Rapid, Room Temperature, High-Density Hydrogen Adsorption on Single-Walled Carbon Nanotubes at Atmospheric Pressure Assi
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Rapid, Room Temperature, High-Density Hydrogen Adsorption on Single-Walled Carbon Nanotubes at Atmospheric Pressure Assisted by a Metal Alloy M.J. Heben, A.C. Dillon, T. Gennett1, J.L. Alleman, P.A. Parilla, K.M. Jones, and G.L. Hornyak. National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401-3393 (USA) 1 Chemistry Department, Rochester Institute of Technology, 85, Lomb Drive, Rochester, NY 146235604 (USA) ABSTRACT Laser-generated, carbon single-walled nanotubes (SWNTs) adsorb hydrogen in a matter of minutes at room temperature and atmospheric pressure in the presence of a Ti-6Al-4V metal alloy. The unusual hydrogen adsorption properties are activated when the SWNTs are sonicated in nitric acid with a Ti-6Al-4V probe. The process cuts the SWNTs and introduces ~15-40 wt% metal alloy into the previously pure single-walled nanotube material. Subsequent hydrogen adsorption occurs in two separate sites with a maximum adsorption capacity of ~7 wt% on a total sample weight basis. Approximately 2.5 wt% hydrogen is evolved at 300 K while the remainder desorbs between 475-850 K. The pure metal alloy adsorbs ~ 2.5 wt% H 2, and evolves hydrogen with increasing temperature in a manner similar to the alloy-doped SWNTs. However, it is clear from studies presented here that the SWNT fraction is quite active in H2 uptake, adsorbing as much as 7 % on a SWNT weight basis. INTRODUCTION Hydrogen can be reacted with oxygen to produce water and energy without the generation of either carbon dioxide or other pollutants in both internal combustion engines and highly efficient fuel cells. It is therefore an ideal candidate to replace fossil fuels as an energy carrier1. Until hydrogen can be inexpensively generated in bulk from renewable wind and solar resources, it may be produced from currently available non-renewable resources such as natural gas. However, the transition to a hydrogen-based energy economy is impeded by the lack of a convenient and cost-effective hydrogen storage system. Although several hydrogen storage options exist, no approach satisfies all of the efficiency, size, weight, cost and safety requirements for use in transportation or utility applications. The ideal system would be capable of reversibly storing hydrogen at a density of 6.5 wt% with only small energy requirements for heating, cooling, or pressurization. The potential advantages of SWNTs over other hydrogen storage materials were demonstrated in 19972. Hydrogen was stabilized on impure SWNT samples by non-dissociative adsorption at room temperature after a brief exposure at 300 torr (~0.4 atm). Hydrogen storage densities of 5-10 wt% were projected for pure samples. Other studies using purified, cut SWNTs concluded that such high storage densities could only be achieved with cryogenic temperatures (80 K) and high pressures (158 atm)3. These latter results are consistent with theoretical investigations based on consideration of van der Waals interactions between H2 and A9.1.1Mat. Res. Soc. Symp. Proc. Vol. 633 © 2001 Materials Research Society
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