▎ 摘　　要

Single Mn atom on nitrogen-doped graphene (MnN4-G) has exhibited good structural stability and high activity for the adsorption and dissociation of an O-2 molecule, becoming a promising single-atom catalyst (SAC) candidate for oxygen reduction reaction (ORR). However, the catalytic activity of MnN4-G for the ORR and the optimal reaction pathway remain obscure. In this work, density-functional theory calculations were employed to comprehensively investigate all the possible pathways and intermediate reactions of the ORR on MnN4-G. The feasible active sites and the most stable adsorption configurations of the intermediates and transition states during the ORR were identified. Screened from all the possibilities, three optimal four-electron O-2 hydrogenation pathways with an ultralow energy barrier of 0.13 eV were discovered that are energetically more favorable than direct O-2 dissociation pathways. Analysis of the free energy diagram further verified the thermodynamical feasibility of the three pathways. Thus, MnN4-G possesses superior ORR activity. This study provides a fundamental understanding of the design of highly efficient SACs for the ORR.