Synergistic effect of diatomic Mo–B site confined in graphene-like C2N enables electrocatalytic nitrogen reduction via novel mechanism

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 N2 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 *N2 seemed thermodynamically unfavorable (ΔGads = 0.61 eV). Our results have revealed that the activation of the inert N≡N triple bond is dominated by the π*-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.