One-pot temperature-controlled hydrothermal synthesis of α-MnO2 nanoparticles decorated thermally reduced graphene oxide composite as high-performance flexible aqueous symmetric supercapacitors

In this study, manganese dioxide (MnO2)/thermally reduced graphene oxide (rGO) symmetric supercapacitors were fabricated. The (MnO2/[email protected]) composites with varying reaction temperatures (100, 120, and 140 °C) were prepared from a one-pot hydrothermal approach. First, we optimize the reaction temperature as 120 °C for the MnO2/rGO composite on its electrochemical behaviour in a two-electrode cell. Then, pure MnO2nanoparticles were synthesized at the same reaction temperature. X-ray diffraction (XRD) analysis revealed the presence of α-MnO2 produced through hydrothermal synthesis. The MnO2/rGO composite formation was confirmed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The scanning electron microscope (SEM) image of the MnO2/[email protected] composite showed that the rGO surface was decorated with flakes-like MnO2 nanoparticles. The electrochemical properties of pure MnO2@120 and the MnO2/[email protected] composite were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge measurements. In a two-electrode symmetric cell configuration, the MnO2/[email protected] exhibits a much larger specific capacitance of 413 Fg−1 at a current 1 mA and delivers maximum specific energy 14.3 Wh kg−1 with a specific power of 260 W kg−1. Moreover, the 99.7% efficiency exhibited by this composite symmetric supercapacitor was found to retain after 5000 charge/discharge cycles at 3 mA current. The excellent supercapacitive performance of our MnO2/rGO composite electrode material prepared via one-pot hydrothermal treatment at a reaction temperature of 120 °C has potential applications for energy storage applications.