Efficient synergistic effect of trimetallic organic frameworks derived as bifunctional catalysis for the rechargeable zinc-air flow battery

Precise design of oxygen electrode catalysts can alleviate the problems of slow kinetic reaction and high overpotential in the rechargeable zinc-air flow batteries (ZAFBs). Herein, an ideal 3D carbon-based material for FeCo alloy inlaid to Fe/Co and N co-doped bamboo-like carbon nanotubes (CNTs) is prepared by means of a one-pot high-temperature pyrolysis strategy of three metal organic frameworks (MOFs) mixed-precursors. The concentration of active metal species, the amount of conductive CNTs and the hierarchical porous structure with high specific surface area in this material are regulated. The optimal catalyst, Fe/12Zn/Co-NCNTs, demonstrates excellent electrochemical activity with a high half-wave potential of 0.879 V for oxygen reduction reaction (ORR) and low overpotential of 340 mV at 10 mA cm−2 for oxygen evolution reaction (OER) in the half-cell. Moreover, the smaller bifunctional ΔE value of Fe/12Zn/Co-NCNTs and Fe/(12Zn/Co)-NCNTs catalyst are 0.693 V and 0.717 V, respectively, less than the commercial Pt/C+IrO2 (ΔE = 0.77 V). The ZAFB yields a high open circuit voltage of 1.518 V, peak power density of 166 mW cm−2, and specific capacity of 809.1 mAh g−1 when employing Fe/12Zn/Co-NCNTs as air cathode because of the synergistic effect that improves both OER and ORR. More importantly, both Fe/12Zn/Co-NCNTs and Fe/(12Zn/Co)-NCNTs as the bifunctional catalysts produce a low charge-discharge voltage gap and high cycle lifespan of more than 320 h at 10 mA cm−2. This work provides a facile strategy for fabricating high-efficiency and low-cost bifunctional electrocatalysts for ZAFBs and other clean energy applications.