Carbon Nanotube Materials for Hydrogen Storage

Carbon single-wall nanotubes (SWNTs) are essentially elongated pores of molecular dimensions and are capable of adsorbing hydrogen at relatively high temperatures and low pressures. this behavior is unique to these materials and indicates that SWNTs are the ideal building block for constructing safe, efficient, and high energy density adsorbents for hydrogen storage applications. In past work wedeveloped methods for preparing and opening SWNTs, discovered the unique adsorption properties of these new materials, confirmed that hydrogen is stablilized by physical rather than chemical interactions, measured the strength of interaction to be approximately 5 times higher than for adsorption on planar graphite, and performed infrared absorption spectroscopy to determine the chemical natureof the surface terminations before, during, and after oxidation. This year we have made significant advances in synthesis and characterization of SWNT materials so that we can now prepare gram quantities of high-purity SWNT samples and measure and control the diameter distribution of the tubes by varying key parameters during synthesis. We have also developed methods which purify nanotubes andcut nanotubes into shorter segments. These capabilities provide a means for opening the (10,10) tubes which were unreactive to the oxidation methods that successfully opened (9,9) tubes, and offer a path towards orgainizing nanotube segments to enable high volumetric hydrogen storage densitites. We also performed temperature programmed desorption spectroscopy on high purity carbon nanotubematerial obtained from our collaborator Prof. Patrick Bernier and finished construction of a high precision Seivert's apparatus which will allow the hydrogen pressure- temperature-composition phase diagrams to be evaluated for SWNT materials.