James C. F. Wang Sandia National Laboratories
William Tumas Los Alamos National Laboratory
Aline Rougier Universite de Picardie Jules Verne
Michael J. Heben National Renewable Energy Laboratory
Etsuo Akiba AIST
EE1: Metal Hydrides I
Tuesday PM, April 18, 2006
Room 2006 (Moscone West)
9:30 AM - **EE1.1
Progress Made by the DOE National Hydrogen Storage Project Towards Addressing the Challenges of Vehicular Storage.
Carole Read 1 , Grace Ordaz 1 , Sunita Satyapal 1 , John Petrovic 2 , George Thomas 3 Show Abstract
1 Office of Hydrogen, Fuel Cells and Infrastructure Technologies, US Department of Energy, Washington, District of Columbia, United States, 2 , Los Alamos National Laboratory-Retired, Cape Canaveral, Florida, United States, 3 , Sandia National Laboratory-Retired on Assignment to DOE, Reno, Nevada, United States
At the present time, there are three primary technology barriers that must be overcome to enable an industry commercialization decision on hydrogen fuel cell vehicles. First, the cost of safe and efficient hydrogen production and delivery must be lowered to be competitive with gasoline without adverse environmental impacts. Second, fuel cell system costs must be lowered while meeting performance and durability requirements. Finally, on-board hydrogen storage systems must be developed that allow a vehicle range of greater than 300 miles while meeting packaging, cost, and performance requirements.The barriers associated with hydrogen production, delivery and fuel cells are essentially cost-driven. However, with regard to the on-board hydrogen storage barrier, no approach currently exists that can meet the technical requirements of a greater than 300-mile range, irrespective of the present cost. Therefore, the focus of hydrogen storage research is on performance. New materials and approaches are needed. To accelerate and focus R&D in hydrogen storage, the DOE has initiated the implementation of a National Hydrogen Storage Project.Storing enough hydrogen on vehicles to achieve greater than 300-mile driving range is clearly a significant challenge. On-board hydrogen storage in the range of 5-13 kg is required to encompass the full platform of light duty vehicles. The average fleet on-board storage requirement is approximately 8 kg.On-board hydrogen storage system targets have been developed through the FreedomCAR Partnership between DOE and the US Council for Automotive Research. These targets are system-driven, based on achieving similar performance and cost levels as current gasoline fuel storage systems. The storage system includes the tank, valves, regulators, piping, mounting brackets, insulation, added cooling capacity, and any other balance-of-plant components in addition to the first charge of hydrogen and any material such as solid sorbent or liquid used to store the hydrogen.The focus of the DOE National Hydrogen Storage Project is on materials-based technologies to meet 2010 targets and with potential to eventually meet 2015 targets. It is important to note that to achieve system-level capacities of 2 kWh/kg (6 wt% hydrogen) and 1.5 kWh/L (0.045 kg hydrogen/L) in 2010, the gravimetric and volumetric capacities of the material alone must clearly be higher than the system-level targets.Recent progress achieved through the R&D activities of the DOE National Hydrogen Storage Project will be highlighted and discussed. An update on the Storage Analysis Working Group and on collaborative storage research activities in support of the International Partnership for the Hydrogen Economy will also be presented. Finally, the state-of-the-art performance of storage system approaches in terms of volumetric and gravimetric capacity will be updated and presented.
10:00 AM - **EE1.2
Concept of Hybrid Containment - High-pressure Metal Hydride Tank.
Daigoro Mori 1 , Katsuhiko Hirose 1 , Norihiko Haraikawa 1 , Nobuo Kobayashi 2 , Tamio Shinozawa 3 , Tomoya Matsunaga 3 , Hidehito Kubo 4 , Keiji Toh 4 , Makoto Tsuzuki 4 Show Abstract
1 Fuel Cell System Development Div., Toyota Motor Corporation, Susono, Shizuoka, Japan, 2 Fuel Cell System Engineering Div., Toyota Motor Corporation, Toyota, Aichi, Japan, 3 Material Engineering Div. 3, Toyota Motor Corporation, Susono, Shizuoka, Japan, 4 Research & Development Dept., Toyota Industries Corporation, Obu, Aichi, Japan
There are many hydrogen storage technologies for automotive applications, but it is difficult to satisfy all the recommendation by each simple containment technology. High-pressure MH tank system is a concept of hybrid containment combined metal hydride with high-pressure hydrogen. It is one of the few options for a realistic tank system for fuel cell vehicles that can store effective hydrogen 7.3 kg with a tank volume of 180 L, and also its possible cruising range is over 700 km or more. Furthermore the high-pressure MH tank can achieve good charge and discharge performance by using hydrogen-absorbing alloy with high dissociation pressure, for example Ti-Cr-Mn alloys. On the other hand, mass reduction of the hydrogen-absorbing alloy is necessary for further popularization of fuel cell vehicles. The current hydrogen storage capacity of Ti-Cr-Mn alloy, 1.9mass%. is not enough for the required specification from the vehicle system. A new type of MH alloy with high dissociation pressure and high capacity, Ti-Cr-V-Mo BCC alloy has been developed for this system. This new alloy can store 2.5mass% of effective hydrogen and it is 40% larger capacity. Conventional BCC alloy, for example Ti-Cr-V alloys also can store hydrogen over 2mass%, but its desorption property at cold temperature decreases due to low dissociation pressure (<0.1MPa). By Mo substitution for V of Ti-Cr-V BCC alloy, dissociation pressure increased considerably. In this study, the hydrogen charge-discharge performance of the high-pressure MH tank with Ti-Cr-V-Mo BCC alloy was investigated.It describes the performance of the high-pressure MH tank designed by using the above-mentioned MH alloy. Furthermore, optimization of the heat exchanger also will be reported. It is necessary to improve the heat exchange performance, if the heat of formation of high capacity hydrogen-absorbing alloy increases according to its capacity. The heat exchanger that assumed 4mass% of hydrogen capacity has been developed and investigated
10:30 AM - **EE1.3
Material Processing and Densification for Complex Hydride Based Storage Systems
Daniel Mosher 1 , Xia Tang 1 Show Abstract
1 Fuel Cells Program, United Technologies Research Center, East Hartford, Connecticut, United States
Complex hydrides such as NaAlH4 hold promise to deliver superior storage capacities per unit mass over conventional metal hydrides, but differences in characteristics affect how these materials must be processed and ultimately incorporated into storage systems. The current presentation will cover the use of alternative forms of catalysts and milling methods for NaAlH4 to achieve improved reaction kinetics for the quantities of materials needed to construct prototype systems. Characterization of the resulting kinetics and its impact on system design will also be discussed. The storage capacity per unit volume for a candidate material is determined not only by the hydrogen capacity per unit mass and solid material density, but also by the ability to densely pack the powder within a storage system structure. To study this material behavior, an apparatus has been developed for evaluating the inherent powder densification characteristics of complex hydrides in order to perform material comparisons and determine the best system fabrication method.
11:00 AM - EE1: MH1
11:30 AM - **EE1.4
Hydrogenation Properties and Crystal Structure of the Single bcc (Ti0.355V0.645)100-xMx alloys with M = Mn, Fe, Co, Ni.
Sylvain Challet 1 , Michel Latroche 1 , Fabien Heurtaux 2 Show Abstract
1 LCMTR UPR209, CNRS, Thiais France, 2 Direction of Research, Renault, Guyancourt France
The hydrogenation properties of the (Ti0.355V0.645)100-xMx (7 ≤ x ≤ 21) alloys with M = Mn, Fe, Co and Ni and the crystallographic structures of their hydrides have been investigated. The limit of solubility of the M element in the solid solution at constant Ti/V ratio increases from Ni to Mn, respectively from 7% to up 14%. For the single phase bcc alloys, the hydrogen capacities reach about 4wt% at room temperature under 2 MPa. The reversible capacity at 298K is low for the (Ti0.355V0.645)93M7 alloys. However, the cell volume reduction induced by the increasing substitution of M element leads to a reversible capacity of about 2wt% at room temperature for the (Ti0.355V0.645)86Fe14 alloy. Moreover, an influence of the M element is observed on the equilibrium pressure since destabilization of the hydride is larger for iron than manganese. The hydrogen sites of the dihydride compound have been determined by neutron diffraction and the evolution of the structural parameters during desorption has been studied. The dihydride exhibits a fcc-type structure (Fm-3m), whereas the monohydride shows a tetragonal one (I4/mmm). The stability domain of the tetragonal phase ranges from 0.75 to 0.92 H/M..
12:00 PM - **EE1.5
Ni-dispersed Hybrid Nanomaterials for Practical Hydrogen Storage Media.
Jeung Ku Kang 1 2 3 Show Abstract
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong Gu, Daejeon, Korea (the Republic of), 2 Materials Process & Simulation Center, California Institute of Technology, Pasadena, California, United States, 3 Center for Ultramicrochemical Process Systems, Korea Advanced Institute of Science and Technology, Yuseong Gu, Daejeon, Korea (the Republic of)
Ni nanoparticles-dispersed hybrid nanomaterials based carbon nanotubes and organic-silica nanotubes are found to be usable for energy storage applications. We find that our Ni-dispersed nanotube shows a high hydrogen storage capacity up to 4.5 wt% H2 at room temperature. Consequently, the Ni-dispersed hybrid nanotube is proposed as a novel nanostructure to solve energy and environmental problems in the earth resulting from using petroleum fuels.
12:30 PM - EE1.6
Interaction of Atomic and Molecular Hydrogen with Ti-Doped Al(100): Hydrogen Dissociation and Formation of Surface Alanes
Peter Sutter 1 , Erik Muller 1 , Percy Zahl 1 , Santanu Chaudhuri 2 1 , James Muckerman 2 Show Abstract
1 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States, 2 Department of Chemistry, Brookhaven National Laboratory, Upton, New York, United States
Hydrogen storage using complex metal hydrides will only be applicable on a large scale if a material with a gravimetric hydrogen density near 10 wt. % is found that can be safely and reversibly hydrogenated near ambient conditions. The pivotal discovery that the decomposition of NaAlH4 to NaH, Al, and hydrogen can be made reversible at reasonable temperatures and pressures by adding Ti  has demonstrated a possible path towards a solution of this problem. Although recent evidence suggests that the active Ti dopants occupy surface or near-surface sites , its role in the different elementary steps of the re-hydrogenation (‘refueling’) reaction remains largely unknown.We have begun a comprehensive research effort with focus on the atomistic mechanisms underlying reversible hydrogen storage in Ti-doped NaAlH4, aimed at deriving a knowledge base for rational optimization of this and other related hydrogen storage materials. For sodium alanate, a key step in the re-hydrogenation reaction is the dissociative adsorption of molecular hydrogen on Al or NaH. A specific Al:Ti complex has been predicted recently as an active site for H2 dissociation on extended Al(100) surfaces .Combining high-resolution surface imaging experiments (scanning tunneling microscopy, low-energy electron microscopy) with theory, we study the dissociative adsorption of H2 on Ti-doped Al(100) prepared in ultrahigh vacuum, an idealized model system suitable for direct comparison of experimental observations with first-principles calculations. We will discuss our progress toward identifying catalytically active sites for H2 dissociation on this surface, as well as pathways to the formation of mobile Al-species (surface alanes, AlHx) and their role in facilitating the required large-scale mass transport in the re-hydrogenation of NaH and Al to Na3AlH6 and ultimately NaAlH4.B. Bogdanovic and M. Schwickardi. J. Alloys Comp. 253–254, 1 (1997).J. Graetz, J.J. Reilly, J. Johnson, A.Y. Ignatov, and T.A. Tyson, Appl. Phys. Lett. 85, 500 (2004).S. Chaudhuri and J.T. Muckerman, J. Phys. Chem. B 109, 6952 (2005).
12:45 PM - EE1.7
Thermal Analysis of High-Pressure Metal Hydride Tank for Automotive Application.
Keiji Toh 1 , Hidehito Kubo 1 , Yoshihiro Isogai 1 , Daigoro Mori 2 , Katsuhiko Hirose 2 , Nobuo Kobayashi 3 Show Abstract
1 Research & Development Dept., Toyota Industries Corporation, Obu Japan, 2 Fuel Cell System Development Div., Toyota Mortor Corporation, Susono Japan, 3 Fuel Cell System Engineering Div., Toyota Mortor Corporation, Toyota Japan
A new type of hydrogen storage tank has been developed for fuel cell vehicles FCHV. The tank design is based on the 35MPa high-pressure cylinder vessel and the heat exchanger module including hydrogen absorbing alloy with high dissociation pressure is integrated in it. For hydrogen absorbing alloy, for example, Ti-Cr-Mn alloy with AB2 laves phase is applied. Its effective hydrogen weight capacity is 1.9 wt% and reaction enthalpy Δh is -22 kJ/molH2. To optimize the heat exchanger, thermal analyzing method was developed to predict the amount of hydrogen absorption or desorption. The simulation consists of heat and mass balance. Heat balance is made about the hydrogen absorbing alloy, heat exchanger and coolant each other, also reaction heat of the hydrogen absorbing alloy and compressed heat are considered. The reaction heat is calculated from the equation of reaction rate that is derived experimentally. Furthermore, an additional simulation to predict the charging performance of on-board high-pressure MH tank system by the radiator cooling will be reported. With this simulation, it will become possible to make parameter studies to investigate how the operating conditions influence the performance of tank system.
EE2: Boron-Containing Systems
Tuesday PM, April 18, 2006
Room 2006 (Moscone West)
2:30 PM - **EE2.1
Hydrogen Storage in HNBH Systems.
Liyu Li 1 , Benjamin Schmid 2 , R Smith 1 , Bruce Kay 1 , John Linehan 1 , Wendy Shaw 1 , Nancy Hess 1 , Ashley Stowe 1 , Craig Brown 3 , Luke Daemen 4 , Maciej Gutowski 1 , Tom Autrey 1 Show Abstract
1 , PNNL, Richland, Washington, United States, 2 Materials Science, University of Oregon, Eugene, Oregon, United States, 3 , NIST, Gaithersburg, Maryland, United States, 4 , LANSCE, Los Alamos, New Mexico, United States
We have been investigating the viability of using ammonia borane (NH3BH3) as hydrogen storage material. This material is promising given the high volumetric storage densities, ca. 12 - 19 wt % hydrogen. Ammonia borane (AB) is a stable solid at room temperature that requires heating to release the H2. Thermal decomposition of NH3BH3 at temperatures below 100 C yields H2 and a complex polyaminoborane-like –(NH2BH2)n– material (PAB). The solid phase thermal reaction involves a bimolecular dehydrocoupling reaction to yield a new B-N bond, i.e., HNB-H --- HNBH to yield HNB-NBH in contrast to our observations of the catalytic pathway involves the intramolecular abstraction of H-H from a single H-NB-H molecule to yield N=B intermediate. At temperatures above 150 C the PAB decomposes to yield a second equivalent of H2, concurrent with formation of a polyiminoborane-like –(NHBH)n– material (PIB) and borazine c-(NHBH)3. Borazine is a volatile inorganic analog of benzene, which is undesirable in the H2 feed. While AB provides a theoretically high volumetric and gravimetric density, three additional physical obstacles must be overcome: (i) increasing the rates of H2 release at lower temperatures, (ii) preventing borazine formation and (iii) demonstrating the potential for reversibility. The work presented in this symposium will highlight our success in lower the temperature of hydrogen release from ammonia borane (<80 C) and to minimize the formation of borazine from polyammonia borane decomposition using mesoporous silica scaffold (SBA-15). Three notable observations are described in this work: (i) increased rates of H2 release, (ii) modifications of the non-volatile polymeric products that change the thermodynamics of hydrogen release and (iii) minimized formation of borazine.
3:00 PM - **EE2.2
High Level Computational Chemistry Approaches to the Prediction of the Energetic Properties of Chemical Hydrogen Storage Systems.
David Dixon 1 , Myrna Hernandez-Matus 1 , Daniel Grant 1 Show Abstract
1 Chemistry Department, The University of Alabama, Tuscaloosa, Alabama, United States
High level first principles quantum chemical calculations on massively parallel supercomputers have been used to predict the heats of formation and other energetic properties of materials for chemical hydrogen storage systems. The calculations were done at the molecular orbital theory (MP2 and CCSD(T)) levels with the correlation-consistent basis sets extrapolated to the complete basis set level as well as at the density functional theory (DFT) level with extended basis sets. These values can be used to predict the suitability of such compounds for hydrogen storage for the transportation sector. The amine boranes such as BH3NH3 and the salt [BH4-][NH4+] have been found to have suitable thermodynamic properties for hydrogen storage. In addition, we have found that the isoelectronic compounds AlH3NH3 and AlH3PH3 as well as the salts [BH4-][PH4+], [AlH4-][NH4+], and [AlH4-][PH4+] can serve as hydrogen storage systems based on their thermodynamic properties. We have explored the cyclic compounds c-(XH2YH2)3 and c-(XHYH) for X = B and Al and Y and N and P to determine the role of these cyclic compounds in chemical hydrogen storage systems. We will discuss the role of organic compounds such as the carbenes as potential chemical hydrogen systems. We will discuss dehydrogenation mechanisms for the boron amines and the energetics of a wide range of reactions important in the regeneration process to make B-H bonds from B-O bonds as well as for the regeneration of N-H and B-H bonds in boron amines and C-H bonds in organic chemical hydrogen storage systems, for example, those derived from cyanocarbons. The critical role of reliable predictions of energetics in designing new materials for hydrogen storage will be emphasized.
3:30 PM - **EE2.3
Chemical Hydrogen Storage Using Organic Materials.
David Thorn 1 , Daniel Schwarz 1 , Jonathan Webb 2 , Thomas Cameron 1 , Brian Scott 1 , P. Hay 3 , William Tumas 1 Show Abstract
1 Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Department of Chemistry, Queen's University, Kingston, Ontario, Canada, 3 Theory Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Owing to their thermodynamic stability, nearly all organic compounds are incapable of releasing hydrogen at P > 1 atm at 298 K, and their C-H bonds are incapable of reducing non-superacid protons (H+) to H2. However, C-H bonds which are flanked by at least two heteroatoms (N or O) are much more "hydridic" than usual. We show that such C-H bonds are capable of reducing mildly acidic protons, and even water, to H2 at ambient temperature, and discuss the possible roles of materials containing such C-H bonds in hydrogen storage materials.
4:00 PM - EE2: Boron
4:30 PM - EE2.4
Mechanistic Studies of Hydrogen Release from Solid Amine Borane Materials.
Mark Bowden 1 , Tim Kemmitt 1 , Wendy Shaw 2 , Nancy Hess 2 , John Linehan 2 , Maciej Gutowski 2 , Benjamin Schmid 2 , Tom Autrey 2 Show Abstract
1 , Industrial Research Ltd, Lower Hutt New Zealand, 2 , Pacific Northwest National Laboratory, Richland, Washington, United States
We are working to develop a fundamental understanding of the chemical and physical properties of amine borane complexes. These materials, especially ammonia borane (AB) NH3BH3, have a high gravimetric density of hydrogen (0.195 kg H2/kg). AB is isoelectronic with ethane yet is a solid at ambient temperatures with a density of 0.75 gm/cc providing a volumetric density of 0.146 kg H2/liter. AB is composed of a network of non-classical dihydrogen bonds formed between the protic hydrogen atoms on nitrogen and the hydridic hydrogens on boron (N—Hδ+ ….. δ-H—B). The polar dihydrogen bond may be a critical feature leading to the formation of molecular hydrogen in solid state AB at temperatures below 80°C. However, there is little mechanistic understanding to test the reaction mechanism of hydrogen formation. In this work we present experimental studies designed to elucidate the critical reaction intermediates and pathways leading to hydrogen formation from amine borane complexes in the solid state. We show the time dependent release of hydrogen from AB can be described by a solid state nucleation and growth kinetic model. Further analysis of the reaction products, using D-labeled amine boranes, by TPDMS to monitor the volatile products and 11B NMR to monitor the nonvolatile products suggests hydrogen formation proceeds by a bimolecular pathway involving ionic intermediates.
4:45 PM - EE2.5
Room-Temperature Hydrogen Generation Based on Catalytic Dissociation and Hydrolysis of Ammonia-Borane.
Qiang Xu 1 , Manish Chandra 1 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan
Hydrogen, H2, is a globally accepted clean fuel. The use of hydrogen fuel cells in vehicles or in portable electronic devices requires lightweight H2 storage or “on-board” hydrogen generation. There have been a large number of reports on H2 storage [1,2] and on “on-board” reforming of hydrocarbons into H2 . However, all the methods are not suitable for portable applications due to the low volumetric and gravimetric efficiency of hydrogen storage and the difficulties in operation of high-temperature reforming processes of hydrocarbons as well as to the safety issue. Significant reports dealing with sodium borohydride (NaBH4) as a potential carbon-free portable hydrogen source are available, whereas this system needs a highly basic solution [4-7]. For portable hydrogen generation systems, in particular, the most important are safety, ease to control and high kinetics of the hydrogen release along with a high hydrogen content. Here we report a new excellent catalytic system suitable for use as a portable hydrogen source from the above points of view, which is based on transition metal-catalyzed dissociation and hydrolysis of ammonia-borane complex (NH3BH3) at room temperature . NH3BH3 dissolves in water to form a solution stable in the absence of air. The addition of a catalytic amount of suitable metal catalysts such as Pt, Rh, and Pd into the solutions with various concentrations leads to rigorous release of hydrogen gas with an H2 to NH3BH3 ratio up to 3.0, corresponding to 8.9 wt% of the starting materials NH3BH3 and H2O. The Pt catalysts are the most active and no significant deactivation was observed for the recycled catalysts. This new system possesses high potential to find its application to portable fuel cells.References: P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, Nature 420 (2002) 302.N.L. Rosi, J. Eckert, M. Eddaoudi, D.T. Vodak, J. Kim, M. O’Keeffe, O.M. Yaghi, Science 300 (2003) 1127. G.A. Deluga, J.R. Salge, L.D. Schmidt, X.E. Verykios, Science 303 (2004) 993. H.I. Schlesinger, H.C. Brown, A.E. Finholt, J.R. Gilbreath, H.R. Hoekstra, E.K. Hyde, J. Am. Chem. Soc. 75 (1953) 215. C.M. Kaufman, B. Sen, J. Chem. Soc., Dalton Trans. (1985) 307. S.C. Amendola, S.L. Sharp-Goldman, M.S. Janjua, M.T. Kelly, P.J. Petillo, M. Binder, J. Power Sources 85 (2000) 186.Z.P. Li, B.H. Liu, K. Arai, S. Suda, J. Electrochem. Soc. 150 (2003) A868. M. Chandra, Q. Xu, J. Power Sources, in press (doi:10.1016/j.jpowsour.2005.05.043).
5:00 PM - EE2.6
Mechano-chemical Synthesis and Characterization of New Complex Hydrides for Hydrogen Storage.
Sesha Srinivasan 1 , Elias Stefanakos 1 Show Abstract
1 Clean Energy Research Center, College of Engineering, University of South Florida, Tampa, Florida, United States
Mechano-chemical synthesis has been employed to prepare new light weight complex borohydrides. The precursor complex borohydrides such as NaBH4 and LiBH4 have been used since these materials posses high hydrogen storage capacity of 13.0 and 19.6 wt.%. This advanced materials based technology will meet the US-DOE grand challenge technical targets. The thermal calorimetric and gravimetric analysis of these complex borohydrides exhibits the hydrogen decomposition temperature (Tdec) of 100-150° C with theoretical capacity of ~8.0-10.0 wt%. The catalysts (e.g. ZnCl2, TiF3) doping and destabilization of the borohydride by reacting with binary hydride (MgH2) reveals the enhancement of decomposition kinetics and reversible dehydrogenation-rehydrogenation behavior.
5:15 PM - **EE2.7
Catalyst and Reactor Development for Hydrogen Generation from Sodium Borohydride
Ying Wu 1 Show Abstract
1 , Millennium Cell Inc., Eatontown, New Jersey, United States
Sodium borohydride (NaBH4) offers promising hydrogen storage capacity and ready release of hydrogen gas suitable for a variety of applications. When a heterogeneous catalyst is used in hydrogen generation from NaBH4, the solution is passed over a supported solid-phase catalyst in a fixed-bed reactor. With generation of hydrogen, NaBH4 is converted to the by-product sodium metaborate, NaB(OH)4. The overall energy density of such a hydrogen storage system heavily depends on performance of the catalyst reactor. Efforts have been made to understand the catalyst performance under a number of reactor conditions, with reactor pressure ranging from ambient to approximately 10 bar, The rate of hydrogen generation is dependent on not only the intrinsic activity of the catalyst but more importantly, on the effective mass transport and heat management in the reactor. In this paper, we will report the latest data on catalyst performance evaluation, improved reactor design, and process modeling results wherever applicable. A unique reactor design in which the catalyst bed is integrated with a heat exchanger for auto thermal operation has been demonstrated. It was capable of operating in a self-sustained fashion. In a vertical down flow configuration, the reactor was successfully operated at three times higher liquid hourly space velocity than a reactor not integrated with a heat exchanger. Similar results were obtained in a horizontal reactor configuration. Over 200% enhancement in reactor throughput was achieved at 99% NaBH4 conversion. Increased reactor throughput and operating window not only allows one the use of much smaller reactor, but also leads to significant increases in the responsiveness of the reactor to a wide range of hydrogen flow demands. Furthermore the increased throughput offers the potential for significant reduction in the size requirement of down-stream components such as the gas-liquid separator. These effects will also be discussed briefly.
5:45 PM - EE2.8
Carbon NanoTubes Functionalized with Monolayer Coatings as Low Cost Catalysts for Producing Hydrogen from NaBH4
Raquel Peña-Alonso 1 3 , Adriana Sicurelli 1 , Emanuela Callone 1 , Antonio Miotello 2 , Giovanni Carturan 1 , Gian Domenico Soraru 1 , Rishi Raj 3 Show Abstract
1 Ingegneria dei Materiali e Tecnologia Industriale - Facolta di Ingegneria, Universita di Trento, Trento Italy, 3 Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 2 Fisica - Facolta di Scienze, Universita di Trento, Trento Italy
EE3: Poster Session: Hydrogen Storage
Wednesday AM, April 19, 2006
Salons 8-15 (Marriott)
9:00 PM - EE3.1
Investigation of the Dynamics of Hydrogen in Lithium Borohydride using Qausielastic Neutron Scattering.
Michael Hartman 1 , Jack Rush 1 , Terry Udovic 1 Show Abstract
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Lithium borohydride, LiBH4, is a complex metal hydride that shows great promise as a hydrogen storage medium with a volumetric hydrogen density of 122 kg H/m3 and a gravimetric hydrogen density of 18.5 wt. %. While numerous NMR, Raman, and infrared investigations have been reported in the literature, neutron scattering investigations of LiBH4 have been limited due to the large neutron absorption cross-section of naturally occurring lithium and boron. We have recently synthesized an isotopically-enriched lithium borohydride, containing 7Li and 11B, which eliminates the large neutron absorption cross-section that arises from the presence of 6Li and 10B. Quasielastic neutron scattering (QENS) has been performed on this isotopically-enriched material to gain an improved fundamental understanding of the hydrogen dynamics in both the low-temperature and high temperature (T > ~384K) crystalline phases. The results of the QENS investigation are presented along with a discussion of the dynamics of hydrogen within LiBH4.
9:00 PM - EE3.15
Quantitative Structure-Uptake Relationship of Metal-Organic Frameworks as Hydrogen Storage Material
Daejin Kim 1 , Tae-Bum Lee 1 , Seung-Hoon Choi 1 , Sang Beom Choi 2 , Jihye Yoon 2 , Jaheon Kim 2 Show Abstract
1 , Insilicotech Co., Ltd., Seongnam, Gyeonggi-Do, Korea (the Republic of), 2 Department of Chemistry, Soongsil University, Seoul Korea (the Republic of)
We have investigated the relationship between the structures of metal-organic frameworks (MOFs) and their hydrogen uptake capabilities. The QSPR (quantitative structure-property relationship) method was used to find out which structural factors would affect the quantities of hydrogen molecules adsorbed on the MOFs. The derivatives of the organic links, more specifically the functionalized aromatic moieties induced noticeably different polarization effect on the framework surface for a series of MOFs having the identical framework topology and similar lattice constants each other. In addition the same approach has been applied to the typical MOFs showing different framework structures to examine the influence of the topological changes. Langmuir-Freundlich model was used to adapt the saturated hydrogen adsorption values from the experimental isotherms measured at low pressure, which was incorporated as a parameter into QSPR analysis. These studies indicate that the polar surface area of MOF is a very important indicator to predict the adsorption amount of hydrogen molecule into the MOFs. To figure out the quantitative interaction strengths between hydrogen molecule and MOF, the specific values of electrostatic potential surface were calculated. We call this specific analysis procedure QSUR(Quantitative Structure-Uptake Relationship).
9:00 PM - EE3.16
Structure and Dynamics of Methane in MOF5
Wei Zhou 1 2 , Taner Yildirim 1 Show Abstract
1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 MSE, UPENN, Philadelphia,, Pennsylvania, United States
Metal-organic framework (MOF) compounds, which consist ofmetal-oxide clusters connected by organic linkers, are a relatively new class of nano-porous material that show promise for hydrogen storage applications because of their tunable pore size and functionality. In this talk,we present a detailed study of Methane storage in MOF5 using elastic and inelastic neutron scattering (INS) along with first-principles total energy calculations. We also carried out isotherm measurements as a function of pressure (up to 50 Atm.) and temperature. The INSspectrum shows very rich features which will be used todetermine the interaction between the methane molecules and the MOF5-host lattice. Such information will beimportant to tune MOF structures further for better storage capacity and dynamics.
9:00 PM - EE3.19
Nanocrystalline Silicon for Hydrogen Storage.
Doinita Neiner 1 , Christopher Chervin 1 , Hsiang Chiu 1 , Michael Blessent 1 , Susan Kauzlarich 1 Show Abstract
1 Chemistry, UC Davis, Davis, California, United States
Hydrogen constitutes the primary candidate for a clean, efficient and environmental friendly fuel. Early studies on bulk silicon revealed hydrogen emission upon annealing. The surface to volume ratio for a nanomaterial increases as its size decreases. This makes nanocrystalline silicon a serious candidate for hydrogen storage. Preparation of hydrogen capped silicon nanoparticles have been attempted by both solid state and solution reaction routes. The precursors are NaSi and Mg2Si and as hydrogen sources ammonium halides have been used. The X-ray powder patterns of the resulted materials correspond to nc-Si. SEM/TEM images indicate that these materials are on the nanometer scale.
9:00 PM - EE3.2
Local Coordination Environments of Transition Metal Dopants in Complex Metal Hydrides.
Jason Graetz 1 , Santanu Chaudhuri 1 , Alexander Ignatov 1 , James Reilly 1 , Tina Salguero 2 , John Vajo 2 , James Muckerman 1 Show Abstract
1 , Brookhaven National Laboratory, Upton, New York, United States, 2 , HRL Laboratories, Malibu, California, United States
The demonstration of reversible hydrogen cycling in Ti-doped sodium aluminum hydride has generated considerable interest in the complex metal hydrides. Since this discovery there have been a number of studies focused on improving the catalytic effects and understanding the role of the dopant in the alanates. Recent experiments have shown that the Ti atoms are well dispersed in this system and form Ti-Al clusters on/near the surface with a local structure similar to that of TiAl3. However, the mechanism by which NaAlH4 is activated in the presence of a small amount of a transition metal is still not well understood. In this study x-ray absorption spectroscopy and first-principles calculations are used to investigate the atomistic transport mechanisms of the reversible complex metal hydrides (sodium alanate and lithium borohydride). In the case of the alanates, our results suggest that the catalytic role of the transition metal atoms is due to a lowering of the potential energy barrier to the formation of the aluminum hydride species. Although Al metal has a low affinity for hydrogen, when doped with Ti the surface characteristics change significantly. Our calculations show that the Al(001) containing two next-nearest-neighbor Ti atoms on/near the surface dissociates molecular hydrogen. Preliminary absorption studies on the doped, destabilized borohydride have revealed a number of similarities with the alanates. Our results indicate that in the Ti-doped borohydrides the Ti is present as a divalent species with a local atomic structure similar to TiB2. In addition, the possibility of long-range metal (Al or B) transport via alane/borane formation will be discussed.
9:00 PM - EE3.20
H Adsorption On Rh (110) Surface.
Shao-Ping Chen 1 Show Abstract
1 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
We have used the density functional theory to study the H adsorption phenomena on Rh (110) surface with H coveragefrom 0.33 to 2.00 mono-layers. We found H atom favors the three-fold coordinated site as observed experimentally.We confirmed the existence of 1x3-H, 1x2-H,1x2-2H, 1x3-2H, 1x1-2H ordered structures. We also found that the proposed1x3-2H, 1x2-2H structures for coverage of 0.66 and 1.0 were not the lowest energy configuration. We have proposed new 1x3-2H and 1x2-2H structures which need to be tested by future experiments
9:00 PM - EE3.21
Using a Focused Ion Beam to Characterize the Microstructure of Porous Lanthanum Strontium Manganite (LSM) Electrodes.
Aijie Chen 1 , Danijel Gostovic 2 , Robert DeHoff 3 , Kevin Jones 4 Show Abstract
1 Materials Science and Engineering, Univ. of Florida, Gainesville, Florida, United States, 2 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 3 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 4 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
The relationship between the microstructure and electrical properties of lanthanum strontium manganite (LSM) /yttria stabilized zirconia (YSZ) solid oxide fuel cells was studied. Previous studies have shown that cathode polarization depends on aspects of its morphology such as homogeneity, porosity, pore connectivity density and the triple-phase boundary (TPB) length. In this study a dual-beam focused ion beam (FIB) system was employed to automatically slice serial sections of the electrode parallel to the surface with a narrow (2000Å) and reproducible spacing. A 3-D map of microstructure was then developed. The connectivity density of the three dimensional pore network was characterized by applying the volume tangent count to the set of serial sections produced. At a given volume fraction of porosity, the TPB boundary length decreased with increasing pore size. A Branch-node-chart model was developed to quantify 3-D connectivity of the pore networks by reconstructing 3-D geometry from 2-D sections. Microstructure evolution include porosity, connectivity and TPB length were quantified with respect to different annealing times between 15 min and 720 min at annealing temperature 1100°C. Analytical transmission electron microscopy was used to analyze atom migration and tertiary phase formation at the interface. La and Mn were found to be the diffusing species at the interface.
9:00 PM - EE3.22
Engineered Thin Film Structures for Model Hydrogen Storage Materials
Stephen Kelly 1 , Raj Kelekar 2 , Hermione Giffard 1 , G. Olson 3 , John Vajo 3 , B. Clemens 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Applied Physics, Stanford University, Stanford, California, United States, 3 , HRL Laboratories, LLC, Malibu, California, United States
Metal hydrides are an attractive medium for hydrogen storage. They store hydrogen by bonding it chemically to a reactive metal and release it when the hydride phase becomes less thermodynamically stable than the two phase system. Magnesium stores hydrogen reversibly with a theoretical maximum of 7.6 wt% as MgH2 but with very slow kinetics and relatively low equilibrium pressure at reasonable temperatures. Magnesium provides a good model system to investigate because of the relative simplicity of the hydriding reaction, its low cost and abundance, and its relative safety.We have engineered, fabricated and analyzed thin film structures of magnesium and its alloys that show promise as efficient hydrogen storage materials in order to gain an understanding of the fundamental processes that occur on hydrogen charging and discharging. Some of the materials systems that we investigated include pure magnesium thin films with Pd and Ti/Pd capping layers, monolithic thin films of Mg2Si and Mg2Si/Ge, multilayers of Mg/Pd, Mg/Mg2Si and Mg2Si/Pd, and epitaxial Mg thin films with Pd capping layers. Using UHV sputter deposition, we were able to engineer precise film structures, compositions and arrangements that varied on the nanoscale as well as control the location and dispersion of catalyst materials such as Pd and Ti. We analyzed our samples using various x-ray diffraction (XRD) techniques as well as resistivity measurements and Auger Electron Spectroscopy (AES). In-situ resistivity measurements and XRD scans performed while charging and discharging samples show that film orientation, microstructure and texture play a large role in the hydriding and dehydriding kinetics of the thin film samples. As a result of our studies, we determined the structural orientation correlation between the magnesium and magnesium hydride structures in thin films. We found, through the use of epitaxial thin films of magnesium, that the structures align such that MgH2 (110)  // Mg (001).
9:00 PM - EE3.24
Carbide Derived Carbon Designed for Efficient Hydrogen Storage
Ranjan Dash 1 , Gleb Yushin 1 , Giovanna Laudisio 2 , Taner Yildirim 3 , Jacek Jagiello 4 , John Fischer 2 , Yury Gogotsi 1 Show Abstract
1 Dept of Materials Sc and Engg, Drexel Univ, Philadelphia, Pennsylvania, United States, 2 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 4 , Quantachrome Instruments, Boynton Beach, Florida, United States
Carbide derived carbons (CDCs) have BET specific surface area (SSA) up to 2300 m2/g [1, 2] and open pore volume up to 80% represent a new class of porous carbons produced by thermo chemical etching of metal atoms from carbides. Tuning the pore size with high sensitivity by using different starting carbides [1, 3, 4] and synthesis temperatures  allows the design of carbon materials with enhanced with enhanced carbon-hydrogen interaction and thus increased hydrogen storage capacity . Our systematic investigation of a large number of CDCs with various pore size distributions and SSA experimentally showed how smaller pores (1 nm or below) increase both the heat of adsorption and the total volume of adsorbed H2 at ambient pressure. Values over 3 wt.% and 30 kg/m3 have been demonstrated in CDC; these are higher that that can be stored using metal-organic frameworks (MOF-5) and single or multi-walled carbon nanotubes at 77K and atmospheric pressure. The isosteric heat of hydrogen adsorption was obtained by applying Clausius-Clapeyron equation on adsorption isotherms of 77 and 87 K. Similarly, the obtained values of up to 11 kJ/mole considerably exceeded that of metal-organic frameworks and single-walled carbon nanotubes. References1. Gogotsi Y, Nikitin A, Ye H, Zhou W, Fischer JE, Yi B, Foley HC, Barsoum MW: Nanoporous Carbide-Derived Carbon with Tunable Pore Size. Nature Materials 2003, 2:591-594.2. Yushin G, Nikitin A, Gogotsi Y: Carbide-Derived Carbon. In: Gogotsi Y, editor. Handbook of Nanomaterials, CRC Press, 237-280, 20053. Dash RK, Nikitin A, Gogotsi Y: Microporous Carbon Derived From Boron Carbide. Microporous and Mesoporous Materials 2004, 72:203-208.4. Dash RK, Yushin G, Gogotsi Y: Synthesis, Structure and Porosity Analysis of Microporous and Mesoporous Carbon Derived from Zirconium Carbide. Microporous and Mesoporous Materials 2005, 86:50-57.5. Gogotsi Y, Dash RK, Yushin G, Yildirim T, Laudisio G, Fischer JE: Tailoring of Nanoscale Porosity in Carbide-Derived Carbons for Efficient Hydrogen Storage. Journal of American Chemical Society 2005, in press.
9:00 PM - EE3.25
Investigation of Hydrogen Adsorption/Desorption Reactions by Thin-Film DSC.
Lawrence Cook 1 , Richard Cavicchi 1 , Christopher Montgomery 1 , Peter Schenck 1 , Leonid Bendersky 1 , Frank Biancaniello 1 , Winnie Wong-Ng 1 , Martin Green 1 , Stephen Semancik 1 Show Abstract
1 , NIST, Gaithersburg, Maryland, United States
One of the major challenges in developing hydrogen-fueled transportation has to do with on-board storage of hydrogen in a safe, economical fashion. R&D efforts have concentrated on low atomic number hydrides – yet, currently the most promising materials still do not meet the required energy density goals. Research to date suggests that relatively minor doping can have a significant effect on hydriding properties; also, there are many chemistries that have yet to be evaluated. Clearly, the overall research effort would benefit from a screening tool to more efficiently and rapidly differentiate among the large array of potential materials. For this purpose, we are developing a combinatorial method of which thin-film differential scanning calorimetry (DSC) is an essential part. In this paper we report on the use of thin-film DSC to detect enthalpic changes associated with gas-phase reactions. For the hydriding experiments, we have constructed a stainless-steel DSC chamber capable of hydrogen pressures to 500 Pa and vacuum to 10-4 Pa. A six-sensor thin-film DSC device is incorporated within this chamber. Each of the DSC sensors consists of dual 60 μm x 100 μm pads with embedded thermopiles situated on a suspended MEMS platform. On one side of the sensor, a thin film of the materials to be measured is deposited by pulsed laser deposition or other suitable methods. Enthalpic changes during gas adsorption/desorption are measured by a differential method. Tests indicate enthalpies of reaction of less than 100 nJ can be detected on thin-film samples of less than 1 ng. Progress in the measurement of hydriding reactions for selected systems will be discussed.
9:00 PM - EE3.26
Growth of Carbon Nanotubes on Anodized Titanium Oxide Template by Catalytic Chemical Vapor Deposition & Electrochemical Hydrogen Storage Thereof.
Pradeep Pillai 1 , K. S. Raja 1 , Manoranjan Misra 1 Show Abstract
1 Material Science & Metallurgical Engineering, University Of Nevada, Reno, Nevada, United States
It is reported that 5-10 wt.% of H2 can be stored in Carbon Nanotubes (CNTs). Also TiO2 nanotubes produced by simple hydrothermal process, have been reported to store up to ~2 wt.% H2 at room temperature. If CNTs and nano-porous titanium oxide could be combined then it is highly probable to obtain an excellent hydrogen storage material.Nanoporous titanium oxide (NT) templates were prepared by anodizing titanium foils in an acidified fluoride solution. Cobalt catalyst was deposited at the bottom of the nano-porous titanium oxide template by pulse reverse electro-deposition method. Chemical Vapor Deposition (CVD) technique by cracking acetylene at 650oC was used for the production of carbon nanotubes. The electrochemical storage of hydrogen was measured on (NT)/CNT assembly using a three-electrode system in 30% KOH. Hydrogen charging and discharging experiments were carried out for more than 10 cycles. For comparison, plain titanium sample, Nanoporous Titanium oxide (NT), Cobalt deposited NT and the NT/CNTs assembly were investigated individually. The discharge capacity was found by integrating the product of discharge current and time. The amount of hydrogen stored was calculated from the measured discharge capacity. Plain titanium sample gave a discharge capacity of 78.92mAh/g while nanoporous titanium oxide (NT) sample gave a capacity of 419mAh/g. The discharge capacity for the Co deposited NT sample was found to be 705mAh/g.The NT/CNT assembly showed the highest value of discharge capacity of 1756.17mAh/g which corresponds to 6.53wt.% of hydrogen stored. Further work is in progress in studying the effect of size of the nanotubes on the storage capacity of the assembly.
9:00 PM - EE3.27
Effect of Pd on the Hydrogen Adsorption Capacity of Activated Carbon Fibers
Nidia Gallego 1 , Frederick Baker 1 , Cristian Contescu 1 , Dan Edie 2 Show Abstract
1 Carbon Materials Technology Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina, United States
First-principles calculations at Oak Ridge National Laboratory (ORNL) on interactions between hydrogen and graphite provided the fundamental basis for experimental work on metal-doped, activated carbon fibers (produced at Clemson University). Measurements at ORNL revealed that the Pd-doped fibers exhibited a hydrogen storage capacity of about 2 wt% at ambient temperature and a pressure of 2 MPa, corresponding to a H/Pd atomic ratio of about 50:1. This represented an order of magnitude increase over the hydrogen storage capacity of the corresponding Pd-free carbon fibers under similar conditions. Further modeling work indicated that, provided the high energy barrier for initial sorption could be overcome, hydrogen could be stored by intercalation between graphene layers. On the basis of these preliminary findings, it is hypothesized that metal-assisted hydrogen storage in nanostructured carbon is the result of catalytic activation (dissociation) of molecular hydrogen and surface diffusion of hydrogen atoms, followed by storage on carbon structural defects through either chemical bonding or intercalation. Furthermore, that the key to enhancing hydrogen storage in metal-doped carbon materials, including activated carbon fibers, is obtaining a fine dispersion of nanosized metal particles throughout the carbon material.As part of the effort to obtain a better understanding of the atomistic mechanisms of metal-assisted hydrogen storage in nanostructured carbon materials, in-situ X-ray diffraction techniques have been applied to study the adsorption of hydrogen on Pd-doped activated carbon fibers. Preliminary data obtained at ambient temperature and in the pressure range of 0-0.1 MPa revealed that the adsorption of hydrogen on the carbon fibers was accompanied by Pd hydride formation as the cell pressure was rapidly increased to 0.1 MPa. Upon reduction of the cell pressure to 0 MPa, the hydride rapidly decomposed at ambient temperature, confirming that the adsorption of hydrogen on the Pd-doped carbon fibers was totally reversible in this low pressure range. Further work is underway to carry out similar in-situ X-ray diffraction studies in the higher pressure range of 0-0.5 MPa (and later to 2 MPa).In this paper, results of the first principles computations for simulation of hydrogen interactions with graphite-like structures will be presented, and correlated with experimental data (gravimetric and X-ray diffraction) for the adsorption of hydrogen on Pd-doped activated carbon fibers produced from an isotropic pitch precursor. Fundamental studies to relate pitch chemistry to the nanostructure of activated carbon fibers, and subsequently to hydrogen uptake on the Pd-doped activated carbon fibers, will be discussed.
9:00 PM - EE3.28
Modification of Surface of Micron size Diamond Powder to Enhance for Hydrogen Storage.
Alexis Sotomayor-Rivera 1 , Tushar Ghosh 1 , Mark Prelas 1 Show Abstract
1 Nuclear Science and Engineering Institute, University of Missouri-Columbia, Columbia, Missouri, United States
Micron size diamond powder was doped with boron in order to change its various chemical properties. Diamond possesses several technologically important properties including extreme hardness, high electrical resistance, chemical inertness, high thermal conductivity, high electron and hole mobilities, and optical transparency. Because of its small size, boron atom can be incorporated in the diamond powder. Boron atoms diffuse into carbon atoms during the heating process. The introduction of boron atoms affects the structure and properties of the diamond powder including resistance to oxidation. Following doping with boron, the diamond powder will be irradiated in a neutron flux at the Missouri University Research Reactor (MURR) with the objective of creating micro-porous diamond powder that can be used as a storage media for hydrogen. Prompt Gamma Neutron Activation Analysis was used to determine the concentration of boron in the diamond powder. Scanning electron microscopy (SEM), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TGA) were also employed to study the morphology and structure of the diamond particles.
9:00 PM - EE3.29
Hydrogen Storage Behaviors of Palladium Deposited Carbon Nanotubes via Electrochemical and Sputter Deposition Method.
Yong-Won Lee 1 , Guangyu Zhang 2 , David Mann 3 , Karl Gross 4 , Hongjie Dai 2 , Bruce Clemens 1 Show Abstract
1 Materials Science & Engineering, Stanford University, Stanford, California, United States, 2 Chemistry, Stanford University, Stanford, California, United States, 3 Applied Physics, Stanford University, Stanford, California, United States, 4 , Hy-Energy, LLC., Newark, California, United States
A Sieverts’ apparatus for studying hydrogen storage behaviors in small sized samples has been implemented by employing very small volume reservoir and sample vessel. The hydrogen storage capacity and uptake kinetics of various types of carbon nanotube samples were measured in the hydrogen charging pressure range of 1 to 30 bar at room temperature; PECVD SWNTs, hipCO SWNTs, and HWCVD MWNTs. Then palladium nanoparticles were deposited on carbon nanotube samples via electrochemical method from PdCl2 solution and UHV sputter deposition method. The existence of Pd nanoparticles was confirmed with high-resolution TEM and XPS analysis. The changes in hydrogen storage behavior by two different deposition methods was studied and compared.
9:00 PM - EE3.3
Solid State NMR Studies of the Aluminum Hydride Phases.
Son-Jong Hwang 1 , Robert Bowman 2 , Jason Graetz 3 , J. Reilly 3 Show Abstract
1 Division of Chemistry & Chemical engineering, California Institute of Technology, Pasadena, California, United States, 2 , Jet Propulsion Laboratory, Pasadena, California, United States, 3 Department of Energy Science and Technology, Brookhaven National Laboratory, Upton, New York, United States
With a hydrogen gravimetric capacity over 10 wt.%, AlH3 would be an extremely attractive hydrogen storage material for low temperature fuel cells if its hydrogen absorption and desorption properties could be improved. At least three distinct polymorphic AlH3 phases can be produced by organometallic synthesis methods where the most thoroughly investigated and stable polymorph is denoted as α-AlH3. Several solid state NMR techniques including magic-angle-spinning (MAS) and multiple-quantum (MQ) MAS experiments have been used to characterize various AlH3 samples. MAS-NMR spectra for the 1H and 27Al nuclei have been obtained on a variety of AlH3 samples that include the β- and γ- phases as well as the α-phase. While the dominant components in these NMR spectra correspond to the aluminum hydride phases, other species were found that include Al metal, molecular hydrogen (H2), as well as peaks that can be assigned to Al-O species in different configurations. The occurrence and concentration of these extraneous components are dependent upon the initial AlH3 phase composition and preparation procedures. Both the β-AlH3 and γ-AlH3 phases were found to generate substantial amounts of Al metal when the materials were stored at room temperature while the α-phase materials do not exhibit these changes. The roles of Al metal and H2 gas formation on relative stabilities of the AlH3 polymorphs will be discussed.
9:00 PM - EE3.30
Hydrogen Desorption in Novel Carbon Cryogel - Hydride Composites.
A. Feaver 1 , Patrick Shamberger 1 , T. Autrey 2 , G. Cao 1 Show Abstract
1 Materials Science & Engineering, University of Washington, Seattle, Washington, United States, 2 , Pacific Northwest National Laboratory, Richland, Washington, United States
9:00 PM - EE3.31
Hydrogen Storage Properties and Phase Variation Studies in the Destabilized CaH2+Si System.
Hui Wu 1 , Terrence Udovic 1 , John Rush 1 Show Abstract
1 Neutron Center, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Many light-metal hydrides are known to have relatively high hydrogen-storage capacities (>5wt%), but most of them are too stable for practical applications and have sluggish sorption kinetics. Recently, more attention has been given to this class of hydrides in terms of (i) improving the kinetics through adding catalysts or preparing nanocrystalline hydrides using extended ball milling, and (ii) modifying the hydrogen-cycling thermodynamics using additives that could destabilize the metal hydrides by forming alloys or compounds in the hydrogenated and/or dehydrogenated states. Here we present a study of the hydrogen-storage properties of ball-milled mixtures of CaH2+Si powders via absorption/desorption isotherms in conjunction with x-ray and neutron powder diffraction, neutron vibrational spectroscopy, and neutron prompt-gamma activation analysis. A CaSi alloy forms upon initial dehydrogenation at 650 oC. Subsequent hydrogenation of this alloy leads to a CaSiHx ternary phase. The hydrogen-storage properties of this system will be discussed and correlated with the changes in crystal structures and composition ranges of these calcium silicide and calcium-silicon hydride phases.
9:00 PM - EE3.32
Decoration of Single-Walled Carbon Nanohorns for Hydrogen Storage.
Hui Hu 1 , Bin Zhao 1 , Alex Puretzky 1 , David Styers-Barnett 1 , Christopher Rouleau 1 , Hongtao Cui 1 , David Geohegan 1 Show Abstract
1 Condensed Matter Sciences Division and the Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
The development of novel carbon based materials is very important for hydrogen storage. The unique structure of single-walled carbon nanohorns (SWNHs), such as nanometers size, closed single-walled carbon structure, numerous defect sites, and variable-morphology aggregate structures, make them excellent candidates for gas adsorption and supports for metal catalyst clusters. The size of the metal particles and control of nanohorn morphology are important to study hydrogen storage mechanisms such as spillover. Here we compare two methods for the controlled decoration of SWNHs for hydrogen storage measurements.The SWNHs used in the study were synthesized by laser ablation of pure carbon targets using a high-power (600 W) industrial Nd:YAG laser facility at Oak Ridge National Laboratory. The decoration of SWNHs with metal nanoparticles, such as Pt, Pd, Ti and Ni, was achieved by two methods. The first method is the chemical synthesis of metal nanoparticles in the presence of solublized, as-prepared SWNHs. The second method is the direct production of metal decorated SWNHs by laser vaporization of composite targets containing carbon and the metal of interest. SEM, high-resolution TEM and TGA were used to characterize and compare the metal nanoparticle-decorated SWNHs from these two methods. The factors evaluated for hydrogen storage efficiency have included the size of metal nanoparticles on SWNHs, the degree of metal deposition homogeneity, the mass to volume ratio of SWNHs targets, the stability of metal nanoparticles under hydrogen cycling. Of special interest in these studies is the question whether residual organic groups from the chemical synthesis of the nanoparticles help or hinder hydrogen storage efficiency. The metal nanoparticle decoration inside the opened SWNHs, which was obtained by either thermal treatment or chemical oxidation, was also conducted to increase the surface area of SWNHs for hydrogen storage. Research supported by the U. S. Department of Energy (EERE) through the Center on Carbon-Based Hydrogen Storage and by the U. S. Department of Energy, Division of Material Science, Basic Energy Sciences.
9:00 PM - EE3.4
In situ NMR Studies of amine boranes: Dynamics and Mechanisms of Hydrogen Formation.
Wendy Shaw 1 , John Linehan 1 , Benjamin Schmid 1 , Ashley Stowe 1 , Tom Autrey 1 Show Abstract
1 , Pacific Northwest National Labs, Richland, Washington, United States
We have been developing in-situ spectroscopic methods to study the mechanism of hydrogen formation from amine borane materials. In previous work we discovered that a mesoporous silica scaffold significantly enhances the rate of hydrogen release from ammonia borane compared to the bulk material. In this presentation we will share our results from high field 11B and 1H NMR to monitor the evolution of the nonvolatile polymeric products as hydrogen is released from ammonia borane as a function of temperature to 423K. This approach permits a direct comparison of the rates of hydrogen release as well as a comparison of the nonvolatile boron containing products formed from thermal decomposition of the bulk AB material and the AB material embedded in the mesoporous silica scaffold. Static D NMR using deuterium labeled ammonia borane was used to study properties of the ammonia borane at the interface of the mesoporous silica. This approach provides an experimental measure of the rotational barriers about the B-N bond for the ammonia borane at both the higher temperature (>225K) tetragonal phase and the lower temperature (<225K) orthrombic phase. The NMR results for AB in the scaffold suggest the presence of a new amorphous mobil phase at the silica interface. PNNL is operated by Battelle Memorial Institute for the U.S. Department of Energy. A portion of this work was done at the EMSL, a user facility operated by PNNL for the USDOE.
9:00 PM - EE3.5
Cold Neutron Prompt Gamma-ray Activation Analysis for Characterization of Hydrogen Storage and Fuel Cell Materials.
Rick Paul 1 Show Abstract
1 Analytical Chemistry Division, NIST, Gaithersburg, Maryland, United States
Prompt gamma-ray activation analysis (PGAA) has great potential for analyzing materials that may impact the hydrogen economy. An instrument for cold neutron PGAA, located at the NIST Center for Neutron Research (NCNR), has proven useful for the measurement of hydrogen and other elements in a variety of such materials. Neutrons, chilled by passage through liquid hydrogen at 20 K, pass through a neutron guide to the PGAA station. Gamma rays, emitted by the sample upon neutron irradiation, are measured by a high purity germanium detector. The detection limit for hydrogen is less than 10 mg/kg for most materials. PGAA has been used to study materials with hydrogen storage potential. Hydrogen mass fractions up to 1.5 % have been measured in carbon nanotubes. Other potential H storage materials characterized by PGAA include lithium magnesium imides (Li2Mg(NH)2) and hydrides with formula ZrBe2Hx. PGAA has also been used to measure hydrogen uptake by solid proton conductors, and to characterize stoichiometries of Nafion films, which have potential for use as membranes in hydrogen fuel cells. A future upgrade to the instrument will improve detection limits and applicability of the method.
9:00 PM - EE3.6
Synthesis Process of Mg-Ti BCC Hydrogen Storage Alloys by Means of Ball Milling.
Kohta Asano 1 , Hirotoshi Enoki 1 , Etsuo Akiba 1 Show Abstract
1 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba, Ibaraki, Japan
Mg and Mg based alloys attract attention as on board hydrogen storage and transportation because of their high hydrogen storage capacity (Mg: 7.6 mass%, Mg2Ni: 3.8 mass%), low cost and light weight. Our group has successfully synthesized Mg-Ti alloys with a body centered cubic (BCC) structure by means of ball milling. BCC structure is a coarse packing structure and has many interstitial sites for hydrogen in comparison with the closest packing structures as a face centered cubic (FCC) and a hexagonal close packed (HCP). Mg-Ti BCC alloys synthesized by our group hardly absorbed hydrogen. To improve the hydrogen absorption and desorption properties of Mg-Ti alloys from the view point of nanostructures the synthesis process of Mg-Ti alloys by means of ball milling was investigated.After 50 h milling of Mg and Ti powder in an argon atmosphere, the plate-like particles were stuck on a milling pot and balls. After 75 h milling, these plate-like particles were peeled off a milling pot and balls and the spherical particles with the mean diameter of 1 mm were formed. Observations by optical microscope and chemical analysis by SEM-EDX showed that numerous concentric Ti layers were disposed in Mg spherical particles. After 150 h milling, these spherical particles were crushed into small particles and X-ray diffraction with Cu Kα radiation showed that the structure of Mg-Ti alloys was BCC structure. The structure of Mg and Ti is HCP structure. However, the mechanical properties between Mg and Ti are significantly different. Because Ti is harder than Mg, Ti acts as abrasives for Mg stuck on a milling pot and balls. The difference in the mechanical properties among raw materials is an essential factor for synthesis of Mg based alloys by means of ball milling.
9:00 PM - EE3.7
Chemisorption of H2 on a CuPt3 Cluster.
Hector Luna 1 , Sidonio Castillo 1 , Alfonso Anguiano 2 Show Abstract
1 Ciencias Basicas, Universidad Autonoma Metropolitana, Ciudad de Mexico, Distrito Federal, Mexico, 2 DEPI, ITTLA, Tlalnepantla de Baz, Estado de Mexico, Mexico
The study of the interaction of a pyramidal tetramer of CuPt3 with the H2 is reported here through ab initio self-consistent field (SCF) calculations, plus configuration interaction (CI) calculations. The CuPt3-H2 interaction was carried out in Cs symmetry. The lowest three electronic states X 2A'', A 2A' and a 4A' of the bare cluster were considered to study this interaction. For the H2 approaching toward a Pt vertex, results show that the CuPt3 pyramid cluster in its X 2A'', A 2A'and a 4A' states can spontaneously capture and break the H2. For the H2 approaching toward a Cu vertex, where H2 is located in the Cs reflecting plane, the CuPt3 cluster in its X 2A'', a 4A', electronic states shows capture of the hydrogen molecule with no energy barrier; moreover, in this approach the CuPt3 cluster in its a 2 A' electronic state shows spontaneous capture and dissociation of the hydrogen molecule. For the H2 approaching toward a Cu vertex, where the Cs reflecting plane bisects the H2 molecule, the CuPt3 cluster in two of its lowest-lying states X 2A'', a 4A', is able to capture the hydrogen molecule with no energy barrier. The CuPt3+H2 interactions show a lower H2 activation than that which was obtained in the equivalent Pt4+H2 interactions.
9:00 PM - EE3.8
Capture and Dissociation of the H2 Molecule by an AuPt3 Cluster.
S. Castillo 1 , Hector Luna 1 , Armando Cruz 2 , Enrique Garcia 1 Show Abstract
1 Ciencias Basicas, Universidad Autonoma Metropolitana, Ciudad de Mexico, Distrito Federal, Mexico, 2 Catalisis Molecular, Instituto Mexicano del Petroleo, Ciudad de Mexico, Distrito Federal, Mexico
9:00 PM - EE3.9
Structural and Hydriding/Dehydriding Properties of HoMn2Hx with Cubic and Hexagonal Laves Phase Structure.
Yoshikazu Makihara 1 , Youichi Iwata 1 , Kazumi Umeda 1 , Yoshio Miyairi 1 , Hironobu Fujii 2 Show Abstract
1 Mechanical and Electronic System Engineering, Kyushu-Kyoritsu University, Kitakyushu Japan, 2 Natural Science Center for Basic Research and Development, Hiroshima University, Higashi-Hiroshima Japan
Structural and hydrogen absorption/desorption properties of HoMn2Hx (0≦x<3) with cubic C15-type and hexagonal C14-type Laves phase structure have been investigated by powder X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA) and pressure-composition isotherms (PCT) measurements. The C15-type HoMn2 was elaborated by arc melting the constituent metals, and then the C14-type one was successfully prepared by annealing the C15-type HoMn2 in Ar atmosphere at 1173K for a week. After an activation process in vacuum at 343K, they were hydrogenated at room temperature, and then annealed in a hydrogen atmosphere at 433K in order to obtain a homogeneous hydride. The hydrogen content of the hydride was controlled by adjusting the hydrogen pressure in the range from 0.1 to 1.0 MPa. With increasing the hydrogen content, the lattice parameters at room temperature of the hydrides increase non-linearly for the C15-type hydrides, while linearly for the C14-type ones, where the expansion of the unit cell volume reaches to about 30% for the hydride with x≈3.0. The hydrogen absorbed in both the C15- and C14-type hydrides were discharged around 493K in an Ar atmosphere without any changes of crystal system and decomposition. The DTA profile of the C15-type hydride with x=2.95 shows an endothermic reaction around 373K which may correspond to a spinodal decomposition, in addition to the main dehydriding reaction around 491K. On the other hand, two endothermic reactions around 449K and 488K are observable in the DTA profile of the C14-type hydride with x=2.86, which correspond to two steps of dehydriding reactions. The structural changes in the desorption process for both types of hydrides were investigated in detail by XRD measurement. The PCT measurement at room temperature shows two plateaus for the C14-type HoMn2 in the absorption process, while one plateau for the C15-type one. Based on the experimental results mentioned above, structural effects on the hydriding/dehydriding properties of the HoMn2 are discussed.
James C. F. Wang Sandia National Laboratories
William Tumas Los Alamos National Laboratory
Aline Rougier Universite de Picardie Jules Verne
Michael J. Heben National Renewable Energy Laboratory
Etsuo Akiba AIST
EE4: Metal Hydrides II
Wednesday AM, April 19, 2006
Room 2006 (Moscone West)
9:30 AM - **EE4.1
Bader Analysis on Mg-Based High-Pressure Hydrides
Hitoshi Takamura 1 , Yasuyuki Goto 1 , Kamegawa Atsunori 1 , Masuo Okada 1 Show Abstract
1 Department of Materials Science, Tohoku University, Sendai, Miyagi, Japan
Novel hydrides and intermetallic compounds have been extensively explored in Mg-M systems by using Giga-pascal high-pressure, where M denotes rare-earth and transition metals. To date, a number of novel high-pressure hydrides such as MgY2H8 and Mg3MnH6 have been prepared under 2 to 5 GPa by using a cubic-anvil-type apparatus. Even though their crystal structures, hydrogen content, and electronic structures have been clarified, the nature of bonding between hydrogen and metal elements remains unknown. In this study, Bader analysis was performed to clarify the nature of bonding in the novel Mg-based high-pressure hydrides. Bader analysis enables ones to divide molecules or crystals into atoms by defining zero flux surfaces. The zero flux surfaces can be obtained by searching points at which ▽ρ = 0 holds. As a result, this analysis gives ones information on a shape of atoms including hydrogen and electronic charges belonging to the atoms as well as ionicity and covalency of bonding. To perform Bader analysis, it is crucial to obtain good electronic charge density. The first-principles calculations were conducted by using WIEN2k package; Bader analysis was performed by using the "atoms in molecules" program in the package. The analysis was also adopted for conventional hydrides such as TiH2 and MgH2 and amides. Compared to the conventional hydrides, the nature of bonding in the Mg-based high-pressure hydrides will be discussed in the context of the shape of hydrogen, ionicity, and covalency.
10:00 AM - **EE4.2
Advantages of High Surface Area Catalysts on MgH2 Sorption Properties.
Vinay Bhat 2 , Aline Rougier 2 , Luc Aymard 2 , G Nazri 1 , Jean-Marie Tarascon 2 Show Abstract
2 LRCS, UPJV, 33 rue St Lue, 80039, Amiens France, 1 , General Motors, R&D, Warren, Michigan, United States
10:30 AM - EE4.3
Hydrogen Storage in Magnesium Based Thin Films
Hasan Akyildiz 1 , Macit Ozenbas 1 , Tayfur Ozturk 1 Show Abstract
1 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
It is well known that Mg satisfies the most requirements of storage medium for stationary as well as for mobile applications. This is except for its high stability and sluggish reaction kinetics. Recently considerable progress has been made with the use of powder processing techniques to accelerate the reaction rate. The problem with regard to its stability, however, still remains to be solved. To develop MgH2 of reduced stability it is necessary to modify its chemistry. Thin film processing is a flexible method with which the chemistry of the basic system can be modified quite easily. Moreover, films of the same chemistry may be produced in amorphous or in crystalline state. In the current work a variety of thin films were produced via thermal evaporation, all based on Mg, in pure, co-deposited or in multilayered form, some coated with Pd. The films under the experimental conditions employed were crystalline with columnar grains with some degree of preferred orientation. In multi-component systems, the films in the as-deposited state were made of individual elements, but upon hydrogenation at temperatures greater than 473 K, the elements react with each other yielding the intermetallic phases. The study showed that, of the systems studied in this work, Mg-Cu multilayer yielded the most favorable result as a useful storage system, for Mg portion of the film can be converted totally into MgH2, this occurring at temperatures not greater than 473 K. The study implies that if the as-deposited structure were to be used and preserved as hydrogen storage medium, there is a narrow temperature window for hydrogenation.
10:45 AM - EE4.4
Hydrogen Storage in Metastable MgyTi(1-y) Thin Films.
P. Vermeulen 1 , R.A.H. Niessen 2 , P.H.L. Notten 1 2 Show Abstract
1 , Eindhoven University of Technology, Eindhoven Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands
It has been extensively discussed that hydrogen storage will determine the feasibility of a hydrogen economy to a large extend. A gravimetric storage capacity of at least 6 wt.% was set by the U.S. Department of Energy to accomplish the essential breakthroughs in this field . Recently, Niessen et al. showed that 6.5 wt.% of hydrogen can be reversibly absorbed and desorbed at high rates using Mg0.80Ti0.20 alloys . To determine the effect of the Ti-content on the hydrogen storage properties, MgyTi(1-y) thin films with y ranging from 0.50 to 1.00 were prepared by electron beam deposition. XRD measurements of the as-deposited thin films confirmed that crystalline single-phase alloys were obtained in all cases, which is remarkable as Ti does not form stable alloys with Mg under standard alloying conditions . Galvanostatic discharging reveals an optimum reversible hydrogen storage capacity (Qd) of approximately 1600 mAh/g for the Mg0.80Ti0.20 composition. Moreover, it is possible to distinguish two composition regions, a Mg-poor region (y ≤ 0.80) characterized by a excellent rate-capability and a Mg-rich region (y > 0.80) characterized by a poor rate-capability. An approximately similar compositional dependence of Qd for MgySc(1-y) alloys was reported in the past . Here, it was argued that the crystal structure of the hydride induces a profound change in hydrogen transport characteristics. The analogous dependence of the MgyTi(1-y) materials presented here, suggests that the crystal structure is most likely responsible for the inferior reversible hydrogen storage properties of the MgyTi(1-y) alloys with y beyond 80 at.%. In order to discuss the effect of the Ti-content in more detail, the hydrogenation responses of the MgyTi(1-y) thin films were analysed. These charging curves are comprised of two plateaus. Furthermore, the width of the first plateau increased with increasing Ti-content, which may suggest that segregation is induced. However, in spite of the high thermodynamic stability of TiH2, experimentally TiH is found in all cases. The MgyTi(1-y) thin films with 0.70 ≤ y ≤ 0.90 indicate MgH2 formation. Contrastingly, the electrochemical response of the Mg0.50Ti0.50 and Mg0.95Ti0.05 thin films implies MgH formation. As these observations are in contradiction with the intrinsic thermodynamic properties of both TiH2 and MgH2, it suggests that segregation upon hydriding the thin films does not occur. References U.S. Department of Energy, Multi-Year Research, Development and Demonstration, Plan: Planned program activities for 2003-2010, http://www.eere.energy.gov/hydrogenandfuelcells/mypp/ (Aug. 2005) R.A.H. Niessen and P.H.L. Notten, Electrochem. Solid-State Lett., 8, A534-A538 (2005).  Villars (Edt), Pearson’s Handbook Desk Edition, Vol. 2, 2336, ASM International (1997). P.H.L. Notten, M. Ouwerkerk, H. van Hal, D. Beelen, W. Keur, J. Zhou and H. Feil, J. Power Sources, 129, 45-54 (2004).
11:00 AM - EE4: MH2
11:30 AM - **EE4.5
Kinetics and Thermodynamics of Destabilized Hydride Systems.
John Vajo 1 , Tina Salguero 1 , Sky Skeith 1 , Gregory Olson 1 Show Abstract
1 , HRL Laboratories, LLC, Malibu, California, United States
Many light element hydrides with high gravimetric hydrogen densities but low equilibrium hydrogen pressures can be thermodynamically destabilized by the addition of elements or compounds that form alloys or new compounds during dehydrogenation. This lowers the enthalpy of the dehydrogenated state, which increases the equilibrium hydrogen pressure and effectively destabilizes the hydride. Using this approach we have developed several destabilized systems with hydrogen capacities of 5 to 10 wt % and equilibrium hydrogen pressures of 1 bar at temperatures from 25 to 225 °C. For example, we have found that LiBH4 can be destabilized by the addition of MgH2. In this case, dehydrogenation yields LiH and MgB2. In contrast, pure LiBH4 dehydrogenates to LiH and B. The exothermic formation of MgB2 lowers the dehydrogenated state enthalpy and increases the equilibrium hydrogen pressure by more than a factor of ten compared to pure LiBH4. With MgH2, the theoretical hydrogen capacity is 11.2 wt % and we have experimentally achieved reversible storage of >9 wt %. We have also found that LiBH4 can be destabilized, with at least partial reversibility, by other Mg compounds including MgF2, MgS, and MgSe. In these cases, dehydrogenation yields LiF, Li2S, and Li2Se, respectively. Although the thermodynamics of these destabilized systems are very attractive for hydrogen storage in transportation applications, we find that the kinetics are slow. Typically, temperatures of >300 °C are required for hydrogenation or dehydrogenation to occur in ~1 hr. To lower the reaction temperatures in the LiBH4/MgH2 system, we have tested several transition metals as potential catalysts including Ti, V, Sc, Cr, and Nb. For Ti, we have tested several Ti sources including TiCl2, TiCl3, TiCl3Cp (Cp = cyclopentadienyl), and TiF3. While addition of catalysts does lower the reaction temperatures slightly, Ti, V, Cr, and Nb all behave similarly and for Ti the behavior is independent of the Ti source. In contrast, Sc appears to completely poison the hydrogenation of LiH + 0.5MgB2. The dehydrogenation reaction pathway also depends on the temperature and hydrogen pressure. Thus, the destabilizing additives do not always react with the hydride in a concerted fashion leading to the stabilized dehydrogenated state. In this talk we will give several examples of destabilized hydride systems, discuss the kinetic limitations and our approaches to accelerating the hydrogen exchange reactions at temperatures <200 °C.
12:00 PM - EE4.6
On the Road to Make New Metal Hydrides.
Ewa Ronnebro 1 , Eric Majzoub 1 Show Abstract
1 Analytical Materials Science Department, Sandia National Laboratories, Livermore, California, United States
12:15 PM - EE4.7
Prediction of the Formation Enthalpy and Free Energy ofAB2H8 hydrides (A=Mg,Ca and B=B,Al).
Roland Stumpf 1 Show Abstract
1 , Sandia National Laboratories, Livermore, California, United States
12:45 PM - EE4.9
Study on the Ternary Mg-Ca-N-H Materials.
Yongfeng Liu 1 , Zhitao Xiong 1 , Jianjiang Hu 1 , Guotao Wu 1 , Ping Chen 1 Show Abstract
1 Physics, Surface Science, Singapore Singapore
Ternary Mg-Ca-N-H samples have been prepared by ball milled Mg(NH2)2 and CaH2 (1:1) with planetary ball mill machine, and the structure and reaction mechanism with increasing temperate were studied. The results indicated only hydrogen can be released during ball milled, and the amount of hydrogen released was increased with increasing ball milling time. After ball milling 72 hours, ~ 3.5 H atom were found to be detached, which is equivalent to ~ 3.5wt% of the starting material. Results of volumetric release and soak testing on the sample collected after 12 hours of ball milling, which only released ~ 0.6wt% of hydrogen, show that hydrogen desorption starts at temperature right above 50°C. At temperature of 200°C, ~ 1.9wt% of hydrogen was desorbed. DSC measurement on the hydrogen desorption from the post-12h milled sample reveals that the overall heat of desorption is ~ 28kJ/mol-H2, which indicates that Mg-Ca-N-H system could be a potential lower temperature hydrogen storage material. Moreover, the high-pressure release testing reveals that hydrogen could not desorb from the post-12h milled sample at temperature below 200°C when 80 bars of hydrogen was applied. As temperature increased to 300°C more than 3.0wt% of hydrogen was released, revealing that the equilibrium hydrogen desorption pressure is higher than 80 bars at temperature of 300°C. All these results indicate the reversibility of the Mg-Ca-N-H system. However, the difficulties in recharging the sample with hydrogen should be due to the high kinetic barrier. The kinetic investigations reveal a rather high activation energy in desorbing hydrogen from the Mg-Ca-N-H sample.
EE5: Carbon and Modified-Carbons
Wednesday PM, April 19, 2006
Room 2006 (Moscone West)
2:30 PM - **EE5.1
Hydrogen Storage in Novel Carbon-based Nanostructured Materials
Anne Dillon 1 , Calvin Curtis 1 , Philip Parilla 1 , Jeff Blackburn 1 , Tom Gennett 1 , Kim Jones 1 , Jeff Alleman 1 , Lin Simpson 1 , Yufeng Zhao 1 , Yong_Hyun Kim 1 , Shengbai Zhang 1 , Michael Heben 1 Show Abstract
1 Center for Basic Sciences, National Renewable Energy Laboratory, Golden, Colorado, United States
Hydrogen can be generated by a variety of means including the electrolysis of water using electricity derived from wind power, photovoltaics or by thermo-chemical processing of biomass. Hydrogen can then be reacted with oxygen in fuel cells to generate electricity, combusted in an engine to generate mechanical energy, or simply burned to generate heat. In each of these cases, water is produced in a virtually pollution-free process. The widespread use of hydrogen as an energy carrier will transform our society in much the same way that personal computing technologies have. Unfortunately, before hydrogen can be employed in the transportation sector, numerous technical hurdles must still be overcome. Furthermore, the United States Department of Energy's (DOE) Office of Energy Efficiency and Renewable Energy and the Office of Basic Sciences have concluded that vehicular hydrogen storage is the cornerstone technology for implementing hydrogen in the transportation sector. None of the current vehicular storage methods meet both the DOE volumetric and gravimetric targets for vehicular storage. Also an ideal binding energy that would allow for reversible hydrogen storage at near ambient conditions is ~10-40 kJ/mol. This binding energy is stronger than that expected for physisorption but significantly weaker than chemisorption. Recent theoretical studies(1) in our lab have shown that scandium will complex with the twelve five-membered rings in a boron-doped fullerne (C48B12). It is then possible to stabilize five H2 dihydrogen ligands with a binding energy of ~ 30 kJ/mol. The resulting C48B12[ScH(H2)5]12 has a reversible hydrogen capacity of 8.77 wt.%. Also, known metallocarbohedrenes including Ti8C12 and Ti14C13 have been predicted to bind dihydrogen molecules with a desirable binding energy for vehicular storage(2). Rational synthetic methods to experimentally demonstrate that dihydrogen may be stabilized on novel carbon-based nanostructures are currently being explored. Both gas phase synthesis and conventional wet chemical techniques are promising venues to demonstrate near ambient dihydrogen adsorption on light-weight materials. These experimental efforts will be discussed in detail.(1) Y. Zhao, Y.-H. Kim, A. C. Dillon, M. J. Heben, and S. B. Zhang, Phys. Rev. Lett. 94, 155504-1-4 (2005).(2) Y. Zhao, A. C. Dillon, Y.-H. Kim, M. J. Heben, and S. B. Zhang, Preprints of Symp, Amer. Chem. Soc. 50, 452-456 (2005).
3:00 PM - **EE5.2
Structure and Interaction Models for Carbon-based Retainment of Hydrogen.
Pavel Krasnov 1 , Feng Ding 1 , Boris Yakobson 1 Show Abstract
1 Dep. of ME&MS, and Dept. of Chemistry, Rice University, Houston, Texas, United States
Challenges of hydrogen storage include search for the carrier materials with (i) high density of binding sites and (ii) proper binding energy range, in order to ensure (i) sufficient hydrogen content and (ii) reversibility of containment-release cycles. With these goals in mind we perform theoretical evaluation of several conceptual systems, which can be--approximately--implemented with carbon nanotubes and fullerenes in the experimentalists' disposal. Currently we pursue three important topics. First is the feasibility to achieve hydrogen binding on metal-decorated nanotubes, following recent demonstration by our NREL partners of high efficiency of metal-C60 complexes. For this, we perform density functional theory (DFT) computations of scandium complexes with nanotubes and molecular hydrogen. We find that interaction of H in these complexes is weaker than the covalent binding while stronger than purely van-der-Waals physisorption. Therefore, the binding of H by scandium-doped nanotubes can be reversible, yet sufficient to prevent any spontaneous undesirable release at ambient conditions. The H-capacity of scandium-doped nanotubes is ~6.0%, raising to nearly 7.5% for very narrow tubes due to better spacing of the metal atoms. We perform further analysis of the potential barriers between the Sc binding sites at the adjacent hexagons, important for prevention of metal aggregation at operating temperatures. Second, we explore an ultimate foam-surface, negative-curvature assembly of C60‘s welded into a supramolecular diamond type Bravais lattice (Vanderbilt and Tersoff, 1992). In such foam, H can interact with both sides of the C-network, and the presence of heptagons must additionally enhance the interactions, since the breaking of aromaticity increases the chemical activity. Molecular dynamics (MD) simulations of hydrogen in the foam are performed with classical potential gauged by ab initio calculations. Interaction with the C-foam is also evaluated by DFT calculations with plane-wave basis. Third, we investigate the phenomenon of spillover of hydrogen through metal cluster (e.g., Pd) onto SWNT exterior. MD simulations are performed using tight-binding approximation. The main purpose is to gain insight into dissociation of molecules and transport through the metal cluster, followed by H binding to the nanotubes. This work is supported by the U.S. Department of Energy.
3:30 PM - EE5.3
Ab Initio Study of Hydrogen Storage on CNT
Zhiyong Zhang 1 , Henry Liu 1 , Kyeongjae Cho 1 Show Abstract
1 , Stanford University, Stanford, California, United States
Since the first report of hydrogen storage in CNT, there have been intensive experimental and theoretical efforts to understand the characteristics of CNT as a hydrogen storage material under various conditions. Hydrogen interacts with CNT either through physisorption or chemisorption. Due to the weak nature of the physisorption of H on CNT, it is more likely that H is chemisorbed on CNT in a viable hydrogen storage material based on CNT . With a one to one ratio of H to C, up to 7.69 wt% of chemisorbed H can be stored on CNT. Unfortunately, due to the widely different experimental conditions and nanotube samples used, there is no clear consensus on the actual capacity of CNTs for hydrogen storage. Some of the key issues of the hydrogen storage on CNT include: (1) how does the binding energy change as a function of coverage, nanotube size, and chirality? (2) What is the most likely dissociative adsorption pathway of hydrogen on CNT? (3) How to modify the CNT to enhance the dissociative adsorption of hydrogen on CNT? We will use first principles ab initio simulation methods to provide answers to these issues. In our study we considered the hydrogen chemisorption capacity on CNT as a function of coverage. It is found that binding energy is a strong function of the coverage pattern of H on CNT. We have identified the optimal configurations of H on CNT at different coverage’s and based on the calculations, we discuss the most likely coverage pattern and the maximum storage capability of H on CNT through chemisorption. We will also present our results for CNTs of different sizes. To understand the mechanism of dissociative adsorption of H on CNT, we studied various pathways and identified the most likely dissociative adsorption pathway with an energy barrier around 1.3 eV. We found that adsorbed hydrogen can act as auto catalysts for further hydrogen dissociative adsorption on CNT. It has been proposed that catalysts are needed for the breakup of hydrogen and then hydrogen can diffuse on the CNT to reach the maximum coverage. To understand the diffusion mechanism we identified various diffusion pathways of H on CNT and their implication for the so called spillover mechanism will be discussed. Furthermore, we studied the catalytic effects of transition metal clusters on CNT and doping CNT with N. It is found that doping CNT with N can substantially improve the dissociative adsorption of hydrogen on CNT. Finally we will present the results of the structures of metal clusters on CNT, as well as the catalytic effects of transition metal clusters on hydrogen dissociative adsorption on CNT.  S. Park, D. Srivastava, and K. Cho, “Generalized Chemical Reactivity of Curved Surfaces: Carbon Nanotubes,” Nano Lett. v.3, no.9, p.1273-1277 (2003).
3:45 PM - EE5.4
Volumetric Sorption Measurements On Small Samples At Low Temperatures.
Philip Parilla 1 , Lin Simpson 1 , Jeff Blackburn 1 , Anne Dillon 1 , Tom Gennett 2 , Katherine Gilbert 1 , Michael Heben 1 Show Abstract
1 Basic Sciences Center, National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Chemistry Department, Rochester Institute of Technology, Rochester, New York, United States
With the recent emphasis on developing new hydrogen storage materials for the push toward a hydrogen economy, fast and accurate hydrogen capacity measurements are needed to screen the numerous types of test samples. Having an ability to perform measurements on small masses (5 - 10 mg) facilitates the research both by reducing the effort required to produce enough material for testing and by increasing measurement throughput since small samples have shorter degassing, sorption and desorption times. Here, we report on an instrument developed to provide the above features and additionally having an isolation valve for the sample container thereby allowing for sample transfer without exposure to the laboratory ambient. The design of this system focuses on single-point measurements to allow fast screening/high throughput for the samples (about 4 samples/day). The system is capable of temperatures up to ~ 1300 K for desorption and down to 77 K for low temperature sorption measurements. The maximum pressure capability is currently ~3 bar. Typically prior to measurement, any degassing is performed at a separate high vacuum station (maximum temperature ~ 1300 K) and the sample later transferred to the volumetric apparatus in the sealed container without exposure to air. Degassing at another system allows for higher sample throughput by having the volumetric instrument just utilized for the sorption measurements. Alternatively, the volumetric systems is also capable of an in situ degas and degassing in a flowing gas such as helium. Critical components for the exact control of temperature gradients from room temperature to the liquid nitrogen bath as well as methods used to minimize the effect of the falling liquid nitrogen level will be described. Experimental procedure, instrument calibration, accuracy estimates, and instrument verification will be discussed. Finally, example data with carbon-based samples will be used to show the functioning of the instrument. Funding provided by the US Department of Energy's Office of Energy Efficiency and Renewable Energy within the Center of Excellence on Carbon-based Hydrogen Storage 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.
4:00 PM - EE5: Carbon
4:30 PM - **EE5.5
Metal Poly(Dihydrogen) Complexes for Hydrogen Storage.
Gregory Kubas 1 , Jeffrey Cross 1 Show Abstract
1 Chemistry, Los Alamos National Lab, Los Alamos, New Mexico, United States
Our discovery of transition metal dihydrogen complexes nearly 25 years ago has led to a new field of chemistry. Over 500 complexes of the type M(H2)(L)n are known for all of the metals from Ti to Pt (L = ancillary ligand). Many contain reversibly bound H2 at or near room temperature and pressure, which is ideal for hydrogen storage. However the weight percent hydrogen is low primarily because of the ancillary ligand weight. Only a few complexes are known to contain two H2 ligands (none with more). We are seeking synthesis of hydrogen-rich metal complexes of the type M(H)x(H2)n containing theoretically predicted multiple H2 ligands (up to n = 6) and no ancillary ligands. Protonation of metal alkyl or aryl complexes, e.g. M(R)2, in ionic liquids under hydrogen atmosphere is one potential pathway. The organo group R should be eliminated as alkane or arene, leaving a "naked" metal cation capable of binding multiple H2 and/or hydride ligands. Such species are known in the gas phase with up to seven or eight bound H2 groups per first-row metal, and if they prove to be unstable in the condensed phase, they could possibly be incorporated into solid phase materials such as zeolites and fullerenes. Protonation of anionic metal polyhydrides is another pathway to poly-H2 complexes, which may be stable under moderate H2 pressures. The binding of H2 should be highly reversible in such systems, leading to facile hydrogen storage.
5:00 PM - EE5.6
Hydrogen Storage and Spillover in New Mesoporous Platinum-Carbon Nanocomposite.
Seong Ihl Woo 1 , Hee Jung Jeon 1 , Kwang Seok Oh 1 , Myoung Rae Kim 1 Show Abstract
1 Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
5:15 PM - EE5.7
Metastable Structures and Recombination Pathways for Atomic Hydrogen on the Graphite (0001) Surface.
Liv Hornekaer 1 , Zeljko Sjlivancanin 2 , Wei Xu 1 , Roberto Ortero 1 , Eva Rauls 1 , Bjoerk Hammer 1 , Flemming Besenbacher 1 Show Abstract
1 institute of physics and astronomy, University of Aarhus, DK-8000 Aarhus C Denmark, 2 , Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne Switzerland
5:30 PM - EE5.8
Hydrogen Adsorption in Carbon based Materials – a Quantitative Study using Nuclear Magnetic Resonances
Alfred Kleinhammes 1 , Shenghua Mao 1 , Marcelo Behar 1 , Yue Wu 1 Show Abstract
1 Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill , North Carolina, United States
The capability of newly developed or already existing materials for adsorbing H2 molecules need to be evaluated in a consistent and exact matter if such materials should be selected for H2 storage applications. Nuclear magnetic resonance (NMR) spectra sensitively distinguish between molecules contained in the gas, H2 adsorbed on surfaces as well as hydrogen containing contaminants through their distinct spectral features. In addition to spectral analysis relaxation techniques are used to distinguish various contributions. The selectivity and sensitivity of the technique qualifies NMR as the tool to assess quantitatively the adsorption of H2 on and within materials. A high pressure cell based on a sapphire sample tube that can sustain H2 pressures higher than 100 atmospheres is used to study the insitu H2 loading of carbon based materials in an NMR probe. The adsorbed H2 is measured as a function of H2 pressure for loading and unloading. Materials for H2 storage being investigated include conducting polymer networks, doped and undoped carbon nanotubes, MOFs. Funding provided by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy within the Center of Excellence on Carbon-based Hydrogen Storage Materials as part of DOE’s National Hydrogen Storage Grand Challenge
5:45 PM - EE5.9
Capillary Densification of Hydrogen in Nanoporous, Amorphous Carbons.
Steve Lustig 1 , Mark Shiflett 1 , David Corbin 1 , Pratibha Gai 1 , Kostantinos Kourtakis 1 Show Abstract
1 Central Research & Development, DuPont, Wilmington, Delaware, United States
We have studied the effect of synthesis conditions on the nanostructure of advanced carbons that show moderate to excellent H2 storage. We have performed in situ studies of the dynamic pyrolysis of palladium catalyzed multifunctional polymers (MFP) in nitrogen environments, to understand the effect of process parameters and to utilize the results in the development of optimum nanostructures to meet the storage requirements. Carbon sorbents have been synthesized from polysaccharides including chitosan, chitin, and cellulose. Pyrolysis in a hydrogen atmosphere at 1373 K and 24 h has lead to microporous carbons with an optimum surface area and pore volume exceeding 2000 m2 g-1 and 2.0 cc g-1, respectively. Gravimetric microbalance studies indicate that these materials physically absorb hydrogen and store between 7 to 10 mass percent at 10 bar and 100 K. TEM micrographs indicate that the amorphous carbon shows additional ordering with prolonged hydrogen treatment from 2 to 24 h which has proven beneficial in increasing hydrogen storage. X-ray diffraction, TEM analysis, and porosimetry measurements also indicate that extending hydrogen exposure beyond 24 h leads to decreasing hydrogen storage due to the continuation of a loss in carbon relative to metal contaminants (P, Ca, Na) in the starting materials and increased crystallinity. Comparison of the results have shown that for advanced carbons derived from polymers or natural products treated with hydrogen at high temperatures, the optimum nanostructure is substantially disordered (turbostratic) graphite, whereas for materials derived from MFP, it is primarily amorphous carbon. The experiments have also revealed the optimum temperature region for operation.
James C. F. Wang Sandia National Laboratories
William Tumas Los Alamos National Laboratory
Aline Rougier Universite de Picardie Jules Verne
Michael J. Heben National Renewable Energy Laboratory
Etsuo Akiba AIST
EE6: New Approaches to Hydrogen Storage
Thursday AM, April 20, 2006
Room 2006 (Moscone West)
9:00 AM - **EE6.1
Tuning Clathrate Hydrates: Application to Hydrogen Storage.
Huen Lee 1 , Jong-won Lee 1 3 , Do-Youn Kim 1 , Jeasung Park 1 , Yu-Taek Seo 2 , Huang Zeng 3 , Igor Moudrakovski 3 , Christopher Ratcliffe 3 , John Ripmeester 3 Show Abstract
1 Chemical & Biomolecular Eng., KAIST, Daejeon Korea (the Republic of), 3 Steacie Institute for Molecular Sciences, National Research Council Canada, Ottawa, Ontario, Canada, 2 Conversion Process Research Center, Korea Institute of Energy Research, Daejeon Korea (the Republic of)
The efficient storage of hydrogen will be a key factor in establishing a hydrogen-based economy, requiring the handling of large quantities of hydrogen gas at safe pressures. Strategies have been explored where hydrogen can either be bound chemically, adsorbed in materials with permanent void space, or be stored in hybrid materials that combine some of these elements. Each approach has problems, either from technical considerations or from materials cost. A recently reported clathrate hydrate of hydrogen, requiring only water and gas, indeed does meet the storage and cost requirements, however, the extreme pressures (~2 kbar) required to produce the material make it impractical. Here we report how clathrate hydrates can be tuned to give a reasonable hydrogen storage capacity while requiring only modest pressures for synthesis and storage.We carried out initial studies on materials produced from 5.56 mol% THF solution in water, which gives a clathrate of composition THF●17H2O. when cooled below the melting point of 277.3 K. The THF hydrate was then pressurized with H2 gas at various pressures up to ~ 120 bars, and examined for structure, cage populations and composition by powder X-ray diffraction (PXRD), Raman and NMR spectroscopy, and direct measurement of the H2 released on decomposition. From the PXRD results, the material was confirmed to be a sII hydrate according to its phase behavior. The Raman spectra show four transitions due to rotational fine structure associated with the high-pressure H2 gas, and a broad band that can be identified with H2 inside hydrate cages. The hydrate H2 line is shifted to lower frequency compared to the free gas, as has also been observed for O2 and N2 hydrates. 1H NMR spectroscopy was used to monitor H in the product of its reaction with perdeuteriated THF hydrate (THF-d8●17D2O), so that only H2 signals and residual protons in water and THF would be observed. The analysis of NMR spectroscopy confirmed earlier experiments that led to the suggestion of double occupancy of the small cages by H2. Although the hydrate lattice is tunable for higher levels of storage, the yield is relatively low, making the analysis more difficult. However, one may expect that by replenishing the THF consumed during hydrate formation, the yield can be increased considerably. A number of features remain to be explored, including the actual guest distribution in the high H2-loading region, and the actual boundaries on the composition, pressure and temperature phase diagram for the mixed hydrate with high H2 storage levels.
9:30 AM - **EE6.2
Hydrogen Storage and Delivery in a Liquid Carrier Infrastructure
Guido Pez 1 , Alan Cooper 1 , Bernard Toseland 1 , Karen Campbell 1 Show Abstract
1 Corporate Science and Technology Center, Air Products and Chemicals Inc., Allentown, Pennsylvania, United States
We have approached the problem of hydrogen storage within the vision of an H2-regenerable two-way liquid carrier hydrogen delivery infrastructure. The carrier is a readily transportable liquid which is catalytically hydrogenated at a H2-source site and correspondingly is catalytically dehydrogenated in an appropriate reactor at a fixed or mobile point of use.The significant material challenges will be discussed with reference to an early prototype carrier composition, perhydro-N-ethyl carbazole – an ambient temperature liquid which can reversibly store and at 180-200 degree C deliver ~5.6 wt% of its contained hydrogen.
10:00 AM - **EE6.3
Evading the Choice Between High-pressure Hydrogen Storage and High Temperature Reforming on Fuel Cell Vehicles: Reforming of Ethanol to Hydrogen and Methane at Low Temperature and a High Efficiency Scheme for Utilization.
David Morgenstern 1 , James Fornango 1 Show Abstract
1 Catalyst Discovery Team, Monsanto Co., St. Louis, Missouri, United States
At this time, the weight, cost, and startup time requirements for vehicular fuel cells can be met only by PEM fuel cells supplied with hydrogen. This fact imposes a choice of either storing hydrogen on board the vehicle, perhaps aided by advanced hydrogen storage materials, or producing it from a liquid fuel by onboard reforming. In many respects, the onboard reforming option is attractive. There is no need for drivers to handled pressurized hydrogen, a national hydrogen infrastructure is not required, and cruising range is greatly improved. Despite these advantages, onboard reforming was abandoned by the Department of Energy in 2004. Reforming of most fuels of interest, such as gasoline, natural gas, and ethanol, requires temperatures of about 800°C, and relatively large catalyst masses. This results in problems of thermal efficiency, cost and poor startup, among other issues identified by the DOE.We have developed a catalyst for an unexplored low-temperature reforming pathway of ethanol. Ethanol is an attractive fuel because it is renewable and available in large quantities in the US and elsewhere. Traditional high temperature reforming of ethanol produces six moles of hydrogen per mole of ethanol, but the low-temperature pathway produces only two moles after water-gas shift, along with a mole of methane.CH3CH2OH + H2O → CH4 + CO2 + 2H2Nickel sponge, often termed “Raney nickel” plated with copper has proven to be active for the reaction and stable for hundreds of hours. Water-gas shift activity is poor, and a downstream water-gas shift catalyst bed would likely be required. The catalyst is compact, thermally conductive and uses only inexpensive base metals. Combined with the low reforming temperature, we anticipate that these properties of the catalyst will eliminate the problems that have stymied high temperature onboard reforming.In order to be competitive with the efficiency of high temperature reforming, the fuel value of the methane must be exploited in an internal combustion engine (ICE). We believe that low temperature ethanol reformate could be used to fuel a powertrain looking much like today’s hybrid vehicles, in which torque supplied by an ICE is supplemented by an electric motor. The gas mixture would pass through a fuel cell unit where electricity is generated from the hydrogen. The effluent, containing methane and unreacted hydrogen, would be burned in the ICE. The reformer would be heated by the ICE exhaust. Such a vehicle would start up as quickly as a conventional car, since the ICE would start when the key is turned, immediately supplying heat to the reformer. In this approach, the waste heat from the engine is not wasted, resulting in improved activity. Our calculations indicate that the efficiency of such a vehicle would be equivalent to a more conventional, fuel-cell only vehicle on a tank-to-wheels basis.
10:30 AM - EE6: New App
11:00 AM - **EE6.4
Combined Neutron Scattering and First-principles Study of Novel Hydrogen Storage Materials.
Taner Yildirim 1 Show Abstract
1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
11:30 AM - **EE6.5
Combinatorial Development of Cost-Effective Catalysts for Solid State Hydride Materials
Xiao-Dong Xiang 1 Show Abstract
1 , Intematix Corporation, Fremont, California, United States
The kinetics of dehydrogenation and regeneration of solid-state materials capable of storing hydrogen with high-capacity volume and weight ratios is of vital importance to the realization of using hydrogen as an energy carrier alternative to fossil fuel. We have investigated the catalysis efficiency of various transition metals and related metal alloys in chemical hydrides and metal hydrides using combinatorial development technology. The combinatorial technology makes it possible to accelerate study of the catalysis properties of a variety of metals and their alloys in hydride materials. This approach has led to discovery of several promising catalyst candidates that exhibit better catalytic performance than or equivalent to that of precious metals in a few different hydride material systems, respectively.
12:00 PM - EE6.6
Decomposition Kinetics and Thermodynamics of the α, β and γ Polymorphs of Aluminum Hydride.
Jason Graetz 1 , James Reilly 1 Show Abstract
1 Energy Sciences and Technology, Brookhaven National Laboratory, Upton, New York, United States
Aluminum hydride (AlH3) is a covalently bonded, metastable solid at room temperature with a large gravimetric and volumetric hydrogen capacity (10.1 wt.% and 149 kg/m3, respectively). The high capacity and rapid kinetics has generated considerable interest in using AlH3 as an H2 source in low temperature fuel cells. In this study the kinetics and thermodynamics of the α, β and γ polymorphs of aluminum hydride (AlH3) were investigated. Polymorphs of AlH3 were prepared by organometallic synthesis. The freshly synthesized, nonsolvated AlH3 exhibited hydrogen capacities approaching 10 wt.% at desorption temperatures less than 100° C. The decomposition kinetics were determined by measuring isothermal hydrogen evolution between 60 and 140° C. Decomposition was most rapid for the γ polymorph, followed by the β and α phases. Our results indicate that the rate of decomposition is controlled by nucleation and growth of the aluminum phase. The large activation energies measured for AlH3 (~100 kJ/mol for α-AlH3) suggest that the decomposition may occur via an activated complex of approximately 9 AlH3 molecules (1-2 unit cells for α-AlH3). The thermal stability of α, β and γ-AlH3 was determined using differential scanning calorimetry and ex situ x-ray diffraction. We demonstrate that the decomposition of the β polymorphs occurs by an initial β → α phase transition followed by the decomposition of α-AlH3 at a temperature of around 100° C. Similarly, thermal decomposition of the γ phase revealed a γ → α transition at ~100° C followed by the decomposition of the α phase. The transformation from the less stable β and γ phases to the α phase is exothermic and is therefore likely to occur spontaneously at room temperature. A formation enthalpy of approximately -10 kJ/mol AlH3 was measured for α-AlH3, which is in good agreement with previous experimental and calculated results.
12:15 PM - EE6.7
Predicting New Hydrides: A Combined Monte Carlo and ab-inito Approach.
Eric Majzoub 1 , Vidvuds Ozolins 2 , Roland Stumpf 1 , Ewa Ronnebro 1 Show Abstract
1 MS 9403, Sandia National Laboratories, Livermore, California, United States, 2 , University of California, Los Angeles, California, United States
12:30 PM - EE6.8
Formation and Decompositon Reactions of Sr2AlH7.
Etsuo Akiba 1 , Hirotoshi Enoki 1 , Qingan Zhang 2 Show Abstract
1 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki Japan, 2 School of Materials, Anhui University of Technology, Maanshan, Anhui, China
Sr2AlH7 was successfully synthesized by hydrogenation of an intermetallic compound SrAl2 by the authors. In addition, this hydride was synthesized by hydrogenation of Sr2Al alloys. In this report, we tried to prepare Sr2AlH7 from commercially available SrH2, Al powder and hydrogen gas. Formation of the hydride has not been observed yet. It is due to poor mixing of the raw materials. The decomposition process of the hydride will also be discussed.
12:45 PM - EE6.9
Quantum Dynamics of H2 in Metal-Organics Frameworks MOF5
Yun Liu 1 , Taner Yildirim 1 Show Abstract
1 NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Metal-organic framework (MOF) compounds are a new family of highly crystalline, nanoporous materials in which thesize and chemical functionality of the pores can be tailored systematically. Despite to their promise in hydrogen storage, our understanding of hydrogen-host lattice interaction is still very limited. Recently we have carried out a detailed inelastic neutron scattering study of MOF5 as a function of hydrogenloading and temperature. The INS spectrum indicates several sharp features due to orho-para transition and H2-phonons and their coupling. In this talk, we present a detailed analysis of these features which are very sensity to the H2-MOF interaction and therefore provide a local probe to measure the H-MOF potential accurately. Needless to say, obtaining such an accurate potential for H2-MOF is critical to improve these materials for higher hydrogen storage capacity. The INS spectrum is calculated by solving 3dimensional Schrodinger equation for an H2 molecule at the adsorption sites of MOF5 lattice for differentrotational states. We also study the effect of thecoupling between rotational quantum numbers andthe center of mass vibrations.
EE7: Metal Hydrides III
Thursday PM, April 20, 2006
Room 2006 (Moscone West)
2:30 PM - **EE7.1
Thermodynamic and Kinetic Invesitgations on the Reversible Hydrogen Storage over Li-Mg-N-H System.
Ping Chen 1 , ZHitao Xiong 1 , Guotao Wu 1 , Lefu Yang 1 , Jianjiang Hu 1 , Weifang Luo 2 Show Abstract
1 Physics Department, National University of Singapore, Singapore Singapore, 2 , Sandia National Laboratories, Livermore, California, United States
The chemical interaction between magnesium amide and lithium hydride follows the reaction of Mg(NH2)2 + 2LiH = Li2MgN2H2 + 2H2. Theoretically, more than 5.5wt.% of hydrogen can be reversibly absorbed. The isotherm of hydrogen desorption from the system presents one pressure plateau and one slope region indicating different thermodynamic properties. The overall reaction heat of the abovementioned reaction is ~ 44 kJ/mol-H2. Whereas, the heat of desorption of hydrogen within the pressure plateau is ~39kJ/mol-H2. Estimated from the thermodynamic data the temperature for hydrogen desorption at 1.0 bar equilibrium pressure should be lower than 100 degree C. However, the relatively large activation energy sets a high barrier for the hydrogen desorption. Isotopic exchange technique has been applied to identify the reaction mechanism. Both isothermal and non-isothermal kinetic measurements have been performed to distinguish the origin of kinetic barrier.
3:00 PM - **EE7.2
Recent Development on Li-Mg-N-H Storage System.
Weifang Luo 1 , Jim Wang 1 , Karl Gross 1 , Shane Sickafoose 1 , Ken Stewart 1 Show Abstract
1 , Sandia National Laboratories, Livermore, California, United States
The Mg-Li-N-H system is a very promising hydrogen storage material due to its high capacity, reversibility and moderate operating conditions. The plateau pressure of this new system is about 30 bars at 200oC with H capacity of 5.2 wt%. Reaction mechanism for this system has been investigated by Powder X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) analysis for samples at various degrees of hydrogenation. These results provide information about the structural changes during absorption/desorption. The mixture of (2LiNH2 + MgH2) can convert to (Mg(NH2)2+2LiH) when heated at 220oC and 100 bar of hydrogen without undergoing desorption. Based on the fact that there are two distinct parts appearing in all of the pressure-composition isotherms (180 to 220oC), a reaction mechanism is proposed. There are two reactions taking place in hydrogen isothermal absorption/desorption for the material starting with (2LiNH2 + MgH2) or (Mg(NH2)2+2LiH), i.e., a single solid-phase reaction, corresponding to the sloping region for hydrogen weight percent (Hwt %) smaller than 1.5%, and a multiple-phase reaction, corresponding to a plateau region for Hwt %> 1.5 in the isotherms. During hydrogen absorption/desorption, the single-phase reaction corresponds to the forming/consuming of -NH2 which is bonded to Li and the multiple-phase reaction corresponds to forming/consuming Mg(NH2)2 and LiH. Issues of the side-reaction, forming ammonia, will be discussed.Key words: Hydrogen storage materials; Powder XRD; FTIR analysis; Thermodynamic and structural characterization.
3:30 PM - EE7.3
Potential of Li-Al-N-H Materials for Hydrogen Storage.
Jun Lu 1 , Zhigang Fang 1 , Hong Sohn 1 Show Abstract
1 Metallurgical Engineering, University of Utah, Salt Lake City, Utah, United States
Although there have been numerous materials studied as candidates for hydrogen storage applications, none of the materials known to date has demonstrated a sufficient hydrogen capacity or efficiency at required operating temperature ranges. There are still considerable opportunities for the discovery of new materials or material systems that will lead to advances in science as well as commercial technologies in this area. LiAlH4 is one of the most promising materials owing to its high hydrogen content. In the present work, we investigated the dehydrogenation properties of the combined system of 2LiAlH4/LiNH2 under argon. Thermogravimetric analysis (TGA) of the decomposition of 2LiAlH4/LiNH2 mixtures without any catalysts indicated that a large amount of hydrogen (~ 8.1 wt%) can be released between 85 and 320 C under a heating rate of 2 C/min in three dehydrogenation reaction steps. It was determined that LiNH2 effectively destabilizes LiAlH4 by reacting with LiH during the dehydrogenation process of LiAlH4. We also investigated other Li-Al-N-H systems, including 2LiAlH4/LiNH2, Li3AlH6/3LiNH2, and Li3AlH6/3LiNH2. TGA results showed that all of these systems released large amounts of hydrogen between 100 and 320 C. Preliminary results indicate that the reversibility is approximately 4wt%.
4:30 PM - **EE7.5
Reversibility and Phase Compositions of Destabilized Hydrides Formed from LiH.
Robert Bowman 1 , Son-Jong Hwang 2 , C. Ahn 2 , Anne Dailly 2 , M. Hartman 3 , T. Udovic 3 , J. Rush 3 , J. Vajo 4 Show Abstract
1 , Jet Propulsion Laboratory, Pasadena, California, United States, 2 , California Institute of Technology, Pasadena, California, United States, 3 , NIST, Gaithersburg, Maryland, United States, 4 , HRL, Laboratories, LLC, Malibu, California, United States
The novel approach of destabilizing hydrogen rich but strongly bound hydrides such as LiH via alloying with elements (i.e., Si) or compounds (i.e., MgB2) has been recently shown to improve substantially their potential as hydrogen storage materials in fuel cell powered vehicles. A reversible hydrogen storage capacity totaling around 5.0 wt.% was measured with mixtures of LiH and silicon powders where this LiH+Si system produces a 4-to-5 order-of-magnitude increase in the equilibrium pressure compared to just LiH alone for temperatures below 800 K. Similar behavior has also been seen for the LiH+Ge system whereas somewhat different effects have been found from LiH+MgB2 mixtures. Volumetric measurements of the hydrogen absorption and desorption isotherms have been obtained for these three systems The phase compositions at the various stages of reaction for these samples have been examined by Magic Angle Spinning-nuclear magnetic resonance (MAS-NMR) of the 7Li, 1H, 11B, and 29Si nuclei, powder x-ray diffraction (XRD), Raman spectroscopy, and neutron scattering methods. The initial mixtures of LiH with Si or Ge were found to convert into known Li-Si or Li-Ge intermetallic phases. A previously unknown ternary Li-Si-H phase has been found and characterized using MAS-NMR, neutron vibration spectroscopy, and neutron diffraction. Raman spectra clearly demonstrated that crystalline silicon or germanium reforms from the Li-Si or Li-Ge phases upon hydrogen absorption. While the absorption reactions are certainly reversible over portions of the Li-Si-H composition range, incomplete recovery of the original LiH + Si phases was also observed sometimes. The distributions of the silicide and hydride phases for various stages of reaction are discussed within the context of destabilization processes involving intermediate hydride and alloy phases that alter observed thermodynamic parameters. Prompt gamma activation analysis has been employed to provide a quantitative measure of the hydrogen contents of the LiH-Si and LiH-Ge systems at different levels of dehydrogenation. Results of these various studies are discussed along with their implications for the use of these Li-based systems as hydrogen storage media.
5:00 PM - **EE7.6
Recent Progresses on Complex- and Perovskite-hydrides for Hydrogen Storage.
Shin-ichi Orimo 1 , Yuko Nakamori 1 , Kazutaka Ikeda 1 , Hai-Wen Li 1 Show Abstract
1 Institute for Materials Research, Tohoku University, Sendai Japan
Currently, two effective methods, ‘substitution of M elements’ and ‘preparation of appropriate mixtures’, are being investigated for complex hydrides (M-N-H and M-B-H with M = Ia and IIa elements) with the primary aim of destabilizing the hydrides for promoting the dehydriding reactions. In the former method, an effective way for the destabilization was to partially substitute Li with other elements that have larger electronegativity, such as Mg. Experimental results on the dehydriding reactions of LiNH2 and LiBH4 with/without Mg substitutions prove that the dehydriding temperatures become lower with the increasing Mg concentrations. In the latter method, the actual destabilization of the mixture of Mg(NH2)2 and 4LiH, and that of LiBH4 and 2LiNH2 as compared to the individual (complex-) hydrides was confirmed.On perovskite hydrides, formation ability of LixNa1-xMgH3 with x = 0 - 1.0 was experimentally studied, and NaMgH3 (x = 0) with the perovskite-type structure was successfully synthesized just by mechanical milling. Reversible hydriding and dehydriding reactions were experimentally confirmed on NaMgH3 at 673 K. The diffraction peaks corresponding to the structure shift to higher angles due to the partial substitution of Na by Li (x = 0.5), while there is no evidence of the perovskite-type structure in LiMgH3 (x = 1.0). The experimental results are reasonably explained/predicted from the viewpoint of the geometric restrictions of ions, which are described by so-called Goldschmidt’s tolerance factors.
5:30 PM - EE7.7
Powder Diffraction Study of Li and Mg amides and imides.
Yumiko Nakamura 1 , Magnus Sorby 1 , Satoshi Hino 2 , Haiyan Leng 2 , Takayuki Ichikawa 2 , Hironobu Fujii 2 , Hendrik Brinks 1 , Bjorn Hauback 1 Show Abstract
1 Department of Physics, Institute for Energy Technology, Kjeller Norway, 2 Materials Science Center, N-BARD, Hiroshima University, Higashi-Hiroshima Japan
5:45 PM - EE7.8
In Depth Investigation of Hydrogen Storage and Absorption/Release Kinetics in Metal Ammine Complexes and Nanoscaffolds
Brian Mosher 1 , Samuel Mao 2 , Gang Chen 3 , Taofang Zeng 1 Show Abstract
1 , North Carolina State Univ., Raleigh, North Carolina, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Metal ammine complexes have recently become an apparent means to safe, condensed hydrogen storage. However, through the use of metal hydrides, even more effective metal ammine complexes can be created, storing and releasing significantly more hydrogen than current materials. We compare the absorption/release kinetics and overall hydrogen storage capacity of several metal hydrides and show their high potential as new media for efficient hydrogen storage.Furthermore, we present a detailed investigation of the pore size effects of molecular sieves on hydrogen storage. Molecular sieves have recently been established as a means of storing hydrogen rich materials. Pore size effects on combined hydrogen and ammonia physiosorption/release kinetics are presented. Composition of the nanoporous materials, more specifically, Al/Si ratio and cation type also effect physiosorption of hydrogen and ammonia. These compositional effects are also presented.