Boosting bifunctional oxygen electrocatalysis with atomically dispersed Fe and Co dual-metal sites for flexible zinc-air batteries

Rechargeable zinc-air batteries (ZABs) hold enormous promise as energy conversion and storage system of the next generation. Here, through utilizing the Co/ZIF-8@F127 precursor and a coordinated strategy that includes 'post-absorption' and 'dual-pyrolysis', a Fe/CoNx-C possesses a hierarchical porous N-doped carbon with an ultrahigh specific area and rich defects to stabilize accessible dual metallic active sites. With a narrow potential gap of 0.71 V, the Fe/CoNx-C catalyst demonstrates excellent bifunctional electrocatalytic activity toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Noteworthily, scanning electrochemical microscopy (SECM) was used to visualize the local electrocatalytic ORR activity of CoNx-C and Fe/CoNx-C. For the applications of zinc-air batteries, the Fe/CoNx-C-based cathode provides a high peak power density of 134.97 mW cm-2 for aqueous ZABs. Moreover, quasi-solid-state ZABs (including flexible ZAB and cell ZAB)-based on Fe/ CoNx-C as cathode catalyst demonstrate satisfying flexibility and durability. The theoretical calculation results further elucidate the synergistic effect that the engagement of Fe atoms in the electron transfer process of the FeN4@CoN4 system reduces the energy barrier of the rate-determining-step in ORR and OER, hence facilitating the reversible oxygen electrocatalytic kinetics.