Effect of ammonium persulfate on the growth of MnO2 nanostructures prepared via hydrothermal synthesis for supercapacitor applications

Abstract In this work, we present the hydrothermal synthesis of MnO2 nanostructures with various morphologies for supercapacitor applications. Varying molar ratios of MnCl2·4H2O and (NH4)2S2O8 were mixed in 15 mL of deionized water. Hydrothermal treatment was done at 120 °C for 12 h. XRD results revealed that tetragonal β-MnO2 was formed for all samples. SEM images show that at an equimolar ratio (1:1), rod-like nanostructures with diameters around 45 nm and 0.65 µm in length were formed. Increasing the ratio to 1:0.5 resulted to the formation of hollow urchin-like microstructures with rods of length and diameter of about 1 µm and 82 nm as primary structures. The average diameter of the whole urchin was measured to be around 6.7 µm. Cyclic voltammetry was employed to calculate the specific capacitance of the fabricated nanostructured electrodes at 5 mV/s scan rate. The highest specific capacitance was obtained at 1:0.75 MnCl2·4H2O to (NH4)2S2O8 ratio with a value of 87.07F/g.