▎ 摘　　要

Metal-air battery, represented by zinc-air battery (ZAB), is recognized as a promising secondary battery technology with great energy density. Since the catalyst in the air-electrode must simultaneously catalyze oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), mass transfer structure of the air-electrode catalyst would significantly affect the ZAB performance. A facile selectively etching strategy is therefore proposed to in situ adjusting the mass transfer structure of the CoFe OER/ORR bi functional catalyst encapsulated in graphene cage. This graphene encapsulated CoFe catalyst with optimized mass transfer channel exhibits superior OER and ORR activity to IrO2 and Pt/C, respectively. The corresponding ZAB performance is therefore tripled compared with that equipped with Pt/C-IrO2 catalysts in terms of maximum power density (206 mW/cm(2)). Together with the satisfied stability, this facilely synthesized CoFe catalyst shows promising application potential in metal-air batteries. (C) 2020 Elsevier Ltd. All rights reserved.