A series of efficient bifunctional electrocatalyst composed of nitrogen-doped graphene-cobalt oxide nanoparticles nano-hybrids (Co-N/G) are fabricated by one-pot hydrothermal synthesis, which involves in-situ growth of cobalt oxides nanocrystals and nitrogen doping into graphene. 2, 4, 6-Triaminopyrimidine used as nitrogen precursor could anchor cobalt oxides nanoparticles on graphene oxide as active centers for oxygen electrode reactions. The TEM, Raman, XRD and XPS confirm the germination of nitrogen doped graphene and nano-sized cobalt oxides. The optimized Co-N/G catalyst consists of the highest contents of pyridinic nitrogen and CoO, which efficiently catalyze both ORR and OER. The strong coupling between cobalt oxides and N-graphene endows Co-N/G 600 with a low reversible overvoltage of 0.96 V between ORR and OER in alkaline medium, which is superior to novel catalysts such as Pt/C (1.24 V), IrO2 (1.43 V) and RuO2 (1.35 V), rendering it bi-catalyst efficient and economical for reversible oxygen electrode reactions. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.