Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D6: Predictive Materials Design for Alternative Energy Storage |
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Sponsoring Units: DCOMP Chair: Zhenyu Zhang, Oak Ridge National Laboratory Room: 406 |
Monday, March 16, 2009 2:30PM - 3:06PM |
D6.00001: First-Principles Studies of Phase Stability and Reaction Dynamics in Complex Metal Hydrides Invited Speaker: Complex metal hydrides are believed to be one of the promising materials for developing hydrogen storage systems that can operate under desirable conditions. At the same time, these are also a class of materials that exhibit intriguing properties. We have applied state-of-the-art computational techniques to study the structural, dynamic, and electronic properties of these materials. This talk will focus on the critical role played by the Ti catalyst in helping hydrogen cycling in the alanates, which remains a challenging topic for this hydrogen storage material. We have performed a series of calculations to address the hydrogen interaction on the aluminum surface in the presence of the Ti ``dopant,'' focusing on the effect of near-surface alloying on the Al(100) surface. It is found that Ti occupies subsurface sites near the Al surface. This subsurface Ti arrangement not only enhances H binding with the Al surface layer, but also improves H mobility on the surface. Based on existing experimental data and our preliminary results, we propose a model in which the catalyst does not enter the bulk, but facilitates hydrogen dissociation-recombination near the surface. In the dehydrogenation cycle, the catalyst kinetically facilitates the release and decomposition of AlH$_3$ from the solid-state alanate. In the hydrogenation cycle, the catalyst helps the adsorption of hydrogen and the formation of AlH$_3$ oligomers on Al surfaces. The implication of Ti as a catalyst for the hydrogenation reactions will be discussed. [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:42PM |
D6.00002: Energy Storage in Nanostructured Materials Invited Speaker: Renewably produced energy by solar and wind technologies should be stored properly for practical use because of their intermittent generation of electricity. The energy can be stored in materials in forms of chemical, electrical, or thermal energies. The current energy-storage materials technologies, however, suffer from their inevitable low energy densities, compared to liquid fuels such as gasoline and ethanol, and thus end up to high cost due to material limitation. In order to overcome the fundamental limit, many scientists and researchers have studied nanostructured materials with more surface areas, tunable storage mechanisms, and better kinetic processes. Because electronic and mechanical properties of nanostructured materials are simply not a miniature of their bulk counterparts, a careful material design is required based on microscopic understanding of the energy storing process. In this talk, I will discuss our recent theoretical efforts and development to understand energy storage mechanisms in nanostructured materials for hydrogen, battery, and electrochemical capacitor applications. We have pioneered dihydrogen adsorption in nanostructured materials with the Kubas coordination [1-3] and lately developed efficient van der Waals potentials within the density functional theory approach [4]. Also very recently we have unraveled reversible lithium intercalation mechanisms in MoO$_{3}$ nanoparticles for Li-ion battery electrodes [5], and been developing a microscopic theory of electrochemical and capacitive energy storage. \\[4pt] [1] Y. Zhao et al., Phys. Rev. Lett. \textbf{94}, 155504 (2005) \\[0pt] [2] Y.-H. Kim et al., Phys. Rev. Lett. \textbf{96}, 016102 (2006) \\[0pt] [3] Y. Y. Sun, Y.-H. Kim, and S. B. Zhang, J. Am. Chem. Soc. \textbf{129}, 12606 (2007) \\[0pt] [4] Y. Y. Sun, Y.-H. Kim, K. Lee, and S. B. Zhang, J. Chem. Phys. \textbf{129}, 154102 (2008) \\[0pt] [5] S.-H. Lee et al., Adv. Mater. \textbf{20}, 3627 (2008) [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 4:18PM |
D6.00003: Nanomaterials for Hydrogen Storage Invited Speaker: The success of a hydrogen economy critically rests on our ability to find materials that can store hydrogen with large gravimetric and volumetric densities and operate at near ambient conditions. To meet the large gravimetric density requirement, the storage materials must be lighter than Al. Unfortunately, in these light materials hydrogen is bound either too strongly or too weakly, thus leading to poor thermodynamics. I will discuss how the chemistry of these elements can be manipulated at the nanoscale so that hydrogen can be stored in quasi-molecular form with binding energies that are appropriate for near ambient conditions. Examples will include functionalized carbon fullerenes and nanotubes and doped AlN nanostructures. Using carbon nanostructures as catalysts I will demonstrate unambiguously the dehydrogentation mechanism of sodium alanate. A cluster perspective of the intermediate phases in the dehydrogenation of borohydrides will also be presented. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:54PM |
D6.00004: Fundamental design of hydrogen storage structures and systems. Invited Speaker: Fundamental simulations of hydrogen interactions with host structures offer indispensable insights to the understanding and design of hydrogen storage materials for practical applications. First-principles approaches were applied to selected materials of high promise, e.g., doped/defective carbon, doped hydrides and metal/amine complexes. Several candidates show large capacities for hydrogen -- over the 6-9 mass-percentage threshold considered for applications. Recent progress on carbon nanostructures show the importance of defects and doping on extra hydrogen uptake, and a small change of C-C interspacing on the mode-switching of hydrogen sorption. Work on the molecular analogues of the basic structural unit of boron-nitride indicates that transition metal (TM) atom doping can boost both the gravimetric and thermodynamic capacities of hydrogen in these materials. The H2 binding to the TM dopants is Kubas-like in nature, though the maximum binding capacity at the TM doped sites does not follow the 18-electron rule. Progress in the Li-N-H system shows that the N-Li bond is weaker than one of the N-H bonds in LiNH2, and consequently LiNH2 can dissociate into: Li+ and (NH2)-, or (LiNH)- and H+. Hence, NH3 may evolve as a transient gas, if it is not sufficiently captured by a reactive component, e.g. LiH. Molecular dynamics calculations indicate that hydrogen deliveries are possible close to fuel-cell operation conditions. Comparison is also made with experiment where possible. [Preview Abstract] |
Monday, March 16, 2009 4:54PM - 5:30PM |
D6.00005: First principles design of electric-field-assisted high capacity hydrogen storage media Invited Speaker: Hydrogen has been viewed as a highly appealing energy carrier for renewable energy. To achieve economic feasibility hydrogen storage materials with high gravimetric and volumetric densities must be developed. However, no materials so far satisfy the essential criteria for economically feasible hydrogen storage. Therefore, there are necessities of breakthrough ideas and methods for developing new materials. In this talk, I will discuss the novel idea of electric-field-assisted hydrogen storage in nanostructures. Its central ingredient is to create high and strongly delocalized electric fields that are strong enough to attract hydrogen through polarization. Using quantum mechanical first-principles calculations, it has been shown that high electric fields can be easily established in a region close to the surface of nanostructures by electronic doping [1] or in charge compensated ways. The charging idea and its underlying physical mechanism can be generalized to many other related nanoscale materials that are of interest for hydrogen storage, as exemplified by alkaline-earth-metal coated carbon nanostructures [2] and charge transferred organic crystals [3]. \\[4pt] [1] M. Yoon, S. Yang, E. Wang, and Z. Zhang, Nano Lett. \textbf{7}, 2578 (2007).\\[0pt] [2] M. Yoon, S. Yang, C. Hicke, E. Wang, D. Geohegan, and Z. Zhang, Phys. Rev. Lett. \textbf{100}, 206806 (2008).\\[0pt] [3] M. Yoon and M. Scheffler (in preparation). [Preview Abstract] |
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