Novel electrode materials for electrochemical capacitors: Part II. Material characterization of sol-gel-derived and electrodeposited manganese dioxide thin films

Material characterization of sol-gel-derived and electrodeposited MnO2 thin films showed that their microstructures are highly porous in nature. While sol-gel-derived films are nanoparticulate, electrodeposited films showed m acropores of random and irregular platelike structures, comprising much den ser surface layers and highly porous underlying layers. On the basis of cal culated and theoretical density values of 1 and 4.99 g/cm(3), respectively, the porosity of sol-gel-derived MnO2 films was determined to be as high as 80%, which is substantially higher than electrodeposited films at 67%. Apa rt from their higher specific capacitance, sol-gel-derived MnO2 films appea red to exhibit higher cycling stability and reversibility than electrodepos ited MnO2 films. In the case of sol-gel films, thinner films appeared to ex hibit higher cycling stability than thicker films. There was less alteratio n in surface morphology and microstructure, and the rate of loss in charge- storage capacity upon voltammetric cycling was not as significant for sol-g el MnO2 thin films.