Highly Dispersive Co@N-C Catalyst as Freestanding Bifunctional Cathode for Flexible and Rechargeable Zinc-air Batteries

The design of efficient cathode with great cycle performance, high flexibility, and low cost is essential for the commercialization of zinc-air battery (ZAB). Herein, we report the exploration of freestanding bifunctional cathode with rationally designed structures, namely, tiny Co nanoparticles embedded in N-doped carbon nanofiber aerogels, which have desired features including uniform Co dispersity, balanced distribution of N-C species, hierarchically porous structure with increased fraction of meso- to micropores, and moderate amounts of defects. Accordingly, the as-fabricated cathodes exhibit positive half-wave potential of 0.82 V for oxygen reduction and small overpotential of 350 mV at 10 mA cm(-2) for oxygen evolution, respectively, which deliver smaller reversible oxygen electrode index (0.76 V) than the commercial Pt/C+RuO2 (0.80 V) and most Co-based electrocatalysts ever reported. Impressively, the as-constructed liquid rechargeable ZAB behaves high peak power density (160 mW cm(-2)), large specific capacity (759.7 mAh g(-1) at 10 mA cm(-2), tested after 120 h of OCV tests), and robust stability over 277 h. Moreover, the as-assembled quasi-solid-state ZAB using such freestanding cathode represents excellent mechanical flexibility and outstanding cycle performance, regardless of being serviced under extremely bending conditions from 0 degrees to 180 degrees, underscoring their promising applications as durable bifunctional cathode for portable metal-air batteries.