Enhanced activity of microwave synthesized hierarchical MnO2 for high performance supercapacitor applications

In this study, exclusive affect of microwave mediated synthesis on the physicochemical and electrochemical properties of alpha-MnO2 have been differentiated from that of alpha-MnO2 synthesized in conventional-reflux method. The TG, XRD, BET and SEM analyses show improved physicochemical properties like additional lattice K+ ions, better crystallinity, high surface area (155 m(2) g(-1)) as well as pore volume (0.67 cm(3) g(-1)) and hierarchical porous ball-like morphology of the microwave-synthesized alpha-MnO2. The CV studies show lower polarization resistance and higher rate pseudocapacitance (258 Fg(-1) at 100 mVs(-1)) of microwave-synthesized alpha-MnO2 as compared to its reflux-synthesized counterpart (168 Fg(-1) at 100 mVs(-1)). The CP studies show better high rate charge-discharge performance (146 Fg(-1) at 16 Ag-1), longer cyclic stability (91.4% capacitance retention after 400 charge-discharge cycles at 16 Ag-1) and higher Coulombic efficiency (similar to 100%) of microwave-synthesized alpha-MnO2 as compared to the reflux-synthesized sample (80 Fg(-1) at 16 Ag-1; 74.1% capacitance retention after 400 charge-discharge cycles at 16 Ag-1: 85% Coulombic efficiency). Further, due to facile mass transfer in the perfectly porous matrix, the microwave-synthesized alpha-MnO2 shows lower equivalent series resistance and better frequency response (higher specific capacitance at elevated operating frequency) as revealed from the impedance studies. (C) 2012 Elsevier B.V. All rights reserved.