Nanotubular materials for supercapacitors

Different types of multi-walled (MWNTs) and single-walled nanotubes (SWNTs) have been considered as active electrode materials for the storage of energy In supercapacitors. Due to their unique mesoporosity, these materials have a high ability for the accumulation of charges in the electrode/electrolyte interface. MWNTs supply twice higher values of capacitance in comparison to SWNTs. The nanotubular materials of high purity point out a box-like shape of voltammetry characteristics that proves an entirely electrostatic attraction. Pseudocapacitance effects are observed if metallic particles are: present and after additional functionalization of the nanotubes or deposition of conducting polypyrrole (PPy). The value of capacitance obtained from nanotubes modified by PPy reaches 170 F/g, about twice that given either by the nanotubes (ca, 80 F/g) or by pure PPy (ca. 90 F/g). The open entangled network of the nanocomposite seems to favour a better efficiency for the formation of the electrical layer in PPy. (C) 2001 Elsevier Science B.V. All rights reserved.