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-NH3) 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-NH3 catalyst leads to excellent ORR and enhanced OER activities. The as-synthesized Fe/SNCFs-NH3 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-NH3 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.

Automated summary

In this study, a Fe-N-4/C catalyst immobilized on a carbon fiber membrane was synthesized, showing excellent catalytic activity for oxygen reduction and evolution reactions through sulfur doping to modulate atomic configurations. The catalyst demonstrated superior electrochemical performance and cycling stability, outperforming commercial Pt/C and most reported M-N-x/C catalysts. The findings offer promising prospects for flexible electronic device applications.