Porous WO3 Research Articles

Sintering Driven Void Formation in PS@WO3 Core-Shell Composites: A Photodegradation Enhancement Strategy

Background: Polystyrene nanospheres are used as a substrate for the hydrothermal coating of tungsten trioxide (WO3) to form a core-shell composite of PS@WO3. The core-shell structure is used for the next sintering step. This produces porous WO3. The focus of this study is on the role of porous WO3 in enhancing photocatalytic performance. Methods: The hydrothermal method was employed for coating, and the surface morphology, as well as the structural properties of WO3-coated PS spheres, were systematically investigated using SEM and XRD analyses. Additionally, the sintering process was introduced to enhance the material by inducing rupture in the PS sphere core, creating voids that significantly increased the material's surface area. Results: The evaluation of the effect of sintering temperature on photodegradation efficiency highlighted the crucial role of sintering temperature. Un-sintered and 300°C sintered WO3, both having a hexagonal crystalline structure, exhibited superior degradation efficiencies compared to samples sintered at higher temperatures (400°C and 500°C). In particular, the 300°C sintered WO3 outperformed its un-sintered counterpart despite identical crystalline structures. The performance of the PS@WO3 composite was assessed to determine the enhanced role of porous WO3. The porous WO3 obtained, in particular by the sintering of the core-shell PS@WO3 composites at 300°C, showed a remarkable improvement in the degradation efficiency. These composite demonstrated over 95% efficiency within 10 minutes and achieved near complete (100%) degradation for a further 10 minutes, surpassing the performance of pure WO3. It is important to clarify that while the final product was predominantly WO3 after the sintering process, the inclusion of PS served a critical purpose in creating voids during sintering. The PS@WO3 composite structure used as a resource for the preparation of porous WO3, even with a potentially reduced PS composition, has been found to play a significant role in influencing the surface area of the material, and consequently the photocatalytic performance. Conclusion: The study has highlighted the importance of crystalline structure and sintering conditions in optimizing the efficiency of photocatalytic materials. The porous WO3 obtained, in particular by the sintering of the core-shell PS@WO3 composites at 300°C, showed promising potential for applications under UV and visible LED light irradiation. These results provide valuable insights for the development of advanced photocatalytic materials with improved performance, highlighting WO3 as the key contributor to the observed improvements.

Microporous tungsten oxide spheres coupled with Ti3C2Txnanosheets for high-volumetric capacitance supercapacitors.

In the contemporary landscape of technological advancements, the burgeoning demand for portable electronics and flexible wearable devices has necessitated the development of energy storage systems with superior volumetric performance. Tungsten oxide (WO3), known for its high density and theoretical capacitance, is a promising electrode material for supercapacitors. However, low conductivity and poor cycling stability are still the key bottlenecks for its application. Herein, a novel composite comprising hollow porous WO3 spheres (HPWS) derived by template method was electrostatic self-assembled on the surface of the Ti3C2Tx nanosheets. The resulting electrodes exhibited ultra-high volumetric capacitance of 1930 F cm-3 at 1 A g-1 and rate capability of 46% at 50 A g-1, attributed to enhanced ion accessibility from microporous structure and electron transport from conductive network of Ti3C2Tx even at a high packing density of 3.86 g cm-3. Utilizing HPWS/Ti3C2Tx as the negative electrode and porous carbon as the positive electrode, the assembled asymmetric supercapacitor achieved an energy density of 31 Wh kg-1 at a power density of 650 W kg-1 with over 107% capacitance retention after 5000 cycles. This work provides a promising approach for developing next-generation supercapacitors with ultra-high volumetric capacitance.

A Versatile Synthesis Platform Based on Polymer Cubosomes for a Library of Highly Ordered Nanoporous Metal Oxides Particles.

Polymer cubosomes (PCs) have well-defined inverse bicontinuous cubic mesophases formed by amphiphilic block copolymer bilayers. The open hydrophilic channels, large periods, and robust physical properties of PCs are advantageous to many host-guest interactions and yet not fully exploited, especially in the fields of functional nanomaterials. Here, the self-assembly of poly(ethylene oxide)-block-polystyrene block copolymers is systematically investigated and a series of robust PCs is developed via a cosolvent method. Ordered nanoporous metal oxide particles are obtained by selectively filling the hydrophilic channels of PCs via an impregnation strategy, followed by a two-step thermal treatment. Based on this versatile PC platform, the general synthesis of a library of ordered porous particles with different pore structures , tunable large pore size (18-78nm), high specific surface areas (up to 123.3m2g-1 for WO3) and diverse framework compositions, such as transition and non-transition metal oxides, rare earth chloride oxides, perovskite, pyrochlore, and high-entropy metal oxides is demonstrated. As typical materials obtained via this method, ordered porous WO3 particles have the advantages of open continuous structure and semiconducting properties, thus showing superior gas sensing performances toward hydrogen sulfide.

Nanostructured porous WO3 for photoelectrochemical splitting of seawater

Seawater, due to its salinity, can serve as an electrolyte in photoelectrochemical (PEC) systems, which have the potential to enable solar-driven production of hydrogen and oxidizing species. In this study several micrometer thick and highly porous nanostructured WO3 films were formed and their performance in photoanodic oxidation of chloride and sulfate ions, the most abundant anionic species in seawater, was investigated. Layers were characterized using scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, and BET surface area measurements. The study demonstrates that efficient PEC performance is achieved through optimal light absorption by sufficiently thick WO3 layers (3–5 μm), a highly porous structure that facilitates electrolyte permeation and ionic transport and provides a large electrochemically active interfacial area, and a nanosheet morphology where the sheet thickness is shorter than the hole diffusion length in WO3. The Faradaic efficiency of ClO- + ClO2- generation in neutral chloride-based electrolytes was found to be close to 100 %, but decreased significantly with photoelectrolysis time, presumably, due to the formation of higher chlorine oxo compounds. In addition, photocurrent stability and dissolution of WO3 photoanodes in acidic sulfate and neutral chloride media was compared. Though dissolution of WO3 in 0.5 M NaCl was found to be up to 3 times higher, photocurrent decay was more significant in 0.5 M H2SO4. The phenomenon was attributed to effective hole scavenging by surface-adsorbed Cl- ions, which prevents passivation of the photoelectrode surface due to formation of W(VI) peroxospecies.

Gas-fed photoelectrochemical reactions sustained by phosphotungstic acid as an inorganic surface electrolyte

Phosphotungstic acid (H3PW12O40) can function as a surface solid electrolyte for porous WO3 photoanode in gas-phase photoelectrochemical reactions such as water vapour splitting and methane conversion in the absence of liquid electrolytes.

Amorphous/ordered porous crystalline stacked WO3 films fabricated by electrodeposition-assisted sol–gel and its application to electrochromic devices

WO3 is currently the most widely used and promising electrochromic material, but the preparation of WO3 thin films with excellent optoelectronic properties is a formidable challenge. The amorphous WO3/ordered porous crystalline WO3 stacked films (a-WO3/OP-c-WO3) were prepared by electrodeposition-assisted sol–gel method with polystyrene (PS) spheres as the templates. The microstructure and properties of a-WO3/OP-c-WO3 films were significantly influenced by electrodeposition time (150 s ∼ 300 s). The optimized a-WO3/OP-c-WO3 films exhibited even better electrochromic properties (at 633 nm) with high cycling stability, superior optical modulation (53.9 %), fast response time (3.9 s/6.1 s for bleaching /coloration), and especially high coloration efficiency (51.3 cm2/C), compared with OP-c-WO3 film (25.1 cm2/C) and a-WO3 film (35.2 cm2/C), which is unique synergistic effect between the top layer of a-WO3 and the bottom layer of OP-c-WO3 film. The ordered porous structure allows the film to fully contact with the electrolyte, thereby providing a greater specific surface area and more active sites for the electrochemical reaction. The electrochromic device (EDC) prototype assembled with a-WO3/OP-c-WO3 laminated film as the electrochromic layer has better electrochromic properties.

Anodic Oxidation of Tungsten under Illumination-Multi-Method Characterization and Modeling at the Molecular Level.

Tungsten oxide has received considerable attention as photo-anode in photo-assisted water splitting due to its considerable advantages such as significant light absorption in the visible region, good catalytic properties, and stability in acidic and oxidative conditions. The present paper is a first step in a detailed study of the mechanism of porous WO3 growth via anodic oxidation. In-situ electrochemical impedance spectroscopy (EIS) and intensity modulated photocurrent spectroscopy (IMPS) during oxidation of W illuminated with UV and visible light are employed to study the ionic and electronic processes in slightly acidic sulfate-fluoride electrolytes and a range of potentials 4-10 V. The respective responses are discussed in terms of the influence of fluoride addition on ionic and electronic process rates. A kinetic model is proposed and parameterized via regression of experimental data to the EIS and IMPS transfer functions.

Graphene dot-embedded porous WO3 photoanode for highly efficient photoelectrochemical water splitting

The development of semiconductor photoanodes with improved photoelectrochemical (PEC) efficiency and stability for the purpose of realizing solar water splitting is a crucial challenge that carries substantial practical implications. In this study, GQDs/WO3 composite porous photoanodes were fabricated using a pulsed anodization method in an aqueous electrolyte containing hydroxyl GQDs. The morphology and crystal structure of the as-prepared GQDs/WO3 porous films were characterized by SEM, TEM, XRD, XPS, Raman spectra, and FTIR. The successful embedding of GQDs into the WO3 walls to form tightly bound heterojunctions was confirmed. It was investigated how the GQD content influenced the photoelectrochemical properties of the GQDs/WO3 heterojunctions. The optimal photocurrent densities observed in the GQDs/WO3 samples (10-WO3) were found to be three times higher compared to those obtained from pure WO3 porous films. This significant enhancement clearly indicates the positive impact of GQDs on the PEC performance. The boosted PEC activity of the GQDs/WO3 heterojunction photoanode was attributed to the fact that the introduction of GQDs promotes more efficient light absorption, charge separation, and transport processes within the heterojunction structure. Moreover, the GQDs/WO3 composites photoelectrodes exhibited excellent PEC stability, predicting its enormous potential for practical applications.

(Digital Presentation) Large-Scale Synthesis of Nanoporous Tungsten Oxide for Supercapacitor Application

The development of materials delivering high specific capacitance and energy density is a major challenge for supercapacitors. Due to high redox activity, several metal oxides like RuO2, MnO2, MoO3, Fe3O4, WO3 and CoOx have been broadly utilized as the active material for pseudo-capacitors. Among these, tungsten oxide (WO3), being less toxic, chemically stable, and abundantly available, has become a potential candidate and is widely investigated for pseudo-capacitors. However, some modifications are required to bring its performance to a commercial scale. Various approaches like composites with carbon and other oxides, doping, confinement, and porosity improvement are followed to improve their performances. But there is a need to find the potential of solely WO3 for supercapacitors. Looking forward to it, we have synthesized highly porous pure WO3 using the solution-based nanoprecipitation method. Our approach offers the possibility of large-scale production of porous materials with tunable pore sizes and structures compared to the traditionally used solvent evaporation-induced self-assembly (EISA) method. Herein, we used PS-b-PAA block copolymer as pore creating agent, which was removed after giving thermal treatment. The prepared material was analyzed using Brunauer-Emmett-Teller (BET) and exhibited a high specific surface area of 55.5 m2 g-1 with an average pore diameter of 3.7 nm. A detailed crystallographic and morphological analysis of these materials was carried out to check the feasibility of our material for energy storage applications. Furthermore, electrochemical investigations were carried out in 3E and 2E device configurations. The electrochemical studies demonstrate that porous WO3 has achieved a specific capacitance of 555 F g-1 at 10 mV s-1 scan rate. Figure 1

Preparation of ordered nanoporous WO3 thin films and the mechanism of large room-temperature ferromagnetism

Undoped porous WO3 nanofilms with large surface area were fabricated on porous anodic alumina substrates by magnetron sputtering. The nanofilms exhibited significant room-temperature ferromagnetism, at least one order of magnitude stronger than other reported undoped WO3 films. By controlling the oxygen partial pressure and the sputtering time during the deposition process, the saturation magnetization of the samples could be tuned over a large range, from 0.1 to 21.7 emu/cm3. Obvious magnetic anisotropy was found in the porous samples, indicating that the magnetic behavior is related to the regular pore structure perpendicular to the surface. Moreover, the first theoretical evidence that the Curie temperature of the sample is higher than room temperature was provided. When annealed in argon, the WO3 nanofilms turned black and showed a combination of a narrowed bandgap and enhanced ferromagnetism. These interesting phenomena are explained based upon the concept of hydrogen-like impurity states associated with oxygen vacancies.

Hierarchical Porous WO3@SiO2 Self-Standing Monolithic Catalysts and Their Efficient Cycling “Cosolvent-Free” Friedel–Crafts Alkylation/Acylation Catalytic Properties

Hierarchical Porous WO₃@SiO₂ Self-Standing Monolithic Catalysts and Their Efficient Cycling “Cosolvent-Free” Friedel–Crafts Alkylation/Acylation Catalytic Properties

Enhanced electrochemical performance of WO3 thin films prepared from polyvinyl alcohol-modified nanoparticle ink

Tungsten oxide (WO3) is a potential material in catalysis, sensors, electrochromic devices, etc. In this research work, porous WO3 thin films are prepared on FTO-glass employing spin coating of WO3 nanoparticle's ink modified with polyvinyl alcohol (PVA) in the concentration range of 0 to 25.0 wt%. This study explored the change in structure and morphology of WO3 thin films with varying PVA concentration in ink composition and their effect on the ability to intercalate and de-intercalate Li+ ions as a function of applied bias. The wettability of ink on FTO-glass improved by raising its PVA content. All WO3 thin films exhibited a monoclinic structure. Scanning electron microscopy images indicated that the porosity of WO3 thin films gradually increased with increasing PVA concentration up to 25 wt% but the thin film became highly nonuniform at a very high concentration of additive. WO3 thin film prepared with ink having 10 wt% of PVA had optimum porosity and uniformity, therefore, yielded better electrochemical performance compared with all other samples. The addition of an optimum amount of PVA to ink is found to be an effective approach to modulating ink's characteristics and inducing porosity in thin films which eventually improves their redox reaction characteristics.

Selective Electrochromic Regulation for Near-Infrared and Visible Light via Porous Tungsten Oxide Films with Core/Shell Architecture.

Dual-band electrochromic smart windows have become a research hotspot owing to their unique ability to selectively control near-infrared (NIR) and visible (VIS) light. However, the design and exploitation of dual-band electrochromic films are still an extreme challenge due to the scarcity of relevant high-performance materials. To solve this issue, we here proposed a type of porous WO3 film with nanowires/nanoparticles core/shell architecture as a promising candidate, endowing smart windows with a dual-band electrochromic feature. Moreover, the mechanism of the dual-band electrochromism is illustrated by the response of the transmittance spectra in Li+-based or TBA+-based electrolytes to distinguish the electrochemical behavior and the cyclic voltammetry to determine the degree of diffusion-limited kinetics. Our results indicate that the dual-band electrochromic performance is credited to the progressive electrochemical reduction procedure, in which the capacitive charging process gives rise to NIR regulation and the following ion intercalation contributes to VIS light modulation. Furthermore, we develop a dual-band electrochromic energy storage prototype device utilizing the porous WO3 film. This work describes a judicious strategy for designing dual-band electrochromic films, promoting the evolution of dual-band electrochromic technology.

Porous WO3·2H2O film with large optical modulation and high coloration efficiency for electrochromic smart window

Porous WO3·2H2O film with large optical modulation and high coloration efficiency for electrochromic smart window

Position-Selective Growth of WO3 Nanosheets for NH3 Gas Sensors

In this study, chemical vapor deposition of WO3 via graphene-catalyzed thermal transport is utilized to prepare position-selective WO3 micro/nanostructures. The effects of growth temperature and oxygen concentration on the structure, morphology, surface chemical states, and electrical properties are studied. The growth temperature and oxygen concentration are found to alter the resulting morphology and electrical properties. The combined application of high temperature and high oxygen concentration results in porous WO3 nanosheets with active surfaces. The prepared nanosheets are utilized for room-temperature NH3 gas sensing, and they exhibit good sensitivity, response time, and recovery time.

Fabrication of Large-Area, Affordable Dual-Function Electrochromic Smart Windows by Using a Hybrid Electrode Coated with an Oxygen-Deficient Tungsten Oxide Ultrathin Porous Film.

Electrochromic (EC) devices are not commercialized extensively owing to their high cost. The best large-area devices in the market suffer from not reaching a distinct dark-colored state. These devices appear more like a blue tinted glass. While a better performance demands the use of appropriate components, the cost-effectiveness of such components is crucial for commercialization. Specifically, the utilization of cost-effective electrodes, thin WO3 coatings, and inexpensive electrolytes are essential for reducing the cost of EC devices. Here, we report a high-performing porous WO3 thin film (∼130 nm) achieved by optimizing the DC sputtering process parameters. This way, an affordable dual-function EC energy-storage device was fabricated, showing 84% transmittance modulation and a high power density of 3036 mW/m2, thus functioning simultaneously as a transparency switching energy-storage device. With a large-area (900 cm2) device, we have demonstrated that the need for expensive ITO electrodes and Li+ ion-based electrolytes can be eliminated by using a hybrid electrode (ITO/Al-mesh) and multivalent Al3+ ion-based electrolytes while not compromising the device performance. The findings of this study may revolutionize the EC device industry and their commercialization owing to inexpensive ingredients and scalable processing.

Chemical reduction of porous WO3 and TiO2 photoelectrocatalysts by atomic hydrogen

The donor properties of atomic hydrogen were exploited to chemically reduce nanoparticle-based WO3 and TiO2 electrodes giving rise to a n-type doping of the semiconductors. For this purpose, a reactor system allowing for meticulous materials processing under high vacuum conditions and for the controlled electrode transfer into an aqueous electrolyte was designed and hydrogen doping-induced activity-changes in water photooxidation were studied. The chemical reduction of monoclinic WO3 electrodes leads to increased charge carrier separation at the semiconductor/electrolyte interface. Importantly, the beneficial doping effect is quite stable. However, bronze formation has a negative impact on the photoelectrocatalytic activity of WO3 electrodes upon strong sample reduction. For anatase TiO2 nanoparticle films de-doping of the reduced film is fast due to the small particle size. Correspondingly, the beneficial doping effect is transient. The small particle size allows, however, to estimate the number and energetic distribution of trapped electrons in hydrogen doped films.

Boosting coloration efficiency in an electrochromic device using an ITO/Ag/ITO multilayered electrode and porous WO3 chromic layer

ABSTRACT High-performance electrochromic devices (ECDs) were fabricated by introducing indium tin oxide/silver/indium tin oxide (IAI) multilayers as a transparent conducting oxide (TCO) electrode in conjunction with microstructural tailoring of tungsten trioxide (WO3) as an electrochromic (EC) layer. A 15-nm-thick Ag film with a preferential orientation of (111) and smooth morphology resulted in a high optical transmittance of 90.9% and sheet resistance 16.7 Ω/sq, making it a suitable TCO. In addition, the open network WO3 film used as an EC layer was deposited by carefully controlling the chamber pressure during the sputtering process. A high chamber pressure (2.0 Pa) resulted in a WO3 film with the lowest mass density (5.72 g/cm3) and a rough morphology. Half-cell ECDs consisting of a TCO bottom electrode (BE)/WO3 stack immersed in LiClO4 electrolyte were fabricated to verify the impact of using the IAI multi-layer stack and tailored WO3 film as a TCO and EC layer, respectively. Significant enhancement in terms of coloration efficiency was achieved for the ECDs by adopting the IAI TCO and open network WO3 EC layer compared to counterpart devices with an ITO TCO or dense WO3 EC film. This can be explained by the facile carrier extraction (injection) and transport of Li ions.

Dual-band electrochromic film based on mesoporous h-WO3/o-WO3·H2O/r-TiO2 for high performance smart windows

Porous three-dimensional electrochromic films composed of orthorhombic WO 3 ·H 2 O, hexagonal WO 3 , and rutile TiO 2 array (h-WO 3 /o-WO 3 ·H 2 O/r-TiO 2 , WWT) were controllably synthesized by a facile two-step hydrothermal technique. Due to the hydrophilicity and array structure of TiO 2 , the generation of high-quality o-WO 3 ·H 2 O was significantly promoted, which can reduce the energy barrier to ion diffusion and increase the ion flux by introducing structural water in the interlayer region of WO 3 . The formation of porous 3-dimensional structure and WO 3 –TiO 2 heterojunction increases the effective contact area, alters the distribution of energy bands, and promotes charge transport, resulting in significantly improved electrochromic properties. An impressive dual-band electrochromic performance with high optical modulation of 68.4% at 633 nm and 59.8% at 1600 nm was achieved in WWT film, respectively, with a fast switching speed (11s/3.3 s at 633 nm and 3 s/9.4 s at 1600 nm for coloring/bleaching), high coloration efficiency (46 cm 2 C −1 at 633 nm and 136.8 cm 2 C −1 at 1600 nm), and a satisfactory cycling stability at the same time. Dual-band electrochromic film and device with high optical modulation was obtained by hydrothermal synthesizing porous three-dimensional h-WO 3 /o-WO 3 ·H 2 O/r-TiO 2 composite film. • High performance dual-band electrochromic films and device are obtained. • The films composed of orthorhombic WO 3 ·H 2 O, hexagonal WO 3 , and rutile TiO 2 array. • TiO 2 promoted the formation of o-WO 3 ·H 2 O due to the hydrophilicity and array structure. • The layered structure of o-WO 3 ·H 2 O reduced ion diffusion barrier and increased ion flux. • The h-WO 3 /o-WO 3 ·H 2 O/r-TiO 2 film has high optical modulation of 68.4% at 633 nm and 59.8% at 1600 nm.

Enhancement reversibility and electrochromic efficiency of porous WO3 films by sparking method under electric/magnetic field

• The film prepared under an electric field provided extremely fluffy morphology. • The film prepared under combined electric/magnetic fields revealed denser morphology. • Dense/porous double-layer WO 3 films were designed and fabricated by sparking method. • The reversibility has been improved from 16.1% to 83.7%. • Enhanced 7-fold optical modulation and 9-fold coloration efficiency. This article reports on the morphological design to enhance reversibility and electrochromic performance of porous WO 3 films synthesized by sparking method using electric field (E = 6 kV/cm) and magnetic field (B = 500 mT). The excellent H + ion exchange between liquid electrolyte and the WO 3 films was influenced by extremely fluffy morphology as observed by sparking under an electric field— WO 3 with E sample. The morphology of the films becomes denser when sparked under a combination of electric and magnetic fields—WO 3 with (E + B) sample—which reduces the diffusion pathway and improves electron transfer within the films. Finally, we designed and fabricated dense/porous double-layer WO 3 films (WO 3 with (E + B)/E sample) to integrate their advantages to enhance 7-fold optical modulation and 9-fold coloration efficiency. Furthermore, the reversible efficiency increased from 16.1 % to 83.7 % compared to WO 3 with E sample.