Single Mo1(Cr1) Atom on Nitrogen-Doped Graphene Enables Highly Selective Electroreduction of Nitrogen into Ammonia

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 (M1) supported on nitrogen-doped graphene (N3-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 Mo1/N3-G and Cr1/N3-G as candidate electrocatalysts for nitrogen reduction reaction (NRR). The theoretically predicted selectivities (overpotentials) are 40% (0.34 V) and 100% (0.59 V) on Mo1/N3-G and Cr1/N3-G, respectively. The electroreduction of nitrogen proceeds via distal-to-alternating hybrid mechanism with two spectator dinitrogen molecules. The high stability, high selectivity to ammonia, and relatively low overpotentials for NRR suggest Mo1(Cr1)/N3-G as the most promising electrocatalyst among those studied for electroreduction of nitrogen.