ELECTROCHEMICAL REDUCTION OF BETA-MNO2, RAMSDELLITE, GAMMA-MNO2 AND EPSILON-MNO2

The electrochemical reduction of four different forms of MnO2 (ramsdel lite, beta-MnO2, gamma-MnO2 and epsilon-MnO2) was made in KOH 1N and 7 N, under potentiostatic control. The structural disorder (De Wolff's d efauts and microtwinning) and stoichiometry defects are the origin of higher reduction potential observed for gamma- and epsilon-MnO2. The w ide peak observed in the KOH 1N voltammogram for gamma- and epsilon-Mn O2 is assigned to H+/e- insertion process, and not observed for ordere d and stoichiometric forms ramsdellite and beta-MnO2. For KOH 7N, a st ep is defined in all cases and related to the dissolution of MnO2.