Photoelectrochemical Water-splitting Devices Research Articles

Solution Processing Silicon Heterojunction Photocathode for Efficient and Stable Hydrogen Production.

Efficient and stable photocathodes are crucial for the development of photoelectrochemical (PEC) water-splitting devices. Silicon heterojunction (SHJ) solar cell is one of the most advanced photovoltaic cells. However, due to the instability of its outermost indium tin oxide (ITO) layers in the electrolyte, a protective layer needs to be introduced on its surface. Previously reported high-quality protective layers almost all involved the use of expensive thin film manufacturing techniques such as atomic layer deposition (ALD). In this work, for the first time, a new strategy is proposed of modifying SHJ-based photocathode with yttrium hydroxide (Y(OH)3) through two-step solution methods to simultaneously improve the stability and activity. The optimized SHJ photocathode exhibits a high applied bias photon-to-current efficiency (ABPE) of 8.4% under simulated 100mWcm-2 (1 Sun) with an AM 1.5G filter in 0.5m KOH. Furthermore, the obtained SHJ photocathode demonstrates excellent stability of at least 110h at 0.3V versus RHE. In this work, combining facile direct current magnetron sputtering with a solution treatment technique provides a novel design strategy, which lowers the threshold for preparing high-quality protective layer, and paves the way for developing economic, efficient, and stable SHJ-based PEC devices.

Self-assembled monolayer mediated fast charge transport of Sb2(S,Se)3 photocathode enabling high-performance unbiased water splitting

The photoelectrochemical (PEC) water splitting system, capable of generating green hydrogen fuel, is crucial for achieving carbon net zero. However, the performance of the photocathode, responsible for the hydrogen evolution reaction, remains suboptimal. We propose bottom interface engineering using a self-assembled monolayer (SAM) to enhance the quality of the Sb2(S,Se)3 absorber layer. The SAM, composed of (3-aminopropyl)triethoxysilane (APTES), is introduced on the Au substrate to enhance adhesion between the substrate and the Sb2(S,Se)3 absorber. Notably, the APTES treatment facilitates the formation of strong electrophile functional groups on the substrate, which predominantly attract tartrate-Sb-Se ionic clusters in the precursor ink. This interaction between the precursor and the substrate induces preferential nucleation of Sb2Se3 near the substrate, followed by Sb2S3 formation at a later stage near the top surface. The APTES-treated Sb2(S,Se)3 photocathodes exhibit a steep band energy gradient, resulting in a photocurrent density of 16 mA cm–2, an onset potential of 0.24 V versus the standard hydrogen electrode, and stability of 24 h in neutral electrolyte (0.5 M K-Pi, pH 6.13). By combining the APTES-treated Sb2(S,Se)3 photocathode with a perovskite photoanode, the co-planar PEC–PEC water splitting device achieves a remarkable solar-to-hydrogen efficiency of 6.5 % under unbiased conditions, along with operating stability for over 120 min. This study suggests that SAM treatment-based interface engineering could be a potential breakthrough in improving the performance of chalcogenide photocathodes in solar-driven water splitting systems.

Embedding biocatalysts in a redox polymer enhances the performance of dye-sensitized photocathodes in bias-free photoelectrochemical water splitting

Dye-sensitized photoelectrodes consisting of photosensitizers and molecular catalysts with tunable structures and adjustable energy levels are attractive for low-cost and eco-friendly solar-assisted synthesis of energy rich products. Despite these advantages, dye-sensitized NiO photocathodes suffer from severe electron-hole recombination and facile molecule detachment, limiting photocurrent and stability in photoelectrochemical water-splitting devices. In this work, we develop an efficient and robust biohybrid dye-sensitized NiO photocathode, in which the intermolecular charge transfer is enhanced by a redox polymer. Owing to efficient assisted electron transfer from the dye to the catalyst, the biohybrid NiO photocathode showed a satisfactory photocurrent of 141±17 μA·cm−2 at neutral pH at 0 V versus reversible hydrogen electrode and a stable continuous output within 5 h. This photocathode is capable of driving overall water splitting in combination with a bismuth vanadate photoanode, showing distinguished solar-to-hydrogen efficiency among all reported water-splitting devices based on dye-sensitized photocathodes. These findings demonstrate the opportunity of building green biohybrid systems for artificial synthesis of solar fuels.

TiO2 nanorod arrays/Ti3C2T x MXene nanosheet composites with efficient photocatalytic activity

Semiconductor photocatalysis holds significant promise in addressing both environmental and energy challenges. However, a major hurdle in photocatalytic processes remains the efficient separation of photoinduced charge carriers. In this study, TiO2 nanorod arrays were employed by glancing angle deposition technique, onto which Ti3C2T x MXene was deposited through a spin-coating process. This hybrid approach aims to amplify the photocatalytic efficacy of TiO2 nanorod arrays. Through photocurrent efficiency characterization testing, an optimal loading of TiO2/Ti3C2T x composites is identified. Remarkably, this composite exhibits a 40% increase in photocurrent density in comparison to pristine TiO2. This enhancement is attributed to the exceptional electrical conductivity and expansive specific surface area inherent to Ti3C2T x MXene. These attributes facilitate swift transport of photoinduced electrons, consequently refining the separation and migration of electron–hole pairs. The synergistic TiO2/Ti3C2T x composite showcases its potential across various domains including photoelectrochemical water splitting and diverse photocatalytic devices. As such, this composite material stands as a novel and promising entity for advancing photocatalytic applications. This study can offer an innovative approach for designing simple and efficient photocatalytic materials composed of MXene co-catalysts and TiO2 for efficient water electrolysis on semiconductors.

Designing idealised devices for bias-free solar water splitting

This perspective categorizes unbiased photoelectrochemical (PEC) configurations and outlined their strengths and weaknesses, exploring the path to an ideal PEC water-splitting device design, crucial for practical solar-to-hydrogen conversion.

3D printing of MAX/PLA filament: Electrochemical in-situ etching for enhanced energy conversion and storage

Two-dimensional (2D) MXenes are promising materials for a variety of sustainable energy-related applications such as photoelectrochemical water splitting and energy storage devices. Among the MXene family, the Ti3C2Tx is mostly prepared by selective etching of Al from the Ti3AlC2 MAX phase using hydrofluoric acid (HF) or in-situ produced HF as an etchant. However, the severe toxicity, handling of HF acid as well as the oxidation and degradation of freshly synthesized MXenes when stored as aqueous suspensions obstruct the large-scale production of MXenes. 3D printing is an innovative and versatile technology utilized for a plethora of applications in the field of energy applications. Thus, integration of 3D printing technology with the synthesis procedure of MXene will provide a new outlook for large-scale production and the long-storing capability of MXene. Herein, we fabricated a novel MAX (Ti3AlC2)/polylactic acid (PLA) filament for fused deposition modeling (FDM) 3D printing followed by etching of the 3D-printed MAX/PLA electrode into 3DP-etched-MAX employing chronoamperometry technique consecutively in 9 M HCl and 4 M NaOH as electrolytes. The 3D printed electrochemically etched MAX (3DP-etched-MAX) electrode shows promising behaviour for the photoelectrochemical hydrogen evolution reaction (HER) and capacitive performance. In general, this work demonstrates a path of production of large-scale manufacturing of MAX/PLA filament and 3DP-etched-MAX electrodes without using toxic HF for energy conversion and energy storage applications. This work paves the way to fabricate other novel MAX filaments and electrodes for several applications beyond energy conversion and storage.

Rationally designed core-shell of 2D-g-C3N4/Cu2O nanowires heterojunction photocathode for efficient photoelectrochemical water splitting

Copper oxide (Cu2O) is a promising candidate as a high-performance photocathode due to its remarkable cost-to-efficiency ratio for photoelectrochemical (PEC) water splitting. However, fully exploiting the potential of planar Cu2O photocathodes for an efficient PEC performance remains a fundamental challenge owing to the poor light absorption and limited carrier diffusion length. To address these challenges, a graphitic carbon nitride (g-C3N4)/2D-Cu2O nanowires (NWs) with core-shell heterojunction photocathode has developed. The PEC water-splitting analysis reveals that the g-C3N4/Cu2O core-shell NWs photocathode boosted the photocurrent density from 0.83 mA/cm2 to 2.33 mA/cm2 at 0 VRHE (3-fold enhancement) compared with bare Cu2O. The formation of a g-C3N4 shell over the Cu2O core resulted in improved light harvesting as well as facile charge transport from the electrode to the electrolyte. Computational studies also revealed an impressive Gibbs free energy of 0.20 eV for the g-C3N4/Cu2O interface, highlighting its potential as an efficient PEC water-splitting device. These findings demonstrate that incorporating nanostructuring and overlayer strategies can remarkably enhance the PEC performance of Cu2O photocathodes, paving the way for more efficient and cost-effective water-splitting technologies.

Scaling up BiVO4 Photoanodes on Porous Ti Transport Layers for Solar Hydrogen Production.

Commercialization of photoelectrochemical (PEC) water-splitting devices requires the development of large-area, low-cost photoanodes with high efficiency and photostability. Herein, we address these challenges by using scalable fabrication techniques and porous transport layer (PTLs) electrode supports. We demonstrate the deposition of W-doped BiVO4 on Ti PTLs using successive-ionic-layer-adsorption-and-reaction methods followed by boron treatment and chemical bath deposition of NiFeOOH co-catalyst. The use of PTLs that facilitate efficient mass and charge transfer allowed the scaling of the photoanodes (100 cm2 ) while maintaining ~90 % of the performance obtained with 1 cm2 photoanodes for oxygen evolution reaction, that is, 2.10 mA cm-2 at 1.23 V vs. RHE. This is the highest reported performance to date. Integration with a polycrystalline Si PV cell leads to bias-free water splitting with a stable photocurrent of 208 mA for 6 h and 2.2 % solar-to-hydrogen efficiency. Our findings highlight the importance of photoelectrode design towards scalable PEC device development.

Investigation of the Solar Hydrogen Sensitivity of GeSe Thin Film Photoelectrode with Photoelectrochemical Environment.

GeSe photovoltaic thin films are very promising for photoelectrochemical (PEC) hydrogen evolution. The GeSe-based PEC water splitting device is a system containing a photoelectrode, electrolyte, and other packages, and the performance of the GeSe photoelectrode inside the system is very sensitive to the PEC system environment, such as the electrolyte temperature, pH, and concentration. Here, we reveal how the electrolyte environment at the electrolyte/photoelectrode interface influences the optoelectronic/PEC properties of GeSe photoelectrodes. It was found that the photocurrent density of the GeSe photoelectrode increased with temperature between 10 and 50 °C but decreased when the temperature was over 50 °C. In addition, the pH values of the electrolyte were inversely proportional to the photocurrent density of the GeSe photoelectrode. Moreover, the PEC performance improved as the sodium ion concentration of the electrolyte increased. The results in this work should provide a new direction for further optimizing the performance of photoelectrodes.

TiO2 Nanotubes Decorated with Mo2C for Enhanced Photoelectrochemical Water-Splitting Properties.

The presence of Ti3+ in the structure of TiO2 nanotube arrays (NTs) has been shown to enhance the photoelectrochemical (PEC) water-splitting performance of these NTs, leading to improved results compared to pristine anatase TiO2 NTs. To further improve the properties related to PEC performance, we successfully produced TiO2 NTs using a two-step electrochemical anodization technique, followed by annealing at a temperature of 450 °C. Subsequently, Mo2C was decorated onto the NTs by dip coating them with precursors at varying concentrations and times. The presence of anatase TiO2 and Ti3O5 phases within the TiO2 NTs was confirmed through X-ray diffraction (XRD) analysis. The TiO2 NTs that were decorated with Mo2C demonstrated a photocurrent density of approximately 1.4 mA cm-2, a value that is approximately five times greater than the photocurrent density exhibited by the bare TiO2 NTs, which was approximately 0.21 mA cm-2. The observed increase in photocurrent density can be ascribed to the incorporation of Mo2C as a cocatalyst, which significantly enhances the photocatalytic characteristics of the TiO2 NTs. The successful deposition of Mo2C onto the TiO2 NTs was further corroborated by the characterization techniques utilized. The utilization of field emission scanning electron microscopy (FESEM) allowed for the observation of Mo2C particles on the surface of TiO2 NTs. To validate the composition and optical characteristics of the decorated NTs, X-ray photoelectron spectroscopy (XPS) and UV absorbance analysis were performed. This study introduces a potentially effective method for developing efficient photoelectrodes based on TiO2 for environmentally sustainable hydrogen production through the use of photoelectrochemical water-splitting devices. The utilization of Mo2C as a cocatalyst on TiO2 NTs presents opportunities for the advancement of effective and environmentally friendly photoelectrochemical (PEC) systems.

Enhancing the photoelectrochemical activity and stability of plate-like WO3 photoanode in neutral electrolyte solution using optimum loading of BiVO4 layer and NiFe–LDH electrodeposition

Tungsten trioxide (WO3) is an attractive candidate that can be used as a photoanode in the photoelectrochemical (PEC) water splitting device. However, WO3 photoanode is known for its high thermodynamic and chemical stability only in strong acidic (low pH) electrolyte solution and its relatively wide bandgap energy (2.8 eV) leads to insufficient absorption of visible light. The current study explored a WO3/BiVO4 heterojunction photoanode, consisting of plate-like WO3 covered with a uniform and highly porous BiVO4 thin layer, with electrodeposition of NiFe–LDH as a co-catalyst for oxygen evolution reaction. This top layer of BiVO4 nanostructure not only exhibited an enhancement in absorption of visible light but also protected the underneath plate-like WO3 from being attacked by the neutral environment of electrolyte solution (pH=∼7), resulting in significant improvement in its stability. The electrodeposition of NiFe–LDH using an acidic aqueous electrolyte solution (pH=3.7) was employed to overcome the sluggish kinetics of water oxidation on the surface of BiVO4. To overcome the weakness of the chemical dissolution of BiVO4 nanostructure in strong acidic solution, the electrodeposition time was carefully optimized for 50 s, leading to a uniform distribution of co-catalyst on the surface of WO3/BiVO4 heterostructure without the dissolving of BiVO4 in the acidic media. The WO3/BVO5/NiFe50 photoanode with the highest PEC performance (photocurrent density of around 1.78 mA/cm2 at 1.23 V vs. RHE) could maintain around 75% of its initial photocurrent after 24 h.

Photoelectrochemical Water Splitting at Elevated Pressure: A Model-Based Evaluation

Photoelectrochemical (PEC) water splitting is one of the few truly renewable pathways towards “green” H2. Although PEC water splitting demonstration devices have been mainly operated at atmospheric pressure, most applications and processes that use H2 require it to be supplied at elevated pressure. Although PEC-generated H2 can be pressurized afterwards with e.g. mechanical compression, operating the PEC water-splitting device itself at elevated pressure offers an intriguing alternative and several possible advantages. For example, bubble formation is strongly reduced at elevated pressure, which lowers bubble-induced electrode deactivation and bubble-induced product crossover rate.[1,2] In addition, the optical reflection and diffraction losses induced by bubbles can be minimized.[3] Finally, the electrochemical production of hydrogen at higher pressure requires only a small (though not insignificant) increase of the thermodynamic cell voltage (29 mV for 10-fold increase in pressure).[4] The main disadvantage of a higher pressure is the increasing mechanical demands on the cell design, and the challenge is to find a pressure range at which optimum conditions will be achieved.To evaluate these pressure-induced effects, we have developed a two-dimensional multiphysics model that considers semi-empirical pressure-dependent bubble characteristics (e.g., bubble formation efficiency, bubble diameter) and their impacts on the multi-phase flow, electrochemistry, and mass transport in a membrane-free PEC water-splitting device. Based on the simulation results, a quantitative comparison between two technical approaches to generate pressurized H2 from a PEC device, namely operating PEC water-splitting at atmospheric vs. elevated pressure, has been conducted, as shown in the schematic diagram in Fig. 1a. Various performance loss factors in a PEC water-splitting device were considered, including bubble-induced product crossover, optical loss, and pH gradient-induced concentration overpotential. These losses (translated to kWh unit) were then compared with the specific work required to mechanically compress H2 from the collection pressure (p 1 in Fig. 1a) to 700 bar (p 2 in Fig. 1a). Our results show that bubble-induced optical loss is the predominant factor among all the losses considered. The overall loss diminishes as pressure increases, as shown in Fig. 1b. By comparing the benefit of conducting PEC water-splitting at elevated pressure (defined as the amount of losses avoided vs. operation at 1 bar) with the thermodynamic cell voltage penalty (see Fig. 1c), we found that no significant benefit can be gained by operating beyond 6 – 8 bar. Therefore, this pressure range represents a desirable range for the operation of a membrane-free PEC water-splitting device. Keywords : (photo)electrochemistry, water splitting, elevated pressure, multiphysics modeling, quantitative evaluation.

Monolithically Integrated BiVO4/Si Tandem Devices Enabling Unbiased Photoelectrochemical Water Splitting

AbstractA photoelectrochemical (PEC) water splitting device based on a dual‐junction monolithic tandem cell that utilizes NiOOH/FeOOH/BiVO4/SnO2/Ta:SnO2 (TTO)/tunnel oxide passivated contact (TOPCon) Si is reported. The PEC device achieves a maximum photocurrent density of 1.4 mA cm−2 (equal to a solar‐to‐hydrogen conversion efficiency of 1.72%) in 1.0 m potassium borate solution (pH 9) when illuminated with air mass 1.5 G simulated solar irradiation, which is the highest value among dual‐junction monolithic photoelectrochemical cells except for III–V materials. The TOPCon Si not only works as an appropriate bottom photoelectrode for subsequent high‐temperature BiVO4 processing but also offers a high photovoltage of 590 mV. Transparent and conductive TTO grown by pulsed laser deposition serves as a recombination layer to achieve effective integration. In addition, the TTO provides chemical and physical protection, allowing the surface of the TOPCon Si to exhibit 24 h of tandem cell stability under weak base electrolyte conditions. The SnO2 hole‐blocking layer inserted between TTO and BiVO4 enhances the charge separation of BiVO4, allowing the device to achieve high efficiency. Artificial leaf‐type monolithic tandem cells consisting of NiFe/BiVO4/SnO2/TTO/TOPCon Si/Ag/Ti/Pt with a solar‐to‐hydrogen efficiency of 0.44% are also demonstrated.

Exploiting the complete efficacy of 3D-nitrogen-doped ZnO nanowires photoanode via type-II ZnS core-shell formation toward highly stable photoelectrochemical water splitting

The hierarchical 3D-zinc oxide (ZnO) nanowires (NWs) photoanode promises high cost-to-efficiency ratios toward photoelectrochemical (PEC) water splitting owing to their enthralling characteristics. However, minimal visible light harvesting, and sluggish surface oxidation kinetics severely hinder the water-splitting efficiencies along with the resistance to photo-corrosion. We report a unique strategy of constructing type-II heterostructure of N-doped ZnO NWs with ultrathin zinc sulfide (ZnS) layer to form a core-shell structure that provides dual benefits of accelerating the charge transfer process and significantly enhancing the resistance to photo-corrosion of N-doped ZnO NWs. The PEC water splitting analyses showed that the optimal ZnS/N:ZnO core-shell NWs photoanode exhibited a photocurrent density of 0.85 mA cm−2 at 1.23 Vs RHE which was 3-fold higher than N:ZnO NWs photoanode. The ZnS shell encapsulation effectively protects the N:ZnO NWs core over a period of ∼16 h from detrimental photo-corrosion with 76% photocurrent density retention. Additionally, the integration of multilateral tactics of staggered heterojunction and core-shell formation provided higher photoconversion efficiencies over N:ZnO NWs. The reported approach may provide an alternative to address the sluggish surface kinetics that bothers the chemical stability, prolong the charge lifetime, and thus open up wide opportunities in the construction of efficient and highly stable PEC water-splitting devices.

Life cycle net energy assessment of sustainable H2 production and hydrogenation of chemicals in a coupled photoelectrochemical device

Green hydrogen has been identified as a critical enabler in the global transition to sustainable energy and decarbonized society, but it is still not economically competitive compared to fossil-fuel-based hydrogen. To overcome this limitation, we propose to couple photoelectrochemical (PEC) water splitting with the hydrogenation of chemicals. Here, we evaluate the potential of co-producing hydrogen and methyl succinic acid (MSA) by coupling the hydrogenation of itaconic acid (IA) inside a PEC water splitting device. A negative net energy balance is predicted to be achieved when the device generates only hydrogen, but energy breakeven can already be achieved when a small ratio (~2%) of the generated hydrogen is used in situ for IA-to-MSA conversion. Moreover, the simulated coupled device produces MSA with much lower cumulative energy demand than conventional hydrogenation. Overall, the coupled hydrogenation concept offers an attractive approach to increase the viability of PEC water splitting while at the same time decarbonizing valuable chemical production.

Recent research progress on operational stability of metal oxide/sulfide photoanodes in photoelectrochemical cells

Photoelectrochemical (PEC) water splitting can directly convert solar energy into hydrogen energy for storage, effectively ending the energy crisis and solving environmental problems. With their modification by many researchers, photoanodes have rapidly improved in PEC performance. Nevertheless, the poor stability of PEC water-splitting devices has not been effectively corrected, seriously hindering their practical application and large-scale commercialization. In this review, we provide a detailed introduction to the photocorrosion mechanism of photoanodes and characterizations of stability, summarizing the current research progress on the stability of metal oxide/sulfide photoanode materials. According to the specificity of each semiconductor, the corrosion mechanism and modification strategy of each photoanode are discussed in detail. Finally, we summarize the deficiencies in the current stability research and propose influencing factors and possible solutions that need to be considered in the photocorrosion research field of photoanodes. This review can provide a reference for the stability research of photoanodes based on metal oxides and sulfides, especially for the design of efficient and stable metal sulfide-based photoanodes.

A Transparent, High-Performance, and Stable Sb2 S3 Photoanode Enabled by Heterojunction Engineering with Conjugated Polycarbazole Frameworks for Unbiased Photoelectrochemical Overall Water Splitting Devices.

Developing low-cost, high-performance, and durable photoanodes is essential in solar-driven photoelectrochemical (PEC) energy conversion. Sb2 S3 is a low-bandgap (≈1.7eV) n-type semiconductor with a maximum theoretical solar conversion efficiency of ≈28% for PEC water splitting. However, bulk Sb2 S3 exhibits opaque characteristics and suffers from severe photocorrosion, and thus the use of Sb2 S3 as a photoanode material remains underexploited. This study describes the design and fabrication of a transparent Sb2 S3 -based photoanode by conformably depositing a thin layer of conjugated polycarbazole frameworks (CPF-TCzB) onto the Sb2 S3 film. This structural design creates a type-II heterojunction between the CPF-TCzB and the Sb2 S3 with a suitable band-edge energy offset, thereby, greatly enhancing the charge separation efficiency. The CPF-TCzB/Sb2 S3 hybrid photoanode exhibits a remarkable photocurrent density of 10.1mAcm-2 at 1.23V vs reversible hydrogen electrode. Moreover, the thin CPF-TCzB overlayer effectively inhibits photocorrosion of the Sb2 S3 and enables long-term operation for at least 100h with ≈10% loss in photocurrent density. Furthermore, a standalone unbiased PEC tandem device comprising a CPF-TCzB/Sb2 S3 photoanode and a back-illuminated Si photocathode can achieve a record solar-to-hydrogen conversion efficiency of 5.21%, representing the most efficient PEC water splitting device of its kind.

Dual textured BiVO4/Sb:SnO2 heterostructure for enhanced photoelectrochemical Water-splitting

Heterostructure engineering, combining dissimilar materials into a single substrate, allows the alteration of the optical, electrical, and electrochemical properties of photoelectrodes for photoelectrochemical (PEC) water splitting. Herein, we successfully synthesized a novel dual-textured BiVO4 / Sb:SnO2 heterostructure as a photoanode for PEC water-splitting devices. Sb:SnO2 (ATO) nanorods (NRs) with a [001] growth orientation were first grown on a fluorine-doped tin oxide substrate by a hydrothermal method. Subsequently, the BiVO4 (BVO) seed layer was deposited on the ATO NRs using a solution spin-coating followed by a second hydrothermal growth to synthesize the dual-textured BVO/ATO heterostructure (dt-BAH). The resultant dt-BAH photoanode was composed of (001)-textured BVO on the [001]-oriented single-crystalline ATO NRs, and their interface exhibited intimate junctions. In addition, the textured BVO exhibited two different facets of (001) and (101). Notably, the synthesized dt-BAH photoanode showed a considerable enhancement in charge collection performance, resulting in a photocurrent density approximately four times higher than that of the textured BVO grown on the randomly oriented ATO nanoparticle film (single-textured BAH). Our results provide new insights into heterostructure design for the development of efficient photoelectrodes.

(Invited) Solar Fuels Produced by Compound Semiconductors

Energy crisis is a broad and complex global topic. Natural resources such as gas and oil are in limited in supply. Development towards renewable resources is one of the most important technologies in the world. Currently, photocatalytic and photoelectrochemical (PEC) water splitting devices under the irradiation of sunlight have received much attention for the production of renewable hydrogen from water. Solar energy conversion and storage through photoelectrolysis of water using semiconductors as both light absorber and energy converter to store solar energy in simple chemical bond, H2, become highly desirable approaches to solving the energy shortage challenge. We focus on the effort to develop an efficient GaAs-based PEC water splitting device. The multifunctional designs for compound semiconductor photoelectrodes provide the potential for the future development in the renewable energy market.

Photocorrosion of WO3 Photoanodes in Different Electrolytes.

Photocorrosion of an n-type semiconductor is anticipated to be unfavorable if its decomposition potential is situated below its valence band-edge position. Tungsten trioxide (WO3) is generally considered as a stable photoanode for different photoelectrochemical (PEC) applications. Such oversimplified considerations ignore reactions with electrolytes added to the solvent. Moreover, kinetic effects are neglected. The fallacy of such approaches has been demonstrated in our previous study dealing with WO3 instability in H2SO4. In this work, in order to understand parameters influencing WO3 photocorrosion and to identify more suitable reaction environments, H2SO4, HClO4, HNO3, CH3O3SH, as electrolytes are considered. Model WO3 thin films are fabricated with a spray-coating process. Photoactivity of the samples is determined with a photoelectrochemical scanning flow cell. Photostability is measured in real time by coupling an inductively coupled plasma mass spectrometer to the scanning flow cell to determine the photoanode dissolution products. It is found that the photoactivity of the WO3 films increases as HNO3 < HClO4 ≈ H2SO4 < CH3O3SH, whereas the photostability exhibits the opposite trend. The differences observed in photocorrosion are explained considering stability of the electrolytes toward decomposition. This work demonstrates that electrolytes and their reactive intermediates clearly influence the photostability of photoelectrodes. Thus, the careful selection of the photoelectrode/electrolyte combination is of crucial importance in the design of a stable photoelectrochemical water-splitting device.