Zn‒air battery operated with a 3DOM trimetallic spinel (Mn0.5Ni0.5Co2O4) as the oxygen electrode

Abstract A bifunctional electrocatalyst for oxygen reactions based on a trimetallic spinel with three‒dimensionally ordered macroporous (3DOM) morphology was synthesized. The 3DOM structure was achieved using the colloidal‒crystal template method. The 3DOM material had a spinel‒like crystal structure with a Mn0.5Ni0.5Co2O4 trimetallic composition and a BET surface area of 67.74 m2 g‒1. The presence of three different metals with multiple valences in the same crystalline structure, the distribution of pores that facilitate mass transport, and the promotion of oxygen vacancies (Ov) resulted in a highly active bifunctional electrocatalyst for oxygen reduction (ORR) and evolution (OER) reactions. The 3DOM material presented a half‒wave potential (E1/2) of 0.76 V (vs. RHE) for the ORR and 1.63 V @ 10 mA cm−2 during the OER, obtaining a differential potential (ΔE = Ej=10 − E1/2) of ΔE = 0.87 V. In addition, the 3DOM catalyst possessed stability; it maintained 100% of its original current after 10 h for the ORR. It was found during the Zn‒air battery tests that the use of a trimetallic spinel enabled to obtain an open circuit voltage of 1.38 V and a maximum power density of 117 mW cm−2. Additionally, this spinel displayed excellent bifunctional behavior, with superior stability to benchmarked Pt/C and IrO2/C catalysts after being operated for 21 h during charge‒discharge processes.