Identifying TM-N4 active sites for selective CO2-to-CH4 conversion: A computational study

Abstract

Electrochemical CO2 reduction reaction (CO2RR) to generate CH4 is more desirable than CO. Herein, we investigate the potential of CO2-to-CH4 conversion on the representative single-atom catalysts (SACs), single transition metal atom with four coordinated nitrogen atoms embedded in graphene (TM-N4) by first-principle calculations. Interestingly, the CH4 product can be formed more favorably on TM-N4 through the key intermediate of *HCOOH instead of the traditional *CO. Among all TM-N4 candidates, Mn-, Fe-, and Ru-N4 stand out with the low limiting potentials of −0.31, −0.42, and −0.30 V, respectively. The analysis of electronic structures and charge variation shed light on the CO2RR activity origin. Moreover, it is suggested that Mn-N4 and Ru-N4 possess high CH4 selectivity owing to the suppressed hydrogen evolution reaction (HER), while the dominant HER prohibits the CH4 formation on Fe-N4. This work will provide more insights into the underlying mechanism of CO2RR and promote the explorations of TM-N4 for CO2-to-CH4 conversion.