Electrosynthesis of manganese oxide films

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Abstract
Nanostructured manganese oxide films for electrochemical supercapacitors were obtained by cathodic electrosynthesis from aqueous NaMnO4 solutions. The proposed deposition mechanism is based on cathodic reduction of MnO4− species. The amount of the deposited material has been controlled by the variation of deposition time at a constant current density. Obtained films were studied by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis, thermogravimetric and differential thermal analysis. It was found that the composition and microstructure of the films depend on the concentration of NaMnO4 in the solutions used for deposition. The films prepared from the 0˙02M NaMnO4 solutions were crack free and porous with typical pore size of about 100–200 nm. Cyclic voltammetry and chronopotentiometry data for the films tested in the 0˙1M Na2SO4 solutions showed capacitive behaviour in the voltage window of 0–1˙0 V versus standard calomel reference electrode. The highest specific capacitance of ∼220 F g−1 was obtained for 90 μg cm−2 films at a scan rate of 2 mV s−1 using Ni substrates. The capacitance decreased with increasing scan rate. The charge storage mechanism is discussed.

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