Temperature dependent surface morphological modifications of hexagonal WO3 thin 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.

Anode Materials for Proton Batteries: Progress and Prospects

A proton battery is considered as a promising energy storage solution with the merits of fast kinetics, high safety, low cost, and environmental benignity. The realization of these merits depends on the exploration of the appropriate and high-performance electrode materials. Although many anode materials of proton batteries have been reported, a dedicated summary of the progress, challenges, and prospects of anode materials for proton batteries has not been reported. Through discussions on the proton storage mechanisms, advantages and limitations of various anode materials, optimization strategies to boost their proton storage capability, and their potential applications, this review seeks to provide a comprehensive theoretical foundation and practical guidance for future research and development of proton battery technology. First, the preparation methods and proton storage mechanism of anode materials have been discussed. Then, the limitations and optimization strategies have been summarized. After that, the next section elaborately focuses on the proton storage performance of different types of anode materials. Finally, the challenges and prospects of anode materials for proton batteries have been proposed. This review aims to provide insight into the efficient design and optimization of anode materials for practical applications of proton batteries.

A novel efficient electrochemical sensor for detecting paracetamol contaminants in polluted water using an active electrode from tungsten oxide nanoplates

Herein, electrochemical sensing of paracetamol in polluted water was achieved using facile-synthesized tungsten oxide nanoparticles. Ion exchange resin has been used as a sustainable preparation route, while the prepared nanoparticles have been characterized by XRD and SEM analyses. Orthorhombic WO3·H2O nano-plates have been synthesized via a facile preparation method, where the crystal size has been calculated as 25-33 nm, and these results were used to create a 3D model of the prepared WO3·H2O nano-plates. An active electrochemical sensor layer of the prepared WO3·H2O has been used to detect paracetamol in water with a concentration range of 0-50 mg L-1. The tungsten oxide nanoplates show high sensitivity with a detection-limit of 66 μM and sensitivity of 12.85 μA μM-1. Kinetic models have been investigated, where pseudo 1st and 2nd order models were used to study the sensing mechanism. Both experimental results and mathematical calculations have been combined and used to provide suggested sensing mechanisms. The current investigations may be the key factor of future, economic and eco-friendly environmental sensors for industrial wastewater treatment.

Recent Development on Transition Metal Oxides-Based Core-Shell Structures for Boosted Energy Density Supercapacitors

In recent years, nanomaterials exploration and synthesis have played a crucial role in advancing energy storage research, particularly in supercapacitor development. Researchers have diversified materials, including metal oxides, chalcogenides, and composites, as well as carbon materials, to enhance energy and power density. Balancing energy density with electrochemical stability remains challenging, driving intensified efforts in advancing electrode materials. This review focuses on recent progress in designing and synthesizing core-shell materials tailored for supercapacitors. The core-shell architecture offers advantages such as increased surface area, redox active sites, electrical conductivity, ion diffusion kinetics, specific capacitance, and cyclability. The review explores the impact of core and shell materials, specifically transition metal oxides (TMOs), on supercapacitor electrochemical behavior. Metal oxide choices, such as cobalt oxide as a preferred core and manganese oxide as a shell, are discussed. The review also highlights characterization techniques for assessing structural, morphological, and electrochemical properties of core-shell materials. Overall, it provides a comprehensive overview of ongoing TMOs-based core-shell material research for supercapacitors, showcasing their potential to enhance energy storage for applications ranging from gadgets to electric vehicles. The review outlines existing challenges and future opportunities in evolving TMOs-based core-shell materials for supercapacitor advancements, holding promise for high-efficiency energy storage devices.

Superior Cyclic Stability and Capacitive Performance of Cation- and Water Molecule-Preintercalated δ-MnO2/h-WO3 Nanostructures as Supercapacitor Electrodes

The large number of active sites in the layered structure of δ-MnO2 with considerable interlayer spacing makes it an excellent candidate for ion storage. Unfortunately, the δ-MnO2-based electrode has not yet attained the exceptional storage potential that it should demonstrate because of disappointing structural deterioration during periodic charging and discharging. Here, we represent that stable Na ion storage in δ-MnO2 may be triggered by the preintercalation of K ions and water molecules. Furthermore, the sluggish reaction kinetics and poor electrical conductivity of preintercalated δ-MnO2 layers are overcome by the incorporation of h-WO3 in the preintercalated δ-MnO2 to form novel composite electrodes. The composites contain mixed valence metals, which provide a great number of active sites along with improved redox activity, while maintaining a fast ion transfer efficiency to enhance the pseudocapacitance performance. Based on our research, the composite prepared from preintercalated δ-MnO2 with 5 wt % h-WO3 provides a specific capacitance of up to 363.8 F g-1 at a current density of 1.5 A g-1 and an improved energy density (32.3 W h kg-1) along with an ∼14% increase in capacity upon cycling up to 5000 cycles. Hence, the interaction between the preintercalated δ-MnO2 and h-WO3 nanorods results in satisfactory energy storage performance due to the defect-rich structure, high conductivity, superior stability, and lower charge transfer resistance. This research has the potential to pave the way for a new class of hybrid supercapacitors that could fill the energy gap between chemical batteries and ideal capacitors.

Synthesis and Capacitive Properties of Mesoporous Tungsten Oxide Films Prepared by Ultrasonic Spray Deposition

Mesoporous tungsten trioxide (WO3) films are prepared by the combination of the template-assisted sol-gel method and ultrasonic spraying deposition (USD) for supercapacitors, and then the surface morphology and electrochemical performance of the films are studied. Compared to WO3 prepared by the traditional hydrothermal synthesis and spin coating method, the films obtained by USD exhibit advantages such as low cost, minimal material usage, and suitability for large-area in-line manufacturing. Additionally, the mesoporous structure of USD-produced films is also supportive of ion transportation. Due to the high specific surface area of WO3 films deposited by USD, it is a material capable of use in a high-performance energy storage device. Through the control of spray coats, the film thickness and specific capacitance can be effectively controlled. Electrochemical measurements show that the mesoporous WO3 films possess excellent electrochemical performance with a maximum specific capacitance of 109.15 F/g at 0.5 A/g. The cycling performance up to 5000 cycles of mesoporous WO3 films is due to the stable nature of nanocrystalline produced by the combination of USD and sol-gel chemistry.

Enhanced Performance of WO3/SnO2 Nanocomposite Electrodes with Redox-Active Electrolytes for Supercapacitors

For effective supercapacitors, we developed a process involving chemical bath deposition, followed by electrochemical deposition and calcination, to produce WO₃/SnO₂ nanocomposite electrodes. In aqueous solutions, the hexagonal WO₃ microspheres were first chemically deposited on a carbon cloth, and then tin oxides were uniformly electrodeposited. The synthesized WO₃/SnO₂ nanocomposite was characterized by XRD, XPS, SEM, and EDX techniques. Electrochemical properties of the WO₃/SnO₂ nanocomposite were analyzed by cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy in an aqueous solution of Na₂SO₄ with/without the redox-active electrolyte K₃Fe(CN)₆. K₃Fe(CN)₆ exhibited a synergetic effect on the electrochemical performance of the WO₃/SnO₂ nanocomposite electrode, with a specific capacitance of 640 F/g at a scan rate of 5 mV/s, while that without K₃Fe(CN)₆ was 530 F/g. The WO₃/SnO₂ nanocomposite catalyzed the redox reactions of [Fe(CN)₆]³/[Fe(CN)₆]^4- ions, and the [Fe(CN)₆]^3-/[Fe(CN)₆]^4- ions also promoted redox reactions of the WO₃/SnO₂ nanocomposite. A symmetrical configuration of the nanocomposite electrodes provided good cycling stability (coulombic efficiency of 99.6% over 2000 cycles) and satisfied both energy density (60 Whkg^-1) and power density (540 Wkg^-1) requirements. Thus, the WO₃/SnO₂ nanocomposite prepared by this simple process is a promising component for a hybrid pseudocapacitor system with a redox-flow battery mechanism.

Pivotal Role of the Granularity Uniformity of the WO3 Film Electrode upon the Cyclic Stability during Cation Insertion/Extraction

Delicate design and precise manipulation of electrode morphology has always been crucial in electrochemistry. Generally, porous morphology has been preferred due to the fast kinetic transport characteristics of cations. Nevertheless, more refined design details such as the granularity uniformity that usually goes along with the porosity regulation of film electrodes should be taken into consideration, especially in long-term cation insertion and extraction. Here, inorganic electrochromism as a special member of the electrochemical family and WO₃ films as the most mature electrochromic electrode material were chosen as the research background. Two kinds of WO₃ films were prepared by magnetron sputtering, one with a relatively loose morphology accompanied by nonuniform granularity and one with a compact morphology along with uniform particle size distribution, respectively. Electrochemical performances and cyclic stability of the two film electrodes were then traced and systematically compared. In the beginning, except for faster kinetic transport characters of the 50 W-deposited WO₃ film, the two electrodes showed equivalent optical and electrochemical performances. However, after 5000 CV cycles, the 50 W-deposited WO₃ film electrode cracked seriously. Strong stress distribution centered among boundaries of the nonuniform particle clusters together with the weak bonding among particles induced the mechanical damage. This discovery provides a more solid background for further delicate film electrode design.

All Transition Metal Selenide Composed High-Energy Solid-State Hybrid Supercapacitor

Transition metal selenides (TMSs) have enthused snowballing research and industrial attention due to their exclusive conductivity and redox activity features, holding them as great candidates for emerging electrochemical devices. However, the real-life utility of TMSs remains challenging owing to their convoluted synthesis process. Herein, a versatile in situ approach to design nanostructured TMSs for high-energy solid-state hybrid supercapacitors (HSCs) is demonstrated. Initially, the rose-nanopetal-like NiSe@Cu₂ Se (NiCuSe) positive electrode and FeSe nanoparticles negative electrode are directly anchored on Cu foam via in situ conversion reactions. The complementary potential windows of NiCuSe and FeSe electrodes in aqueous electrolytes associated with the excellent electrical conductivity results in superior electrochemical features. The solid-state HSCs cell manages to work in a high voltage range of 0-1.6 V, delivers a high specific energy density of 87.6 Wh kg^-1 at a specific power density of 914.3 W kg^-1 and excellent cycle lifetime (91.3% over 10 000 cycles). The innovative insights and electrode design for high conductivity holds great pledge in inspiring material synthesis strategies. This work offers a feasible route to develop high-energy battery-type electrodes for next-generation hybrid energy storage systems.

Computation and Investigation of Two-Dimensional WO3·H2O Nanoflowers for Electrochemical Studies of Energy Conversion and Storage Applications

The aim of this study is to prepare a two-dimensional (2D) WO3·H2O nanostructure assembly into a flower shape with good chemical stability for electrochemical studies of catalyst and energy storage applications. The 2D-WO3·H2O nanoflowers structure is created by a fast and simple process at room condition. This cost-effective and scalable technique to obtain 2D-WO3·H2O nanoflowers illustrates two attractive applications of electrochemical capacitor with an excellent energy density value of 25.33 W h kg-1 for high power density value of 1600 W kg-1 and good hydrogen evolution reaction results (low overpotential of 290 mV at a current density of 10 mA cm-2 with a low Tafel slope of 131 mV dec-1). A hydrogen evolution reaction (HER) study of WO3 in acidic media of 0.5 M H2SO4 and electrochemical capacitor (supercapacitors) in 1 M Na2SO4 aqueous electrolyte (three electrode system measurements) demonstrates highly desirable characteristics for practical applications. Our design for highly uniform 2D-WO3·H2O as catalyst material for HER and active material for electrochemical capacitor studies offers an excellent foundation for design and improvement of electrochemical catalyst based on 2D-transition metal oxide materials.

An asymmetric supercapacitor based on controllable WO3 nanorod bundle and alfalfa-derived porous carbon

A novel asymmetric supercapacitor (ASC) is assembled on the basis of an inerratic hexagonal-like WO₃ nanorod bundle as a negative electrode and graphene-like alfalfa-derived porous activated carbon (APAC) as the positive electrode in 1 M H₂SO₄ aqueous electrolyte. The WO₃ nanostructures prepared at pH of 1.6, 1.8, 2.0, 2.5 and 3.0 display hexagonal disc-like, nanorod bundle, inerratic hexagonal-like, sphere-like, and needle-shaped nanorod morphology. WO₃-2.0, which was prepared at a pH of 2.0, exhibits high specific capacitance (415.3 F g⁻¹ at 0.5 A g⁻¹). APAC-2, which had the mass ratios of dried alfalfa and ZnCl₂ as 1 : 2, showed a 3D porous structure, large surface area (1576.3 m² g⁻¹), high specific capacitance (262.1 F g⁻¹ at 0.5 A g⁻¹), good cycling stability with 96% of initial specific capacitance after 5000 consecutive cycles. The ASC assembled with WO₃-2.0 and APAC-2 exhibits high energy density (27.3 W h kg⁻¹ at a power density of 403.1 W kg⁻¹), as well as good electrochemical stability (82.6% capacitance retention after 5000 cycles). Such outstanding electrochemical behavior implies that the electrode materials are promising for practical energy-storage systems.

A asymmetric supercapacitor is assembled on the basis of an inerratic hexagonal-like WO₃ nanorod bundle as a negative electrode and graphene-like alfalfa-derived porous activated carbon as the positive electrode in 1 M H₂SO₄ aqueous electrolyte.

Three-dimensional hierarchical porous lignin-derived carbon/WO3 for high-performance solid-state planar micro-supercapacitor

The development of advanced energy storage systems, such as rechargeable batteries and supercapacitors (SCs), is one of the great challenges related to energy demand with the rapid development of world economy. Herein, a three-dimensional hierarchical porous lignin-derived carbon/WO₃ (HPC/WO₃) was prepared by carbonization and solvothermal process. This electrode material for supercapacitor can be operated at a wide voltage window range of -0.4 V to 1.0 V. More importantly, 3HPC/WO₃ with ultrahigh mass loading (~3.56 mg cm^-2) has excellent specific capacitance of 432 F g^-1 at 0.5 A g^-1 and cycling stability of 86.6% after 10,000 cycles at 10 A g^-1. The as-assembled asymmetrical supercapacitor shows an energy density of 34.2 W h kg^-1 at a power density of 237 W kg^-1 and energy density of 16 W h kg^-1 at a power density is 14,300 W kg^-1. A solid-state planar micro-supercapacitor (MSC) was fabricated using HPC/WO₃ nanocomposites. Moreover, the calculated specific capacity of MSC was 20 mF cm^-2 in polyvinyl alcohol-sulfuric acid gel electrolyte. Overall, through the reasonable design of HPC/WO₃ nanocomposite materials and the efficient assembly of MSCs, the performance of the device was greatly improved, thus providing a clear strategy for the development of energy storage devices.

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.

The CdIn2 S4 /WO3 Nanosheet Composite Has a Significantly Enhanced Photo-electrochemical Cathodic Protection Performance and Excellent Electron Storage Capability

Photo-electrochemical cathodic protection (CP) technology is considered to be a green metallic corrosion protection technology that uses solar energy to protect from corrosion and does not consume any anode materials. In this work, a CdIn₂ S₄ /WO₃ nanocomposite photoelectrode was prepared, and its photo-electrochemical CP performance and mechanism were studied and analyzed. WO₃ has a well band matching with CdIn₂ S₄ , leading to a significantly enhanced photo-electrochemical CP performance of the nanocomposite. Meanwhile, as confirmed in this work, the CdIn₂ S₄ /WO₃ nanocomposite can store photoinduced electrons under light illumination through intercalation reactions and changing the valence state of tungsten. Moreover, it can discharge in the dark state to provide continuous CP for the coupled metals. This research will promote the practical application process of the photo-electrochemical CP technology.

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.

Crystal facet-dependent activity of h-WO3 for selective conversion of furfuryl alcohol to ethyl levulinate

The use of WO3 as an acid catalyst has received extensive attention in recent years. However, the correlation between the catalytic activity and the predominantly exposed surface with varied acidic sites needs further understanding. Herein, the effects of the Brønsted and Lewis acid sites of different crystal facets of WO3 on the catalytic conversion of furfuryl alcohol (FA) to ethyl levulinate (EL) in ethanol were investigated in detail. A yield of EL up to 93.3% over WO3 with the (110) facet exposed was achieved at 170 °C, while FA was mainly converted to polymers over (001) faceted nanosheets and nanobelts with exposed (002) and (100) facets. This was attributed to the different distribution of the acidic sites on different exposed crystal facets. The (110) faceted WO3 possessed abundant and strong Brønsted acid sites, which favored the conversion of FA to EL, while the (100) faceted WO3 with stronger Lewis acid sites and weaker Brønsted acid sites mainly led to the formation of polymers. In addition, the (110) faceted WO3 showed excellent sustainability in comparison with the (100) faceted counterpart.

Electrical and Structural Dual Function of Oxygen Vacancies for Promoting Electrochemical Capacitance in Tungsten Oxide

Intrinsic defects, including oxygen vacancies, can efficiently modify the electrochemical performance of metal oxides. There is, however, a limited understanding of how vacancies influence charge storage properties. Here, using tungsten oxide as a model system, an extensive study of the effects of structure, electrical properties, and charge storage properties of oxygen vacancies is carried out using both experimental and computational techniques. The results provide direct evidence that oxygen vacancies increase the interlayer spacing in the oxide, which suppress the structural pulverization of the material during electrolyte ion insertion and removal in prolonged stability tests. Specifically, no capacitive decay is detected after 30 000 cycles. The medium states and charge storage mechanism of oxygen-deficient tungsten oxide throughout electrochemical charging/discharging processes is studied. The enhanced rate capability of the oxygen-deficient WO3- x is attributed to improved charge storage kinetics in the bulk material. The WO3- x electrode exhibits the highest capacitance in reported tungsten-oxide based electrodes with comparable mass loadings. The capability to improve electrochemical capacitance performance of redox-active materials is expected to open up new opportunities for ultrafast supercapacitive electrodes.

A WO3/PPy/ACF modified electrode in electrochemical system for simultaneous removal of heavy metal ion Cu2+ and organic acid

Heavy metal ions and organic acids are common pollutants in electroplating wastewater. Effective and economic treatment of such wastewater needs novel technologies. In this study, WO₃/PPy-1/ACF electrode was prepared using a hydrothermal modification method and it has large specific area (788.27 m² g^-1), high areal capacitance (2.58 F cm^-2 under 5 mA cm^-2 charge and discharge) and excellent conductivity. The modified electrode was used in an electrochemical system with activated carbon fiber felt (ACF) as counter electrode. The system simultaneously and successfully removed 97.8 % Cu²⁺ and 80.1 % citric acid (CA) from a simulated electroplating wastewater (typically 100 mg L^-1 Cu²⁺ and 800 mg L^-1 CA) in five- hour optimized operation. The influence of operating parameters (circulating inflow rate, applied voltage and influent pH) on the treatment performance was compared. There is interplay between Cu²⁺ reductive deposition and CA oxidation. The synergetic electrochemical treatment mechanism involves formation of hydrogen peroxide, free radicals, and catalytic effect of Cu species was proposed. This electrochemical system which is low-cost, easy to operate and highly efficient, may be applicable in treating acid-wash or electroplating wastewater, containing heavy-metal ions and organic acids.

An Easy and Ecological Method of Obtaining Hydrated and Non-Crystalline WO3-x for Application in Supercapacitors

In this work, we report the synthesis of hydrated and non-crystalline WO₃ flakes (WO_3−x) via an environmentally friendly and facile water-based strategy. This method is described, in the literature, as exfoliation, however, based on the results obtained, we cannot say unequivocally that we have obtained an exfoliated material. Nevertheless, the proposed modification procedure clearly affects the morphology of WO₃ and leads to loss of crystallinity of the material. TEM techniques confirmed that the process leads to the formation of WO₃ flakes of a few nanometers in thickness. X-ray diffractograms affirmed the poor crystallinity of the flakes, while spectroscopic methods showed that the materials after exfoliation were abundant with the surface groups. The thin film of hydrated and non-crystalline WO₃ exhibits a seven times higher specific capacitance (C_s) in an aqueous electrolyte than bulk WO₃ and shows an outstanding long-term cycling stability with a capacitance retention of 92% after 1000 chronopotentiometric cycles in the three-electrode system. In the two-electrode system, hydrated WO_3−x shows a C_s of 122 F g⁻¹ at a current density of 0.5 A g⁻¹. The developed supercapacitor shows an energy density of 60 Whkg⁻¹ and power density of 803 Wkg⁻¹ with a decrease of 16% in C_sp after 10,000 cycles. On the other hand, WO_3−x is characterized by inferior properties as an anode material in lithium-ion batteries compared to bulk WO₃. Lithium ions intercalate into a WO₃ crystal framework and occupy trigonal cavity sites during the electrochemical polarization. If there is no regular layer structure, as in the case of the hydrated and non-crystalline WO₃, the insertion of lithium ions between WO₃ layers is not possible. Thus, in the case of a non-aqueous electrolyte, the specific capacity of the hydrated and non-crystalline WO₃ electrode material is much lower in comparison with the specific capacity of the bulk WO₃-based anode material.

Review on Recent Progress in the Development of Tungsten Oxide Based Electrodes for Electrochemical Energy Storage

Current progress in the advancement of energy-storage devices is the most important factor that will allow the scientific community to develop resources to meet the global energy demands of the 21st century. Nanostructured materials can be used as effective electrodes for energy-storage devices because they offer various promising features, including high surface-to-volume ratios, exceptional charge-transport features, and good physicochemical properties. Until now, the successful research frontrunners have focused on the preparation of positive electrode materials for energy-storage applications; nevertheless, the electrochemical performance of negative electrodes is less frequently reported. This review mainly focuses on the current progress in the development of tungsten oxide-based electrodes for energy-storage applications, primarily supercapacitors (SCs) and batteries. Tungsten is found in various stoichiometric and nonstoichiometric oxides. Among the different tungsten oxide materials, tungsten trioxide (WO₃ ) has been intensively investigated as an electrode material for different applications because of its excellent charge-transport features, unique physicochemical properties, and good resistance to corrosion. Various WO₃ composites, such as WO₃ /carbon, WO₃ /polymers, WO₃ /metal oxides, and tungsten-based binary metal oxides, have been used for application in SCs and batteries. However, pristine WO₃ suffers from a relatively low specific surface area and low energy density. Therefore, it is crucial to thoroughly summarize recent progress in utilizing WO₃ -based materials from various perspectives to enhance their performance. Herein, the potential- and pH-dependent behavior of tungsten in aqueous media is discussed. Recent progress in the advancement of nanostructured WO₃ and tungsten oxide-based composites, along with related charge-storage mechanisms and their electrochemical performances in SCs and batteries, is systematically summarized. Finally, remarks are made on future research challenges and the prospect of using tungsten oxide-based materials to further upgrade energy-storage devices.

Synthesis of three-dimensional hierarchical furball-like tungsten trioxide microspheres for high performance supercapacitor electrodes

A hierarchical furball-like WO₃ electrode material, based on stainless-steel mesh, was successfully synthesized via a simple in situ hydrothermal method. The electrode materials obtained are made from a self-assembled nanorod core and a connected/quasi-connected nano-thorn network shell, and could help utilize all the surface or near-surface regions for faradaic reaction. Furthermore, the furball-like WO₃ special microstructure provides a more effective charge storage area, exhibiting a high specific capacitance of 8.35 F cm⁻² and excellent cycling stability (93.4% of its initial value after 10 000 cycles). These performances indicate this furball-like WO₃ material would be a promising candidate for high performance supercapacitors.

Furball-like tungsten trioxide microspheres with significant specific capacitance and remarkable cycle stability.

Nitrogen-doped carbon integrated nickel–cobalt metal phosphide marigold flowers as a high capacity electrode for hybrid supercapacitors

The fabrication of advanced MOF-derived multicomponent NiCoP/NC marigold flowers electrode for high-performance hybrid supercapacitors.

Synthesis of Three-Dimensional Hierarchical Urchinlike Tungsten Trioxide Microspheres for High-Performance Supercapacitor Electrode

In this work, hierarchical three-dimensional (3D) urchinlike WO3 microspheres with a self-assembled nanorod core, and a connected and quasiconnected nanothorn network shell were synthesized with the hydrothermal method. For the surface or near-surface regions of pseudocapacitive materials that are involved in the Faradaic reaction, the urchinlike WO3 special microstructure provided more effective charge-storage area, exhibiting a high specific capacitance of 488.78 F g−1, low average equivalent-series resistance of 0.966 Ω cm−2, and excellent cycling stability (84.75% of its initial value after the 10,000 cycles). This performance indicates the urchinlike WO3 microspheres are promising electrode materials for high-performance supercapacitors.

Fabrication of Mo-Doped WO₃ Nanorod Arrays on FTO Substrate with Enhanced Electrochromic Properties

Well-oriented and crystalline WO₃ nanorod arrays (WNRAs) decorated with Mo were synthesized on fluorine doped tin oxide (FTO) substrate by the hydrothermal method. The effects of Mo doping, hydrothermal reaction time, and hydrothermal temperature on the morphologies and electrochromic properties of as-prepared WNRAs were studied thoroughly. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and chronoamperometry techniques were used to characterize the structures and properties of obtained WNRAs. The results demonstrate that the average diameter of the as-prepared WNRAs ranged from 30 to 70 nm. During the decoration of Mo on the WNRAs, the growth density of as-prepared WNRAs decreased and the surfaces became rough. However, the decorated Mo on WNRAs synthesized at 180 °C for 5 h with a Mo/W mole ratio of 1:40 exhibited better electrochromic properties than single WNRAs. They exhibited high optical modulation (61.7%), fast bleaching/coloring response times (3 s/9 s), high coloration efficiency values (73.1 cm²/C), and good cycling stability.

Fabrication of WO3·2H2O/BC Hybrids by the Radiation Method for Enhanced Performance Supercapacitors

In this study, we described a facile process for the fabrication of tungsten oxide dihydrate/bamboo charcoal hybrids (WO₃·2H₂O/BC) by the γ-irradiation method. The structural, morphological, and electrochemical properties of WO₃·2H₂O/BC hybrids were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. The combination of BC (electrical double layer charge) and WO₃·2H₂O (pseudocapacitance) created a combined effect, which enhanced the specific capacitance and superior cyclic stability of the WO₃·2H₂O/BC hybrid electrode. The WO₃·2H₂O/BC hybrids showed the higher specific capacitance (391 F g⁻¹ at 0.5 A g⁻¹ over the voltage range from −1 to 0 V), compared with BC (108 F g⁻¹) in 6 M KOH solution. Furthermore, the hybrid electrode showed superior long-term performance with 82% capacitance retention even after 10,000 cycles. The experimental results demonstrated that the high performance of WO₃·2H₂O/BC hybrids could be a potential electrode material for supercapacitors.

Enhanced electrochromic and energy storage performance in mesoporous WO3 film and its application in a bi-functional smart window

Construction of multifunctional photoelectrochemical energy devices is of great importance to energy saving. In this study, we have successfully prepared a mesoporous WO3 film on FTO glass via a facile dip-coating sol-gel method; the designed mesoporous WO3 film exhibited advantages including high transparency, good adhesion and high porosity. Also, multifunctional integrated energy storage and optical modulation ability are simultaneously achieved by the mesoporous WO3 film. Impressively, the mesoporous WO3 film exhibits a noticeable electrochromic energy storage performance with a large optical modulation up to 75.6% at 633 nm, accompanied by energy storage with a specific capacity of 75.3 mA h g-1. Furthermore, a full electrochromic energy storage window assembled with the mesoporous WO3 anode and PANI nanoparticle cathode is demonstrated with large optical modulation and good long-term stability. Our research provides a new route to realize the coincident utilization of optical-electrochemical energy.

Facile synthesis of hierarchical mesoporous weirds-like morphological MnO2 thin films on carbon cloth for high performance supercapacitor application

The mesoporous nanostructured metal oxides have a lot of capabilities to upsurge the energy storing capacity of the supercapacitor. In present work, different nanostructured morphologies of MnO₂ have been successfully fabricated on flexible carbon cloth by simple but capable hydrothermal method at different deposition temperatures. The deposition temperature has strong influence on reaction kinetics, which subsequently alters the morphology and electrochemical performance. Among different nanostructured MnO₂ thin films, the mesoporous weirds composed thin film obtained at temperature of 453K exhibits excellent physical and electrochemical features for supercapacitor application. The weirds composed MnO₂ thin film exhibits specific surface area of 109m²g^-1, high specific capacitance of 595Fg^-1 with areal capacitance of 4.16Fcm^-2 at a scan rate of 5mVs^-1 and high specific energy of 56.32Whkg^-1. In addition to this, MnO₂ weirds attain capacity retention of 87 % over 2000 CV cycles, representing better cycling stability. The enhanced electrochemical performance could be ascribed to direct growth of highly porous MnO₂ weirds on carbon cloth which provide more pathways for easy diffusion of electrolyte into the interior of electroactive material. The as-fabricated electrode with improved performance could be ascribed as a potential electrode material for energy storage devices.