Effect of the hydrothermal synthesis temperature on the capacitive performance of α-MnO2 particles

A hydrothermal method was used to synthesise alpha-MnO2 particles, with manganese sulfate as the metal precursor and potassium permanganate as the oxidising agent. The alpha-MnO2 samples synthesised by hydrothermal treatment at 120 degrees C (alpha-120) and 140 degrees C (alpha-140) for 2 h exhibited different sample morphologies. The sample morphology consisted of a mixture of rose-like microflower and needles, and X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) characterisation and Fourier transform infrared spectroscopy (FT-IR) were carried out on both the alpha-120 and alpha-140 samples. The results show that the only MnO2 phase obtained in the synthesis was alpha-MnO2. The electrochemical properties of the samples were analysed by cyclic voltammetry (CV) using a 0.1 M Na2SO4 electrolyte solution at scan rates ranging from 5 to 100 mV s(-1). The specific capacitance of the system was calculated from the CV curves. The ct-120 and ct-140 samples had specific surface areas of 128 m(2) g(-1) and 95 m (2) g(-1), respectively, and specific capacitances at a scan rate of 5 mV s(-1) of 112.8 F g(-1) and 34.86 F g(-1), respectively. The specific capacitance decreased as the scan rate increased for both samples.