NiMn2O4-based Ni-Mn bimetallic oxides as electrocatalysts for the oxygen reduction reaction in Al–air batteries

To date, research on air battery catalysts has been mainly focused on finding materials with a high oxygen reduction reaction (ORR) catalytic activity. However, the high cost of platinum catalysts restricts their commercialization. Herein, we report a simple hydrothermal-calcination method to fabricate low-cost NiMn2O4 -based Ni-Mn bimetallic oxides. The Ni-Mn-600 sample showed a high onset potential (1.01 V vs. RHE), which was more positive than that for 20 wt% Pt/C (0.97 V vs. RHE), and its half-wave potential (0.78 V vs. RHE) was comparable to that for 20 wt% Pt/C (0.84 V vs. RHE). Moreover, Ni-Mn-600 as an Al-air battery air–cathode catalyst exhibited a high discharge plateau of 1.42 V and peak power density of 100.45 mW cm−2, which outperformed those for 20 wt% Pt/C (1.34 V and 76.10 mW cm−2). The high ORR electrocatalytic activity of Ni-Mn-600 may be attributed to the nanorod morphology and high ratio of (Mn3++Mn4+)/Mn2+ and Ni3+/Ni2+. This work demonstrated that NiMn2O4-based Ni-Mn bimetallic oxides as cathode catalysts have good research prospects in aluminum-air batteries and other energy applications.