Manganese Oxide Coated Carbon Materials as Hybrid Catalysts for the Application in Primary Aqueous Metal-Air Batteries

One of the major challenges of metal-air batteries is the impeded oxygen reduction reaction (ORR) during discharge occurring at the gas diffusion electrode (GDE) of the battery. Due to the impeded ORR, high overpotentials emerge and result in a loss of energy efficiency. In order to improve the latter, suitable catalysts have to be employed. Transition metal oxides like manganese oxides (e.g., MnO2, Mn2O3, Mn3O4, Mn5O8, MnOOH) [1,2] are known as good and inexpensive materials for the ORR in alkaline media. A drawback of manganese oxide catalysts is the poor electrical conductivity. Hence, the approach presented in this work aims to enhance the catalytic activity of Mn3O4 and gamma-MnO2 by the incorporation of conductive carbon material into the pure manganese oxide. The resulting hybrid catalysts are prepared either by impregnation of Super C 65, Vulcan XC 72, and Kuraray YP 50F via a sol-gel technique employing a MnO2 precursor sol or by direct precipitation of Mn3O4 or gamma-MnO2 particles in the presence of the carbon materials mentioned above. Investigations by rotating disc electrode (RDE) show a noticeably higher catalytic activity of the hybrid catalysts than for the pure materials. For verification of the results measured by RDE, screen printed GDEs are prepared and tested in Zn-air full cells.