WO3 Photoanode Research Articles

Enhanced photoelectrochemical water oxidation of WO3/R-CoO and WO3/B-CoO photoanodes with a type II heterojunction

Tungsten trioxide (WO3) has been conceived as a promising photoanode material for photoelectrochemical (PEC) water oxidation. Therefore, many efforts have been made to improve its PEC performances. Herein, a novel heterojunction is fabricated through combining rocksalt CoO (R-CoO) or blende CoO (B-CoO) nanosheets with WO3 nanoplates using a spin-coating method. The typical type II heterojunctions, e.g., WO3/R-CoO and WO3/B-CoO, both have exhibited higher photocurrent densities than pristine WO3 photoanode. The photocurrent densities of WO3/R-CoO, WO3/B-CoO and WO3 are 0.53 mA cm−2, 0.45 mA cm−2 and 0.31 mA cm−2 at 1.23 V vs. reversible hydrogen electrode, respectively. For the WO3/R-CoO photoanode, the surface charge separation efficiency is 50.95% and the photoconversion efficiency is 0.062%, which are both higher than the WO3 and WO3/B-CoO photoanodes. The enhanced PEC performances are due to the type II heterojunction between WO3 and R-CoO (or B-CoO), which facilitates the absorption of visible light and charge transport. The better performance of WO3/R-CoO than that of WO3/B-CoO may be due to the deeper valence band position of R-CoO. Our work demonstrates that R-CoO (or B-CoO) can couple with WO3 to form a type II heterojunction to improve the PEC water oxidation performance.

The effect of nanoparticulate PdO co-catalysts on the faradaic and light conversion efficiency of WO3 photoanodes for water oxidation.

WO3 photoanodes offer rare stability in acidic media, but are limited by their selectivity for oxygen evolution over parasitic side reactions, when employed in photoelectrochemical (PEC) water splitting. Herein, this is remedied via the modification of nanostructured WO3 photoanodes with surface decorated PdO as an oxygen evolution co-catalyst (OEC). The photoanodes and co-catalyst particles are grown using an up-scalable aerosol assisted chemical vapour deposition (AA-CVD) route, and their physical properties characterised by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and UV-vis absorption spectroscopy. Subsequent PEC and transient photocurrent (TPC) measurements showed that the use of a PdO co-catalyst dramatically increases the faradaic efficiency (FE) of water oxidation from 52% to 92%, whilst simultaneously enhancing the photocurrent generation and charge extraction rate. The Pd oxidation state was found to be critical in achieving these notable improvements to the photoanode performance, which is primarily attributed to the higher selectivity towards oxygen evolution when PdO is used as an OEC and the formation of a favourable junction between WO3 and PdO, that drives band bending and charge separation.

Photooxidation of Water with Thin Film Tungsten Oxides

Tungsten oxide semiconductors are used to photooxidize water. Students prepare WO3, CuWO4, and mixed composition thin film photoanodes. The syntheses are simple, allowing for the quick production of a range of materials. Photoanodes are tested in a photoelectrochemical cell assembled from common equipment, allowing for the direct comparison of photoanode performance. Composite photoanodes perform best, leading to a discussion of what limits overall performance in these materials. Additional instrumental methods such as SEM, EDS, XRD, and diffuse reflectance UV–vis spectrophotometry, if available, can be incorporated readily into the experiment, providing additional insights into material properties. Students are introduced to solid-state chemistry, semiconductors, and the photooxidation of water in the context of the hydrogen economy.

Surface oxygen vacancies on WO3 nanoplate arrays induced by Ar plasma treatment for efficient photoelectrochemical water oxidation

The construction of surface defects on semiconductor oxide photoanodes has been identified as a promising route for attaining improved photoelectrochemical (PEC) performance. Here, Ar plasma treatment has been used to etch the surface of hydrothermally synthesized WO3 nanoplate array films, which generated surface oxygen vacancies (Ovs) with the concomitant reduction of surface W6+ to W5+/W4+. As a result, the visible-light absorption and photogenerated charge separation of WO3 was enhanced, as evidenced by X-ray photoelectron spectroscopy (XPS), UV/Vis diffuse-reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. A WO3 photoanode subjected to Ar plasma treatment for 120 s exhibited a photocurrent density of 1.32 mA cm−2 and an O2 evolution rate of 1.0 μmol cm−2·min−1 under simulated solar light irradiation at a bias potential of 1.23 V vs. reversible hydrogen electrode, approximately 1.7- and 5-times higher, respectively, than those of a pristine sample. This improvement is mainly attributed to the facilitative effect of surface oxygen vacancy defects, which promote electron–hole generation and separation rates and decrease the interfacial charge-transfer resistance between the WO3 photoanode and electrolyte. Our Ar plasma surface modification also has potential for developing other photoanodes for efficient PEC performance.

Tuning the Electronic Structure of Monoclinic Tungsten Oxide Nanoblocks by Indium Doping for Boosted Photoelectrochemical Performance.

Photoelectrochemical (PEC) water oxidation, a desirable strategy to meet future energy demands, has several bottle-necks to resolve. One of the prominent issues is the availability of charge carriers at the surface reaction site to promote water oxidation. Of the several approaches, metal dopants to enhance the carrier density of the semiconductors, is an important one. In this work, we have studied the effect of In-doping on monoclinic WO3 nanoblocks, growing vertically over fluorine-doped tin oxide (FTO) without the aid of any seed layer. X-ray photoelectron spectroscopy (XPS) data reveals that In3+ ions are partially occupying the W6+ ions in In-doped WO3 photoanode. In3+ ions are offering better performance by adding additional charge carriers for amplifying the expression of the number of carriers. The maximum current density value of 2.18 mA/cm2 has been provided by the optimized In-doped WO3 photoanode with 3 wt% indium doping at 1.23 V vs. RHE, which is ∼3 times higher than that of undoped monoclinic WO3 photoanode. Mott-Schottky (MS) analysis reveals charge carrier density (ND ) for In-doped WO3 photoanode has been enhanced by a factor of 3. An average Faradic yield of ∼90 percent has been achieved which can serve as a model system using In3+ as a dopant for an inexpensive and attractive method for enhanced WO3 based PEC water oxidation.

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.

Multifunctional WO3/NiCo2O4 heterojunction with extensively exposed bimetallic Ni/Co redox reaction sites for efficient photoelectrochemical water splitting

AbstractThe enhanced separation and injection efficiencies of photogenerated carriers is essential to improve the photoelectrochemical (PEC) performance of WO3 photoanode. In this work, we firstly synthesized WO3/NiCo2O4 heterojunction through simple hydrothermal‐annealing method as well as investigate the effect and mechanism of NiCo2O4 on WO3 for PEC performances. The measurements demonstrate that the nano‐needle NiCo2O4 grown on the surface of WO3 induces the bimetallic Ni/Co redox reaction sites extensively exposed to the electrolyte, which is beneficial to enhance the PEC performances of WO3 photoanode, such as photocurrent density improved by four times (0.84 mA/cm2 at 1.23 V vs. RHE) as well as more negative initial potential (∼280 mV) in contrast to bare WO3. Further investigation shows the remarkable enhancement of PEC performances is attributed to improved surface reaction kinetics, the enhanced injection efficiency and separation efficiency of photogenerated carriers due to the co‐catalyst effect of NiCo2O4 and the formation of WO3/NiCo2O4 heterojunction. This work provides reference for application of heterojunction with co‐catalyst function, which is beneficial to the development and application of similar structures.

Sol-gel synthesis of highly reproducible WO3 photoanodes for solar water oxidation

Although monoclinic WO3 is widely studied as a prototypical photoanode material for solar water splitting, limited success, hitherto, in fabricating WO3 photoanodes that simultaneously demonstrate high efficiency and reproducibility has been realized. The difficulty in controlling both the efficiency and reproducibility is derived from the ever-changing structures/compositions and chemical environments of the precursors, such as peroxytungstic acid and freshly prepared tungstic acid, which render the fabrication processes of the WO3 photoanodes particularly uncontrollable. Herein, a highly reproducible sol-gel process was developed to establish efficient and translucent WO3 photoanodes using a chemically stable ammonium metatungstate precursor. Under standard simulated sunlight of air mass 1.5 G, 100 mW cm−2, the WO3 photoanode delivered photocurrent densities of ca. 2.05 and 2.25 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), when tested in 1 mol L−1 H2SO4 and CH3SO3H, respectively. Hence, the WO3 photoanodes fabricated herein are one of the WO3 photoanodes with the highest performance ever reported. The reproducibility of the fabrication scheme was evaluated by testing 50 randomly selected WO3 samples in 1 mol L−1 H2SO4, which yielded an average photocurrent density of 1.8 mA cm−2 at 1.23 VRHE with a small standard deviation. Additionally, the effectiveness of the ammonium metatungstate precursor solution was maintained for at least 3 weeks, when compared with the associated upper-limit values of peroxytungstic and tungstic acid based precursors after 3 d. This study presents a key step to the future development of WO3 photoanodes for efficient solar water splitting.

Efficient urine removal, simultaneous elimination of emerging contaminants, and control of toxic chlorate in a photoelectrocatalytic-chlorine system

Urine, which is an important waste biomass resource, is the main source of nitrogen in sewage and contains large quantities of emerging contaminants (ECs). In this study, we propose a new method to efficiently remove urine, simultaneously eliminate ECs, and control the generation of toxic chlorate during urine treatment using a photoelectrocatalytic-chlorine (PEC-Cl) system. A type-II heterojunction of WO3/BiVO4 was used as a photoanode to generate chlorine radicals (Cl•) by decreasing the oxidation potential of WO3 valence band for the highly selective conversion of urine to N2 and the simultaneous degradation of ECs in an efficient manner. The method presented surprising results. It was observed that the amount of toxic chlorate was significantly inhibited by circumventing the over-oxidation of Cl− by holes or hydroxyl radicals (•OH). Moreover, the removal of urea nitrogen reached 97% within 90 min, while the degradation rate of trimethoprim in urine was above 98.6% within 60 min, which was eight times more than that in the PEC system (12.1%). Compared to the bare WO3 photoanode, the toxic chlorate and nitrate generated by the WO3/BiVO4 heterojunction photoanode decreased by 61% and 44%, respectively. Thus, this study provides a safe, efficient, and environmentally-friendly approach for the disposal of urine.

WO3 homojunction photoanode: Integrating the advantages of WO3 different facets for efficient water oxidation

Abstract The manipulation of the surface property of WO3 photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics. Here, we report a WO3(002)/m-WO3 homojunction film that is composed of an upper WO3 layer with predominant (002) facet (WO3(002)) and a lower WO3 layer with multi-crystal facets (m-WO3) as a photoanode for solar water oxidation. Due to the synergistic effect of WO3(002) layer and m-WO3 layer, better water oxidation activity and stability are achieved on the WO3(002)/m-WO3 homojunction film relative to the m-WO3 and WO3(002) film. Specifically, the improved water oxidation performance on the WO3(002)/m-WO3 homojunction film is attributed to the followings. In thermodynamics, the band position differences between WO3(002) layer and m-WO3 layer lead to the formation of WO3(002)/m-WO3 homojunction, which has positive function of improving their charge separation and transfer. In kinetics, the upper WO3(002) layer of the WO3(002)/m-WO3 film has superior activity in the adsorption and activation of water molecules, water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway, and the corrosion of photoanode from the H2O2 intermediate is restrained. The present work provides a new strategy to modify the WO3 photoanodes for thermodynamically and kinetically efficient water oxidation.

Oxygen vacancy engineering with flame heating approach towards enhanced photoelectrochemical water oxidation on WO3 photoanode

Abstract Oxygen vacancies are a double-edged sword for photoelectrochemical (PEC) devices and a comprehensive understanding on their role in PEC processes is important. Although there is existing work that illustrates their effect on PEC processes, clarifying the influence of surface and bulk oxygen vacancies, respectively, on the PEC performance is challenging. Herein, we present the fabrication of WO3 photoanodes with tunable bulk and surface oxygen vacancy with a novel two-step flame heating approach that is proving to be a powerful platform for this purpose. We found that both the conductivity and trapping state density of the WO3 photoanode increase with bulk oxygen vacancy density, leading to a volcano-like relationship between the kinetics of charge separation/transport and bulk oxygen vacancy density. Moreover, both the interfacial charge transfer rate constant and the charge recombination rate constant on the surface of the WO3 photoanode increase with surface oxygen vacancy density, which also leads to a volcano-like relationship between the charge injection efficiency and surface oxygen vacancy density. By tuning the surface and bulk oxygen vacancy density simultaneously, the PEC performance of the WO3 photoanode was increased by ca. 10 times, which illustrates the strength of delicate oxygen vacancy engineering in optimizing PEC devices.

Fabrication of WO3 photoanode on crystalline Si solar cell for water splitting

An integrated device of solar cell and photocatalysis (p-Si fronted solar cell/ CoSi2/WO3) has been used as photoanode for water splitting. The WO3 had been synthesized by co-electrodeposition of CoW on the p-Si fronted solar cell and followed by the annealing and acid treatment. The XRD and SEM show the amorphous structure for both as-depostion and after treatment samples. After the treatment, XPS and the ellipsometer spectroscopy shows that the CoSi2 and WO3 was formed with the band gap of 1.32 eV and 2.67 eV, respectively. Without additional power, we had demonstrated that the p-Si fronted solar cell/CoSi2/WO3 can achieve ~ 0.046 mA/cm2 photocurrent.

Bi electrodeposition on WO3 photoanode to improve the photoactivity of the WO3/BiVO4 heterostructure to water splitting

In view of the urgency to replace fossil fuel-based energy sources with sustainable and renewable sources, much has been done to discover new materials and/or production methods that can provide devices capable of converting solar energy into chemical or electrical energy. This work describes the electrodeposition of Bi on WO3 film and its subsequent conversion to BiVO4 with the addition of NH4VO3 and heat treatment. In this way, a WO3/BiVO4 heterojunction is obtained. With this methodology, it is possible to observe the formation of BiVO4 nanostructures with pillar shapes and a photocurrent increase of 300 times compared to films obtained by drop-casting. At 1.23 V vs RHE (Reversible Hydrogen Electrode), the photocurrent achieved with the photoanode reaches 2.1 ± 0.3 mA cm−2, which is 35 times higher than pure BiVO4 and 23 times higher than pure WO3. Transient absorption spectroscopy studies show an increase in the time constants for the recombination of charge carriers to the WO3/BiVO4 heterojunction. Electrodeposition is a relatively simple, easy to use, and scalable technique. So, it is expected that its use for the production of photoelectrodes will be more widespread.

Activity of sol-gel derived nanocrystalline WO3 films in photoelectrochemical generation of reactive chlorine species

Conventional chlor-alkali method used for production of chlorine gas and chlorine-based disinfectants is among the most energy-intensive processes in chemical industry, therefore, more sustainable alternatives with lower carbon footprint are sought. Photoelectrochemical (PEC) generation of reactive chlorine species (Cl2, HClO, ClO−) is a promising technology in the area of water disinfection and purification, as it combines the advantages of (i) using the renewable solar energy; (ii) possibility to produce disinfectants on-site and on-demand and (iii) eliminates the need for sophisticated infrastructure for storage and handling of chlorine species.In the present study nanocrystalline tungsten (VI) oxide layers were formed on conducting glass substrate using simple sol-gel synthesis technique and polytethylene glycol as a structure-directing agent. It is shown that addition of PEG in moderate amounts favours formation of the structure of interconnected nanocrystalline particles, which ensures effective separation and transport of photogenerated charge carriers and, therefore, is crucial for the photoelectrochemical activity of the films. This is corroborated by the analysis of SEM and XRD data, revealing the influence of polytethylene glycol from the initial stages of WO3 phase crystallization. Faradaic efficiency of photoelectrochemical hypochlorite formation is shown to be about 30%, and antimicrobial effect of PEC chlorination with WO3 photoanodes is demonstrated on Gram-positive Bacillus sp. and Gram-negative E.coli C41(DE3) bacteria.

Photocatalytic Production of Hypochlorous Acid over Pt/WO3 under Simulated Solar Light

The production of hypochlorous acid (HClO) over a visible-light active photocatalyst was achieved for the first time in an aqueous solution of NaCl under simulated solar light. Approximately 17.6 μM of HClO was accumulated after 1 h of photoirradiation by employing the photocatalytic oxidation of Cl– with O2 reduction over the Pt cocatalyst-loaded WO3. The quantum efficiency of the HClO production was 2.3% at 420 nm. Moreover, the photoelectrochemical HClO production on the WO3 photoanode was also investigated to elucidate the photocatalytic reaction mechanism. The initial faradaic efficiency of the process reached 96%, indicating high selectivity toward the production of HClO over the WO3 surface in an aqueous NaCl solution. It was found that the highly photocatalytic performance over Pt-loaded WO3 was primarily attributed to the higher oxygen reduction and lower H2O2 formation abilities in comparison to other cocatalysts.

3D core-shell WO3@α-Fe2O3 photoanode modified by ultrathin FeOOH layer for enhanced photoelectrochemical performances

Abstract The solar light absorption efficiency as well as the carrier separation and transfer efficiency in the bulk and on the surface of the photoanodes are still the main challenges for efficient photoelectrochemical (PEC) water splitting. Hence, in this work, a 3D core-shell WO3@α-Fe2O3 photoanode modified by ultrathin FeOOH layer was designed and fabricated for the first time to maximize respective merits of 1D WO3 (excellent electron transport pathways), α-Fe2O3 (strong visible light absorption) and FeOOH (a hole transfer) to achieve efficient PEC performances. As a result, the as-fabricated WO3@α-Fe2O3/FeOOH photoanode exhibits a 120 mV negatively shift in onset potential and yields a photocurrent density of 1.12 mA/cm2 at 1.23 V vs. RHE, which is 1.72 and 3.73 times than that of WO3@α-Fe2O3 and WO3 photoanodes, respectively. Moreover, this work may provide an effective strategy of maximizing the advantages of each component in the composite photoelectrode to achieve effective PEC performance.

PVP Treatment Induced Gradient Oxygen Doping in In2S3 Nanosheet to Boost Solar Water Oxidation of WO3 Nanoarray Photoanode

AbstractThe photoelectrochemical performance of the WO3 photoanode is limited by the severe charge recombination in the bulk phase and at the WO3/electrolyte interface. Herein, In2S3 nanosheets are integrated onto the surface of the WO3 nanowall array photoanode, followed by a facile polyvinylpyrrolidone (PVP) solution treatment. The PVP treatment results in sulfur vacancies and a gradient oxygen doping into In2S3 from surface to interior, which induces the formation of a gradient energy band distribution. The gradient band structured In2S3 and type II band alignment at the WO3/In2S3 interface simultaneously create a channel that favors photogenerated electrons to migrate from the surface to the conductive substrate, thereby suppressing bulk carrier recombination. Meanwhile, the sulfur vacancies and oxygen doping contribute to increased charge carrier concentration, prolonged carrier lifetime, more active sites, and small interfacial transfer impedance. As a consequence, the PVP treated WO3/In2S3 heterostructure photoanode exhibits a significantly enhanced photocurrent of 1.61 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE) and negative onset potential of 0.02 V versus RHE.

Multilayer WO3/BiVO4 Photoanodes for Solar-Driven Water Splitting Prepared by RF-Plasma Sputtering

A series of WO3, BiVO4 and WO3/BiVO4 heterojunction coatings were deposited on fluorine-doped tin oxide (FTO), by means of reactive radio frequency (RF) plasma (co)sputtering, and tested as photoanodes for water splitting under simulated AM 1.5 G solar light in a three-electrode photoelectrochemical (PEC) cell in a 0.5 M NaSO4 electrolyte solution. The PEC performance and time stability of the heterojunction increases with an increase of the WO3 innermost layer up to 1000 nm. A two-step calcination treatment (600 °C after WO3 deposition followed by 400 °C after BiVO4 deposition) led to a most performing photoanode under back-side irradiation, generating a photocurrent density of 1.7 mA cm−2 at 1.4 V vs. SCE (i.e., two-fold and five-fold higher than that generated by individual WO3 and BiVO4 photoanodes, respectively). The incident photon to current efficiency (IPCE) measurements reveal the presence of two activity regions over the heterojunction with respect to WO3 alone: The PEC efficiency increases due to improved charge carrier separation above 450 nm (i.e., below the WO3 excitation energy), while it decreases below 450 nm (i.e., when both semiconductors are excited) due to electron–hole recombination at the interface of the two semiconductors.

First demonstration of photoelectrochemical water splitting by commercial W–Cu powder metallurgy parts converted to highly porous 3D WO3/W skeletons

Hydrogen evolution through photoelectrochemical (PEC) water splitting by tungsten oxide-based photoanodes, as a stable and environmental-friendly material with moderate band gap, has attracted significant interest in recent years. The performance of WO3 photoanode could be hindered by its poor oxygen evolution reaction kinetics and high charge carrier recombination rate. Additionally, scalable and cost-effective commercial procedure to prepare nanostructured electrodes is still challenging. We present, for the first time, a novel and scalable method to fabricate highly efficient self-supported WO3/W nanostructured photoanodes from commercial W–Cu powder metallurgy (P/M) parts for water splitting. The electrodes were prepared by electrochemical etching of Cu networks followed by hydrothermal growth of WO3 nanoflakes. Interconnected channels of W skeleton provided high active surface area for the growth of WO3 nanoflakes with a thickness of ~40 nm and lateral dimension of ~250 nm. The optimized photoelectrode having 35% interconnected porosity exhibited an impressive current density of 4.36 mA cm−2 comprising a remarkable photocurrent of 1.71 mA cm−2 at 1.23 V vs. RHE under 100 mW cm−2 simulated sunlight. This achievement is amongst the highest reported photocurrents for WO3 photoelectrodes with tungsten substrate reported so far. Impedance and Mott-Schottky analyses evidenced fast charge transfer, low recombination rate, and accelerated O2 detachment provided by optimum 3D porous WO3/W electrode. Due to the nature of the commercial P/M parts and low-temperature hydrothermal processing, the procedure is cost-effective and scalable which can pave a new route for the fabrication of highly porous and efficient water splitting electrodes.

Engineering band edge properties of WO3 with respect to photoelectrochemical water splitting potentials via a generalized doping protocol of first-row transition metal ions

The photoelectrochemical (PEC) water splitting efficiency of WO3 is limited because to its wide band gap, which allows limited absorption of incident sunlight and its unsuitable band edge positions with respect to overall water splitting potentials. Therefore, band edge engineering of WO3 is essential for reducing the band gap and altering band edge positions via substitutional doping of metal ions. Hence, we report a facile and generalized protocol for synthesizing first row transition metal ion (V, Cr, Mn, Fe, Co, Ni, Cu and Zn,) -doped WO3 thin films and explore their band-edge and PEC water-splitting properties. The detailed characterization results show that irrespective of the type of dopant, the morphology is found to change upon doping, whereas the crystal phase, crystal facet, band gap, charge-transfer resistance, carrier density, and oxygen vacancy formation depend on the type of dopant. The band-edge positions of doped WO3 are plotted with respect to a reference hydrogen electrode, revealing a reduction and widening of the band gap and an upward and downward shift in conduction and valence band-edge positions induced by dopants. Overall, our results provide valuable insights into fabricating highly engineered WO3 photoanodes for efficient future PEC water-splitting capabilities.