A Composite Bifunctional Oxygen Electrocatalyst for High-Performance Rechargeable Zinc-Air Batteries

Rechargeable zinc-air batteries are considered as next-generation energy storage devices because of their ultrahigh theoretical energy density of 1086 Wh kg^-1 (including oxygen) and inherent safety originating from the use of aqueous electrolyte. However, the cathode processes regarding oxygen reduction and evolution are sluggish in terms of kinetics, which severely limit the practical battery performances. Developing high-performance bifunctional oxygen electrocatalysts is of great significance, yet to achieve better bifunctional electrocatalytic reactivity beyond the state-of-the-art noble-metal-based electrocatalysts remains a great challenge. Herein, a composite Co₃ O₄ @POF (POF=framework porphyrin) bifunctional oxygen electrocatalyst is proposed to construct advanced air cathodes for high-performance rechargeable zinc-air batteries. The as-obtained composite Co₃ O₄ @POF electrocatalyst exhibits a bifunctional electrocatalytic reactivity of ΔE=0.74 V, which is better than the noble-metal-based Pt/C+Ir/C electrocatalyst and most of the reported bifunctional ORR/OER electrocatalysts. When applied in rechargeable zinc-air batteries, the Co₃ O₄ @POF cathode exhibits a reduced discharge-charge voltage gap of 1.0 V at 5.0 mA cm^-2 , high power density of 222.2 mW cm^-2 , and impressive cycling stability for more than 2000 cycles at 5.0 mA cm^-2 .