Abstract

The results of investigation of Mn2+ electrooxidation mechanism in the presence of acetate ions have been presented. The kinetic measurements were supplemented by quantum-chemical modeling. The calculated value of the redox potential of Mn(H2O)(5)Ac/Mn(H2O)(5)Ac system was compared with experimental data obtained at pH 5.2. The similar values have given a reason to assume the direct electrooxidation of ion Mn2+ to Mn3+ like complex Mn(H2O)(5)Ac. The process occurs according to inner-sphere mechanism due to direct contact of the complex with the electrode through the carboxyl group. The quantum-chemical calculations have shown the impossibility of elimination of second electron without considerable reorganization of the complex Mn(H2O)(5)Ac. The final product of electrooxidation of Mn2+ acetate complex, manganese dioxide, was formed as a result of Mn(H2O)(5)Ac disproportionation with subsequent hydrolysis of the Mn(H2O)(5)Ac complex. In weakly acidic solution (pH above 4) due to reducing the number of Mn(H2O)(5)Ac complexes, electrooxidation of manganese ions were occurred by a similar mechanism to the acid sulphate solution, i.e. by radicals, produced by electrooxidation of water molecules.

Authors

Vargalyuk, Viktor F.;  Poltavets, Veronika V.;  Shevchenko, Ludmila V.

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