Defect-rich carbon fiber electrocatalysts with porous graphene skin for flexible solid-state zinc-air batteries

Rechargeable flexible Zn-air batteries have attracted great attentions as promising next-generation energy storage devices for portable and wearable electronics. Bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts on the air electrode are critical for improving the energy storage performance of Zn-air batteries. Free-standing electrocatalysts with superb OER/ORR reactivity render promising flexible power sources for the wearable and stretchable devices. In this contribution, a metal-free electrocatalyst based on surface modification of flexible carbon cloth is proposed. A coaxial cable-like structure with carbon fiber skeleton coated by nanostructured porous and defect-rich graphene skin is in situ fabricated through a facile H-2 etching approach. With abundant heteroatoms and defects as active sites, the nanocarbon shells coated carbon cloth exhibits excellent OER/ORR bifunctional activity. The OER and ORR current densities on graphene skin modified carbon fiber are 20 and 3 times higher than those of pristine carbon cloth, respectively. This emerging carbon cloth derived electrocatalyst with porous graphene skin also serves as the air electrode in a rechargeable flexible solid-state Zn air battery with polymer gel electrolyte, and demonstrates stable charge/discharge cycling even under bending. This strategy of constructing nanostructures directly on carbon fibers benefits the rational design of flexible and functionalized materials for electrocatalytic energy applications.