Carbon Nanotubes: Electrochemical Modification
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Carbon nanotubes (CNTs) are important because of their outstanding structural, mechanical, and electronic properties, and are finding applications in molecular electronics, chemical sensors, scanning probes, special capillaries, supercapacitors, energy storage devices, and electromechanical actuators. CNTs are expected to exhibit superior electrochemical properties in comparison with other carbon materials that are widely used in electrochemical applications. Because CNTs have length scales similar to those of biological molecules such as enzymes and proteins, they can act as effective biosensing electrodes. Furthermore, potential applications such as Coulter counters, bioelectrochemical sensors, as well as electrochemical hydrogen and lithium storage have stimulated an increasing amount of research into the electrochemical properties of CNTs.
Chemical functionalization is developing to be an effective tool to broaden the application spectrum of CNTs. Until now, functionalization of CNTs has been accomplished by three different approaches, namely, thermally activated chemistry, photochemical functionalization, and electrochemical modification (ECM). Among these, ECM offers the specific advantage that the energy level of a chosen nanotube can be selectively tuned, allowing one to functionalize the tubes in a controlled manner.
To devise novel ECM schemes, it is essential to investigate the electrochemical properties of CNTs, such as their charging and discharging behaviors in various media, electron transfer (ET) rates for different redox couples, etc. In the following entry, the electrochemical characteristics of various types of nanotube electrodes are first presented. Then various ECM methods reported until now are reviewed. The modification of bulk CNTs is detailed first, followed by the modification of individual nanotubes. Finally, various (electro)chemical applications of pristine and electrochemically modified CNTs are discussed.