Spatial carrier separation in cobalt phosphate deposited ZnIn₂S₄ nanosheets for efficient photocatalytic hydrogen evolution

Developing photocatalyst with effective charge separation and fast surface reaction kinetics is crucial to high-efficiency photocatalytic H₂ evolution. Herein we spatially separate the reductive and oxidative reaction sites of ZnIn₂S₄ nanosheet and accelerate the hole transfer process by simply depositing cobalt phosphate (CoH_xPO_y, noted as Co-Pi), a non-precious co-catalyst, on its basal plane. Theoretical calculations combined with comprehensive characterizations reveal that Zn vacancies induced deep local energy levels serve as hole trap states to pin the photogenerated holes on (0 0 1) surface of ZnIn₂S₄. Upon Co-Pi deposition, Co atoms preferentially bond with S atoms nearby the Zn vacancies of ZnIn₂S₄. Taking advantage of the formation of Co-S bonds, Co-Pi acts as a hole receptor to extract the trapped holes effectively. As the photocatalytic activity of ZnIn₂S₄ is caused by active S atoms on its edge side, deposition of Co-Pi on planar side of nanosheets helps electron-hole migration to different facets. As a result of inert facet activation and spatial carrier separation, Co-Pi/ZnIn₂S₄ exhibits a superior photocatalytic H₂ evolution rate of 10.19 mmol g^-1h⁻¹ under visible light, which is superior to most of reported ZnIn₂S₄-based photocatalysts. This work will provide novel insights into the activation of inert basal planes of two-dimensional photocatalysts.