Computational screening of single transition-metal atoms anchored to g-C9N4 as catalysts for N2 reduction to NH3.

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-C9N4) monolayer has been systematically investigated. We find that TMs can bind tightly to g-C9N4 and form single-atom catalysts (SACs) with high thermodynamic stability. The four candidates, Nb, Ta, W and Re@g-C9N4, not only exhibit high NRR catalytic activity but also effectively inhibit the competitive HER. Among them, Nb@g-C9N4 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-C9N4 is via the enzymatic mechanism, while Ta@g-C9N4 tends to be through the distal mechanism. In addition, the decomposition potential of the g-C9N4 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.