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Gold/Mining/Energy : Global Thermoelectric - SOFC Fuel cells (GLE:TSE) -- Ignore unavailable to you. Want to Upgrade?

To: Rockwell60 who wrote (2709)	7/21/1999 2:41:00 PM
From: Scoobah	Read Replies (1) \| Respond to of 6016

Nothing questionable about it, just other people's wrong assumptions, which I am not obligated to correct. I am not here hyping stock, but promoting the industry, you won't find me giving investment advice to the public; and there is no law against the dissemination of public information. below is something sent to me on Nanotubes, Science Magazine July 2, 1999 High H2 Uptake by Alkali-Doped Carbon Nanotubes Under Ambient Pressure and Moderate Temperatures P. Chen, X. Wu, J. Lin, L. Tan* Physics Department, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260 Lithium- or potassium-doped carbon nanotubes can absorb ~20 or ~14 weight percent of hydrogen at moderate (200° to 400°C) or room temperatures, respectively, under ambient pressure. These values are greater than those of metal hydride and cryoadsorption systems. The hydrogen stored in the lithium- or potassium-doped carbon nanotubes can be released at higher temperatures, and the sorption-desorption cycle can be repeated with little decrease in the sorption capacity. The high hydrogen-uptake capacity of these systems may be derived from the special open-edged, layered structure of the carbon nanotubes made from methane, as well as the catalytic effect of alkali metals. * To whom correspondence should be addressed. Hydrogen has been recognized as an ideal energy carrier, but to make it truly useful, end-user H2 storage must be improved. In particular, high storage capacity is desirable when H2 is used as the energy carrier in high-energy density rechargeable batteries and in H2/O2 fuel cells. For these applications, metal hydridation is the existing method above room temperatures and below 20 to 40 atm of pressure, but these materials are heavy and expensive (1, 2). Cryoadsorption, in which activated carbon is often used as a sorbent, shows its advantages in the moderate size and weight of carbon, but suffers from the severe conditions (liquid nitrogen temperatures and 20 atm of pressure) required to hold the physically adsorbed H2 (3, 4). In any case, the H2 uptake by these systems is less than 6 weight % (Table 1), far lower than that of gasoline or diesel (17.3 weight %). More recently, carbon nanotubes were reported to be a more effective material for H2 uptake. Dollin et al. found that single wall carbon nanotube (SWNT) soots could absorb about 5 to 10 weight % of H2 at 133 K and 300 torr (5). Chambers et al. observed that at 120 atm and room temperature, graphite nanofibers with herringbone structure could store 67 weight % of H2 (6). Ye et al. used high-purity SWNT and obtained 8.25 weight % of H2 adsorption at 80 K and 100 atm (7). All the above H2-uptake systems require high pressure or subambient temperatures, or both. Here we introduce a H2 storage system that uses alkali metal-doped carbon nanotubes (CNTs) as sorbents and operates at ambient pressure and moderate temperatures The H2 uptake can achieve 20 weight % for Li-doped CNT at 653 K, or 14 weight % for K-doped CNT at room temperature. These values correspond to ~160 (for Li-doped CNT) or 112 kg of H2/m3 (for K-doped CNT), respectively, and are comparable to those of gasoline and diesel. Table 1. Comparison of H2 storage properties of various systems. W i: H2-uptake capacity (weight % H2); V i: H2 density (g/liter). System Tabsorb (K)Pabsorb (atm)H2 density Energy density WiVikWh/KgkWh/liter CNT 298-7731 0.43.20.1330.106 Li-doped CNT 473~6731 20.01806.666.0 Graphite 473~673114.0 2804.669.32 K-doped CNT <313114.012.6 4.664.2 Graphite <31315.0601.662.0 FeTi-H >26325<2960.583.18 NiMg-H >523 25<4811.052.69 Cryoadsorption ~7720~5 ~201.660.67 Isooctane/gasoline >233117.3 11712.78.76 The CNTs used in this study were made from catalytic decomposition of CH4 (8). After purification, almost all of the catalyst particles were removed. More than 90% of the product was in the form of multiwalled CNTs, and 70% was in the diameter range of 25 to 35 nm. The structure of a CNT is formed by the piling up of graphene sheets in the shape of circular cones with a hollow center. The doping of Li and K to the CNT was carried out by solid-state reactions between CNT and Li- or K-containing compounds, such as carbonates or nitrates. For comparison, Li- and K-doped graphite were prepared by the same procedures. The graphite sample was obtained from Merck with an average diameter of 50 µm. The specific surface area of CNT and graphite is 130 and 8.6 m2/g, respectively. The Li/C and K/C ratio of these alkali-doped carbon materials was about 1/15 as measured by x-ray photoelectron spectroscopy. The density of Li-doped carbon materials was ~0.9 g/cm3 for CNT and ~2.0 g/cm3 for graphite. Hydrogen uptake was measured by thermogravimetery analysis (TGA), with purified H2 (>99.99%) as the purging gas. Hydrogen absorption-desorption was confirmed by temperature- programmed desorption (TPD), with H2 being the only desorption product of the H2-saturated carbons. In situ Fourier transform infrared spectroscopy (FTIR) was applied to analyze the detailed mechanism of the process. All the above investigations were performed mainly on Li-doped samples because they are stable under ambient conditions. Samples for TGA were initially heated in situ at 873 K for 1 hour in a flow of purified H2 (99.99%) to remove absorbed water and contaminants. The Li-doped samples were cooled from 873 to 300 K and then heated again to 873 K linearly (5° per minute). The H2 uptake began at temperatures around 773 K and ended at 423 K (Fig. 1A). When the temperature was increased again, the sample further increased its weight, reaching a maximum value corresponding to a total of 14.5 weight % H2 at 673 K. Further increasing the temperature resulted in the H2 desorption, and the sample weight returned to its original value at 773 K In the above hydrogenation-dehydrogenation cycle, the system did not reach the equilibrium (saturation) state. When the Li-doped CNT sample was maintained at 653 K for 2 hours, the H2 uptake reached 20 weight % H2 at ambient pressure.