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!501

The state of the titanium catalyst species formed upon doping and hydrogen cycling of NaAlH4 with Ti-catalysts was studied by X-ray diffraction analysis. After doping with TiCl3, Ti is present as an hcp-Ti(Al) solid solution, while for the Ti(OBu)4 doped system, Ti exists as an XRD-amorphous phase. Cycling of hydrogen for 1.5 times results in transformation of these initially different Ti compounds into similar compounds, whose composition is dependent on the temperature. Thus, if low temperatures were used during the cycling process (up to 175 °C) an amorphous Al-Ti alloy formed, while upon using high temperatures (200 °C and higher) Ti was present as an AlxTi intermetallic. Correlation of the XRD and hydrogen desorption curves shows that the most active catalyst species in the present system is the amorphous Al-Ti alloy, whereas a decreased catalytic activity is found for the AlxTi intermetallic. © 2004 Elsevier B.V. All rights reserved.

Cycling of hydrogen for 1.5 times results in transformation of these initially different Ti compounds into similar compounds, whose composition is dependent on the temperature. Thus, if low temperatures were used during the cycling process (up to 175 °C) an amorphous Al-Ti alloy formed, while upon using high temperatures (200 °C and higher) Ti was present as an AlxTi intermetallic.

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In this work, effects of partial substitution of Mg, Ni with AB2 in Mg-based alloy and subsequent surface modification by further ball-milling with carbon nanotubes (CNTs) on electrochemical properties were investigated. Mg1.9(AB2)0.1Ni0.8 (AB 2=LaNi2, LaNiCo and LaNiMn) alloys were prepared by solid-state diffusion method, the nanocrystalline Mg-based alloys were prepared by ball-milling the mixture of obtained Mg1.9(AB2) 0.1Ni0.8 alloys and nickel powder. It was found that the electrochemical capacities of nanocrystalline Mg1.9(AB 2)0.1Ni1.8 alloys were measured to be 460-490mAh/g. The nanocrystalline Mg-based alloys containing carbon nanotubes (10wt.%) obtained by ball-milling after 60min were demonstrated to show improved electrochemical properties with respect to the original nanocrystalline Mg-based alloys. The electrochemical reaction activity was detected by electrochemical impedance spectra (EIS). Raman and X-ray photoelectron spectroscopy (XPS) proved the interaction between Mg1.9(AB 2)0.1Ni1.8 alloys and carbon nanotubes after ball-milling, which resulted in an increase in the surface Ni/Mg ratio. © 2003 Elsevier B.V. All rights reserved.

In this work, effects of partial substitution of Mg, Ni with AB2 in Mg-based alloy and subsequent surface modification by further ball-milling with carbon nanotubes (CNTs) on electrochemical properties were investigated. It was found that the electrochemical capacities of nanocrystalline Mg1.9(AB 2)0.1Ni1.8 alloys were measured to be 460-490mAh/g.

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The reaction of gaseous hydrogen with hydride-forming metals and alloys often involves a hydride layer formed on the metallic surface. Under proper steady state conditions, this layer is moving into the bulk metal, retaining constant thickness and velocity. In this work, the kinetics of the moving hydride layer is analyzed, using a model combining the four main sequential steps: adsorption (chemisorption), penetration, diffusion and reaction, in which the hydrogen is transferred from the gas phase into the reaction site. The model yields the rate of absorption during the steady state hydriding process (proportional to the hydride layer velocity) as a function of the pressure, the rate constants of the system (adsorption, desorption, penetration, decomposition, diffusion and interface emission) and the critical concentrations of hydrogen in the hydride, Cmax, Cp and Cmin (the last is associated with the equilibrium absorption pressure Peq). According to the model, for sufficiently high pressures, the rate is pressure-independent. A simple expression for the pressure independent rate is derived. The conditions leading to rates limited by one of the four sequential steps are analyzed and demonstrated. Relatively simple expressions are derived for the rate's pressure dependence. It is shown that for the interface and diffusion controlled cases the general pressure dependence is of the form: Rate-1∝[(P/Peq)1/2-1]-1. For the adsorption controlled case the pressure dependence is Rate∝(P-Peq). Based on the model, a numerical procedure is proposed for a system, removed from an initial steady state, describing the time-dependent approach to the new steady state determined by the applied change. The model is successfully tested for a real case, the uranium-hydrogen system, which is shown to obey the interface control rate equations.

Under proper steady state conditions, this layer is moving into the bulk metal, retaining constant thickness and velocity. A simple expression for the pressure independent rate is derived.

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!504

A hydrogen engine-fuel system is being developed as an alternative for powering underground mining machinery. A diesel was converted to a spark-ignited hydrogen engine and operated with a metal hydride, solid-state hydrogen storage system. Performance and emissions data show that hydrogen can be used as an ultralow emission fuel for underground mining. A special method of fuel control has overcome abnormal combustion problems frequently experienced with hydrogen fuel. The turbocharged, after-cooled engine maintains NOX emissions (the only significant pollutant) below 0.7 gram per kilowatt-hour. Power and fuel consumption are comparable to the naturally aspirated, prechambered diesel version of the engine. Hydrogen fuel is released from a metal hydride storage container by heat from the engine coolant. Through proper design, hydride containment can limit the leakage of hydrogen, in a worst-case accident, to acceptable levels. Copyright © 1984 Society of Automotive Engineers, Inc.

Performance and emissions data show that hydrogen can be used as an ultralow emission fuel for underground mining. Through proper design, hydride containment can limit the leakage of hydrogen, in a worst-case accident, to acceptable levels.

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The effect of sequential and continuous high-energy impact mode in the magneto-mill Uni-Ball-Mill 5 on the mechano-chemical synthesis of nanostructured ternary complex hydride Mg2FeH6 was studied by controlled reactive mechanical alloying (CRMA). In the sequential mode the milling vial was periodically opened under a protective gas and samples of the milled powder were extracted for microstructural examination whereas during continuous CRMA the vial was never opened up to 270 h duration. MgO was detected by XRD in sequentially milled powders while no MgO was detected in the continuously milled powder. The abundance of the nanostructured ternary complex hydride Mg 2FeH6, produced during sequential milling, and estimated from DSC reached ∼44 wt.% after 188 h, and afterwards it slightly decreased to ∼42 wt.% after 210 and 270 h. In contrast, the DSC yield of Mg 2FeH6 after continuous CRMA for 270 h was ∼57 wt.%. Much higher yield after continuous milling is attributed to the absence of MgO. This behavior provides strong evidence that MgO is a primary factor suppressing formation of Mg2FeH6. The DSC hydrogen desorption onset temperatures are close to 200 °C while the desorption peak temperatures for all powders are below 300 °C and the desorption process is completed within the range 10-20 min. Within the investigated nanograin size range of ∼5-13 nm, the DSC desorption onset and peak temperatures of β-MgH2 and Mg2FeH6 do not exhibit any trend with nanograin (crystallite) size of hydrides. TPD hydrogen desorption peaks from the powders containing a single ternary complex hydride Mg2FeH6, are very narrow, which indicates the presence of small but well-crystallized hydride particles. Their narrowness provides good evidence that the phase composition, bulk hydrogen distribution and hydride particle size distribution are very homogeneous. The overall amount of hydrogen desorbed in TPD from single-hydride Mg2FeH6 powders is somewhat higher than that observed in DSC and TGA desorption. The powder milled sequentially for 270 h and desorbed in a Sieverts-type apparatus at 250 and 290 °C, yielded about a half of the hydrogen content obtained during DSC and TGA tests. No desorption of hydrogen was detected in a Sieverts-type apparatus at 250 and 290 °C after 128 and 70 min, respectively, from the powder continuously milled for 270 h. The latter easily desorbed 3.13 and 2.83 wt.% hydrogen in DSC and TGA tests, respectively. © 2004 Elsevier B.V. All rights reserved.

Much higher yield after continuous milling is attributed to the absence of MgO. This behavior provides strong evidence that MgO is a primary factor suppressing formation of Mg2FeH6.

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Various properties of metal hydrides and their use in energy storage and conversion systems are discussed. Metal hydrides can be classified in terms of the hydrogen bonding to the metal. For the alloy side of the hydride family, hydrogen is usually bound in the interstitial sites in a metallic state with usually minor distortions of generally stable H-free alloy structure. Metal hydrides are being considered for applications involving the absorption and desorption of hydrogen gas, as many of them can readily absorb and desorb hydrogen gas around room temperature and near atmospheric H 2 pressure.

For the alloy side of the hydride family, hydrogen is usually bound in the interstitial sites in a metallic state with usually minor distortions of generally stable H-free alloy structure. Metal hydrides are being considered for applications involving the absorption and desorption of hydrogen gas, as many of them can readily absorb and desorb hydrogen gas around room temperature and near atmospheric H 2 pressure.

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The PuNi3-type intermetallic compounds LaNi3, CaNi3, La0.5Ca0.5Ni3, LaCaMgNi9, La0.5Ca1.5MgNi9, CaTiMgNi9, LaCaMgNi6Al3 and LaCaMgNi6Mn3 have been prepared using a powder-metallurgy-sintering method. The hydrogenation behaviour of these materials has been studied through the gas-solid reaction. The as-prepared compounds were easily activated at room temperature under a hydrogen pressure of 3.3 MPa. The pressure-composition-temperature (P-C-T) curves show a single plateau region with the exception of LaNi3-H, which shows no plateau, and La0.5Ca1.5MgNi9-H, which shows two plateaus. All of these alloys can absorb/desorb hydrogen by 1.8 wt.% under the conditions studied. X-ray diffraction (XRD) analysis reveals that LaNi3H4.5 is in the amorphous state, and the other hydrides are accompanied by different expansions of the unit cell volume of the host alloy.

The PuNi3-type intermetallic compounds LaNi3, CaNi3, La0.5Ca0.5Ni3, LaCaMgNi9, La0.5Ca1.5MgNi9, CaTiMgNi9, LaCaMgNi6Al3 and LaCaMgNi6Mn3 have been prepared using a powder-metallurgy-sintering method. The as-prepared compounds were easily activated at room temperature under a hydrogen pressure of 3.3 MPa.

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!508

The International Energy Agency Agreement on the Production and Utilization of Hydrogen is marking its 25th anniversary. This summarizes the R&D activities in currently active Annex 17 - Solid and Liquid State Hydrogen Storage Materials. Task 17 was chartered in 2001 and sets as its main target the development of reversible hydrogen storage media capable of delivering 5 wt.% H at less than 80°C. Eleven countries and the EC are official participants: Australia, Canada, European Commission, Japan, Italy, Lithuania, Norway, Spain, Sweden, Switzerland, the United Kingdom and the United States. The eleven national participations are represented by 33 research centers representing universities, national laboratories and industries. Internationally collaborative R&D are being performed under about 32 projects divided among three categories of H-storage media: hydrides, carbon and combined hydrides plus carbon. Included in the Task 17 activities is the IEA/DOE/SNL Hydride Information Center, an extensive series of online databases of hydride properties and applications (hydpark.ca.sandia.gov).

This summarizes the R&D activities in currently active Annex 17 - Solid and Liquid State Hydrogen Storage Materials. Internationally collaborative R&D are being performed under about 32 projects divided among three categories of H-storage media: hydrides, carbon and combined hydrides plus carbon.

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The H2Fuel Bus is the world's first hydrogen-fueled electric hybrid transit bus (see Figure1.). It was a project developed through a public/private partnership involving several leading technological and industrial organizations, with primary funding by the Department of Energy (DOE). The primary goals of the project were to gain valuable information on the technical readiness and economic viability of hydrogen fueled buses and to enhance the public awareness and acceptance of emerging hydrogen technologies. The bus completed its field-testing and was placed into public service on September 4, 1998 by Augusta Public Transit in Augusta, Georgia. The bus employs a hybrid Internal Combustion (IC) engine/generator and battery powered electric drive system, with onboard storage of hydrogen in metal hydride beds. The initial operating results demonstrated an overall energy efficiency (miles/BTU) twice the range of a similar diesel-fueled bus, while doubling the range of an all-electric vehicle by providing in-transit recharging of the batteries. Subsequent data showed that the power controller was not optimized for maximum battery life and, therefore, some efficiency was lost. Correction of that condition would provide a daily range of at least 120 miles in a hybrid hydrogen/electric-operating mode. The project developed reduced engine tail-pipe emissions, with NOx measured at less than 0.2 ppm. In addition todemonstrating the inherent safety of a solid-state hydrogen storage system, the project also addressed permit, liability, and safety issues, including a safety risk assessment of the metal hydride storage system. State-of-the-art technology in battery system management was likewise demonstrated. Copyright © 1999 Society of Automotive Engineers, Inc.

The bus employs a hybrid Internal Combustion (IC) engine/generator and battery powered electric drive system, with onboard storage of hydrogen in metal hydride beds. The project developed reduced engine tail-pipe emissions, with NOx measured at less than 0.2 ppm.

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The processes occurring in the course of two sequential hydrogen discharging and recharging cycles of Ti-doped sodium alanate were investigated in parallel using XRD analysis and solid-state NMR spectroscopy. Both methods demonstrate that in hydrogen storage cycles (Eq. (1)) the majority phases involved are NaAlH4, Na3AlH6, Al and NaH. Only traces of other, as yet unidentified phases are observed, one of which has been tentatively assigned to an Al-Ti alloy on the basis of XRD analysis. The unsatisfactory hydrogen storage capacities heretofore observed in cycle tests are shown to be due entirely to the reaction of Na3AlH6 with Al and hydrogen to NaAlH4 (Eq. (1), 2nd hydrogenation step) being incomplete. Using XRD and NMR methods it has been shown that a higher level of rehydrogenation can be achieved by adding an excess of Al powder. © 2002 Elsevier Science B.V. All rights reserved.

The processes occurring in the course of two sequential hydrogen discharging and recharging cycles of Ti-doped sodium alanate were investigated in parallel using XRD analysis and solid-state NMR spectroscopy. Using XRD and NMR methods it has been shown that a higher level of rehydrogenation can be achieved by adding an excess of Al powder.

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The activity of the "Hydrogen Group" of Padova University, addressed to the study of materials for solid state hydrogen storage, is illustrated. Various Mg-based materials have been considered and are being studied: a) MgH2 and 0.5% mol Nb2O5 mixture ball milled under argon atmosphere; b) Mg-Ni-Fe intermetallic compounds prepared by short time ball milling of ribbons obtained by melt spinning and by long time ball milling of a mixture of MgH2, Ni and Fe powders; c) MgH2 ball milled in argon with Mm-Ni-Al (Mm = La-rich mishmetal) and Zr-Cr-Fe catalyst alloys. All the samples have been structurally characterized by X-ray diffraction (Rietveld refinement) before and after hydrogen absorption/desorption cycling and tested with a Sievert apparatus as regarding their thermodynamic and kinetic properties.

Various Mg-based materials have been considered and are being studied: a) MgH2 and 0.5% mol Nb2O5 mixture ball milled under argon atmosphere; b) Mg-Ni-Fe intermetallic compounds prepared by short time ball milling of ribbons obtained by melt spinning and by long time ball milling of a mixture of MgH2, Ni and Fe powders; c) MgH2 ball milled in argon with Mm-Ni-Al (Mm = La-rich mishmetal) and Zr-Cr-Fe catalyst alloys. All the samples have been structurally characterized by X-ray diffraction (Rietveld refinement) before and after hydrogen absorption/desorption cycling and tested with a Sievert apparatus as regarding their thermodynamic and kinetic properties.

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!512

General Motors (GM) Corp. and Sandia National Laboratories have launched a partnership to design and test an advanced method for storing hydrogen based on metal hydrides. GM and Sandia, a National Nuclear Security Administration lab, have embarked on a four year, $10 million program for the project. Researchers also hope to create a tank design that could be adaptable to any type of solid-state hydrogen storage. The project will be conducted in two phases: in phase one, the program will study engineering designs for a sodium alanate storage tank, and in phase two, the promising tank designs will be subjected to rigourous testing, after that fabrication of the storage tanks will be done.

General Motors (GM) Corp. and Sandia National Laboratories have launched a partnership to design and test an advanced method for storing hydrogen based on metal hydrides. The project will be conducted in two phases: in phase one, the program will study engineering designs for a sodium alanate storage tank, and in phase two, the promising tank designs will be subjected to rigourous testing, after that fabrication of the storage tanks will be done.

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The concerns about fossil fuel resources depletion and the need of reducing the climate affecting emissions make more and more attractive a future widespread use of hydrogen as energy vector. Hydrogen represents an important option also to store energy in a long term scenario of fluctuating power generation from renewables sources (solar and wind). However, independently from the primary energy sources used for its production in medium and long term (fossil fuel with carbon dioxide sequestration, nuclear, renewables), R&D efforts must be focused henceforward on hydrogen related technologies, like fuel cells and advanced storage systems. Fuel cells, in particular, represent the ideal system to convert the hydrogen chemical energy into electricity with high efficiencies. The CESI experience on a grid connected PEFC system fuelled with hydrogen stored in metal hydrides is outlined in this presentation with emphasis on all the aspects related to subsystem interlacing. A 6,5 Nm3 capacity hydrogen storage was developed at CESI starting from commercial metal hydride powders supplied by LabTech Ltd. The heat transfer during the charge - discharge cycles and the useful hydrogen output were optimised in view of the coupling with a PEFC stack/module operating near ambient pressure. Three Independence 1000 PEFC modules were supplied by ReliOn and carefully characterised at CESI laboratories. This module is a rather open system and a lot of parameters can be acquired at operating conditions including all the cell and cartridges voltages, currents and temperatures. The module responses to an external electric load were investigated both in steady state conditions, by increasing gradually the load, and during steep load changes. The actual hydrogen consumption was measured at different operating conditions and LHV and HHV efficiencies were obtained as a function of the power output. The PEFC modules were connected to the local grid through a 3.3 kW DC-AC converter (inverter) that was supplied by SGS Future based on CESI specifications. The inverter efficiency exceeded 90%. A control system was set up in a LabVIEW™ environment to manage the hydrogen storage charge and discharge cycles and to test the PEFC - inverter system behaviour on different load profiles. Experimental results on the integrated system are presented and discussed. A few critical aspects related to each subsystem and to their interfaces are analysed This work was carried out in the frame of the research on the Italian Electrical System "Ricerca di Sistema", Ministerial Decrees of January 26, 2000 and April 17, 2001.

Hydrogen represents an important option also to store energy in a long term scenario of fluctuating power generation from renewables sources (solar and wind). A 6,5 Nm3 capacity hydrogen storage was developed at CESI starting from commercial metal hydride powders supplied by LabTech Ltd.

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Although recently there have been many reports on the in-situ structural characterization of hydrogen storage alloys, these studies were all conducted under equilibrium states. In practice, however, hydrogen storage alloys alternate hydrogen absorption and desorption processes ceaselessly. Therefore, in functional situations where hydrogen storage alloys are utilized, their hydrogen absorption properties cannot be evaluated precisely by applying the results of observations made under equilibrium states. We assessed the hydrogen absorption behavior and phase transformation of LaNi 5 during the hydrogen absorption process using our newly developed time-resolved in-situ XRD system for vapor-solid phase reaction. This system, which comprises a chamber for performing in-situ XRD measurements, a Sieverts' component for measuring hydrogenation speed, and a PSPC (position-sensitive proportional counter) X-ray detector, enables sequential XRD measurement in an in-situ atmosphere. Over a period of several minutes, we observed the phase transformation of the master alloy of LaNi 5 into a hydride of LaNi 5H 6 during the hydrogen absorption process and evaluated the process sequentially at intervals of a few seconds. Our results showed that the actual phase transformation during the process of hydrogen storage differs from what had been characterized previously under an equilibrium state. It was also made clear that the lattice volume of the hydride produced remains unchanged between the onset of hydride formation and attainment of the equilibrium state. © 2005 The Japan Institute of Metals.

Although recently there have been many reports on the in-situ structural characterization of hydrogen storage alloys, these studies were all conducted under equilibrium states. We assessed the hydrogen absorption behavior and phase transformation of LaNi 5 during the hydrogen absorption process using our newly developed time-resolved in-situ XRD system for vapor-solid phase reaction.

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The proceedings contain 49 papers from the conference on Advanced Materials for Energy Conversion II. The topics discussed include: fuel cell materials and components; international hydrogen storage R&D in IEA; solid state and surface phenomena in energy transformation materials; hydrogen storage properties of Li-based complex hydrides; structural and thermodynamic aspects of atlantes for hydrogen storage; advances in hydrogen storage; reaction of hydrogen with an organic hydrogen getter; and in-situ production of nano-structured ceramics by spray solution.

The proceedings contain 49 papers from the conference on Advanced Materials for Energy Conversion II. The topics discussed include: fuel cell materials and components; international hydrogen storage R&D in IEA; solid state and surface phenomena in energy transformation materials; hydrogen storage properties of Li-based complex hydrides; structural and thermodynamic aspects of atlantes for hydrogen storage; advances in hydrogen storage; reaction of hydrogen with an organic hydrogen getter; and in-situ production of nano-structured ceramics by spray solution.

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