Fe/Fe₂O₃ nanoparticles anchored on Fe-N-doped carbon nanosheets as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Electrocatalysts with high catalytic activity and stability play a key role in promising renewable energy technologies, such as fuel cells and metal-air batteries. Here, we report the synthesis of Fe/Fe₂O₃ nanoparticles anchored on Fe-N-doped carbon nanosheets (Fe/Fe₂O₃@Fe-N-C) using shrimp shell-derived N-doped carbon nanodots as carbon and nitrogen sources in the presence of FeCl₃ by a simple pyrolysis approach. Fe/Fe₂O₃@Fe-N-C obtained at a pyrolysis temperature of 1, 000 ℃ (Fe/Fe₂O₃@Fe-N-C-1000) possessed a mesoporous structure and high surface area of 747.3 m²·g^-1. As an electrocatalyst, Fe/Fe₂O₃@Fe-N-C-1000 exhibited bifunctional electrocatalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline media, comparable to that of commercial Pt/C for ORR and RuO₂ for OER, respectively. The Zn-air battery test demonstrated that Fe/Fe₂O₃@Fe-N-C-1000 had a superior rechargeable performance and cycling stability as an air cathode material with an open circuit voltage of 1.47 V (vs. Ag/AgCl) and a power density of 193 mW·cm^-2 at a current density of 220 mA·cm^-2. These performances were better than other commercial catalysts with an open circuit voltage of 1.36 V and a power density of 173 mW·cm^-2 at a current density of 220 mA·cm^-2 (a mixture of commercial Pt/C and RuO₂ with a mass ratio of 1:1 was used for the rechargeable Zn-air battery measurements). This work will be helpful to design and develop low-cost and abundant bifunctional oxygen electrocatalysts for future metal-air batteries.