Nano-sized spherical MnO2 electrodes were galvanostatically deposited onto graphite substrates at various anodic current densities and they were then subjected to heat treatment at 200 °C for 2 h in air. The structure, morphology and specific surface area of the prepared films were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and nitrogen adsorption-desorption analyses. The pseudocapacitive property of the electrodes was found using cyclic voltammetry, chronopotentiometry and ac impedance measurements. The results revealed that the active surface area and the energy storage performance were enhanced with the increase in the deposition current density. A maximum areal capacitance of 0.42 F cm−2 at 5 mA cm−2 was obtained for the film deposited at 25 mA cm−2. To further improve the charge storage property, a CNT/MnO2 composite electrode was fabricated via the electrodeposition of manganese oxide on an as-prepared electrophoretically CNTs-coated graphite substrate. Owing to the good electrical conductivity and unique structure of CNTs, the composite electrode exhibited an optimum areal capacitance of 0.59 F cm−2 at 5 mA cm−2 and superior cycling stability of 93.2% after 1000 cycles at a current rate of 10 mA cm−2.
