Ji-Cheng Zhao General Electric Company
Ian M. Robertson University of Illinois
Shin-ichi Orimo Tohoku University
Z1: Hydrogen Storage Systems and Safety
Monday AM, November 27, 2006
Independence E (Sheraton)
9:30 AM - **Z1.1
Hydrogen Storage for Hydrogen-Powered Vehicles: Goals and Progress of the U.S. National Hydrogen Storage Project
Sunita Satyapal 1 , Grace Ordaz 1 , John Petrovic 2 , Carole Read 1 , George Thomas 3 Show Abstract
1 Office of Hydrogen, Fuel Cells and Infrastructure Technologies, U.S. Department of Energy, Washington, District of Columbia, United States, 2 (Retired), Los Alamos National Laboratory/DOE, Washington, District of Columbia, United States, 3 (Retired- on assignment to DOE), Sandia National Laboratory/DOE, Washington, District of Columbia, United States
The development of hydrogen fuel cell vehicles is one of the Department of Energy’s (DOE's) key long-term strategies for energy, environmental and economic security. Hydrogen storage is a critical enabling technology for the successful commercialization of hydrogen-powered vehicles, which must possess a driving range of greater than 300 miles in order to meet customer requirements in the North American market and to compete effectively with other automotive technologies. However, the storage of sufficient quantities of on-board hydrogen within vehicular weight, volume, and system cost constraints is a major scientific and technological challenge. Vehicular hydrogen storage targets have been established through the FreedomCAR & Fuel Partnership, a partnership among the DOE, the U.S. Council for Automotive Research and major energy companies. The DOE has established the National Hydrogen Storage Project to meet these challenging targets, with Centers of Excellence in Metal Hydrides, Chemical Hydrogen Storage, and Carbon-based Materials, as well as independent projects in the areas of new concepts/materials, hydrogen storage testing, and storage system analyses. Recent technical progress achieved in hydrogen storage through the R&D activities of The National Hydrogen Storage Project will be highlighted and discussed. Progress towards meeting targets and key challenges under investigation through collaboration with the DOE Office of Science will be summarized. The results of hydrogen storage systems analyses and round robin hydrogen storage testing will also be presented, as well as new activities through the International Partnership for the Hydrogen Economy (IPHE) and the International Energy Agency (IEA). The timeline, key milestones and future plans of DOE’s hydrogen storage research, development and demonstration program will be provided.
10:00 AM - **Z1.2
Performance of On-Board Hydrogen Storage Systems.
Rajesh Ahluwalia 1 , Romesh Kumar 2 Show Abstract
1 Nuclear Engineering, Argonne National Laboratory, Argonne, Illinois, United States, 2 Chemical Engineering Division, Argonne National Laboratory, Argonne, Illinois, United States
To be viable, an on-board hydrogen storage system for automotive fuel cells must meet some critical performance requirements besides specific energy (1.5-3 kWh/kg or 4.5-9% H2 by weight), energy density (1.2-2.7 kWh/L or 0.036-0.081 kg H2/L) and cost ($6/kWh or $200/kg in 2007, decreasing to $2/kWh or $67/kg by 2015). For example, the system must be able to deliver hydrogen as needed by the fuel cell system, up to 0.02 g/s per kW of the fuel cell system’s rated power, regardless of how much hydrogen remains in the storage tank. It must do so while maintaining a minimum delivery pressure of 8 bar (in 2007; 3 bar by 2015), as dictated by the hydrogen metering device or the fuel cell stack operating pressure. The system must be capable of being refueled at a rate of 0.5 kg H2/min (in 2007; 2 kg/min by 2015). There are additional requirements in regard to the operating ambient temperature (–20oC to 50oC in 2007, –40oC to 60oC by 2015), hydrogen delivery temperature (from –30,oC to +85oC in 2007, from –40oC to +85oC by 2015), start time to full flow (15 s in 2007, decreasing to 5 s by 2015), and transient response time for 10% to 90% and from 90% to 0% of rated flow (1.75 s in 2007, decreasing to 0.75 s by 2015).While these are system-level targets, most of the developmental activity in hydrogen storage materials only measures the properties and characteristics of the storage media, that too with the media available only in small quantities for the time being. We have developed a modeling tool that can be used to evaluate how well such a storage medium would perform vis-à-vis the performance requirements listed above. This modeling tool can also be used to determine the target properties of a developmental hydrogen storage material such that it would meet these system requirements. This paper introduces the modeling tool and illustrates its usefulness by applying it to a reversible complex metal hydride system and demonstrating how the material’s storage capacity, sorption kinetics, thermal conductivity, and enthalpy of sorption/desorption affect the overall system characteristics such as recoverable hydrogen storage capacity, refueling time, minimum full-flow rate of hydrogen, minimum hydrogen delivery pressure, hydrogen refueling pressure and on-board heat transfer requirements.We then analyze a liquid hydrocarbon-based hydrogen carrier that, similar to the metal hydrides, requires a heat source for the on-board dehydrogenation reaction but is be regenerated off-board. For this system, we discuss different concepts for the catalytic dehydrogenation reactor and its thermal integration with the fuel cell system. For both systems, we present initial results on the overall fuel cycle efficiency, taking into account the on-board and off-board energy requirements for release of hydrogen, material regeneration, and heat rejection.
10:30 AM - Z1.3
Fiber Optic Hydrogen Detectors Containing Mg-based Metal Hydrides.
Martin Slaman 1 , Bernard Dam 1 , Matieu Pasturel 1 , Dana Borsa 1 , Herman Schreuders 1 , Ronald Griessen 1 Show Abstract
1 Condensed matter, VU-Amsterdam, Amsterdam, NH, Netherlands
One of the main issues for the public acceptance of hydrogen is safety. In this context an important role is played by detectors that can detect a hydrogen leak well below the lower explosion limit of 4% hydrogen in air. Currently available hydrogen detectors are not optimally suited for many applications since they are large, work at relatively high temperature and have electrical leads at the potentially explosive measuring spots. In addition many of them are too expensive. These disadvantages can be circumvented by using optical fiber hydrogen sensors . The so-called “ metal-hydride switchable mirrors” discovered in our group  are especially well suited for this type of sensors since hydrogen ab/desorption induces very large optical changes. The optical fiber sensor described here consists of a glass fiber with a switchable mirror layer sputtered on the end face. This layer consists of a thin (~ 30 nm) layer of Mg-Ni [3, 4] or Mg-Ti  covered with a relatively thick (30 to 100 nm) transition metal layer, which is capped with a few nm of Pd. These particular layer stacks become black on hydrogenation: the reflectivity changes by a factor 10 . Using a light emitting diode as light source at one end of the glass fiber, the presence of hydrogen at the other end of the fiber can easily be detected at a large distance without the problems mentioned above. The active detector surface area is of the order of micrometers and a cheap detector array can read hundreds of fibers simultaneously. Our fiber optic hydrogen sensors detect less than 10% of the lower explosion limit of hydrogen in air within seconds, due to a drop in absolute optical reflection of more than 55%. The detection is hydrogen specific, reversible and stable in a temperature range from 260 to 333 K. Note, that our detectors work well at temperatures below 273 K because no water is involved in the hydrogen transport within the metal layers, in contrast to WO3 – based optic fiber sensors.M.A. Butler, Sensors and Actuators B, Chemical 22 (1994) 155-163. J.N. Huiberts, et al., Nature 380 (1996) 231-234. W. Lohstroh, et al.: Self-organized layered hydrogenation in black Mg2NiHx switchable mirrors, Phys. Rev. Lett. 93 197404 (2004). M. Pasturel, M. Slaman, D.M. Borsa, H. Schreuders, B. Dam, R. Griessen, Stabilized switchable ‘black state’ in Mg2Ni / Ti / Pd thin films for optical hydrogen sensing, accepted by Appl. Phys. Lett. (2006).M. Slaman, B. Dam, M. Pasturel, D.M. Borsa, H. Schreuders, J.H. Rector, R. Griessen, Fiber optic hydrogen detectors containing Mg-based metal hydrides, submitted to Sensors and Actuators (2006).
11:30 AM - **Z1.5
Production of Borohydrides as the Regenerative Hydrogen Storage Material.
Seijirau (Seiji) Suda 1 Show Abstract
1 ICHST, MERIT, Chino-shi, Nagano-ken, Japan
Borohydrides have been known from their high H-contents, mostly higher than 10 mass% that is generated either by thermal decomposition or hydrolysis. B-based minerals such as Tincal, Kernite, Colemanite, and Asharite are feasible to synthesize NaBH4 (and KBH4), CaBH4, and Mg(BH4)2 as the hydrogen storage materials.Production and regeneration of NaBH4 have been experimentally demonstrated by 2 different processes by using Mg and Al as O-acceptor; (1) Mg-porocess: NaBO2 + 2H2 + 2Mg -> NaBH4 + 2MgO (2) Al-process: :NaBO2 + 2H2 + 4/3Al -> NaBH4 + 2/3Al2O3In these reactions, NaBO2 (anhydrous borate) can be obtained both from NaBO2●4H2O and NaBO2●10H2O where these materials can be recovered from B-based minerals. Feasibliity studies will be extended to NaBH4 and Mg(BH4)2 production based on B-based minerals in this presentation,
12:00 PM - Z1.6
Combustion-Assisted Hydrolysis of Sodium Borohydride for Hydrogen Generation
Victor Diakov 1 , Moiz Diwan 1 , Evgeny Shafirovich 1 , Arvind Varma 1 Show Abstract
1 School of Chemical Engineering, Purdue University, West Lafayette, Indiana, United States
Fuel cells are attractive power sources for portable applications, since they provide much higher specific energy than batteries. In this context, direct methanol fuel cells (DMFC) are suggested as power sources for small scale applications but have drawbacks, such as low power density, methanol crossover, electrode poisoning and methanol toxicity. Hydrogen fuel cells do not have any methanol-related problems and provide higher power density and double conversion efficiency as compared to DFMCs. Their deployment, however, is hindered by the lack of efficient methods for hydrogen storage. Sodium borohydride (NaBH4) is an efficient hydrogen-storing compound but its use requires either expensive catalysts (e.g. Ru) or mixing with solid oxidizers (e.g. Sr(NO3)2, NH4ClO4), which may produce harmful byproducts. To solve this problem, we propose borohydride/metal/water mixtures for combustion-based generation of hydrogen. In the proposed mixtures, the highly exothermic reaction of metal (Al or Mg) with water assists hydrolysis of NaBH4, eliminating the need of catalyst. Upon ignition, such mixtures exhibit self-sustained propagation of combustion wave with simultaneous release of hydrogen stored in sodium borohydride and water. Combustion of these mixtures was studied in a stainless-steel reaction chamber using digital video recording, pressure monitoring, thermocouple measurements, gas chromatography, mass spectrometry and powder XRD analysis. It was found that Al powder should be nano-scale to provide mixture ignition, while micro-scale Mg ensures stable self-sustained combustion. For both Al and Mg, increasing metal fuel loading significantly stimulates combustion. Condensed products include sodium metaborate (NaBO2) and metal oxide (Al2O3 or MgO). The evolved gas is essentially hydrogen (~99%). The efficiency of hydrogen generation is 74-77 % for the mixtures with Al and 88-92% for the mixtures with Mg. The lower efficiency for Al is likely caused by the larger surface oxide content in the passivated Al nanoparticles. The maximum observed H2 yield is ~7 wt% for both systems.The proposed method could be used to develop hydrogen fuel cell power systems with high specific energy, high power density, no catalyst, simple design (no liquid fuel flow) and safe reaction products, suitable for portable applications.
12:15 PM - Z1.7
Impact of Solid Ammonia Borane Fuel Formulation on an On-Board Storage and Hydrogen Release System
Scot Rassat 1 , Arthur Chin 2 , Chris Aardahl 1 , Joseph Magee 3 , R. Smith 1 , Gary VanSciver 2 , S. Autrey 1 , Frank Lipiecki 2 , Abhi Karkamkar 1 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 Engineering Division, Rohm and Haas Company, Croydon, Pennsylvania, United States, 3 Rohm and Haas Technical Center, Rohm and Haas Company, Spring House, Pennsylvania, United States
In the current vision of the hydrogen economy, fuel cell vehicles using hydrogen fuel will replace automobiles relying on gasoline powered internal combustion engines. A wide range of candidate on-board hydrogen storage methods are being evaluated including pressurized hydrogen gas tanks, liquefied hydrogen, and a host of storage materials from which hydrogen gas H2 can be extracted. A portion of the current research within the US Department of Energy (DOE) Center of Excellence for Chemical Hydrogen Storage focuses on solid ammonia borane (AB), a chemical hydrogen storage material that releases hydrogen gas by thermally decomposing the fuel on-board the vehicle. It is a particularly promising hydrogen storage material because it contains a large fraction by weight of releasable hydrogen gas.The work reported here addresses physical and thermochemical properties of solid AB as they impact the safety and systems engineering aspects of an on-board storage and hydrogen release system. The AB fuel formulation including purity and packing density affects fuel stability during storage and system factors such as reactor design, individual component volumes, system volumetric density, and system gravimetric density. Here, it is demonstrated that appropriate analysis of the Avrami reaction kinetics can be used to understand fuel stability issues and hydrogen release for continuous hydrogen delivery. Model results were confirmed through the use of accelerated rate calorimetry experiments, showing that processing temperature and fuel purity have a large effect on the ability to use AB as a safe hydrogen carrier. These results will help enable AB fuel formulations that are both stable for on-board storage and sufficiently reactive to release H2 at the rates required for fuel cell operation.
12:30 PM - Z1.8
NaAlH4 Densification to Improve Hydrogen Storage System Volumetric Performance.
Sarah Arsenault 1 , Ming Cao 1 , Daniel Mosher 1 , Salvatore Saitta 1 Show Abstract
1 , United Technologies Research Center, East Hartford, Connecticut, United States
Lightweight, compact hydrogen storage has been one of the major bottlenecks in developing fuel cell systems applicable to powering ground vehicles. In this study, experimental examinations have been performed to evaluate vibratory densification of nanometer-scale hydride powder particles, which directly affects the volume and weight of storage systems based on complex hydrides such as NaAlH4. A unique apparatus including biaxial vibration and a tube test section to quantify the densification of a column of powder was developed for this study. Comprehensive testing has been carried out to identify the optimal vibration and processing conditions achieving the highest densities. The study investigates the effectiveness of 1-dimensional, 2-dimensional vibration and the impact of frequency patterns (constant frequency and frequency sweeping) as well as the effects of various hydride milling techniques. Offering fundamental understanding of nano-powder densification, this experimental investigation provides guidelines for further study of vibration-based hydride powder densification.
12:45 PM - Z1.9
Hydrogen Storage in Hypercrosslinked Organic Polymers
Andrew Cooper 1 , Colin Wood 1 , Jun-Young Lee 1 , Darren Bradshaw 1 , Abbie Trewin 1 , Bien Tan 1 , Matthew Rosseinsky 1 Show Abstract
1 Chemistry, University of Liverpool, Liverpool United Kingdom
We present here a method for producing microporous hypercrosslinked polymer resins which adsorb more than 3 wt. % hydrogen at 77 K and 15 bar. This represents the highest level of hydrogen adsorption yet observed for an organic polymer . The widespread use of hydrogen as a fuel is limited presently by the lack of a convenient, safe, and cost-effective method of H2 storage. A large number of materials have been investigated as physisorptive H2 adsorbents including carbon, zeolites, and metal-organic frameworks (MOFs). None of these materials meets the current criteria of size, recharge kinetics, cost, and safety required for use in transportation systems. The storage of hydrogen in porous materials by physisorption is very challenging because of the fundamentally weak interactions which exist between gas and sorbent at temperatures well above the critical temperature for H2 (–240.17 C). This has prompted researchers to develop MOFs with very high internal surface areas or which exhibit kinetic trapping behaviour . Organic polymers are attractive as potential H2 adsorbents because they are synthetically very versatile and can be composed entirely of light elements. An major advantage associated with organic polymers – for example, with respect to activated carbon – is the very broad scope for synthetic variation of both chemical functionality and structural topology. A significant challenge, however, is the relatively limited number of synthetic routes to access organic polymers with high surface areas (>1000 m2/g) and pores in the micropore range. Hypercrosslinked polymers represent a class of predominantly microporous organic materials which can exhibit high surface areas . The permanent porosity in hypercrosslinked materials results from extensive cross-linking reactions which prevent the polymer chains from collapsing into a dense, non-porous state. The most well-studied hypercrosslinked materials are "Davankov-type" resins which are prepared by post-cross-linking of polystyrenic networks. These materials can exhibit apparent BET surface areas as high as 2090 m2/g12 and have been used widely as sorbents and in chromatography.In this paper we describe a broad strategy for preparing microporous organic polymer networks with a range of surface functionalities. We believe that this may be an enabling methodology to prepare high surface area, light-element based materials with increased adsorption enthalpies for the storage of hydrogen at more practicable temperatures. The results are partly rationalized by DFT modelling of the interactions between dihydrogen and the monomeric building blocks. J.-Y. Lee, C. D. Wood, D. Bradshaw, M. J. Rosseinsky and A. I. Cooper, Chem. Commun., 2006, 2670-2672. X. B. Zhao, B. Xiao, A. J. Fletcher, K. M. Thomas, D. Bradshaw and M. J. Rosseinsky, Science, 2004, 306, 1012. V. A. Davankov and M. P. Tsyurupa, Reactive Polym., 1990, 13, 27.
Z2: Metal Hydrides
Monday PM, November 27, 2006
Independence E (Sheraton)
2:30 PM - **Z2.1
Tailoring of Metal Borohydrides for Hydrogen Storage Applications
Yuko Nakamori 1 , Kazutoshi Miwa 2 , Haiwen Li 1 , Nobuko Ohba 2 , Shin-ichi Towata 2 , Shin-ichi Orimo 1 Show Abstract
1 Institute for Materials Research, Tohoku University, Sendai Japan, 2 Toyota Central R&D Labs, Tohoku University, Nagakute Japan
A series of metal borohydrides M(BH4)n with high gravimetric and volumetric hydrogen densities is a candidate for hydrogen storage materials. One of the important issues for the research of metal borohydrides is controlling their stabilities for lowing the hydrogen desorption temperatures. We have been investigating the thermodynamical stabilities of metal borohydrides theoretically and experimentally [1-2]. The results of first-principles calculations revealed that the charge compensation by Mn+ is a key feature for the stabilities of M(BH4)n. It was also expected that selecting Mn+ having larger electronegativity χP is effective for lowering the hydrogen desorption temperature. In order to confirm the relation experimentally, a series of M(BH4)n were mechanically and chemically synthesized, and then the hydrogen desorption reactions were investigated by thermal desorption analyses. The detected hydrogen desorption temperature Td correlates with χP; Td decreases with increasing the value of χP. The χP of M is a useful indicator to estimate the stabilities of complex hydrides. The intermediate compound of M(BH4)n [3-4] will be also discussed. Y. Nakamori, H.-W. Li, K. Miwa, S. Towata, S. Orimo, Mater. Trans., in press. Y. Nakamori, K. Miwa, A. Ninomiya, H.-W. Li, N. Ohba, S. Towata, A. Züttel, S. Orimo, Phys. Rev. B, communicated. S. Orimo, Y. Nakamori, N. Ohba, K. Miwa, M. Aoki, S. Towata, A. Züttel, Appl. Phys. Lett., in press. N. Ohba, K. Miwa, M. Aoki, T. Noritake, S. Towata, Y. Nakamori, S. Orimo, A. Züttel, cond-mat/0606228 (http://arxiv.org/abs/cond-mat/0606228)
3:00 PM - **Z2.2
Hydrogen Storage in Doped Light Weight Hydrides and Reactive Hydride Composites.
Martin Dornheim 1 , Gagik Barkhordarian 1 , Nico Eigen 1 , Ulrike Boesenberg 1 , Xiumei Qi 1 , Claude Keller 1 , Oliver Metz 1 , Thomas Klassen 2 , Ruediger Bormann 1 Show Abstract
1 Department of Nanotechnology, Institute for Materials Research, GKSS-Research Centre Geesthacht, Geesthacht Germany, 2 Institute of Materials Science, Helmut-Schmidt-University, University of the Federal Armed Forces, Hamburg Germany
So far metal hydrides have not been considered competitive for hydrogen storage in most mobile applications because of sluggish reaction kinetics, too low gravimetric hydrogen storage densities or large reaction enthalpies, which necessitate complicated heat management systems. However, recent developments in this area are promising and will be reviewed and discussed in this presentation.The preparation of nanocrystalline hydrides using high-energy ball milling as well as the discovery of suitable catalysts/dopants enabled the preparation of novel lightweight materials for hydrogen storage with much higher gravimetric hydrogen storage densities and fast ab- and desorption kinetics. Hydrogen absorption and desorption now is possible in metal oxide catalyzed MgH2 within 90 seconds. In catalyzed NaAlH4 hydrogenation also takes place within a few minutes. While there is still a large number of other light metal hydrides with even higher gravimetric hydrogen storage densities, these fail to be reversible under moderate temperature pressure conditions. New concepts are required to exploit these compounds. One exciting, successful and promising novel approach is the concept of the Reactive Hydride Composites (RHC). Such composite systems show high gravimetric hydrogen storage densities and reduced total reaction enthalpies as well as significantly improved ab- and desorption kinetics compared to the pure hydrides. Reversibility is successfully achieved for RHC reactions of Mg with several borohydrides, which had previously been considered as irreversible using moderate hydrogen pressures and temperatures.
4:30 PM - **Z2.3
Development of Transition Metal Borohydride Complexes as Hydrogen Storage Materials
Craig Jensen 1 , Jennifer Eliseo 1 , Godwin Severa 1 Show Abstract
1 , University of Hawaii, Honolulu, Hawaii, United States
The development of high capacity, hydrogen storage materials that can be recharged under moderate conditions is a key barrier to the realization of a hydrogen economy. Recently, considerable progress has been made toward the development of lithium and other Group I and II borohydrides as hydrogen storage materials. However, the dehydrogenation of these compounds is plagued by serve kinetic limitations, competing side reactions and/or irreversibility that preclude the practical utilization of these compounds even as a component of a hydrogen carrier for vehicular applications. Many transition metal borohydride complexes have highly attractive gravimetric hydrogen densities. However, most well known transition metal borohydride complexes such as Zr(BH4)4 and Zn(BH4)2 are inadequate hydrogen absorbants as they have very high vapor pressures under the conditions required for dehydrogenation. Additionally, the elimination of diborane often competes with dehydrogenation and typically highly stable, transition metal borides are obtained upon dehydrogenation that cannot be directly hydrogenated under practical conditions. As an attempt to circumvent these problems, we have synthesized a class of stabilized transition metal borohydride complexes. The characterization of these complexes by infrared and 11B NMR spectroscopy and X-ray diffraction will be presented together with studies of their dehydrogenation and re-hydrogenation behavior.
5:00 PM - Z2.4
Simultaneous in-situ X-ray Diffraction and Mass Spectrometric Studies of Hydrogen Storage Materials.
Job Rijssenbeek 1 , Yan Gao 1 , Grigorii Soloveichik 1 , Jonathan Hanson 2 Show Abstract
1 , GE Global Research, Niskayuna, New York, United States, 2 Department of Chemistry, Brookhaven National Laboratory, Upton, New York, United States
5:15 PM - Z2.5
Studies of Sc and Ti Doped NaAlH4.
Robert Bowman 1 2 , Son-Jong Hwang 2 , Mark Conradi 3 , Timothy Ivancic 3 , Hendrik Brinks 4 Show Abstract
1 , Jet Propulsion Laboratory, Pasadena, California, United States, 2 , Caltech, Pasadena, California, United States, 3 Dept. of Physics, Washington U., St. Louis, Missouri, United States, 4 , Institute for Energy Technology, Kjeller Norway
The roles of dopants such as TiCl3 and ScCl3 on the behavior of the alanate phases remain unresolved in spite of extensive experimental and theoretical studies over the past several years. Both bulk and surface processes have been proposed for the enhanced rates of hydrogen desorption and desorption by these hydrides upon doping. We have prepared NaAlH4 samples with additives of TiCl3 and ScCl3 then subjected these materials to hydrogen absorption and desorption cycles. High resolution x-ray diffraction (HR-XRD) and various solid state nuclear magnetic resonances (NMR) techniques have been used to assess the phase compositions and other properties of both as-prepared and cycled alanate samples. Magic angle spinning (MAS) NMR spectra were obtained from the 1H, 23Na, and 27Al nuclei to identify the different alanates as well as other phases. Due to the favorable NMR properties of 45Sc, it was possible to obtain its MAS-NMR spectra even though the initial Sc content of this dopant was only ~2 wt.%. Hence, NMR was used to track the progression of this species during preparative steps (i.e., mechanical ball milling) and hydrogen cycling to provide new insights into its role on the kinetics of alanate phase conversions and stability. The observations from the combined HR-XRD and NMR experiments will be discussed in terms of various models and mechanisms suggested for the influences of Ti and Sc on alanate behavior.
5:30 PM - Z2.6
Crystal and Electronic Structures of Li-N-H and Related Hydrogen Storage Materials.
Jinbo Yang 1 4 , Q. Cai 2 , Xujun Wang 1 , William James 1 3 , William Yelon 1 3 Show Abstract
1 Materials Research Center, University of Missouri-Rolla, Rolla, Missouri, United States, 4 Physics Department, University of Missouri-Rolla, Rolla, Missouri, United States, 2 Physics Department, University of Missouri-Cloumbiala, Columbia, Missouri, United States, 3 Chemistry Department, University of Missouri-Rolla, Rolla, Missouri, United States
5:45 PM - Z2.7
First-Principles Studies of Thermodynamic and Structural Properties of the Li-Mg-N-H System
Alireza Akbarzadeh 1 , Vidvuds Ozolins 1 , Chris Wolverton 2 Show Abstract
1 Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 , Ford Research and Advanced Engineering, Dearborn, Michigan, United States
Amides have emerged as promising hydrogen storage materials after Chen et al.  reported reversible H2 extraction from Li2NH above 200 C. Recently, Nakamori et al.  have reported a significant decrease of dehydriding temperature in LiNH2 upon adding Mg. These authors predict that Mg(NH2)2 could store up to 9.1 wt.% H2 according to the following reaction: 3Mg(NH2)2 + 12LiH ↔ 4Li3N + Mg3N2 + 12H2 .Using first-principles density functional calculations we investigate the thermodynamics, structural properties and lattice dynamics of known crystalline compounds in the Li-Mg-N-H system. From the calculated thermodynamic functions - reaction enthalpies, vibrational energies and entropies – we investigate the phase diagram of this system as a function of temperature and hydrogen pressure and predict the thermodynamically favored sequence of decomposition reactions. We also report results of extensive searches for stable crystal structures of hypothetical ordered Li-Mg amides and imides. This project is supported by DOE grants DE-FC36-04GO14013 and DE-FG02-05ER46253. P. Chen et al., Nature, 420 (2002) 302 Y. Nakamori et al., J. Alloys Comp., 404-406 (2005) 396
Ji-Cheng Zhao General Electric Company
Ian M. Robertson University of Illinois
Shin-ichi Orimo Tohoku University
Z3: Chemical & Metal Hydrides
Tuesday AM, November 28, 2006
Independence E (Sheraton)
9:00 AM - **Z3.1
Intermediates in the Transformation of Complex Hydrides.
Maximilian Fichtner 1 Show Abstract
1 Institute for Nanotechnology, Research Center Karlsruhe, Karlsruhe Germany
9:30 AM - **Z3.2
Amineborane Based Chemical Hydrogen Storage.
Larry Sneddon 1 , Martin Bluhm 1 , Chang Yoon 1 , Mark Bradley 2 Show Abstract
1 Chemistry, U of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Chemistry, Widener University, Chester, Pennsylvania, United States
The development of efficient methods for hydrogen storage is a major hurdle that must be overcome to enable the use of hydrogen as an alternative energy carrier. Although many molecular hydride complexes have certain features that might be attractive for chemical hydrogen storage, the high hydrogen capacities needed for transportation applications exclude most compounds. Amineboranes such as ammonia borane, NH3BH3, (19.6 wt% hydrogen) and ammonia triborohydride, NH3B3H7, (17.8 wt%) are thus unique in their ability to store and deliver large amounts of hydrogen through dehydrogenation and/or hydrolysis reactions. We report here our studies demonstrating that the rate and the extent of hydrogen release from both ammonia borane and ammonia triborohydride can be significantly increased through the use of metal catalysts, ionic liquids and/or chemical additives.
10:00 AM - **Z3.3
Experimental and Computational Investigations of NBH Chemical Hydrogen Storage Compounds.
Abhijeet Karkamkar 1 , Nancy Hess 1 , Mark Bowden 2 , Wendy Shaw 1 , Donald Camaioni 1 , Jun Li 1 , Shawn Kathman 1 , Greg Schenter 1 , Maciej Gutowski 3 , Tom Autrey 1 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , Indusrial Research Ltd., Lower Hutt New Zealand, 3 , Heriot-Watt University EH14 4AS, Edinburgh United Kingdom
Amine boranes are attractive candidates for the storage of high volumetric and gravimetric densities of hydrogen for fuel cell powered devices. The parent compound, ammonia borane (NH3BH3, 19wt% H2), isoelectronic with ethane, is a solid molecular crystal under standard conditions. Ammonia borane is stable at room temperature but will release up to 2 moles of hydrogen in two discrete steps at temperatures between 100 and 160 C. Our group has been investigating the thermal and catalytic mechanisms of amine borane decomposition leading to hydrogen formation. We believe that the interactions between the hydridic BH and protic NH hydrogen are responsible for the relatively low activation barriers for hydrogen formation. In this presentation we will discuss our experimental and computational research aimed at developing a fundamental understanding of the chemical and physical properties of these hydrogen rich materials. This work was supported by the Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.
10:30 AM - Z3.4
Hydrogen Storage and Absorption/Release Kinetics in Nanocomposites of Ammine Complexes and Mesoporous Silica
Yanjia Zuo 1 , Brian Mosher 1 , Yi He 1 , Sam Mao 2 , Gang Chen 3 , Taofang Zeng 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States, 2 , Lawrence Berkeley Natioanl Laboratory, Berkeley, California, United States, 3 , MIT, Cambridge, Massachusetts, United States
The development of hydrogen-fueled vehicles and portable electronics requires new materials that can store large amounts of hydrogen at ambient temperature and relatively low pressures with small volume, low weight, and fast kinetics for recharging. We have been developing a method for hydrogen storage by combining chemisorption and physorption in nanocomposite materials. Magnesium hydrides have been successfully incorporated in silica aerogels. In this study, we further incorporate magnesium hydrides into other nanoporous materials with doped catalysts. One is the highly ordered mesoporous material of SBA-15. We have also tested incorporating borate ammonia (BH3NH3) with mesoporous silica aiming to obtain stable and reusable materials for hydrogen storage. Nanoparticles of Ru, Ni, Pt etc, are added to the composites as catalysts. The effects of nanoporous structure and the catalysts on kinetics and thermodynamics of hydrogen release are also investigated.
10:45 AM - Z3.5
New Routes for Aluminum Hydride Regeneration.
Jason Graetz 2 , Santanu Chaudhuri 2 , Yongjae Lee 2 , James Reilly 2 Show Abstract
2 , Brookhaven National Laboratory, Upton, New York, United States
The high volumetric/gravimetric hydrogen density and low heat of decomposition of aluminum hydride make it a promising material for solid-state hydrogen storage. However, a critical challenge exists to regenerate or recycle the hydride from the spent Al and H2 gas. The key scientific obstacle lies in overcoming the low enthalpy of hydride formation when reforming the hydride from Al metal. A better understanding of alane chemistry is necessary to develop new methods to lower the free energy of formation and the equilibrium pressure of the hydrogenation reaction.As part of this effort, pressure-induced structural, electronic and thermodynamic changes in α-AlH3 were investigated using synchrotron x-ray powder diffraction. Although no first-order structural transitions were found up to 7 GPa, a monoclinic distortion was observed at pressures above 5 GPa. The reduced cell volume is accommodated by an increase in AlH6 octahedral tilting and a decrease in the Al-H bond distance at high pressures. Density functional theory calculations of the total free energy change between 0-100 GPa indicate that the hydride becomes progressively more destabilized at high pressures with respect to the Al metal. Thus, the direct high-pressure hydrogenation of Al metal is severely restricted by the thermodynamics of the reaction, which do not improve with pressure. However, it may be possible to reduce the hydrogenation pressure by including a second species in the reaction, such as another metal or a solvent, to lower the total free energy change. For example, by introducing a solvent the formation enthalpy may become more negative due to the heat of solvation. Further, the possibility that the formation entropy may become less positive for solvated AlH media will also be discussed. Preliminary results from our study of solvated-hydride systems will be presented.
11:30 AM - **Z3.6
Reversible Hydrogen Storage in Li-Al-N-H System.
Ping Chen 1 , Zhitao Xiong 1 , Guotao Wu 1 , Jianjiang Hu 1 , Yongfeng Liu 1 , Chaw Keong Yong 1 Show Abstract
1 Physics, National University of SIngapore, Singapore Singapore
Step-wise solid-state reaction between LiNH2 and LiAlH4 at a molar ratio of 2/1 was investigated. It was observed that 4 H atoms were detached from the mixture of LiNH2-LiAlH4 (2/1) after mechanical ball milling. The transformation of tetrahedral [AlH4]- in LiAlH4 to the octahedral [AlH6]3- in Li3AlH6 was observed during the ball milling treatment. In addition, the interaction between LiNH2 and LiAlH4 leading to the Al-N bonding was manifested by solid-state 27Al NMR measurements. Heating the post-milled sample to 673K resulted in the liberation of additional 4 H atoms. Thus, a total number of 8 H atoms were detached per [2LiNH2-1LiAlH4], which led to the formation of the final product Li3AlN2. The subsequent hydrogenation testing revealed that 5.17wt% of hydrogen can be recharged at temperatures below 603K.
12:00 PM - **Z3.7
Novel Combinations of High Density Hydrogen Storage Materials
Andrea Sudik 1 , Jun Yang 1 , Devin Halliday 1 , Donald Siegel 1 , Andy Drews 1 , Roscoe Carter 1 , Christopher Wolverton 1 Show Abstract
1 Physical and Environmental Sciences, Ford Motor Company, Dearborn, Michigan, United States
Practical hydrogen storage for mobile applications requires materials that contain large amounts of hydrogen, have low decomposition temperatures, and fast kinetics for absorption and desorption. One of the most promising classes for reversible hydrogen storage is represented by complex hydrides. In particular the group I, II and III elements such as Li, Na, Mg, B, Al, and N form a large number of metal-hydrogen complexes. Unfortunately, the majority of these materials based on row 2 elements have been deemed practically inadequate for on-board storage applications due to irreversibility and/or the significantly high temperatures (Tdes) required for hydrogen release. Since there is a direct correlation between Tdes and deltaH, there has been a great deal of research focused on identifying methods of optimizing these values while simultaneously preserving the high gravimetric densities associated with these materials. Mixtures of high-density hydrides such as LiBH4/MgH2, LiNH2/LiBH4, and LiNH2/MgH2 have recently emerged as a successful approach toward improved thermodynamic properties (with deltaH values in the 'ideal' 20 to 50 kJ/molH2 range) relative to their individual component reactions. However, in practice, appropriate thermodynamics is not enough to guarantee that hydrogen will evolve at the expected Tdes and at a purity and rate that is suitable to power the vehicle. We present a combined experimental/computational approach for new combinations of high density hydrogen storage materials. Experimental data for these materials include kinetic desorption, powder X-ray, FT-IR, and MS and computational results are mainly based on density functional theory calculations. We demonstrate reactions with improved hydrogen storage properties in terms of reversibility, kinetics, and hydrogen purity, while preserving high hydrogen density and favorable thermodynamics. Additionally, we show that our experimental results can be corroborated, clarified, and even guided using computational means.
12:30 PM - Z3.8
Reduced Dehydriding Temperature in Quaternary Li-B-N-H with Ni and NiCl2 Additives.
Frederick Pinkerton 1 , Martin Meyer 1 , Gregory Meisner 1 , Michael Balogh 2 Show Abstract
1 Materials and Processes Laboratory, General Motors R&D Center, Warren, Michigan, United States, 2 Chemical and Environmental Sciences Laboratory, General Motors R&D Center, Warren, Michigan, United States
We have examined the effect of adding small quantities of Ni, Fe, or Zn, or their dichlorides, on the dehydrogenation temperature of the new quaternary hydride material LiB0.33N0.67H2.67 (“Li3BN2H8”). Ball milled samples of doped LiB0.33N0.67H2.67 were synthesized by incorporating Ni in the form of 45 μm Ni powder, 0.37 μm thick Ni flake, high surface area Raney Ni, 40 nm diameter Ni metal nanoparticles, or NiCl2. NiCl2 proved to be especially effective as a dehydrogenation promoter. Compared to additive-free Li-B-N-H, for which hydrogen release begins above 250 C, the addition of 5-11 wt% (0.9-1.9 mole %) NiCl2 decreased the hydrogen release temperature by more than 100 C. Transmission electron microscopy on Li-B-N-H + 11 wt% NiCl2 revealed uniformly dispersed nanoparticles with diameters less than 8 nm within the Li-B-N-H matrix, consistent with reduction of the NiCl2 to metallic Ni or a Ni intermetallic compound during synthesis by ball milling. Other forms of Ni proved less effective than NiCl2 in a manner strongly dependent on the morphology of the Ni particles; as the particle size decreased and the corresponding specific surface area increased, the temperature of dehydrogenation decreased. Small, highly dispersed Ni nanoparticles having a large total contact area with the Li-B-N-H matrix were most effective, from which we surmise that Ni likely acts as a dehydrogenation catalyst for the Li-B-N-H quaternary phase. Additive-free Li-B-N-H melted completely above 190 C and released hydrogen directly from the liquid state above 250 C, forming a mixture of Li3BN2 polymorphs. In contrast, hydrogen release from Li-B-N-H + 5 wt% NiCl2 was accompanied by partial melting above 190 C plus formation of an unidentified hydrogen-poor solid intermediate phase. The remaining hydrogen desorbed near 300 C to again form Li3BN2 polymorphs. Mass spectrometry of the evolved gas during dehydrogenation of Li-B-N-H + 5 wt% NiCl2 showed that the total amount of NH3 released concurrently with the H2 was reduced by an order of magnitude compared to the additive-free material. We attribute this improvement to higher hydrogen release kinetics at lower temperatures, where thermally activated NH3 release remains slow. Addition of 5 wt% FeCl2 reduced the dehydrogenation temperature by 36 C, but Fe, Zn, and ZnCl2 additives did not produce significant improvement.
12:45 PM - Z3.9
Decrease the Hydrogen Desorption Temperature of LiNH2 Through Doping: A First Principles Study.
Hongmei Jin 1 , Ping Wu 2 Show Abstract
1 Computational Materials Science, Institute of High Performance Computing, Singapore Singapore, 2 Computational Materials Science, Institute of High Performance Computing, Singapore Singapore
a theoretical approach to investigate the possibility of reducing desorption temperature of LiNH2 by partial element substitution will be presented. The approach was based on first principles study of electronic structure of LiNH2 and (Li, Mg)NH2. Results of LiNH2 study showed that LiNH2 is non metallic, the bonding between Li and N is ionic, and the bonding between N and H is strongly covalent. Results of (Li, Mg)NH2 study showed that the bonding nature of Li-N and N-H is the same as in LiNH2, but the bond strength of N-H was reduced. In addition, the system becomes metal like after substitution. These two major differences can be used to explain the experimental observation that the hydrogen desoprtion temperature was reduced by Mg substitution. More important, they might be used as criteria to predict the behavior of other substitution element. Based on these two criteria, effect of substitution elements Na, K, Al, B, C, Si, P, Ga, Ge, In and Sn are investigated. Results showed that the desorption temperature of LiNH2 might be reduced by partial Li substitution with Al. But if Al is used to partial replace N atom, the desorption temperature may not be changed. This approach may be used in the design of dopants for alternative energy applications.
Z4: Combinatorial Screening & Hydride Structures
Tuesday PM, November 28, 2006
Independence E (Sheraton)
2:30 PM - **Z4.1
Hydrogenography: High-throughput Optical Measurements of Hydride Formation Enthalpies.
Ronald Griessen 1 , Robin Gremaud 1 , Chase Broedersz 1 , Herman Schreuders 1 , Bernard Dam 1 Show Abstract
1 Condensed Matter Physics, Vrije Universiteit, Amsterdam Netherlands
Hydrogenography is a novel technique based on the optical changes induced by hydrogen ab- and desorption in metal films. Hydrogenography on thin films with a compositional gradient has the great advantage that it allows the simultaneous measurement of a huge number of samples (up to thousands) of different elemental compositions on only one wafer (each pixel of the recording camera corresponds essentially to one alloy composition). This enormously facilitates the search for new metal-hydrides with specific physical properties . The compositional gradient thin films necessary for hydrogenography are synthesised by co-sputtering on a 3 in wafer from three (up to six) off-centered magnetron sources. The hydride formation during ex-situ hydrogen exposition at well-defined temperatures and hydrogen gas pressures is monitored by the transparency of the films. Since all complex hydrides found so far have an electronic bandgap their transparency is a good indicator of the amount of absorbed hydrogen. Hydrogenography is thus applicable to a large class of potential light-weight hydrogen storage materials.As an illustration of our technique I describe how hydrogenography is used to optimize Magnesium-Transition metal hydrides . Some of these hydrides have gravimetric hydrogen capacities approx. 4 times higher than that of conventional NiMH batteries. From the simultaneous measurements of the enthalpy of formation of thousands of Mg-Ti-Ni hydrides we are able to determine the compositions with the best capacity and ab/desorption kinetics. The hydrogen sorption kinetics is directly amenable to the experiment as the optical transmission is continuously recorded during hydrogen ab/desorption. Hydrogenography is also of great help in the search and optimisation of catalytic layers . Furthermore, it can be also used for the optimisation of optical fiber hydrogen safety sensors  and smart solar collectors . R. Gremaud et al.: Structural and optical properties of MgxAl1-xHy gradient thin films: a combinatorial approach, Applied Physics A: Mat. Science & Processing 84 (2006) 77 R.A.H. Niessen and P.H.L. Notten, Electrochemical hydrogen storage characteristics of thin film MgX (X = Sc, Ti, V, Cr) compounds, Electrochem. Solid-State Lett 8 (2005) A534  A. Borgschulte et al.: Catalytic activity of noble metals promoting hydrogen uptake, J. of Catalysis 229 (2006) 263 M. Pasturel et al.:Stabilized switchable ‘black state’ in Mg2Ni/Ti/Pd thin films for optical hydrogen sensing, Appl. Phys. Lett. (2006) in press D. M. Borsa et al.: Mg–Ti–H thin films for smart solar collectorsAppl. Phys. Lett. 88 (2006) 241910
3:00 PM - **Z4.2
Discovery and Mechanistic Understanding of Metal Hydrides using Thermography, Gravimetric Analysis and in-situ Synchrotron XRD
John Lemmon 1 , Jun Cui 1 , Yan Gao 1 , Tom Raber 1 , Job Rijssenbeek 1 , Gosia Rubinsztajn 1 , Grigorii Soloveichik 1 , Ji-Cheng Zhao 1 Show Abstract
1 , GE Global Research Center, Niskayuna, New York, United States
The search for new high capacity reversible hydrogen storage materials for mobile applications presents several challenges to modern Physics and Chemistry. These include discovering new materials within in a limited range of thermodynamic, kinetic and molecular weight parameters. To increase the efficiency of discovery we have developed a bulk high throughput synthesis and screening technique, in which promising storage materials can be rapidly identified with semi-quantitative results. Several techniques for multi-sample synthesis have been attempted over a four-year program, however this paper will be limited to multi-sample high-energy ball milling for sample preparation. Screening for hydrogen storage properties was accomplished by thermal imaging of bulk sample, in which semi-quantitative thermodynamic and storage properties can be achieved. Quantitative storage properties for promising materials were obtained using a multi-sample gravimetric technique that allows sample being characterized under more extreme conditions. Phase identification and pathways for hydride sorption and desorption were investigated using in-situ XRD with a residual gas analyzer. Several alloys and inter-metallic systems have been investigated using this discovery cycle. In this paper recent results in the Al-Li-Si and Mg-Al phase space will be discussed.
3:30 PM - Z4.3
A Thin Film/Cantilever-based Method for the High-Throughput Screening of Hydrogen Storage Materials.
Jialin Cao 1 , Alan Savan 1 , Michael Ehmann 1 , Alfred Ludwig 1 2 Show Abstract
1 Combinatorial Materials Science, caesar, Bonn Germany, 2 Institute of Materials, Ruhr-University , Suita, Osaka Japan
A new high-throughput characterization method is described for the development of hydrogen storage alloys using combinatorial libraries of thin films deposited on micromachined substrates, which consist of single crystalline Si cantilevers. A UHV sputter deposition system designed for fabricating combinatorial materials libraries is used for the deposition of thin films for hydrogen storage (Pd, Mg, Ti, Cr, Mg-based composition spreads). The mechanical stress change due to hydrogenation, leads to a curvature change of the film/cantilever combinations. These curvature changes are measured simultaneously on sets of cantilevers with an optical method. In a special gas phase loading apparatus equipped with a 50 mm diameter window, the pressure can be varied from vacuum to a hydrogen pressureranging between 0.105 and 5.1 MPa, and the temperature can be varied from 20 to 450°C. Complementary to the gas phase screening, an electrochemical apparatus was designed and used for the electrochemical hydrogenation of thin film electrodes on Si cantilevers. Isobaric and isothermal measurements of the thin film/substrate combinations are presented.
3:45 PM - Z4.4
Combinatorial Search for Thin Film Alanates by in situ Optical Spectrometry.
Robin Gremaud 1 , Erdny Batyrev 1 , Martin Slaman 1 , Herman Schreuders 1 , Bernard Dam 1 , Ronald Griessen 1 Show Abstract
1 Faculty of Sciences, Department of Physics and Astronomy, Condensed Matter Physics, Vrije Universiteit, Amsterdam Netherlands
Hydrogenography, i.e. real-time optical spectrometry of hydrides, is a novel technique that exploits the optical changes induced by hydrogen absorption in metal thin films . This technique has the great advantage of delivering the formation enthalpy as well as the kinetics of typically 103 metal-hydride alloys simultaneously [2, 3], facilitating the search for new metal-hydrides with suitable physical properties for hydrogen storage.Thin films with a compositional gradient of metals (Na, Li, Al) are deposited by off-centered RF/DC magnetron co-sputtering. So far, the hydride formation of metal thin films with compositional gradient has been studied ex situ, a Pd caplayer providing the necessary protection against oxidation. This approach proved to be not applicable for highly oxidizing elements such as Li and Na. Therefore we set up an UV/VIS fiber optic spectrometer to measure the optical transmission and reflection of light-weight metal-hydrides in situ after deposition. The hydrogen pressure can be varied over a broad range (10-10 < p(H2) < 103 mbar) to determine the stability as well as the kinetics of hydrogenation of the various compounds present.We investigate the behavior of X-Al (X = Li, Na) gradient thin films upon hydrogenation and compare them with X-Al-H gradients films reactively sputtered with hydrogen. The optical properties of NaH and LiH are also determined and provide the necessary data for comparison with the Al-containing gradient samples.Additionally, the surface of the gradient thin films is investigated by scanning probe microscopy and Auger spectroscopy to study the modifications of catalyst surfaces upon hydrogenation. Thermal desorption spectroscopy will be combined with hydrogenography results to establish the hydrogen desorption rate and the amount of absorbed hydrogen.R. Gremaud et al.: Structural and optical properties of MgxAl1-xHy gradient thin films: a combinatorial approach, Applied Physics A: Mat. Science & Processing 84 (2006) 77 A. Borgschulte et al.: Catalytic activity of noble metals promoting hydrogen uptake, J. of Catalysis 229 (2006) 263R. Gremaud et al.: An optical combinatorial method to optimize the thermodynamics and kinetics of hydrides, in preparation.
4:30 PM - Z4.5
Combinatorial Thin Film Deposition and Infrared Emission Characterization of Hydrogen Storage Materials.
Leonid Bendersky 1 , Hiroyuki Ohuchi 2 , Edwin Heilweil 1 , Lawrence Cook 1 , Alexander Shapiro 1 , Peter Schenck 1 , Daniel Josell 1 Show Abstract
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , University of Maryland, College Park, Maryland, United States
4:45 PM - Z4.6
Pressure Cycling Effect Studies of Li-Based Complex Hydrides
Dhanesh Chandra 1 , Wen-Ming Chien 1 , Joshua Lamb 1 Show Abstract
1 Chemical & Metallurgical Engineering Department, University of Nevada, Reno, Reno, Nevada, United States
5:00 PM - **Z4.7
In-situ Diffraction Studies of Novel Hydrogen Storage Materials.
Bjorn Hauback 1 , Hendrik Brinks 1 , Yumiko Nakamura 1 , Magnus Sorby 1 , Hilde Grove 1 Show Abstract
1 Physics Department, Institute for Energy Technology, Kjeller Norway
Efficient and safe storage of hydrogen remains as the most challenging unsolved problem for the introduction of the Hydrogen Economy. During the last years significant achievements have been obtained among several classes of light-weight metal hydrides, and in particular compounds based on aluminium, nitrogen, magnesium and boron. The processes for absorption and desorption of hydrogen in these compounds normally involve several steps and also intermediate phases. Structural phase transitions and phase changes during hydrogen absorption and desorption can be studied by in-situ synchrotron X-ray and neutron diffraction experiments. Such experiments contribute to the understanding of the details about the development of the different phases during hydrogenation and dehydrogenation. In addition, better understanding of how additives (e.g. Ti-based compounds in the alanates) influence the kinetics, reversibility and development of intermediate phases can also obtained. Here we will present and discuss in-situ desorption experiments using synchrotron X-rays (SNBL at ESRF) and neutron diffraction (JEEP II at IFE) for different Al- and N-based metal hydrides, including alanates, alane and amides/imides. The experiments are either carried out at a constant heating rate or at isothermal conditions.Support from The Research Council of Norway and the European Commission (FP6 projects STORHY and NESSHY) are acknowledged.
5:30 PM - Z4.8
Structural Properties of Mg0.7Ca0.3Ni2Dx.
Yumiko Nakamura 1 2 , Naoyoshi Terashita 3 , Bjørn Hauback 2 , Etsuo Akiba 1 Show Abstract
1 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan, 2 Department of Physics, Institute for Energy Technology, Kjeller Norway, 3 , Japan Metals & Chemicals Co. Ltd., Oguni-machi Japan
Some of the authors have been found (Mg,Ca)Ni2 Laves phase alloys (MgCu2 type), which reversibly absorb and desorb hydrogen around room temperature. The capacity is not larger than 0.8 H/M (~1.7 wt%), but this shows feasibility of hydrogen storage with Mg-containing compounds under ambient conditions.In this talk, structural properties of Mg0.7Ca0.3Ni2Dx(Hx) are reported. The structural change during hydrogenation was studied by in situ powder X-ray diffraction. The structure of Mg0.7Ca0.3Ni2D~2 was determined by powder neutron diffraction. Hydrogen occupation will be discussed from results of Rietveld refinement and radial distribution function analysis. N. Terashita et al., J. Alloys and Comp., 327 (2001) 275.
Ji-Cheng Zhao General Electric Company
Ian M. Robertson University of Illinois
Shin-ichi Orimo Tohoku University
Z5: Carbon and Nanotubes
Wednesday AM, November 29, 2006
Independence E (Sheraton)
9:30 AM - **Z5.1
Mechanistic Understanding of Hydrogen Storage in Carbon-based Materials
Hansong Cheng 1 , Alan Cooper 1 , Guido Pez 1 Show Abstract
1 , Air Products and Chemicals, Allentown, Pennsylvania, United States
Recent theoretical and experimental studies of hydrogen storage in boron-doped graphitic carbons and hydrogen spillover onto several carbon-based materials have generated great research interest. To understand the underlying mechanisms governing these chemical/physical processes, we have undertaken a series of theoretical studies based on first-principles atomistic simulations. Surprisingly large H2 adsorption energies in boron-doped carbon materials have been reported . NMR and neutron scattering data for H2 in a few selected boron-doped carbon materials also exhibit unusual features. For boron-doped graphitic carbons, we calculate the vibrational spectra, NMR chemical shifts, and evaluated H2 adsorption energies. In parallel, an enhanced hydrogen storage capacity was also reported for H2 in several carbon-based composite materials, such as carbon nanotubes, graphite fibers and metal organic framework (MOF) compounds, via an atomic hydrogen spillover process . Hydrogen atoms, generated by dihydrogen dissociation via transition metal catalysts, have been proposed to react with the unsaturated carbon atoms in the carbon or MOF materials to form C-H bonds. For composite metal/carbon materials, we performed ab initio molecular dynamics simulations to investigate the dissociative chemisorption of H2 and H2 spillover using several transition metal catalysts. Dissociation probabilities and average H desorption energies were calculated. Atomic hydrogen diffusion in graphitic carbon materials and the spillover dynamics were also investigated. The series of theoretical studies provide useful physical insight into the probable operative hydrogen mechanisms for these materials. Nondissociative Adsorption of H2 Molecules in Light-Element-Doped Fullerenes. Y.-H. Kim, Y. Zhao, A. Williamson, M. J. Heben, and S. B. Zhang, Phys. Rev. Lett. 96, 016102 (2006). Adsorption of Spillover Hydrogen Atoms on Single-Wall Carbon Nanotubes. F. H. Yang, A. J. Lachawiec Jr., R. T. Yang, J. Phys. Chem. B. 110, 6236 (2006).
10:00 AM - Z5.2
Theory and Simulation of Hydrogen Absorption in Graphene Layers.
Rachel Aga 1 , Maja Krcmar 1 2 , James Morris 1 3 , Chong Long Fu 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Grand Valley State University, Allendale, Michigan, United States, 3 , University of Tennessee, Knoxville, Tennessee, United States
We have used first-principles calculations to demonstrate that hydrogen uptake in graphite can be dramatically improved by altering the spacing between layers. In the dilute limit, H2 molecules between graphene sheets have unfavorably high energy. However, the initial molecules promote a dramatic expansion of the interlayer spacing, which reduces the absorption energy and promotes further absorption. Significantly, both H2 absorption energy and graphite interlayer spacing show a non-linear dependence on hydrogen concentration; a substantial decrease in the H2 absorption energy together with a significant expansion in the graphite interlayer spacing occurs within a very narrow H/C atom ratio. These results are used to derive an effective interaction potential between carbon and hydrogen molecules. The potential is used in grand canonical Monte Carlo simulations to investigate the pressure and temperature dependence of hydrogen storage in graphene layers. This research is sponsored by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, US Department of Energy under Contract No. DE-AC05-00OR-22725 with UT-Batelle.
10:15 AM - Z5.3
Hydrogen Adsorption in Ti, Co and Pt Decorated Carbon Nanotubes
Yubing Wang 1 , Zafar Iqbal 1 Show Abstract
1 Chemistry, New Jersey Institute of Technology, Newark, New Jersey, United States
Electrochemically-induced hydrogen adsorption on self-assembled free-standing sheets or vertically aligned films of single wall carbon nanotubes (SWNTs)on a metallized Si substrate decorated with Ti, Co and Pt have been studied. Decoration was carried out by pulsed electrodeposition or microwave-decomposition of metal precursors to obtain nanometer sized particles on the nanotube sidewalls and tips. Raman and fourier transform infrared (FTIR) spectroscopy in combination with thermopower and temperature programmed desorption measurements were used to understand the adsorption mechanism in terms of recent calculations on metal functionalized nanotubes by Yildirim and Ciraci . Hydrogen in Co-decorated SWNTs appears to be chemisorbed as indicated by the appearance of a C-H stretching line in the FTIR spectrum. Thermopower measurements suggest that hydrogen uptake is associated with partial charge transfer. Raman spectroscopy shows a reproducible downshift of the SWNT tangential stretching mode consistent with charge transfer or chemisorption, and a substantial decrease in resonance-enhanced intensity of the Raman lines with electrochemical charging. T. Yildirim and S. Ciraci, Phys. Rev. Lett. vol.94, 175501 (2005)
10:30 AM - Z5.4
Hydrogen Storage Properties of Laser- and arc-generated Boron-doped Carbon Nanotubes.
Jeff Blackburn 1 , Anne Dillon 1 , Thomas Gennett 2 , Phil Parilla 1 , Yong-Hyun Kim 1 , Yufeng Zhao 1 , Shangbai Zhang 1 , Yanfa Yan 1 , Kim Jones 1 , Lin Simpson 1 , Jeff Alleman 1 , Michael Heben 1 Show Abstract
1 , National Renewable Energy Lab, Golden, Colorado, United States, 2 chemistry department, Rochester Institute of Technology, Rochester, New York, United States
Doping of carbon nanotubes with a heteroatom such as boron affords control over the electronic properties of the nanotubes. Recent theoretical studies suggest that boron-doped carbon fullerenes may show promise as hydrogen adsorbents. These studies propose a three-center bond between boron dopants and hydrogen molecules with a binding energy of ~38 kJ/mol, ideal for hydrogen storage. Essential to this binding is the localized empty pz orbital of the boron dopant. Inspired by these findings, we explore the hydrogen storage properties of boron-doped carbon nanotubes experimentally. One of the major early stumbling blocks for hydrogen storage measurements on SWNTs was the preparation of highly pure samples. Recently, large hydrogen storage capacities have been reported for SWNTs rigorously purified with acid and oxidative treatments. While the laser vaporization method is generally recognized to produce SWNTs of very high purity with low defect density, efforts to directly dope SWNTs with significant amounts of B using laser vaporization have been largely unsuccessful. To this end, we have recently developed a synthetic procedure for the high yield synthesis of B-SWNTs by pulsed laser vaporization using a NiB catalyst. The B-SWNTs may be purified by a combination of acid reflux and oxidative treatments. Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) confirm boron incorporation as sp2 bonded species at doping levels of 1 – 2% in the B-SWNTs. The synthetic method has also been recently extended to the arc discharge method for B-SWNT production.We have studied the hydrogen storage properties of the laser- and arc-generated B-SWNTs with volumetric adsorption techniques as well as hydrogen nuclear magnetic resonance (NMR) spectroscopy and inelastic neutron scattering (INS). Multiple adsorption sites contribute to the hydrogen NMR and INS spectra of the B-SWNTs, with significant differences relative to undoped C-SWNTs. The results are evaluated to experimentally determine the binding energy of hydrogen molecules on the B sites. NMR spectroscopic studies were done in collaboration with Alfred Kleinhammes, Shenghua Mao, and Yue Wu from the University of North Carolina, Chapel Hill. Inelastic neutron scattering studies were done in collaboration with Craig Brown, Dan Neumann, and Y. Liu at the National Institute of Standards (NIST) in Maryland. Work was supported by the DOE/EERE/Hydrogen Program through the Center of Excellence on Carbon-based Hydrogen Storage Materials and by DOE/OS/BES.
10:45 AM - Z5.5
Tunable Hydrogenation of Fullerenes with Endohedral Dopants.
Yufeng Zhao 1 , Michael Heben 1 , S. Zhang 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
11:30 AM - Z5.6
Activation of Carbide Derived Carbons (CDC) for Effective Hydrogen Storage
Giovanna Laudisio 1 , Ranjan Dash 2 , Jonathan Singer 1 , Gleb Yushin 2 , Wei Zhou 3 1 , Taner Yildirim 3 , Yury Gogotsi 2 , John Fischer 1 Show Abstract
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
A breakthrough in storage systems is necessary for a successful hydrogen-based economy. A real improvement in designing materials for hydrogen storage was to refute the widely-held belief that hydrogen physisorption is directly proportional to BET specific surface area (SSA). Our recent findings on carbide derived carbons (CDC), a new class of porous carbons, demonstrate that large SSA and total pore volume for a given pore size are necessary for high hydrogen uptake . Thus a large volume of small open pores with narrow size distribution is the key for improving substantially physisorption on carbon structure. Pore size in CDC can be controlled by using different starting carbides and chlorination temperatures [2,3]. CDC’s have SSA up to 2000 m2/g and up to 80% open pore volume available to hydrogen without any meso or macro pores. Activation is a well known process for developing surface area and porosity. In particular physical activation with CO2 is reported to produce opening of narrow microporosity . In this work we report the application of CO2 and NH3 activation to different CDCs and the effect on hydrogen storage and heat of adsorption. This work was supported by the US DOE, Grant No. DE-FC36-04GO14280. corresponding author: email@example.com. Gogotsi, Y., Dash, R., K., Ysuhin, G., Laudisio, G., Fischer, J., E., J. Am. Chem. Soc. 2005, 127, (46), 16006-7.2. Gogotsi, Y., Nikitin, A., Ye, H., Zhou, W., Fischer, J., E., Yi, B., Foley, H., F., Barsoum, M., W., Nature mat. 2003, 2, 591-594.3. Yushin, G., Nikitin, A., Gogotsi, Y, Carbide-derived carbon. CRC Press: 2006; p 69-105.4. Rodriguez-Reinoso, F., Molina-Sabio, M., Gonzales, M., T., Carbon 1995, 33, (1), 15-23.
11:45 AM - Z5.7
Hydrogen Storage in Novel Carbon-based Nanostructured Materials
Erin Whitney 1 , Calvin Curtis 1 , Chai Engtrakul 1 , Mark Davis 1 , Kim Jones 1 , Philip Parilla 1 , Lin Simpson 1 , Anne Dillon 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
One of the biggest challenges facing a future hydrogen economy is that of onboard vehicular hydrogen storage. Since neither compression of hydrogen to 10,000 p.s.i. or liquid hydrogen will satisfy the United States Department of Energy’s 2015 targets, novel carbon-based nanostructured materials have emerged as potential candidates for vehicular storage. We present the synthesis and characterization of “bucky dumbbell,” a new organometallic compound comprised of two buckyballs complexed to a central iron atom. This work was inspired by previous experimental exploration of hydrogen storage on singled-wall nanotubes (SWNT) and iron-decorated multi-walled nanotubes (MWNT), as well as theoretical work predicting the formation of stable scandium-decorated buckyballs and boron-doped species. The buckyballs act as stabilizing ligands because of their symmetric arrangement of cyclopentadiene rings, which have been shown to complex with transition metals but would otherwise polymerize without the presence of the buckyball matrix. This new compound has been characterized using both 13C solid-state NMR and Raman spectroscopy, and electron spin paramagnetic resonance spectroscopy reveals the presence of Fe3+. Temperature-programmed desorption has revealed a new hydrogen binding site via the appearance of a peak centered at approximately -50 °C, indicating the hydrogen is stabilized at a temperature significantly above that expected for physisorption but still lower than that of C-H bond formation. Comparison with C60 under the same hydrogen exposure and heating conditions shows almost no hydrogen adsorption, and the exact binding energy (or desorption activation energy, Ed) for the bucky dumbbell shows an enhanced value of ~6.2 kJ/mol. Initial volumetric analyses conducted at 77K and 3 bar show a storage capacity of ~0.4 wt%. The synthesis and analysis of other novel fullerene-based organometallic hydrogen complexes will also be discussed.
12:00 PM - Z5.8
Structure Characterization of Carbide-Derived Carbons (CDC) for Optimal Hydrogen Storage by X-ray Scattering.
Jonathan Singer 1 , Giovanna Laudisio 1 , Alexander Seletsky 1 , Ranjan Dash 2 , Gleb Yushin 2 , Wei Zhou 3 , Taner Yildirim 3 , Yury Gogotsi 2 , John Fischer 1 Show Abstract
1 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
One of the greatest challenges facing the hydrogen-based economy is the need to store hydrogen safely and compactly. Porous systems present an attractive solution to this problem. Recent work demonstrated that in addition to high surface area, the key property for hydrogen storage in porous materials is a high total volume of micropores. Our examination of carbide-derived carbons (CDC) obtained from several precursors has revealed them to possess both of these qualities,1 in addition to having highly tunable properties controllable by carbide selection, chlorination temperature, and the use of post-treatments.2,3 Direct atom-scale experiments of porous materials which might accurately and reliably measure volume, size and shape of the pores are problematic, so indirect methods such as gas sorption are generally employed. We recently demonstrated the effectiveness of small angle X-ray scattering (SAXS) in confirming and reinforcing model-dependent conclusions drawn from gas sorption isotherms.4 In order to further explore the evolution of CDC structure under various synthesis conditions and post-treatments and its effect on hydrogen storage we will present a combination of SAXS techniques with diffuse scattering obtained from conventional X-ray powder diffraction.This work was supported by the US DOE, Grant No. DE-FC36-04GO14280. Corresponding author: firstname.lastname@example.org. Gogotsi, Y., Dash, R., K., Ysuhin, G., Laudisio, G., Fischer, J., E., J. Am. Chem. Soc. 2005, 127, (46), 16006-7.2. Gogotsi, Y., Nikitin, A., Ye, H., Zhou, W., Fischer, J., E., Yi, B., Foley, H., F., Barsoum, M., W., Nature mat. 2003, 2, 591-594.3. Yushin, G., Nikitin, A., Gogotsi, Y, Carbide-derived carbon. CRC Press: 2006; p 69-105.4. Laudisio, G., Dash, R. K., Singer, J. P., Yushin, G., Gogotsi, Y., Fischer, J. E., Langmuir 2006, in press.
12:15 PM - Z5.9
The Tailoring of Single-Walled Carbon Nanohorns for Hydrogen Storage
Hui Hu 1 , Bin Zhao 2 , Alexander Puretzky 1 , David Styers-Barnett 2 , Christopher Rouleau 1 , David Geohegan 1 , Yun Liu 3 , Craig Brown 3 , Dan Neumann 3 , Houria Kabbour 4 , Channing Ahn 4 , John Zielinski 5 , Charles Coe 5 , Alan Cooper 5 , Lin Simpson 6 , Anne Dillon 6 , Philip Parilla 6 , Michael Heben 6 Show Abstract
1 Materials Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , National Institute of Standard Technology, Gaithersburg, Maryland, United States, 4 Department of Materials Science, California Institute of Technology, Pasadena, California, United States, 5 , Air Products and Chemicals Inc., Allentown, Pennsylvania, United States, 6 , National Renewable Energy Laboratory , Golden, Colorado, United States
Single-Walled Carbon Nanohorns (SWNHs) are single-walled, closed-shell carbon structures which form ball-shaped aggregates (~50-100 nm in diameter). Their unique nanostructures make SWNHs promising candidates for hydrogen storage. Here we report the effects of chemical and thermal processing treatments to adjust the surface area and tune the pore sizes of the SWNHs as a basis for optimizing hydrogen storage, and assess the role of metal nanoparticle decoration on spillover storage. The SWNHs used in these studies were synthesized by laser ablation of carbon targets using a high-power (600 W) industrial Nd:YAG laser with adjustable pulse-width at Oak Ridge National Laboratory. The nanohorn length, the diameter of their aggregates, and their pore size distributions depend upon the laser pulse width used for their synthesis. Post-processing by chemical and thermal treatments permits adjustment of the nanostructure as well as access to the inner empty space of SWNHs to achieve efficient hydrogen uptake. The hydrogen uptake of opened SWNHs (2.5 wt%) is three times that of unopened SWNHs (0.8 wt%) at 77K. Based on BET measurements, opened SWNHs have surface areas (1892 m2/g) up to 4 times that of un-opened SWNHs (450 m2/g), indicating increased access to external pores. Thermal and oxidative processing treatments can also be used to increase the prevalence of folded graphitic structures in the samples as media for spillover storage. Two methods - the laser ablation of C/Pt targets, and wet chemistry using sodium citrate – will be described for the decoration of SWNHs with metal nanoparticles (Pt, Pd, etc.). TEM and STEM images show that wet chemistry method gives more uniform decoration of Pt nanoparticles with sizes between 1-3 nm. Both thermogravimetric and prompt gamma activation analysis demonstrate metal loadings of SWNHs/Pt can achieve 15-20 wt%. Decoration chemistry for Pd nanoparticles will be described and compared with the Pt decoration techniques and comparative hydrogen isotherm data will be presented. Pd-decorated opened SWNHs have been previously shown to increase hydrogen storage by factor of 4 compared with opened SWNHs.Our preliminary results of neutron scattering measurements have shown spillover effects in chemically-decorated SWNH/Pt materials. For comparison, unopened SWNHs decorated with clean metal catalysts by the in situ laser vaporization technique will be described to understand the effects of residual organics (surfactants, citrate groups, etc.) resulting from the chemical decoration method on the spillover storage. Research supported by the U. S. Department of Energy (EERE) through the Carbon-Based Hydrogen Storage Center of Excellence and by the U. S. Department of Energy, Division of Material Science, Basic Energy Sciences.
12:30 PM - Z5.10
Carbide-derived Carbons: Effect of Pore Size on Hydrogen Uptake and Heat of Adsorption.
Gleb Yushin 1 , Ranjan Dash 1 , Daniel Vriehof 1 , Yury Gogotsi 1 , Taner Yildirim 2 , Giovanna Laudisio 3 , Jonathan Singer 3 , John Fischer 3 Show Abstract
1 Materials Science and Engineering, A.J. Drexel Nanotechnology Institute, Drexel University, Philadelphia, Pennsylvania, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Z6: Carbon and MOFs
Wednesday PM, November 29, 2006
Independence E (Sheraton)
2:30 PM - **Z6.1
Nanostructured Absorbents for Hydogen Storage
Jeffrey Blackburn 1 , Calvin Curtis 1 , Anne Dillon 1 , Thomas Gennett 2 , Michael Heben 1 , Yong Hyun Kim 1 , Philip Parilla 1 , Lin Simpson 1 , Erin Whitney 1 , Shengbai Zhang 1 , Yufeng Zhao 1 Show Abstract
1 , National Renewable Energy Lab, Golden, Colorado, United States, 2 , Rochester Institute of Technology, Rochester, New York, United States
Hydrogen is viewed as a clean energy alternative that could one-day replace fossil fuels in powering vehicles. For this vision to become a reality, significant advances will be required in a wide array of hydrogen related technologies. For hydrogen storage, the U.S. Department of Energy has set a goal of achieving system gravimetric and volumetric storage densities exceeding 6 wt% and 45 kg H2/m3, respectively, to facilitate large scale commercial deployment of hydrogen fuel on several low-demand vehicle platforms by the year 2010 . A generic approach to the problem based on nanoscience considerations can offer a new perspective on this problem . In this approach, one considers how suitable binding sites for hydrogen can be designed and arranged in space with sufficient density, using a light host material, to simultaneously achieve high gravimetric and volumetric performance. To minimize energy input requirements during the charge/discharge cycle, and therefore optimize system efficiency, the “suitable” binding sites should stabilize hydrogen with energies in the range of 10 – 50 kJ/mol. We will discuss theoretical and experimental results on carbon nanotubes, fullerenes, and other nanostructured adsorbent materials, and explore the role of composition, doping, and local environment in tuning hydrogen storage properties. We will also describe the research activities in the DOE Center of Excellence for Carbon-Based Hydrogen Storage Materials which is focused on developing new solutions for hydrogen storage on-board vehicles. The Center is researching systems that reversibly stabilize sufficient hydrogen to meet the DOE targets, and builds on existing experimental and theoretical evidence for (i) dissociative adsorption that is weaker than typical C-H bond formation, and (ii) non-dissociative adsorption that is stronger than pure physisorption. In the first case we consider reversible hydrogen spillover, while in the second the goal is molecular adsorption via structural/chemical modifications to the physisorption potential as well as complexation of dihydrogen. The Center consists of projects at Air Products and Chemicals, Inc., California Institute of Technology, Duke University, Lawrence Livermore National Laboratory, National Institute of Standards and Technology, National Renewable Energy Laboratory, Oak Ridge National Laboratory, Pennsylvania State University, Rice University, University of Michigan, University of North Carolina (Chapel Hill), and the University of Pennsylvania.1. http://www.eere.energy.gov/hydrogenandfuelcells/mypp/2. http://www.sc.doe.gov/bes/hydrogen.pdf
3:00 PM - Z6.2
Hydrogen Sorption Properties of MIL-53, 100 and 101 Compounds: Correlation with the Surface Area and the Microporosity.
Houria Kabbour 1 , Anne Dailly 2 3 , Channing Ahn 1 Show Abstract
1 Materials Science, Caltech, Pasadena, California, United States, 2 Chemical & Environmental Sciences Laboratory, General Motors Corporation, Warren, Michigan, United States, 3 College of Engineering, Purdue University, West Lafayette, Indiana, United States
3:15 PM - Z6.3
Molecular Simulation Study on Catenation Effects on Hydrogen Uptake Capacity of MOFs.
Dong Hyun Jung 1 , Tae-Bum Lee 1 , Daejin Kim 1 , Ji Hye Yoon 2 , Sang Beom Choi 2 , Jaheon Kim 2 , Seung-Hoon Choi 1 Show Abstract
1 , Insilicotech Co. Ltd., Seongnam, Gyeonggi-Do, Korea (the Republic of), 2 Chemistry, Soongsil University, Seoul Korea (the Republic of)
3:30 PM - Z6.4
High Capacity Hydrogen Storage using Novel Nanotubes.
Sheng Meng 1 2 , Efthimios Kaxiras 2 , Zhenyu Zhang 1 Show Abstract
1 Condensed Matter Sciences Division, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 2 Physics Department, Harvard University, Cambridge, Massachusetts, United States
4:30 PM - Z6.6
Hydrogen storage in Palladium and Platinum-doped SWNTs by spill-over mechanism
Yong-Won Lee 1 , Ranadeep Bhowmick 1 , Bruce Clemens 1 Show Abstract
1 MSE, stanford university, Stanford, California, United States
Single-wall carbon nanotubes have intriguing potential for hydrogen storage since each carbon atom is on a surface site, and calculations have indicated that hydrogen bonding strength can be tuned by adjusting nanotube diameter. However, exposure to molecular hydrogen has resulted in only modest hydrogen uptake, as opposed to exposure to atomic hydrogen where significant hydrogen bonding has been observed. This has motivated studies of metal-doped SWNT in order to facilitate catalysis of hydrogen molecule disassociation. The hydrogen storage capacity of metal catalyst-doped single-wall carbon nanotube (SWNT) was measured using a volumetirc Sieverts apparatus to 30 Bar of pressure at room temperature. The base material is commercially available HiPco (high pressure CO conversion) SWNT containing 5 wt% of Fe. Additional metal catalyst doping was performed through electrochemical (EC) and UHV sputter (Sp) deposition techniques. The un-doped SWNT showed a reversible hydrogen uptake capacity of 0.17 wt %. The Pd-doped SWNTs by EC and Sp deposition methods showed 0.53 and 0.72 wt% uptake concentration (after adjustment for the hydrogen stored on the Pd), which is an increase of a factor of 3 to 4 over the undoped material. For the case of Pt catalyst, the uptake capacities of EC and Sp-doped samples were also increased to 0.40 and 0.51 wt%, respectively. The storage capacity of SWNT portion was significantly enhanced for both samples by the presence of catalyst metals. The relationship between the uptake capacity and metal content was investigated by varying the Sp-doped Pt thickness from 0.2 to 3.0 nm. Raman spectroscopy and transmission electron microscopy were also performed to suggest possible spill-over uptake mechanism.
4:45 PM - Z6.7
Hydrogen Adsorption in Boron doped Graphite and Single Walled Carbon Nanotubes probed by 1H Nuclear Magnetic Resonance Measurements
Shenghua Mao 1 , Alfred Kleinhammes 1 , Qiang Chen 1 , Yue Wu 1 , Michael Chung 2 , Jeff Blackburn 3 , Michael Heben 3 Show Abstract
1 Department of Physics and Astronomy and Curriculum in Applied and Materials Science, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Department of Materials Science and Engineering, Pennsylvania State Univeristy, University Park, Pennsylvania, United States, 3 , National Renewable Energy Laboratory (NREL), Golden, Colorado, United States
Theoretical models and simulations show that the binding energy of hydrogen in doped carbonaceous materials is enhanced over the adsorption energy of pure graphite or single walled carbon nanotubes (SWNTs). Boron doped carbon is an example which is actively studied. Unfortunately the amount of boron which can be doped into graphite or SWNTs is small at present (a few percent). Conventional volumetric or weight based techniques might not detect adsorption caused by a minority site. 1H nuclear magnetic resonance (NMR), however, is a technique which allows to sensitively probe the interaction of hydrogen with a minority site (here boron) while monitoring the majority site (carbon matrix) as well. The distinction between hydrogen in different sites is made through spectral inspection or through relaxation measurements. The amount of hydrogen associated with the boron site is quantitatively measured as a function of pressure. The isotherm is analyzed via a Langmuir model to extract the adsorption energy. Hydrogen adsorption in samples of boron doped SWNTs (NREL) and boron doped graphite (Penn State) are measured using 1H NMR as a function of temperature and pressures up to 100 atmospheres in situ. In case of boron doped graphite 2d exchange measurements are reported as well. 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
5:00 PM - Z6.8
Direct Observation of Hydrogen Binding to Unsaturated Metal Sites in a Metal-organic Framework.
Yun Liu 1 2 , Craig Brown 1 3 , Dan Neumann 1 , Mircea Dinca 4 , Jeffrey Long 4 , Anne Dailly 5 6 Show Abstract
1 , NIST Center for Neutron Research, Gaithersburg, Maryland, United States, 2 Department of Material Science and Engineering, University of Maryland, College Park, Maryland, United States, 3 , Indiana University Cyclotron Facility, Bloomington, Indiana, United States, 4 Department of Chemistry, University of California, Berkeley, California, United States, 5 Chemical & Environmental Sciences Laboratory, General Motors Corporation, Warren, Michigan, United States, 6 College of engineering, Purdue University, West Lafayette, Indiana, United States
Metal-organic frameworks (MOFs) attract considerable research interests due to their potential applications as hydrogen storage materials. Although their large surface area renders the potential to store large amount of hydrogen, most of the pore volume in MOFs can only be used at either extremely high pressure or very low temperature due to the small hydrogen binding energy. Therefore, to maximize the amount of adsorbed hydrogen molecules accessible at room temperature and with reasonable applied pressure, approaches to enhance the hydrogen molecule binding energy are needed. A new type of MOF has been synthesized with the tritopic bridging ligand 1,3,5-benzenetristetrazolate (BTT3-). The isosteric heat of adsorption of 10.1 kJ/mol for initial hydrogen uptake is achieved in this material, which is much larger than that in known MOFs. The hydrogen adsorption sites in this material were investigated using neutron powder diffraction at the NIST Center for Neutron Research. We found that the first and second hydrogen binding sites are responsible for the enhanced binding energy. We show for the first time that a hydrogen molecule binds to an unsaturated metal center in MOFs.
5:15 PM - Z6.9
Carbon Mmembranes: A Viable Technology for the Recovery and Purification of Hydrogen Gas.
Anna Merritt 1 , Ramakrishnan Rajagopalan 2 , Henry Foley 1 2 3 Show Abstract
1 Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Chemistry Department, The Pennsylvania State University, University Park , Pennsylvania, United States
Z7: Poster Session: Hydrogen Storage
Wednesday PM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - Z7.1
The Effect of Sn Element on Hydrogen Storage Characteristics of Mg2-xSnxNi(x=0, 0.05, 0.1, 0.15, 0.2)Alloys.
Jin Guo 1 , Cunke Huang 1 , Kun Yang 1 , Guangxu Li 1 , Weiqing Jiang 1 Show Abstract
1 College of Physics Science and Technology, Guangxi University, Nanning, Guangxi, China
9:00 PM - Z7.10
Pd-doped Multiwall Carbon Nanotubes as a H2 Storage Material.
Huanan Duan 1 , Ivan Mardilovich 2 , Jianyu Liang 1 , Yihua Ma 2 Show Abstract
1 Dept. of Mechanical engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States, 2 Dept. of Chemical engineering, Worcester Polytechnic Institute, Worcester, Massachusetts, United States
9:00 PM - Z7.11
Modified Electronic Properties of Pd in PdCu Bimetallic Layers for Improved Pd – H Interaction.
Manika Khanuja 1 , Bodh Mehta 1 , Sonnada Shivaprasad 2 Show Abstract
1 Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, India, 2 Surface Physics and Nanostructures, National Physical Laboratory, New Delhi, Delhi, India
9:00 PM - Z7.12
Development of Environmental Cell and its Application to Hydrogen Storage Materials.
Kohya Okudera 1 , Koichi Hamada 1 , Takanori Suda 1 , Somei Ohnuki 1 Show Abstract
1 Grad. School of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan
High-resolution and “environmental cell” microscopy were applied for surveying the reaction of hydrides in Vanadium and Magnesium based alloys, which are candidate for hydrogen storage materials of advanced hydrogen energy systems. For clarify the hydrogenation process, in-situ experiment was carried out by using 200 kV TEM equipped with a newly developed environmental cell, which is enable to observe transmitted image and electron-diffraction under gas reaction under hydrogen enviroment of 0.1 MP at room temperature. In case of Vanadium, bending fringe was created under hydrogen-gas of 0.1 MPa, which means that hydrogen reaction is not so quick in this case, and the local stress due to the hydrogen solution caused the fringes. In case of Magnesium, the gas reacted with the powders and showed the swelling, where the surface steps with several ten nm become to more straight, and also SADP showed the formation of MgH2. In-situ experiment for hydrogenation reaction by using the environmental cell has started recently, therefore the precise studies will be continued, as well as its improvement, especially in the transparence films.
9:00 PM - Z7.13
Hydrogen Storage of Polyol Reduced Mg-Ni Nanoparticles.
Chien-Hsing Hsu 1 , Jie-Syuan Liu 1 , Wei-Li Yuan 1 Show Abstract
1 Chemical Engineering, Feng Chia University, Taichung Taiwan
A chemical reduction method, the polyol process, was used to prepare the Mg-Ni nano-intermetallic alloys for hydrogen storage. There are two advantages for this method: (1) a higher quantity of the sample can be prepared (2) the preparation conditions such as reduction temperature, reaction time, protecting reagent (PVP, polyvinylpyrrolidone) concentration can be adjusted to control the particle size and to produce the nano-single metal or nano-intermetallic alloy. In addition, the chemical reduction method can be used on materials difficult to reduce such as Mg and Ti. Firstly, a total of 0.05 mole metal acetate including magnesium acetate and nickel acetate was dissolved in 50∼200 ml ethylene glycol as weak reduction reagent with various Mg/Ni molar compositions. Secondly, 30 g of polyvinylpyrrolidone (PVP, MW=10000) was dissolved to disperse the Mg-Ni nanoparticles. Thirdly, the two prepared mixtures were mixed and stirred completely with a magnetic stone for 30 min. Then in the fourth step, the mixture was refluxed at 180∼190°C. When the temperature had reached the set temperature, the reflux procedure was continued for an additional 10 min. Fifthly, the PdCl2 with 0.01 molar ratio of (Pd/metal) dissolved in 10 ml ethylene glycol was further added and the reflux continued for one hour at a set temperature. Sixthly, the as-synthesized product was thoroughly washed with a 85% ethanol solution and centrifuged at 9000 rpm speed several times. In the final step, the nano-intermetallic Mg–Ni alloy was dried at a temperature below 70°C to avoid burning off. At a concentration ratio of 3:2 (0.03 mol magnesium acetate and 0.02 mol nickel acetate), the mean particle size was 72.1 nm measured by dynamic light scattering (DLS); the redox peaks were less than 1.0 V apart, measured by cyclic voltammetry (CV) and relative to Ag/AgCl reference; XRD results showed peaks of Mg2Ni, Mg, and Ni with 32% Mg and 50% Ni from analysis of inductively coupled plasma (ICP); and the hydrogen storage capacity was found to reach 1.1 wt%. The results show the potential of low cost manufacture of metal hydrides by polyol process.
9:00 PM - Z7.14
Thermodynamic Study of Nanoscale Metal Hydride for Hydrogen Storage
Vincent Berube 1 , Gregg Radtke 2 , Gang Chen 2 , Millie Dresselhaus 2 Show Abstract
1 Physics, MIT, Cambridge, Massachusetts, United States, 2 Mechanical engineering, MIT, Cambridge, Massachusetts, United States
Metal and complex hydrides may be the most promising options for hydrogen storage that reach the 2015 DOE targets for volumetric and gravimetric storage. Slow desorption kinetics and high release temperature must be overcome to make automotive applications feasible. Reducing the enthalpy of formation by destabilizing the hydride reduces the heat loss during the hydration phase and allows desorption at a lower temperature. We show that at nanoscale, the increased surface to volume ratio may help reduce the enthalpy of formation by creating a higher energy surface upon hydriding. The expected change of enthalpy of formation for different geometries at nanoscale is considered. We show that the reduction of enthalpy of formation is non-negligible only at very small sizes (radius less than 2nm for Mg nanoparticles) that currently cannot be achieved experimentally. Other possible mechanisms responsible for lowering the heat released upon hydriding are considered. For example, additional surface and subsurface sites of lower binding energy may decrease the enthalpy of formation by reducing the average binding energy while increasing the storage capacity. The effect of the excess enthalpy at the grain boundary of nanoparticles is also investigated. These nanoscale effects are studied and their magnitude estimated for magnesium hydride.
9:00 PM - Z7.15
NaAlH4 Morphological Evolution during Air Exposure
Ejiroghene Oteri 1 , Kristan Moore 2 , Tabbetha Dobbins 1 2 Show Abstract
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 Dept. of Physics, Grambling State University, Grambling, Louisiana, United States
This research entails the study of sodium alanate (NaAlH4) particle morphological and powder surface area changes during exposure to atmospheric conditions. Sodium alanate powders were high energy ball milled with and without the transition metal salt TiCl4. The particle morphology and size analysis were conducted using microscopy based and laser light scattering techniques. Phase data were determined using powder x-ray diffraction. The results attempt to track changes in alanate powders during transfer to the microscope and hence establish the upper time limit for air exposure during morphology study of sodium alanate doped and undoped powders.
9:00 PM - Z7.17
Hydrogen Adsorption in Modified and Conventional Carbon Nanotubes.
Renato Bonadiman 1 , Márcio Lima 1 , Monica de Andrade 1 , Carlos Bergmann 1 Show Abstract
1 Materials Department, Federal University of Rio Grande do Sul, Porto Alegre Brazil
9:00 PM - Z7.18
Encapsulation of NaAlH4 in Polymers with Titanium Metal Adsorbed on the Surface.
Vimal Kamineni 1 , Yuri Lvov 1 , Tabbetha Dobbins 1 Show Abstract
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States
9:00 PM - Z7.19
Design, Synthesis, Structure Characterization and Hydrogen Sorption of Microporous Metal Organic Frameworks (MMOFs)
Long Pan 1 , JeongYong Lee 1 , Jing Li 1 Show Abstract
1 Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, United States
There has been an increasing demand in developing clean and efficient energy carriers/sources to replace fossil fuels. Hydrogen, as an alternative energy carrier, has significant advantages superior to fossil fuels. It is the most abundant element in the universe and has a very high energy density. It can be generated from renewable energy sources such as water, solar and wind power. The sole byproduct of its energy generation process is water, which is environmentally clean. However, due to its low volumetric energy density, adequate storage of hydrogen becomes a key issue that must be addressed if the hydrogen economy is to be developed. While extensive efforts have been made to improve the hydrogen storage technologies currently being investigated, none is yet capable of meeting the gravimetric and volumetric targets required for large scale commercialization. There is, therefore, a strong need to explore new materials with enhanced sorption properties, in addition to continuing research in the more traditional technologies. In this presentation we will describe our recent development on microporous metal organic frameworks (MMOFs), a subclass of MOFs that have small pores in the range of several angstroms. We will discuss the rational design and synthesis, crystal growth and structure analysis, hydrogen sorption studies at low and high temperature/pressure, and the pore properties of these materials.
9:00 PM - Z7.2
Milling and Additive Effects on Hydrogen Desorption Reactions of Li-N-H and Li-Mg-N-H Hydrogen Storage Systems.
Mitsuru Matsumoto 1 , Yoshitsugu Kojima 1 3 , Shin-ichi Towata 1 , Yuko Nakamori 2 , Shin-ichi Orimo 2 Show Abstract
1 Materials Department, Toyota Central R&D Labs., Inc., Nagakute-cho, Aichi, Japan, 3 Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan, 2 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan
Hydrogen desorption reactions of the mixtures of (i) lithium amide and lithium hydride (LiNH2/LiH), and (ii) magnesium amide and lithium hydride (Mg(NH2)2/4LiH) were studied. Titanium compounds and nano-particles including fullerene (C60), were doped to those hydrogen storage mixtures respectively. The hydrogen desorption reactions were monitored by means of temperature programmed desorption (TPD) technique under an Ar atmosphere. The reaction of LiNH2/LiH was accelerated by adding either 1 mol% of Ti species or 0.2 mol% of fullerene (C60), while those additives did not show significant acceleration effects on the reaction of Mg(NH2)2/4LiH. Kinetic studies revealed the enhanced hydrogen desorption reaction rate constant of TiCl3 doped LiNH2/LiH, k = 3.1 x 10-4 s-1 at 493 K, and the prolonged ball-milling further improved reaction rate, k = 1.1 x 10-3 s-1 at the same temperature. For the dehydrogenation reaction of TiCl3 doped LiNH2/LiH, the activation energies estimated by Kissinger plot (95 kJ mol-1) and Arrhenius plot (110 kJ mol-1) were in reasonable agreement each other. The LiNH2/LiH mixture without additive exhibited slower hydrogen desorption process and the kinetic traces deviated from single exponential behavior. The results indicated the Ti(III) additives change the hydrogen desorption reaction mechanism of the LiNH2/LiH mixture.
9:00 PM - Z7.20
High Surface Area Nanoporous Carbon Derived from Polyfurfuryl Alcohol/polyethylene Glycol Blends.
Ramakrishnan Rajagopalan 2 , Christopher Burket 1 , Henry Foley 1 2 Show Abstract
2 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 1 Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
9:00 PM - Z7.21
Role of Annealing for Improving Hydrogen Storage Properties of Ti-Cr-V Alloy.
Kota Washio 1 , Yasuhiro Munekata 1 , Somei Ohnuki 1 , Hironobu Arashima 2 , Hideaki Ito 2 Show Abstract
1 Grad. School of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan, 2 Muroran Res Inst, Japan Steel Works, Muroran, Hokkaido, Japan
9:00 PM - Z7.22
Hydrogen Desorption Properties of a New Mg(NH2)2-LiAlH4 System.
Yongfeng Liu 1 Show Abstract
1 , Physics, Singapore Singapore
9:00 PM - Z7.23
The Effect of Equal Channel Angular Pressing on Hydrogen Storage Properties of a Mg-Ni Alloy
Eugen Rabkin 1 , Vladimir Skripnyuk 1 , Eli Buchman 1 , Yuri Estrin 2 , Mikhail Popov 2 , Scott Jorgensen 3 Show Abstract
1 Department of Materials Engineering, Technion, Haifa Israel, 2 , Technical University of Clausthal, Clausthal-Zellerfeld Germany, 3 , General Motors R&D Center , Warren, Michigan, United States
A multi-pass equal channel angular pressing (ECAP) technique was applied to as-cast eutectic Mg-Ni alloy to refine its microstructure down to sub-micrometer size of Mg and Mg2Ni grains. This was achieved after 10 ECAP passes. The Mg grains exhibited a supersaturation in Ni, which was non-homogeneously distributed across the grains. All alloys studied exhibited a gravimetric hydrogen storage capacity of about 6 wt. %. The pressure-composition isotherms for the hydrogenation of as-cast and ECAP processed alloys were determined. It was shown that equilibrium hydrogen desorption pressure increases with increasing number of ECAP passes, the alloy processed by 10 passes exhibiting approximately 50% pressure increase over its as-cast counterpart. The ECAP-processed alloy exhibited an excellent hydrogen desorption kinetics, desorbing 5 wt. % of hydrogen in less than 5 min at the temperature lower than 573 K. It was also shown that in terms of hydrogen desorption pressure, the ECAP treated Mg-Ni alloy outperforms the alloys of similar composition whose nanoscale structure was by alternative processing techniques.
9:00 PM - Z7.24
X-ray Absorption Spectroscopy (XAS) and Small-angle X-ray Scattering (SAXS) Studies on Transition Metal Doped Sodium Alanate (NaAlH4)
Tabbetha Dobbins 1 2 Show Abstract
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 Dept. of Physics, Grambling State University, Grambling, Louisiana, United States
This research is aimed at understanding the role of transition metal dopants in the sodium alanates (NaAlH4) using the combined characterization of small-angle x-ray scattering (SAXS) and x-ray absorption spectroscopy (XAS). Sodium alanate powders were high energy milled both with and without transition metal salt (i.e. TiCl3, ZrCl4, and VCl3) dopant additions. Variation in phases formed, particle sizes and powder surface occurring during milling was tracked. This work attempts to establish a link between dopant chemistry and powder morphological evolution.
9:00 PM - Z7.25
Ti-catalyzed Hydrogen Dissociation: Consequences for Reversible Hydrogen Storage in Doped Sodium Alanate.
Erik Muller 1 , Peter Sutter 1 , Percy Zahl 1 , James Muckerman 2 , Santanu Chaudhuri 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
9:00 PM - Z7.3
Complex Hydrides Studied by Raman Spectroscopy and Thermal Conductivity Measurements under Pressure.
Bertil Sundqvist 1 , Alexandr Talyzin 1 , Ove Andersson 1 Show Abstract
1 Department of Physics, Umeå University, Umeå Sweden
Hydrogen has been suggested as a replacement for oil or gasoline as a possible future energy carrier in mobile applications, and one of the safest and most efficient ways to store hydrogen is considered to be in the form of solid, hydrogen-rich materials. Two examples of such materials are the alkali metal alanates, AAlH4, and the alkali metal borohydrides, ABH4, where A is an alkali metal. Theoretical calculations show that these materials should show rich structural pressure-temperature phase diagrams, and there are predictions that some high-pressure phases should have quite high hydrogen densities. We have investigated several materials of this type under high pressure, using both Raman spectroscopy up to 17 GPa at room temperature and thermal conductivity and DTA measurements over the range 100-400 K below 2 GPa. Both types of method can be used to find structural phase transformations. We discuss the phase diagrams of several materials, combining our own data with old and new experimental and theoretical data from literature sources to map phase boundaries and, where possible, structures. Data for the thermal conductivity of several materials are also presented. Such data are very important for future applications, especially for reversible hydrogen storage where large amounts of heat must be deposited into the material to discharge hydrogen and removed from the material on recharging with hydrogen.
9:00 PM - Z7.4
Research on Computer Optimization of low-cost Hydrogen Storage Alloy Containing B Prepared by Strip Casting and its Microstructure and Performance.
Hong Guo 1 , Weiping Han 1 , Chengdong Li 1 Show Abstract
1 Research Center for Non-ferrous Metals Composites, Beijing General Research Institute for Non-ferrous Metals, Beijing China
9:00 PM - Z7.5
Crystal Structure Analysis in the Dehydrogenation Process of Mg(NH2)2-LiH System.
Tatsuo Noritake 1 , Masakazu Aoki 1 , Shin-ichi Towata 1 , Yuko Nakamori 2 , Shin-ichi Orimo 2 Show Abstract
1 Materials Department, TOYOTA Central R&D Labs., Inc., Nagakute, Aichi, Japan, 2 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan
Mg(NH2)2-LiH system which have the properties of reversible hydrogenation and dehydrogenation is one of the promising candidates for new hydrogen storage materials. For understanding of the reversible reaction mechanism, we investigated the crystal structure changes in 3Mg(NH2)2-12LiH system using the pressure-composition (p-c) isotherm measurement and synchrotron X-ray diffraction. The sample was prepared by the hydrogenation of Mg3N2 + 4Li3N. At the several dehydrogenation stages of the p-c isotherm measurement at temperature 523 K, the sample was taken out and X-ray diffraction measurement was performed. By the amount of desorbed hydrogen, the reaction was expressed as the following formula, Mg(NH2)2 + 4LiH → LixMg(NH2)2-x(NH)x + (4-x)LiH + xH2 (x = 0~2). The crystal structures of LixMg(NH2)2-x(NH)x, similar to CaF2-type one, formed during the dehydrogenation reaction were determined by Rietveld analysis. As a result, it is considered that the dehydrogenation process might relate to the diffusion of Li+ ion in cation sites of Mg(NH2)2.  Y. Nakamori et al., Appl. Phys. A 80, 1–3 (2005)  M. Aoki et al., J. Alloys Compd. in press
9:00 PM - Z7.6
Relations between Microstructure of Mg/Cu Super-laminates and Kinetics of Hydrogen Absorption/desorption.
Koji Tanaka 1 , Nobuhiko Takeichi 1 , Hideaki Tanaka 1 , Nobuhiro Kuriyama 1 , Tamotsu Ueda 2 , Makoto Tsukahara 2 , Hiroshi Miyamura 3 , Shiomi Kikuchi 3 Show Abstract
1 Res. Inst. for Ubiquitous Enegy Devices, Natl. Inst. of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka, Japan, 2 , IMRA Material R&D Co.Ltd., Kariya, Aichi, Japan, 3 , IUniversity of Shiga Prefecture, Hikone, Shiga, Japan
Hydrogen storage materials have attracted more and more attention with the advance of R & D activities of fuel cell vehicles. Magnesium is expected as one of hydrogen storage media because it can store a large amount of hydrogen up to 7.6 mass%, as MgH2. However, MgH2 is too stable to release hydrogen smoothly; a practical decomposition rate is given at the temperatures above 673K, which is too high for practical applications. Thus, various Mg-based alloys and compounds have been investigated to improve the rate and lower the temperature of dehydrogenation. Recently, co-authors Ueda et al. reported that Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473K.The Mg/Cu super-laminates were prepared by a repetitive fold and roll method using conventional two-high rolling mill. Hydrogen storage properties of the super-laminates were investigated by using a Sieverts’ method. Initial activation at 573 K leads the super-laminates to absorb hydrogen at 473K. In order to clarify the process of hydrogenation and dehydrogenation at 473K, we performed (1) in-situ XRD analyses to observe phase transformations of the super-laminates, (2) TEM observations of nano-structures of the super-laminates and Mg2Cu powder prepared by conventional casting method, and (3) thermogravimetry of the super-laminates and powder during dehydrogenation.The results of in-situ XRD analyses suggest that the reaction mechanism is as follows. In the hydrogenation process for the super-laminates at 573K, Mg2Cu is formed at the interface between Mg and Cu layers through interdiffusion and then the Mg2Cu decomposes into MgH2 and MgCu2. In the dehydrogenation process at 573K, the MgH2 releases hydrogen and returns to metallic Mg. The Mg reacts with MgCu2, and Mg2Cu is formed again. Through the sequence, Mg2Cu phase absorbs and desorbs hydrogen reversibly in parallel with disproportionation and recombination of intermetallic phase at 473K. TEM observations reveal that the as-rolled Mg/Cu super-laminates have laminated structures in sub-micrometer-order composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation keep laminated structure and have uniformly distributed pores with a sub-micrometer diameter. On the other hand, the cast Mg2Cu powder after initial activation has pores only beneath the surface oxide layers. The results of thermogravimetric measurements show that the temperature at maximum dehydrogenation rate decreases in order of the flaky Mg/Cu super-laminates, cast Mg2Cu powder and MgH2 powder. It is considered that these characteristic structures of the activated super-laminates enhance the diffusion of hydrogen and enables hydrogenation and dehydrogenation at 473K. It is concluded that the nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics, which would contribute to achieve high performance hydrogen storage materials.
9:00 PM - Z7.7
Hydrogen Degradation and Its Mechanism of Fcc Metals for High-Pressure Hydrogen Storage Tank
Kenichi Takai 1 Show Abstract
1 Mechanical Engineering, Sophia University, Tokyo Japan
High-resistance metals to hydrogen degradation have been required since hydrogen pressure in a storage tank for a fuel cell vehicle varies from 35 MPa to 70 MPa, and that in the tank for hydrogen refueling station increases to above 100 MPa. FCC metals used under the high-pressure hydrogen for fuel-cell constituent materials such as SUS 316L, Inconel 625, and pure Aluminum were prepared, because of the low susceptibility to hydrogen degradation. Three principal aspects regarding the fcc metals are present here: (1) to analyze hydrogen desorption properties of fcc metals obtained by thermal desorption spectrometry (TDS), (2) to find out the condition of electrolysis hydrogen charging corresponding to various hydrogen pressures, since the charging under high-pressure hydrogen is much danger and more expensive than the electrolysis hydrogen charging, and (3) to clarify the degradation susceptibility using slow strain rate technique (SSRT) and its mechanism. The fcc metals were solution heat treated, charged under the electrolysis and high-pressure hydrogen, then analyzed hydrogen content and the states. The electrolysis hydrogen charging enables us to substitute high-pressure hydrogen atmosphere such as hydrogen refueling station using Sieverts rule since hydrogen state absorbed by the electrolysis and high-pressure conform without the surface damage. The maximum hydrogen pressure on Inconel 625 surface achieves to approximately 600MPa by the electrolysis charging. The strain to failure of Inconel 625 is critically dependent on hydrogen content and decreases with increasing hydrogen content. The fracture surfaces transform from ductile to brittle with increasing hydrogen. In contrast, the strain to failure of SUS 316L remains constant regardless of high hydrogen content. The fracture surfaces remain ductile up to 93.1 mass ppm hydrogen content. The strain to failure of the aluminum is critically dependent on hydrogen content and decreases with increasing hydrogen content. The strain to failure of the aluminum decreases with strain rate of SSRT.
9:00 PM - Z7.8
The Energetics of Hydrogen Adsorbed in Nanoporous Silicon. An ab initio Simulational Study.
Ariel Valladares 1 , Alexander Valladares 2 , R. Valladares 2 , A. Calles 2 Show Abstract
1 Condensed Matter, IIM-UNAM, Mexico, D.F. 04510 Mexico, 2 Physics, Facultad de Ciencias-UNAM, Mexico, D.F. 04510 Mexico
Porous carbon has been consistently considered a promising material to store hydrogen. Both carbon and silicon, being group IV elements, may have similar properties when the tetrahedral bonding phase of carbon (diamond) is considered. However, in general carbon displays a rich variety of bonds that makes it very versatile; these bonds lead to different types of molecules or solids not encountered in silicon or silicon compounds. Therefore, nanoporous silicon should have a more tetrahedrally dominated structure and its internal surfaces may show a different density of dangling bonds than nanoporous carbon, where bond rearrangement due to hybridization of the sp2 and sp1 type may play a role in the total number of dangling bonds existing on its internal surfaces. A priori we expect nanoporous silicon to have a larger density of dangling bonds than nanoporous carbon; therefore nanoporous silicon may be a more efficient material to store hydrogen than nanoporous carbon. In this work we report studies of a porous atomic structure of silicon with 50 % porosity that, due to the size of the supercell falls within the regime of nanoporous silicon. This structure is generated using a novel ab initio molecular dynamics procedure that leads to more realistic materials . The sample has been hydrogenated both by attaching hydrogens to the dangling bonds and relaxing it, and by placing hydrogen within the cavity of the pore and applying a molecular dynamics process at 300 K to see if the hydrogen is either physisorbed or chemisorbed. The total energy of the supercell was obtained before and after the hydrogen incorporation. From these values the average energy per hydrogen atom was then deduced. We compare our results to CH bond energies and hydrogen chemisorption in carbon ; conclusions are drawn. A. Valladares et al., submitted to Symposium QQ, MRS, Fall Meeting 2006. E.R.L. Loustau et al., Journal of Non-Cryst. Solids, 352 1332 (2006).
9:00 PM - Z7.9
Clathrate Hydrogen Storage Examined with Inelastic Neutron Scattering and Raman Vibrational Spectroscopy.
Timothy Jenkins 1 , Russell Hemley 1 , Ho-kwang Mao 1 , Wendy Mao 2 1 , Burkhard Militzer 1 , Viktor Struzhkin 1 Show Abstract
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States, 2 LANSCE, Los Alamos National Lab, Los Alamos, New Mexico, United States
Ji-Cheng Zhao General Electric Company
Ian M. Robertson University of Illinois
Shin-ichi Orimo Tohoku University
Z8: Mg and Mg-based Hydrides
Thursday AM, November 30, 2006
Independence E (Sheraton)
9:30 AM - **Z8.1
Mg Based Alloys for Hydrogen Storage.
Etsuo Akiba 1 , Hirotoshi Enoki 1 , Huaiyu Shao 1 , Masachika Shibuya 1 , Kohta Asano 1 Show Abstract
1 ETRI, AIST, Tsukuba, Ibaraki, Japan
10:00 AM - Z8.2
Development of Nanocrystalline Al-Mg Alloys for Hydrogen Storage.
Fereshteh Ebrahimi 1 , Sankara Tatiparti 1 , Mahesh Tanniru 1 , Darlene Slattery 2 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Florida Solar Energy Center (FSEC), Cocoa, Florida, United States
Magnesium alanate has a theoretical gravimetric hydrogen capacity of 9.3wt%, which makes it an attractive complex metal hydride for hydrogen storage. Furthermore it has a reasonable desorption temperature (<200C) and is less ignitable than sodium alanate. Recent results on hydrogenation of a supersaturated Al-Mg thin film have revealed that magnesium alanate can be formed directly from the alloy when Al/Mg ratio is close to 2.We have synthesized nanocrystalline supersaturated Al-Mg alloy powders on graphite substrates via electrodeposition using organometallic electrolytes. The Al-Mg powder was fabricated in a glove box with less than 1ppm oxygen and was transferred to hydrogenation chamber without exposure to atmosphere. The morphology, grain size, composition and structure of the powders were characterized using electron microscopy and x-ray diffraction techniques. The thermal stability and propensity to intermetallic formation of the powders was evaluated by annealing the powders up to 300C. In this presentation the results of microstructural analysis before and after hydrogenation will be discussed.The financial support by NASA (Grant NAG-2930) and NSF (Grant DMR-0605406) is greatly appreciated.
10:15 AM - Z8.3
Activated Reactive Evaporation of Mg2NiH4 and MgH2 Thin Films.
Ruud Westerwaal 1 , M. Slaman 1 , W. Lohstroh 2 , A. Borgschulte 3 , B. Dam 1 , R. Griessen 1 Show Abstract
1 FEW - Vaste - stoffysica, Vrije University, Amsterdam Netherlands, 2 Institute for Technology, Forschungszentrum Karlsruhe GmbH, Karlsruhe Germany, 3 , GKSS - Research Center Geesthacht GmbH WTP, Geesthacht Germany
10:30 AM - Z8.4
Catalytic Effects of Transition Metals and Carbon Nanotubes on Hydrogen Storage in Magnesium.
Xiangdong Yao 1 2 , C. Wu 3 , A. Du 1 4 , Yinghe He 2 , P. Wang 3 , Huiming Cheng 3 , Sean Smith 1 4 , J. Zou 5 , Gaoqing Lu 1 Show Abstract
1 ARC Centre for Functional Nanomaterials, The University of Queensland, Brisbane, Queensland, Australia, 2 School of Engineering, James Cook University, Townsville, Queensland, Australia, 3 National Laboratory of Materials Science, Institute of Metal Research, Shenyang China, 4 Centre for Computational Molecular Science, Institute of Metal Research, Shenyang China, 5 Centre for Microscopy and Microanalysis and School of Engineering, The University of Queensland, St. Lucia, Queensland, Australia
10:45 AM - Z8.5
Novel Mg-Ti based Materials for Hydrogen Storage.
Peter Kalisvaart 1 , Peter Notten 1 2 Show Abstract
1 Chemical Engineering, Eindhoven University of Technology, Eindhoven, Noord Brabant, Netherlands, 2 , Philips Research Laboratories, Eindhoven, Noord Brabant, Netherlands
To meet the ever-increasing energy demands of the future, the hydrogen economy has been proposed as a viable alternative to fossil fuels. One of the major technological challenges that need to be accomplished is the development of a safe hydrogen storage material that is cheap, lightweight and releases its hydrogen at close-to-ambient temperatures and pressures.Recently, MgSc alloys were identified as high-capacity storage materials [1,2] Electrochemically reversible hydrogen storage capacities of up to 1500 mAh/g and 1790 mAh/g (~6.5 wt%!) for Mg80Sc20 Pd-doped bulk materials and Pd-coated thin films respectively. However, the high cost of Sc (>10 USD/g) makes practical application of this material unlikely. For thin films made by e-beam deposition, it proved possible to synthesize a large variety of non-equilibrium compositions with 3d-transition metals as cheap substitutes for Sc . A maximum capacity for Mg80Ti20 of 1750 mAh/g was found, almost equal to Mg80Sc20, with similarly favourable discharge kinetics. However, the mutual equilibrium solid solubility of Ti and Mg is less than 1 at% even at elevated temperatures, which makes the synthesis of a bulk equivalent of these materials very difficult.Mechanical alloying has been proved to be a very versatile way of producing all kinds of non-equilibrium materials . In the present study, attempts to synthesise bulk Mg-Ti alloys by high-energy ball-milling are reported. Mg and Ti, with up to 5 at% of Ni, were successfully reacted to new intermetallic phases with a Face-Centred-Cubic structure. Subsequent activation with Pd resulted in electrochemically reversible capacities up to 550 mAh/g for (Mg65Ti35)0.95Ni5 doped with 5at% of Pd. The fact that the capacity is so much lower than in the thin film case suggests that not all the resulting intermetallic phases are active for hydrogen storage. Therefore, it can be concluded that synthesis of bulk Mg-Ti based materials is possible by mechanical alloying and that further optimisation of the materials composition will very likely lead to even higher capacities than those reached until now.  P. H. L. Notten, M. Ouwerkerk, H. van Hal, D. Beelen, W. Keur, J. Zhou and H. Feil, J. Power Sources, 129, 45 (2004). W. P. Kalisvaart, R. A. H. Niessen and P. H. L. Notten, J. Alloys Compd., In Press,, doi:10.1016/j.jallcom.2005.09.042 (2006). R. A. H. Niessen and P. H. L. Notten, Electrochemical and Solid-State Letters, 8, 10, A534 (2005). P. Vermeulen, R. A. H. Niessen and P. H. L. Notten, Electrochemistry Communications, 8, 1, 27 (2005). C. Suryanarayana, Progress in Materials Science, 46, 1-2, 1-184 (2001)
11:30 AM - Z8.6
In-Situ High-resolution Observation for Decomposition of MgH2-(Ni) Hydride.
Somei Ohnuki 1 , Naoki Shiomi 1 , Kohya Okudera 1 , Koichi Hamada 1 , Takanori Suda 1 , Y. Kawai 2 , Yoshitsugu Kojima 2 Show Abstract
1 Grad. School of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan, 2 , Toyota Central R&D Labs., Inc., Nagakute Japan
11:45 AM - Z8.7
Hydrogen Desorption from MgH2 Based Nano-Micro Composites.
Nadica Abazovic 1 , Ennio Bonetti 2 , Vittoria Contini 1 , Anna Lisa Fiorini 2 , Rita Mancini 1 , Amelia Montone 1 , Luca Pasquini 2 , Marco Vittori Antisari 1 Show Abstract
1 UTS Materiali e Nuove Tecnologie, ENEA, Roma Italy, 2 Department of Physics, University of Bologna, Bologna Italy
The desorption behaviour of composite materials based on MgH2 has been studied with particular attention to the onset temperature of the hydride mixture decomposition.Micro and nano-composite materials have been prepared by ball milling mixtures of MgH2 with other phases like Mg2Ni, LaNi5 and pure Pd, all compounds having concentrations as high as 30%. All the added compounds can form hydride phases which release their hydrogen content at a temperature lower than MgH2. The purpose was to explore the eventual setting up of synergic effects able to support a lowering of the actual desorption temperature of MgH2. Materials with a different degree of microstructural refinement were obtained by synthesis under different processing conditions, varying milling time and intensity. The structural evolution of the composites has been investigated by X-Ray Diffraction and Scanning Electron Microscopy, while the hydrogen desorption has been studied by Thermo-Gravimetric and Differential Thermal Analysis techniques. In the case of MgH2-Pd, a few samples have been realized by Inert Gas Condensation (IGC) in order to compare the behaviour of materials with the same composition and very different microstructures.First results show that the addition of a defined amount of such phases and a suitable mechanical processing procedure appear to provide channels for an easy de-hydrogenation of MgH2, at a temperature lower than the one characteristic of the pure phase. The desorption channels appear to maintain their activity even after some exposure to the atmosphere. All the measured desorption temperature data are consistent with the constraint imposed by the equilibrium of MgH2 with gaseous hydrogen so that it results that the additives mainly affect the entity of the kinetic barriers limiting the decomposition process. Several samples show an onset of the decomposition reaction, studied by TG-DTA in inert gas at atmospheric pressure, as low as 230 °C.
12:00 PM - Z8.8
Continuum Model for the Optimization of Hydrogen Sorption Kinetics.
Andreas Borgschulte 1 , Gagik Barkhordarian 3 , Robin Gremaud 2 , Ronald Griessen 2 Show Abstract
1 Hydrogen & Energy, EMPA, Dübendorf/Zürich Switzerland, 3 Institute for Materials Research, GKSS-Research Center Geesthacht GmbH, Geesthacht Germany, 2 FEW, Condensed Matter Physics, Vrije Universiteit Amsterdam, Amsterdam Netherlands
12:15 PM - Z8.9
Nanostructured Magnesium for Hydrogen Storage.
Rudy Wagemans 1 , Joop van Lenthe 2 , Krijn de Jong 1 , Petra de Jongh 1 Show Abstract
1 Inorganic Chemistry and Catalysis, Utrecht University, Utrecht Netherlands, 2 Theoretical Chemistry, Utrecht University, Utrecht Netherlands
12:30 PM - Z8.10
Microstructure of the MgH2 Synthesized by Hydriding Chemical Vapor Deposition.
Itoko Saita 1 , Takeshi Toshima 1 , Satoshi Tanda 1 , Tomohiro Akiyama 2 Show Abstract
1 Graduate school of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan, 2 Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo, Hokkaido, Japan
Magnesium has been considered as a competent hydrogen storage media because it stores the largest amount of hydrogen as much as 7.6 mass% in the form of MgH2, and due to the inexpensive and abundant raw material. However, it is hardly achieved to prepare highly pure MgH2 by the conventional method of solid-gas reaction between solid magnesium and hydrogen even under the conditions of repeating hydrogenation/dehydrogenation, adding second element as a catalyst, or pulverizing into micro- or nano-orders because of the low hydrogen diffusivity. Therefore, we have proposed and succeeded to synthesize MgH2 by novel method dubbed “Hydriding Chemical Vapor Deposition (HCVD)” . In the HCVD, the magnesium as raw material was heated and evaporated in highly pressurized hydrogen at 4 MPa and the gaseous mixture of the magnesium vapor and the hydrogen was cooled on a substrate, depositing MgH2 as the product. Very interestingly, the HCVDed MgH2 was made of single crystals with fibrous figures, which showed the diameter less than 500 nm and the length larger than 100 μm. The results appealed a revolutionary productive route for metal hydride, which offers more benefits for simplifying the productive procedure, minimizing processing time, saving energy, and upgrading the product. However, further detail of the HCVDed product had not been studied. Therefore the aim of this study was to examine the HCVDed MgH2 in hydrogen storage and to observe the microstructure of the HCVDed MgH2 after the hydrogen desorption and absorption. As the results of Pressure-Composition-Isotherm (PCT) measurement, the HCVDed MgH2 reversibly absorbed and desorbed 7.6 mass% hydrogen, as much as the theoretical maximum hydrogen capacity of magnesium, without any activation treatment. In addition, the absorption and desorption took for 2 hours and 1 hour, respectively. This result revealed that the hydrogen charging-releasing rate of the HCVDed MgH2 was relatively large, and the HCVDed MgH2 had high activity for hydrogen storage despite very low hydrogen diffusivity of magnesium that usually prevents magnesium from being activated enough by the current activation treatment. The decomposition pressure of the HCVDed MgH2 was slightly lower, 0.07 MPa at 560 K, than the reported value, 0.1 MPa at 563 K. According to the observation by Scanning Electron Microscope, the fibrous figure of the HCVDed MgH2 was kept even after the hydrogen releasing and charging though the fiber had been shortened during hydrogen release.  I. Saita et al., Mater. Trans., 47 (2006) 931-934.
12:45 PM - Z8.11
Thermo-chemistry of Li- and B-doped MgH2 Clusters.
Paul Kung 1 , Alexander Goldberg 1 , Jian-jie Liang 1 Show Abstract
1 , Accelrys Inc., San Diego, California, United States
Difficulty in finding efficient, inexpensive hydrogen storage materials is one of the major obstacles in realizing the new hydrogen economy worldwide. One material that has potential is MgH2. The recent work of Johnson et al. showed that MgH2 could be further enhanced by doping with LiBH4.In this work, we used all-electron DMol code based on density functional theory to investigate the H-desorption thermo-chemistry of Li2B2Mg20H48 nanoparticles. We found that thermo-chemically stable nanoparticles of the nominal composition of LiBMg10H24/LiBMg10 can exist and our calculation validate the experimental results seen to date. In particular, we found configurations of the nominal composition of LiBMg10H24 that gives higher enthalpy of H-sorption/desorption, as compared to the parent materials.------------- Johnson et al., Chem. Commun., 22, 2823 (2005). see, e.g., J. J. Liang, Appl. Phys. A, 80, 173 (2005). B. Delley, J. Chem. Phys. 92, 508 (1990). MS DMol is a product of Accelrys Inc.
Z9: Hydrogen Storage Modeling & Analysis
Thursday PM, November 30, 2006
Independence E (Sheraton)
2:30 PM - **Z9.1
Theory and Modeling of Materials for Hydrogen Storage
Gerbrand Ceder 1 , Tim Mueller 1 , Caetano Miranda 1 Show Abstract
1 DMSE, MIT, Cambridge, Massachusetts, United States
Computational materials science tools such as density functional theory (DFT) are playing an increasingly important role in searching for and characterizing promising hydrogen storage materials. We have applied a full range of first-principles characterization and optimization techniques to predict and calculate the structure, energetic, phase stability and thermodynamics of novel hydrogen storage materials (lithium imide and ammonia-borane). Lithium imide (Li2NH) is a candidate material for hydrogen storage but its structure has proven difficult to fully characterize. The structure of lithium imide is believed to resemble the anti-fluorite structure, with lithium cations and NH anions.1 To find the orientation of the N-H bonds we have created a model Hamiltonian that expresses the energy of lithium imide as a function of the N-H bond orientations. Using this Hamiltonian it is possible to identify favorable interactions and rapidly search for low-energy structures. This search predicts the existence of a new candidate ground state structure for lithium imide. Density functional theory calculations confirm that this new structure has lower formation energy than any previously considered structure. We present this structure and compare it to published experimental data on lithium imide. In addition to this, the thermodynamic, structural and electronic properties of ammonia-borane complexes have been fully characterized by first principles calculations within DFT. The calculated thermodynamic functions (free energy, enthalpy and entropy), obtained within harmonic approximation, are in good agreement with the available experimental data. The enthalpies of the hydrogen release reactions for all decomposition products reported experimentally have been determined by including the zero point energy and finite temperature effects. Those results provide important information about the regeneration process of ammonia-borane complexes. The borazine-cyclotriborazane (poly-borazylene) cycle has a strong exothermic decomposition character (~ -10 kcal/mol), which implies the necessity of an alternative chemical process to recover ammonia-borane. Hydrogen bonding in both systems has been characterized by electronic structure analysis. This is valuable information for the study of catalytic hydrogen release from metal and chemical hydrides. 1K. Ohoyama, Y. Nakamori, S. Orimo, et al., Journal of the Physical Society of Japan 74, 483 (2005).
3:00 PM - Z9.2
Estimating the Enthalpy of Formation of Complex Hydrides using First Principles and Global Optimization Techniques.
Eric Majzoub 1 , Vidvuds Ozolins 2 Show Abstract
1 MS 9403, Sandia National Laboratories, Livermore, California, United States, 2 Engineering and Applied Science, UCLA, Los Angeles, California, United States
Rapid thermodynamic assessment of candidate hydride materials is important for reducing the time needed for materials development in the area of hydrogen storage. Many promising materials fall in the class of complex ionic hyrdides, such as NaAlH4, or Mg(BH4)2, where the anionic complexes AlH4- and BH4- are charge balanced in a cation matrix. Many such materials are made available through wet chemical and perhaps solid state synthesis routes. From electronic structure studies of many of these materials, it is known that electrostatics dominates the cohesive energy, from which one can calculate an estimate of the enthalpy of decomposition. First-principles calculations of the cohesive energy requires a crystal structure for input. We have developed a global optimization technique using Metropolis Monte Carlo with minimization and basin-hopping, to m