Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session D30: Focus Session: Hydrogen Storage I |
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Sponsoring Units: DMP Chair: Channing Ahn, California Institute of Technology Room: D139 |
Monday, March 15, 2010 2:30PM - 3:06PM |
D30.00001: High-Density Hydrogen Storage and Lithium Super-Ionic Conduction in Metal Borohydrides Invited Speaker: Development of high-density hydrogen storage materials is a critical issue for fuel cell technologies. Candidates for the materials are metal borohydrides, (M(BH4)n with M = Li, Na, K, Cu, Mg, Mn, Zn, Sc, Ti, Y, Zr, and Hf; n = 1-4). The thermodynamical stabilities of the metal borohydrides were systematically investigated by using both the first-principles studies and hydrogen desorption measurements. Then, the Pauling electronegativity of M was found to be an indispensable indicator for appropriately producing/designing the metal borohydrides, including multi-cation (for example; Li-Zr and Li-K) systems. It was also discovered that the electrical conductivity of lithium borohydride, LiBH4, drastically jumped by three orders of magnitude due to the structural transition. The hexagonal phase above 388 K exhibited a high electrical conductivity of the order of 10$^{-3}$ S/cm, lithium super(fast)-ionic conduction. The hexagonal phase of LiBH4 can be thermodynamically stabilized by anion substitutions even at room temperature. Therefore, some of the metal borohydrides (and their multi-anion systems) might be new candidates also for solid-electrolytes. [Preview Abstract] |
Monday, March 15, 2010 3:06PM - 3:18PM |
D30.00002: Structural, Electronic, and Hydriding Properties of Li$_{2}$MgSi Jan Herbst, Martin Meyer An investigation of Li$_{2}$MgSi, with particular emphasis on its potential as a hydrogen storage material, is reported. A cubic P$\overline{4}$3m crystal structure, differing from previous determinations, is established. We find that the material reversibly sorbs $\sim $2.8 mass{\%} hydrogen at T $\sim $ 300\r{ }C according to the reaction Li$_{2}$MgSi + H$_{2}$ $\leftrightarrow \quad \raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $Mg$_{2}$Si + 2LiH + $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $Si. Electronic structure calculations indicate that Li$_{2}$MgSi is a semiconductor with a small, indirect gap of $\sim $0.2 eV. [Preview Abstract] |
Monday, March 15, 2010 3:18PM - 3:30PM |
D30.00003: Thermodynamic and kinetic size effects for hydrogen-desorption in catalytically-doped magnesium hydride: Nanoparticle versus bulk surface effects Jason Reich, L.-L. Wang, D. D. Johnson Using density-functional methods with simulated annealing, we show that there are no size effects for hydrogen desorption energies in nanoparticles (NPs) of MgH2. Recently reported exothermic desorption energies in MgH2-doped NP (Mg30XH62) are shown to be spurious, resulting from metastable NP configurations before dehyrogenation. We confirm that the 93-atom NPs are amorphous, with structures that are sensitive to the presence of dopants, found via simulated annealing techniques. We find that dehydrogenation energies are similar between bulk surfaces and nanoparticles, showing that the thermodynamics is unchanged by particle size as desorption is determined only by the local hydrogen-metal bond. We then discuss the effects of nanoparticle size and presence of dopants on the kinetic barriers between NPs and bulk surfaces. The takehome message is: In modeling desorption events, especially within amorphous NPs, metastable, local minimum must be carefully avoided, and, in doing so, an accurate and physically reasonable picture emerges for the thermodynamic and kinetic behavior. [Preview Abstract] |
Monday, March 15, 2010 3:30PM - 3:42PM |
D30.00004: Quantum Monte Carlo Simulation of Nanoscale MgH2 Cluster Thermodynamics Zhigang Wu, Mark Allendorf, Jeffrey Grossman We calculated the desorption energy of MgH$_{2}$ clusters using the quantum Monte Carlo (QMC) approach, which can provide desorption energies with chemical accuracy (within $\approx 1$ kcal/mol) and therefore a valuable benchmark for such hydrogen-storage simulations. Compared with these QMC results, the widely used density-functional-theory (DFT) computations cannot reach a consistent and suitable level of accuracy across the thermodynamically tunable range for MgH$_{2}$ clusters, for a wide range of exchange-correlation functionals. Furthermore, our QMC calculations show that the DFT error depends substantially on cluster size. These results suggest that in simulating metal-hydride systems it is crucial to apply accurate methods that go beyond traditional mean-field approaches as a benchmark of their performance for a given material, and QMC is an appealing method for such a benchmark due to its high level of accuracy and favorable scaling ($N^{3}$) with number of electrons. [Preview Abstract] |
Monday, March 15, 2010 3:42PM - 3:54PM |
D30.00005: Regeneration of AlH$_{3}$ studied with Raman and Infrared Spectroscopy David Lacina, J. Wegrzyn, J.J. Reilly, Jason Graetz Aluminum hydride compounds are known to exhibit a 10{\%} by weight hydrogen storage capacity that makes them suited for technologies that require hydrogen as a fuel. The current challenge associated with this material is how to regenerate the hydride from the spent fuel and H$_{2}$ gas. We employ a two-step process to regenerate the hydride compound which first requires the formation of a stable aluminum hydride adduct using a tertiary amine. This is followed by a second step consisting of adduct separation and hydride recovery, involving transamination to create a less stable adduct. We present results which show that alane-amines can be formed by hydrogenation of catalyzed aluminum in a solvent at low pressures using one of several tertiary amines. Raman and infrared spectroscopy was performed on the products of these reactions to better understand the structure of the alane amines that are formed, as well as the hydrogenation reactions that take place. A vibrational analysis of the regeneration products performed with Raman and infrared spectroscopy is presented and will help clarify the molecular and vibrational structures of these alane amine adducts. [Preview Abstract] |
Monday, March 15, 2010 3:54PM - 4:06PM |
D30.00006: Discovering the Optimal Route for Alane Synthesis on Ti doped Al Surfaces Using Density Functional Theory Based Kinetic Monte Carlo Methods Altaf Karim, James T. Muckerman Issues such as catalytic dissociation of hydrogen and the mobility of alane species on Ti-doped Al surfaces are major challenges in the synthesis of aluminum hydride. Our recently developed modeling framework (DFT-based KMC simulation) enabled us to study the steady-state conditions of dissociative adsorption of hydrogen, its diffusion, and its reaction with Al adatoms leading to the formation of alane species on Ti-doped Al surfaces. Our studies show that the doping of Ti atoms in the top layer of Al surfaces significantly reduces the mobility of alane species. On the other hand, the doping of Ti atoms beneath the top layer of Al surfaces enhances the mobility of alane species. The arrangement of dopant Ti atoms in different layers not only affects the diffusion barriers of alane species but it also affects hydrogen dissociation barriers when Ti-Ti pairs are arranged in different ways in the top layer. Using our theoretical methods, we identified a few configurations of dopant Ti atoms having lower barriers for alane diffusion and hydrogen dissociation. Further, we discovered the optimal values of Ti concentration, temperature, and pressure under which the rate of alane formation is maximized. [Preview Abstract] |
Monday, March 15, 2010 4:06PM - 4:18PM |
D30.00007: Comparative analysis of the hydrogen-vacancy interaction in Mg and Al based on density functional theory Lars Ismer, Anderson Janotti, Min Sik Park, Chris G. Van de Walle The interactions of vacancies (V) with atomic hydrogen (H) in the bulk of the metal are expected to play an important role in H-storage as well as H-embrittlement. Using density functional theory we have studied the H-V interactions in hcp-Mg and fcc-Al, two prototypic systems for H storage. We show that a single V can in principle host up to 9 H atoms in Mg and 10 in Al. In going beyond previous theoretical studies we further evaluate the concentration of the H-V complexes for different H loading conditions -- ranging from low pressures to high pressures of H2 gas. We find significant differences between Mg and Al. In the case of Al, up to 15 {\%} of H atoms are trapped in single vacancies even for very low H pressures, which strongly slows down the diffusion of H atoms. In the case of Mg, these trapping effects are negligible for low H pressures. However, vacancies containing multiple H atoms and H-induced superabundant vacancy formation are predicted to occur in Mg at much lower H loading pressures (about 1 GPa) than in Al (about 10 GPa). [Preview Abstract] |
Monday, March 15, 2010 4:18PM - 4:30PM |
D30.00008: Theoretical investigation of hydrogen interaction in Covalent Organic Framework - 1 Pornjuk Srepusharawoot, Ralph H. Scheicher, C. Moys\'es Ara\'ujo, Andreas Blomqvist, Rajeev Ahuja Density functional theory (DFT) and second-order M{\o}ller-Plesset perturbation theory (MP2) are carried out to calculate the non-dissociative hydrogen adsorption energies of covalent organic framework-1 (COF-1). Our DFT results show that a hydrogen molecule prefers to adsorb on top of oxygen of boroxine (B$_{3}$O$_{3})$ ring and C---C bridge site of benzene ring when a single H$_{2}$ is interacting with the COF-1. Moreover, the trend of adsorption energy obtained from the DFT calculations is found to be in good agreement with the MP2 binding energy trend. However, hydrogen molecules prefer to trap on top of oxygen at B$_{3}$O$_{3}$ ring and carbon atom at C$_{6}$H$_{4}$ ring at high hydrogen loadings. By performing \textit{ab initio} molecular dynamics simulations, we observed that H$_{2}$ molecules are able to stay at their initial adsorption sites due to blocking by occupancy of hydrogen molecules at the adsorption sites. (See also \textit{J. Phys. Chem. C}, \textbf{113}, 8498 (2009)) [Preview Abstract] |
Monday, March 15, 2010 4:30PM - 4:42PM |
D30.00009: First Principles Simulations of Hydrogen Storage via Spillover in MOF-5 Donald Siegel Metal organic frameworks (MOF) have attracted considerable attention as hydrogen storage materials due to their high surface areas and ability to adsorb large quantities of hydrogen by weight ($\sim $12 wt. {\%} at 100bar). However, as a consequence of the weak H$_{2}$-MOF bonding interaction ($\sim $5 kJ/mol H$_{2})$, this uptake occurs only at cryogenic temperatures; at room temperature, gravimetric capacities do not exceed $\sim $0.5 wt. {\%}. As an ideal storage system would operate under ambient conditions, renewed interest in these materials has been sparked by recent experiments demonstrating RT uptake of $\sim $4 wt. {\%} via the so-called ``spillover'' mechanism [JACS \textbf{128}, 8136 (2006)]. In contrast to the conventional mechanism of MOF-based storage, where \textit{molecular} H$_{2}$ bonds directly to the MOF, spillover employs a hydrogen dissociation catalyst to generate \textit{atomic} hydrogen (H), presumably resulting in stronger H-MOF bonding. Recent computational studies of spillover have reported conflicting results regarding the nature of this interaction. In an effort to resolve these ambiguities and clarify the thermodynamics of MOF-based spillover, DFT calculations are used to evaluate binding energies for several H adsorption configurations on MOF-5. Importantly, our calculations avoid the cluster approximation to the MOF geometry--a source of significant uncertainty in previous studies--and account for finite-temperature contributions to the free energy of adsorption. [Preview Abstract] |
Monday, March 15, 2010 4:42PM - 4:54PM |
D30.00010: Energetics and dynamics of H$_2$ adsorbed in metal-organic frameworks from a van der Waals density functional approach Lingzhu Kong, Nour Nijem, Yonggang Zhao, Yves J. Chabal, Jing Li, David C. Langreth We performed van der Waals-density-functional calculations of the hydrogen adsorption in metal-orgnic frameworks.\footnote{M. Dion et al. PRL 92,246401(2004); T. Thonhauser et al. PRB 76,125112(2007).} The quantum dynamic behavior of the adsorbed dihydrogen is studied. The low-lying energy levels of the hindered rotational, frustrated translational and vibrational motions are calculated and compared with experimental inelastic neutron scattering and IR measurements. A consistent picture is obtained. Zero point energies due to the rotational and translational motions are estimated to be around 10 meV and 15 meV, respectively. The zero-point corrected binding energies agree with the measured isosteric heat of adsorption. [Preview Abstract] |
Monday, March 15, 2010 4:54PM - 5:06PM |
D30.00011: Understanding the kinetics of adsorption in narrow channel metal organic frameworks Wei Zhou, Jason Simmons, Taner Yildirim Advancements in the controlled synthesis of metal organic frameworks (MOFs) have lead to impressive increases in hydrogen storage capacities and enhanced binding energies that may offer higher temperature operation. Given that the optimum pore size for hydrogen adsorption is on the order of 7 Angstroms, diffusion of hydrogen into these materials can play an important role in their ultimate implementation. In this presentation we use a combination of experimental and computational techniques, including gas sorption and neutron scattering measurements and detailed first-principles calculations, to better understand the kinetic limitations to adsorption in narrow channel MOF. In particular we show that the adsorption is diffusion limited with a significant activation barrier of $\sim $70 meV, and that this barrier is phonon-mediated. This work demonstrates the importance of considering kinetic effects in addition to pore volume and heats of adsorption when optimizing MOF materials for hydrogen storage. [Preview Abstract] |
Monday, March 15, 2010 5:06PM - 5:18PM |
D30.00012: On the Hydrogen Storage Capacity Limitations of Carbon Nanotube Bundles Dimitrios Maroudas, Andre Muniz Exposure of single-walled carbon nanotubes (SWCNTs) to atomic hydrogen leads to chemisorption of H atoms on the SWCNT walls, enabling the use of SWCNTs as hydrogen storage media with a theoretical storage capacity of 7.7 wt{\%}. Experimental studies, however, have reported inconsistent hydrogen storage capacities that are usually well below this limit. To explain the experimental measurements, we have developed an analytical model that describes the effect of SWCNT swelling upon hydrogenation on the hydrogen storage capacity of SWCNT bundles. The model is properly parameterized using a large set of atomistic simulation results for the dependence of SWCNT swelling on the degree of hydrogenation as measured by the coverage of the SWCNTs by chemisorbed atomic H. The model generates experimentally testable hypotheses, which can be used to explain the lower H storage capacities reported for SWCNT bundles and the experimentally observed nonuniform hydrogenation of SWCNT bundles. It also provides recommendations for optimal SWCNT arrangement in bundles to maximize their hydrogen storage capacity. [Preview Abstract] |
Monday, March 15, 2010 5:18PM - 5:30PM |
D30.00013: Hydrogen clathrates of ammonia borane Maciej Gutowski, Alexander Abramov The concept of hierarchical hydrogen storage is illustrated by clathrates built from ammonia borane (AB) and loaded with molecular hydrogen. These new materials would have two levels of hydrogen storage: (i) physisorbed H$_{2}$ and (ii) hydrogen chemically bound in AB. The advantages of these materials would be: (i) fast kinetics and (ii) high hydrogen density. We developed a construction principle for clathrates of AB and performed electronic structure calculations for isolated cages and for periodic structures. Hydrogen capacity of the most stable periodic structure (cantitruncated cubic honeycomb) is estimated to be 21~wt{\%}, 19 wt{\%} chemically bound in AB and 2~wt{\%} of H$_{2 }$physisorbed in cages of AB. We developed a statistical model of clathrate phase equilibria that is based on calculated guest-host interactions, entropy of guest molecules in spherical cages, and corrections for nonideality of gases. Application of the model to known hydrates showed quantitative agreement between experimental and theoretical data. We predicted stability of hydrogen clathrates of ammonia borane at ambient pressure and T=77~K. Further stabilization by formation of double clathrates and semi-clathrates will be discussed. [Preview Abstract] |
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