Enhancing Oxygen Reduction Reaction Electrocatalytic Performance of Nickel-Nitrogen-Carbon Catalysts through Coordination Environment Engineering†

Abstract

Single-atom catalysts (SACs) have attracted significant attention due to their high atomic utilization and tunable coordination environment. However, the catalytic mechanisms related to the active center and coordination environment remain unclear. In this study, we systematically investigated the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalytic activities of NiN₄, NiN₃, NiN₃H₂, NiN₄X, NiN₃X, and NiN₃H₂X (X denotes axial ligand) through density functional theory (DFT) calculations. This study unveils two distinct reaction pathways for ORR and OER, involving proton-electron pairs adsorbed from both the solution and the catalyst surface. The overpotential is the key parameter to evaluate the catalytic performance when proton-electron pairs are adsorbed from the solution. NiN₃ and NiN₃H₂ show promise as pH-universal bifunctional electrocatalysts for both ORR and OER. On the other hand, when proton-electron pairs are adsorbed from the catalyst surface, the reaction energy barrier becomes the crucial metric for assessing catalytic activity. Our investigation reveals that NiN₃H₂ consistently exhibits optimal ORR activity across a wide pH range, regardless of the source of proton-electron pair (solvent or catalyst surface).