Michio Sugawara

Oxygen reduction catalysis of Mn–Co spinel oxides on agraphite electrode in alkaline solution

Binary Mn–Co spinel oxides have been applied as catalysts for oxygen reduction on graphite electrodes in alkaline solution. Oxides with cation deficiencies were obtained by heating the homogeneous citrate and carbonate precursors with different atomic ratios of Mn/Co (0–1.5) at 400–600 °C in an O 2 atmosphere. The oxygen reduction was studied by a rotating ring-disk electrode method, and these oxides loaded onto graphite showed catalytic activity for the direct four-electron reduction of oxygen. It is considered that cation deficiencies in the oxide catalysts contribute to the appearance of catalytic activity.

Preparation of thin films of MnO2 and CeO2 by a modified chemical bath (oxidative-soak-coating) method

Thin films of MnO2 and CeO2 were deposited on glass substrates directly from aqueous solutions in a temperature range from 313 to 333 K by a modified chemical bath deposition technique. The principle of the film deposition was based on the oxidation of Mn2+ and Ce3+ ions in homogeneous solutions and subsequent heterogeneous nucleation of MnO2 and CeO2 on the substrates. We have named this method as “oxidative-soak-coating” method. The film thicknesses after a 24-hour deposition were 1 μm and 60 nm, respectively. Thin films consisting of Mn3O4 and MnOOH were also deposited by changing the pH of the starting solutions for the deposition of MnO2. The effects of the composition of the starting solution, deposition temperature, and the compatibility of the substrates to the film substances were investigated.