Carbon Nanotubes and Nanoribbons

Single-walled carbon nanotubes (SWNTs) are composed of single hollow tubes having a diameter between 0.4 and 2 nm. Multiwalled carbon nanotubes (MWNTs) 

FIGURE 7.5 TEM images of untreated CNTs (a, b ACNT) and activated with KOH and thermally treated at SOO C using different KOH/ACNT weight ratios of 3 (c, d ACNT-3) and 5 (e, f ACNT-5). (From Xu et al., 2008. Electrochim. Acta 53, 7730-7735, with permission.) 

The electrochemical response of CNTs is dominated by double-layer charging with only a small contribution of faradaic pseudocapacitance due to surface oxides (Frackowiak and Beguin, 2000 Kavan et al., 2001), so that faradaic processes are essentially absent. In contact with aqueous electrolytes, however, weak peaks may eventually appear. These peaks are presumably due to faradaic pseudocapacitance associated with oxygen-containing surface functionalities on CNTs and/or 

The appearance of weak voltammetric peaks in contact with nonaqueous electrolytes can be attributed to water traces (Claye et al., 2000) or to Li+ insertion (Barisci et al., 2000b). Lithium insertion into SWNTs exhibits fast kinetics and absence of staging, and l.i ions are presumably accommodated in nanochannels occurring inside the nanotube bundles and ropes (Claye et al., 2000). 

Correlation between spectral and electrochemical features for CNTs has been studied by Kavan et al. (2004). Spectral features for SWNTs in the near infrared-visible region can be explained in terms of resonance enhancement and optical band-gap excitation in a one-dimensional conductor with Van Hove singularities in the electronic density of states (Kavan et al., 2000). Chemical redox processes can modify the population of such states so that the electronic structure of SWNTs can be tuned by chemical doping with molecules having different redox potentials or by controlling the interfacial potential of SWNTs in contact with an electrolyte solution, as studied in detail by Kavan et al. (2001). 

---