Fabrication of three-dimensional porous graphene-manganese dioxide composites as electrode materials for supercapacitors

Three dimensional (3D) porous graphene-MnO2 (PGR-MnO2) composites as electrode materials for supercapacitors were fabricated via deposition of MnO2 particles on 3D PGR produced from freeze-drying method. Field emission scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize morphologies and composition of the produced PGR-MnO2 composites. By immersing PGR into 0.1 M KMnO4/K2SO4 for different time, it was found that MnO2 particles with the size of about 200 nm were formed and uniformly distributed on the GR sheets. The obtained PGR-MnO2 composites still remained 3D interpenetrating porous structures. Electrochemical methods including cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge were carried out to investigate electrochemical properties and capacitive performance. The results showed that the PGR-MnO2-2 h composite (immersing the PGR into 0.1 M KMnO4/K2SO4 for 2 h) gave the best capacitive performance among these produced composites. The PGR-MnO2-2 h composite gave the maximum specific capacitance of 800 F g(-1) with the maximum energy density of 40 W h kg(-1) at the current density of 0.1 A g(-1). The good capacitive performance was attributed to the unique 3D porous structure of the PGR-MnO2 composites and the synergistic effect of GR with high conductivity and MnO2 particles with good pseudocapacitive properties. (C) 2014 Elsevier B.V. All rights reserved.