Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session P14: Focus Session: Hydrogen Storage I: Media |
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Sponsoring Units: FIAP Chair: Frederick E. Pinkerton, GM Research and Development Center Room: LACC 403B |
Wednesday, March 23, 2005 11:15AM - 11:51AM |
P14.00001: A Variety of Metal-N-H System for Hydrogen Storage Invited Speaker: Metal nitrides and imides exhibit strong affinity towards hydrogen molecules. Such strong interactions enable these substances to be used as potential materials for hydrogen storage. In the previous investigations, maximum of 11.5wt{\%} and 7.0 wt{\%} of hydrogen storage capacities have been determined in lithium nitride and lithium imide, respectively. However, relatively high operating temperatures place a serious restriction onto the application of those substances. It is clear that to lower down the operation temperatures the composition and structure of the subject material have to be altered in order to sit within a suitable thermodynamic range. Successful attempts have been made by introducing Mg or Ca into the Li2NH binary system, in which considerable reduction in hydrogen absorption and desorption temperatures and uprising H2 desorption plateau pressures have been achieved. Ternary imide Li2MgN2H2, as an example, could reversibly store 5.8wt{\%} of hydrogen at 180ÂșC with desorption plateau pressure higher than 10 bars. Previous investigations reveal that the hydrogen-rich phase of Li-N-H and Li-Mg-N-H systems comprise of metal amides and hydrides. It is probably the great potential for the union of H$^{\delta +}$ in amide and H$^{\delta -}$ in hydride to H2 that drives the two chemicals to react and give out hydrogen. According to this hypothesis, a serial of new Metal-N-H systems can be developed by reacting various amides with hydrides. Interaction between amide of Li or Mg with LiAlH4, MgH2, NaH and CaH2, respectively, has been investigated by an in situ planetary ball mill, TPD, volumetric Release-Soak techniques and FTIR etc. Novel Metal-N-H systems have been developed accordingly, among which three systems can release substantial amount of hydrogen (more than 5.0wt{\%}) near ambient temperature.. [Preview Abstract] |
Wednesday, March 23, 2005 11:51AM - 12:03PM |
P14.00002: Glassy materials as a hydrogen storage medium Seung-Hoon Jhi, Young-Kyun Kwon The adsorption of molecular hydrogen on a glassy material and its relatives is studied with a use of pseudopotential density functional method. The binding energy and distance of adsorbed hydrogen is particularly calculated. It is found that the desorption temperature of hydrogen in layered boron oxide is significantly higher than that in carbon nanotubes as much as twice, which is attributed to heteropolar bonding in boron oxide. The effect of water addition to boron oxide on hydrogen adsorption is also investigated. Our results indicate that water may reduce the surface area of boron oxide but does little affect the hydrogen adsorption energy. We also calculated an optimum pore size for hydrogen diffusion into boron oxide. Current study demonstrates a pathway to the finding of a new class of materials for hydrogen storage media that can hold hydrogen at ambient conditions through physisorption. [Preview Abstract] |
Wednesday, March 23, 2005 12:03PM - 12:15PM |
P14.00003: Enhanced hydrogen affinity in single-walled carbon nanotubes relative to activated carbons M.K. Haas, A.C. Cooper, C.G. Coe, J.M. Zielinski, G.P. Pez The present body of work represents a meticulous and thorough investigation of single-walled carbon nanotube properties and processing in relation to hydrogen storage. Nanotube samples were characterized by Raman spectroscopy, light scattering, microscopy, TGA, ICP, differential pressure adsorption (DPAU), and BET surface area. A reproducible carbon nanotube cutting method was developed and characterized. A number of nanotube variables, such as average length, were then evaluated for their effects on hydrogen capacity. Thorough characterization reveals the strongly variable nature of carbon nanotube materials. Diameter, length, purity, structural integrity, as well as secondary and tertiary morphology must be determined in order to establish any structure-property relationships. Measurements of hydrogen capacity indicate that commercially available single-walled carbon nanotubes in their pristine, non-functionalized form are not a viable hydrogen storage option. However, it is also clear that single-walled carbon nanotubes have a higher affinity for hydrogen than do activated carbons. At a given BET surface area, activated carbons have a fraction of the hydrogen capacity of single-walled carbon nanotubes. This information, in addition to Air Product's experimental modeling results, leads to a promising path forward. In particular, experiments with smaller diameter nanotubes and charge transfer intercalation are planned. [Preview Abstract] |
Wednesday, March 23, 2005 12:15PM - 12:27PM |
P14.00004: New Reversible Complex Metal Hydrides J. Graetz, J.J. Reilly, Y. Lee, T. Vogt Novel, reversible complex metal hydrides with the general formula $A_{3-x}A'_x$AlH$_6$ ($A$, $A' =$ Na, Li, K, Mg, Ca) were synthesized and structurally characterized using synchrotron x-ray diffraction. The hydrogen absorption/desorption characteristics and thermodynamic properties were studied using pressure-composition isotherms. These results demonstrate that the partial substitution of the alkali metal can change the equilibrium pressures substantially. As an example, the substitution of one Li for Na in Na$_3$AlH$_6$ cryolite to form Na$_2$LiAlH$_6$ elpasolite increases the dissociation enthalpy by $6.5 \pm1.6$ kJ/mol H$_2$. This thermodynamic change lowers the plateau pressure by 30 bar at 518 K. Similar trends were observed in the potassium cryolite and elpasolite phases. This form of thermodynamic tuning may be applied to other, high capacity alanates (e.~g. LiAlH$_4$ and Mg(AlH$_4$)$_2$), which are currently hindered by reaction enthalpies that are largely unfavorable for PEM fuel cell applications. [Preview Abstract] |
Wednesday, March 23, 2005 12:27PM - 12:39PM |
P14.00005: Hydrogen storage in BN cage Puru Jena, Qiang Sun, Qian Wang Recently hydrogen is being considered as a potential candidate to meet the increasing energy need of both the developing and developed world. To this end it is important to find efficient means for storing hydrogen. Carbon nanotubes, especially single-wall tubes, were initially considered to be better candidates for hydrogen storage than other materials. However, the early experiments have met with some controversy and very different results for the hydrogen storing capacity of carbon nano-tubes have been reported. To search for other non-carbon system, we studied (H$_{2})_{n}$@B$_{36}$N$_{36}$ cage by using first-principles method. It has been found that H$_{2}$ can go into the cage through the hexagonal face. The maximum number of H$_{2}$ that can be inserted into the cage without breaking the cage is 18, resulting in a weight percentage of 4{\%}. However, the storage of H$_{2}$ in BN cage needs external energy, which increases with n$^{2}$ (n is the number of hydrogen molecules) while the HOMO-LUMO gap decreases as n$^{3}$. The energy cost is associated with the increase in the B-N bond length and decrease in the H-H bond length as n increases. [Preview Abstract] |
Wednesday, March 23, 2005 12:39PM - 12:51PM |
P14.00006: Effect of Mg Doping in NaAlH$_4$ Rajeev Ahuja, Sa Li, C. Moyses Araujo, Puru Jena First principles calculations based on density functional theory have been carried out to search for suitable catalysts that can lower the hydrogen desorption temperature from sodium-alanate (NaAlH$_{4})$. We focus here on the possibilities of doping Mg in bulk sodium alanate. The result shows that Mg prefers to occupy the Na site and weakens the covalent bond between Al and H. The energy needed to remove a hydrogen atom from (Mg,Na)AlH$_{4}$ is found to be significantly lower than that from NaAlH$_{4}$. The effect is similar to Ti doping which is supposedly the best catalyst found to date for hydrogen desorption from sodium alanate. Furthermore, the Mg doping is shown to promote the formation of Na vacancy which in turn plays an important role in the hydrogen desorption process. [Preview Abstract] |
Wednesday, March 23, 2005 12:51PM - 1:03PM |
P14.00007: Cohesion of Mg$_2$FeH$_6$ and Related Complex Hydrides David Singh, Samed Halilov, R. Gupta, M. Gupta The stability and bonding of complex K$_2$PtCl$_6$ structure hydrides is analyzed using results of density functional calculations. The cohesion is dominated by ionic contributions. The 18-electron rule generally followed in these compounds results from their ionic character combined with crystal field effects. Density functional results for the formation energies are presented and implications for hydrogen storage are discussed. [Preview Abstract] |
Wednesday, March 23, 2005 1:03PM - 1:15PM |
P14.00008: New Quaternary Hydride Li$_{3}$BN$_{2}$H$_{8}$ with $>$10 wt{\%} Hydrogen: I. Material Synthesis and Structural Characterization Gregory P. Meisner, Frederick E. Pinkerton, Martin S. Meyer, Michael P. Balogh, Matthew Kundrat We report a new quaternary hydride Li$_{3}$BN$_{2}$H$_{8}$ synthesized from mixed LiNH$_{2}$ and LiBH$_{4}$ powders in a 2:1 molar ratio by ball milling. X-ray diffraction (XRD) results show that as milling time increases, the LiNH$_{2}$ and LiBH$_{4}$ diffraction peaks weaken and a new set of peaks emerges. At 40 min, the sample is substantially converted to the new phase, with only a small remnant of LiNH$_{2}$ in the XRD pattern. After 300 min the conversion is complete, and continued milling up to 960 min produces no further change. The final XRD pattern appears to be single phase, except for a small amount of Li$_{2}$O impurity, and has a background intensity that is essentially unchanged with milling time, implying that ball milling does not produce an amorphous phase. All of the observed XRD peaks can be indexed as a single BCC quaternary phase with a =10.76 {\AA}. Our \textit{in-situ} XRD data show that Li$_{3}$BN$_{2}$H$_{8}$ forms when mixed LiNH$_{2}$ and LiBH$_{4}$ powders are heated to above $\sim $95$^{\circ}$C without ball milling, then melts at $\sim $190$^{\circ}$C, and finally forms a mixture of solid Li$_{3}$BN$_{2}$ polymorphs upon H$_{2}$ gas release above $\sim $250$^{\circ}$C. [Preview Abstract] |
Wednesday, March 23, 2005 1:15PM - 1:27PM |
P14.00009: New Quaternary Hydride Li$_{3}$BN$_{2}$H$_{8}$ with $>$10 wt{\%} Hydrogen: II. Hydrogen Desorption Measurements Frederick E. Pinkerton, Gregory P. Meisner, Martin S. Meyer, Michael P. Balogh, Matthew Kundrat We report thermogravimetric, volumetric, and calorimetric measurements of hydrogen desorption from the new quaternary hydride Li$_{3}$BN$_{2}$H$_{8}$ (11.9 wt{\%} theoretical hydrogen capacity). Li$_{3}$BN$_{2}$H$_{8}$ releases $\ge $10 wt{\%} hydrogen at temperatures above $\sim $250$^{\circ}$C. Simultaneous mass spectrometry residual gas analysis shows that a small amount of ammonia (2-3 mole{\%} of the generated gas) is released concurrently. Independent volumetric and gravimetric measurements are in excellent agreement regarding the quantities of hydrogen and ammonia released. Differential scanning calorimetery and in-situ x-ray diffraction show that Li$_{3}$BN$_{2}$H$_{8}$ melts at $\sim $190$^{\circ}$C, thus hydrogen evolution occurs from the molten state. It dehydrides to the solid product Li$_{3}$BN$_{2}$, and the evolved gas satisfactorily accounts for all of the available hydrogen content. Preliminary calorimetric measurements suggest that hydrogen release is exothermic, and, hence, not easily reversible; to date, rehydriding has not been achieved. [Preview Abstract] |
Wednesday, March 23, 2005 1:27PM - 1:39PM |
P14.00010: Towards 9 weight percent, reversible, room temperature hydrogen adsorbents: Hydrogen saturated organometallic bucky balls Yufeng Zhao, Yong-Hyun Kim, A. C. Dillon, M.J. Heben, S. B. Zhang A new concept for high-capacity hydrogen absorbents is introduced by first-principles calculations. Transition metal (TM) atoms bound to fullerenes are proposed as a medium for high density, room temperature, ambient pressure storage of hydrogen. TMs bind to C60 or C48B12 by charge transfer interactions to produce stable organometallic bucky balls (OBBs) and bind to multiple dihydrogen molecules through the so-called Kubas interaction [1]. A particular scandium OBB can bind as many as eleven hydrogen atoms per TM, ten of which are bound in the form of dihydrogen molecular ligands that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is around 0.3 eV/H2, which is ideal for use on-board vehicles. The theoretical maximum retrievable H2 storage density is about 9 weight percent. This work was supported by the U.S. DOE EERE, BES/MS, and BES/CS under contract No. DEAC36-99GO10337. [1] G.J. Kubas, J. Organometallic Chem. 635, 37 (2001). [Preview Abstract] |
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