Synthesis of porous δ-MnO2 nanosheets and their supercapacitor performance

In this work, a hydrothermal method has been exploited to synthesize porous δ-MnO2 nanosheets. The influence of hydrothermal temperature on the synthesis of δ-MnO2 has been investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM) and electrochemical methods. The results show that the pure δ-MnO2 appears at the hydrothermal temperature from 130 to 170 °C, and the hydrothermal temperature has a great influence on the morphology and BET surface area of as-prepared samples. The δ-MnO2 prepared at 150 °C delivers high specific capacitances of 411 F g−1 at a scan rate of 5 mV s−1 and 332.7 F g−1 at a current density of 0.5 A g−1. The excellent supercapacitor performance is attributed to the porous nanosheets structure, which brings a large specific surface area, increases the active sites, and shortens the ion diffusion distance in δ-MnO2 electrodes. It is suggested that the optimal synthesizing temperature is 150 °C in order to obtain pure δ-MnO2 with good electrochemical performance by hydrothermal method.