Carbon nanotubes electrochemical performance

In the third paper by French and Ukrainian scientists (Khomenko et al.), the authors focus on high performance a-MnCVcarbon nanotube composites as pseudo-capacitor materials. Somewhat surprisingly, this paper teaches to use carbon nanotubes for the role of conductive additives, thus suggesting an alternative to the carbon blacks and graphite materials - low cost, widely accepted conductive diluents, which are typically used in todays supercapacitors. The electrochemical devices used in the report are full symmetric and optimized asymmetric systems, and are discussed here... 

Work on the nanostructuring of electrodes with carbon nanotubes by Gooding and coworkers [96, 97] has demonstrated that superior electrochemical performance can be achieved with carbon nanotubes that are vertically aligned compared with being... 

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. 

Carbon nanotubes inevitably contain defects, whose extent depends on the fabrication method but also on the CNT post-treatments. As already seen, oxidizing treatments, such as acid, plasma or electrochemical, can introduce defects that play an important role in the electrochemical performance of CNT electrodes. For instance, Collins and coworkers have published an interesting way to introduce very controlled functionalization points or defects on individual SWNTs by electrochemical means [96]. Other methodologies to introduce artificial defects comprise argon, hydrogen and electron irradiation. Under this context, a number of recent works have appeared with the goal of tailoring the electrochemical behavior of CNT surfaces by the controlled introduction of defects [97, 98]. 

In order to guarantee an efficient performance of the CNT-based electrochemical devices, attention has to be paid not only to CNT synthesis and purification but also to the way that the CNT electrode is built up. There have been many studies in the literature dealing with CNT dispersions either on conducting substrates or forming composites. In this subsection we will address the different carbon-nanotube deposition techniques and carbon-nanotube arrangements on different electrode surfaces. 

Effects of Air Exposure of a Pyrolytic Carbon Electrode and Multiwalled Carbon Nanotubes on Their Electrochemical Performance in Terms of Fe2+/Fe3+ Redox Behavior... 

It is well known that catalyst support plays an important role in the performance of the catalyst and the catalyst layer. The use of high surface area carbon materials, such as activated carbon, carbon nanofibres, and carbon nanotubes, as new electrode materials has received significant attention from fuel cell researchers. In particular, single-walled carbon nanotubes (SWCNTs) have unique electrical and electronic properties, wide electrochemical stability windows, and high surface areas. Using SWCNTs as support materials is expected to improve catalyst layer conductivity and charge transfer at the electrode surface for fuel cell oxidation and reduction reactions. Furthermore, these carbon nanotubes (CNTs) could also enhance electrocatalytic properties and reduce the necessary amount of precious metal catalysts, such as platinum. 

Portet C, Yushin G, Gogotsi Y (2007) Electrochemical performance of carbon onions, nanodiamonds, carbon black and multi walled nanotubes in electrical double layer capacitors. Carbon 45(13) 2511-2518... 

Electrodeposition of Pt on multiwall carbon nanotubes (MWNT) has been reported by Wang et al.27 In their process, a layer of Co was first electrodeposited on a carbon paper. The purpose of Co film was to catalyze the growth of the subsequent MWNTs layer. A chemical vapor deposition (CVD) technique was used to deposit MWNTs on the Co film. Platinum was then electrodeposited on the MWNT layer. The electrolyte used contained H2PtCl6 and H2SO4. The electrodeposition of Pt was performed under potentiostatic condition using 0 V vs. saturate calomel electrode (SCE). The particle size achieved with this technique was approximately 25 nm that is too large in comparison with other chemical and electrochemical methods. 

Su, L.-H.. Zhang, X.-G., and Liu, Y. 2008. Electrochemical performance of Co-Al layered double hydroxide nanosheets mixed with multiwall carbon nanotubes. Journal of Solid State Electrochemistry 12, 1129-1134. 

Raymundo-Pinero, E., Khomenko, V., Frackowiak, E., and Beguin, F. (2005). Performance of manganese oxide/carbon nanotubes composites as electrode materials for electrochemical capacitors. J. Electrochem. Soc., 152, A229-A235. 

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