W/Br co-doped Zn(O,S) with Zn/O bi-vacancy defects and heterovalent states for enhanced photocatalytic hydrogen evolution

To reveal the role of bi-vacancy defects and heterovalent states in oxysulfide catalysts for enhancing the photocatalytic hydrogen evolution reaction (PHER), we demonstrate a Br/W co-doped Zn(O,S) catalyst (labeled as Br/W-ZnOS) featuring abundant anionic oxygen vacancies (V O )/cationic zinc vacancies (V Zn ) bi-defects and heterovalent W 5+ /W 6+ states via a facile hydrolysis method. The co-doping of Br and W induces lattice distortions that enable neighboring atoms to leave the lattice, creating surfaces enriched with anionic V O and cationic V Zn defects. The synergistic effect between dual defects forms an efficient electron-hole separation system, enhancing the efficiency of electron-hole pair separation. Density functional theory calculation (DFT) demonstrates that the combination of Br/W co-doping and vacancies significantly reduces the water dissociation barrier and optimizes the surface ∗H generation rate of the photocatalyst. Thus, Br/W-ZnOS exhibits a PHER rate of 3415.7 μmol h −1 , which is 12.5 times higher than the undoped Zn(O,S) catalyst, and achieves an apparent quantum yield (AQY) of 15.41 % at 365 nm, while maintaining good stability with a PHER activity of 3288.1 μmol h −1 after five repeated cycles. This research provides a promising strategy for designing oxysulfide catalysts with synergistically engineered defects for efficient PHER.