Photoanodes For Photoelectrochemical Water Splitting Research Articles

Nitrogen-doped CdS/TiO2 nanorods heterojunction photoanode for efficient and stable photoelectrochemical water splitting

Photoelectrochemical water splitting represents a promising route for converting solar energy into hydrogen, but sluggish reaction kinetics associated with inefficient charge separation and migration, and poor stability limit solar-to-hydrogen conversion. In this work, we develop a N-doped-CdS/TiO2-nanorods heterojunction photoanode for photoelectrochemical water splitting by anchoring CdS on TiO2 nanorods followed by nitrogen doping. The light harvesting is significantly enhanced and the charge separation and migration are promoted due to the formed heterojunction and nitrogen doping, which greatly enhances the water oxidation reaction. As a result, the photoelectrochemical cell with the optimized N-doped-CdS/TiO2-nanorods heterojunction photoanode yields a hydrogen production rate of 42.6 μmol cm−2 h−1, which is 2.51 times higher than that of the TiO2-nanorods photoanode. In particular, doping nitrogen atoms into CdS greatly alleviates the photocorrosion problem. Therefore, the newly-developed photoanode exhibits excellent stability under a continuous 10-h running.

Fe-N Co-Doped BiVO4 Photoanode with Record Photocurrent for Water Oxidation.

Bismuth vanadate (BVO) ranks among the most promising photoanodes for photoelectrochemical (PEC) water splitting. Nonetheless, slow charge separation and transport, besides the sluggish water oxidation kinetics, are key barriers to its photoefficiency. Here, we present a co-doping strategy that significantly improves the charge separation performance of BVO photoanodes. We found that, under standard one sun illumination, the Fe-N co-doped BVO photoanode (Fe-N-BVO) by N-coordinated Fe precursor reaches a record photocurrent density of 7.01 mA cm-2 at 1.23 V vs RHE after modified a surface co-catalyst (FeNiOOH), and exhibits an outstanding stability. By contrast, much lower photocurrent density is obtained for the N-doped, Fe-doped and Fe/N-doped BVO photoanode with separated N and Fe precursors. The detailed experimental characterizations show that the high activity of the Fe-N co-doped BVO photoanode is attributed to the enhanced photo-induced bulk charge separation, as well as the accelerated surface water oxidation kinetics. XPS, EXAFS and DFT calculations clearly show that, instead of formation of deep trapping state in the individually doped BVO, the co-doping of Fe-N into BVO generates Fe-based electronic states just below the bottom of conduction band and N-derived states just above the top of valence band. Such modulations in electronic structure enable the efficient trap of the electrons and holes to enhance the separation of photo-induced carriers, but hinder the charge recombination originated from the deep trapping sites.

Oxygen vacancy mediated TiO2-x-MoS2/FTO heterostructure as an efficient photoanode for photoelectrochemical water splitting

To achieve a complete water splitting cycle, solar-assisted oxidation plays a crucial role. Discovering efficient photoanodes capable of absorbing visible light is essential to enable cost-effective solar energy conversion. This study devised an efficient hydrothermal method to synthesize a TiO2-MoS2 heterostructure with an oxygen vacancy on FTO (fluorine-doped tin oxide). The structure, morphology, optical properties, and photoelectrocatalytic behavior of the TiO2-x-MoS2 heterostructure using various techniques. The oxygen vacancy state can create a new sublevel state below the conduction band of TiO2, which narrows the band gap to a lower level and thus extends the absorption edge into the visible region. The strategy of oxygen vacancy resulted in a photocurrent density of 0.6 mA cm-2, which is 3 times higher than pure TiO2. Also, the TiO2-x-MoS2 heterostructure exhibits a photocurrent density of 2.6 mA cm−2 and higher O2 evolution than pure TiO2 in a 1.0 M KOH solution under UV–Vis irradiation. Compared to unmodified TiO2 nanorods, TiO2-x-MoS2 electrodes exhibit an increase of 13 times in photoelectrochemical activity and have a low overpotential. This is due to accelerated electron transfer kinetics at the TiO2-x-MoS2 interface, an enhanced density of charge carriers, a reduced rate of charge recombination, and a highly wettable surface.

Structural and photoelectrochemical properties of fibrous silica-titania (FST) photocatalyst for water splitting

Photoelectrochemical (PEC) water splitting is an ecologically friendly technique that uses effective photoanodes to generate hydrogen (H2). The microemulsion approach was used to develop a distinctive form displaying fibrous silica-titania (FST) photoanode. We examined the photocatalytic attributes of FST, hematite (Fe2O3), and zinc oxide (ZnO). XRD, N2 adsorption-desorption, FESEM, TEM, FTIR, XPS, UV–vis/DRS, and EIS were used to investigate the FST, Fe2O3, and ZnO. By using these techniques, a bicontinuous concentric lamellar arrangement with an ample surface area has been developed within FST. Characterization results demonstrate that FST has superior catalytic activity when compared to Fe2O3 and ZnO. The FST photoanode has an improved photocurrent density of 11.75 mA/cm2 and a 14.1% Solar-to-hydrogen (STH %) efficacy, which is greater than ZnO and Fe2O3, which performed at 4.7 mA/cm2 and 2.8 mA/cm2 with 5.6% and 3.36% STH efficiency, respectively. Moreover, we also compared the Solar-to-hydrogen (STH %) effectiveness of FST with different of TiO2 photoanodes. We absorbed that the band gap is decreased when Ti is added to the silica matrix, which facilitates the formation of Si–Ti bonds. FST displays a remarkable closeness of its conduction band (CB) to the hydrogen reduction potential in comparison to ZnO and Fe2O3, allowing for quick electron transfer and rapid production of H2. The geometry of FST design provides a novel way for producing robust and exceptionally productive photoanodes for PEC water splitting.

Synergistic Surface Engineering of BiVO4 Photoanodes for Improved Photoelectrochemical Water Oxidation.

Surface engineering of BiVO4 photoanodes is effective and feasible for photoelectrochemical (PEC) water splitting. To achieve superior PEC performance, however, more than one surface engineering method is usually indispensable, for which a positive synergistic effect is vital and thus highly desired. Herein, it is reported that the incorporation of borate moieties into ultrathin p-type NiOx catalysts can induce the reconfiguration of surface catalytic sites to form new highly active species, in addition to enhanced fast charge separation and transfer. The photocurrent density of BiVO4 photoanodes is enhanced from 1.49 to 5.76 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) under AM 1.5G illumination, which is achieved by successive modifications of NiOx and borate moieties. It is found that BO3 groups anchored to Ni atoms by replacing the surface hydroxyl sites of NiOx catalysts not only increase the relative ratio of Ni3+ species to facilitate charge transfer but also provide efficient active sites for H2O molecule adsorption and oxidation reactions. This work demonstrates the positive synergistic effect of these two surface engineering methods and provides an effective pathway to construct highly efficient and stable photoanodes for PEC water splitting.

Narrow Band Gap Base Metal Double Perovskite Oxides Through Copper Doping of Ba2Ca0.66Nb1.33O6

This work examines the influence of copper doping on the structure, optoelectronic properties, and photocatalytic performance of transition metal double perovskite oxides of the Ba2Ca0.67Nb1.33O6 (BCN) family. A solid-state synthesis method was used to achieve partial substitution of Cu2+ in the Nb5+ site (Ba2Ca0.67Nb1.33-xCuxO6-δ, x = 0.05, 0.13, 0.26) and Ca2+ site (Ba2Ca0.67-xCuxNb1.33O6-δ, x = 0.13). The incorporation of copper in BCN resulted in significant changes in the structure and optoelectronic properties. Major differences were observed when Cu atoms occupied the Nb-site versus the Ca-site. The parent compound and Ca-site doped compounds crystallized in a P3 1 space group while Nb-site doped compounds showed increasing Fm3 mixed phase character. Cu doping resulted in a dramatic shift of the absorption band edge towards the visible region. Ca-site doping resulted in a primary band edge shift from 3.8 eV to 2.1. For the Nb-site doped compounds, the primary band-edge remained at 3.8 eV but a secondary band-edge appeared which progressively shifted to smaller energies as Cu doping increased. Ba2Ca0.67Nb1.20Cu0.13O6-δ and Ba2Ca0.67Nb1.07Cu0.26O6-δ exhibited strong absorption of near-infrared photons of wavelength well beyond 800 nm. The double perovskite oxides were utilized as photoanodes for photoelectrochemical water splitting, exhibiting both a visible photoresponse (until wavelengths as low as 520 nm) and good photochemical stability. This work showcases the possibility of forming new low band gap multi-element inorganic semiconductor oxides constituted entirely of base metals and oxygen.

P–N homojunction and heteroatom active site engineering over Fe2O3 nanorods for highly efficient photoelectrochemical water splitting

Limited charge transfer and slow oxygen evolution (OER) kinetics significantly impede the practical realization of photoanodes for photoelectrochemical (PEC) water splitting. Here, pn-type-Fe2O3 homojunction photoanode catalysts with P active sites are designed by doping phosphorus (P) into outer lattice of n-type Fe2O3 nanorods (pn-P-Fe2O3). The optimized pn-P-Fe2O3 photoanode shows the maximum photocurrent density of 2.61 mA/cm2 at 1.23 VRHE, and the value is 6.4 times greater than that of pristine Fe2O3. Experimental and theoretical results clearly show that the P–N homogeneous junctions constructed in Fe2O3 through P-doping increase active sites for H2O adsorption and activation, reduce OER reaction energy barrier, and promote effective separation of photogenerated electron-hole pairs and water splitting kinetics. This not only makes the photoelectric water decomposition performance outstanding, but also produces excellent durability. This work provides a novel simple and environmentally friendly strategy for designing effective photoanodes for PEC water splitting.

Synthesis, characterization and photoelectrochemical performance of Bi2Fe4O9 thin films

Mullite-type Bi2Fe4O9 has been little explored in thin film form as a photoanode for photoelectrochemical water splitting. In this study, Bi2Fe4O9 thin films have been prepared using the sol-gel technique from a simple precursor solution based on the corresponding metal salts, acetic acid, and polyvinyl alcohol. The films were deposited by dip-coating onto fluorine-doped tin oxide substrates and dried at 350 °C, repeating the dipping-drying cycle six times, and finally sintered at 600 °C. The films were characterized by GIXRD, revealing the formation of the material in its orthorhombic phase. Raman spectroscopy showed the Ag and B1g vibrational modes, validating the formation of the bismuth iron oxide. UV–Vis transmittance measurements revealed that the material exhibits two optical transitions: a direct band gap of 2.86 eV and an indirect band gap of 1.98 eV. FESEM micrographs and AFM images showed a uniform nanostructured surface morphology. The photoelectrochemical properties of the Bi2Fe4O9 films were studied using cyclic voltammetry and chronoamperometry with front side illumination, demonstrating the stability of the material in aqueous media and the generation of photocurrent in the presence of H2O2. Furthermore, results from intensity-modulated photocurrent spectroscopy (IMPS) revealed that the photocurrent is limited by both bulk and surface recombination and a short hole diffusion length.

Fabrication of WO3/Co3O4 nanorods as a p-n heterojunction photoanode for efficient photoelectrochemical oxygen evolution

Developing efficient photoelectrocatalysts is seen as a promising method for generating hydrogen through photoelectrochemical (PEC) water splitting. In this study, the WO3/Co3O4 heterojunction was fabricated on FTO substrates, serving as an effective photoanode for PEC water splitting. The p-type Co3O4 nanoparticles were loaded onto n-type WO₃ nanorods to create a p-n heterojunction, thereby reducing charge recombination due to the internal electric field at the heterointerface. Under LED illumination (∼80 mW/cm2), the photocurrent density of the WO3/Co3O4 photoanode reached 161.1 μA/cm2 at 1.23 V vs. RHE, which is 2.3 times higher than that of bare WO3 photoanode. The results show that loading Co3O4 onto WO3 nanorods significantly increased the absorption of visible light, boosted charge carrier density, and enhanced surface reaction kinetics. This work indicates the construction of p-n heterojunction photoanodes for achieving effective photoelectrochemical performance.

Promoting the Photoelectrochemical Properties of BiVO4 Photoanode via Dual Modification with CdS Nanoparticles and NiFe-LDH Nanosheets.

Bismuth vanadate (BiVO4) has long been considered a promising photoanode material for photoelectrochemical (PEC) water splitting. Despite its potential, significant challenges such as slow surface water evolution reaction (OER) kinetics, poor carrier mobility, and rapid charge recombination limit its application. To address these issues, a triadic photoanode has been fabricated by sequentially depositing CdS nanoparticles and NiFe-layered double hydroxide (NiFe-LDH) nanosheets onto BiVO4, creating a NiFe-LDH/CdS/BiVO4 composite. This newly engineered photoanode demonstrates a photocurrent density of 3.1 mA cm-2 at 1.23 V vs. RHE in 0.1 M KOH under AM 1.5 G illumination, outperforming the singular BiVO4 photoanode by a factor of 5.8 and the binary CdS/BiVO4 and NiFe-LDH/BiVO4 photoanodes by factors of 4.9 and 4.3, respectively. Furthermore, it exhibits significantly higher applied bias photon-to-current efficiency (ABPE) and incident photon-to-current efficiency (ICPE) compared to pristine BiVO4 and its binary counterparts. This enhancement in PEC performance is ascribed to the formation of a CdS/BiVO4 heterojunction and the presence of a NiFe-LDH OER co-catalyst, which synergistically facilitate charge separation and transfer efficiencies. The findings suggest that dual modification of BiVO4 with CdS and NiFe-LDH is a promising approach to enhance the efficiency of photoanodes for PEC water splitting.

Interface charge transfer and photoelectrochemical properties of SnS2 nanosheets/WO3 heterojunction

Photoelectrochemical water splitting holds great promise as a technology for converting solar energy into hydrogen fuel. In this study, SnS2 nanosheets were vertically aligned and grown in situ on WO3 substrate using chemical vapor deposition (CVD) to create a SnS2/WO3 heterojunction photoanode. The resulting photoanode was then subjected to various characterizations, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to examine its morphology and structure. The introduction of SnS2 significantly improved the absorption of visible light and carrier density. At 1.4 V (vs. RHE), the photocurrent density of the SnS2/WO3 heterojunction reached 1.86 mA cm−2, which was three times higher than that of pure WO3. KPFM analysis revealed that charge transfer occurred at the SnS2/WO3 heterojunction interface, under light illumination, electrons are transferred from the conduction band of SnS2 to the conduction band of WO3, forming a type-II heterojunction. This work provides an important reference for the development of efficient photoanodes for photoelectrochemical water splitting.

Modulating built-in electric field via Bi-VO4-Fe interfacial bridges to enhance charge separation for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting on semiconductor electrodes is considered to be one of the important ways to produce clean and sustainable hydrogen fuel, which is a great help in solving energy and environmental problems. Bismuth vanadate (BiVO4) as a promising photoanode for photoelectrochemical water splitting still suffers from poor charge separation efficiency and photo-induced self-corrosion. Herein, we develop heterojunction-rich photoanodes composed of BiVO4 and iron vanadate (FeVO4), coated with nickel iron oxide (NiFeOx/FeVO4/BiVO4). The formation of the interface between BiVO4 and FeVO4 (Bi-VO4-Fe bridges) enhances the interfacial interaction, resulting in improved performance. Meanwhile, high-conductivity FeVO4 and NiFeOx oxygen evolution co-catalysts effectively enhance bulk electron/hole separation, interface water’s kinetics and photostability. Concurrently, the optimized NiFeOx/FeVO4/BiVO4 possesses a remarkable photocurrent density of 5.59 mA/cm2 at 1.23 V versus reversible hydrogen electrode (vs RHE) under AM 1.5G (Air Mass 1.5 Global) simulated sunlight, accompanied by superior stability without any decreased of its photocurrent density after 14 h. This work not only reveals the crucial role of built-in electric field in BiVO4-based photoanode during PEC water splitting, but also provides a new guide to the design of efficient photoanode for PEC.

Insights into interface engineering of g-C3N4/NaNbO3 heterojunction for photoelectrochemical water splitting

Green hydrogen is a very attractive energy source, a widely studied strategy among scientists to produce it is using metal oxide semiconductors as photoanodes for photoelectrochemical water splitting. The main challenge is to produce a photocatalyst that is stable and efficient enough to be commercially viable. In this sense, several different combinations of materials have been studied. Here, we report the preparation of g-C3N4/NaNbO3 coupled to Pt-based species (Pt-g-C3N4/NaNbO3) and its potential application as a photoanode for water photosplitting. NaNbO3 was chosen for its suitable properties, g-C3N4 was used to enhance the visible light activity, and Pt species were added to perform as a co-catalyst avoiding recombination of photogenerated charges. The main innovations are the reduced time and energy-consuming procedure to prepare NaNbO3 and the direct polymerization of the g-C3N4 on the NaNbO3. Results demonstrate the successful synthesis of the Pt-g-C3N4/NaNbO3 heterojunction; however, the resultant system showed low efficiency, probably for forming a layer of g-C3N4 on the top of NaNbO3 and electrically active surface states at the semiconductor/solution interfaces. Besides that, this study contributes valuable insights into the design of photoelectrodes for sustainable hydrogen production, especially due to the detailed research on the formation of the heterojunction.

Exploring the role of ZnS as passivation layer on SrTiO3/Bi2S3 heterojunction photoanode for improved solar water splitting

Sustainable energy harvesting has emerged as a frontier research area and relentless efforts are being put in to tackle the tenacious issues of global warming and energy crisis. Photoelectrochemical (PEC) water splitting is regarded as a promising technology to produce H2. In this study, we report facile fabrication of ZnS modified SrTiO3/Bi2S3 (STO) heterojunction photoanode for PEC water splitting. Ternary heterojunction photoanode was fabricated using sol-gel followed by SILAR methods. Coupling of wide band gap STO with narrow band gap Bi2S3 photosensitizer extends the absorption edge while the ZnS passivation layer improves electrode stability by preventing direct contact of Bi2S3 with electrolyte and providing an active energy state for facile charge transfer to improve charge separation. Decreased rate of recombination and elongated lifetime of photogenerated charge carriers resulted in enhanced charge carrier dynamics. STO/Bi2S3/ZnS photoanodes displayed a photocurrent density (J) of 1.89 mA.cm−2 at 1.23 V vs RHE and HC-STH of 1.19% at 0.42 V vs RHE in neutral medium while the corresponding values in basic medium were J = 5.08 mA cm−2 at 1.23 V RHE and HC-STH 4.8% at 0.71 V vs RHE; considerably higher than bare STO and binary STO/Bi2S3 electrodes. The superior performance in basic medium could be attributed to the presence of hole scavengers. The improved photostability >3000 s was attributed to ZnS deposition. To better under the role of hole scavengers the quantification of O2 and H2 was undertaken.

Fabrication of ZnO Scaffolded CdS Nanostructured Photoanodes with Enhanced Photoelectrochemical Water Splitting Activity under Visible Light.

CdS, characterized by its comparatively narrow energy band gap (∼2.4 eV), is an appropriate material for prospective use as a photoanode in photoelectrochemical water splitting. Regrettably, it encounters several obstacles for practical and large-scale applications, including issues such as bulk carrier recombination and diminished conductivity. Here, we have tried to address these challenges by fabricating a novel photoelectrode (ZnO/CdS) composed of one-dimensional ZnO nanorods (NRs) decorated with two-dimensional CdS nanosheets (NSs). A facile two-step chemical method comprising electrodeposition along with chemical bath deposition is employed to synthesize the ZnO NRs, CdS NSs, and ZnO/CdS nanostructures. The prepared nanostructures have been investigated by UV-visible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. The fabricated ZnO/CdS nanostructures have shown enhanced photoelectrochemical properties due to the improvement of the semiconductor junction surface area and thereby enhanced visible light absorption. The incorporation of CdS NSs has been further found to promote the rate of the charge separation and transfer process. Subsequently, the fabricated ZnO/CdS photoelectrodes achieved a photocurrent conversion efficiency 3 times higher than that of a planar ZnO NR photoanode and showed excellent performance under visible light irradiation. The highest applied bias photon-to-current conversion efficiency (% ABPE) of about ∼0.63% has been obtained for the sample with thicker CdS NSs on ZnO NRs with a photocurrent density of ∼1.87 mA/cm2 under AM 1.5 G illumination. The newly synthesized nanostructures further demonstrate that the full photovoltaic capacity of nanomaterials is yet to be exhausted.

Enhanced bulk and interfacial charge transfer in Fe:VOPO4 modified Mo:BiVO4 photoanodes for photoelectrochemical water splitting

Bismuth vanadate (BiVO4) is a promising photoanode material for photoelectrochemical (PEC) water oxidation. However, its performance is greatly hindered by poor bulk and interfacial charge transfer. Herein, to address this issue, iron doped vanadyl phosphate (Fe:VOPO4) was grafted on molybdenum doped BiVO4 (Mo:BiVO4) for significantly enhancing charge transfer and oxygen evolution kinetics simultaneously. Consequently, the resultant Fe:VOPO4/Mo:BVO4 photoanode exhibits a remarkable photocurrent density of 6.59 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (VRHE) under AM 1.5G illumination, over approximately 5.5 times as high as that of pristine BiVO4. Systematic studies have demonstrated that the hopping activation energy of small polarons is significantly reduced due to the Mo doping, resulting in accelerated bulk charge transfer. More importantly, the deposition of Fe:VOPO4 promotes the interfacial charge transfer between Mo:BiVO4 and Fe:VOPO4 via the construction of V−O−V and P−O bonds, in addition to facilitating water splitting kinetics. This work provides a general strategy for optimizing charge transfer process, especially at the interface between photoanodes and cocatalysts.

Advancements in cadmium-based photoanodes for photoelectrochemical water splitting: A short review

Photoelectrochemical (PEC) water splitting, which directly converts sunlight into storable hydrogen fuel, has emerged as a promising technology in pursuing renewable energy. This process relies on semiconductor materials functioning as photoelectrodes to harness solar energy and drive water electrolysis into hydrogen and oxygen. However, PEC systems’ efficiency and cost-effectiveness face formidable challenges, primarily centred around developing robust and efficient photoanodes. Cadmium-based catalysts, belonging to the II-VI n-type semiconductor family, exhibit exceptional properties conducive to PEC applications, such as tunable band gaps and superior light absorption capabilities. Yet, their practical utility has been hindered by issues related to photocorrosion and inadequate charge carrier separation. Recent breakthroughs in cadmium-based photoanodes have addressed these limitations through innovative strategies. In regards to this matter, this review provides a comprehensive overview of recent advancements in cadmium-based photoanodes, shedding light on their innovative applications in PEC water splitting.

Effect of aging times of fibrous silica cadmium sulfide photoanodes for enhanced photoelectrochemical water splitting

The use of photoelectrochemical (PEC) water splitting to produce hydrogen from solar sources is an alluring potential address to the world’s energy and environmental problems. Cadmium Sulfide (CdS) is a potentially visible light response photoanode of PEC water splitting, but practical use remains a significant barrier due to its low charge carrier separation efficiency. To address this disadvantage, modifications to the morphology of CdS is necessary. Herein, fibrous silica cadmium sulfide (FSCdS) photoanode for PEC water splitting was synthesized using microemulsion method reported in this study. In this study, it will be focused on the effect of aging times which is 6 hours and 8 hours on the structure of FSCdS towards the PEC water splitting. The physicochemical and electrical properties of the photoanodes were investigated using XRD, UV-Vis DRS, FTIR and EIS Nyquist Plot. FSCdS-6H had a higher photocurrent density of 22.1 mA/cm2 at 1.23 VRHE and a higher solar-to-hydrogen (STH) efficiency of 27.2% when compared to FSCdS-8H with 13.0 mA/cm2 and STH of 16.0%. This is due to the better crystallinity, higher Si-Cd-S interaction, and lower electron hole recombination rate of FSCdS-6H photoanode. Fabrication of fibrous silica-based photoanodes revealed significant insight for the creation of highperformance photoanodes for improved PEC water splitting performance.

Modification of hydrothermally synthesized α-Fe2O3 nanorods with g-C3N4 prepared from various precursors as photoanodes for hydrogen production

α-Fe2O3 nanorods and g-C3N4 are coupled as photoanodes for photoelectrochemical water splitting. The effects of precursors of g-C3N4 on the photoelectrochemical responses of the composites are emphasised.

One-Step Dry Coating of Hybrid ZnO-WO3 Nanosheet Photoanodes for Photoelectrochemical Water Splitting with Composition-Dependent Performance.

In this study, the potential of zinc oxide (ZnO), tungsten oxide (WO3), and their composites (ZnO-WO3) as photoanodes for photoelectrochemical (PEC) water splitting was investigated. ZnO-WO3 nanocomposites (NCs) were deposited on fluorine-doped tin oxide substrates at room temperature using a one-step dry coating process, the nanoparticle deposition system, with no post-processes. Different compositions of ZnO-WO3 NCs were optimized to enhance the kinetics of the PEC water-splitting reaction. Surface morphology analysis revealed the transformation of microsized particle nanosheets (NS) powder into nanosized particle nanosheets (NS) across all photoanodes. The optical characteristics of ZnO-WO3 photoanodes were scrutinized using diffuse reflectance and photoluminescence emission spectroscopy. Of all the hybrid photoanodes tested, the photoanode containing 10 wt.% WO3 exhibited the lowest bandgap of 3.20 eV and the lowest emission intensity, indicating an enhanced separation of photogenerated carriers and solar energy capture. The photoelectrochemical results showed a 10% increase in the photocurrent with increasing WO3 content in ZnO-WO3 NCs, which is attributed to improved charge transfer kinetics and carrier segregation. The maximum photocurrent for a NC, i.e., 10 wt.% WO3, was recorded at 0.133 mA·cm-2 at 1.23V vs. a reversible hydrogen electrode (RHE). The observed improvement in photocurrent was nearly 22 times higher than pure WO3 nanosheets and 7.3 times more than that of pure ZnO nanosheets, indicating the composition-dependence of PEC performance, where the synergy requirement strongly relies on utilizing the optimal ZnO-WO3 ratio in the hybrid NCs.