▎ 摘　　要

The development of nonprecious metal catalysts with highly efficient and durable activities is of great importance for high performances of zinc-air batteries. Herein, the N-doped graphene wrapped Fe3C/Fe2O3 heterostructure has been designed as a bifunctional oxygen catalyst for zinc-air batteries. In the synthesis process of the catalyst, graphene oxide (GO) can assemble with graphitic carbon nitride (g-C3N4) and FeOOH nanorods by the pi-pi stacking and hydrogen bonds, respectively. The assembly of GO, g-C3N4 and FeOOH nanorods results in nanostructure of carbon layers coated iron species and leads to outstanding durability in both alkaline and acidic media. The synergistic effect of nitrogen doping and Fe3C/Fe2O3 heterostructure allows the catalyst (Fe3C/Fe2O3@NGNs) to display high oxygen reduction and evolution reaction activities. The liquid zinc-air battery assembled with the catalyst presented a remarkable peak power density (139.8mWcm(-2)), large specific capacity (722 mAh g(-1)) and excellent charging-discharging cycling performance. The quasi-solid-state zinc-air battery with the catalyst exhibited an impressive open-circuit voltage and a peak power density. Therefore, the Fe3C/Fe2O3@NGNs catalyst is expected to have a bright future for practical applications in energy conversion devices. (C) 2019 Elsevier Ltd. All rights reserved.