S-doped CoMn2O4 with more high valence metallic cations and oxygen defects for zinc-air batteries

The strategy of introducing heteroatom sulfur (S) in the cobalt manganese spinel oxides (CoMn2O4) is employed to boost the bifunctional electrocatalyst. The optimized sample of S– CoMn2O4 shows overpotentials shifts of 60 mV at 10 mA cm−2 for the oxygen evolution reaction (OER) and 40 mV for the oxygen reduction reaction (ORR). X-ray photoelectron spectroscopy results reveal that the S-doping can significantly increase highly active Mn4+, Co3+, and oxygen defects, while density functional calculation results suggest that metal-oxygen covalency of S–CoMn2O4 can enhance the shrinking energy difference of Co 3d-O 2p and Mn 3d-O 2p centers, which can explain the enhancement of OER/ORR activities. What's more, the S–CoMn2O4 based zinc-air battery displays excellent open voltage of 1.52 V, power density of 108.3 mW cm−2, specific capacity of 808.2 mA h g−1 at 10 mA cm−2, and good cycling stability. This work shows that the doping of heteroatom in the spinel materials can provide a feasible pathway to obtain optimized bifunctional catalysis for power sources devices.