Half-unit-cell ZnIn2S4 monolayer with sulfur vacancies for photocatalytic hydrogen evolution

Abstract Two-dimensional (2D) photocatalytic materials have attracted extensive attention due to the unique properties different from those of their bulk. 2D ZnIn 2 S 4 nanosheets with the intrinsic bilayer in one-unit-cell with interlayer force generally perform better than that of the bulk in photocatalytic hydrogen evolution. Here, we for the first time demonstrate that the half-unit-cell ZnIn 2 S 4 monolayer possesses an excellent photocatalytic performance compared with the one-unit-cell bilayer owing to its increased carrier lifetime. Meanwhile, sulfur vacancies are introduced in the half-unit-cell ZnIn 2 S 4 monolayer to trap the photo-generated electrons and further prolong the carrier lifetime. First-principle calculations reveal that sulfur vacancies in the ZnIn 2 S 4 monolayer induce more charge carriers at the valence band maximum to participate in the photocatalytic activity. As expected, the photocatalytic hydrogen production rate of the monolayer ZnIn 2 S 4 with sulfur vacancies is up to 13.478 mmol/g/h under the visible light irradiation, which is much higher than the available values reported of ZnIn 2 S 4 so far. These findings provide a new strategy for optimization of 2D photocatalysts to enhance photocatalytic hydrogen evolution.