▎ 摘　　要

The bifunctional catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of importance to the development of electrochemical energy systems such as reversible fuel cells, metal-air batteries, and water electrolyzers. Here, using the first-principles methods based on density functional theory (DFT), the Co and N codoped graphene systems (CoNx-gra, x = 1-4) with high ORR activity were further suggested as efficient OER catalysts. It was found that the activity on Co site of CoNx-gra towards ORR and OER would be affected by both the N-dopant concentration and configuration. The extrapolated overpotential of 0.37 V for either ORR or OER on CoNx-gra systems is comparable to those of noble metal benchmark catalysts. The origin of the activity stems from moderate hybridization between Co 3d orbital and p-orbital from O species, governed by the neighboring N coordination environment. Our results highlight the potential application of transition metal and non-metal codoped graphene as efficient non-precious bifunctional catalysts. (C) 2018 Elsevier Ltd. All rights reserved.