3D Hierarchical ZnIn2S4 Nanosheets with Rich Zn Vacancies Boosting Photocatalytic CO2 Reduction

Zinc vacancy (V-Zn) is successfully introduced into 3D hierarchical ZnIn2S4 (3D-ZIS). The photo-electrochemical experiments demonstrate that the charge separation and carrier transfer are more efficient in the 3D-ZIS with rich V-Zn. Of note, for the first time, it is found that V-Zn can decrease the carrier transport activation energy (CTAE), from 1.14 eV for Bulk-ZIS (Bulk ZnIn2S4) to 0.93 eV for 3D-ZIS, which may provide a feasible platform for further understanding the mechanism of photocatalytic CO2 reduction. In situ Fourier transform infrared (FT-IR) results reveal that the presence of rich V-Zn ensures CO2 chemical activation, promoting single-electron reduction of CO2 to CO2-. In addition, in situ FT-IR and CO2 temperature programmed desorption results show that V-Zn can promote the formation of surface hydroxyl. To the best of current knowledge, there are no reports on the photoreduction of CO2 simply by virtue of 3D-ZIS with V-Zn and few literature reports on the photocatalytic reduction of CO2 concerned with CTAE. Additionally, this work finds that surface hydroxyl may play a crucial role in the process of CO2 photoreduction. The work may provide some novel ways to ameliorate solar energy conversion performance and a better understanding of photoreaction mechanisms.