Co<sub>3</sub>Fe<sub>7</sub> Alloy Nanoparticles Encapsulated\nin N‑Doped Carbon as Oxygen-Reduction Electrocatalysts for\nRechargeable Zinc-Air Batteries

Bimetallic alloy catalysts have become highly sought-after\nstar\ncatalysts in the oxygen reduction reaction (ORR) due to their excellent\ncatalytic activity and stability. In this study, an optimal catalyst\n(Co<sub>3</sub>Fe<sub>7</sub>@NC-800) involving Co<sub>3</sub>Fe<sub>7</sub> alloy nanoparticles encapsulated by N-doped carbon shield\nwas constructed by employing Co-ZIF and <i>g</i>-C<sub>3</sub>N<sub>4</sub> assisted with Fe ions as source precursors through\nan impregnation-calcination method. The catalyst demonstrates a remarkable\n4e<sup>–</sup> ORR activity in alkaline electrolyte with a\nhigh half-wave potential (<i>E</i><sub>1/2</sub>) of up\nto 0.94 V, a large limiting current density (<i>J</i><sub>L</sub>) of 5.81 mA·cm<sup>–2</sup>, and good durable\nstability, surpassing the benchmark Pt/C catalyst. It simultaneously\ndisplays moderate oxygen evolution reaction (OER) activity with an\noverpotential of 355.6 mV at 10 mA·cm<sup>–2</sup> (<i>E</i><sub>J=10</sub>). Driven by a small oxygen potential gap\nΔ<i>E</i> of 0.646 V, the rechargeable zinc-air battery\n(ZAB) applied this catalyst as air cathode delivers a high power density\nof 141.7 mW·cm<sup>–2</sup> and specific capacity of 800\nmAh·g<sub>Zn</sub><sup>–1</sup>, an excellent rate capability,\nand a good cycling stability over 200 h at 5 mA·cm<sup>–2</sup>. The superior ORR activity and good ZAB performance perhaps result\nfrom the synergy of abundant available active sites mediated by Co<sub>3</sub>Fe<sub>7</sub> bimetallic alloy nanoparticles and N-doped\ncarbon defects. This work will expand the application of non-noble\nmetal ORR catalysts for future metal-air batteries in energy systems.