In-situ enriching active sites on co-doped Fe-Co4N@N-C nanosheet array as air cathode for flexible rechargeable Zn-air batteries

The sluggish oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) kinetics in air cathode severely refrain the development of the reversible Zn-air battery. Herein, we report the design and synthesis of co-doped Fe-Co4N@N-C nanosheet array derived from MOF precursor on carbon cloth as the dual-functional electrocatalyst to boost the reaction kinetics. The Fe, N co-doping significantly promotes the generation of abundant Pyridinic-N-M active sites for ORR due to the strong coordination effect between metal center and pyridinic nitrogen. The enriched Co3+ sites concurrently motivate the formation of targeted *OOH intermediates during OER with decreased charge transfer resistance. Such electrocatalyst therefore delivers high catalytic activity for both ORR and OER. When applied as air cathode for liquid Zn-air battery, the device exhibits a high specific energy density of 934 Wh kg(-1) with excellent cycling stability, which is superior to the referenced Pt and Ru-based Zn-air batteries. Flexible solid-state Zn-air battery can also achieve a high volumetric power density of 72 mW cm(-3) and good cycling durability under different bending states. This work gives a facile and cost-efficient strategy to construct bifunctional flexible electrode with enriched active sites for Zn-air batteries.