Double-layered gas diffusion electrodes with a fixed gas supplying-layer have been prepared by hot-pressing using hydrophobic acetylene black; AB (I), semi-hydrophobic acetylene black; AB (II), AB (II) with manganese oxide (mixture of Mn5O8 and Mn3O4), active carbon, and active carbon with AB (I) as reaction-layer materials, and their oxygen-reduction performance was examined in 6M KOH solution. The electrodes consisting of AB (II), AB (II) with manganese oxide, and active carbon with AB (I)

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... ibited a stable and good pclarization behavior throughout experiments, because of a favorable wettability which was effective to hold stable three phase boundaries, i.e., oxygen dissolving sites in the reaction-layer. In addition, as active carbon and particularly manganese oxide particles had a high electrochemical activity and HO2 ion decomposition ability, a most excellent oxygen-reduction performance was found in the electrode containing manganese oxide, which was followed by the electrode consisting of active carbon with AB (I). On the other hand, the electrode consist of AB (I) or active carbon only gave a poor performance, because of a little or an excessive electrolyte penetration into the reaction-layer by which the formation of three phase boundaries was limited.