Long-Life Rechargeable Zn Air Battery Based on Binary Metal Carbide Armored by Nitrogen-Doped Carbon

Developing low-cost and high-performance bifunctional oxygen electrocatalysts is essential for commercial realization of regenerative fuel cells and rechargeable metal air batteries. Iron carbide (Fe3C) is an ideal electrocatalyst candidate; however, its poor oxygen evolution reaction (OER) activity and stability make it serve only as a unifunctional oxygen reduction reaction (ORR) electrocatalyst. Here, we report a robust bifunctional electrocatalyst consisting of manganese–iron binary carbide (MnxFe3–xC) nanoparticles armored by nitrogen-doped graphitic carbon (MnxFe3–xC/NC). Synthesis involved facile pyrolysis of a trimetallic (Fe, Mn, Zn) zeolitic imidazolate framework. Incorporation of Mn modulated the electronic properties of Fe3C and the surrounding carbon, enhancing ORR and OER activities. MnxFe3–xC, well-armored by carbon layers, displayed high resistance to oxidation and corrosion. The assembled Zn-air battery (ZAB) exhibited a large peak power density (160 mW cm–2 at 250 mA cm–2) with an energy density of up to 762 mWh gZn–1, high open-circuit voltage of 1.5 V, and impressive long-term stability over 1000 cycles, indicating that MnxFe3–xC is one of the most stable earth abundant (cobalt-free) bifunctional electrocatalysts for rechargeable ZABs currently available.