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

Vacancies have been demonstrated to be significant for CO 2 reduction reaction (CO 2 RR) over ZnS, but anion vacancies were easily refilled with oxygen species and could work as both H 2 and CO evolution sites, aggravating the competition between hydrogen evolution reaction (HER) and CO 2 RR. In this study, cation vacancies (V Zn ) were proposed as new active sites on the ZnS surface. With no cocatalyst, the V Zn -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 CO 2 RR pathways into formate and proved that the surface V Zn could greatly lower the barrier of CO 2 RR and suppress the proton adsorption, elucidating the origin of the highly selective CO 2 RR in the presence of competitive HER. This work gives an in-depth understanding of the cation vacancies and inspiration to develop efficient photocatalysts.