Fe3O4 Encapsulated in Porous Carbon Nanobowls as Efficient Oxygen Reduction Reaction Catalyst for Zn-Air Batteries

Abstract Zn-air batteries have received extensive attention because of their high energy density, environmental friendliness, low cost and safety. It is vital to develop cost-effective and stable electrocatalysts for oxygen reduction reaction for Zn-air batteries. Herein, Fe 3 O 4 encapsulated in porous carbon nanobowls (Fe 3 O 4 @PCN) for oxygen reduction reaction are prepared by simple soft-template approach and calcination subsequently. The optimized catalyst 4Fe 3 O 4 @PCN-800 with uniformly doped Fe 3 O 4 nanoparticles and large surface area exhibits excellent catalytic performance and long-term durability. It displays 66 mV higher half-wave potential (0.911 V) than that of 20 wt. % Pt/C catalysts in 0.1 M KOH electrolyte. It also shows excellent durability, only 5 mV attenuation of halfwave potential after 10,000 potential cycles. In addition, 4Fe 3 O 4 @PCN-800 possesses better methanol resistance than Pt/C, negligible current density fluctuation in the basic electrolyte with 3M methanol. Impressively, when being employed as a cathode catalyst in both aqueous and solid-state Zn-air batteries, 4Fe 3 O 4 @PCN-800 presents higher open-circuit voltage, higher capacity and peak power density, and more stable discharge voltage plateaus than those of Pt/C. Furthermore, the solid-state Zn-air batteries with the optimal synthesized catalyst exhibit encouraging flexibility, which have enormous potential in the application of flexible and wearable power sources.