Die kinetic der aktiven manganelektrode

Abstract

At active manganese, polarization curves and the course of the potential after changes of cd have been measured in neutral and weakly acid manganese sulphate and chloride solutions containing the respective ammonium salts as the base electrolyte. A method for depositing active manganese with well reproducible electrochemical properties has been developed. The pH-independent cathodic stationary polarization curves, after elimination of the concentration polarization for the diffusion-limited supply of manganese ions, are shown to be additive superpositions of a Tafel line for hydrogen evolution with a slope of 120 mV/decade of cd and a Tafel line for deposition of manganese with a slope of 29 mV/decade. The reaction order with respect to manganese ions was found to be y(Mn2+) = 1·5. A stationary polarization curve for the dissolution of active manganese does not exist, because of irreversible changes in the surface during anodic polarization resulting in deposition of only hydrogen after the re-application of the cathodic polarization. The anodic and cathodic transient polarization curves were Tafel lines with slopes close to 58 mV/decade.The results can be explained using the conception that bivalent manganese ions are transferred at certain points on the metal surface, eg half-crystal positions, the surface activity of which is a function of overvoltage.