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

Two-dimensional (2D) photocatalytic materials have attracted extensive attention due to the unique properties different from those of their bulk. 2D ZnIn2S4 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 ZnIn2S4 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 ZnIn2S4 monolayer to trap the photo-generated electrons and further prolong the carrier lifetime. First-principle calculations reveal that sulfur vacancies in the ZnIn2S4 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 ZnIn2S4 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 ZnIn2S4 so far. These findings provide a new strategy for optimization of 2D photocatalysts to enhance photocatalytic hydrogen evolution.