Bifunctional CoNx embedded graphene electrocatalysts for OER and ORR: A theoretical evaluation

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.