Synthesis of Flake-Like MnO₂/CNT Composite Nanotubes and Their Applications in Electrochemical Capacitors

MnO₂/CNT composite nanotubes with nanometer-sized flake-like MnO₂ on carbon nanotubes' surfaces have been synthesized through an easy and efficient solution-based method. Similarly, Mn₃O₄/CNT composite nanotubes have also been synthesized by using the same method but different heat treatment process. The structures and compositions of the two types of composite nanotubes are characterized by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption isotherms. Electrochemical measurements indicate that the MnO₂/CNT composites nanotubes exhibit significantly enhanced supercapacitance performance compared with the Mn₃O₄/CNT composite nanotubes, the as-synthesized MnO₂ nanoparticles and commercial MnO₂. The possibilities of the enhanced properties are illustrated on the basis of analysis of XRD and X-ray photoelectron spectroscopy measurements. Our results presented here can give clear evidence of the superiority of nanocrystalline MnO₂ to nanocrystalline Mn₃O₄ toward the applications as electrode materials in electrochemical capacitors.