Facile one-step hydrothermal syntheses and supercapacitive performances of reduced graphene oxide/MnO2 composites

Reduced graphene oxide (rGO)/MnO2 composites were synthesized by a facile one-step hydrothermal reaction of GO and KMnO4 in ammonia solution, and then used as electrode materials for supercapacitors containing electrolytes of 1 M Na2SO4 aqueous solution. The structures and morphologies of composites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectra and N2 adsorption-desorption isotherms. To assess the supercapacitive performances of these materials, cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy tests of two-electrode supercapacitors were performed. GO was reduced to form rGO and 30-50 nm sized MnO2 nanoparticles were in-situ grown on the rGO sheets to obtain rGO/MnO2 composites simultaneously during the hydrothermal reaction. The influences of mass ratios of GO and KMnO4 on the electrochemical performances of supercapacitors were investigated. In comparison with pure MnO2-based supercapacitor, supercapacitors based on rGO/MnO2 composites show better performances because both the specific surface areas and the electrical conductivities of electrode materials were increased by the introduction of rGO. When the mass ratio of GO and KMnO4 is 2:1, rGO/MnO2 composite electrode shows the highest capacitance of 205.7 F/g at a constant current density of 0.15 A/g in a two-electrode supercapacitor. Additionally, the supercapacitor exhibits high rate capability and long cyclic durability.