Electrospun MOF-Based FeCo Nanoparticles Embedded in Nitrogen-Doped Mesoporous Carbon Nanofibers as an Efficient Bifunctional Catalyst for Oxygen Reduction and Oxygen Evolution Reactions in Zinc-Air Batteries

Low-price, high-performance and strong-stability electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly significant in the application of clean energy devices like rechargeable zinc-air batteries and renewable fuel cells. In this paper, a Prussian blue analogue Co3[Fe(CN)6]2·nH2O (Co-Fe PBA), as a well-known member of the metal–organic framework family, was electrospun into polyacrylonitrile (PAN) nanofibers to obtain composite Co-Fe PBA@PAN nanofibers. Nitrogen-doped carbon nanofibers encapsulated FeCo alloy nanoparticles (FeCo-NCNFs-Ts, T = 700, 800, 900 °C) were synthesized by pyrolysizing Co-Fe PBA@PAN precursor at different temperatures under an argon atmosphere. The effects of different calcination temperatures and mass ratios between Co-Fe PBA and PAN on ORR/OER catalytic activity were explored. Among FeCo-NCNFs-Ts, FeCo-NCNFs-800 had the highest bifunctional electrocatalytic performance with a lower reversible overvoltage of 0.869 V between ORR (E1/2) and OER (Ej = 10 mA cm–2), excellent stability and methanol durability, which even exceeded those of Pt/C and RuO2. The superb bifunctional activity for FeCo-NCNFs-800 was comparable to that of non-noble electrocatalysts reported in recent literatures. Moreover, the zinc-air battery based on the FeCo-NCNFs-800 air-cathode catalyst had a high power density of 74 mW cm–2 and strong cycling stability (125 cycles for 42 h), which can be comparable to a Pt/C-RuO2 zinc-air battery. The impressive bifunctional activity on ORR and OER for the FeCo-NCNFs-800 catalyst in the zinc-air battery can be attributed to the synergistic effects of the one-dimensional fibrous structure, FeCo alloy nanoparticles, Co-N (pyridinic-N) active sites, and numerous mesopores.