Facial synthesis of MnO2/three dimensional graphene composite and its application in supercapacitors

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 CO32-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{C}}{{\text{O}}_{\text{3}}}^{{\text{2}} - }$$\end{document} 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.