Heterogeneous Two-Atom Single-Cluster Catalysts for the Nitrogen Electroreduction Reaction

The electrocatalytic dinitrogen reduction reaction (NRR) is promising to realize the decentralized production of ammonia by using renewable energies, which contrasts with the energy-intensive Haber–Bosch process. The key to achieve it is to find stable, efficient and selective catalysts. Recently, the heterogeneous single-cluster catalysts (SCCs) have emerged as a promising class of catalysts for electrochemical reactions due to their atomically precise active site, abundant active atoms and atomic level controllability. Herein, the NRR catalyzed by the two-atom SCCs consisting of homonuclear 3d transition metal (TM) dimers over the N-doped graphene, denoted as M2-N6G, is systematically investigated by using density functional theory (DFT). Our results indicate that the ability of metal dimer to capture N2 is related to the reducibility of the catalyst and the orbital interaction between the N-2p states and the TM-3d states. Subsequently, comparing with those metals which overbind N2 through side-on configurations, the M2-N6G SCCs with end-on adsorption of N2 work better. Furthermore, we obtain a linear relationship between the adsorption free energies of *N2H (ΔadsG*NH2) and that of *NH2 (ΔadsG*NH2). Based on this scaling relationship, we propose a compromised strategy for screening efficient two-atom SCCs for NRR. Finally, by comparing the stability, activity and selectivity of various M2-N6G SCCs, the Cr2-N6G and Mn2-N6G are predicted to be most active for NRR with low limiting potential and high suppression to hydrogen evolution reaction (HER). The present work not only provides experimentally synthesizable electrocatalyst candidates for NRR, but also gives insight into the development of the two-atom SCCs.