Hierarchical cobalt-nitrogen-doped carbon composite as efficiently bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

•A bifunctional carbon-based catalyst with heavy nitrogen content was fabricated.•Hierarchically microporous structure was constructed.•Cobalt element well dispersed in the catalyst.•The catalyst exhibits excellent ORR and OER catalytic activity in alkaline electrolyte.•Zn-air battery shows superior performance with excellent durability and rechargeability.