Atomic Fe–N4/C in Flexible Carbon Fiber Membrane as Binder-Free Air Cathode for Zn–Air Batteries with Stable Cycling over 1000 h

Noble-metal-free, durable, and high-efficiency electrocatalysts for oxygen reduction and evolution reaction (ORR/OER) are vital for rechargeable Zn–air batteries (ZABs). Herein, a flexible and free-standing carbon fiber membrane immobilized with atomically dispersed Fe–N 4 /C catalysts (Fe/SNCFs-NH 3 ) is synthesized and used as air cathode for ZABs. The intertwined fibers with hierarchical nanopores facilitate the gas transportation, electrolyte infiltration and electron transfer. The large specific surface area exposes a high concentration of Fe–N 4 /C sites embedded in the carbon matrix. Modulation of local atomic configurations by sulfur doping in Fe/SNCFs-NH 3 catalyst leads to excellent ORR and enhanced OER activities. The as-synthesized Fe/SNCFs-NH 3 catalyst demonstrates a positive half-wave potential of 0.89 V and a small Tafel slope of 70.82 mV dec –1 , outperforming the commercial Pt/C (0.86 V/94.74 mV dec –1 ) and most reported M–N x /C (M = Fe, Co, Ni) catalysts. Experimental characterizations and theoretical calculations uncover the crucial role of S doping in regulating ORR and OER activities. The liquid-state ZABs with Fe/SNCFs-NH 3 catalyst as air cathode deliver a large peak power density of 255.84 mW cm –2 and long-term cycle durability over 1000 h. Solid-state ZAB shows stable cycling at various flat/bent/flat states, demonstrating great prospects in flexible electronic device applications.