Boosting photo-assisted efficient electrochemical CO2 reduction reaction on transition metal single-atom catalysts supported on the C6N6 nanosheet

CO2 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 CO2 reduction reaction (CO2RR) to form C-1 products (CO, HCOOH, CH3OH, CH4) needs to be quite efficient. Herein with the help of density functional theory, CO2RR towards C-1 products was investigated on a transition metal (TM = Fe, Co, Ni) embedded C6N6 framework. The stable geometry of the catalysts, CO2 adsorption configurations, and CO2RR mechanisms were systematically studied for all the systems considered. The possible different adsorption configurations and adsorption energy calculations indicated that CO2 could be chemically adsorbed on the Co@C6N6 system. On the other hand, physical adsorption of CO2 is more preferable on Fe@C6N6 and Ni@C6N6 systems. As a competitive reaction, hydrogen evolution reaction (HER) was investigated and the systems were found to show more selectivity for CO2RR than for HER. OCHO formation turned out to be more favorable than COOH formation as initial protonation intermediates for CO2RR on the TM@C6N6 systems. The present work demonstrates that the Co@C6N6 catalyst can favor the electrocatalytic CO2RR among all systems. In addition, the photocatalytic activity of the systems was also investigated. The systems are found to be active for photoreduction of CO2 to CH3OH and CH4 in the presence of reducing agents such as H-2 and H2O 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.