▎ 摘　　要

Structural modulation of the active site with atomic-level precision is of great importance to meet the activity and selectivity challenges that electrocatalysts are commonly facing. In this work, we have designed a metal (M)-nonmetal diatomic site embedded in graphene-like C2N (denoted as Mo-B@C2N), where the electrocatalytic N-2 reduction reaction (eNRR) was thoroughly explored using density functional theory combined with the computational hydrogen electrode method. Compared to M-M diatomic sites, the Mo-B site can generate a pronounced synergistic effect that led to eNRR proceeding via a novel quasi-dissociative reaction mechanism that has not been reported relative to the conventional enzymatic, consecutive, distal, and alternating associative mechanism. This newly uncovered mechanism in which N-N bond scission takes place immediately after the first proton-coupled electron transfer (PCET) step (i.e., *NH-*N + H+ + e(-) -> *NH2*N) has demonstrated much advantage in the PCET process over the four conventional mechanism in terms of thermodynamic barrier, except that the adsorption of side-on *N-2 seemed thermodynamically unfavorable (& UDelta;G(ads) = 0.61 eV). Our results have revealed that the activation of the inert N & EQUIV;N triple bond is dominated by the pi*-backdonation mechanism as a consequence of charge transfers from both the B and Mo sites and, unexpectedly, from the substrate C2N itself as well. Moreover, the hybrid Mo-B diatomic site demonstrated superior performance over either the Mo-Mo or B-B site for driving eNRR. Our study could provide insight into the delicate relationships among atomic site, substrate, and electrocatalytic performance. Published under an exclusive license by AIP Publishing.