A Facile and Scalable Strategy for Fabrication of Superior Bifunctional Freestanding Air Electrodes for Flexible Zinc-Air Batteries

The large-scale fabrication of efficient and inexpensive bifunctional catalysts is highly desirable but very challenging for oxygen reduction reaction and oxygen evolution reaction (ORR-OER) in metal-air batteries. Here, a facile and scalable approach for the fabrication of hierarchically porous air electrode consisting of cobalt nanoparticles embedded in bamboo-like nitrogen-rich carbon nanotubes (Co/N@CNTs), which are in situ grown onto the surface of carbon nanotube macrofilm (CNMF) through a catalytic growth of crosslinked carbon nanotubes is reported. The resulting hybrid macrofilm (Co/N@CNTs@CNMF) can be directly used as a freestanding air electrode without adding any binder or addivities. More importantly, when incorporated in a zinc-air battery (ZAB), the Co/N@CNTs@CNMF electrode demonstrates drastically enhanced ORR and OER activity while maintaining excellent durability during cycling. Further, when it is used to assemble an all-solid-state ZAB, the cell also displays excellent mechanical flexibility, implying promising perspectives as power sources for wearable electronics.