Hierarchical CoO Nano-Micro Arrays Featuring Superior Activity as Cathode in a Flexible and Rechargeable Zinc-Air Battery.

All-solid-state zinc-air batteries are characterized as low cost and have high energy density, providing wearable devices with an ideal power source. However, the sluggish oxygen reduction and evolution reactions in air cathodes are obstacles to its flexible and rechargeable application. Herein, a strategy called MOF-on-MOF (MOF, metal-organic framework) is presented for the structural design of air cathodes, which creatively develops an efficient oxygen catalyst comprising hierarchical CoO nanoparticles anchored in nitrogen-doped carbon nano-micro arrays on flexible carbon cloth (CoO@N-CNMAs/CC). This hierarchical and free-standing structure design guarantees high catalyst loading on air cathodes with multiple electrocatalytic activity sites, undoubtedly boosting reaction kinetics, and energy density of an all-solid-state zinc-air battery. The integrated CoO@N-CNMAs/CC cathode in an all-solid-state zinc-air battery exhibits a high open circuit potential of 1.461 V, a high capacity of 815 mAh g Zn at 1 mA cm, a high energy density of 1010 Wh kg Zn, excellent cycling stability as well as outstanding mechanical flexibility, significantly outperforming the Pt/C-based cathode. This work opens a new door for the practical applications of rechargeable zinc-air batteries in wearable electronic devices.