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

Abstract

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° to 180°, underscoring their promising applications as durable bifunctional cathode for portable metal–air batteries.