Abstract
Abstract At a rotating disc electrode covered with manganese dioxide, changes of mass were measured at 40 °C with a quartz frequency balance and, at a ring electrode, changes of the flux of hydrogen ions. Several effects are discussed which might interfere with the determination of mass changes from frequency changes, in particular effects due to unilateral normal pressure and tangential stress. Kinetic experiments as a function of electrolyte composition show that manganese(II) ions and oxygen ions are transferred in statistically independent charge transfer reactions. In equilibrium, the water content of the oxide is determined by the variable state of oxidation of the oxide. Theoretical expressions were developed which together with the experimental results yield the following conclusions: The exchange current of manganese ions is much greater than the exchange current of oxygen ions. Manganese ions are transferred without water, but several water molecules are transferred with an oxygen ion. In addition, water is transferred in a neutral particle current. Proton transfer between the oxide and the electrolyte proceeds at a negligible rate.
Published Version
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