Hydrothermal Synthesis, Characterization And Supercapacitance Of Nanostructured MnO₂

Based on the hydrothermal techniques, we prepared MnO₂ nanorods, orchid-like MnO₂ nanostructure and hydrangea-like MnO₂ nanostructures. The morphologies were characterized by X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectra (XPS). The structures, morphologies and electrochemical properties of the prepared MnO₂ are discussed in this paper. The formation mechanisms have also been discussed based on the experimental results. The major contents can be summarized as follows:1.β-MnO₂ has been synthesized via a hydrothermal method with the reactions between (NH)₄S₂O₈ and MnSO₄. The reaction temperature, reaction time and acidity influenced on the aggregation of nanoclusters, but didn't cause the transformation of lattice structure of MnO₂.2. Theα-MnO₂ nanorods with diameters of 100nm and lengths of 1.2um have been fabricated via a hydrothermal method, using KClO₃ as the oxidant. When we changed the reaction temperature, the as-obtained MnO₂ presented abundant morphologies and we got the snow-likeβ-MnO₂.3. The orchid and hydrangea-like MnO₂ nanostructures doped by Cr and vanadium were successfully synthesized by a facile, mild hydrothermal route in aqueous KClO₃ solution, respectively. It was found that the additives did not bring out a new phase and not cause the transformation of lattice structure of MnO₂. But the additives played an important role in forming the different morphologies. While the Zn, Co, Ni doped MnO₂ didn't cause the transformation of lattice structure and morphology of MnO₂.4. Electrochemical properties of the synthesized nanostructured samples were studied by using cyclic voltammetry in (NH₄)₂SO₄ aqueous electrolyte. It was found that the metal doped MnO₂ presented good electrochemical performance with the specific capacitance of 250F/g at the scan rate of 2mV/s. The composite MnO₂ presented excellent electrochemical performance as supercapacitor electrode materials.