Boosting photo-assisted efficient electrochemical CO 2 reduction reaction on transition metal single-atom catalysts supported on the C 6 N 6 nanosheet.

CO 2 reduction to value-added chemicals turns out to be a promising and efficient approach to resolve the increasing energy crisis and global warming. However, the catalytic efficiency of CO 2 reduction reaction (CO 2 RR) to form C 1 products (CO, HCOOH, CH 3 OH, CH 4 ) needs to be quite efficient. Herein with the help of density functional theory, CO 2 RR towards C 1 products was investigated on a transition metal (TM = Fe, Co, Ni) embedded C 6 N 6 framework. The stable geometry of the catalysts, CO 2 adsorption configurations, and CO 2 RR mechanisms were systematically studied for all the systems considered. The possible different adsorption configurations and adsorption energy calculations indicated that CO 2 could be chemically adsorbed on the Co@C 6 N 6 system. On the other hand, physical adsorption of CO 2 is more preferable on Fe@C 6 N 6 and Ni@C 6 N 6 systems. As a competitive reaction, hydrogen evolution reaction (HER) was investigated and the systems were found to show more selectivity for CO 2 RR than for HER. OCHO formation turned out to be more favorable than COOH formation as initial protonation intermediates for CO 2 RR on the TM@C 6 N 6 systems. The present work demonstrates that the Co@C 6 N 6 catalyst can favor the electrocatalytic CO 2 RR among all systems. In addition, the photocatalytic activity of the systems was also investigated. The systems are found to be active for photoreduction of CO 2 to CH 3 OH and CH 4 in the presence of reducing agents such as H 2 and H 2 O as they possess appropriate absorption spectrum in the visible region as well as suitable band edge positions. These findings open a way for designing single atom catalysts for important catalytic reactions.