2D/3D WO3/BiVO4 heterostructures for efficient photoelectrocatalytic water splitting

Developing novel photoanodes with high efficiency for photoelectrochemical (PEC) water splitting has become the key to solar energy conversion and storage realm. Herein, 3D worm-like bismuth vanadate (BiVO₄) is grafted on 2D thin tungsten trioxide (WO₃) underlayer by electrodeposition to form mixed–dimensional structured photoanode, resulting in significant improvement of the photocatalytic performance and the charge separation efficiency. Characterization results prove that the mixed–dimensional structured can boost the photocatalytic activity by suppressing back reaction and charge recombination of the bulk BiVO₄. Simultaneously, the electrical conductivity of photoanode can be increased by W⁶⁺ doping. Furthermore, a robust catalyst NiCo₂O_x is coated onto the surface of WO₃/BiVO₄ photoanode, exhibiting a desirable photocurrent of 3.85 mA cm^?2 at 1.23 V vs. RHE and an excellent stability over 3 h. Both the excellent photocurrent density and great operational stability of this 2D/3D WO₃/BiVO₄ photoanode make it a promising material for practical applications.     

Reasonable regulation of kinetics over BiVO4 photoanode by Fe–CoP catalysts for boosting photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting using earth-abundant semiconductor offer a promising strategy to produce the sustainable clean energy. Herein, we successfully engineered BiVO₄ photoanode with Fe-doped CoP oxygen evolution catalysts (BiVO₄–Fe/CoP) for the first time. Fe/CoP catalysts could significantly break the kinetic limitations of BiVO₄, contributing to the enhanced charge injection efficiencies and charge carrier density. The rational heterostructure has boosted the photocurrent density and incident photon-to-current conversion efficiency (IPCE) to 2.16 mA/cm² and 43% (7 times than that of the bare BiVO₄), respectively. Meanwhile, the BiVO₄–Fe/CoP photoanode also exhibited the desirable long-term stability during PEC water oxidation for 4 h. The results prove the feasibility of BiVO₄–Fe/CoP configuration, which further provided a novel approach towards the development of efficient PEC water oxidation system.     

Recent trends and outlooks on engineering of BiVO4 photoanodes toward efficient photoelectrochemical water splitting and CO2 reduction: A comprehensive review

Photoelectrochemical (PEC) water splitting, and carbon dioxide (CO₂) utilization devices have attracted immense attention as sustainable technologies for the generation of hydrogen (H₂) fuel and value-added chemicals feedstock. Among numerous semiconductors, bismuth vanadate (BiVO₄) has emerged as a promising photoanode owing to its fascinating features such as high chemical stability, straddling band alignment with water redox levels, eco-friendly, and cost-effectiveness. However, sluggish oxidation kinetics, photo-corrosive nature, low electronic conductivity, and short carrier diffusion length limit its commercialization on the PEC horizon. To mitigate these inadequacies, several strategies have emerged such as novel heterojunctions, doping with unique materials, interface modulation, morphology, facet orientation, co-catalyst loading for surface engineering, etc. to realize the outstanding cost-to-efficiency ratios and long-term stability of PEC devices. The review highlights the recent advancement in BiVO₄-based photoanodes in last five years (2018–2022) and their utilization in the single absorber and unexplored tandem PEC systems towards boosted water splitting and CO₂ reduction. A discussion on theoretical studies of BiVO₄-based PEC systems elucidates the microscopic mechanism of promotion effect of the bulk/interface/surface strategies on surface catalysis as well as interfacial charge transfer in boosting oxidation kinetics. Moreover, this review addresses the versatility of the BiVO₄-based photoanode for the novel yet commercially viable PEC applications. This review will provide a broad avenue in designing highly durable, and scalable BiVO₄-based systems toward various PEC energy conversion devices.     

Coupling surface modification with cocatalyst deposition on BiVO4 photoanode to enhance charge transfer for efficient solar-driven water splitting

Bismuth vanadate (BiVO₄) has attracted wide attention as photoanode in water-splitting photoelectrochemical (PEC) devices. However, its catalytic performance is greatly limited by the serious charge recombination on the surface states. Herein, borate modified BiVO₄ plus additional CoPi cocatalyst (B-BVO/CoPi) is developed as photoanode for PEC cell via a simple soaking and electrodeposition process. Based on the electrochemistry tests and material characteristics, the borate groups [B(OH)₄] ^– is able to effectively prevent the charge recombination, while the outer CoPi cocatalyst enhance the activity toward oxygen evolution reaction. Therefore, the designed B-BVO/CoPi photoanode could obtain a high current density of 2.67 mA cm⁻² at 1.23 V_RHE with an onset potential of 0.29 V_RHE, much higher than pristine BiVO₄ (0.78 mA cm⁻², 0.52 V_RHE). This work may provide a new insight for constructing multifunctional modified photoanodes for efficient solar conversion.     

rGO decorated semiconductor heterojunction of BiVO4/NiO to enhance PEC water splitting efficiency

Monoclinic phase of BiVO₄ is a promising photoanode material for photoelectrochemical (PEC) water splitting, but its sluggish water oxidation kinetics and frequent bulk charge recombination greatly reduce its efficiency of PEC water splitting. A novel BiVO₄/NiO/rGO photoanode was very simply prepared by electrodeposition, solution immersion and spin coating methods, in particular, the solution immersion method to loading NiO has never been reported in PEC research. Compared with BiVO₄, the photocurrent density of the ternary photoanode reaches 1.52 mA/cm² at 1.23 V vs RHE, which is 2.41 and 1.39 times higher than that of pure BiVO₄ and binary BiVO₄/NiO photoanode, respectively. The onset potential of the ternary photoanode shows a significant cathodic shift of 130 mV compared with the BiVO₄ photoanode. Moreover, the measured incident photon-to-current efficiency (IPCE) value reaches 50.52% at λ = 420 nm. The improvement is attributed to the type-II heterojunction formation that enhances the separation efficiency of electron/hole and the rGO decoration that accelerates the electron transfer and provides more active sites for gas adsorption.     

Rational design of W-doped BiVO4 photoanode coupled with FeOOH for highly efficient photoelectrochemical catalyzing water oxidation

Developments of promising photocatalyst for PEC water oxidation gain significant interest in the research field of PEC water splitting. The BiVO₄ has been envisioned as suitable photocatalyst material for the PEC water oxidation due to suitable bandgap with favorable band edge positions. Nevertheless, the poor electron-hole separation and low charge transfer efficiency of BiVO₄ yield sluggish surface catalysis reaction. Herein, facile electrodeposition and annealing techniques are proposed to fabricate W-doped BiVO₄ photoanode coupled with FeOOH (W–BiVO₄/FeOOH) for efficient photocatalytic water oxidation. This synthesis is simple, cost-effective and less time consuming. The doping concentration of W and deposition time of FeOOH are optimized to improve photocatalytic ability of BiVO₄. At 1.23 V vs. reversible hydrogen electrode (RHE) under 1 sun illumination, the W–BiVO₄/FeOOH photoanode exhibits a high photocurrent density of 2.2 mA/cm², which is seven folds higher than that of the pristine BiVO₄ photoanode (0.31 mA/cm² 1.23 V vs. RHE). The enhanced photocatalytic ability of W–BiVO₄/FeOOH photoanode is due to the enhanced charge transport properties and synergistic effects of W doping and FeOOH deposition. The excellent long-term stability with the photocurrent density retention of 90% after continuous light illumination for 1000 s is also achieved for the W–BiVO₄/FeOOH photoanode.     

Fabrication of BiVO4 photoanode catalyzed with bimetallic sulfide nanoparticles for enhanced photoelectrochemical water oxidation

The photoelectrochemical water oxidation ability of BiVO₄ is usually restrained by its low separation efficiency of the photogenerated charge and slow kinetics for water oxidation. Here, FeCoS₂ bimetallic sulfide nanoparticles are successfully coated on BiVO₄ photoanode to address these problems. The photocurrent density of FeCoS₂/BiVO₄ photoanode is 3.08 times that of BiVO₄ photoanode. Furthermore, the charge separation efficiency can reach 75% and the charge injection efficiency reaches nearly 78%. The onset potential of FeCoS₂/BiVO₄ shifts 300 mV negatively, while the incident photon-to-electron conversion efficiency value of FeCoS₂/BiVO₄ is 2.86 folds of BiVO₄. The enhancement benefits from the loading of FeCoS₂, which promotes the separation of photogenerated electron and hole, and inhibits the recombination of photogenerated charge and hole.     

BiVO4 photoanode decorated with cobalt-manganese layered double hydroxides for enhanced photoelectrochemical water oxidation

Bismuth vanadate (BiVO₄) is being widely identified as a leading n-type semiconductor material for photoelectrochemical (PEC) water splitting. Nevertheless, achieving efficient PEC water oxidation process through BiVO₄ photoanode still faces serious challenge such as severe electron-hole recombination. In this case, PEC activity of BiVO₄ photoanode was enhanced by decoration of three-dimensional CoMn-layered double hydroxide (CoMn-LDH) nanoflakes on the BiVO₄ surface via a facile electrodeposition process. It was suggested that CoMn-LDH played a synergistic effect on broadening internal light absorption, which accelerated injection of holes carrier to electrolyte and alleviated the electron-hole recombination, resulting in expediting faster PEC water oxidation reaction kinetics. Consequently, the photocurrent density of BiVO₄/CoMn-LDH photoanode achieved 2.69 mA cm⁻² at 1.23 V_RHE, 2.45 times higher than the pristine BiVO₄. What's more, 220 mV negative-shift took place on onset potential that was further decreased to 0.31 V_RHE. The vastly enhanced PEC performance was also prioritized to those of Co and Mn single relatives. This work demonstrated that the synergistic BiVO₄/CoMn-LDH as a capable candidate material, can be utilized for effective PEC water splitting.     

Photodeposited CoOx as highly active phases to boost water oxidation on BiVO4/WO3 photoanode

Surface decoration of photoanodes with oxygen evolution cocatalysts is an efficient approach to improve the photoelectrochemical water splitting performance. Herein, ultrafine CoO_x was selectively immobilized on the surface of BiVO₄/WO₃ photoanode by using the photogenerated holes to in-situ oxidize Co₄O₄ cubane. The composited photoanode (CoO_x/BiVO₄/WO₃) displayed an enhanced photoelectrochemical (PEC) water oxidation performance, with a photocurrent density of 2.3 mA/cm² at 1.23 V_RHE under the simulated sunlight irradiation, which was 2 times higher than that of bare BiVO₄/WO₃. The characterization results for the morphological, optical and electrochemical properties of the photoelectrodes revealed that, the enhanced PEC performances could be attributed to the improved charge carrier separation/transport behaviors and the promoted water oxidation kinetics when the photoelectrodes were loaded with CoO_x.     

Enhanced photoelectrochemical water oxidation on BiVO4 by addition of ZnCo-MOFs as effective hole transfer co-catalyst

Solar-driven water splitting is one of greenways for massive conversion of sustainable and nonpolluting energy applied to meet global energy crisis. Photocatalysts are greatly explored to improve photoelectrochemical (PEC) water oxidation efficiency. Bismuth vanadate (BiVO₄) has been extensively used as photocatalyst for water oxidation, but its passive oxygen evolution kinetics and charge carrier recombination lead to inferior PEC performance under light illumination. Tuning interfacial charge separation and transfer is an eminent way to stimulate water oxidation characteristics of BiVO₄. Herein, a BiVO₄/zinc cobalt metal-organic framework (ZnCoMOF) composite is firstly proposed as photocatalyst for water oxidation. ZnCoMOF nanosheets are loaded on BiVO₄ surface as co-catalyst via solvothermal process. Effects of solvothermal duration and mole ratio of zinc and cobalt are investigated. The optimal BiVO₄/ZnCoMOF electrode shows a photocurrent density of 3.08 mA cm^?2 at 1.23 V vs. reversible hydrogen electrode (RHE), which is 4.21 times greater than that of BiVO₄ electrode. The redox properties of high valence metal ions in ZnCoMOF are used to store photoexcited holes and transfer them to the water oxidation process in the BiVO₄/ZnCoMOF system. This work demonstrates that PEC performance of BiVO₄ can be largely improved via controlling water oxidation kinetics and refining charge recombination and transport properties.     

Photoanode of LDH catalyst decorated semiconductor heterojunction of BiVO4/CdS to enhance PEC water splitting efficiency

BiVO₄ is an ideal photoanode material for solar-driven photoelectrochemical (PEC) water splitting but it easily suffers from the recombination of photogenerated electrons and holes due to its low carrier mobility thus cause low efficiency of PEC water splitting. Herein, the BiVO₄/CdS/NiCo-LDH photoanode was prepared by combining methods of metal organic decomposition, chemical and electrodeposition. The photoanode photocurrent density reaches 2.72 mA cm⁻² at 1.23 V (vs. RHE), which is 3.6 folds of pure BiVO₄ photoanode and onset potential shifts 450 mV toward cathodic. The incident photon-to-electron conversion efficiency (IPCE) value is 2.86 folds of BiVO₄, the calculated photon–to–current efficiency (ABPE) is 1.24% at 0.62 V (vs. RHE). The obtained results are higher than that of most BiVO₄ based photoanodes published so far. The enhancement benefits from increase of visible light absorption capacity, enhancement of separation efficiency of photoexcited electron-hole and fast transfer of holes accumulated on electrode/electrolyte surface for water oxidation, which has been confirmed by calculating carrier density and carrier transport rate.     

Plasmonic Bi nanoparticle decorated BiVO4/rGO as an efficient photoanode for photoelectrochemical water splitting

We report the application of plasmonic Bi nanoparticles supported rGO/BiVO₄ anode for photoelectrochemical (PEC) water splitting. Nearly, 2.5 times higher activity was observed for Bi-rGO/BiVO₄ composite than pristine BiVO₄. Typical results indicated that Bi-rGO/BiVO₄ exhibits the highest current density of 6.05 mA/cm² at 1.23 V, whereas Bi–BiVO₄ showed the current density of only 3.56 mA/cm². This enhancement in PEC activity on introduction of Bi-rGO is due to the surface plasmonic behavior of BiNPs, which improves the absorption of radiation thereby reduces the charge recombination. Further, the composite electrode showed good solar to hydrogen conversion efficiency, appreciable incident photon-to-current efficiency and low charge transfer resistance. Hence, Bi-rGO/BiVO₄ provides an opportunity to realize PEC water splitting.     

An efficient tandem photoelectrochemical cell composed of FeOOH/TiO2/BiVO4 and Cu2O for self-driven solar water splitting

An integrated solar water splitting tandem cell without external bias was designed using a FeOOH modified TiO₂/BiVO₄ photoanode as a photoanode and p-Cu₂O as a photocathode in this study. An apparent photocurrent (0.37 mA/cm² at operating voltage of +0.36 V_RHE) for the tandem cell without applied bias was measured, which is corresponding to a photoconversion efficiency of 0.46%. Besides, the photocurrent of FeOOH modified TiO₂/BiVO₄–Cu₂O is much higher than the operating point given by pure BiVO₄ and Cu₂O photocathode (∼0.07 mA/cm² at +0.42 V_RHE). Then we established a FeOOH modified TiO₂/BiVO₄–Cu₂O two-electrode system and measured the current density-voltage curves under AM 1.5G illumination. The unassisted photocurrent density is 0.12 mA/cm⁻² and the corresponding amounts of hydrogen and oxygen evolved by the tandem PEC cell without bias are 2.36 μmol/cm² and 1.09 μmol/cm² after testing for 2.5 h. The photoelectrochemical (PEC) properties of the FeOOH modified TiO₂/BiVO₄ photoanode were further studied to demonstrate the electrons transport process of solar water splitting. This aspect provides a fundamental challenge to establish an unbiased and stabilized photoelectrochemical (PEC) solar water splitting tandem cell with higher solar-to-hydrogen efficiency.     

Hierarchical mesoporous SnO2/BiVO4 photoanode decorated with Ag nanorods for efficient photoelectrochemical water splitting

Bismuth vanadate has been extensively investigated as a potential visible light photoanode for PEC water splitting. The performance of BiVO₄ is restricted by fast charge recombination and slow oxygen evolution reaction kinetic. To address these issues, hierarchical SnO₂ (HSN) mesoporous support is developed via a novel sol-electrophoretic approach, and BiVO₄ film is decorated with silver nanorods (Ag NRs). The photocurrent density of HSN/BiVO₄ photoanode is 3.98 mA/cm² at 1.23 V vs. reversible hydrogen electrode (RHE) and onset potential (V_onset) of 0.5 V vs. RHE. The PEC performance is attributed to the appropriate band alignment between SnO₂ and BiVO₄, as well as the hierarchical structure of SnO₂. Ag-HSN/BiVO₄ photoanode shows photocurrent density of 4.30 mA/cm² at 1.23 V vs. RHE and V_onset of 0.28 V vs. RHE. The enhanced photocurrent and negatively shifted V_onset can be attributed to radiative localized surface plasmon resonance decay and catalytic effect of Ag NRs, respectively.     

Molybdenum doped bilayer photoanode nanotubes for enhanced photoelectrochemical water splitting

Conversion of solar energy into hydrogen energy via photoelectrochemical (PEC) water splitting is one of the most promising approaches for generation of clean and sustainable hydrogen energy in order to address the alarming global energy crisis and environmental problems. To achieve superior PEC performance and solar to hydrogen efficiency (STH), identification, synthesis, and development of efficient photoelectrocatalysts with suitable band gap and optoelectronic properties along with high PEC activity and durability is highly imperative. With the aim of improving the performance of our previously reported bilayer photoanode of WO₃ and Nb and N co-doped SnO₂ nanotubes i.e. WO₃-(Sn_0.95Nb_0.05)O₂:N NTs, herein, we report a simple and efficient strategy of molybdenum (Mo) doping into the WO₃ lattice to tailor the optoelectronic properties such as band gap, charge transfer resistance, and carrier density, etc. The Mo doped bilayer i.e. (W_0.98Mo_0.02)O_3-(Sn_0.95Nb_0.05)O₂:N revealed a higher light absorption ability with reduced band gap (1.88 eV) in comparison to that of the undoped bilayer (1.94 eV). In addition, Mo incorporation offered improvements in charge carrier density, photocurrent density, with reduction in charge transfer resistance, contributing to a STH (～3.12%), an applied bias photon-to-current efficiency (ABPE ～ 8% at 0.4 V), including a carrier density (N_d ～ 7.26 × 10²² cm^?3) superior to that of the undoped bilayer photoanode (STH ～2%, ABPE ～ 5.76%, and N_d ～5.11 × 10²² cm^?3, respectively). The substitution of Mo⁶⁺ for W⁶⁺ in the monoclinic lattice, forming the W–O–Mo bonds altered the band structure, realizing further enchantments in the PEC reaction and charge transfer kinetics. Additionally, doped bilayer photoanode revealed excellent long term PEC stability under illumination, suggesting its robustness for PEC water splitting. The present work herein provides a simple and effective Mo doping approach for generation of high performance photoanodes for PEC water splitting.     

Membrane electrode assembly-based photoelectrochemical cell for hydrogen generation

A novel photoelectrochemical cell (PEC) for generation of hydrogen via photocatalytic water splitting is proposed and investigated. At the heart of the PEC is a membrane electrode assembly (MEA) integrated with Degussa P25 TiO₂ powder as a model photocatalyst for the photoanode and Pt catalyst powder for the dark cathode, respectively. It serves as a compact photocatalytic reactor for water splitting as well as an effective separator for the generated hydrogen and oxygen. The unique characteristic of the MEA-based PEC is that the use of co-catalyst, sacrificial reagent and supporting electrolyte in the cell is totally not required. The novel PEC can be operated without addition of water in the cathode compartment resulting in improved photo conversion efficiency. In addition, the application of a Degussa P25/BiVO₄ mixed photocatalyst was found to significantly enhance the hydrogen generation. Further improvements for the MEA-based PEC utilizing solar energy are also proposed.     

Photoelectrochemical performance of bismuth vanadate photoanode for water splitting under concentrated light irradiation

Photoelectrochemical (PEC) water splitting is a promising way to convert solar energy into hydrogen energy. It is typically carried out at room temperature (RT) and 1 sun illumination. The PEC water splitting under concentrated light is expected to be an effective route to improve PEC performance, but there are few studies on it. Herein, CoPi/Mo:BiVO₄ photoanode was selected to investigate the effect of concentrated light and the reaction temperature on its PEC performance. It was revealed that CoPi/Mo:BiVO₄ showed enhanced PEC performance under concentrated light. The photocurrent density was enhanced with increased light intensity and increased reaction temperature. At a high temperature (60 °C), the normalized photocurrent density (3.31 mA cm⁻² at 1.23 V vs. RHE) was found to be optimal at 4 suns, which was attributed to the synergistic effect of concentrating light and heating. It is proved that concentrated light can effectively improve the PEC performance, which has important guiding significance to realize the low-cost and efficient PEC water splitting.     

Bi2S3 entrenched BiVO4/WO3 multidimensional triadic photoanode for enhanced photoelectrochemical hydrogen evolution applications

The catalytic reactivity and photoactivity of WO₃ and BiVO₄ oxide semiconductors have general obstacles as electrodes in emergent photo-electrochemical (PEC) hydrogen evolution applications. The present work comprises the integration of photocatalyst with wide visible photon absorption material which is vital for hydrogen evolution in photo-electrocatalytic water splitting. Herein, the 1D WO₃ NWs have been integrated with stable water oxidation photocatalysts of BiVO₄ and Bi₂S₃ as a photoanode (Bi₂S₃/BiVO₄/WO₃) for photoelectrochemical hydrogen evolution reactions. The morphological variations in the Bi₂S₃/BiVO₄/WO₃ heterostructure manifest catalytic activity and rapid charge transfer characteristics owing to band alignment and a wide range of visible photon absorption. The optimized Bi₂S₃/BiVO₄/WO₃ multidimensional photoanode accomplishes a superior photocurrent density of 1.52 mA/cm², a seven-fold higher than pristine WO₃ photoanode counterpart (0.2 mA/cm²) at 1 V vs. RHE. A prodigious lowest onset potential of ?0.01 V vs. RHE) has been achieved which enables very high solar to hydrogen conversion. The photoelectrode with entangled morphology such as nanosheets, nanocrystals and nanorods expanded their surface to volume ratio having enhanced catalytic performance. The hybrid photoanodes have demonstrated the lowest charge transfer resistance of 360 Ohm/cm² with a 7-fold rise in hydrogen evolution performance. The resultant triadic Bi₂S₃/BiVO₄/WO₃ heterostructure appeared to be an emerging stable photo-electro catalyst for hydrogen evolution applications.     

Efficient suppression of surface charge recombination by CoP-Modified nanoporous BiVO4 for photoelectrochemical water splitting

BiVO₄ is a promising photoanode material for water splitting due to its substantial absorption of solar light as well as favorable band edge positions. However, the poor water oxidation kinetics of BiVO₄ results in its insufficient photocurrent density. Herein, we demonstrate the use of CoP nanoparticles for facile surface modification of nanoporous BiVO₄ photoanode in potassium borate buffer solution (pH 9.0), which can generate a tremendous cathodic shift of ~430 mV in the onset potential for photoelectrochemical water oxidation. In addition, a remarkable photocurrent density of 4.1 mA cm^?2 is achieved at 1.23 V vs. RHE under AM 1.5G illumination. The photoelectrochemical measurement using sodium sulfite as a hole scavenger clearly shows that the greatly improved performances are attributed to the efficient suppression of interfacial charge recombination through loading of CoP catalyst. Moreover, the maximum surface charge injection yield can reach >81% at 1.23 V vs. RHE and the maximum IPCE of CoP/BiVO₄ can reach 75.8% at 420 nm, suggesting the potential application of CoP-modified BiVO₄ photoanode for overall solar water splitting in cost-effective tandem photoelectrochemical cells.     

Experimental and first-principles studies of BiVO4/BiV1-xMnxO4-y n-n+ homojunction for efficient charge carrier separation in sunlight induced water splitting

Though bismuth vanadate (BiVO₄) is extensively used as a photoactive material, its performance in harnessing solar energy is limited by ineffective separation of photo-excited charge carriers. We demonstrate here a concept of n-n⁺ homojunction of BiVO₄/BiV_1-xMn_xO_4-y, which improves its charge separation efficiency. Using first-principles theoretical calculations, we determine the effect of Mn substitution on oxygen vacancy formation energies and associated changes in the electronic structure of BiVO₄. Showing that Mn substitution pushes the Fermi level of BiVO₄ towards its conduction band, we predict that the associated enhanced bending of bands at the homojunction (BiVO₄/BiV_1-xMn_xO_4-y) facilitates efficient separation of charge carriers. With Mott-Schottky experiments, we verify the increased band bending at the n-n⁺ homojunction, and show that the maximum photocurrent density measured in a sample with n-n⁺ homojunction is ten times higher than that obtained of the pristine sample. Secondly, Mn substitution in BiVO₄ also reduces the oxygen vacancy formation energy, promoting higher concentration of O-vacancies, further enhancing the photoelectrochemical response.