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

A hydrothermal method was used to synthesise α-MnO2 particles, with manganese sulfate as the metal precursor and potassium permanganate as the oxidising agent. The α-MnO2 samples synthesised by hydrothermal treatment at 120 °C (α-120) and 140 °C (α-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 α-120 and α-140 samples. The results show that the only MnO2 phase obtained in the synthesis was α-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 α-120 and α-140 samples had specific surface areas of 128 m2 g‒1 and 95 m2 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.