▎ 摘　　要

Atomically dispersed metals and their environments strongly influence their electrocatalytic activities. In this work, we synthesized a series of cobalt/nitrogen doped graphene (Co-NG) catalysts. Cobalt atom dispersion and aggregation on NG's basal plane, bond states of cobalt and nitrogen along with graphene basal plane defect and their impacts on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities and kinetics were intensively studied. We found that a geometrically controlled formation of active Co-N and Co-C sites in the NG's basal plane is the key issue for improving interfacial Faradic reaction kinetics and thus enhancing hydrogen evolution. Differently, chemical bonding of finely dispersed cobalt atoms with oxygen, nitrogen and carbon together improves interfacial water oxidation kinetics for achieving high OER activity. (C) 2018 Elsevier Ltd. All rights reserved.