Regulating the coordination environment through doping N atoms for single-atom Mn electrocatalyst of N2 reduction with high catalytic activity and selectivity: A theoretical study

Electrochemical N-2 reduction reaction (NRR) is a promising way for ammonia synthesis, and developing novel electrocatalyst with high catalytic activity and selectivity is an urgent matter. Herein, the catalytic performances of single-atom Mn catalysts supported with nitrogen-doped graphene substrates (Mn-sA@V-x-N-y, x = s, d. y = 0, 1, 2, 3, 4.) for NRR have systematically investigated through density functional theory (DFT) calculations. The catalytic activity and selectivity of Mn-sA@V-x-N-y were discussed through reaction path, Gibbs free energy variation, hydrogen evolution reaction (HER), electron transfer and projected density of states. The result reveals the adsorption energy of N-2 and catalytic activity of Mn-sA@V-x-N-y were effectively regulated through modulating the coordination environment of Mn atom. Mn-sA@V-s-N-1 has the highest catalytic activity and selectivity among all studied catalysts for NRR at room temperature. Mn-sA@V-s-N-1 can facilitate NRR by the distal mechanism, and the potential determining step is *N-2 + H+ + e(-) ->*NNH with a free energy variation of 0.77 eV. Simultaneously, HER is suppressed by the high selectivity of N-2 adsorption on Mn-sA@V-s-N-1. This adjusting method can provide a guideline for developing robust electrocatalyst for NRR.