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

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 (001) 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.