Efficient WO3 Research Articles

Electrosynthesis of highly efficient WO3-x/graphene (photo-)electrocatalyst by two-electrode electrolysis system for oxygen evolution reaction

Integration of non-noble transition metal oxides with graphene is known to construct high-activity electrocatalysts for oxygen evolution reduction (OER). In order to avoid the complexity of traditional synthesis process, a facile electrochemical method is elaborately designed to engineer efficient WO3-x/graphene (photo-)electrocatalyst for OER by a two-electrode electrolysis system, where graphite cathode is exfoliated into graphene and tungsten wire anode evolves into VO-rich WO3-x profiting from formed reductive electrolyte solution. Among as-prepared samples, WO3-x/G-2 shows the best electrocatalytic performance for OER with an overpotential of 320 mV (without iR compensation) at 10 mA/cm2, superior to commercial RuO2 (341 mV). With introduction of light illumination, the activity of WO3-x/G-2 is greatly enhanced and its overpotential decreases to 290 mV, benefiting from additional reaction path produced by photocurrent effect and extra active sites generated by photogenerated carriers (h+). Characterization results indicate that both VO-rich WO3-x and graphene contribute to the efficient OER performance. The activity of WO3-x for OER is decided by the synergistic effect between VO concentration and particle size. The graphene could not only disperse WO3-x nanoparticles, but also improve the holistic conductivity and promote electron transmission. This work supports a novel method for engineering WO3-x/graphene composite for highly efficient (photo-)electrocatalytic performance for OER.

Surfactant assisted approach to development of efficient WO3 photoanode for natural dye sensitized solar cell

Herein, the single-step hydrothermal route has been successfully implemented to design a surfactant-assisted WO3 photoanode for dye-sensitized solar cell (DSSC). The influence of surfactant on growth and photoresponse properties of the dye-sensitized WO3 have been studied. Optical absorption study shows a direct allowed type of electronic transition with band gap energy lies in the range of 2.82–2.38 eV. The formation of pure hexagonal crystal with tuning in the surface morphology from nanospheres to nanoflowers were obtained in the structural and morphological investigation. The compositional analysis confirms the formation of stoichiometric films with respective valence states of W+6 and O2–. Photovoltaic performance of dye-sensitized WO3 demonstrates improved photocurrent from 1.53 to 2.61 mA/cm2 corresponding to photovoltage of 690–764 mV. The best photo-conversion efficiency of 3.52% was obtained for the W-SDS sample of DSSC. The IPCE measurement are well supported to PEC performance of the DSSC. The stability of the prominent W-SDS photoanode was performed to confirm the suitability and reproducibility of photoelectrode. The charge transfer properties of DSSC were analyzed by electrochemical impedance spectroscopy (EIS).

Efficient WO3−x nanoplates photoanode based on bidentate hydrogen bonds and thermal reduction of ethylene glycol

In this study, an efficient WO3−x nanoplates photoanode was generated based on bidentate hydrogen bonds and in subsequent thermal reduction of ethylene glycol (EG). An appropriate number of controllable oxygen vacancies (Ov) was generated in-situ on the surface of the WO3 nanoplates without deep defects by bidentate hydrogen bonds. Density functional theory (DFT) calculations indicate that the distance between two alcoholic hydrogens (5.124 Å) in EG matches that of the diagonal oxygens (5.483 Å) in the WO3 (002) surface, which allows EG to combine through the most stable bidentate hydrogen bonds with O–H intervals of approximately 2.5 Å. Diagonal oxygens are captured directly from the surface, leaving Ov owing to the special hydrogen-bond structure and moderate reducibility of EG under appropriate thermal conditions. The photocurrent density of the WO3−x nanoplates improves considerably to 2.07 from the 0.91 mA cm−2 of pristine WO3 with the introduction of Ov, which demonstrates the superior surface reaction kinetics from the reduced holes-to-water resistance and increase in surface injection efficiency. DFT calculations of the oxygen evolution reaction reveal that surface Ov could substantially decrease the reaction energy barrier for a lower overpotential of 0.494 V compared to that of WO3 (1.037 V), which is consistent with the reduction in the Tafel slope from 412 to 243 mV dec−1. Therefore, this study provides an innovative method to obtain an efficient WO3 photoanode based on the treatment of EG.

Morphology control of WO3 nanoplate film on W foil by oxalic acid for photocatalytic gaseous acetaldehyde degradation

WO3 film with reasonable morphology could be a promising photocatalytic material for indoor air purification. Herein, we constructed WO3 nanoplate film for photocatalytic degradation of gaseous acetaldehyde. The WO3 nanoplate film was prepared by nitric acid corrosion of W foil using oxalic acid for morphology regulation. SEM, XRD, and XPS evidenced that the monoclinic phase WO3 nanoplates grew on W foil. The oxalic acid anchored on the specific faces of the tungsten oxide hydrate facilitated for forming high quality larger and thinner WO3 nanoplates. UV–vis diffuse reflection spectra (DRS) manifested that the oxalic acid modulated WO3 nanoplate films possess smaller absorption edge and wider solar light absorption region. The oxalic acid contributed to obtain efficient WO3 nanoplate film photocatalyst for gaseous acetaldehyde decomposition under simulated solar light irradiation, which was response for the increased crystallinity and more surface reactive sites as well as the enhanced light absorption. The morphology modulation by oxalic acid will pave the way for synthesis of practical WO3 films in environment purification.

One-Step Rapid and Scalable Flame Synthesis of Efficient WO3 Photoanodes for Water Splitting.

Photoelectrochemical water splitting is a promising approach for the carbon-free production of hydrogen using sunlight. Here, robust and efficient WO3 photoanodes for water oxidation were synthesized by the scalable one-step flame synthesis of nanoparticle aerosols and direct gas-phase deposition. Nanostructured WO3 films with tunable thickness and band gap and controllable porosity were fabricated by controlling the aerosol deposition time, concentration, and temperature. Optimal WO3 films demonstrate superior water oxidation performance, reaching a current density of 0.91 mA at 1.24 V vs. reversible hydrogen electrode (RHE) and an incident photon-to-current conversion efficiency (IPCE) of ca. 61 % at 360 nm in 0.1 m H2 SO4 . Notably, it is found that the excellent performance of these WO3 nanostructures arises from the high in situ restructuring temperature (ca. 1000 °C), which increases oxygen vacancies and decreases charge recombination at the WO3 /electrolyte interface. These findings provide a scalable approach for the fabrication of efficient photoelectrodes based on WO3 and other metal oxides for light-driven water splitting.

Highly enhanced photocatalytic activity of WO3 thin films loaded with Pt–Ag bimetallic alloy nanoparticles

This study provides a novel approach to design efficient WO3 photocatalysts decorated by bimetallic Pt–Ag alloy nanoparticles.

Efficient WO3 photoanodes fabricated by pulsed laser deposition for photoelectrochemical water splitting with high faradaic efficiency

In this work, we present a systematic study on the synthesis of monoclinic γ-WO3 obtained using pulsed laser deposition (PLD). A photocurrent of 2.4mA/cm2 (60% of the optical maximum for a 2.7eV gap material) was obtained for films as thick as 18μm. FE-SEM images revealed that WO3 films were actually formed by an array of oriented columns. Efficient hole extraction toward the electrolyte was observed and attributed to a possible accommodation of the electrolyte between the WO3 columns, even for relatively compact films. This feature, combined with the detailed optical absorption and IPCE characterization, allowed us to implement a double-stack configuration of WO3 photoanodes which resulted in a remarkable photocurrent density of 3.1mAcm−2 with 1 sun AM1.5G illumination in 0.1M H2SO4 electrolyte. Faradaic efficiencies of more than 50% was obtained without co-catalyst, which is one the highest values reported for pure WO3. By adding a 3nm layer of Al2O3 by ALD, a faradaic efficiency of 80% was reached without diminishing the photocurrent density.

Efficient Anodically Grown WO3 for Photoelectrochemical Water Splitting

The potentiostatic anodization of metallic tungsten has been investigated in different solvent/electrolyte compositions with the aim of improving the photoelectrochemical performances of the tungsten oxide layer. Among the explored electrolytes, the anodization in the NMF/H2O/NH4F solvent mixture was found to produce the most efficient WO3 photoanodes, which, combining spectral sensitivity, high electrochemically active surface and improved charge transfer kinetics, outperform, under simulated solar illumination, most of the reported nanocrystalline substrates produced by anodization in aqueous electrolytes and by sol gel methods. While the preparation of the photoelectrodes is a slow process at room temperature (20°C), it could be greatly accelerated (x 10) by carrying out the anodization at 40-50°C, thus proving to be a fast and convenient approach to the production of high performing WO3 photoactive substrates directly connected to a metal electron collector.

Indium-free transparent organic light emitting diodes with Al doped ZnO electrodes grown by atomic layer and pulsed laser deposition

We present highly efficient transparent organic light emitting diodes (OLEDs) with Al doped ZnO (AZO) electrodes prepared by atomic layer deposition and pulsed laser deposition (PLD). The power and current efficiencies exceed 27 lm/W and 44 cd/A at a brightness level of 100 cd/m2, respectively. At the same time, the transmissivity of the devices is above 73% in the visible part of the spectrum. Owing to an efficient WO3 buffer layer and an optimized PLD process for the deposition of the top AZO electrode, the OLEDs show leakage current densities as low as 3×10−5 mA/cm2 at a reverse bias of 6 V. Therefore, our study paves the way for indium-free, see-through OLED displays.