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Silicon heterojunction (SHJ) solar cell is an advanced and mature photovoltaic cell. Development of photoelectrochemical (PEC) water splitting devices for hydrogen fuel production using SHJ solar cells is considered as a promising approach to address energy crisis. To achieve this goal, it is necessary to deposit passivation layer and cocatalyst layer on the photoelectrode. However, the development of low‐cost and scalable preparation methods for high‐quality passivation and cocatalyst layer continues to be a significant challenge. Herein, an efficient passivation layer and hydrogen evolution reaction (HER) catalyst are successfully fabricated via solution processed methods. To improve the HER activity of Ni3S2, a Ni3S2‐based nanoheterostructure of crystalline Ni3S2, Ni, and amorphous Y(OH)3 is constructed. The optimized photocathode exhibits excellent PEC‐HER performance, which achieves a saturated photocurrent of −35.5 mA cm−2 and an applied bias photon‐to‐current efficiency (ABPE) of 8.4 ± 0.1% under simulated AM1.5G one‐sun illumination and more than 120 h of continuous water splitting. This study paves a way for the design and large‐scale manufacturing of cost‐efficient SHJ photocathode devices. [ABSTRACT FROM AUTHOR]

BiVO4 faces significant challenges for widespread application in photoelectrochemical (PEC) water oxidation due to its poor hole transport ability, high surface defect density, and sluggish water oxidation reaction kinetics. Employing interfacial engineering to assist in energy level modulation is an effective strategy to address these challenges. Herein, a CuCrO2 hole transport layer (HTL) is coupled and further grew NiCo‐MOF in situ to prepare a NiCo‐MOF‐CuCrO2‐BiVO4 composite photoanode. The novel composite photoanode not only achieves a photocurrent density of 5.75 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (vs RHE) but also maintains stable operation for over 24 h. Comprehensive physicochemical characterization and density‐functional theory calculations confirm that the built‐in electric field generated by the p–n heterojunction formed between the CuCrO2 HTL and BiVO4 photoanode enhances the hole transport ability. Moreover, the NiCo‐MOF chelated on the photoanode surface not only passivates the surface defect states but also accelerates the kinetics of the water oxidation reaction. Under the synergistic effect of dual modification, the PEC water oxidation performance of the BiVO4 photoanode is dramatically improved. This pioneering work presents a MOF/HTL/BiVO4 configuration that provides a blueprint for the future development of integrated photoanodes for efficient solar energy conversion. [ABSTRACT FROM AUTHOR]

TiO2 is one of the most studied semiconductor materials for the photoelectrochemical water splitting to hydrogen production, but it only responds to ultraviolet light. The introduction of organic compound is one of the common means to expand the visible light response of TiO2. In this work, rutile TiO2 nanowire arrays (NWs) were grown on conductive glass by a modified solvothermal method using oleic acid as the key additive. The obtained TiO2 NWs are characterized using x-ray diffraction, x-ray photoelectron spectroscopy, infrared spectroscopy and electrochemical characterization. The results show that the carboxyl groups arising from oleic acid are chemically bonded with the TiO2 NWs in the form of chelating bidentate, which increases the visible light absorption range and active sites of TiO2, and reduces the transfer resistance between the photoelectrode and the electrolyte. The photocurrent density is doubled to 0.17 mA cm−2 at 1.23 V vs. RHE. This work provides a novel idea for the design of metal oxide semiconductor photoanodes by adsorbing organic compounds. [ABSTRACT FROM AUTHOR]

Hydrogen fuel produced from water splitting using sunlight remains one of the cleanest and most sustainable energy sources. However, photoelectrochemical hydrogen production faces several challenges, including poor sunlight absorption, deficient charge carrier lifetime and transfer rates, and very sluggish kinetics of the water oxidation half‐reaction. To address these challenges, researchers have concentrated on enhancing the efficiency of photoelectrochemical water splitting. A critical factor in this enhancement is a deeper understanding of the fundamental processes involved in photoabsorption and the subsequent oxidation evolution reaction. The advent of ultrafast lasers has enabled the detailed tracking of charge carriers within materials after sunlight absorption, including their separation and migration to the surface for water oxidation. Ultrafast transient absorption spectroscopy is a powerful technique that allows real‐time observation of the behavior of excited states and charge carriers on femtosecond to nanosecond timescales. Recent studies utilizing ultrafast transient absorption spectroscopy are explored to investigate the dynamics of charge carriers in photoelectrochemical water splitting, providing insights into the mechanisms that lead to the design of enhanced photoanodes with improved efficiency. [ABSTRACT FROM AUTHOR]

Exploiting the Bragg mirror effect of photonic crystal photoelectrode is desperately desired for photoelectrochemical water splitting. Herein, a novel TiO2 nanotube photonic crystal bi-layer structure consisting of a top nanotube layer and a bottom nanotube photonic crystal layer is presented. In this architecture, the photonic bandgap of bottom TiO2 nanotube photonic crystals can be precisely adjusted by modulating the anodization parameters. When the photonic bandgap of bottom TiO2 nanotube photonic crystals overlaps with the electronic bandgap of TiO2, the bottom TiO2 nanotube photonic crystal layer will act as a Bragg mirror, leading to the boosted ultraviolet light absorption of the top TiO2 nanotube layer. Benefiting from the promoted UV light absorption, the TiO2 NT-115-NTPC yields a photocurrent density of 1.4 mA/cm2 at 0.22 V vs. Ag/AgCl with a Faradic efficiency of 100%, nearly two times higher than that of conventional TiO2 nanotube arrays. Furthermore, incident photon-to-current conversion efficiency is also promoted within ultraviolet light region. This research offers an effective strategy for improving the performance of photoelectrochemical water splitting through intensifying the light–matter interaction. [ABSTRACT FROM AUTHOR]

Incorporation of chromium (Cr) nanoparticle onto LaFeO3 (LFO) photocathode to improve optical and photocatalytic activities have been successfully demonstrated. The plain LFO photocathode was prepared by spin-spray gun deposition, following the Cr-incorporated nanoparticle onto the photocathode by spin coating method. It is observed that the photocathode with the optimal composition of 1.5 mmol Cr nanoparticle enhanced the crystal growth of orthorhombic crystal structure predominantly on (121) orientation with the formation of well-connected crystal grain architecture. The structure demonstrated strong optical absorption and a high current density of -60.52 µA cm− 2 at -0.5 V (vs. Ag/AgCl) more than twice to the untreated LFO film which recorded a maximum photocurrent of -21.83 µA cm− 2 at -0.5 V (vs. Ag/AgCl). This subsequently led to suppressed surface recombination, lower charge resistance and good stability in the strong alkaline electrolyte. The enhancement provided that incorporating a transition metal element with plain LFO would be applicable for producing efficient photosensitive devices, particularly for photoelectrochemical (PEC) water splitting applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Photoelectrochemical solar to hydrogen production is a promising way to achieve carbon neutrality, but severe charge recombination in photoanodes limits the conversion efficiency. Herein, Au nanoparticles and Co(OH)x co‐sensitized bismuth vanadate (BiVO4) to construct AuCo(OH)x/BiVO4 photoanode for significantly enhancing the performance of photoelectrochemical water splitting. This process significantly improves the bulk charge carrier separation efficiency, the surface kinetics of water oxidation, and the electron density of BiVO4 photoanode through Au surface plasmon resonance (SPR) and Co(OH)x oxygen evolution catalysts effect. Additionally, the enhancement of the *O and the *OOH generation accelerate the oxygen evolution reaction kinetics. Consequently, the constructed AuCo(OH)x/BiVO4 photoanode demonstrates an excellent photocurrent of 6.2 mA cm−2 at 1.23 V versus reversible hydrogen electrode and a stable continuous output within 42 h. This work contributes to developing high‐efficiency and high‐stability photoanodes for solar H2 production through SPR effect and oxygen evolution catalysts. [ABSTRACT FROM AUTHOR]

Limited charge transfer and slow oxygen evolution (OER) kinetics significantly impede the practical realization of photoanodes for photoelectrochemical (PEC) water splitting. Here, pn-type-Fe 2 O 3 homojunction photoanode catalysts with P active sites are designed by doping phosphorus (P) into outer lattice of n-type Fe 2 O 3 nanorods (pn-P-Fe 2 O 3). The optimized pn-P-Fe 2 O 3 photoanode shows the maximum photocurrent density of 2.61 mA/cm2 at 1.23 V RHE , and the value is 6.4 times greater than that of pristine Fe 2 O 3. Experimental and theoretical results clearly show that the P–N homogeneous junctions constructed in Fe 2 O 3 through P-doping increase active sites for H 2 O 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. • The homojunction photoanode catalyst with P active sites is designed by P doping. • The photocurrent density of pn-P-Fe 2 O 3 is 6.4 times higher than pristine Fe 2 O 3. • P active sites and the P–N homojunction reduce the energy barrier of OER. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting by TiO 2 photoanode for clean hydrogen production is limited by the poor charge separation and inert oxygen evolution reaction (OER) kinetics issues for now. In this work, a band-matched heterophase homojunction (TiO x /N–TiO 2) by amorphous TiO x and N-doped TiO 2 nanotube arrays is constructed by two-step anodic oxidation and impregnation. The photocurrent density of TiO x /N–TiO 2 reaches 0.69 mA/cm2 at 1.23 V vs. RHE, which is 1.86 folds than bare TiO 2. The enhanced charge carriers' injection/separation efficiency, smaller Tafel slope (37.79 mF dec−1) and larger electrochemical active surface area (ECSA) (1.98 mF cm−2) of TiO x /N–TiO 2 indicate that N doping and heterophase homojunction with amorphous TiO x effectively facilitate the surface OER kinetics and charge carriers' transportation. TiO x /N–TiO 2 is annealed with a transformation of the surface amorphous TiO x layer into anatase TiO 2 (a-TiO x /N–TiO 2) to study the role of amorphous TiO 2 in PEC water splitting. The photocurrent density and applied bias photon-to-current efficiency (ABPE) for a-TiO x /N–TiO 2 decrease, even lower than the pristine TiO 2. This is due to the reduction of surface oxygen vacancies, which causes the slowdown of OER kinetics and the weakening of charge carrier transportation ability. That is favorable for a better understanding of the OER kinetics and charge carriers' transportation enhancement mechanism by the surficial modification on the semiconductor during the PEC water splitting. A band-matched heterophase homojunction (TiO x /N–TiO 2) by amorphous TiO x and N-doped TiO 2 nanotube arrays is constructed. The increased charge carriers' injection/separation efficiency, smaller Tafel slope and larger electrochemically active surface area of TiO x /N–TiO 2 indicate N doping and heterophase homojunction with amorphous TiO x enhance the surface OER kinetics and charge carriers' transportation. TiO x /N–TiO 2 is annealed with a transformation of the surface amorphous TiO x layer into anatase TiO 2 (a-TiO x /N–TiO 2) to study the role of amorphous TiO x. The photocurrent density and applied bias photon-to-current efficiency (ABPE) for a-TiO x /N–TiO 2 decrease, even lower than the pristine TiO 2. This is due to the reduction of surface oxygen vacancies, which causes the slowdown of OER kinetics and the weakening of charge carrier transportation ability. [Display omitted] • TiO x /N–TiO 2 heterophase homojunction system with suitable band alignment is constructed. • The charge carriers' transportation is improved by N doping and TiO x /N–TiO 2 heterophase homojunction. • Amorphous TiO x heterophase homojunction is favorable for oxygen evolution reaction kinetics acceleration. • The PEC performance decrease by the amorphous TiO x disappearance further reveals the mechanism of OER kinetics enhancement. [ABSTRACT FROM AUTHOR]

Electronic structure regulation is a prevailing approach to modifying the electrocatalysts in the oxygen evolution reaction (OER), yet its impact on the co‐catalysts modified photoanodes remains uncertain. Herein, B‐modified NiFe‐LDH (NiFeB‐hydx) co‐catalyst in situ is immobilized onto Ti‐Fe2O3 and emphasizes the effect of lower‐valence Ni (Ni2‐δ) in the photoelectrochemical (PEC) process. A flexible adjustment in the oxidation state of Ni from +2 to 0 by manipulating the Ni content and the corresponding B quantity is achieved. Interestingly, the Ni0 significantly reduces the onset potential low to 0.53 VRHE, albeit leading to wasted holes due to incomplete redox transition. An optimal amount of Ni2‐δ effectively facilitates the redox transition of Ni and achieves a delicate balance between hole extraction and consumption, substantially enhancing the PEC performance. Density functional theory calculations verifies the electron enrichment of Ni and the corresponding benefits for enhancing OER. Furthermore, introducing FeOOH as a hole transfer layer on Ti‐Fe2O3 induces a pronounced band bending effect, remarkably promoting the meticulously engineered NiFeB‐hydx/FeOOH/Ti‐Fe2O3 photoanode to a photocurrent density of 3.29 mA cm−2 at 1.23 VRHE. NiFeB‐hydx/FeOOH can be universally applied to the BiVO4 photoanode, resulting in doubled photocurrent density (4.8 mA cm−2 at 1.23 VRHE). [ABSTRACT FROM AUTHOR]

[Display omitted] 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 (BiVO 4) 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 BiVO 4 and iron vanadate (FeVO 4), coated with nickel iron oxide (NiFeO x /FeVO 4 /BiVO 4). The formation of the interface between BiVO 4 and FeVO 4 (Bi-VO 4 -Fe bridges) enhances the interfacial interaction, resulting in improved performance. Meanwhile, high-conductivity FeVO 4 and NiFeO x oxygen evolution co-catalysts effectively enhance bulk electron/hole separation, interface water's kinetics and photostability. Concurrently, the optimized NiFeO x /FeVO 4 /BiVO 4 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 BiVO 4 -based photoanode during PEC water splitting, but also provides a new guide to the design of efficient photoanode for PEC. [ABSTRACT FROM AUTHOR]

Photoelectrochemically active WO3 films were fabricated by electrodeposition from an acidic (pH 2), hydrogen-peroxide-containing electrolyte at −0.5 V vs. SCE. WO3-TiO2 composites were then synthesized under the same conditions, but with 0.2 g/L of anatase TiO2 nanoparticles (⌀ 36 nm), mechanically suspended in the solution by stirring. After synthesis, the films were annealed at 400 °C. Structural characterization by XRD showed that the WO3 films exhibit the crystalline structure of a non-stoichiometric hydrate, whereas, in WO3-TiO2, the WO3 phase was monoclinic. The oxidation of tungsten, as revealed by XPS, was W6+ for both materials. Ti was found to exist mainly as Ti4+ in the composite, with a weak Ti3+ signal. The efficiency of the WO3 films and composites as an oxygen evolution reaction (OER) photo-electrocatalyst was examined. The composite would generate approximately three times larger steady-state photocurrents at 1.2 V vs. SCE in a neutral 0.5 M Na2SO4 electrolyte compared to WO3 alone. The surface recombination of photogenerated electron–hole pairs was characterized by intensity-modulated photocurrent spectroscopy (IMPS). Photogenerated charge transfer efficiencies were calculated from the spectra, and at 1.2 V vs. SCE, were 86.6% for WO3 and 62% for WO3-TiO2. Therefore, the composite films suffered from relatively more surface recombination but generated larger photocurrents, which resulted in overall improved photoactivity. [ABSTRACT FROM AUTHOR]

A photovoltaic wittichenite semiconductor of Cu3BiS3, due to its optimal bandgap, high light absorption coefficient, and various advantages of low cost and environmental‐friendliness, has been considered a competitive candidate for solar absorber materials of photocathode for photoelectrochemical water splitting. However, the presence of various deleterious defects in the Cu3BiS3 lattice and its high conduction band minimum are detrimental factors that restrict further enhancements in the conversion efficiency of Cu3BiS3‐based photocathode. Herein, a one‐step solution‐based Ag element doping strategy is proposed to improve the crystalline quality of Cu3BiS3 films, which includes enlarging the grain size and reducing the intergranular gaps. Additionally, the Ag‐doped Cu3BiS3 layer can form a more favorable band alignment with the buffer layer. Ultimately, the fabricated composite Cu3BiS3‐based photocathode doped with 3% Ag delivers a remarkable photocurrent density of 13.6 mA cm−2 under 0 VRHE, an applied bias photon‐to‐current efficiency of 2.85%, and long‐term stability exceeding 12 h. Furthermore, with the assistance of a BiVO4 photoanode, the tandem cell also achieves an unbiased solar‐to‐hydrogen efficiency of 2.64%, with no significant decline observed within 20 h. [ABSTRACT FROM AUTHOR]

Although various kinds of cocatalyst are developed and decorated on the bismuth vanadate (BiVO4) photoanode, its photoelectrochemical (PEC) water splitting performance is limited owing to severe charge recombination and sluggish oxygen evolution reaction (OER). Herein, a high‐entropy hydroxide electrocatalyst (FeCoNiMoCrOOH) is constructed as a co‐catalyst deposited on BiVO4 with a good PEC activity and stability in potassium borate buffer, addressing substantial charge recombination and poor surface oxygen evolution reaction of the material. FeCoNiMoCrOOH synthesized by a simple electrodeposition stacking strategy, delivers an overpotential of 172 mV at 10 mA cm−2 with a stability of 600 h under alkaline conditions, representing one of the best performances on high‐entropy‐based catalysts. The FeCoNiMoCrOOH/BiVO4 photoanode shows a photocurrent density of 5.23 mA cm−2 at 1.23 VRHE with 100 h durability in potassium borate buffer. Experimental investigations and theoretical calculations demonstrate that the synergistic effect of Mo and Cr in FeCoNi catalyst effectively decreases the dissolution Fe, Co, and Ni after long‐term operation, increases the charge transfer kinetics, and promotes OER and PEC performances, therefore enhancing the photocorrosion resistance of BiVO4. This work provides a new avenue to design high entropy‐based electrocatalysts boosting solar water splitting activity and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] Photoelectrochemical (PEC) water splitting is an effective and sustainable method for solar energy harvesting. However, the technology is still far away from practical application because of the high cost and low efficiency. Here, we report a low-cost, stable and high-performing industrial-Si-based photoanode (n -Indus-Si/Co -2mA-xs) that is fabricated by simple electrodeposition. Systematic characterizations such as scanning electron microscopy, X-ray photoelectron spectroscopy have been employed to characterize and understand the working mechanisms of this photoanode. The uniform and adherent dispersion of co-catalyst particles result in high built-in electric field, reduced charge transfer resistance, and abundant active sites. The core–shell structure of co-catalyst particles is formed after the activation process. The reconstructed morphology and modified chemical states of the surface co-catalyst particles improve the separation and transfer of charges, and the reaction kinetics for water oxidation greatly. Our work demonstrates that large-scale PEC water splitting can be achieved by engineering the industrial-Si-based photoelectrode, which shall guide the development of solar energy conversion in the industry. [ABSTRACT FROM AUTHOR]

Photoelectrochemical water splitting is regarded as one of the most efficient methods for hydrogen production, with photoelectrode materials playing a crucial role in enhancing its efficiency. To further improve the effectiveness of hydrogen production via photoelectrochemical water splitting, a lattice Boltzmann method (LBM) with multiple relaxation times (MRT) is employed to simulate the evolution of bubble growth, coalescence, and detachment on the photoelectrode surface. This simulation takes into account factors such as bubble detachment diameter, contact angle of the photoelectrode surface, and the spatial distribution of nucleation sites. According to simulation results, when the gravity coefficient increases, the bubble detachment diameter decreases, a contact angle between 120° and 140° is found to be optimal for bubble detachment. When the contact angle is less than 90°, the bubbles typically adhere to the surface of nucleation sites. The bubble detachment time decreases gradually as the contact angle ranges from 120° to 160°, and the bubble detachment time drops by 1.8 ms and 0.2 ms, respectively. When the distance between two nucleation sites was 5 μm, 10 μm, 15 μm, and 20 μm, and the bubble detachment time was 3 ms, 2.2 ms, 3 ms, and 2.9 ms, respectively. The bubble detachment time could be effectively reduced by appropriately increasing the distance between nucleation sites in a certain range. This study elucidates the behavior of bubbles on photoelectrode surfaces during photocatalytic water decomposition, providing valuable insights for optimizing photoelectrode design and improving the efficiency of hydrogen production. [ABSTRACT FROM AUTHOR]

BiVO4 has garnered substantial interest as a promising photoanode material for photoelectrochemical water‐splitting due to its narrow band gap and appropriate band edge positions for water oxidation. Nevertheless, its practical use has been impeded by poor charge transport and sluggish water oxidation kinetics. Here, a hybrid composite photoanode is fabricated by uniformly embedding SnS2 nanoparticles near the surface of a BiVO4 thin film, creating a type II heterostructure with strong interactions between the nanoparticles and the film for efficient charge separation. This structure forms via eutectic melting during atomic layer deposition of SnS2 with subsequent phase separation between SnS2 and BiVO4 at room temperature, offering greater advantages and flexibilities over conventional exsolution techniques. Furthermore, the SnS2/BiVO4 hybrid composite is coated with a thin amorphous ZnS passivation layer to accelerate charge transfer process and enhance long‐term stability. The optimized BiVO4/SnS2/ZnS photoanode exhibits a photocurrent density of 5.44 mA cm−2 at 1.23 V versus RHE, which is 2.73 times higher than that of the BiVO4 photoanode, and a dramatic improvement in photostability retention at 1.23 V versus RHE, increasing from 55% to 91% over 24 hours. This method of anchoring nanoparticles onto host materials proves highly valuable for energy and environmental applications. [ABSTRACT FROM AUTHOR]

In this study, we developed well-aligned ZnO nanoflowers coated with poly-10,12-pentacosadiyonic acid (p-PCDA@ZnO) and modified with Pt nanoparticle (Pt/p-PCDA@ZnO) hybrid photoanodes for highly efficient photoelectrochemical (PEC) water splitting. The scanning electron microscope (SEM) image shows that thin films of the p-PCDA layer were well coated on the ZnO nanoflowers and that Pt nanoparticles were on it. The photoelectrochemical characterizations were made under simulated solar irradiation AM 1.5. The current density of the p-PCDA@ZnO and the Pt/p- PCDA@ZnO was 0.227 mA/cm2 and 0.305 mA/cm2, respectively, and these values were three times and four times higher compared to the 0.071 mA/cm2 of the bare ZnO nanoflowers. The UV–visible spectrum showed that the absorbance of coated p-PCDA films was extended in visible light region, which agrees with the enhanced PEC data for p-PCDA@ZnO. Also, adding Pt nanoparticles on top of the films as co-catalysts enhanced the PEC performance of Pt/p-PCDA@ZnO further. This indicates that Pt/p- PCDA@ZnO has a great potential to be implemented in solar water splitting. [ABSTRACT FROM AUTHOR]

The superior kinetics of charge carriers and greater visible light absorption are important factors for enhancing photoelectrochemical performance. Herein, the core–shell heterostructure has been developed by encapsulating single-phase MnZnO3 over TiO2 nanotubes by aerosol-assisted chemical vapor deposition approach. The fabricated photoanodes have been characterized by employing various techniques including X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and photoluminescence. Moreover, the mechanism for electron/hole transfer has been focused by a brief electrochemical investigation. The bilayer 1D/2D TiO2@MnZnO3 photoanode exhibited higher current density (2 mA cm−2) as compared to pristine TiO2-nanotubes (0.174 mA cm−2) at 1.52 V vs RHE. The superior photoactivity of heterostructure is attributed to the rapid transfer of photogenerated charge carriers via the Type-II mechanism. Furthermore, the reduced band gap (2.05 eV) accounts for good absorption in the visible region of light, while the interfacial electric field allowed the improved charge separation. The synergistic strategy in the present work demonstrates the promising significance of a heterojunction interface to optimize photovoltaic devices. [ABSTRACT FROM AUTHOR]

Despite achievements in the remarkable photoelectrochemical (PEC) performance of photoelectrodes based on organometal halide perovskites (OHPs), the scaling up of small-scale OHP-based PEC systems to large-scale systems remains a great challenge for their practical application in solar water splitting. Significant resistive losses and intrinsic defects are major obstacles to the scaling up of OHP-based PEC systems, leading to the PEC performance degradation of large-scale OHP photoelectrodes. Herein, a scalable design of the OHP-based PEC systems by modularization of the optimized OHP photoelectrodes exhibiting a high solar-to-hydrogen conversion efficiency of 10.4% is suggested. As a proof-of-concept, the OHP-based PEC module achieves an optimal PEC performance by avoiding major obstacles in the scaling up of the OHP photoelectrodes. The constructed OHP module is composed of a total of 16 OHP photoelectrodes, and a photocurrent of 11.52 mA is achieved under natural sunlight without external bias. The successful operation of unassisted solar water splitting using the OHP module without external bias can provide insights into the design of scalable OHP-based PEC systems for future practical application and commercialization.

[Display omitted] The recombination of photogenerated electron-hole pairs of the photoanode seriously impairs the application of bismuth vanadate (BiVO 4) in photoelectrochemical water splitting. To address this issue, we prepared a Yb:BiVO 4 /Co 3 O 4 /FeOOH composite photoanode by employing drop-casting and soaking methods to attach Co 3 O 4 /FeOOH cocatalysts to the surface of ytterbium-doped BiVO 4. The prepared Yb:BiVO 4 /Co 3 O 4 /FeOOH photoanode demonstrates a high photocurrent density of 4.89 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), which is 5.1 times that of bare BiVO 4 (0.95 mA cm−2). Detailed characterization and testing demonstrated that Yb doping narrows the band gap and significantly enhances the carrier density. Furthermore, Co 3 O 4 serves as a hole transfer layer to expedite hole migration and diminish recombination, while FeOOH offers additional active sites and minimizes surface trap states, thus boosting stability. The synergistic effects of Yb doping and Co 3 O 4 /FeOOH cocatalyst significantly improved the reaction kinetics and overall performance of PEC water oxidation. This work provides a strategy for designing efficient photoanodes for PEC water oxidation. [ABSTRACT FROM AUTHOR]

Commercialization of photoelectrochemical (PEC) water-splitting technology is hindered by the slower kinetics of oxygen evolution in the currently available photoanodes. Light absorption, charge-separation, and charge-transfer efficiencies determine the kinetics of the oxygen evolution reaction (OER) at semiconductor photoanode surfaces. All these parameters can be maximized by nanotexturing the photoanode surface through morphological (cones, pyramids, grids, etc.) control and crystallographic (facets) orientation. The primary objective of texturing on conducting substrates is to improve the photoconversion efficiency in PEC devices through an increased surface area and light absorption. Laser-assisted ablation and melt-fusion additive techniques allow for rapid iteration of morphological architecture designs for optimized light absorption properties. This work reviews various ultrafast laser techniques employed for fabricating nanotextured surfaces and their impact on PEC performance. Compared with conventional electrode fabrication techniques, laser-based surface nanotexturing techniques provide a cost-effective, rapid design, and validation method for the research and development of photoelectrochemical water splitting technologies. [ABSTRACT FROM AUTHOR]

A novel method for the production of a biofuel precursor and additive (γ-valerolactone) using in-situ generated hydrogen is reported. Firstly, a potential non-carbon fuel as hydrogen is generated from water through a photoelectrochemical approach employing a set of TiO 2 nanostructures synthesized by hydrodynamic anodization. Secondly, this system was coupled with a reactor in a way that the hydrogen produced reacts with levulinic acid in the presence of a ruthenium catalyst to yield γ-valerolactone. The preparation procedure of TiO 2 nanostructures was optimized and the influence of factors such as the rotation speed and the anodization media was investigated. The best photoelectrochemical performance corresponds to the nanostructure synthesized in lactic acid and using hydrodynamic conditions at a rotation speed of 1000 rpm. The optimal nanostructure was used as a photocatalyst for hydrogen production by water splitting, with the generated hydrogen being directly used for the transformation of levulinic acid into γ-valerolactone in the presence of a ruthenium catalyst supported on alumina. Using this optimal TiO 2 and the ruthenium catalyst, a yield to γ-valerolactone of 93 % was obtained in only 5 h at 60 °C and atmospheric pressure. [Display omitted] • Optimization of photoelectrochemical water splitting with titania nanostructures. • Tandem process: photoelectrocatalysis and conventional heterogeneous catalysis. • In-situ generated hydrogen for biofuel production. • Clean fuels: hydrogen and γ-valerolactone. [ABSTRACT FROM AUTHOR]

The current study employs both theoretical and experimental methods to investigate the effect of Ti and Co doping on the WO 3 nanocomposite with MoS 2 photoanode's photoelectrochemical (PEC) water-splitting reaction. A simple hydrothermal and sol-gel method was adopted for the preparation of samples. The Ti-doped WO 3 –MoS 2 (1.96 at %) sample showed the maximum optical absorption with a photocurrent density of 1.15 mA/cm2 at 1.6 V vs Ag/AgCl. The improvement in photocurrent density may be ascribed to the upward shifting of the conduction band edge towards the H+/H 2 redox potential as well as the presence of a large number of active sites in MoS 2. A high value of flat band potential of −0.3 V vs Ag/AgCl was achieved in Ti-doped WO 3 –MoS 2 , which was confirmed by Mott-Schottky measurements with the corresponding lowest charge transfer resistance at the semiconducting electrode/electrolyte interface. Furthermore, density functional theory calculations have also indicated that on doping WO 3 with Ti and Co, there is a slight upward shift in the conduction band minimum, without any significant change in the valence band maximum, with respect to the Fermi level. This study provides new insight into the impact of transition metal doping and nanocomposite of chalcogenide materials for WO 3 -based PEC electrodes. [Display omitted] • Ti and Co-doped WO 3 nanorods and MoS 2 nanoflowers were prepared using a cost-effective sol-gel and hydrothermal method. • MoS 2 plays a crucial role in boosting the PEC response due to the presence of a large number of active sites. • Improved charge carrier separation and enhanced PEC response were achieved in 1.96 at% Ti-doped WO 3 –MoS 2 sample. • DFT calculations showed that on doping WO 3 with Ti and Co, a slight upward shift in CBM, without any notable change in VBM, with respect to Fermi level. [ABSTRACT FROM AUTHOR]

[Display omitted] To reveal the mechanism of charge transfer between interfaces of BiVO 4 -based heterogeneous materials in photoelectrochemical water splitting system, the cocatalyst was grown in situ using tannic acid (TA) as a ligand and Fe and Co ions as metal centers (TAFC), and then uniformly and ultra-thinly coated on BiVO 4 to form photoanodes. The results show that the BiVO 4 /TAFC achieves a superior photocurrent density (4.97 mA cm−2 at 1.23 V RHE). The charge separation and charge injection efficiencies were also significantly higher, 82.0 % and 78.9 %, respectively. From XPS, UPS, KPFM, and density functional theory calculations, Ligand-to-metal charge transfer (LMCT) acts as an electron transport highway in TAFC ultrathin layer to promote the concentration of electrons towards metal center, leading to an increase in the work function, which enhances the built-in electric field and further improves the charge transport. This study demonstrated that the LMCT pathway on TA-metal complexes enhances the built-in electric field in BiVO 4 / TAFC to promote charge transport and thus enhance water oxidation, providing a new understanding of the performance improvement mechanism for the surface-modified composite photoanodes. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) offer remarkable versatility, combining ordered structures, high porosity, and tailorable functionalities in nanoscale reaction spaces. Herein, we report the synthesis of a series of isostructural, photoactive Wurster‐type COFs achieved by manipulating the chemical and electronic nature of the Wurster aromatic amine building blocks. A series of donor‐acceptor‐donor (D‐A‐D) Wurster building block molecules was synthesized by incorporating heteroaromatic acceptors with varying strengths between triphenylamine donor groups. These tailored building blocks were integrated into a 2D COF scaffold, resulting in highly crystalline structures and similar morphologies across all COFs. Remarkably, this structural uniformity was also achieved in the synthesis of homogeneous and oriented thin films. Steady‐state photoluminescence revealed a tunable red‐shift in film emission exceeding 100 nm, demonstrating effective manipulation of their optical properties. Furthermore, photoelectrochemical (PEC) water splitting studies exhibited a doubled current density (8.1 μA cm−2 at 0.2 VRHE) for the COF with the strongest acceptor unit. These findings highlight the potential of Wurster D‐A‐D COFs in photoelectrochemical water splitting devices and pave the way for further exploration of chemical functionality‐reactivity‐property relationships in this promising class of photoactive materials. [ABSTRACT FROM AUTHOR]

The scale-up of photoelectrochemical water splitting and CO 2 reduction is currently hindered by the excessive band gap of metal oxide photoanodes. Metal sulfides 2D nanostructured morphology offer improved optoelectronic properties and catalytic capabilities in the oxygen evolution reaction (OER). This study demonstrates for the first time visible spectra absorption capabilities of Sn x S y photoanodes, fabricated by facile non-vacuum techniques and post-annealed in a sulfur atmosphere, yielding SnS 2 multilayer nanosheets with visible-light absorption down to 900 nm wavelengths. Optimal annealing (500 °C) resulted in >1 V photovoltages, photocurrents surpassing 1.6 mA/cm2 at 1.23V RHE , incident photon-to-current conversion efficiency (IPCE) of 75% at 330 nm. Photon conversion in the 500–900 nm range (down to 1.37 eV) is correlated with phase transformation from orthorhombic α-SnS to Sn 2 S 3 and further hexagonal SnS 2. IPCE is key for describing effective phase transformation and photon conversion at wavelengths below the dominant direct band gap for the SnS 2 , suggesting potential indirect transitions or confinement in the low-dimensional nanosheets. SnS 2 nanosheets fabricated by solution-processed means, hold great potential for large-scale, cost-effective, and efficient photoelectrochemical devices. [Display omitted] • 1.06 V and 1.6 mA/cm2 are photogenerated, converting 75% of 330 nm photons. • Crystallographic phase transition α-SnS to Sn 2 S 3 and SnS 2 creates 2D nanosheets. • 2D SnS 2 nanosheets have photoelectrochemical conversion in the visible range. • Maximum performance is obtained by 2D SnS 2 nanosheets. • Photon conversion below the direct band gap is attributed to indirect transitions. [ABSTRACT FROM AUTHOR]

Gamma radiation can cause structural defects in metal oxide thin films, affecting their conversion efficiency. This study focuses on synthesizing and characterizing Tungsten oxide (WO3) films for photo-electrochemical (PEC) water-splitting applications. The pristine WO3 film was irradiated with a Co-60 gamma source to improve its photocatalytic activity and was named G-WO3. The resulting G-WO3 thin films showed a decrease in the optical direct band gap and showed higher photocurrent density and lower charge transfer resistance for PEC applications. The carrier charge density (Nd) values were found to be increased after γ-radiation. The synthesized G-WO3 thin films possess good stability and reusability for photo-electrochemical water-splitting applications. [ABSTRACT FROM AUTHOR]

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In this paper, a CuSCN hole transport layer (HTL) is introduced between BiVO 4 and NiFeO x oxygen evolution cocatalyst (OEC) to form BiVO 4 /CuSCN/NiFeO x photoanode. Characterization and DFT calculations suggest that the high PEC performance is attributed to the incorporation of CuSCN as a HTL, which effectively facilitates charge transfer and accelerates the water oxidation kinetics, resulting in an enhanced PEC water splitting performance (5.65 mA cm−2 at 1.23 V vs. RHE). [Display omitted] • BiVO 4 /CuSCN/NiFeO x photoanode prepares by inserting CuSCN between BiVO 4 and NiFeO x. • The CuSCN promotes the transfer of holes from BiVO 4 to NiFeO x OEC. • The CuSCN exhibits enhanced OER activity and accelerates water oxidation kinetics. • BiVO 4 /CuSCN/NiFeO x photoanode achieves enhanced PEC water splitting performance. Modification of oxygen evolution co-catalyst (OEC) on the surface of bismuth vanadate (BiVO 4) can effectively improve the kinetics of water oxidation, but it is still limited by the small hole extraction driving force at the BiVO 4 /OEC interface. Modulating the BiVO 4 /OEC interface with a hole transfer layer (HTL) is expected to facilitate hole transport from BiVO 4 to the OEC surface. Herein, a copper(I) thiocyanate (CuSCN) HTL is inserted between BiVO 4 and NiFeO x OEC to create BiVO 4 /CuSCN/NiFeO x photoanode, resulting in a significant enhancement of photoelectrochemical (PEC) water splitting performance. From electrochemical analyses and density functional theory (DFT) simulations, the markedly enhanced PEC performance is attributed to the insertion of CuSCN as an HTL, which promotes the extraction of holes from BiVO 4 surface and boosts the water oxidation kinetics. The optimal photoanode achieves a photocurrent density of 5.6 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (vs. RHE) and an impressive charge separation efficiency of 96.2 %. This work offers valuable insights into the development of advanced photoanodes for solar energy conversion and emphasizes the importance of selecting an appropriate HTL to mitigate recombination at the BiVO 4 /OEC interface. [ABSTRACT FROM AUTHOR]

Photoelectrochemical water splitting is a promising technique for converting solar energy into low‐cost and eco‐friendly H2 fuel. However, the production rate of H2 is limited by the insufficient number of photogenerated charge carriers in the conventional photoelectrodes under 1 sun (100 mW cm−2) light. Concentrated solar light irradiation can overcome the issue of low yield, but it leads to a new challenge of stability because the accelerated reaction alters the surface chemical composition of photoelectrodes. Here, it is demonstrated that loading Pt nanoparticles (NPs) on single crystalline GaN nanowires (NWs) grown on n+‐p Si photoelectrode operates efficiently and stably under concentrated solar light. Although a large number of Pt NPs detach during the initial reaction due to H2 gas bubbling, some Pt NPs which have an epitaxial relation with GaN NWs remain stably anchored. In addition, the stability of the photoelectrode further improves by redepositing Pt NPs on the reacted Pt/GaN surface, which results in maintaining onset potential >0.5 V versus reversible hydrogen electrode and photocurrent density >60 mA cm−2 for over 1500 h. The heterointerface between Pt cocatalysts and single crystalline GaN nanostructures shows great potential in designing an efficient and stable photoelectrode for high‐yield solar to H2 conversion. [ABSTRACT FROM AUTHOR]

The application of BiVO4 in photoelectrochemical water splitting for efficient clean hydrogen energy production encounters challenges arising from the sluggish kinetics of water oxidation. Motivated by the synergistic interplay of metal sites and ligands on the catalyst surface, we utilized the photoelectric deposition technique to introduce amorphous nanothin layers of cobalt–iron double hydroxide (referred to as CoFe-LDH) onto the Fe-doped BiVO4 surface. Fe dopants lead to a size reduction of BiVO4 nanoparticles while enlarging the specific surface area and pore volume, thus increasing the reaction sites, which is favorable for photoelectrochemical water splitting. The unique dual-layered structure of CoFe-LDH not only enhances the mobility of charge carriers but also addresses surface defects through passivation. Additionally, it optimizes the exposure of active sites on the surface and expedites the flow of charge carriers, effectively mitigating recombination. The CoFe/Fe-BiVO4 photoanode demonstrates outstanding photocatalytic performance, achieving a substantial photocurrent of 2.56 mA cm–2 (at 1.23 V vs RHE) and an impressive incident photon current conversion efficiency (IPCE) of 52.1% at 400 nm, which is approximately a 270% increment in photocurrent and a remarkable 2.2-fold improvement in IPCE compared to those of the unmodified sample. In addition, the charge surface transport efficiency increases from 16.8% to 62.5% at 1.23 V vs RHE after modification of the cobalt–iron hydroxide bilayer. This study not only emphasizes the promising results of employing binary polymetallic co-catalysts but also provides a strategic pathway to improve semiconductor-based photoelectrodes in various photoelectrochemical applications. [ABSTRACT FROM AUTHOR]

Cuprous oxide (Cu2O) is a promising photocathode material for unbiased solar water splitting cells. To improve the onset potential of Cu2O photocathodes, numerous efforts have been devoted to exploring a suitable n-type buffer layer material. However, previous studies mostly focused on optimizing the band alignment between the absorber and buffer layer, ignoring the role of surface states as reaction intermediates. Moreover, the high cost of Ga element and complicated multilayer process in current Ga2O3-based devices impede their large-scale application. In this work, the photoelectrochemical (PEC) performance of Cu2O photocathodes was investigated by coating an amorphous and crystalline WO3 buffer layer with an annealing temperature of 100 and 200 °C, respectively. It is found that the onset potential of the Cu2O photocathode anodically shifts from 0.7 to 0.95VRHE with an amorphous WO3 coating, while a poorer PEC performance is observed on the electrodes with crystalline WO3 coating. Further analysis indicates that the porous structure and photocapacitive surface states on the amorphous WO3 layer provide a special electron-transfer pathway into the electrolyte, which is eliminated in the crystalline WO3 layer. Our study offers a strategy for enhancing the photovoltage of photocathodes instead of optimizing band alignment. [ABSTRACT FROM AUTHOR]

[Display omitted] The photoelectrochemical (PEC) performance of BiVO 4 is limited by sluggish water oxidation kinetics and severe carrier recombination. Herein, a novel high-performance BiVO 4 /NiFe-NOAQ photoanode is prepared by a simple one-step hydrothermal method, using BiVO 4 and 1-Nitroanthraquinone (NOAQ) as raw materials. The BiVO 4 /NiFe-NOAQ photoanode has an excellent photocurrent density of 5.675 mA cm−2 at 1.23 V RHE , which is 3.35 times higher than that of the pure BiVO 4 (1.693 mA cm−2) photoanode. The BiVO 4 /NiFe-NOAQ shows a significant improvement in charge separation efficiency (86.12 %) and charge injection efficiency (87.86 %). The improvement is ascribable to the NiFe-NOAQ form a type II heterojunction with BiVO 4 to inhibit carrier recombination. More importantly, the kinetic isotope experiment suggests that the proton-coupled electron transfer (PCET) process can enhance the charge transfer of BiVO 4 /NiFe-NOAQ. The contact angle measurements show that modifying functional groups enhanced the hydrophilicity of BiVO 4 /NiFe-NOAQ, which can further accelerate the PCET process. The XPS and PL results as well as the tauc plot indicate that the strong electron-withdrawing ability of –NO 2 which can promote the extension of π conjugation, results in more π electron delocalization and produces more efficient active sites, thus achieving efficient photoelectrochemical water oxidation. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting is a promising energy conversion strategy for directly converting solar energy into green hydrogen fuel. Constructing an efficient PEC device, finding an efficient photoanode material with a suitable band gap and favorable band-edge positions is essential. Tantalum nitride (Ta3N5) meets these fundamental requirements, and its theoretical maximum solar-to-hydrogen (STH) conversion efficiency can reach 15.9%. Consequently, it has been widely applied as a photoanode material for the PEC oxygen evolution reaction (OER). However, severe bulk and interface charge recombination, along with sluggish water oxygen kinetics, seriously limits its STH conversion efficiency for PEC water splitting. Herein, this feature article briefly reviews recent advances by our research group in improving the STH conversion efficiency of the Ta3N5 photoanode using various strategies, including defect engineering, construction of a gradient band structure, interface engineering, and surface modification of self-healing OER cocatalyst. Up to now, the obtained half-cell STH efficiency has exceeded 4%, providing a solid foundation for the development of tandem PEC devices for unbiased solar-driven overall water splitting toward practical application. [ABSTRACT FROM AUTHOR]

Bismuth vanadate (BiVO4) has emerged as a highly prospective material for photoanodes in photoelectrochemical (PEC) water oxidation. However, current limitations with this material lie in the difficulties in producing stable and continuous BiVO4 layers with efficient carrier transfer kinetics, thereby impeding its widespread application in water splitting processes. This study introduces an accessible fabrication approach that yields continuous, monoclinic nanostructured BiVO4 films, paving the way for their use as photoanodes in efficient PEC water oxidation for hydrogen production under solar light conditions. The fabrication involves the intercalation of vanadium (V) ions into Bi2O3 films at 450 °C. Upon interaction with V ions, the film undergoes a transformation from tetragonal Bi2O3 to monoclinic scheelite BiVO4. This synthesis method enables the fabrication of single monoclinic phase BiVO4 films with thicknesses up to 270 nm. The engineered monoclinic BiVO4 film, devoid of any pinholes that could cause carrier loss, exhibits a robust photocurrent of 1.0 mA/cm2 at 1.23 VRHE in a neutral electrolyte, without requiring additional modifications or doping. Moreover, we demonstrate that the incorporation of a cobalt phosphate (Co–Pi) cocatalyst into the BiVO4 photoanode significantly enhances the lifetime of photogenerated holes by a factor of 9, resulting in a further elevation of the photocurrent to 2.9 mA/cm2. This remarkable PEC enhancement can be attributed to the surface state passivation by the Co–Pi cocatalyst. Our fabrication approach opens up a facile route for producing large-scale, highly efficient BiVO4 photoanodes for PEC water splitting technology. [ABSTRACT FROM AUTHOR]

The interface of two-dimensional transition metal dichalcogenides hosts collective interactions between the electronic structures that tune the charge density wave (CDW) states and the photoelectrochemical (PEC) properties of heterostructures. This work reports the influence of the interface on the CDW and PEC of a sputtered Bi2Se3/TiSe2 heterostructure on Ti metal foils. The hexagonal nanoflakes on the spiral-pyramid-like surface morphology of pristine TiSe2 confirm the Bi2Se3 decoration on the TiSe2 sample. The stoichiometric growth of TiSe2 and Bi2Se3 was revealed from X-ray photoelectron spectroscopy and Raman spectroscopy. The temperature-dependent Raman spectroscopy demonstrates the evolution of EgCDW and A1gCDW optical phonon modes with increased CDW phase transition temperature for the Bi2Se3/TiSe2 heterostructure. The enhancement of photoresponsive properties of the Bi2Se3/TiSe2 heterostructure under a solar light intensity of 100 mW/cm2 (AM = 1.5 G) in 0.5 M Na2SO4 electrolyte solution toward suitable water splitting was validated from the PEC measurements. This engineered heterostructure can pave the futuristic path to studying light-active electrodes with tunable CDW properties of pristine TiSe2 and Bi2Se3/TiSe2 heterostructures grown on flexible Ti substrates. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting for hydrogen generation is one of most promising approach to settle today's energy crisis. 1D metal nitrides have been developed as competitive photoanode candidates due to the suitable bandgap, short carrier diffusion length, and excellent chemical stability, but achieving the maximum PEC performance is still challenging owing to their sluggish oxidation evolution reaction (OER) kinetics and serious bulk carrier recombination. Heterostructuring 1D metal nitrides with other materials have been reported in various literatures. In this review, recent progress in 1D metal nitrides-based heterojunctions as efficient photoanodes for PEC water oxidation has been comprehensively presented, with a focus on photoanodes improved strategies for enhancing carrier transport including band alignment engineering, intermediate layer deposition and co-catalyst anchoring. Finally, the critical perspectives on fundamental challenges in the development of 1D metal nitrides-based heterostructures is outlined. • PEC water splitting is one of most promising approach for hydrogen generation. • 1D metal nitrides as photoanode for efficient PEC water oxidation. • Ta 3 N 5 and InGaN nanostructures are the competitive photoanodes. • Heterostructring 1D metal nitrides based on enhancing carrier transport. [ABSTRACT FROM AUTHOR]

We demonstrate the key role played by the structural transformation of MOF cocatalyst on BiVO 4 photoanode in PEC water splitting. Owing to the significantly reduced overpotential and enhanced hole extraction, the highest photocurrent density of 4.0 mA/cm2 at 1.23 V RHE have been obtained. [Display omitted] • A facile electrochemical activation method was developed to transform CoZn-MOFs to CoOOH on BiVO 4 photoanode. • CoOOH cocatalyst with rich active sites could significantly enhance the hole extraction and reduce the OER overpotential. • The highest photocurrent density of 4.0 mA/cm2 at 1.23 V RHE have been obtained in this work. • This work provides a new insight in understanding the key role of the structural transformation of MOF cocatalyst. Photoelectrochemical (PEC) water splitting has been widely investigated for solar-to-hydrogen conversion. However, issues like high charge recombination rate and slow surface water oxidation kinetics severely hinder its (PEC) conversion efficiency. Herein, we constructed MOF-derived CoOOH cocatalyst on BiVO 4 photoanode, using a feasible electrochemical activation strategy. The BiVO 4 -based photoanode obtained shows a high photocurrent density of 3.15 mA/cm2 at 1.23 V RHE and low onset potential. Detailed experiments and theoretical calculations show that during the activation of CoZn-MOFs, there was a partial breakage of 2-methylimidazole (mIM) linker, an increase in the oxidation state of Cobalt ion (Co), and increased O2–. The high PEC performance is mainly attributed to the MOF-derived CoOOH, which provides rich active sites for hole extraction and reduces the overpotential for oxygen evolution reaction. Furthermore, when CoZnNiFe-LDHs were decorated on BiVO 4 using the ions exchange method, the photocurrent density of BiVO 4 /CoZnNiFe-LDHs photoanode got to 4.0 mA/cm2 at 1.23 V RHE , accompanied with high stability. This study provides insights into understanding the key role played by the structural transformation of MOF cocatalyst in PEC water splitting processes. [ABSTRACT FROM AUTHOR]

The rise of concentration resistance caused by bubble growth is a key factor affecting the photoelectrochemical water splitting efficiency. In this research, we employed an electrochemical workstation, a synchronized measuring system, and a CCD camera to investigate the in-situ evolution of oxygen bubbles on the surfaces of TiO 2 -NTAs and C/TiO 2 -NTAs electrodes. The connection among the critical nucleation, growth and departure behavior of a single bubble on the photoanode surface and photocurrent curves at different solution pH (1–13) has been investigated. For TiO 2 -NTAs, it was found that strong alkalinity significantly reduces the voltage required for critical bubble nucleation. The photocurrent rises approximately 1.5 times when the control voltage is 0.10 V (vs. Ag/AgCl) by pH increasing from 1 to 13 and while the bubble evolution cycles decline by approximately 3.2 times. The photocurrent rises by 10.4 times compared with pH = 9 and by 7.3 times compared with pH = 13 when the control voltage is 0.71 V (vs. RHE), respectively. We also found that the oxygen bubble evolution of C/TiO 2 -NTAs is similar to TiO 2 -NTAs. When pH = 3–13, the average photocurrent of C/TiO 2 -NTAs electrode is higher than that of TiO 2 -NTAs, and the average bubble evolution cycles are lower than those of TiO 2 -NTAs at the same pH. According to the results, carbon films can rise the absorption capacity of TiO 2 -NTAs and significantly improve the effectiveness of photogenerated holes and electrons departure. Meanwhile, based on the oxygen bubble force balance model on the photoanode surface, the concentration Marangoni force rises with the increase of pH, which leads to the growth of bubble departure diameter. The outcomes demonstrate that oxygen bubbles on the photoanode surface can be successfully eliminated in strongly alkaline settings. • Photocurrent roughly shows an increasing trend at a constant voltage as pH rises. • Bubble cycles roughly show a decreasing trend at a constant voltage as pH rises. • Gas production efficiency increases about 5 times as pH rises from 1 to 13. • Concentration Marangoni force on the bubble rises with the increase of pH. [ABSTRACT FROM AUTHOR]

Slow oxygen evolution kinetics and severe corrosion limit the further application of BiVO4 photoelectrodes in photoelectrochemical water splitting. Here, BiVO4/Co-Pi/Ni(OH)2 photoanodes were synthetized with the aim of improving their photoelectric conversion efficiency and stability. Compared with a pure BiVO4 photoanode, the BiVO4/Co-Pi/Ni(OH)2 photoanode enhanced the photocurrent from 1.1 to 4.5 mA/cm² at 1.23 V versus the reversible hydrogen electrode. In addition, Ni(OH)2 acted as a corrosion protection layer on the surface of the photoanode, allowing the BiVO4/Co-Pi/Ni(OH)2 photoanode to exhibit excellent stability. [ABSTRACT FROM AUTHOR]

A key factor in the photoelectrochemical (PEC) performance of photoelectrodes is the efficient separation and transfer of photogenerated charges. Herein, a novel photoanode comprising three‐dimensional (3D) WO3 nanoplate@ZnO nanosheet hierarchical type‐II heterojunction arrays (3D WO3@ZnO HHAs) is designed and constructed via modification of the WO3 nanoplate arrays with ZnO nanosheets. The synthesized materials are characterized viaX‐ray diffraction (XRD), ultraviolet and visible spectrophotometry (UV–vis), scanning electon microscopy (SEM), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) analyses. Photoelectrochemical (PEC) test results reveal that the synthesized 3D WO3@ZnO HHAs photoanode exhibits reduced charge transfer resistance, improved electron‐hole pair life, and enhanced photocurrent density (≈4.5 times increase in comparison to that of the bare WO3). The increased light capture and high surface area in contact with the electrolyte as well as the enhanced charge transfer through the synergy between morphology and band structures may be responsible for the improved PEC characteristics. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water splitting presents a promising approach for harnessing solar energy and converting it into hydrogen energy. However, the limited water oxidation activity of semiconductor photoanodes has severely hampered the overall conversion efficiency. In this study, a hollow dodecahedral structure of NiCo-LDH (HD-NiCo-LDH) was designed using the metal-organic framework ZIF-67 as a precursor. HD-NiCo-LDH was employed to modify the BiVO4 photoanode, serving as an oxygen evolution cocatalyst. HD-NiCo-LDH can enhance light absorption, accelerate photogenic hole extraction, promote photogenic charge separation and improve the kinetics of water oxidation reaction. Significantly, the unique hollow dodecahedral structure of HD-NiCo-LDH possesses a larger specific surface areas, which provides additional active sites for the water oxidation reaction and facilitates the adsorption of water molecules. The photocurrent density of the optimized HD-NiCo-LDH/BiVO4 photoanode reaches 4.54 mA/cm2 at 1.23 V vs. RHE, which is 3.3 times greater than the bare BiVO4 photoanode. This presented work introduces an innovative design concept for photoanodes supported by oxygen evolution cocatalysts with multi-active sites.

Titanium dioxide (TiO2) has been considered as one of the most promising photocatalysts for photoelectrochemical (PEC) water splitting. Therefore, numerous efforts have been devoted to improving its PEC water splitting performance. In this study, TiO2 nanorod/nanoflower (NRF) films with controlled morphology were synthesized on fluorine-doped tin oxide (FTO) glass substrates by following a facile one-step hydrothermal method. The TiO2 NRF films were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectrometer (EDS), and ultraviolet-visible (UV-Vis) spectrophotometer. FE-SEM showed that the TiO2 films are composed of a simultaneous growth of a primary layer of TiO2 nanorod arrays (NRAs) and a second layer of TiO2 nanoflowers (NFs). The proposed growth mechanism highlighted the influence of precursor concentration on nucleation sites, affecting the preferred crystallographic plane growth of rutile TiO2 and nanorod alignment on the FTO substrate. Intriguingly, TiO2 NRF films prepared with 1.0 mL of titanium butoxide exhibited a maximum photocurrent density of 3.58 mA.cm−2 at 1.23 V versus (vs.) the reversible hydrogen electrode (RHE), along with a maximum photoconversion efficiency of 0.69%. The enhanced photocurrent density and photoconversion efficiency were attributed to the optimum thickness in the range of 4.52-7.31 µm, which caused the film to be formed with a unique morphology of the primary layer with well-vertically aligned nanorods and the second layer of flowers consisting of numerous rods stacked on top of one another. This study demonstrates the importance of designing semiconductors with 1D nanorod/3D nanoflower structures as high-performance photoelectrodes for PEC water splitting. Copyright © 2024 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Photoelectrochemical (PEC) performance of photoanode is limited by the cascade-dynamic processes, mainly including light absorption, charge separation, and surface reaction. This work adopted a strategy of nanocones modification on FTO substrate (FTO-NC) to enhance light utilization and photoelectrons collection for improved PEC water splitting. Comparative studies showed that FTO-NC enhanced the light scattering, promoting the conversion process of photon to electron/hole and enlarging the effective surface area of BiVO 4 for surface reaction. Meanwhile, cooperative Mo-doping and Co-MOF decoration improved the bulk electron transportation in BiVO 4 , hole migration towards the electrode surface, and accelerated the water oxidation reaction of photogenerated holes. The photocurrent density of FTO-NC/BiVO 4 -Mo/MOFs reached 3.56 mA cm−2, 6.14 times that of pristine BiVO 4. The IPCE of FTO-NC/BiVO 4 -Mo/MOFs photoanode achieve 60% at 1.23 V vs. RHE, demonstrating a significantly enhanced light utilization performance. This work presents new insight into boosting cascade-dynamic processes through collaborative strategies for highly efficient PEC water-splitting. [Display omitted] • FTO-NC had high light scattering effect for increasing light absorption of BiVO 4. • The photocurrent of FTO-NC/BiVO 4 -Mo/MOFs was increased by 6.14 times than FTO-BiVO 4. • FTO-NC/BiVO 4 -Mo/MOFs showed 2.7-times higher η transfer than FTO-BiVO 4. [ABSTRACT FROM AUTHOR]

ZnIn2S4 has been regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting. However, its severe charge recombination and low carrier transport efficiency limit practical applications in PEC water splitting. A novel ZnIn2S4/Au/PB photoanode was prepared by using the in‐situ photodeposition of Au nanoparticles and electrodeposition of Prussian blue (PB) nanoparticles onto ZnIn2S4 nanosheets. The photocurrent density of the prepared ternary photoanode reached 0.42 mA/cm2 at 1.23 VRHE, which is 6 times higher than pure ZnIn2S4. The introduction of Au nanoparticles remarkably improved the efficiency of carrier transport and separation. Additionally, the application of PB onto ZnIn2S4 resulted in an extended spectrum of light absorption. The incident photon‐to‐current efficiency (IPCE) value recorded was 24.6 % at 350 nm. This improvement can be attributed to the formation of a Z‐type heterojunction. [ABSTRACT FROM AUTHOR]