Manganese oxide films for electrochemical supercapacitors

Manganese oxide films for electrochemical supercapacitors were obtained by cathodic electrodeposition from aqueous KMnO4 solutions. The amount of the deposited material has been controlled by the variation of the 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 shown that the deposition process resulted in the formation of the nanostructured manganese oxide KxMnO2+y(H2O)z (x=0.35±0.04). The films were porous with typical pore size of about 100–200nm. Cyclic voltammetry and chronopotentiometry data for the films tested in the 0.1M Na2SO4 solutions showed capacitive behavior in the voltage window of 0–1.0V versus SCE. The highest specific capacitance (SC) of ∼353F/g was obtained for 45μg/cm2 film at a scan rate of 2mV/s. The capacitance decreased with increasing scan rate and film thickness. Heat treatment at 200°C resulted in the reduced porosity and improved crystallinity of the films. Compared to the as-prepared films, the films heat treated at 200°C exhibited lower SC at scan rates below 10mV/s and higher SC at scan rates above 10mV/s.