LAUSR

Nanostructured MnO2 has been synthesized using a simple and rapid microwave-assisted hydrothermal (MHT) technique through the decomposition of KMnO4 in a hydrochloric acid solution. The effects of hydrothermal temperature and ramp rate were examined and discussed. It was found that a lower temperature (140°C) favors the formation of cauliflower-like δ-MnO2 particles while a higher temperature (160°C, 180°C, or 200°C) favors the formation of α-MnO2 nanorods. The dimensions of the obtained MnO2 nanorods were affected by the ramp rate. The cauliflower-like δ-MnO2 particles have higher specific surface areas than the α-MnO2 nanorods. Supercapacitors having the obtained MnO2 as the electrodes were evaluated using cyclic voltammetry and electrochemical impedance spectroscopy in a 1 mol·L−1 Na2SO4 solution within a potential window of −0.1-0.9 V. The cauliflower-like δ-MnO2 electrodes give higher capacitance, up to 202 F/g, than the nanorods α-MnO2 electrodes, at most 61 F/g.