Construction of type-II BiVO₄/FeCoMOF p–n heterojunction for enhanced photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting is a highly promising approach for sustainable hydrogen production. BiVO₄ (BVO) possesses an appropriate bandgap and excellent optical properties; however, its poor carrier transport and sluggish water-oxidation kinetics severely limit the utilization of holes, leading to low PEC efficiency. Herein, we rationally design a p–n heterojunction with a stepwise type-II energy band configuration through the in-situ growth of p-type FeCoMOF on n-type BVO. This architecture promotes the efficient and selective separation of photogenerated electrons and holes, enabling the BVO/FeCoMOF photoanode to achieve enhanced PEC water oxidation performance. The optimized photoanode delivers a remarkable photocurrent density of 6.2 mA·cm⁻² at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is 3.8 times higher than that of bare BVO photoanode, and exhibits significantly enhanced operational stability compared to the bare BVO. Furthermore, gas-evolution tests confirm highly stoichiometric water splitting, yielding an H₂/O₂ ratio close to 2:1, along with a Faradaic efficiency exceeding 92%. Detailed physicochemical characterization, including intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated photovoltage spectroscopy (IMVS), and in-situ Kelvin probe force microscopy (KPFM), confirm that the construction of the type-II p–n heterojunction effectively promotes the hole transfer from BVO to the FeCoMOF layer, enhances the charge-separation efficiency, and prolongs the carrier lifetime. Furthermore, the FeCoMOF modification significantly reduces the interfacial reaction resistance and enhances the charge utilization efficiency, thereby further improving the PEC performance. This work provides new insights into the rational design of high-performance photoelectrode.