▎ 摘　　要

MnO2 nanoparticle/three dimensional graphene composite (MnO2/3DG) was synthesized by a hydrothermal template-free method and subsequent ultrasonic treatment in KMnO4 solution. The MnCO3/3DG particles can be detected after the hydrothermal process, which may be produced through the reaction between Mn2+ and due to the decarboxylation of GO under the hydrothermal condition. The final product MnO2/3DG displayed high specific capacitance (324 F g(- 1) at 0.4 A g(-1)) and good cycle stability (91.1% capacitance retention after 5000 cycles). Furthermore, the asymmetric supercapacitor assembled with MnO2/3DG and activated carbon (AC) exhibits an energy density of 33.78 Wh kg(-1) at the powder density of 380 W kg(-1). The excellent supercapacitance of the MnO2/3DG composite may be due to the high pseudocapacitance of the dispersed MnO2 nanoparticles and the conductive graphene with three dimensional porous microstructure.