▎ 摘　　要

Searching for new types of electrocatalysts with high stability, activity, and selectivity is essential for the production of ammonia via electroreduction of nitrogen. Using density functional theory (DFT) calculations, we explore the stability of single metal atoms (M-1) supported on nitrogen-doped graphene (N-3-G); the competitive adsorption of dinitrogen and hydrogen; and the potential competition of first dinitrogen protonation and hydrogen adsorption on metal sites. Consequently, we identify Mo-1/N-3-G and Cr-1/N-3-G as candidate electrocatalysts for nitrogen reduction reaction (NRR). The theoretically predicted selectivities (over-potentials) are 40% (0.34 V) and 100% (0.59 V) on Mo-1/N-3-G and Cr-1/N-3-G, respectively. The electroreduction of nitrogen proceeds via distal-toalternating hybrid mechanism with two spectator dinitrogen molecules. The high stability, high selectivity to ammonia, and relatively low overpotentials for NRR suggest Mo-1, (Cr-1)/N-3-G as the most promising electrocatalyst among those studied for electroreduction of nitrogen.