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 Mn 2ϩ with and without the presence of Bi 3ϩ was studied using voltammetric and in situ spectroelectrochemical techniques at boron-doped diamond ͑BDD͒ electrodes in 1.0 M HClO 4 . Electrochemical oxidation of only Mn 2ϩ resulted in the formation of mostly MnO 2 with MnO 4Ϫ produced as a minor product. The MnO 2 film formed on the electrode surface, which is an inevitable part of Mn 2ϩ oxidation, shows a blocking effect on the formation of MnO 4 Ϫ , and reduces the overall current efficiency of MnO 4 Ϫ production. Higher Mn 2ϩ concentrations result in less MnO 4 Ϫ production due to the formation of more MnO 2 . The addition of Bi 3ϩ increased the current efficiency of MnO 4 Ϫ production. The Bi 3ϩ is oxidized to Bi͑V͒, which acts as an electrocatalyst in MnO 4 Ϫ production. The Bi͑V͒ oxidizes MnO 2 , formed on the electrode surface, to MnO 4 Ϫ . This increases the production of MnO 4 Ϫ by removing the blocking film to provide an active electrode ͑bare BDD͒ surface, which is available for further Mn 2ϩ oxidation.

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Bismuth Doped PbO₂ Coatings: Morphology and Electrocatalytic Properties

“…For Bi-PbO 2 a further loss of electrocatalytic activity occurs in the interval 1.7 ÷ 1.85 V. As the potential is increased further, R ct decreases by about an order of magnitude, and at 1.9 V it becomes lower than for unmodified PbO 2 , under the same electrodeposition conditions (see PbO 2 -c in Table 2). It is noteworthy that this potential corresponds to the oxidation of Bi(III) to Bi(V) (E °=2.0±0.2 V) [49] whose build-up can lead to increased water oxidation.…”