CNT-composite electrodes

The first CNT-modified electrode was reported by Britto et al. in 1996 to study the oxidation of dopamine [16]. The CNT-composite electrode was constructed with bro-moform as the binder. The cyclic voltammetry showed a high degree of reversibility in the redox reaction of dopamine (see Fig. 15.3). Valentini and Rubianes have reported another type of CNT paste electrode by mixing CNTs with mineral oil. This kind of electrode shows excellent electrocatalytic activity toward many materials such as dopamine, ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid [39], hydrogen peroxide, and NADH [7], Wang and Musameh have fabricated the CNT/Teflon composite electrodes with attractive electrochemical performance, based on the dispersion of CNTs within a Teflon binder. It has been demonstrated that the electrocatalytic properties of CNTs are not impaired by their association with the Teflon binder [15]. 

Among those several different types of transducers based on CNTs, the CNT-composite electrode, which was the first CNT electrode tested in 1996, is still widely used with different composite materials such as conducting polymers, nanoparticles, sol-gel, etc. The usefulness of these electrodes is based on their high sensitivity, quick response, good reproducibility, and particularly long-term stability. We expect to see continued research activities using CNT-composite electrodes. 

FIGURE8.27 Impedance spectra of a symmetric capacitor based on PPy/CNT composite electrodes (20 wt% of CNT) in 1 mol L 1 H2S04, before (a) and after (b) performing 500 galvanostatic charge-discharge cycles at a maximum voltage of 0.8 V. (From Khomenko, V., et al., Appl. Phys. A, 82, 567, 2006. With permission.)... 

The values of specific capacitance and cell resistance obtained with symmetric two-electrode capacitors built with a-Mn02/CNTs composite electrodes are presented in Table 8.3. The addition of nanotubes to a-Mn02 causes a drastic decrease of cell resistance and an increase of specific capacitance referred to the mass of a-Mn02 H20. However, when the specific capacitance is referred to the total mass of the composite electrode material, to be realistic, a CNTs loading higher than 10-15 wt% does not improve the electrodes performance. Therefore, 10-15 wt% of CNTs conducting additive seems to be an optimal amount both on the point of view of electrodes capacitance... 

Fig. 12. Evolution of the ESR for a supercapacitor assembled with activated carbon/CNTs composite electrodes in organic medium, as a function of the CNTs content in the composite [52]. Reprinted with permission from C. Portet, P.L. Tabema, P. Simon and E. Flahaut, J. Power Sounc., 139 (2005) 371.

FIGURE 3.2 Nyquist plots of AC impedance of the nano-MnOj/CNTs composite electrodes with different current collectors in different electrolytes. (With kind permission from Springer Science+Business Media Pseudocapacitive behaviors of nanostructured manganese dioxide/carbon nanotubes composite electrodes in mild aqueous electrolytes Effects of electrolytes and current collectors, Journal of Solid State Electrochemistry, 12,2008,1101-1107, Wang, Y. Q., A. B. Yuan, and X. L. Wang.)... 

Figure 3.5 Capacity retention of Fe203-filled CNT and Fe203-loaded CNT composite electrodes. Reprinted with permission from Ref 14.

Fig. 5. Schematic representation of electrochemical detection by CNTs composite electrode. Adpted from Teles Fonseca, 2008.

Lee, H. et al. 2011. Fabrication of polypyrrole (PPy)-carbonnanotube (CNT) composite electrode on ceramic fabric for supercapacitor apipUcations. Electrochimica Acta, 56,7460-7466. 

Along with the development of CNT electrodes through modification of conventional electrodes by CNTs with and without chemical modification, CNT composite electrodes have been investigated for biosensing applications. For instance, Hrapovic et al. reported that electrochanical sensors made of SWCNTs mixed with 2-3 nm small platinum nanoparticles displayed a remarkably improved sensitivity toward hydrogen peroxide. In this study, Nation, a perfluorosulfonated polymer, was used to solubilize SWCNTs and interact with Pt nanoparticles to form a network that connected Pt nanoparticles to the nanotube electrode surface (Figure 6.10A). 

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