Hierarchically Designed 3D Holey C2N Aerogels as Bifunctional Oxygen Electrodes for Flexible and Rechargeable Zn-Air Batteries.

The future of electrochemical energy storage spotlights on the designed formation of highly efficient and robust bifunctional oxygen electrocatalysts that facilitate advanced rechargeable metal-air batteries. We introduce a scalable facile strategy for the construction of a hierarchical three-dimensional sulfur-modulated holey C2N aerogels (S-C2NA) as bifunctional catalysts for Zn-air and Li-O2 batteries. The S-C2NA exhibited ultrahigh surface area (∼1943 m2 g-1) and superb electrocatalytic activities with lowest reversible oxygen electrode index ∼0.65 V, outperforms the highly active bifunctional and commercial (Pt/C and RuO2) catalysts. Density functional theory and experimental results reveal that the favorable electronic structure and atomic coordination of holey C-N skeleton enable the reversible oxygen reactions. The resulting Zn-air batteries with liquid electrolytes and the solid-state batteries with S-C2NA air cathodes exhibit superb energy densities (958 and 862 Wh kg-1), low charge-discharge polarizations, excellent reversibility, and ultralong cycling lives (750 and 460 h) than the commercial Pt/C+RuO2 catalysts, respectively. Notably, Li-O2 batteries with S-C2NA demonstrated an outstanding specific capacity of ∼648.7 mA h g-1 and reversible charge-discharge potentials over 200 cycles, illustrating great potential for commercial next-generation rechargeable power sources of flexible electronics.