Controllable Fabrication of Co3−xMnxO4 with Tunable External Co3+/Co2+ Ratio for Promoted Oxygen Reduction Reaction

Co 3− x Mn x O 4 is a bimetal oxide with excellent electrochemical activity in alkaline solution, has been regarded as a promising alternative in the field of ion-air batteries and proton exchange membrane fuel cell (PEMFC). Herein, we report a simple solvothermal-calcination method to fabricate Co 3− x Mn x O 4 with tunable external Co 3+ /Co 2+ and Mn 3+ /Mn 2+ ratio. The tunable ratio of element valence in the bimetal results in a higher exposure of active center for oxygen redox reaction (ORR), and thus lead to a better ORR activity, which was confirmed by X-ray photoelectron spectroscopy characterizations and electrochemical measurements. Specially, Co 1.8 Mn 1.2 O 4 with a Co 3+ /Co 2+ ratio of 2.08 showed an overpotential of 0.37 V at benchmark ORR current density of 3 mA/cm 2 in 0.1 M KOH, which is lower than that of pure oxide (Mn 3 O 4 0.53 V and Co3O4 0.56 V). In addition, the as prepared Co 1.8 Mn 1.2 O 4 exhibited a positive half-wave potential (0.83 V vs RHE) due to their more active sites, promotes charge transfer, adsorption and desorption of oxygen species. This work provides a strategy for the design and fabrication of earth-abundant, low-cost electrocatalysts for PEMFC in practical applications. Graphic Abstract Co 3− x Mn x O 4 was fabricated by tuning external Co 3+ /Co 2+ and Mn 3+ /Mn 2+ ratio, and the activity initially shows a positive correlation with the ration of Co 3+ /Co 2+ in Co 3− x Mn x O 4 .