Carbon nanotubes and their composites in electrochemical applications

Abstract

This paper presents various applications of carbon nanotubes as components of electrode materials for such electrochemical use as electrochemical capacitors, fuel cells, hydrogen electrosorption and accumulators. Generally, carbon nanotubes give exceptional improvement of electrode performance due to their mesoporous and well conducting networks. The cell resistance is drastically reduced and the transport of ions is greatly enhanced. In addition to their good conductivity, carbon nanotubes can be flexible and stretchable which is crucial for cyclability of electrodes, especially if volumetric changes of electrode material occur during operation. Consequently, they serve as excellent support for conducting polymers (e.g. polyaniline, polypyrrole) and metal oxides (e.g. MnO₂) giving attractive capacitor electrodes. The presence of nanotubes in carbon precursor rich in heteroatoms, e.g. nitrogen from melamine or oxygen, also supplies an interesting carbonized composite with a good charge propagation for supercapacitor use. Furthermore, carbon nanotubes have been tested for hydrogen electrosorption giving a very moderate hydrogen capacity (0.27 wt.%). However, modification of nanotubes can enhance hydrogen storage. On the other hand, carbon nanotubes can serve as an excellent additive to many electrode materials for improvement of conductivity and cell performance. They could be a good support of the catalytic particles for fuel cell application as well.