Single-walled carbon nanotubes hold great promises as hydrogen storage medium. Their unique architecture makes them the best carbon-based adsorbent for hydrogen. It has been predicted theoretically that gravimetric density of up to 16 weight percent of H2 and volumetric density of 160 kg/m3 of H2 can be stored in (10,10) SWNT. This value exceeds greatly the US Department of Energy¹s energy density target of 6.5 weight percent and 62 kg/m3 for an economically viable vehicular hydrogen storage medium. This value has never been obtained experimentally in a reproducible way, creating much controversy in the field. This is because of the lack of controls in the synthesis of SWNT, the lack of understanding of the effects of chemical modifications through the purification processes, and the lack of understanding of how molecular hydrogen interacts with SWNT. Recently, we began an intensive research program aiming at resolving these issues. The presentation will focus on the following two aspects: Controlled synthesis and large-scale production of SWNT and effect of purification on the hydrogen uptake. Controlled synthesis and large-scale production is effected using a novel aerosol-based CVD approach employing mixed metal nanoparticles prepared in-situ the hydrocarbon feedstock. The effect of purification on the hydrogen storage capacity is studied through series of experiments employing Raman and proton NMR spectroscopy and N2 adsorption isotherms. It appears that the entry ports of SWNT become functionalized during purification and that these functional groups prevent H2 from entering the tubes. Experiments to eliminate the blocking groups and to confirm the high hydrogen uptake capacity of SWNT are under way.
Steacie Institute for Molecular Sciences, National Research Council of Canada
100 Sussex Drive, Room 1047, Ottawa, ON K1A 0R6 CANADA