Development of Hydrogen Storage Technique by Using Carbon Nanotubes

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The high hydrogen storage capacity of carbon nanotubes has been reported for single-walled carbon nanotubes (SWNTs) and metal-doped graphite nanofibers. Because of its impact in applications in fuel cell vehicles, intensive experimental and theoretical works have been performed. Some of the most striking reports are questionable and molecular dynamics simulations in this research project cannot explain the hydrogen storage capacity of SWNTs more than 1 wt %. Hence, the generation of high-purity SWNTs is the key issue to solve this discrepancy. In addition to the laser-furnace technique, we developed a new CVD technique for bulk high-purity generation of SWNTs. By using alcohols such as ethanol and methanol as the carbon sources in catalytic CVD, high-purity SWNTs without metal particles, amorphous carbon or MWNTs can be synthesized at relatively low reaction temperatures of 600 -800 For the bulk generation of SWNTs, Fe/Co bimetal catalysts supported on USY zeolite was employed. The diameter and chirality distributions, which were examined by resonant Raman scatterings and near infrared fluorescence spectroscopy, could be quite narrow at lower CVD temperatures. Combined with the molecular dynamics simulation of the nanotube growth process, the determination mechanism of chirality by the nanotube cap structure was demonstrated. In addition to the bulk generation by using zeolite, Fe/Co or Co/Mo nano-particles directly located on quartz or silicon substrate by dip-coating can be used as efficient catalysts. With this latter system, detailed characterization of catalysts and the growth of vertically aligned SWNTs mat on a quartz substrate were demonstrated. With this latter system, virtually metal-free SWNTs were generated for the further clarifications of hydrogen storage examinations.