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

Abstract

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 C₁ products (CO, HCOOH, CH₃OH, CH₄) needs to be quite efficient. Herein with the help of density functional theory, CO₂RR towards C₁ 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 H₂ 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.