RuO 2 /CNT nanocomposites with well-dispersed RuO 2 nanoparticles (diameter <2 nm) on the carbon nanotubes' surface, synthesized through an easy and efficient solution-based method, have been investigated for potential application in electrochemical capacitors (ECs) as electrode materials. The electrochemical results demonstrate that the supporting material of CNT can significantly promote the supercapacitance performance of RuO 2 . The RuO 2 nanoparticles in the composite with a RuO 2 /CNT mass ratio of 6:7 could achieve a specific capacitance of as high as 953 F g -1 . The results also demonstrate that the resulted RuO 2 /CNT nanocomposites are superior electrode materials for ECs with a high specific capacitance and significantly enhanced highpower and high-energy capabilities as well as improved cycling performance compared with bare RuO 2 . At a power density of 5000 W kg -1 , the RuO 2 /CNT composite (RuO 2 /CNT ) 6:7 in wt %) can still deliver an energy density of 16.8 Wh kg -1 , which is about 5.8 times larger than that of bare RuO 2 (2.9 Wh kg -1 ). The much improved electrochemical performances could be attributed to the dispersive action and good electronic conductivity of CNTs as well as the pinning effect for nanosized RuO 2 particles on the CNTs' surfaces.

Well-organized carbon nanotube (CNT)@TiO 2 core/porous-sheath coaxial nanocables are synthesized by controlled hydrolysis of tetrabutyl titanate in the presence of CNTs, and investigated with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and electrochemical experiments. The CNT@TiO 2 coaxial nanocables show excellent rate capability and cycling performance compared with both pure CNT and pure TiO 2 when used as anode materials for lithium-ion batteries (LIBs). Both the specific capacity in the CNT core and that in the TiO 2 sheath are much higher than that of the TiO 2 -free CNT and that of the CNT-free TiO 2 sample, respectively. These results demonstrate that the coaxial cable morphology provides a clever solution to the ionic-electronic wiring problem in LIBs as well as the synergism of the two cable wall materials. On one hand, the CNT core provides sufficient electrons for the storage of Li in TiO 2 sheath. On the other hand, the CNT itself can also store Li whereby this storage kinetics is, in turn, improved by the presence of the nanoporous TiO 2 because the only very thin protection layer on TiO 2 (unlike free CNT) enables rapid access of Li-ions from the liquid electrolyte. This fascinating symbiotic behavior and the fact that the cable morphology leads to an efficient use of this symbiosis makes this solution match the requirements of LIBs extremely well.

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.