Electrosynthesis of manganese oxide films

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.