Electrochemical properties of PEDOT/WO3 composite films for high performance supercapacitor application

Fabricating stable protective layer on orthorhombic tungsten oxide anode for long-lifespan pseudocapacitors by trace of aluminum ion electrolyte additives

Orthorhombic tungsten oxide (WO3·H2O) has been considered as a promising anode material due to its layered crystal structure and high capacity. However, the instability of its crystal structure usually results in poor cyclic stability of the battery/capacitor. Herein, a novel strategy of introducing aluminum ion (Al3+) additives for designing hybrid electrolyte is demonstrated to enhance the cycling stability of WO3·H2O. Aluminum ions may participate in the redox reaction and contribute extra capacitance. More importantly, the Al3+ ions can facilitate fast phase transformation of metastable orthorhombic tungsten oxides to stable monoclinic phase, but also participate in the construction of stable protective layer during the long-term cycling, forming a protective layer at the surface of tungsten oxide for alleviating the dissolution and structural damage. The WO3·H2O is electrodeposited on the exfoliated graphite foil (Ex-GF) and shows a specific capacitance of 395 mF cm-2 at 2 mA cm-2 in the LiCl + AlCl3 hybrid electrolyte (pH = 2.93), and the capacitance remains 91.8 % after 10,000 charge/discharge cycles, indicating that the WO3·H2O/Ex-GF electrode material exhibits excellent stability in supercapacitors. The density functional theory (DFT) calculations further demonstrate whether the adsorption energy or intercalation energy of Li+ at the monoclinic WO3 is lower than the orthorhombic WO3·H2O. This result suggests that the electrochemical performance of WO3·H2O, which operates on a pseudocapacitive reaction mechanism, can be enhanced through the phase transformation from the orthorhombic phase to the monoclinic phase during the cycling. Hence, this ion additive approach can adjust the interface composition and protect internal active material, and can be extended to the stability improvement of other metal oxide electrodes.

Electropolymerization of PPy, PEDOT, and PANi on WO3 nanostructures for high-performance anodes in Li-ion batteries

In this research work, four distinct WO3 electrodes were synthesized and coated with three different polymers, known as polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) in poly(4-styrenesulfonate) (PEDOT:PSS) and polyaniline (PANi), using electropolymerization techniques. The morphological features of the samples were thoroughly characterized through Field Emission Scanning Electron Microscopy (FE-SEM) and Atomic Force Microscopy (AFM) analyses. Additionally, contact angle measurements and electrochemical characterizations were used to verify the performance of each electrode, aiding in the prediction of their suitability for energy storage applications in lithium-ion batteries. The electrodes were subsequently employed as anodes in lithium-ion batteries, and charge-discharge cycles were performed to analyze its specific capacity, and the Electrochemical Impedance Spectroscopy (EIS) technique was employed to analyze its behavior both before and after cycling. The results revealed superior performance for WO3 electrodes with PEDOT:PSS coating electropolymerized during 100 min at 0.4 mA. This comprehensive investigation not only sheds light on the synthesis and morphological characteristics of WO3 electrodes but also highlights the crucial role of PEDOT:PSS in enhancing electrochemical behavior for efficient energy storage applications.

Optimizing Electrodeposition of Polyaniline on Various Woven Steel Mesh Sizes for Enhanced Supercapacitor Performance

The development of efficient supercapacitors hinges on the innovation of superior electrodes, which are pivotal in augmenting their energy storage capabilities. Supercapacitors, recognized for their high-power density and extended cycle life, play a crucial role as sustainable solutions in addressing energy storage challenges. A fundamental aspect of supercapacitor functionality involves the electrode material, which works in concert with other key components such as the current collector, separator, and electrolyte. This study focuses on evaluating the impact of the current collector material on the performance of symmetric supercapacitors. We investigated the electropolymerization of polyaniline on woven steel mesh current collectors of varying mesh sizes, ranging from 20 to 200 mesh per inch, using assorted deposition conditions. The electrochemically modified woven steel meshes were utilized to construct symmetric supercapacitors. The electrochemical performance of the assembled supercapacitors, configured in a two-electrode system, was investigated using a variety of electrochemical techniques to better understand the kinetics of electrolyte ion migration. Notably, the 20-mesh size, characterized by the fewest pores per inch, demonstrated superior performance with an optimum capacitance of 4730 mF/cm2, an energy density of 317.8 μWh/cm2, and a power density of 400 μW/cm2 at a current density of 1 mA/cm2.

Fabrication and Characterization of a Poly(3,4-ethylenedioxythiophene)@Tungsten Trioxide-Graphene Oxide Hybrid Electrode Nanocomposite for Supercapacitor Applications

With the rapid development of nanotechnology, the study of nanocomposites as electrode materials has significantly enhanced the scope of research towards energy storage applications. Exploring electrode materials with superior electrochemical properties is still a challenge for high-performance supercapacitors. In the present research article, we prepared a novel nanocomposite of tungsten trioxide nanoparticles grown over supported graphene oxide sheets and embedded with a poly(3,4-ethylenedioxythiophene) matrix to maximize its electrical double layer capacitance. The extensive characterization shows that the poly(3,4-ethylenedioxythiophene) matrix was homogeneously dispersed throughout the surface of the tungsten trioxide-graphene oxide. The poly(3,4-ethylenedioxythiophene)@tungsten trioxide-graphene oxide exhibits a higher specific capacitance of 478.3 F·g-1 at 10 mV·s-1 as compared to tungsten trioxide-graphene oxide (345.3 F·g-1). The retention capacity of 92.1% up to 5000 cycles at 0.1 A·g-1 shows that this ternary nanocomposite electrode also exhibits good cycling stability. The poly(3,4-ethylenedioxythiophene)@tungsten trioxide-graphene oxide energy density and power densities are observed to be 54.2 Wh·kg-1 and 971 W·kg-1. The poly(3,4-ethylenedioxythiophene)@tungsten trioxide-graphene oxide has been shown to be a superior anode material in supercapacitors because of the synergistic interaction of the poly(3,4-ethylenedioxythiophene) matrix and the tungsten trioxide-graphene oxide surface. These advantages reveal that the poly(3,4-ethylenedioxythiophene)@tungsten trioxide-graphene oxide electrode can be a promising electroactive material for supercapacitor applications.

Electrochromic-Induced Rechargeable Aqueous Batteries: An Integrated Multifunctional System for Cross-Domain Applications

Multifunctional electrochromic-induced rechargeable aqueous batteries (MERABs) integrate electrochromism and aqueous ion batteries into one platform, which is able to deliver the conversion and storage of photo-thermal-electrochemical sources. Aqueous ion batteries compensate for the drawbacks of slow kinetic reactions and unsatisfied storage capacities of electrochromic devices. On the other hand, electrochromic technology can enable dynamically regulation of solar light and heat radiation. However, MERABs still face several technical issues, including a trade-off between electrochromic and electrochemical performance, low conversion efficiency and poor service life. In this connection, novel device configuration and electrode materials, and an optimized compatibility need to be considered for multidisciplinary applications. In this review, the unique advantages, key challenges and advanced applications are elucidated in a timely and comprehensive manner. Firstly, the prerequisites for effective integration of the working mechanism and device configuration, as well as the choice of electrode materials are examined. Secondly, the latest advances in the applications of MERABs are discussed, including wearable, self-powered, integrated systems and multisystem conversion. Finally, perspectives on the current challenges and future development are outlined, highlighting the giant leap required from laboratory prototypes to large-scale production and eventual commercialization.

Recent progress in electrochromic energy storage materials and devices: a minireview

Integration of several functionalities into one isolated electrochemical body is necessary to realize compact and tiny smart electronics. Recently, two different technologies, electrochromic (EC) materials and energy storage, were combined to create a single system that supports and drives both functions simultaneously. In EC energy storage devices, the characteristic feature of EC materials, their optical modulation depending on the applied voltage, is used to visually identify the stored energy level in real time. Moreover, combining energy-harvesting and EC storage systems by sharing one electrode facilitates the realization of further compact multifunction systems. In this minireview, we highlight recent groundbreaking achievements in EC multifunction systems where the stored energy levels can be visualized using the color of the device.

Proton-insertion-pseudocapacitance of tungsten bronze tunnel structure enhanced by transition metal ion anchoring

The one-dimensional channel array of hexagonal tungsten bronze (WO₃) offers an electron transfer matrix, but its overwhelming H⁺ adsorption hinders it from being a good supercapacitor electrode material. Inspired by the Volcano plot on the relation between transition-metal and free energy of H-adsorption, we propose a new strategy to anchor transition metal ions (Zn²⁺, Cu²⁺, Ni²⁺, Ag⁺, Au³⁺ and Ir³⁺) into the WO₃ lattice to improve proton-insertion based pseudocapacitance. Among the variety of transition metals, Zn²⁺ exhibits the optimal O 2p band center, which matches well with the best experimental capacitive behavior. The molar ratio of Zn/WO₃ ranges from 0.2 to 0.6. The specific capacitance for Zn²⁺-anchored WO₃ (390 F g^-1) reaches 202% of that of WO₃ (193 F g^-1) at 0.5 A g^-1 with robust stability (259 F g^-1 at 3 A g^-1 for 3000 cycles). Density functional theory confirms that O 2p is shifted down by the d-filling cations, which corresponds to alleviated O-H interaction and facilitated H⁺ desorption. The band tuning by transition-metal-ion incorporation would break new ground on developing high-capacitance metal oxide supercapacitors.

Ice-Templated Large-Scale Preparation of Two-Dimensional Sheets of Conjugated Polymers: Thickness-Independent Flexible Supercapacitance

Two-dimensional (2D) organic materials hold great promise for use in a multitude of contemporary applications due to their outstanding chemical and physical properties. Herein, 2D sheets of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) are prepared from a commercially available PEDOT:PSS suspension using ice as a template. The 2D PEDOT:PSS sheets grow in the boundaries of ice crystals as the polymers are "squeezed" out of the suspension when the water solidifies. The mechanical robustness of the sheets can be enhanced by incorporating WO₃ nanowires, and the PSS component can be conveniently removed with a concentrated solution of H₂SO₄ to afford stable suspensions of PEDOT or WO₃@PEDOT sheets, either of which can be converted into flexible films with tunable thicknesses via filtration. Swagelok- or pouch-type supercapacitor devices prepared from the WO₃@PEDOT films exhibit outstanding energy-storage characteristics, including high rate capability, thickness-independent energy storage (e.g., 701 mF cm^-2 is achieved with a 1-mm-thick film), high resistance toward mechanical deformation, and good cycling stability. Additionally, a high energy density of 0.083 mWh cm^-2 is measured for a device prepared using a 1-mm-thick film at a high power density of 10 mW cm^-2. The methodology described establishes an efficient and readily scalable approach for accessing 2D organic sheets.

Interactions in Electrodeposited Poly-3,4-Ethylenedioxythiophene-Tungsten Oxide Composite Films Studied with Spectroelectrochemistry

Cyclic voltammograms and optical absorption spectra of PEDOT/WO₃ composite films were recorded in order to identify possible interactions and modes of improved performance of the composite as compared to the single materials. Changes in the shape of redox peaks related to the W(VI)/W(V) couple in the CVs of WO₃ and the composite PEDOT/WO₃ films indicate electrostatic interactions between the negatively charged tungsten oxide species and the positively charged conducting polymer. Smaller peak separation suggests a more reversible redox process due to the presence of the conducting polymer matrix, accelerating electron transfer between tungsten ions. Electronic absorption spectra of the materials were analyzed with respect to changes of the shapes of the spectra and characteristic band positions. There are no noticeable changes in the position of the electronic absorption bands of the main chromophores in the electronic spectra of the composite film. Obviously, the interactions accelerating the redox performance do not show up in the optical spectra. This suggests that the existing electrostatic interactions in the composite do not significantly change the opto-electronic properties of components of the composite but resulted in the redistribution of fractions of polaron and bipolaron forms in the polymer.

Advances in Electrochemical Energy Devices Constructed with Tungsten Oxide-Based Nanomaterials

Tungsten oxide-based materials have drawn huge attention for their versatile uses to construct various energy storage devices. Particularly, their electrochromic devices and optically-changing devices are intensively studied in terms of energy-saving. Furthermore, based on close connections in the forms of device structure and working mechanisms between these two main applications, bifunctional devices of tungsten oxide-based materials with energy storage and optical change came into our view, and when solar cells are integrated, multifunctional devices are accessible. In this article, we have reviewed the latest developments of tungsten oxide-based nanostructured materials in various kinds of applications, and our focus falls on their energy-related uses, especially supercapacitors, lithium ion batteries, electrochromic devices, and their bifunctional and multifunctional devices. Additionally, other applications such as photochromic devices, sensors, and photocatalysts of tungsten oxide-based materials have also been mentioned. We hope this article can shed light on the related applications of tungsten oxide-based materials and inspire new possibilities for further uses.

Oxidative Spin-Spray-Assembled Coordinative Multilayers as Platforms for Capacitive Films

The spin-spray-assisted layer-by-layer (LbL) assembly technique was used to prepare coordinative oxidative multilayers from Ce(IV), inorganic polyphosphate (PP), and graphene oxide (GO). The films consist of successive tetralayers and have a general structure (PP/Ce/GO/Ce)n. Such oxidative multilayers have been shown to be a general platform for the electrodeless generation of conducting polymer and melanin-type films. Although the incorporation of GO enhances the film growth, the conventional dip LbL method is very time consuming. We show that the spin-spray method reduces the time required to grow thick multilayers by the order of magnitude and the film growth is linear from the beginning, which implies a stratified structure. We have deposited poly(3,4-ethylenedioxothiophene), PEDOT, on the oxidative multilayers and studied these redox-active films as models for melanin-type capacitive layers for supercapacitors to be used in biodegradable electronics, both before and after the electrochemical reduction of GO to rGO. The amount of oxidant and PEDOT scales linearly with the film thickness, and the charge transfer kinetics is not mass transfer-limited, especially after the reduction of GO. The areal capacitance of the films grows linearly with the film thickness, reaching a value of ca. 1.6 mF cm-2 with 20 tetralayers, and the specific volumetric (per film volume) and mass (per mass of PEDOT) capacitances are ca. 130 F cm-3 and 65 F g-1, respectively. 5,6-Dihydroxyindole can also be polymerized to a redox-active melanin-type film on these oxidative multilayers, with even higher areal capacitance values.

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

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.

Self-Standing Hydrogels Composed of Conducting Polymers for All-Hydrogel-State Supercapacitors

Conducting polymer hydrogels that are capable of contacting with electrolytes at the molecular level, represent an important electrode material. However, the fabrication of self-standing hydrogels merely composed of conducting polymers is still challenging owing to the absence of reliable methods. Herein, a novel and facile macromolecular interaction assisted route is reported to fabricate self-standing hydrogels consisting of polyaniline (PANi: providing high electrochemical activity) and poly(3,4-ethylenedioxythiophene) (PEDOT: enabling high electronic conductivity). Owing to the synergistic effect between them, the self-standing hydrogels possess good mechanical properties and electronic/electrochemical performances, making them an excellent potential electrode for solid-state energy storage devices. A proof-of-concept all-hydrogel-state supercapacitor is fabricated, which exhibits a high areal capacitance of 808.2 mF cm^-2 , and a high energy density of 0.63 mWh cm^-3 at high power density of 28.42 mW cm^-3 , superior to many recently reported conducting polymer hydrogels based supercapacitors. This study demonstrates a novel promising strategy to fabricate self-standing conducting polymer hydrogels.

Intelligent electrochromic-supercapacitor based on effective energy level matching poly(indole-6-carboxylicacid)/WO3 nanocomposites

A high-quality electrochromic-supercapacitor based on poly(indole-6-carboxylicacid)/WO₃ nanocomposites can intelligently monitor the energy storage state by changing the color of the device.

Anchoring carbon layers and oxygen vacancies endow WO3−x/C electrode with high specific capacity and rate performance for supercapacitors

Herein, novel hierarchical carbon layer-anchored WO_3−x/C ultra-long nanowires were developed via a facile solvent-thermal treatment and a subsequent rapid carbonization process. The inner anchored carbon layers and abundant oxygen vacancies endowed the WO_3−x/C nanowire electrode with high conductivity, as measured with a single nanowire, which greatly enhanced the redox reaction active sites and rate performance. Surprisingly, the WO_3−x/C electrode exhibited outstanding specific capacitance of 1032.16 F g⁻¹ at the current density of 1 A g⁻¹ in a 2 M H₂SO₄ electrolyte and maintained the specific capacitance of 660 F g⁻¹ when the current density increased to 50 A g⁻¹. Significantly, the constructed WO_3−x/C//WO_3−x/C symmetric supercapacitors achieved specific capacitance of 243.84 F g⁻¹ at the current density of 0.5 A g⁻¹ and maintained the capacitance retention of 94.29% after 5000 charging/discharging cycles at the current density of 4 A g⁻¹. These excellent electrochemical performances resulted from the fascinating structure of the WO_3−x/C nanowires, showing a great potential for future energy storage applications.

A high-performance supercapacitor electrode comprising hierarchical carbon layer-anchored WO_3−x/C nanowires with inner abundant redox reaction active sites and numerous oxygen vacancies is presented.