Understanding the role of central metal and coordination environment of single atom catalysts embedded in graphene flakes on CO 2 RR performance

Single atom catalysts are promising for enhancing performance of electrocatalytic CO 2 reduction reaction (CO 2 RR). Herein, first-principle calculations were conducted to investigate the mechanism of two electron/proton transfers during CO 2 RR on two types of structures of single metal atom with four coordinated nitrogen atoms (M‒N 4 , M = Fe, Co, Ni, and Cu), namely metal phthalocyanine (MPc) and metal anchored nitrogen-containing carbon (M‒NC). Our results demonstrate that nitrogen-containing carbon plane effectively immobilizes and activates metal centers. The physical adsorption of CO 2 suggests that the initial activation of CO 2 proceeds through a concerted proton-electron transfer step. M‒NC surfaces exhibit higher favorability toward reactions of CO 2 → *COOH and CO 2 → *HCOO compared to MPc with the same metal center. Noteworthily, MPc structures featuring pyrrolic N coordination environment exhibit greater stability, whereas M‒NC with pyridinic N coordination environment demonstrate higher activity in the initial reduction of CO 2 . CoPc and Fe‒NC are the optical catalysts for achieving high CO 2 RR performance in the formation of CO and HCOOH, respectively. The strong binding of *COOH/*HCOO on catalyst can effectively reduce the reaction energy required for its subsequent reduction. The results of this study provide profound insights into the intricate coordination environment and the distinct role by various metal centers in M‒N x materials. Graphical abstract Both central metals and coordination environment of single atom catalysts have great influence on CO 2 RR. Metal anchored nitrogen-containing carbon catalysts are more favorable for activation of CO 2 while metal phthalocyanine catalysts exhibit higher stability. CoPc and Fe‒NC are the optical catalysts for achieving high CO 2 RR performance in the formation of CO and HCOOH, respectively.