In this work, -MnO2 nanoparticles and -MnO2 urchin-like nanostructures have been successfully
synthesized by the microwave-assisted reflux as short as 5 min under neutral and acidic conditions,
respectively. The crystal structure, morphology and chemical composition of the MnO2 products were
investigated be X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron
microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and
N2 adsorption–desorption. -MnO2 nanoparticles showed a smaller particle size, a higher specific surface
area, and a larger pore volume than those of -MnO2 urchin-like nanostructures. The electrochemical
performance was investigated by using cyclic voltammetry and galvanostatic charge–discharge techniques.
-MnO2 nanoparticles obtained from the neutral condition exhibited a capacitance of 311 F g−1
at a current density of 0.2 A g−1, which is much higher than that of -MnO2 urchin-like nanostructures
(163 F g−1). The specific capacitance retention and coulombic efficiency after 5000 cycles at 1 A g−1 were
about 93% and almost 100% for -MnO2 nanoparticles, respectively, suggesting that it is a promising
electrode material for supercapacitors.