▎ 摘　　要

Exploration of sustainable electrocatalysts toward oxygen reduction reaction (ORR) with high catalytic activity remains a key challenge in the development of metal-air batteries and fuel cells. In this work, a hybrid electrocatalyst composed of cobalt (Co/CoOx) nanoparticles encapsulated in Co/N-doped mesoporous graphene (Co/CoOx@Co/N-graphene) is reported for efficient ORR catalysis. The catalyst is rationally designed and synthesized via a facile combination of spontaneous one-pot polymerization of dopamine in the presence of graphene oxide (GO) and Co2+ ions and the subsequent carbonization process. The morphology, doping nature and ORR activity of the as-prepared catalyst are systematically investigated. It is found that there are abundant Co/N active sites and Co/CoOx nanoparticles in this hybrid catalyst, leading to a synergistic enhancement effect for improved ORR activity. In an alkaline environment, this Co/CoOx@Co/N-graphene catalyst displays Pt/C-comparable ORR activity in terms of half-wave potential and four-electron reduction selectivity, and higher limiting current density, better methanol tolerant ability and long-term durability. When being evaluated in a Zn-air battery, it demonstrates superior performance to the commercial Pt/C catalyst.