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Abstract

In this work the mechanisms of electrooxidation of Mn2+ to MnO2 were investigated in perchlorate, sulphate and acetate solutions. Density functional theory (DFT), as a quantum modeling method, was used for identification of red-ox potentials of one-electron oxidation of the aquacomplexes [Mn2+(H2O)(6)], [Mn2+(H2O)(5)(SO42-)]. The calculated values were significantly higher than the measured potentials of the initial stages of complexes oxidation on Pt electrode. The thermodynamical possibilities of formation of oxocomplexes and the kinetic measurements were analyzed. Based on this data it has been found that in perchlorate and sulphate solutions (pH 4) Mn2+-iones were oxidized due to the interaction with adsorbed center dot OH-radicals, produced by the water-splitting reaction. For strongly acid sulphate solutions (pH 1) it was observed the convergence of values of the potential of water-splitting reaction (1,2 V) and the potential of oxidation of [Mn2+(H2O)(5)(HSO4-)] complex (1,13V). This points to simultaneous implementation of two reaction paths: the direct electrooxidation of Mn2+-iones and the oxidation due to the interaction with center dot OH-radicals. The calculated value of potential of electrooxidation of monoacetate aquacomplex of Mn2+-iones is notably low (0,66 V). This poin to the only electrooxidation path of the reaction. The calculated data have been confirmed by the kinetic measurements. The particles [Mn3+(H2O)(5)(Ac-)] rapidly disproportionate to MnO2 and [Mn2+(H2O)(5)(Ac-)] due to the features of carboxyl group.

Authors

Poltavets, Veronyka V.;  Vargalyuk, Viktor F.;  Seredyuk, Volodymir A.;  Shevchenko, Ludmila, V

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