Tuning Single-Atom Catalysts of Nitrogen-Coordinated Transition Metals for Optimizing Oxygen Evolution and Reduction Reactions

Single-atom catalysts based on Earth-abundant elements have recently emerged as one of the most promising alternatives to the precious-metal-based catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Here, we use density functional theory calculations to investigate the OER and ORR catalytic activities of 3d single metal atoms coordinated by nitrogen atoms on carbon substrates. It is found that the adsorption energies of all reaction intermediates increase monotonically with the number of d electrons. By constructing the linear scaling relationships between the adsorption energies of reaction species, a volcano pattern is observed and the optimal conditions for high catalytic activity are obtained. Among the atom/substrate combinations, the Co atom on the pyridine-N-4 substrate exhibits the lowest theoretical overpotentials for both reactions. Furthermore, we propose that the trend in catalytic activity is mainly governed by the filling of the antibonding state between the metal atom and the reaction intermediate *O.