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

•α-MnO2 nanorods forest were prepared without any surfactants by DC reactive sputtering for the first time.•BET surface area of the α-MnO2 nanorods is 164.2 m2 g−1.•α-MnO2 exhibits specific capacitance of 346 F g−1.•α-MnO2 nanorods supercapacitor electrode delivered high energy density 38.92 Wh kg−1.

In this work, a facile and novel approach is presented to maintain stoichiometry, to achieve stable nanostructure and high surface area manganese oxide (α-MnO2). The synthesis of α-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 α-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 α-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 α-MnO2 with (2 × 2) tunnel is obtained. The mesopores in α-MnO2 provide wide channels, which is extremely suitable to transport ions into micropores present in α-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 (346 F g−1 at 0.71 A g−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.

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