Fe-based species anchored on N-doped carbon nanotubes as a bifunctional electrocatalyst for acidic/neutral/alkaline Zn–air batteries

Exploring efficient and durable bifunctional catalysts in pH-universal media is critical for versatile fuel cells. Herein, Fe-based species anchored on N-doped carbon nanotubes (Fe/Fe3C@N-C) are used for bifunctional oxygen electrocatalysts. The composite electrocatalyst exhibits low potential gaps (ΔE, ΔE = Ej=10 - E 1/2) in a pH-universal environment. The estimated values are about 0.70, 1.07,and 1.10 V in alkaline, neutral, and acidic medias. A neutral Zn-air battery (ZAB) is constructed using an Fe/Fe3C@N-C composite as the air electrode, which exhibits a favorable performance in energy storage with an open-circuit potential (OCP) of 1.42 V and a high power density of 80 mW cm-2. The ZAB also has superior cycling stability with only a 0.5% decay after 1200 charge-discharge cycles at 2 mA cm-2. While the assembled ZAB in acidic media indicates an OCP of 1.40 V, a power density of 23 mW cm-2, and 612 discharge-charge cycles. The ZAB is rechargeable and has a cycling lifespan of 120 h. This work provides potential applications of Fe/Fe3C@N-C as air electrodes for advanced pH-universal media based on ZABs for future energy storage devices.