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.

The exploration of cheap, efficient, and durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desired to push forward the commercialization of rechargeable metal–air batteries. Here, bifunctional ORR/OER electrocatalysts based on Co_xP (0 < x < 2, i.e., Co₂P, Co₂P/CoP mixture, and CoP) nanoparticles (NPs) anchored on N,P-doped carbon framework (Co_xP@NPC) are developed via one-step carbonization of the mixture of as-synthesized ZIF-67 and melamine–phytic acid supermolecular aggregate (MPSA). The stoichiometric ratio of resultant Co_xP NPs can be rationally designed by adjusting the introduced ratio of ZIF-67 to MPSA, enabling their fabrication in a controlled manner. It is found that the as-synthesized Co₂P@NPC exhibits the best bifunctional ORR/OER activity among the Co_xP@NPC analogues, with a reversible oxygen electrode index (ΔE = E_j10 − E_1/2) down to ~0.75 V. The constructed Zn–air battery based on Co₂P@NPC delivers a peak power density of 157 mW cm⁻² and an excellent charge-discharge stability with negligible voltage decay for 140 h at 10 mA cm⁻², superior to those based on Pt/C+RuO₂ and most Co_xP-based electrodes ever reported.