An efficient α-MnO2 nanorods forests electrode for electrochemical capacitors with neutral aqueous electrolytes

In this work, a facile and novel approach is presented to maintain stoichiometry, to achieve stable nanostructure and high surface area manganese oxide (alpha-MnO2). The synthesis of alpha-MnO2 nanorods forest has been carried out using reactive DC magnetron sputtering technique without use of surfactant/wet chemical procedure. The structural parameters, vibrational response and surface morphology of the alpha-MnO2 nanorods are characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform Infrared spectroscopy (FT-IR), X-ray Photoluminescence spectroscopy (XPS), Field emission scanning electron microscopy (FE-SEM), Transmission electron miscopy (TEM) and BET surface area. The alpha-MnO2 nanorods have smooth surface and uniform diameters. The high surface area with lower lattice energy of poly nano-crystalline structure is expected to enhance the utilization ratio of electrode materials and facile de-intercalation process. The Mn-O-Mn bonded, MnO6 octahedral based and the well-developed tetragonal alpha-MnO2 with (2 x 2) tunnel is obtained. The mesopores in alpha-MnO2 provide wide channels, which is extremely suitable to transport ions into micropores present in alpha-MnO2. The electrochemical measurements are performed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD) techniques. The MnO2 electrode exhibits high specific capacitance (346Fg(-1) at 0.71 Ag-1 in 1 M aqueous Na2SO4) and good cycling stability (86.6% retention after 1500 cycles). The present approach opens a new avenue to design an efficient chemical reaction free nanorods. (C) 2016 Published by Elsevier Ltd.