Electrochemical Oxidation of Mn[sup 2+] on Boron-Doped Diamond Electrodes with Bi[sup 3+] Used as an Electron Transfer Mediator

Abstract

Electrochemical oxidation of Mn2+with and without the presence of Bi3+was studied using voltammetric and in situ spectro-electrochemical techniques at boron-doped diamond (BDD) electrodes in 1.0 M HClO4. Electrochemical oxidation of only Mn2+resulted in the formation of mostly MnO2with MnO4-produced as a minor product. The MnO2film formed on the electrode surface, which is an inevitable part of Mn2+oxidation, shows a blocking effect on the formation of MnO4-, and reduces the overall current efficiency of MnO4-production. Higher Mn2+concentrations result in less MnO4-production due to the formation of more MnO2. The addition of Bi3+increased the current efficiency of MnO4-production. The Bi3+is oxidized to Bi(V), which acts as an electrocatalyst in MnO4-production. The Bi(V) oxidizes MnO2, formed on the electrode surface, to MnO4-. This increases the production of MnO4-by removing the blocking film to provide an active electrode (bare BDD) surface, which is available for further Mn2+oxidation. © 2004 The Electrochemical Society. All rights reserved.