Bare WO3 Research Articles

Electrochemical properties of WO3-reduced graphene oxide composite powders prepared by one-pot spray pyrolysis process

In this work, we report the preparation of WO3-reduced graphene oxide (rGO) composite powders by spray pyrolysis process using a stable graphene oxide colloidal solution with ammonium tungstate. The ultrafine WO3 nanocrystals below 10 nm in size are dispersed within the rGO matrix. The bare WO3 powders prepared from the aqueous spray solution of ammonium tungstate are spherical and do not aggregate. The bare WO3 and WO3-rGO composite powders show monoclinic and cubic crystal structures, respectively. The initial discharge capacities of the bare WO3 and WO3-rGO composite powders at a current density of 100 mA g−1 are 771 and 941 mA h g−1, respectively, and their initial Coulombic efficiencies are 67 and 65%, respectively. The discharge capacities of the bare WO3 and WO3-rGO composite powders at the 300th cycle are 282 and 546 mA h g−1, respectively.

Commercially Available WO3 Nanopowders for Photoelectrochemical Water Splitting: Photocurrent versus Oxygen Evolution

WO3 photoanodes with remarkable photocurrent densities are presented. These photoanodes were prepared from three different commercially available WO3 nanopowders. Doctor blading of the nanopowders followed by a short annealing in air led to nanostructured films. The best photoanode showed a photocurrent density of 3.5 mA cm-2 at 1.23 V vs. RHE in 1 m CH3 SO3 H under AM 1.5 G illumination (100 mW cm-2 ), surpassing values reported so far for bare WO3 photoanodes. The study also showed that the photocurrent was strongly dependent on the electrolyte, indicating oxidation of the electrolyte rather than of water. Oxygen evolution measurements performed in different electrolytes revealed that the amounts of oxygen were highly dependent on the electrolyte. By comparing the photocurrent values in the different electrolytes with the amount of evolving oxygen, it was found that the electrolyte producing the highest photocurrent was the electrolyte with the lowest oxygen evolution. Stability measurements showed that the more oxygen is produced, the less stable is the photoanode. These results clearly underline the difficulty to correlate the photocurrent values with oxygen evolution, drawing the attention to one of the major limitations of photoelectrochemical water splitting.

Efficient solar water oxidation by WO3 plate arrays film decorated with CoOx electrocatalyst

We report the synthesis and photoelectrochemical characterization of CoOx oxygen evolution catalyst modified two-dimensional (2D) WO3 plate arrays photoelectrode. The 2D-WO3 plate arrays were prepared perpendicularly on the FTO substrate by hydrothermal method. The CoOx nanoparticles were deposited on the surface of WO3 plate arrays on FTO by chemical deposition process. The CoOx nanoparticles are distributed on the surface of WO3 plates with a diameter of about 20 nm. The CoOx/WO3 film shows enhanced photoelectrochemical performance than the bare WO3 film. The highest incident-photon-to-current-efficiency (IPCE) value increases from 24.9% to 49.1% when introducing CoOx. The deposited CoOx electrocatalyst on WO3 surface can transfer holes effectively through the cobalt ion valency cycle, suppress the hole's accumulation and recombination at the electrode surface, achieve the superior kinetics and consequently enhance the overall solar water oxidation efficiency.

Branched Tungsten Oxide Nanorod Arrays Synthesized by Controlled Phase Transformation for Solar Water Oxidation

AbstractBranched (NH4)0.33⋅WO3 nanorods have been successfully synthesized by applying a simple hydrothermal approach with ammonium oxalate as capping agents. After annealing them in different atmospheres, the (NH4)0.33⋅WO3 nanorods were converted to WO3 nanorods. Atmosphere‐dependent morphology evolution and phase transformation by annealing of (NH4)0.33⋅WO3 were observed. The branched WO3 nanorods produce a higher photoelectrochemical activity than the bare WO3 nanorods without branches obtained under similar conditions, and the improvement of efficiency by branched nanorods was ascribed to the better light‐trapping characteristics and increase in surface area, which facilitates holes transfer at the WO3/electrolyte interface. The possible formation mechanisms of branched nanorods have been explored and the results show that the synergistic interaction between ammonium ion (NH4+) and acetate ion (−COO−) contributes to the formation of branched (NH4)0.33⋅WO3 nanorods.

Significant enhancement of the photoelectrochemical activity of WO3 nanoflakes by carbon quantum dots decoration

This work reports on single-crystal WO3 nanoflakes decorated with carbon quantum dots (CQDs) for efficient photoelectrochemical energy conversion system. The promising photoanodes can be fabricated via seed-mediated solvothermal method in combination with subsequent impregnation-assembling. A photocurrent density of 1.46 mA cm−2 at 1.0 V vs. Ag/AgCl can be achieved for the CQDs/WO3 electrode when performing linear sweep voltammetry measurements in 1 M H2SO4 solution under AM 1.5G illumination, which is about two times higher than that of the bare WO3 electrode. The enhancement of photoelectrochemical performance is ascribed to the enhanced light harvesting ability of CQDs and its accelerating charge transfer across the interface between CQDs/WO3 electrode and electrolyte. The improved activity indicates the potential of CQDs/WO3 as an efficient electrode for photoelectrochemical solar energy conversion.

Aerosol-Assisted CVD-Grown PdO Nanoparticle-Decorated Tungsten Oxide Nanoneedles Extremely Sensitive and Selective to Hydrogen.

We report for the first time the successful synthesis of palladium (Pd) nanoparticle (NP)-decorated tungsten trioxide (WO3) nanoneedles (NNs) via a two-step aerosol-assisted chemical vapor deposition approach. Morphological, structural, and elemental composition analysis revealed that a Pd(acac)2 precursor was very suitable to decorate WO3 NNs with uniform and well-dispersed PdO NPs. Gas-sensing results revealed that decoration with PdO NPs led to an ultrasensitive and selective hydrogen (H2) gas sensor (sensor response peaks at 1670 at 500 ppm of H2) with low operating temperature (150 °C). The response of decorated NNs is 755 times higher than that of bare WO3 NNs. Additionally, at a temperature near that of the ambient temperature (50 °C), the response of this sensor toward the same concentration of H2 was 23, which is higher than that of some promising sensors reported in the literature. Finally, humidity measurements showed that PdO/WO3 sensors displayed low-cross-sensitivity toward water vapor, compared to bare WO3 sensors. The addition of PdO NPs helps to minimize the effect of ambient humidity on the sensor response.

Synthesis of Shape-Tailored WO₃ Micro-/Nanocrystals and the Photocatalytic Activity of WO₃/TiO₂ Composites.

A traditional semiconductor (WO3) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO3 microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectance spectroscopy (DRS). These methods contributed to the detailed analysis of the crystal morphology and structural features. The synthesized bare WO3 photocatalysts were totally inactive, while the P25/WO3 composites were efficient under UV light radiation. Furthermore, the maximum achieved activity was even higher than the bare P25’s photocatalytic performance. A correlation was established between the shape of the WO3 crystallites and the observed photocatalytic activity registered during the degradation of different substrates by using P25/WO3 composites.

Carbon Materials as Additives to WO3 for an Enhanced Conversion of Simulated Solar Light

We have explored the impact of the incorporation of nanoporous carbons as additives to tungsten oxide on the photocatalytic degradation of two recalcitrant pollutants: rhodamine B and phenol, under simulated solar light. For this purpose, WO3/carbon mixtures were prepared using three carbon materials with different properties (in terms of porosity, structural order and surface chemistry). Despite the low carbon content used (2 wt. %), a significant increase in the photocatalytic performance of the semiconductor was observed for all the catalysts. Moreover, the influence of the carbon additive on the performance of the photocatalysts was found to be very different for the two pollutants. Carbon additives of hydrophobic nature increased the photodegradation yield of phenol compared to bare WO3, likely due to the higher affinity and stronger interactions of phenol molecules towards basic nanoporous carbons. Oppositely, the use of acidic carbon additives led to higher rhodamine B conversions due to increased acidity of the WO3/carbon mixtures and the stronger affinity of the pollutant for acidic catalyst’s surfaces. As a result, the photooxidation of rhodamine B is favored by means of a coupled (photosensitized and photocatalytic) degradation mechanism. All these results highlight the importance of favoring the interactions of the pollutant with the catalyst’s surface through a detailed design of the features of the photocatalyst.

Preparation of cobalt coated TiO2 and WO3–TiO2 nanotube films via photo-assisted deposition with enhanced photocatalytic activity under visible light illumination

Highly ordered TiO2 and WO3–TiO2 nanotubes were prepared by one-step electrochemical anodizing method and cobalt has been successfully deposited on these nanotubes by photo-assisted deposition process. The morphology, crystal structure, elemental composition and light absorption capability of samples were characterized by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray spectrometer and ultraviolet–visible spectroscopy methods. All cobalt loaded samples show an appearance of red shift relative to the unloaded samples. The degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of these novel visible-light-responsive photocatalysts. Results showed that the photocatalytic activity of bare WO3–TiO2 samples is higher than that with undoped TiO2 sample. Compared with unmodified TiO2 and WO3–TiO2, the Co/TiO2 and Co/WO3–TiO2 samples exhibited enhanced photocatalytic activity in the degradation of methylene blue. Kinetic research showed that the reaction rate constant of Co/WO3–TiO2 is approximately 2.26 times higher than the apparent reaction rate constant of bare WO3–TiO2. This work provides an insight into designing and synthesizing new TiO2–WO3 nanotubes-based hybrid materials for effective visible light-activated photocatalysis. The catalysts prepared in this study exhibit industrially relevant interests due to the low cost and high photocatalytic activity.

Morphology engineering of WO3/BiVO4heterojunctions for efficient photocatalytic water oxidation

Four types of nanostructural WO3/BiVO4 heterojunctions were designed by depositing a BiVO4 layer onto WO3 scaffolds with different morphologies and investigated to understand the influence of heterojunction morphology on their photoelectrochemical performances. The architecture of WO3 scaffolds was controlled by adjusting the solvents used in their solvothermal synthesis. The solvent was found to exert a great influence on the architecture of the obtained WO3 scaffolds. Methanol leads to the formation of block-like nanostructures and ethanol facilitates the formation of nanorods, while isopropyl alcohol and ethylene glycol give rise to the formation of triangular nanowalls and 3D hierarchical nanostructures, respectively. Monoclinic WO3 nanostructures were obtained via removal of ammonium or structural water by annealing the samples obtained at 510 °C in air. A BiVO4 layer was then deposited on the monoclinic WO3 scaffolds with different morphologies by spin-coating to form WO3/BiVO4 heterojunction films, which show significantly enhanced photocurrents compared to their corresponding bare WO3 scaffolds. Among these WO3/BiVO4 nanostructure heterojunctions, the one based on a rod-like WO3 nanostructure shows the best photoelectrochemical (PEC) performance, which can be ascribed to its optimal rod-like morphology, for the construction of WO3/BiVO4 heterojunction regarding efficient charge carrier transfer and collection, while the other one based on WO3 nanowalls exhibits better stability and a higher photocurrent in a long-run test, indicating that morphology engineering significantly influences the activity and stability of WO3-based heterojunctions.

Visible light responsive Zeolite/WO3–Pt hybrid photocatalysts for degradation of pollutants in air

Adsorbent–photocatalyst hybrids based on WO3 and Pt as cocatalyst immobilized on different type of zeolites were prepared. Their performance for the degradation of pollutants under UV and Vis light was analyzed. Two types of zeolites (ZSM-5 and Zeolite Y) with Si/Al ratios ranging between 5 and 280 were selected as hierarchical microporous materials acting as adsorbents. The incorporation of platinum on tungsten oxide was done by means of the photodeposition method. Pt-loaded WO3 was dispersed on the zeolites and subjected to a lyophilization process. Their photocatalytic properties towards the abatement of representative pollutants e.g., acetic acid, acetaldehyde and trichloroethylene, were analyzed under different operating conditions in batch and continuous flow photoreactors. Raw materials and hybrid photocatalysts were characterized by N2 adsorption–desorption, XRD, UV–vis spectroscopy, XPS and TEM microscopy. The adsorption ability of the photocatalysts towards the selected pollutants was studied under dynamic conditions. The textural properties of the photocatalysts were not the main factor controlling their adsorption ability. The incorporation of WO3–Pt on the zeolite results in Vis light responsive materials. Monoclinic WO3 crystal phase was identify in all zeolitic materials. Large WO3–Pt aggregates were detected on Zeolite Y (ca. 300nm) with low Si/Al content in contrast with highly disperse phase for ZSM-5 (SiO2/Al2O3=280) (ca. 100nm). All WO3–Pt hybridized zeolites showed photoactivity for the degradation of the studied pollutants under Vis light, improving the performance of bare WO3–Pt. The results shown in this work reveal the influence of the hydrophobicity of the siliceous material for the adsorption of reaction intermediates or byproducts and as a consequence for the determination of the rates of CO2 formation under static conditions. A F(Static) function, dependent of the Si/Al ratio and the BET area, to correlate the difference trend of the amount of CO2 released produced by the hybrid composites, under static and dynamic conditions is proposed.

A highly efficient BiVO4/WO3/W heterojunction photoanode for visible-light responsive dual photoelectrode photocatalytic fuel cell

A highly efficient BiVO4/WO3/W heterojunction photoanode was fabricated based on the nanoporous WO3 film, which was prepared on the tungsten plate by anodic oxidation, in order to facilitate the electrons transfer from BiVO4 to WO3 by providing a natural connection between WO3 film and W substrate. Then, a visible-light responsive dual photoelectrode photocatalytic fuel cell (PFC) consisted of BiVO4/WO3/W photoanode and Pt modified commercial buried junction silicon (Pt/BJS) photocathode was constructed. The results showed that the optimized BiVO4/WO3/W photoanode obtained a photocurrent of 2.01mA/cm2 at 0.6V (vs Ag/AgCl) in 0.1M KH2PO4 (pH 7) electrolyte under simulated AM1.5 solar light, which was 180% and 205% higher than that of bare WO3 film and bare BiVO4 film, respectively. The established dual photoelectrode PFC showed high converting performance of organics into electricity. For example, a short-circuit current density of 0.26mAcm−2, which is higher than most of the reported visible-light responsive dual photoelectrode PFC systems, was obtained with the open-circuit voltage of 0.78V and maximum power output of 2.0×10−4 Wcm−2 in 20mgL−1 tetracycline hydrochloride. Furthermore, a removal ratio of 78% after 4h was achieved with a stable output photocurrent in the degradation process.

Enhanced toluene sensing performance of gold-functionalized WO3·H2O nanosheets

Au nanoparticle-functionalized composites have been proven to be promising materials for gas sensing applications. We successfully synthesized tungsten oxide (WO3·H2O) nanosheets by a facile and effective hydrothermal process and decorated Au nanoparticles on their surface for ultra-high sensitivity levels to toluene gas. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Spectrometer (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Gas-sensing measurements revealed superior toluene sensing properties of Au nanoparticle-functionalized WO3·H2O nanosheets (Au-WO3·H2O) compared with bare WO3·H2O. The maximum response value of Au-WO3 reached 50–100ppm toluene at 300°C, which was nearly four times as high as that of bare WO3. Meanwhile, Au-WO3·H2O exhibited the shorter response/recovery time, better selectivity and lower operating temperature to toluene gas than those of bare WO3·H2O. Also, the mechanism involved in improving the toluene sensing properties of WO3·H2O by Au nanoparticle-functionalization was discussed.

Enhancement of gas-sensing characteristics of hydrothermally synthesized WO3 nanorods by surface decoration with Pd nanoparticles

Enhancement of the gas-sensing characteristics of nanostructured metal oxides by surface decoration with noble metal nanoparticles has recently received significant attention as a powerful technique for improving gas-sensing performance. Herein, we introduce a facile method of decorating tungsten oxide (WO3) nanorods by palladium (Pd) nanoparticles to achieve enhanced NH3 gas-sensing performance. The WO3 nanorods were synthesized by a scalable hydrothermal method followed by thermal calcination to activate surface bonding for Pd decoration. Decoration of Pd nanoparticles on the surface of WO3 was achieved through reduction of the complex Na2PdCl4 using Pluronic as both surfactant and reducing agent. The materials obtained were characterized by SEM, EDS, HRTEM, and XRD. The gas-sensing characteristics of bare WO3 and Pd–WO3 nanorods were tested for NH3, CO, H2, CO2, and CH4 detection at different temperatures. Results revealed that decoration of Pd nanoparticles on the surface of WO3 nanorods significantly enhances the NH3 gas-sensing characteristics of the metal oxide. The transient stability of the sensor determined after 10 on/off cycles of switching from air to gas demonstrated the effective reusability of the fabricated device.

Preparation of three dimensional graphene foam–WO3 nanocomposite with enhanced visible light photocatalytic activity

Three dimensional graphene foam (3D GF) was synthesized by chemical vapor deposition (CVD) on a nickel foam skeleton. After dissolving the nickel foam, the obtaining 3D GF was used as a highly porous conductive substrate for nucleation and growth of WO3 particles. Scanning electron microscopy (SEM) and Raman spectroscopy was employed to ensure the quality of the prepared GFs and to judge about the 3D GF–WO3 chemical structure. The WO3 characteristic Raman peaks centered at 726, and 809 cm−1 are slightly broadened and displaced to lower wavelength in the 3D GF–WO3 nanocomposite, as compared to the corresponding peaks of the bare tungsten oxide. This phenomenon confirms the formation of W–C and W–O–C bonds in composite material which is important for faster transferring the photoexcited electrons to graphene 3D network as an exceptional electron acceptor. The 3D GF−WO3 composite material was applied in photocatalytic degradation of Rhodamine B dye. It was observed that the annealed samples show an excellent photocatalytic performance relative to the as-prepared 3D GF−WO3 samples and bare WO3, which is ascribed to the lower electron/hole recombination through the formation of W–C and W–O–C bonds.

Ultra-Efficient Photocatalytic Properties in Porous Tungsten Oxide/Graphene Film under Visible Light Irradiation.

Recently, a growing amount of effort has been devoted to solving the widespread problem of pollution. Photocatalysts have attracted increasing attention for their widespread environmental applications. Here, a classic and simple electrospun technique is used to directly fabricate a porous a tungsten oxide nanoframework with graphene film as a photocatalyst for degradation of pollutants. The as‐synthesized film simultaneously possesses substantial adsorptivity of aromatic molecules, extensive light absorption range, significant light trapping, and efficient charge carrier separation properties, which remarkably enhance photocatalytic activity. In the photodegradation of Rhodamine B, a significant photocatalytic enhancement in the reaction rate is observed, which has superior photocatalytic activity compared to other bare WO3 and TiO2 nanomaterials under visible‐light irradiation.

Enhanced visible-light photocatalytic activity and the mechanism study of WO3 nanosheets coupled with Ag3PO4 nanocrystals

Highly efficient visible-light-driven Ag3PO4/WO3 photocatalysts with different mole fractions of Ag3PO4 nanocrystals have been synthesized via an in situ precipitation method. Characterization results showed the in situ growth of finely distributed Ag3PO4 nanocrystals on the surface of the WO3 nanosheets. Under visible light irradiation, the Ag3PO4/WO3 photocatalysts exhibited enhanced photocatalytic activity compared with bare Ag3PO4 or WO3 for the degradation of methyl blue, and the highest activity was reached by the Ag3PO4/WO3 hybrid photocatalyst with 20at% of Ag3PO4. The observed improvement in photocatalytic activity is associated with the extended absorption in the visible light region resulting from the attached Ag3PO4 nanocrystals, and the effective separation of photo-induced carriers at the Ag3PO4/WO3 interfaces. In addition, on the basis of the quenching effects of different scavengers and estimated energy band positions, the mechanism of enhanced photocatalytic activity is proposed.

A novel Z-scheme WO3/CdWO4 photocatalyst with enhanced visible-light photocatalytic activity for the degradation of organic pollutants

A novel Z-scheme WO3/CdWO4 photocatalyst was developed and used for the degradation of different organic pollutants. It exhibited enhanced photocatalytic performance much higher than that of bare WO3 and CdWO4.

Dodecyl ethyl dimethyl ammonium bromide capped WO3nanoparticles: efficient scaffolds for chemical sensing and environmental remediation

The current work revealed the comparative analysis of bare and surface functionalized tungsten trioxide (WO3) nanoparticles that can be successfully utilized as competent photocatalysts for the degradation of organic dyes and as efficient electron transporters for the fabrication of highly sensitive electrochemical sensors in aqueous medium. The room temperature synthesis of WO3 nanoparticles with good crystallinity was carried out in the presence of dodecylethyldimethyl ammonium bromide (DEDMAB) as the template by a wet chemical process. The surface functionalized nanoparticles possess a controllable band gap and act as an effectual substrate for electrochemical sensing of hydrazine. The sensitivity values of the fabricated sensor range from 9.39 μA μM(-1) cm(-2) with the limits of detection ranging from 28.8 μM. Furthermore, surface modulated particles also exhibited enhanced photocatalytic performance in the photodegradation of Congo red dye with an efficiency of 98.67% compared to bare WO3 nanoparticles without any modification. The comparison of the current responses and photodegradation activity of the bare and capped WO3 particles illustrates an excellent sensitivity, selectivity and operational stability of the as-functionalized nanoparticles.

Electrochemical properties of tungsten sulfide-carbon composite microspheres prepared by spray pyrolysis.

Tungsten sulfide (WS2)–carbon composite powders with superior electrochemical properties are prepared by a two-step process. WO3-carbon composite powders were first prepared by conventional spray pyrolysis, and they were then sulfidated to form WS2-carbon powders. Bare WS2 powders are also prepared by sulfidation of bare WO3 powders obtained by spray pyrolysis. Stacked graphitic layers could not be found in the bare WS2 and WS2–carbon composite powders. The amorphous bare WS2 and WS2–carbon composite powders have Brunauer–Emmett–Teller (BET) surface areas of 2.8 and 4 m2 g−1, respectively. The initial discharge and charge capacities of the WS2–carbon composite powders at a current density of 100 mA g−1 are 1055 and 714 mA h g−1, respectively, and the corresponding initial Coulombic efficiency is 68%. On the other hand, the initial discharge and charge capacities of the bare WS2 powders are 514 and 346 mA h g−1, respectively. The discharge capacities of the WS2–carbon composite powders for the 2nd and 50th cycles are 716 and 555 mA h g−1, respectively, and the corresponding capacity retention measured after first cycle is 78%.