Electrosynthesis of manganese oxide films

Nanostructured manganese oxide films for electrochemical supercapacitors were obtained by cathodic electrosynthesis from aqueous NaMnO 4 solutions. The proposed deposition mechanism is based on cathodic reduction of MnO 4 − 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 NaMnO 4 in the solutions used for deposition. The films prepared from the 0˙02M NaMnO 4 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 Na 2 SO 4 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.