Symposium Organizers
Etsuo Akiba National Institute of Advanced Industrial Science and Technology
William Tumas National Renewable Energy Laboratory
Ping Chen National University of Singapore
Maximilian Fichtner Karlsruhe Institute of Technology
Shengbai Zhang Rensselaer Polytechnic Institute
W1: Computation
Session Chairs
Jisoon Ihm
Shengbai Zhang
Zhenyu Zhang
Monday PM, November 30, 2009
Back Bay D (Sheraton)
9:15 AM - **W1.1
First-Principles Discovery of Novel Hydrogen Storage Materials and Reactions.
Christopher Wolverton 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractPractical hydrogen storage for mobile applications requires materials that exhibit high hydrogen densities, low decomposition temperatures, and fast kinetics for absorption and desorption. Unfortunately, no reversible materials are currently known that possess all of these attributes. Here we present an overview of our recent efforts aimed at developing a first-principles computational approach to the discovery of novel hydrogen storage materials. We have developed computational tools which enable accurate prediction of decomposition thermodynamics, crystal structures for unknown hydrides, and thermodynamically preferred decomposition pathways. We present examples that illustrate each of these three capabilities. Specifically, we focus on recent work on crystal structure and dehydriding reactions of borohydride materials, such as Mg(BH4)2, MgB12H12, and (NH4)2B12H12. In addition, we illustrate work on ab-initio molecular dynamics simulations of the Li4BN3H10 hydride showing how this tool can be used to elucidate unsuspected kinetic pathways for hydrogen release.
9:45 AM - **W1.2
Recent Development in Designing Metal-decorated Hydrogen-storage Nanostructures.
Jisoon Ihm 1
1 Physics , Seoul National University, Seoul Korea (the Republic of)
Show AbstractUsing first-principles electronic structure calculations, we perform a combinatorial search for hydrogen storage materials among low-dimensional nanomaterials and metal organic frameworks (MOFs) decorated with extra metal atoms. In the model systems we study, hydrogen molecules are stored by being attached to certain metal atoms which are bound to a backbone matrix consisting of carbon-based nanomaterials or MOFs. Stable structures are obtained by relaxing positions of constituting atoms via the energy minimization procedure. High gravimetric as well as volumetric storage capacity under ambient conditions is shown to be possible with appropriate choices of elements and structures. Transition metal atoms can bind hydrogen molecules through the simultaneous electron donation and back-donation which is usually called a ``Kubas interaction''. This interaction is extremely useful for the room-temperature hydrogen storage applications and provides the optimal H2 binding energy of 0.3 eV including the zero-point energy correction. We show that there exists competition between the exchange field and the ligand(crystal) field splitting, and the high storage capacity is achievable only when the ligand field dominates. Other metal atoms such as calcium may bind hydrogen molecules through the dipole interaction as well which is induced by the ionization of the metal atoms.We also report recent theoretical progress in the field using a new formalism for estimating the storage capacity. Experimental H2 uptake data are analyzed based on this equilibrium thermodynamics formalism and novel interpretations of the data are presented.
10:15 AM - **W1.3
Design Principles of Exposed Metal-Organic Frameworks toward Enhanced Hydrogen Physisorption.
Yong-Hyun Kim 1
1 Graduate School of Nanoscience and Technology (WCU), Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractMetal-organic framework (MOF) materials provide high-surface areas of ~5000 m2/g BET vaules, where H2 molecules can be physisorbed up to 7.5 wt% at 77 K and 80 bar [1]. Because physisorption is a surface reaction, the physisorption-based H2 storage is as fast and reversible as traditional liquid and high-pressure gas-tank storages. In spite of its promise, however, pure physisorption of H2 suffers from a weak interaction (0.04-0.05 eV per H2) with materials and thus operates only at cryogenic temperatures. At room temperature, storage performance of the same MOFs drops to less than 1 wt%. In order to improve the room-temperature performance, one needs to design MOF materials that have enhanced H2 physisorption sites. In this regard, transition metal (TM)-exposed MOFs such as those based on Mn and Cu [2,3] have been investigated. The octahedrally-coordinated TM centers are easily exposed by post-processing such as degassing or dehydration, and the exposed TM sites adsorb H2 with increased energy gains up to ~0.1 eV per H2. Yet, the binding is not enough for room-temperature operation. It is therefore important to deduce design principles of TM-exposed MOFs to get enhanced physisorption greater than 0.2 eV per H2, based on microscopic understanding of dihydrogen interaction mechanisms.From results of first-principles calculations, we have proposed a series of design principles to achieve high hydrogen adsorption energies greater than 0.2 eV in TM-exposed MOFs [4,5]. (i) Instead of late-TMs such as Mn and Cu, early TMs such as Sc, Ti, and V can store H2 strongly, attributing to sigma-d(z2) coupling. In particular, Ti- and V-incorporated MOFs can adsorb hydrogen molecules as strongly as 0.3-0.4 eV per H2. (ii) Fe is also a good hydrogen storage element. The hydrogen adsorption energy is as large as 0.3 eV per H2, after Fe’s local symmetry is lowered. (iii) Late-TMs can couple well with hydrogen in paddle-wheel diatomic configurations, via unique sigma-s coupling. In this talk, we will discuss details of the underlying mechanisms of enhanced hydrogen physisorption.[1] A. G. Wong-Foy, A. J. Matzger, and O. M. Yaghi, J. Am. Chem. Soc. 2006, 128, 3494–3495.[2] M. Dincă, A. Dailly, Y. Liu, C. M. Brown, D. A. Neumann, and J. R. Long, J. Am. Chem. Soc. 2006, 128, 16876-16883.[3] V. K. Peterson, Y. Liu, C. M. Brown, and C. J. Kepert, J. Am. Chem. Soc. 2006, 128, 15578–15579.[4] Y. Y. Sun, Y.-H. Kim, and S. B. Zhang, J. Am. Chem. Soc. 2007, 129, 12606–12607.[5] Y.-H. Kim, Y. Y. Sun, W. I. Choi, J. Kang, and S. B. Zhang, submitted.
10:45 AM - W1.4
On Accuracy of Density Functionals for Designing Molecular Hydrogen Storage Materials.
Yiyang Sun 1 , Kyuho Lee 2 , Lu Wang 1 3 , Zhongfang Chen 4 , Shengbai Zhang 1
1 Physics, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Physics, Rutgers University, Piscataway, New Jersey, United States, 3 Physics, Dalian University of Science and Technology, Dalian China, 4 Chemistry, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractRecent theoretical calculations and experiments have suggested that metal-functionalized nano and porous materials are promising for storing molecular hydrogen (H2) at near ambient conditions. Optimizing the storing capacities (both gravimetric and volumetric) for massive H2 storage, such as onboard vehicles, is of great current interest. Theoretical design of H2 sorbents relies on accurate description of the interaction between metal and H2. However, the strength of such interactions (typically 10-40 kJ/mol) falls in a gray area, where it is uncertain if the widely used density-functional theory (DFT) calculations are accurate enough. For weaker interactions, mainly van der Waals interactions, it is well-known that common DFT calculations fail. For stronger interactions, e.g., covalent bonding, DFT has been shown successful for many years. In this work, we carry out benchmark calculations with high-level quantum chemistry calculations at MP2 and CCSD(T) levels, including most interesting elements that have been proposed for H2 storage. It is hoped that this benchmark could facilitate the search for a “good” density functional suitable for theoretical design of H2 storage materials.
11:30 AM - **W1.5
Predictive Modeling of Low-Dimensional Materials for Solar Energy Conversion and Storage.
Zhenyu Zhang 1
1 Department of Physics and Astronomy, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractAdvanced materials, in particular materials of reduced dimensionality, are playing an essential role in exploration of alternative and sustainable energy sources. In this talk, I will try to highlight the importance of interdisciplinary science and synergetic efforts between theory and experiment in designing advanced materials for enhanced solar energy utilization, as exemplified by a few examples. The first is the formulation of non-compensated n-p codoping as a novel enabling concept for narrowing the bandgap of oxide semiconductors for a variety of catalytic applications, including photolysis for hydrogen production and environmental cleanup. Next we will outline some guiding principles in predictive design of light-element based nanomaterials as potential high-capacity media for hydrogen storage. Collectively, these examples hopefully help to convey the vital importance of fundamental understanding and control of the elemental energy carriers and their conversion from one form to another.Supported by USDOE and USNSF.
12:00 PM - W1.6
First Principles Simulations of Hydrogen Storage via Spillover in MOF-5.
Don Siegel 1 2
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 , Ford Motor Company, Dearborn, Michigan, United States
Show AbstractMetal organic frameworks (MOF) represent an important class of candidate hydrogen storage materials due to their ability to adsorb large quantities of hydrogen by weight, approaching 12 wt% (total, P = 100bar). However, as a consequence of the weak (~5kJ/mol) H2-MOF bonding interaction, this uptake occurs only at cryogenic temperatures; at room temperature, gravimetric storage densities generally do not exceed ~0.5 wt. %. As an ideal storage system would operate under near-ambient conditions, much interest has been generated by recent experiments reporting RT storage in MOFs of 3-4 wt. % via the so-called "spillover" mechanism [JACS 128, 8136 (2006)]. In contrast to conventional MOF-based storage, where molecular hydrogen bonds directly to the MOF, spillover employs a hydrogen dissociation catalyst to generate atomic hydrogen. Although stronger bonding between atomic H and the MOF receptor is cited as the basis for increased ambient temperature storage, recent computational studies of spillover have reported conflicting results regarding the strength and nature of this interaction. In an effort to resolve these ambiguities and clarify the thermodynamics of MOF-based spillover, periodic density functional theory calculations are used to evaluate binding energies for several H adsorption configurations on MOF-5. Importantly, our calculations avoid the cluster approximation to the MOF geometry – a source of significant uncertainty in previous studies – and account for finite-temperature contributions to the free energy of adsorption. We conclude by placing our thermodynamic data in context with those available from previous calculations and experiments.
12:15 PM - W1.7
First Principles Calculations on Storage Capacity of Hydrogen Storage Materials.
Hiroshi Mizuseki 1 , Natarajan Venkataramanan 1 , Ryoji Sahara 1 , Yoshiyuki Kawazoe 1
1 , Institute for Materials Research, Tohoku Univ., Sendai, Miyagi, Japan
Show AbstractDoping with alkali metal elements increases the hydrogen storage capacity of many materials. Inspired by these findings, we have explored the hydrogen storage properties of lithium doped Metal Organic Frameworks (MOFs) and BN fullerenes. Binding energy of alkali atoms on BN fullerenes were identical to C60. However, the binding on BN fullerene occurs at the bridge site near the tetragonal site. Alkali adsorption can be adsorbed to a maximum of six sites. Each Li atom was found to hold up to 3 hydrogen molecules. Ab initio MD studies shows that these materials have working temperature between 300K and 400K. In the case of the MOF materials, Li-doping significantly improves the hydrogen uptake. Each Li atom doped was found to hold three H2 molecules firmly due to the charge induced dipole interaction. The most stable position for the Li atom was found to be on the benzene ring, forming a Li-benzene complex and each benzene ring was able to hold two Li atoms [1]. 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, Int. J. Mol. Sci. 10, 1601 (2009).
12:30 PM - W1.8
A Comparison of Atomistic Modeling of Hydrogen Adsorption in Nanoporous Carbon with Recent Experimental Results.
Lujian Peng 1 , James Morris 2 1 , Vinay Bhat 2 , Cristian Contescu 2 , Nidia Gallego 2 , Wojtek Dmowski 1 , Takeshi Egami 1 2
1 , University of Tennessee, Knoxville, Tennessee, United States, 2 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractWe present recent experimental studies and associated atomistic simulations of hydrogen adsorption in nanoporous carbon. Promising evidence of significant hydrogen adsorption in nanoporous carbon has been revealed by experiments that show a heat of adsorption is near 15 kJ/mol. Grand Canonical Monte Carlo simulations of expanded graphite shows heats of adsorptions that can approach the experimental value, and that have the same behavior as a function of density. This suggests that pores formed of separated graphitic sheets may give rise to favorable hydrogen physisorption. Tight-binding simulations of nanoporous carbon show evidence of such pores. We use such simulations to examine the binding of H2 molecules in the disordered structure, and how structural changes and densities affect the physisorption. These results will be compared with careful diffraction studies of different carbon structures with different absorption properties.This research has been sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-00OR-22725 with UT-Battelle.
12:45 PM - W1.9
Room Temperature Hydrogen Storage Via a Kubas-like Interaction in Titanium-Doped Silica (Ti-HMS): A Combined Experimental and Theoretical Investigation.
Jason Simmons 1 , Taner Yildirim 1 2 , Ahmad Hamaed 3 , David Antonelli 3
1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Department of Materials Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 Department of Chemistry and Biochemistry, University of Windsor, Windsor, Ontario, Canada
Show AbstractNumerous first-principles calculations have suggested that transition metal atoms incorporated onto high surface area materials could enable significant room temperature storage via a Kubas-like interaction. Such a binding mechanism would offer an ideal isoteric heat of hydrogen adsorption in between that of standard physisorbers and chemisorbers. Thus far, direct experimental evidence for such interactions has been lacking. Here we demonstrate that Ti(III)-benzyl complexes grafted onto porous silica hosts (Ti-HMS) can provide Kubas-active sites for room temperature hydrogen storage. Using a combination of experimental techniques, including gas sorption measurements and neutron vibrational spectroscopy, and first-principles calculations we are able to better understand the nature of the titanium sites as well as to thoroughly probe the hydrogen-titanium interactions. Interestingly we found that hydrogen storage in Ti-HMS via the Kubas interaction is thermally activated, proceeding only near room temperature, and is stable over long periods of time. This assessment is further supported by first-principles reaction-path calculations. In Ti-HMS, the Ti-center is coordinated by both the methyl and phenyl moieties of the benzyl ligand. Introduction of hydrogen causes the Ti-phenyl coordination to relax, allowing hydrogen to access the Kubas-active Ti-center. Surprisingly, the calculations indicate that the free and adsorbed hydrogen have similar ground-state energies separated by a small energy barrier (< 0.25 eV), a feature that should make the removal of the adsorbed hydrogen possible under relatively mild conditions. Thus, Ti-HMS represents the first system in which Kubas-like hydrogen storage is possible near room temperature, providing experimental support for previous theoretical predictions.
W2: Adsorption
Session Chairs
Monday PM, November 30, 2009
Back Bay D (Sheraton)
2:30 PM - **W2.1
Hydrogen Sorption Materials Development.
Lin Simpson 1 , A. Dillon 1 , T. Gennett 1 , K. O'Neill 1 , C. Engtrakul 1 , J. Blackburn 1 , Y. Zhao 1 , J. Bult 1 , A. Groves 1 , P. Parilla 1 , E. Whitney 1 , C. Curtis 1 , Y. Kim 2 , S. Zhang 3 , M. Heben 4
1 , NREL, Golden, Colorado, United States, 2 , Korea Advanced Institute of Science and Technology, Seoul Korea (the Republic of), 3 , Rensselaer Polytechnic Institute, Troy, New York, United States, 4 , University of Toledo, Toledo, Ohio, United States
Show AbstractThe National Renewable Energy Laboratory (NREL) works with DOE as the technical lead for the Hydrogen Sorption Center of Excellence (HSCoE) to develop sorbent materials that can meet DOE’s reversible storage technical targets. Since sorption based materials typically meet the vast majority of the technical targets, most of our efforts are focused on improving capacity and reducing cost via scalable, reproducible, and inexpensive synthesis. In general, sorbent materials may be able to meet the DOE targets via multiple approaches using different sorption mechanisms. NREL’s efforts have focused on the rational design and synthesis of nanostructured materials where the sorption sites are optimized to allow access to and binding of the hydrogen with enthalpies higher than typical physisorption (i.e., 3-5 kJ/mol) but low enough (i.e., less than 40 kJ/mol) so that reversibility at ambient temperature and heat removal during refilling are not issues. The use of sorbent-based materials greatly simplifies the refueling/regeneration process, thus lowering system costs and weight.NREL is developing sorbent materials with lightweight elements. In addition to optimizing the geometric structures for maximum site access and sorption, NREL is constructing multiple element materials with the constituents arranged in optimal ways to enhance hydrogen storage. NREL will provide detailed hydrogen capacity/performance and reproducible processing information for some of our promising hydrogen storage materials. This will include detailing systematic studies of the sorption behavior of chemically and thermally processed nanomaterials and correlating this performance with structural/composition information. In addition to providing results on dihydrogen adsorption materials, NREL will also detail our efforts on developing spillover materials.ACKNOWLEDGEMENTSFunding for this effort was provided by the US Department of Energy's Office of Energy Efficiency and Renewable Energy within the Center of Excellence on Hydrogen Sorption Materials as part of DOE's National Hydrogen Storage Grand Challenge, and by the Office of Science, Basic Energy Sciences, Materials Science and Engineering under subcontract DE-AC36-99GO10337 to NREL.
3:00 PM - W2.2
Metal Supported Nanocones for Hydrogen Spillover: Optimizing Metal Dispersion.
Paolo Matelloni 1 , Gavin Walker 1 , David Grant 1
1 Dept of Mechanical, Materials and Manuf. Engineering, University of Nottingham, Nottingham United Kingdom
Show AbstractCarbon nanocones are the fifth allotropic form of carbon synthesized in 1997. They consist of curved graphite sheets with one to five pentagonal rings located at the tip. It has been proved the correlation between the number or pentagons and the cone angle. Theoretically, only five discrete pentagonal disclinations can define the tip of the carbon cone resulting in five predicted cone angles (19.2°, 38.9°, 60°, 86.6°, and 123.6°). The lengths of the nanocones vary between 300 and 800 nm with a maximum base diameter between 1 and 2μm. The wall thickness is in the range 20–50 nm. These structures are similar to nanohorns which also have long cone-shaped tips with cone angles of about 20° and large tube-diameters of about 2–4 nm. They have been selected for investigating hydrogen storage capacity, because earlier temperature programmed desorption experiments found a significant amount of hydrogen was evolved at ambient temperatures. The aim of this work was to study the effect of metal catalysts on hydrogen uptake of nanocones. Pre-treatment of carbon nanocones with hydrogen peroxide has been carried out in order to enhance their dispersion in water for subsequent metal decoration by an incipient wetness technique. Two methods of reducing the metal catalyst have been applied: with 10% flow of hydrogen at room temperature and with an aqueous solution of NaBH4. In situ X-ray diffraction analysis confirmed the complete reduction has taken place and transmission electron microscopy has been used to study of the influence of the reduction technique and the metal loading on the particle size. Conditions have been identified for the controlled deposition of very fine dispersions of ca.1nm diameter metal clusters. Furthermore, the reduction with NaBH4 leads to the formation of Pd2B alloy confirmed by ToF SIMS. Finally hydrogen adsorption has been investigated. For the uptake of hydrogen at room temperature, it has been found that the catalysts are very active for the dissociation of hydrogen, proving to be a facile reaction at this temperature. Hydrogen capacities were measured and an increase was observed with metal loading up to 15 wt.%.
3:15 PM - W2.3
Hydrogen Binding Energy Tuning with the Interlayer Distance of Metal Intercalated Graphite.
Aditi Herwadkar 1 , Yufeng Zhao 1
1 , NREL, Golden , Colorado, United States
Show Abstract The adsorption of hydrogen on carbon structures and nanostructures offers a way to reduce the storage pressure of hydrogen with respect to compression storage while achieving interesting gravimetric storage densities. One of the more readily available carbon structures, activated carbons, can achieve reproducible, high gravimetric storage densities under cryogenic operating conditions: 5.6% at 3.5 MPa and 77 K, in excess of the normal density that would be present in the pore volume under compression at the same temperature and pressure. To this we discuss and compare the adsorption of hydrogen on graphene layer with 8% B substituting C atoms. In our model we have used Li atoms as active metal centers. Using first principle plane wave calculations we show that Boron substitution in graphene sheets enhances both Li-sheet charge transfer and hydrogen binding. Enhanced charge transfer leads to better metal dispersion and hence increases the Li density from 1/18 in the un-doped case to 1/9 in the doped case. Here in particular we present gravimetric sorption measurements to estimate the H2 storage capacity. These estimates are calculated with the Grand Canonical Monte Carlo simulations. With the current system we could achieve reproducible, excess sorption of 6.4% at 2.7 MPa and 77 K with interlayer distance of 7.73 A the adsorption. With our calculations we also show that the binding energy can be tuned by changing the interlayer distance which in turn changes the H2 adsorption.
3:30 PM - W2.4
Hydrogen Adsorption in Nanostructured Graphite Intercalation Compounds from Electrospun Polymer Nanofibers.
Arthur Lovell 1 3 , Zeynep Kurban 1 3 , Derek Jenkins 2 , Stephen Bennington 1 3 , Neal Skipper 3 , Felix Fernandez-Alonso 1 3
1 ISIS, STFC Rutherford Appleton Laboratory, Didcot United Kingdom, 3 London Centre for Nanotechnology, University College London, London United Kingdom, 2 Micro and Nano Technology Centre, STFC Rutherford Appleton Laboratory, Didcot United Kingdom
Show AbstractThe prospects for solid state hydrogen storage are currently marred by the lack of materials in which hydrogen binds with intermediate enthalpy between physi- and chemisorption. H2 binding in high surface area structures is characterised by fast kinetics and reversibility, but poor storage density and cryogenic operating temperatures. Conversely, hydrides have good H storage density, but impractically high desorption temperatures and slow release rates. Nanostructuring provides a promising route to improving the thermodynamics and kinetics of hydrogen desorption by increasing surface area and lowering hydrogen diffusion times. Furthermore, the binding strength of H2 in physisorptive hosts is known to be enhanced under controlled charge doping. The understanding of how these effects combine anticipates the synthesis of storage materials with good hydrogen density and rapid cycling under near-ambient conditions.
The electrospinning of nanofibers from polymer solutions has attracted attention as a cheap and scalable bulk nanostructuring method, making it ideal for hydrogen storage research. We have used this route to produce and characterize charge-doped nanostructured carbons, by intercalating potassium into electrospun nanofibers following air stabilization and carbonization at high temperatures. Neutron spectroscopy of H2 has been performed at 1.5K in the resulting turbostratic graphite intercalation compounds (GICs) of stoichiometry KC24, and combined with constant-volume desorption measurements to obtain the sorption enthalpy. The librational spectra as a function of hydrogen loading were compared with our recent results in the homologous bulk turbostratic GIC. The reduction in the degree of crystallinity in the nanostructured intercalate leads to a greater width in the hydrogen tunneling bandhead at 0.6 meV, as the K-H2 interaction potential is mediated by inhomogeneities in the host matrix. Further work will focus on the nature of these, the turbostratic nanofibers as a host for other donor species, and the potential of the electrospinning technique for the synthesis of other materials including nanostructured complex hydrides.
3:45 PM - W2.5
Exploration of Hydrogen Molecule Binding in Covalent Organic Framework-1 through Ab initio Calculations.
Ralph Scheicher 1 , Pornjuk Srepusharawoot 1 2 , C. Moyses Araujo 1 3 , Andreas Blomqvist 1 , Udomsilp Pinsook 4 5 , Rajeev Ahuja 1 3
1 Condensed Matter Theory Group, Department of Physics and Materials Science, Uppsala University, Uppsala Sweden, 2 Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen Thailand, 3 Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH), Stockholm Sweden, 4 Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok Thailand, 5 ThEP, Commission on Higher Education, Bangkok Thailand
Show AbstractNon-dissociative adsorption of molecular hydrogen on materials with a high surface area represents a potentially promising route towards the dual goal of safely storing hydrogen and ensuring favorable kinetics for its release. In this work [1], we have used both density functional theory (DFT) and Hartree-Fock plus second-order Møller-Plesset perturbation theory (MP2) to systematically investigate the hydrogen physisorption energies at all possible adsorption sites in the Covalent Organic Framework-1 (COF-1), a porous crystalline material [2]. When considering only a single H2 interacting with the COF-1 structure, the most favorable adsorption sites identified from our DFT results are found to be directly above an oxygen atom in the B3O3 ring and on top of the midpoint of a C-C bond in the benzene ring. These binding preferences are slightly altered when higher hydrogen loading levels are considered, so that H2 molecules then become preferentially trapped directly above the carbon atoms of the benzene ring. The trend and hierarchy of physisorption energies obtained from the DFT method is found to be in good agreement with the MP2 results, lending support to the qualitative accuracy of the DFT calculations. The observation of a rise in binding energies upon an increase in the number of hydrogen molecules loaded into the system is interpreted by us as a cooperative phenomenon emerging from long-range attractive H2-H2 interactions. Ab initio molecular dynamics simulations carried out at three different temperatures (77 K, 150 K, and 300 K) reveal that for higher hydrogen loading levels, the occupancy (and hence non-availability) of binding sites can limit the mobility of the hydrogen molecules and thus contribute effectively to the trapping of H2 molecules in the COF-1 system. [1] Pornjuk Srepusharawoot, Ralph H. Scheicher, C. Moysés Araújo, Andreas Blomqvist, Udomsilp Pinsook, and Rajeev Ahuja, J. Phys. Chem. C 113, 8498–8504 (2009). [2] Adrien P. Côté, Annabelle I. Benin, Nathan W. Ockwig, Michael O'Keeffe, Adam J. Matzger, and Omar M. Yaghi, Science 310, 1166–1170 (2005).
4:30 PM - **W2.6
Increase the Hydrogen Uptake of Metal-Organic Frameworks (MOFs).
Hong-Cai (Joe) Zhou 1
1 Chemistry, Texas A&M University, College Station, Texas, United States
Show AbstractFor any potential hydrogen-storage system, raw uptake capacity must be balanced with the kinetics and thermodynamics of uptake and release. MOFs provide unique systems with large overall pore volumes and surface areas, adjustable pore sizes, and tunable framework–adsorbate interaction by ligand functionalization and metal choice. These materials can potentially fill the niche between other physisorbents such as activated carbon, which have similar uptake at low temperatures but low affinity for hydrogen at ambient temperature, and chemical sorbents such as hydrides, which have high hydrogen uptakes but undesirable release kinetics and thermodynamics. Although MOFs have high hydrogen uptake at 77 K and under applicable pressure, the hydrogen uptake at room temperature is very low. The reason is that the hydrogen affinity of common MOFs is relatively low. To increase hydrogen uptake of MOFs, studies to increase both the surface area and the heat of hydrogen adsorption have been carried out in our laboratory. In this presentation, a series of MOFs designated as Porous Coordination Networks (PCNs) including MOFs with entatic metal centers, aligned open metal coordination sites, interpenetration, and mesocavities with microwindows will be discussed. References Zhao, D.; Yuan, D.; Sun, D.; Zhou, H.-C. J. Am. Chem. Soc. 2009, 131, 9186-9188. Ma, S.; Yuan, D.; Chang, J.-S.; Zhou, H.-C. Inorg. Chem. 2009, 48, 5398-5402. Ma, S.; Simmons, J. M.; Sun, D.; Yuan, D.; Zhou, H.-C. Inorg. Chem. 2009, 48, 5263-5268. Ma, S.; Eckert, J.; Forster, P. M.; Yoon, J. W.; Hwang, Y. K.; Chang, J.-S.; Collier, C. D.; Parise, J. B.; Zhou, H.-C. J. Am. Chem. Soc. 2008, 130, 15896-15902. Wang, X.-S.; Ma, S.; Forster, P. M.; Yuan, D.; Eckert, J.; Lopez, J. J.; Murphy, B. J.; Parise, J. B.; Zhou, H.-C. Angew. Chem., Int. Ed. 2008, 47, 7263-7266. D. Zhao, D. Yuan, and H.-C. Zhou. Energy Environ. Sci., 2008, 1, 222.
5:00 PM - W2.7
Highly Porous Metal-Organic Framework Containing A Novel Organosilicon Linker – A Promising Material For Hydrogen Storage.
Michael Froeba 1 , Stephanie Wenzel 1 , Michael Fischer 1 , Frank Hoffmann 1
1 Department of Chemistry, University of Hamburg, Hamburg Germany
Show AbstractThe synthesis and characterization of the new metal-organic framework PCN-12-Si (isoreticular to PCN-12) is reported (1). PCN-12-Si comprises dicopper paddle-wheel units located at the vertices of a cuboctahedron, which are connected by the new linker 5,5’-(dimethylsilanediyl)diisophthalate. The microporous MOF has a high specific surface area of BET = 2430 m2/g and a high specific micropore volume of Vp = 0.93 cm3/g (p/p0 = 0.18). The activated form of PCN-12-Si shows a remarkable hydrogen storage capacity. Volumetric low pressure hydrogen physisorption isotherms at 77 K reveal an uptake of 2.6 wt.-% H2 at 1 bar. Furthermore, theoretical GCMC simulations were carried out. The simulated low pressure isotherm is in excellent agreement with the experimental one. Simulations for the high pressure regime predict an excess hydrogen uptake of 4.8 wt.-% at 30 bar, which corresponds to an absolute amount adsorbed of 5.5 wt.-%. In addition, the potential field of H2 inside PCN-12-Si was derived from the simulations and analyzed in detail, providing valuable insights concerning the preferred adsorption sites on an atomic scale.(1) S.E. Wenzel, M. Fischer, F. Hoffmann, and M. Froeba, Inorg. Chem. 2009, in press.
5:15 PM - W2.8
Investigation of Metal Hydride Nanoparticles Templated in Metal Organic Frameworks.
Raghunandan Bhakta 1 , Julie Herberg 2 , Aaron Highley 1 , Richard Behrnes 1 , Mark Allendorf 1
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractHydrogen is proposed as an ideal carrier for storage, transport, and conversion of energy. However, its storage is a key problem in the development of hydrogen economy. Metal hydrides hold promise in effectively storing hydrogen. For this reason, metal hydrides have been the focus of intensive research. The chemical bonds in light metal hydrides are predominantly covalent, polar covalent or ionic. These bonds are often strong, resulting in high thermodynamic stability and low equilibrium hydrogen pressures. In addition, the directionality of the covalent/ionic bonds in these systems leads to large activation barriers for atomic motion, resulting in slow hydrogen sorption kinetics and limited reversibility. One method for enhancing reaction kinetics is to reduce the size of the metal hydrides to nano scale. This method exploits the short diffusion distances and constrained environment that exist in nanoscale hydride materials. In order to reduce the particle size of metal hydrides, mechanical ball milling is widely used. However, microscopic mechanisms responsible for the changes in kinetics resulting from ball milling are still being investigated. The objective of this work is to use metal organic frameworks (MOFs) as templates for the synthesis of nano-scale NaAlH4 particles, to measure the H2 desorption kinetics and thermodynamics, and to determine quantitative differences from corresponding bulk properties. Metal-organic frameworks (MOFs) offer an attractive alternative to traditional scaffolds because their ordered crystalline lattice provides a highly controlled and understandable environment. The present work demonstrates that MOFs are stable hosts for metal hydrides and their reactive precursors and that they can be used as templates to form metal hydride nanoclusters on the scale of their pores (1 – 2 nm).We find that using the MOF HKUST-1 as template, NaAlH4 nanoclusters as small as 8 formula units can be synthesized inside the pores. A detailed picture of the hydrogen desorption is investigated using a simultaneous thermogravimetric modulated-beam mass spectrometry instrument. The hydrogen desorption behavior of NaAlH4 nano-clusters is found to be very different from bulk NaAlH4. The bulk NaAlH4 desorbs about 70 wt% hydrogen ~250°C. In contrast, confinement of NaAlH4 within the MOF pores dramatically increases the rate of H2 desorption at lower temperatures. About ~80% of the total H2 desorbed from MOF-confined NaAlH4 is observed between 70 to 155°C. In addition to HKUST-1, we find that other MOFs (e.g. MIL-68 and MOF-5) can be infiltrated with hydrides (LiAlH4, LiBH4) or hydride precursors (Mg(C4H9)2 and LiC2H5) without degradation. By varying pore dimensions, metal centers, and the linkers of MOFs, it will be possible to determine whether the destabilization of metal hydrides is dictated only by the size of the metal hydride clusters, their local environment in a confined space, or by catalytic effects of the framework.
5:30 PM - W2.9
Unexpected Quantum Effects observed by NMR for Adsorbed Hydrogen in Interpenetrating MOFs at High Temperature.
Alfred Kleinhammes 1 , Robert Anderson 1 , Liqing Ma 2 , Wenbin Lin 2 , Yue Wu 1
1 Department of Physics and Astronomy and Curriculum in Applied and Materials Sciences, University of North Carolina, Chapel Hill, North Carolina, United States, 2 Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractAdsorbed hydrogen molecules behave as free rotors at all but the lowest temperatures. However, in hydrogen adsorbed in interpenetrating metal organic frameworks (MOFs) the NMR spectra deviate from the normally observed Gaussian line shape and show a distinct Pake pattern at temperatures below 180 K. The Pake powder pattern is due to the (only partially averaged) intra-molecular dipolar interaction. The H2 molecules experience a strong crystal field that lifts the degeneracy of the rotational energy levels giving rise to a preferred axis of rotation. Spectra are recorded as a function of temperature, between 100 K and 180 K, and of pressure of up to 100 atm.. Spectral width decreases with increasing temperature and pressure, presumably due to various averaging processes. Spin lattice relaxation measurements are performed to shed light on the molecular dynamics. Besides being of interest from a fundamental aspect, the measurements point to a novel method of trapping hydrogen between the pliable walls of interpenetrating MOFs after guest (solvent) molecules have been removed and replaced with hydrogen. The binding energy of trapped H2 molecules exceeds conventional van der Waals interaction but the hydrogen remains fairly mobile at all temperatures studied. Hydrogen in MOFs with subtly different ligands extending between interpenetrating frames experience crystal fields of different strength.
W3: Poster Session: Metal Hydrides, Simulation, Absorbers and Other Hydrides
Session Chairs
Etsuo Akiba
Shengbai Zhang
Tuesday AM, December 01, 2009
Exhibit Hall D (Hynes)
9:00 PM - W3.1
First-principles Calculations of Phonon and Thermodynamic Properties of Hydrogen Storage α-LaNi5H.
Masahiko Katagiri 1 , Shigeki Saito 1 , Hiroshi Ogawa 2
1 Computational Materials Science Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2 Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Show AbstractMany researchers have studied the LaNi5 hydrogen storage alloys as feasible candidates with high hydrogen-storage capacities for future clean-energy systems. These alloys have three phases: α-phase LaNi5H, β-phase LaNi5H3~4, and γ-phase LaNi5H6~7. The investigation of the LaNi5 hydrogen storage mechanism have led to the development of hydrogen gas-battery applications, while theoretical computations from first-principles and molecular dynamics calculations have recently played an important role in determining the electronic and structural properties at the nanometer scale.The theoretical calculations of the electronic, structural, and thermodynamic properties for bulk LaNi5 and LaNi5-H1~7 hydrides have been performed by many research groups using density functional theory (DFT) calculations. Recently, Herbst et al. and Yu et al. calculated the thermodynamic properties of bulk LaNi5 using DFT calculations [1, 2]. The phonon dispersion curve, the phonon density of states, and the thermodynamic properties were then estimated. However, the phonon contribution from the thermodynamics properties for the hydrogenation process of LaNi5 has not been explained by the first-principles method. Phonon calculations based on first-principles energy potentials using a supercell force constants matrix are an accurate and efficient method to investigate the structural and thermodynamic properties of LaNi5H hydride.LaNi5 hydride has a lot of interstitial hydrogen and α-β-γ phase La-Ni lattices. In this letter, we provide calculational results of the phonon and thermodynamic properties of α-phase LaNi5H with 4h, 6m, 12n, and 12o hydrogen in the Wickoff positions, determined by X-ray diffraction measurements, because α-phase LaNi5H is a basic condition. The initial state of the hydrogen storage process can first be determined by theoretical modeling. Here, the frozen-phonon approach with a DFT potential surface was applied to estimate the phonon density of states in the Brillouin zone of LaNi5H. Then, the phonon contributions of the internal and free energies were calculated based on the density of states. In this study, frequency shifts from the phonon contribution of the internal energies of 12n < 6m < 12o < 4h appeared in specific modes originated by interstitial hydrogen and in the upper-edge modes with nickel lattice motion. Moreover, the stability of 12n interstitial hydrogen in α-LaNi5 due to the wide XZ storage space was explained by its phonon amplitudes and the charge density around nickel-bonded hydrogen.[1] J. F. Herbst, and L. G. Hector Jr., J. Alloys Compounds, vol. 446, pp. 188 (2007).[2] Y. Yu, H. Han, Y. Zhao, W. Xue, and T. Gao, Sol. Stat. Commun., vol. 148, pp. 1 (2008).
9:00 PM - W3.10
Calculated Properties of Hydrogenated Single Layers of BN, BC2N and Graphene: Graphane and its BN-containing Analogues.
James Morris 1 2 , Frank Averill 1 2 , Lujian Peng 2 , Valentino Cooper 1
1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of Tennessee, Knoxville, Tennessee, United States
Show AbstractCarbon is an attractive material for hydrogen adsorption, due to its light weight, variety of structures, and ability to both physisorb and chemisorb hydrogen. Recently, fully hydrogenated graphene layers (“graphane”) have been predicted to exist [J.O. Sofo et al., Phys. Rev. B 75, 153401 (2007)], and experimentally observed [D.C. Elias et al., Science 323, 610 (2009)]. In this work, we examine analogues of graphane, in particular BN and BC2N. Unlike graphene, these materials have a band gap without hydrogenation. The hydrogenation of BN is metastable, but the fully hydrogenated compound BNH2 is energetically unfavorable to decomposition into BN+H2, in sharp contrast with graphane. BC2NH4 is energetically very close to the graphene form of BC2NH4 + 2 H2 molecules. This suggests that the strength of the hydrogen binding may be controlled by controlling the carbon content in the graphene layer. We further examine the relative binding strengths of individual hydrogen atoms on these materials, to identify the desorption process. Molecular dynamic simulations of desorption of hydrogen from graphane will be presented, examining the cooperativity of the desorption process. This research has been sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC05-00OR-22725 with UT-Battelle.
9:00 PM - W3.12
Large H Absorption in Nd2Ni2In; Magnetism in a New Structure Type.
Ladislav Havela 1 , Silvie Maskova 1 , Stanislav Danis 1 , Olha Stelmahovych 1 2 , Khrystyna Miliyanchuk 1 2
1 Department of Condensed Matter Physics, Charles University, Prague 2 Czechia, 2 Faculty of Chemistry, Ivan Franko National University, Lviv Ukraine
Show AbstractSome f-Electron compounds reversibly absorb/desorb a large amount of H. U-based ternaries of the U2T2X type were found to absorb up to 2 H atoms/f.u., preserving the tetragonal symmetry of the Mo2FeB2 structure type [1]. Such H doping can be used for tuning of the 5f magnetism, which is critically dependent on the U-U spacing. Much higher H absorption was found for the rare-earth analogues, absorbing about 4 H atoms/f.u. at low H pressures [2]. The crystal structure reacts, besides large expansion (> 15%), by a sizeable orthorhombic distortion. The present study of Nd2Ni2In demonstrates that even higher hydride, with approx. 6 H at./f.u. and the volume expansion 21.6%, can be synthesized at H pressures of several bar H. The desorption study reveals three distinct stages, corresponding to 4, 2, and 0 H at. f.u., appearing at approx. 240 oC, 520 oC, and 720 oC, respectively. No trace of a binary Nd hydride has been detected. Nd2Ni2In undergoes magnetic ordering at 8 K [2]. The triangular rare-earth lattice can give rise to magnetic frustration in case of antiferromagnetic interactions. This is probably the reason why weak magnetic fields (< 0.3 T) can achieve ferromagnetic alingnment of Nd moments. In Nd2Ni2InH6, the Néel temperature decreases to 3.5 K. The frustration is apparently removed by the orthorhombic distortion and magnetic field does not induce fast the ferromagnetic alignment. The paramagnetic Curie temperature becomes more negative, decreasing from -4.5 K in Nd2Ni2In to -8 K. Low temperature heat-capacity data are in progress so as to test a possible loss of metallicity. [1] L. Havela et al., J. Alloys Comp. 466-447, 606 (2007).[2] M. Dzevenko et al., J. Alloys Comp. 477, 182 (2009).
9:00 PM - W3.13
Quartz Crystal Microbalance for Investigating Nanoscale Hydrogen Storage Materials.
Nicola Naujoks 1 , Lorand Romanszki 1 , Christoph Langhammer 1 , Michael Zaech 1 , Igor Zoric 1 , Bengt Kasemo 1
1 Applied Physics, Chalmers Institute of Technology, Göteborg Sweden
Show AbstractReducing the geometrical dimensions of hydrogen storing materials to the nanoscale is expected (and shown) to result in improved thermodynamic and kinetic properties [1]. Studying this effect, however, demands highly sensitive measurement techniques. One approach to investigate hydrogen uptake and desorption characteristics of thin films and nanoscale particles is the use of a Quartz Crystal Microbalance (QCM). The QCM is an extremely sensitive mass sensor, relying on measuring shifts in resonance frequency of a piezoelectric oscillator crystal induced by mass-changes on the sensor. With a sensitivity in the range of ng/cm2 the minute changes occurring during hydride formation in thin films can be measured accurately, provided that temperature and pressure are controlled precisely. This has been shown for both metal films [2] and nanoparticles [3]. QCM-based measurements allow for the determination of both the kinetics and the thermodynamics of the investigated material.To be studied in a QCM setup, the sample structures have to be fabricated directly onto the surface of quartz sensor. The feasibility of the QCM technique to investigate hydrogenation of thin metal films is demonstrated at the example of Pd covered Mg thin films (in the range of 30-100nm), where we obtained thermodynamic data in term of pressure-composition-isothems. Applying this technique to the investigation of hydrogen storage in nanoparticles (NP) requires a method of attaching a sufficiently large amount of NPs onto the crystal (a 2d disperse layer on the sensor surface suffers from a limited sensitivity of the QCM). We will present first results on hydrogenation of Pd NPs embedded in SiO2 based porous supports (grown by wet-chemistry approaches) that are coated onto the crystal, thereby allowing a larger number of particles to be accessed by the H2 gas. Experiments are performed in a QCM gas cell setup that enables measurements over a wide range of temperatures (up to 150C) and pressures, allowing wide flexibility in choice of material to be investigated.Our group has recently extended this scheme towards detecting hydrogen uptake in metal nanostructures in connection with complementary optical techniques using localized surface plasmon resonances (LSPR) [3]. This allows for studying the influence of geometrical parameters, such as film thickness, and size and shape of the nanostructures, on the kinetics and thermodynamics of the studied material.We will show how QCM and complementary optical techniques can help in determining the influence of geometrical parameters on hydrogen uptake and desorption, on the example of Mg-based storage materials.References[1]V. Berube, G. Radtke, M. Dresselhaus, and G. Chen, Int. J. Energy Res. 31 (2007) 637.[2] A. Krozer, and B. Kasemo; J. Less Comm. Met. 160 (1990). 323.[3]C. Langhammer, I. Zoric, and B. Kasemo, Nano Lett. 7 (2007) 3122.
9:00 PM - W3.14
Hydrothermal Synthesis and Applications of Low-dimensional Strontium Compounds.
Tolulope Salami 1 , Stephanie Patterson 1 , Victoria Jones 1
1 Chemistry, Valdosta State University, Valdosta, Georgia, United States
Show AbstractPorous materials are extremely important materials with a wide array of applications in catalysis, ion exchange, energy storage and drug delivery, just to mention a few. A variety of porous materials have been synthesized using templating and structural directing agents, such as biological molecules, neutral molecules and cationic molecules. Our research involves the use of a relatively new and unexplored templating technique, using small organic and inorganic anions. (Such as NO3-, SO4-, disulfonic acids, phosphonic acids etc.). We will report the synthetic conditions, physical properties and potential applications of some newly synthesized strontium compounds. The structures are primarily layered compounds. The intercalation properties of these materials are still being investigated.
9:00 PM - W3.15
Hydrogen Storage Properties and Local Structures of (La0.6RE0.4)5Ni19 Compounds with Block-stacking Superstructures.
Ryo Ishikawa 1 , Eiji Abe 1
1 Department of Materials Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
Show AbstractRElNim (RE: rear earth, 3≤l/m≤4) compounds with block-stacking superstructures have attracted a lot of attentions as new hydrogen storage materials, because they are able to store a relatively large amount of hydrogen (~2.0wt.%) under normal temperatures and pressures. These compounds are constructed by the stacking of the “structural blocks”, which are represented by Haucke-unit (RENi5) and Laves-unit (RE2Ni4) with their stacking ratio of n:1 (n=1, 2, 3, ...). Partially substituting the La site with Mg in the LalNim provided a successful example of alloy designs to improve the hydrogen storage properties, suggesting a further possibility of exploring a new dopant X element for the (La, X)lNim compounds. While concerning the substitution, it also becomes important to understand a role of dopant atoms with respect to their favorable substitution sites and how they alter block-unit structures, since these local structural issues should be closely related to the hydrogen-storage properties. In the present work, we synthesize various (La,RE)5Ni19 compounds with RE=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er and evaluate their hydrogen-storage properties based on PCT measurements (at 303K, PH2<5MPa). We further investigate local structural changes of the compounds before/after hydrogenation using atomic-resolution scanning transmission electron microscopy (STEM), which is a powerful method for characterizing local chemistry through the atomic-number dependent Z-contrast and spectroscopy (EDS/EELS) combined with a focused electron beam less than 1 Å. (La0.6RE0.4)5Ni19 compounds were prepared by arc melting of pure metals. The annealed ingots (1023K or 1223K for 10 days) were crushed and again annealed at 473K for 1 hour in vacuum, and then they were submitted to PCT measurements under PH2=5MPa at 303K. For atomic-resolution STEM observations, we used a spherical aberration (Cs)-corrected 200kV STEM (JEM-2100F and ARM-200F) equipped with EDS and EELS.As preliminary results, we identified two representative hydrogenation behaviors for the compounds with RE=Y and Er. For the (La,Y)5Ni19 alloy, its PCT curve shows two plateau pressures, PH2=3.2×10-3MPa (~0.3H/M) and 3.2MPa(~1.1H/M), while there is only one plateau pressure, PH2=0.4MPa (~1.1H/M), for the (La,Er)5Ni19 alloy. STEM investigations of these alloys revealed significant structural differences that can be represented by a local chemical order particularly at the Laves-unit. That is, Y-containing Laves-unit forms a robust hydride that will never release hydrogen, while Er-containing Laves-unit is almost able to capture/release hydrogen at room temperatures. These results indicate that local chemistry at the Laves-unit is a key factor to control the hydrogen-storage property of the block-stacking compounds. We will describe further details of microstructural changes induced by hydrogenation and discuss the structure-property relationships of the hydrogen-storage block-stacking compounds.
9:00 PM - W3.16
Identification of Planar Defects in a Hydrogen-discharged LaNi5 by Advanced Scanning Transmission Electron Microscopy.
Junya Yamamoto 1 , Ryo Ishikawa 1 , Eiji Abe 1
1 Dept. of Materials, University of Tokyo, Tokyo Japan
Show AbstractAfter a hydrogen charge-discharge process of the LaNi5 compound, a considerable amount of structural defects are known to be introduced due to formation-annihilation of the LaNi5Hx hydrides during the process. From some of the previous electron microscopy studies, characteristic defects are shown to be a-type sessile dislocations and the planar defects almost lying on the (11-20) planes of the hexagonal lattice. The latter, planar defects do reveal significant diffraction contrast by bright-field TEM imaging, but a nature of these defects has been remained unsolved. In the present work, we use advanced scanning transmission electron microscopy (STEM) to identify these unique planar defects. We have successfully figured out that these defects are vacancy-concentrated region composed of the 2x(11-20) planes (2 atomic-layer thickness), which are carefully derived from angle-resolved annular dark-field imaging and electron energy loss spectroscopy (EELS) at atomic-scale. Origin of these vacancy-concentrated layers can be reasonably attributed to “crystalline mosaicness” that is caused by a lattice expansion-shrink cycle during the formation-annihilation of the hydrides. Details will be described at the meeting.
9:00 PM - W3.17
Hydrogen Storage Properties and Crystal Structure of Mg-V-Na Hydride Prepared by Gigapascal Hydrogen Pressure Method.
Nobuhiko Takeichi 1 , Kenji Shida 1 , Junmin Yan 1 , Hideaki Tanaka 1 , Nobuhiro Kuriyama 1 , Tetsuo Sakai 1
1 , AIST, Ikeda, OSAKA, Japan
Show AbstractMagnesium is a promising material for hydrogen storage media because of the high hydrogen capacity 7.6 mass%. However, the high thermodynamic stability of MgH2 prevents dehydrogenation at ambient temperature. Therefore, various Mg-based alloys and compounds have ever been investigated to improve the reaction kinetics through metallurgical methods such as elemental substitution, mechanical alloying and laminate composites.Ultrahigh-pressure technique (UHP) using multi-anvils would be one of the useful methods to prepare novel hydrides. Our group reported that Mg-TM (TM: transition metal) hydrides with face-centered cubic (fcc) structure, prepared with a cubic anvil press, show reversibly and speedy absorb and desorb hydrogen at 523 K. In this study, we found new Mg-V-Na hydrides by the technique. In addition, we investigated hydrogen storage properties and crystal structure of the hydrides.Initial mixture pellet of 6MgH2+VH2+nNaH (n=0-1.0) 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 K for 1 hour under 8 GPa. The constituent phases in the samples were examined by X-ray diffraction analysis. Moreover the crystal structures were analyzed based on XRD data obtained at the beam-line BL19B2 in SPring-8. Hydrogen storage properties were examined by a differential scanning calorimeter and pressure-composition isotherms measurements. In the Mg-V-Na system, the new fcc-type hydride was synthesized with small amount of impurity, MgO, MgH2 and VH2. The yield of the fcc-type hydride was significantly improved with increase of NaH content, and the highest yield 82.69 % was achieved when the additive amount n=1.0.The fcc-type hydride showed reversible hydrogen release and restoration at 620 and 600 K, respectively. It showed lower hydrogen releasing temperature than MgH2. The reversible hydrogen storage capacities were in the range of 2 - 3.7 mass% on the pressure-composition isotherms at 573 K.Rietveld refinements based on the synchrotron XRD data of samples indicated that the structure of fcc-type hydride, Mg6VNanHx, can be described by the atomic positions: Mg at 24d (0, 0.25, 0.25), V at 4a (0,0,0), and Na at 4b (0.5, 0.5, 0.5) using space group Fm-3m. These metal atoms form Ca7Ge-type structure. While H atoms occupy the two tetrahedral sites of 32f (0.106, 0,106, 0.106) and 32f (0.363, 0.363, 0.363). The lattice constant of Mg6VHx and Mg6VNaHx were 0.9437 and 0.9482 nm, respectively. This crystallographic information reveals that the nearest distance between Mg and H atoms was 0.199 nm, which is longer than that between Mg and H atoms in MgH2, 0.194 nm. It is considered that this structure improves remarkably the reaction kinetics and hydrogen storage properties.This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO).
9:00 PM - W3.18
Hydrogen Absorption/Desorption Characteristics in Mg-Al Powders.
Mahesh Tanniru 1 , Fereshteh Ebrahimi 1 , Darlene Slattery 2
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Florida Solar Energy Center, Cocoa, Florida, United States
Show AbstractAlloying with different elements is one solution to reduce the Mg-H bond strength and thereby lowering the desorption temperature of MgH2. Theoretical studies have predicted that the addition of Al to MgH2 reduces the formation/dissociation enthalpy of the hydride. We have fabricated Mg-Al powders with nominal compositions of 8at% Al by the electrodeposition technique and studied the phase evolution during the development of pressure-composition-temperature curves. In addition, the pressure-temperature isotherms were used to construct Van’t Hoff plots, from which the enthalpies of magnesium hydride formation and dissociation were calculated and compared to those for pure magnesium powder. Structural and compositional analysis revealed that initially, during hydrogenation, the magnesium hydride rejects the Al, thus causing the formation of a high volume fraction of the Mg17Al12 intermetallic compound. As pressure is increased beyond the equilibrium pressure for magnesium hydride formation, this intermetallic phase hydrogenates and results in the development of the fcc-Al and the Al3Mg2 intermetallic phases. The latter intermetallic eventually hydrogenates such that at 10MPa pressure only the magnesium hydride and the fcc-Al phases were found in the microstructure. During dehydrogenation of the magnesium hydride, the hcp-Mg phase nucleates and consumes the fcc-Al phase such that at atmospheric pressure the microstructure consists of the hcp-Mg and the Mg17Al12 phases. Analysis of the pressure-composition isotherms indicated that the enthalpy and entropy of hydride formation/dissociation are not affected significantly by the addition of Al. This finding is attributed to the absence of Al in the MgH2 lattice at high temperatures and under equilibrium test conditions.
9:00 PM - W3.19
In-situ TEM Observation for Reaction Mechanism in MgH2 Hydrogen Storage Material.
Akifumi Ono 1 , Shigehito Isobe 1 , YongMing Wang 1 , Naoyuki Hashimoto 1 , Somei Ohnuki 1
1 , Hokkaido University, Sapporo Japan
Show AbstractTo develop hydrogen storage materials with high volumetric/gravimetric density of hydrogen is one of key issues for realizing onboard fuel cell vehicles in hydrogen energy economy. MgH2 has an advantage: its high hydrogen capacity of 7.6 wt.%, and does two disadvantages: slow kinetics and stable thermodynamics in hydrogen absorption/desorption reaction. Recent studies have suggested that Nb2O5 can drastically make the kinetics fast as catalysis. In our work, we performed in-situ TEM (Transmission Electron Microscopy) with an environmental cell, which is especially designed to control the “in-situ” condition, in order to microscopically examine the reaction and catalysis mechanism. With the environmental cell, we can observe the reaction in 0 ~ 0.2MPa hydrogen atmosphere and room temperature ~ 150°C. In addition, HVEM (High Voltage Electron Microscope) of 1300keV was performed to obtain high resolution images. Sample was prepared by ball-milling MgH2 powder with 1mol% Nb2O5 powder at room temperature for 20 hours under hydrogen atmosphere of 1.0MPa. Lattice images of MgH2 were confirmed at room temperature, and then lattice images of Mg were observed with increase of temperature up to 200 °C. The hydrogen desorption reaction was surely observed by in-situ HVEM.
9:00 PM - W3.2
Atomistic Simulation on Hydrogen Storage in Metallic Nanoparticles.
Hiroshi Ogawa 1 , Megumi Kayanuma 1 , Masahiko Katagiri 2
1 RICS, AIST, Tsukuba, Ibaraki, Japan, 2 , NIMS, Tsukuba, Ibaraki, Japan
Show AbstractNanoclusters have been considered as potential candidates for hydrogen storage materials because their large fraction of surface area is advantageous for hydrogen absorption and desorption. Behaviors of hydrogen in nanoclusters or nanocrystals have been studied experimentally in the last decade. [1] In this study, dynamics of hydrogen atoms in metallic bcc and fcc nanoparticles were investigated by classical molecular dynamics (MD) simulation. A structure model composed of 10 nm, spherical nanoparticle and surrounding hydrogen gas was adopted to simulate the hydrogen storage in a nanoparticle. Hydrogen atoms were initially arranged as an f.c.c. crystal with octahedral shape, and formed monoatomic gas phase after starting MD. Simulation was carried out at 300K by changing the parameters of M-H potential function. Distribution of absorbed hydrogen atoms in nanoparticle was found to show different profiles depending on the assumed potential parameters of M-H pairs. In cases of weak M-H interaction, hydrogen atoms distribute homogeneously inside a nanoparticle. If the radius parameter of M–H pairs is too large, hydrogen atoms cannot be absorbed in a nanoparticle. As the third case, formation of thin, hydrogen-rich layer at the nanoparticle surface was observed. [2] Surface layers are caused by small lattice deformation due to hydrogenation and prevent migration of hydrogen atoms into a nanoparticle. Such a surface layer was observed in the experiment. [3] In these cases, self-diffusion coefficient of hydrogen atoms in the lattice was found to decrease steeply near a specific H/M ratio. Lattice deformation due to hydrogenation also induced grain boundary formation in some cases. [4] In a typical case, the nanoparticle was divided into five subgrains. Most of the grain boundaries were twin boundaries and located parallel to each other. Distances between the boundaries increases with time due to the force imbalances between surface and interface tensions. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".References: [1] A. Pundt et al., J. Alloy Comp., 293-5 (1999) 480. [2] H. Ogawa et al., Mater. Trans., 49 (2008) 1983. [3] Y. Ishido et al., Denki Kagaku, 46 (1978) 620. [4] H. Ogawa et al., Int. J. Nanosci, 8 (2009) 39.
9:00 PM - W3.20
Ordered Block Copolymer Templates for the Preparation of Nanoscale Metal Hydrides.
Xiangfeng Liu 1 2 , Christopher Jost 1 2 , David Peaslee 1 2 , Eric Majzoub 1 2
1 Department of Physics and Astronomy , University of Missouri-St. Louis, St. Louis, Missouri, United States, 2 The Center for Nanoscience, University of Missouri-St. Louis, St. Louis, Missouri, United States
Show AbstractPoor thermodynamics and kinetics of most light metal hydrides limit their practical application as a hydrogen storage medium. Recent modeling and preliminary experiments predict the particle size of metal hydrides plays an important role in hydrogenation/dehydrogenation and that tuning of the thermodynamics and kinetics can be achieved by controlling the particle size and distribution of metal hydrides. Block copolymer templates are widely used for the synthesis of nanoparticles due to their flexibility in size control and chemical composition. In this study, polystyrene-b-polymethylmethacrylate (PS-b-PMMA) and polystyrene-b-polybutadiene diblock copolymers (PS-b-PB), which self-assembles into a cylindrical phase in a polystyrene matrix, were used to prepare highly ordered nanoporous templates with the pore size of about 20 nm by selective etching PMMA or PB blocks. The resulting pores were characterized by means of atomic force microscopy (AFM), high-resolution scanning electron microscope (SEM), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). These ordered block copolymer templates were infiltrated with nanoscale metal hydrides (NaAlH4, and MgH2) and the dehydrogenation thermodynamics and kinetics were investigated using a temperature-controlled quartz crystal microbalance in-situ vacuum chamber.
9:00 PM - W3.21
Hydrogen Absorption and Thermal Aging of Nanoporous Palladium.
Markus Ong 1 , David Robinson 1 , Benjamin Jacobs 1 , Mary Langham 1 , Stephen Fares 1
1 Energy Nanomaterials, Sandia National Laboratories, Livermore, California, United States
Show AbstractNanoporous materials can offer improved charging and discharging kinetics for hydrogen storage applications due to their high surface area. Additionally, complications from helium retention may be reduced when tritium is stored. We have synthesized nanoporous palladium and palladium alloy powders in a scalable fashion by chemical reduction of palladium salts in a concentrated aqueous surfactant. Particle diameters are approximately 50 nm and each particle is perforated by 3 nm pores, as determined by electron tomography. This study investigates the hydrogen absorption properties of these materials at various temperatures and the effects of thermal and hydrogen environments on their nanostructures. Pore collapse and particle sintering can be induced, especially at high temperatures and extended times. Quantitative analysis by porosimetry of the palladium particles indicates minimal change in pore size and specific area when heated in vacuum to 150 °C, but progressive degradation can accumulate at higher temperatures. Complementary qualitative analysis by transmission electron microscopy show that pore collapse in palladium can occur dramatically on very short time scales around 400 °C during in situ heating. Particles produced with palladium alloyed with higher melting point metals results in greater stability and higher pore density.
9:00 PM - W3.22
Formation of a Microstructure in the Multicomponent Laves Phase Alloys.
Leonid Bendersky 1 , Ke Wang 1 , William Boettinger 1 , Dale Newbury 2 , Ursula Kattner 1 , Chun Chiu 1 , Kwo Young 3 , Benjamin Chao 3
1 Materials Science & Engineering Laboratory, NIST, Gaithersburg, Maryland, United States, 2 Chemical Science & Technology Laboratory, NIST, Gaithersburg, Maryland, United States, 3 Ovonic Hydrogen Systems, Energy Conversion Devices Inc., Rochester Hills, Michigan, United States
Show AbstractMulticomponent AB2-type alloys with A=(Ti,Zr) and B=(Ni,Mn,V,Cr,Co) based on Laves phases are considered for their applications in Ni-metal hydride batteries and for vehicular/stationary hydrogen storage. For optimization of hydrogen capacity and kinetics of charge/discharge different research groups studied modifications of the Laves phases, i.e., varying ratio of Ti and Zr on A-site, variation of components on B-site, or stabilization of different Laves crystal structures. For a number of alloys improvements in electrochemical properties was attributed to the presence of a secondary catalytic phase of a Zr-Ni system in addition to the major AB2 Laves phase; these catalytic phases were identified as mainly Zr7Ni10 and Zr9Ni11. The close proximity among various phases enhances the synergetic effect of promoting necessary electrochemical properties in the application as a metal hydride electrode in nickel metal-hydride battery.In this work we discuss formation of phases and microstructural details of the as-cast Zr21Ti12.5V10Cr5.5Mn5.1Co5.0Ni40.2 alloy. The work analyses the solidification path, which leads to the microstructure of C14 dendrites coated with epitaxial C15, by utilizing the constituent ternary diagrams of the Ni-Cr-Ti-Zr quaternary. We also show that the secondary interdendritic phase results from the decomposition of a high-temperature B2 phase to Zr7Ni10 and Zr9Ni11-type phases, which leads to a complex hierarchical microstructure.
9:00 PM - W3.23
Novel Nanostructuring Approaches to Study Catalysis in Hydrides.
Shathabish Narase Gowda 1 , Tabbetha Dobbins 1 2
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 Physics, Grambling State University, Grambling, Louisiana, United States
Show AbstractThe main restraint to the development of an ideal hydrogen storage system is the lack of understanding of catalysis in hydrides. In the present work, the hydrides, LiBH4 and NaAlH4, are studied by nano-confinement into porous Al2O3 templates and MoFs. The key technical objectives addressed here are: (1) To explore polyelectrolyte self assembly as a new approach to catalyst design (2) Understanding the effective catalyst geometries (traditional bulk introduction by high energy milling Vs surface overlay after embedding in polyelectrolyte self assembly), (3) To enhance catalytic activity by modifying the pore surface before hydride insertion, (4) To quantitatively study the effect of catalyst and catalyst geometries on long range diffusion within the hydrides both in time and length scales. Overall, this work will clearly elucidate whether catalysis is a bulk mediated or a surface mediated phenomena and the effect of various transition metal catalysts on mass transport and desorption kinetics of hydride based storage systems, in general. These results will be a circumstantial resource for choosing the right catalyst for the new wave of novel hydrides that are being probed.
9:00 PM - W3.24
Raman and Visible Absorption Study of TbH3 Under High Pressure.
Tetsuji Kume 1 , Naoki Shimura 1 , Hiroyasu Shimizu 1 , Shigeo Sasaki 1 , Akihiko Machida 2 , Tetsu Watanuki 2 , Katsutoshi Aoki 2 , Kenichi Takemura 3
1 , Gifu University, Gifu Japan, 2 , Japan Atomic Energy Agency, Hyogo Japan, 3 , National Institute for Materials Sci., Tsukuba Japan
Show AbstractFor hexagonal rare-earth trihydrides RH3, the pressure induced transition to fcc structure has been systematically investigated[1]. The transition pressure is known to depend on the atomic size of the metal[1]; the smaller molar volume of RH3 gives rise to the higher transition pressure. Recent x-ray diffraction experiments[2,3] demonstrated the existence of the intermediate phase of YH3 (ScH3) around 10-20 (25-40) GPa between the hexagonal and high-pressure fcc phases. Raman spectroscopic study on YH3[3] has suggested that the hydrogen atoms are highly disordered in the intermediate phase. However, there is no systematic study for clarifying the pressure region of the intermediate phase for various RH3. Insulator-metal transition as well as the structural transition have been investigated for YH3[4], and were suggested to occur at the almost the same pressure as the phase transition to the fcc phase [4]. In this paper, we present high pressure Raman and visible absorption study on TbH3, which were performed for better understanding of the intermediate phase and the insulator-metal transition of RH3.
The sample of TbH3 was prepared in a diamond anvil cell (DAC) by hydrogenating a Tb foil in the small sample chamber of DAC filled with fluid hydrogen. The fluid hydrogen was loaded using a gas loading apparatus. Raman spectra were measured in a backscattered geometry using a spectrometer (JASCO NR1800). Radiation of 532 nm from a solid-state laser was incident with a power of 5 mW. The optical absorption was measured using an absorption measurement system[4].
Raman spectra have been measured at high pressures up to around 20 GPa. At 8 GPa, obvious spectral changes were found on the Tb and H vibrational signals. Taking into account the previous Raman results on YH3[4], the present spectral changes were found to be associated with the transition to the intermediate phase. The visible absorption spectra of TbH3 were obtained at high pressures up to 10 GPa. An analysis for the band edge allowed us to estimate the optical gap Egopt to be approximately 1.3 eV at 0.4 GPa. The Egopt shifted to lower energies with pressure. An extrapolation of the pressure dependence of the Egopt suggested the metallization pressure to be about 20 GPa. The systematic discussion by referring other RH3 will be made, focussing the structural and insulator-metal phase transition under the high pressure.
[1] M. Tkacz, T. Palasyuk, J. Alloys Compd. 446-447, 593 (2007).
[2] A. Machida et al., Phys. Rev. B 76, 052101 (2007).
[3] A. Ohmura et al., J. Alloys Compd., 446-447, 598 (2007).
[4] T. Kume et al., Phys. Rev. B 76, 024107 (2007).
9:00 PM - W3.25
Physico-Chemical Study of a NH3-BH3 Based Reactive Composition for Hydrogen Generation.
Jerome Helary 1 , Nicolas Salandre 1 , Denis Autissier 1 , Jerome Saillard 1 , Didier Poullain 1 , Arnaud Beaucamp 1
1 Explosives dpt, CEA-DAM Le Ripault, Monts France
Show AbstractHydride materials are an attractive option to achieve the challenge of hydrogen storage, particularly in the case of one-shot or security devices. Among all the hydrides, ammonia borane (NH3BH3) has a very high theoretical hydrogen content (19.6%), which can be easily released through a fair heating. The decomposition reaction could become self-heated by adding a thermal auxiliary, such as ammonium nitrate, closely mixed with the ammonia borane.The first part of this study consists in safety tests in order to reveal the higher oxidizing rate allowing a safe use of the composition. Differential scanning calorimetry was employed to explore the thermal stability. Impact sensitivity and thermo-mechanical limit tests were carried out. For the lower oxidizer concentrations, the reaction is not kept going, but for higher rates (i.e. 10% as classically described in the literature) it could become highly sensitive, not to say explosive. Such a behavior is unacceptable for industrial or commercial applications. Nevertheless a compromise exists between reactivity and security.The thermal behavior was studied by thermogravimetric analysis and reveals decomposition in two steps. The first one is close to 100°C and the second one around 130°C. The ammonia borane reaches its melting point before the beginning of the decomposition; in this way it gives hydrogen and amino-borane. Afterwards the decomposition of amino-borane into imino-borane produces the second hydrogen release.TGA coupled with a mass spectrometer was used to determine the nature of the gases produced during the degradation of the NH3BH3/NH4NO3 mixed compositions. It was observed that hydrogen was the main gas that evolved during the heating. In a second time we have tried to identify the nature of impurities. Depending of their nature, they could be harmful for a long-term working fuel cell battery. All the impurities have been identified. Gas chromatography (microGC) could be used successfully to improve the characterization of decomposition products. In this case the gas have been generated in a closed combustion bomb and collected in a steel cylinder for a later analysis.Different ammonia-borane sources, providing various purities and costs, were tested and their influence on gas quality evaluated.Some experiments have been carried out to establish the role of the ammonium nitrate through the analysis of the decomposition mechanisms. The energy necessary to the self combustion of the mixture probably results from the reaction between the oxidizer and a small part of produced hydrogen.We will present an early demonstration of the encouraging possibilities of this system trough a basic laboratory model, including an electrically initiated gas generator and a fuel cell battery.
9:00 PM - W3.26
Calcium Amidoborane Ammine Complex – A New Hydrogen Storage Material.
Yong Shen Chua 1 , Guotao Wu 3 , Zhitao Xiong 3 , Teng He 3 , Ping Chen 1 2 3
1 Department of Chemistry, National University of Singapore, Singapore Singapore, 3 , Dalian Institute of Chemical Physics, Dalian China, 2 Department of Physics, National University of Singapore, Singapore Singapore
Show AbstractCompounds or complexes with high hydrogen content are potential hydrogen storage materials. Ammonia borane (AB) has been extensively investigated recently, owing to its high hydrogen capacity (19.6 wt%) and moderate dehydrogenation temperature, which promise for the application as a hydrogen storage material. However, high kinetics barriers and borazine emission during dehydrogenation process make it challenging to realize its application for onboard purpose. In order to improve the dehydrogenation performance, considerable efforts have been given to the chemical modification of AB. Reacting alkali metal or alkali earth metal hydride with AB can produce lithium amidoborane (LiAB), sodium amidoborane (NaAB) and calcium amidoborane (CaAB), in which all these AB derivatives show superior dehydrogenation performance compare to pristine AB. In this presentation, we are going to report a new derivative of AB, namely calcium amidoborane ammine complex. The structure and thermal decomposition of this material have been investigated by X-Ray Diffraction (XRD), Nuclear Magnetic Resonance (NMR), Temperature-Programmed-Desorption (TPD), Differential Scanning Calorimetric (DSC) and volumetric release. Hydrogen desorption from this complex starts at a temperature around 70 oC and more than 8 wt% of H2 can be released.
9:00 PM - W3.29
Roles of Surface Oxide Layer in Hydrogen Desorption Processes by AlH3 and LiBH4.
Shunsuke Kato 1 , Andreas Borgschulte 1 , Michael Bielmann 1 , Kazutaka Ikeda 2 , Shin-ichi Orimo 2 , Andreas Zuettel 1
1 , EMPA, Dübendorf Switzerland, 2 , Tohoku University, Sendai Japan
Show AbstractLight-weight hydrides have great potential in efficient hydrogen storage, especially, for mobile applications [1]. For instance, AlH3 and LiBH4 exhibit high gravimetric densities of 10 mass% and 18 mass%, respectively. Under technical conditions, e.g. inside a hydrogen tank, surface contamination of the hydrogen storage material by impurity gasses has to be taken into account since the surface composition is determining the hydrogen sorption kinetics [2, 3]. This study focuses on two different families of hydrides, namely, covalent-like and complex hydrides, whose formation enthalpy are 10 kJ/mol for AlH3 [4] and 194 kJ/mol for LiBH4 [5]. The surface composition is investigated by X-ray Photoelectron Spectroscopy (XPS) and the hydrogen desorption is analyzed by means of Thermal Desorption Spectroscopy (TDS). The oxide layers formed on AlH3 kinetically hinder the decomposition. The desorption of the hydrogen and diborane by-product from LiBH4 is significantly affected by the surface oxidation. The role of the surface oxide layer is analyzed with respect to the hydrogen desorption mechanisms.[1] L. Schlapbach, A. Züttel, Nature 414 (2001) 353.[2] A. Borgschulte, M. Bielmann, A. Züttel, G. Barkhordarian, M. Dornheim, R. Bormann, Appl. Surf. Sci. 254 (2008) 2377.[3] H. Uchida, Int. J. Hydrogen Energy 24 (1999) 861.[4] J. Graetz, J.J. Reilly, J. Alloys Compd. 424 (2006) 262.[5] A. Züttel, A. Borgschulte, S. Orimo, Scripta Mater. 56 (2007) 823.
9:00 PM - W3.30
Hydriding and Dehydriding Kinetics of Sodium Alanate at Constant Pressure Thermodynamic Driving Forces.
Hongwei Yang 1 , Andrew Goudy 1
1 Department of Chemistry, Delaware State University, Dover, Delaware, United States
Show AbstractA study was done to compare the absorption and desorption kinetics of the first two decomposition steps in NaAlH4. In the first step NaAlH4 decomposes forming Na3AlH6. In the second step the Na3AlH6 decomposes forming NaH. This comparison was made using a novel procedure in which the ratio of the equilibrium plateau pressure (Pm) to the opposing pressure (Pop), or the N-value, was the same. This represents the first time that such a comparison has been made in a complex hydride displaying two decomposition steps. Since the Gibbs free energy change is proportional to Ln(Pm/Pop), it was concluded that these experiments were carried out under constant thermodynamic driving forces. It was found that under these conditions, the first decomposition step occurs about an order of magnitude faster than the second decomposition step. Experiments were also done to compare absorption and desorption rates for the second decomposition step. It was found that, using the same N-value, the absorption rates were about twenty times faster than desorption. Modeling studies showed that the absorption kinetics are most likely controlled by reaction at a moving boundary. Desorption reactions displayed a more complex behavior in which no single model described the entire process. Indications are that nucleation and growth controls the reaction rate in the early stages but that diffusion through a product layer may control the rate in latter stages.
9:00 PM - W3.31
The Study of the Destabilized Effect in NaAlH4 Using TiN.
Whitney Ukpai 1 , Tabbetha Dobbins 1 2
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 Dept. of Physics, Grambling State University, Grambling, Louisiana, United States
Show AbstractDestabilized metal hydride systems are gaining increased attention due to their ability to undergo a lowered hydrogen desorption reaction temperature (moving toward targeted temperatures set by the Dept. of Energy). LiBH4 has been destabilized using MgH2 (Vajo, Skeith, and Mertens) with a demonstrated lowering of the hydrogen desorption reaction by 90 C (compared to LiBH4 alone). This research reports on the potential for destabilization of NaAlH4 using TiN as a destabilizer phase. The samples prepared were NaAlH4 with varying concentrations of TiN (specifically, 25mol%, 50mol%, and 75mol% concentrations were used). The destabilizer was introduced to the hydride powder system using high energy ball milling (SPEX 8000M mill in WC mill media). After high energy milling, the hydrogen desorption reaction was lowered to 100 C to 112 C (compared to 186 C for pure NaAlH4), determined using mass spectrometry (RGA Analog Scan) with 25 mol% concentration of TiN.
9:00 PM - W3.32
Characterizing Catalysts in Li-N-H System by X-ray Absorption Spectroscopy.
Shigehito Isobe 1 , Satoshi Hino 2 , Takayuki Ichikawa 2 , Yoshitsugu Kojima 2 , Somei Ohnuki 1
1 Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan, 2 Institute for Advanced Materials Research, Hiroshima Univeristy, Higashi-Hiroshima, Hiroshima, Japan
Show AbstractLithium-Nitrogen-Hydrogen (Li-N-H) systems have been reported as one of the attractive hydrogen storage systems [1, 2]. So far it was clarified that some catalysts, especially titanium (Ti) based compounds, were significantly effective for improving the hydrogen storage kinetics in the Li-N-H system [3]. In our works, the chemical bonding states and local environmental structures of the titanium compounds in LiH and LiNH2 mixture were examined by X-ray absorption spectroscopy (XAS) measurement as the characterization of the catalysts. The results of X-ray absorption near-edge structure (XANES) indicated that the Ti atoms in the Ti compounds, which had the catalytic effect on the kinetics of the hydrogen desorption properties, had a common electronic (chemical bonding) state [4]. Additionally, this common electronic state of the Ti catalysts agrees with that of TiCl3(NH3)5. This results indicated that TiCl3(NH3)5 could be identified as the state of the Ti catalysts in the Li-N-H system.1. P. Chen, Z. Xiong, J. Luo, J. Lin, K. L. Tan, Nature 420 (2002) 302.2. T. Ichikawa, S. Isobe, N. Hanada, H. Fujii, J. Alloys Compd. 365 (2004) 271.3. S. Isobe, T. Ichikawa, N. Hanada, H. Leng, M. Fichtner, O. Kircher, H. Fujii, J. Alloys Compd. 404 (2005) 439.4. S. Isobe, T. Ichikawa, Y. Kojima, H. Fujii, J. Alloys Compd. 446-447 (2007) 360-362
9:00 PM - W3.33
Hydrogen Desorption and Absorption Properties of Ternary Nitride LiCaN.
Toshihisa Izuhara 1 , Naoki Ito 1 , Hiroyuki Takeshita 1
1 Faculty of Chemistry, Materials and Bioengineering , Kanasi University, Suita, Osaka, Japan
Show AbstractRecently, many research works has been focused on inorganic solid metal hydrides for large amount of hydrogen storage. Chen et al. reported Li-N-H hydrogen storage system which was composed of the mixture of LiNH2 and LiH. This mixture has high hydrogen storage capacity of 5.6mass% by the reaction of Li2NH + H2 ↔ LiNH2 + LiH [1]. Among them, the mixture of Mg(NH2)2 with LiH has more high hydrogen capacity of 5.5mass% by the reaction of Mg(NH2)2 +2 LiH ↔ Li2Mg(NH)2 +H2. However, Lu et al. reported that the mixture of LiNH2 and MgH2 released 8.1mass% of H2 by the reaction of LiNH2 + MgH2 → LiMgN + H2 [2]. These things suggested that some of other nitrides such as LiCaN, LiZnN and Li3AlN2 have the same antifluorite-type structure as LiMgN, which makes we expect to find new hydrogen storage nitrides. In this study, we aim to search for novel hydrogen storage materials by evaluating hydrogenation properties of ternary nitride LiCaN. The mixture of Li3N and Ca3N2 in the molar ratio of 1 to 1 was heated up to 873K for 86.4ks under helium atmosphere. Hydrogenations of samples were measured by Sieverts’ method. Dehydrogenation properties measured with thermogravimetry-mass spectroscopy (TG-MS). Constituent phases were identified by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Thermodynamic properties of hydrogen desorption and absorption was measured by differential scanning calorimetry (DSC).LiCaN were prepared at 873K for 86.4ks by the solid state reaction of Li 3N and Ca 3N 2. LiCaN was heated up to the temperature of 673K under hydrogen atmosphere at 3MPa. CaNH phase was observed in this hydrogenated sample by the XRD. This hydrogenation sample was released hydrogen about 3.6mass%H2 at the temperature of 873K under He flow atmosphere by the TG-MS. LiCaN phase was observed in the sample after TG-MS. And more, LiCaN sample observed exothermic and endothermic peaks at the temperature from 600K to 650K under hydrogen atmosphere at 13MPa by the DSC. From these facts, LiCaN can reversibly absorbed and desorbed hydrogen.[1] P. Chen et al., Nature, 420 (2002), 302-304. [2] J. Lu et al., J. Phys. Chem. C, 111 (2007), 12129-12134.
9:00 PM - W3.34
In-site TEM Observation for Reaction of LiH and NaH with NH3 by Means of Environmental Cell.
Hiroko Hirasawa 1 , Shigehito Isobe 1 , Yongming Wang 1 , Naoyuki Hashimoto 1 , Somei Ohnuki 1 , Takayuki Ichikawa 2 , Yoshitsugu Kojima 2
1 , Hokkaido University, Sapporo Japan, 2 , Hiroshima University, Higashi Hiroshima Japan
Show AbstractFor realizing hydrogen energy system in the near future, we have to establish advanced hydrogen storage and transportation methods. Nowadays, light weight hydrides, such as LiH and NaH, have been studied as promising hydrogen storage materials for onboard fuel cell vehicle. LiH and NaH can be reacted with NH3 to produce H2, LiNH2 and NaNH2, respectively. The reaction formulae are “LiH + NH3 ↔ H2 + LiNH2”, “NaH + NH3 ↔ H2 + NaNH2”. In this work, we performed in-situ TEM (Transmission Electron Microscopy) with an environmental cell, which is especially designed to control the “in-situ” condition, in order to microscopically examine the reactions. With the environmental cell, we can observe the reaction in 0 ~ 0.2MPa hydrogen atmosphere and room temperature ~ 150°C. Samples were prepared by ball-milling each powder of LiH and NaH under 1.0 MPa hydrogen gas atmosphere for 10 hours. We observed the samples under NH3 gas of 0.1 and 0.01 MPa at room temperature by TEM with the environmental cell. It was confirmed that LiH, NaH reacted with NH3 to generate LiNH2, NaNH2. Moreover, we observed volume expansion of the nano-particles due to the reactions. In both cases of LiH and NaH, the reaction rates with the condition of “under NH3 gas of 0.1 MPa” are faster than “that of 0.01 MPa”.
9:00 PM - W3.35
Offshore Sodium Metal Production with Electrolysis by Wind Power or Solar Cell for Hydrogen Power Generation.
Masataka Murahara 1
1 , Tokyo Institute of Technology, Meguro-ku, Tokyo, Japan
Show AbstractSodium metal reacts with water violently and generates an enormous amount of hydrogen instantaneously; therefore, sodium metal can play an important role as a storage material in hydrogen power generation. Resources for fossil and nuclear fuel are deposited in the limited areas over the world and its reserves are limited, whereas sodium is inexhaustible resources and exists as a salt in seawater and as a rock salt on the Continents. Sodium (specific gravity, 0.971) is lighter than water and is stored safely in kerosene for electric power generation. Sodium metal is, therefore, prepared electrolytically from seawater or rock salt by wind power generation when a strong wind blows constantly or by solar cell when hours of sunlight is long in summer and kept in kerosene; which is added water to produce a large amount of hydrogen instantly for power generation according to demand when there is no wind or when hours of sunlight is short in winter.For offshore wind power generation, transmission loss is a serious problem and must be minimized. The transmission loss and the installation cost of power-transmission line increase in proportion to the line length. In order to solve the two problems, a temporary storage is needed for the electricity generated by wind. Conventionally, the seawater is desalinated and electrolyzed to produce hydrogen at sea; namely, by changing into hydrogen, the electric power produced by wind turbines is transported to land. Hydrogen itself is light, but it requires a very heavy iron cylinder for storage. Hydrogen absorption alloy is now under development, but it is also heavy; the frequency of its absorption and discharge is very low. Thus, a new method of offshore sodium production by seawater electrolysis is proposed. Seawater contains water most and sodium second. Sodium is prepared electrolytically from seawater by wind or solar cell power generation and is stored in kerosene; which is transported to a thermoelectric power plant on land, where the sodium is added water to generate hydrogen for operating a hydrogen combustion turbine. The sodium hydroxide, a by-product, is supplied to the soda industry as a raw material. When oversupplied, the sodium hydroxide is melted again and electrolyzed to reproduce sodium metal. It is exactly the sodium fuel cycle. This sodium fuel cycle is a recycle system, which endlessly produces and reuses fuel, same as the nuclear fuel cycle that remanufactures uranium and plutonium by reprocessing the used nuclear fuel at the power plant; however, the sodium fuel cycle does not generate high level nuclear waste as the nuclear fuel cycle does. By the offshore seawater electrolysis, not only sodium but also fresh water, magnesium, calcium, sodium hydroxide, chlorine, oxygen, hydrogen, hydrochloric acid, and sulfuric acid are isolated and recovered as by-products. Thus, sodium is an economical, renewable, and sustainable fuel that discharges neither CO2 nor radiation.
9:00 PM - W3.36
Hydrogen Embrittlement in Metals: From Continuum Concepts to Atomistics.
Jun Song 1 , William Curtin 1
1 Division of Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractHydrogen embrittlement is a pervasive mode of degradation in many metallic systems that can occur via several mechanisms. Here, the competition between dislocation emission and cleavage at a crack tip in Ni is evaluated in the presence of H. At this level, embrittlement is predicted when the critical stress intensity required for emission rises above that needed for cleavage, eliminating crack tip plasticity and blunting as toughening mechanisms. Continuum predictions for emission and cleavage are made using computed generalized stacking fault energies and surface energies in a model Ni-H system. A Coupled Atomistic/Discrete-Dislocation (CADD) multiscale model is then used to investigate actual crack tip behavior in the presence of controlled arrays of H atoms around the crack tip. The continuum models are accurate at low H concentrations, below the embrittlement point, but at higher H concentrations the models deviate from the atomistic behavior. Specially at high H concentration around the crack tip, the dislocation emission is greatly altered and the set of dislocations nucleated may change. Our results highlight the directions and issues that are critical in clarifying the mechanism underlying the hydrogen embrittlement process.
9:00 PM - W3.6
Electrochemical Hydrogen Insertion into Carbon Inter-layers and the Enhancement of such Insertion by Catalytic Poisoning.
Janak Kafle 1 , Deyang Qu 1
1 , UMass Boston, Boston, Massachusetts, United States
Show AbstractHydrogen, which can be produced from renewable energy sources and burn pollution-free, could eventually replace fossil fuels and dramatically reduce the emission of greenhouse gases. Safe and reversible storage of hydrogen is one of the crucial technically challenges for the application of hydrogen as primary energy source. The phenomena of hydrogen adsorption into Pd was first reported by Graham, similar behavior has been reported at various transition metal electrodes such as Fe, Ti, Zr and especially mischmetal alloys, which have been used as anode materials for rechargeable Ni-MH battery, the chemistry played a historical role of replacing the once widely used toxic Ni-Cd batteries. Recently, hydrogen was also found to be adsorbed into carbon inter-layers electrochemically and potentialities of using carbon material as the vehicle for the storage of hydrogen has been discussed. It is also well known that cathodic H sorption into metals or alloys can be greatly enhanced by the presence of so-called “catalytic poison” e.g. H2S, thiourea etc. The mechanism of such catalytic poison is still under debate. It is the first time that such enhancement of hydrogen adsorption by the catalytic poison is reported on a carbon electrode.In this report, the mechanism for safe and reversible storage of hydrogen in porous carbonaceous materials by electrochemical decomposition of water in alkaline electrolyte is proposed. Atomic H was found inserted into the micro domains of defective graphene layers. The capacity of hydrogen storage increases with the increase of the interlayer distance of carbon sheets. Hydrogen insertion in carbonaceous materials occurs at ambient conditions. Static potential acts as an electrochemical valve which can retain the hydrogen in the carbon structure from leakage during storage.The amount of hydrogen inserted into carbon inter-layer was found to be significantly increased by the surface catalytic poison. The enhancement of H electro-sorption on carbon electrode was observed for the first time. For example, more than 30% of hydrogen was demonstrated inserted into the carbon inter-layers for the electrode with exposure to thiourea. The hypothesis of the mechanism is that electrosorbed H is formed by the electrolysis, the H residing on the surface could either diffuse close to each other on the surface of the carbon electrode, recombine and form H2; or could intercalate into the interlayer of carbon. Adsorption of catalytic poisons generally blocks electrode surface sites, competitively diminishing the coverage by adsorbed H which is the intermediate resulting from discharge of H+ in the cathodic H2 evolution reaction. Those poison species could serve as geometrical spacer, which impede the two adsorbed Hs to get close enough to form H2. Thus, the catalytic poisons which reduce the factional coverage by adsorbed H, can actually enhance H insertion into the electrode.
9:00 PM - W3.7
New Insights on Functionalization of Metal-Organic Frameworks.
Andreas Blomqvist 1 , Pornjuk Srepusharawoot 1 2 , C. Moyses Araujo 1 3 , Ralph Scheicher 1 , Rajeev Ahuja 1 3
1 Department of Physics and Materials Science, Uppsala University, Uppsala Sweden, 2 Department of Physics, Khon Kaen University, Khon Kaen Thailand, 3 Department of Materials and Engineering, Royal Institute of Technology, Stockholm Sweden
Show AbstractThrough a systematic investigation of the interactions of alkali, alkaline earth, and transition metals with metal-organic framework-5 we will provide key insights on possibilities and problems arising during the functionalization of metal-organic frameworks (MOF). Storing molecular hydrogen in high surface materials such as metal-organic frameworks requires low temperature and/or high pressure. This is due to the weak dispersive binding interaction between the surface and the hydrogen molecules. In order to lower the pressure and raise the temperature at which hydrogen can be stored, the hydrogen adsorption has to include other than purely dispersive interactions.It was shown, both experimentally [1] and theoretically [2,3], that Li-decoration could improve the hydrogen storage properties of metal-organic frameworks. The improvement, however, is not sufficient to make MOFs a practically useful hydrogen storage material. Moreover, the functionalization of MOFs is not a straightforward procedure. Therefore it is important to gain more knowledge on the interactions between MOFs and potential functionalizing atoms or molecules.Using ab initio calculations we show how alkali, alkaline earth, and transition metals interact with different sites of the metal-organic framework and how they can improve the hydrogen uptake properties. Furthermore using ab initio molecular dynamics simulations we show that functionalization of the metal-oxide cluster can destabilize and even destroy the metal-organic framework. This will be of interest when choosing the precursors for designing new and improved metal-organic frameworks. References: [1] L. K. Mulfort and J. T. Hupp, J. Am. Chem. Soc. 129, 9604 (2007); [2] S. S. Han and W. A. Goddard III, J. Am. Chem. Soc., 129, 8422 (2007); [3] A. Blomqvist et al., Proc. Natl. Acad. Sci. U.S.A., 104, 20173 (2007)
9:00 PM - W3.8
Controlled Formation of Porous Coordination Polymer Particles (CPPs) for Hydrogen Storage.
Won Cho 1 , Hee Jung Lee 1 , Moonhyun Oh 1
1 Department of Chemistry, Yonsei University , Seoul Korea (the Republic of)
Show AbstractPorous coordination polymers have received great attention owing to their useful applications in catalysis, recognition, and separation. In particular, there is a huge interest in the storage of gas molecules, that is, H2, CO2. Although the majority of coordination polymer materials, including metal-organic frameworks (MOFs), are concentrated on macro-scaled crystalline products, for structural studies based on single crystal X-ray analysis, we and others have recently reported the synthetic strategies for the preparation of nano- and micro-sized coordination polymer particles (CPPs). A sophisticated understanding of coordination polymer particle formation, as well as the concomitant size and morphology control, is central for the practical application of these materials. However, the fine control of CPP growth has not been well studied. Herein, we wish to report the size and morphology controlled formation of porous coordination polymer particles through modulating the growth rate of different facets of crystalline CPP. We found that the blocking efficiency during CPP growth can be controlled by the amount of surfactant used. The N2 sorption isotherm of CPPs prepared shows type I behavior typical for microporous materials. The hydrogen storage capacity of CPPs prepared will be also presented.
9:00 PM - W3.9
A Novel Polymeric Approach by Utilizing Functionalized Poly(ether ether ketone) for Hydrogen Storage Applications.
Rolando Pedicini 1 , Gaetano Squadrito 1 , Giosue Giacoppo 1 , Ada Sacca 1 , Enza Passalacqua 1
1 , CNR-ITAE, Messina Italy
Show AbstractHydrogen storage is an important tool for the extensive use of hydrogen as an energy carrier. The development of hydrogen as a reliable energy vector is strongly connected to the cost, performance and level of safety of the storage system components. Up to date, none of the proposed hydrogen storage systems appears able to match DOE targets [1]. Among the materials for chemical and physical storage of H2, metal hydride appears to be more promising for applications. Moreover, many other materials have been proposed, but few research works were devoted to polymer based materials [2,3], that are generally low cost and weight, easy to be managed and manufactured. For this reason, a novel approach to hydrogen storage was considered.Polymer properties can be modified by introducing suitable functional groups, according to the particular application field such as magnetic support materials, ion conducting polymers, selective transport and so on. In this work, a Poly(ether ether ketone) (PEEK) was chosen as a base polymeric matrix with the aim to produce a both low cost and low weight hydrogen storage material. The polymer was functionalized with a metallic compound bonded to the polymer chain allowing the hydrogen storage. Here we report the functionalisation process and the preliminary results on hydrogen storage capability of the synthesized polymer.The polymer was characterized by Scanning Electron Microscopy, X-ray diffraction, BET method surface area, Transmission Electron Microscopy and Gravimetric Hydrogen Adsorption measurements.The metallic compound introduction modifies the morphology of the material and supplies an increased surface area for hydrogen chemisorptions, revealing a 1.2%wt/wt hydrogen adsorption capability at 77K. Preliminary results by gravimetric measurements showed that by increasing the temperature and over, hydrogen storage capability was reduced but not disappeared, for example a 0.3%wt/wt at 50°C and 80 bar was obtained. These very promising results showed the approach effectiveness, for this reason deeper studies are in progress.References[1]W.R. Schmidt, Hydrogen storage in polymer-dispersed metal hydrides (PDMH), Proceedings of the 2001 DOE Hydrogen Program Review NREL/CP-570-30535.[2]S.J. Cho, K. Choo, D.P. Kim, J.W. Kim, H2 sorption in HCl-treated polyaniline and polypyrrole, Catal. Today 2007, 120, 336–340.[3]J. Germain, J. Hradil, J.M.J. Frechet, F. Svec, High Surface Area Nanoporous Polymers for ReversibleHydrogen Storage, Chem. Mater. 2006, 18, 4430-4435.[4]B. Panella, L. Kossykh, U.D. Weglikowskab, M. Hirscher, G. Zerbi, S. Roth, Volumetric measurement of hydrogen storage in HCl-treated polyaniline and polypyrrole, Synth. Met. 2005, 151, 208–210.
Symposium Organizers
Etsuo Akiba National Institute of Advanced Industrial Science and Technology
William Tumas National Renewable Energy Laboratory
Ping Chen National University of Singapore
Maximilian Fichtner Karlsruhe Institute of Technology
Shengbai Zhang Rensselaer Polytechnic Institute
W4: Metal Hydrides I
Session Chairs
Etsuo Akiba
Hitoshi Takamura
Tuesday AM, December 01, 2009
Back Bay D (Sheraton)
9:30 AM - **W4.1
The Fundamental Study of the Structural and Electronic Properties of Metal Hydrides Using Synchrotron Radiation X-rays.
Akihiko Machida 1 , Hiroyuki Saitoh 1 , Yoshinori Katayama 1 , Katsutoshi Aoki 1
1 Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Sayo-gun, Hyogo, Japan
Show AbstractSynchrotron radiation (SR) x-rays experiments are powerful and useful for understanding the chemical and physical properties of hydrogen storage materials. SR x-rays enable us to investigate the structural and electronic properties of materials that change often dramatically on hydrogenation and/or dehydrogenation. We have made SR x-ray diffraction measurements for aluminum-hydrogen system at hydrogen pressures up to 10 GPa and temperatures up to 800 °C, and observed for the first time the hydrogenation and dehydrogenation reaction process of aluminum. AlH3 is one of promising materials for hydrogen storage due to its large hydrogen capacity of 10 wt%. In spite of the stable condition of AlH3 thermodynamically predicted (above ~0.7 GPa at room temperature), the hydrogenation reaction of pristine aluminum metal has not been reported. The hydride has been synthesized only by organometallic method. Oxide layer on aluminum surface seems to prevent aluminum metal from hydrogenation. It is expected that the chemical potential of hydrogen fluid steeply elevated by compression and heating would allow hydrogenation reaction eventually. We have observed hydrogenation and/or dehydrogenation processes using in-situ SR x-ray diffraction experiments. The high pressure and temperature state of hydrogen fluid was achieved with a multi-anvil high pressure apparatus installed in BL14B1 at SPring-8. The sample chamber, which was filled with aluminum foils (purity 6N), was placed in a hydrogen sealing capsule along with internal hydrogen sources.The reflection peaks from α-AlH3 with a rhombohedral lattice was first observed at a pressure of 8.9 GPa and temperature of 600 °C. The oxide layer may be removed partially with the reactive hydrogen fluid at such high pressure-temperature conditions. With further heating to 680 °C, the reflection peaks vanished, indicating decomposition of AlH3 into aluminum metal and hydrogen fluid. The reflection peaks of AlH3 reappeared upon successive cooling to 600 °C. We succeeded in observation of the hydrogenation-dehydrogenation cycle. After aluminum metal experienced the hydrogenation and dehydrogenation cyclic reaction several times, the hydrogenation conditions became moderate. The hydride formed at 4.9 GPa and 330 °C half of the initial conditions. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under Advanced Fundamental Research on Hydrogen Storage Materials.
10:00 AM - W4.2
Phase Transformation in Yttrium-Hydrogen System Studied by TEM.
Ke Wang 1 , Jason Hattrick-Simpers 1 , Leonid Bendersky 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show AbstractPhase transformations in epitaxial single-crystal yttrium films grown on (0001)Ti//(0001)Al2O3 substrates and hydrogenated for different times were characterized using transmission electron microscopy (TEM). After short time of hydrogen charging, dense twin lamellae form during α(Y(H))-to-β(YH2) phase transition with twin boundaries predominately parallel to the interface between Y and a substrate. High densities of Shockley partial dislocations are present at the twin boundaries, their glides during phase transformation are responsible for the formation of twin lamellae. Cracking along the twin boundaries was evident in longer time hydrogenation samples, which is caused by the voids nucleated on the YH2 twin boundaries during β(YH2)-to-γ(YH3) transition. No γ phase was observed in TEM samples because of the unstable nature of the phase during TEM sample preparation and exposure to high vacuum of the microscope column during TEM observation.
10:15 AM - W4.3
Electronic Structure and Magnetic Properties of Iron Hydride.
Takao Tsumuraya 1 , Tatsuya Shishidou 1 , Tamio Oguchi 1 2
1 ADSM, Hiroshima University, Higashihiroshima Japan, 2 IAMR, Hiroshima University, Higashihiroshima Japan
Show AbstractInteraction of hydrogen with transition-metal atoms is of broad interest and fundamental importance for understanding the properties of transition-metal alloy hydrogen storage materials, including phase transformations, electronic structure and superabundant vacancy formation. [1, 2] Iron hydride FeH consists of double hexagonal closed-packed (dhcp) Fe lattice. Structural transformation from bcc-Fe to dhcp-FeH has been experimentally observed under hydrogen pressure above about 3.5 GPa. [3, 4] The hydride is thermodynamically stable only at the high-pressure condition and rapidly decomposed into bcc-Fe and gaseous hydrogen under ambient condition. Fortunately, the hydride can be retained in a metastable state at ambient pressure by cooling under high hydrogen pressure. The “quenched” metastable FeH shows a ferromagnetic phase with dhcp Fe lattice. [5] Magnetic properties are very sensitive to external variables such as pressure. To investigate the magnetic properties of the hydride depending on applied hydrogen pressure, Mössbauer spectroscopy and x-ray magnetic circular dichroism (XMCD) at Fe K-edge have been carried out recently. In this study, we present a theoretical investigation and interpretation of the experimental results for understanding the electronic structure and the magnetic properties from first-principles calculations. Our approach is based on density functional theory in its spin-polarized form with the generalized gradient approximation. One-electron Kohn-Sham equations are solved with the all-electron full-potential linearized augmented plane wave (FLAPW) method. [1] Y. Fukai, K. Mori and H. Shinomiya, J. Alloys Comp. 348, 105 (2003).[2] V. E. Antonov, J. Alloys Comp. 330-332, 110 (2002). [3] I. Choe, R. Ingalls, J. M. Brown, Y. Sato-Sorensen and R. Mills, Phys. Rev. B 44, 1 (1991). [4] J. V. badding, R. J. Hemley, H. K. Mao, Science 253, 421 (1991). [5] V. E. Antonov, K. Cornell, V. K. Fedotov, A. I. Kolesnikov, E. G. Ponyatovsky, V. I. Shiryaev and H. Wipf, J. Alloys Comp. 264, 214 (1998).
10:30 AM - W4.4
Infrared Imaging and PCI Method of Studying Growth Rate of a Hydride Phase.
Zhuopeng Tan 1 2 , Chun Chiu 1 , Jason Hattrick-Simpers 1 , Leonid Bendersky 1
1 Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Materials Science and Engineering, University of Maryland at College Park, College Park, Maryland, United States
Show Abstract A method of studying growth rate of hydrides using in-situ infrared imaging of wedge-shaped films is presented. Hydrogenation experiments with Pd-capped Mg-TM(Ti, Mn, Fe, Ni, Cu, Zn, Zr, Ru), films having thickness gradient of 300 nm/cm were conducted at 373K and 3 bar H2 gas pressure. The infrared imaging combined with structural characterizations of Mg-Ti films demonstrated two growth modes; fast formation of a ~150 nm-thick layer of MgH2 under Pd followed by dramatically slower growth. This method was validated for a variety of samples with different thickness gradients and compositions, and is expected to be applicable for evaluating hydrogenation kinetics and microstructural requirements of different hydrogen storage materials. In addition to the kinetics study, quantitative thermodynamics analysis has been conducted using film’s PCI measurement with a sensitivity of ~1.5μg.
10:45 AM - W4.5
Thermodynamic and Kinetic Characterization of H-D Exchange on Metals.
Weifang Luo 1 , Donald Cowgill 1 , Rion Causey 1
1 , Sandia National Laboratory, Livermore, California, United States
Show AbstractA Sieverts’ apparatus coupled with an RGA is an effective method to detect composition variations during isotopic exchange. This experimental setup provides a tool for the thermodynamic and kinetic characterization of H-D isotope exchange on metals. The equilibrium properties, i.e. the H-D separation factors alpha and equilibrium constants KHD, are obtained and found to be very close to those in the literature. The exchange rate can be determined from the exchange profiles and a kinetic model is proposed and exchange activation energy will be determined. Both exchange directions, H2+MD and D2+MH, will be discussed. The thermodynamic and kinetic understanding the H-D exchange behavior will provide useful information for hydrogen isotope separation applications.
11:30 AM - **W4.6
Structural and Hydrogenation Properties of Hydrogen Storage Alloys.
Yumiko Nakamura 1 , Jin Nakamura 1 , Kenji Iwase 1 , Junko Matsuda 1 , Kouji Sakaki 1 , Etsuo Akiba 1
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show AbstractHydrogen 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. Structural changes and hydrogen occupation during hydrogenation/dehydrogenation were studied using in situ X-ray and neutron diffraction. Introduction of lattice defects was investigated using in situ positron annihilation methods and transmission electron microscopy (TEM). Relation among lattice expansion, hydrogen occupation, introduction of lattice defects and hydrogenation properties will be discussed based on the obtained results for (RE,Mg)-TM intermetallic compounds (RE: rare-earth metal, TM: transition metal) and Ti,V-based solid solution alloys.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).
12:00 PM - W4.7
Local Structure Analysis in LaNi5 Based Alloys by In-Situ Coincidence Doppler Broadening Measurement.
Kouji Sakaki 1 , Yumiko Nakamura 1 , Etsuo Akiba 1
1 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractWe have reported that vacancies and dislocations are introduced by hydrogenation in LaNi5 around room temperature based on positron annihilation lifetime measurements. Their densities and thermal stability were influenced by the additional third elements into LaNi5.[1] Vacancy recovery during dehydrogenation at room temperature was also observed in LaNi4.93Sn0.27 and LaNi5Cu by the in-situ positron lifetime measurement.[2] The coincidence Doppler broadening (CDB) measurement is a new technique using positron annihilation that can identify the elements around the lattice defects from the energy spectrum of positron annihilation gamma ray. In this study, we tried to analyze the local structure around the lattice defects using the in-situ CDB measurement and the positron lifetime measurement simultaneously. Introduction and recovery of the lattice defects during hydrogenation and dehydrogenation in LaNi5, LaNi4Cu and LaNi5Cu was studied.Before hydrogenation, all samples did not have any lattice defects that the positron annihilation methods can detect. During hydrogenation, increase of the mean positron lifetime, which originated from the lattice defect formation, was observed with increasing hydrogen content in all samples. CDB spectrum was converted into a ratio curve obtained by dividing the original spectrum by that of reference. The change of CDB ratio curves showed that the numbers of positrons which were annihilate with core electrons of La increased by hydrogenation. This indicates that vacancies were introduced to Ni sites during hydrogenation considering that Ni vacancies at 2c and 3g sites would be surrounded by both La and Ni atoms, while La vacancy would be surrounded by only Ni atoms in LaNi5. Recovery of the vacancies was not suggested in the CDB ratio curve and positron lifetime for LaNi5 during dehydrogenation. On the other hands, in LaNi5Cu the mean positron lifetime and CDB ratio curve returned to their initial state during dehydrogenation. It indicates that almost all introduced Ni vacancies could recover during dehydrogenation in LaNi5Cu. While some of vacancies were recovered and the other still remained in a lattice in LaNi4Cu during dehydrogenation. The difference of vacancy recovery must originate from the local structure around introduced vacancies.This work was supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".[1] K. Sakaki, E. Akiba, M. Mizuno, H. Araki, Y. Shirai: J. Alloy. Compd., 473 (2009) 87-93.[2] K. Sakaki, R. Date, M. Mizuno, H. Araki, Y. Nakamura, Y. Shirai, R. C. Bowman Jr., E. Akiba: J. Alloy. Compd., 477 (2009) 205-211.
12:15 PM - W4.8
Local Structure and Transport Properties of Ca4ZrH10 Prepared under High Pressure.
Hitoshi Takamura 1 , Takaaki Nakamura 1 , Shin-ichi Hashimoto 1 , Hideki Maekawa 1
1 Department of Materials Science, Tohoku University, Sendai, Miyagi, Japan
Show AbstractCa4ZrH10 having a BiF3-type structure can be prepared by using high-pressure synthesis on the order of GPa. In this study, the local structure and transport properties including hydrogen dynamics of Ca4ZrH10 were investigated by means of Raman and NMR spectroscopy. Ca4ZrH10 was prepared by using a cubic-anvil-type apparatus at 800 oC under 5 GPa. The hydrogen content was controlled by adding hydrogen source during preparation and/or heat treatment after preparation. For NMR spectroscopy, tetramethyl silane (TMS) was used as references for 1H. Based on XRD analysis, Ca4ZrH10 was found to be prepared as a single phase under high pressure; a lattice constant was a = 0.53143 nm. In a Raman spectrum of Ca4ZrH10, a sharp peak at around 220 cm-1 and a broad peak at around 500 cm-1 were observed. Compared to those of other metal hydrides having the same structure, those shifts were attributed to a cation breathing mode and a symmetrical stretching mode of T-site hydrogen, respectively. In addition, a broad and weak Raman signal presumably due to hydrogen occupying distorted O-sites was observed. A chemical shift of 1H in Ca4ZrH10 was approximately 5 ppm. By using a high-temperature NMR probe, the temperature dependence of spin-lattice relaxation time (T1), which gives information on hydrogen dynamics, was also investigated. This work has been supported in part by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".
12:30 PM - W4.9
Experimental Evaluation of the Effect of Al on Stability of Magnesium Hydride.
Fereshteh Ebrahimi 1 , Mahesh Tanniru 1 , Darlene Slattery 2
1 Materials Science and Engineering, University of florida, Gainesville, Florida, United States, 2 , Florida Solar Energy Center, Cocoa Beach, Florida, United States
Show AbstractComputational studies have revealed that the incorporation of Al in the magnesium hydride crystal will cause its destabilization by reducing its enthalpy of formation/dissociation. The objective of this work was to evaluate whether Al could indeed be dissolved in magnesium hydride and it would result in its destabilization. In this study, Mg-8at%Al alloy powders were fabricated via the electrodeposition technique. The powders were hydrogenated at 180, 210 and 280C at 1MPa pressure. Detailed compositional and structural analyses of the phases revealed that noticeable amount of Al can be trapped in the hydride structure at 180C hydrogenation temperature, which caused in a measurable expansion of the hydride lattice. The amount of Al in the magnesium hydride decreased sharply with increasing temperature suggesting that the hydride phase has very low solubility for Al. When Al was entrapped owing to its slow diffusion at low hydrogenation temperatures, the hydrogen release was found to take place at temperatures as low as 120C, confirming the destabilization effect of Al on magnesium hydride. This work has been supported by NSF under grant number DMR-0605406.
12:45 PM - W4.10
Hydrogenation Properties of Pr Thin Films, Nanocrystalline Layers and Size-selected Nanoparticles.
Shubhra Kala 1 2 , Bodh Mehta 2 , Frank Kruis 1
1 Faculty of Engineering, Institute for Nano Structures (NST), Duisburg, NRW, Germany, 2 Department of Physics, Indian Institiute of Technology Delhi, New Delhi, Delhi, India
Show AbstractHydrogen induced changes in the structural, electrical and optical properties of rare earth metals have been widely studied in bulk, alloys and multilayer structures. In this study, the effect of nanoparticle character on these properties have been investigated by comparing the hydrogenation properties of Pr nanocrystalline layers and size-selected Pr nanoparticles with the thin film counter parts. Nanocrystalline layers have been prepared by using an inert gas evaporation method. Size-selected Pr nanoparticles have been prepared using an integrated deposition set up consisting of a spark generator for initial formation of primary Pr agglomerates in the carrier gas, a UV charger for charging the agglomerates, a differential mobility analyzer for size selection, a furnace for in-flight sintering for transforming the agglomerates into well-formed, single crystalline, spherical Pr nanparticles, which are finally deposited onto substrates using an electrostatic precipitator. It will be shown that this method is ideally suitable for synthesizing nanoparticles of rare earth metals (and other materials, highly susceptible towards oxidation) in the size range of 5-20 nm with a geometric standard deviation less than 1.15. A detailed structural and topographic comparison of these samples has been done using transmission electron microscopy techniques. Monocrystalline nanoparticles are stable in air during post deposition exposure in comparison to those having defects and grain boundaries. Faster electrical switching with a response time of ~ 95 seconds and higher electrical contrast between hydrogen loaded and deloaded states have been observed in case of nanocrystalline layers. Optical absorption studies show that a single absorption edge at 2.91 eV, in case of Pr nanocrystalline layers, which indicates a complete conversion of Pr to PrH3-δ in comparison to two absorption edges corresponding to PrH2+ε and PrH3-δ states observed in thin films. As a consequence of presence of single absorption feature in the loaded state along-with the blue shift in the absorption edge, extension in the constant transmittance region towards higher energy take place in nanocrystalline layers. During deloading, effective hydrogen desorption from nanocrystalline layers results in a large shift in absorption edge and consequently a higher optical contrast (~ 56 %) between loaded and deloaded states. The observed improvements in switching characteristics will be explained in terms of blue shift in the absorption edge due to quantum confinement effect, enhanced surface effect at smaller dimension, interparticle gaps and relatively loose adhesion of the nanocrystalline layers to the substrate.
W5: Metal Hydrides and Other Hydrides
Session Chairs
Yumiko Nakamura
Gwo-Ching Wang
Tuesday PM, December 01, 2009
Back Bay D (Sheraton)
2:30 PM - **W5.1
Tuning thermodynamics of M-H (nano-)systems with elastic constraints.
Ronald Griessen 1 , Andrea Baldi 1 , Yevheniy Pivak 1
1 Physics/FEW, VU university, Amsterdam Netherlands
Show AbstractBy means of a simple model, we show that the thermodynamic properties of hydrogen absorption in nanostructured metals can be tuned by means of elastic constraints. This applies in particular to the plateau pressure P in pressure-composition isotherms. For a planar bilayer made of a H absorbing metal (m) elastically coupled to a less or non H-absorbing material (c) the ratio of the plateau pressures P(clamped)/P(free) is predicted to depend on the ratio (E(m)D(m)/[E(c)D(c)] where E(i) and D(i) are the Young's modulus and the layer's thickness, respectively of layer i. Large increases of plateau pressures can be reached by coating a soft H-absorbing metal with a thin hard material with a lower H affinity. A typical case is that of a Mg layer capped by a transition metal such as Ni or Pd. At 333 K the plateau pressure P(clamped) of a 20 nm Mg film capped with 20 nm Pd is ~ 200 times higher than the plateau pressure P(free) of a free Mg layer. For nanoclusters the model predicts even stronger destabilization effects. For a Mg nanocluster of 10 nm radius covered with a MgO layer of only 1.7 nm thickness, we calculate P(clamped)/P(free) = 300 at 333 K.These predictions are quantitatively in agreement with pressure-composition isotherms measured by hydrogenography [1] on bi-layers and multilayers of Mg and transition metals [2]. Our results provide the basis for the development of new hydrogen storage materials with attractive thermodynamic properties. They also show that the infinite range of the elastic H-H interaction in metal-hydrides can lead to a drastic influence of the imposed elastic boundary conditions on their thermodynamic properties. [1]R. Gremaud, C.P. Broedersz, D.M. Borsa, A. Borgschulte, P. Mauron, H. Schreuders, J.H. Rector, B. Dam and R. Griessen: Hydrogenography: An optical combinatorial method to find new light-weight hydrogen storage materialsAdvanced Materials 19 (2007) 2813-2817 [2] A. Baldi, M. Gonzalez-Silveira, V. Palmisano, B. Dam and R. Griessen: Destabilization of the Mg-H system through elastic constraints, Phys. Rev. Lett. 102 (2009) 226102
3:00 PM - **W5.2
Novel Ultrathin Mg Nanoblades for Hydrogen Storage.
Gwo Ching Wang 1 , Fu Tang 2 , Toh Ming Lu 1
1 Physics, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractVarious simple metal hydrides, complex metal hydrides, metal organic framework compounds, and activated carbon aerogels, have been studied for hydrogen storage. Some have high storage capacity but have drawbacks for example, high temperature or slow kinetics of hydrogen absorption/desorption or limited hydrogenation/de-hydrogenation cycles. We present a fresh approach to metal-catalyst systems using a unique morphology of ultrathin Mg nanoblades as a candidate for hydrogen storage. The isolated crystalline ultrathin nanoblades were made from oblique angle vapor deposition [1] and not from ball milling that may produce contaminations and strains. Each nanoblade has a large surface-area-to-mass ratio that is in orders of magnitude higher than that of a continuous film made by normal vapor incident deposition. Since the Mg nanoblades are thin (~20 nm), hydrogen will diffuse through their entire thickness to form hydride, and the time required for hydrogenation and de-hydrogenation processes in these nanoblades will be short. The gaps between vertically standing isolated nanoblades can easily accommodate volume expansion between Mg and MgH2 during cycling to extend durability and cycle lifetime. Our preliminary studies of Pd coated Mg nanoblades show a low hydrogen absorption/ desorption temperature of T < 100 oC [2]. The catalyst Pd provides lower hydrogen absorption and desorption barriers on the Mg surface. The near surface structural evolution in the de-hydrogenation process of air exposed Pd coated Mg nanoblades was characterized in situ from room temperature to ~300 oC using surface sensitive reflection high energy electron diffraction (RHEED) [3]. With RHEED, we are able to detect structural compositions and crystal sizes smaller than ~2 nm. At room temperature the dominant structures near surface were Pd and MgH2. When the temperature increased to ~200 oC the MgH2 was nearly depleted and Mg6Pd alloys started to form and co-exist with Mg. Further fundamental understanding of hydrogenation/de-hydrogenation properties of Pd coated Mg nanoblades could help us in designing promising nanoscale metal hydrides that have functional properties for hydrogen storage.Work partially supported by the NSF 0506738. [1] F. Tang, T. Parker, H.-F. Li, G.-C. Wang, and T.-M. Lu, "Unusual magnesium crystalline nanoblades grown by oblique angle vapor deposition", J. of Nanosci. and Nanotechnol. 7, 3239 (2007).[2] F. Tang, T. Parker, H.-F. Li, G.-C. Wang, and T.-M. Lu, "Pd catalyst effect on low temperature hydrogen desorption from hydrided ultrathin Mg nanoblades", Nanotechnology 19, 465706 (2008). [3] F. Tang, W. Yuan, T.-M. Lu, and G.-C. Wang, "In situ RHEED study of dehydrogenation process of Pd coated Mg nanoblades", J. of Appl. Phys. 104, 033534 (2008).
3:30 PM - W5.3
Enhanced Hydrogen Storage Properties of Magnesium Nanotrees with Nanoleaves.
Mehmet Cansizoglu 1 , Tansel Karabacak 1
1 Applied Science, University of Arkansas at Little Rock, Little Rock, Arkansas, United States
Show AbstractHydrogen storage in advanced solid state materials has been an intense area of research due to many drawbacks in conventional high pressure or cryogenic liquid hydrogen storage methods. A practical hydrogen storing material is required to have high storage capacity and fast dehydrogenation kinetics. Among many solid state materials for hydrogen storage, magnesium hydride (MgH2) combines a hydrogen capacity of 7.6 wt % with the benefit of the low cost of production and abundance. The main difficulties for implementing MgH2 are slow absorption/desorption kinetics and high reactivity towards air and oxygen, which are also common issues in most lightweight metal hydrides. Previously, improvements in hydrogen storage and release properties have been reported by using nanostructured magnesium that can be obtained through various fabrication methods including ball-milling, mechanical alloying, and vapor transport. In this study, we investigate the hydrogen absorption and desorption properties of magnesium “nanotrees” fabricated by glancing angle deposition (GLAD) technique, and also conventional Mg thin films deposited at normal incidence. Mg nanotrees are about 15 µm long, 10 µm wide, and incorporate “nanoleaves” of about 25 nm in thickness and 1,2 µm in lateral width. A quartz crystal microbalance (QCM) gas absorption/desorption measurement system has been used for our hydrogen storage studies. Nanostructured and thin film Mg have been deposited directly on the surface of the gold coated unpolished quartz crystal samples. QCM hydrogen storage experiments have been performed at temperatures ranging between 100-300 oC, and at H2 pressures of 10 and 30 bars. Our QCM measurements revealed that Mg nanotrees can absorb hydrogen at lower temperatures and faster compared to Mg thin film. In addition, Mg nanotrees can reach hydrogen storage values of about 7.0 wt %, which is close to the theoretical maximum storage value, at temperatures as low as 100 oC. The significant enhancement in hydrogen absorption properties of our Mg nanotrees is believed to originate from novel physical properties of their nanoleaves. These nanoleaves are very thin (~25 nm) and both surfaces are exposed to hydrogen enhancing the diffusion rate of hydrogen together with a decreased diffusion length. Based on X-ray diffraction measurements, individual nanoleaves have non-close-packed crystal planes that can further enhance the hydrogen absorption kinetics. In addition, our nanostructured Mg have been observed to quite resistant to surface oxidation, which is believed to due to the single crystal property of the Mg nanoleaves, that further improves the absorption kinetics of hydrogen.
3:45 PM - W5.4
Hydrogen Sorption in Magnesium Nanoparticles: Size- and Surface-related Phenomena.
Luca Pasquini 1 , Elsa Callini 1 , Emanuela Piscopiello 2 , Amelia Montone 3 , Torben Jensen 4 , Marco Vittori Antisari 3 , Ennio Bonetti 1
1 Dept. of Physics, University of Bologna, Bologna Italy, 2 C.R. Brindisi, ENEA, Brindisi Italy, 3 C.R. Casaccia, ENEA, Rome Italy, 4 Dept. of Chemistry and iNANO, University of Aarhus, Aarhus Denmark
Show AbstractThe aim of this work is the investigation of the metal-hydride transformation in magnesium (Mg) nanoparticles both as a function of particle size and in response to surface functionalization by transition metal clusters.Mg nanoparticles were synthesized by the inert-gas condensation technique, which yields single crystals with six-fold symmetry whose average size can be controlled by tuning the inert gas pressure. After the synthesis the nanoparticles were passivated by slow exposure to oxygen, obtaining a core-shell morphology where a metallic core is coated by a MgO shell of about 4 nm thickness. The material structure was investigated by Transmission Electron Microscopy (TEM), also in Scanning (STEM) and High Resolution (HRTEM) mode, and by X-Ray Diffraction (XRD). The sorption kinetics were analysed by a volumetric Sievert apparatus, which also allowed for a determination of the activation energies.Small nanoparticles (≈35 nm) display interesting kinetics with gravimetric capacity of 4.5 wt.% at saturation, limited by the oxide fraction. Hydride formation proceeds by one-dimensional growth controlled by diffusion through the hydride, while the reverse transformation to metal involves interface-controlled three-dimensional growth of nuclei formed at constant rate. On the contrary, large nanoparticles (≈450 nm) exhibit very low reactivity due to reduced probability of hydrogen dissociation/recombination and nucleation at the particle surface. For this reason, large nanoparticles were surface-decorated by Pd through in situ evaporation in the inert-gas condensation chamber. This procedure results in Pd clusters of 3-4 nm located over a portion of the MgO shell, as shown by STEM, HRTEM and XRD. This treatment results in dramatically improved hydrogen sorption behavior, even if the total amount of Pd is only 2 at.%. In fact, previously inert nanoparticles now exhibit metal-hydride transformation with fast kinetics and gravimetric capacity above 5 wt.%. The kinetics analysis yields a similar activation energy for absorption and desorption, and hints at a one-dimensional nuclei growth which reflects the decoration geometry.Real-time diffraction studies using Synchrotron Radiation were carried out during hydrogen sorption on the Pd-decorated nanoparticles. We clearly show that a Mg-Pd intermetallic phase is formed after the first heating treatment and takes active part in the transformation. Further experiments, presently in progress, on the pressure-dependence of the hydrogen sorption kinetics and on the effect of other transition metals, will also be presented to provide a comprehensive picture of hydrogen sorption in this class of nanostructured storage materials.ReferencesL. Pasquini et al., Appl. Phys. Lett. 94, 041918 (2009)E. Callini et al., Appl. Phys. Lett. 94, 221905 (2009)
4:30 PM - W5.5
Study of Mg-TM (Mn, Ni, Ta, Ti) Thin Films for Hydrogen Storage Application.
Nilima Hullavarad 1 , Shiva Hullavarad 1
1 OFFICE OF ELECTRONIC MINIATURIZATION, UNIVERSITY OF ALASKA FAIRBANKS, Fairbanks, Alaska, United States
Show AbstractMagnesium alloys have been widely used for hydrogen storage applications and as electrodes in MH-Ni batteries due to high hydrogen uptake of 7.6 wt.% for pure Mg and 3-6 wt.% for Mg-TM (transition metal) alloys. In this work, we present the hydrogen storage properties of Mg-TM (Mn, Ni, Ta, Ti) thin films. The Mg-TM thin films are grown by RF co-evaporation sputtering technique. The thin films are characterized by X-Ray Diffraction for identifying the phases responsible for maximized hydrogen adsorption and desorption kinetics during recycling. Scanning Electron Microscopy/Electron Back Scattered Diffraction studies will be carried out to understand the grain alteration and phase changes during the hydrogen adsorption/desorption kinetics. The results obtained from SEM/EBSD measurements will be presented to understand the interaction between the component hydrides and grain fields at phase boundaries. We will present the Pressure - Composition- isotherm (PCT) measurements for optimized Mg-TM (Mn, Ni, Ta, Ti) composition alloys.
4:45 PM - W5.6
Rapid and Reversible Hydrogen Sorption in Mg-Ti-Fe Thin Films.
David Mitlin 1 2 , Beniamin Zahirisabzevar 1 2 , Babak Shalchi Amirkhiz 1 2 , Chris. T Harrower 1 2 , Helmut Fritzsche 3
1 , University of Alberta, Edmonton, Alberta, Canada, 2 , National Research Council Canada, Edmonton, Alberta, Canada, 3 , National Research Council Canada, SIMS, Canadian Neutron Beam Centre, Chalk River, Ontario, Canada
Show AbstractThis study focused on the hydrogen sorption properties of the 1.5 micrometer thick Mg-10at.%Fe-10Ti, Mg-15at.%Fe-15Ti, and Mg-20at.%Fe-20Ti films. We show that the alloys display remarkable sorption behavior: At 200°C the films are capable of absorbing nearly 5 wt.% hydrogen (capacity being dependent on the composition) in seconds, and desorbing in minutes. This sorption behavior appears be remarkably stable. For example in the Mg-15at.%Fe-15at.%Ti alloy there is no kinetic or capacity degradation even after 100 absorption/desorption cycles. X-ray diffraction analysis indicates that the sorbed microstructure consists of α-MgH2 (the majority phase) and FeTiH1.9. We envision these alloys becoming the material of choice for a variety of applications such as optical hydrogen sensing, switchable mirrors and solar absorbers.
5:00 PM - W5.7
Magnetic Switching Due to Absorption of Hydrogen in Co/Pd Multilayers with Perpendicular and In-plane Magnetic Anisotropies.
Kineshma Munbodh 1 , Samuel Ducatman 2 , Felio Perez 1 , David Lederman 1
1 Physics, West Virginia University, Morgantown, West Virginia, United States, 2 Physics, Grinnell College, Grinnell, Iowa, United States
Show AbstractCo/Pd multilayers with thin cobalt thickness (2-6 Å) have been fabricated by d. c. sputtering technique Al2O3 (110) in an argon atmosphere. The morphological and structural characterizations revealed smooth surfaces, layered structure and highly oriented growth in the [111] direction. The magnetic and electronic transport properties were measured in a hydrogen and helium atmospheres at room temperature using a vibrating sample magnetometer and a four-point technique with current-in-plane configuration, respectively. All samples exhibited significant changes on the magnetic and transport properties as a function of H2 absorption, however, a large diversity of behaviors and dependences with the external magnetic field were observed. These preliminary results show that these devices may be used as effective corrosion resistant hydrogen sensors and hydrogen storage devices.This work was supported by the U.S. Department of Energy.
5:15 PM - W5.8
Investigation of Carbon Supported Nanocrystalline Mg(Ni) for Hydrogen Storage.
Sankara Sarma Tatiparti 1 , Rene Bogerd 1 , Krijn de Jong 1 , Petra de Jongh 1
1 Inorganic Chemistry and Catalysis, Utrecht University, Utrecht Netherlands
Show AbstractMagnesium hydride (MgH2) is a potential hydrogen storage material with high gravimetric and volumetric capacities. However, its on-board vehicular application is hindered by slow sorption kinetics and high desorption temperature. These problems can be addressed by extensive ball-milling and the addition of dopants. Alternatively, we explore nanosizing magnesium by melt-infiltration of porous carbon supports and doping with nickel. Two different preparation methods were employed namely co-melt infiltration (CMI) and incipient wetness impregnation (IWI) of carbon with Ni followed by Mg melt infiltration. Structural and sorption characteristics were investigated using X-ray diffraction (XRD), electron microscopy, N2- physisorption, temperature programmed desorption (TPD), Extended X-Ray Absorption Fine Structure (EXAFS) and equilibrium sorption measurements.For MgH2 loadings up to ~ 15 wt% the addition of nickel resulted in crystallites of 10-30 nm size in the porous carbon. Different H2 desorption signatures were observed by varying nickel contents. For a composition of Mg0.77Ni0.23, the addition of Ni resulted in Mg2NiH4-like (150-250 °C) and MgH2-like (350-400 °C) behaviour during hydrogen desorption. In the case of IWI the contribution of hydrogen desorption from MgH2-like crystallites was much smaller than would be expected based on the stoichiometry. This was attributed to effective quenching of non-equilibrium magnesium and nickel compositions during melt infiltration. At higher MgH2 loadings of about 50 wt%, CMI resulted in bulk MgH2-like behaviour (> 400 °C) during hydrogen desorption. Surprisingly, in the case of IWI dehydrogenation behaviour between that of Mg2NiH4 and MgH2 was observed. This was attributed to excellent nanoscale mixing of Mg and Ni in case of IWI making it the preferred process at higher loadings.
5:30 PM - W5.9
On the Role of Defects and Catalyst Particles in Speeding Up The Reaction of Mg with H2.
Amelia Montone 1 , Annalisa Aurora 1 , Daniele Mirabile Gattia 1 , Marco Vittori Antisari 1
1 Department of Advanced Physical Technologies and New Materials , ENEA Research Center Casaccia, Rome Italy
Show AbstractThe dehydrogenation and hydrogenation reaction kinetics of MgH2 is widely studied owing to the potentiality of the hydride as reversible storage medium for hydrogen. Main promising results have been reached by intensive plastic deformation and catalyst introduction -generally performed by ball milling- that were able to overtake the classical reaction rate limiting steps. A metallographic approach together with kinetics analysis was used to provide sharp information on the role of localized features like catalyst particles and defects in the H2 sorption reaction.The spatial distribution of the different present phases can in fact provide important issues in the phase transformation like nucleation site, nucleation rate that are difficult to assess by indirect methods.A method based on Low Voltage Scanning Electron Microscopy (SEM) observation of cross sectional samples made of partially transformed material, constituted by a mixture of Mg and MgH2 has been developed. The different Secondary Electron (SE) yield displayed by the insulating MgH2 and by the metallic Mg in suitable SEM condition produces a clear artificial contrast between the two phases that allowed distinguishing the details of the microstructure, and in particular the distribution of the growing phases. At this purpose, three kind of materials have been studied, in order to understand the role of the catalyst and of defects in the MgH2↔Mg + H2 reaction: as received MgH2, 10h milled MgH2 and 10h milled MgH2 with 5wt% of Fe, acting as reaction accelerator. The samples have been subjected to partial phase transformation in both absorption and desorption so that they are constituted by a dispersion of about 10% of the transformed phase in the parent matrix.The metallographic analysis easily has shown the differences in term of mechanism of reaction between the absorption and desorption process. The nucleation of the new phase in absorption reaction (MgH2 in this case) occurs in the bulk for all three samples while the particle or agglomerate surface do not appear to have any particular role in the nucleation. The structural defects induce the precipitation of the forming MgH2 and an increasing of defect density simply reflects a higher nuclei density. When the catalyst particle is added, the identical microstructure is maintained so the catalyst behaves like a further structural defect. On the contrary, the decomposition of pure MgH2 starts at the sample surface and not at bulk defects while Fe catalyst specifically assists the nucleation in the bulk, as demonstrated by the systematic presence of Mg around the Fe particles.This kind of information, coupled with the classical kinetic analysis allowed a better understanding of the details of the phase transformation that can be so described even beyond the definition of the reaction rate limiting step.
5:45 PM - W5.10
Stresses and Hydride Formation Accompanying High Rates of Hydrogen Absorption into Aluminum During Dissolution.
Kurt Hebert 1 , Guiping Zhang 2 3 , Kai-Ming Ho 2 3 , Cai-Zhuang Zhang 2 3 , Gery Stafford 4
1 Chemical & Biological Engineering, Iowa State University, Ames, Iowa, United States, 2 Physics, Iowa State University, Ames, Iowa, United States, 3 , Ames Laboratory - USDOE, Ames, Iowa, United States, 4 Metallurgy Division, NIST, Gaithersburg, Maryland, United States
Show AbstractHydrogen charging during Al dissolution in alkaline solutions is accompanied by large rates of formation of aluminum hydride and voids, along with highly elevated H chemical potential near the metal surface [1,2]. This presentation reports progress in a combined experimental and modeling effort seeking to understand the dynamics of H absorption and formation of H-related defects in this system. Cantilever-deflection experiments, using Al thin films on borosilicate glass substrates, were carried out to characterize the evolution of near-surface stress during the initial stages of alkaline dissolution. Large rates of tensile deflection of ~ 5 N/m-s were observed during exposure to solutions at pH 12-13. The time dependence of the tensile shift correlated with the appearance of hydride, suggesting the hypothesis that vacancies incorporate in the hydride phase, as a consequence of the attractive interaction between vacancies and hydrogen [3]. We describe a mathematical model based on these observations, for the purpose of predicting stress and electrochemical potential transients. The model considers H diffusion due to stress and concentration gradients, formation of the vacancy-hydride phase, and stresses due to elastic and plastic deformation. In the model, much of the H formed during Al dissolution (3 H atoms per Al) enters the metal, and reacts to form the vacancy-hydride phase. The high efficiency of hydride formation effectively couples the dissolution rate of Al atoms to that of vacancy generation, so that a net tensile stress arises due to lattice contraction accompanying the vacancies. [1] S. Adhikari et al., J. Electrochem. Soc., 155, C16 (2008); [2] H. K. Birnbaum et al., J. Alloys Cmpd., 253, 260 (1997); [3] C. Wolverton et al., Phys. Rev. B, 69, 144109 (2004).
Symposium Organizers
Etsuo Akiba National Institute of Advanced Industrial Science and Technology
William Tumas National Renewable Energy Laboratory
Ping Chen National University of Singapore
Maximilian Fichtner Karlsruhe Institute of Technology
Shengbai Zhang Rensselaer Polytechnic Institute
W6: Complex Hydrides I
Session Chairs
Maximilian Fichtner
Sabrina Sartori
Wednesday AM, December 02, 2009
Back Bay D (Sheraton)
9:30 AM - **W6.1
Stability and Dynamics of Metal Borohydrides.
Shin-ichi Orimo 1
1 Institute for Materials Research, Tohoku University, Sendai Japan
Show AbstractDevelopment of hydrogen storage materials is a critical issue for hydrogen energy applications. Candidates for the materials are metal borohydrides, such as LiBH4, Mg(BH4)2, Ca(BH4)2, and Y(BH4)3; including their intermediate compounds [Appl. Phys. Lett., 87 (2006) 021920; Phys. Rev. B, 74 (2006) 075110; 77 (2008) 104114; Acta Mater., 56 (2008) 1342]. Also, the electrical conductivity of LiBH4 was reported to drastically increase by three orders of magnitude due to the structural transition [Appl. Phys. Lett., 91 (2007) 224103]. The hexagonal phase above 388 K exhibited a high electrical conductivity of the order of 10−3 Scm−1, “lithium super(fast)-ionic conduction”. The conduction can be the origin of the occurrence of the large conductive loss and also of the microwave-induced hydrogen desorption [Appl. Phys. Lett., 88 (2006) 112104; 90 (2007) 232907]. Just recently, the hexagonal, that is, lithium super(fast)-ionic conduction phase of LiBH4 was well stabilized even at room temperature [J. Am. Chem. Soc., 131 (2009) 894; Appl. Phys. Lett., 94 (2009) 084103; 94 (2009) 141912].
10:00 AM - W6.2
Hydrogen Storage Behavior of LiBH4/MgH2 Confined in Nanoporous Scaffolds.
John Vajo 1 , Adam Gross 1 , Shu Zhang 2 , Sky Skeith 1 , Ping Liu 1 , Craig Jensen 2
1 , HRL Laboratories, Malibu, California, United States, 2 Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii, United States
Show AbstractThe LiBH4/MgH2 destabilized hydrogen storage system has high hydrogen capacity (11.4 wt% and 95 g/l) and a moderate dehydrogenation enthalpy (ΔH = 41 kJ/mol-H2 with an equilibrium hydrogen pressure of 1 bar at ~225 °C). However, the rates of hydrogen exchange are much too slow for practical use, requiring temperatures of ~ 400 °C for dehydrogenation and ~300 °C for hydrogenation. High-energy mechanical milling and catalytic additives can improve the kinetics but, thus far, have lowered reaction temperatures by less than ~50 °C. Recently, nanoporous scaffolds have been considered as hosts for hydride materials in order to improve kinetics by reducing diffusion distances and increasing surface and interfacial areas. For LiBH4, an increase in the dehydrogenation rate by a factor of 60x (at 300 °C) was observed when the hydride was incorporated within a carbon aerogel scaffold with a peak in the pore size distribution at 13 nm. In the same scaffold, a dehydrogenation rate of 25 wt%/hr was observed for MgH2 (at 250 °C); this rate is comparable to the best kinetics for MgH2 that are obtained with catalytic additives.Currently, we have been investigating the incorporation and kinetics of the combined 2LiBH4 + MgH2 system in carbon aerogels. Using a carbon aerogel with 13 nm pores, incorporation was initially performed sequentially with LiBH4 (or MgH2) incorporated first, followed by MgH2 (or LiBH4). Lithium borohydride was incorporated directly from molten LiBH4 at ~290 °C. Magnesium hydride was formed within the pores by hydrogenating a solution of dibutyl magnesium (MgBu2) dissolved in heptane. However, the 2LiBH4 + MgH2 dehydrogenation reaction products and the cycling behavior suggested that when loaded sequentially, the LiBH4 and the MgH2 are not well mixed within the aerogel pores. These results have led us to attempt to incorporate both hydrides simultaneously by using a solvent, such as diethyl ether that dissolves both LiBH4 and MgBu2.In this presentation, we will describe our efforts to achieve incorporation of LiBH4 + 2MgH2 with the proper stoichiometry, with intimate mixing on small length scales, and without byproducts. We will also compare the kinetics in the aerogel to those of bulk samples.
10:15 AM - W6.3
Determination of the Phase Behavior of (LiNH2)c(LiBH4)1-c Quaternary Hydrides through in situ X-ray Diffraction.
Jonathan Singer 1 , Martin Meyer 2 , Richard Speer 3 , John Fischer 1 , Frederick Pinkerton 2
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Materials and Processes Laboratory, General Motors Research and Development Center, Warren, Michigan, United States, 3 Chemical and Environmental Sciences Laboratory, General Motors Research and Development Center, Warren, Michigan, United States
Show AbstractOne of the largest obstacles for automotive application of fuel cells is effective on-board hydrogen storage, which necessitates the development of a material with both high gravimetric and volumetric hydrogen capacity. Light metal hydrides, a promising group of materials, possess very high theoretical hydrogen capacities and operate at non-cryogenic temperatures; however, the dehydrogenation process often leaves hydrogen containing products, such as metal imides or lithium hydride, or releases other gas species, such as ammonia or diborane. In addition, light metal hydrides often decompose at temperatures much higher than the maximum operating temperatures of fuel cells. Recently, a material of nominal composition Li3BN2H8, formed by combining LiNH2 and LiBH4 in a 2:1 ratio, has garnered attention due to its high hydrogen release at relatively low temperatures (up to 11.9 wt% hydrogen on heating above ~200-250 °C) and its anticipated decomposition, releasing only hydrogen, into Li3BN2. While expected to exist in a single “Li3BN2H8” α-phase within a solubility region between the 2:1 and 3:1, it is shown that single-phase 2:1 Li3BN2H8 samples decompose with time into a combination of an α-phase composition enriched in LiNH2 compared to Li3BN2H8 and the 1:1 β-phase Li2BNH6. This motivated a more detailed examination of the equilibrium phase behavior of the α-phase by in situ X-ray diffraction (XRD) of samples from the (LiNH2)c(LiBH4)1-c system with c in the range 0.667-0.750 (corresponding to LiNH2:LiBH4 = 2:1 to 3:1). To best determine the equilibrium compositions, samples were prepared in two ways: either by high-energy ball-milling (HEBM) for 10 minutes (to produce well mixed LiNH2:LiBH4 samples) or HEBM for 300 minutes (to produce non-equilibrium milled α-phases). The complete equilibrium composition range of the α-phase at 50 °C is shown to be LiNH2:LiBH4 = ~2.62:1-2.83:1, or c=0.724-0.739. Based on higher temperature observations, it may be concluded that the α-phase forms peritectically from LiBH4 rich liquid and LiNH2 at ~220 °C. Utilizing these and previous observations, an approximate phase diagram in the composition range c=0.5-0.75 and temperature range T=0-250 °C was generated. Because samples that were previously thought to be 2:1 single α-phase had likely separated into a mixture of α and β-phase material, mixtures of phases with an overall composition of 2:1, but excluding the β-phase, were investigated to see whether the desirable hydrogen release could be achieved while avoiding the undesirable decomposition behavior of the β-phase. This was accomplished via a 1:1 mixture of a 3:1 milled sample and LiBH4.
10:45 AM - W6.5
In-situ Study of the Thermal Decomposition of 4 Using Raman Microscopy.
Daniel Reed 1 , David Book 1
1 Metallurgy and Materials, University of Birmingham, Birmingham, W. Midlands, United Kingdom
Show AbstractWith relatively high gravimetric and volumetric hydrogen storage capacities, borohydrides have attracted interest as potential hydrogen storage media. Lithium borohydride has a maximum theoretical gravimetric hydrogen storage density of 18.4 wt%, and has been shown to be reversible when heated to 600°C in 350 bar hydrogen1. It is hoped that a greater understanding of the decomposition and reformation mechanisms, may lead to the development of LiBH4-based materials that can absorb and desorb hydrogen under less extreme conditions. However, these studies have proved a challenge: currently most in-situ investigations have used x-ray diffraction or neutron diffraction however these cannot readily give information on non-crystalline or liquid phases. The preparation of samples measured ex-situ via XRD, NMR2 and Raman3 have shown the reaction products and stable intermediates during the thermal decomposition, however, it is very difficult to detect short lived intermediate (or byproduct) species. Raman spectroscopy has the advantages that: materials with only short-range order can be analysed; and by focusing the laser on regions in a sample the reaction path can be monitored with changing temperature with a rapid scan rate.After heating lithium borohydride through its phase change and melting point, shifts in peak position and peak width were observed, which agreed with other studies4. A sample was also heated to 500°C (under 1 bar Ar) to decompose the sample. A number of intermediates and reaction products have been predicted and observed ex situ. This work shows the in situ formation of lithium dodecaborane (Li2B12H12) and amorphous boron from liquid lithium borohydride. It is therefore possible to determine at what temperatures certain intermediates and products form. (1)Orima, S.; Nakamori, Y.; Kitahara, G.; Miwa, K.; Ohba, N.; Towata, S.; Zuttel, A. Journal Of Alloys And Compounds 2005, 404, 427-430.(2)Her, J. H.; Yousufuddin, M.; Zhou, W.; Jalisatgi, S. S.; Kulleck, J. G.; Zan, J. A.; Hwang, S. J.; Bowman, R. C.; Uclovict, T. J. Inorganic Chemistry 2008, 47, 9757-9759.(3)Miwa, K.; Ohba, N.; Towata, S.; Nakamori, Y.; Orimo, S. Phys. Rev. B 2004, 69.(4)Gomes, S.; Hagemann, H.; Yvon, K. Journal Of Alloys And Compounds 2002, 346, 206-210.
11:30 AM - W6.6
Nanoconfined LiBH4 Prepared by Melt Infiltration: Synthesis and H2 Sorption Properties.
P. Ngene 1 , P. Adelhelm 1 , K. de Jong 1 , P. de Jongh 1
1 Iorganic Chemistry and Catalysis, Utrecht University, Utrecht Netherlands
Show AbstractLiBH4 has attracted much attention as a potential H2 storage material due to its high H2 content. However, thermodynamics and kinetics of its H2 sorption must be improved before it can be used for automobile applications. Nanosizing, destabilization with other materials and the use of suitable catalysts are among the techniques being investigated to improve the sorption properties. We discuss the effects of nanoconfinement and the addition of suitable catalysts on the H2 sorption properties for the LiBH4/ordered mesoporous silica (SBA-15) and LiBH4 (Ni)/nanoporous carbon system. Ni nanoparticles were deposited onto the carbon by impregnation with an aqueous precursor solution followed by heat treatments, while the melt infiltration process was performed by mixing the required amounts of LiBH4 and the porous material and heating to 295 °C under 100 bar H2 in an autoclave. Structural and H2 sorption properties of the composites were preformed by N2 physisorption, TEM, XRD, SAXS, EXAFS, TPD and gravimetric sorption measurements.Nitrogen physisorption data of SBA-15 after melt infiltration with different amounts of LiBH4 shows a decrease in the pore volume. The total pore volume loss is proportional to LiBH4 loading and close to the volume of LiBH4 in the mixture. XRD did not show any crystalline lithium silicates. As also SAXS confirmed that the long range order of the SBA-15 mesopores was maintained after melt infiltration under H2 pressure, this proves that under H2 pressure, molten LiBH4 can fully fill the mesopores of SBA-15. However, upon melting the LiBH4 in the presence of SBA-15 under Ar, clearly reaction took place during melting, and the structure of the SBA-15 was destroyed. The nanoconfined LiBH4 had enhanced H2 sorption properties compared to the bulk, with desorption starting at 150 °C in the LiBH4 /SBA-15 composite. However upon dehydrogenation, lithium silicates were formed, limiting the reversibility. We therefore moved to nanoporous carbon as a support. In this case, especially in the presence of Ni, reversible H2 uptake at mild conditions of 20 bar and 250 °C was achieved.Our study shows that melt infiltration is an effective method for the preparation of nanoconfined LiBH4 in mesoporous SiO2 only if carried out under H2 pressure. This proves that there is no fast direct reaction between molten LiBH4 and SiO2. The confined LiBH4 has enhanced H2 sorption properties compared to the bulk, however the formation of lithium silicates during dehydrogenation limits the reversibility. In the case of nanoconfinement in carbon reversibility under mild conditions was achieved, especially after addition of Ni.
11:45 AM - W6.7
Reversible Borohydride for Hydrogen Storage.
Pabitra Choudhury 1 2 , Venkat Bhethanabotla 1 2 , Elias Stefanakos 2
1 Chemical and Biomedical Engineering, University of South Florida, Tampa, Florida, United States, 2 Clean Energy Research Center, College of Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractMaterials that are light weight, low cost and have high hydrogen storage capacity are essential for on-board vehicular applications. Some reversible complex hydrides are alanates and amides but they have lower capacity than the DOE 2010 target. High capacity, light weight, reversibility and fast kinetics at lower temperature are the primary desirable aspects for any type of hydrogen storage material. Borohydride complexes as hydrogen storage materials have recently attracted great interest. Understanding the above parameters for designing efficient complex borohydride materials requires modeling across different length and time scales. A direct method lattice dynamics approach using ab initio force constants is utilized to calculate the phonon dispersion curves. This allows us to establish stability of the crystal structure at finite temperatures. In this study, a density functional theory study with the gradient generalized approximation (GGA) and augmented plane wave method (PAW) is performed to find the hydrogen storage properties for the reversible complex borohydride material (LiNH2)2 - LiBH4 - (MgH2) system. Using combined ab initio and lattice dynamics methods, the structural stability of the reactants and products in the reaction steps are confirmed and thermodynamic properties such as enthalpy of reactions and Gibbs energy are calculated of these dehydrogenation reactions. To apply the above formalism to the above system, we begin by identifying reactants and products with known crystal structures that have Li, Mg, B, N and H as their constituents. These compounds are listed in Table 1. These will be compared with the experimental results and validated the theoretically predicted dehydrogenation reactions. Hydrogen storage capacity predicted for this complex borohydride will also be presented from the de-sorption behavior observed at different temperatures.
12:00 PM - W6.8
Reversible Hydrogen Storage with Magnesium Borohydride.
Godwin Severa 1 , Craig Jensen 1 , Ewa Ronnebro 2
1 Chemistry, University of Hawaii, Honolulu, Hawaii, United States, 2 Metal hydride center of excellency, Sandia National labs, Livermore, California, United States
Show AbstractThe development of high capacity, reversible hydrogen storage materials is a key barrier to the realization of a hydrogen economy. Mg(BH4)2 has 14.8 wt % H2 capacity and undergoes stepwise dehydrogenation to give MgB2 as seen in equations 1-3. Thermodynamic calculations indicate that it should be 6 Mg(BH4)2 → 5 MgH2 + MgB12H12 + 13 H2 (1)5 MgH2 + MgB12H12 → 5 Mg + 5 H2 + MgB12H12 (2)5 Mg + MgB12H12 → 6 MgB2 + 6 H2 (3)possible to hydrogenate MgB2 to Mg(BH4)2 at moderate temperatures and pressures. However no full recycling has been accomplished experimentally and only the reverse of the processes in equation 2 have been achieved. This has been attributed to the high kinetic stabilization of MgB12H12. Thus it was of interest to explore whether the re-hydrogenation process can be achieved at high pressures and to explore cycling pathways avoiding MgB12H12. We have found that ball-milled mixtures of MgB2 with catalytic additives can be hydrogenated at 350-400 degrees celcius and 700-950 atm. Analysis of the product mixture by XRD showed the product of the hydrogenation to be Mg(BH4)2. We also confirmed the identity of the product by magic angle spinning (MAS) 11B NMR spectroscopy. Only a very minor signal is observed for MgB12H12, in the 11B NMR indicating that it represents <5 % of the product mixture. Thermolysis of the product gives >12 wt % H2 indicating >85 % conversion to Mg(BH4)2. We have also found that hydrogenation also occurs under a much lower hydrogen pressure of 120 atm but significantly lower yields of Mg(BH4)2 are obtained. Results of these studies and their mechanistic implications will be presented.
12:15 PM - W6.9
Sorption Properties of the NaBH4/MgH2 System: Dehydrogenation Mechanism and Pathway.
Sebastiano Garroni 1 , Enric Menendez 2 , Alberto Lopez Ortega 3 , Marta Estrader 3 , Chiara Milanese 5 , Pau Nolis 4 , Josep Nogues 3 , Santiago Surinach 1 , María Dolores Baro 1
1 Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain, 2 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Dresden Germany, 3 , Centre d’Investigació en Nanociència i Nanotecnologia (ICN-CSIC), Bellaterra, Barcelona, Spain, 5 C.S.G.I., Dipartimento di Chimica Fisica "M. Rolla", Università di Pavia, Pavia Italy, 4 Servei de Ressonància Magnètica Nuclear (SeRMN), Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
Show AbstractNanostructured NaBH4/MgH2 composites have established themselves as promising materials for hydrogen storage applications due to their high gravimetric capacity, large hydrogen volumetric density and rather low dehydrogenation temperature compared to that one corresponding to the single compounds. Actually, further research on the NaBH4/MgH2 system could lead to an enhanced understanding of more complex reactive hydride composites, such as Ca(BH4)2/MgH2 or LiBH4/MgH2. As-received NaBH4 and MgH2 powders were mixed, in a 2 to 1 molar ratio (2NaBH4/MgH2), and ball-milled to obtain nanostructured composites. The milling processes were carried out for diverse times, under Ar atmosphere, in a Spex mill with a ball-to-powder mass ratio of 10:1. In-situ synchrotron X-ray powder diffraction indicates that the dehydrogenation process starts at around 320 C, with the desorption of the MgH2 to Mg, and proceeds with the chemical dismutation of NaBH4 in NaH and a possible intermediate specie, such as Na2B12H12 [1]. In fact, solid-NMR seems to confirm the existence of this transitional compound. However, the temperature onset of the dehydrogenation process of the NaBH4 counterpart has not yet been fully elucidated and, since it is difficult to establish from either X-ray diffraction or thermogravimetric analysis, magnetic characterization is proposed as an alternative technique, which takes advantage of the superconducting nature of the MgB2 phase, to further study dehydrogenation processes. Furthermore, the influence of diverse additives, such as TiCl4, VCl3, Mg(OH)2, NaBF4 or MgF2, on the storage properties of NaBH4/MgH2 composites were also investigated. The thermal desorption profiles clearly evidence a two-step process, the first corresponding to the dissociation of MgH2 and the second to the gradual dehydrogenation of NaBH4. Interestingly, all the mixtures release an overall amount of H2 close to that one expected to the full dissociation of the systems, which is indeed much higher than the target value required by the US Department of Energy [2]. In order to check the reversibility behavior of the specimens, absorption tests were also performed, confirming that complete absorption was not achieved in any mixture. Moreover, X-ray powder diffraction evidences the formation of perovskite-type hydrides, such as NaMgH3, and the presence of small amounts of free Mg during absorption. Finally, it should be noted that MgF2 plays a significant catalytic role in the sorption properties, leading to the mixture with fastest kinetics. [1] S. Garroni et al. Hydrogen desorption mechanism of 2NaBH4 + MgH2 compositeprepared by high-energy ball milling. Scr. Mater. 60, 1129–1132 (2009)[2] http://www.sc.doe.gov/bes/hydrogen.pdf
12:30 PM - W6.10
Effect of Transition Metal Fluorides on Ca(BH4)2 Sorption Properties.
Christian Bonatto Minella 1 , Gagik Barkhordarian 1 , Ulrike Boesenberg 1 , Rapee Gosalawit 1 , Claudio Pistidda 1 , Carine Rongeat 2 , Oliver Gutfleisch 2 , Martin Dornheim 1 , Ruediger Bormann 1 , Torben R. Jensen 3 , Yngve Cerenius 4 , Magnus Sorby 5 , Bjorn C. Hauback 5
1 Nanotechnology, GKSS Research Center Geesthacht, Geesthacht Germany, 2 , IFW, Dresden Germany, 3 Department of Chemistry, University of Aarhus, Aarhus Denmark, 4 MAX-lab, Lund University, Lund Sweden, 5 Physics Department, Institute for Energy Technology, Kjeller Norway
Show AbstractCa(BH4)2 is one of the most interesting hydrogen storage material because its high gravimetric (11.5 wt%) and volumetric (~130 kg m-3) hydrogen density [1]. Its good thermodynamic and decomposition temperature, that is lower than LiBH4, makes it promising for mobile applications.Some transition metal fluorides and chlorides have shown to positively affect the partial reversible formation of Ca(BH4)2 [2] and shift to lower temperatures the hydrogen desorption steps. In this work a scanning of the effect of several selected Transition Metal fluorides on Ca(BH4)2 is investigated, in order to improve its sorption kinetics and to achieve a full reversible system. Ca(BH4)2 was obtained drying the Ca(BH4)2-2THF adduct at 200°C in vacuum. Five different samples were prepared milling Ca(BH4)2 with 0.05 mol of TiF3, TiF4, VF3, VF4, NbF5. Volumetric measurements, calorimetric analysis, X-ray diffraction and infrared spectroscopy were used to characterize the specimens. Samples were desorbed in static vacuum heating from room temperature to 450°C and the desorbed powders were afterwards absorbed at 350°C and 145 bar for 18 hours. Only the samples milled with TiF4 and NbF5 led to a partial reversible formation of Ca(BH4)2. In-situ X-ray diffraction was used to observe the reaction pathway for the specimens with TiF4 and NbF5 in order to understand the reaction mechanism. Both the experiments were carried out in dynamic vacuum, heating from room temperature to 450°C and then cooling down. The starting material is composed by different abundance of α-Ca(BH4)2, β-Ca(BH4)2 and CaF2, formed after milling. After the polymorphic transformation from α to β at 160°C, the β-Ca(BH4)2 decomposes to a likely Ca-B-F-H phase not yet indexed. This phase transforms, around 400 °C, to CaF2-xHx phase [3], likely confirmed by the rise of the 200 reflection. At this temperature other two peaks show up and they could belong to a TM non stoichiometric hydride likely responsible of the reversibility. It has been shown for MgH2 with transition metals fluorides additives the formation of a TM-hydride layer that helps the reversibility and the kinetics [4]. The ICSD database does not help in finding the correct phases and furthermore there could be an exchange between fluorine and hydrogen which leads to the formation of new phases.This work shows the positive effect of TiF4 and NbF5 in reversible formation of Ca(BH4)2, even though partial, and describe the decomposition reaction by means of in-situ X-ray diffraction never done so far up to our knowledge.
12:45 PM - W6.11
On the Reversibility of Hydrogen-storage Reactions in Ca(BH4)2: Characterization via Experiment and Theory.
Lin-Lin Wang 1 , Dennis Graham 1 , Ian Robertson 1 , Duane Johnson 1
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractWith 11.6-wt% H2, Ca(BH4)2 is a promising hydrogen-storage candidate material provided the issue of reversibility can be addressed. We investigate theoretically and experimentally the structure and reversibility of Ca(BH4)2 in (de)hydrogenation reactions, including an intermediate CaB12H12 phase. Our first-principles calculations predict several polymorphs of CaB12H12 that compete in energy (<100 meV/CaB12H12 or 1 kJ/mol-H2 in dehydrogenation reaction), making an amorphous intermediate material likely. Our experimental microchemical analysis and structural characterization of the dehydrogenated Ca(BH4)2 show that the intermediate phase is indeed amorphous-like with a broad peak around the expected Ca-Ca signal. The calculated reaction formation enthalpies versus H-content reveal limited reversibility, as CaB12H12 is energetically very favorable. Our results suggest the (de)hydrogenation process via CaB12H12 intermediates is reversible, but, due to its stability, full release of H2 between Ca(BH4)2 and CaB6 is not possible except at high temperature and pressure. Thus, Ca(BH4)2 has limited viability as a reversible on-board storage material for vehicular applications.
W7: Complex Hydrides II
Session Chairs
Eric Majzoub
Shin-ichi Orimo
Wednesday PM, December 02, 2009
Back Bay D (Sheraton)
2:30 PM - **W7.1
Carbon Nanomaterials as Catalyst for Hydrogen Uptake and Release in Complex Hydrides.
Ragaiy Zidan 1 , Matthew Wellons 1 , Polly Berseth 1 , Puru Jena 2
1 Energy Security Directorate, Savannah River National Laboratory, Aiken, South Carolina, United States, 2 , Virginia Commonwealth University, Richmond, Virginia, United States
Show AbstractCarbon nanomaterials have been commonly associated with use as storage materials. A novel view is formulated; the employment of carbonaceous nanomaterials as catalysts for hydrogen uptake and release. A synergistic approach involving experiment and first-principles theory was taken and not only shows that carbon nanostructures can be used as catalysts for hydrogen uptake and release in complex metal hydrides such as NaAlH4 and LiBH4, but also provides an unambiguous understanding of how the catalysts work. Experimental work shows carbon nanostructure-catalyzed hydrogen uptake and release for sodium alanate (NaAlH4) and lithium borohydride (LiBH4). A survey of carbon material (fullerene, carbon nanotubes, and graphene) NaAlH4 nanocomposites demonstrated varying degrees of catalytic activity. Partial reversibility of hydrogen was observed for NaAlH4 and LiBH4. Computation simulations showed that the underlying mechanism relies on the electronegativity of the carbon-based nanomaterials which exerts a destabilizing effect on complex metal hydride systems by withdrawing electrons. The thus generated electron-deficient environment weakens the chemical bonds of hydrogen (e.g., the Al-H bond in NaAlH4). Based on our experimental observations and theoretical calculations it appears the curvature of the carbon nanostructure plays a role in the catalytic process.
3:00 PM - W7.2
Nanosized Hydrides Infiltrated in Carbon Scaffolds.
Sabrina Sartori 1 , Kenneth Knudsen 1 , Zhirong Zhao-Karger 2 , Maximilian Fichtner 2 , Bjorn Hauback 1
1 , Institute for Energy Technology, Kjeller Norway, 2 , Institute of Nanotechnology, KIT , Karlsruhe Germany
Show AbstractOne of the main challenges for the introduction of a hydrogen-based economy is storage of hydrogen. Hydrogen storage in solid materials is considered among the most attractive methods. During the last years much emphasis has been placed on the synthesis of nanosized metals and alloys. The massive changes in surface to volume ratio occurring at nanoscale dimensions, combined with quantum confinement, lead to physical properties that differ substantially from typical bulk behaviour [1,2]. In the field of H-storage in metal hydrides, the rationale behind such “nanoengineering” approaches is based not only on kinetic enhancement by increasing the hydrogen diffusivity and reducing the diffusion distance, but also on the fact that the increase of surface energy (when the particle size is reduced) may result in a change in the thermodynamics. It has recently been reported that nano-crystalline metal and metal-hydrogen alloys with grain sizes less than 20 nm possess many properties that differ from those of conventional coarse-grained materials [3-5]. So far, no evidence has been shown that complex hydrides infiltrated in microporous carbon are indeed nanodispersed. In this contest, small-angle neutron scattering (SANS) performed at the JEEP II reactor at IFE and small angle X-ray scattering (SAXS) performed at ESRF, Grenoble, are useful tools to extract information about the distribution of hydrogen-containing structures, in particular the size-range distribution. In this work carbon nanostructures were used to host and “shield” against agglomeration high H-capacity complex metal hydride nanoparticles. Carbon nanofibers (CNF) and activated carbons (AC) were among the porous carbon chosen to host the hydrides. The infiltration method has been proved successful in modifying the size of the hydride particles, as confirmed by scanning electron microscopy and X-ray diffraction data. The size of the particles for the infiltrated samples has been estimated by SANS measurements to be mainly in the range < 4 nm. The results suggest that the smallest pores of the scaffold are partially or fully filled and that this type of scaffold acts as an effective dispersing agent for the metal hydrides. [1] T. Tsuzuki, P.G. McCormick, Mechanochemical synthesis of nanoparticles, J. Mater. Sci. 39, 5143-5146 (2004).[2] M. Fichtner, Nanotechnology 20, 204009 (2009).[3] J. J. Vajo and G. L. Olson, Scr. Mater. 56, 829 (2007).[4] J. J. Vajo, T. T. Salguero, A. F. Gross, S. L. Skeith, and G. L. Olson, J. Alloys Compd. 446-447, 409 (2007).[5] M. Fichtner, Z. Zhao-Karger, J. Hu, A. Roth, and P. Weidler, Nanotechnology 20, 204029 (2009).
3:15 PM - W7.3
The Importance of the Surface Chemistry and Pore Size Distribution of Carbon Scaffolds on the Hydrogen Sorption Kinetics of Infiltrated LiBH4.
Adam Gross 1 , Theodore Baumann 2 , Ping Liu 1 , John Vajo 1
1 , HRL Laboratories, LLC, Malibu, California, United States, 2 Chemistry & Materials Science Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractFabricating nanoscale hydrogen storage materials is desirable because the small length scales and high surface areas provide a means to potentially overcome the slow hydrogen dissociation and diffusion rates that limit sorption kinetics in many bulk metal hydrides. A porous host may act as a template for nanoscale metal hydrides where the pore structure determines the length scale of the hydrides and the pore walls prevent sintering upon hydrogen cycling. We and other groups have filled porous carbon materials with metal hydrides and observed enhanced kinetics, although the kinetics can vary significantly with the template. We will present the hydrogen sorption behavior of several porous carbon materials filled with LiBH4 and correlate pore morphology with kinetics. Carbons aerogels and mesoporous carbon were fabricated with a range of pore sizes, different pore distributions, and inverse cast or directly synthesized structures and used as templates for nanostructured hydrides. These templates were then filled with LiBH4 by wicking from a melt. There is a well known trend of smaller pore sizes resulting in faster kinetics; however, we find significant differences in the dehydrogenation rates of hydrides incorporated in different carbon structures with similar pore dimensions. For example, the dehydrogenation rate of LiBH4 at 300 °C was 2x faster in a aerogel with a peak in the pore size distribution at 5 nm containing ~25% pore volume micropores (<2 nm) than in a similar aerogel containing <5% pore volume micropores. This kinetic disparity may be caused by the presence of micropores or by differences in surface chemistry between the two aerogels. Furthermore, we observe significantly faster dehydrogenation in reverse cast mesoporous carbon as compared to hexagonal mesoporous carbon, which may result from greater connectivity between pores in the inverse structure. We will also present kinetic differences observed when surface chemistry was modified by pyrolysis temperature and chemical treatments. The goal of our work is to identify and understand chemical variables of porous carbon materials that are important in optimizing hydrogen exchange kinetics.
3:30 PM - W7.4
Thermodynamics of Nano-cluster Complex Hydrides Using First-principles Density Functional Theory.
Eric Majzoub 1 , Vidvuds Ozolins 2 , Fei Zhao 2
1 Physics, University of Missouri, St. Louis, St. Louis, Missouri, United States, 2 Materials Science and Engineering, University of California, Los Angeles, California, United States
Show AbstractThe equilibrium plateau pressure of a metal hydride compound at a given temperature is a characteristic thermodynamic quantity, and determines the application and engineering required for a hydrogen storage system. While recent interest has focused on complex metal hydrides such as NaAlH4 and Ca(BH4)2, these compounds are not as easily tunable (as are the interstitial metallic hydrides) through alloying with other metal atoms due to the strongly ionic character of the cohesive energy. However, the complex hydrides are superior on a wt.% hydrogen basis, and are the preferred materials for vehicular transport. In order to address thermodynamic tunability, we investigate these materials at the nano-scale, where the ratio of surface to bulk atoms impacts the energetics. Recent theoretical work by Wagemans et al. [1] and others indicate that small clusters of MgH2, for example, can significantly lower the desorption enthalpy with respect to bulk. Small metal or hydride clusters may be incorporated into nanoporous frameworks such as block polymer templates, for example, to prevent agglomeration and perhaps even improve tunability through particle/surface interactions. We present theoretical results for desorption energetics of small nano-clusters of NaAlH4, and Ca(BH4)2. Prototype geometries for the clusters were generated using a well-validated electrostatic ground state approach to a global optimization of the total energy using a recently developed non-conventional Monte Carlo random walk in energy space. First-principles density functional theory applied to the prototype clusters was used for full free energy calculations of the clusters and decomposition products. [1] J. Am. Chem. Soc., 127, 16675, 2005.
3:45 PM - W7.5
Thermal Studies of Alkali-transition Metal Borohydrides.
Godwin Severa 2 , Sesha Srinivasan 1 , Yogi Goswami 1 , Elias Stefanakos 1 , Craig Jensen 2
2 Department of Chemistry, University of Hawaii, Honolulu, Hawaii, United States, 1 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States
Show AbstractIn this paper, we report the thermal studies pertaining to hydrogen decomposition from solid state alkali-transition metal borohydrides. Some of the borohydride families such as NaMn(BH4)3, LiMn(BH4)3 and LiSc(BH4)4 which are synthesized using single step approach employing mechano-chemical milling. The thermo-gravimetric analysis of these systems show a mass reduction (weight loss ~ 8-12 wt.%) due to hydrogen decomposition at low temperatures of 80-120 oC. The occurrence of endothermic transition at these decomposition temperatures confirms the dehydrogenation process. We have found the enthalpy of hydrogen decomposition (ΔH) which is fairly close to the theoretical predictions. In addition, the thermal programmed desorption (TPD) of these alkali-transition metal borohydrides indicate the thermal conductivity signal changes due to hydrogen decomposition process which compliments the DSC and TGA observations.Keywords: Complex Hydrides, Hydrogen Storage, Thermogravimetric Analysis, Temperature Programmed Desorption, Differential Scanning Calorimetry
4:30 PM - W7.6
Synthesis and Characterization of Novel Double-Cation Borohydrides.
Stefano Deledda 1 , Nadir Aliouane 1 , Jon Fonnelop 1 , Christoph Frommen 1 , Isabel Llamas-Jansa 1 , Klaus Lieutenant 1 , Sabrina Sartori 1 , Heidi Ostby 1 , Magnus Sorby 1 , Bjorn Hauback 1
1 Physics Departement, Institute for Energy Technology, Kjeller Norway
Show AbstractDue to the high gravimetric and volumetric hydrogen densities, metal borohydrides M(BH4)n are among the most attractive candidates for hydrogen storage materials and have been the subject of an extensive R&D effort in the scientific community. It has been shown that the thermodynamic stability is directly related to the charge transfer from the cation Mn+ and that there exists a linear relation between the temperature of desorption Td and Pauling electronegativity χP of M [1], the higher χP, the lower Td. It was also shown that the desorption temperature of double-cation borohydrides MM′(BH4)n is correlated to the averaged value of χP for the two cations. This has been proven to be useful for tailoring the properties of borohydrides containing cations with high and low χP, respectively, and tuning Td to values suitable for hydrogen storage applications [2,3].This contribution focuses on IFE’s current research activities on the synthesis and characterization of double-cation borohydrides MM′(BH4)n (M = Li, Na; M′= 3d or 4d transition metals, e.g. V, Ti, Cr, Co, Ni, Zn, Y, Nb, Rh, Cd). A systematic series of screening experiments aimed at synthesizing MM′(BH4)n by ball milling techniques and according to the mechanochemical reaction m M(BH4) + M′Cln → Mm-nM′(BH4)m + n MCl. Ball milling was carried out at ambient and cryogenic temperatures and the structural properties were investigated by Powder X-ray Diffraction, Powder Neutron Diffraction, in-situ Synchrotron Powder X-ray Diffraction. Raman spectroscopy was also employed for the characterization of highly disordered or amorphous systems. The thermal stability of the as-milled systems was investigated by Differential Scanning Calorimetry and Temperature Programmed Desorption.It will be shown that, due to the complexity of the systems, the synthesis of double-cation borohydrides is challenging and not always straightforward. For instance, ball milling of VCl3 + LiBH4 proceeds with evolution of gas(es) and results in a mixture of LiCl and an unidentified amorphous phase. In contrast, ball milling of LiBH4 with YCl3 leads to the formation of a crystalline Li-Y borohydride. The latter undergoes a structural phase transition upon annealing below 450 K in 100 bar H2. Upon heating, the Li-Y borohydride decomposes in several steps at temperatures between 475 and 600 K. References.[1] Y. Nakamori, K. Miwa, A. Ninomiya, H. Li, N. Ohba, S. Towata, A. Züttel, and S. Orimo, Phys. Rev. B 74 (2006) 45126.[2] H.-W. Li, S. Orimo, Y. Nakamori, K. Miwa, N. Ohba, S. Towata, and A. Züttel, J. Alloys Comp. 446-447 (2007) 315.[3] H. Hagemann, M. Longhini, J.W. Kaminski, T.A. Wesolowski, R. Černý, N. Penin, M.H. Sørby, B.C. Hauback, G. Severa, and C.M. Jensen, J. Phys. Chem. A 112 (2008) 7551.
4:45 PM - W7.7
Structure and Stability of Multivalent Metal Tetraborohydrides.
Zbigniew Lodziana 1 , Andreas Zuttel 1
1 , EMPA, Dubendorf Switzerland
Show AbstractThe tetrahydroborates, also called borohydrides or in short boranates, are compounds containing metal cations and BH4 groups. In general the number of BH4 groups per metal atom reflects the valency of the cation. Recently the borohydrides are studied intensively because of their high gravimetric hydrogen content, which makes them potential hydrogen storage materials.Borohydrides of univalent and divalent cations form ionic solids, and numerous crystalline phases and variety of their physicochemical properties are well known and understood at low temperatures. Structural and thermodynamic properties of complex hydrides with tri- or tetravalent cations are relatively less known, even though these compounds were intensively studied in their gas/molecular phases in the past.We report theoretical studies, based on density functional theory, of the structure and stability of borohydrides with trivalent (Sc, Y, Ti) and tetravalent (Ti, Zr) metals. Depending on the ionic radii, some compounds form molecular crystals consisting of stoichiometric units (Al(BH4)3, Zr(BH4)4) which are bonded together via weak Van der Waals forces to form crystalline structure. Compounds of scandium or yttrium on the other hand form ionic structures, similarly to borohydrides of mono- and divalent metals. The charge transfer toward BH4 group ranges from 0.75e for Al(BH4)3 to 0.52e for Zr(BH4)4. Covalent contribution to molecular bonding is analyzed and related to the orientation of borohydride groups.We show that compounds containing Al, Sc Ti and Zr are thermodynamically unstable at ambient conditions with respect to decomposition to metal hydride, hydrogen and boron, however if the main decomposition products consist of BxHy groups this compounds are kinetically stable at favorable temperatures below 500K.Consequences of the crystalline structure and inter-atomic bonding for synthesis of novel borohydrides containing mixed metal cations are discussed.
5:00 PM - W7.8
In-situ Raman Study of Complex Hydride Powders.
Jason Hattrick-Simpers 1 , Chun Chiu 1 , Michael Niemann 3 , James Maslar 2 , Sesha Srinivasan 3 , Yogi Goswami 3 , Elias Stefanakos 3 , Leonid Bendersky 1
1 Materials Science and Engineering Lab, National Institute of Standards and Technology, Gaithersbug, Maryland, United States, 3 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States, 2 Chemical Science & Technology Laboratory, National Institute of Standards and Technology, Gaithersbug, Maryland, United States
Show AbstractDirect measurements of the structure of many complex hydrides during their hydrogenation/dehydrogenation processes is hindered by the poor X-ray scattering efficiency of the light elements Li, B, N, and H that are often the primary constituents. Raman spectroscopy, however, is a measure of the local ordering of a material and is generally quite sensitive to vibrations of the B-H and N-H variety. Here we will demonstrate direct observation and evolution of the Raman modes of an assortment of complex hydrides, such as LiBH4, Mg(BH4)2, and a novel nanoscale Li-Mg-B-N-H powder during hydrogen loading and desorption in a high-pressure high-temperature optical cell. We will discuss a proposed de-hydrogenation pathway in the Li-Mg-B-N-H powder, as well as show the presence of a previously unreported reversible high-temperature phase transformation. Approximations of the kinetic curves determined by monitoring the N-H bands during desorption/absorption cycles will be compared with traditional kinetic measurements as determined by a Sieverts apparatus.
5:15 PM - W7.9
Molecular Vibrations as the Origin of Solid State Effects in Borohydrides.
Andreas Borgschulte 1 , Robin Gremaud 1 , Andreas Zuettel 1 , Timmy Ramirez-Cuesta 2
1 Laboratory 138 Hydrogen & Energy, Empa Switzerland, Duebendorf Switzerland, 2 ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot United Kingdom
Show AbstractThe understanding of the hydrogen dynamics is one of the most exciting challenges in the research on metal-hydrogen systems; its knowledge is a starting point to describe phenomena like optical,electronic and transport properties and mechanisms, and thermodynamics. In (d-metal) metallic hydrides, these phenomena can be satisfyingly approximated within one-electron pictures [1]. Accordingly, the electronic structure changes are similar to those caused by alloying of two metals, and the vibrational properties of e.g. PdD_(0.63) are a text book example of phonon dispersions of lattice vibrations in a binary compound [2]. However, in alkali and alkaline earth borohydrides M(BH4)n, the pseudo-molecule BH4 is ionically bound to the ionized alkali- or alkaline earth atom. phonons in these can be well approximated by so-called 'internal' and 'external' vibrations, where 'internal' refers to the characteristic vibrations of the BH4 ion, and 'external' refers to the vibrational properties of the whole crystal structure. Accordingly, the labelling of the internal vibrations is based on the vibrational modes of a free BH4 tetrahedral molecule, as the effect of the crystal field is small. Due to the preferred local bonding, vibrational effects can change significantly on different time- and length scales. This has consequences on the dynamics of borohydrides in first instance, e.g. coupling between modes, but affects the kinetic and thermodynamical properties of these compounds as well. We will demonstrate these effects on the diffusional properties of LiBH4, and the impact of anharmonicities and coupling of the vibrational modes on the entropy of Ca(BH4)2.Three complementary techniques of vibrational spectroscopy, i.e. inelastic neutron scattering (INS), Raman scattering and infrared spectroscopy are used to characterize phonons in the tetrahydroborates LiBH4 and Ca(BH4)2 [3,4]. The use of labelled compounds enables us to assign modes and to follow changes due to diffusion processes and phase transformations. [1] L. Schlapbach, F. Meli, and A. Z{\"u}ttel, in Intermetallic Compounds, Principles & Practice, (Eds.: J. H. Westbrook and R. L. Fleischer) John Wiley & Sons Ltd., Chichester 1994.[2] J. M. Rowe, J. J. Rush, H. G. Smith, M. Mostoller, H. E. Flotow, Phys. Rev. Lett. 33, 1927 (1974).[3] F. Buchter, Z. Lodziana, Ph. Mauron, A. Remhof, O. Friedrichs, A. Borgschulte, A. Züttel, D. Sheptyakov, Th. Strässle, and A. J. Ramirez-Cuesta, Phys. Rev. B 78, 094302 (2008).[4] A.-M. Racu, J. Schoenes, Z. Lodziana, A. Borgschulte, and A. Züttel, J. Phys. Chem. A 2008, 112, 9716.
5:30 PM - W7.10
Investigation of Interaction of Hydrogen with Defects in Zirconia.
Oksana Melikhova 1 , Jan Kuriplach 1 , Jakub Cizek 1 , Ivan Prochazka 1 , Gerhard Brauer 2 , Wolfgang Anwand 3
1 Low Temperature Physics, Charles University, Prague Czechia, 2 Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, Dresden Germany, 3 Institut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, Dresden Germany
Show AbstractZirconia-based materials are promising for many practical applications, including heat-resistance structural and functional ceramics, solid oxide fuel cells, oxygen sensors, as well as applications in nuclear fuel and waste confinement. In such applications, it is often necessary to employ the cubic zirconia phase that can be stabilized at ambient temperature by adding yttria. Due to such doping, a large amount of point defects is introduced in yttria stabilized zirconia (YSZ). But defects’ structure, behavior and overall role is yet far from being understood. Because the presence of hydrogen can hardly be avoided in any YSZ preparation technique, an interaction of hydrogen with point defects in zirconia should be taken into account in YSZ defect studies. Indeed, the recent nuclear reaction analyses confirm the presence of hydrogen in a wide range of zirconia based materials. In the present work, we concentrate on open volume defects that can be studied by means of positron annihilation techniques. In order to elucidate the nature of positron trapping sites observed experimentally in zirconia, the structural relaxations of several types of vacancy-like defects in zirconia were performed and positron characteristics for them were calculated. Relaxed atomic configurations of studied defects were obtained by means of an ab initio pseudopotential method within the supercell approach. Positron characteristics, like the positron lifetime and binding energy to defects, are calculated using self-consistent electron densities and potentials taken from ab initio calculations. Theoretical calculations indicated that neither the oxygen vacancies nor their neutral complexes with substitutional yttrium atoms are capable of positron trapping. On the other hand, the zirconium vacancies are deep positron traps and are most probably responsible for the saturated positron trapping observed in YSZ single crystals. However, the calculated positron lifetime for the zirconium vacancy is apparently longer than the experimental values corresponding to single-component spectra measured for several cubic YSZ single crystals with varying yttria content. On the basis of structure relaxations, we found that the zirconium vacancy – hydrogen complexes represent deep positron traps with the calculated lifetime close to the experimental one. In the zirconium vacancy – hydrogen complexes the hydrogen atom forms an O-H bond with one of the nearest neighbor oxygen atoms. The calculated bond length is close to 1 Å.
5:45 PM - W7.11
Neutron Scattering Characterization of Hydrogen Interaction with Pure and Metal Cluster Decorated Metal Oxides.
J. Larese 1 2 , Paige Landry 1 , Andrew Lupini 2 , Michael Felty 1
1 Chemistry, University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States
Show AbstractUnderstanding the physical properties of nm scale, metal-decorated metal oxides for use in energy related catalysis and nanotechnology is a prerequisite for designing materials with prescribed behavior. We report our recent activities related to the synthesis and characterization of metal oxides (MO) decorated with metal clusters. Composition controlled, MO powders with the general composition M1-x Rx O (where M, R = Mg and Zn) and various morphologies (cubes, rods, tetrapods) have been produced using a novel gas phase method. Metal clusters including Pd, Au and Cu have been deposited from solution or gas phase and subsequently reduced. The interaction of molecular hydrogen with the pure and decorated materials has been investigated using high-resolution adsorption isotherms and neutron scattering methods. We will discuss our recent findings and emphasize how the microscopic dynamics of adsorbed hydrogen is affected by the MO support and the presence of the metal cluster. We find that both the support and the presence of the metal cluster can dramatically impact the microscopic dynamics if the molecular hydrogen. Our presentation will underscore the significant promise these combined systems hold for use in providing basic knowledge concerning energy storage and conversion and ultimately for technological applications.This work was supported by U.S. DOE Basic Energy Science, with contract no. DE-AC05-00OR22725 with ORNL.
W8: Poster Session: Complex and Chemical Hydrides
Session Chairs
Ping Chen
Maximilian Fichtner
Thursday AM, December 03, 2009
Exhibit Hall D (Hynes)
9:00 PM - W8.1
The Application of Modeling to the Calculation of the P-C-Isotherms for Hydrogen Storage Materials.
Vasileios Tserolas 1 , Masahiko Katagiri 1 , Hidehiro Onodera 1 , Hiroshi Ogawa 2
1 , National Institute for Materials Science, Tsukuba Japan, 2 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractIt has been suggested that metal hydrides are the most promising materials for hydrogen storage, especially the lightweight metal alloy hydrides. Getting high hydrogen uptake is only a part of the problem. It will also be needed to obtain controlled hydrogen release under practical conditions of temperature and pressure, and rapid hydrogen filling of the storage medium by recycling. Recently, it has been emphasized that efficient hydrogen storage via the gas phase is also one of the key factors, enabling the future hydrogen economy, which will be based on the extensive use of hydrogen-driven fuel cells in a wide range of stationary and portable applications. The recent developments in the field of fuel cells and more particularly hydrogen storage under solid form have underlined the usefulness of the Pressure-Composition-Isotherms (PCIs). Such a curve will define the capacity of storing hydrogen for a given metal hydride as a function of the temperature and the pressure.For the calculation of PCIs by computer simulations, we first consider a lattice gas, statistical mechanics approach. By using the grand canonical partition function, we obtain a relation between the pressure of gaseous hydrogen and the number of hydrogen atoms in the metal. The average number of hydrogen atoms is simply given by a Fermi-Dirac like distribution function. In order to calculate site energies, the hydrogen-induced lattice expansion has to be taken into account. Increasing the hydrogen concentration makes all interstitial sites more favourable, for hydrogen and results in an infinite range attractive H-H interaction. Because of the long-range nature of interactions, the lattice expansion depends primarily on the total number of hydrogen atoms in the bulk. Moreover, the density functional method (DFT) can be used to estimate the site energies and the lattice expansion parameter for metal hydrides.The PCIs of various metal hydride materials have been simulated at different temperatures. The simulations demonstrate good agreement with the experimental data reported for these materials. As expected, the plateau pressure increases with increasing temperatures. It also becomes more difficult to insert hydrogen atoms at higher temperatures, which is generally accepted to occur. The intent of these calculations is to screen potential materials purely in terms of their reaction thermodynamics and storage capacity. These properties are useful for screening candidate materials that can have practical use.
9:00 PM - W8.10
Theoretical Analysis of the Hydrogen Storage Capacity of Single-walled Carbon Nanotubes.
Andre Muniz 1 , Dimitrios Maroudas 1
1 Department of Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractSingle-walled carbon nanotubes (SWCNTs) have been considered as hydrogen storage media. The exposure of SWCNTs to a hydrogen plasma leads to the chemisorption of atomic hydrogen onto their graphene walls. Experimental studies have reported storage capacities obtained by this process as high as 7 wt %, which corresponds to a H coverage of almost 100%, i.e., the theoretical maximum value. However, in many experiments, lower H storage capacities have been reported consistently and the reasons for these discrepancies are not clear. A fundamental understanding of the structural changes undergone by SWCNTs upon hydrogenation is required for the interpretation of these experimental results. Toward this end, in this presentation, we report results of a computational atomic-scale analysis of the effects of atomic hydrogen chemisorption on the structure and deformation of SWCNTs and SWCNT bundles. The analysis is based on classical molecular-dynamics (MD) and Monte Carlo (MC) simulations of structural and compositional relaxation, as well as targeted first-principles density functional theory (DFT) calculations that complement and validate the classical simulation results. We find that H chemisorption induces structural changes in SWCNTs associated with sp2-to-sp3 bonding transitions, which cause deformation and amorphization of the SWCNT graphene wall. A particularly important finding is the swelling of the nanotubes, consistent with experimental observations. The corresponding computed radial and axial strains depend on the H coverage and on the SWCNT diameter and chirality. There is a critical H coverage (typically >= 30%), beyond which the radial and axial SWCNT strains start increasing linearly with H coverage and sp3-hybridized C atoms prevail; at sub-critical coverages, the strain levels are negligible and sp2-hybridized C atoms dominate. When SWCNTs arranged in bundles are exposed to atomic hydrogen, the swelling of the individual SWCNTs causes a decrease in the inter-tube spacing within the bundle, which may hinder H diffusion through the interstitial space of the bundle. This mass-transfer limitation may cause the non-uniform hydrogenation of the SWCNTs throughout the bundle and, consequently, a decrease in the total amount of hydrogen that can be stored in the bundles. For this phenomenon, we present an analytical model, which is parameterized according to the atomic-scale computations of SWCNT swelling. The model provides estimates of the maximum tube wall coverage as a function of the bundle density and the properties of the individual nanotubes in the bundle. The model predictions are assessed by comparisons with large-scale MD/MC simulations of hydrogenation of SWCNT bundles.
9:00 PM - W8.11
Noble-Metal Doped Core Shell Materials as Efficient Hydrogen Spillover Catalysts for Carbon Based Substrates.
Amy Groves 1 , Kevin O'Neill 1 , Justin Bult 1 , Phillip Parilla 1 , Calvin Curtis 1 , Lin Simpson 1 , Thomas Gennett 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractHydrogen spillover arises in hydrogen-catalyzed reactions on substrate supported metal catalysts. In the process hydrogen molecules dissociate on the metal catalyst and while some hydrogen atoms remain attached to the metal, others diffuse to the support and are said to spillover. Hydrogen spillover has been shown to be an important process in both sorption and heterogeneous catalysis. This work has centered on the use of core shell noble metal spillover catalysts attached to high surface area activated carbon, boron-doped carbon templated materials and carboranes. The core shell complexes of Pt, Ni/Pd and Ru were synthesized via a previously published microemulsion process. Finally, through a series of physio-chemical processes the core-shell spillover catalysts were attached to the surface of the various carbon-boron substrates. The characterization (TEM) of noble – metal core – ceria shell nanoparticles intimately dispersed upon various substrates indicate the use of a CTAB – toluene reverse micelle solution phase process led to the most uniform coatings on the substrate surfaces. Typically, the isolated core–shell nanoparticles were on the order of 2 – 4 nanometers. The hydrogen sorption properties of the resultant materials were evaluated via low to high pressure volumetric adsorption at room temperature from 1 – 140 bar. While the kinetics of the volumetric hydrogen sorption are still slow, the total volumetric and gravimetric sorption properties of these materials has improved drastically from their individual components to a level comparable to those observed for the direct attachment of the catalysts to the carbon substrate surface (1 – 1.5% w/w H2 @ 100 bar, 35° C for comparable Pt loadings.). Therefore, this is a unique dual spillover whereby the core – shell oxide known spillover substrate acts as the catalyst for spillover to a carbon – based substrate. The desorption kinetics of this material appear to be dependent on the base substrate, with improved rates observed for both hydrogen adsorption and desorption on the modified boron-doped materials. The hydrogen sorption properties of the various materials along with our efforts to maximize the adsorption/desorption kinetics, full characterization of the materials including isotope exchange reactions will be discussed.
9:00 PM - W8.12
Chemical Vapor Synthesis of Boron Substituted Carbon for Hydrogen Storage.
Justin Bult 1 , Jeffrey Blackburn 1 , Thomas Gennett 1 , Kevin O'Neill 1 , Lin Simpson 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractBoron doped carbon materials have shown significant potential for hydrogen storage. Active boron sites incorporated in a graphitic lattice have been theorized to have a hydrogen binding energy of 10-15 kJ/mol, the desired range for near ambient storage. Furthermore, incorporated boron has been established as a stabilizing site for deposited metals that provide multiple hydrogen binding and/or catalyze dissociation for spillover. One common method for producing boron-substituted carbon involves Chemical Vapor Deposition (CVD) using boron trichloride (BCl3) and benzene co-reactants at high temperature to form BCx films. A deleterious result of this synthesis is the production of hydrogen chloride (HCl). The HCl bi-product significantly interferes with the hydrogen accessibility of the pore structure and limits the yield of active boron sites, thus diminishing the materials storage properties. To mitigate the effects of the HCl, a new CVD process was developed utilizing direct liquid injection of triethylborane, a non-halogen containing boron precursor. To further enhance the degree of boron activity an airless sample transfer system was employed to avoid boron oxide formation. Three carbon substrate materials were used in this study, high surface area activated carbon, high surface area zeolite templated carbon, and multiwall carbon nanotubes. Following CVD processing, the boron-substituted carbon materials were analyzed via Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopy (XPS) to investigate the state of hydrogen binding and each material’s efficacy for solid-state hydrogen storage. The results of these experiments and characterization will be presented.
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Are Slit Pores in Carbonaceus Materials Real?
Cristina Romero 1 , R. Valladares 2 , Alexander Valladares 2 , Ariel Valladares 1
1 Materia Condensada, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, Mexico, D.F. 04510, Mexico, 2 Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal 70-542, Mexico, D.F. 04510, Mexico
Show AbstractNanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. The slit pore model is one of the oldest models proposed to describe porous carbon. Developed by Emmet in 1948 [1] it has been recurrently used and in its most basic form consists of two parallel graphene layers separated by a distance that is taken as the width of the pore. Its simplicity limits its applicability since experimental evidence suggests that the walls of the carbon pores have widths of a few graphene layers [2] but it makes it appealing for computational simulations due to its low computational cost. Using a previously developed ab initio approach to generate porous semiconductors [3] we have obtained porous carbonaceous materials with walls made up of a few layers (four layers), in agreement with experimental results, separated by distances comparable to those used in the slit pore model [4]. This validates the idea of a modified slit pore model obtained without the use of ad hoc suppositions. Structures will be presented, analyzed and compared to available experimental results. [1] P. H. Emmett, Chem. Rev. 43, 69 (1948).[2] H. Marsh, D. Crawford, T.M. O’Grady, A. Wennerberg, Carbon 20, 419 (1982).[3] Ariel A. Valladares, Alexander Valladares and R. M. Valladares, Mater. Res. Soc. Symp. Proc. 988E, 97 (2007).[4] Iván Cabria, María J. López, Julio A. Alonso, Carbon 45, 2649 (2007).
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Structural Studies of Carbon Aerogels and Their Metal-Doped Derivatives for Hydrogen Storage Applications.
Dafei Kang 1
1 , Michigan State University, East Lansing, Michigan, United States
Show AbstractCarbon aerogels (CAs) and their metal-doped derivatives represent a novel category of materials capable of promising hydrogen storage capabilities. In this work, a structural study of pure CAs prepared chemically with various conditions is presented, together with that of CAs doped with a range of different metal nanoparticles. Of particular importance are the results acquired with high-resolution transmission electron microscopy that reveal a very unique hierachical structure of mesoporosity and microporosity. Metal particles were found to be dispersed very evenly across the bulk of the CA substrate without any sign of undesirable agglomeration.
9:00 PM - W8.16
Metal – Organic Frameworks Having Novel Fulvalene Linkers.
Amy Groves 1 , Calvin Curtis 1 , Kevin O'Niell 1 , Chaiwat Engtrakul 1 , Lin Simpson 1 , Anne Dillon 1 , Thomas Gennett 1
1 , National Renewable Energy Laboratory (NREL), Golden, Colorado, United States
Show AbstractThe hydrogen storage capabilities of several types of metal-organic frameworks (MOFs) containing 6 membered ring linkers is well documented. Specifically, MOFs with Zn4(μ4-O) structural building unit (SBU) based MOFs having demonstrated gravimetric hydrogen storage capacities of about 0.5 %w/w at 298K and 10 MPa (1). In this work, the design, synthesis and characterization of a new set of novel MOF materials, based on the well precedented group of metal-organic frameworks that utilize the Zn4(μ4-O) SBU, where the linkers are modified from 6 to 5 membered ring systems, will be discussed. This incorporation of 5 membered rings, instead of typical arenes is achieved through the use of the fulvalene dianion (C10H82-), and the synthesis and isolation of its dicarboxylic acid and bis-pyridine derivatives. These linkers have similar size requirements as the corresponding arene linkers. Based on the theoretical work of Ahuja and co-workers on MOF-5 (2), where the linker is 1,4 benzenedicarboxylate, the alkali metal / naphthelenide reduction of such MOFs are predicted to increase the hydrogen storage three fold at 300K. However, these reduced arene MOFs, to date, have never been isolated, due to instability, which is thought to be reduction of the metal SBU leading to structure collapse. An advantage of these new linkers is the ease of incorporation of either alkali or transition metals, and ultimately the effective isolation of the reduced site from the SBU metal core. The synthetic barriers, and how to work around them, that these linkers present as one tries to isolate the correct isomers and monomeric species, will be discussed. The synthetic and crystallization approaches to making fulvalene based MOFs will be outlined. Finally, the conditions for optimum hydrogen storage for each case will be presented.Acknowledgements We are grateful for support from: The Office of Energy Efficiency and Renewable Energy – Hydrogen, Fuel Cell, and Infrastructure Technologies Program, under Department of Energy Grant No. DE-AC36-08GO28308. References1. Y. Li, R. T. Yang. J. Am. Chem. Soc. 128, 8136 (2006).2. A. Blomqvist, C. Moysés Araújo, P. Srepusharawoott, R. Ahuja. Proc. Nat. Acad. Sci., 104, 20173 (2007).
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Lattice Defects Introduced during Hydrogen Absorption-Desorption Cycles in LaNi5-based Alloys.
Junko Matsuda 1 , Yumiko Nakamura 1 , Etsuo Akiba 1
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki Japan
Show AbstractLaNi5-based alloys have been used as negative electrode materials of rechargeable nickel-metal hydride (Ni-MH) batteries because of their quick activation and excellent electrochemical charge/discharge kinetics. Inui et al. have observed a-type edge dislocations in LaNi5 with Burgers vectors of the 1/3<11-20> introduced during absorption-desorption cycles [1]. They suggested that these a-type dislocations were misfit dislocations formed at the interfaces between the LaNi5 matrix and hydride, based on their result of uniaxial compression deformation: the easiest slip system was {1-100}[0001], observed over 1073K. However, the structure model at the interface for the nucleation and growth of hydrides has not been understood in detail.In this work, lattice defects induced during hydrogen absorption-desorption cycles in the LaNi5–based alloys with various substitution elements and their contents have been investigated by transmission electron microscopy (TEM). LaNi5-xMx(M=Fe, Cu, Si, Sn, Al) were prepared by arc-melting the raw metals (minimum purity 99.9%) in a water-cooled copper crucible under an argon atmosphere. The pressure-composition isotherms were measured at 298K using a conventional Sieverts apparatus. TEM samples were prepared as follows: brass tubes filled with the compound of the alloy particles and epoxy resin were thinned by mechanically grinding, dimpling and finally ion milling with the cold stage using liquid nitrogen. Hitachi High-Technologies H9000NAR was used for TEM observation. Energy dispersive X-ray spectroscopy (EDS) was performed with JEOL JEM-2010F for chemical analysis. The c-type dislocations with Burgers vectors of <0001> as well as dense a-type dislocations were observed after one absorption-desorption cycle in LaNi5, LaNi4.5Cu0.5, LaNi5-xFex(x<1.2) and LaNi5-xAlx(x<0.25). In contrast, any lattice defects have not been practically observed in LaNi4.5Si0.5, LaNi4.75Sn0.25 and LaNi5-xAlx(x>0.25) even after five-cycles. Dislocation densities related to the pressure hysteresis observed in the first absorption and desorption: the density of the dislocations was high when the pressure hysteresis was large. Furthermore, both a-type and c-type dislocations have the Burgers vectors on the (01-10) plane. This suggests that these (01-10) planes are the interface between the hydrides and solid solution matrix during reactions.This work was supported by The New Energy and Industrial Technology Development Organization (NEDO) under Advanced Fundamental Research on Hydrogen Storage Materials (HYDRO-STAR).[1] H. Inui, T. Yamamoto, M. Hirota, M. Yamaguchi; J. Alloys and Compounds 330-332 (2002) 117-124.
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Structural Investigation of Light Element Amorphous Hydrides by Solid-State NMR Techniques.
Keiji Shimoda 1 , Tessui Nakagawa 1 , Taisuke Ono 1 , Ken-ichi Kojima 2 , Takayuki Ichikawa 1 , Yoshitsugu Kojima 1
1 , Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima Japan, 2 , Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima Japan
Show AbstractStructural characterization of light element hydrides, a candidate of effective hydrogen storage, provides basic information to understand the hydrogen absorption/desorption mechanisms. The crystalline hydride phases have been commonly investigated by using high-energy x-ray and neutron diffraction techniques. However, these compounds often become low- or non-crystalline composite phases during milling or heating processes, which are difficult to fully characterize by the diffraction methods. Solid-state nuclear magnetic resonance (NMR) spectroscopy is also one of useful analytical methods and detects the local structure on the specific element even for complex amorphous materials. We will show our research examples of the structural characterization of non-crystalline borohydrides and the amorphization of an Al-amide during thermal decomposition using multi-nuclear solid-state NMR techniques.7Li, 11B, 23Na, and 27Al magic-angle spinning (MAS) NMR spectra were acquired on JEOL JNM-ECA600 (14.1 T) with a spinninig rate of 15 kHz. The resonance frequencies are 233.2, 192.5, 158.7, and 156.3 MHz, respectively. These light elements are half-interger quadrupole nuclei (spin I = 3/2, or 5/2), therefore, triple-quantum (3Q) MAS NMR technique were also applied that allow us to obtain high-resolution spectra.1. ScH2 + MBn (M = Mg, Ca) system: We prepared nanocomposites of 2ScH2 + 3MgB2, and 2ScH2 + CaB6 by using mechanical milling technique under H2 pressure to examine the hydrogen storage properties of the products. TG-MS profiles showed that the hydrogenation proceeded by the milling at H2 pressure. 11B MAS and 3QMAS spectra clarified that the composites after milling consisted of low-crystalline ScB2 and non-crystalline Mg- or Ca-borohydrides (M(BH4)2) and that H2 desorption was coming from the decomposition of the borohydrides.2. Metal Al-amide:A composite of LiAl(NH2)4 and LiH by mechanical milling releases a large amount of hydrogen below 130°C. To understand the indivisual reaction pathways, we investigated the thermal decomposition reaction of LiAl(NH2)4 by using 7Li and 27Al MAS and 3QMAS techniques. The LiAl(NH2)4 was synthesized by milling LiH and Al metal mixture in liquid NH3. TG-MS and XRD profiles indicated that LiAl(NH2)4 decomposed into NH3 and a non-crystalline material, which is suitable to apply multi-nuclear NMR analysis.
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First Principle Study on the Thermodynamics of Hydrogen in Iron and Steels.
Roman Nazarov 1 , Tilmann Hickel 1 , Joerg Neugebauer 1
1 Computational Materials Design, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf Germany
Show AbstractThe amount of hydrogen that can be stored in a metal sensitively depends on the chemical composition, defect concentration and the microstructure of the host material. In particular, point defects are often discussed as trapping centers for hydrogen. The resulting hydrogen-vacancy complexes are often detrimental to the structural materials integrity. An example is hydrogen embrittlement which is particularly pronounced in modern high-strength steels such as high-manganese austenitic steels. To understand and eventually prevent such materials failure it is critical to develop theoretical tools which allow an accurate description of the amount of hydrogen which can be dissolved in such a material and its interaction with vacancies.To address this question we have employed density-functional theory (DFT) using GGA-PBE together with thermodynamic concepts. In a first step we have used DFT to calculate the formation energy of isolated and hydrogen loaded vacancies assuming various magnetic configurations. Our results show that in the presence of hydrogen, the equilibrium vacancy concentration significantly increases due to the lower formation energy of vacancy-hydrogen complexes. The large change in formation energy due to hydrogen addition that causes this increase is related to the fact that up to 6 hydrogen atoms can be incorporated into a single vacancy.Based on our ab-initio results we developed a thermodynamic model which defines the concentrations of vacancies, of hydrogen in different interstitial positions and of vacancy-hydrogen complexes as a function of pressure, temperature and external hydrogen chemical potential. Applying this model we find dramatically increased equilibrium vacancy concentrations and total hydrogen concentrations in the crystal, in particular if the material is exposed to a very hydrogen-rich atmosphere.In a final step we considered the energetic barriers for hydrogen diffusion using the “drag” method. We observe a much higher diffusion barrier for a hydrogen atom migrating from a vacancy to the closest octahedral site than for the diffusion in pure bulk between octahedral sites which practically remains unchanged even for pores near a vacancy. This finding has an important consequence: It demonstrates that vacancies in austenitic steels serve as effective but extremely short range trapping centers for hydrogen.
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Study of Mg-Ni-Ti Laminate Hydrogen Storage Material.
Yusuke Sasaki 1 , Hiroyuki Takeshita 1 , Shinya Hattori 1 , Kouji Tanaka 2
1 Faculty of Chemistry,Materials and Bioengineering, Kansai University, Suita, Osaka, Japan, 2 , Nathional Institute of Advanced Industrial Science and Technology(AIST), Ikeda, Osaka, Japan
Show AbstractMagnesium is one of promising materials for hydrogen storage due to its high gravimetric hydrogen content (7.6mass%) but both thermodynamic and kinetic properties must be improved for practical application. Many authors reported that mechanical deformation such as ball milling is effective for the improvement of hydrogen desorption properties of MgH2 [1]. Griessen et al. [2] reported that thin film of Mg-Ni-Ti alloy prepared by DC/RF magnetron co-sputtering reversibly react with hydrogen at low temperatures below 313K. However, for practical application, deformation and formation of thin film should be achieved by another method which is suitable for mass production, for example, laminate-rolling. (In laminate-rolling, the following procedure is repeated; laminated metal plate is cold-rolled in order that the thickness of each plate is decreased, and the rolled material is cut and piled up, and then cold-rolled again. The deformed material with very thin film layer of several nm in thickness can be obtained by this method.) The improvement of dehydrogenation properties of Mg-based hydrogen storage alloys by laminate-rolling are reported by Ueda et al. [3] and Takeichi et al. [4]. In the present study, the dehydrogenation properties of pure Mg and Mg-Ni-Ti alloy prepared by laminate rolling were examined in order to know the possibility of the application of laminate rolling to these materials and the mechanism of the improvement.Mg foil (98% purity, 50μm in thickness, Mitsubishi steel) was cut to 50mm×30mm in size, piled up, sandwiched with Cu plate, and cold-rolled. When the length of the sample became to twice longer than that of before rolling, it was cut to the same size as the foil before rolling and piled up again. This procedure was repeated until single-layered thickness comes to 1.5nm. For Mg-Ti and Mg-Ni-Ti laminate sample, Ti and Ni was deposited on Mg foil by ion plating. Then, the Ti- and Ni- deposited Mg foil was cold rolled by the above described procedure. For comparison, MgH2-TiH2 mixtures were prepared from MgH2 powder(98% purity, Johnson Mattey) and TiH2 powder(99% purity, HIGH PURITY CHEMICALS) using mechanical ball-milling. Hydrogenation and dehydrogenation properties were examined by DSC, TG-DTA-MS and PCT measurements. From the result of DSC, the desorption temperature of Mg laminate was found at 736.2K. This desorption temperature was lower than that of Mg foil by 754K. But the absorption temperature insignificantly changed. In the result of XRD, the intensity of diffraction peak from MgH2 decreases in order of laminate and Mg foil. From these results, the reaction rate of Mg could be judged to be improved by laminate rolling. [1] J.F. Stampfer Jr., J.F. Suttle, J. Am. Chem. Soc, 82 (1960), 3504. [2] J. J. LIANG, Appl. Phys. A, 80 (2005), 173-178. [3] T. T. Ueda, M. Tsukahara et al., J. Alloys Compd., 386 (2005), 253. [4] N. Takeichi et al., J. Alloys Compd. 446-447 (2007), 543-548.
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Formation of Intermetallic Compound in Super-laminated Mg/Al Composite and its Hydrogenation Properties.
Hiroshi Miyamura 1 , Chisa Goh 1 , Shiomi Kikuchi 1 , Nobuhiko Takeichi 2 , Koji Tanaka 2 , Hideaki Tanaka 2 , Nobuhiro Kuriyama 2
1 Materials Science, University of Shiga Prefecture, Hikone, Shiga Prefecture, Japan, 2 Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology(AIST), Ikeda, Osaka Prefecture, Japan
Show AbstractSuper lamination technique is a kind of foil metallurgy. Its process consists of the repetition of stacking and rolling metal foils, and finally obtaining nano-layered composite materials. Some of hydrogen storage alloys prepared by this technique show better reaction properties than conventionally cast materials. In the present study, formation capability and hydrogenation properties of the Mg17Al12 intermetallic compound prepared by a combination of the super lamination technique and heat treatment were investigated, and the properties were compared with the materials prepared by sintering of a mixture of Mg and Al powders.High purity Mg and Al films with each thickness of 40 μm and 20 μm were stacked in alternating layers and made into a laminate composite by repetitive stacking and rolling under an ambient condition. Thus, a super laminate composite with each layer thickness less than 1 μm was successfully obtained. By heat treatment of the laminate composite in vacuum at 673 K, a uniform compound of Mg17Al12 was obtained in less than 10 minutes. On the other hand, sintering of the conventionally available Mg and Al powders with particle size about a few micrometers at the same temperature resulted in a mixture of intermetallic compounds and residual starting materials, and uniform compound could not be obtained within the sintering period less than 120 minutes.In order to study the formation kinetics of the compounds in super laminates, some Mg-Al diffusion couples with a Mo wire as the Mg/Al boundary marker were prepared. The samples were heat treated at 673 K for various periods, and the growth rates of the compounds formed on the boundary were evaluated by the observation of their thickness, by use of a SEM with EDX. It was found that Mg2Al3 and Mg17Al12 compounds were formed and grew from the initial Mg/Al boundary, and both of the compounds strongly grew towards Mg side, not to Al side. The difference in growth path distance towards the Mg side was extremely larger than that towards Al side. This indicates that the initial thickness of Al layer determines the time required to complete the compound formation, and accounts for the residual materials in the powder sintered composite, because the contaction of Al particles in the powder compact before sintering reaches more than several ten micrometers, whereas no such long path of Al contaction does not exist in the super laminate composite. This shows that the super lamination technique is one of the effective and costly methods for preparing the intermetallic compounds for hydrogen storage in a short period.Hydrogenation behavior of the materials was studied by use of a Sieverts’ type apparatus. The Mg17Al12 compound prepared by the heat treatment of a super laminate could reversibly absorb hydrogen via a disproportionation reaction, and decomposed into Mg2Al3 and MgH2. Overall hydrogen storage capacity of the Mg17Al12 compound reached up to about 0.8 at 673 K.
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Hydrogenation and Dehydrogenation Properties of Mg-Cu, Mg-Al Eutectic Alloy.
Ho Shin 1 , Yuma Eto 1 , Koji Tanaka 2 , Hiroyuki Takeshita 1
1 Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka, Japan, 2 Nano materials sience group, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan
Show AbstractMg has 7.6 mass% of high gravimetric hydrogen density, an abundance of resources and inexpensive price compared with other functional materials. Owing to these merits, it has been the major subject of study. However, it is unsuitable for practical application due to thermodynamic stability and slow kinetics of Mg hydride. Therefore, many ways such as fabrication of nanocrystalline or addition of catalyst have been proposed to solve the problems of Mg hydride system. Copper and aluminum are inexpensive and can be easily obtained as well as Mg. The alloys with eutectic compositions in Mg-Cu, Mg-Al system can transform from solid state to liquid state at lower temperatures than Mg and diffusion rate of Mg atoms which kinectically relates to form hydride closely can be expected to be improved by lowering melting temperature[1], [2]. These alloys with eutectic composition also can be expected to improve reaction rate by its structural refinement. Therefore, the aim of present study is to observe hydriding/ dehydriding properties of eutectic composition in Mg-Cu and Mg-Al system. We purchased Mg, Cu and Al foil from Takeuchi Metal Foil & Powder Co., Strem Chemical, Inc. and for domestic use as starting materials to make laminate alloys. Mg, Cu and Al powders from Rare metallic Co. Ltd. and Wako Pure Chemical industries were also prepared. Mg-14.5mol%Cu and Mg-31mol%Al alloys with eutectic composition were prepared by repetitive-rolling or sintering process and then they were analyzed with fluorescent X-ray spectrometer to confirm the composition. The measurements of hydrogen absorption and desorption properties were performed by differential scanning calorimetry (DSC) at 5K/min in heating and cooling rate under hydrogen pressure of 4MPa and by thermogravimetry differential - thermal analysis - mass spectrometry (TG-DTA-MS). The microstructure and morphology of the obtained samples were examined by scanning electron microscopy (SEM) and the constituent phases were analyzed by X-ray diffraction (XRD). Both of eutectic Mg-Cu and Mg-Al alloys exhibited hydrogenation/dehydrogenation at lower temperature than pure Mg, which indicates improvement of reaction kinectics and thermodynamics was accomplished for hydriding and dehydriding of Mg.[1] A. Andreasen, Int. J. Hydrogen Energy,33(2008), 7489-7497., [2] N.Takeichi et al., J. Alloys Compd., 446-447(2007), 543-548.
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Hydrogen Desorption Behavior of the MgH2-Ni/Al2O3 Composite Prepared by High Energy Ball Milling.
Natsuki Yamasaki 1 , Jyunpei Miki 1 , Yasuhiro Kodera 1 , Manshi Ohyanagi 1 , Zuhair Munir 2
1 , Ryukoku University, Otsu , Shiga, Japan, 2 , University of California, Davis, Davis, California, United States
Show AbstractThe effect of the Ni/Al2O3 composite addition on the hydrogen desorption kinetics of the magnesium hydride (MgH2) was observed. The Ni/Al2O3 composite was prepared by the oxygen reduction of the NiO/Al2O3 composite using hydrogen. The reduction from NiO to Ni was characterized by X-ray diffraction analysis. The reduction reaction of NiO was completed at 400 °C for 6 h under 0.2 MPa of hydrogen. The MgH2 and 50wt% Ni/Al2O3 were mechanically milled using a gear driven planetary ball mill for 10 min. In the case of the specimen heated with 5 °C/min under 0.001 MPa of hydrogen, the onset temperature of hydrogen desorption of the MgH2-Ni/Al2O3 was 195 °C, which is 25 °C lower than that of MgH2-Al2O3. From the results of the hydrogen desorption measurement at 250 °C for 1000 s, the MgH2-Ni/Al2O3 released approximately 80 % of relative hydrogen storage capacity (3.8 wt%), when the MgH2-Al2O3 desorped only 5%.
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Electrochemical Charge for the Formation of Metal Hydrides from LiH+M (M=Mg, Al).
Nobuko Hanada 1 , Hiroshi Suzuki 1 , Kenichi Takai 1
1 Department of Engineering and Applied Sciences, Sophia University, Tokyo Japan
Show AbstractThe electrochemical method is one of the useful methods to charge hydrogen under moderate condition into the storage materials, which thermodynamically require high pressure and temperature for the hydrogenation. Electrochemical hydrogen charge into light materials of Magnesium and Aluminum in non-aqueous solution has been investigated. Recently, Oumellal et al. has used MgH2 as negative electrode in Li ion battery on the anode reaction of MgH2 + 2Li+ + 2e- → Mg + 2LiH [1]. Based on this reaction, we have tried to form MgH2 from 2LiH + Mg or AlH3 from 3LiH + Al. The samples of 2LiH + Mg, 3LiH + Al and AlH3 are ball milled for 1~10 hours. The samples ball milled are mixed with Acetylene black and PTFE (or PVDF) as positive electrodes. Lithium metal and EC/EMC (1:1) + LiPF6 (1M) are used as a negative electrode and an electrolyte, respectively.The charge curve of 2LiH + Mg ball milled for 2 h doesn’t show a plateau of the voltage and immediately increases to 3 V (vs Li+/Li) at less than the composition of 0.1 mole Li. MgH2 phase is not observed after the charging by XRD measurement. The charge curve of 2LiH + Mg ball milled for 10 h shows the plateau of voltage until the composition of 0.7 mole fraction of Li around at 0.55 V which is the same as the theoretical value (0.53 V) of this reaction. The formation of MgH2 phase is observed in the XRD profiles after the charging. It indicates that good mixing state and small crystalline size by the longer ball milling leads the long reactivity between Mg and LiH to form MgH2 by electrochemical charge. In the charge curve of 3LiH + Al ball milled for 10 h, the short plateau of voltage is observed until the composition of 0.03 mol fraction of Li around at 0.9 V corresponding to the theoretical value of 0.87 V. But AlH3 phase is not detected by XRD measurement. On the other hand, after discharging of AlH3 ball milled for 1 h until at 0.7 mole fraction of Li, the Al and LiH phases are observed in addition to AlH3 phase. It indicates that the reaction of AlH3 + 3Li+ + 3e− → Al + 3LiH proceeds as the discharge reaction of AlH3.[1] Y. Oumellal, A. Rougier, G. A. Nazri, J-M. Tarascon and L. Aymard, Nature Materials, 7 (2008) 916.
9:00 PM - W8.25
Observation of Hydrogen Absorption by Pd Thin Film using in situ Scanning Probe Microscopy.
Itoko Saita 1 , Kouji Sakaki 1 , Yumiko Nakamura 1 , Etsuo Akiba 1
1 , AIST, Tsukuba, Ibaraki, Japan
Show AbstractTo describe the hydrogen absorption mechanism of solid-state hydrogen storage materials, it is essential to understand hydrogen-surface interaction that is the first step of hydrogen absorption by the materials. Some of the authors have worked on in situ observation of metal hydride surface. They developed a scanning probe microscope (SPM) which enabled observation under hydrogen atmosphere and succeeded in observing the atomic image of graphite even under 1 MPa hydrogen [1]. In this study, we investigated the surface reaction of Pd thin film under hydrogen atmosphere using the in situ SPM. A film 50 nm thick was prepared on mica substrate using a sputtering machine. Tens-nanometer grains having round shape were observed on the surface of as-prepared film. When the film was exposed to hydrogen, the grains changed their shapes from rounded one to noncircular one composed of rectilinear outlines. At low magnification, buckling of tens-micrometer wide was observed on the film under hydrogen atmosphere. Those structure changes were observed when the hydrogen pressure was above the absorption pressure of Pd thin film. This demonstrates that the surface structure change was caused by the lattice expansion due to hydrogen absorption. Ref. [1] Y.Suzuki et al., Ultramicroscopy, 99 (2004) 221–226. Acknowledgement: This work was supported by AIST Nano-Processing Facility and New Energy and Industrial Technology Development Organization (NEDO) under the “Advanced Fundamental Research on Hydrogen Storage Materials (Hydro-Star)”.
9:00 PM - W8.26
New Multinary Complex Hydrides for Reversible Hydrogen Storage.
Anthony D'Angelo 1 , Michael Niemann 1 , Sesha Srinivasan 1 , Yogi Goswami 1 , Elias Stefanakos 1
1 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States
Show AbstractThe multinary hydride structure consisting of LiBH4, LiNH2 and MgH2 has been shown to reversibly store approximately 6wt.% at 150oC by optimizing the processing conditions of the structure. The hydrogen sorption properties such as kinetics and storage capacity of this multinary structure are significantly improved via the addition of Nb2O5¬. The materials are processed using solid state mechano chemical synthesis techniques and extensively characterized for their thermal, chemical and structural properties using differential scanning calorimetry, thermal gravimetric analysis, x-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy as well as thermal programmed desorption. It is found that the order of addition of Nb2O5 and its concentration optimization are essential to fine tuning the hydrogen sorption properties of the multinary hydride. Furthermore, the addition of nano-sized iron was found to greatly enhance the rate of hydrogen release, while the addition of nano-sized nickel is found to have a large effect on reducing the temperature required for hydrogen release. Various other nano-sized additives and their effect on the hydrogen sorption behavior are presented.
9:00 PM - W8.27
Self-decomposition Characteristic and Phase Transition of Amorphous Mg(NH2)2.
Masahiro Heishi 1 , Hideaki Watanabe 2 , Tukasa Shirai 3 , Hiroyuki Takesita 4
1 Graduate Course of Engineering, Kansai University Graduate school, Suita, Osaka, Japan, 2 Materials Science and Engineering, Kansai University, Suita, Osaka, Japan, 3 Materials Science and Engineering, Kansai University, Suita, Osaka, Japan, 4 Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka, Japan
Show AbstractLiH-Mg(NH2)2 system has attracted considerable attention as a potential hydrogen storage candidate because of its high hydrogen storage capacity. But further improvement of kinetic properties is required for this system. It is important that constituents in this mixture more actively migrates to accelerate reaction rate. We consider self-decomposition temperature of Mg(NH2)2 might affect hydrogen desorption temperature of Mg(NH2)2 and LiH mixture. Furthermore, it is considered that melting point of Mg(NH2)2 might affect hydrogen desorption temperature of those mixture. Because constituent atoms and ions can quickly migrate, when Mg(NH2)2 becomes liquid, hydrogen desorption from those mixture might be improved. Therefore, we aim to reveal phase transition related melting of amorphous Mg(NH2)2 phase by in-situ observation using XRD.Mg(NH2)2 was synthesized by ball milling of Mg powder (99% purity, RAREMETALLIC Co.) at 300rpm for 72ks in NH3 gas-liquid mixture of 1MPa, or by ball milling MgH2 powder (98% purity, Jonson Matthey Co.) at 350rpm for 50.4ks in the NH3 mixture. Thermal properties of Mg(NH2)2 samples were determined by DSC. The constituent phases of the samples after synthesis and DSC measurement were respectively identified by XRD and FT-IR. The self-decomposition of these samples was analyzed by TG-DTA-MS. In DSC profiles of the samples synthesized by mechanochemical method, an exothermic peak at 540-600K and on endothermic one at 620-650K respectively corresponding to crystallization and melting of Mg(NH2)2 were observed during heating at the first cycle. After endothermic peak at 620-650K the sample was cooled down to room temperature, but we peak corresponding to solidification was observed, implying the decomposition of Mg(NH2)2. XRD and FT-IR profiles showed the existence of amorphous Mg(NH2)2 phase in the sample after the first cycle. The sample after DSC measurement at first cycle exhibited the some features as amorphous Mg(NH2)2 prepared by ball milling, that is, decomposition started at lower temperatures and temperature range for decomposition was wider quite different from crystalline Mg(NH2)2.From these results, it can be judged that amorphous Mg(NH2)2 is crystallized by rising temperature, and then transformed to vitrified Mg(NH2)2 in cooling, which implies. That Mg(NH2)2 can easily form amorphous phase by supercooling of liquid.
9:00 PM - W8.28
Dehydrogenation and Poisoning of LiBH4-based Hydrogen Storage System.
Hiroyuki Takeshita 1 , Yong Li 1 , Seito Niwa 1 , Makoto Ikeda 1
1 Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka, Japan
Show AbstractInorganic hydrogen storage materials including complex hydrides are promising candidate of hydrogen storage of fuel cell powered automobiles because of their high gravimetric hydrogen storage capacities. Among them, LiBH4 has extremely high capacity of 13.5 mass% but the thermodynamic and kinetic improvement of its hydrogen desorption are required. In addition, it can be seriously damaged by other active gas species in the atmosphere, oxygen, water vapor and carbon dioxide. Therefore, the breakthrough is required about these problems for the application of the LiBH4-based hydrogen storage system to hydrogen storage. The present study deals with the improvement of kinetic and thermodynamic hydrogen desorption properties of LiBH4 by the mixing of MgH2 and Al, as well as its poisoning against water vapor.LiBH4 and MgH2 powder purchased from Johnson Matthey Catalysts and Al powder purchased from Wako Pure Chemical Industries were used as starting materials. They were put into hardened Cr-steel vessel with hardened Cr-steel balls, and then well-mixed and mechanically alloyed with Fritsch P-6 planetary ball mill machine. On the other hand, the poisoning of LiBH4 by water vapor was performed by holding the sample kept at 298K in the flow of helium gas mixed with water vapor generated from LiBO2-2H2O. H2O content and exhaust gas after passing the sample were respectively monitored with dew-point meter and quadrupole mass filter. The constituent phases were analyzed by XRD and FT-IR, and hydrogen desorption properties were measured with TG-DTA-MS and high pressure DSC instruments.The LiBH4-MgH2-Al sample exhibited 80K lower hydrogen desorption temperature than LiBH4-MgH2 one and 10 mass% of gravimetric hydrogen storage capacity below 773K. The constituent phases were LiBH4, MgH2 and Al before hydrogen desorption, which means that there were no phase formed during mechanical grinding and alloying, and LiH, (Mg, Al)B2 and Al phases after dehydrogenation. The (Mg, Al)B2 phase has the same crystal structure as MgB2 and appeared even at almost zero of partial hydrogen pressure (in helium gas), which implies that Al can assist the formation of MgB2-type phase, causing hydrogen desorption at lower temperature. On the other hand, LiBH4 changed to its hydrate by poisoning treatment, although small amount of hydrogen gas emission was observed during the treatment. The poisoned sample exhibited significant weight decrease of 3 to 10 mass% below 383K, mainly due to hydrogen emission, according to the content of the hydrate phase formed. The results imply that excess LiBH4 can contribute to the protection of main hydrogen storage materials against water vapor by its self-sacrifice effect, as well as it can work as hydrogen generation source. LiBH4-based hydrogen storage materials such as LiBH4-MgH2-Al which were covered with excess LiBH4 might have the potential applicable to storage of hydrogen with purity of commercial-grade.
9:00 PM - W8.29
Time and Frequency Resolved Hydrogen Dynamics in LiBH4.
Robin Gremaud 1 , Esben Ravn Andresen 2 , Timmy Ramirez-Cuesta 4 , Keith Refson 4 , Zbigniew Lodziana 1 , Paul Hug 3 , Andreas Zuettel 1 , Peter Hamm 2 , Andreas Borgschulte 1
1 Hydrogen & Energy, Empa, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf Switzerland, 2 Physikalisch-Chemisches Institut, Universität Zürich, Zürich Switzerland, 4 ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon United Kingdom, 3 Solid State Chemistry, Empa, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf Switzerland
Show AbstractThe conditions for hydrogen uptake and release by LiBH4 remain harsh, despite considerable research effort.[1] A better understanding of the B-H bond and of the hydrogen diffusion mechanism is therefore needed to obtain a real breakthrough in the (de)hydrogenation reversibility and kinetics of the system.[2] Hydrogen absorption in hydrides is in general a multi-step process.[3] In LiBH4, gaseous hydrogen has to dissociate, diffuse in the material and form stable BH4- molecular units. It is debated what is the diffusing species (H2, H, H+, H- or BH4) responsible for the mass transport.Hydrogen diffusion mechanismWe use Raman scattering mapping associated to H/D isotope exchange to investigate the diffusion mechanisms. Interdiffusion profiles reveal that at low temperatures, diffusion of BH4-/BD4- is the only transport mechanism. Deuterium exchange within the BH4- unit is a slower process arising close to the melting point. Combining vibrational properties ab initio calculations of the partially H/D exchanged LiB(H1-xDx)4 structures and Raman, neutron and infrared spectroscopy data, we are able to detect each individual B(H4-nDn)- unit (n = 1,..,4). This full isotope scrambling demonstrates that even though the BH4- unit is very stable, single hydrogen atoms are successively exchanged in the complex units. The exchange occurs most probably at low-concentration defects or at the surface, as the bulk-sensitive NMR technique could not evidence atomic H jumps.[4] Net transport of atomic hydrogen in LiBH4therefore results from a combination of local H-exchange and subsequent mass transport by BH4- units.B-H bondDue to the light elements involved, the vibrational properties of LiBH4 are strongly influenced by potential anharmonicity. We present here the first example of (two-dimensional) infrared pump-probe spectroscopy (2D-IR) on a complex hydride. 2D-IR provides a direct measure of the vibrational lifetime and of the anharmonicities for each B(H4-nDn)- unit. Furthermore, we show that 2D-IR measurements are sensitive to vibrational energy redistribution from local BH4- vibrations to long-range, low-frequency phonon modes. We demonstrate that we can disentangle the signal from BH4- vibrations and the signal caused by the low-frequency phonons – essentially a “heat signal” that can be described by an increase of temperature. The induced, ultrafast temperature-jump opens new prospects for extending nonlinear infrared spectroscopic measurements to studying non-equilibrium effects in hydrides. [1] P. Mauron, F. Buchter, O. Friedrichs, A. Remhof, A.; M. Bielmann, C. N. Zwicky and A. Züttel. J. Phys. Chem. B, 112, 906 (2008).[2] O. Friedrichs, A. Borgschulte, S Kato, F. Buchter, R. Gremaud, A. Remhof and A. Züttel, A. Chem. Eur. J. 15, 5531 (2009).[3] A. Borgschulte, R. Gremaud and R. Griessen, Phys. Rev. B 78, 094106 (2008).[4] R. L. Corey, D. T. Shane, R. Bowman, M. S. Conradi, J. Phys. Chem. C 112, 18706 (2008).
9:00 PM - W8.3
Towards Understanding Palladium Doping of Carbon Supports: A First-principles Molecular Dynamics Investigation.
Samir Mushrif 1 , Alejandro Rey 1 , Gilles Peslherbe 2
1 Chemical Engineering, McGill University, Montreal, Quebec, Canada, 2 Chemistry and Biochemistry, Centre for Research in Molecular Modeling (CERMM) and Concordia University, Montreal, Quebec, Canada
Show AbstractPalladium-doped carbon supports are commonly used catalysts in hydrogenation and combustion processes and are candidate materials for carbon nanostructure growth catalysts and hydrogen storage. Palladium doping, using a precursor, is either carried out on a pre-existing carbon support or during the preparation of the carbon support. Experimental studies suggest that the underlying chemistry between the palladium precursor and the aromatic carbons in the support (or its precursor) affects the resulting microstructure and hence the performance of palladium-doped carbon materials. First principles molecular dynamics simulations are performed for a mixture of chrysene, a model polyaromatic carbon compound, and palladium (II) acetylacetonate, a palladium complex often used as a palladium precursor and the details of the electronic structure of the mixture are analyzed along the trajectory with the electron localization function. We demonstrate that the acetylacetonate ligands in palladium (II) acetylacetonate get covalently linked to the carbon atoms in the chrysene molecule, accompanied by the decomposition of palladium (II) acetylacetonate. The two acetylacetonate ligands separate and palladium remains attached to one of them. Palladium also forms a bonded interaction with a carbon atom of the chrysene molecule. The acetylacetonate ligand-chrysene covalent interaction results in the loss of conjugation in the chrysene molecule and in turn gives rise to cross-linking in the neighboring aromatic molecules.
9:00 PM - W8.30
First-Principles Study on Hydrogen Atom Hopping in NaAlH4.
Hao Wang 1 , Akinori Tezuka 1 , Hiroshi Ogawa 1 , Tamio Ikeshoji 1
1 Research Institute for Computational Sciences , National Institute of Advanced Industrial Science and Technology(AIST), Tsukuba, Ibaraki, Japan
Show AbstractSodium alanate, NaAlH4, is presently one of the most promising hydrogen storage materials, which release hydrogen in two stages with Na3AlH6 as the intermediate. To make absorption/desorption reversible under the practical conditions, of the numerous additives that have been investigated, Ti-doping is considered to give favorable kinetics as well as high hydrogen-storage capacity.H diffusion plays an important role on absorption/desorption kinetics. However, what is behind the effect of dopants on H diffusion is still open to question. Substitution of Ti for Al+H at Al site in (NaAlH4)4 is theoretically proven to be thermodynamically favorable in terms of the enthalpy of formation and heat of substitution (Løvvik etal. PRB 71 054103). In this work, we use the First Principles calculations to investigate how H diffuses in bulk NaAlH4 with and without the effect of dopants. We simulate the H transfer from one AlH4- group to a vacancy site in a supercell. In case of Ti-doped supercell, since the break of the symmetry, an appreciate effect range of Ti atom is selected, of which a H atom is simulated to transfer from outside to inside. In order to find Minimum Energy Paths (MEP), the Nudged Elastic Band(NEB) method is applied. The activation energies with and without dopants are discussed and compared to the available experimental data. AcknowledgementsThis work is supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials". First principles calculations were done on AIST Super Cluster using QMAS (PAW DFT code developed by Ishibashi et al.).
9:00 PM - W8.31
Hydrogen Interactions with Ammonia Borane and Its Thermolysis Residues at High Pressures.
Raja Chellappa 1 , Maddury Somayazulu 1 , Viktor Struzhkin 1 , Russell Hemley 1 , Thomas Autrey 2
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States, 2 Fundamental Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractAmmonia borane (AB: NH3BH3) is a chemical hydride with potential to store hydrogen for fuel cell applications due to its high gravimetric (19.6 wt. % H) and volumetric (0.145 kg L-1) hydrogen densities. Upon heating NH3BH3 releases H2 with the formation of polyaminoborane [PAB:(NH2BH2)x] (~5.6 wt. % at 90-100 oC) that further decomposes to polyiminoborane [PIB:(NHBH)x] (~5.5 wt. % >150 oC) as well as other volatles such as borazine (NHBH)3. Both PAB and PIB suffer from the limitation of not being reversible (i.e., reuptake of hydrogen) ; a key requirement for on-board hydrogen storage hindered by unfavorable thermodynamics.In a series of studies at elevated pressures, we have explored the interactions of H2 (D2) with AB, PAB, and PIB to gain insight into dynamics and diffusion in B-N-H compounds. Raman spectroscopy reveals the formation of high hydrogen content AB-H2 complexes at 6.7 and 10 GPa evidenced by the appearance of new ν(H2) modes at these pressures. The origin of these H2 excitations is ascribed to H2 interactions with the N-Hδ+… Hδ--B intermolecular dihydrogen bonding network. Synchrotron x-ray diffraction studies are on-going to identify the structural relationship between the AB-H2 complexes and the corresponding high pressure phases of pure AB. Raman spectroscopy also reveals remarkable reactions between PAB/PIB with H2 and D2 at elevated pressures (2-4 GPa). Under high pressure D2, prior to complexation, a H/D exchange process is observed in PAB, PIB, as well as mixed phases as seen by the formation of HD. Mechanisms for the observed hydrogen interactions will be proposed.
9:00 PM - W8.32
Parallel in-situ Raman/IR Emissivity and PCI Measurement for Screening Hydrogen Storage Materials.
Chun Chiu 1 , Jason Hattrick-Simpers 1 , Leonid Bendersky 1 , James Maslar 1 , Edwin Heilweil 1
1 , NIST, Gaithersburg, Maryland, United States
Show AbstractThe traditional approach in studying hydrogen storage materials relies on synthesizing bulk samples and measuring hydriding/dehydriding reactions with Sieverts-type apparatus, which records pressure-concentration isotherms (PCIs). Although PCI method provides us with in-depth results, it is time consuming; for high-throughput screening of hydrogen storage different methods are required. In our recent study, the use of infra-red (IR) emissivity imaging for studying the in-situ hydrogenation of MgxNi1-x combinatorial films with hydrogen gas has been shown to be a powerful screening tool for metal hydride storage materials. Also, Raman spectroscopy shows promise to be used as a quantifiable in-direct measurement of the presence of different hydride phases. However, the drawback of these screening techniques is that they do not give truly quantitative results of composition and amount of a hydride phase.In the paper we present our initial results on the development of an experimental setup to conduct parallel in-situ Raman/IR emissivity and PCI measurements. In the presented examples we show that the IR emissivity or Raman intensity in thin film or power samples can be correlated with the amount of hydrogen measured in PCI.
9:00 PM - W8.33
A Carbide-based Fuel System (CFS) for the Generation of Syngas.
Louis Carreiro 1 , Alan Burke 1
1 Code 8231, Naval Undersea Warfare Center, Newport, Rhode Island, United States
Show AbstractSolid Oxide Fuel Cells (SOFCs) usually operate on syngas (a mixture of hydrogen and carbon monoxide) derived from the fuel processing (catalytic reforming) of higher hydrocarbons. While liquid hydrocarbons have been the fuel of choice, due to their high energy content and ease of storage, solid fuel sources are also being considered since they offer the distinct advantages of extended shelf-life and non-volatility. One source in particular is a composite mixture of calcium carbide and calcium hydride that when reacted with water forms acetylene and hydrogen, respectively. Further processing of the product gases (hydrogenation followed by steam reforming) yields syngas, which can be utilized by the SOFC. This study examines a unique method for the controlled generation of acetylene and hydrogen via the addition of calcium carbide/calcium hydride/glycerin slurry into water. The acetylene is hydrogenated to ethane using the hydrogen produced from the hydride followed by steam reforming of ethane to carbon monoxide and hydrogen. The effects of particle size, the amount of glycerin coating the particles and the rate of slurry addition to water on the co-generation of acetylene and hydrogen are investigated.
9:00 PM - W8.34
Development of Small Measurement System of Effective Thermal Conductivity for Solid-state Hydrogen Storage Material.
Chan Hyeok Yeo 1 , Hyeon Soo Kim 2 , Sang Hun Hwang 1 , Ki Suk Nahm 1 2 , Yeon Ho Im 1 2
1 Department of Hydrogen and Fuel Cells Engineering, Specialized Graduate School, Chonbuk National University, Jenoju Korea (the Republic of), 2 School of Semiconductor and Chemical Engineering, Chonbuk National University, Jenoju Korea (the Republic of)
Show AbstractTo date, there have been many attempts to develop the solid-state hydrogen storage materials for hydrogen economy. Especially, heat management is one of critical issues in the solid-state hydrogen storage systems because hydrogen storage materials generate or absorb heat during hydrogen absorption/discharge in hydrogen storage vessels. Thermal properties of the hydrogen storage materials need to be investigated to develop the effective hydrogen storage system. In this work, we developed a miniaturized measurement system to investigate the effective thermal conductivity using the minimum amount of solid-state hydrogen storage materials obtained in the initial step of novel material development. The developed system was evaluated using well-known standard material such as LaNi5. Finally, we measured the effective thermal conductivities of carbon nanotubes (CNT), metal doped CNT, and chemical hydrides that have attracted a great deal of research interest as solid-state hydrogen storage materials.
9:00 PM - W8.35
In-situ Monitoring of Hydriding Kinetics using High Resolution Curvature Measurements.
Renaud Delmelle 1 , Joris Proost 1
1 Division of Materials and Process Engineering, Université Catholique de Louvain, Louvain-la-Neuve Belgium
Show AbstractIn this work, the hydriding and dehydriding kinetics of a model Pd thin film system has been monitored in-situ. The key experimental technique consists of a high resolution curvature measurement setup, which continuously monitors the reflections of multiple laser beams coming off a cantilevered thin film sample. After mounting the sample inside a high vacuum chamber, a H-containing gas mixture is introduced to instantaneously generate a given hydrogen partial pressure (pH2) inside the chamber. The resulting interaction of H with the Pd layer then leads to a volume expansion of the thin film system. This induces in turn changes in the sample curvature as a result of internal stresses developing in the Pd film during a hydriding cycle. Based on such high-resolution curvature data obtained in-situ at different pH2, a two-step model for the kinetics of Pd-hydride formation has been proposed. Expressions for the hydrogen adsorption and absorption velocities have been validated by quantifying relevant kinetic and thermodynamic parameters. A strong influence of the Pd thin film quality on the hydriding kinetics has been identified, while this parameter turned out to have a negligible effect on the equilibrium H-uptake. The latter was found to be mainly influenced by the fraction of crystalline α and β phases in the Pd-H film, which depends only on the imposed pH2. Finally, the reversibility of Pd thin film hydriding has been evaluated by monitoring the curvature evolution during multiple hydriding/dehydriding cycles. Significant residual curvature has been observed during such cycling in vacuum, its level remaining constant from cycle to cyle.
9:00 PM - W8.36
Automated Computational Thermochemistry of Nanoalloys and the Implication on Decrepitation in Hydrogen Storage Materials.
Jian-jie Liang 1
1 , Accelrys, San Diego, California, United States
Show AbstractAn automation in computational thermochemistry had been established to sample the configuration-energy space of nanoalloys and their corresponding hydride materials, in order to understand the decrepitation behavior common in the chemically-activated hydrogen storage materials such as the LiMMg10H24 (M=B,Al,Ga) series. The automation was achieved through pipelining a density functional theory (DFT)-based procedure on large ensembles of structure-composition combinations. With the automation, nanoparticles of varying sizes were considered and large numbers of atomic configurations at given particle sizes were computed with respect to their thermochemistry, to establish the relationship between particle size and average thermochemical properties. The results confirmed that, in bulk phases, the decrepitation of the LiMMg10H24/LiMMg10 series is thermochemically driven, with the energy of solid-solution substitutions being as high as ca. 260 KJ/mol per formula unit. The energy of solid-solution substitution decreases as does the particle size, to close to zero when the particle sizes approach the size range of a few nanomemters. Furthermore, the composition of LiAlMg10H24 was identified to be the most energetically favorable in resisting decrepitations.
9:00 PM - W8.37
Experimental and Theoretical Study for Optimizing Hydrogen Interaction with Metal Organic Frameworks.
Nour Nijem 1 , Jean-Francois Veyan 1 , Kunhao Li 2 , Lingzhu Kong 3 , Jing Li 2 , David Langreth 3 , Yves Chabal 1
1 Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States, 2 Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, United States, 3 Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractTo optimize the volumetric density of hydrogen gas in materials, Metal Organic Framework (MOF) materials are being considered because their chemical nature and size of unit cell can be tailored to weakly attract and incorporate an appropriate number of H2 molecules to achieve good hydrogen volumetric and mass density.We have explored the incorporation of hydrogen into different MOF structures using a combination of experimental and theoretical methods based on infrared (IR) absorption spectroscopy and a newly developed DFT-based theory (DFT-VdW). IR spectroscopy is an important tool that probes the interaction of H2 molecules with materials, and can distinguish possible binding sites based on the perturbation of the internal H2 stretch mode. IR measurements are performed at room temperature and high pressures (20-60 atm) on a variety of MOF materials, chosen to distinguish the effects of ligands, metal centers and overall pore size. Starting with samples that have the general formula M(bdc)(ted)0.5 (bdc=1,4-benzenedicarboxylate, ted= triethylenediamine), differing in the metal core M (Ni and Zn) with 3D pores (~7-8 Å), we then study samples with a M(bodc)(ted)0.5 (bodc= bicyclo[2.2.2]octane-1,4-dicarboxylate) , that is with similar crystal and pore structure, but is made of aliphatic ligands instead of aromatic. We also explore M-Formate (M-Fa) MOFs, with M (Ni, Mn) featuring 1D open channels with smaller pore sizes (~5-6 Å) connected by very small apertures ~1.4x5.3 Å in size. Finally, we study more complex structures, such as Zn2(bpdc)2(bpee) made of layers of two-fold interpenetrating Zn(bpdc) (bpdc=4,4’-biphenyldicarboxylate) nets interconnected by bpee (bpee=1,2-bipyridylethene).IR data and theoretical calculations show negligible effect on the hydrogen vibrational shift upon metal substitution for M(bdc)(ted)0.5 structures. In addition, DFT-VdW theoretical calculations for Zn(bdc)ted0.5 shows up to 12 possible binding sites for hydrogen and ~ 37 cm-1 shift of the para- H (4161 cm-1) at low temperatures and pressures consistent with IR measurements. These binding sites are located away from the metal and closer to the organic ligands. Furthermore, changing the aromatic group with an aliphatic lead to a smaller IR shift ~34 cm-1; indicating the dependence on the type of organic ligand. The formats show smaller shifts (30 cm-1 for Ni-Fa and 28 cm-1 for Mn-Fa) with a weak dependence on metal substitution. On the other hand, interpenetrating structures such as Zn2(bpdc)2(bpee) give a high IR peak intensity, although the shift (~37 cm-1 ) is still determined by the type of ligand interaction. In all cases, the loading is reasonably low (~10% saturation) so that H2-H2 interactions are negligible compared to H2-host interactions, leading to linear intensity dependence.
9:00 PM - W8.38
Synthesis, Characterization and H2 Storage of Functionalized MOF-5.
Jie Yang 1 , Anna Grzech 2 , Theo Dingemans 1 , Fokko Mulder 2
1 Faculty of Aerospace Engineering, Delft University of Technology, Deflt Netherlands, 2 Department of Radiation, Radionuclides and Reactors, Faculty of Applied Sciences, Delft University of Technology, Delft Netherlands
Show Abstract Developing safe and reliable hydrogen storage technologies that meet performance and cost requirements is critical to achieving a future hydrogen economy.[1] Recently, Metal-Organic Frameworks (MOFs) have been considered as a class of promising hydrogen storage materials due to their hydrogen storage capacity, chemical stability and light weight. Current hydrogen storage capacities of MOFs, however, cannot meet the Department of Energy criteria of 6.0 wt%. Increasing effort has been put forth to investigate the synthesis, the physical and chemical properties of MOFs. Our work focuses on elucidating the role of substituent type, i.e. size and electrostatic considerations, and the effect on the hydrogen storage capability of MOF-type frameworks. The results, in combination with computer modeling efforts, will be used to understand and design better MOFs architectures for hydrogen storage.[2-4] In this paper, we will discuss our recent results on (polar) halogen and (non-polar) methyl modifications of MOF-5 frameworks. The two halogens, i.e. Bromine (Br) or Chlorine (Cl) were introduced into the aromatic moiety of MOF-5 using 2-bromoterephthalic acid and 2-chloroterephthalic acid by solvothermal as-synthesis. The MOFs were characterized by XRD, TG-DTA, and FT-IR. Powder-XRD results suggest the two MOFs, labeled by us Br-MOF-5 and Cl-MOF-5, have structures comparable to MOF-5. They also show high thermal stabilities (5% wt loss at 623-673 K). MOF-5, Br-MOF-5 and Cl-MOF-5 show different hydrogen storage capacities at 77 K and low pressure (below 2 bar). Hydrogen storage capacities are 1.48 wt. % on MOF-5, 1.07 wt. % on Br-MOF-5 and 0.34 wt. % on Cl-MOF-5 at 77K and 1 bar, respectively. The results clearly indicate that halogen substitutions on the aromatic moiety of MOF-5 affect the hydrogen storage capacities of MOF-5 type frameworks. In this presentation the role of halogen substitution, on the hydrogen storage capacity of MOF-5, will be discussed in detail and contrasted with non-polar methyl MOF-5 analogs.Keywords: Metal-organic frameworks, Hydrogen capacity, Halogen substitutionsReference[1] N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O. M. Yaghi, Science 2003, 300. [2] T. Gadzikwa, B-S. Zeng, J.T. Hupp, S.T. Nguyen, Chem. Commun, 2008, 3672.[3] F.M. Mulder, T.J. Dingemans, M. Wagemaker, G.J. Kearley, Chem.Phys. 2005, 317, 113.[4] F.M. Mulder, T.J. Dingemans, H.G. Schimmel, A.J. Ramirez-Cuesta, G.J. Kearley, Chem. Phys. 2008, 351, 72.
9:00 PM - W8.39
Ab-Initio Based Grand Canonical Monte-Carlo Simulation on Hydrogen Storage in Metal-Organic Frameworks and Covalent-Organic Frameworks.
Sang Soo Han 1 2 , William Goddard 2
1 , Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 2 , California Institute of Technology, Pasadena, California, United States
Show AbstractHydrogen is well-recognized as a future energy carrier, however its application in on-board vehicles as an energy carrier is limited due to hydrogen storage. A grand challenge in hydrogen storage technology is to develop materials capable of reversible storage greater than 6% by weight at ambient temperatures and pressures. Here, we will present metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) of Prof. Omar Yaghi in UCLA for hydrogen storage. To predict their hydrogen storage capacities, we used a grand canonical Monte-Carlo simulation with ab-initio derived force fields which reproduces well experimental H2 adsorption isotherms. These simulations show that hexagonal MOFs are better than cubic ones due to higher surface area and free volume, and increasing the number of aromatic rings in the organic fragment of MOF structure dramatically increases the H2 uptake capacity. For example, a hexagonal IRMOF-2-60 binds 9.7 wt% H2 storage at 77 K and 70 bar, the highest known value for 77 K. We also used the theory to predict the effect of doping Li into the MOFs, which leads to substantial H2 uptake even at ambient temperatures. For example, IRMOF-2-96-Li leads to 6.0 wt% H2 storage at 273 K and 100 bar, the first material to attain the 2010 DOE target. Moreover, we will show the H2 uptake properties of various COFs and discuss other strategies (appropriate pore size, impregnation, Kubas binding, etc.) to improve hydrogen storage.This research was performed for the Hydrogen Energy R&D Center, one of the 21st Century Frontier R&D program, funded by the Minstry of Education, Science and Technology of Korea.
9:00 PM - W8.4
Theoretical Study on N Doping in Carbon Materials for Hydrogen Storage.
Megumi Kayanuma 1 , Tamio Ikeshoji 1 , Hiroshi Ogawa 1
1 RICS, AIST, Ibaraki Japan
Show Abstract Carbon materials with a large surface area such as activated carbons and carbon nanotubes can store some amount of hydrogen by physisorption. A novel microporous carbon proposed by Kyotani et al have very high surface area with uniform micropores and its hydrogen storage capacity is up to 2.2 wt % at 34 MPa [1]. However, for practical use, much higher capacity is desired. Recent experimental and theoretical studies suggest that nitrogen substitution of carbon nanomaterials change their various properties. Nitrogen substitution of carbon nanotube increases hydrogen absorption capacity [2], although doping microporous carbon with nitrogen has no positive effect for hydrogen uptake [1]. In this study, we examined how nitrogen doping affects physisorption of hydrogen molecule on curved or flat surfaces of graphene fragment by using ab initio molecular orbital calculations. We assumed three simple and small model compounds, [5]circulene (corannulene), [6]circulene (coronene), and [7]circulene (pleiadannulene) by referring to the study by Kyotani et al which shows that their microporous carbons consist of non-stacked, nanometer-sized, curved graphene sheets [3]. Since physisorption is based on van der Waals interaction, adsorption energy on carbon materials may be proportional to their polarizabilities. We substituted carbon atoms in the model compounds by nitrogen in various patterns and searched the best position for high polarizability. Geometry optimization and calculation of the polarizability were done at HF/6-31G(d) level using GAMESS program package. We found several structures with high polarizability and calculated their binding energies with hydrogen molecule at MP2 level. When two nitrogen atoms are substituted for carbon atoms, polarizabilities of model compounds are changed according to the positions of nitrogen atoms. In general, substituted compounds having lower total energy exhibit small or negative change in the polarizability compared with the original pure carbon compound. There are several substitution positions of nitrogen atoms which show higher polarizability than the original compound by about 10 %, although their total energies are relatively high. This result suggests that the physisorption amount of hydrogen molecule on porous carbon can be improved by nitrogen doping at the specific positions. This work has been supported by of NEDO (New Energy and Industrial Technology Development Organization) project “Advanced Fundamental Research on Hydrogen Storage Materials (Hydro-Star)”.Ref. [1] H. Nishihara, P.-X. Hou, L.-X. Li, M. Ito, M. Uchiyama, T. Kaburagi, A. Ikura, J. Katamura, T. Kawarada, K. Mizuuchi, T. Kyotani J. Phys. Chem. C 113 (2009) 3189. [2] B. Viswanathan, M. Sankaran Diamond & Related Materials 18 (2009) 429. [3] H. Nishihara, Q.-H. Yang, P.-X. Hou, M. Unno, S. Yamauchi, R. Saito, J. I. Paredes, A. Martínez-Alonso, J. M. D. Tascón, Y. Sato, M. Terauchi, T. Kyotani Carbon 47 (2009) 1220.
9:00 PM - W8.40
Theoretical Study of Hydrogen Storage in Clathrate Hydrate.
Rodion Belosludov 1 , Oleg Subbotin 1 2 , Hiroshi Mizuseki 1 , Vladimir Belosludov 1 2 , Yoshiyuki Kawazoe 1
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk Russian Federation
Show AbstractAfter a report that the clathrate hydrate of cubic structure II (CS-II) can store around 4.96 wt%, the interest in hydrogen hydrates as potential hydrogen storage materials has risen [1]. However, the extreme pressure required to stabilize the pure hydrogen clathrate makes it impractical. The formation pressure of hydrogen clathrate can be significantly reduced by adding second “large” guest molecule, such as tetrahydrofuran (THF) [2]. This addition is resulted in filling large cages by THF and hence the reduction in the mass of hydrogen storage.Among the several types of gas hydrate structures, some of them, such as hydrate with cubic structure I (CS-I), can hypothetically store more hydrogen than the hydrate of structure CS-II. Therefore, for practical application of gas clathrates as hydrogen storage materials, it is important to know the region of stability of these compounds as well as the hydrogen concentration at various pressures and temperatures. In order to accurately estimate the thermodynamic properties of hydrogen hydrates, we developed a method based on the solid solution theory of van der Waals and Platteeuw with some modifications that include multiple occupancies, host relaxation, and the description of the atoms or small molecules behavior in the cavities [3]. Using this approach, the phase diagram (P,T) of the pure hydrogen clathrate of structure CS-II has been constructed in agreement with the recent experimental diagram [1]. It has been also estimated that the pure hydrogen hydrate of CS-I structure can store more hydrogen but this structure is thermodynamically unstable as comparable with hexagonal ice. Therefore, the H2-Propane-H2O (hydrate CS-II structure) and the H2-Methane-H2O (hydrate CS-I and CS-II structures) systems have been investigated with different propane, methane and H2 concentration. The calculations showed that the formation pressure of hydrogen hydrates was significantly reduced in the presence of propane as in the case of THF. However, in the case of propane there is possibility of increasing the amount of hydrogen stored (around 4 wt% of hydrogen at 270 K) at small concentration of propane in gas phase. In the case of mixture hydrogen-methane hydrate, it was found that the CS-II hydrates can be stabilized at lower pressure than the pure hydrogen CS-II hydrate [4]. Moreover, the methane can support to stabilization of CS-I hydrate and the thermodynamic region of stability is strongly depends on the concentration of methane in gas phase. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Advanced Fundamental Research Project on Hydrogen Storage Materials”.REFERENCES[1] V.V. Struzhkin et al. Chem. Rev. 107 (2007) 4133-4151.[2] L.J. Florusse et al. Science 306 (2004) 469-471.[3] V.R. Belosludov et al. Materials Transactions, 29 (2007) 704-710.[4] V.R. Belosludov et al. Int. J. Nanoscience, 1-2 (2009) 57-63.
9:00 PM - W8.41
A Density Functional Theory Study of Sodium Alanate Nanoparticles.
Tim Mueller 1 , Gerbrand Ceder 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Somerville, Massachusetts, United States
Show AbstractSodium alanate (NaAlH
4) is a widely-studied hydrogen storage material, with a theoretical gravimetric capacity of 5.6%. Bulk sodium alanate releases hydrogen at temperatures well above 100° C, outside the target temperature range for PEM fuel cells. However it has recently been shown that for 2-10 nm sodium alanate nanoparticles the peak desorption temperature is 70° C [1], within the target range for PEM fuel cells. The activation energy for hydrogen release in nanoparticles is significantly lower than the bulk activation energy for reasons that remain unknown. We apply computational methods to better understand the thermodynamics and kinetics of hydrogen release from sodium alanate nanoparticles. Using density functional theory, we generate cluster-expansion Hamiltonians that enable us to calculate the size-dependent shapes and energies of sodium alanate nanoparticles and their decomposition products. Our calculations reveal low-energy surfaces and edges that might be important for hydrogen storage and release reactions. In addition, we will present the calculated hydrogen storage reaction energy as a function of particle size.
1. Balde, C.P., et al., Sodium alanate nanoparticles - Linking size to hydrogen storage properties. Journal of the American Chemical Society, 2008. 130(21): p. 6761-6765.
9:00 PM - W8.42
Improvement in Power Density of Rechargeable Air Battery using Hydrogen Storage Alloy.
Masatsugu Morimitsu 1 , Takahito Kondo 1 , Naoki Osada 1 , Koji Takano 2
1 , Doshisha University, Kyoto Japan, 2 , Kyushu Electric Power, Inc., Fukuoka Japan
Show AbstractThis paper presents our recent development on an air secondary battery using hydrogen storage alloy as the negative electrode. The positive electrode consists of nickel, PTFE, and pyrochlore-type oxide, Bi2Ir2O7-Z, and a coin shape of metal hydride(MH)-air secondary battery has been designed, assembled, and evaluated. The battery shows stable charge and discharge voltages during constant current operation even at high current density and achieves a high power density, 81 W dm-3, which is comparable to commercial nickel-hydrogen secondary batteries.
9:00 PM - W8.5
A Molecular-Dynamics Study on Metal-Immersed Hydrogen Fluids.
Yasushi Takeuchi 1
1 , National Institution for Materials Science, Tsukuba Japan
Show AbstractMolecular dynamics (MD) simulations on hydrogen fluids containing metal atoms were carried out. H-H interactions under the influence of metal atoms are studied. Implications for hydrogen-storage alloys are discussed, especially taking emphases on H-H interactions and their effects on the preference sites of hydrogen.
9:00 PM - W8.6
New Type of Reversible Hydrogen Storage Material at Low Temperature.
Pabitra Choudhury 1 3 , Sesha Srinivasan 3 2 , Bhethanabotla Venkat 1 3 , Yogi Goswami 1 3 , Elias Stefanakos 2 3
1 Department of Chemical Engineering, University of South Florida, Tampa, Florida, United States, 3 Clean Energy Research Center, University of South Florida, Tampa, Florida, United States, 2 Department of Electrical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractIn this study, a promising new type of complex borohydride (Li-Mn-B-H) was evaluated for on-board hydrogen storage. This new complex hydride was prepared from the precursor materials via. solid state mechano-chemical process. The B-H stretch occurrence at 2374 cm-1 in addition to two other B-H bonding bands of LiBH4 (2228 and 2297 cm-1) from the FTIR investigation confirm the formation of new type of complex borohydride at room temperature. Gas chromatography studies of both undoped and doped (Li-Mn-B-H) system demonstrate that the evolved gas is mainly hydrogen and does not contain members of borane family. Though this complex borohydride exhibits high theoretical hydrogen storage capacity (~8 wt.%) at lower temperature (<150 oC), the reversible hydrogenation and dehydrogenation cycling is not promising. The new type of system uptakes up to 3.0 wt% hydrogen at 100 oC and release all the hydrogen at 150 oC for one cycle only and diminish cyclic capacity subsequently. The cyclic reversibility can be improved by ad-mixing optimum amount (10mol %) of MgH2. The destabilization strategy has been adopted to convert this new material to become reversible, and these results will also be presented.
9:00 PM - W8.7
Mechanism of Specific Hydrogen Adsorption on Lithium-Doped Mesoporous Silica.
Masaru Kubo 1 , Hiroshi Ushiyama 1 , Atsushi Shimojima 1 , Tatsuya Okubo 1
1 , The University of Tokyo, Tokyo Japan
Show Abstract The development of safe and efficient methods to hydrogen storage is eager for the use of hydrogen with fuel cells in vehicle applications. The use of hydrogen physisorption on porous materials is one of the promising methods; however, the hydrogen uptake is generally limited because of the weak interactions. In order to increase the hydrogen uptake, it is important to incorporate specific adsorption sites on the pore surfaces. We have recently found that lithium-doped mesoporous silica (Li-MPS) has a specific hydrogen adsorption capability at ambient temperature [1]. It could adsorb hydrogen 4~5 times more than undoped mesoporous silica at room temperature. However the mechanism has not been well understood yet. If this mechanism is elucidated, a new method for incorporating adsorption sites into the porous materials would be proposed. In this work, adsorption models were constructed from the experimental results, and the detail of the reaction path for the formation of Li-MPS and the mechanism of specific hydrogen sorption on Li-MPS were investigated using the quantum calculation to these models. Li-MPS was prepared by impregnating mesoporous silica (MPS) with LiCl ethanol solution, followed by heat treatment at 773 K at heat up rate of 4 K/min in argon flow of 100 cm3/min. During the heat treatment, since Cl species were released in the form of ethylchloride, Li cations and delocalized electrons remained on the surface of silica. Inferred from 7Li MAS NMR and FT-IR, remained Li cations would be stabilized in the form of ≡Si-OLi groups instead of silanol groups. The H2 uptakes of Li-MPS and MPS at 77 K and 1 atm were 0.80 wt% and 0.50 wt%, respectively. Also the adsorption enthalpy of Li-MPS was 4.8 kJ/mol, which is in good agreement with quantum calculation result (5.1 kJ/mol). The calculation suggests that the specific hydrogen adsorption of H¬2 to Li-MPS is due to the orbital interaction that is induced by the electron transfer from HOMO of H2 molecules to the LUMO of Li cation.[1] Chino N. et al., Journal of Physical Chemistry B, 2005, 109, 8574-8579.
Symposium Organizers
Etsuo Akiba National Institute of Advanced Industrial Science and Technology
William Tumas National Renewable Energy Laboratory
Ping Chen National University of Singapore
Maximilian Fichtner Karlsruhe Institute of Technology
Shengbai Zhang Rensselaer Polytechnic Institute
W9: Complex Hydrides III
Session Chairs
Thursday AM, December 03, 2009
Room 306 (Hynes)
9:30 AM - **W9.1
Metal Ammonia Boranes.
Anthony Burrell 1 , Himashinie Diyabalanage 1 , Roshan Shrestha 1 , Kate Ryan 2 , Martin Jones 2 , William David 3
1 , Los Alamos National Lab, Los Alamos, New Mexico, United States, 2 Chemistry, Oxford University, Oxford United Kingdom, 3 ISIS, Rutherford Appleton Laboratory, Didcot United Kingdom
Show AbstractAmmonia-borane (NH3BH3), a potential candidate for effective chemical hydrogen storage, garnered much interest due to its high hydrogen storage capacity of 19.6 wt% and low molecular weight, which are ideal features for hydrogen storage material. Even though ammonia-borane has a high molecular hydrogen storage capacity, only 2/3 of this hydrogen is readily accessible. The modification of ammonia-borane is desirable to improve many of the properties of this promising hydrogen storage material. We have undertaken a systematic study of ammonia-borane derivatives that can quickly release hydrogen and be reprocessed using hydrogen pressure. The materials we have prepared are derivatives of ammonia-borane where a new covalent bond between the nitrogen and a metal or a main group element, has been formed (eg: M(NH2BH3)n, where; M = Li, K, Ca, Mg, Ti, Sc etc. n = 1-6). They have significantly different thermal properties than ammonia-borane, undergo loss of H2 without significant foaming, a common problem associated with solid NH3BH3 and offer several advantages over NH3BH3 including better thermal stability and more controlled hydrogen release over a wider temperature range.
10:00 AM - **W9.2
Structure, Dynamics and Thermodynamics of Ammonia Borane and its Amidoborane Derivatives.
Bill David 1 2 , Kate Ryan 1 2 , Martin Jones 1 2 , Peter Edwards 2 , Tom Autrey 3 , Avery Luedtke 3 , Takeshi Yamada 4 , Osamu Yamamuro 4
1 ISIS, STFC, Chilton United Kingdom, 2 Inorganic Chemistry Laboratory, University of Oxford, Oxford United Kingdom, 3 Fundamental Science Directorate, Pacific Northwest National Laboratory, Richland, Washington, United States, 4 ISSP, University of Tokyo, Tokyo Japan
Show AbstractAmmonia borane (NH3BH3) and its amidoborane derivatives (LiNH2BH3 and NaNH2BH3) have been extensively studied as prototypic hydrogen storage materials. In this talk, we present detailed structural, dynamic and thermodynamic analysis of ammonia borane and lithium amidoborane as a function of temperature. Ammonia borane, in particular, is shown to behave in a complex manner in the solid state. The subtleties of this behaviour shed light on the importance of dihydrogen bonding in ammonia borane. This bonding motif is, however, absent in the isostructual compounds, LiNH2BH3 and NaNH2BH3, and thus dihydrogen bonding is not an essential property for hydrogen decomposition. However, ammonia borane and the alkali-metal amidoboranes both contain protic and hydritic hydrogens which are believed to be important in promoting hydrogen formation on decomposition. The importance of the two distinct forms of hydrogen will be addressed in general terms for lightweight chemical hydrides as potential hydrogen storage materials.
10:30 AM - **W9.3
Dynamics and Phase Transformations in Ammonia Borane and Related Compounds by Anelastic Spectroscopy and Calorimetry.
Rosario Cantelli 1 , Annalisa Paolone 1 2 , Oriele Palumbo 1 3 , Pasquale Rispoli 1 , Tom Autrey 4 , Abhijeet Karkamkar 4
1 Physics, Sapienza University of Rome, Rome Italy, 2 , Laboratorio Regionale SuperMAT, CNR-INFM, Salerno Italy, 3 , CNISM c/o Sapienza University of Rome, Rome Italy, 4 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractAmmonia borane, NH3BH3, has a very interesting hydrogen content of 19% wt and moderate dehydrogenation temperatures (less than 100 °C). However, the rates of H2 release at temperatures below 85 °C need to be increased, borazine formation must be prevented, and regeneration must be made more energy efficient for applications in fuel cells.An anelastic spectroscopy study of this material displayed the presence of thermally activated relaxation processes at about 100 K (for a sample vibration frequency of ~1 kHz), due to the dynamics of a very mobile species with pre-exponential factors of the relaxation rate typical of point defect relaxation. From a comparative analysis of our results with NMR data and theoretical estimates, we attributed the measured processes to the torsional and rotational motions of the NH3 and BH3 groups of the ammonia-borane complex. A systematic study of the structural phase transition occurring around 220 K in NH3BH3 and in its partially and fully deuterated anologues was also performed by combining anelastic spectroscopy and differential scanning calorimetry. The transition is accompanied by a latent heat which denotes a 1st order character. On the deuterated sample the enthalpy variation is reduced and the transition is shifted towards higher temperatures. Both NH3BH3 and its deuterated compounds display a temperature hysteresis between cooling and heating which varies with the temperature rate and is reduced to ~0.5 K in quasi-static conditions . In addition, the modulus and energy-loss measurements showed that the width of the transformation is rather small (a fraction of K), thus indicating that the coexistence region between the two phases is very narrow. During isothermal ageing, the transformation of the low-temperature orthorhombic phase into the high-temperature tetragonal one occurs with a time constant of ~16 minutes in NH3BH3 and increases in the deuterated compound, showing a drastic slowing down of kinetics induced by sample deuteration.Recently it was reported that artificial assembling of ammonia borane consisting in the infusion of NH3BH3 into mesoporous silica scaffolds increases the desorption rates of hydrogen and decreases both the contamination of hydrogen from borazine and the dehydrogenation enthalpy. We studied to which extent the basic physical properties of ammonia borane are modified when this compound is dispersed as a single monolayer inside porous silica channels. In particular we showed that nano-confining of NH3BH3 prevents the structural phase transition readily observed in bulk NH3BH3. The occurrence of different electronic and lattice interactions in nano-confined hydrogen storage systems could provide an alternative approach to modify the physical characteristics of other bulk hydrogen storage materials to obtain enhanced dehydrogenation and rehydrogenation properties.
11:30 AM - **W9.4
Quantitative Measurements of Ammonia in the Dehydrogenation of Alkali Metal Amidoboranes.
Zhitao Xiong 1 , Ping Chen 1 , Jianping Guo 1
1 , Dalian Institute of Chemical Physics, Dalian China
Show AbstractA new type of hydrogen storage material, namely alkali metal amidoborane, was recently synthesized by reacting ammonia borane (NH3BH3, AB in short) with alkali metal hydrides (i.e. LiH and NaH) either by mechanical milling [1-3] or wet-chemical process [4, 5]. The substitution of one H of NH3 in NH3BH3 by alkali metal leads to the alteration of polarity and intermolecular interactions (specifically the dihydrogen bonding) of NH3BH3. Consequently, those alkali metal amidoboranes exhibit improved dehydrogenation profiles compared with pristine AB.For N-containing hydrogen storage materials there is always concern on the formation of by product-NH3 in the dehydrogenation process. In this study, NH3 evolutions in the thermal decomposition of lithium and sodium amidoboranes were measured quantitatively. It was found that when heating LiNH2BH3 and NaNH2BH3 in a dynamic heating system, i. e., in TPD system where gaseous products are blew away instantaneously by carrier gas, the NH3 desorbed are around 3000-4000ppm. However, when heated in a close system at temperatures below 100C the NH3 concentrations are drastically decreased to 200ppm or less. It appears that NH3, upon formation, can further react with reactant and produce H2. Our experimental results show that when heating NaNH2BH3 in NH3 in a NaNH2BH3/NH3 molar ratio of 5/1 in a closed system, only 7% NH3 survived at the completion of reaction.Reference1. Z. T. Xiong, C. K. Yong, G. T. Wu, P. Chen, W. Shaw, A. Karkamkar, T. Autrey, M. O. Jones, S. R. Johnson, P. P. Edwards, W. I. F. David, Nature Materials, 2008, 7, 1382. H. Wu, W. Zhou, T. Yildirim, J. Am. Chem. Soc., 2008, 130, 148343. J. Spielmann, G. Jansen, H. Bandmann, S. Harder, Angewandte Chemie International Edition, 2008, 47, 62904. Z. T. Xiong, G. T. Wu, Y. S. Chua, J. J. Hu, T. He, W. L. Xu and P. Chen, Energy Environ. Sci., 2008, 1, 360-3635. Z. T. Xiong, Y. S. Chua, G. T. Wu, W. L. Xu, P. Chen, W. Shaw, A. Karkamkar, J. Linehan, T. Smurthwaite and T. Autrey, Chem. Commun., 2008, 43, 5595
12:00 PM - **W9.5
B,N-hydrides: Characterization and Chemistry.
Paul Anderson 1
1 School of Chemistry, University of Birmingham, Birmingham United Kingdom
Show AbstractComplex hydrides of the light alkali metals, such as Li4BH4(NH2)3, Li2BH4NH2 and Na2BH4NH4, contain the anions BH4− and NH2−, and release relatively large amounts of hydrogen (up to 13.5% by weight) at moderate temperatures, which may be reduced further through the addition of suitable transition metal catalysts. In spite of these desirable features, the potential usefulness of this class of materials is currently compromised by a number of less favourable aspects, such as a tendency for hydrogen desorption to be accompanied by the release of NH3 and a lack of reversibility.For the lithium phases the major product of hydrogen desorption is one or more polymorphs of Li3BN2. As the B:N ratio in this compound does not match that of either amide–borohydride material, ammonia release can occur as a means of compensation, but may be effectively suppressed through means as diverse as the presence of excess LiBH4 or LiNH2 to adjust the B:N ratio, the use of catalysts or careful control of the desorption conditions. The stability of Li3BN2, however, remains a major obstacle to rehydriding.Ammonia borane has also received a significant amount of attention in the field of hydrogen storage. This is due to an even higher gravimetric hydrogen content of 19.6 wt% and a high volumetric hydrogen density of 145 kg H2 m−3. However, only approximately 6.5 wt% of this hydrogen can be released in the temperature range 70 – 120°C. Furthermore, on decomposition ammonia borane releases undesirable gases such as borazine, which would poison fuel cells and the hydrogen release is found to be irreversible.The reaction of alkali and alkaline earth metal hydrides with ammonia borane leads to the synthesis of a variety of new phases, which exhibit modified decomposition pathways and onset temperatures of hydrogen desorption as low as 35°C. The characterization of these new phases has been investigated by powder X-ray diffraction, temperature programmed desorption, intelligent gravimetric analysis, Raman spectroscopy and solid state 11B NMR, with a view to determining their chemical compositions and structures, and elucidating the often complex reaction pathways involved in their formation and decomposition.
12:30 PM - **W9.6
Ammonium Borohydride: Properties Arising from Storing Hydrogen on both Anionic and Cationic Sites.
Abhi Karkamkar 1 , Shawn Kathmann 1 , Greg Schenter 1 , Nancy Hess 1 , Tom Autrey 1
1 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractWe will discuss the synthesis, stability, structure and hydrogen desorption properties of ammonium borohydride. This unique borohydride complex releases greater than 20 wt% hydrogen, at temperatures ranging between 40 -160 °C, in three moderately exothermic steps. The NH4BH4 complex crystallizes at room temperature and standard pressure in a rock-salt structure. The experimental lattice parameters provide an estimate of the volumetric density, ca. 154 g hydrogen/liter of NH4BH4. The high volumetric capacity is comparable to many metal hydrides, however, as NH4BH4 has hydrogen stored on both the cationic and anionic sites which leads to a significantly greater gravimetric density (244 gm hydrogen/kg).
W10: Complex Hydrides IV
Session Chairs
Tom Autrey
Anthony Burrell
Thursday PM, December 03, 2009
Room 306 (Hynes)
2:30 PM - **W10.1
Sorption Mechanism and Thermodynamics of Complex Hydrides.
Andreas Zuettel 1
1 , EMPA, Zurich Switzerland
Show AbstractThe stability of complex hydrides is described based on the enthalpy of formation of the elemental hydrides, i.e. described by the Pauling electronegativity and the enthalpy of formation of the complex, i.e. an empirical equation by Miwa using the electronegativity of the cation atom. The mechanism of the hydrogen absorption and desorption in complex hydrides is not known yet. In the conventional view the complex hydride with a general formula of Mx+[TH4-]x (M = Li, Na, Mg, Ca…; T = Al, B, N and x is the stoichiometry) releases H- to form MHx + x●TH3 [1,2]. The stability of the AlH3 < BH3 < NH3, therefore, alanates decompose into hydrogen and aluminum while boranates tend to liberate beside hydrogen also B2H6 and the ammonium spontaneously decomposes into NH3. Therefore, the thermodynamics i.e. stability and kinetics, is calculated based on the intermediate products identified. The stability of the TH4- is determined by the localisation of the electron on the T-atom. As a consequence the stability of the complex hydride strongly depends on the electronegativity of the cation. However, this approach is only able to describe the stability of the forth hydrogen atom in the anion. The stability of the neutral and “hypothetical” TH3 is crucial for the decomposition process.The appearance or the induced creation of intermediate products in the hydrogen desorption reaction is a possibility to destabilize the complex hydrides and to facilitate the reversible hydrogen absorption.
3:00 PM - **W10.2
Stability of Hydrogen Clathrates of Ammonia Borane.
Maciej Gutowski 1
1 Chemistry, Heriot-Watt University, Edinburgh, Scotland United Kingdom
Show AbstractWe have developed a concept of hierarchical hydrogen storage. It is illustrated by clathrates built from ammonia borane and loaded with molecular hydrogen. These new hypothetical materials would have two levels of hydrogen storage: (i) physisorbed H2 and (ii) hydrogen chemically bound in ammonia borane. The advantages of these materials would be: (i) the fast kinetics of release and uptake of physisorbed hydrogen and (ii) very high gravimetric and volumetric hydrogen density. We developed a construction principle for clathrates of ammonia borane, performed electronic structure calculations for isolated cages and for periodic structures built from these cages. Finally, we developed a statistical model of clathrate phase equilibria that is based on calculated guest-host interactions, entropy of guest molecules in spherical cages, and corrections for nonideality of gases. We demonstrated that due to entropic effects, hydrogen storage in clathrate materials requires smaller hydrogen binding energy than in common solid systems (e.g. borohydrides). In addition we demonstrated that pressures required for room temperature hydrogen storage in small cages of hydrate structures are practically unattainable. Finally, clathrates of ammonia borane loaded with hydrogen should be more stable than the experimentally observed hydrogen hydrates, which results from different sizes of cages in hydrates and in ammonia borane clathrates.
4:00 PM - **W10.3
Low Energy Regeneration Routes for Kinetically Stabilized Hydrides.
Jason Graetz 1 , James Reilly 1 , David Lacina 1 , James Wegrzyn 1
1 Energy Sciences and Technology, Brookhaven National Lab, Upton, New York, United States
Show AbstractKinetically stabilized hydrides exhibit a low heat of reaction and rapid hydrogen evolution rates at low temperatures making them well suited for mobile PEM fuel cell applications. However, a critical challenge exists to regenerate or recycle these hydrides from the spent fuel and H2 gas in a low cost process. In this effort we demonstrate a low energy route to regenerate the kinetically stabilized hydrides (LiAlH4 and AlH3) at low pressure without the need for mechanical milling. We employ a two-step regeneration process, which involves initially forming a stabilized hydride adduct using amines and ethers, followed by adduct separation and hydride recovery.The regeneration of LiAlH4 involves the direct formation of the stabilized hydride adduct (LiAlH4-4THF) from catalyzed aluminum (Al*), LiH and THF. The stabilized adduct is separated in a low temperature desolvation step to recover crystalline LiAlH4. The regeneration of AlH3 involves the direct formation of an alane amine (AlH3-NR3), followed by amine exchange (transamination), separation and AlH3 recovery. We demonstrate that AlH3 can be formed by direct hydrogenation of Al* in a liquid medium at low pressures and temperatures using a number of different tertiary amines (NR3 = trimethylamine, triethylenediamine, dimethylethylamine, quinuclidine and hexamine). We note that this simple regeneration procedure may be broadly applicable to other kinetically stabilized hydrides (e.g. Mg(AlH4)2).
4:30 PM - W10.4
Heat Propagation in LiNH2.
Biswajit Paik 1 , Masami Tsubota 1 , Takayuki Ichikawa 1 , Yoshitsugu Kojima 1
1 IAMR, Hiroshima University, Higashi Hiroshima Japan
Show AbstractSince Chen et al (1) established amide-imide as a model hydrogen storage system, a significant amount of study has been carried out with LiNH2, including its phases (2) and structure (3, 4), thermodynamics (5), kinetics of H-sorption (6) etc. Nevertheless, to propose a feasible option of hydrogen storing based on amide-imide system we need to study its thermal properties too; as the Hydrogen charging/discharging in this system is believed to follow a sorption mechanism triggered by the thermal activation. In heat-system designing we require to know some basic thermal parameters. In the present work we aim to study the thermal properties of Li-amide and the variation of these parameters within a temperature range 30-150 degree C. The thermal parameter in the present study includes: thermal diffusivity (α), specific heat capacity (Cp), and thermal conductivity (κ). The samples used in the present study are commercially available Li-amide powders and the single crystals prepared from this powder by the melting method. The powders are mechanically pressed (within a pressure range of 1.25 to 1.75 GPa) to make tablets which are then subjected to the thermal studies. Thermal diffusivity has been measured by the temperature wave analysis (TWA) method (7) whereas the specific heat is estimated from the Differential Scanning Calorimeter (DSC). The thermal conductivity is estimated from these values using the relationship, α=κ/Cp.ρ where ρ is density of LiNH2. The thermal diffusivity estimated at room temperature in the single crystal of Li-amide is 6.5x10-7 m2s-1 which is higher than the Li-amides of tablets (α<5x10-7 m2s-1). It is also observed at ambient temperature that the diffusivity values decrease with the increased mechanical pressure applied to make the tablets. However, with temperature the diffusivity decreases in all these samples. Specific heat capacity of Li-amide has been observed to decrease with temperature (up to 150 degree C in this study). The estimated thermal conductivity (κ) for Li-amide single crystal varies marginally within 1.5 W/mK (at room temperature) to 1.2 W/mK (at 150 degree C) as a result of the increasing specific heat and a decreasing thermal diffusivity.The result obtained in this study can be analyzed in terms of the lattice contribution in thermal conductivity (8) and the heat transport through a medium with the layered microstructure(9). References1. P. Chen et al, Nature, 420(2002), 302-3042. W.I.F. David et al, J.Am.Chem.Soc., 129(2007), 1594-16013. M.H. Sørby et al, J.Alloy.Comp, 428(2007), 297-3014. T. Ichikawa and S. Isobe, Z.Kristallogr., 223(2008), 660-6655. A.R. Akbarzadeh et al, Adv.Mat., 19(2007), 3233-32396. H.Y. Leng et al, J.Power Source, 156(2006), 166-1707. J. Morikawa et al, J.Appl.Phys., 103(2008), 0635228. R. Mévrel et al, J.Eur.Ceram.Soc., 24(2004), 3081-30899. N. Muñoz Aguirre et al, phys.stat.sol. (b), 220 (2000), 781-787
4:45 PM - W10.5
Alane Formation on Ti-doped Al(100) and Al(111) Surfaces.
Irinder Chopra 1 , Jean-Francois Veyan 1 , S. Chaudhuri 2 , Yves Chabal 1
1 Material Science and Engineering, University of Texas at Dallas, Dallas, Texas, United States, 2 , Washington State University, Spokane, Washington, United States
Show AbstractComplex metal hydrides, such as NaAlH4, are being considered as candidates for hydrogen storage as they have the potential to reversibly release and recapture hydrogen at relatively mild conditions. Alane Clusters (AlxHy) are the mass transport intermediates in the hydrogen reactions involved in hydrogen uptake and release on aluminum surfaces. Ti doping of aluminum surfaces may help lower the temperature and the pressure for the hydrogen adsorption on and desorption from aluminum surfaces. Thus understanding the surface chemistry behind the formation and evolution of alane clusters as a function of Ti doping is important. We have undertaken a comprehensive study of H interaction with Ti-doped Al (100) and Al(111) surfaces to understand the mechanisms underlying this reversible behavior important for hydrogen storage. Using in-situ infrared absorption spectroscopy we have shown that the nature of the alane formation is critically dependent on the structure of the undoped surfaces (no Ti). Al(100) surfaces require higher atomic hydrogen doses as compared to Al(111) surfaces for similar surface saturations of alanes. The nature of the alane formation is also dependent on both H exposure and sample temperature. At low temperatures (~90K), small alanes such as AlH3 and Al2H6 are predominant. At higher temperatures (~ 250K), larger alanes are formed1. For Ti-doped Al(100) surfaces, alane formation is observed when dosing with atomic hydrogen at 90K. For low Ti doping, the formation of both low and high mass alanes is observed. Increasing Ti doping (>0.3ML) inhibits the formation of higher mass alanes. On Ti-doped surfaces, the surface kinetics of hydrogen and alanes is critically dependent on the nature of the surface and Ti doping concentration. For instance, the mobility of the hydrogen and alanes is higher on Al(111) surfaces than on Al(100) surfaces. Increasing the Ti doping inhibits the mobility of the various species and thus inhibits formation of higher mass alanes. Thus, this study of alane formation on the Ti doped Al(100) and Al(111) surface as a function of H exposures, substrate temperatures, crystal orientation and the optimum Ti coverage makes it possible to explore the mechanism and optimum conditions for efficient alane formation. 1 Formation and Bonding of Alane Clusters on Al(111) Surfaces Studied by Infrared Absorption Spectroscopy and Theoretical Modeling Chaudhuri, S.; Rangan, S.; Veyan, J.-F.; Muckerman, J. T.; Chabal, Y. J.J. Am. Chem. Soc.; (Article); 2008; 130(32); 10576-10587.
5:00 PM - W10.6
Formation and Migration of Native Defects in NaAlH4.
Gareth Wilson-Short 1 , Anderson Janotti 1 , Khang Hoang 1 , Chris Van de Walle 1
1 Materials Department, University of California, Santa Barbara, California, United States
Show AbstractNaAlH4 is an interesting hydrogen storage material. While its theoretical hydrogen capacity by weight (5.6 %) is not sufficient for automotive applications, it may be useful in other applications. More importantly, as one of the most widely studied hydrogen storage materials, it serves as a prototype for fundamental investigations of kinetics. Reversible absorption and desorption at reasonable temperatures is accomplished by adding a small amount of titanium or other transition metal impurities. The mechanism of this kinetic improvement has remained controversial. In recent work, based on first-principles calculations, we have suggested that titanium acts as an electronically active impurity, promoting the diffusion of hydrogen [1]. Desorption of hydrogen and decomposition of NaAlH4 requires not only mass transport of hydrogen but also of aluminum and/or sodium. This process is likely to be mediated by native defects. We have therefore investigated the structure and stability of native defects in NaAlH4 based on first-principles density functional theory. For relevant defects, migration enthalpies are also calculated. These allow us to estimate diffusion activation energies for the various defects that may be responsible for mass transport. We find that most of the relevant defects exist in charge states other than neutral, and that consideration of these charge states is essential for a proper description of migration and kinetics. Our results differ from some of the previous theoretical treatments, and we propose specific new mechanisms to explain the observed activation energies and their dependence on the presence of impurities.[1] A. Peles and C. G. Van de Walle, Phys. Rev. B 76, 214101 (2007).This work is supported by the Department of Energy.
5:15 PM - W10.7
NaAlH4 and NaH/Carbon Nanocomposites for Hydrogen Storage.
Philipp Adelhelm 1 , Jinbao Gao 1 , Krijn de Jong 1 , Petra de Jongh 1
1 Inorganic Chemistry and Catalysis, Utrecht University, Utrecht Netherlands
Show AbstractMetal hydrides are promising materials for the on-board storage of hydrogen, as they allow the storage of large quantities of hydrogen in a small volume at moderate temperatures and pressures. However, most of the metal hydrides are thermodynamically too stable and release hydrogen at temperatures that are too high for practical applications. Furthermore, kinetics are often slow leading to hydrogen release/uptake at insufficient rates and often poor reversibility. Kinetics can be improved by extensive ball-milling, and the addition of dopants. However, for many systems no effective catalysts have been found, and the impact of the dopants is often poorly understood, which is also due to the heterogeneous nature of ball milled materials. In an alternative approach to improve kinetics and possibly to alter the thermodynamics, we reduce the particle size to the low nanometers scale using melt infiltration of a nanoporous support. In this project we focussed on NaAlH4/carbon nanocomposites. The NaAlH4 and NaH/carbon nanocomposites were synthesized by melt infiltration of porous carbons under protective atmosphere, similar to the synthesis described earlier for Mg, or under high H2 pressure. Different carbon materials (activated carbon, graphitic carbon, graphite) with a wide range in porosity and structural characteristics were used for this purpose. The weight fraction of active material in the nanocomposite was typically between 10-60 wt%. Hydrogenation was conducted in an tubular oven (RT, 1 bar H2) or in an autoclave (RT, 50 bar H2) 325 oC. The structural properties of the composite materials were characterized by XRD, N-physisorption, and NMR. Hydrogen sorption properties were investigated using thermally programmed desorption (TPD), and gravimetric and volumetric H2 sorption measurements. Structural characterization evidenced the filling of the pores of the carbon by NaAlH4 and showed that no bulk NaAlH4 remained after the melt infiltration synthesis, although a small amount of metallic Al was observed. It is known that NaAlH4 shows very slow kinetics and very limited reversibility in the absence of catalysts. Surprisingly, we found that for the nanocomposites in the absence of such catalysts the dehydrogenation of NaAlH4 was reversible, even under relatively mild conditions. Furthermore a strong indication for a change in the thermodynamic equilibrium was found, which motivated us to study especially the NaH/nanoporous carbon system in more detail. It was observed that intimate contact with the carbon allowed the reversible hydrogen release from NaH at much lower temperatures than for bulk NaH. As NaH is a decomposition product during dehydrogenation of NaAlH4 these findings are also relevant to improve the hydrogen desorption properties and storage capacity of NaAlH4.
5:30 PM - W10.8
Improvement of Hydrogenation Properties for the LiH-NH3 System by Mechanical Milling.
Masami Tsubota 1 , Kyoichi Tange 2 , Satoshi Hino 1 , Shigehito Isobe 1 , Kosei Nakamura 2 , Masashi Nakatake 3 , Hikaru Yamamoto 2 , Hiroki Miyaoka 1 , Takayuki Ichikawa 1 2 , Yoshitsugu Kojima 1 2
1 Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan, 2 Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan, 3 Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan
Show AbstractRecently, the search for alternative fuel has been spurred because of the global issues such as the fossil fuel depletion, an overall increase in the world’s energy consumption and the emission of carbon dioxide. In order to distribute the primary energy sources, the suitable secondary energy should be developed. One of the forerunners is hydrogen, which is proposed to greatly reduce the emission of carbon dioxide and therefore play a major role in tackling global warming. Storing hydrogen in high-density, easily-controlled and safe is a difficult problem. Storage in the form of metal hydrides has been studied for four decades, and more recently so-called chemical hydrides composed of light elements like alanate systems, borohydride systems, amide/imide systems have been developed. Some chemical hydrides have promising hydrogen storage properties, however, almost all hydrides suffer from crucial problems about the slow kinetics and the difficulty in rehydrogenation.Ammonia NH3 is also thought to be a hydrogen storage material. NH3 has the advantages of a high hydrogen density with 17.6 mass% and 0.12 kgH2/L, a well-developed technology for synthesis, decomposition, and transportation. Moreover, it emits no CO2 at the end user. Although it has a disadvantage of the toxicity of NH3, the problem of handling could be overcome by reacting NH3 with materials or absorbing NH3 into materials. The reaction between NH3 and alkaline metal hydride MH to form amide MNH2 and H2 is an example for the former. Here, we demonstrate the drastic improvement of the reactivity between metal hydrides and ammonia and its mechanism.The samples used in the present study are commercially available lithium hydride LiH and milled one. The effects of milling on the structural properties were investigated by synchrotron radiation X-ray diffraction, X-ray photoelectron emission spectroscopy (XPS) experiments. It was found that milled LiH reacted with ammonia even at room temperature and the reverse reaction also took place at 200 °C. Thus, the mechanical pretreatment drastically improved the reactivity to form hydrogen and amide [1, 2]. The XPS results showed that a hydroxide phase existed on the surface of LiH and the milling reduced the hydroxide phase from the surface.References[1] Y. Kojima et al., Mater. Res. Soc. Symp. Proc. 1042 (2008) S06-01.[2] Y. Kojima et al., J. Mater. Res. in press (2009).
5:45 PM - W10.9
Superionicity in Li-N-H Hydrogen Storage Materials and How it is Affected by the Hydrogen Content.
C. Moyses Araujo 1 2 , A. Blomqvist 1 , Ralph Scheicher 1 , Ping Chen 3 4 , Rajeev Ahuja 1 2
1 Department of Physics and Materials Science, Uppsala University, Uppsala Sweden, 2 Department of Materials Science and Engineering, Royal Institute of Technology (KTH), Stockholm Sweden, 3 Department of Physics and Department of Chemistry, National University of Singapore, Singapore Singapore, 4 , Dalian Institute of Chemical Physics, Dalian China
Show AbstractThe hydrogenation of Li3N has been demonstrated to represent a promising approach to achieve a suitable hydrogen storage material [1]. In this system, the hydrogen absorption and release processes take place in the following two-step reaction without the need for any catalyst: Li3N + 2H2 ↔ Li2NH + LiH + H2 ↔ LiNH2 + 2LiH. (1)The hydrogen is, thus, stored in the mixture of lithium amide (LiNH2) and lithium hydride (LiH) with a remarkable theoretical storage capacity of 10.5wt%. However, the involved thermodynamic and kinetic properties still require further improvement before this approach could be considered suitable for on-board applications. To design ways of overcoming these limitations it is necessary to understand the mechanisms of the reactions in (1), which requires knowledge about the crystal structures of the various reactants and products. In this work, we have employed extensive ab initio molecular dynamics simulations to investigate temperature-dependent phenomena in Li3N, Li2NH and LiNH2. It was found [2] that the order-disorder transition observed in Li2NH at around 400 K [3] is associated with a melting of the cation (Li+) sublattice forming a superionic state. The corresponding states are further investigated in the other two compounds, Li3N and LiNH2. The former is found to undergo a similar transition but at higher temperatures around 700 K whereas the latter does not display any phase transformation until the whole lattice melts at around 1000 K. These results shed light on the fundamental understanding of the underlying mechanisms of the reactions in (1), and might furthermore broaden possible technological applications of Li2NH towards batteries and fuel cells.References1. P. Chen, Z. Xiong, J. Luo, J. Lin, and K. L. Tan, Nature 420, 302 (2002).2. C. Moysés Araújo, A. Blomqvist, Ralph H. Scheicher, P. Chen, and R. Ahuja, Phys. Rev. B 79, 172101 (2009).3. M. P. Balogh et al., J. Alloys Compd. 420, 326 (2006).