Functionalization Of Carbon Nanotubes And Electrochemical Performance Of Its Composite Materials

In this paper, hydrothermal method was carried out to synthesize highly water-dispersible nanotubes. It was used to functionalization of carbon nanotubes in a mixture of nitric and sulfuric acids. Electrochemical properties of functionalized carbon nanotubes and layered double hydroxides composites were investigated. The major works have been described as follows:(1) The acid concentration, hydrothermal time and hydrothermal temperature were discussed. By optimizing the processing conditions we obtain the functionalized carbon nanotubes which have the best stability in water. The optimized condition is:the concentration of sulfuric acid is 10.3 mol·L-1, the concentration of nitric acid is 4.6 mol·L-1, hydrothermal time is 3 h and hydrothermal temperature is 120℃. (2) Multilayer thin films (Co-Al LDHNS/MWCNTs)n comprising negatively charged functionalized carbon nanotubes and positively charged Co-Al LDHs nanosheet, were prepared by the electrostatic layer-by-layer adsorption technique. UV-vis spectra and QCM studies showed the multilayer films increased uniformly. The electrochemical properties of (Co-Al LDHNS/MWCNTs)n multilayer thin films were studied. The area specific capacitance values of (Co-Al LDHNS/MWCNTs)n multilayer thin films enhanced almost linearly with increasing in the number of bilayers. A specific capacitance value of 201 F·g-1 was obtained for (Co-Al LDHNS/MWCNTs)5 multilayer thin film, and the capacitance decreased slightly over 1000 cycles. With charge-discharge current increased from 2 A·g-1 to 8 A·g-1, the retention of the capacitance was 85%, indicating that the multilayer thin films electrode has an excellent high-rate capability.