The rational exploitation of non-precious metal catalyst with high activity,strong durability and low cost for the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is of vital importance for metal-air batteries.Herein,a composite of Co3O4 nanoparticles confined in three-dimensional(3D)N-doped porous carbon(Co-NpCs)was prepared by a simple freeze-drying and in situ pyrolysis method.The effect of different dosages of Co(NO3)2 on the catalytic performance was discussed.The Co-NpC-12％exhibits the best catalytic performance(E1/2= 0.78 V,better stability than 20％Pt/C)in ORR and in OER among all the as-synthesized samples.Furthermore,it also exhibits the best bifunctional activity(AE = 0.849 V).The excellent properties of Co-NpCs are mainly due to the synergy between Co3O4 and carbon.Firstly,a high Co3O4 loading amount can boost the defect level of the N-doped hierarchical porous carbon and expose more active sites.Secondly,the unique in situ pyrolysis guarantees a large-area contact between Co3O4 and carbon as well as a strong C-O-Co bonding,which promotes charge transfer,avoids the peeling of Co3O4 nanoparticles and effectively improves the stability of the material.This work is expected to offer a feasible strategy to produce metal oxide/carbon nanocomposite and push forward the devel-opment of bifunctional electrocatalyst with high activity and stability.