•A facile route was developed to fabricate Co3O4@NMC OER/ORR catalysts.•Co3O4@NMC (1:3) exhibits a considerable ORR/OER activity and stability.•Accelerated kinetic charge transfer process is the main reason for catalysis. A nanocomposite with mesoporous Co3O4 loaded on nitrogen-doped mesoporous carbon (Co3O4@NMC) has been constructed by a facile post-grinding process. The electro-catalytic experimental results show that Co3O4@NMC (1:3) can be regarded as the low-cost alternative ORR/OER bi-functional catalyst compared with commercial noble Pt/C + IrO2 catalysts. The potential difference (ΔE) between between E1/2 and Ej10 for Co3O4@NMC (1:3) sample is only 21 mV larger. Moreover, we observed no obvious degeneration in both ORR and OER activity during ADT tests. The enhancement of electro-catalytic activity can be attributed to the effective charge transfer process as suggested by the Tafel analysis due to the synergistic effect.