Tailoring the special hole transfer layer between BiVO₄ and oxygen evolution co-catalysts interfaces for boosting photoelectrochemical water splitting

Tailoring the hole transport layer (HTL) between BiVO₄ (BVO) and oxygen evolution co-catalysts (OECs) interfaces is a leading strategy to improve the performance of photoelectrochemical (PEC) water splitting. Nevertheless, the limited driving force at the BVO/OECs interfaces severely hinders the transport of charge carriers. In this study, we designed a specialized defective transition metal oxide (Vo-MnO_x) as the HTL. The integrated photoanode (BVO/Vo-MnO_x/CoFe(OH)_x) exhibits an impressive photocurrent density at 1.23 V vs. RHE, along with an outstanding η_surface value of 91.91 %. These remarkable outcomes are due to the fact that Vo-MnO_x as HTL effectively enhances the interface driving force and charge migration ability, which is largely attributed to the ability of Vo to accumulate electrons and accelerate rapid cyclic transitions of multivalent Mn. Satisfactorily, microscopic perspective studies reveal that the distinctive Vo-MnO_x can efficiently promote photogenerated charge transfer, as shown in dynamic carrier analysis using scanning photoelectrochemical microscope (SPECM). Additionally, the oxygen evolution reaction model suggests that a defective HTL can improve surface catalytic kinetics. This work provides valuable insights into the role of Vo in regulating the valence state changes in PEC water splitting.