Facile synthesis of ternary spinel Co–Mn–Ni nanorods as efficient bi-functional oxygen catalysts for rechargeable zinc-air batteries

Facile synthesis of high efficient bi-functional oxygen catalysts is important for large-scale application of rechargeable metal-air batteries. Herein, an ethanol-water mediated co-precipitation approach is applied to fabricate Co–Mn–Ni (CMN) ternary spinel oxides with uniform 1D structure. Their catalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are investigated by the rotating ring-disk electrode (RRDE) techniques. The ternary spinel oxide with the Co/Mn/Ni atomic ratio of 2:3:1 (CMN-231) exhibits the best bi-functional activities among the as-prepared ternary, binary and unitary spinel oxides (△E is as low as 0.88 V), which can be attributed to its reasonable element composition, mesoporous nanorod structure, strong oxygen-adsorption ability and good charger-transfer capability. In addition, the CMN-231 catalyst demonstrates a strong stability during long-term operation. This well-designed catalyst is applied in a homemade zinc-air battery, and exhibits good charge–discharge performances (voltage gap is 0.9 V at 50 mA cm−2) and remarkable cycling stability.