▎ 摘　　要

Development of efficient bifunctional electrocatalysts for reversible oxygen reduction (ORR) and the oxygen evolution reaction (OER) is of prime importance in rechargeable metal-air batteries. In this work, a relatively unexplored and mechanistically unclear nickel-based catalyst has been explored as an ORR and OER catalyst using density functional theory (DFT) investigations. A detailed reaction mechanism involving four-coordination and three-coordination Ni-N-C configurations on a graphene substrate have been investigated, together with the effects of OH ligand binding on Ni-N-C-gra towards ORR and the OER. Through our simulations, we identified the existence of strong influences of the N and C co-ordination environment around the Ni atoms, and the OH ligand affinity determines the overall bifunctional ability of Ni-based catalyst systems. After a detailed analysis, the four-coordination NiC(4)shows excellent bifunctional catalytic potential (eta(ORR)= 0.48 V,eta(OER)= 0.40 V), while NiN3, NiN2C and NiNC(2)have excellent OER catalytic performance (eta(OER)= 0.23, 0.20 and 0.42 V). Analysis of the effects of OH ligand reveals that Ni(OH)N-3, Ni(OH)NC(2)and Ni(OH)C(3)show efficient ORR catalytic performance (eta(ORR)= 0.45, 0.43 and 0.42 V). The calculations in our study reveal that the co-ordination of N and C with Ni greatly affects the bifunctional activity; hence, fine tuning of the C and N contents is highly essential during the catalyst synthesis process.