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

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 SACsviadensity 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, MC(4)and MN(4)followed the same volcano curve of activity, where FeB(4)was optimal with a limiting potential of -0.55 V. On MB4, the H adsorption energies were weaker than on widely studied MC(4)and MN(4)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 FeB(4)at 0 Vvs.RHE, and hence the ammonia production should be more feasible than hydrogen evolution on FeB4. This work not only reported MB(4)as a potential NRR electrocatalyst, where FeB(4)was the most outstanding, but also generalized the descriptor-based approach to the rational design of widely studied SACs.