The rational design of single-atom catalysts for electrochemical ammonia synthesis via a descriptor-based approach

Abstract

Single-atom catalysts (SACs) have been widely studied in electrocatalysis towards renewable energy conversion. Herein, we present a general descriptor-based strategy for the rational design of SACs via density functional theory calculations. Taking the electrochemical nitrogen reduction reaction (NRR) as an example, we firstly revealed the scaling relations for adsorption energies of intermediates on a series of 4-B (MB₄), 4-C (MC₄) and 4-N (MN₄) coordinated SACs. Based on this, the activity of the NRR was described by the adsorption free energy of *NH. It's found that MB₄, MC₄ and MN₄ followed the same volcano curve of activity, where FeB₄ was optimal with a limiting potential of −0.55 V. On MB₄, the H adsorption energies were weaker than on widely studied MC₄ and MN₄ due to the highly occupied H 1s–d antibonding state, which resulted in a higher NRR selectivity of MB₄. More strikingly, kinetic calculations suggested that the activation energy of the NRR (0.99 eV) is lower than that of the HER (1.10 eV) on FeB₄ at 0 V vs. RHE, and hence the ammonia production should be more feasible than hydrogen evolution on FeB₄. This work not only reported MB₄ as a potential NRR electrocatalyst, where FeB₄ was the most outstanding, but also generalized the descriptor-based approach to the rational design of widely studied SACs.