Cation Vacancy-Initiated CO2 Photoreduction over ZnS for Efficient Formate Production

Vacancies have been demonstrated to be significant for CO2 reduction reaction (CO2RR) over ZnS, but anion vacancies were easily refilled with oxygen species and could work as both H2 and CO evolution sites, aggravating the competition between hydrogen evolution reaction (HER) and CO2RR. In this study, cation vacancies (VZn) were proposed as new active sites on the ZnS surface. With no cocatalyst, the VZn-rich ZnS acquired a high selectivity of formate production (>85%) in inorganic aqueous solution. In situ attenuated total reflection-infrared (ATR-IR) spectroscopy and first-principle calculations have clarified the CO2RR pathways into formate and proved that the surface VZn could greatly lower the barrier of CO2RR and suppress the proton adsorption, elucidating the origin of the highly selective CO2RR in the presence of competitive HER. This work gives an in-depth understanding of the cation vacancies and inspiration to develop efficient photocatalysts.