Carbon nanotubes electron transfer rate

To summarize, one can say that the electrochemical performance of CNT electrodes is correlated to the DOS of the CNT electrode with energies close to the redox formal potential of the solution species. The electron transfer and adsorption reactivity of CNT electrodes is remarkably dependent on the density of edge sites/defects that are the more reactive sites for that process, increasing considerably the electron-transfer rate. Additionally, surface oxygen functionalities can exert a big influence on the electrode kinetics. However, not all redox systems respond in the same way to the surface characteristics or can have electrocatalytical activity. This is very dependent on their own redox mechanism. Moreover, the high surface area and the nanometer size are the key factors in the electrochemical performance of the carbon nanotubes. 

Figure 3.13 (a) Values of charge-transfer resistance of different systems based on carbon, using the redox probe Fe(CN)6 . (b) Nyquist plot of different carbon nanotube composites in the presence of the redox couple, (c) Table with the electron-transfer rate constants calculated from cyclic voltammet data by using Nicholson method. Adapted with permission from Ref [103]. Copyright, 2008, Elsevier. 

Both reflectance FT-IR spectra and the dependence of the reduction peak current on the scan rate revealed that cat adsorbed onto the SWNTs surfaces. The redox wave corresponds to the Fe(lll)/Fe(ll) redox center of the heme group of the cat adsorbate. Compared to other types of carbonaceous electrode materials (e.g. graphite and carbon soot), the electron-transfer rate of cat redox reaction was greatly enhanced at the SWNTs-modified electrode. The catalytic activity of cat adsorbate at the SWNTs appeared to be retained, as the addition of H2O2 produced a characteristic catalytic redox wave. The facile electron-transfer reaction of cat could be attributed to the unique properties of SWNTs (e.g. the excellent electrical conductivity of SWNTs, the enhanced surface area arising from the high aspect ratio of the nanotubes, and the amenability of SWNTs for the attachment of biomolecules). 

GUell, A. G. Ebejer, N. Snowden, M. E. McKelvey, K. Macpherson, J. V. Unwin, P. R., Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks. Proceedings of the National Academy of Sciences 2012, 109, 11487-11492. 

Carbon nanotubes (CNTs) show remarkable electrical, chemical, mechanical, and stmctural properties and have found their applications in various disciplines, such as in material [55, 56] and surface [57] sciences. CNTs have been shown to improve the conductivity behavior of electrodes [58-60]. CNTs improve electron transfer rates when used to modify electrodes, and have even exhibited some electrocatalytic properties which are attributed to the reactive open ends of the tubes [61, 62]. CNTs can cause reduction in overpotentials and surface fouling on electrodes as well as an increase in the voltammetric signals [34, 63-65]. 

CNT randomly dispersed composites Many soft and rigid composites of carbon nanotubes have been reported [17]. The first carbon-nanotube-modified electrode was made from a carbon-nanotube paste using bromoform as an organic binder (though other binders are currently used for the paste formation, i.e. mineral oil) [105]. In this first application, the electrochemistry of dopamine was proved and a reversible behavior was found to occur at low potentials with rates of electron transfer much faster than those observed for graphite electrodes. Carbon-nanotube paste electrodes share the advantages of the classical carbon paste electrode (CPE) such as the feasibility to incorporate different substances, low background current, chemical inertness and an easy renewal nature [106,107]. The added value with CNTs comes from the enhancement of the electron-transfer reactions due to the already discussed mechanisms. 

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