The mechanism of the manganese dioxide electrode

✍ Scribed by K.E. Heusler; A. Grzegorzewski

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 567 KB
• Volume: 35
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(90)87041-y

✦ Synopsis

steady-state polarization curves of manganese dioxide were measured at 40" C in 1 M sodium sulfate solutions, pH 4-6, containing between 0.5 mM and 0.25 M manganese sulfate. According to transient measurements at the rotating ring-disc electrode and the rotating quartz frequency balance the exchange current densities for manganese ions are several orders of magnitude larger than the exchange current densities for oxygen ions. Changes of the state of oxidation with the overpotential and with the composition of the electrolyte penetrated into the bulk.

The experiments agree to the mechanism of statistically independent, parallel transfer reactions of manganese (II) ions and hydrated oxygen ions. The rate determining step of the slow oxygen ion transfer is the reaction with the lattice of adsorbed oxygen ions originating from a potential dependent equilibrium with hydrogen ions and water. A limiting anodic current density nearly independent of pH and concentration of manganese sulfate is explained by the saturation of the surface with adsorbed oxygen ions.