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

High-Performance Electrochromic Devices Based on Size-Controlled 2D WO3 Nanosheets Prepared Using the Intercalation Method

It is difficult to obtain ultrathin two-dimensional (2D) tungsten trioxide (WO3) nanosheets through direct exfoliation from bulk WO3 in solution due to the strong bonding between interlayers. Herein, WO3 nanosheets with controllable sizes were synthesized via K+ intercalation and the exfoliation of WO3 powder using sonication and temperature. Because of the intercalation and expansion in the interlayer distance, the intercalated WO3 could be successfully exfoliated to produce a large quantity of individual 2D WO3 nanosheets in N-methyl-2-pyrrolidone under sonication. The exfoliated ultrathin WO3 nanosheets exhibited better electrochromic performance in an electrochromic device than WO3 powder and exfoliated WO3 without intercalation. In particular, the prepared small WO3 nanosheets exhibited excellent electrochromic properties with a large optical modulation of 41.78% at 700 nm and fast switching behavior times of 9.2 s for bleaching and 10.5 s for coloring. Furthermore, after 1000 cycles, the small WO3 nanosheets still maintained 86% of their initial performance.

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.

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.

Synthesis and applications of WO3 nanosheets: the importance of phase, stoichiometry, and aspect ratio

Tungsten trioxide (WO₃) is an abundant, versatile oxide that is widely explored for catalysis, sensing, electrochromic devices, and numerous other applications. The exploitation of WO₃ in nanosheet form provides potential advantages in many of these fields because the 2D structures have high surface area and preferentially exposed facets. Relative to bulk WO₃, nanosheets expose more active sites for surface-sensitive sensing/catalytic reactions, and improve reaction kinetics in cases where ionic diffusion is a limiting factor (e.g. electrochromic or charge storage). Synthesis of high aspect ratio WO₃ nanosheets, however, is more challenging than other 2D materials because bulk WO₃ is not an intrinsically layered material, making the widely-studied sonication-based exfoliation methods used for other 2D materials not well-suited to WO₃. WO₃ is also highly complex in terms of how the synthesis method affects the properties of the final material. Depending on the route used and subsequent post-synthesis treatments, a wide variety of different morphologies, phases, exposed facets, and defect structures are created, all of which must be carefully considered for the chosen application. In this review, the recent developments in WO₃ nanosheet synthesis and their impact on performance in various applications are summarized and critically analyzed.

Solution Processing of Topochemically Converted Layered WO3 for Multifunctional Applications

Solution processing of nanomaterials is a promising technique for use in various applications owing to its simplicity and scalability. However, the studies on liquid-phase exfoliation (LPE) of tungsten oxide (WO₃ ) are limited, unlike others, by a lack of commercial availability of bulk WO₃ with layered structures. Herein, a one-step topochemical synthesis approach to obtain bulk layered WO₃ from commercially available layered tungsten disulfide (WS₂ ) by optimizing various parameters like reaction time and temperature is reported. Detailed microscopic and spectroscopic techniques confirmed the conversion process. Further, LPE was carried out on topochemically converted bulk layered WO₃ in 22 different solvents; among the solvents studied, the propan-2-ol/water (1 : 1) co-solvent system appeared to be the best. This indicates that the possible values of surface tension and Hansen solubility parameters for bulk WO₃ could be close to that of the co-solvent system. The obtained WO₃ dispersions in a low-boiling-point solvent enable thin films of various thickness to be fabricated by using spray coating. The obtained thin films were used as active materials in supercapacitors without any conductive additives/binders and exhibited an areal capacitance of 31.7 mF cm^-2 at 5 mV s^-1 . Photo-electrochemical measurements revealed that these thin films can also be used as photoanodes for photo-electrochemical water oxidation.

An Aqueous Exfoliation of WO3 as a Route for Counterions Fabrication-Improved Photocatalyticand Capacitive Properties of Polyaniline/WO3Composite

In this paper, we demonstrate a novel, electrochemical route of polyaniline/tungsten oxide (PANI)/WO₃) film preparation. Polyaniline composite film was electrodeposited on the FTO (fluorine-doped tin oxide) substrate from the aqueous electrolyte that contained aniline (monomer) and exfoliated WO₃ as a source of counter ions. The chemical nature of WO₃ incorporated in the polyaniline matrix was investigated using X-ray photoelectron spectroscopy. SEM (scanning electron microscopy) showed the impact of WO₃ presence on the morphology of polyaniline film. PANI/WO₃ film was tested as an electrode material in an acidic electrolyte. Performed measurements showed the electroactivity of both components and enhanced electrochemical stability of PANI/WO₃ in comparison with PANI/Cl. Thus, PANI/WO₃ electrodes were utilized to construct the symmetric supercapacitors. The impact of capacitive and diffusion-controlled processes on the mechanism of electrical energy storage was quantitatively determined. Devices exhibited high electrochemical capacity of 135 mF cm⁻² (180 F g⁻¹) and satisfactory retention rate of 70% after 10,000 cycles. The electrochemical energy storage device exhibited 1075.6 W kg⁻¹ of power density and 12.25 Wh kg⁻¹ of energy density. We also investigated the photocatalytic performance of the deposited film. Photodegradation efficiencies of methylene blue and methyl orange using PANI/WO₃ and PANI/Cl were compared. The mechanism of dye degradation using WO₃-containing films was investigated in the presence of scavengers. Significantly higher efficiency of photodecomposition of dyes was achieved for composite films (84% and 86%) in comparison with PANI/Cl (32% and 39%) for methylene blue and methyl orange, respectively.