Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X24: Hydrogen Storage: Complex Hydrides |
Hide Abstracts |
Sponsoring Units: DMP Chair: John Vajo, HRL Laboratories Room: 326 |
Thursday, March 19, 2009 2:30PM - 3:06PM |
X24.00001: "Developments in the application of borohydrides for hydrogen storage" Invited Speaker: |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X24.00002: First-Principles Determination of Crystal Structures, Phase Stability, and Reaction Thermodynamics in the Li-Mg-Al-H Hydrogen Storage System Alireza Akbarzadeh, Chris Wolverton, Vidvuds Ozolins First-principles DFT calculations have been used to investigate the crystal structures, thermodynamic stability, and decomposition pathways of Li-Mg-Al-H hydrogen storage compounds. We find that the recently discovered LiMg(AlH$_4)_3$ compound is marginally stable with respect to decomposition into LiAlH$_4$ and Mg(AlH$_4)_2$; however, we also find that LiMg(AlH$_4)_3$ is unstable with respect to H$_2$ release and decomposes exothermically into LiMgAlH$_6$, Al, and H$_2$ in excellent agreement with measurements. Using ICSD crystal structures database, we predict that the hypothetical MgAlH$_5$ compound should assume the orthorhombic BaGaF$_5$ prototype structure. We also discuss that phonon vibrations have sizeable effects on the enthalpies and entropies of hydrogen release reactions of Li-Mg-Al-H compounds. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X24.00003: Hydrogen Storage in Cu-Li-Mg Alloys M. Helena Braga, George Chertkov, Alice Acatrinei, Saurabh Kabra, Luke Daemen CuMg$_{2}$ has an orthorhombic crystal structure (Fddd) and does not form a hydride. However CuLi$_{x}$Mg$_{2-x}$ (x $\sim $ 0.11) has a hexagonal crystal structure (P6$_{2}$22), just like NiMg$_{2}$, a compound known for its hydrogen storage properties. A comparison between the phase diagrams of the systems Cu-Mg and Ni-Mg shows that these binary systems form compounds with similar stoichiometry. NiMg$_{2}$ is formed by peritectic reaction of the elements at 759 $^{\circ}$C (1032 K) and CuMg$_{2}$ at 568 $^{\circ}$C (841 K) by congruent melting. Since the energy of formation of the hydride is related to that of the primary alloy, it was hypothesized that CuLi$_{x}$Mg$_{2-x}$ might also be a hydrogen storage material similar to NiMg$_{2}$. Presumably, its advantage would be that it would release hydrogen at a lower temperature (possibly close to room temperature). In order to determine the properties of the hydrogenated (and deuterated) CuLi$_{x}$Mg$_{2-x}$ material, absorption/desorption experiments were performed at several temperatures and under different pressures of H$_{2}$ (and D$_{2})$. Neutron diffraction patterns and neutron vibrational spectra were collected to elucidate the behavior of hydrogen in the Li-doped CuMg$_{2}$ intermetallic. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X24.00004: Structural Discrimination via DFT: Monoclinic Mg$_{2}$NiH$_{4}$ Jan Herbst, Louis Hector, Jr. Mg$_{2}$NiH$_{4}$ is a semiconductor and forms an ordered low temperature monoclinic phase and a disordered high temperature cubic modification. Two distinct structures for the monoclinic phase from neutron diffraction studies of the deuterated analog, which we designate as LTI and LTII, are available in the published literature. We calculate the enthalpy of formation $\Delta $H with density functional theory (DFT) for both using three different approximations for the exchange-correlation energy functional. Phonon spectra are calculated as well. DFT unequivocally identifies LTII as preferable since $\Delta $H obtained for it is in better agreement with experiment and its phonon spectrum contains no anomalies. Structures approximating LTII derived from analyses of soft modes in LTI and in Mg-substituted CaMgNiH$_{4}$ are also discussed. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X24.00005: Control of thermodynamics and kinetics through anion substitution in metal borohydrides Young-Su Lee, Yoonyoung Kim, Jae-Hyeok Shim, Young Whan Cho High thermal stability of metal borohydrides is one of the bottlenecks in adopting them for practical hydrogen storage materials. For this reason, much effort has been put toward lowering their thermal stability. One of the common routes taken to achieve this aim is to mix with other borohydrides or alantes of less thermal stability hoping to make a compound or an alloy of intermediate stability. Recent studies have proposed a possibility where F$^{-}$ or Cl$^{-}$ anions could incorporate into the lattice of alanates or borohydrides replacing H$^{-}$ or BH$_{4}^{-}$ anions, thus modifying the thermal stability of these materials. We present here a combined experimental and theoretical study on the anion substitution in Ca(BH$_{4})_{2}$ and LiBH$_{4}$. Both thermodynamic and kinetic aspect will be discussed. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X24.00006: First-Principles Study of the Li-Mg-N-H System: Compound Structures and Hydrogen Storage Properties Kyle Michel, Vidvuds Ozolins The Li-Mg-N-H system is studied with the addition of the Li4Mg(NH)3, MgNH, and Li4NH compounds using first-principles density-functional theory (DFT) calculations. A structure for the mixed imide Li4Mg(NH)3 is proposed, belonging to the Imm2 space group. A new structure for Li2Mg(NH)2 is given that has Pca21 symmetry; this compound has been previously reported as having Iba2 symmetry. The stability of the Li4Mg-imide is studied with respect to its decomposition reactions. The static, zero-point (ZPE), and vibrational energies of all relevant compounds belonging to this system are reported along with their predicted lowest-energy structures. Dehydrogenation reactions are presented that involve these phases and which are found to be spontaneously occurring within 400 K of room temperature. It is predicted that mixing LiH, LiNH2, and Li2Mg(NH)2 at 505 K will form Li4Mg(NH)3 with the release of 2.04 wt. {\%} H2. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X24.00007: De(Re)-hydrogenation Mechanisms of B-N-H Complexes at Elevated Pressure Raja Chellappa, Maddury Somayazulu, Viktor Struzhkin, Russell Hemley, Thomas Autrey The goal of identifying a hydrogen storage material that possesses reversible hydrogen removal/addition characteristics with favorable thermodynamics and kinetics still remains elusive. In case of chemical {\&} complex hydrides, it is increasingly realized that some ``destabilization'' is desired by altering the stiochiometry (dopants) or physical properties via mechanical preprocessing. In this study, a combined pressure-temperature approach (few GPa and 77-400 K) that has been used with great success for synthesizing novel hydrogen clathrates is extended to understand de(re)-hydrogenation mechanisms of B-N-H compounds. For example, Ammonia Borane (NH$_{3}$BH$_{3})$ has very high hydrogen content (19 wt.{\%}) however its thermal polymeric residue does not re-uptake hydrogen. We will present some in situ Raman spectroscopy results from our attempts to create novel hydrogen complexes with this residue as well as with the parent compound. In general, the physics {\&} chemistry of hydrogen interactions at high pressure with light element compounds containing hydrogen has been unexplored and this study is an attempt towards bridging that gap. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X24.00008: First-Principles Prediction of Hydrogen Storage Energetics in the Li-B-N-H System Wenhao Sun, Christopher Wolverton, Vidvuds Ozolins In this talk, we describe recent efforts using first-principles density functional theory (DFT) based methods to elucidate the reaction energetics and phase stability in the Li-B-N-H hydrogen storage system. We have calculated DFT total energies of a large number of phases in this system, including Li$_{4}$BN$_{3}$H$_{10}$, Li$_{2}$BNH$_{6}$, and their decomposition products. We then use these DFT energies in the recently developed ``grand canonical linear programming'' (GCLP) approach to automatically detect the thermodynamically preferred decomposition paths of these compounds as functions of temperature and H$_{2}$ pressure. Using the combined DFT+GCLP approach we calculate thermodynamic phase diagrams in the LiBH$_{4}$ -- LiNH$_{2}$ phase space. Some phases (e.g., Li$_{3}$BN$_{2}$, BN) are found to be very energetically stable, but are often only seen experimentally at very high temperatures, presumably due to hindered kinetics. By removing these phases from the DFT+GCLP calculations and examining the resultant phase diagrams, we can provide insight into the experimental reaction mechanisms. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X24.00009: First-Principles Molecular Dynamics Simulations of Liquid Li$_{4}$BN$_{3}$H$_{10}$:Structural Characterization and Dynamics of Hydrogen Release David Farrell, Christopher Wolverton The recently discovered Li$_{4}$BN$_{3}$H$_{10}$ compound is a promising hydrogen storage material due to its high capacity for hydrogen desorption ($>$10 wt.\%) and favorable thermodynamics for low-temperature H$_2$ release. However, elevated temperatures are necessary for appreciable H$_2$ desorption, pointing to kinetic limitations. Further, Li$_{4}$BN$_{3}$H$_{10}$ is liquid at these H$_2$ release temperatures. In an effort to characterize the liquid structure and uncover the atomistic mechanisms for H$_2$ release, we have performed first-principles molecular dynamics simulations of liquid Li$_{4}$BN$_{3}$H$_{10}$. Our calculations give the temperature-dependent liquid structure, which we compare in detail with that of the crystalline solid. We are also able to ascertain the latent heat of melting, an important contribution to understanding the thermodynamics of H$_2$ release from this material. Finally, we present preliminary work on the atomistic mechanisms of hydrogen desorption from the liquid based on temperature accelerated molecular dynamics. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X24.00010: Hydrogen Desorption Behavior of Nickel-Chloride-Catalyzed Stoichiometric Li$_{4}$BN$_{3}$H$_{10}$ Frederick Pinkerton, Martin Meyer Li-B-N-H quaternary hydrides with the $\alpha $-phase crystal structure form over a range of compositions between Li$_{3}$BN$_{2}$H$_{8}$ and Li$_{4}$BN$_{3}$H$_{10}$ and have up to 11.9 wt{\%} hydrogen capacity. Previous work focused on the non-equilibrium Li$_{3}$BN$_{2}$H$_{8}$ composition created by ball milling because it has maximum hydrogen release and minimum NH$_{3}$ co-generation. Here we report the hydrogen and NH$_{3}$ release characteristics of $\alpha $-phase material having the equilibrium Li$_{4}$BN$_{3}$H$_{10}$ composition. In the absence of a dehydrogenation catalyst, H$_{2}$ and NH$_{3}$ were released simultaneously in roughly equal quantities by weight (or about 10{\%} NH$_{3}$ by volume) at temperatures above 240 \r{ }C. Adding Ni in the form of NiCl$_{2}$ as a dehydrogenation catalyst reduced the H$_{2}$ release temperature by 122 \r{ }C. NH$_{3}$ release, in contrast, still occurred only at the higher temperature. As a result, decomposition occurred in two steps separated in temperature, dominated by H$_{2}$ gas at low temperature and NH$_{3}$ at high temperature. The two gases clearly evolved in two distinct reactions that are coincident in uncatalyzed Li$_{4}$BN$_{3}$H$_{10}$, but can be separated by a dehydrogenation catalyst. We expect that NH$_{3}$ co-generation could be completely eliminated at sufficiently low dehydrogenation temperatures. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X24.00011: Thermochemical Investigations of Nano-phase Ammonia Borane: Effect of Higher Loading Abhi Karkamkar, Ashley Stowe, Tom Autrey Chemical hydrogen storage materials that release H$_{2}$ by thermolysis without generating CO$_{2}$ offer an attractive option. The ammonia borane is an attractive compound containing more than 18 wt{\%} hydrogen. However, the kinetics of hydrogen release in not favorable in bulk materials where H$_{2}$ is released at 114 $^{\circ}$C. We recently reported use of SBA-15 as scaffold material to form a nanophase ammonia borane species which liberated H$_{2}$ at significantly lower temperatures. Hydrogen formation from bulk AB is slightly exothermic (-5 kcal/mol). The reaction enthalpy ($\Delta $H) for release of H$_{2}$ from AB adsorbed into SBA-15 (1:1 w/w) was determined to be nearly thermoneutral---dramatically lower than the bulk material. A near thermoneutral reaction suggests that there would be less restrictive heat management issues, greater thermal stability and potentially a lower energy input requirement for regeneration of AB. One drawback which results for nano-phase AB is that while the hydrogen release properties are enhanced, the gravimetric hydrogen density is reduced by a 50{\%} for the 1 to 1 by mass ratio material. We here report on our efforts to increase the gravimetric hydrogen density of nano-phase AB by developing higher loading conditions of AB adsorbed into mesoporous silica (MCM-41). [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X24.00012: Hydrogen storage in ammonia borane: {\em Ab initio} study of the de- and rehydrogenation mechanisms Kiseok Chang, David Tom\'anek, Eunja Kim, Philippe F. Weck Using {\em ab initio} density functional calculations, we study the microscopic mechanism of hydrogen release from ammonia borane (NH$_3$BH$_3$) and the reverse process leading to its subsequent recharging with hydrogen. Our total energy surfaces indicate the most favorable pathways to thermally convert the NH$_3$BH$_3$ molecular solid to the energetically preferred polymer NH$_2$BH$_2$ and molecular hydrogen. To prevent formation of undesirable side-products such as the cyclic compound borazine (N$_3$B$_3$H$_6$) or other complexes that would prevent subsequent rehydrogenation, we propose to enclose AB in narrow carbon nanotubes. In this constrained space, we investigate possible rehydrogenation pathways using atomic and molecular hydrogen as well as selected protonation agents. [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