Anodic WO3 Research Articles

Surface Engineering of Anodic WO3 Layers by In Situ Doping for Light-Assisted Water Splitting.

This study presents a novel approach to fabricating anodic Co-F-WO3 layers via a single-step electrochemical synthesis, utilizing cobalt fluoride as a dopant source in the electrolyte. The proposed in situ doping technique capitalizes on the high electronegativity of fluorine, ensuring the stability of CoF2 throughout the synthesis process. The nanoporous layer formation, resulting from anodic oxide dissolution in the presence of fluoride ions, is expected to facilitate the effective incorporation of cobalt compounds into the film. The research explores the impact of dopant concentration in the electrolyte, conducting a comprehensive characterization of the resulting materials, including morphology, composition, optical, electrochemical, and photoelectrochemical properties. The successful doping of WO3 was confirmed by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence measurements, X-ray photoelectron spectroscopy (XPS), and Mott-Schottky analysis. Optical studies reveal lower absorption in Co-doped materials, with a slight shift in band gap energies. Photoelectrochemical (PEC) analysis demonstrates improved PEC activity for Co-doped layers, with the observed shift in photocurrent onset potential attributed to both cobalt and fluoride ions catalytic effects. The study includes an in-depth discussion of the observed phenomena and their implications for applications in solar water splitting, emphasizing the potential of the anodic Co-F-WO3 layers as efficient photoelectrodes. In addition, the research presents a comprehensive exploration of the electrochemical synthesis and characterization of anodic Co-F-WO3, emphasizing their photocatalytic properties for the oxygen evolution reaction (OER). It was found that Co-doped WO3 materials exhibited higher PEC activity, with a maximum 5-fold enhancement compared to pristine materials. Furthermore, the studies demonstrated that these photoanodes can be effectively reused for PEC water-splitting experiments.

Photocatalytic fuel cell with cathodic P-BiVO4/CQDs and anodic WO3 for efficient Cr(VI) reduction and stable electricity generation

Developing efficient and sustainable photoelectrodes in photocatalytic fuel cell (PFC) system remains a major challenge. In this work, a PFC system (WO3|P-BiVO4/CQDs) was established based on WO3 photoanode and P-BiVO4 photocathode loaded with carbon quantum dots (CQDs) for Cr(VI) reduction with simultaneous electricity production. The photocatalytic performance of the constructed PFC system was characterized by various analytical methods. With the introduction of CQDs, both Cr(VI) reduction and maximum power density (Pmax) have been significantly enhanced. When the loading amount of CQDs was 150 μL, its Cr(VI) reduction rate and maximum power density (Pmax) were respectively 90 % and 0.10 mW/cm2 within 180 min of illumination, superior to the WO3|P-BiVO4 system. This was attributed to the decoration of CQDs, which broadened the light absorption range, increased the isolation efficiency of charge carriers and ultimately enhanced the ability of the fabricated PFC system. The superior stability and practicability were also demonstrated by five cyclic experiments. In addition, the plausible mechanism was proposed. This work offers an important reference for the application of the PFC system in wastewater treatment.

Enhanced photoelectrochemical hydrogen production via linked BiVO4 nanoparticles on anodic WO3 nanocoral structures

In this study, heterostructured BiVO4/WO3 with linked BiVO4 nanoparticles and anodic WO3 nanocorals was fabricated. This heterostructure shows enhanced photoelectrochemical performances, especially, in H2 production.

BiVO4-modified anodic nanocoral WO3 structures for enhancement of photoelectrochemical performance

Nanostructuring of metal oxides is a straightforward strategy for enhancing photoelectrochemical (PEC) performance. The present work demonstrates the anodization of W metal to determine the optimum WO3 nanostructure for use in photoanodes. Anodization was performed in a fluoride-containing 1 M Na2SO4 electrolyte. Under optimum conditions, WO3 nanocoral structures were fabricated. The forming mechanism of the nanocoral structures was elucidated by the generation and development of nanobubbles at the metal/oxide interface. To enhance the PEC performance, BiVO4 layers were coated on the anodic WO3 nanocoral structures and annealed at 500 °C in air atmosphere. The prepared BiVO4/WO3 nanocoral layers were characterized by SEM, XRD, EIS and UV–vis spectroscopy. They were then used as photoanodes for PEC and IPCE measurements. Consequently, photocurrent density was improved to 0.42 mA/cm2 at 1.23 V vs. RHE and IPCE at 400 nm (21%) was enhanced by 21 times due to the producing band alignment between BiVO4 and WO3.

Anodic nanoporous WO3 modified with Bi2S3 quantum dots as a photoanode for photoelectrochemical water splitting

Although anodic nanoporous (ANP) WO3 has gained a lot of attention for photoelectrochemical water splitting (PEC-WS), there is still a lack of efficient WO3-based photoanodes with sufficient light absorption and good e−/h+ separation and transfer. The decoration of ANP WO3 with narrow bandgap semiconductor quantum dots (QDs) can enhance charge carrier transfer while reducing their recombination, resulting in a high PEC efficiency. In this study, ANP WO3 was synthesized via an anodic oxidation process and then modified with Bi2S3 QDs via successive ionic layer adsorption and reaction (SILAR) process and examined as a photoanode for PEC-WS under ultraviolet–visible illumination. The ANP WO3 photoanode modified with ten cycles of Bi2S3 QDs demonstrated the highest current density of 16.28 mA cm−2 at 0.95 V vs RHE, which is approximately 19 times that of pure ANP WO3 (0.85 mA cm−2). Furthermore, ANP WO3/Bi2S3 QDs (10) photoanode demonstrated the highest photoconversion efficiency of 4.1 % at 0.66 V vs RHE, whereas pure ANP WO3 demonstrated 0.3 % at 0.85 V vs RHE. This can be attributed to the proper number of Bi2S3 QDs significantly enhancing the visible light absorption, construction of type-II band alignment with WO3, and improved charge separation and migration. The modification of ANP WO3 with nontoxic Bi2S3 QDs as a prospective metal chalcogenide for enhancing visible light absorption and PEC-WS performance has not yet been investigated. Consequently, this study paves the path for a facile technique of designing effective photoelectrodes for PEC-WS.

Pretexturing and Anodization of W for Fabricating Ordered Anodic Porous WO3

Ordered anodic porous WO3 was prepared by the anodization of a W substrate with a depression pattern under a constant voltage of 18 V in concentrated phosphoric acid at 120 °C. However, the behavior of hole formation induced in depressions was found to be strongly affected by the depth and diameter of the depressions. Multiple holes were formed in a shallow depression during the initial stage of anodization, whereas only one hole was formed in a deep depression. In addition, when the depression diameter was small, the growth of fine holes around the induced holes was observed. Since the fine holes formed on the surface of anodic porous WO3 prevented the induced holes from growing in the depth direction, the formation of large-diameter depressions allowed the induced holes to grow deeper. The obtained ordered anodic porous WO3 can be used for various applications such as in photocatalysis and electrochromic devices.

Anodic WO3 layers sensitized with hematite operating under the visible light spectrum

Tungsten oxide has been considered one of the most promising photoanode materials for photoelectrochemical (PEC) water splitting. WO3 possesses a relatively narrow band gap (2.5–2.8 eV) and superior charge transport properties. In this paper, for the first time, anodic WO3 layers were sensitized with Fe2O3 by electrodeposition and re-annealing method. The influence of FeCl3 concentration in the electrolyte used for the electrodeposition process on the morphology, semiconducting and photoelectrochemical properties was investigated. Since the band gap of hematite is narrower when compared to tungsten oxide, its modification/sensitization with hematite is a promising way to transfer WO3 photoactivity to the visible light region. To sum up, a successfully performed synthesis of Fe2O3-WO3 and Fe2O3–C,N-WO3 heterojunctions resulted in a shift of the material photoresponse towards the visible light region even to the wavelength of 550 nm. The best results were achieved for the Fe2O3–C,N-WO3 sample, that exhibits IPCE values about 1.6 times higher at 450 nm and 12 times higher at 480 nm in comparison to pristine anodic WO3.

Synthesis and characterization of anodic WO3 layers in situ doped with C, N during anodization

In this work, for the first time, anodic C,N-WO3 layers were obtained by in situ doping during anodic oxidation of metallic tungsten. The effects of applied potential (40, 50, and 60 V), and hexacyanoferrate (III) ion concentration (0, 15 and 60, 120, and 180 mM) in the electrolyte on the resulting oxide morphology, phase composition, and photoelectrochemical performance were investigated. To obtain a photoactive oxide phase, as-received samples were annealed at 500°C in air for 2 h. The synthesized materials were subjected to complex physicochemical characterization using SEM, EDS, XRD, and XPS. In addition, the semiconducting properties of prepared samples were characterized using the Mott-Schottky analysis. The anodic C,N-WO3 layers were used as photoanodes for water splitting experiments. The best photoelectrochemical performance was observed for the samples obtained in 1 M (NH4)2SO4 and 0.075 M NH4F with 120 mM K3[Fe(CN)6] at 50 V for 4 h.

An aqueous aluminum-ion electrochromic full battery with water-in-salt electrolyte for high-energy density

Electrochromic batteries (EBs) have been developed as a technical breakthrough to solve the energy issues of storage and saving. Multivalent-ions (Zn2+, Mg2+ and Al3+) have recently demonstrated attractive properties for EBs due to their multiple-electron redox nature. However, still now, reported multivalent-ion EBs are typically assembled with a small-area metallic anode and a large-area electrochromic cathode. Non-uniformity of coloration and unstable metal plating/stripping hinder the developments of these devices. Additionally, insufficient energy/power density of EBs is a huge technical challenge needed to be overcome. In this work, we demonstrated a new aqueous aluminum-ion electrochromic full battery (AIEFB) to overcome the challenges. Systematic studies of density functional theory calculation, molecular dynamics simulation, electrochemical analysis, and mechanical measurements were conducted to optimize electrode materials and electrolyte. A water-in-salt (WIS) Al(OTF)3 electrolyte and a new electrochromic material couple of anodic amorphous WO3 (a-WO3) and cathodic indium hexacyanoferrate (InHCF) were exploited for AIEFB. The AIEFB demonstrated advantages of a high average discharge potential (1.06 V), an attractive energy density of 62.8 mWh m−2 at a power density of 2433.8 mW m−2, a high transmittance modulation of 63% at 600 nm, and a distinct transparent-to-deep blue coloration during the Al-ion shuttling processes.

Visible-light sensitization of anodic tungsten oxide layers with CuWO4

Anodic tungsten oxide is an attractive material for photoelectrochemical water splitting under solar irradiation, however due to several limitations, it absorbs only UV light and, therefore, one of the challenges is to transfer its photoresponse to the visible light region. In this paper, for the first time, it is proposed sensitization of anodic WO3 layers with copper tungstate by a wet impregnation method. The CuWO4–WO3 materials are obtained by immersion of anodic layers in a copper acetate solution and annealing at 500 °C in air atmosphere. As-received materials are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), and Raman spectroscopy, Mott–Schottky measurements and photoelectrochemical (PEC) tests. Proposed visible-light sensitization with CuWO4 results in an enhanced photoelectrochemical response to visible light. Moreover, narrowing of the band gap (from 2.88 to 2.47 eV) with a prolonged impregnation time is also observed.

Enhanced Visible Light Active WO3 Thin Films Toward Air Purification: Effect of the Synthesis Conditions.

Taking our current environmental situation in the world into consideration, people should face growing problems of air and water pollution. Heterogeneous photocatalysis is a highly promising tool to improve both air and water quality through decomposition/mineralization of contaminants directly into harmless CO2 and H2O under ambient conditions. In this contribution, we focused on the synthesis of self-assembly WO3 thin films via an electrochemical approach in the aqueous electrolyte containing fluoride ions toward air purification. The effect of preparation conditions such as applied potential (10–50 V), anodization time (15–120 min), concentration of H2SO4 (0.5–1.5 M) and NaF (0.1–1.0 wt.%) on the morphology, photocurrent response, and photocatalytic activity addressed to removal of air pollutant in the presence of as-prepared WO3 samples were thoroughly examined and presented. The results revealed the growth of nanoplatelets and their gradual transformation into flower-like structures. The oxide layers and platelet thickness of the WO3 samples were found to be proportionally related with the synthesis conditions. The photocatalytic ability toward air purification was evaluated by degradation of toluene from air mixture using low-powered LEDs as an irradiation source (λmax = 415 nm). The highest photoactivity was achieved in presence of the sample which possessed a well-ordered, regular shape and repeatable distribution of flower buds (100% of degradation). The results have confirmed that the oxide layer thickness of the anodic WO3 significantly affected the photocatalytic activity, which increased with the increasing thickness of WO3 (to 1.05 μm) and then had a downward trend. The photocurrent response evidenced that the well-organized sample had the highest ability in photocurrent generation under UV-Vis and Vis irradiation. Finally, a possible growth mechanism of WO3 NFs was also discussed.

Improving Photoelectrochemical Properties of Anodic WO3 Layers by Optimizing Electrosynthesis Conditions.

Although anodic tungsten oxide has attracted increasing attention in recent years, there is still a lack of detailed studies on the photoelectrochemical (PEC) properties of such kind of materials grown in different electrolytes under various sets of conditions. In addition, the morphology of photoanode is not a single factor responsible for its PEC performance. Therefore, the attempt was to correlate different anodizing conditions (especially electrolyte composition) with the surface morphology, oxide thickness, semiconducting, and photoelectrochemical properties of anodized oxide layers. As expected, the surface morphology of WO3 depends strongly on anodizing conditions. Annealing of as-synthesized tungsten oxide layers at 500 °C for 2 h leads to obtaining a monoclinic WO3 phase in all cases. From the Mott-Schottky analysis, it has been confirmed that all as prepared anodic oxide samples are n-type semiconductors. Band gap energy values estimated from incident photon−to−current efficiency (IPCE) measurements neither differ significantly for as−synthesized WO3 layers nor depend on anodizing conditions such as electrolyte composition, time and applied potential. Although the estimated band gaps are similar, photoelectrochemical properties are different because of many different reasons, including the layer morphology (homogeneity, porosity, pore size, active surface area), oxide layer thickness, and semiconducting properties of the material, which depend on the electrolyte composition used for anodization.

Functional Blocking Layer of Twisted Tungsten Oxide Nanorod Grown by Electrochemical Anodization for Photoelectrochemical Water Splitting

Using electrochemical anodization of tungsten foil in a fluorinated-based electrolyte, the twisted WO3 nanorods (T-WO3 NRs) were grown, and the film properties were controlled by post-annealing conditions. The anodized WO3 material was composed of two distinct layers; the T-WO3 NRs which functions as an active layer for the PEC reaction and another compact WO3 (C-WO3) barrier which acts as a blocking layer for the charge transport. From more resistance of thicker C-WO3 layer, to minimize the formation of the C-WO3 layer under constant applied voltage, we performed rapid-thermal annealing under air ambient as a post-thermal treatment. As the post-annealing time increased, the thickness of T-WO3 NRs layer remained at approximately 680 nm, but the C-WO3 thickness gradually increased from about 91 nm at 1 min to 633 nm at 120 min. Unexpectedly, the anodic WO3 film having a compact layer thickness of about 475 nm exhibited the highest PEC performance, corresponding to a photocurrent density of 0.75 mA cm−2 at 1.23 V vs reversible hydrogen electrode, subsequently followed by anodic WO3 films with less thick compact layers. This suggests that the C-WO3 layer promotes the charge separation/transfer events by formation of cascading band alignments between the T-WO3 NR and C-WO3 layers.

Enhanced Rhodamine B and coking wastewater degradation and simultaneous electricity generation via anodic g-C3N4/Fe0(1%)/TiO2 and cathodic WO3 in photocatalytic fuel cell system under visible light irradiation

Degradation of pollutants can be integrated with electricity generation in Photocatalytic fuel cell under light irradiation or self-powered fuel cell in the dark. In fuel cell driven by electrode reactions, the electrode reduction and oxidation transforms chemical energy in pollutants into electrical energy. In this work, Rhodamine B and coking wastewater were treated, using an efficient Z-scheme g-C3N4/Fe0(1%)/TiO2 as an anodic catalyst and WO3 as a cathodic catalyst. After 100 min of reaction in a single chamber fuel cell with 10 Ω of external resistance, in 0.05 M Na2SO4 electrolyte, the paired stainless-steel electrodes loaded respectively with g-C3N4/Fe0(1%)/TiO2 and WO3, degraded 98% Rhodamine B and generated 0.95 V cell voltage under 50 W visible-light irradiation, while removed 60% RhB and generated 0.5 V without light. To investigate the PFC performance of g-C3N4/Fe0(1%)/TiO2 in treating real coking wastewater, at optimal pH 2, 91% chemical oxygen demand (COD) and 89% total organic carbon (TOC) were removed and generated 0.3 V cell voltage. The influence of pH on photocatalytic degradation performance and cell voltage are evaluated. The high cell voltage is attributed to the very low impedance of the g-C3N4/Fe0(1%)/TiO2 loaded anode. The excellent electrochemical properties of paired electrodes help in generating higher current density, due to the increased photocatalyst activity of the tridimensional catalyst as proved by electron spinning resonance spectrum, photoluminescence, and Electric Impedance Spectrum analysis.

Preparation of anodic nanoporous WO3 film using oxalic acid as electrolyte

Abstract In this work, nanoporous WO 3 was formed by anodization in oxalic acid. Various oxalic acid concentrations (0.01–0.4 M) and anodization times (1–240 min) on the formation of nanoporous WO 3 were investigated. Uniform nanoporous WO 3 with pore diameter size of 70 nm and pore wall thickness of 19 nm was produced by using 0.05 M oxalic acid and 120 min anodization time. Meanwhile, a partially porous structure or film dissolution occurred on the samples prepared using other oxalic acid concentrations and anodization times. In addition to the nanoporous layer, a compact layer embedded with nanobubbles was formed underneath the nanoporous layer. The as-anodized nanoporous film was amorphous and it transformed to monoclinic WO 3 after annealing in argon (Ar) and nitrogen (N 2 ) gases. N was doped into WO 3 after annealing in N 2 and it suppressed the grain growth. The N-doped WO 3 which possesses thinner pore wall showed higher electrochromic current density value than the film annealed in Ar.

Tungsten Oxide Nanoplate Film as a Highly Active Solar-Driven Photocatalyst

A WO3 nanoplate-like film with an average edge width of approximately 20 nm and thickness of approximately 250 nm was fabricated via electrochemical anodization of W film at 60 V in a bath with electrolytes composed of ethylene glycol and 0.7 wt% NH4F. The influence of applied potential on the morphology of the anodic oxide was investigated. The growth of the nanoplate-like morphology might be attributed to the competition between electrochemical oxide formation and chemical etching by the corrosive [WFn](n-6) complex ions at minimal applied potential of 60 V. In addition, the presence of tungstite (WO3H2O) with an orthorhombic structure was observed within the WO3 nanoplate-like film, which has a layered structure with sheets of distorted W–O octahedral units sharing corners. All of the anodic WO3 nanostructured films were annealed and their electrochemical ability was investigated under solarillumination. A maximum photocurrent density of 1.50 mA/cm2 was observed for the WO3 nanoplate-like film because more incident photons could be harvested to generate photo-induced charge carriers under solar-illumination. Keywords: Electrochemical anodization, photoelectrochemical, solar-illumination, WO3 nanoplate.

Anodic WO3 mesosponge @ carbon: a novel binder-less electrode for advanced energy storage devices.

A novel design for an anodic WO3 mesosponge @ carbon has been introduced as a highly stable and long cyclic life Li-ion battery electrode. The nanocomposite was successfully synthesized via single-step electrochemical anodization and subsequent heat treatment in an acetylene and argon gas environment. Morphological and compositional characterization of the resultant materials revealed that the composite consisted of a three-dimensional interconnected network of WO3 mesosponge layers conformally coated with a 5 nm thick carbon layer and grown directly on top of tungsten metal. The results demonstrated that the carbon-coated mesosponge WO3 layers exhibit a capacity retention of 87% after completion of 100 charge/discharge cycles, which is significantly higher than the values of 25% for the crystalline (without carbon coating) or 40% for the as-prepared mesosponge WO3 layers. The improved electrochemical response was attributed to the higher stability and enhanced electrical conductivity offered by the carbon coating layer.

Electropolymerization of Aniline onto Anodic WO3 Film: An Approach to Extend Polyaniline Electroactivity Beyond pH 7

Generally, the redox activity of polyaniline (PANI) can only be retained in acidic media at pH < 3. This high acidity requirement has been a large obstacle in many applications such as biosensor, marine antifouling, and anticorrosion. In this study, composite film systems of PANI and tungsten trioxide (WO3) were fabricated by the electropolymerization of aniline onto anodic WO3 film. For the first time, we found that the prepared PANI/WO3 film possesses excellent electrochemical activity and cycling stability in neutral solutions. The morphology and composition of the PANI/WO3 films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), whereas their electroactivity was evaluated by cyclic voltammetry. Particularly, the long-term stability of their electroactivity upon cycling was investigated in detail. The good electroactivity and high redox stability of the PANI/WO3 films in neutral ...

NH4-doped anodic WO3 prepared through anodization and subsequent NH4OH treatment for water splitting

Tungsten trioxide (WO3) prepared by anodization of a W foil was doped with NH4 through NH4OH treatment at 450°C. Since aqueous NH4OH was used during doping instead of NH3 gas, the treatment step does not require complicated annealing facilities. Moreover, the state of doped N is a form of NH3-W instead of W2N, which lowers the bandgap but increases photocorrosion. We found that incorporation of NH4 into WO3 leads to reduction of the bandgap from 2.9eV to 2.2eV, regardless of the amount of NH4OH treatment, lowering the onset potential and increasing the current density at fixed potential for oxygen evolution reaction under illumination. Scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were employed to investigate the surface morphologies, crystallinities of tungsten oxides and existence of NH4 doping, respectively. The bandgap energy was determined by UV–Vis spectroscopy to measure the transmittance and refraction. The water splitting performance of each sample was measured by electrochemical linear sweep voltammetry in a 3-electrode configuration under illumination.

The Effect of Crystallinity of Nanoporous WO&lt;sub&gt;3&lt;/sub&gt; on the Intercalation and Deintercalation of Li&lt;sup&gt;+&lt;/sup&gt;

Nanoporous anodic WO3 was annealed at three different times of 1h, 2h, and 3h at a constant temperature of 500oC. This was to investigate the intercalation and deintercalation behaviour of Li+ in this annealed nanoporous oxide. The as-anodised WO3 is amorphous and after annealing, monoclinic WO3 was observed with much higher degree of crystallinity when the time of annealing was increased from 1h to 3h. By electrodiffusion of Li+ in the nanoporous structure, an ion exchange between fully oxidized states (W6+) which is the octahedral coordination dominates (WO6) and Li+ could happen. This causes changing of the colour of the yellowish WO3 to bluish WO3.Li2O. This work showed the effect of annealing time on intercalation of Li+ ion with WO3, however crystallinity can play a good role for electron movement, it cause a decrease in Li+ ion interaction with WO3.