Poltavets V. Electrochemical formation and properties of electrode materials based on MnO2.

The aim of research was to establish the patterns of the anodic oxidation of Mn2+ ions and to identify the factors regulating the chemical composition and properties of the MnOx oxide films. It was shown that, depending on the acidity of the solution, the composition of the internal coordination sphere of manganese aquacomplexes, the nature of the electrode material and the value of the anodic polarization, various mechanisms of electro-oxidation of Mn2+ ions can be implemented. In perchlorate and sulphate solutions in the area of φ < φ0Mn2+/Mn3+ the following path prevails: Mn2+ + • → MnO+ MnO(OH) - e → MnO2, but in the area φ > φ0Mn2+/Mn3+ the path is supplemented with the reaction of direct electrooxidation of Mn2+ ions. In acetate and acrylate solutions only direct electrooxidation of monosubstituted aquacomplexes MnL+ to MnL2+ takes place. The compound MnL2+subsequently disproportionate and simultaneously all products hydrolyze to MnO(OH) and MnO2 The phase composition and morphology of electrolytic MnOx films depends on the temperature of electrolyte. Up to 50 °C, the film has amorphous structure, above 50 °C it has polycrystalline structure. The composition of the main components of the MnOx film has been established: the mixture of MnO(OH)(H2O)2 and MnO2(H2O)2. It has been shown that the catalytic properties of MnOx films toward oxygen-transfer reactions depend on the ratio of Mn3+ and Mn4+ compounds. Maximum catalytic activity was observed at x = 1,895. The possibility of applying high-resistant MnOx films on a steel base and using Fe/ MnOx electrodes in electrical devices based on charge cycling has been confirmed. Keywords: anodic oxidation, aqua complexes of manganese, properties of MnOx films.