▎ 摘　　要

Development of earth-abundant, efficient and stable catalysts for hydrogen evolution reaction (HER), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysis is an important subject in replacing precious metals to solve energy and environmental issues. Herein, we report a highly active trifunctional electrocatalyst for hydrogen and oxygen electrodes comprising Co/CoOx nanoparticles embedded onto nitrogen-doped carbon-graphene obtained by the pyrolysis of graphene oxide supported cobalt metal-organic framework (ZIF-67) under a nitrogen atmosphere. The as-prepared Co@NC-G-700 catalyst shows robust and highly active HER in both acid and base electrolyte with low overpotential (140 and 136 mV at 10 mA cm(-2), respectively). In addition, this catalyst exhibits excellent ORR performance, including a positive half-wave potential (similar to 0.83 V vs RHE), a low Tafel slope of 47.9 mV dec(-1), outstanding stability, and strong tolerance to CH3OH crossover. Furthermore, Co@NC-G-700 displays a good oxygen evolution reaction activity in alkaline media with an overpotential of only 322 mV at a current density of 10 mA cm(-2). The surface Co-N-x sites should be responsible for the efficient HER and ORR, while Co-O-Co, Co-N-C, and Co-O-C sites might work together in OER. (C) 2018 Elsevier Ltd. All rights reserved.