Dual Cu and S vacancies boost CO2 photomethanation on Cu1.95S1-x: Vacancy-regulated selective photocatalysis

Tuning product selectivity and improving activity are significant in CO2 photoreduction. Herein, we demonstrate that introducing Cu and S dual vacancies on copper sulfide surfaces can improve the CO2 photoreduction activity and completely switch the selectivity from CO to CH4. Experimental results reveal that Cu and S vacancies can attain a favorable CH4 production of 12.42 μmol g−1 h−1 with 100 % selectivity. Meanwhile, the single S vacancies also exhibit an approx. 4-fold CO yield (13.63 μmol g−1 h−1) compared with vacancy-free Cu2S (3.48 μmol g−1 h−1). Mechanism research indicates that the single S vacancies could promote the CO2 → COOH* → CO* pathway to improve the CO yield, while the simultaneously introducing of Cu and S dual vacancies can further lower the energy barriers of CO2 → COOH* → HCOOH* → CHO* pathway to promote the stepwise protonation of CO2, which in turn strengthen the selectivity of CO2-to-CH4 photoreduction.