, K.-B. Kim, Effect of poly(3,4-ethylenedioxythiophene) (PEDOT) on the pseudocapacitive properties of manganese oxide (MnO2) in the PEDOT/MnO2/multiwall carbon nanotube (MWNT) composite. Electrochim. Acta 106, 135-142 (2013). https://doi.org/10.1016/j.electacta.2013.05.058
[130] G. Cai, P. Darmawan, M. Cui, J. Wang, J. Chen, S. Magdassi, P.S. Lee, Highly stable transparent conductive silver grid/PEDOT:PSS electrodes for integrated bifunctional flexible electrochromic supercapacitors. Adv. Energy Mater. 6, 1501882 (2016). https://doi.org/10.1002/aenm.201501882
[131] D. Yang, Y. Song, Y.-J. Ye, M. Zhang, X. Sun, X.-X. Liu, Boosting the pseudocapacitance of nitrogen-rich carbon nanorod arrays for electrochemical capacitors. J. Mater. Chem. A 7, 12086-12094 (2019). https://doi.org/10.1039/c9ta01973a
[132] Y. Huang, J. Tao, W. Meng, M. Zhu, Y. Huang, Y. Fu, Y. Gao, C. Zhi, Super-high rate stretchable polypyrrole-based supercapacitors with excellent cycling stability. Nano Energy 11, 518-525 (2015). https://doi.org/10.1016/j.nanoen.2014.10.031
[133] J.G. Ibanez, M.E. Rincon, S. Gutierrez-Granados, M. Chahma, O.A. Jaramillo-Quintero, B.A. Frontana-Uribe, Conducting polymers in the fields of energy, environmental remediation, and chemical-chiral sensors. Chem. Rev. 118, 4731-4816 (2018). https://doi.org/10.1021/acs.chemrev.7b00482
[134] G. Sabouraud, S. Sadki, N. Brodie, The mechanisms of pyrrole electropolymerization. Chem. Soc. Rev. 29, 283-293 (2000). https://doi.org/10.1039/a807124a
[135] J. Jang, Conducting Polymer Nanomaterials and Their Applications (Springer, Berlin, 2006), pp. 189-260.
[136] S.C. Erwin, L. Zu, M.I. Haftel, A.L. Efros, T.A. Kennedy, D.J. Norris, Doping semiconductor nanocrystals. Nature 436, 91-94 (2005). https://doi.org/10.1038/nature03832
[137] T.F. Otero, J.G. Martinez, Structural and biomimetic chemical kinetics: Kinetic magnitudes include structural information. Adv. Funct. Mater. 23, 404-416 (2013). https://doi.org/10.1002/adfm.201200719
[138] T. Liu, Y. Li, Addressing the achilles' heel of pseudocapacitive materials: Long‐term stability. InfoMat (2020). https://doi.org/10.1002/inf2.12105
[139] Y. Shi, L. Peng, Y. Ding, Y. Zhao, G. Yu, Nanostructured conductive polymers for advanced energy storage. Chem. Soc. Rev. 44, 6684-6696 (2015). https://doi.org/10.1039/c5cs00362h
[140] B. Anothumakkool, A.T.A. Torris, S.N. Bhange, M.V. Badiger, S. Kurungot, Electrodeposited polyethylenedioxythiophene with infiltrated gel electrolyte interface: A close contest of an all-solid-state supercapacitor with its liquid-state counterpart. Nanoscale 6, 5944-5952 (2014). https://doi.org/10.1039/c4nr00659c
[141] Y. Xie, Y. Liu, Y. Zhao, Y.H. Tsang, S.P. Lau, H. Huang, Y. Chai, Stretchable all-solid-state supercapacitor with wavy shaped polyaniline/graphene electrode. J. Mater. Chem. A 2, 9142-9149 (2014). https://doi.org/10.1039/c4ta00734d
[142] S. Lehtimaki, M. Suominen, P. Damlin, S. Tuukkanen, C. Kvarnstrom, D. Lupo. Preparation of supercapacitors on flexible substrates with electrodeposited PEDOT/graphene composites. ACS Appl. Mater. Interfaces 7, 22137-22147 (2015). https://doi.org/10.1021/acsami.5b05937
[143] Y. Huang, M. Zhu, Z. Pei, Y. Huang, H. Geng, C. Zhi, Extremely stable polypyrrole achieved via molecular ordering for highly flexible supercapacitors. ACS Appl. Mater. Interfaces 8, 2435-2440 (2016). https://doi.org/10.1021/acsami.5b11815
[144] N. Kurra, M.K. Hota, H.N. Alshareef, Conducting polymer micro-supercapacitors for flexible energy storage and Ac line-filtering. Nano Energy 13, 500-508 (2015). https://doi.org/10.1016/j.nanoen.2015.03.018
[145] N. Hui, F. Chai, P. Lin, Z. Song, X. Sun, Y. Li, S. Niu, X. Luo, Electrodeposited conducting polyaniline nanowire arrays aligned on carbon nanotubes network for high performance supercapacitors and sensors. Electrochim. Acta 199, 234-241 (2016). https://doi.org/10.1016/j.electacta.2016.03.115
[146] X.-Y. Peng, F. Luan, X.-X. Liu, D. Diamond, K.-T. Lau. pH-controlled morphological structure of polyaniline during electrochemical deposition. Electrochim. Acta 54, 6172-6177 (2009). https://doi.org/10.1016/j.electacta.2009.05.075
[147] B. Yao, L. Yuan, X. Xiao, J. Zhang, Y. Qi et al., Paper-based solid-state supercapacitors with pencil-drawing graphite/polyaniline networks hybrid electrodes. Nano Energy 2, 1071-1078 (2013). https://doi.org/10.1016/j.nanoen.2013.09.002
[148] Y. Wang, Y. Shi, L. Pan, Y. Ding, Y. Zhao, Y. Li, Y. Shi, G. Yu, Dopant-enabled supramolecular approach for controlled synthesis of nanostructured conductive polymer hydrogels. Nano Lett. 15, 7736-7741 (2015). https://doi.org/10.1021/acs.nanolett.5b03891
[149] Z. H. Huang, Y. Song, X.X. Xu, X.X. Liu, Ordered polypyrrole nanowire arrays grown on a carbon cloth substrate for a high-performance pseudocapacitor electrode. ACS Appl. Mater. Interfaces 7, 25506-25513 (2015). https://doi.org/10.1021/acsami.5b08830
[150] S. Huang, Y. Han, S. Lyu, W. Lin, P. Chen, S. Fang, A facile one-step approach for the fabrication of polypyrrole nanowire/carbon fiber hybrid electrodes for flexible high performance solid-state supercapacitors. Nanotechnology 28, 435204 (2017). https://doi.org/10.1088/1361-6528/aa84cb
[151] J. Huang, R.B. Kaner. Nanofiber formation in the chemical polymerization of aniline: A mechanistic study. Angew. Chem. Int. Ed. 43, 5817-5821 (2004). https://doi.org/10.1002/anie.200460616
[152] N.R. Chiou, C. Lu, J. Guan, L.J. Lee, A.J. Epstein, Growth and alignment of polyaniline nanofibres with superhydrophobic, superhydrophilic and other properties. Nat. Nanotechnol. 2, 354-357 (2007). https://doi.org/10.1038/nnano.2007.147
[153] K. Wang, J. Huang, Z. Wei, Conducting polyaniline nanowire arrays for high performance supercapacitors. J. Phys. Chem. C 114, 8062-8067 (2010). https://doi.org/10.1021/jp9113255
[154] Y.-J. Ye, Z.-H. Huang, Y. Song, J.-W. Geng, X.-X. Xu, X.-X. Liu, Electrochemical growth of polyaniline nanowire arrays on graphene sheets in partially exfoliated graphite foil for high-performance supercapacitive materials. Electrochim. Acta 240, 72-79 (2017). https://doi.org/10.1016/j.electacta.2017.04.025
[155] H.-P. Cong, X.-C. Ren, P. Wang, S.-H. Yu, Flexible graphene–polyaniline composite paper for high-performance supercapacitor. Energy Environ. Sci. 6, 1185-1191 (2013). https://doi.org/10.1039/c2ee24203f
[156] M. Yu, Y. Ma, J. Liu, S. Li, Polyaniline nanocone arrays synthesized on three-dimensional graphene network by electrodeposition for supercapacitor electrodes. Carbon 87, 98-105 (2015). https://doi.org/10.1016/j.carbon.2015.02.017
[157] G.F. Chen, X.X. Li, L.Y. Zhang, N. Li, T.Y. Ma, Z.Q. Liu, A porous perchlorate-doped polypyrrole nanocoating on nickel nanotube arrays for stable wide-potential-window supercapacitors. Adv. Mater. 28, 7680-7687 (2016). https://doi.org/10.1002/adma.201601781
[158] G. Lu, G. Shi, Electrochemical polymerization of pyrene in the electrolyte of boron trifluoride diethyl etherate containing trifluoroacetic acid and polyethylene glycol oligomer. J. Electroanal. Chem. 586, 154-160 (2006). https://doi.org/10.1016/j.jelechem.2005.10.020
[159] D.P. Dubal, S.H. Lee, J.G. Kim, W.B. Kim, C.D. Lokhande, Porous polypyrrole clusters prepared by electropolymerization for a high performance supercapacitor. J. Mater. Chem. 22, 3044-3052 (2012). https://doi.org/10.1039/c2jm14470k
[160] D.W. Wang, F. Li, J. Zhao, W. Ren, Z.G. Chen et al., Fabrication of graphene/polyaniline composite paper via in situ anodic electropolymerization for high-performance flexible electrode. ACS Nano 3, 1745-1752 (2009). https://doi.org/10.1021/nn900297m
[161] J. Han, Y. Dou, J. Zhao, M. Wei, D.G. Evans, X. Duan, Flexible CoAl LDH@PEDOT core/shell nanoplatelet array for high-performance energy storage. Small 9, 98-106 (2013). https://doi.org/10.1002/smll.201201336
[162] G. Lu, L. Qu, G. Shi, Electrochemical fabrication of neuron-type networks based on crystalline oligopyrene nanosheets. Electrochim. Acta 51, 340-346 (2005). https://doi.org/10.1016/j.electacta.2005.04.043
[163] X. He, W. Yang, X. Mao, L. Xu, Y. Zhou et al., All-solid state symmetric supercapacitors based on compressible and flexible free-standing 3D carbon nanotubes (CNTs)/poly(3,4-ethylenedioxythiophene) (PEDOT) sponge electrodes. J. Power Sources 376, 138-146 (2018). https://doi.org/10.1016/j.jpowsour.2017.09.084
[164] H. Park, J.W. Kim, S.Y. Hong, G. Lee, D.S. Kim, J.h. Oh et al., Microporous polypyrrole-coated graphene foam for high-performance multifunctional sensors and flexible supercapacitors. Adv. Funct. Mater. 28, 1707013 (2018). https://doi.org/10.1002/adfm.201707013
[165] C. Wang, Y. Ding, Y. Yuan, A. Cao, X. He, Q. Peng, Y. Li, Multifunctional, highly flexible, free-standing 3D polypyrrole foam. Small 12, 4070-4076 (2016). https://doi.org/10.1002/smll.201601905
[166] D.-Y. Feng, Z. Sun, Z.-H. Huang, X. Cai, Y. Song, X.-X. Liu, Highly loaded manganese oxide with high rate capability for capacitive applications. J. Power Sources 396, 238-245 (2018). https://doi.org/10.1016/j.jpowsour.2018.06.026
[167] T. Zhai, S. Xie, M. Yu, P. Fang, C. Liang, X. Lu, Y. Tong, Oxygen vacancies enhancing capacitive properties of MnO2 nanorods for wearable asymmetric supercapacitors. Nano Energy 8, 255-263 (2014). https://doi.org/10.1016/j.nanoen.2014.06.013
[168] Z. Sun, S. Firdoz, E. Y. Yap, L. Li, X. Lu, Hierarchically structured MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors. Nanoscale 5, 4379-4387 (2013). https://doi.org/10.1039/c3nr00209h
[169] W. Wei, X. Cui, W. Chen, D.G. Ivey, Phase-controlled synthesis of MnO2 nanocrystals by anodic electrodeposition: Implications for high-rate capability electrochemical supercapacitors. J. Phys. Chem. C 112, 15075-15083 (2008). https://doi.org/10.1021/jp804044s
[170] W. Wei, X. Cui, X. Mao, W. Chen, D.G. Ivey, Morphology evolution in anodically electrodeposited manganese oxide nanostructures for electrochemical supercapacitor applications—effect of supersaturation ratio. Electrochim. Acta 56, 1619-1628 (2011). https://doi.org/10.1016/j.electacta.2010.10.044
[171] F. Grote, Y. Lei, A complete three-dimensionally nanostructured asymmetric supercapacitor with high operating voltage window based on PPy and MnO2. Nano Energy 10, 63-70 (2014). https://doi.org/10.1016/j.nanoen.2014.08.019
[172] S.B. Singh, T.I. Singh, N.H. Kim, J.H. Lee, A core–shell MnO2@Au nanofiber network as a high-performance flexible transparent supercapacitor electrode. J. Mater. Chem. A 7, 10672-10683 (2019). https://doi.org/10.1039/c9ta00778d
[173] Q. Li, X.F. Lu, H. Xu, Y.X. Tong, G.R. Li, Carbon/MnO2 double-walled nanotube arrays with fast ion and electron transmission for high-performance supercapacitors. ACS Appl. Mater. Interfaces 6, 2726-2733 (2014). https://doi.org/10.1021/am405271q
[174] H. Xia, J. Feng, H. Wang, M.O. Lai, L. Lu, MnO2 nanotube and nanowire arrays by electrochemical deposition for supercapacitors. J. Power Sources 195, 4410-4413 (2010). https://doi.org/10.1016/j.jpowsour.2010.01.075
[175] J. Duay, S.A. Sherrill, Z. Gui, E. Gillette, S.B. Lee, Self-limiting electrodeposition of hierarchical MnO2 and Mn(OH)2/MnO2 nanofibril/nanowires: Mechanism and supercapacitor properties. ACS Nano 7, 1200-1214 (2013). https://doi.org/10.1021/nn3056077
[176] X. Lu, M. Yu, G. Wang, T. Zhai, S. Xie, Y. Ling, Y. Tong, Y. Li, H-TiO2@MnO2//H-TiO2@C core-shell nanowires for high performance and flexible asymmetric supercapacitors. Adv. Mater. 25, 267-272 (2013). https://doi.org/10.1002/adma.201203410
[177] E. Eustache, C. Douard, R. Retoux, C. Lethien, T. Brousse, MnO2 thin films on 3D scaffold: Microsupercapacitor electrodes competing with “bulk” carbon electrodes. Adv. Energy Mater. 5, 1500680 (2015). https://doi.org/10.1002/aenm.201500680
[178] L. Yuan, X.H. Lu, X. Xiao, T. Zhai, J. Dai et al., Flexible solid-state supercapacitors based on carbon nanoparticles/MnO2 nanorods hybrid structure. ACS Nano 6, 656-661 (2012). https://doi.org/10.1021/nn2041279
[179] S.H. Lee, H. Lee, M.S. Cho, J.-D. Nam, Y. Lee, Morphology and composition control of manganese oxide by the pulse reverse electrodeposition technique for high performance supercapacitors. J. Mater. Chem. A 1, 14606-14611 (2013). https://doi.org/10.1039/c3ta12828h
[180] X. Lu, D. Zheng, T. Zhai, Z. Liu, Y. Huang, S. Xie, Y. Tong, Facile synthesis of large-area manganese oxide nanorod arrays as a high-performance electrochemical supercapacitor. Energy Environ. Sci. 4, 2915-2921 (2011). https://doi.org/10.1039/c1ee01338f
[181] T. Beyazay, F. Eylul Sarac Oztuna, U. Unal, Self-standing reduced graphene oxide papers electrodeposited with manganese oxide nanostructures as electrodes for electrochemical capacitors. Electrochim. Acta 296, 916-924 (2019). https://doi.org/10.1016/j.electacta.2018.11.033
[182] Q. Chen, Y. Meng, C. Hu, Y. Zhao, H. Shao, N. Chen, L. Qu, MnO2-modified hierarchical graphene fiber electrochemical supercapacitor. J. Power Sources 247, 32-39 (2014). https://doi.org/10.1016/j.jpowsour.2013.08.045
[183] H. Gao, F. Xiao, C.B. Ching, H. Duan, High-performance asymmetric supercapacitor based on graphene hydrogel and nanostructured MnO2. ACS Appl. Mater. Interfaces 4, 2801-2810 (2012). https://doi.org/10.1021/am300455d
[184] S.H. Kazemi, M.A. Kiani, M. Ghaemmaghami, H. Kazemi, Nano-architectured MnO2 electrodeposited on the Cu-decorated nickel foam substrate as supercapacitor electrode with excellent areal capacitance. Electrochim. Acta 197, 107-116 (2016). https://doi.org/10.1016/j.electacta.2016.03.063
[185] M. Kundu, L. Liu, Direct growth of mesoporous MnO2 nanosheet arrays on nickel foam current collectors for high-performance pseudocapacitors. J. Power Sources 243, 676-681 (2013). https://doi.org/10.1016/j.jpowsour.2013.06.059
[186] L. Li, X. Zhang, G. Wu, X. Peng, K. Huo, P.K. Chu, Supercapacitor electrodes based on hierarchical mesoporous MnOx/nitrided TiO2 nanorod arrays on carbon fiber paper. Adv. Mater. Interfaces 2, 1400446 (2015). https://doi.org/10.1002/admi.201400446 [187] S.-M. Li, Y.-S. Wang, S.-Y. Yang, C.-H. Liu, K.-H. Chang et al., Electrochemical deposition of nanostructured manganese oxide on hierarchically porous graphene–carbon nanotube structure for ultrahigh-performance electrochemical capacitors. J. Power Sources 225, 347-355 (2013). https://doi.org/10.1016/j.jpowsour.2012.10.037
[188] W. Li, K. Xu, B. Li, J. Sun, F. Jiang et al., MnO2 nanoflower arrays with high rate capability for flexible supercapacitors. ChemElectroChem 1, 1003-1008 (2014). https://doi.org/10.1002/celc.201400006
[189] Y.-H. Lin, T.-Y. Wei, H.-C. Chien, S.-Y. Lu, Manganese oxide/carbon aerogel composite: An outstanding supercapacitor electrode material. Adv. Energy Mater. 1, 901-907 (2011). https://doi.org/10.1002/aenm.201100256
[190] Z. Pan, Y. Qiu, J. Yang, F. Ye, Y. Xu, X. Zhang, M. Liu, Y. Zhang, Ultra-endurance flexible all-solid-state asymmetric supercapacitors based on three-dimensionally coated MnOx nanosheets on nanoporous current collectors. Nano Energy 26, 610-619 (2016). https://doi.org/10.1016/j.nanoen.2016.05.053
[191] Z. Qi, A. Younis, D. Chu, S. Li, A facile and template-free one-pot synthesis of Mn3O4 nanostructures as electrochemical supercapacitors. Nano-Micro Lett. 8, 165-173 (2016). https://doi.org/10.1007/s40820-015-0074-0
[192] A. Rafique, A. Massa, M. Fontana, S. Bianco, A. Chiodoni, C.F. Pirri, S. Hernandez, A. Lamberti, Highly uniform anodically deposited film of MnO2 nanoflakes on carbon fibers for flexible and wearable fiber-shaped supercapacitors. ACS Appl. Mater. Interfaces 9, 28386-28393 (2017). https://doi.org/10.1021/acsami.7b06311
[193] W. Wei, X. Cui, W. Chen, D.G. Ivey, Electrochemical cyclability mechanism for MnO2 electrodes utilized as electrochemical supercapacitors. J. Power Sources 186, 543-550 (2009). https://doi.org/10.1016/j.jpowsour.2008.10.058
[194] Z. Ye, T. Li, G. Ma, X. Peng, J. Zhao, Morphology controlled MnO2 electrodeposited on carbon fiber paper for high-performance supercapacitors. J. Power Sources 351, 51-57 (2017). https://doi.org/10.1016/j.jpowsour.2017.03.104
[195] Y. Zheng, W. Pann, D. Zhengn, C. Sun, Fabrication of functionalized graphene-based MnO2 nanoflower through electrodeposition for high-performance supercapacitor electrodes. J. Electrochem. Soc. 163, D230-D238 (2016). https://doi.org/10.1149/2.0341606jes
[196] B. Yao, S. Chandrasekaran, J. Zhang, W. Xiao, F. Qian, C. Zhu, E.B. Duoss, C.M. Spadaccini, M.A. Worsley, Y. Li, Efficient 3D printed pseudocapacitive electrodes with ultrahigh MnO2 loading. Joule 3, 459-470 (2019). https://doi.org/10.1016/j.joule.2018.09.020
[197] Y. Song, T. Liu, B. Yao, M. Li, T. Kou et al., Ostwald ripening improves rate capability of high mass loading manganese oxide for supercapacitors. ACS Energy Lett. 2, 1752-1759 (2017). https://doi.org/10.1021/acsenergylett.7b00405
[198] Z.-H. Huang, Y. Song, X.-X. Liu, Boosting operating voltage of vanadium oxide-based symmetric aqueous supercapacitor to 2V. Chem. Eng. J. 358, 1529-1538 (2019). https://doi.org/10.1016/j.cej.2018.10.136
[199] A.M. Engstrom, F.M. Doyle, Exploring the cycle behavior of electrodeposited vanadium oxide electrochemical capacitor electrodes in various aqueous environments. J. Power Sources 228, 120-131 (2013). https://doi.org/10.1016/j.jpowsour.2012.11.075
[200] A. Ghosh, E.J. Ra, M. Jin, H.-K. Jeong, T.H. Kim, C. Biswas, Y.H. Lee, High pseudocapacitance from ultrathin V2O5 films electrodeposited on self-standing carbon-nanofiber paper. Adv. Funct. Mater. 21, 2541-2547 (2011). https://doi.org/10.1002/adfm.201002603
[201] R.S. Ingole, B.J. Lokhande, Electrochemically synthesized mesoporous architecture of vanadium oxide on flexible stainless steel for high performance supercapacitor. J. Mater. Sci.-Mater. Electron. 28, 10951-10957 (2017). https://doi.org/10.1007/s10854-017-6875-9
[202] C.-H. Lai, C.-K. Lin, S.-W. Lee, H.-Y. Li, J.-K. Chang, M.-J. Deng, Nanostructured Na-doped vanadium oxide synthesized using an anodic deposition technique for supercapacitor applications. J. Alloy Compd. 536, S428-S431 (2012). https://doi.org/10.1016/j.jallcom.2011.12.038
[203] E. Armstrong, M. O'Sullivan, J. O'Connell, J.D. Holmes, C. O'Dwyer, 3D vanadium oxide inverse opal growth by electrodeposition. J. Electrochem. Soc. 162, D605-D612 (2015). https://doi.org/10.1149/2.0541514jes
[204] D.L. da Silva, R.G. Delatorre, G. Pattanaik, G. Zangari, W. Figueiredo, R.-P. Blum, H. Niehus, A.A. Pasa, Electrochemical synthesis of vanadium oxide nanofibers. J. Electrochem. Soc. 155, E14 (2008). https://doi.org/10.1149/1.2804856
[205] Y.R. Lu, T.Z. Wu, C.L. Chen, D.H. Wei, J.L. Chen, W.C. Chou, C.L. Dong, Mechanism of electrochemical deposition and coloration of electrochromic V2O5 nano thin films: An in situ X-ray spectroscopy study. Nanoscale Res. Lett. 10, 387 (2015). https://doi.org/10.1186/s11671-015-1095-9
[206] D. Rehnlund, M. Valvo, K. Edström, L. Nyholm, Electrodeposition of vanadium oxide/manganese oxide hybrid thin films on nanostructured aluminum substrates. J. Electrochem. Soc. 161, D515-D521 (2014). https://doi.org/10.1149/2.0511410jes
[207] K. Takahashi, S.J. Limmer, Y. Wang, G. Cao, Synthesis and electrochemical properties of single-crystal V2O5 nanorod arrays by template-based electrodeposition. J. Phys. Chem. B 108, 9795-9800 (2004). https://doi.org/10.1021/jp0491820
[208] Y. Wang, K. Takahashi, H. Shang, G. Cao, Synthesis and electrochemical properties of vanadium pentoxide nanotube arrays. J. Phys. Chem. B 109, 3085-3088 (2005). https://doi.org/10.1021/jp044286w
[209] J.-D. Xie, H.-Y. Li, T.-Y. Wu, J.-K. Chang, Y.A. Gandomi, Electrochemical energy storage of nanocrystalline vanadium oxide thin films prepared from various plating solutions for supercapacitors. Electrochim. Acta 273, 257-263 (2018). https://doi.org/10.1016/j.electacta.2018.04.007
[210] H. Drosos, A. Sapountzis, E. Koudoumas, N. Katsarakis, D. Vernardou. Effect of deposition current density on electrodeposited vanadium oxide coatings. J. Mater. Chem. 159, E145-E147 (2012). https://doi.org/10.1149/2.017208jes
[211] Q. Qu, Y. Zhu, X. Gao, Y. Wu, Core-shell structure of polypyrrole grown on V2O5 nanoribbon as high performance anode material for supercapacitors. Adv. Energy Mater. 2, 950-955 (2012). https://doi.org/10.1002/aenm.201200088
[212] J.G. Wang, H. Liu, H. Liu, W. Hua, M. Shao, Interfacial constructing flexible V2O5@polypyrrole core-shell nanowire membrane with superior supercapacitive performance. ACS Appl. Mater. Interfaces 10, 18816-18823 (2018). https://doi.org/10.1021/acsami.8b05660
[213] T.M. McEvoy, K.J. Stevenson, Elucidation of the electrodeposition mechanism of molybdenum oxide from iso- and peroxo-polymolybdate solutions. J. Mater. Res. 19, 429-438 (2011). https://doi.org/10.1557/jmr.2004.19.2.429
[214] V.S. Saji, C.W. Lee, Molybdenum, molybdenum oxides, and their electrochemistry. ChemSusChem 5, 1146-1161 (2012). https://doi.org/10.1002/cssc.201100660
[215] W. Zhang, H. Li, C.J. Firby, M. Al-Hussein, A.Y. Elezzabi, Oxygen-vacancy-tunable electrochemical properties of electrodeposited molybdenum oxide films. ACS Appl. Mater. Interfaces 11, 20378-20385 (2019). https://doi.org/10.1021/acsami.9b04386
[216] H. Farsi, F. Gobal, H. Raissi, S. Moghiminia, The pH effects on the capacitive behavior of nanostructured molybdenum oxide. J. Solid State Electrochem. 14, 681-686 (2009). https://doi.org/10.1007/s10008-009-0828-z
[217] H. Farsi, F. Gobal, H. Raissi, S. Moghiminia, On the pseudocapacitive behavior of nanostructured molybdenum oxide. J. Solid State Electrochem. 14, 643-650 (2009). https://doi.org/10.1007/s10008-009-0830-5
[218] T. Tsumura, Lithium insertion/extraction reaction on crystalline MoO3. Solid State Ionics 104, 183-189 (1997). https://doi.org/10.1016/s0167-2738(97)00418-9
[219] C.R. Clayton, Y.C. Lu, Electrochemical and XPS evidence of the aqueous formation of Mo2O5. Surf. Inter. Anal. 14, 66-70 (1989). https://doi.org/10.1002/sia.740140114
[220] C. Liu, Z. Xie, W. Wang, Z. Li, Z. Zhang, The Ti@MoOx nanorod array as a threedimensional film electrode for micro-supercapacitors. Electrochem. Commun. 44, 23-26 (2014). https://doi.org/10.1016/j.elecom.2014.04.007
[221] C. Liu, Z. Xie, W. Wang, Z. Li, Z. Zhang, Fabrication of MoOx film as a conductive anode material for micro-supercapacitors by electrodeposition and annealing. J. Electrochem. Soc. 161, A1051-A1057 (2014). https://doi.org/10.1149/2.081406jes
[222] K.K. Upadhyay, T. Nguyen, T.M. Silva, M.J. Carmezim, M.F. Montemor, Electrodeposited MoOx films as negative electrode materials for redox supercapacitors. Electrochim. Acta 225, 19-28 (2017). https://doi.org/10.1016/j.electacta.2016.12.106
[223] D.D. Yao, J.Z. Ou, K. Latham, S. Zhuiykov, A.P. O’Mullane, K. Kalantar-zadeh, Electrodeposited α- and β-phase MoO3 films and investigation of their gasochromic properties. Cryst. Growth Des. 12, 1865-1870 (2012). https://doi.org/10.1021/cg201500b
[224] F. Wang, Z. Liu, X. Wang, X. Yuan, X. Wu, Y. Zhu, L. Fu, Y. Wu, A conductive polymer coated MoO3 anode enables an Al-ion capacitor with high performance. J. Mater. Chem. A 4, 5115-5123 (2016). https://doi.org/10.1039/c6ta01398h
[225] S. Sun, X. Liao, Y. Sun, G. Yin, Y. Yao, Z. Huang, X. Pu, Facile synthesis of a α-MoO3 nanoplate/TiO2 nanotube composite for high electrochemical performance. RSC Adv. 7, 22983-22989 (2017). https://doi.org/10.1039/c7ra01164d
[226] X. Xiao, T. Ding, L. Yuan, Y. Shen, Q. Zhong et al., WO3x/MoO3x core/shell nanowires on carbon fabric as an anode for all-solid-state asymmetric supercapacitors. Adv. Energy Mater. 2, 1328-1332 (2012). https://doi.org/10.1002/aenm.201200380
[227] G.-R. Li, Z.-L. Wang, F.-L. Zheng, Y.-N. Ou, Y.-X. Tong, ZnO@MoO3 core/shell nanocables: Facile electrochemical synthesis and enhanced supercapacitor performances. J. Mater. Chem. 21, 4217-4221 (2011). https://doi.org/10.1039/c0jm03500a
[228] J.-C. Liu, H. Li, M. Batmunkh, X. Xiao, Y. Sun et al., Structural engineering to maintain the superior capacitance of molybdenum oxides at ultrahigh mass loadings. J. Mater. Chem. A 7, 23941-23948 (2019). https://doi.org/10.1039/c9ta04835a
[229] X.F. Lu, Z.X. Huang, Y.X. Tong, G.R. Li, Asymmetric supercapacitors with high energy density based on helical hierarchical porous NaxMnO2 and MoO2. Chem. Sci. 7, 510-517 (2016). https://doi.org/10.1039/c5sc03326h
[230] H. Zheng, J.Z. Ou, M.S. Strano, R.B. Kaner, A. Mitchell, K. Kalantar-zadeh, Nanostructured tungsten oxide-properties, synthesis, and applications. Adv. Funct. Mater. 21, 2175-2196 (2011). https://doi.org/10.1002/adfm.201002477
[231] B. Yang, H. Li, M. Blackford, V. Luca, Novel low density mesoporous WO3 films prepared by electrodeposition. Curr. Appl. Phys. 6, 436-439 (2006). https://doi.org/10.1016/j.cap.2005.11.035
[232] S. Wang, X. Feng, J. Yao, L. Jiang, Controlling wettability and photochromism in a dual-responsive tungsten oxide film. Angew. Chem. Int. Ed. 45, 1264-1267 (2006). https://doi.org/10.1002/anie.200502061
[233] P. Shen, N. Chi, K.-Y. Chan, Morphology of electrodeposited WO3 studied by atomic force microscopy. J. Mater. Chem. 10, 697-700 (2000). https://doi.org/10.1039/a908348k
[234] Z. Sun, X.G. Sang, Y. Song, D. Guo, D.Y. Feng, X. Sun, X.X. Liu, A high performance tungsten bronze electrode in a mixed electrolyte and applications in supercapacitors. Chem. Commun. 55, 14323-14326 (2019). https://doi.org/10.1039/c9cc06845g
[235] G. Yang, X.-X. Liu, Electrochemical fabrication of interconnected tungsten bronze nanosheets for high performance supercapacitor. J. Power Sources 383, 17-23 (2018). https://doi.org/10.1016/j.jpowsour.2018.02.035
[236] T. Pauporté, A simplified method for WO3 electrodeposition. J. Electrochem. Soc. 149, C539-C545 (2002). https://doi.org/10.1088/2053-1583/ab1e0a
[237] S.H. Baeck, K.S. Choi, T.F. Jaramillo, G.D. Stucky, E.W. McFarland, Enhancement of photocatalytic and electrochromic properties of electrochemically fabricated mesoporous WO3 thin films. Adv. Mater. 15, 1269-1273 (2003). https://doi.org/10.1002/adma.200304669
[238] A.K. Srivastava, M. Deepa, S. Singh, R. Kishore, S.A. Agnihotry, Microstructural and electrochromic characteristics of electrodeposited and annealed WO3 films. Solid State Ionics 176, 1161-1168 (2005). https://doi.org/10.1016/j.ssi.2004.10.006
[239] M. Deepa, A.K. Srivastava, T.K. Saxena, S.A. Agnihotry, Annealing induced microstructural evolution of electrodeposited electrochromic tungsten oxide films. Appl. Surf. Sci. 252, 1568-1580 (2005). https://doi.org/10.1016/j.apsusc.2005.02.123
[240] M. Deepa, M. Kar, S.A. Agnihotry, Electrodeposited tungsten oxide films: Annealing effects on structure and electrochromic performance. Thin Solid Films 468, 32-42 (2004). https://doi.org/10.1016/j.tsf.2004.04.056
[241] C. Yao, B. Wei, H. Li, G. Wang, Q. Han, H. Ma, Q. Gong, Carbon-encapsulated tungsten oxide nanowires as a stable and high-rate anode material for flexible asymmetric supercapacitors. J. Mater. Chem. A 5, 56-61 (2017). https://doi.org/10.1039/c6ta08274b
[242] Y. Zeng, M. Yu, Y. Meng, P. Fang, X. Lu, Y. Tong, Iron-based supercapacitor electrodes: Advances and challenges. Adv. Energy Mater. 6, 1601053 (2016). https://doi.org/10.1002/aenm.201601053
[243] Q. Xia, M. Xu, H. Xia, J. Xie, Nanostructured iron oxide/hydroxide-based electrode materials for supercapacitors. ChemNanoMat 2, 588-600 (2016). https://doi.org/10.1002/cnma.201600110
[244] J. Chen, J. Xu, S. Zhou, N. Zhao, C.-P. Wong, Amorphous nanostructured FeOOH and Co–Ni double hydroxides for high-performance aqueous asymmetric supercapacitors. Nano Energy 21 145-153 (2016). https://doi.org/10.1016/j.nanoen.2015.12.029
[245] X.-F. Lu, X.-Y. Chen, W. Zhou, Y.-X. Tong, G.-R. Li, α-Fe2O3@PANI core–shell nanowire arrays as negative electrodes for asymmetric supercapacitors. ACS Appl. Mater. Interfaces 7, 14843-14850 (2015). https://doi.org/10.1021/acsami.5b03126
[246] J. Liu, M. Zheng, X. Shi, H. Zeng, H. Xia, Amorphous FeOOH quantum dots assembled mesoporous film anchored on graphene nanosheets with superior electrochemical performance for supercapacitors. Adv. Funct. Mater. 26, 919-930 (2016). https://doi.org/10.1002/adfm.201504019
[247] J. Sun, Y. Huang, C. Fu, Y. Huang, M. Zhu, X. Tao, C. Zhi, H. Hu, A high performance fiber-shaped PEDOT@MnO2//C@Fe3O4 asymmetric supercapacitor for wearable electronics. J. Mater. Chem. A 4, 14877-14883 (2016). https://doi.org/10.1039/c6ta05898a
[248] M.-S. Wu, R.-H. Lee, Electrochemical growth of iron oxide thin films with nanorods and nanosheets for capacitors. J. Electrochem. Soc. 156, A737-A743 (2009). https://doi.org/10.1149/1.3160547
[249] K.A. Owusu, L. Qu, J. Li, Z. Wang, K. Zhao et al., Low-crystalline iron oxide hydroxide nanoparticle anode for high-performance supercapacitors. Nat. Commun. 8 14264 (2017). https://doi.org/10.1038/ncomms14264
[250] W. Fu, E. Zhao, X. Ren, A. Magasinski, G. Yushin, Hierarchical fabric decorated with carbon nanowire/metal oxide nanocomposites for 1.6V wearable aqueous supercapacitors. Adv. Energy Mater. 8, 1703454, (2018). https://doi.org/10.1002/aenm.201703454
[251] Y.C. Chen, Y.G. Lin, Y.K. Hsu, S.C. Yen, K.H. Chen, L.C. Chen, Novel iron oxyhydroxide lepidocrocite nanosheet as ultrahigh power density anode material for asymmetric supercapacitors. Small 10, 3803-3810 (2014). https://doi.org/10.1002/smll.201400597
[252] X. Tang, R. Jia, T. Zhai, H. Xia, Hierarchical Fe3O4@Fe2O3 core-shell nanorod arrays as high-performance anodes for asymmetric supercapacitors. ACS Appl. Mater. Interfaces 7, 27518-27525 (2015). https://doi.org/10.1021/acsami.5b09766
[253] Y. Li, J. Xu, T. Feng, Q. Yao, J. Xie, H. Xia, Fe2O3 nanoneedles on ultrafine nickel nanotube arrays as efficient anode for high-performance asymmetric supercapacitors. Adv. Funct. Mater. 27, 1606728 (2017). https://doi.org/10.1002/adfm.201606728
[254] T. Deng, W. Zhang, O. Arcelus, J.G. Kim, J. Carrasco et al., Atomic-level energy storage mechanism of cobalt hydroxide electrode for pseudocapacitors. Nat. Commun. 8, 15194 (2017). https://doi.org/10.1038/ncomms15194
[255] V. Gupta, S. Gupta, N. Miura, Potentiostatically deposited nanostructured CoxNi1x layered double hydroxides as electrode materials for redox-supercapacitors. J. Power Sources 175, 680-685 (2008). https://doi.org/10.1016/j.jpowsour.2007.09.004
[256] Y. Zeng, Z. Lai, Y. Han, H. Zhang, S. Xie, X. Lu, Oxygen-vacancy and surface modulation of ultrathin nickel cobaltite nanosheets as a high-energy cathode for advanced Zn-ion batteries. Adv. Mater. 30, 1802396 (2018). https://doi.org/10.1002/adma.201802396
[257] Y. Zeng, Y. Meng, Z. Lai, X. Zhang, M. Yu et al., An ultrastable and high-performance flexible fiber-shaped Ni-Zn battery based on a Ni-NiO heterostructured nanosheet cathode. Adv. Mater. 29, 1702698 (2017). https://doi.org/10.1002/adma.201702698
[258] M. Huang, M. Li, C. Niu, Q. Li, L. Mai, Recent advances in rational electrode designs for high-performance alkaline rechargeable batteries. Adv. Funct. Mater. 29, 1807847 (2019). https://doi.org/10.1002/adfm.201807847
[259] Y. Liu, N. Fu, G. Zhang, M. Xu, W. Lu, L. Zhou, H. Huang, Design of hierarchical Ni-Co@Ni-Co layered double hydroxide core-shell structured nanotube array for high-performance flexible all-solid-state battery-type supercapacitors. Adv. Funct. Mater. 27, 1605307 (2017). https://doi.org/10.1002/adfm.201605307
[260] G. Nagaraju, S. Chandra Sekhar, L. Krishna Bharat, J.S. Yu, Wearable fabrics with self-branched bimetallic layered double hydroxide coaxial nanostructures for hybrid supercapacitors. ACS Nano 11, 10860-10874 (2017). https://doi.org/10.1021/acsnano.7b04368
[261] T. Wang, B. Zhao, H. Jiang, H.-P. Yang, K. Zhang et al., Electro-deposition of CoNi2S4 flower-like nanosheets on 3D hierarchically porous nickel skeletons with high electrochemical capacitive performance. J. Mater. Chem. A 3, 23035-23041 (2015). https://doi.org/10.1039/c5ta04705f
[262] H. Xu, C. Zhang, W. Zhou, G.R. Li, Co(OH)2/RGO/NiO sandwich-structured nanotube arrays with special surface and synergistic effects as high-performance positive electrodes for asymmetric supercapacitors. Nanoscale 7, 16932-16942 (2015). https://doi.org/10.1039/c5nr04449a
[263] G. Xiong, P. He, D. Wang, Q. Zhang, T. Chen, T.S. Fisher, Hierarchical Ni-Co hydroxide petals on mechanically robust graphene petal foam for high-energy asymmetric supercapacitors. Adv. Funct. Mater. 26, 5460-5470 (2016). https://doi.org/10.1002/adfm.201600879
[264] Hierarchical multicomponent electrode with interlaced Ni(OH)2 nanoflakes wrapped zinc cobalt sulfide nanotube arrays for sustainable high-performance supercapacitors. Adv. Energy Mater. 7, 1701228 (2017). https://doi.org/10.1002/aenm.201701228
[265] X. Lu, X. Huang, S. Xie, T. Zhai, C. Wang et al., Controllable synthesis of porous nickel–cobalt oxide nanosheets for supercapacitors. J. Mater. Chem. 22, 13357-13364 (2012). https://doi.org/10.1039/c2jm30927k
[266] H. Li, Y. Gao, C. Wang, G. Yang, A simple electrochemical route to access amorphous mixed-metal hydroxides for supercapacitor electrode materials. Adv. Energy Mater. 5, 1401767 (2015). https://doi.org/10.1002/aenm.201401767
[267] X. Xia, J. Tu, Y. Zhang, J. Chen, X. Wang, C. Gu, C. Guan, J. Luo, H.J. Fan, Porous hydroxide nanosheets on preformed nanowires by electrodeposition: Branched nanoarrays for electrochemical energy storage. Chem. Mater. 24, 3793-3799 (2012). https://doi.org/10.1021/cm302416d
[268] W. Guo, C. Yu, S. Li, X. Song, H. Huang et al., A universal converse voltage process for triggering transition metal hybrids in situ phase restruction toward ultrahigh-rate supercapacitors. Adv. Mater. 31, 1901241 (2019). https://doi.org/10.1002/adma.201901241
[269] J.C. Chen, C.-T.Hsu, C.-C. Hu, Superior capacitive performances of binary nickel–cobalt hydroxide nanonetwork prepared by cathodic deposition. J. Power Sources 253, 205-213 (2014). https://doi.org/10.1016/j.jpowsour.2013.12.073
[270] R. Li, S. Wang, Z. Huang, F. Lu, T. He, NiCo2S4@Co(OH)2 core-shell nanotube arrays in situ grown on Ni foam for high performances asymmetric supercapacitors. J. Power Sources 312, 156-164 (2016). https://doi.org/10.1016/j.jpowsour.2016.02.047
[271] H. Pourfarzad, M. Shabani-Nooshabadi, M. R. Ganjali, H. Kashani, Synthesis of Ni–Co-Fe layered double hydroxide and Fe2O3/graphene nanocomposites as actively materials for high electrochemical performance supercapacitors. Electrochim. Acta 317, 83-92 (2019). https://doi.org/10.1016/j.electacta.2019.05.122
[272] Z. Li, H. Duan, M. Shao, J. Li, D. O'Hare, M. Wei, Z.L. Wang, Ordered-vacancy-induced cation intercalation into layered double hydroxides: A general approach for high-performance supercapacitors. Chem 4, 2168-2179 (2018). https://doi.org/10.1016/j.chempr.2018.06.007
[273] G. Lee, J.W. Kim, H. Park, J.Y. Lee, H. Lee et al., dynamically stretchable, planar supercapacitors with buckled carbon nanotube/Mn-Mo mixed oxide electrodes and air-stable organic electrolyte. ACS Nano 13, 855-866 (2019). https://doi.org/10.1021/acsnano.8b08645
[274] K. Okamura, R. Inoue, T. Sebille, K. Tomono, M. Nakayama, An approach to optimize the composition of supercapacitor electrodes consisting of manganese-molybdenum mixed oxide and carbon nanotubes. J. Electrochem. Soc. 158, A711 (2011). https://doi.org/10.1149/1.3578039
[275] Y.-H. Li, Q.-Y. Li, H.-Q. Wang, Y.-G. Huang, X.-H. Zhang et al., Synthesis and electrochemical properties of nickel–manganese oxide on MWCNTs/CFP substrate as a supercapacitor electrode. Appl. Energy 153, 78-86 (2015). https://doi.org/10.1016/j.apenergy.2014.09.055 [276] H. Zhou, X. Zou, K. Zhang, P. Sun, M.S. Islam, J. Gong, Y. Zhang, J. Yang, Molybdenum-tungsten mixed oxide deposited into titanium dioxide nanotube arrays for ultrahigh rate supercapacitors. ACS Appl. Mater. Interfaces 9, 18699-18709 (2017). https://doi.org/10.1021/acsami.7b01871
[277] E. Karaca, D. Gökcen, N.Ö. Pekmez, K. Pekmez, Electrochemical synthesis of PPy composites with nanostructured MnOx, CoOx, NiOx, and FeOx in acetonitrile for supercapacitor applications. Electrochim. Acta 305, 502-513 (2019). https://doi.org/10.1016/j.electacta.2019.03.060
[278] C.H. Ng, H.N. Lim, Y.S. Lim, W.K. Chee, N.M. Huang, Fabrication of flexible polypyrrole/graphene oxide/manganese oxide supercapacitor. Int. J. Energy Res. 39, 344-355 (2015). https://doi.org/10.1002/er.3247
[279] L. Chen, L.-J. Sun, F. Luan, Y. Liang, Y. Li, X.-X. Liu, Synthesis and pseudocapacitive studies of composite films of polyaniline and manganese oxide nanoparticles. J. Power Sources 195, 3742-3747 (2010). https://doi.org/10.1016/j.jpowsour.2009.12.036
[280] J. Kim, H. Ju, A.I. Inamdar, Y. Jo, J. Han, H. Kim, H. Im, Synthesis and enhanced electrochemical supercapacitor properties of Ag–MnO2–polyaniline nanocomposite electrodes. Energy 70, 473-477 (2014). https://doi.org/10.1016/j.energy.2014.04.018
[281] Z. Su, C. Yang, C. Xu, H. Wu, Z. Zhang et al., Co-electro-deposition of the MnO2–PEDOT:PSS nanostructured composite for high areal mass, flexible asymmetric supercapacitor devices. J. Mater. Chem. A 1, 12432 (2013). https://doi.org/10.1039/c3ta13148c
[282] Z. Wang, J. Du, M. Zhang, J. Yu, H. Liu et al., Continuous preparation of high performance flexible asymmetric supercapacitor with a very fast, low-cost, simple and scalable electrochemical co-deposition method. J. Power Sources 437, 226827 (2019). https://doi.org/10.1016/j.jpowsour.2019.226827
[283] P. Asen, S. Shahrokhian, A. Iraji zad, One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor. Int. J. Hydrog. Energy 42, 21073-21085 (2017). https://doi.org/10.1016/j.ijhydene.2017.07.008
[284] M.H. Bai, L.J. Bian, Y. Song, X.X. Liu, Electrochemical codeposition of vanadium oxide and polypyrrole for high-performance supercapacitor with high working voltage. ACS Appl. Mater. Interfaces 6, 12656-12664 (2014). https://doi.org/10.1021/am502630g
[285] M.-Y. Zhang, Y. Song, D. Guo, D. Yang, X. Sun et al., Strongly coupled polypyrrole/molybdenum oxide hybrid films via electrochemical layer-by-layer assembly for pseudocapacitors. J. Mater. Chem. A 7, 9815-9821 (2019). https://doi.org/10.1039/c9ta00705a
[286] J.-W. Geng, Y.-J. Ye, D. Guo, X.-X. Liu, Concurrent electropolymerization of aniline and electrochemical deposition of tungsten oxide for supercapacitor. J. Power Sources 342, 980-989 (2017). https://doi.org/10.1016/j.jpowsour.2017.01.029
[287] Y. Wang, S. Dong, X. Wu, M. Li, One-step electrodeposition of MnO2@NiAl layered double hydroxide nanostructures on the nickel foam for high-performance supercapacitors. J. Electrochem. Soc. 164, H56-H62 (2016). https://doi.org/10.1149/2.0861702jes
[288] Z. Zeng, P. Sun, J. Zhu, X. Zhu, Porous petal-like Ni(OH)2−MnOx nanosheet electrodes grown on carbon fiber paper for supercapacitors. Surf. Inter. 8, 73-82 (2017). https://doi.org/10.1016/j.surfin.2017.04.011
[289] B.-X. Zou, Y. Liang, X.-X. Liu, D. Diamond, K.-T. Lau, Electrodeposition and pseudocapacitive properties of tungsten oxide/polyaniline composite. J. Power Sources 196, 4842-4848 (2011). https://doi.org/10.1016/j.jpowsour.2011.01.073
[290] X. Fan, X. Wang, G. Li, A. Yu, Z. Chen, High-performance flexible electrode based on electrodeposition of polypyrrole/MnO2 on carbon cloth for supercapacitors. J. Power Sources 326, 357-364 (2016). https://doi.org/10.1016/j.jpowsour.2016.05.047
[291] C.-C. Hu, C.-Y. Hung, K.-H. Chang, Y.-L. Yang, A hierarchical nanostructure consisting of amorphous MnO2, Mn3O4 nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors. J. Power Sources 196, 847-850 (2011). https://doi.org/10.1016/j.jpowsour.2010.08.001
[292] P. Tang, L. Han, L. Zhang, Facile synthesis of graphite/PEDOT/MnO2 composites on commercial supercapacitor separator membranes as flexible and high-performance supercapacitor electrodes. ACS Appl. Mater. Interfaces 6, 10506-10515 (2014). https://doi.org/10.1021/am5021028
[293] N. Zhao, H. Fan, M. Zhang, C. Wang, X. Ren et al., Preparation of partially-cladding NiCo-LDH/Mn3O4 composite by electrodeposition route and its excellent supercapacitor performance. J. Alloy. Compd. 796, 111-119 (2019). https://doi.org/10.1016/j.jallcom.2019.05.023
[294] D.V. Zhuzhelskii, E.G. Tolstopjatova, S.N. Eliseeva, A.V. Ivanov, S. Miao, V.V. Kondratiev, Electrochemical properties of PEDOT/WO3 composite films for high performance supercapacitor application. Electrochim. Acta 299, 182-190 (2019). https://doi.org/10.1016/j.electacta.2019.01.007
[295] S.-Q. Wang, X. Cai, Y. Song, X. Sun, X.-X. Liu, VOx@MoO3 nanorod composite for high-performance supercapacitors. Adv. Funct. Mater. 28, 1803901 (2018). https://doi.org/10.1002/adfm.201803901
[296] G.-F. Chen, Z.-Q. Liu, J.-M. Lin, N. Li, Y.-Z. Su, Hierarchical polypyrrole based composites for high performance asymmetric supercapacitors. J. Power Sources 283, 484-493 (2015). https://doi.org/10.1016/j.jpowsour.2015.02.103
[297] J. Yang, C. Yu, X. Fan, S. Liang, S. Li, H. Huang, Z. Ling, C. Hao, J. Qiu, Electroactive edge site-enriched nickel–cobalt sulfide into graphene frameworks for high-performance asymmetric supercapacitors. Energy Environ. Sci. 9, 1299-1307 (2016). https://doi.org/10.1039/c5ee03633j
[298] J. Zeng, J. Liu, S.S. Siwal, W. Yang, X. Fu, Q. Zhang, Morphological and electronic modification of 3D porous nickel microsphere arrays by cobalt and sulfur dual synergistic modulation for overall water splitting electrolysis and supercapacitors. Appl. Surf. Sci. 491, 570-578 (2019). https://doi.org/10.1016/j.apsusc.2019.06.182
[299] B.D. Falola, L. Fan, T. Wiltowski, I.I. Suni, Electrodeposition of Cu-doped MoS2 for charge storage in electrochemical supercapacitors. J. Electrochem. Soc. 164, D674-D679 (2017). https://doi.org/10.1149/2.0421712jes
[300] B.D. Falola, T. Wiltowski, I.I. Suni, Electrodeposition of MoS2 for charge storage in electrochemical supercapacitors. J. Electrochem. Soc. 163, D568-D574 (2016). https://doi.org/10.1149/2.0011610jes
[301] X. Zhang, J. Gong, K. Zhang, W. Zhu, J.-C. Li, Q. Ding, All-solid-state asymmetric supercapacitor based on porous cobalt selenide thin films. J. Alloys Compd. 772, 25-32 (2019). https://doi.org/10.1016/j.jallcom.2018.09.023
[302] W. Chen, C. Xia, H.N. Alshareef, One-step electrodeposited nickel cobalt sulfide nanosheet arrays for high-performance asymmetric supercapacitors. ACS Nano 8, 9531-9541 (2014). https://doi.org/10.1021/nn503814y
[303] K.R. Prasad, K. Koga, N. Miura, Electrochemical deposition of nanostructured indium oxide:  High-performance electrode material for redox supercapacitors. Chem. Mater. 16, 1845-1847 (2004). https://doi.org/10.1021/cm0497576
[304] A. Albu-Yaron, C. Lévy-Clément, A. Katty, S. Bastide, R. Tenne, Influence of the electrochemical deposition parameters on the microstructure of MoS2 thin films. Thin Solid Films 361-362, 223-228 (2000). https://doi.org/10.1016/s0040-6090(99)00838-x
[305] W. Deng, X. Feng, Y. Xiao, C. Li, Layered molybdenum (oxy) pyrophosphate (MoO2)2P2O7 as a cathode material for sodium-ion batteries. ChemElectroChem 5, 1032-1036 (2018). https://doi.org/10.1002/celc.201800005
[306] B. Wen, N.A. Chernova, R. Zhang, Q. Wang, F. Omenya, J. Fang, M.S. Whittingham, Layered molybdenum (oxy)pyrophosphate as cathode for lithium-ion batteries. Chem. Mat. 25, 3513-3521 (2013). https://doi.org/10.1021/cm401946h
[307] C. Masquelier, L. Croguennec, Polyanionic (phosphates, silicates, sulfates) frameworks as electrode materials for rechargeable Li (or Na) batteries. Chem. Rev. 113, 6552-6591 (2013). https://doi.org/10.1021/cr3001862
[308] R. Murugavel, A. Choudhury, M.G. Walawalkar, R. Pothiraja, C.N. Rao, Metal complexes of organophosphate esters and open-framework metal phosphates: Synthesis, structure, transformations, and applications. Chem. Rev. 108, 3549-3655 (2008). https://doi.org/10.1021/cr000119q
[309] R. Sahoo, D.T. Pham, T.H. Lee, T.H.T. Luu, J. Seok, Y.H. Lee, Redox-driven route for widening voltage window in asymmetric supercapacitor. ACS Nano 12, 8494-8505 (2018). https://doi.org/10.1021/acsnano.8b04040
[310] Y. Yang, H. Hou, G. Zou, W. Shi, H. Shuai, J. Li, X. Ji, Electrochemical exfoliation of graphene-like two-dimensional nanomaterials. Nanoscale 11, 16-33 (2018). https://doi.org/10.1039/c8nr08227h
[311] S. Yang, P. Zhang, F. Wang, A.G. Ricciardulli, M.R. Lohe, P.W.M. Blom, X. Feng, Fluoride-free synthesis of two-dimensional titanium carbide (MXene) using a binary aqueous system. Angew. Chem. Int. Ed. 57, 15491-15495 (2018). https://doi.org/10.1002/anie.201809662
[312] M. Le Thai, G.T. Chandran, R.K. Dutta, X. Li, R.M. Penner, 100k cycles and beyond: Extraordinary cycle stability for MnO2 nanowires imparted by a gel electrolyte. ACS Energy Lett. 1, 57-63 (2016). https://doi.org/10.1021/acsenergylett.6b00029
[313] P. Zhang, F. Wang, S. Yang, G. Wang, M. Yu, X. Feng, Flexible in-plane micro-supercapacitors: Progresses and challenges in fabrication and applications. Energy Storage Mater. 28, 160-187 (2020). https://doi.org/10.1016/j.ensm.2020.02.029
[314] A. Emrani, P. Vasekar, C.R. Westgate, Effects of sulfurization temperature on CZTS thin film solar cell performances. Sol. Energy 98, 335-340 (2013). https://doi.org/10.1016/j.solener.2013.09.020
[315] J.G. Werner, G.G. Rodríguez-Calero, H.D. Abruña, U. Wiesner, Block copolymer derived 3-D interpenetrating multifunctional gyroidal nanohybrids for electrical energy storage. Energy Environ. Sci. 11, 1261-1270 (2018). https://doi.org/10.1039/c7ee03571c
[316] T. Liu, F. Yang, G. Cheng, W. Luo, Reduced graphene oxide-wrapped Co9-xFexS8 /Co,Fe-N-C composite as bifunctional electrocatalyst for oxygen reduction and evolution. Small 14, 1703748 (2018). https://doi.org/10.1002/smll.201703748
[317] H. Niu, Y. Zhang, Y. Liu, B. Luo, N. Xin, W. Shi, MOFs-derived Co9S8-embedded graphene/hollow carbon spheres film with macroporous frameworks for hybrid supercapacitors with superior volumetric energy density. J. Mater. Chem. A 7, 8503-8509 (2019). https://doi.org/10.1039/c8ta11983j
[318] X.M. Lin, J.H. Chen, J.J. Fan, Y. Ma, P. Radjenovic et al., Synthesis and operando sodiation mechanistic study of nitrogen-doped porous carbon coated bimetallic sulfide hollow nanocubes as advanced sodium ion battery anode. Adv. Energy Mater. 9, 1902312 (2019). https://doi.org/10.1002/aenm.201902312
[319] R. Kumar, S. Sahoo, E. Joanni, R.K. Singh, R.M. Yadav et al., A review on synthesis of graphene, h-BN and MoS2 for energy storage applications: Recent progress and perspectives. Nano Res. 12, 2655-2694 (2019). https://doi.org/10.1007/s12274-019-2467-8

Citation Information

Lv, H., Pan, Q., Song, Y. et al. A Review on Nano-/Microstructured Materials Constructed by Electrochemical Technologies for Supercapacitors. Nano-Micro Lett. 12, 118 (2020). https://doi.org/10.1007/s40820-020-00451-z

History

Received: 22 March 2020 / Accepted: 22 April 2020 / Published online: 30 May 2020


Additional Info

  • Type of Publishing: JOUR - Journal
  • Title: A Review on Nano-/Microstructured Materials Constructed by Electrochemical Technologies for Supercapacitors
  • Author: Lv, H., Pan, Q., Song, Y. et al.
  • Year: 2020
  • Volume: 12
  • Journal Name: Nano-Micro Letters
  • ISSN: 2150-5551
  • URL: http://dx.doi.org/10.1007/s40820-020-00451-z
  • Abstract: The article reviews the recent progress of electrochemical techniques on synthesizing nano/microstructures as supercapacitor electrodes. With a history of more than a century, electrochemical techniques have evolved from metal plating since their inception to versatile synthesis tools for electrochemically active materials of diverse morphologies, compositions, and functions. The review begins with tutorials on the operating mechanisms of five commonly used electrochemical techniques, including cyclic voltammetry, potentiostatic deposition, galvanostatic deposition, pulse deposition, and electrophoretic deposition, followed by thorough surveys of the nano/microstructured materials synthesized electrochemically. Specifically, representative synthesis mechanisms and the state-of-the-art electrochemical performances of exfoliated graphene, conducting polymers, metal oxides, metal sulfides, and their composites are surveyed. The article concludes with summaries of the unique merits, potential challenges, and associated opportunities of electrochemical synthesis techniques for electrode materials in supercapacitors.
  • Publish Date: Saturday, 30 May 2020
  • Start Page: 118
  • DOI: 10.1007/s40820-020-00451-z