The shape-controlled star-like and rod-like γ-MnO2 nanocrystals are prepared by vitriolization of synthesized manganese oxides with the adjustment of the molar ratio of Mn precursors in the ammonia solution. The properties of the product, γ-MnO2, are investigated by scanning electron microscopy, X-ray powder diffraction, transmission electron microscopy, etc. The prepared rod-like γ-MnO2 nanocrystals have a high surface area of 129 cm2 g−1. Charge/discharge tests of the obtained nanorods particle shows a capacitance of 218 F g−1 but with a high capacitance of 261 F g−1 at the first cycle. The star-like nanoparticles show a better stability with less capacitance loss.
The scheme of the phase transition of the manganese oxides.