The peculiarities of electrooxidation of Mn<sup>2+</sup> to MnO<sub>2</sub> in acetate electrolyte
Keywords:Mn2 acetate complexes, electrooxidation, quantum-chemical modeling
AbstractThe 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)5Ac]+/[Mn(H2O)5Ac]2+ 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)5Ac]+. 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)5Ac]2+. The final product of electrooxidation of Mn2+ acetate complex, manganese dioxide, was formed as a result of [Mn(H2O)5Ac]2+ disproportionation with subsequent hydrolysis of the [Mn(H2O)5Ac]3+ complex. In weakly acidic solution (pH above 4) due to reducing the number of [Mn(H2O)5Ac]+ 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.
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