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 (CoHxPOy, 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.