▎ 摘　　要

Pristine MnO2 and MnO2/graphene (abbreviated as Mn and MnG) nanocomposite has been prepared through a facile hydrothermal method under mild conditions. The morphology and nanostructure of the prepared composite are individualized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman microscope, Brunauer-Emmet-Teller and X-ray photoelectron spectroscopy (XPS). XRD results reveal the pure tetragonal phase of alpha-MnO2 with the space group of I4/m. TEM images show spherical morphology for pure Mn and layered structure for MnG. The results of N-2 adsorption-desorption analysis indicates the specific surface area of the prepared nanomaterials and it was found to be 92 m(2)/g and 134 m(2)/g for the pure Mn and MnG nanocomposites. The XPS spectrum shows the confining states of different elements present in the composites. Electrochemical execution of the synthesized composite electrodes was evaluated using both two and three-electrode system. We have achieved maximum specific capacitance of 1537 Fg(-1) at the charging current of 20 Ag-1 with high steadiness was observed up to 6000 cycles. The fabricated ASC devices manifest a maximum energy density of 22 Wh kg(-1) with long standing cyclic stability of 90.5% capacitance retention after 5000 cycles.