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.