Metal-organic-framework-derived Fe, Co, N-tri-dopped porous carbon as oxygen electrocatalysts for Zn-air batteries

To commercialize the rechargeable zinc-air (Zn-air) battery, it is desirable but challenging to design highly active, low-cost, stable, and earth-rich bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) to replace rare, expensive, and unstable noble-metal electrocatalysts. Herein, two MOFs are combined under electrostatic interaction and pressure by the way of Ball milling. Then, after post-processing including calcination, acid pickling, and N doping, the bimetal (Fe and Co) and N triple-doped porous carbon electrocatalyst (MIL/ZIF-4-700 °C-NH3) is prepared. Noteworthily, the MIL/ZIF-4-700 °C-NH3 has bimetallic active sites, high contents of pyridine N and graphite N, large surface area, mesoporous structure, and conductive carbon skeletons, which decide the excellent ORR performance. For ORR, the half-wave potential (E1/2 = 0.902 V vs. RHE) of MIL/ZIF-4-700 °C-NH3 is 27 mV higher than that of 20 wt% Pt/C (E1/2 = 0.875 vs. RHE). And the catalyst has also excellent methanol tolerance and stability. The Zn-air battery with MIL/ZIF-4-700 °C-NH3 as cathode catalyst has higher peak power density (176.5 mW cm−2) than that with 20 wt% Pt/C (141.8 mW cm−2) and 20 wt% Pt/C + RuO2 (94.4 mW cm−2) as cathode catalyst. Meanwhile, the Zn-air battery with MIL/ZIF-4-700 °C-NH3 as cathode catalyst exhibits perfect charge-discharge stability (longer than 540 h).