Computational screening of single transition-metal atoms anchored to g-C 9 N 4 as catalysts for N 2 reduction to NH 3 .

The electrocatalytic nitrogen reduction reaction (NRR) is considered to be the most desirable strategy for ammonia production but still faces many challenges in terms of high activity and high selectivity. Based on density functional theory (DFT) calculations, the catalytic performance of a series of (3d, 4d and 5d series) transition metals atoms (TMs) anchored on a novel graphitic carbon-nitrogen (g-C 9 N 4 ) monolayer has been systematically investigated. We find that TMs can bind tightly to g-C 9 N 4 and form single-atom catalysts (SACs) with high thermodynamic stability. The four candidates, Nb, Ta, W and Re@g-C 9 N 4 , not only exhibit high NRR catalytic activity but also effectively inhibit the competitive HER. Among them, Nb@g-C 9 N 4 is the most promising NRR catalyst with a lowest limiting potential of -0.21 V. The optimal reaction path for Nb, W and Re@g-C 9 N 4 is via the enzymatic mechanism, while Ta@g-C 9 N 4 tends to be through the distal mechanism. In addition, the decomposition potential of the g-C 9 N 4 monolayer is higher than the limiting potential of all four SACs, ensuring the feasibility of the experimental implementation. This work identifies efficient NRR catalysts and provides a feasible screening scheme.