Z.Zak Fang University of Utah
Hongcai (Joe) Zhou Texas A&M University
Ewa Ronnebro Pacific Northwest National Laboratory
N3: Poster Session: Hydrogen Storage and Carbon Capture Technology
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
1:00 AM -
N3.1 Transferred to N8.7
N2: Complex Metal Hydrides and Amidoboranes II
Tuesday PM, April 26, 2011
Room 2011 (Moscone West)
2:30 PM - **N2.1
Investigations on Multi-component Amidoboranes for Hydrogen Storage.
Zhitao Xiong 1 , Guotao Wu 1 , Ping Chen 1 Show Abstract
1 , Dalian Institute of Chemical Physics, Dalian China
One of the key technological challenges facing fuel cell vehicle is to pursue high capacity hydrogen storage material. Metal amidoboranes (MNH2BH3) were synthesized recently through reacting ammonia borane (AB) with hydrides and exhibited improved desorption performances comparing to their parent material. However, the dehydrogenation remains exothermic and consequently is an irreversible storage process. Research effort has to be continued in attempt to tune the thermodynamics to enable endothermic desorption and one of the feasible ways is to change the composition of storage material. In this study, by simultaneously reacting AB with two different hydrides in tetrahydrofuran a series of multi-component amidoboranes were synthesized successfully. For example, after adding LiH-MgH2 and LiH-CaH2 hydride mixtures respectively to AB-THF solution (LiH/MH2/AB molar ratio of 2/1/4) and stirring the suspensions vigorously at ambient temperature 1 equiv hydrogen per AB was evolved from each system and the resulting white solids having the formula of Li2Mg(NH2BH3)4 and Li2Ca(NH2BH3)4 were both found to be single phase. The structures were resolved and their dehydrogenations were investigated. Other amidoboranes synthesized in this work were LiNa(NH2BH3)2, Na2Mg(NH2BH3)4 and Na2Ca(NH2BH3)4. Performing reaction of CaH2-MgH2 mixture with AB-THF solution, however, gave no desired product. 2 equiv hydrogen per AB, instead of 1, were evolved and the reaction seems not to stop at the formation of CaMg(NH2BH3)4.
3:00 PM - N2.2
New Fuel Blends for High-capacity Hydrogen Storage.
Ewa Ronnebro 1 , Young Joon Choi 1 , Abhijeet Karkamkar 1 , Tom Autrey 1 , Mark Bowden 1 , Guosheng Li 1 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Hydrogen storage is a key technology in development of alternative energy infrastructures and for continuous operation of Proton Exchange Membrane (PEM) fuel cells. We have been exploring new fuel blends based on hydrides mixed with ammonia borane (AB), NH3BH3, to obtain high-capacity (ca 7-14 wt% H2) chemical hydride materials systems with desirable hydrogen release features, in particular improved thermodynamics and faster kinetics. Metal hydrides and borohydrides have endothermic H-release at high temperatures while AB has exothermic H-release in conjunction with release of volatile species (i.e. borazine, ammonia, diborane) from side reactions at temperatures closer to the operation of a PEM fuel cell. When mixing AB with a hydride by ball milling, we found that the H-release becomes less exothermic and that the amount of volatile species could be reduced which is important for applications. The decomposition reactions were studied by X-ray diffraction, NMR, thermal gravimetry, calorimetry and mass spectroscopy along with engineering materials properties, such as thermal diffusitivity and kinetics. We found that the choice of fuel blend is crucial to control impurity levels and hydrogen release features.
3:15 PM - N2.3
New High-capacity Hydrogen Storage Materials Based on Ammonia Borane and Multiple Metal Hydrides: Synthesis and Characterization.
Young Joon Choi 1 , Ewa Roennebro 1 Show Abstract
1 Energy Storage Group , Pacific Northwest National Laboratory, Richland, Washington, United States
Ammonia borane (AB = NH3BH3) is one of the most attractive materials for chemical hydrogen storage due to its high hydrogen contents with 19.6 wt % capacity, however, impurity levels of borazine, ammonia and diborane in conjunction with foaming and exothermic hydrogen release calls for finding ways to mitigate the decomposition reactions. Our approach involves mixing AB with alkali metal hydrides such as LiH, NaH, MgH2 and CaH2 which have endothermic hydrogen release in order to control the heat release from AB upon decomposition. The composite materials were prepared by mechanical ball milling, and their H2 release properties were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The formation of volatile products from decomposition side reactions, such as borazine (N3B3H6) was determined by mass spectrometry (MS). Sieverts type pressure-composition-temperature (PCT) gas-solid reaction instrument was adopted to observe the kinetics of the H2 release reactions of the combined systems and neat AB. We found that enthalpy and impurity levels are dependent on the choice of combinations of metal hydrides mixed with AB.
3:30 PM - N2.4
Mixed Metal Amidoboranes and Borohydride Ammonia Borane Complexes for Hydrogen Storage
Hui Wu 1 2 , Wei Zhou 1 2 , Frederick Pinkerton 3 , Martin Meyer 3 , Gadipelli Srinivas 1 4 , Taner Yildirim 1 4 , Terrence Udovic 1 , John Rush 1 2 Show Abstract
1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 3 Chemical Sciences and Materials Systems Laboratory, General Motors Research and Development Center, Warren, Michigan, United States, 4 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Ammonia borane (AB) is a promising material that has been extensively studied for hydrogen storage. However, its onboard applications are subject to improvement in dehydrogenation kinetics, purity of gas released, and regeneration. This work has investigated several novel AB-related chemical hydrides, aiming to advance the dehydrogenation properties of pristine AB. Examples include a new family of borohydride ammonia borane complexes such as Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2 and the first example of mixed metal amidoboranes (NaMg (NH2BH3)x). The structures of these compounds have been successfully determined using a combination of x-ray diffraction and first-principles calculations. The dehydrogenation studies show that more than 10 wt%, and 11 wt% hydrogen can be released from Li2(BH4)2NH3BH3 and Ca(BH4)2(NH3BH3)2, respectively, and about 8.5 wt% hydrogen can be released from NaMg(NH2BH3)x below 200°C with dramatically enhanced kinetics of dehydrogenation and the improved purity of hydrogen gas released compared to the pure AB. The crystal structures and the chemistry behind will be discussed together with the correlations between their bonding variation and the dehydrogenation properties.
3:45 PM - N2.5
Efficient Hydrogen Release from Ammonia Borane Confined Metal-organic Frameworks.
Srinivas Gadipelli 1 2 , Jamie Ford 1 2 , Taner Yildirim 1 2 Show Abstract
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Ammonia borane (NH3BH3, AB) has recently received much attention as a promising hydrogen storage medium among a very large number of candidate materials because of its satisfactory air stability, relatively low molecular mass (30.7 g/mol), and remarkably high energy storage densities (gravimetric and volumetric hydrogen capacities are 19.6 % mass fraction and 140 g/L, respectively) . However, the direct use of pristine AB as a hydrogen energy carrier in on-board/fuel cell applications is prevented by its very slow dehydrogenation kinetics below 100oC and the concurrent release of detrimental volatile by-products such as ammonia, borazine and diborane. Many different methods  have been adopted to promote efficient H2 generation from AB, including catalytic hydrolysis in aqueous solution, ionic liquids, or organic solvents and thermodynamic modifications by formation of hybrid structures with transition metals, alkali-, or alkaline-earth metal/hydrides or nanoconfined phases using porous scaffolds. However, more work needs to be done to explore the potential role that catalysts can play to further improve the controllable H2 release kinetics under moderate conditions while at the same time preventing the generation of volatile by-products.Herein we demonstrate that an excellent catalytic activity of MOF-74  in the solid-state form when AB is introduced into the pores. The AB is infiltrated into the pores by solution blending method. MOF-74 has a rigid framework with open pore structure of high surface area (>1000 m2/g) that is composed of one-dimensional (1D) hexagonal channels with a nominal diameter of ~12 Å running parallel to the DOBDC ligands. The confinement of AB inside the pores of MOF-74 (AB-MOF-74) resulted in drastically improved desorption kinetics at significantly reduced temperatures that are suitable for operating temperatures of polymer electrolyte fuel cell. Our system also offers clean hydrogen delivery by suppressing the detrimental byproducts of ammonia, borazine and diborane. Our systematic investigation shows that the dehydrogenation properties of the AB-MOF-74 system dependent on the level of AB loading, indicating the significant role of AB-AB interactions on the dehydrogenation kinetics ..A. Staubitz, A. P. M. Robertson, I. Manners, Chem. Rev. 110 (2010) 4079..S. R. Caskey, A. G. Wong-Foy, A. J. Matzger, J. Am. Chem. Soc. 130 (2008) 10870..Gadipelli Srinivas, Jamie Ford, Wei Zhou, Hui Wu, Terrence J. Udovic and Taner Yildirim, Nanoconfinement and Catalytic Dehydrogenation of Ammonia Borane by Metal-Organic Framework-74 (To be published).
4:30 PM - **N2.6
Structural Studies of Hydrogen Storage Alloys using X-ray/Neutron Diffraction and Total Scattering.
Yumiko Nakamura 1 , Hyunjeong Kim 1 , Saishun Yamazaki 1 , Kouji Sakaki 1 , Thomas Proffen 2 , Etsuo Akiba 1 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Hydrogen storage alloys are one of the most promising materials to achieve on-board hydrogen storage for fuel cell vehicles. They have advantages in volumetric capacity, good kinetics and good stability for absorption/desorption cycles, but a disadvantage in gravimetric capacity. Approach to excellent materials for practical use needs fundamental understanding of reactions between materials and hydrogen. We have studied structural properties of hydrogen storage alloys and tried to find relations between structural and hydrogenation properties. This talk will focus on crystal and local structures and hydrogen occupation of Mg containing materials, which are expected to provide prospects for new light-weighted materials. Hydrogenation and dehydrogenation of (Mg,Ca)Nix (x = 2, 3) have been studied using in situ X-ray and neutron diffraction. (Mg,Ca)Ni2 is C15 Laves phase (MgCu2-type), and (Mg,Ca)Ni3 consists of cells with MgZn2-type and CaCu5-type structures stacking along the c-axis in a ratio of 1:1. Hydrogen occupation and accompanied structural changes depend on the ratios of Ni/(Mg,Ca) and Mg/Ca. A Mg-Co alloy synthesized by mechanical alloying, which was difficult to characterize by conventional methods, has been studied using X-ray and neutron total scattering and the PDF (Pair Distribution Function) method. Neutron and X-ray PDFs show quite different patterns, reflecting that Mg and Co have the opposite contrast for neutron and X-ray. Analysis of the local structure indicates that the material contains two 1-2 nm domains with different compositions and local structures, i.e. Mg-rich and Co-rich domains. The PDFs of the hydrogenated sample suggests that the only Mg-rich domains absorb hydrogen. Part of this work was supported by the New Energy and Industrial Technology Development Organization (NEDO) under Advanced Fundamental Research on Hydrogen Storage Materials (HYDRO-STAR).
5:00 PM - N2.7
Novel Synthesis of Alkali Metal Fulleride Complexes Leading to Reversible Hydrogen Storage Materials.
Douglas Knight 1 , Ragaiy Zidan 1 Show Abstract
1 Chemical Science Division, Savannah River National Laboratory, Aiken, South Carolina, United States
Discovery of materials capable of reversibly storing hydrogen is one of the key challenges researchers face in the current hydrogen storage development. So many of the materials explored today seem desorb hydrogen at high temperatures and reabsorb hydrogen only under extreme pressures and temperatures. Studies have shown that carbonaceous nanomaterials may act as a catalytic scaffold when combined with metal hydrides, proving to be beneficial to the materials hydrogen sorption kinetics. Our study reveals how the combination of C-60 fullerene with alkali metal hydrides will result in the formation of a material that is capable of reversible hydrogen storage. While these types of metallo-fullerides have been studied for their superconductive properties, we present a more straightforward route to their synthesis as well as a detailed account of these materials hydrogen sorption properties. Of the materials presented, results include stoichiometric effects, comparison of mono- and bi-metallic materials, and the result of catalytic additives such as the insertion of titanium or nickel into the metallo-fulleride complexes. These materials not only demonstrate reversible hydrogen storage over several cycles, they also have shown to reabsorb over three times the amount of hydrogen as was in the parent compounds. The materials’ hydrogen desorption performance is measured at temperatures up to 653K under 1 bar hydrogen with the hydrogen absorption measured at temperatures up to 523K under 120 bar hydrogen using a standard Sieverts apparatus. Additional thermal characteristics examined by thermal gravimetric analysis (TGA) coupled with residual gas analysis (RGA) and further characterization performed by powder X-ray diffraction and FTIR Spectroscopy.
5:15 PM - N2.8
Nanoconfinement Effects of Varying Pore Size and Loading Fraction in Lithium Borohydride-carbon Aerogel Systems.
Margaret Bacon 1 , Michael Hartman 1 Show Abstract
1 Nuclear Engineering & Radiological Sciences, University of Michigan, Ann Arbor, Michigan, United States
Though alkali borohydrides are a class of material with inherently high volumetric and gravimetric capacities for hydrogen, their high thermodynamic stability and slow sorption kinetics are obstacles to deployment of these materials for on-board hydrogen storage in vehicles. Confinement of hydrogen storage materials within nanostructured frameworks is a promising approach to improving sorption kinetics and is the focus of the work presented here. Incorporation of lithium borohydride, LiBH4, into nanoporous carbon aerogels (CAs) has been reported to yield decreased activation energy for hydrogen diffusion, decreased in dehydrogenation temperature, and increased cycling capacity. Nanoconfinement studies of mesoporous silica infiltrated with ammonia borane suggest that an optimal ratio of hydrogen storage material to structuring material may be found, a possibility which motivates our studies of LiBH4 in CAs. Results of our previous work with nanoconfined LiBH4 suggest that activation energy decreases as sample loading fraction decreases. For CAs with average pore size of 13 nm, full pore loading reduced activation energy by half relative to the neat material, and partial loading of 3.5% reduced activation energy by half again. We present here the results of our most recent neutron scattering experiments with intermediate loading fractions of LiBH4 in 13 nm CAs. Another confinement effect is that activation energy decreases as aerogel pore size decreases. We present here the results of neutron scattering experiments with full loadings of LiBH4 in 4 nm and 25 nm CAs. We have combined the results of experiments employing various loading fractions or various CA pore sizes with those of our previous experiments in order to achieve a fuller understanding of the correlation between sample composition and materials properties, in an effort to meet the goal of optimizing the LiBH4-CA system for hydrogen storage applications.
5:30 PM - N2.9
Theoretical and Experimental Evidences of an Alkali Silanide as Reversible Hydrogen Sstorage Material.
Jean-Noel Chotard 1 , Wan Si Tang 1 , Pascal Raybaud 2 , Raphael Janot 1 Show Abstract
1 , LRCS UMR 6007 CNRS, Amiens France, 2 , IFP Energies nouvelles, Solaize France
In the search of potential new materials for reversible hydrogen storage, the hydrogenation properties of different M-Si alloys (M=alkaline or alkaline-earth metal) have been investigated by both theoretical and experimental approaches. Thanks to density functional theory (DFT) calculations, the hydrogenation enthalpies of some M-Si silicides into M-Si-H silanides have been predicted favorable for reversible hydrogen storage under moderate pressure and temperature conditions. In particular a promising silicon-based hydride with high gravimetric capacities is reported. This hydride has been obtained either by direct solid-gas hydrogenation of the M-Si alloy, or by reactive ball-milling under hydrogen pressure. Its hydrogen absorption-desorption processes have been carefully investigated by complemental experimental techniques such as thermogravimetry, volumetry, DSC calorimetry and mass spectroscopy. We will show that this compound is able to absorb more than 4 wt% of hydrogen at 100°C with very suitable thermodynamic properties (e.g. 1 bar hydrogen equilibrium pressure at about 140°C). The hydride undergoes a structural transition near room temperature as revealed by DSC. The complete crystallographic structures of the hydrogenated material have been solved on a deuterated sample thanks to neutronic diffraction experiments (HRPT, PSI-Villigen, Switzerland). We will show that the Si-D distances are very short (~1.46 Å as encountered with silanes) leading to a significant covalent character of the Si-H bonding. The relationship between the hydrogenation properties and the crystallographic structures of the hydride will be discussed and closely correlated with DFT calculations.
N3: Poster Session: Hydrogen Storage and Carbon Capture Technology
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - N3.10
Microstructural Modification upon Hydrogen Cycling of MgH2 Nanocomposites.
Marco Vittori Antisari 1 , Amelia Montone 1 , Annalisa Aurora 1 , Daniele Mirabile Gattia 1 Show Abstract
1 Materials Technology, ENEA, Rome Italy
Hydrogen is considered an important energy carrier for a carbon-free management of the energy. One of the main problems for its technological application is related to a safe and compact storage, and intensive study of hydrides has been carried out in the last years, in order to synthesize materials able to store hydrogen at solid state. In particular, MgH2 system is attractive due to a high theoretical gravimetric capacity, to the reversibility of the reaction with hydrogen and to a relatively low cost of the material. Nanostructured MgH2 based systems are able to reduce the working temperature and to speed up the reaction rate with H2. Kinetics behaviour of hydrogen sorption reaction is influenced by sample microstructure. In fact, catalyst particles dispersed into the bulk and the presence of defects in ball milled powders allow to move the nucleation site from the surface of the powder particles to the material bulk both during the hydride formation and hydride decomposition. However, most of the experimental results are relative to materials just processed while less is known on the microstructure evolution during service where a large number of cycles consisting in charging with hydrogen followed by hydrogen desorption, are expected. Here are reported experimental results relative to the modifications of the microstructure and of the reaction kinetics as a consequence of cycling with hydrogen both catalysed and pure Mg powders, simulating the cyclic behaviour of a hydrogen tank. More than 50 cycles of hydrogen absorption and desorption have been carried out. The material performances have been characterized by the maximum hydrogen storage capacity, while the reaction speed has been studied by analyzing the reaction rates. The microstructure of the samples after a large number of cycles has been studied by Scanning Electron Microscopy, both on the powder sample and on cross sectional samples exposing the material bulk. MgH2 and MgH2 with 5wt% of Fe have been studied, in order to understand the role of the catalyst on the cyclic ageing behaviour. The samples have been subjected to repeated cycles of hydrogen adsorption and desorption in a Sievert’s volumetric apparatus at different temperature and pressure conditions. Experimental results show the strong effect induced by the cyclic processing with hydrogen; in particular Mg is progressively extracted by the MgO shell surrounding the powder particles giving rise to a complex powder particle structure where a fraction is constituted by pure Mg not surrounded by the MgO crust. The Mg extraction from the MgO shell leaves the catalyst particles inside the particles. The strategy of catalyst dispersion in materials for technological applications has to take into account this kind of in service modification. Moreover this can represent a new synthetic route in nanofabrication with the purpose of synthesizing MgO boxes containing functionally active particles.
6:00 PM - N3.11
Ab-initio Study of Hydrogen Storage in Palladium Nanoclusters.
Bac Phung 1 , Hiroshi Ogawa 1 Show Abstract
1 Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Pd is known as an archetypical hydrogen storage metal and stores hydrogen under ambient conditions. The hydrogen storage properties of Pd nanoparticles vary depending on the particle sizes and the stabilizers. The hydrogen solubility and equilibrium pressure for the formation of palladium hydride decrease with a decrease in the particle size . In our research, density functional theory (DFT) calculations for the surface adsorption and subsurface absorption of hydrogen on Palladium clusters are performed. We investigate the hydrogen-site specific effects and how the hydrogen storage properties of Pd clusters change with the cluster size. The nudged elastic band method was used to find the minimum energy path and the corresponding energy barriers for hydrogen diffusion process. The hydrogen diffusion barriers are calculated for interstitial sites, from the surface to the subsurface of Pd icosahedral clusters and compared to those of bulk and Pd (111) surface systems , which can provide us an interpretation of the stability of the hydrogenated Pd clusters. The energy profiles along the H diffusion paths in Pd clusters and Pd icosahedral surface are presented. ReferencesM. Yamauchi, H. Hobayashi, H. Kitagawa, Chem. Phys. Chem., Vol. 10, 2566-2576 (2009).  R. A. Olsen, P. H. T. Philipsen, and E. J. Baerends, G. J. Kroes, O. M. Lovvik, J. Chem. Phys. 106 (22), 9286-9296 (1997). AcknowledgementsThis work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".
6:00 PM - N3.12
Large Increase in Volumetric Hydrogen Uptake of MOF-5 via Powder Densification.
Justin Purewal 1 2 , Dongan Liu 1 2 , Andrea Sudik 1 , Don Siegel 2 , Stefan Maurer 3 , Ulrich Mueller 3 Show Abstract
1 Research and Advanced Engineering, Ford Motor Company, Dearborn, Michigan, United States, 2 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Chemicals Research and Engineering, BASF, Ludwigshafen Germany
The metal-organic framework MOF-5 has attracted significant attention due to its ability to store large quantities of H2 by mass, up to ~10 wt % absolute at 80 bar. On the other hand, since MOF-5 is typically obtained as a bulk powder, it exhibits a low volumetric density and poor thermal conductivity—both of which are undesirable characteristics for a hydrogen storage material. At present it is not clear whether materials processing (densification, composite formation, etc.) can overcome these deficiencies, or what impact processing has on structure and other properties. In this study, bulk MOF-5 powder was processed into pellets of varying density by mechanical compaction. We find that compaction can yield a greater than 300% increase in volumetric hydrogen capacity at 77 K compared to the bulk powder, with only a small decrease in gravimetric capacity. Total pore volume decreases with density due to the amorphization of the porous MOF-5 crystal structure, although this decrease is not measurable for pellets with a density below 0.3 g/cc. The thermal conductivity of pellets prepared from pure MOF-5 is slightly below the single crystal value of 0.32 W/m K. Addition of a graphite binder to the pellets is shown to enhance the thermal conductivity. The combined effect of density and graphite additive on surface area, hydrogen adsorption, crush strength and thermal conductivity is summarized.
6:00 PM - N3.13
Experimental Evidence of Super Densification of Adsorbed Hydrogen by In-situ Small Angle Neutron Scattering (SANS).
Dipendu Saha 1 , Lilin He 2 , Nidia Gallego 3 , Yuri Melnichenko 4 , Cristian Contescu 5 Show Abstract
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Neutron Scattering Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Entrapping hydrogen molecules within the nanopores of solid adsorbents serves a unique alternative for on-board storing of hydrogen for transportation purposes. The key advantage of utilizing the physisorption process for hydrogen storage is the higher density values achieved with the adsorbed gas, compared to that of the compressed phase, translating into higher storage capacities at lower pressures. The necessary condition for superior adsorption is the presence of narrow micropores (< 7 A) which serves the most suitable environment of hydrogen adsorption. Despite numerous theoretical calculations or indirect experimental findings, there was no direct experimental result that measured the density of adsorbed hydrogen or compared the same with varying pore sizes. In the present study, we employed in-situ small angle neutron scattering (SANS) on adsorbed hydrogen over polyfurfuryl alcohol-derived activated carbon (PFAC), at room temperature and pressures up to ~200 bar, to provide for the first time direct experimental measurements of the effect of pore size and pressure on the density of the adsorbed hydrogen. SANS studies were carried out at the General-Purpose Small-Angle Neutron Scattering spectrometer, at the High Flux Isotope Reactor, at Oak Ridge National Laboratory. The measurements covered the Q-range from 0.01 to 0.7 Å-1, covering to pores in the range of 8 to 34 Å of the PFAC material. The results indicated that the density of the adsorbed hydrogen, over the Q-range studied, increases with increasing pressure, and achieves values significantly higher than the bulk hydrogen density under similar conditions of pressure and temperature, and it approaches the liquid hydrogen density at the higher pressure studied, of ~200 bar. Our study also revealed that the densification factor (the ratio of the density of the adsorbed gas to the density of bulk gas at a given pressure) is higher in the narrower pores than in the wider pores, confirming theories and experimental indications that narrow micropores present in nanoporous adsorbents are most optimal for hydrogen adsorption.Research sponsored by the Materials Sciences and Engineering Division, and by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy.
6:00 PM - N3.14
Phloroglucinol Based Microporous Polymeric Organic Frameworks for H2 and CO2 Adsorption.
Alexandros Katsoulidis 1 , Mercouri Kanatzidis 1 Show Abstract
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Microporous organic polymers is a rapidly growing category of materials that have been mainly synthesized with coupling and condensation reactions. These metal free polymers possess disordered networks of various rings whose inefficient packing imposes open porous structures. They have attracted considerable attention for applications in several fields such as gas storage, catalysis and separations. Herein a new family of microporous polymeric organic frameworks (POF)s is described. These POFs are assembled from phlorglucinol (1,3,5-trihydroxybenzene) and several benzaldehyde derivatives under solvothermal conditions using bakelite type chemistry of forming C-C bonds without any catalyst. The materials exhibit semiconductor like optical absorption properties with energy gaps in the range of 1.5 to 2.5 eV. The new materials form as uniform spherical particles and exhibit surface areas up to 917 m2g-1 comprising solely of micropores. The micropores have a very uniform size as the gas adsorption isotherms of these amorphous materials are reminiscent of those of crystalline microporous zeolites. Their micropores are internally decorated with a large number of –OH reactive groups which are available for functionalization. The materials are stable in aqueous environment under acidic, pH=1, and basic, pH=13, conditions. The POFs capture at atmospheric pressure as much as 18% and 9% of their mass CO2 at 273 and 298K respectively. The sodium functionalized POF exhibit heat of adsorption for H2 of 9 kJ/mol at low coverage.
6:00 PM - N3.15
Classical MD Simulation of Hydrogen Absorption in f.c.c. and b.c.c. Nanoparticles.
Hiroshi Ogawa 1 , Phung Thi Viet Bac 1 Show Abstract
1 NRI, AIST, Tsukuba, Ibaraki, Japan
Hydrogen absorption in metallic nanoparticles was investigated by classical molecular dynamics (MD) simulation. We used a simple model composed of an isolated f.c.c. or b.c.c. nanoparticle and surrounding hydrogen atoms in a cubic, periodic MD cell. The simulated particle sizes are 1, 1.4, 2, 4, 6, 8 and 10 nm which correspond to about 50 to 44000 atoms. The f.c.c. and b.c.c. lattices were simulated by the manybody potential proposed by Finnis and coworkers for Ni and Fe, and the M-H interaction was assumed to vary by two (energy and radius) parameters from the reference function proposed by Ruda et al. for Ni-H and Fe-H. MD simulation was carried out 300 K and other temperatures for more than 100 ps. In cases of f.c.c. nanoparticles, atomic configuration with five-fold symmetries was observed in both hydrogen-free and hydrogenated particles smaller than 2 nm. Critical particle size of the transition from f.c.c. to icosahedral seems to vary by hydrogenation. The f.c.c. structure was fundamentally maintained in larger particles than 4 nm, although lattice deformation occurred in strong M-H interaction cases. No icosahedral symmetry but b.c.t. transition was observed in b.c.c. nanoparticles. These structure changes induce variation of particle shapes and formation of grain boundaries. Number of absorbed H atoms in a nanoparticle was found to be dependent on both particle size and assumed M-H interaction. It increases with increasing particle size and M-H bond strength. Absorption site of hydrogen atoms in f.c.c. nanoparticles moved from O-site to T-site with increasing M-H bond strength. Present results on lattice structure and absorbing site in hydrogenated nanoparticles were understood by the surface effect in small particles and lattice deformation induced by strong M-H bonds. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".
6:00 PM - N3.16
Theoretical Study of Hydrogen Storage Materials Using All-electron Mixed-basis Program TOMBO.
Ryoji Sahara 1 2 , Hiroshi Mizuseki 1 , Marcel Sluiter 2 , Kaoru Ohno 3 , Yoshiyuki Kawazoe 1 Show Abstract
1 , Institute for Materials Research, Tohoku University, Sendai Japan, 2 , Delft University of Technology, Delft Netherlands, 3 , Yokohama National University, Yokohama Japan
Metal-Organic Frameworks (MOFs) are one of the promising candidates for hydrogen storage materials  with hydrogen storage capacity higher than 6 wt.% (45 kg/m3). In the present study, we propose a simple model of MOFs that can expand hydrogen storage capacity by lithium cation doping and clarify the mechanisms of enhancing hydrogen adsorption energy. We use TOhoku Mixed-Basis Orbitals ab initio simulation package TOMBO [2, 3] which has been developping by our research group. It enables us to study based on ”all-electron mixed-basis approach” with smaller number of plane waves. Here we studied the binding enegy for calixarene with Li ligand. We found that the adsorption of Li atoms improves hydrogen storage function properties of these systems. That is, the system without Li ligand by 1.74 wt.% and makes binding energy much higher than the systems without lithium doping. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials". References: O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi and J. Kim, Science. 300 (2003) 1127-1129.  K. Ohno, K. Esfarjani and Y. Kawazoe, Computational Materials Science From ab initio to Monte Carlo Methods, Springer Series in Solid-State Sciences 129 (Springer-Verlag, Berlin, Heidelberg, 1999), pp. 42-46.  M. S. Bahramy, M.H.F. Sluiter, and Y. Kawazoe, Phys. Rev. B73 (2007), 045111.
6:00 PM - N3.17
A Molecular Dynamics Study of Hydrogen Diffusion in Aluminum Including Dislocations.
Kenji Nishimura 1 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Aluminum trihydride is promising as a hydrogen storage material, e.g., for automotive application, due to its high storage capacity with gravimetric densities of more than 10 wt %. In order to understand the kinetics of hydrogen storage, measuring the diffusion rate of hydrogen in aluminum is important. However, a consensus on the physical mechanisms and numerical values of hydrogen diffusion coefficients in aluminum is still lacking. We have studied hydrogen diffusion in systems including screw and edge dislocations by molecular dynamics simulations to clarify the hydrogenation and dehydrogenation processes of aluminum. The Embedded Atom Method (EAM) potential developed by Tanguy and Megnin is used in this study. The hydrogen diffusivity in aluminum has been estimated at several temperatures from 650 K to 900 K, the highest temperature being 39 K below the melting point with this potential. The pre-exponential factor and activation energy of the hydrogen diffusion are obtained from Arrhenius plot. The hydrogen diffusion along the screw dislocation is found to be significantly faster than diffusion along the edge dislocation, and both diffusivities agree well with experimental data.
6:00 PM - N3.18
Dehydrogenation of Sodium Amidoborane: Characterization by Solid-State NMR Spectroscopy.
Keiji Shimoda 1 , Yu Zhang 1 , Hiroki Miyaoka 1 , Takayuki Ichikawa 1 , Yoshitsugu Kojima 1 Show Abstract
1 , Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima Japan
Structural characterization of hydrogen storage materials on thermal decomposition process provides essential information for understanding the hydrogenation/dehydrogenation mechanisms. Much attention has been paid to ammonia borane (AB; NH3BH3) and its derivatives metal amidoborane (MAB; MNH2BH3, M = Li, Na, etc.) because of their high hydrogen capacity and accessible dehydrogenation starting from ~100 °C [1,2]. Although many researchers have made great efforts to clarify their hydrogen desorption mechanisms, they are partly unsuccessful because the pyrolysis products are difficult to be characterized due to their amorphous features. In the present work, the thermal decomposition of sodium amidoborane (NaAB; NaNH2BH3) was investigated in details by using multinuclear 11B and 23Na MAS/3QMAS NMR techniques.NaAB was prepared from NaH and NH3BH3 reagents (Sigma-Aldrich) by ball milling synthesis method. The thermal gas desorption properties were examined by thermogravimetry (TG) coupled with quadrupole mass spectrometry (MS) up to 200 °C under He flow with a heating ramp of 1 °C/min. Solid-state nuclear magnetic resonance (NMR) spectroscopy was applied on 11B and 23Na nuclei, whose resonance frequencies are 192.6 and 158.7 MHz at an external magnetic field of 14.1 T. Magic-angle spinning (MAS) spectra were acquired with a spinning rate of 15 kHz. Triple-quantum (3Q) MAS NMR technique was also applied that allow us to obtain high-resolution spectra for the half-integer quadrupole nuclei (11B and 23Na; spin I = 3/2).23Na MAS/3QMAS NMR spectra suggested the formation of NaH and an amorphous Na-N-B-H phase as decomposition products above ~80 °C, although NaAB was prepared from NaH and NH3BH3 by ball milling at room temperature. Based on the quantitative analyses of 23Na MAS spectra, we proposed a decomposition reaction up to 200 °C as follows: NaNH2BH3 → Na0.5NBH0.5 + 0.5NaH + 2.0H2. The hypothetical phase Na0.5NBH0.5 is amorphous, where the basic molecular unit of the original NaAB is polymerized into a [–B=N–]n network structure. It was also found that the diammoniate of diborane (DADB) and polyaminoborane (PAB) were not formed during the decomposition of NaAB, which are considered to be key compounds on the pyrolysis of AB .  F. Baitalow, J. Bauman, G. Wolf, K. Jaenicke-Röβler and G. Leitner, Thermochim. Acta., 2002, 391, 159.  Z. Xiong, C. K. Yong, G. Wu, P. Chen, W. Shaw, A. Karkamkar, T. Autrey, M. O. Jones, S. R. Johnson, P. P. Edwards and W. I. F. David, Nature Mat., 2008, 7, 138.  A. C. Stowe, W. J. Shaw, J. C. Linehan, B. Schmid and T. Autrey, Phys. Chem. Chem. Phys., 2007, 9, 1831.
6:00 PM - N3.19
Rapid, High-capacity Hydrogen Storage in Air-stable Magnesium Nanocomposites.
Hoi Ri Moon 1 2 , Ki-Joon Jeon 3 , Ruminski Anne 2 , Bian Jiang 4 , Christian Kisielowski 5 , Jeffrey Urban 2 Show Abstract
1 Interdisciplinary School of Green Energy, Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of), 2 The Molecular Foundry, Material Science Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 3 Environmental Energy Technologies Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 4 , FEI Company, Hillsboro, Oregon, United States, 5 National Center for Electron Microscopy and Helios SERC, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Hydrogen is a promising alternative energy source that can potentially facilitate the transition from fossil fuels to sources of clean energy due to its prominent advantages such as high energy density (142 MJ/kg), natural abundance, light weight, and low environmental impact (water is the sole combustion product). While recent research has yielded several innovations in hydrogen generation, hydrogen storage has not advanced apace and critically limits the viability of hydrogen as a fuel. This problem originates from the challenge of producing a material capable of simultaneously optimizing two conflicting criteria-absorbing hydrogen strongly enough to form a stable thermodynamic state, but weakly enough to release it on-demand with a small temperature rise. Many materials under development, including metal-organic frameworks, nanoporous polymers, and other carbon-based materials, physisorb only a small amount of hydrogen (typically 1-2 wt. %) at room temperature. Metal hydrides were traditionally thought to be unsuitable materials due to their high bond formation enthalpies (e.g. MgH2 has a ΔHf ~75 kJ/mol) resulting in unacceptably slow hydrogen uptake and release kinetics. However, recent theoretical calculations and thin-film studies have shown that microstructuring of these materials can enhance the kinetics by decreasing diffusion path lengths for hydrogen and decreasing the required thickness of the poorly permeable hydride layer that forms during absorption. In this work, we present the synthesis of an air-stable composite material comprised of metallic Mg nanocrystals (NCs) in a gas-barrier polymer matrix that enables both the storage of a high density of hydrogen (up to 6 wt.% of Mg, 4 wt% for the composite) and rapid kinetics (loading in < 30 mins. at 200 degrees C).
6:00 PM - N3.2
First-principles Study of Cobalt Hydrides.
Yasuyuki Matsuura 1 , Tatsuya Shishidou 1 , Tamio Oguchi 1 2 Show Abstract
1 , ADSM, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan, 2 , ISIR, Osaka University, Ibaraki, Osaka, Japan
At high pressures of hydrogen, cobalt forms ferromagnetic hydrides CoHx . As the pressure increases, the solubility of hydrogen monotonically increases. At around temperatures of 250–350°C, the concentration of hydrogen in the hcp phase is x∼0.6 at 7 GPa. At higher pressures, an fcc-based hydride with x∼1.0 is formed. At ambient pressure and 120 K, hydrogen atoms in the solution with x≤0.26 are randomly distributed over octahedral interstitial sites . In the solution with x=0.34 (x≥0.38), hydrogen atoms occupy every third (second) layer. In the ordered structures, the Co layers separated by hydrogen move apart while those with no hydrogen in between get closer with each other. The magnetic moments of the hcp-based hydrides are oriented to the c-axis, and are decreased with increasing hydrogen concentration at a rate of about 0.36 μB per hydrogen atom. In this study, we optimize the structural parameters, namely the lattice constants and internal coordinates for several structures, and investigate the structural stability and related electronic properties by using first-principles calculations. The full-potential linearized augmented plane wave method with the generalized gradient approximation is adopted. V. E. Antonov: J. Alloys Compd. 330-332 (2002) 110. V. K. Fedotov, V. E. Antonov, T. E. Antonova, E. L. Bokhenkov, B. Dorner, G. Grosse, and F. E. Wagner: J. Alloys Compd. 291 (1999) 1.
6:00 PM - N3.20
Characterization of AgInSbTe-SiO2 Nanocomposite Thin Film for Hydrogen Gas Sensor Applications.
Chin-Hung Wang 1 , Kuo-Chang Chiang 1 , Tsung-Eong Hsieh 1 Show Abstract
1 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Hydrogen (H2) gas sensor characteristics of AgInSbTe (AIST)-SiO2 nanocomposite thin film is presented. AIST-SiO2 nanocomposite layers with various thicknesses were first deposited on Si substrates by target-attachment sputtering method. A rapid thermal annealing at 400oC was then followed to induce the crystalline AIST phase in nanocomposite layer. After the deposition of Ag electrodes, the sensor samples were transferred to a test chamber with controlled ambient and temperature. The gas-sensing characteristics of samples were evaluated in temperatures ranging from room temperature to 200oC by measuring the electrical conductance in air and an N2/H2 ambient (H2 content = 200 ppm). It was found that the H2 sensor characteristics become pronounced in the samples containing sufficiently thin AIST-SiO2 nanocomposite layers (e.g., the thickness ≤30 nm). This implies the sensor mechanism is mainly contributed by the reduction/oxidation reactions at the surface of AIST-SiO2 nanocomposite layer. Further, a maximum sensor response = 71.8% with 90% response time = 1 min and 90% recovery time = 1.1 min, respectively, could be achieved in the 30-nm thick AIST-SiO2 nanocomposite sample heated at 100oC. This clearly illustrates the feasibility of AIST-SiO2 nanocomposite layer to H2 sensor fabrications.Microstructure analysis revealed the metallic Sb2Te nanocrystal (NC) is the dominant phase in AIST-SiO2 nanocomposite layer. Nevertheless, the finely dispersed Sb2Te NCs may react with surrounding oxide to form antimony oxides, e.g., Sb2O3 and Sb2O5. Further, the composition depth profile identified the aggregation of TeO2 phase at the surface of AIST-SiO2 nanocomposite layer. As the oxygen vacancies are generated via nonstoichiometric reactions of oxide phases, electrons simultaneously form in the nanocomposite layer. In particular, segregation of TeO2 results in abundant electrons in the vicinity of nanocomposite surface. Such a carrier reservoir facilitates the reduction/oxidation reactions, consequently leading to the H2 sensor characteristics in sufficiently thin AIST-SiO2 nanocomposite layers. In comparison with the sensor technologies utilizing nanorods or nanowires, the sensor comprised of AIST-SiO2 nanocomposite layers apparently exhibits a simplified fabrication process and device structure. A promising application of AIST-SiO2 nanocomposite thin film to H2 gas sensor can thus be expected.
6:00 PM - N3.21
Preparation, Characterization, and Thermal Decomposition Reactions of Hexaamminealuminum Borohydride.
Daniel Hillesheim 1 , Claudia Rawn 1 , Benjamin Hay 1 , Gilbert Brown 1 Show Abstract
1 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Ammonia adducts of complex metal hydrides such as Al(NH3)6(BH4)3, first reported in 1967 (Bird, et.al. J. Chem. Soc., 1967, 664) are under investigation as high hydrogen content storage materials. While IR and elemental analysis conform to the previously published data, the X-ray powder diffraction pattern differs in several key areas. The IR and Raman modes are calculated for the gas-phase compound and compare favorably to the experimental data. The temperature programmed desorption under ambient and reduced pressure conditions is also reported. Coupled TGA-MS data reveals that the first weight loss event (onset ~150 °C) is comprised of borazine (N3B3H6) with corresponding hydrogen evolution. The material was also synthesized with ND3 and the kinetic isotope effect and the product distribution of the initial desorption process has been quantified.Research sponsored by the Office of Energy Efficiency and Renewable Energy, Office of Hydrogen and Fuel Cell Technologies, in conjunction with the MHCoE. ORNL is managed by UT-Battelle, LLC for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.
6:00 PM - N3.22
Kinetics and Materials Properties Measurements of Ammonia Borane Hydrogen Storage System.
Young Joon Choi 1 , Ewa Roennebro 1 Show Abstract
1 Energy Storage Group , Pacific Northwest National Laboratory, Richland, Washington, United States
Among the class of candidates for chemical hydrogen storage in PEM fuel cell applications, ammonia borane (NH3BH3) is considered as one of the most promising materials due to its high hydrogen contents with 19.6 wt.% capacity. This material is selected by the Hydrogen Storage Engineering Center of Excellence (HSECoE) for systems engineering. Therefore, to provide the modelers with necessary information, we investigated the engineering materials properties of ammonia borane (neat AB), the mixtures of ammonia borane and methyl cellulous (AB/MC), and their decomposed products as spent fuel. Sieverts type pressure-composition-temperature (PCT) gas-solid reaction instrument was adopted to characterize the kinetics of H2 release reactions of neat AB and AB/MC at various target temperatures and H2 back pressures. The formation of volatile products such as borazine (N3B3H6) during the H2 release was determined by quantitative analysis on the impurities in the PCT cold trap as well as mass spectrometry (MS). The activation energy and the enthalpy change of dehydrogenation of the samples were determined by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Other materials property requirements needed for systems modeling in the HSECoE, such as thermal conductivity, bulk density and form factor, will be discussed.
6:00 PM - N3.23
Lithium- and Titanium-Doped Graphene Oxide: Novel Hydrogen Storage Materials.
Benjamin Estes 1 , Paige Landry 1 , Hangning Chen 1 , John Larese 1 Show Abstract
1 Chemistry, University of Tennessee, Knoxville, Tennessee, United States
Thermally exfoliated graphite oxide (TEGO), a graphene precursor, has been reacted with butyllithium to prepare lithium-oxygen groups covalently bound to single- and few-layer graphitic materials. These materials may be considered as a model for LiO-doped graphene and other lithium-oxygen containing carbonaceous hydrogen storage materials. Titanium-doped and mixed Ti/Li-doped graphite oxide materials have also been prepared. Hydrogen uptake in comparison to bare TEGO has been measured at low temperature for Li-, Ti-, and Li/Ti- doped oxidized graphene. These materials have also been characterized by XPS, FTIR, Raman and SSNMR. While these low surface area materials are not viable hydrogen storage materials based on DOE targets, their increased affinity towards hydrogen compared to bare TEGO provide further evidence that LiO and TiO doping may be viable routes to the production of higher surface area materials that may indeed meet future hydrogen storage needs.
6:00 PM - N3.24
Crystal Structure and Hydrogen Storage Properties of Novel Mg-Zr-(Li, Na, K) Hydrides Prepared by Gigapascal Hydrogen Pressure Method.
Nobuhiko Takeichi 1 , Kenji Shida 1 , Xiao Yang 1 , Nobuhiro Kuriyama 1 , Tetsuo Sakai 1 Show Abstract
1 , AIST, Ikeda, OSAKA, Japan
Magnesium is one of the promising elements for hydrogen storage media because of the high hydrogen capacity, 7.6 mass%, as MgH2. However, MgH2 is thermodynamically too stable for practical use and needs high temperatures such as 573K. Therefore, Mg-based alloys and compounds have ever been investigated in order to improve the reaction kinetics of hydrogenation and dehydrogenation at elevated temperature. Ultrahigh-pressure technique using multi-anvils would be one of the useful methods to synthesize novel Mg-based hydrides. Our group have reported that Mg-transition metal hydrides with face-centered cubic (FCC) structure, prepared by this method, show reversible hydrogen storage properties at 523 K. In this study, we have succeeded to synthesize a series of novel Mg-Zr-A hydrides (A=Li, Na and K) by the UHP technique. In addition, we investigated crystal structure and hydrogen storage properties of the hydrides. Initial mixture pellet, 6MgH2+ZrH2+xAH (A=Li, Na and K; x=0~1), was sealed in an NaCl capsule together with hydrogen source. The capsule was inserted into an octahedral pyrophyllite cell. Then, the assembly was compressed up to 8 GPa by using a high-pressure generating and held at 873 ~ 1073 K for 1 hour under 8 GPa. The crystal structures were analyzed based on X-ray diffraction data obtained at the beam-line BL19B2 in SPring-8. The structure was refined by use of the Rietveld program RIETAN-2000. Hydrogen storage properties were examined by a differential scanning calorimeter and pressure-composition isotherms measurements. In the Mg-Zr-H system, the Mg-Zr hydride with FCC structure was formed under 8 GPa and 873 K. Under 8 GPa and 973 K, the Mg-Zr hydride with monoclinic structure was formed with small amount of impurity, MgO and γ-MgH2, where FCC-type hydride was not formed. The monoclinic hydride is more stable than FCC-type hydride under high temperature region. In the Mg-Zr-Li system, the quaternary hydrides were formed and these kept the same crystal structure, FCC structure, up to x = 1.0. Mg, Zr and Li atoms are sharing the 4a site using space group Fm-3m. While in the Mg-Zr-Na system, the quaternary hydrides were formed and these kept FCC structure, up to x = 0.3. With addition of 0.5 NaH, Ca7Ge-type super lattice phase was formed instead of FCC-type. In case of the Mg-Zr-K system, two kinds of FCC-type hydrides with small and large lattice constant were formed. The large lattice constants were increased with increasing the KH content. The nearest-neighbor distance between Mg and H atoms in Mg-Zr-A hydrides is longer than that between Mg and H atoms in MgH2. Mg-Zr-A hydrides can reversibly absorb and desorb a large amount of hydrogen, ~ 4 mass%, at 523 ~ 573 K. We will discuss that the reason for the improvement of the hydrogen storage properties, the relationship between crystal structure and those properties. This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO).
6:00 PM - N3.25
Novel Hydrogen Storage Materials: An Atomic Scale Computational Approach.
Hiroshi Mizuseki 1 , Natarajan Venkataramanan 1 , Ryoji Sahara 1 , Gang Chen 1 , Mohammad Khazaei 1 , Yoshiyuki Kawazoe 1 Show Abstract
1 , Institute for Materials Research, Tohoku Univ., Sendai, Miyagi, Japan
Doping with alkali metal elements increases the hydrogen storage capacity of many materials. Inspired by these findings, we have explored the hydrogen storage properties of alkali doped fullerene, BN fullerene, BN sheet, and TiNi nanocluster. Calculations based on DFT show that alkali metal dopants significantly improves the average binding energy of hydrogen molecules . Moreover, Na-functionalized calixarene molecule was found to hold six hydrogen molecules inside its cavity . In the case of carbon nanohorn, Each Li atom on the outer sidewall could bind three hydrogen molecules, while the small room inside the nanohorn limits the adsorbed hydrogen molecules to be eight at maximum. The hydrogen binding energy attracted by Li atoms would not be altered much if both sidewalls are decorated by Li atoms. The total storage capacity could be 5.8 wt.% with 8 and 36 hydrogen molecules respectively adsorbed surrounding the Li atoms on the inner and the outer sidewalls, which has the average binding energy per H2 > 200 meV . In this presentation we will also present the storage capacities and adsorption properties of graphene[4, 5], BN sheet[5, 6], BN fullerene, and TiNi nanocluster. A part of this work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Advanced Fundamental Research Project on Hydrogen Storage Materials”.1. N. S. Venkataramanan, R. Sahara, H. Mizuseki, and Y. Kawazoe, J. Phys. Chem. C. 112, (2008), 19676.2. N. S. Venkataramanan, R. Sahara, H. Mizuseki, and Y. Kawazoe, Comput. Mater. Sci. 49 (2010) S263.3. G. Chen, Q. Peng, H. Mizuseki, and Y. Kawazoe, Comput. Mater. Sci. 49 (2010) S378.4. M. Khazaei, M. S. Bahramy, A. Ranjbar, H. Mizuseki, and Y. Kawazoe, Carbon 47, (2009), 3306-3312.5. M. Khazaei, M. S. Bahramy, N. S. Venkataramanan, H. Mizuseki, and Y. Kawazoe, J. Appl. Phys. 106, (2009), 094303.6. N. S. Venkataramanan, M. Khazaei, R. Sahara, H. Mizuseki, and Y. Kawazoe, Chem. Phys. 359, (2009), 173-178.7. N. S. Venkataramanan, R. V. Belosludov, R. Note, R. Sahara, H. Mizuseki, and Y. Kawazoe, Chem. Phys. in press.8. N. S. Venkataramanan, R. Sahara, H. Mizuseki, and Y. Kawazoe, J. Phys. Chem. A, 114, (2010), 5049.
6:00 PM - N3.3
Synthesis of Sub-nanometer Porous Membranes with Molecular Level Control over Pore Chemistry.
Rami Hourani 1 , Rob van der Weegen 2 , Nana Zhao 1 , Beverly Zhang 1 , Brett Helms 2 , Ting Xu 1 3 4 Show Abstract
1 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 2 Organic and Macromolecular Synthesis Facility, The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Department of Chemistry, University of California, Berkeley, California, United States, 4 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Thin films containing sub-nanometer channels aligned normal to the surface constitute promising materials for selective separation and transport to meet growing demands in renewable energy, environmental sustainability and life sciences. The membrane selectivity is determined by the shape, size, and surface chemistry of the through channels. Our studies focus on generating sub-nanometer porous membranes with channels mimicking natural transmembrane proteins for carbon caption and water desalination. We developed chemical approaches to synthesize nanotubes based on cyclic peptides where the shape and surface chemistry of the nanotubes can be tailored. This was achieved by incorporating artificial amino acids, such as 3-amino-2-methylbenzoic acid, in the primary peptide sequence. NMR, CD and TEM clearly demonstrated molecular modifications of interior of nanotubes with diameters ranging from 0.4-1.5nm. We also developed a new approach to co-assemble nanotubes with diblock copolymers in thin films to generate sub-nanometer porous membranes with nanotubes oriented normal to the surface by directing the growth of nanotubes within a confined geometry. The presented directed synergistic co-assembly of nanotube subunits and block copolymers may allow one to direct the formation of nanotubes within the nanoscopic domains established by the BCPs so as to manipulate the spatial organization and macroscopic orientation of nanotubes. This process takes full advantage of nanoscopic assembly of copolymers and the reversibility of organic nanotube growth and is compatible with existing technologies for thin film fabrication. Initial transport studies showed the resultant sub-nanometer membranes are size selective and exhibit significant enhanced mass transport with a similar magnitude seen in single wall carbon nanotubes.
6:00 PM - N3.4
Addition of Lithium Cations to Improve Selective Carbon-dioxide Adsorption in Micro-porous Materials.
Brad Hauser 1 , Youn-Sang Bae 2 , Omar Farha 1 , Randall Snurr 2 , Joseph Hupp 1 Show Abstract
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois, United States
The removal of carbon dioxide from methane in natural gas applications is an important process. Contamination of natural gas streams with CO2 causes pipeline corrosion and decreases energy density. Additionally, the separation of carbon dioxide from nitrogen is required for the treatment of flute gas emissions from coal-fired power plants. High CO2 selectivity and capacity are essential when selecting an adsorbent for energy efficient adsorptive separation processes such as pressure-swing adsorption (PSA).Recently, microporous materials such as metal-organic frameworks (MOFs) and metal free porous polymers have shown promise in the fields of gas storage and gas separations. These microporous materials are attractive because they possess extremely high internal surface areas, low density and can be synthesized with diverse functionality. These diverse functionalities can be exploited to tune the material for selective affinity towards certain guests. Addition of lithium cations is shown to enhance the selectivity of CO2 versus CH4 in microporous materials. This presentation will show multiple routes to post-synthetic incorporation of lithium cations into metal-organic and metal-free polymeric frameworks. Methods using both chemical reduction through alkali metal doping, and cation exchange are employed. Gas adsorption isotherms have been measured for both the materials before and after incorporation of lithium cations, and the mixed-gas adsorption predicted from the single-component isotherms. Also, the incorporation of amine and nitro functional groups into prototypical metal-organic frameworks is explored as a means to increase CO2 binding energy and enhance selectivity for CO2 versus nitrogen.
6:00 PM - N3.5
Microstructural Evolution during Hydrogen Sorption Cycling of Magnesium-transitionMetal Nanolayered Composites.
Peter Kalisvaart 1 2 , Alan Kubis 1 2 , Mohsen Danaie 1 2 , Babak Shalchi Amirkhiz 1 2 , David Mitlin 1 2 Show Abstract
1 Chemical&Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 , National Institute of Nanotechnology, Edmonton, Alberta, Canada
A detailed study of the microstructural evolution of Mg-FeTi multilayered hydrogen storage materials during extended cycling at low (200 oC) and high (300 oC) temperatures will be presented. A 28 nm Mg-5 nm FeTi multilayer has comparable performance to a cosputtered material with an equivalent composition (Mg-10%Fe-10%Ti), which is included as a baseline case. At 200 oC, the FeTi layers act as a barrier, preventing agglomeration of Mg particles. At 300 oC, the initial structure of the multilayer is preserved up to 35 cycles, followed by fracturing of the Mg layers in the in-plane direction and progressive delamination of the FeTi layers as observed with SEM and TEM. Concurrently, an increase in the Mg grain size was observed from 32 to 76 nm between cycle 35 and 300. As a result, the absorption kinetics deteriorate with cycling, although 90% of the total capacity is still absorbed within 2 minutes after as many as 300 cycles. The desorption kinetics, on the other hand, remain rapid and stable and complete desorption of 4.6 wt.% H is achieved in 1.5 minutes at ambient desorption pressure. Interestingly, the materials’ behavior is not only influenced by the ‘bilayer’ (Mg+FeTi) thickness, but also independently by the thickness of the catalyst layers. When the Mg/FeTi ratio is kept constant, but the bilayer thickness increased to 100 nm, 85 nm Mg/15 nm FeTi, the Mg layers are found to agglomerate into large particles ‘sandwiched’ between intact catalyst layers. The kinetics rapidly deteriorate, most notably in absorption, thus demonstrating the severe diffusion limitations in Mg hydride. However, similar behavior upon cycling is observed even when the Mg thickness is reduced down to 56 and 28 nm while keeping the FeTi thickness at 15 nm. Thus, there seems to be an interplay between the mechanical rigidity of the catalytic phase and the behavior of the storage phase, which could offer guidance for the design of other composite materials for energy storage.
6:00 PM - N3.7
Characterization of Membranes for Hydrogen Purification Applying a Membrane / Gas-sensor Combination.
Ravi Mohan Prasad 1 , Michael Huebner 2 , Odile Merdrignac Conanec 3 , Aleksander Gurlo 1 , Ralf Riedel 1 , Nicolae Barsan 2 , Udo Weimar 2 Show Abstract
1 Fachbereich Material- und Geowissenschaften, Technische Universitaet Darmstadt, Darmstadt Germany, 2 Faculty of Mathematics and Natural Sciences, Department of Chemistry, Tuebingen University, Tuebingen Germany, 3 Institut de Chimie de Rennes, Universite de Rennes 1, Rennes Cedex France
The growing interest in the use of hydrogen as main fuel has increased the need for pure hydrogen production and purification. There are several poisoning by-products (CO, H2O, CO2..) associated with the production of hydrogen which might damage the production rate. Therefore, separation of hydrogen from other gases is an important step in the hydrogen production process . Membrane-related approaches are considered to be one of the most promising technologies for the production of high-purity hydrogen. The present work concentrates on the characterization of membrane performance applying a novel membrane/gas-sensor combination. As a case study, the high-temperature separation and sensing of hydrogen and carbon monoxide was monitored by employing a combination of a microporous ceramic membrane and a semiconducting metal nitride based gas-sensor. Selective extraction of H2 from the product side during hydrogen production in membrane reactors can facilitate complete CO conversion in a single-step under the thermodynamically unfavourable but kinetically favourable high temperature conditions . Therefore, we used CO instead of CO2 which is produced at lower temperature (< 500°C) during water-gas-shift reaction. GaN - used as sensing material - was obtained by nitridation of Ga2O3 with ammonia at 900°C for 24 hours  and then screen printed onto alumina substrates provided with Pt electrodes and heater and annealed under nitrogen (400-600°C). GaN was chosen for the present study because it shows higher stability in harsh reducing conditions when compared to that of SnO2 . The amorphous Si3N4 ceramic membrane was obtained by ammonolysis of commercially available polysilazane. Dip coating method of the preceramic polymer was used to form a ceramic membrane on the top of the GaN, which was finally pyrolysed under ammonia at 800°C. The results of XRD and NMR characterisation and N2 sorption isotherm analysis confirm the formation of amorphous microporous Si3N4 ceramic. Gas sensing properties of uncoated and Si3N4-coated GaN were studied at 350 and 530°C in nitrogen towards different H2 (40-900 ppm) and CO (10-120 ppm) concentrations. The uncoated GaN showed very high signals towards CO in oxygen-free background whereas the membrane coated sensor showed almost no signal to CO. The H2 sensor signals remained unaffected confirming high permeance of H2 through Si3N4 membrane compared to CO permeance. Hence, membrane/gas-sensor combination could be used as one of the models for getting an impression of the performance of microporous ceramic membrane in a fast and economic way before using it in membrane-reactor.Financial support by German Research Foundation (DFG) is greatly acknowledged.References N.W. Ockwig et al., Chem. Rev., 2007, 107, 4078-4110 G.Q. Lu et al., J. Colloid Interf. Science, 2007, 314, 589-603 M. Kerlau et al., Sens. Actuators B, 2006, 115, 4-11 R.M. Prasad et al., Sens. Actuators B, 2010, 149, 105-109
6:00 PM - N3.8
ab initio Calculations on MH+NH3 Hydrogen Storage System.
Aki Yamane 1 , Fuyuki Shimojo 2 , Kozo Hoshino 1 , Takayuki Ichikawa 3 4 , Yoshitsugu Kojima 3 4 Show Abstract
1 Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, Hiroshima, Japan, 2 Graduate School of Science and Technology, Kumamoto University, Kumamoto, Kumamoto, Japan, 3 Graduate School of Advanced Sciences of Matter, Hiroshima University, Hiroshima, Hiroshima, Japan, 4 Institute for Advanced Materials Research, Hiroshima University, Hiroshima, Hiroshima, Japan
To realize a society based on hydrogen energy, it is required to develop high-performance hydrogen storage systems.Ammonia (NH3), which contains 17.6 mass% of hydrogen and easily liquefies at about 1 MPa of pressure, can be regarded as one of the most excellent hydrogen storage and transport materials.MH+NH3 ↔ MNH2+H2 (M = Li, Na, and K) systems are hydrogen storage systems based on NH3 and metal hydride(MH).The hydrogen desorption reaction of these systems are exothermic and proceeds at room temperature, and the reverse reaction also proceeds at relatively low temperatures and pressures .Though the hydrogen storage capacity decreases in order of M = Li, Na, and K, the reaction yield increases in order of M = Li, Na, and K .The purpose of this study is to reveal the microscopic mechanism of H2 desorption from MH+NH3 by ab initio calculations.We set a system consisting of an M2H2 cluster and an NH3 molecule, where we regard M2H2 cluster as a model of disordered MH surface.To estimate the height of the potential barrier of the H2 desorption reaction, we decreased the distance between a H atom in M2H2 and another H atom in NH3 (this reaction process is consistent  with the experimental results  on Li-N-H hydrogen storage system).We found that the potential barrier of the H2 desorption from M2H2+NH3 depends on M and its height decreases in order of M = Li, Na, and K.This result is consistent with the M dependence of the reaction yield of these systems.This work is supported by the Grants of the NEDO project 'Advanced Fundamental Research on Hydrogen Storage Materials' in Japan. Y. Kojima et al., J. Mater. Res. 24 (2009) 2185 H. Yamamoto et al., Int. J. Hydrogen Energy 34 (2009) 9760 S. Isobe et al., J. Phys. Chem. B 109 (2005) 14855 A. Yamane et al., J. Mol. Struct.: THEOCHEM, 944 (2010) 137
6:00 PM - N3.9
Multiple Scale Modeling of Hydrogen Adsorption in Simulated Nanoporous Carbon Structures.
Lujian Peng 1 , Valentino Cooper 2 , James Morris 2 1 Show Abstract
1 Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee, United States, 2 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
We have introduced an efficient and accurate approach to estimate the hydrogen physisorption in amorphous carbons at room temperature and moderate pressure. The method accurately reproduces previous results of an expanded graphite model. Extensive tight binding molecular dynamics simulations have been performed to model amorphous carbons at various densities. The numerical calculations suggest the theoretical hydrogen uptake is close to 1.5 wt% at 298 K and 5 MPa in low density amorphous carbons. Suitable heats of adsorption for hydrogen storage (12-20 kJ/mol) are predicted for these materials. We investigate the relationship between hydrogen uptake and carbon bond distribution, pore size distribution, and pore connectivity. To improve the accuracy of this method, we examine the binding energy of hydrogen molecules to carbon structures using recently developed van der Waals-density functional electronic methods that account for dispersion interactions, and use this binding information to directly examine hydrogen adsorption. Comparisons with adsorption, diffraction and small-angle neutron scattering experiments will be discussed. Research supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.
Z.Zak Fang University of Utah
Hongcai (Joe) Zhou Texas A&M University
Ewa Ronnebro Pacific Northwest National Laboratory
N8: Metal and Intermetallic Hydrides, Sorption, and Other Hydrogen Storage Materials II
Thursday PM, April 28, 2011
Room 2011 (Moscone West)
2:30 PM - **N8.1
Round-robin Results on Measuring High-surface-area Materials For Hydrogen Storage and Critical Calibration Issues.
Philip Parilla 1 , Kevin O'Neill 1 , Katherine Hurst 1 , Jeffery Blackburn 1 , Chaiwat Entrakul 1 , Justin Bult 1 , Lin Simpson 1 , Thomas Gennett 1 Show Abstract
1 5200, NREL, Golden, Colorado, United States
For the class of hydrogen storage media consisting of high-surface-area materials, there is an intrinsic difficulty in calibrating the measurement for accurate determination of adsorption capacity. There are several issues, among them, precise calibration of the free space, proper verification of the instrument, non-ideality of the gases, uniformity, stability and measurement of the temperature and the problem of helium adsorption during calibration. Whether using the volumetric or gravimetric methods, helium adsorption will produce an error in the skeletal density determination and result in an inaccurate free space or buoyancy correction respectively. In order to help the hydrogen storage community address these issues, a round-robin measurement project is underway to gauge the variability in capacity results for two standard materials. A similar round-robin program in Europe (NESSHY)* yielded a wide variety of results and underscores the need to address the problem. With defined sample preparation and measurement protocols, measurements near room temperature and at liquid nitrogen were tested up to pressures of 200 bar. Results of the round-robin testing are presented and discussed. Specific issues that create systematic errors are explored in detail. Here we will focus on issue with the volumetric method and discuss proper calibration techniques and data analysis procedures. Experimental procedure, accuracy estimates, and instrument verification will be discussed as well as example data will be shown. This work was performed under DOE contract DE-AC36-08GO28308 and the DOE Fuel Cell Technologies Program* Claudia Zlotea, Pietro Moretto, Theodore Steriotis, International Journal of Hydrogen Energy 34 (2009) 3044 – 3057
3:00 PM - N8.2
Porous Metal (Ni) Nanospheres with Tunable Structures as a Novel Hydrogen Storage Material.
Hiesang Sohn 1 , Qiangfeng Xiao 1 , Yunfeng Lu 1 Show Abstract
1 Chemical and Biomolecular Engineering, UCLA, Los Angeles, California, United States
Although hydrogen (H2) is an attractive energy carrier due to its abundance and environmental benignity, its attractiveness as a fuel is undermined owing to difficulty of onboard storage. After many systems for reliable and safe H2 storage were proposed, it is regarded as proper approach to store H2 as a metal hydride form. To maximize the storage capacity, it is crucial to design and synthesize porous host metal as a H2 storage media with optimized structure and with high surface area. Nevertheless, there were quite limited studies on fabrication of porous metal with tunable structure and on the investigation of the morphological effect of porous metal on H2 uptake property owing to difficulty in making porous metal with high surface area. We fabricated porous metal (nickel) nanospheres with various morphologies based on aerosol-assisted method and measured their H2 uptake property. Various morphologies for nickel nanosphere, ranging from non-hollow to hollow porous structure, were obtained by judicious selection of precursor material (metal salts and organic ligand), and by controlling of their stoichiometric mixing ratio. After morphological analyses of the formation and growing of porous nickel nanosphere with different structure by electronic imaging (TEM), it was found that the structure of nanosphere were mainly determined by kinetics of surface enrichment process during the thermal decomposition in the aerosol reactor. In addition, the mole ratio between metal (Ni) salt and organic ligand and thermal degradation behavior of organic ligand also played a key role to determine the structure by influencing on diffusion kinetics inside of the aerosol. The crystalline structure of the nanosphere was investigated by X-ray diffraction and the surface porosity was illustrated via N2 sorption behavior. Based on morphological, structural analyses and gas sorption behavior, it was confirmed that various porous hollow metal nanosphere products were successfully fabricated with tunable surface area (116~260 m2/g) as well as tunable structure (non-hollow to hollow porous nanosphere). The effect of morphological difference of the porous nickel nanospheres on the H2 uptake capacity was carried out at low pressure (1 atm) and room temperature (298 K). Porous nickel nanospheres show high H2 uptake (0.06 ~ 0.14 wt%) compared to that of commercial Ni powder (0.02 wt%) at the same test condition. Although the surface area, morphology and crystalline structure comprehensively influence on the H2 uptake, morphology was found to be very influential factor after normalization of other parameters, and higher H2 uptake (0.12~0.14 wt%) were obtained by porous nickel nanosphere with hollow structure. Since the procedure developed in the study offer advantages including facile control of material’s morphology and applicability to other metal or metal complexes, these results would provide insight to design novel material for high capacity H2 storage.
3:15 PM - N8.3
Hydrogen Adsorption Properties on Porous Materials at around the Critical Temperature.
Takayuki Ichikawa 1 , Akira Kubota 1 , Hiroki Miyaoka 1 , Yoshitsugu Kojima 1 Show Abstract
1 , Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
In the research field of hydrogen storage materials, hydrogen adsorption on a surface of porous materials has been widely studied, in which the pore size and surface area of the materials have been tried to be controlled. In recent years, it has been reported that the activated carbon with a high surface area of about 3000 m2/g exhibits a maximum hydrogen storage capacity of ~5 mass% at 77 K [1,2] and of ~ 1 mass% at a room temperature under 10 MPa hydrogen pressure. Thus, many researchers in this field have focused on how the pore size and the surface area can be controlled to obtain high enough hydrogen storage capacity. On the other hand, Panella et al. focused on the adsorption potential of hydrogen on the surface of the materials by means of cryogenic techniques below 77 K . However, they reported on the hydrogen desorption properties on elevating temperature from 20 K under high vacuum condition. Furthermore, almost all the studies were performed at 77 K.
In this work, we have investigated the hydrogen adsorption properties at around the critical temperature of hydrogen, 33 K. After precisely controlling the temperature with a deviation of ±0.1 K, the volumetric capacities of hydrogen storage were measured by Sieverts systems. From the results, it was confirmed that about 10 mass% of hydrogen can be adsorbed on the activated carbon at 28 K as an excess hydrogen capacity. This capacity was obviously larger compared with the case of blank measurement at 28 K, suggesting that the amount of adsorbed hydrogen was larger than the gaseous hydrogen excluded due to the volume of sample. With increasing temperature from 28K to 38K, the hydrogen capacities were gradually decreased without any apparent gap even though hydrogen straddles the critical temperature.
 M. Hirscher and B. Panella, J. Alloy. Compd.,2005; 399 404-406
 Y. Kojima, et al. J. Alloy. Compd.,2006; 421 204-208
 B. Panella, et al. Microporous Mesoporous Mat.,2007; 103 230-234
3:30 PM - N8.4
High Specific Surface Area Microporous Materials for Hydrogen Storage at Cryogenic Conditions.
Maurice Schlichtenmayer 1 , Barbara Streppel 1 , Michael Hirscher 1 Show Abstract
1 , Max Planck Institute for Metals Research, Stuttgart Germany
Physisorption of hydrogen in microporous materials is a potential solution for the storage of hydrogen in mobile applications due to its high gravimetric storage density, fast kinetics and complete reversibility. An important parameter for the characterization of porous materials is the specific surface area, which is most commonly measured with nitrogen gas using the Langmuir- or BET-method and lies in the order of 1000 m2/g for most microporous materials. A linear correlation was found between the specific surface area of adsorption materials and their hydrogen uptake, giving roughly 1 wt% of excess uptake at 77 K per 500 m2/g of specific surface area (Chahine’s rule). Here, materials with BET surface areas higher than 3000 m2/g have been investigated in the temperature range from 77 K to room temperature and for pressures up to 2.5 MPa. All materials are compared regarding their excess hydrogen uptakes, which is mostly found in the literature, and their total uptakes, which includes adsorbed hydrogen and hydrogen gas in the pores. This total uptake is the relevant parameter for application in a storage system. These results are evaluated with respect to the operating conditions of a tank system, assuming a minimum back pressure of 0.2 MPa, a maximum tank pressure of 2 MPa and cryogenic temperatures, which results in the so-called usable capacity. Furthermore, the usable capacity of a storage material can be correlated to its heat of adsorption. Materials with high heat of adsorption show a high usable capacity at high operating temperatures and long dormancy times, but a low usable capacity at low operating temperatures, and vice versa for materials with lower heats of adsorption.
3:45 PM - N8.5
High Surface Area Boron Doped Carbon with Slow Hydrogen Desorption Kinetics.
Justin Bult 1 , Jeffrey Blackburn 1 , Justin Lee 1 , Kevin O'Neill 1 , Katherine Hurst 1 , Chaiwat Engtrakul 1 , Philip Parilla 1 , Lin Simpson 1 , Thomas Gennett 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Boron doped turbostratic carbon is shown to have altered hydrogen sorption kinetics and improved hydrogen storage properties compared to base activated carbon (CM-Tec™). The high surface area sp2 bonded boron doped carbon is synthesized by using chemical vapor deposition to deposit a 10 nm thick layer of BCX on the activated carbon substrate. These materials show uniquely slow kinetic desorption as measured by temperature programmed desorption. Furthermore, the BCX material shows improved storage capacity on a per unit area basis greater than that expected by the “Chahine rule” for physisorbed hydrogen. It is postulated that an intercalated hydrogen species can be adsorbed and stored within the unique pore structure generated by the boron dopant induced curvature. This is supported by the significant decrease in the hydrogen storage capacity observed at approximately 100 K and below, indicating a change in accessible surface area as a function of temperature. The storage values observed could be a result of one of two mechanisms; hydrogen dissociation on BCX edge planes or pure physisorption into precisely sized pores generated by the boron dopant in the graphitic plane. Both mechanisms would have the potential to produce a lower temperature bound for hydrogen accessibility either due to insufficient reaction energy or structural changes in the pore dimensions. Characterization of the boron doped carbon in the context of its hydrogen storage capacity and mechanism of storage will be discussed. Furthermore, the effect this unique kinetic behavior has on its use and performance in the noble metal catalyzed spillover process will be presented.  Sha, X.; Cooper, A.; Bailley III, W.; Cheng, H. Revisiting Hydrogen Storage in Bulk BC3. J. Phys. Chem. C 2010, 114, 3260-3264
4:30 PM - N8.6
Novel Hydrogen-Dense Boron- and Nitrogen-based Storage Materials and Their Applicability in Hydrolytic Dehydrogenation.
Umit Demirci 1 , Julien Hannauer 1 2 , Christophe Geantet 2 , Philippe Miele 3 , Jean-Marie Herrmann 2 Show Abstract
1 , Laboratoire des Multimateriaux et Interfaces / Universite Lyon 1, Villeurbanne France, 2 , Institut de Recherches sur la Catalyse et l’Environnement de Lyon / Université Lyon 1, Villeurbanne France, 3 , Institut Europeen des Membranes / Universite Montpellier 2, Montpellier France
With oil reserves running low and oil demand rising, there is a demand for sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to diversified merits of hydrogen as energy carrier . Chemical hydrides, especially boron-based ones – the most typical examples of this class of materials are certainly sodium borohydride (SB) and ammonia borane (AB) –, have been widely investigated owing to their high hydrogen content . Such materials can be dehydrogenated by solvolysis [2,3] and/or hydrolysis [2,4]. However, none has achieved effective gravimetric hydrogen storage capacities high enough at low temperature (< 85 °C) to be implemented in technological (especially, automotive) applications [1,2].One has to recognize that today a significant breakthrough in the field of solid-state hydrogen storage materials is necessary. Novel, hydrogen dense, ‘unstable’ materials have to be found to be envisaged for on-board vehicular applications which criteria are severe . Despite limited performances in terms of effective storage capacities, AB is still very attractive. In fact, it is very attractive as it is a promising, reactive parent material for designing novel boron- and nitrogen-based materials. For example, amidoboranes such as LiNH2BH3 has already showed to be a potential hydrogen storage material, its dehydrogenation being mainly done through thermal activation . Involved since several years in the field of boron- and nitrogen-based materials, we are today working on designing novel, hydrogen-dense boron and nitrogen-based compounds, i.e. AB derivatives, intended to be dehydrogenated in higher extent and at temperatures much lower than AB does, with dehydrogenation being achieved either by solvolysis or thermolysis. MRS 2011 spring meeting will thus be an exciting opportunity to show the high potential of the novel materials we develop and, to present and discuss our most impressive results in terms of dehydrogenation and effective storage capacities. Eberle et al,. Angew. Chem. Int. Ed., 2009, 48, 6608 U.B. Demirci, P. Miele, Energy Environ. Sci., 2009, 2, 627 Hannauer J.et al, Energy Environ. Sci., 2010, 3, 1796 Benzouaa R. et al., Thermochimica Acta, 2010, 509, 81 U.S. Department of Energy Hydrogen Program, 2007, NREL/MP-150-42220. Xiong et al. Nature Mater., 2008, 7, 138
4:45 PM - N8.7
Electrospinning Complex Hydrides for Hydrogen Storage.
Arthur Lovell 1 2 , Zeynep Kurban 2 1 , Stephen Bennington 1 2 , Derek Jenkins 3 , Neal Skipper 2 , Kate Ryan 4 , Martin Jones 4 , Bill David 1 4 Show Abstract
1 ISIS, STFC-Rutherford Appleton Laboratory, Didcot United Kingdom, 2 London Centre for Nanotechnology, University College London, London United Kingdom, 3 MNTC, STFC-Rutherford Appleton Laboratory, Didcot United Kingdom, 4 Inorganic Chemistry, University of Oxford, Oxford United Kingdom
We have used co-axial electrospinning to encapsulate and nanostructure complex hydrides in composite permeable polymer fibres. With this one-step process, we are able to address the twin challenges of solid state hydrogen storage: improving H2 release properties while reducing hydride oxidation and contamination of the fuel stream with reaction byproducts. Our investigations using ammonia borane and polystyrene have shown that a variety of core-shell fibre structures and microbeads can be synthesised, controlled by a solution-selection model we developed to optimise the co-axial spinning parameters such as solution miscibility, vapour pressure, viscoelasticity and electrical conductivity. We present details of the process and the dehydrogenation characteristics of the resulting materials.
5:00 PM - N8.8
Reversible Storage of Molecular Hydrogen in Type II Clathrate Silicon.
David Baker 1 , Carolyn Koh 1 , George Nolas 2 , P. Craig Taylor 1 Show Abstract
1 Physics, Colorado School of Mines, Golden, Colorado, United States, 2 Physics, University of South Florida, Tampa, Florida, United States
Previously studied for its superconducting properties, clathrate silicon in the Type II structure now shows promise as a viable storage medium for molecular hydrogen. Three clathrate silicon samples of composition Na1.3Si136, Na7.9Si136, and Na22.7Si136, provided by the University of South Florida, exposed to a molecular hydrogen atmosphere at 70 MPa exhibit reversible hydrogen uptake as evidenced by temperature programmed desorption (TPD) measurements. In addition there is evidence that increasing concentration of intercalated sodium atoms within the clathrate structure correlates with increasing hydrogen uptake. Thus, of the samples analyzed, Na22.7Si136 shows the most promise as a storage material, with a 0.06 wt% hydrogen fraction as measured via TPD. In addition to hydrogen, the TPD results indicate the presence of water and other small molecules as contaminants within the samples, the elimination of which could increase total hydrogen storage beyond that currently measured. These TPD results, in concert with electron paramagnetic resonance spectroscopy results, indicate that these samples store molecular hydrogen within the structure itself. Furthermore, these results show that clathrate silicon offers clear advantages as a material that is stable at room temperature and atmospheric pressure and provides a reversible, mechanical hydrogen storage mechanism.
5:15 PM - N8.9
Reversibility of H2 Sorption in NaAlH4 / Carbon System.
Jinbao Gao 1 , Krijn de Jong 1 , Petra de Jongh 1 Show Abstract
1 chemistry, utrecht university, Utrecht Netherlands
To satisfy the requirements for on board hydrogen storage, major interest was shifted to high H2 content compounds, such as complex metal hydrides containing up to 18 wt% H2 and mixed metal hydride systems. Most of these multi-component systems exhibit slow kinetics for H2 release and uptake. Furthermore, the obtained reversible H2 capacities in these systems are far below the theoretical values. A promising approach to improve H2 sorption kinetics and even alter thermodynamics is to reduce particles size to the low nanometer scale and confine them in a porous material. Although this also largely improved the reversibility, still loss of H2 storage capacity was observed during cycling. For instance, LiBH4 incorporated into different porous carbon showed improved reversibility, but 30% ~ 55% capacity loss was found for different samples after three cycles . Also for NaAlH4 encapsulated in microporous carbon fibers 45~% capacity loss was observed after three cycles .Previously, we prepared nanosized NaAlH4 confined mainly in the 2-3 nm pores of carbon by melt infiltration, and found nanoconfined NaAlH4 shows partial reversibility without a metal-based catalyst . However, significant loss of capacity was observed during the initial cycle, while the hydrogen capacity became stable upon further cycling.It is at first sight surprising to find that 2.4 wt% H2 can be reabsorbed with only 24 bar H2 pressure and 150 oC for 3 h. For bulk NaAlH4, rehydrogenation involves interdiffusion of several solid phases (NaH, Al, Na3AlH6), and only 0.6 wt% reversible H2 capacity can be obtained even with 150 bar H2 pressure and 170 oC in the absence of a metal-based catalyst. This has commonly been ascribed to the hypothesis that H2 absorption is limited by solid state transfer of decomposition products, especially Al. In our nanoconfined NaAlH4/C system, it is expected that phase segregation and mass transfer could be restricted by confinement from the pores of carbon. Nevertheless, relatively large Al grains were formed during decomposition. Interestingly, XRD results indicate that part of solid Al has a remarkable mobility under mild conditions, and can partially be reconverted into nanoconfined (and non-crystalline) NaAlH4 inside the small pores. Some Al seems inert, despite what pressure and temperature are used for rehydrogenation. In this contribution, we discuss which factors limit the reversibility and how full cycling can be achieved in a nanoconfined NaAlH4/C system. The understanding of this will also have relevance for other complex hydrides systems. Gross, A.F., Vajo, J.J., Van Atta, S. L. and Olson, G. L., 2008, J. Phys. Chem. C, 112(14) Lohstroh, W., Roth, A., Hahn, H., Fichtner, M., 2010, Chem. Phys. Chem., 11(4)  Gao, J., Adelhelm, P., et al., 2010, J. Phys. Chem. C, 114(10)