Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Z24: Hydrogen Storage: Dopants and Catalysts |
Hide Abstracts |
Sponsoring Units: DMP Chair: Fred Pinkerton, GM Research Room: 326 |
Friday, March 20, 2009 11:15AM - 11:27AM |
Z24.00001: Effect of Ti Dopant on Surface Diffusion of Isolated Alane Species: A Comparison between Al (111) and Al (100) surfaces Altaf Karim, James Muckerman Our density functional theory-based kinetic Monte Carlo simulations show that an embedded Ti atom creates a well in the potential energy surfaces of Al(111) and Al(100) as probed by hydrogen and other isolated alane species. Hydrogen adatoms become trapped around Ti atoms on an Al(111) surface, whereas Al adatoms do not exhibit any significant effect of the potential energy well created by the Ti atoms. In contrast to the case of Al(111), Al adatoms on an Al(100) surface also become trapped around the Ti atoms for a longer period of time compared to the hydrogen adatoms on this surface. Therefore, Ti sites on Al(100) become poisoned by the presence of Al adatoms around them for long periods of time, thereby blocking further dissociative adsorption of hydrogen. The overall diffusion of Al adatoms on an Al(100) surface is significantly lower compared to the Al(111) surface. This fact suggests that the Ti-doped Al(111) surface is perhaps more conducive to the production of alane species than the Ti-doped Al(100) surface despite its higher activation barrier for the dissociation of molecular hydrogen. [Preview Abstract] |
Friday, March 20, 2009 11:27AM - 11:39AM |
Z24.00002: Hydrogen adsorption on Al (100) facilitated by surface alloying with Sc Feng Zhang, Yan Wang, M. Y. Chou We report first-principles investigations of hydrogen adsorption on the Al (100) surface modified by alloying with Sc, as the first step to understand the catalytic role of scandium in the hydrogenation process in Sc-doped NaAlH4. Sc prefers to stay at subsurface sites with or without adsorbed hydrogen. The adsorption energy on the Sc-modified surface is 0.5 eV/H2 lower than that on the pure Al surface, while the dissociation barrier of H2 is similar for the two systems. The structure with two H atoms adsorbed on two nearest-neighbor bridge sites is at least 0.3 eV more stable than other structures; but no additional activation energy is required for H to diffuse among these structures. Electronic structures are also examined to explain these alloying-induced effects. [Preview Abstract] |
Friday, March 20, 2009 11:39AM - 11:51AM |
Z24.00003: Hydrogen-related defects and the role of metal additives in complex hydrides Khang Hoang, Chris G. Van de Walle Complex hydrides such as NaAlH$_{4}$ and Li$_{4}$BN$_{3}$H$_{10}$ doped with selected transition metals (e.g., Ti, Ni, and Pt) are promising hydrogen storage materials. The mechanism of the enhancement in (de)hydrogenation rates caused by these metals is, however, not well understood. We have carried out first-principles studies based on density functional theory of hydrogen vacancies and interstitials, which play an important role in the (de)hydrogenation processes. We find that these defects are always charged; their formation energy therefore depends on the Fermi level. The metallic impurities can also exist in different charged states and, therefore, modify the Fermi level, thus changing the defect concentrations. Our first-principles results shed light on the role of transition-metal impurities in hydrides and lead to the design of storage materials with improved characteristics. [Preview Abstract] |
Friday, March 20, 2009 11:51AM - 12:03PM |
Z24.00004: First-principles and Tight-binding Calculations in the Pd-H System A. Shabaev, D.A. Papaconstantopoulos Using the linearized augmented plane wave(LAPW) method we have generated a large database of electronic structure results that include fcc, bcc, NaCl, CsCl, Cu3Au, Fluorite crystal structures as well as supercell configurations with various hydrogen occupations for the Pd-H system. The formation energies and energy bands from this database were used to construct a tight-binding model that reproduces well the above LAPW results and, in addition, is transferable to other crystal lattices including random occupation of crystal sites as well as treating vacancies. We calculate the phonon frequencies, elastic constants, the density of states, coefficient of thermal expansion, mean-squared displacement and the energy of vacancies formation in Pd. The objective of this work is to be able to perform electronic structure calculations for systems containing up to a few thousand atoms where first- principles calculations are computationally intractable. This approach is used in both static and dynamic calculations and enables us to vary the amount of hydrogen entering into the Pd matrix. [Preview Abstract] |
Friday, March 20, 2009 12:03PM - 12:15PM |
Z24.00005: Nitrogen and Hydrogen on a Palladium-covered proton conductor: a first principle study of Ammonia catalysis Lorenzo Paulatto, Stefano de Gironcoli Being liquid at ambient conditions Ammonia would be an ideal Hydrogen vector. However, the industrial Haber process for Ammonia synthesis involves high pressures ($\approx 100$~bar) and temperatures ($450-500$~$^{\circ}$C), making the process very expensive. Recently, ambient pressure Ammonia production, in the $570-750$~$^{\circ}$C temperature range, has been reported at the Palladium cathode of a proton conducting cell-reactor [1]. The rate limiting step in the Haber process is N$_2$ dissociation, while the observed limiting factor in Ref. [1] appears to be the proton transfer through the conductor and it has been proposed that Nitrogen hydrogenation may in this case precede dissociation. We use first-principles techniques to study Nitrogen, Hydrogen and Ammonia interaction with flat and stepped Pd surfaces, in presence of external electric fields. Our aim is to study the effect of electrochemically provided protons on the catalysis of the reaction. [1]{G. Marnellos and M. Stoukides, Science 282, 98 (1998); G. Marnellos, S. Zisekas, and M. Stoukides, J. of Catalysis 193, 80–87 (2000)} [Preview Abstract] |
Friday, March 20, 2009 12:15PM - 12:27PM |
Z24.00006: Synthesis and Characterization of Au and Pd Decorated ZnO Powders Paige Landry, Hangning Chen, Andi Barbour, Michael Felty, John Z. Larese We report our synthesis and characterization of ZnO nanopowders decorated with Pd and Au clusters. Ultrapure ZnO powders are readily produced. Pd and Au nanoclusters are deposited from solution and reduced using hydrogen gas. Characterization of these materials using high resolution adsorption isotherms and inelastic neutron scattering have been performed.~Particular attention has been paid to the adsorption of hydrogen and deuterium on these pure and decorated materials. Preliminary results indicate that hydrogen preferentially adsorbs to the Pd metal sites. Our results will underscore the significant promise of these combined systems for use in providing basic knowledge and for technological applications. [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