Single-, double-, and triple-atom catalysts on graphene-like C2N enable electrocatalytic nitrogen reduction: insight from first principles

Abstract

The electrocatalytic nitrogen reduction reaction (eNRR) is widely regarded as a viable route to artificial N₂ fixation towards NH₃ production under ambient conditions. Herein, using density functional theory and the computational hydrogen electrode method, we systematically explored the eNRR on M_n@C₂N (M = Fe, Co, Ni, Cr, Mo, and W; n = 1, 2, and 3), representing single-, double-, and triple-atom catalysts on graphene-like C₂N. Our results demonstrate that *NH_x intermediates on M_n@C₂N are highly stable for n = 3 and unstable for n = 1, rendering M₂@C₂N as the optimal candidate for driving the eNRR due to its moderate binding with NH_x (x = 0, 1, 2, 3). With the ensemble size of M_n increasing from n = 1 to 3, the N-affinity of active sites can be enhanced to a certain extent, constrained by the oxidation state of M_n^δ+. The limiting potential (U_L) of the eNRR yields a well-defined trend on either the M₁ (i.e., MN₂) or M₂ (i.e., N₃MMN₃) active site and is critically dependent on the N-affinity of M_n^δ+, contrasting to that (U_L) on the M₃ site which is both metal- and ensemble-size-dependent. Our study provides theoretical guidance for rational design of atomic active sites driving efficiently the eNRR.