Thermally tuning FeCoNiCrMn high-entropy alloy in carbon nanofibers for superior bifunctional oxygen electrocatalysis toward flexible zinc-air batteries.

Developing efficient, durable, and low cost bifunctional oxygen electrocatalysts remains a key challenge for the commercialization of flexible zinc-air batteries (ZABs). Herein, a strategy is reported that enables the in situ confinement of FeCoNiCrMn high-entropy alloy (HEA) nanoparticles within electrospun carbon nanofibers (CNFs) through combined electrospinning and controlled graphitization. Thermal optimization reveals that the sample carbonized at 800 °C (FeCoNiCrMn/CNFs-800) attains an optimal balance between graphitization, crystallinity, and active-site accessibility, resulting in exceptional bifunctional activity. FeCoNiCrMn/CNFs-800 exhibits superior oxygen evolution reaction (OER) performance with a low overpotential of 230 mV at 10 mA cm-2, outperforming commercial RuO2. It also demonstrates outstanding oxygen reduction reaction (ORR) activity, featuring a half-wave potential of 0.80 V, which yields a remarkably small bifunctional overpotential gap (ΔE) of only 0.66 V. When integrated as an air cathode in a flexible ZAB, FeCoNiCrMn/CNFs-800 endows the device with a peak power density of 88 mW cm-2, a specific capacity of 826 mAh gZn-1, and durable cycling stability exceeding 88 h at 5 mA cm-2. This work highlights the critical role of thermal regulation in tailoring HEA/carbon composites and provides an effective materials design strategy for next-generation flexible energy storage devices.