The electrochemical impedance measurements of carbon nanotubes

The two types of carbon nanotube electrodes have been studied as a function of frequency and the open circuit cell voltage. Nyquist plots measured from the closed carbon nanotubes electrodes at different potentials include only one semicircle that is attributed the adsorption phenomenon at the surface only. However, the Nyquist plots measured from the opened carbon nanotubes electrodes at different potentials include two semicircles. The presence of two semicircles in the high and intermediate frequency ranges can be ascribed to a charge-transfer reaction, which involves an adsorbed intermediate species. The diffusion of lithium-ions into the opened carbon nanotubes can occur around the inner core space and the outer surface that may lead to rapid diffusion. On the contrary, diffusion into the closed carbon nanotubes occurs only at the outer surface which may lead to slow diffusion. (C) 2001 Published by Elsevier Science B.V.