Shape-controlled synthesis of hierarchical hollow urchin-shape α-MnO₂ nanostructures and their electrochemical properties

3D hierarchical hollow urchin-shape α-MnO₂ nanostructures have been synthesized using a simple one-step hydrothermal process in an acidic KMnO₄ solution without employing any templates or surfactants. The structure and morphology of the products were characterized by XRD, FTIR, SEM and TEM. The hierarchical hollow urchins were found to be assembled from single crystalline α-MnO₂ nanotubes. The formation mechanism of the unique superstructure was investigated systemically by varying the synthesis conditions. Electrochemical studies indicated that these α-MnO₂ nanotubes-assembled hollow urchins exhibited favorable performance compared to the α-MnO₂ nanorods-assembled microspheres as electrode materials in supercapacitor. Due to the distinct architecture of macroporous hollow structure and nanotubular building blocks, the sample delivered a specific capacitance of 123 F g^-1 with superior rate capability.