Preparation of manganese dioxide using Ag+ ions as an electrocatalyst

The production of manganese dioxide by the conventional electrolytic process is based on the direct oxidation of Mn2+ ions on an anode in sulfuric acid solution. The process is complicated. A new method for the preparation of manganese dioxide has been reported recently by the authors. This method uses Ag+ ions to electrocatalyze the anodic oxidation of Mn2+ ions. To show the difficulty in the direct anodic oxidation of Mn2+ ion and the electrocatalytic mechanism of Ag+ ions, the anodic oxidation behaviour of Mn2+ and Ag+ ions and the electrocatalytic behaviour of Ag+ ions on the anodic oxidation of Mn2+ ion are studied using a rotating ring disc electrode, a.c. impedance and voltammetry techniques. Mn3+ ion or MnO2 will be formed when Mn2+ ion is oxidized on an anode, as determined by the sulfuric acid concentration. Mn2+ ion is oxidized on the surface with OH groups and some compounds with Mn2+ or Mn3+ are formed before Mn3+ ions or MnO2 are produced. This causes difficulties in the preparation of Mn3+ ions or MnO2. Ag+ ions can be oxidized easily on an anode to form Ag2+ ions. In turn, Mn2+ ions can be oxidized easily by the Ag2+ ions. Thus, the anodic oxidation of Mn2+ ions can be e electrocatalyzed by using Ag2+ ions. This is a homogeneous electrocatalysis and allows MnO2 to be prepared in a convenient process.