Defect Engineering toward Atomic Co-N_x -C in Hierarchical Graphene for Rechargeable Flexible Solid Zn-Air Batteries

Rechargeable flexible solid Zn-air battery, with a high theoretical energy density of 1086 Wh kg^-1 , is among the most attractive energy technologies for future flexible and wearable electronics; nevertheless, the practical application is greatly hindered by the sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics on the air electrode. Precious metal-free functionalized carbon materials are widely demonstrated as the most promising candidates, while it still lacks effective synthetic methodology to controllably synthesize carbocatalysts with targeted active sites. This work demonstrates the direct utilization of the intrinsic structural defects in nanocarbon to generate atomically dispersed Co-N_x -C active sites via defect engineering. As-fabricated Co/N/O tri-doped graphene catalysts with highly active sites and hierarchical porous scaffolds exhibit superior ORR/OER bifunctional activities and impressive applications in rechargeable Zn-air batteries. Specifically, when integrated into a rechargeable and flexible solid Zn-air battery, a high open-circuit voltage of 1.44 V, a stable discharge voltage of 1.19 V, and a high energy efficiency of 63% at 1.0 mA cm^-2 are achieved even under bending. The defect engineering strategy provides a new concept and effective methodology for the full utilization of nanocarbon materials with various structural features and further development of advanced energy materials.