Gholam-Abbas Nazri General Motors R&D Centre
Chen Ping National University of Singapore
Aline Rougier Laboratoire de Reactivite et Chimie des Solides
Azarnoush Hosseinmardi Magna Steyr
S1: Metal Hydride Hydrogen Storage I
Monday PM, November 26, 2007
Room 309 (Hynes)
9:30 AM - **S1.1
Crystal Structures and Hydrogenation Behaviors of the RMn (3≤n<5) ''Superlattice” Alloys.
Etsuo Akiba 1 , Y. Chai 1 , Jin Nakamura 1 , Hirotoshi Enoki 1 , Kouji Sakaki 1 , Kohta Asano 1 , Yumiko Nakamura 1 Show Abstract
1 ETRI, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki Japan
RMn (3≤n<5) (R= rare earth, M=transition metal) type intermetallic compounds with various stacking structures were reported by Kadir et al. . Kohno et al. reported that (La, Mg)(Ni, Co)n (n=3.0-4.0) alloys have higher discharge capacity and significant rate capability than conventional AB5-type alloys . This type of intermetallic compounds consists of [AB5] and [A2B4] layers. Both AB5 and AB2 Laves phase alloys are the most popular hydrogen absorbing alloys. Today, this type of alloy that was named as the “superlattice alloy” by SANYO is used for the negative electrode of commercially available Ni-hydrogen batteries.In this study, the crystal structures of La4MgNi19 and its full hydride were refined using powder neutron diffraction. The metallic sublattice kept the same structure with hydrogenation and dehydrogenation. Mg selectively occupied the La site in the [A2B4] layer same as we have already reported using single crystal analysis . The structural change for La0.7Mg)0.3Ni2.8Co0.5 with hydrogenation and dehydrogenation was measured using in-situ X-ray diffraction. The alloy is composed of more than 80 % of Ce2Ni7-type La3Mg(Ni,Co)14 and other minor phases of PuNi3-type La2Mg(Ni,Co)9, Pr5Co19-type La4Mg(Ni,Co)19 and LaNi5-type phase. Metal sublattice of the Ce2Ni7-type phase was stable with hydrogenation and dehydrogenation up to H/M = 1.0. The lattice expansion was isotropic and volumetric expansion with hydrogenation was 22.7%. K. Kadir et al. J. Alloys Comp., 257, 115 (1997). T. Kohno et al., J. Alloys Comp., 311, L5 (2000). H. Hayakawa et al., Meter. Trans., 46, 1393 (2005).
10:00 AM - S1.2
Phase Transformation and Structural Properties of La(Ni5-xCox) Hydrides.
Yumiko Nakamura 1 , Etsuo Akiba 1 Show Abstract
1 ETRI, AIST, Tsukuba, Ibaraki, Japan
La(Ni5-xCox) have a CaCu5 structure for any ratio of Ni and Co, while Ni-rich (x ≦ 1) and Co-rich (x ≧ 2) compositions take different phase transformation upon hydrogenation . In particular, the alloys for x = 2 and 3 form four hydrides subsequently: α (hexagonal), β (orthorhombic), γ (orthorhombic), and δ (hexagonal). The first three are similar to hydrides of LaCo5. We found the δ phase unique to x = 2, 3 using in situ X-ray diffraction .In this study, the crystal structure of δ-La(Co3Ni2)D6 was investigated using powder neutron diffraction. The data was collected under 3 MPa of D2 on the 90-deg banks of Sirius at KENS (Tsukuba, Japan). Hydrogen occupation and lattice expansion are discussed in comparison with other hexagonal La(Ni, M)5 hydrides. Y. Nakamura, T. Nomiyama, E. Akiba, J. Alloys Compd., 413 (2006) 54.
10:15 AM - S1.3
A Numerical Analysis of the Influence of the Effective Thermal Conductivity on the Cooling Mechanisms of Ti-Cr-V(-Fe) Solid Solution Metal Hydride Beds in Hydrogen Storage Vessels.
Sang-kun Oh 1 , Kyung-Woo Yi 1 , Sung-Wook Choi 2 Show Abstract
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Minerals & Materials Processing Research, Korea Institute of Geoscience & Mineral Resources, Daejeon Korea (the Republic of)
Storage of hydrogen in metal hydride alloys is a promising technology which offers high potential storage density in a safe solid state. A major factor to be considered for the use of these alloys in storage applications is the significant amount of heat which is released during the exothermic hydrogen absorption process, as well as the consequent need for effective cooling methods. Various difficulties are involved in large-scale experimentation of these phenomena in storage vessels. Therefore numerical analysis of simulation models is a more practical and effective approach. The thermal conductivity of a metal hydride bed has a major impact on its thermal profile during the hydrogen absorption process. Because of the complex nature of the metal hydride powders, an accurate simulation model requires the use of an effective thermal conductivity value (Kef) which reflects the conductivity of the bed as a whole. This value takes into account both the metal hydride material itself and the gas occupying the spaces between the powder particles. In this study, we incorporate experimentally obtained Kef values for Ti-Cr-V and Ti-Cr-V-Fe solid solutions into numerical model simulations to predict the heating mechanisms and temperature profiles for various bed formations of these alloys. The results are then used as a reference to define appropriate parameters for simulation models which take the hydride powder and gas elements into account separately, in order to treat the metal hydride beds more accurately as porous media. Based on the resulting thermal profiles, a number of possible cooling facilitation methods and their effects on the alloy bed are investigated through additional numerical simulations.We were able to conclude through these simulations that higher effective conductivities result in significantly enhanced cooling behavior for most configurations of Ti-Cr-V and Ti-Cr-V-Fe beds. Consequently, a number of methods are proposed to increase the effective thermal conductivity Kef, and thereby facilitate the cooling of the beds.
10:30 AM - S1.4
Direct Production of the Ni–Ti–Zr Icosahedral Phase for Hydrogen-storage Applications by Rapid Quenching from the Melt.
Andraz Kocjan 1 , Paul McGuiness 1 , Aleksander Recnik 1 , Spomenka Kobe 1 Show Abstract
1 Department for nanostructured materials, Joseph Stefan Institute, Ljubljana Slovenia
Our study focused on the formation of Ti40Zr40Ni20 icosahedral (i-phase) quasicrystals directly from the melt and their subsequent characterization and high-pressure hydrogenation. The samples were produced in an inert-gas melt-spinning device from a series of arc-melted precursor buttons of approximately 9 grams. The buttons were melted at 1400°C in a boron-nitride crucible with a 1.5-mm nozzle so as to produce broad melt-spun ribbons at various wheel speeds. By varying the wheel speeds we were able to produce a range of crystallographic structures, from amorphous, through quasicrystalline, to crystalline. The structures were crystalline at 12 m/s, quasicrystalline at 22 m/s and amorphous above 28 m/s. Initially, we studied the dependence of ribbon thickness (d) and saturation magnetization (Ms) on the wheel speed. The ribbon thickness showed the expected exponential reduction with wheel speed, from 120 microns to 30 microns, while the Ms exhibited a surprisingly modest change with wheel speed; varying between 0.03 and 0.02 emu/g. The XRD analysis showed that depending on the cooling rate (controlled by the wheel speed) it was possible to freeze the icosahedral phase directly from the melt, without the need for any subsequent heat-treatment steps, at 22 m/s. We believe this represents the first report of such direct formation of the icosahedral phase for this material. Using the same procedure to test the range of formation wheel speeds for a comparable system we also produced the samples containing up to 3 atomic % copper. Using transmission electron microscopy we have confirmed that the ribbons contain nanosized particles of Ti40Zr40Ni20 icosahedral phase imbedded in an amorphous matrix with same composition. The average particle size of the i-phase was approximately 20 nm. The 5-fold symmetry was confirmed by selected-area electron diffraction and high-resolution TEM having the crystallite oriented close to the symmetry axis. Both our XRD measurements and the TEM observations have provided direct evidence for the quasicrystalline ordering of Ti40Zr40Ni20 by rapid quenching from melt. To test the hydrogen-absorption properties of the icosahedral phase we crushed ribbons into finer particles to provide fresh, new surfaces to aid hydrogen dissociation at the metal surface. The uptake of hydrogen was found to be critically dependent on the surface state of the Ni–Ti–Zr ribbons; even modest exposure to the atmosphere produced a protective layer of oxide on the surface that practically prevented any hydrogen being taken up by the icosahedral phase. However, when the ribbons were crushed in a protective argon atmosphere it became possible to 95% charge the phase with hydrogen. The extent of hydrogen charging was determined from the shift in the XRD peaks, and we observed a near-linear dependence between the [H]/[M] ratio and the quasi-lattice constant aq. The calculated expansion of aq was 6% and the corresponding [H]/[M] value was 1.5.
10:45 AM - S1.5
Improving the Packing Density of Adsorbed Hydrogen and a Novel Configuration of Hydrogen Molecules in MOF-74.
Yun Liu 1 2 , Houria Kabbour 3 , Craig Brown 1 4 , Dan Neumann 1 , Channing Ahn 3 Show Abstract
1 Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 3 Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States, 4 Indiana University Cyclotron Facility, Indiana University, Bloomington, Indiana, United States
Metal-organic frameworks (MOFs) are promising hydrogen storage candidates due to their high surface areas. To achieve technologically relevant levels, the hydrogen packing density as well as the total available surface area are critical metrics. MOF-74 is used as a model material showing significant packing density. The hydrogen adsorption sites in MOF-74 are identified for the first time using neutron powder diffraction and a shorter H2-H2 interaction distance is observed than is expected given the nearest neighbor distance of solid H2. Of significance is the presence of coordinatively unsaturated metal centers. Inelastic neutron scattering spectra measured at different temperatures reveal large binding energy differences between some adsorption sites. Moreover, the adsorbed hydrogen molecules form a one-dimensional nanotube-like structure. These results extend our insights into physisorbed hydrogen molecules in micro-porous media including MOFs, carbon nanotubes/nanohorns and amorphous carbons.
11:45 AM - S1.7
Positron Lifetime Dtudy of the Lattice Defect Formation by Hydrogenation in Ti-based BCC Alloys.
Kouji Sakaki 1 , Kenji Iwase 1 , Yumiko Nakamura 1 , Yasuharu Shirai 2 , Etsuo Akiba 1 Show Abstract
1 Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan, 2 Department of Materials Science and Engineering, Osaka University, Suita Japan
Ti-based BCC alloys developed by Iba and Akiba in 1995  have twice larger gravimetric hydrogen capacity than that in conventional hydrogen storage alloys such as AB5 and AB2 type alloys. Ti-based BCC alloys are one of the candidates for hydrogen storage media in fuel cell vehicles. Although these have higher gravimetric density of hydrogen, the decrease of capacity with cycles should be improved for the practical use. Our previous results for AB5 alloys suggested that the concentration of the lattice defects introduced by hydrogenation is close related with the cyclability . In this study, we investigated the introduction of the lattice defects in Ti45Cr55-xMox (x=15, 30) alloys and their thermal stability by the positron lifetime measurement.In-situ positron lifetime measurement showed that lattice defects started to be introduced even in the hydrogen solid solution region and they remained after dehydrogenation. Further hydrogenation to hydride-phase region increased the concentration of lattice defect. The annealing experiments showed that introduced lattice defects were vacancy and dislocation. The onset temperatures of their migration were 573 and 1173 K, respectively. They were completely recovered around 773 and 1573K, respectively.The release behavior of the residual hydrogen that is settled down in the activated sample even after evacuation was investigated by TG-DTA measurement in Ti45Cr25Mo30. The release of the residual hydrogen started around 550 K and then was completed below 773 K. This temperature region well agrees with the vacancy migration temperature. It suggests that the vacancy introduced by hydrogenation is coupled with the residual hydrogen. Similar result has been reported in LaNi5 alloy .We found the reversible phenomenon of vacancy introduction and recovery during hydrogenation and dehydrogenation in LaNi4.93Sn0.27 . If we appended this reversible property into Ti-based BCC alloys, we could dramatically improve the hydrogen storage capacity and degradation behaviors of Ti-based BCC alloys. H. Iba and E. Akiba: J. Alloys Compd. 231 (1995) 508. Kouji Sakaki, Ryosuke Date, Masataka Mizuno, Hideki Araki, Yumiko Nakamura, Yasuharu Shirai, Robert C. Bowman, Jr. and Etsuo Akiba: to be published. K. Sakaki, H. Araki and Y. Shirai: Mater. Trans. 43 (2002) 1494.
12:00 PM - S1.8
Effects of Carbon Nanostructures and AB2 Alloy Additives on Hydrogen Storage Properties of Magnesium.
Sundara Ramaprabhu 1 , Srinivas G Srinivas 1 Show Abstract
1 , Indian Institute of Technology Madras, Chennai India
12:15 PM - S1.9
Carbon Nanotube/Zr-based Alloy Nanocomposites as Electrode Material for Nickel-metal Hydride Batteries.
Sundara Ramaprabhu 1 , G. Srinivas Srinivas 1 Show Abstract
1 , Indian Institute of Technology Madras, Chennai India
12:45 PM - S1.11
Investigation of Hydrogen Storage Using Combinatorial Thin Films and IR Imaging.
Hiroyuki Oguchi 1 , Ichiro Takeuchi 1 , Daniel Josell 2 , Edwin Heilweil 2 , Leonid Bendersky 2 Show Abstract
1 Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Hydrogen storage is one of the stumbling blocks for the practical use of hydrogen as a new source of energy for transportation. Absorption and desorption of hydrogen by a storage material depends on the materials precise composition and microstructural state. Combinatorial thin films with continuously changing composition provide an opportunity for studying a wide range of compositions and microstructures (amorphous, nanocrystalline, single crystal, multiphases) on a single substrate. Here we report preparation, characterization and hydrogenation of MgxNi1-x thin films with a Pd overlayer. Mg-rich MgxNi1-x, has good gravimetric density of hydrogen. Capping the film with a Pd layer is known to both prevent oxidization and catalyze hydrogenation reaction. These 200 nm-thick, square-shape films have compositional variation in one in-plane direction and variation in Pd thickness (from 0 to 20 nm) in the other direction. Therefore rapid study of hydrogen absorption/desorption properties of various compositions with various thicknesses of Pd catalytic layer is possible in just one experiment. Structures of the films were characterized by scanning x-ray and cross-sectional TEM. Hydrogen absorption/desorption of the films was monitored with an infrared (IR) CCD camera that could image the full area of the substrate. The observed changes in infrared intensity were attributed to changing electronic states of the MgxNi1-x thin films upon accommodation of hydrogen. In the study reaction temperature and kinetics dependence on the alloy composition and Pd layer thickness were obtained.
S2: Metal Hydride Hydrogen Storage II
Monday PM, November 26, 2007
Room 309 (Hynes)
2:30 PM - S2.1
The Effect of Specific Surface Area and Chemistry of Inco Nano Ni on the Improvement of Hydrogen Storage Properties of MgH2.
Robert Varin 1 2 3 , Tom Czujko 1 2 3 , Zbigniew Wronski 1 2 3 , Eric Wasmund 1 2 3 Show Abstract
1 Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, Canada, 2 CANMET Energy Technology Centre, Natural Resources Canada, Ottawa, Ontario, Canada, 3 , INCO Special Products, Mississauga, Ontario, Canada
2:45 PM - S2.2
Hydrogen Storage in Mg-2 wt.% Multiwall Carbon Nanotubes Composite Processed by Equal Channel Angular Pressing.
Eugen Rabkin 1 , Vladimir Skripnyuk 1 , Yuri Estrin 2 3 , Leonid Bendersky 4 , Arnaud Magrez 5 , Efrain Carreno-Morelli 6 Show Abstract
1 , Technion, Haifa Israel, 2 , Monash University, Clayton, Victoria, Australia, 3 , CSIRO Division of Manufacturing and Materials Technology, Clayton, Victoria, Australia, 4 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 5 , Swiss Federal Institute of Technology, Lausanne Switzerland, 6 , University of Applied Sciences of Western Switzerland, Sion Switzerland
A Mg-based composite material containing 2 wt.% of multiwall carbon nanotubes (MWCNT) was synthesized by hot isostatic pressing of a mixture of Mg powder with MWCNT. In addition, the as-sintered composite was processed by one or two passes of equal channel angular pressing (ECAP). The hydrogen storage properties of the prepared materials were determined by volumetric method and compared with those of pure Mg. It was found that addition of MWCNT to Mg eliminates the pressure hysteresis and increases the slope of the pressure plateau in the "pressure-composition" isotherms measured at 573 K. The kinetics of hydrogen desorption is also significantly enhanced. The hydrogen desorption pressure in the middle of plateau region for the as-sintered composite is by about 50% higher than that for pure Mg. Surprisingly, ECAP processing of the as-sintered composite lowers hydrogen desorption pressure, although it still remains higher than for pure Mg. This is in contrast with the results of previous studies in which it was shown that ECAP processing of Mg-based alloys increases hydrogen desorption pressure. Transmission electron microscopy observations of the ECAP processed composite indicate that the changes in morphology of Mg-MWCNT interface upon ECAP may be responsible for the deterioration of hydrogenation properties.
3:00 PM - S2.3
MgH2 - Aerogel Composite for Hydrogen Storage.
Yanjia Zuo 1 , Chunwei Wu 1 , Sam Mao 2 , Taofang Zeng 1 Show Abstract
1 Mechanical Engineering, North Carolina State Univ., Raleigh, North Carolina, United States, 2 , Berkeley National Laboratory, Berkeley, California, United States
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, which has high specific surface areas (600–1000 m2/g), large pore volumes (1–4 cm3/g), and nano-pore radius (around 10 nm). In this study, we further incorporate magnesium hydrides into other nanoporous materials with doped catalysts. BET shows that MgH2/aerogel still has a surface area of 877.9m2/g and pore size of 6.36 nm. Low decomposition temperature (260C0) and promising capacity of hydrogen were also confirmed from XRD and DSC.
3:15 PM - S2.4
Insights from First Principles Simulation into the Mechanisms of Catalysed Hydrogen Release from MgH2 Surfaces via Nickel Doping and Ammonia-Borane Adsorption.
Stephen Shevlin 1 , Zheng Guo 1 Show Abstract
1 Materials, Queen Mary, University of London, London United Kingdom
Energy consumption intimately linked to CO2 emission, a major human contributor to climate change and thus currently of major worldwide concern. In order to combat this a switchover to cleaner fuels, of which hydrogen is a prime alternative, must be made. However in order to store hydrogen safely solid-state materials must be used. Magnesium hydride has long being considered as a prospective hydrogen storage material due to it’s cost, gravimetric, and volumetric properties, but to date applications have been limited because of poor thermodynamic properties leading to high temperature hydrogen release. Catalysis can aid this. In this talk we will present the results of first principles ab initio simulations on two different types of catalyst acting on magnesium hydride: transition metal dopants and molecules that possess hydrogen species that are electron acceptors. Transition metal dopants are well known to catalyse hydrogen release, while molecules that possess hydrogen electron acceptors should dehydrogenate metal hydrides that store hydrogen in electron donor form. The energetics of nickel substitution into bulk MgH2 and onto different surfaces of MgH2, and the effects of these dopants on hydrogen removal energies and the dehydrogenated structure will be presented. NiHx cluster formation is observed directly following Ni substitution, suggesting that in experimental systems solid solution (Ni, Mg)Hx is formed. The diffusion rates of hydrogen diffusion throughout bulk MgH2 and Ni-doped MgH2 will be calculated and compared. Additionally we present results on the chemisorption of the prospective hydrogen storage material ammonia-borane (H3BNH3) onto the (100) and (110) surfaces of MgH2. We find that the chemisorption of this molecule on the (100) surface is weak whereas on the (110) surface it is strong. Additionally this molecule is unstable with respect to dissociation into BH3 and NH3 components, which are thermodynamically preferred over dissociation into H2BNH2+H2 form. These separate molecular components then attack the MgH2 surface, strongly reducing the removal energy for hydrogen with respect to the removal energy for ideal MgH2 and allowing hydrogen release at lower temperatures. The effects of finite temperature and the rate-limiting step for these dissociation reactions will be discussed.
3:30 PM - S2.5
Composition Dependence of Electrical Resistivity of Magnesium-cobalt Films During Hydridation and Dehydridation.
Yiu Bun Chan 1 , Chung Wo Ong 1 Show Abstract
1 Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hong Kong China
Magnesium-transition metal alloys are interested because of their ability of storing and releasing hydrogen. The reactions involve reversible transitions between a metallic state and a hydride state, which are accompanied by drastic changes in electrical conductivity and optical transmission. Thin films of these materials are further investigated because of the potential of being used in switchable mirrors, hydrogen sensors, and many other conceived applications. In this study, we focused on the Mg-cobalt (Co) thin film system. Film samples were prepared by co-sputtering a Mg target and a Co target. The ratio of the sputtering powers was set such that films of various compositions covering a broad range were fabricated. Each film was covered with a palladium (Pd) overcoat with a thickness less than 10 nm to protect the film from oxidation. The film structure was investigated by using X-ray diffraction (XRD). Except the films containing predominantly one metal, the diffraction patterns of Mg-Co films with other compositions in between only showed broad halos. This suggests that the structure of Mg-Co films is highly disordered and not isostructural to any known stochiometric Mg-Co compounds. X-ray photoelectron spectroscopy (XPS) analysis provided information on the depth profiles of elemental composition. Pd was only detected at shallow depths. Conspicuous amount of oxygen was found in the Pd layer, and started to drop from the Pd/Mg-Co interface with increasing depth. Mg showed a peak value near the Pd/Mg-Co interface and a coherent drop with oxygen content along depth. This leads one to suggest that oxygen atoms can penetrate through the Pd layer and react with Mg, inducing more Mg atoms to diffuse towards the top surface. At deeper regions, the Mg:Co ratio approached some stable value in accordance with the power ratio used to prepare the sample. Prolonged exposure to air resulted in significant oxidation, as reflected by XPS data and the appearance of pits on the film surface. The change of electrical conductivity (σ) of a sample in a small chamber was continuously monitored during hydridation and dehydridation at room temperature. Each cycle consisted of exposure to 15% hydrogen in argon at 105 Pa (10 min), followed by evacuation to rough vacuum and then exposure to air (10 min). In general, the value of σ of a film with a higher Mg content showed a stronger drop in the hydridation process, but the response times for both hydridation and dehydridation processes were longer, such that the range of the change in σ in the subsequent cycles appeared to be smaller.
4:30 PM - **S2.7
A Study of Hydrogen Absorption in Magnesium.
Fereshteh Ebrahimi 1 , Mahesh Tanniru 1 , Ki-Joon Jeon 2 , Chang-Yu Wu 2 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida, United States
The kinetics of hydride formation during the hydrogenation of a Mg powder coated with nano-size nickel catalyst was investigated. The caoting was performed using a dry system (Theta Composer, Tokuju Corp.). Hydrogen absorption experiments were conducted using a custom-made hydrogenation system. TEM analysis of a sample prepared using FIB technique revealed that the hydride formation took place in a zone near the surface of the magnesium particle. The large volume expansion due to the hydride formation caused microcracking along the grain and twin boundaries of the magnesium powder and hence revealed the reacted layer. While XRD and TGA tests confirmed the presence of magnesium hydride, none was found in the thin foil. However, nanocrystalline magnesium was observed in the reacted zone. Consistent with previously reported studies, it is believed that the instability of hydride under the electron beam caused the release of hydrogen and resulted in the development of an extremely fine microstructure. The analysis of hydrogenation results revealed two distinct stages. In this presentation, the processes of nucleation and growth of magnesium hydride and their correlation with the kinetics of hydrogen absorption will be discussed.
5:00 PM - S2.9
Hydrogen Sorption Properties and the Microstructure of Mg-Al Alloys and of MgH2 - Carbon Nanotube Composites.
David Mitlin 1 , Julian Haagsma 1 , Mohsen Danaie 1 , Babak Shalchi 1 , Erik Luber 1 , Colin Ophus 1 , Helmut Fritzsche 3 , Velimir Radmilovic 2 , Ulrich Dahmen 2 Show Abstract
1 Chemical And Materials Engineering, University of Alberta and NINT, Edmonton, Alberta, Canada, 3 Canadian Neutron Beam Centre , Chalk River Laboratories , Chalk River , Ontario, Canada, 2 NCEM, Lawrence Berkeley National Laboratory, University of California, Berkeley, California, United States
This study focuses on Mg-Al alloy thin films, and on high-energy ball milled magnesium hydride powder-carbon nanotube (CNT) composites, as potential candidates for low temperature hydrogen storage. To characterize the sorption properties of these materials we employed gravimetric methods, combined with differential scanning calorimetry and neutron reflectometry. In parallel, we explored the materials’ microstructure in detail, through the use of transmission electron microscopy (TEM) and x-ray diffraction (XRD). We found that we can create metastable Mg-Al alloys that are either supersaturated solid solutions, or amorphous-nanocrystalline composites by room temperature co-sputtering. These materials show tremendously improved absorption and desorption, with appreciable (4.5 - 6wt.%) hydrogen capacity that can be readily charged and discharged at temperatures as low as 150°C. Neutron reflectometry demonstrated that after sorption, the hydrogen is uniformly dispersed throughout the films, and does not segregate to either the film-substrate nor the film-Pd overlayer interface. We also explored the microstructural stability of these alloys during sorption cycling. When testing the hydride powders, we observed that the desorption rate was significantly enhanced by the addition of mixed carbon nanotubes with the catalytic nanoparticles still attached. We also tested amorphous carbon and catalyst particles mixed with the magnesium hydride in the same weight ratio. This addition caused very little improvement in the desorption kinetics, indicating that there is something unique about the CNT-catalyst combination. Combined TEM and XRD analysis of the milled hydride powders indicated that much of the enhanced kinetics due to milling treatment was caused by the introduction of defects, rather than the reduction in the particle or the grain size.
5:15 PM - S2.10
Hydrogen Desorption from Pd Capped Mg Based Switchable Mirrors.
Erdni Batyrev 1 , Ruud Westerwaal 1 , Martin Slaman 1 , Bernard Dam 1 , Ronald Griessen 1 Show Abstract
1 Department of Physics and Astronomy, Condensed Matter Physics, Free University Amsterdam, Amsterdam Netherlands
The hydrogen adsorption properties of Pd are very well-studied. This inspired the use of Pd caplayers to enhance the reversible absorption of hydrogen by an underlying transition metal hydride. The hydrogen desorption from a metal hydride through Pd caplayer appears to be more complex than expected. At room temperature, desorption is severely hampered in UHV, while a bit of oxygen triggers desorption immediately. We measured the optical reflection change of Pd-capped Mg based films to probe the kinetics of the hydrogen absorption and desorption through the Pd caplayers . To measure the optical properties in-situ from the substrate side we deposited the films on the freshly cleaved surface of multimode optical microfiber in a metal MBE-system, at a background pressure of 3×10-8 mbar. The light from a halogen source was reflected from the backside side of the deposited metallic film and guided through the optical fiber to the Ocean Optics USB 2000 CCD spectrometer. The hydrogenation was performed at 1 bar of 5 N purity hydrogen while for dehydrogenation the chamber was pumped to below 10-8 mbar. A huge difference between absorption and desorption kinetics of Pd coated Mg-based films was found. The 100 nm Mg2Ni/10 nm Pd film was loaded in 15 s while the unloading took 32000 s. This is in contrast to a single Pd film of 100 nm where the hydrogen absorption and the desorption kinetics are equally fast in 15 s. Depositing a fresh Pd-layer of only a few nanometers on top of the blocked Pd layer improves the dehydrogenation kinetics by a factor 100 and the film unloads in 674 s. Similarly, a short Ar sputtering of the Pd caplayer removes the blocking mechanism and results in an increased hydrogen desorption. The possible mechanisms of the hydrogen desorption behaviour will be discussed in light of surface/subsurface hydrogen , differences in expansion of Pd and Mg2Ni lattices upon hydrogenation and the effect of surface impurities. Additionally, the role of the driving force for hydrogen diffusion through an intermediate layer will be discussed . These findings offer interesting perspectives for the development of hydrogen storage/sensor technologies. R. Westerwaal et al.: Catalysis of hydrogenation of Pd capped Mg based switchable mirrors, to be published D. Farias et al.: Helium Diffraction Investigations of the Transition of Chemisorbed Hydrogen into Subsurface Sites on Palladium Surfaces, Phys. Stat. Sol. (a) 159, 1997, 255 M. Pasturel et al.: Influence of the chemical potential on the hydrogen sorption kinetics of Mg2Ni/TM/Pd (TM = transition metal) trilayers, Chem. Mater. 19, 2007, 624
5:30 PM - S2.11
Methane Decomposition over Defective Carbonaceous Materials for Hydrogen Generation.
Liping Huang 1 2 3 , Erik Santiso 1 3 , Keith Gubbins 1 3 , Marco Buongiorno Nardelli 2 3 Show Abstract
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Department of Physics, North Carolina State University, Raleigh, North Carolina, United States, 3 Center for High Performance Simulation (CHiPS) , North Carolina State University, Raleigh, North Carolina, United States
5:45 PM - S2.12
Electron Beam Coated Pt-Sn and Pt Thin Film/MWNT Electrocatalysts for Direct Ethanol Fuel Cell.
Imran Jafri 1 , Leela Mohana Reddy 1 , Sundara Ramaprabhu 1 Show Abstract
1 , Indian Institute of Technology Madras, Chennai India
S3: Poster Session: Hydrogen Storage Materials and Technology
Tuesday AM, November 27, 2007
Exhibition Hall D (Hynes)
9:00 PM - S3.1
Thermodynamic Studies of the Palladium Hydrogen System.
Paul Nevitt 1 , Andrew Bailey 1 , Amanda Hynes 1 , Malcolm Pizey 1 , Linda Bulmer 1 Show Abstract
1 , AWE, Berkshire United Kingdom
9:00 PM - S3.10
Ab initio Calculations on Al and Si-substituted Magnesium Hydride.
Tuhina Kelkar 1 , Sourav Pal 1 , Dilip Kanhere 2 Show Abstract
1 Physical Chemistry Division, National Chemical Laboratory, Pune, Maharashtra, India, 2 Department of Physics and Center for Modeling and Simulations, University of Pune, Pune, Maharashtra, India
9:00 PM - S3.11
Hydrogen Degradation Property of Electrochemically Charged Aluminum.
Hiroshi Suzuki 1 , Daisuke Kobayashi 1 , Kenichi Takai 1 , Yukito Hagihara 1 Show Abstract
1 Mechanical Engineering, Sophia University, Tokyo Japan
Degradation property of aluminum due to hydrogen is studied. A safe and efficient method to introduce hydrogen to aluminum is needed to access the material in the application. In this study, we chose the electrolytic charging method instead of high pressure gas to introduce hydrogen. Annealed and polished pure aluminum (99%) is used as a testing material. Hydrogen is introduced by electrolytic charge in aqueous solution. The value of electronic potential and the pH of the solution are chosen from -2.5 to 1.0 V and 2 to 10 so that corrosive, passive and stable state on the Pourbaix diagram is attained. The amount of hydrogen and its existing state in the material is analyzed by hydrogen desorption curves measured by the thermal desorption spectroscopy. Tensile properties are obtained to determine degradation property of the material due to hydrogen. The maximum amount of hydrogen introduced to pure aluminum is 18 mass ppm when charged in passivity region with addition of 0.1 mass % NH4SCN as a hydrogen recombination poison. The hydrogen desorption curves of the charged aluminum showed two peaks, one at less than 100 and the other around 400 degrees centigrade. The existing state of hydrogen corresponding to each peaks are identified as weakly trapped solute hydrogen and free hydrogen molecule located in uniformly distributed blisters of several microns of diameter. The fracture strain of tensile deformation decreased from 0.5 to less than 0.2 due to hydrogen charge. Hydrogen corresponding to the lower peak of desorption curve is released by heating up to 200 degrees, causing slight recovery of the fracture strain. Almost all hydrogen is released by heating up to 500 degrees. But the fracture strain remains the same as that of 200 degrees heated specimen. This indicates that solute hydrogen and blisters affects ductility of aluminum, whereas hydrogen molecule in blisters has no effect. The fracture strain of charged aluminum increases with faster strain rate during tensile deformation, showing inverse tendency compared with uncharged material. The fracture strain becomes constant when tested with strain rate faster than 10-3 s-1, where interaction between solute hydrogen and mobile dislocation becomes small due to large difference between rate of diffusion of hydrogen in the matrix and the average velocity of moving dislocations. Therefore the effect of solute hydrogen on ductility of aluminum comes from its interaction with mobile dislocations. The method to introduce hydrogen and analyze its existing state in aluminum developed in this study is applicable to obtain aluminum hydride that can be used as hydrogen storage material.
9:00 PM - S3.12
Synthesis, Properties and Applications of Porous Metal-Organic Framework Materials.
Gary DiFilippo 1 , Kunhao Li 1 , Wenhua Bi 1 , Jing Li 1 Show Abstract
1 Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey, United States
Metal-Organic Framework (MOF) materials have become a hot topic in recent years due to the myriad of applications they might find uses in, such as gas storage and separation. The draw of these hybrid, porous materials is that they combine the variety found in organic ligands with the properties of metal based compounds. For example, by employing a multitude of different building units, porous MOF materials with specific pore size, shape, and properties for specific application may be synthesized as desired. To increase the diversity and to modify the structures and properties of MOF materials different types of organic linkers are used. In this presentation, I will discuss our use of multiple ligands in structure construction of a new group of MOFs. Typically a dicarboxylate will act as a “linker” to bind with the metal center to form 1D chains or 2D layers, and another type of ligands, such as a dicarboxylate, amine or solvent molecule, will act as a “pillar” to form a three dimensional framework. The synthesis, structure, and properties of some of these materials will be displayed.
9:00 PM - S3.13
Enhancing Photoelectrochemical Hydrogen Production by Using TiO2-MgO Core-Shell-Structured Nanoparticles.
Shin-Tae Bae 1 , Jin Young Kim 1 , Sangwook Lee 1 , Hyun Suk Jung 2 , Taehoon Noh 1 , Kug Sun Hong 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Kookmin University, Seoul Korea (the Republic of)
TiO2-MgO core-shell-structured nanoparticles were prepared, and their photoelectrochemical characteristics for hydrogen production were investigated. The coating of a MgO layer onto TiO2 nanoparticles by the thermal topotactic decomposition of the Mg(OH)2 gel was clearly exhibited by high resolution transmission electron microscopy (HRTEM) and the MgO-modified TiO2 films showed maximum hydrogen production at 0.03 wt % addition of MgO. These photoelectrochemical characteristics with the amount of MgO addition were discussed in terms of competition of two factors such as the blocking effect and the resistivity of MgO coating layer. The MgO layer increased the water photolysis efficiency by retarding the electron-hole recombination, which was explained by the “blocking effect” of MgO coating layer with high band gap energy. On the other hand, the decrease of hydrogen production resulting from large amount of MgO addition was explained by increase in resistivity of MgO coating layer.
9:00 PM - S3.14
Catalyst Addition for Reduced Hydrogen Desorption Temperature of Ball-Milled MgH2.
Aline Rougier 1 , Nadir Recham 1 , Manickam Kandavel 1 , Vinay Bhat 1 , Luc Aymard 1 , Gholam Abbas Nazri 2 , Jean Marie Tarascon 1 Show Abstract
1 , LRCS, Amiens France, 2 , GM, Warren, Michigan, United States
Magnesium is among the most promising materials for hydrogen storage applications since it forms a dihydride providing 7.6 wt.% of hydrogen. Despite its high hydrogen content, the hydride formation is very slow and occurs at very high temperature (above 300 °C). Among the ways to improve its sorption properties, i.e. faster kinetics and reduced desorption temperature, the catalyst addition remains one of the most promising. As a matter of fact, we recently reported the desorption of 4.5 wt%. and 3 wt%. of H2 at temperatures as low as 200 °C and 150 °C for ball-milled MgH2 catalyzed with Nb2O5  and NbF5 , respectively. Investigation of other catalysts reveals that oxy-fluorine compounds are also active. In this presentation, the role of the catalyst on improving the sorption properties of ball-milled MgH2 will be discussed in relation with its chemical and physical nature.  V.V. Bhat, A. Rougier, L. Aymard, G.A. Nazri and,J-M. Tarascon J. of Alloys and Compounds, V. V. Bhat, A. Rougier, L. Aymard, G. Nazri, J.-M. Tarascon, J. of Alloys and Compds., doi:10.1016/j.jallcom.2007.05.084. N. Recham, V.V. Bhat, M. Kandavel, L. Aymard, J-M. Tarascon, and A. Rougier, J. of Alloys and Compounds, submitted.
9:00 PM - S3.15
Carbide-Based Fuel System for Solid Oxide Fuel Cells.
A. Burke 1 , Louis Carreiro 1 Show Abstract
1 Code 8231, Naval Undersea Warfare Center, Newport, Rhode Island, United States
Despite wide-ranging efforts to replace batteries with fuel cells in niche military applications, the transition is proceeding slowly, due in part, to the unique fuel storage requirements associated with fuel cell systems. In the case of underwater applications, such as unmanned undersea vehicle (UUV) propulsion, mass and volume constraints often dictate system energy density and specific energy, which must exceed 300 W-hr/L and 300 W-hr/kg, respectively, in order to compete with state-of-the-art battery technologies. To address this need, a novel carbide-based fuel system (CFS) intended for use with a solid oxide fuel cell (SOFC) is under development that is capable of achieving these energy metrics as well as sequestering carbon dioxide. The proposed CFS consists of a composite of calcium carbide and calcium hydride that when combined with water generates acetylene and hydrogen as the fuel and calcium hydroxide as a carbon dioxide scrubber. The acetylene is hydrogenated to ethane and then further processed by steam reforming to syngas (carbon monoxide and hydrogen) before being utilized by the SOFC. Carbon dioxide effluent from the SOFC is reacted with the calcium hydroxide to produce a storable solid, calcium carbonate, thus eliminating gas evolution from the UUV. In this paper, a system configuration is proposed and discussion follows concerning energy storage metrics, operational parameters and preliminary safety analysis.
9:00 PM - S3.16
First-Principles Study of a Hydrogen Molecule Interaction with Tin (N=3-8 and 13 Atoms) Clusters.
Jorge Medina-Garcia 1 , G. Canto 2 , R. de Coss 3 Show Abstract
1 Nanostructures Department, CICESE-UNAM, Ensenada, Baja California, Mexico, 2 Nanostructures Department, CCMC-UNAM, Ensenada, Baja California, Mexico, 3 Department of Applied Physics, CINVESTAV, Merida, Baja California, Mexico
There are theoretical works that report the use of Titanium atoms in order to increase the Hydrogen storage capacity of nanostructures. Also, some experimental works have been found that using clusters of Ti can be increasing its Hydrogen absorption capacity. Here, we show the energetic and structural properties of bare and Hydrogen decorated Titanium clusters (Tin clusters for n=3-8 and 13). We have performed density functional theory calculations with the SIESTA code. The wave functions are expanded on a Linear Combination of Atomic Orbitals (LCAO). We are employed the Generalized-Gradient Approximation (GGA) for the exchange-correlation. Our results for the bare clusters are in good agreement with works previously published. We consider several positions to hydrogen adsorption on the decorated clusters. We found a dissociative adsorption at the interstitial positions as the most probable in all clusters considered. Also, we show the structural results for the saturation of the interstitial sites on Ti13. Formation energies are showed.
9:00 PM - S3.18
Ti-coated Single-walled Carbon Nanotubes for Hydrogen Storage: A Spectroscopic and Microscopic Study.
Ich Tran 1 , Roberto Felix 1 , Lothar Weinhardt 1 , Marcus Baer 1 , Clemens Heske 1 , Oliver Fuchs 2 , Monika Blum 2 , Jonathan Denlinger 3 Show Abstract
1 Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada, United States, 2 Experimentelle Physik II, Universität Würzburg, Würzburg Germany, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
In recent years, carbon nanomaterials have drawn considerable attention as possible candidates for solid state hydrogen storage. In order to enhance their hydrogen storage capabilities, several theoretical publications have proposed models of transition metal atoms bound to carbon nanomaterials, for example Ti on single-walled carbon nanotubes (SWCNT) . In this contribution we will present an experimental investigation of the interaction between Ti and SWCNT. Thin layers of Ti were deposited onto SWCNT films under ultra-high vacuum conditions and investigated in-situ using photoelectron spectroscopy (PES) as well as scanning tunneling microscopy (STM) and spectroscopy (STS). In addition, synchrotron-based x-ray emission (XES) and x-ray absorption (XAS) experiments were performed ex-situ. The combination of laterally integrating techniques (PES, XES, and XAS) with microscopic approaches (STM and STS) results in a powerful tool chest to characterize the electronic and chemical structure, both at the surface and in the near-surface bulk. After Ti deposition, we observe a dramatic change of the C 1s line in PES, which indicates a strong interaction between Ti and C. In addition, the deposited Ti is found to act as a host for various adsorbates. In particular the formation of TiO and TiO2 can be concluded from the Ti 2p spectra, as well as the presence of carbon-containing adsorbates from the C 1s spectra. These findings, combined with results from XES, XAS, and STM/STS, exemplarily show the challenges associated with using Ti-decorated nanomaterials as a material for hydrogen storage, as will be discussed in this presentation.  T. Yildirim, S. Ciraci, Phys. Rev. Lett. 94, 175501 (2005)
9:00 PM - S3.19
Experimental Study on Feasible Metal Hydrides for Destabilization of Lithium Borohydrides.
Hongwei Yang 1 , Andrew Goudy 1 Show Abstract
1 Department of Chemistry, Delaware State University, Dover, Delaware, United States
Destabilization of lithium borohydrides for reversible hydrogen storage materials has been studied by using different metal hydrides as a destabilizer. First principles calculation predicts that CaH2 may be a potential candidate as destabilizing metal hydrides. In our experimental work, mechanically milled mixtures of LiBH4 and CaH2 are shown to store about 13 wt% hydrogen. The equilibrium pressures of absorption and desorption at the different temperature are measured and a van’s Hoff diagram is plotted, which are compared to those for pure LiBH4. In addition, the kinetics of absorption and desorption of destabilized LiBH4 will be discussed.
9:00 PM - S3.2
Porous Nanocomposites for Making Hydrogen Gas Via Water Photolysis.
S. M. Sarif Masud 1 , Geoffrey Saupe 2 Show Abstract
1 Materials Science and Engineering, University of Texas at El Paso, El Paso, Texas, United States, 2 Department of Chemistry, University of Texas at El Paso, El Paso, Texas, United States
9:00 PM - S3.20
Pt-coated Multiwalled Carbon Nanotube : Promising Hydrogen Storage in Fuel Cells.
A. Halder 1 , Ravishankar Narayanan 1 Show Abstract
1 Materials Research Centre, Indian Institute of Science, Bangalore India
Hydrogen storage is critical for developing energy sources based on fuel cells. Carbon nanotube is a potential medium for hydrogen storage and has unique properties such as light mass density, high surface to volume ratio and high degree of reactivity with hydrogen. But there are certain issues regarding the storage capacity of carbon nanotubes. Transition metals like platinum increase the storage capacity of carbon nanotubes by dissolving hydrogen. Here, we report a novel route to deposit nanoporous platinum on multi-walled carbon nanotube that combines the benefits of both porous platinum and carbon nanotube towards the hydrogen storage. This method relies on the synthesis of nanoporous Pt by fast reduction in a toluene medium containing functionalized carbon nanotubes. Microstructural studies have been carried out using high resolution transmission electron microscopy (TEM). Cyclic voltammetry(CV) studies have been carried out to verify the enhanced hydrogen storage capacity.
9:00 PM - S3.21
Hydrogen Permeability and Microstructures of Melt-Spun and Annealed Nb40Ti30Ni30 Ribbons.
Yuta Seki 1 , Koichi Kita 2 , Kazuhiro Ishikawa 1 , Kiyoshi Aoki 1 Show Abstract
1 Department of materials Science, Kitami Institute of Technology, Kitami, Hokkaido, Japan, 2 , Mithubishi Materials Corporation, Kitamoto, saitama, Japan
Pd-Ag based hydrogen permeation alloys are mainly used for separation and purification of hydrogen gas. However, since Pd is too expensive and a rare metal, it is strongly desired to develop non-Pd based alloys. Because hydrogen flux (J) passing through the alloy membrane is inversely proportional to its thickness, the preparation technique of alloy membranes is also important for the development of non-Pd based alloys.The Nb-TiNi alloys consisting of the bcc-(Nb, Ti) and the B2-TiNi phase show high hydrogen permeability equivalent to that of pure Pd. However, its membrane is prepared by means of complex processes such as cold rolling and intermediate annealing. On the other hand, it is well known that alloy ribbons can at a stroke be obtained by a melt-spinning technique. In the present work, hydrogen permeability, crystal structures and microstructures of melt spun Nb-TiNi alloy ribbons before and after annealing treatments are investigated in order to develop the preparation method of alloy membrane.The Nb40Ti30Ni30 (mol%) alloy ribbons were prepared by a melt-spinning technique. Its thickness was about 40 μm. The ribbon samples were annealed at various temperatures and periods. Microstructural observation and phase identification were carried out using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Chemical composition of the ribbon was measured by an electron dispersion X-ray spectroscope (EDS). Both surfaces of the samples were coated with 190 nm Pd using the DC sputtering machine in order to prevent oxidation and enhance a dissociation and recombination of hydrogen. Hydrogen permeability was measured by using a mass-flow meter in the temperature range of 573 to 673 K at 0.4 MPa H2. The as-spun Nb40Ti30Ni30 ribbon consisted of the bcc-(Nb, Ti) and B2-TiNi phases, but it was too brittle to measure its hydrogen permeability. On the contrary, it showed ductility and hydrogen permeability equivalent to that of pure Pd at 673 K by the heat treatment above 1173 K, This alloy consisted of fine granule (Nb, Ti) and TiNi phases. The grain size and hydrogen permeability of these samples increased with increasing temperature and time. However, the hydrogen embrittlement occurred when its grain size was too large, because the TiNi phase, which mainly contributed resistance against the hydrogen embrittlement, might not absorb the large volume expansion of the (Nb, Ti) phase. From the present work, it was concluded that melt-spinning technique is effective for the preparation of the Nb-TiNi hydrogen permeation alloy membrane.
9:00 PM - S3.22
Development of SEM Metallography for the Study of the Mg-MgH2 Phase Transformation.
Nadica Abazovic 1 , Annalisa Aurora 1 , Daniele Mirabile Gattia 1 , Amelia Montone 1 , Luciano Pilloni 1 , Marco Vittori Antisari 1 Show Abstract
1 FIM, ENEA, Rome Italy
9:00 PM - S3.23
Structure and Conductivity of Sodium Hydride Doped Calcium Nitride Hydride.
Maarten Verbraeken 1 , John Irvine 1 Show Abstract
1 School of Chemistry, University of St Andrews, St Andrews, Fife, United Kingdom
Samples of calcium nitride hydride (Ca2NH) and its solid solution with NaH have been synthesized. The structure and conductivity of these phases have been determined. A synthesis route has been used that has not been reported in literature, previously, resulting in a new Ca2NH phase. This phase is believed to be a conductor of hydride ions, which is a chemically interesting species. The material has potential to be used as an electrolyte in solid state electrolyser cells or hydrogen sensors. Experimental:Ca2NH was synthesised by firing CaH2 in a 5% H2/1% N2/94% Argon atmosphere at 780°C. The samples doped with NaH were obtained by dry mixing powders of CaH2 and NaH followed by firing pressed pellets at 330°C for 16 hours, then at 780°C for 4 hours in the same atmosphere. The samples with 0%, 5%, 10% and 20% NaH doping were analysed with XRD and AC impedance spectroscopy. Results:Ca2-xNaxNH1-x crystallises in the FM3M spacegroup, with a = 5.0788Å for undoped Ca2NH and 5.0718Å for Ca1.60Na0.40NH0.60. The lattice parameter changes linearly with dopant concentration. The H- conductivity of undoped Ca2NH is ~4.0E-5 S/cm at 600°C. The activation energy below 400°C is 87 kJ/mol and decreases to 12 kJ/mol above that temperature.
9:00 PM - S3.24
High Pressure Hydrogen Clathrates Examined under Raman Spectroscopy, X-ray diffraction, and Inelastic Neutron Scattering.
Timothy Jenkins 1 , Russell Hemley 1 , Ho-kwang Mao 1 , Viktor Struzhkin 1 Show Abstract
1 , Carnegie Institution of Washington, Washington, District of Columbia, United States
9:00 PM - S3.25
Evaluation of Hydrogen Absorption/desorption Characteristics of Mg-Al alloys.
Mahesh Tanniru 1 , Sankara Sarma Tatiparti 1 , Nathan Hicks 1 , Fereshteh Ebrahimi 1 , Darlene Slattery 2 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Florida Solar Energy Center, Cocoa, Florida, United States
Hydrogen absorption of light weight metals is being improved by addition of catalysts as well as alloying elements. For example, in case of magnesium different transition metals such as Ni, V, Ti etc. are used to enhance hydrogen uptake kinetics. In this study the effects of Al addition as an alloying element and Ni as a catalyst, on the hydrogen uptake and release behaviors of magnesium are evaluated. We have produced supersaturated solid solutions of Mg-Al alloy powders with 5 to 10% Al using electrodeposition from organometallic based electrolytes. These powders are fine in size and porous in nature. Furthermore, they consist of nanocrystalline grains. These qualities promote fast absorption of hydrogen on the surface, facilitate hydride nucleation and increase diffusivity. The hydrogenation kinetics of these powders were investigated in the temperature range of 50-200°C with and without the presence of nickel coating. A sievert’s type apparatus was employed for the hydrogenation experiments. Due to the thermal instability of supersaturated Mg-Al solid solutions, parallel annealing tests on the as deposited powders were conducted in an inert atmosphere to understand the effect of intermetallic phase formation on the hydrogenation process. The powders were characterized for their composition, morphology, phases and grain size. In this presentation the effect of Ni catalyst on kinetics and Al addition on hydride formation will be discussed. This project is supported by a grant from NSF (DMR-065406).
9:00 PM - S3.26
Solubility and Diffusivity of H in the bcc Alloys Ti35Cr 65-x Vx.
Giovanni Mazzolai 1 Show Abstract
1 Dept. of Physics, University of Perugia, Perugia Italy
9:00 PM - S3.27
Microwave Assisted Desorption of Hydrogen from Sodium Alanate (NaAlH4) for Improved Energy Efficiency in the Retrieval of Stored Hydrogen.
Rahul Krishnan 1 , Larry Hurtt 2 , Dinesh Agrawal 3 , Tabbetha Dobbins 1 4 Show Abstract
1 Institute for Micromanufacturing, Louisiana Tech University, Ruston, Louisiana, United States, 2 , SYNO-Therm Co, Changsha City, Hunan Province, China, 3 Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, United States, 4 Department of Physics, Grambling State University, Grambling, Louisiana, United States
Hydrogen has been desorbed from Sodium Alanate (NaAlH4)using microwave irradiation. Gravimetric analysis shows weight loss from the sample during microwave exposure. Samples subjected to microwave treatment were analyzed for phase composition using powder X-ray diffraction (XRD). The gas evolved upon microwave treatment is confirmed to be hydrogen by mass spectrometry analysis. Microwave heating method is well recognized for its energy efficiency in general. It is expected that in the desorption of H2 from NaAlH4, less energy will be used than in a conventional process. Temperature profiles show that NaAlH4 heats with increasing rates as the input power to the microwave furnace is increased. The particle morphology changes with microwave treatment have been characterized using Ultra-Small Angle X-ray Scattering (USAXS). Additionally, our work shows that adding TiCl2 as a dopant improves the desorption kinetics of NaAlH4 with microwave heating.
9:00 PM - S3.28
The Energetics of Hydrogen Adsorbed in Nanoporous Carbon. An ab initio Simulational Study.
R. Valladares 1 , Alexander Valladares 1 , A. G. Calles 1 , Ariel Valladares 2 Show Abstract
1 Physics Department, Fac. de Ciencias, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico, 2 Condensed Matter Department, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Mexico, D.F., Mexico
Porous carbon has consistently been considered a promising material to store hydrogen. In powder form it has been used for a long time as a reactive cleaning agent to get rid of unwanted byproducts in catalytic processes. Carbon displays a rich variety of bond types that makes it very versatile; these bonds lead to structures of molecules or solids not encountered in other elements belonging to group IV of the Periodic Table. Nanoporous carbon should then manifest some of this richness in structure; in particular the internal surfaces of the pores may show a different density of dangling bonds than those of nanoporous silicon  since bond rearrangement in carbon due to hybridization of the sp2 and sp1 types may play a role in the total number of dangling bonds existing on these surfaces. A priori we expect nanoporous carbon to have a lower density of dangling bonds than nanoporous silicon. In this work we report studies of a porous atomic structure of carbon with 50 % porosity that, due to the size of the supercell falls within the regime of nanoporous carbon. This structure is generated using a novel ab initio molecular dynamics procedure that leads to more realistic materials . As with silicon  our carbon 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 silicon  and carbon ; conclusions are drawn.1. A. A. Valladares et al. Accepted for publication MRS Proceedings Symposium QQ, MRS, Fall Meeting, 2006.2. A. A. Valladares et al. Accepted for publication MRS Proceedings Symposium ZZ, MRS, Fall Meeting, 2006.3. E.R.L. Loustau et al., J. Non-Cryst. Solids 352 1332 (2006).
9:00 PM - S3.29
Activation Energies of the Thermal Decomposition of LiNH2 under NH3 Atmosphere.
Kosei Nakamura 1 3 , Hiroyuki Takeshita 2 , Nobuhiro Kuriyama 3 , Shingo Ikeda 3 , Tetsu Kiyobayashi 3 Show Abstract
1 Graduate School of Engineering, Kansai University, Suita, Osaka, Japan, 3 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka, Japan, 2 Materials and Bioengineering, Kansai University, Suita, Osaka, Japan
After Chen et al. suggested Li3N as a hydrogen storage material (Reaction (1)), LiH-LiNH2 mixture- has been studied because Reaction (2) takes place at lower temperatures than Reaction (1) for application. The peak top temperature of the thermal desorption spectrum (TDS) of Reaction (2) is around 500K.LiNH2 +2LiH ↔ Li2NH + LiH + H2 ↔ Li3N + 2H2 (10.4mass%H2)(1)LiNH2 + LiH ↔ Li2NH + H2 (6.5mass%H2)(2)Although the thermal decomposition of LiH-LiNH2 mixture releases H2 as a major product, a small amount of NH3 is released as a byproduct according to the thermal decomposition of LiNH2 alone (Reaction (3)), whose peak top temperature of TDS is 600-700K.2LiNH2→Li2NH+ NH3(3) The mechanism of NH3-release must be elucidated to prevent the NH3-release because NH3 in the H2 poisons the catalyst of polymer electrolyte membrane fuel cells. The NH3-release also amounts to the irreversible loss of constituent nitrogen element from the mixture which eventually leads to the loss in hydrogen capacity. As for the H2 desorption mechanism of the LiH-LiNH2 mixture, Hu et al. and Ichikawa et al. suggest that the quick reaction of LiH with NH3 (Reaction (4)) promotes the thermal decomposition of LiNH2 in the mixture, making the H2 release 100-200 K lower than the decomposition of LiNH2 (Reaction (3)).LiH+NH3 →LiNH2+H2(4) We have observed the TDS spectrum of the decomposition of LiNH2 under He atmosphere shifted to lower temperature than in case of He+NH3 atmosphere. This observation together with Hu and Ichikawa’s studies implies that the promotion effect of LiH to the decomposition of LiNH2 is brought by the reduction of NH3 atmosphere around LiNH2 in the mixture. In present study we investigate the influence of NH3 product gas on the activation energies of the thermal decomposition of LiNH2 by means of the thermogravimetry, differential thermal analysis and mass spectrometry. NH3 from the decomposition of LiNH2 under He+NH3 shift to higher temperature than under He. Increase in the pressure of NH3 increases the activation energies of Reaction (3) by 40-130kJ/mol.AcknowledgmentThis study is financially supported by New Energy and Industrial Technology Development Organization (NEDO), Japan.References P. Chen, Z. Xiong, J. Luo, K. Ten, Nature, 420 (2002), 302-304  Y. H. Hu., E. Ruckenstein, J. Phys. Chem A, 107 (2003) 9737-9739  T. Ichikawa, N. Hanada, S. Isobe, H. Fujii, J. Alloys Compd., 365 (2004), 271-276 Y. Nakamori, Y. Yokoyama, S. Orimo, J. Alloys Compd. 377 (2004) L1. Y. Kojima, Y. Kawai, Chem. Commun. (2004) 2210. G.P. Meisner, F.E. Pinkerton, M.S. Meyer, M.P. Balogh, M.D. Kundrat, J. Alloys Compd. 24 (2005) 404–406. T. Ichikawa, H. Fujii, N. Hanada, S. Isobe, H. Leng, J. Phys. Chem B, 108 (2004) 7887–7892.
9:00 PM - S3.3
Ultra-high Sensitive pH Sensors Based on Pd Patterned Structures.
Young Tack Lee 1 , Eun Song Yi Lee 2 , Min Hong Juen 2 , Ju Hoon Kang 2 , Kye Jin Joen 1 , Wooyoung Lee 1 2 Show Abstract
1 NCRC (Nanomedical National Core Research Center), Yonsei University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of)
9:00 PM - S3.32
NMR Investigations of Carbon Aerogels for Hydrogen Storage.
Julie Herberg 1 , Robert Maxwell 1 , Ted Baumann 1 , Joe Satcher 1 Show Abstract
1 Chemistry and Material Science, Lawrence Livermore National Laboratory, Livermore, California, United States
A basic understanding of hydrogen sorption behavior in materials will be critical to the transportation sector needs of high gravimetric and volumetric density. An important criterion for effective physisorption is a high surface area that exposes a large number of sorption sites to ad-atom or ad-molecule interaction. Previous work with carbon-based sorbants has shown that the amount of surface excess hydrogen adsorbed at 77 K varies linearly with surface area (1 wt% H2 per 500 m^2/g of surface area)(1). Recent progress has been made in the design of high surface area sorbants, such as activated carbons, carbon aerogels, and metal-organic frameworks (MOFs), that show high gravimetric density of adsorbed hydrogen (1,2). For example, activated carbon aerogels prepared at LLNL have shown a hydrogen uptake as high as 5.3 wt% at 77 K (1). Despite this progress, these materials still fall short of the gravimetric and volumetric storage targets set for the transportation sector. In addition, significant work is required to increase the hydrogen sorption enthalpies if such materials are to be used at practical temperatures. To address these issues, a fundamental understanding of the interaction between molecular hydrogen and the surface of the sorbant is required. We will present 11B NMR and Xenon NMR data to provide insight into understanding the surface of the carbon adsorbents and the interaction between molecular hydrogen and the carbon-supported adsorbent. 1. H. Kabbour, T.F. Baumann, J.H. Satcher et al., The Journal of Chemical Physics in press (2006).2.J.L. Rowsell, E.C. Spencer, J. Eckert et al., Science 309, 1350 (2005).This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory, under contract # W-7405-ENG-48.
9:00 PM - S3.33
Hydrogen Permeability Measurements of Pure Nb and NbTi Solid Solution Alloys Prepared by Arc Melting.
Naoyoshi Ota 1 , Kazuhiro Ishikawa 1 , Kiyoshi Aoki 1 Show Abstract
1 Department of Materials science, Kitami Institute of Technology, Kitami, Hokkaido, Japan
In recent years, non-palladium based hydrogen permeation alloys have actively been investigated by several research groups. Group 5 metals such as V, Nb and Ta showing large hydrogen solubility and high hydrogen diffusivity are promising for hydrogen permeation membranes, because hydrogen permeability is the product of hydrogen solubility and hydrogen diffusivity. However, it is recognized that these metals suffer severe hydrogen brittleness and are pulverized spontaneously during hydrogenation. Then, they are unusable as a hydrogen permeation alloy. However, it is still uncertain why they are easily broken in a hydrogen atmosphere. In other words, there is some possibility that these metals are used as hydrogen permeation alloys. Among 5 metals, Nb shows the highest hydrogen permeability, and is the most cheap and abundant metal. In the present work, pure Nb and Nb1-xTix alloys were prepared by arc melting in an arc melting and their Φ were measured by the gas flow meter.Pure Nb and Nb1-xTix alloys ingots were prepared by arc melting in an Ar atmosphere. Disk samples of 12mm in diameter and 0.7mm in thickness were cut from the ingots by spark erosion method. Both sides of the disk surface were polished with an abrasive paper and a buff, and coated with 190nm thickness Pd by the DC magnetron sputtering machine to avoid oxidation and enhance hydrogen dissociation and recombination. Hydrogen permeation tests were carried out using a mass-flow meter. Microstructural observation and phase identification of the samples were carried out with a scanning electron microscope (SEM) and an X-ray diffractometer (XRD), respectively. Hydrogen permeability of as-cast Nb and Nb1-xTix (x = 0.1, 0.2, 0.3, 0.4 and 0.5) alloys prepared by arc melting were successfully measured using a conventional gas permeation method. Hydrogen permeability at 673K of pure as-cast Nb was 8.3×10-8(mol H2m-1s-1Pa-0.5). Hydrogen permeability at 673 K increased with increasing Ti content at once and decreased, i.e. it showed the maximum value of 20×10-8(mol H2m-1s-1Pa-0.5) for Nb0.7Ti0.3 alloy.We discuss why hydrogen permeability of the as-cast pure Nb and the NbTi alloy is measurable on the basis of the microstructural observation.
9:00 PM - S3.34
Hydrogen Permeation in Nb-TiNi Alloy with Anisotropic Microstructures.
Kazuhiro Ishikawa 1 , Sho Tokui 2 , Kiyoshi Aoki 1 Show Abstract
1 Department of Materials Science, Kitami Institute of Technology, Kitami, Hokkaido, Japan, 2 , Mitsubishi Materials Corporation, Okegawa, Saitama, Japan
Pd alloys are commercially used for a separation and purification of hydrogen, but Pd is expensive and rare in resources. Although V, Nb or Ta has 10-100 times higher hydrogen permeability than that of pure Pd, they show severe the hydrogen embrittlement in a hydrogen atmosphere. Recently, we have found out that coexistence of the B2-TiNi phase with Nb suppress the hydrogen embrittlement. For example, the Nb40Ti30Ni30 (mol %) alloy, consisting of the (Nb, Ti) solid solution and the TiNi phases, shows the higher hydrogen permeability than that of pure Pd without the hydrogen embrittlement. This alloy is a duplex phase one, so that its hydrogen permeability may depend strongly on the microstructure. In other words, its hydrogen permeation performance must drastically be improved by the controlling of the microstructure. In the present work, the relation between the microstructure formed by rolling and subsequent annealing and hydrogen permeability is investigated for developing the high performance hydrogen permeation alloy.The large size Nb-TiNi alloys were prepared using an induction melting under an Ar atmosphere. The alloy ingot was forged and rolled, then annealed at various temperatures for distinct periods for microstructural controlling. The disk sample of 12 mm in diameter was cut from the sheet sample using a spark erosion cutting machine. Microstructural observation and phase identification were carried out using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). After both surfaces of the alloy disk were coated by Pd using a sputtering machine, the hydrogen permeability measurement was carried out using a mass-flow meter.After forging and rolling, an anisotropic microstructure was formed in this alloy. That is, the (Nb, Ti) phase was strongly elongated along the rolling direction and compressed to the vertical one. The value of hydrogen permeability along the rolling direction was 30 times higher than that of along vertical one. In this case, hydrogen atoms could diffuse for long distance in the (Nb, Ti) phase. On the contrary, hydrogen atoms must pass frequently the (Nb, Ti)/TiNi phase boundary. Resulting from further annealing, hydrogen permeability along the rolling direction was reduced. The elongated (Nb, Ti) phase was cut into pieces and changed to spherical morphology, which implied that the continuity of this phase is reduced along the rolling direction. It was concluded that maximum hydrogen permeability can be obtained in the structure in which the (Nb, Ti) phase, which contributes the hydrogen permeability, was elongated along the direction for hydrogen diffusion.
9:00 PM - S3.35
Microstructures and Hydrogen Permeability of Nb-TiNi Alloys with Various Ti/Ni Ratios.
Tetsuya Kato 1 , Kazuhiro Ishikawa 1 , Kiyoshi Aoki 1 Show Abstract
1 Department of Materials Science, Kitami Institute of Technology, Kitami, Hokkaido, Japan
Hydrogen produced by steam reforming includes impurities such as CO and CO2, so that it must be purified by some methods. Pd-based alloys are used for purification of hydrogen gas, but Pd is too expensive and rare in resources, so that non-Pd based alloys are strongly desired. Recently, we have demonstrated that the Nb-TiNi alloys having the Ti/Ni ratio =1.0 show high hydrogen permeability (Φ) and large resistance against the hydrogen embrittlement. However, their performance is insufficient for industrial applications. The value of Φ increases with increasing Nb content in the Nb-TiNi alloys with Ti/Ni ratio=1.0, but the higher Nb content alloys suffer from the hydrogen embrittlement. In the present work, the effect of Ti/Ni ratio on the microstructures, crystal structures and Φ of Nb-TiNi alloys is investigated and discussed on the basis of the experimental data.The Nb-TiNi alloy ingots were prepared by arc melting in an Ar atmosphere. Disk samples of 12mm in diameter and 0.7mm in thickness were cut from the ingots by spark erosion method. Both sides of the disk surface were polished with an abrasive paper and a buff, and coated with 190nm thickness Pd by the DC magnetron sputtering machine to avoid oxidation and enhance hydrogen dissociation and recombination. Hydrogen permeation tests were carried out using a mass-flow meter. Microstructural observation and phase identification of the samples were carried out with a scanning electron microscope (SEM) and an X-ray diffractometer (XRD), respectively. Chemical composition of the samples was determined by an electron dispersion X-ray spectroscope (EDS).In Nb40Ti30+xNi30-x alloys, a brittle NbNi compound is formed in the side of the Ti/Ni ratio <1.0, which reduces both Φ and resistance against the hydrogen embrittlement. On the contrary, the alloys with the Ti/Ni ratios between 1.0 and 1.3 have higher Φ values. The SEM observation indicates that the volume fraction of the (Nb, Ti) phase, which contributes mainly hydrogen permeability, increases with increasing Ti/Ni ratio. This microstructural change can be explained by the phase equilibrium between (Nb, Ti) and TiNi phases, i.e. “lever rule”. Solubility of Nb in the TiNi phase decreases with increasing Ti/Ni ratio. On the other hand, that of Ti or Ni in Nb is almost constant independent of the Ti/Ni ratio. This behavior causes the change of the volume fraction of the (Nb, Ti) phase, which increases However, a brittle Ti2Ni intermetallic compound is also formed in the alloy when the Ti/Ni ratio is above 1.3, which reduces both Φ and ductility of the alloys. Thus, Φ in Nb-TiNi alloys can be controlled by the Ti/Ni ratio at the constant Nb content.
9:00 PM - S3.36
Effect of the Excess Volume of Lattice Defects on the Enthalpy of Formation and Desorption Temperature of Metal Hydrides.
Vincent Berube 1 , Gregg Radtke 2 , Gang Chen 2 , Millie Dresselhaus 1 Show Abstract
1 Physics, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Monday, Nov 26Transfer Oral S2.6 @ 2:45 PM to Poster S3.36Effect of the Excess Volume of Lattice Defects on the Enthalpy of Formation and Desorption Temperature of Metal Hydrides. Vincent Berube
9:00 PM - S3.4
High Hydrogen Permeability of Nb49Zr15Ni36 Alloy Enhanced by Pd Addition.
Huixiang Tang 1 , Kazuhiro Ishikawa 1 , Kiyoshi Aoki 1 Show Abstract
1 Materials Science, Kitami Institute of Technology, Kitami Japan
9:00 PM - S3.5
The Peculiarities of Formation of Alloys Structure in the System Ti-Zr-Hf-H.
Veniamin Shekhtman 1 , Seda Dolukhanyan 1 2 , Anahit Aleksanyan 1 2 , David Mayilyan 1 2 , Ofelia Ter-Galstyan 1 2 , Mikhail Sakharov 1 , Salavat Khasanov 1 Show Abstract
1 Lab. of struct. investigations , Institute of Solid State Physics RAS , Chernogolovka, Moscow district, Russian Federation, 2 , Institute of Chemical Physycs NAN RA, Yerevan Armenia
9:00 PM - S3.6
Hydrogenation-Induced Quantum Criticality in U2Co2In.
Ladislav Havela 1 , Khrystyna Miliyanchuk 1 2 , Laura Pereira 3 Show Abstract
1 Department of Electronic Structures, Charles University, Faculty of Mathematics and Physics, Prague 2 Czech Republic, 2 Department of Inorganic Chemistry, Faculty of Chemistry, Ivan Franko University, Lviv Ukraine, 3 Departamento do Quimica, Instituto Technologico e Nuclear, Sacavem Portugal
High hydrogen absorption can be found in several types of uranium intermetallics. Due to the crucial importance of inter-U spacing for magnetic and other electronic properties, hydrogenation can be used for tuning the ground state, leading typically to stronger magnetic features. An interesting case among the U2T2X compounds, which absorb up to 2 H atoms per f.u., is U2Co2In-H. U2Co2In is a weak Pauli paramagnet. The lattice expansion by 8.4% in U2Co2InH1.9 brings the compound to the verge of magnetism, to the vicinity of the quantum critical point, where the dominance of quantum fluctuations induces non-Fermi liquid phenomena. This hydride is a band metamagnet, i.e. magnetic order is induced only if magnetic field exceeds the critical value of 2.2 T. In lower fields, the specific heat in the C/T vs. T representation exhibits a pronounced low-temperature upturn, which can be described down to T = 0.4 K by additional non-Fermi liquid -T1/2 term. The γ coefficient of the specific heat (244 mJ/mol f.u. K2) proves that the hydride belongs to heavy fermion materials.
9:00 PM - S3.7
Hydrogen Storage Properties and Phase Transition of Mg/Pd Laminate Composites.
Nobuhiko Takeichi 1 , Koji Tanaka 1 , Hideaki Tanaka 1 , Nobuhiro Kuriyama 2 , Tamotsu Ueda 2 , Hiroshi Miyamura 3 , Shiomi Kikuchi 3 Show Abstract
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, OSAKA, Japan, 2 , IMRA Material R&D Co.Ltd., Kariya, Aichi, Japan, 3 , The University of Shiga Prefecture, Hikone, Shiga, Japan
Magnesium is a one of promising materials for hydrogen storage media because it can absorb a large amount of hydrogen as MgH2. However, However, the hydrogen absorption/desorption kinetics is too slow for practical use and needs high temperatures such as 573K. To improve the reaction kinetics and diffusion properties, a reduction of the grain size and an addition of various catalysis have been investigated. Recently, co-author Ueda et al. reported Mg-based laminate composites, prepared by a repetitive-rolling method, can reversible hydrogenation and dehydrogenation at 473K. Pd actively reacts with hydrogen. Therefore, adding Pd to Mg is expected to improve the activation properties and kinetics for hydrogen reaction. In this study, we investigated hydrogen storage properties of Mg/Pd laminate composites and phase transition during hydrogenation/dehydrogenation. The Mg/Pd laminate composites with (Mg/Pd)=6,4,3 and 2.5, where (Mg/Pd) means the ratio of the numbers of Mg to Pd atoms, were prepared by a repetitive fold and roll method using conventional two-high rolling mill. The PC-isotherms were measured with a Sieverts’ apparatus. The phase transformation of Mg/Pd laminate composites during hydrogen absorption and desorption was analyzed by in-situ XRD measurement. The Mg/Pd laminate composites can reversibly absorb and desorb a large amount of hydrogen, up to 1.46~0.9 H/M, at 573K. Except Mg/Pd laminate composites with (Mg/Pd)=2.5, PC-isotherms of the Mg/Pd laminate composites show two plateaux, PL and PH. In case of Mg/Pd laminate composite with (Mg/Pd)=6, PL and PHat 573 K were 0.02 and 2 MPa, respectively. PC-isotherms for the Mg/Pd laminate composite with (Mg/Pd)=2.5 at 573K show single plateau at 2 MPa.During the initial activation process, intermetallic compounds, Mg6Pd, Mg4Pd Mg3Pd and Mg5Pd2, are formed from Mg/Pd laminate composites with (Mg/Pd)=6, 4, 3 and 2.5, respectively. In the lower plateau pressure region, PL, those intermetallic compounds, expect Mg5Pd2, decomposed to Mg5Pd2 and MgPd. In case of Mg6Pd, the reaction equation is expressed as follows: Mg6Pd + (7/2)H2 ↔ (1/2)Mg5Pd2 + (7/2)MgH2.This amount of hydrogen, 1 H/M, corresponds to large low plateau of PC-isotherms of Mg6Pd. In high plateau pressure region, PH, Mg5Pd2 decomposed to MgH2 and MgPd. In case of Mg6Pd, the reaction equation is expressed as follows:(1/2)Mg5Pd2 + (7/2)MgH2 + (3/2)H2 ↔ MgPd + 5MgH2.These reaction equations agree with the PC-isotherms of Mg/Pd laminate composites. From those results, Mg/Pd laminate composites can absorb and desorb hydrogen reversible through complex multistage disproportionation reaction and recombination of Mg and Pd.This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Development for Safety Use and Infrastructure of Hydrogen Program”.
9:00 PM - S3.8
The Effect of Initial Activation on Microstructures of Mg/Cu Super-laminates and Hydrogen Absorption Properties.
Koji Tanaka 1 , Nobuhiko Takeichi 1 , Hideaki Tanaka 1 , Nobuhiro Kuriyam 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 , The University 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. Initial activation at 573 K leads the super-laminates to absorb hydrogen at 473K. In order to clarify the role of initial activation at 573K, we performed TEM observations of nano/micro-structures of the super-laminates that were initial-activated and heat-treated in vacuum at 573K, and compared hydrogen storage properties of those.As-rolled Mg/Cu super-laminates started to absorb hydrogen immediately and the reaction was very fast although initial activated Mg/Cu super-laminates started to absorb immediately and the reaction was much faster. On the other hand, heat-treated Mg/Cu super-laminates started to absorb hydrogen immediately and the reaction was slower than as-rolled Mg/Cu super-laminates although heat-treated Mg/Cu super-laminates for the second hydrogenation started to absorb immediately and the reaction was fast as same as initial activated Mg/Cu super-laminates. And then, heat-treated Mg/Cu super-laminates for the first and the second hydrogenation reached equilibrium state faster than as-rolled and initial-activated Mg/Cu super-laminates, however, the hydrogen content H/M is lower than those. The differences of hydrogen storage properties are caused by the differences of nano/microstructures. Heat-treated Mg/Cu super-laminates have more uniform structures than initial-activated Mg/Cu super-laminates, however, include more MgCu2 phase that is irresponsible to a reaction with hydrogen.Uniform nano/micro structures, and more Mg2Cu and less MgCu2 phases are the key to the improvement of hydrogen storage properties.
9:00 PM - S3.9
Quantitative Analysis of Ammonia Emission During the Cycle-life Measurement of Amide-based Hydrogen Storage Materials.
Shingo Ikeda 1 , Kosei Nakamura 2 1 , Hiroyuki Takeshita 3 , Tetsu Kiyobayashi 1 , Kazuhiko Tokoyoda 4 , Toyoyuki Kubokawa 4 , Nobuhiro Kuriyama 1 Show Abstract
1 Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, Ikeda Japan, 2 Graduate School of Engineering, Kansai University, Suita Japan, 3 Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita Japan, 4 R&D Center, Taiheiyo Cement Corporation, Sakura Japan
Amide-based hydrogen storage materials, such as the LiH-LiNH2 mixture  (termed ‘Li-N system’ hereafter) or LiH-Mg(NH2)2 mixture  (Li/Mg-N system), have received much attention as a promising candidate for a hydrogen storage medium due to the high gravimetric hydrogen capacity in view of applying to the fuel cell vehicles. A big problem in the amide-based system is that a certain amount of ammonia is emitted as a byproduct of hydrogen desorption [3,4]. Ammonia emission affects not only the performance of fuel cells but also the hydrogen capacity because the loss of nitrogen amounts to the loss of hydrogen storage material. Therefore, it is practically important to simultaneously investigate the quantitative relationship between the cyclic properties and the amount of ammonia emission all through the cycle-life measurement. In the present study, we investigated the cyclic properties of the Li-N and Li/Mg-N systems as well as the amount of ammonia emission during the cycle life tests. The Li-N system is prepared by ball-milling the mixture of LiNH2:LiH:TiCl3= 1.0:1.1:0.02 (molar ratio) in which TiCl3 works as a catalyst. The Li/Mg-N system, prepared in Taiheiyo Cement Co Ltd., is of the ball-milled mixture of Mg(NH2)2:LiH= 3:8. The cyclic properties are evaluated with using the Sieverts’ type apparatus. The ammonia gas emitted during the cycles is accumulated in a cold-trap at liquid nitrogen temperature for a couple of cycles and is subsequently quantified with using a mass spectrometer which is calibrated with using three materials as a reference, namely, diluted ammonia gas and thermal decomposition of NH4HCO3 and LiNH2. In the case of the Li-N system, the initial hydrogen capacity of ca. 5mass% decreases exponentially by half after 100 cycles at 300 °C. The concentration of ammonia in the desorbed hydrogen becomes stable at 0.4±0.2 mol% after initial few tens of cycle. (More precise value of ammonia concentration will be presented at the conference, as the final calibration is now under way.) On the other hand, Li/Mg-N system shows good stability through 100 cycles at 200 °C: The initial hydrogen capacity of ca. 4mass% shows a barely appreciable degradation. The ammonia concentration in hydrogen is 0.08±0.04 mol%. The better stability and less ammonia emission of Li/Mg-N system than Li-N system can be attributed to the lower cycling temperature and/or to the difference in their innate properties. In both systems the degree of degradation in hydrogen capacity seems to be explained mainly by the loss of constituent nitrogen due to the ammonia emission.Acknowledgements This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan.References P. Chen et al., Nature, 420 (2002) 302-304. W. Luo, J. Alloys Compd., 381 (2004) 284-287. S. Hino et al., Chem. Commun., (2005) 3038-3040. W. Luo et al., J. Alloys Compd., in press.