Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session P39: Focus Session: Hydrogen Storage III |
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Sponsoring Units: FIAP DMP Chair: Taner Yildirim, NIST Center for Neutron Research Room: Colorado Convention Center 502 |
Wednesday, March 7, 2007 11:15AM - 11:51AM |
P39.00001: Hydrogen Storage in Chemically Reducible Microporous Ti Oxides Invited Speaker: Micro- and mesoporous Ti oxides with controlled pore sizes from 12 {\AA} to 26 {\AA} were synthesized. The hydrogen storage capacity at 77 K was tested as a function of surface area, pore size, and reducing agent. Surprisingly, the oxidation state of the surface Ti species had a greater effect on the storage densities than surface area or pore size. The 12 {\AA} material reduced with bis(toluene) Ti possesses a surface area of less than 500 m$^{2}$/g, but absorbs over 5 wt{\%} and 40 kg/m$^{3}$ of H$_{2}$ reversibly at 77K and 100 atm. The H$_{2}$ binding enthalpies increased from less than 5 kJ/mol to over 8 kJ/mol as the surface oxidation state of the Ti decreased. The enthalpies also increased with surface coverage, which is opposite to all other cryogenic physisorption systems. These results suggest that a Kubas-type $\sigma $ H$_{2}$ complex is involved and that further tuning of the H$_{2}$ binding enthalpies through use of various chemical reagents may achieve even higher storage levels at more moderate temperatures. [Preview Abstract] |
Wednesday, March 7, 2007 11:51AM - 12:03PM |
P39.00002: Novel nanostructured materials with binding ``pockets" for hydrogen storage media Sungjong Woo, Young-Kyun Kwon Hydrogen storage issue is one of the key barrier to the effort to substitute the hydrogen with the conventional fossil fuel. Chemisorption using metal hybrides and physisorption using nanostructured carbon-based materials have suffered several serious problems such as low storage capacity, insufficient binding energy and poor releasing process. In order to overcome such issues, we have investigated novel nanostructured materials of low density that bear hydrogen binding ``pockets", which can significantly enhance molecular hydrogen binding -- physisorption -- compared to carbon-based materials. Using numerical simulation based on the density functional theory, the hydrogen-molecule binding-energies of different candidate materials are calculated and optimized. With the obtained binding energies, we develop nanostructures similar to metal-oxide-framework that maximize the hydrogen capacity of the storage. The statistical properties of the structure, which is necessary to understand the process and efficiency of hydrogen release, are studied. In order to enhance the capacity even further, we synthesize the nanostructure with transition metals and the result will be discussed. [Preview Abstract] |
Wednesday, March 7, 2007 12:03PM - 12:15PM |
P39.00003: ABSTRACT WITHDRAWN |
Wednesday, March 7, 2007 12:15PM - 12:27PM |
P39.00004: Transition Metal-Ethylene Complexes as High-Capacity Hydrogen Storage Media E. Durgun, S. Ciraci, W. Zhou, Taner Yildirim From first-principles calculations, we predict that a single ethylene molecule can form a stable complex with two transition metals (TM) such as Ti. The resulting TM-ethylene complex then absorbs up to ten hydrogen molecules, reaching to gravimetric storage capacity of 14 wt\%. Dimerization, polymerizations and incorporation of the TM- ethylene complexes in nanoporous carbon materials have been also discussed. Our results are quite remarkable and open a new approach to high-capacity hydrogen storage materials discovery. [Preview Abstract] |
Wednesday, March 7, 2007 12:27PM - 12:39PM |
P39.00005: ABSTRACT WITHDRAWN |
Wednesday, March 7, 2007 12:39PM - 12:51PM |
P39.00006: Functionalized Carbon Nanostructures as Potential Hydrogen Storage Media Mina Yoon, Shenyuan Yang, Enge Wang, Zhenyu Zhang Nanoscaled carbon materials have attracted great attention as promising hydrogen storage media due to their light weight and high surface areas. However, a major limitation is the poor hydrogen uptake resulting from the weak interactions of hydrogen molecules with pristine carbon nanostructures. Recent theoretical studies have investigated ways to increase the binding strength of molecular hydrogen by coating and/or substitutional doping of the carbon nanostructures with transition metals, yet experimentalization of these approaches have been difficult because of metal clustering. In this talk, we study hydrogen storage in carbon nanotubes and fullerenes, by functionalizing such structures with tunable charge states. The tunability is achieved via chemical or electron doping. Our study shows that with the proper method of charge doping, the hydrogen binding strength can be substantially increased. In this way, hydrogen uptake of $>$ 6.0 wt \% at ambient conditions can be realized. [Preview Abstract] |
Wednesday, March 7, 2007 12:51PM - 1:03PM |
P39.00007: Theoretical study of hydrogen bonding to metal-coated carbon nanotubes Jeongnim Kim Dihydrogen transition metal complexes and carbon nanostructures are promising hydrogen storage materials~[1]. While the practical storage capacity of pure carbon nanostructures is low, calculations predict a possible hydrogen capacity of above 6~wt.\% for Ti coated nanotubes~[2]. A unique hybridization of Ti-d, H-H $\sigma^*$ and carbon $\pi$-orbitals was attributed for the bonding; light alkali and alkaline metals were excluded as alternatives to Ti [2]. This is at odd with earlier predictions of non-transition-metal complexes and synthesis of alkali-doped carbon nanotubes (CNT) [1]. Quantum Monte Carlo (QMC) methods are well suited to describe the strong correlation effects tha to the weak hydrogen binding and metal-hydrogen interactions. We present QMC study of hydrogen bonding to metal-coated CNT using correlated umbrella samplings. Specifically, we study hydrogen bonding to Ti and Mg at various doping levels on CNT. \newline \newline \noindent [1] R. C. Lochan and M. Head-Gordon, Phys. Chem. Chem. Phys. {\bf 8}, 1357 (2006). \newline \noindent [2] T. Yildirim and S. Ciraci, Phys. Rev. Lett. {\bf 94}, 175501 (2005). [Preview Abstract] |
Wednesday, March 7, 2007 1:03PM - 1:15PM |
P39.00008: Interaction of Transition Metals with Carbon Nanostructures Shenyuan Yang, Mina Yoon, Enge Wang, Zhenyu Zhang Recent theoretical studies have shown that transition-metal (TM) decorated carbon nanotubes and fullerenes may serve as promising media for hydrogen storage. However, one prerequisite for this functionality is that the metal atoms decorate the carbon nanostructures as a homogeneous layer. To date, no experimental evidence supports this feasibility; instead, several subsequent studies indicated strong preference of clustering by the TM atoms. In this talk, we investigate several possible ways to prevent TM clustering on the surfaces of carbon nanostructures, based on first-principles total energy calculations. First, we discuss the energetics and kinetics of various TMs as they interact with carbon nanostructures. We then explore the possibility to suppress or enhance clustering by electron or chemical doping. [Preview Abstract] |
Wednesday, March 7, 2007 1:15PM - 1:27PM |
P39.00009: First principles study of Interaction of H2 with doped Carbon Nanotube and Graphite Surfaces Li Chen, Yiming Zhang, Nikihil Koratkar, Puru Jena, Saroj Nayak Using first principles density functional theory based on gradient corrected approach we have studied interaction of H2 molecule with doped carbon nanotube and graphite surfaces. In agreement with earlier study we find that H2 physorbs on carbon nanotube and graphite surfaces while the binding increases dramatically when H2 binds to Li atoms decorated on carbon nanotube surfaces: the binding further enhances with Li atoms on fullerene doped nanotube pea-pod structures. The increase in binding in the latter structures arises due to charge transfer between the nanotube and dopants and the bonding is primarily in electrostatic in nature. The binding is further improved with decrease in diameter of nanotube suggesting a combination of various effects could be exploited for engineering suitable graphitic surfaces for molecular hydrogen storage. [Preview Abstract] |
Wednesday, March 7, 2007 1:27PM - 1:39PM |
P39.00010: Endohedral Metallofullerenes: A Smart Material for Hydrogen Storage Yufeng Zhao, Michael J. Heben, Anne C. Dillon, Lin Simpson, Jeff Blackburn, Harry C. Dorn, Shengbai B. Zhang We report a first-principle computational study on tunable hydrogenation of the fullerene C$_{60}$ and endohedral metallofullerenes M@C$_{60}$ and M$_{2}$@C$_{60}$ (M = Li, Be, Mg, Ca, Al, and Sc). The interaction between the encapsulated metal atoms and the C$_{60}$ cage leads to a smart-material behavior, which tunes the hydrogen binding in a desired manner as the hydrogenation proceeds. At lower H densities, when H atoms are too strongly bound to pure C$_{60}$, the endohedral dopants weaken the binding. The dopants also enhance the hydrogen binding energy at higher coverages, and enable the degree of hydrogenation to be substantially increased relative to that available with un-modified C$_{60}$. Overall, the encapsulated metals increase the capacity and improve the energy efficiency for hydrogen storage in hydroendofullerides. [Preview Abstract] |
Wednesday, March 7, 2007 1:39PM - 1:51PM |
P39.00011: Computational Study of hydrogen storage characteristics of the Covalent-Bonded Graphites. Noejung Park, Seung-Hoon Jhi, Kyubong Kim, Suklyun Hong We perform electronic structure calculations to investigate hydrogen-storage characteristics of the solid carbon structures which consist of covalent-bonded graphenes. First, we show that some regular or irregular combinations of \textbf{\textit{sp}}$^{2}$-and \textbf{\textit{sp}}$^{3}$-bonded carbon atoms lead to very stable porous carbon structures, which is designated as the covalent-bonded graphites (CBGs). Using the density-functional calculation and the M{\o}ller-Plesset perturbation method we show that the H$_{2}$ molecular bindings in CBGs are stronger than those on the isolated graphene by about 20{\%}. We also suggest the CBGs with appropriate pore sizes can be utilized as framework structures for dispersing metal atoms. Energetics show that the Ti atoms are likely to be adsorbed at vertex sites of the CBGs. The hydrogen adsorption properties on metal atoms dispersed inside the CBGs are also presented. [Preview Abstract] |
Wednesday, March 7, 2007 1:51PM - 2:03PM |
P39.00012: Recombination pathways for atomic hydrogen on the graphite (0001) and single-wall carbon nanotubes Zeljko Sljivancanin, Liv Hornekaer, Eva Rauls, Bjork Hammer Using density functional theory we investigated the lowest energy configurations of two H atoms on a graphite surface, and found two states with an approximately identical binding energy. These states are the dimer A state with two hydrogen atoms adsorbed on two neighbour carbon atoms and the dimer B state with two hydrogen atoms adsorbed on carbon atoms at opposite sides of a carbon hexagon. Hydrogen atoms in the dimer A state will recombine via diffusion into state B and then directly recombine from B. We also studied the corresponding pathways for molecular hydrogen formation from H atoms adsorbed at the single-wall carbon nanotubes and compared results to those obrained for the graphite surface. [Preview Abstract] |
Wednesday, March 7, 2007 2:03PM - 2:15PM |
P39.00013: Hydrogen generation and storage over transition metal-decorated fullerenes and related materials Liping Huang, Erik Santiso, Keith Gubbins, Marco Buongiorno Nardelli Economical ways to generate and store hydrogen are crucial steps towards the hydrogen economy and fuel-cell technologies. By using first-principles density functional theory calculations, we found out that transition metal-decorated fullerenes and related materials can simultaneously dissociate small molecules like water to produce and store hydrogen. Hydrogen production from water will allow us to have a clean hydrogen economy by using renewable source rather than fossil fuels so that we can stop releasing carbon into the atmosphere. Our studies show that the bonding between transition metal and hydrogen is of a combination of chemical and physical adsorption, which is essential for reversible hydrogen uptake/release. Car-Parrinello molecular dynamics simulations demonstrate that these systems are stable and exhibit associative desorption of H$_{2}$ upon heating without breaking the bond between carbon and transition metal. This fulfills another requirement for reversible hydrogen storage. [Preview Abstract] |
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