Oxidation of manganese(II) and reduction of manganese dioxide in sulphuric acid

Oxidation of Mn2+ to MnO2 and reduction of MnO2 on Pt electrode in sulphuric acid was investigated by cyclic voltammetry as a function of the Mn2+ concentration, acid concentration, scan rate, temperature and convection. It was observed that oxidation of Mn(II) to Mn(IV) was mass transfer controlled. High temperature and stirring enhanced the oxidation rate of Mn(II) to Mn(IV). Decreasing acid concentration favours MnO2 deposition while high acid concentrations inhibit the formation of MnO2. The mechanism of MnO2 deposition from Mn(II) is suggested to be an ECE sequence with the formation of an insulating intermediate (MnOOH). Small amounts of deposited MnO2 may be reduced electrochemically at the electrode surface. (C) 2000 Elsevier Science Ltd. All rights reserved.