It is of great significance to explore a bifunctional catalyst that can produce both hydrogen and oxygen to accelerate the development of water-splitting technology. In this work, Co@CoO/NG was obtained via calcinating ZIF-67 and in-situ preparation process, which exhibited excellent performance (water oxidation AQE 10.22% at lambda = 450 nm and oxygen production rate 543198 mu mol g(-1) h(-1) and hydrogen production rate 330 mu mol g(-1) h(-1)). A comprehensive analysis of SEM, XRD, TEM, UV-vis, EIS, and PL showed that Co@CoO/NG-7 prepared has a perfect skeleton and more crystal defects, which can provide more reactive sites. The core-shell structure Co@CoO has a synergistic effect with graphene, which is beneficial to the light absorption, separation of photo-generated charges. Meanwhile, cyclic experiments of water oxidation and water reduction showed that the catalyst exhibited high stability during the reaction process. This study has provided a universal strategy to design efficient bifunctional catalyst for water-splitting. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.