▎ 摘　　要

Downsizing the catalyst to atomic scale provides an effective way to maximize the atom efficiency and enhance activity for electrocatalysis. Here, we report a concept whereby graphene defects trap atomic Ni species (aNi) inside to form an integrity (aNi@defect). X-ray adsorption characterization and density-functional-theory calculation revealed that the diverse defects in graphene can induce different local electronic densities of state (DOSs) of aNi, which suggests that aNi@defect serves as an active site for unique electrocatalytic reactions. As examples, aNi@G585 is responsible for the oxygen evolution reaction (OER), and aNi@G5775 activates the hydrogen evolution reaction (HER). The derived catalyst exhibits exceptionally good activity for both HER and OER, e.g., an overpotential of 70 mV at 10 mA/cm(2) for HER (analogous to the commercial Pt/C) and 270 mV at 10 mA/cm(2) for OER (much superior to that of Ir oxide).