Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A16: Focus Session: Hydrogen Storage I |
Hide Abstracts |
Sponsoring Units: FIAP Chair: Louis G. Hector, General Motors Room: Baltimore Convention Center 312 |
Monday, March 13, 2006 8:00AM - 8:36AM |
A16.00001: Quaternary Li-B-N-H Hydrides: New Hydrogen-Rich Storage Materials Invited Speaker: We have synthesized light metal Li-B-N-H quaternary hydrides by ball milling mixtures of LiNH$_{2}$ and LiBH$_{4}$ for a series of compositions (LiNH$_{2})_{x}$(LiBH$_{4})_{1-x}$ (x = 0.33 to 0.8). We discovered a new quaternary hydride phase, referred to here as $\alpha $ Li-B-N-H, as the primary constituent for amide-rich (x $>$ 0.6) compositions. Although previously tentatively identified as Li$_{3}$BN$_{2}$H$_{8}$, its true equilibrium composition is Li$_{4}$BN$_{3}$H$_{10}$ as determined by single crystal x-ray diffraction (XRD). Li$_{4}$BN$_{3}$H$_{10}$ has a body-centered cubic crystal structure, space group I2$_{1}$3 ({\#} 199) with a = 10.68 {\AA}. In situ XRD data demonstrate that the $\alpha $-phase also forms without ball milling by reacting mixed LiNH$_{2}$ and LiBH$_{4}$ powders at temperatures above about 95$^{o}$C. The $\alpha $ phase melts at about 190\r{ }C and releases hydrogen from the liquid above 250\r{ }C, forming solid Li$_{3}$BN$_{2}$. Using mass spectrometry residual gas analysis (RGA) we observe that NH$_{3}$ is released concurrently, and the quantity of NH$_{3}$ released is strongly dependent on the composition x. Maximum hydrogen release, exceeding 10 wt{\%}, with minimum NH$_{3}$ release (1-3 mole {\%} of the evolved gas) occurs for compositions near LiNH$_{2}$:LiBH$_{4}$ = 2:1 (x = 0.667). Small additions of Ni, Pt, or Pd as powder or metal chloride reduce the dehydrogenation temperature by as much as 112\r{ }C, and also reduce the quantity of NH$_{3}$ released by about an order of magnitude. Differential scanning calorimetry shows an endothermic melting peak above 190\r{ }C, followed by substantial exothermic heat flow above 250\r{ }C associated with hydrogen release and solidification of Li$_{3}$BN$_{2}$. The exothermic hydrogen release suggests that the reverse reaction is not thermodynamically favored. This new quaternary compound and its derivatives nonetheless represent promising research candidates in the search for practical on-board hydrogen storage materials. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A16.00002: Composition dependence of hydrogen and ammonia release in the lithium-boron-nitrogen-hydrogen quaternary system Gregory P. Meisner, Matthew L. Scullin, Frederick E. Pinkerton, Martin S. Meyer, Michael P. Balogh The new quaternary hydride in the lithium-boron-nitrogen-hydrogen (Li-B-N-H) quaternary phase diagram forms by the reaction of lithium amide (LiNH$_{2})$ and lithium borohydride (LiBH$_{4})$ near the approximate composition LiB$_{0.33}$N$_{0.67}$H$_{2.67}$. When heated, the quaternary hydride first melts and then releases greater than 10 wt{\%} hydrogen and a small amount of ammonia (2-3 mole{\%} of the generated gas). We studied hydrogen and ammonia release from the series of reactant mixtures (LiNH$_{2})_{x}$(LiBH$_{4})_{1-x}$ as a function of composition using volumetric, gravimetric, mass spectrometer, and \textit{in situ} x-ray diffraction measurements. We found that maximum hydrogen and minimum ammonia release do occur for x = 0.67. We observe that this composition corresponds to the ternary decomposition end product Li$_{3}$BN$_{2}$ rather than to the true single phase composition of the quaternary hydride as determined from our single crystal x-ray diffraction measurements. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A16.00003: First-principles Study on Li-N-H System for Hydrogen Storage Takao Tsumuraya, Tatsuya Shishidou, Tamio Oguchi Lithium amide ${\rm (LiNH_2)}$ and lithium imide $\mathrm{(Li_2NH)}$ have been noticed as one of the most promising candidates for hydrogen storage due to their high gravimetric densities of hydrogen. As regards the hydrogenating and dehydrogenating processes that involve these lithium hydrides, there is an argument about whether ammonia gas is relevant and it still remains as a matter to be studied. Furthermore, the crystal structure of $\mathrm{Li_2NH}$ is not fully determined yet because of the difficulty in identifying hydrogen positions. Recently, various transition-metal compounds have been examined with ball milling technique for exploring catalysis to promote reaction processes, and they found that some of the Ti compounds show good performance. Measurements of x-ray absorption spectroscopy (XAS) at Ti K edge are currently under way to have a clue for understanding the catalysis mechanism. To address these issues and to get fundamental insights from microscopic level, we performed first-principles calculations by using all-electron full-potential linear augmented plane wave (FLAPW) method. We will discuss structural stability, electronic structure of lithium hydrides $\mathrm{LiNH_2}$ and $\mathrm{Li_2NH} $ and the heat of formation in reaction processes. Structural optimization is carried out to evaluate total energies involved in reaction processes. XAS spectra and electronic structure of Ti compounds are also discussed. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A16.00004: First-principles study of structural properties of Li$_2$NH Amra Peles, Suchismita Sanyal, Mahesh Chandran, Job Rijssenbeek, Mei-Yin Chou Nitrogen containing hydrides have attracted much attention recently as viable candidates for hydrogen storage materials. One example is the amide and imide involved in the reversible chemical reaction $$ {\rm LiNH}_{2} + {\rm LiH} \rightarrow {\rm Li}_{2}{\rm NH} +{\rm H}_{2}. \label{re1} $$ In an effort to understand the reaction mechanism, one needs to have the informations on the structural properties of these compounds. There is a disagreement in the existing literature regarding the crystal symmetry of Li$_2$NH. We present a summary of first-principles investigations of the structural properties of Li$_2$NH in an attempt to identify the lowest energy structure. Calculations were performed within density functional theory framework employing plane waves and projector-augmented-wave potentials. Various crystal structures were obtained by minimazing the total energy and the forces. The stability and energetics of these structures will be discussed. [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A16.00005: Theoretical Investigation of the Li amide/Li imide Hydrogen Storage Reaction Jan Herbst, Louis Hector, Jr. Considerable recent interest has centered on the reaction LiNH$_{2}$ + LiH $\leftrightarrow $ Li$_{2}$NH + H$_{2}$ as a mechanism for hydrogen storage. We have conducted density functional calculations of the electronic structure, vibrational properties, and enthalpy of formation for each component. The long established crystal structures for LiH and LiNH$_{2}$ (Li amide) were employed, while a newly determined orthorhombic structure for Li$_{2}$NH (Li imide) was used. Our 298K results within the generalized gradient approximation for $\Delta $H(LiNH$_{2})$ and $\Delta $H(LiH), as well as for the overall heat of reaction, are in excellent accord with experiment, suggesting that the measured $\Delta $H(Li$_{2}$NH) is inaccurate. Phonon densities of states calculated for the amide and imide compare very favorably with observed infrared and Raman spectra. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A16.00006: More insights into LiNH$_2$-(LiH, MgH$_2$) system from DFT studies C. Moys\'{e}s Ara\'{u}jo, Ralph H. Scheicher, Puru Jena, Rajeev Ahuja First-principles calculations based on density functional theory have been carried out by us to understand the hydrogen desorption reactions for systems involving LiNH$_2$ mixed with either LiH or MgH$_2$. We first determined the crystalline structures and total energies of the reactants and possible products, which have been proposed from experiment. Our results for LiNH$_2$ and Li$_2$NH show good agreement with experimental data. For the mixed compound Li$_2$Mg(NH)$_2$, we have performed geometry optimization by force minimization and in addition also using molecular dynamics and simulated annealing. The circumstance that the crystalline structure of this system has not yet been resolved prevented us from comparing our results with experimental data. However, the calculated reaction enthalpy agrees very well with recent measurements [1]. Furthermore, we have also investigated all involved reactions in the gas phase by carrying out molecular calculations. This approach has allowed us to achieve a better understanding of the reaction mechanisms. We found that reaction energies for the molecular systems follow the same trend as for the bulk systems. [1] Weifang Luo, J. Alloys Comp. 381, 284 (2004). [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A16.00007: In-situ Neutron Diffraction Studies of the Hydrogen storage material Li$_{3}$N Ashfia Huq, James W. Richardson, Evan R. Maxey, Dhanesh Chandra, Wen-Ming Chien The search for alternative fuel has spurred interest in complexes with high hydrogen absorption-desorption capacities. Among these compounds complex metal hydrides have received much attention. More recently it was proposed that simple metal nitrides such as Lithium Nitride (Li$_{3}$N), with its 9 wt {\%} recyclable hydrogen uptake, could be good candidates for reversible hydrogen storage. In this presentation we present the results of detailed structural study of Li$_{3}$N through the temperature range 20K to 673K using Neutron Powder Diffraction. Commercially purchased compound showed a coexistence of alpha and beta phases of Li$_{3}$N. We observed a steady decline of the beta phase above 473K and a very small fraction ($\sim $3 wt {\%}) was frozen in at 673K. This transformation ($\beta $ to $\alpha )$ was not reversible on cooling. We will also present the findings of in-situ neutron diffraction measurements of hydrogen absorption and desorption of the title material. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A16.00008: Characterization of Lithium Borohydride using Neutron Scattering Techniques Michael Hartman, Jack Rush, Terry Udovic Lithium borohydride, LiBH$_{4}$, is a complex metal hydride that shows great promise as a hydrogen storage medium with a volumetric hydrogen density of 122 kg H/m$^{3}$ and a gravimetric hydrogen density of 18.5 wt. {\%}. While numerous NMR, Raman, and infrared investigations have been reported in the literature, neutron scattering investigations of LiBH$_{4}$ have been limited due to the large neutron absorption cross-section of naturally occurring lithium and boron. We have recently synthesized an isotopically-enriched lithium borohydride, containing $^{7}$Li and $^{11}$B, which eliminates the large neutron absorption cross-section that arises from the presence of $^{6}$Li and $^{10}$B. The results of powder neutron diffraction, inelastic neutron scattering, and quasi-elastic neutron scattering investigations on the $^{7}$Li$^{11}$BH$_{4}$ material are presented. These measurements provide a fundamental understanding of the behavior of hydrogen within lithium borohydride, and they provide a basis to understand changes concomitant with the introduction of catalytic or destabilizing compounds. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A16.00009: Structural transitions in NaBH4 under pressure Ravhi Kumar, Andrew Cornelius The structure of the technologically important hydrogen storage compound NaBH$_{4}$ has been investigated under pressures up to 30 GPa by \textit{in situ} angle dispersive high pressure x-ray diffraction using synchrotron x-rays and a diamond anvil cell. Our experimental results show pressure-induced structural transitions of $\alpha $-NaBH$_{4}$ (cubic -- \textit{Fm3m}) to $\beta $ -- NaBH$_{4}$ (tetragonal -- $P42_{1}c)$ at 6.3 GPa and further to orthorhombic phase (\textit{Pnma}) at 8.9 GPa. The high pressure orthorhombic phase is found to be stable up to 30 GPa. The cubic phase is completely recovered on releasing the pressure to the ambient. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700