Rock-Salt-Type MnCo2O3/C as Efficient Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

The search for nonprecious metal-based electrocatalysts with high activity and long durability for the oxygen reduction reaction (ORR) has been long pursued by the renewable energy material community. Here, we designed a new Mn–Co bimetallic oxide MnCo2O3/C with the rock-salt-type structure, derived from a spinel-type precursor MnCo2O4/C under mild reduction using NH3 at 300 °C. In-depth electron microscopic and spectroscopic investigations suggest that MnCo2O3/C predominantly has Mn(II) and Co(II) and can be written as MnO(CoO)2/C. Charge transfer between Mn and Co was probed by electron energy-loss near-edge structure (ELNES) analysis. MnCo2O3/C has a Co-rich core and a thin 1–3 nm Mn shell with a mesoporous morphology. MnCo2O3/C achieved a high ORR activity with a half-wave potential of 0.86 V in 1 M KOH, which was ascribed to the microstructure and the synergistic effects between Mn and Co, serving as co-active sites for the ORR.