Efficient Construction of Heterogeneous Oxides as Robust Bifunctional Electrocatalysts for Zinc-Air Batteries

Metal-air batteries (MABs) have attracted considerable attention. However, the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of air cathode is severe which has obstructed the more extensively application. Here, this study proposes a facile method to obtain heterogeneous oxides catalyst for enhancing the oxygen electrode catalysis where multiple nanosize Co₃O₄, Mn₃O₄ and MnCo₂O₄ (CMMCO) are symbiotic. In this case, the concomitant mono-metal oxide can contribute to atomic ratio modulation effect on MnCo₂O₄ spinel such as Mn²⁺ to Mn³⁺,Co³⁺ to Co²⁺, resulting in Mn high-spin state transformation into low-spin state and oxygen vacancies, further optimizing the adsorption of intermediates. Obviously, built-in electric field at heterojunction interface dramatically facilitates electron transfer. Also, band-gap change determined by orbital overlap indicates the affinity with reactant. For the resulting CMMCO catalyst, an excellent half-wave potential of E_1/2 = 0.82 V for the ORR and low polarization potential (360 mV) for OER at 10 mA cm^-2 are achieved. Based on CMMCO cathodes, the assembled zinc air batteries demonstrate an impressive peak power density of 179 mW cm^-2 and cycling stability. The successful combination between heterogeneous interface regulation and efficient ORR/OER catalysis may provide a pivotal guideline for metal air batteries investigation with low-cost bifunctional catalyst.