LAUSR

Exploring efficient and durable bifunctional catalysts in pH-universal media is urgent for versatile fuel cells. Herein, N-doped graphene nanotube-protected Fe-based species (Fe/Fe3C@N-G) are used for bifunctional oxygen electrocatalysts. The composite electrocatalyst exhibits a low potential gaps (ΔE, ΔE = Ej=10 - E1/2) in pH-universal environment. The estimated values are about 0.70 V, 1.07 V and 1.10 V in alkaline, neutral, and acidic media. Neutral Zn-air battery (ZAB) is constructed by the Fe/Fe3C@N-G composite as an air electrode, exhibiting a favorable performance in energy storage with an open-circuit potential (OCP) of 1.42 V and the high power density of 80 mW/cm2. The ZAB also has a superior cycling stability with only 0.5% decay more after 1200 charge-discharge cycles at 2 mA/cm2. While, the assembled ZAB in acidic media indicates an OCP of 1.40 V, power density of 23 mW/cm2 and 612 discharge/charge cycling. The ZAB is rechargeable which shows a cycling lifespan of 120 h. This work provides potential applications of Fe/Fe3C@N-G as the air electrodes for advanced pH-universal media based on Zn-air batteries for future energy storage devices.