Catalytically grown carbon nanotubes

and their applications

Chunming Niu, Bob Hoch and Howard Tennent

Hyperion Catalysis International, 38 Smith Place, Cambridge, MA 02138

Abstract

Recently, catalytic growth of carbon nanotubes has attracted considerable attention for its potential in commercial production of carbon nanotubes. We have been producing catalytically grown carbon nanotubes in large quantity for more than a decade. Our process is based on chemical conversion of hydrocarbon feedstocks catalyzed by supported transition metal catalysts. It is a simple petrochemical technology, producing carbon nanotubes with high purity of ten nanometers or less in diameters and tens of microns in length. Due to their structural uniformity, our nanotubes are ideal template and building blocks for new nanostructured materials. We have prepared highly crystallized SiC nanofibrils by "topotactic" conversion of carbon nanotubes. The average diameter of SiC nanofibrils is 15 nm. A novel carbon structure has been engineered from nanotubes through a wet chemical process. The new carbon has an open frame porous structure, excellent thermal and chemical stability; and more significantly, it is free of micropores. The later property is important for the development of catalysts with high selectivity and energy storage devices with high power. The new carbon has been prepared in various physical forms, including particles, extrudates and membranes (sheet), to meet specific requirement of different applications. Electrochemical capacitors based on nanotube membrane electrode showed unprecedented power performance. A RC constant of 7 milliseconds was measured from a ten-cell device, which is approaching the value of electrolytic capacitors. We have prepared nanotube-polymer nanocomposites by in situ polymerization. Electrical measurement showed that a conducting network can be formed with polymer matrix at very low nanotube concentration. A resistivity of 650 W-cm was measured from a nanotube-polystyrene nanocomposite containing 0.1% nanotubes. Note that, to reach the same conductivity, a considerable high loading (>10%) is required if current commercial conductive additives, such as carbon black and carbon fibers, was used.