In the present study, nanostructured spherical MnO2 electrodes were galvanostatically deposited onto graphite substrates and then subjected to heat treatment at 200°C for 2 h in air. The electrolyte was an aqueous solution of 0.1 M manganese acetate and 0.05 M sodium acetate. MnO2wasdeposited onto graphite substrate at room temperature by applying a constant current density of 25 mA cm-2 for 20 s. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and nitrogen adsorption-desorption measurement were used to study thestructure and morphology of the prepared films. The pseudocapacitive properties of the as-prepared electrode were investigated using cyclic voltammetry and chronopotentiometry charge-discharge measurements. All the tests were carried out at room temperature in a three-electrode electrochemical cell containing 0.5 M Na2SO4 aqueous solutionusing an Ag/AgCl electrode as a reference electrode and a platinum plate as acounter electrode. According to the electrochemical measurements, the capacitance of MnO2 electrodes arises mainly from pseudocapacitance, which is attributed to the reversible redox reaction between Mn4+ and Mn3+. This transition process is based on the insertion/deinsertion of protons (H3O+) or alkali metal cations into the MnO2 structure.
