▎ 摘　　要

Gaining mechanistic insights into the active site is essential to rational design of a high-performance cathode catalyst for the electrochemical CO2 reduction reaction (CO2 RR). Here, by means of density functional theory and computational hydrogen electrode methods, we investigated synergy of a metallic NiCo dimer anchored on a C2N graphene matrix for promoting the CO2 RR. It is found that heterometallic NiCo@C2N (U-L = -0.25 V) outperforms homometallic Co-2@C2N (U-L = -0.30 V) and Ni-2@C2N (U-L = -0.67 V) for catalyzing the CO2 RR toward CH4 formation owing to its synergy within the dimer. We emphasize the impact of co-adsorbed *H, *OH, and *CO intermediates on the CO2 RR, revealing that multiple competing reaction channels are accessible from viable co-adsorbates. Moreover, strongly-bound *H, *OH, and *CO intermediates are predicted not to deactivate metallic dimer sites for a continuous cycle of the CO2 RR Our study could provide a theoretical basis for optimizing a metallic dimer anchored on a N-doped graphene matrix for achieving a more advanced CO2 RR cathode with enhanced activity and selectivity.