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!401 | The present review of the most recent patents outlines the progress made over the last five years in the search of novel materials and processes that might allow large amounts of hydrogen to be stored on board of vehicles. Worth of note are the results of certain abinitio calculations proving that some compounds not yet synthesized might, actually, show features approaching the requirements of the US Department of Energy. Significant progress has been made concerning the absorption/desorption reversibility of Li-N-H compounds (amides/imides, LiH, Li3N), borohydrides and boranes. These materials, at the actual state of the art, appear still largely inadequate to comply with DOE targets. However, their intrinsic high mass capacity offers wide margin for further research in this area. The achievements made with alanates, magnesium-based hydrides and bcc-alloy hydrides, although of great significance from a point of view of the fundamental research, nonetheless, appear to be of limited impact from a practical point of view, at least for automotive applications. This is mainly due to the relatively low intrinsic mass capacity of these materials. © 2012 Bentham Science Publishers. | Significant progress has been made concerning the absorption/desorption reversibility of Li-N-H compounds (amides/imides, LiH, Li3N), borohydrides and boranes. However, their intrinsic high mass capacity offers wide margin for further research in this area. | _ |
!402 | Light element complex hydrides (e.g. NaBH4) together with metal hydrides (e.g. MgH2) are considered two primary classes of solid state hydrogen storage materials. In spite of drawbacks such as unfavorable thermodynamics and poor kinetics, enhancements may occur in reactive hydride composites by nanostructuring of reactant phases and formation of more stable product phases (e.g. MgB2) which lower overall reaction enthalpy and allow reversibility. One potential system is based on mixing NaBH4 and MgH2 and subsequent ball milling, which in a 2:1 molar ratio can store considerable amounts of hydrogen by weight (up to 7.8 wt%). A study of the 2NaBX4 + MgX2 → MgB2 + 2NaX + 4X 2 (X=D,H) reaction is assessed by means of in-situ neutron diffraction with different combinations of hydrogen and deuterium on the X position. The desorption is established to begin at temperatures as low as 250 °C, starting with decomposition of nanostructured MgX2 due to joint effects of nanostructured MgX2 and its reducing effect at NaBX4. Analyses of background profile, due to the high incoherent neutron scattering of hydrogen, as a function of temperature demonstrate direct correlation of H/D desorption reactions with relative phases amount. © 2010 Materials Research Society. | One potential system is based on mixing NaBH4 and MgH2 and subsequent ball milling, which in a 2:1 molar ratio can store considerable amounts of hydrogen by weight (up to 7.8 wt%). The desorption is established to begin at temperatures as low as 250 °C, starting with decomposition of nanostructured MgX2 due to joint effects of nanostructured MgX2 and its reducing effect at NaBX4. | _ |
!403 | We present a comprehensive study on the controlled phase synthesis and thermal decomposition of Cd(BH2)4, a material for solid state hydrogen storage obtained via the metathesis reaction of LiBH4 with CdCl2. By adjusting the stochiometry of the reactants and controlling the mechanical milling vial temperature, we have isolated the tetragonal (P42mn) low temperature phase and the cubic (Pn3̄m) high temperature phase of the cadmium borohydride. Cd(BH2) 4 has a low thermodynamic stability and decomposes with fast kinetic at 348 K, when heated at 1 K min-1 against a backpressure of 1 bar H2. A semi-quantitative analysis reveals that the decomposition gases are composed of 1:1 H2 + B2H6 and that only Cd remains as solid crystalline phase. © 2012 Elsevier B.V. All rights reserved. | We present a comprehensive study on the controlled phase synthesis and thermal decomposition of Cd(BH2)4, a material for solid state hydrogen storage obtained via the metathesis reaction of LiBH4 with CdCl2. Cd(BH2) 4 has a low thermodynamic stability and decomposes with fast kinetic at 348 K, when heated at 1 K min-1 against a backpressure of 1 bar H2. | _ |
!404 | Sodium alanate NaAlH4 is a very suitable material for solid-state hydrogen storage owing to its relatively high hydrogen capacity (7.5 wt.% H2) and moderate temperatures for reversible H2 release/uptake (100-150 °C) compatible with PEM fuel cells. These temperatures are obtained by adding a dopant. TiCl3, ScCl3 or CeCl3 are known to be efficient dopants but the details of the catalytic mechanism are not fully understood yet. In this work, the H 2 sorption of NaAlH4 doped with TiCl3, ScCl3 or CeCl3 is systematically studied. The doped samples were prepared in one step by reactive ball milling of NaH and Al with 4 mol.% dopant in an H2 atmosphere. The efficiencies of the dopants are different for desorption and absorption, indicating that different catalytic mechanisms and rate limiting steps are taking place during both steps and these are described here. TiCl3 is more efficient for desorption and CeCl3 for absorption. ScCl3 is less efficient than the first two for all reactions. A mixture of TiCl3 and CeCl3 is thus added to NaAlH4 to act at the same time on the desorption and the absorption processes. The results show enhanced overall performances for H2 sorption when using this mixture compared to NaAlH4 milled with TiCl3 or CeCl3 only. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. | In this work, the H 2 sorption of NaAlH4 doped with TiCl3, ScCl3 or CeCl3 is systematically studied. The results show enhanced overall performances for H2 sorption when using this mixture compared to NaAlH4 milled with TiCl3 or CeCl3 only. | _ |
!405 | In the search for suitable solid state hydrogen storage systems, NaAlH 4 (7.4 wt % H2) holds great promise due to its suitable thermodynamical properties. However, hydrogen release and uptake are hampered by high activation energies, most likely due to solid state mass transfer limitations. A recent strategy to improve the hydrogen de- and rehydrogenation properties of NaAlH4 is to reduce the particle size to the nanometer scale. We prepared high loadings of nanosized NaAlH4 confined in the pores of a carbon support by melt infiltration. XRD, nitrogen physisorption, high pressure DSC and solid-state NMR are used to evidence that the molten NaAlH4 infiltrates the carbon support, and forms a nanosized NaAlH4 phase lacking long-range order. The confined NaAlH4 shows enhanced hydrogen dehydrogenation properties and rehydrogenation under mild conditions that is attributed to the nanosize and close contact to the carbon matrix. © 2010 American Chemical Society. | However, hydrogen release and uptake are hampered by high activation energies, most likely due to solid state mass transfer limitations. XRD, nitrogen physisorption, high pressure DSC and solid-state NMR are used to evidence that the molten NaAlH4 infiltrates the carbon support, and forms a nanosized NaAlH4 phase lacking long-range order. | _ |
!406 | Solid-state reversible hydrogen storage systems hold great promise for onboard applications. The key criteria for a successful solid-state reversible storage material are high storage capacity, suitable thermodynamic properties, and fast hydriding and dehydriding kinetics. The LiNH2 + LiH system has been utilized as an example system to illustrate these critical issues that are common among other solid-state reversible storage materials. The progress made in thermodynamic destabilization and kinetic enhancements via various approaches are emphasized. The implications of these advancements in the development of future solid-state reversible hydrogen storage materials are discussed. © TMS 2009. | Solid-state reversible hydrogen storage systems hold great promise for onboard applications. The progress made in thermodynamic destabilization and kinetic enhancements via various approaches are emphasized. | _ |
!407 | Hydrogen adsorption and storage using solid-state materials is an area of much current research interest, and one of the major stumbling blocks in realizing the hydrogen economy. However, no material yet researched comes close to reaching the DOE 2015 targets of 9 wt% and 80 kgm-3 at this time. To increase the physisorption capacities of these materials, the heats of adsorption must be increased to ̃20 kJ mol-1. This can be accomplished by optimizing the material structure, creating more active species on the surface, or improving the interaction of the surface with hydrogen. The main focus of this progress report are recent advances in physisorption materials exhibiting higher heats of adsorption and better hydrogen adsorption at room temperature based on exploiting the Kubas model for hydrogen binding: (η2-H2)-metal interaction. Both computational approaches and synthetic achievements will be discussed. Materials exploiting the Kubas interaction represent a median on the continuum between metal hydrides and physisorption materials, and are becoming increasingly important as researchers learn more about their applications to hydrogen storage problems. | However, no material yet researched comes close to reaching the DOE 2015 targets of 9 wt% and 80 kgm-3 at this time. The main focus of this progress report are recent advances in physisorption materials exhibiting higher heats of adsorption and better hydrogen adsorption at room temperature based on exploiting the Kubas model for hydrogen binding: (η2-H2)-metal interaction. | _ |
!408 | The influence of different high energy milling times and of the addition of catalysts such as Nb2O5, TiCl3 and graphite on the hydrogen absorption/desorption (A/D) kinetics of a mixture of 2LiNH2 + 1.1MgH2 has been studied in the temperature range 220-240 °C. It is found that a prolonged milling time is effective in improving the A/D kinetics, irrespective of the presence or not of any kind of tested additive. The enthalpy of decomposition reaction results to be about 40.4 kJ/mol, as derived from van't Hoff plot using the values of the plateau pressures measured in desorption mode. This thermodynamic parameter fits well with the current literature data. © 2007 Elsevier B.V. All rights reserved. | The enthalpy of decomposition reaction results to be about 40.4 kJ/mol, as derived from van't Hoff plot using the values of the plateau pressures measured in desorption mode. This thermodynamic parameter fits well with the current literature data. | _ |
!409 | Free-standing magnesium-nickel (Mg-Ni) films with extensive nanoscale grain structures were fabricated using a combination of pulsed laser deposition and film delaminating processes. Hydrogen sorption and desorption properties of the films, free from the influence of substrates, were investigated. Oxidation of the material was reduced through the use of a sandwiched free-standing film structure in which the top and bottom layers consist of nanometer-thick Pd layers, which also acted as a catalyst to promote hydrogen uptake and release. Hydrogen storage characteristics were studied at three temperatures, 296, 232, and 180°C, where multiple sorption/desorption cycles were measured gravimetrically. An improvement in hydrogen storage capacity over the bulk Mg-Ni target material was found for the free-standing films. As shown from a Van't Hoff plot, the thermodynamic stability of the nanograined films is similar to that of Mg2Ni. These results suggest that free-standing films, of which better control of material compositions and microstructures can be realized than is possible for conventional ball-milled powders, represent a useful materials platform for solid-state hydrogen storage research. | Free-standing magnesium-nickel (Mg-Ni) films with extensive nanoscale grain structures were fabricated using a combination of pulsed laser deposition and film delaminating processes. These results suggest that free-standing films, of which better control of material compositions and microstructures can be realized than is possible for conventional ball-milled powders, represent a useful materials platform for solid-state hydrogen storage research. | _ |
!410 | MgH2 is a promising material for solid-state hydrogen storage due to its high gravimetric and volumetric storage capacity and its relatively low cost. Severe plastic deformation (SPD) processing techniques are being explored as an alternative to high-energy ball-milling (HEBM) in order to obtain more air resistant materials and reduce processing times. In this work, Mg, MgH2, and MgH2-Fe mixtures were severely mechanically processed by different techniques such as high-pressure torsion (HPT), extensive cold forging, and cold rolling. A very significant grain refinement was achieved when using MgH2 instead of Mg as raw material. The mean crystallite sizes observed ranged from 10 to 30 nm, depending on the processing conditions. Enhanced H-sorption properties were observed for the MgH 2-based nanocomposites processed by HPT when compared with MgH 2 mixtures. Additionally, cold forging and cold rolling also proved effective in nanostructuring MgH2. These results suggest a high potential for innovative application with the use of low cost mechanical processing routes to produce Mg-based nanomaterials with attractive hydrogen storage properties. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. | Severe plastic deformation (SPD) processing techniques are being explored as an alternative to high-energy ball-milling (HEBM) in order to obtain more air resistant materials and reduce processing times. A very significant grain refinement was achieved when using MgH2 instead of Mg as raw material. | _ |
!411 | The development of a viable hydrogen storage system is one of the key challenges that must be met prior to the establishment of a true hydrogen economy. Current hydrogen storage options, such as compressed gas and liquid hydrogen, fall short of meeting vehicle manufacturers' goals for safe and efficient energy storage. The most viable long-term alternative to these options is solid-state storage, which has been proven both safe and efficient. The Savannah River National Laboratory (SRNL), with over 50 years of hydrogen storage expertise and over 25 years of expertise in solid-state storage, is working with the Department of Energy's Hydrogen Storage Center of Excellence in Metal Hydrides to help solve this key challenge. A considerable amount of the Center's current efforts involve research to develop new high capacity hydrogen storage materials. However the overall objective of the Center is to deliver a 1 kg of hydrogen prototype vessel that meets the 2010 U.S. DOE FreedomCAR targets, which includes 6wt% hydrogen in the system. To meet this challenging target, will not only require the development of a new light weight hydrogen storage material but also, will require similar breakthroughs in vessel and system design, engineering and fabrication technology. SRNL is leading this systems engineering and analysis activity for the DOE Metal Hydride Center of Excellence. The SRNL team is comprised of distinguished scientists and engineers from national laboratories, leading universities, and major corporate research centers that have extensive experience in solid-state hydrogen storage systems as well as supporting expertise in heat transfer, systems modeling and component and systems development and manufacturing. To meet the FreedomCAR storage goals, engineering and system development tasks will need to be worked in parallel with material development. This approach will ensure that material development and engineering efforts are coordinated and focused on creating a suitable storage material and a compatible storage container. This approach considers the many required tradeoffs. For example, selection of a hydrogen storage material with a high equilibrium pressure could adversely affect the vessel's pressure design and, in turn, its weight, and perhaps the overall hydrogen charging time. Lower pressure materials would permit the use of lightweight storage containers and even possible conformable tank shapes. The Center's efforts will build on the experience and ongoing work of its lead and partners. The Center will also share its knowledge and expertise to solve emerging safety and engineering issues. The major engineering and system development tasks being carried out by the center include: • Heat transfer modeling and verification • Engineering materials property measurements i.e. kinetics, heat capacity, packing density, cycling performance etc. • Material production scale-up. • Safety issues including risk identification and mitigation. • Subsystem fabrication and testing • Prototype system fabrication and testing • System modeling and integration. • Manufacturability and cost estimates. The accompanying presentation will describe the current hydrogen storage systems engineering challenges in more detail and the approach that the SRNL-led team will follow to help solve these challenges. | The most viable long-term alternative to these options is solid-state storage, which has been proven both safe and efficient. A considerable amount of the Center's current efforts involve research to develop new high capacity hydrogen storage materials. | _ |
!412 | In this paper, we present an accurate sensor used to monitor the concentration of hydrogen in a LaNi 5 solid-state hydrogen storage device. The monitoring technique is based on the variations of the electrical properties of the storage material related to the hydrogen content. The sensor uses the electrical resistance of the sample which is directly linked to the hydrogen concentration. A finite element model is presented to simulate the resistivity variations during hydrogenation. © 2011 IEEE. | In this paper, we present an accurate sensor used to monitor the concentration of hydrogen in a LaNi 5 solid-state hydrogen storage device. A finite element model is presented to simulate the resistivity variations during hydrogenation. | _ |
!413 | Hydrogen vibrational excitation was studied for CaF2-type metal hydrides synthesized from Ti-based BCC solid solution alloys using inelastic incoherent neutron scattering (IINS). Ti1.0V1.1Mn 0.9H4.5 and Ti1.0V1.2Cr 1.1H4.8 showed UNS spectra similar to that reported for TiH2. The first three peaks were isolated but the higher excitation peaks were not clear. Analysis of the spectra using curve-fitting with Gauss functions revealed that the hydrogen vibration of Ti1.0V 1.1Mn0.9H4.5 is harmonic but that of the TÍ0.7V12CrIiH48 is deviated from harmonic, which reflects a trumpet-type potential. The relation between metal-hydrogen distance and vibrational excitation energy for the above two hydrides and Ti1.1Cr 1.4Mo0.9H4.8 was compared with a series of CaF2-type binary metal hydrides. All the hydrides of the Ti-based alloys had lower vibrational excitation energies than the binary metal hydrides for the corresponding metal-hydrogen distances. ©2011 The Japan Institute of Metals. | Hydrogen vibrational excitation was studied for CaF2-type metal hydrides synthesized from Ti-based BCC solid solution alloys using inelastic incoherent neutron scattering (IINS). The relation between metal-hydrogen distance and vibrational excitation energy for the above two hydrides and Ti1.1Cr 1.4Mo0.9H4.8 was compared with a series of CaF2-type binary metal hydrides. | _ |
!414 | Eutectic mixture Mg-11.3 at.% Ni was modified by elements X from the 13th (Al, Ga, In) and 14th group (Si, Ge, Sn and Pb). Phase analysis and distribution of X between primary solid solution Mg-Ni-X and Mg2Ni-X compound was carried out in stabilization annealed samples before hydrogen charging and in hydrided state. In the both states, it was found that X prefers Mg 2Ni-X to Mg-Ni-X solid solution, and that the preference is stronger in the hydrided state. The effect is more pronounced for elements X from the 13th group. Suggested explanation was based on influence of X on the formation enthalpy of hydrides. It was observed that In increases the hydrogen storage capacity of the eutectic mixture. The most likely explanation is based on a strong segregation of In to phase Mg2Ni-X, and on a weak tendency of In to form phases with Mg and Ni. © 2011 Elsevier B.V. All rights reserved. | Eutectic mixture Mg-11.3 at.% Ni was modified by elements X from the 13th (Al, Ga, In) and 14th group (Si, Ge, Sn and Pb). The most likely explanation is based on a strong segregation of In to phase Mg2Ni-X, and on a weak tendency of In to form phases with Mg and Ni. | _ |
!415 | Determination of the minimum total weight is the main criterion in the design of a solid state hydrogen storage device for mobile or portable applications. The design should address additional requirements such as storage capacity, charge/discharge rates, space constraints, coolant temperature and hydrogen supply pressure. The typical metal hydride based storage device studied here consists of several filters to distribute hydrogen gas, and heat exchanger tubes to cool or heat the hydride bed based on whether hydrogen is absorbed or desorbed. The total weight of the system includes hydrogen storage material, heat exchanger tubes and associated heat transfer media, porous sintered filters and the cylindrical outer container. Systematic simulation of the heat and mass transfer during hydrogen sorption has been carried out for different feasible configurations. LaNi5 is used as the representative hydriding alloy in the device as its sorption performance is limited by heat transfer in the bed. The effect of geometric parameters on total system weight and charging time are plotted at specified operating conditions. These plots are used for the design of hydrogen storage devices with minimum system weight satisfying the imposed constraints. © 2009 by ASME. | The design should address additional requirements such as storage capacity, charge/discharge rates, space constraints, coolant temperature and hydrogen supply pressure. Systematic simulation of the heat and mass transfer during hydrogen sorption has been carried out for different feasible configurations. | _ |
!416 | Magnesium hydride (MgH2) is considered to be one of the most promising options for a solid state hydrogen storage material. However, for practical use it is still imperative to find a convenient means of overcoming its slow kinetics and high stability. In this investigation, oxide materials based on TiO2 have been prepared from alkoxide precursors using a sol-gel route. When ball milled with MgH2, the titanium oxide based additives were found to result in significantly reduced onset temperatures of dehydrogenation and increased hydrogenation and dehydrogenation rates. Dehydrogenation onset temperatures as low as 257 °C were observed, which is over 100 °C lower than for milled MgH2 with no additives. In cycling experiments at 300 °C, between pressures of 1 × 10-2 bar H2 and 6 bar H2, reaction rates for dehydrogenation and hydrogenation were found to be up to 15 times quicker than for milled MgH2 with no additives. The Ti based oxide additives were found to change the mechanism of dehydrogenation from milled MgH2 from one of surface control followed by contracting volume, to a two-dimensional Johnson-Mehl-Avrami nucleation and growth mechanism. © 2009 Elsevier B.V. All rights reserved. | Magnesium hydride (MgH2) is considered to be one of the most promising options for a solid state hydrogen storage material. However, for practical use it is still imperative to find a convenient means of overcoming its slow kinetics and high stability. | _ |
!417 | Complex hydrides are very promising candidates for future light-weight solid state hydrogen storage materials. The present work illustrates detailed characterization of such novel hydride materials on different size scales by the use of synchrotron radiation and neutrons. The comprehensive analysis of such data leads to a deep understanding of the ongoing processes and mechanisms. The reaction pathways during hydrogen desorption and absorption are identified by in situ X-ray diffraction (XRD). Function and size of additive phases are estimated using X-ray absorption spectroscopy (XAS) and anomalous small-angle X-ray scattering (ASAXS). The structure of the metal hydride matrix is characterized using (ultra) small-angle neutron scattering (SANS/USANS). The hydrogen distribution in tanks filled with metal hydride material is studied with neutron computerized tomography (NCT). The results obtained by the different analysis methods are summarized in a final structural model. The complementary information obtained by these different methods is essential for the understanding of the various sorption processes in light metal hydrides and hydrogen storage tanks. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. | Complex hydrides are very promising candidates for future light-weight solid state hydrogen storage materials. The reaction pathways during hydrogen desorption and absorption are identified by in situ X-ray diffraction (XRD). | _ |
!418 | [No abstract available] | [No abstract available] | _ |
!419 | Hydrogen is the lightest and most abundant element in the universe. The overall amount of hydrogen on Earth is around 0.74. wt%; it is mostly bound in water and carbon-based materials. The future challenges of a hydrogen-based energy economy include the production, distribution and safe storage of hydrogen. Of these, one of the most important is the safe storage of hydrogen for use by consumers in electronic devices, automotive applications or heating and burning processes. A simple technical- or chemical-based solution, which fulfills all the requirements in terms of size, weight and safety for these different applications, is not yet in sight. Therefore, a number of possible solutions for the storage of hydrogen in a solid state are currently being researched. © 2012 Woodhead Publishing Limited All rights reserved. | A simple technical- or chemical-based solution, which fulfills all the requirements in terms of size, weight and safety for these different applications, is not yet in sight. Therefore, a number of possible solutions for the storage of hydrogen in a solid state are currently being researched. | _ |
!420 | The paper presents a model-based investigation of a metal hydride reactor applied as a solid state hydrogen storage device. The elements of a metal hydride reactor are hydrogen supply duct, internal hydrogen distribution, hydride bed, reactor shell and the flow domain of the heat transfer fluid. Internal hydrogen distribution and hydride bed are porous media. Therefore, hydrogen flows through non-porous and porous regions during its reversible exothermic absorption and endothermic desorption, respectively. The interface between porous and non-porous regions is a discontinuity with respect to energy transport mechanisms. Hence, Danckwerts-type boundary conditions for the energy balance equation are introduced. Application of the first and second law of thermodynamics to the interface reveals that temperature jumps may occur at the hydrogen inlet but are not allowed at the hydrogen outlet. Exemplarily the loading behavior of a metal hydride storage tank based on sodium alanate is analyzed. It is demonstrated and experimentally validated that only Danckwerts-type boundary conditions predict the important cooling effect of the inlet hydrogen on the exothermic absorption process correctly. © 2011 Elsevier Ltd. | The interface between porous and non-porous regions is a discontinuity with respect to energy transport mechanisms. Exemplarily the loading behavior of a metal hydride storage tank based on sodium alanate is analyzed. | _ |
!421 | Hydrogen storage systems utilizing high-pressure metal hydrides (HPMHs) require a highly effective heat exchanger to remove the large amounts of heat released once the hydrogen is charged into the system. Aside from removing the heat, the heat exchanger must be able to accomplish this task in an acceptably short period of time. A near-term target for this 'fill-time' is less than 5 min. In this two-part study, a new class of heat exchangers is proposed for automobile hydrogen storage systems. The first part discussed the design methodology and a 2-D computational model that was constructed to explore the thermal and kinetic behavior of the metal hydride. This paper discusses the experimental setup and testing of a prototype heat exchanger using Ti 1.1CrMn as HPMH storage material. Tests were performed to examine the influence of pressurization profile, coolant flow rate and coolant temperature on metal hydride temperature and reaction rate. The experimental data are compared with predictions of the 2-D model to validate the model, calculate reaction progress and determine fill time. The prototype heat exchanger successfully achieved a fill time of 4 min 40 s with a combination of fast pressurization and low coolant temperature. A parameter termed non-dimensional conductance (NDC) is shown to be an effective tool in designing HPMH heat exchangers and estimating fill times achievable with a particular design. © 2010 Elsevier Ltd. All rights reserved. | In this two-part study, a new class of heat exchangers is proposed for automobile hydrogen storage systems. This paper discusses the experimental setup and testing of a prototype heat exchanger using Ti 1.1CrMn as HPMH storage material. | _ |
!422 | [No abstract available] | [No abstract available] | _ |
!423 | Among the borohydrides proposed for solid state hydrogen storage, Ca(BH4)2 is particularly interesting because of its favourable thermodynamics and relatively cheap price. Composite systems, where other species are present in addition to the borohydride, show some advantages in hydrogen sorption properties with respect to the borohydrides alone, despite a reduction of the theoretical storage capacity. We have investigated the milling time influence on the sorption properties of the CaH2 + MgB2 system from which Ca(BH4)2 and MgH 2 can be synthesized by hydrogen absorption process. Manometric and calorimetric measurements showed better kinetics for long time milled samples. We found that the total substitution of MgB2 with AlB2 in the starting material can improve the sorption properties significantly, while the co-existence of both magnesium and aluminum borides in the starting mixture did not cause any improvement. Rietveld refinements of the X-ray powder diffraction spectra were used to confirm the hypothesized reactions. © 2010 Elsevier B.V. All rights reserved. | Among the borohydrides proposed for solid state hydrogen storage, Ca(BH4)2 is particularly interesting because of its favourable thermodynamics and relatively cheap price. Manometric and calorimetric measurements showed better kinetics for long time milled samples. | _ |
!424 | The results of International IPHE Project “Reversible Solid State Hydrogen Storage and Purification System for FC Power Supply” are presented. The project focused on the thermal and integration aspects of metal hydride technology of hydrogen storage and purification. The experimental part of the project included various system –scale metal hydride devices for purification and storage tests. Basing on the results of mathematical modeling, the optimized from the heat and mass transfer point of view low temperature metal hydride (AB5 type) devices for the purification system were created and tested within the fully automatic purification system with capacity of 3000 st.l/hour. The test results of the 100 kg alloy hydrogen storage device integration with PEM FC also presented. It was shown experimentally, that, taking into account overall energy balance of the integrated system, it is possible to increase the total efficiency of the PEM FC based power supply system with low temperature traditional metal hydride storage. The ways for metal hydride units thermal performance improvement and capacity increase for different cases of the technology application are also presented and discussed. © 2010 18th World Hydrogen Energy Conference 2010, WHEC 2010, Proceedings. All Rights Reserved. | The results of International IPHE Project “Reversible Solid State Hydrogen Storage and Purification System for FC Power Supply” are presented. The ways for metal hydride units thermal performance improvement and capacity increase for different cases of the technology application are also presented and discussed. | _ |
!425 | Metal hydrides are formed when certain metals or alloys are exposed to hydrogen at favorable temperatures and pressures. In order to sustain the sorption of hydrogen during this exothermic process, the generated heat has to be removed effectively. Release of hydrogen is an endothermic process needing supply of heat to the metal hydride matrix. Depending on the application, the heat transfer medium can be either a liquid or a gas. Reduction of the total weight of hydrogen storage devices is essential towards utilization of hydrogen for mobile and portable applications. While a variety of new storage materials with desirable sorption characteristics are being suggested, optimal thermal design of the storage device remains a major challenge. Lack of thermodynamic, transport and thermophysical property data of the material particles and of the bed is another drawback which needs to be addressed. © 2010 by ASME. | In order to sustain the sorption of hydrogen during this exothermic process, the generated heat has to be removed effectively. While a variety of new storage materials with desirable sorption characteristics are being suggested, optimal thermal design of the storage device remains a major challenge. | _ |
!426 | This study explores the use of a high-pressure metal hydride (HPMH), Ti1.1CrMn, to store hydrogen at high pressures (up to 310 bar) and temperatures below 60 °C, conditions that are suitable for automobile fuel cells. However, the exothermic reaction of hydrogen with this material releases large amounts of heat, and the reaction rate depends on the metal hydride temperature, decreasing significantly if the heat is not removed quickly. Therefore, a powerful heat exchanger constitutes the most crucial component of a HPMH hydrogen storage system. For automobiles, this heat exchanger must enable fueling 5 kg of hydrogen in less than 5 min. This is a formidable challenge considering the enormous amount of heat that must be released and the stringent limits on the heat exchanger's weight and volume, let alone a host of manufacturing requirements. Unlike conventional heat exchangers that are designed to exchange heat between two fluids, this heat exchanger is quite unique in that it must dissipate heat between a reacting powder and a coolant. In this first of a two-part study, a systematic heat exchanger design methodology is presented, starting with a 1-D criterion and progressing through a series of engineering decisions supported by computations of fill time. A final design is arrived at that meets the 5-min fill time requirement corresponding to minimum heat exchanger mass, supported by a 2-D computational model of the heat exchanger's thermal and kinetic response. © 2010 Elsevier Ltd. All rights reserved. | For automobiles, this heat exchanger must enable fueling 5 kg of hydrogen in less than 5 min. A final design is arrived at that meets the 5-min fill time requirement corresponding to minimum heat exchanger mass, supported by a 2-D computational model of the heat exchanger's thermal and kinetic response. | _ |
!427 | We demonstrate that NaAlH4 confined within the nanopores of a titanium-functionalized metal-organic framework (MOF) template MOF-74(Mg) can reversibly store hydrogen with minimal loss of capacity. Hydride-infiltrated samples were synthesized by melt infiltration, achieving loadings up to 21 wt %. MOF-74(Mg) possesses one-dimensional, 12 Å channels lined with Mg atoms having open coordination sites, which can serve as sites for Ti catalyst stabilization. MOF-74(Mg) is stable under repeated hydrogen desorption and hydride regeneration cycles, allowing it to serve as a "nanoreactor". Confining NaAlH4 within these pores alters the decomposition pathway by eliminating the stable intermediate Na3AlH6 phase observed during bulk decomposition and proceeding directly to NaH, Al, and H2, in agreement with theory. The onset of hydrogen desorption for both Ti-doped and undoped nano-NaAlH4@MOF-74(Mg) is ∼50 °C, nearly 100 °C lower than bulk NaAlH4. However, the presence of titanium is not necessary for this increase in desorption kinetics but enables rehydriding to be almost fully reversible. Isothermal kinetic studies indicate that the activation energy for H2 desorption is reduced from 79.5 kJ mol-1 in bulk Ti-doped NaAlH4 to 57.4 kJ mol-1 for nanoconfined NaAlH4. The structural properties of nano-NaAlH 4@MOF-74(Mg) were probed using 23Na and 27Al solid-state MAS NMR, which indicates that the hydride is not decomposed during infiltration and that Al is present as tetrahedral AlH4 ® anions prior to desorption and as Al metal after desorption. Because of the highly ordered MOF structure and monodisperse pore dimensions, our results allow key template features to be identified to ensure reversible, low-temperature hydrogen storage. © 2012 American Chemical Society. | MOF-74(Mg) is stable under repeated hydrogen desorption and hydride regeneration cycles, allowing it to serve as a "nanoreactor". However, the presence of titanium is not necessary for this increase in desorption kinetics but enables rehydriding to be almost fully reversible. | _ |
!428 | Exploring and evaluating on-board solid state hydrogen storage systems performance are of great interest for fuel cell electric vehicles development. In this report, we present gravimetric and volumetric capacities of a hydrogen storage system based on a densified MOF-177 adsorbent. This is, to our knowledge, the first thorough study of an engineered industrial scale MOFs for hydrogen storage application. The measurements were performed over the 50-120 K and 0-40 bar ranges, and modeled using micropore filling approaches. The performances of a potential 100 L vessel filled with the densified MOF-177 are inferred from the modeling parameters. A comparison of this technology with the 70 MPa compressed gas hydrogen system shows under which conditions the adsorbent offer advantages in terms of volumetric and gravimetric capacities. Further comparison with AX-21 activated carbon pellets reveals that densified MOF-177 stores about 40% more at 77 K and 35 bar. In order to get a physically sound modeling analysis, we introduced an approach to establish effective saturation pressures for supercritical adsorption. This approach insures a consistency between key model parameters and the observed liquid properties of the adsorbed phase at the lowest temperatures. We show that modeling using temperature-dependent saturation pressures and adsorbed phase densities leads to important differences in the projected usable storage capacities. Such differences can be as much as 25% at 50 K in the high pressure limit, revealing the importance of physical insights in the modeling approach. © 2011 The Royal Society of Chemistry. | Exploring and evaluating on-board solid state hydrogen storage systems performance are of great interest for fuel cell electric vehicles development. We show that modeling using temperature-dependent saturation pressures and adsorbed phase densities leads to important differences in the projected usable storage capacities. | _ |
!429 | Proof-of-principle gas-reservoir MnNiMg electrochromic mirror devices have been investigated. In contrast to conventional electrochromic approaches, hydrogen is stored (at low concentration) in the gas volume between glass panes of the insulated glass units (IGUs). The elimination of a solid state ion storage layer simplifies the layer stack, enhances overall transmission, and reduces cost. The cyclic switching properties were demonstrated and system durability improved with the incorporation a thin Zr barrier layer between the MnNiMg layer and the Pd catalyst. Addition of 9% silver to the palladium catalyst further improved system durability. About 100 full cycles have been demonstrated before devices slow considerably. Degradation of device performance appears to be related to Pd catalyst mobility, rather than delamination or metal layer oxidation issues originally presumed likely to present significant challenges. © 2008. | In contrast to conventional electrochromic approaches, hydrogen is stored (at low concentration) in the gas volume between glass panes of the insulated glass units (IGUs). Addition of 9% silver to the palladium catalyst further improved system durability. | _ |
!430 | Intermetallic compounds are able to store reversibly large amount of hydrogen. The hydride formation usually takes place through a two-phase domain for which an equilibrium plateau is observed between the metallic phase and its hydride. Such phase transformation induces important structural changes such as volume expansion (either isotropic and anisotropic), symmetry lowering, hydrogen ordering and phase transitions. In some cases, change of the electronic structure, from metallic to ionocovalent state, is reported. Finally, amorphization can occur leading to disproportionation of the parent compound. In this overview we give some examples of these different behaviors to illustrate the fascinating structural properties of these materials that are of potential interest from the fundamental point of view and for practical applications like energy storage either by solid-gas or electrochemical routes. © by Oldenbourg Wissenschaftsverlag, München. | Intermetallic compounds are able to store reversibly large amount of hydrogen. In some cases, change of the electronic structure, from metallic to ionocovalent state, is reported. | _ |
!431 | Metal hydrides are likely candidates for the solid state storage of hydrogen. NaAlH4 is the only complex metal hydride identified so far that combines favorable thermodynamics with a reasonable hydrogen storage capacity (5.5 wt %) when decomposing in two steps to NaH, Al, and H2. The slow kinetics and poor reversibility of the hydrogen desorption can be combatted by the addition of a Ti-based catalyst. In an alternative approach we studied the influence of a reduced NaAlH4 particle size and the presence of a carbon support. We focused on NaAlH4/porous carbon nanocomposites prepared by melt infiltration. The NaAlH4 was confined in the mainly 2-3 nm pores of the carbon, resulting in a lack of long-range order in the NaAlH4 structure. The hydrogen release profile was modified by contact with the carbon; even for ∼10 nm NaAlH4 on a nonporous carbon material the decomposition of NaAlH4 to NaH, Al, and H2 now led to hydrogen release in a single step. This was a kinetic effect, with the temperature at which the hydrogen was released depending on the NaAlH4 feature size. However, confinement in a nanoporous carbon material was essential to not only achieve low H2 release temperatures, but also rehydrogenation at mild conditions (e.g., 24 bar H 2 at 150 °C). Not only had the kinetics of hydrogen sorption improved, but the thermodynamics had also changed. When hydrogenating at conditions at which Na3AlH6 would be expected to be the stable phase (e.g., 40 bar H2 at 160 °C), instead nanoconfined NaAlH4 was formed, indicating a shift of the NaAlH 4↔Na3AlH6 thermodynamic equilibrium in these nanocomposites compared to bulk materials. © 2010 American Chemical Society. | Metal hydrides are likely candidates for the solid state storage of hydrogen. NaAlH4 is the only complex metal hydride identified so far that combines favorable thermodynamics with a reasonable hydrogen storage capacity (5.5 wt %) when decomposing in two steps to NaH, Al, and H2. | _ |
!432 | The present work reports the straightforward preparation of sodium amidoborane NaNH2BH3, an ammonia borane derivative (NH3BH3). NaNH2BH3 is a promising solid-state hydrogen storage material, known to dehydrogenate in milder conditions than its parent compound. The preparation was made from sodium hydride NaH and NH3BH3 according to three different energy-efficient routes: namely, ball-milling, grinding in a mortar, and simple mixing with a spatula. In each case, NaNH2BH3 was formed. In other words, it has been demonstrated that the solid-solid reaction between NaH and NH3BH3 can take place by simple contact of these molecules, owing to the basic character of the former and the acidity of the latter. The as-formed materials dehydrogenate to a high extent at low temperature, with ca. 2 equivalent hydrogen H2 (NH3-free in our conditions) evolving at temperatures up to 95 °C. An effective gravimetric hydrogen density of ca. 7.4 wt% was calculated, which may correspond to an effective capacity of 3.7 wt% (assuming the weight of NaNH 2BH3 amounts to 50% of the weight of the whole storage system). Such performance confirms the high potential of amidoboranes as hydrogen storage material, especially when compared to NH3BH 3. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights. | NaNH2BH3 is a promising solid-state hydrogen storage material, known to dehydrogenate in milder conditions than its parent compound. Such performance confirms the high potential of amidoboranes as hydrogen storage material, especially when compared to NH3BH 3. | _ |
!433 | The following composite hydride systems: NaBH4-MgH2, MgH2-LiAlH4, MgH2-VH0.81 and MgH2-NaAlH4, were synthesized in a wide range of compositions by controlled reactive/mechanical (ball) milling in a magneto-mill. In effect, composites having nanometric grain sizes of the constituent phases (nanocomposites) were produced. It is shown that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems such as NaBH4 + MgH2, MgH2 + VH0.81 and MgH2 + LiAlH4 substantially decreases linearly with increasing volume fraction of the constituent having lower desorption temperature according to the well-known composite rule-of-mixtures (ROM). It is also shown that the ROM behavior can break down due to an ineffective milling of a composite. The composite system MgH2 + NaAlH4 does not obey the ROM behavior. © 2008 Elsevier B.V. All rights reserved. | In effect, composites having nanometric grain sizes of the constituent phases (nanocomposites) were produced. It is also shown that the ROM behavior can break down due to an ineffective milling of a composite. | _ |
!434 | This study employed a fast, simple and cost-effective hydriding combustion synthesis (HCS) to prepare nano/submicron Mg based alloys, which are the most promising solid state hydrogen storage materials owing to their high storage capacity (7.6 wt.%) and highest volumetric density. The microstructural and absorption/desorption kinetic properties of the prepared MgH2 samples were characterized and compared with commercially available MgH2 powders. The detailed BET analysis of the HCS prepared samples showed a higher surface area than that of commercial MgH2, which resulted in better absorption/desorption kinetics. The HCS-prepared MgH2 powder absorbed 6.2 wt.% H2 with a rate of 0.31 wt.%/min, whereas it desorbed at a rate of 0.98 wt.%/min. These results highlight the superiority of the HCS method to prepare MgH2 powders over conventional ingot-metallurgy. © 2011 Elsevier B.V. | This study employed a fast, simple and cost-effective hydriding combustion synthesis (HCS) to prepare nano/submicron Mg based alloys, which are the most promising solid state hydrogen storage materials owing to their high storage capacity (7.6 wt.%) and highest volumetric density. The detailed BET analysis of the HCS prepared samples showed a higher surface area than that of commercial MgH2, which resulted in better absorption/desorption kinetics. | _ |
!435 | On the basis of a previously acquired experience on scaling up issues concerning the use of magnesium hydride as a base material for solid-state hydrogen storage, a small reactor was designed and tested in different operating conditions. It contains about 10 g of catalyzed magnesium hydride powder mixed with 5 wt.% aluminium powder and pressed in the form of cylindrical pellets and the heat flow is managed by means of an oil circulation system. Carbon paper is used to ensure good heat conductivity between the pellets and the inner wall of the reactor and between one pellet and another. A number of hydrogen absorption and desorption cycles at different temperatures and pressures was carried out to compare the behaviour of the small reactor with the laboratory data obtained on small amounts (fractions of grams) of powdered and pelletized samples. Data acquisition for gas flow, pressure and temperature in different positions of the reactor allow a good understanding of internal dynamics. The results in terms of hydrogen absorption/desorption kinetics and of stability to ongoing cycles are stimulating, so that the tested small reactor can be considered as a basic element for further studies and improvements. © 2010 Elsevier B.V. All rights reserved. | On the basis of a previously acquired experience on scaling up issues concerning the use of magnesium hydride as a base material for solid-state hydrogen storage, a small reactor was designed and tested in different operating conditions. The results in terms of hydrogen absorption/desorption kinetics and of stability to ongoing cycles are stimulating, so that the tested small reactor can be considered as a basic element for further studies and improvements. | _ |
!436 | Complex hydrides are attractive candidates for solid-state hydrogen storage because of their high hydrogen storage capacities and moderate operation temperatures. However, the fast and efficient transport of reaction heat through the hydride bed is an unsolved problem due to the low intrinsic heat conductivities of complex hydrides. Here, we report on increasing the effective thermal conductivities of a NaAlH 4- and a LiNH 2-MgH 2-based material by admixing expanded natural graphite (ENG) up to 25 mass% and compaction with up to 400 MPa. Thermal conductivities in radial and axial direction, microstructure and phase fractions of these pellets were determined. With increasing ENG content the heat transfer characteristics of both systems were enhanced from less than 1 W m -1 K -1 up to 38 W m -1 K -1. The pelletized hydride-graphite composites can be processed easily and safely compared to loose powders. Further, they have increased volumetric storage capacities of up to 59 g-H 2 l -1 and 54 g-H 2 l -1 compared to the loose powders with 19 g-H 2 l -1 and 18 g-H 2 l -1 for the NaAlH 4- and a LiNH 2-MgH 2-based material, respectively, and they are very suitable for a tubular hydride tank design due to anisotropic heat transfer characteristics. © 2012 Elsevier B.V. All rights reserved. | Here, we report on increasing the effective thermal conductivities of a NaAlH 4- and a LiNH 2-MgH 2-based material by admixing expanded natural graphite (ENG) up to 25 mass% and compaction with up to 400 MPa. The pelletized hydride-graphite composites can be processed easily and safely compared to loose powders. | _ |
!437 | Hydrogen is an ideal energy carrier which is considered for future transport, such as automotive applications. In this context storage of hydrogen is one of the key challenges in developing hydrogen economy. The relatively advanced storage methods such as high-pressure gas or liquid cannot fulfill future storage goals. Chemical or physically combined storage of hydrogen in other materials has potential advantages over other storage methods. Intensive research has been done on metal hydrides recently for improvement of hydrogenation properties. The present review reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response. A group of Mg-based hydrides stand as promising candidate for competitive hydrogen storage with reversible hydrogen capacity up to 7.6 wt% for on-board applications. Efforts have been devoted to these materials to decrease their desorption temperature, enhance the kinetics and cycle life. The kinetics has been improved by adding an appropriate catalyst into the system and as well as by ball-milling that introduces defects with improved surface properties. The studies reported promising results, such as improved kinetics and lower decomposition temperatures, however, the state-of-the-art materials are still far from meeting the aimed target for their transport applications. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclic behavior of metal hydrides. © 2006 International Association for Hydrogen Energy. | The present review reports recent developments of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response. Therefore, further research work is needed to achieve the goal by improving development on hydrogenation, thermal and cyclic behavior of metal hydrides. | _ |
!438 | Complex hydrides exhibit various energy-related functions such as hydrogen storage, microwave absorption, and neutron shielding. Furthermore, another novel energy-related function was recently reported by the authors; lithium fast-ionic conduction, which suggests that complex hydrides may be a potential candidate for solid electrolytes in lithium-ion batteries. This review presents the recent progress in the development of lithium fast-ionic conductors of complex hydrides. First, the fast-ionic conduction in LiBH 4 as a result of clarifying the mechanism of microwave absorption is presented, and then the conceptual development of complex hydrides as a new type of solid-state lithium fast-ionic conductors in LiBH 4-, LiNH 2-, and LiAlH 4-based complex hydrides is discussed. Finally, the future prospects of this study from both application and fundamental viewpoints are described: possible use as solid electrolytes for batteries, formation of ionic liquids in complex hydrides, and similarity between complex hydrides and Laves-phase metal hydrides. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. | Complex hydrides exhibit various energy-related functions such as hydrogen storage, microwave absorption, and neutron shielding. Furthermore, another novel energy-related function was recently reported by the authors; lithium fast-ionic conduction, which suggests that complex hydrides may be a potential candidate for solid electrolytes in lithium-ion batteries. | _ |
!439 | A major technological barrier currently preventing the proposed transition to a "hydrogen economy" is the storage of hydrogen for use as an energy carrier. There are various methods available, but none of these can currently achieve the required storage densities. The use of a reversible solid state hydrogen storage material, however, is one of the most promising potential solutions to this problem. In this opening chapter, we will look at some of the background to this topic, including the use of hydrogen as an energy carrier, the barriers to the widespread use of hydrogen energy in transportation technology, the different methods that can be used for the storage of hydrogen and the use of solid state media. We will then introduce the measurement methods for hydrogen uptake determination and some of the complementary characterisation techniques that can be used. We also discuss the reasons why the accurate characterisation of the storage properties of a material is an important and high profile topic. We will close the chapter by defining some of the terminology used throughout the book. © Springer-Verlag London Limited 2011. | A major technological barrier currently preventing the proposed transition to a "hydrogen economy" is the storage of hydrogen for use as an energy carrier. There are various methods available, but none of these can currently achieve the required storage densities. | _ |
!440 | There are a few different approaches for hydrogen transportation and storage. Hydrogen can be stored as a compressed gas, as a liquid (at 20 K), and in solid state compounds. The first two methods are established technologies with several limitations, the most important being their energy intensive character. Hydrogen storage in metal hydrides is considered one of the most attractive methods. While hydrogen has many obvious advantages, there remains a problem with storage and transportation. Hydrides reduce the risk factors of gaseous or liquid hydrogen. The metal hydrides provide a safe method for fuel storage in hydrogen-powered vehicles. LiBH4 is a complex hydride which consists of 18% mass of hydrogen. Therefore, there are many reasons why hydrogen-storage materials, for example LiBH4, will be used in the future at many ranges. Hydride formation, reaction (absorption and/or chemisorption) between metal (M) and hydrogen (H2) is: M + nH2 [image omitted] MH2n+ Q. | While hydrogen has many obvious advantages, there remains a problem with storage and transportation. The metal hydrides provide a safe method for fuel storage in hydrogen-powered vehicles. | _ |
!441 | Complex hydrides are potential candidates for solid state hydrogen storage due to their high gravimetric hydrogen capacities. The present chapter focuses on the most recent progress in the understanding of the hydrogen storage behavior of light metal-based complex hydrides and their (nano)composites. Hydrides such as sodium (NaAlH4) and lithium (LiAlH4) alanate containing various catalyzing additives, complex hydride (nano)composite systems containing LiAlH4, lithium amide (LiNH2) and magnesium hydride (MgH2) as well as manganese borohydride (Mn(BH4)2), which was synthesized by the mechanochemical activation synthesis (MCAS) are all discussed. In particular, the phenomena of mechanical dehydrogenation and slow hydrogen discharge during a long-term storage after processing by ball milling are thoroughly discussed. Furthermore, isothermal dehydrogenation behavior of the above mentioned complex hydride systems is thoroughly discussed. © 2013 Elsevier B.V. All rights reserved. | In particular, the phenomena of mechanical dehydrogenation and slow hydrogen discharge during a long-term storage after processing by ball milling are thoroughly discussed. Furthermore, isothermal dehydrogenation behavior of the above mentioned complex hydride systems is thoroughly discussed. | _ |
!442 | Hydrogen has the capacity to provide society with the means to carry 'green' energy between the point of generation and the point of use. A sustainable energy society in which a hydrogen economy predominates will require renewable generation provided, for example, by artificial photosynthesis and clean, efficient energy conversion effected, for example, by hydrogen fuel cells. Vital in the hydrogen cycle is the ability to store hydrogen safely and effectively. Solid-state storage in hydrides enables this but no material yet satisfies all the demands associated with storage density and hydrogen release and uptake; particularly for mobile power. Nanochemical design methods present potential routes to overcome the thermodynamic and kinetic hurdles associated with solid state storage in hydrides. In this review we discuss strategies of nanosizing, nanoconfinement, morphological/dimensional control, and application of nanoadditives on the hydrogen storage performance of metal hydrides. We present recent examples of how such approaches can begin to address the challenges and an evaluation of prospects for further development. © CSIRO 2012. | A sustainable energy society in which a hydrogen economy predominates will require renewable generation provided, for example, by artificial photosynthesis and clean, efficient energy conversion effected, for example, by hydrogen fuel cells. Nanochemical design methods present potential routes to overcome the thermodynamic and kinetic hurdles associated with solid state storage in hydrides. | _ |
!443 | Hydrogen generated from clean and renewable energy sources has been considered as an alternate fuel to carbon based fossil fuels for several decades. Although many advances in hydrogen production and usage have been made, storing hydrogen remains a significant challenge. Many drawbacks including energy intensive processes, low volumetric densities, and safety concerns are associated with storing hydrogen as pressured or liquefied. Solid state hydrogen storage is considered to be the most promising method as a safe and effective storage option, but there is still no material or method that satisfies the requirements for a practical approach. A feasible hydrogen storage media should address several issues including targeted storage capacities, thermodynamics and hydrogen sorption kinetics, and safety. Nanostructured materials can provide tailor-made properties for storing and releasing hydrogen to fulfill, at least, the partial requirements. This short review, not a comprehensive review of all the materials or technologies in hydrogen storage, summarizes some of the recent developments in application of nanostructures for solid state hydrogen storage; particular attention has been devoted to the most recent development of nanocomposites with tuned dehydrogenation temperatures and kinetics through the control of pore size and surface chemistry. © (2010) Trans Tech Publications, Switzerland. | Hydrogen generated from clean and renewable energy sources has been considered as an alternate fuel to carbon based fossil fuels for several decades. Many drawbacks including energy intensive processes, low volumetric densities, and safety concerns are associated with storing hydrogen as pressured or liquefied. | _ |
!444 | Mixtures of sodium alanate (NaAlH 4) with the nanometric Ni (n-Ni) additive were processed by controlled ball milling for 15 min in a magneto-mill and subsequently investigated by Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD) and volumetric hydrogen desorption in a Sieverts-type apparatus. The apparent activation energy of the decomposition of Na 3AlH 6, which is the decomposition product in the first dehydrogenation step of NaAlH 4, is equal to ~140 kJ/mol and ~101 kJ/mol for ball milled NaAlH 4 and NaAlH 4 +5 wt% n-Ni, respectively, as determined by the Kissinger method in DSC tests. The apparent activation energy for the decomposition of NaH, which is the decomposition product in the second dehydrogenation step of Na 3AlH 6, is estimated as equal to ~143 kJ/mol and ~226 kJ/mol for ball milled NaAlH 4 and NaAlH 4+5 wt% n-Ni, respectively. It seems that the n-Ni additive accelerates the decomposition of Na 3AlH 6 but decelerates the decomposition of NaH. Volumetric desorption tests indicate a substantial enhancement of the rate of hydrogen desorption at 170 °C for the ball milled NaAlH 4+5 wt% n-Ni nanocomposite as a result of the catalytic action of n-Ni. No reaction of n-Ni with the NaAlH 4 matrix is observed during dehydrogenation at 170-280 °C. The n-Ni catalyst used in the present work compares very favorably with other catalytic additives reported in the literature (e.g., metal chlorides) which were used for the enhancement of dehydrogenation of NaAlH 4. Copyright © 2012 American Scientific Publishers All rights reserved. | Mixtures of sodium alanate (NaAlH 4) with the nanometric Ni (n-Ni) additive were processed by controlled ball milling for 15 min in a magneto-mill and subsequently investigated by Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD) and volumetric hydrogen desorption in a Sieverts-type apparatus. No reaction of n-Ni with the NaAlH 4 matrix is observed during dehydrogenation at 170-280 °C. | _ |
!445 | Reversibility is one of the key features for any hydrogen storage material. Borohydrides such as LiBH4 have been studied or proposed as candidates for hydrogen storage because of their high hydrogen contents (18.4 wt% for LiBH4). Limited success has been made in reducing the dehydrogenation temperature. However, full reversibility has not been realized. It is found that the dehydrogenation mechanism of metal borohydrides differs signicantly from the well-known metal hydrides such as LaNi5H 6 and MgH2 that release hydrogen in a single decomposition step through a solid state transformation of crystalline structure. The dehydrogenation of lithium borohydrides involves solid-liquid-gas reactions. Some of the steps in the multiple step decomposition processes of metal borohydrides are not reversible. Furthermore, the decomposition also produces stable intermediate compounds that cannot be rehydrided easily. Lastly, the volatile gases, such as BH3 and B2H6, evolved in decomposition of the transition metal borohydrides cause unrecoverable boron loss. Although our experiments show the partial reversibility of the doped LiBH4, it was not sustainable during dehydriding-rehydriding cycles because of the accumulation of hydrogen inert species and boron loss. Doping with additives reduces the stability of LiBH4, but it also makes LiBH4 less reversible. It raises reasonable doubt on the feasibility of making metal borohydrides suitable for reversible hydrogen storage. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. | It is found that the dehydrogenation mechanism of metal borohydrides differs signicantly from the well-known metal hydrides such as LaNi5H 6 and MgH2 that release hydrogen in a single decomposition step through a solid state transformation of crystalline structure. It raises reasonable doubt on the feasibility of making metal borohydrides suitable for reversible hydrogen storage. | _ |
!446 | Calcium borohydride is one of the most interesting compounds for solid-state hydrogen storage, in particular because of its high hydrogen capacity. In this paper, the synthesis of Ca(BH4)2 by metathesis reaction via ball milling of a mixture of LiBH4 and CaCl2 is described. The effectiveness of this synthesis technique and the possible substitution of Cl ions in the borohydride phases is analysed depending on the back-pressure used for milling. When performed by ball milling under Ar, the metathesis reaction is not successful. A large quantity of a solid solution Li(BH4)1-xClx remains in the sample and CaHCl is formed rather than Ca(BH4)2. In contrast, the use of H2 back-pressure during milling favours the borohydride phases rather than CaHCl and leads to the formation of a solid solution Ca(BH4)2-yCly where [BH4] - groups are partially substituted by Cl ions. This compound has a similar structure as β-Ca(BH4)2 but with smaller lattice parameters. It is present in the as-milled sample together with LiCl and Li(BH4)1-xClx. The decomposition of the mixture occurs at lower temperature than for pure LiBH4 but higher than for pure Ca(BH4)2. The presence of chlorides in the structure of borohydride compounds changes dramatically the thermal properties of the material prepared and should be considered each time a metathesis reaction is used for synthesis. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. | When performed by ball milling under Ar, the metathesis reaction is not successful. This compound has a similar structure as β-Ca(BH4)2 but with smaller lattice parameters. | _ |
!447 | Ammonia borane (AB) is one of the most attractive hydrides owing to its high hydrogen density (19.5 wt%). Stored hydrogen can be released by thermolysis or catalyzed hydrolysis, both routes having advantages and issues. The present study has envisaged for the first time the combination of thermolysis and hydrolysis, AB being first thermolyzed and then the solid by-product believed to be polyaminoborane [NH2BH2]n (PAB) being hydrolyzed. Herein we report that: (i) the combination is feasible, (ii) PAB hydrolyzes in the presence of a metal catalyst (Ru) at 40 °C, (iii) a total of 3 equiv. H2 is released from AB and PAB-H2O, (iv) high hydrogen generation rates can be obtained through hydrolysis, and (v) the by-products stemming from the PAB hydrolysis are ammonium borates. The following reactions may be proposed: AB → PAB + H2 and PAB + xH 2O → 2H2 + ammonium borates. All of these aspects as well as the advantages and issues of the combination of AB thermolysis and PAB hydrolysis are discussed. © 2010 Elsevier B.V. All rights reserved. | Ammonia borane (AB) is one of the most attractive hydrides owing to its high hydrogen density (19.5 wt%). Stored hydrogen can be released by thermolysis or catalyzed hydrolysis, both routes having advantages and issues. | _ |
!448 | The accuracy of gas phase sorption measurements performed on potential hydrogen storage materials has been the subject of much controversy in recent years, particularly in the case of adsorption by carbon nanostructures. As the technological interest in the solid state storage of hydrogen increases, it has become increasingly necessary to investigate the methods used to determine the sorption properties, and hence the storage capacities, of new and existing materials. In this paper, we briefly review the different techniques available and recent literature on the topic, discuss the possible sources of errors and present some comparative measurements on some AB5 hydrogen-absorbing intermetallics. Equilibrium pressure-composition isotherm data measured on two LaNi5-xAlx samples using commercial gravimetric and volumetric instrumentation were found to be in good agreement with each other. © 2007 Elsevier B.V. All rights reserved. | The accuracy of gas phase sorption measurements performed on potential hydrogen storage materials has been the subject of much controversy in recent years, particularly in the case of adsorption by carbon nanostructures. Equilibrium pressure-composition isotherm data measured on two LaNi5-xAlx samples using commercial gravimetric and volumetric instrumentation were found to be in good agreement with each other. | _ |
!449 | The study of ammonia borane (AB) with controllable dehydrogenations is an active research topic for solid-state hydrogen storage materials. The present work shows that tuning the reactivity of both B-H and N-H bonds in AB by alkaline earth metal chlorides not only results in a significantly decrease in the onset dehydrogenation temperature to 40°C but also suppresses undesirable volatile by-products due to the incorporation of alkaline earth metal chlorides in the AB dehydrogenation process. These results provide further insights into the promotion of hydrogen release from amidoboranes and related borohydride ammine complexes. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | The study of ammonia borane (AB) with controllable dehydrogenations is an active research topic for solid-state hydrogen storage materials. These results provide further insights into the promotion of hydrogen release from amidoboranes and related borohydride ammine complexes. | _ |
!450 | This perspective highlights the state-of-the-art solid-state hydrogen storage and describes newly emerging routes towards meeting the practical demands required of a solid-state storage system. The article focuses both on the physical and chemical aspects of hydrogen storage. Common to both classes of storage material is the concept of nanostructure design to tailor kinetics and thermodynamics; whether this be control of functionalised porosity or crystalline growth on the nanoscale. In the area of chemical storage, different processing and nanostructuring techniques that have been employed to overcome the barriers of slow kinetics will be discussed in addition to new chemical systems that have emerged. The prospects of porous inorganic solids, coordination polymers (metal organic frameworks; MOFs) and other polymeric matrices for physical storage of hydrogen will be highlighted. Additionally the role of inorganic nanostructures as evolving materials "intermediate" between physical and chemical storage systems will be discussed and their place within the fine thermodynamic balance for optimum hydrogen uptake and release considered. © 2012 The Royal Society of Chemistry. | This perspective highlights the state-of-the-art solid-state hydrogen storage and describes newly emerging routes towards meeting the practical demands required of a solid-state storage system. In the area of chemical storage, different processing and nanostructuring techniques that have been employed to overcome the barriers of slow kinetics will be discussed in addition to new chemical systems that have emerged. | _ |
!451 | A short review of the materials under investigation suitable for solid state hydrogen storage is presented, with particular reference to the experimental activity carried out at the laboratory of Hydrogen Group of Padova University. © 2008 Elsevier Ltd. All rights reserved. | A short review of the materials under investigation suitable for solid state hydrogen storage is presented, with particular reference to the experimental activity carried out at the laboratory of Hydrogen Group of Padova University. © 2008 Elsevier Ltd. All rights reserved. | _ |
!452 | We have explored metal halide doping in metal borohydrides in order to modify hydrogen desorption/absorption properties of such high-capacity solid-state hydrogen storage materials. The specific application here is 10 mol% addition of CaX2 (X = F, Cl) to Ca(BH4)2. The materials are analyzed using in-situ X-ray diffraction, differential scanning calorimetry, thermogravimetry, and IR spectroscopy, and the experimental results are compared against theoretical predictions from first-principles. Interestingly, in a fully hydrogenated state, CaCl2 dissolves into Ca(BH4)2 whereas CaF2 exists as a separate phase. During the course of dehydrogenation, CaH2-CaF2 solid solution, CaHCl, and a new Ca-H-Cl compound are observed. In-situ X-ray diffraction study reveals that CaX2 interacts with Ca(BH 4)2 in the early stage of decomposition, which could facilitate a direct decomposition of Ca(BH4)2 into CaH2 and CaB6 without forming intermediate phases such as CaB2Hx which seem to be thermodynamically in close competition with the formation of CaH2 and CaB6. Our first-principles calculation estimates that the decrease in the decomposition temperature due to the CaH2-CaX2 interaction would be less than 10 °C, and therefore the major contribution of CaX2 is to change the dehydrogenation pathway rather than the overall thermodynamics. © 2010 Elsevier B.V. All rights reserved. | The specific application here is 10 mol% addition of CaX2 (X = F, Cl) to Ca(BH4)2. During the course of dehydrogenation, CaH2-CaF2 solid solution, CaHCl, and a new Ca-H-Cl compound are observed. | _ |
!453 | In the future sustainable energy system, the recyclable and none-environmental pollution hydrogen-based energy is widely approved in all fields in the future. However, the severe clag, in the development process of industrialization and generalization of hydrogen-based energy, which is lack of the satisfied hydrogen storage material. Over the last decade, material-workers have had a series of researches on the preparation of solid-state hydrogen storage materials and relative hydrogen storage possibilities . The researches mainly includes the following types: (i) Steady large surface areas, such as carbon structures hydrogen storage material; (ii) All kinds of mental and different types of mental alloys, such as the hydrogen storage material based on the element Mg; (iii) All kinds of organic hydrogen storage materials, etc. This paper mainly presents the above mentioned two types of hydrogen storage materials and introduces the aspects of hydrogen storage property and mechanism, mechanical strength of material, porosity and affinity to hydrogen. ©2010 IEEE. | Over the last decade, material-workers have had a series of researches on the preparation of solid-state hydrogen storage materials and relative hydrogen storage possibilities . The researches mainly includes the following types: (i) Steady large surface areas, such as carbon structures hydrogen storage material; (ii) All kinds of mental and different types of mental alloys, such as the hydrogen storage material based on the element Mg; (iii) All kinds of organic hydrogen storage materials, etc. | _ |
!454 | In recent years, significant research and development efforts were spent on hydrogen storage technologies with the goal of realizing a breakthrough for fuel cell vehicle applications. This article scrutinizes design targets and material screening criteria for solid state hydrogen storage. Adopting an automotive engineering point of view, four important, but often neglected, issues are discussed: 1) volumetric storage capacity, 2) heat transfer for desorption, 3) recharging at low temperatures and 4) cold start of the vehicle. The article shall help to understand the requirements and support the research community when screening new materials. © 2009 International Association for Hydrogen Energy. | In recent years, significant research and development efforts were spent on hydrogen storage technologies with the goal of realizing a breakthrough for fuel cell vehicle applications. This article scrutinizes design targets and material screening criteria for solid state hydrogen storage. | _ |
!455 | Multinary complex hydrides comprised of borohydrides, amides and metal hydrides have been synthesized using the solid state mechano-chemical process. After the optimization of the system, it was found that LiBH4/ LiNH2/MgH2 exhibits potential reversible hydrogen storage behavior (>6 wt.%) at temperatures of 125-175 °C. To further improve the hydrogen performance of the system, various nano additives namely, nickel, cobalt, iron, copper, and manganese were investigated. It was observed that some of these additives (Co, Ni) lowered the hydrogen release temperature at least 75-100 °C in the major hydrogen decomposition step. While other additives acted as catalysts and increased the rate at which hydrogen was released. Combinatorial addition of selected materials were also investigated and found to have both a positive effect on kinetics and reduction in hydrogen desorption temperature. © 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. | While other additives acted as catalysts and increased the rate at which hydrogen was released. © 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. | _ |
!456 | Though complex metal hydrides are potential sources of solid state hydrogen storage, practical usage in transportation and power applications is limited by the slow hydrogen adsorption/desorption kinetics and high temperatures for desorption. Experimental observations on transition metal ion-doped sodium alanates reported significant improvement on the hydrogen kinetics at moderate temperatures. However, the actual dopant behavior is still a topic of discussion and the resulting mechanisms leading to changes in the thermodynamic behavior of doped-metal hydrides are still unknown. This work is focused on studying sodium aluminum hydride (NaAlH4) and the role of titanium ion dopants in the improved kinetics of sodium alanates. Density Functional Theory (DFT) geometry optimization calculations are conducted on unit cells and supercells of NaAlH4. Dopant ions replacing native lattice sites are modeled and the electronic density of states and electron density maps around atomic species analyzed to interpret the effect of dopant ions in the sodium alanate cell. | Though complex metal hydrides are potential sources of solid state hydrogen storage, practical usage in transportation and power applications is limited by the slow hydrogen adsorption/desorption kinetics and high temperatures for desorption. Density Functional Theory (DFT) geometry optimization calculations are conducted on unit cells and supercells of NaAlH4. | _ |
!457 | Several mixtures of LiBH 4 and Mg(BH 4) 2 borohydrides in different stoichiometric ratios (1:0, 2:1, 1:1, 1:2, 0:1), prepared by high energy ball milling, have been investigated with X-ray powder diffraction and thermal programmed desorption (TPD) volumetric analysis to test the dehydrogenation kinetics in correlation with the physical mixture composition. Afterwards mixed and unmixed borohydrides were dispersed on high specific surface area ball milled graphite by means of the solvent infiltration technique. BET and statistical thickness methods were used to characterize the support surface properties, and SEM micrographs gave a better understanding of the preparation techniques. It has been observed by TPD volumetric measurements that the confinement of the reactive borohydrides on the nanoporous supports leads to a lower dehydrogenation temperature compared to unsupported borohydrides. Moreover, a further decrease of the dehydrogenation temperature has been observed by increasing the specific surface area of the support and the pores volume and by using the prepared mixtures instead of pure materials. The dehydrogenation process seems to be favoured by the heterogeneous nucleation on the graphite surface of decomposition products or intermediate phases from melted liquid borohydrides. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | Several mixtures of LiBH 4 and Mg(BH 4) 2 borohydrides in different stoichiometric ratios (1:0, 2:1, 1:1, 1:2, 0:1), prepared by high energy ball milling, have been investigated with X-ray powder diffraction and thermal programmed desorption (TPD) volumetric analysis to test the dehydrogenation kinetics in correlation with the physical mixture composition. Afterwards mixed and unmixed borohydrides were dispersed on high specific surface area ball milled graphite by means of the solvent infiltration technique. | _ |
!458 | The major obstacle in transition to the hydrogen economy is the problem of onboard hydrogen storage. Solid-state hydrogen storage is the safest and most efficient method for hydrogen storage. Most of the metal hydrides exhibit very large volumetric storage density but less than 5 wt % gravimetric hydrogen density. Light metals such as Al, B bind with four hydrogen atoms and form together with an alkali metal an ionic or partially covalent compound called complex hydride. LiBH4 is a complex hydride with 18.5 mass % gravimetric hydrogen density and 121 kg/m3 volumetric hydrogen storage capacity. The desorption temperature of LiBH4 is greater than 470°C, thus making it difficult to use for storage applications. In addition, the conditions for reversible reaction are unfavorable. Modification of thermodynamics of the hydrogenation and dehydrogenation reaction is possible by using additives which could destabilize LiBH4 by stabilizing the dehydrogenated state. This could decrease the heat of reaction and reduce the desorption temperature at the same time, making the conditions for reversible reaction more optimum. Several additives which could destabilize LiBH 4 have been reviewed. © 2010 by Begell House, Inc. | Light metals such as Al, B bind with four hydrogen atoms and form together with an alkali metal an ionic or partially covalent compound called complex hydride. The desorption temperature of LiBH4 is greater than 470°C, thus making it difficult to use for storage applications. | _ |
!459 | Transition from the metallic to the hydride phase is of fundamental importance to achieving hydrogen storage in the solid state. Multi-component metal hydrides belong to one of the promising categories of materials that can potentially offer high hydrogen storage capacity. Despite extensive research on metal hydrides over the past decades, the progress remains limited partly due to the inability of screening a nearly infinite number of possible alloy compositions. High throughput materials fabrication and characterization techniques therefore offer an advantage in studying multi-component alloys and their phase transition to metal hydrides. We fabricated an Mg-Ni-Al and Ca-B-Ti ternary alloy libraries using a continuous combinatorial material synthesis technique, and measured the optical reflectance to examine the formation of metal hydride phase when the alloy library was exposed to hydrogen. The results indicate that mapping the change in reflectance is a viable method to study the kinetics of hydride formation. Monitoring the optical properties provides evidence for the "black state" formed during the transition from α-phase to β-phase. In addition, we found that the fastest reflectance change occurred when the alloy has an Mg to Ni ratio of approximately 2:1, and with low concentration of Al. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. | We fabricated an Mg-Ni-Al and Ca-B-Ti ternary alloy libraries using a continuous combinatorial material synthesis technique, and measured the optical reflectance to examine the formation of metal hydride phase when the alloy library was exposed to hydrogen. In addition, we found that the fastest reflectance change occurred when the alloy has an Mg to Ni ratio of approximately 2:1, and with low concentration of Al. © 2010 Professor T. Nejat Veziroglu. | _ |
!460 | The thermal transformations in the lithium alanate-amide system consisting of lithium aluminum hydride (LiAlH4) and lithium amide (LiNH 2), mixed in a 1:1 M ratio, were investigated using the pressure-composition-temperature analysis, solid-state nuclear magnetic resonance, X-ray powder diffraction, and residual gas analysis. Below 250 °C, the alanate decomposes into Al, LiH and H2, through the formation of Li3AlH6, whereas the amide remains largely intact. The release of gaseous hydrogen corresponds to approximately 5 wt%. Above 250 °C, additional ∼4 wt% of hydrogen is produced through solid-state reactions among LiNH2, LiH and metallic Al, through the formation of intermetallic Li-Al binary alloy and an unidentified intermediate. The overall reaction of the thermochemical transformation of the LiAlH 4-LiNH2 mixture results in the production of Li 3AlN2, metallic Al, LiH and the release of 9 wt% of gaseous hydrogen. The reaction mechanism of the thermal decomposition is different from one identified earlier during mechanical treatment of the same system. Rehydrogenation of the thermally-decomposed products of LiAlH 4-LiNH2 mixture using high hydrogen pressure (180 bar) and heating (275 °C) yields LiNH2 and amorphous aluminum nitride (AlN). © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | The thermal transformations in the lithium alanate-amide system consisting of lithium aluminum hydride (LiAlH4) and lithium amide (LiNH 2), mixed in a 1:1 M ratio, were investigated using the pressure-composition-temperature analysis, solid-state nuclear magnetic resonance, X-ray powder diffraction, and residual gas analysis. Above 250 °C, additional ∼4 wt% of hydrogen is produced through solid-state reactions among LiNH2, LiH and metallic Al, through the formation of intermetallic Li-Al binary alloy and an unidentified intermediate. | _ |
!461 | Large quantities of hydrogen (H2) are released at ambient temperatures as a result of mechanical dehydrogenation during ball milling of complex hydride composites such as (LiAlH4+5 wt.% nanometric Fe), (nLiAlH4+LiNH2; n=1, 3, 11.5, 30), (nLiAlH 4+MnCl2; n=1, 3, 8, 13, 30, 63) and (LiNH 2+nMgH2; n=0.5-2.0). For both the (nLiAlH 4+LiNH2) and (LiAlH4+5 wt.% nanometric Fe) composites the second constituent strongly destabilizes LiAlH4 during milling by different mechanisms. For (nLiAlH4+MnCl2) two concurrent mechanisms are observed: (i) a reaction between both constituents during ball milling leading to the formation of LiCl, amorphous Mn and H2, and (ii) a catalytic-like induced decomposition of LiAlH4 into Li 3AlH6, Al and H2. For the (LiNH 2+nMgH2; n=0.5-2.0) composite system, the pathway of hydride reactions depends on the molar ratio n and total milling energy consumed during ball milling. Some composite systems slowly self-discharge H2 at room temperature (RT), 40 and 80°C, after ball milling with an additive. Technical parameters such as specific energy-usable are estimated for LiAlH4-based complex hydride composite systems and are compared with both US DOE hydrogen powered car targets and Li-ion batteries benchmarks. © 2012 Published by Elsevier Ltd. | Some composite systems slowly self-discharge H2 at room temperature (RT), 40 and 80°C, after ball milling with an additive. Technical parameters such as specific energy-usable are estimated for LiAlH4-based complex hydride composite systems and are compared with both US DOE hydrogen powered car targets and Li-ion batteries benchmarks. | _ |
!462 | The feasibility of scaling up the production of a Mg-based hydride as material for solid state hydrogen storage is demonstrated in the present work. Magnesium hydride, added with a Zr-Ni alloy as catalyst, was treated in an attritor-type ball mill, suitable to process a quantity of 0.5-1 kg of material. SEM-EDS examination showed that after milling the catalyst was well distributed among the magnesium hydride crystallites. Thermodynamic and kinetic properties determined by a Sievert's type apparatus showed that the semi-industrial product kept the main properties of the material prepared at the laboratory scale. The maximum amount of stored hydrogen reached values between 5.3 and 5.6 wt% and the hydriding and dehydriding times were of the order of few minutes at about 300 °C. © 2008 International Association for Hydrogen Energy. | Magnesium hydride, added with a Zr-Ni alloy as catalyst, was treated in an attritor-type ball mill, suitable to process a quantity of 0.5-1 kg of material. The maximum amount of stored hydrogen reached values between 5.3 and 5.6 wt% and the hydriding and dehydriding times were of the order of few minutes at about 300 °C. | _ |
!463 | A short review of the materials under investigation suitable for solid state hydrogen storage is presented, with emphasis on the experimental activity carried out at the laboratory of Hydrogen Group of Padova University. | A short review of the materials under investigation suitable for solid state hydrogen storage is presented, with emphasis on the experimental activity carried out at the laboratory of Hydrogen Group of Padova University. | _ |
!464 | In this study, we have developed and characterized various Mg-V-Ni compositions with respect to hydrogen storage. The study was conducted using magnesium as the base material with additions of 5 atomic% of nickel and vanadium in the range of 2.5-10 atomic%. The various compositions were synthesized using high-energy ball milling with different milling times. The compositions were characterized using scanning electron microscopy, energy-dispersive X-ray spectrometry, and X-ray diffraction, and the hydriding-dehydriding characteristics studied using the Sievert method. It was found that the maximum reversible hydrogen storage capacity in the Mg-V-Ni system is 5.71 mass %. Furthermore, it was found that 6 mass% of hydrogen is absorbed within the first 5 min at 210°C. This lowered hydriding temperature is associated with the presence of vanadium as a catalyst. The hydriding enthalpy of the optimized (highest storage capacity) Mg-V-Ni composition has been measured using differential scanning calorimetry as 79.15±3.56 kJ/mol of H2 and the hydriding entropy was obtained as 141.18 ± 6.35 J/mol of H2 K. © 2012 by Begell House, Inc. | In this study, we have developed and characterized various Mg-V-Ni compositions with respect to hydrogen storage. Furthermore, it was found that 6 mass% of hydrogen is absorbed within the first 5 min at 210°C. | _ |
!465 | Manganese borohydride (Mn(BH 4) 2) is considered to be a high-capacity (∼10 wt %) solid-state hydrogen storage candidate, but so far has not been shown to exhibit reversible hydrogenation. This study presents the calculated crystal structure and electronic structure of Mn(BH 4) 2 from density-functional theory within the generalized gradient approximation and thermodynamic properties from the direct method lattice dynamics. A thermodynamically stable phase of Mn(BH 4) 2 is identified. The calculation of Gibbs energy at finite temperatures suggests that the stable phase is of I4 jm2 symmetry. The formation energy of Mn(BH 4) 2 for the I4 j m2 symmetry solid is -28.93 kJ/f.u. at 0 K including zero-point energy corrections, and the standard state enthalpy of formation is predicted to be -58.89 kJ/f.u. The most feasible dehydrogenation reaction is found to be Mn(BH 4) 2 ) Mn + 2B+ 4H 2, which is an endothermic reaction at decomposition temperature. The spin-polarized electronic density of states shows that manganese borohydride has a half-metallic nature due to the presence of half-filled 3d electrons from Mn. The electronic structure calculations and analysis show that the interaction between Mn atoms and BH4 complexes has an ionic character, while the internal bonding of BH 4 is essentially covalent., © 2009 American Chemical Society. | Manganese borohydride (Mn(BH 4) 2) is considered to be a high-capacity (∼10 wt %) solid-state hydrogen storage candidate, but so far has not been shown to exhibit reversible hydrogenation. at 0 K including zero-point energy corrections, and the standard state enthalpy of formation is predicted to be -58.89 kJ/f.u. | _ |
!466 | In recent years there has been considerable interest in sodium alanate as a prototypical complex hydride for solid-state hydrogen storage. Much effort has gone into understanding the rate-limiting processes in its hydrogen release and absorption reactions. The diffusion of metal species has been suggested as a possible kinetic bottleneck in Ti-doped materials. In this paper, we outline an approach for calculating the diffusivity of defects in complicated lattices using a combination of first-principles density-functional theory calculations and stochastic kinetic Monte Carlo methods. We apply this methodology to the diffusion of metal defects in NaAlH4 and Na3AlH 6 that have been predicted to exist in large concentrations. We find that of the metal defects that exist in the largest concentrations, a neutral AlH3 vacancy is the most mobile in NaAlH4 (ΔH mig = 0.34 eV, D0 = 1.30 × 10-2 cm 2/s, and DT=400K = 7.55 × 10-7 cm 2/s) and that a negatively charged Na vacancy is the most mobile in Na3AlH6 (ΔHmig = 0.33 eV, D0 = 6.67 × 10-3 cm2/s, and DT=400K = 4.96 × 10-7 cm2/s). At T = 400 K, the calculated diffusion rates are an order of magnitude lower for charged AlH4 vacancies in NaAlH4 (ΔH = 0.44 eV, D0 = 1.41 × 10-2 cm2/s, and DT=400K = 3.92 × 10 -8 cm2/s) and charged Na vacancies in NaAlH4 (ΔH = 0.43 eV, D0 = 2.96 × 10-3 cm 2/s, and DT=400K = 1.19 × 10-8 cm 2/s). This information is necessary for understanding the kinetics of mass transport during the hydrogen release and absorption reactions of NaAlH4. © 2011 American Chemical Society. | Much effort has gone into understanding the rate-limiting processes in its hydrogen release and absorption reactions. The diffusion of metal species has been suggested as a possible kinetic bottleneck in Ti-doped materials. | _ |
!467 | Our hydrogen-powered lawn mower [Yvon K, Lorenzoni J-L. Hydrogen powered lawn mower. Int J Hydrogen Energy 1993; 18, 345-48] has been operated without major interruption during the past 14 years. The commercial model was originally running on gasoline and was adapted to hydrogen by making small adjustments to the carburettor and by installing a hydrogen reservoir containing solid-state metal hydrides. During the evaluation period the only maintenance work was changing the lubricating oil of the engine once a year, and reactivating the metal hydride powder by external heating after an accidental inlet of air into the reservoir. There occurred no technical failure, and there was no safety incident, neither during operation nor during recharging of hydrogen. This demonstrates that a hydrogen-operated device of this type is mature for use by greater public. Cost and marketing issues are discussed. © 2006 International Association for Hydrogen Energy. | Int J Hydrogen Energy 1993; 18, 345-48] has been operated without major interruption during the past 14 years. The commercial model was originally running on gasoline and was adapted to hydrogen by making small adjustments to the carburettor and by installing a hydrogen reservoir containing solid-state metal hydrides. | _ |
!468 | The recent advances on the effects of microstructural refinement and various nano-catalytic additives on the hydrogen storage properties of metal and complex hydrides obtained in the last few years in the allied laboratories at the University of Waterloo (Canada) and Military University of Technology (Warsaw, Poland) are critically reviewed in this paper. The research results indicate that microstructural refinement (particle and grain size) induced by ball milling influences quite modestly the hydrogen storage properties of simple metal and complex metal hydrides. On the other hand, the addition of nanometric elemental metals acting as potent catalysts and/or metal halide catalytic precursors brings about profound improvements in the hydrogen absorption/desorption kinetics for simple metal and complex metal hydrides alike. In general, catalytic precursors react with the hydride matrix forming a metal salt and free nanometric or amorphous elemental metals/intermetallics which, in turn, act catalytically. However, these catalysts change only kinetic properties i.e. the hydrogen absorption/desorption rate but they do not change thermodynamics (e.g., enthalpy change of hydrogen sorption reactions). It is shown that a complex metal hydride, LiAlH4, after high energy ball milling with a nanometric Ni metal catalyst and/or MnCl2 catalytic precursor, is able to desorb relatively large quantities of hydrogen at RT, 40 and 80 °C. This kind of behavior is very encouraging for the future development of solid state hydrogen systems. © 2010 by the authors. | The research results indicate that microstructural refinement (particle and grain size) induced by ball milling influences quite modestly the hydrogen storage properties of simple metal and complex metal hydrides. It is shown that a complex metal hydride, LiAlH4, after high energy ball milling with a nanometric Ni metal catalyst and/or MnCl2 catalytic precursor, is able to desorb relatively large quantities of hydrogen at RT, 40 and 80 °C. | _ |
!469 | In order to enable the commercial acceptance of solid-state hydrogen storage materials and systems it is important to understand the risks associated with the environmental exposure of various materials. In some instances, these materials are sensitive to the environment surrounding the material and the behavior is unique and independent to each material. The development of testing procedures to evaluate a material's behavior with different environmental exposures is a critical need. In some cases material modifications may be needed in order to reduce the risk of environmental exposure. We have redesigned two standardized UN tests for clarity and exactness; the burn rate and self-heating tests. The results of these and other UN tests are shown for ammonia borane, NH 3BH 3, and alane, AlH 3. The burn rate test showed a strong dependence on the preparation method of aluminum hydride as the particle size and trace amounts of solvent greatly influence the test results. The self-heating test for ammonia borane showed a failed test as low as 70 °C in a modified cylindrical form. Finally, gas phase calorimetry was performed and resulted in an exothermic behavior within an air and 30%RH environment. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | The self-heating test for ammonia borane showed a failed test as low as 70 °C in a modified cylindrical form. Finally, gas phase calorimetry was performed and resulted in an exothermic behavior within an air and 30%RH environment. | _ |
!470 | Hydrogen is important as a new source of energy for automotive applications. It is clear that the key challenge in developing this technology is hydrogen storage. Current methods for hydrogen storage have yet to meet all the demands for onboard applications. High-pressure gas storage or liquefaction cannot fulfill the storage criteria required for on-board storage. Solid-state materials have shown potential advantages for hydrogen storage in comparison to other storage methods. In this article, the most popular solid-state storage materials and methods including carbon based materials, metal hydrides, metal organic frameworks, hollow glass microspheres, capillary arrays, clathrate hydrates, metal nitrides and imides, doped polymer and zeolites, are critically reviewed. The survey shows that most of the materials available with high storage capacity have disadvantages associated with slow kinetics and those materials with fast kinetics have issues with low storage capacity. Most of the chemisorption-based materials are very expensive and in some cases, the hydrogen absorption/desorption phenomena isirreversible. Furthermore, a very high temperature is required to release the adsorbed hydrogen. On the other hand, the main drawback in the case of physisorption-based materials and methods is their lower capacity for hydrogen storage, especially under mild operating conditions. To accomplish the requisite goals, extensive research studies are still required to optimize the critical parameters of such systems, including the safety (to be improved), security (to be available for all), cost (to be lowered), storage capacity (to be increased), and the sorption-desorption kinetics (to be improved). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. | Hydrogen is important as a new source of energy for automotive applications. Furthermore, a very high temperature is required to release the adsorbed hydrogen. | _ |
!471 | Owing to their high uptake capacity at low temperature and excellent reversibility kinetics, metal-organic frameworks have attracted considerable attention as potential solid-state hydrogen storage materials. In the last few years, researchers have also identified several strategies for increasing the affinity of these materials towards hydrogen, among which the binding of H 2 to unsaturated metal centers is one of the most promising. Herein, we review the synthetic approaches employed thus far for producing frameworks with exposed metal sites, and summarize the hydrogen uptake capacities and binding energies in these materials. In addition, results from experiments that were used to probe independently the metal-hydrogen interaction in selected materials will be discussed. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA. | Owing to their high uptake capacity at low temperature and excellent reversibility kinetics, metal-organic frameworks have attracted considerable attention as potential solid-state hydrogen storage materials. Herein, we review the synthetic approaches employed thus far for producing frameworks with exposed metal sites, and summarize the hydrogen uptake capacities and binding energies in these materials. | _ |
!472 | Reactive Hydride Composites (RHCs), ball-milled composites of two or more different hydrides, are suggested as an alternative for solid state hydrogen storage. In this work, dehydrogenation of 2NaBH4 + MgH2 system under vacuum was investigated using complementary characterization techniques. At first, thermal programmed desorption of as-milled composite and single compounds was used to identify the temperature range of hydrogen release. RHC samples annealed at various temperatures up to 500 °C were characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. It was found that the dehydrogenation reaction under vacuum is likely to proceed as follows: 2NaBH4 + MgH2 (>250 °C) → 2NaBH4 + 1/2MgH2 + 1/2Mg + 1/2H2 (>350 °C) ↔ 3/2NaBH4 + 1/4MgB2 + 1/2NaH + 3/4Mg + 7/4H2 (>450 °C) → 2Na + B + 1/2Mg + 1/2MgB 2 + 5H2. In addition, presence of NaMgH3 phase suggests the occurrence of secondary reactions. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights. | RHC samples annealed at various temperatures up to 500 °C were characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. It was found that the dehydrogenation reaction under vacuum is likely to proceed as follows: 2NaBH4 + MgH2 (>250 °C) → 2NaBH4 + 1/2MgH2 + 1/2Mg + 1/2H2 (>350 °C) ↔ 3/2NaBH4 + 1/4MgB2 + 1/2NaH + 3/4Mg + 7/4H2 (>450 °C) → 2Na + B + 1/2Mg + 1/2MgB 2 + 5H2. | _ |
!473 | Hydrogen storage in solid hydrides is the most attractive method of on-board hydrogen storage in fuel cell for cars. Mg metal exhibits a high-storage capacity by weight and has been considered a group of potentially attractive candidates for solid-state hydrogen storage. In this study, mechanochemical synthesis of nanocrystalline Mg-based hydrogen storage composites from various starting materials in specialized hydrogen ball mills has been achieved. The reactive synthesis process and the hydrogen desorption behaviors of the composite hydrides were investigated by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry (TG-DSC). The results show that nano-sized MgH2 and Mg(AlH4)2 could be directly synthesized by pure Mg and pretreated Al powder, as well as Mg-Li-Al alloy powder. Alloying element Li could remarkably promote the synthesis of magnesium alanate, the product composite hydrides releasing 6.2wt% H2 through multi-step decompositions, of which the starting endothermic peaks are as low as 65 °C. © (2009) Trans Tech Publications, Switzerland. | In this study, mechanochemical synthesis of nanocrystalline Mg-based hydrogen storage composites from various starting materials in specialized hydrogen ball mills has been achieved. The results show that nano-sized MgH2 and Mg(AlH4)2 could be directly synthesized by pure Mg and pretreated Al powder, as well as Mg-Li-Al alloy powder. | _ |
!474 | There are four R&D programs on hydrogen and fuel cell in Korea. Two of them are supported by MEST (Ministry of Education, Science and Technology) and others are funded by MKE (Ministry of Knowledge Economy). The hydrogen production technologies examined in Korea cover 3 main bases, fossil fuel, renewable energy including photo-catalytic, bio-hydrogen technology, and high temperature gas-cooled reactor. In October 2003, Korean government launched Hydrogen Energy R&D Center (HERC) as a member of the 21st Century Frontier R&D programs supported by the Ministry of Education, Science and Technology (MEST). The HERC has conducted research on the key technologies for the production, storage, and utilization of hydrogen energy for expediting realization of hydrogen economy based on renewable energy sources. The main purposes of this paper are to overview the current status of research programs for hydrogen storage technologies conducted by Hydrogen Energy R&D Center based on the patent applications as well as research topics and to introduce specific achievements in each research program. © 2011 by ASME. | The hydrogen production technologies examined in Korea cover 3 main bases, fossil fuel, renewable energy including photo-catalytic, bio-hydrogen technology, and high temperature gas-cooled reactor. In October 2003, Korean government launched Hydrogen Energy R&D Center (HERC) as a member of the 21st Century Frontier R&D programs supported by the Ministry of Education, Science and Technology (MEST). | _ |
!475 | We have examined the effect of adding small quantities of Fe, Ni, and Zn, or their dichlorides, on the dehydrogenation temperature of the new quaternary hydride material LiB0.33N0.67H2.67. NiCl2 proved to be an especially effective dehydrogenation promoter. The hydrogen release temperature, represented by the temperature T1/2 at which the hydrogen release reaction is half completed, decreased by ΔT1/2 = -104 °C for 5 wt% NiCl2 addition and by ΔT1/2 = -112 °C for 11 wt% NiCl2 addition compared to that of additive-free LiB0.33N0.67H2.67. This represents a significant improvement over the maximum temperature reduction of ΔT1/2 = -90 °C achieved previously with Pt/Vulcan carbon additive (Pt nanoparticles supported on a Vulcan carbon substrate). Transmission electron microscopy on LiB0.33N0.67H2.67 + 11 wt% NiCl2 revealed uniformly dispersed nanoparticles with diameters less than 8 nm within the LiB0.33N0.67H2.67 matrix, consistent with reduction of the NiCl2 to metallic Ni during synthesis by ball milling. Mass spectrometry of the evolved gas showed that the total amount of NH3 released concurrently during dehydrogenation of LiB0.33N0.67H2.67 + 5 wt% NiCl2 was reduced by an order of magnitude compared to the additive-free material, and by a factor of four compared to LiB0.33N0.67H2.67 + 5 wt% Pt/Vulcan carbon. In contrast to additive-free LiB0.33N0.67H2.67, which melts completely above 190 °C and releases hydrogen from the liquid state only above about 250 °C, hydrogen release from LiB0.33N0.67H2.67 + 5 wt% NiCl2 is accompanied by partial melting above 190 °C plus transformation to a new, hydrogen-poor solid intermediate phase. Addition of 5 wt% FeCl2 gave ΔT1/2 = -36 °C, but Fe, Zn, and ZnCl2 additives did not produce significant improvement. © 2006 Elsevier B.V. All rights reserved. | Transmission electron microscopy on LiB0.33N0.67H2.67 + 11 wt% NiCl2 revealed uniformly dispersed nanoparticles with diameters less than 8 nm within the LiB0.33N0.67H2.67 matrix, consistent with reduction of the NiCl2 to metallic Ni during synthesis by ball milling. Addition of 5 wt% FeCl2 gave ΔT1/2 = -36 °C, but Fe, Zn, and ZnCl2 additives did not produce significant improvement. | _ |
!476 | In times of severe shortage of fossil fuels new strategies have to be developed to assure future mobility. Fuel cell driven automotives with hydrogen as an energy carrier is one alternative discussed for the substitution of gasoline in the long term. Both the generation as well as the storage of hydrogen are technical challenges which have to be solved before hydrogen technology can be a real alternative for mobile applications. This perspective paper highlights the state-of-the art in the field of hydrogen storage, especially in solids, including the technical limitations. New potential research fields are discussed which may contribute to future energy supply in niche applications. © 2011 The Royal Society of Chemistry. | Both the generation as well as the storage of hydrogen are technical challenges which have to be solved before hydrogen technology can be a real alternative for mobile applications. New potential research fields are discussed which may contribute to future energy supply in niche applications. | _ |
!477 | Lightweight complex hydrides have attracted attention for their high storage hydrogen capacity. NaAlH4 has been widely studied as a hydrogen storage material for its favorable reversible operating temperature and pressure range for automotive fuel cell applications. The increased understanding of NaAlH4 has led to an expanded search for high capacity materials in mixed alkali and akali/alkaline earth alanates. In this study, promising candidates in the Na-Li-Mg-Al-H system were evaluated using a combination of experimental chemistry, atomic modeling, and thermodynamic modeling. New materials were synthesized using solid state and solution based processing methods. Their hydrogen storage properties were measured experimentally, and the test results were compared with theoretical modeling assessments. © 2007 Elsevier B.V. All rights reserved. | Lightweight complex hydrides have attracted attention for their high storage hydrogen capacity. The increased understanding of NaAlH4 has led to an expanded search for high capacity materials in mixed alkali and akali/alkaline earth alanates. | _ |
!478 | Hydrogen is expected to play an important role as an energy carrier in a future, more sustainable society. However, its compact, efficient, and safe storage is an unresolved issue. One of the main options is solid-state storage in hydrides. Unfortunately, no binary metal hydride satisfies all requirements regarding storage density and hydrogen release and uptake. Increasingly complex hydride systems are investigated, but high thermodynamic stabilities as well as slow kinetics and poor reversibility are important barriers for practical application. Nanostructuring by ball-milling is an established method to reduce crystallite sizes and increase reaction rates. Since five years attention has also turned to alternative preparation techniques that enable particle sizes below 10 nanometers and are often used in conjunction with porous supports or scaffolds. In this Review we discuss the large impact of nanosizing and -confinement on the hydrogen sorption properties of metal hydrides. We illustrate possible preparation strategies, provide insight into the reasons for changes in kinetics, reversibility and thermodynamics, and highlight important progress in this field. All in all we provide the reader with a clear view of how nanosizing and -confinement can beneficially affect the hydrogen sorption properties of the most prominent materials that are currently considered for solid-state hydrogen storage. Light metal hydrides are an important option for compact, safe, and efficient on-board hydrogen storage. However, slow kinetics, poor reversibility, and low equilibrium pressures hamper their practical application. We review the impact of nanosizing and -confinement; recent strategies with a large impact on the hydrogen sorption properties of relevant light metal hydrides. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. | Since five years attention has also turned to alternative preparation techniques that enable particle sizes below 10 nanometers and are often used in conjunction with porous supports or scaffolds. Light metal hydrides are an important option for compact, safe, and efficient on-board hydrogen storage. | _ |
!479 | Polymer-stabilized cobalt(0) nanoclusters were prepared from the reduction of cobalt(II) chloride in the presence of poly(N-vinyl-2-pyrrolidone)(PVP) stabilizer in methanol solution. PVP-stabilized cobalt(0) nanoclusters were found to be stable in solution and could be isolated as solid material and characterized by TEM, XPS, FT-IR, and UV-visible electronic absorption spectroscopy. PVP-stabilized cobalt(0) nanoclusters were employed as catalyst in the hydrolysis of sodium borohydride and ammonia-borane, which have been considered as solid-state hydrogen storage materials for portable fuel cell applications. PVP-stabilized cobalt(0) nanoclusters were found to be highly active catalyst in both hydrolysis reactions, even at room temperature. Kinetic studies show that the catalytic hydrolyses of sodium borohydride and ammonia-borane are both first order with respect to catalyst and substrate concentration in aqueous medium. The effect of the NaOH concentration on the catalytic activity of the PVP-stabilized cobalt(0) nanoclusters in the hydrolysis of sodium borohydride was also studied. The activation parameters of these hydrolysis reactions were determined from the evaluation of the kinetic data. The PVP-stabilized cobalt(0) nanoclusters provide a lower activation energy for the hydrolysis of sodium borohydride both in aqueous medium(E a = 63 ± 2 kJ·mol-1) and in basic solution(Ea = 37 ± 2 kJ·mol-1) compared to the value reported for bulk cobalt(Ea = 75 kJ · mol -1). © 2009 American Chemical Society. | PVP-stabilized cobalt(0) nanoclusters were employed as catalyst in the hydrolysis of sodium borohydride and ammonia-borane, which have been considered as solid-state hydrogen storage materials for portable fuel cell applications. PVP-stabilized cobalt(0) nanoclusters were found to be highly active catalyst in both hydrolysis reactions, even at room temperature. | _ |
!480 | Magnesium may be the most promising solid-state hydrogen storage material owing to its high storage capacity (7.6 wt%) and highest volumetric density (2 times of liquid H2). On the other hand, suffers from its sluggish absorption/desorption characteristics. In the present study, the simple/cost-effective hydriding combustion synthesis (HCS) was used to prepare highly-active Mg-based-samples. The preparative parameters of HCS were varied, and its effects on the micro-structural and hydrogen storage properties were determined. The results and its analysis showed that the simple HCS process possesses a multifaceted dependence on a range of experimental factors and affect the final product. The estimated dependence enabled us to explain the combined effect of individual experimental factors on the prepared samples. The Mg-Ni-C sample prepared at 610°C with 6%wt-nano-Ni and 4 wt%-multi-walled-CNTs as reactants, resulted in sample with a surface area as high as 19.01 m2/g and a desorption capacity of 5.77 wt%, highlighting the promising characteristics of HCS to prepare highly-active Mg-based-materials. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | Magnesium may be the most promising solid-state hydrogen storage material owing to its high storage capacity (7.6 wt%) and highest volumetric density (2 times of liquid H2). The Mg-Ni-C sample prepared at 610°C with 6%wt-nano-Ni and 4 wt%-multi-walled-CNTs as reactants, resulted in sample with a surface area as high as 19.01 m2/g and a desorption capacity of 5.77 wt%, highlighting the promising characteristics of HCS to prepare highly-active Mg-based-materials. | _ |
!481 | EDen is a European project, supported by FP7 - JTI FCH. It aims to develop an innovative embedded system for the storage of energy, thank to combination and thermal integration between a SOFC (capable to work like SOE) and a innovative solid state hydrogen storage tank. In the proposed work, the objective is the optimization through modeling of behavior and physical performance for hydrogen storage solution in solid-state material (Mg-based metal hydrides). The candidate material for hydrogen storage, and final pellet (utilized inside tank) have been defined through the identification of best physics, to better describe gas' diffusion phenomena and thermal exchange inside the storage tank. Copyright © 2013 Delta Energy and Environment. | EDen is a European project, supported by FP7 - JTI FCH. It aims to develop an innovative embedded system for the storage of energy, thank to combination and thermal integration between a SOFC (capable to work like SOE) and a innovative solid state hydrogen storage tank. | _ |
!482 | Metal hydrides are formed when certain metals or alloys are exposed to hydrogen at favorable temperatures and pressures. In order to sustain the sorption of hydrogen during this exothermic process, the generated heat has to be removed effectively. Release of hydrogen is an endothermic process needing supply of heat to the metal hydride matrix. Depending on the application, the heat transfer medium can be either a liquid or a gas. Reduction of the total weight of hydrogen storage devices is essential toward utilization of hydrogen for mobile and portable applications. While a variety of new storage materials with desirable sorption characteristics are being suggested, optimal thermal design of the storage device remains a major challenge. Lack of thermodynamic, transport, and thermophysical property data of the material particles and of the bed is another drawback which needs to be addressed. © 2012 American Society of Mechanical Engineers. | In order to sustain the sorption of hydrogen during this exothermic process, the generated heat has to be removed effectively. While a variety of new storage materials with desirable sorption characteristics are being suggested, optimal thermal design of the storage device remains a major challenge. | _ |
!483 | Minimization of total weight is the major criterion in the design of a solid state hydrogen storage device for mobile or portable applications. The design should also address the requirements such as storage capacity, charge/discharge rates, space constraints, coolant temperature and hydrogen supply pressure. To achieve this, one should be able to reliably predict the dynamic performance of the storage device. In this paper, a parametric study of hydrogen sorption in an aircooled annular cylindrical hydrogen storage device with external fins is reported. LaNi5, which has excellent hydrogen storage properties is used as the hydriding material. The influence of different geometric parameters such as hydride bed thickness and fin height, and operational parameters such as hydrogen supply pressure and cooling air temperature are studied. | Minimization of total weight is the major criterion in the design of a solid state hydrogen storage device for mobile or portable applications. LaNi5, which has excellent hydrogen storage properties is used as the hydriding material. | _ |
!484 | Magnesium is a promising material for solid state hydrogen storage, since it has low cost and its hydride can store reversibly up to 7.6 wt.% of hydrogen. Fast H-sorption kinetics at around 300 °C can be achieved after processing Mg-based mixtures by high energy ball milling (HEBM), which produces nanostructured composite powders. Severe plastic deformation (SPD) processing techniques are being explored as an alternative to HEBM in order to obtain more air-resistant materials and to reduce the time and energy required for processing. In this paper, MgH2 and MgH2-Fe mixtures were severely mechanically processed by extensive cold forging (CF) and cold rolling (CR). A very significant grain refinement (up to 10 nm) was achieved, which is comparable to the values typically obtained after processing by HEBM. Enhanced H-sorption properties were observed for these mechanically processed MgH 2-based nanocomposites in comparison with commercial magnesium hydride. The obtained compacts after CR and CF presents a much lower specific surface area than the ball-milled powders and therefore show higher air-resistance. These results are promising from the point of view of applications since it reveals the potential of the use of low cost mechanical processing routes to produce Mg-based nanomaterials for hydrogen storage. © 2011 Elsevier B.V. All rights reserved. | Fast H-sorption kinetics at around 300 °C can be achieved after processing Mg-based mixtures by high energy ball milling (HEBM), which produces nanostructured composite powders. Enhanced H-sorption properties were observed for these mechanically processed MgH 2-based nanocomposites in comparison with commercial magnesium hydride. | _ |
!485 | Due to their extensive present, important and versatile potential applications, metal hydrides (MH) are among the most investigated solid-state systems. Theoretical, numerical and experimental studies have provided a considerable knowledge about their structure and properties, but in spite of that, the basic electronic principles of various interactions present in MH have not yet been completely resolved. Even in the simplest MH, i.e. alkali hydrides (Alk-H), some trends in physical properties, and especially their deviations, are not well understood. Similar doubts exist for the alkaline-earth hydride (AlkE-H) series, and are even more pronounced for complex systems, like transition metal-doped AlkE-H, alanates and borohydrides. This work is an attempt of explaining some trends in the physical properties of Alk-H and AlkE-H, employing the Bader analysis of the charge distribution topology evaluated by first-principle all-electron calculations. These results are related to some variables commonly used in the explanation of experimental and calculated results, and are also accompanied by simple tight-binding estimations. Such an approach provides a valuable insight in the characteristics of M-H and H-H interactions in these hydrides, and their possible changes along with external parameters, like temperature, pressure, defect or impurity introduction. The knowledge of these basic interactions and processes taking place in simple MH are essential for the design and optimisation of complex MH-systems interesting for practical hydrogen storage applications. © 2010 World Scientific Publishing Company. | Due to their extensive present, important and versatile potential applications, metal hydrides (MH) are among the most investigated solid-state systems. Theoretical, numerical and experimental studies have provided a considerable knowledge about their structure and properties, but in spite of that, the basic electronic principles of various interactions present in MH have not yet been completely resolved. | _ |
!486 | This overview will highlight features of the main classes of hydrogen storage materials based on their crystal structures. High-pressure techniques have proven to be a useful approach to rapidly discover light-weight, high-capacity hydrogen storage materials in the solid state. Focus will be on three different materials systems; magnesium-based transition metal hydrides, alanates and borohydrides, their crystal structures and properties, prepared by high-pressure sintering, high-energy ball milling or in a cubic anvil. © 2010 Elsevier Ltd. | High-pressure techniques have proven to be a useful approach to rapidly discover light-weight, high-capacity hydrogen storage materials in the solid state. Focus will be on three different materials systems; magnesium-based transition metal hydrides, alanates and borohydrides, their crystal structures and properties, prepared by high-pressure sintering, high-energy ball milling or in a cubic anvil. | _ |
!487 | Light metal borohydrides are considered as promising materials for solid state hydrogen storage. Because of the high hydrogen content of 11.5 wt % and the rather low dehydrogenation enthalpy of 32 Kj·mol-1H 2, Ca(BH4)2 is considered to be one of the most interesting compounds in this class of materials. In the present work, the effect of selected TM-fluoride (TM = transition metal) additives on the reversible formation of Ca(BH4)2 was investigated by means of thermovolumetric, calorimetric, Fourier transform infrared spectroscopy, and ex situ, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD) measurements. Furthermore, selected desorbed samples were analyzed by 11B{1H} solid state magic angle spinning nuclear magnetic resonance (MAS NMR). Under the conditions used in this study (145 bar H 2 pressure and 350 °C), TiF4 and NbF5 were the only additives causing partial reversibility. In these two cases, 11B{1H} MAS NMR analyses detected CaB6 and likely CaB12H12 in the dehydrogenation products. Elemental boron was found in the decomposition products of Ca(BH4)2 samples with VF4, TiF3, and VF3. The results indicate an important role of CaB6 for the reversible formation of Ca(BH4)2. © 2011 American Chemical Society. | Light metal borohydrides are considered as promising materials for solid state hydrogen storage. Furthermore, selected desorbed samples were analyzed by 11B{1H} solid state magic angle spinning nuclear magnetic resonance (MAS NMR). | _ |
!488 | Magnesium hydride (MgH2) is an attractive candidate for solid-state hydrogen storage applications. To improve the kinetics and thermodynamic properties of MgH2 during dehydrogenation- rehydrogenation cycles, a nanostructured MgH2-0.1TiH2 material system prepared by ultrahigh-energy-high-pressure mechanical milling was investigated. High-resolution transmission electron microscope (TEM) and scanning TEM analysis showed that the grain size of the milled MgH 2-0.1TiH2 powder is approximately 5-10 nm with uniform distributions of TiH2 among MgH2 particles. Pressure-composition-temperature (PCT) analysis demonstrated that both the nanosize and the addition of TiH2 contributed to the significant improvement of the kinetics of dehydrogenation and hydrogenation compared to commercial MgH2. More importantly, PCT cycle analysis demonstrated that the MgH2-0.1TiH2 material system showed excellent cycle stability. The results also showed that the ΔH value for the dehydrogenation of nanostructured MgH2-0.1TiH2 is significantly lower than that of commercial MgH2. However, the ΔS value of the reaction was also lower, which results in minimum net effects of the nanosize and the addition of TiH2 on the equilibrium pressure of dehydrogenation reaction of MgH2. © 2009 American Chemical Society. | To improve the kinetics and thermodynamic properties of MgH2 during dehydrogenation- rehydrogenation cycles, a nanostructured MgH2-0.1TiH2 material system prepared by ultrahigh-energy-high-pressure mechanical milling was investigated. High-resolution transmission electron microscope (TEM) and scanning TEM analysis showed that the grain size of the milled MgH 2-0.1TiH2 powder is approximately 5-10 nm with uniform distributions of TiH2 among MgH2 particles. | _ |
!489 | Metal hydrides are one of the most promising technologies in the field of hydrogen storage due to their high volumetric storage density. Important reaction steps take place at the very surface of the solid during hydrogen absorption. Since these reaction steps are drastically influenced by the properties and potential contamination of the solid, it is very important to understand the characteristics of the surface, and a variety of analytical methods are required to achieve this. In this work, a TiMn2-type metal hydride alloy is investigated by means of high-pressure activation measurements, X-ray photoelectron spectroscopy (XPS), secondary neutral mass spectrometry (SNMS) and thermal desorption mass spectrometry (TDMS). In particular, TDMS is an analytical tool that, in contrast to SIMS or SNMS, allows the hydrogen content in a metal to be quantified. Furthermore, it allows the activation energy for desorption to be determined from TDMS profiles; the method used to achieve this is presented here in detail. In the results section, it is shown that the oxide layer formed during manufacture and long-term storage prevents any hydrogen from being absorbed, and so an activation process is required. XPS measurements show the oxide states of the main alloy elements, and a layer 18 nm thick is determined via SNMS. Furthermore, defined oxide layers are produced and characterized in UHV using XPS. The influence of these thin oxide layers on the hydrogen sorption process is examined using TDMS. Finally, the activation energy of desorption is determined for the investigated alloy using the method presented here, and values of 46 kJ/mol for hydrogen sorbed in UHV and 103 kJ/mol for hydrogen originating from the manufacturing process are obtained. © 2009 Springer-Verlag. | In this work, a TiMn2-type metal hydride alloy is investigated by means of high-pressure activation measurements, X-ray photoelectron spectroscopy (XPS), secondary neutral mass spectrometry (SNMS) and thermal desorption mass spectrometry (TDMS). In the results section, it is shown that the oxide layer formed during manufacture and long-term storage prevents any hydrogen from being absorbed, and so an activation process is required. | _ |
!490 | Hydrogenation properties and mechanical stability of pellets made starting from compressed ball-milled MgH2 powders mixed with catalysts (Nb2O5 and graphite) and a binding agent (aluminium powder) have been investigated. Structural characterization with X-ray diffraction and gas-solid reaction kinetic and thermodynamic tests with a Sievert's apparatus have been done on the samples up to 50 hydrogen absorption/desorption (a/d) cycles. The best cycling behaviour and mechanical strength stability have been observed for pellets of catalysed MgH2 powders added with 5 wt% aluminium annealed in vacuum at 450 °C before starting the a/d cycles. This mechanical stability to cycles has been attributed to the formation of a solid solution of aluminium in magnesium. © 2010 Professor T. Nejat Veziroglu. | Structural characterization with X-ray diffraction and gas-solid reaction kinetic and thermodynamic tests with a Sievert's apparatus have been done on the samples up to 50 hydrogen absorption/desorption (a/d) cycles. The best cycling behaviour and mechanical strength stability have been observed for pellets of catalysed MgH2 powders added with 5 wt% aluminium annealed in vacuum at 450 °C before starting the a/d cycles. | _ |
!491 | LiAlH 4 containing 5 wt.% of nanometric Fe (n-Fe) shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H 2) during high energy ball milling reaching ∼3.5 wt.% H 2 after 5 h of milling. In contrast, no H 2 desorption is observed during low energy milling of LiAlH 4 containing n-Fe. Similarly, no H 2 desorption occurs during high energy ball milling for LiAlH 4 containing micrometric Fe (μ-Fe) and, for comparison, both the micrometric and nanometric Ni (μ-Ni and n-Ni) additive. X-ray diffraction studies show that ball milling results in a varying degree of the lattice expansion of LiAlH 4 for both the Fe and Ni additives. A volumetric lattice expansion larger than 1% results in the profound destabilization of LiAlH 4 accompanied by continuous H 2 desorption during milling according to reaction: LiAlH 4 (solid) → 1/3Li 3AlH 6 + 2/3Al + H 2. It is hypothesized that the Fe ions are able to dissolve in the lattice of LiAlH 4 by the action of mechanical energy, replacing the Al ions and forming a substitutional solid solution. The quantity of dissolved metal ions depends primarily on the total energy of milling per unit mass of powder generated within a prescribed milling time, the type of additive ion e.g. Fe vs. Ni and on the particle size (micrometric vs. nanometric) of metal additive. For thermal dehydrogenation the average apparent activation energy of Stage I (LiAlH 4 (solid) → 1/3Li 3AlH 6 + 2/3Al + H 2) is reduced from the range 76 to 96 kJ/mol for the μ-Fe additive to about 60 kJ/mol for the n-Fe additive. For Stage II dehydrogenation (1/3Li 3AlH 6 → LiH+1/3Al + 0.5H 2) the average apparent activation energy is within the range 77-93 kJ/mol, regardless of the particle size of the Fe additive (μ-Fe vs. n-Fe). The n-Fe and n-Ni additives, the latter used for comparison, provide nearly identical enhancement of dehydrogenation rate during isothermal dehydrogenation at 100 °C. Ball milled (LiAlH 4 + 5 wt.% n-Fe) slowly self-discharges up to ∼5 wt.% H 2 during storage at room temperature (RT), 40 and 80 °C. Fully dehydrogenated (LiAlH 4 + 5 wt.% n-Fe) has been partially rehydrogenated up to 0.5 wt.% H 2 under 100 bar/160°C/24 h. However, the rehydrogenation parameters are not optimized yet. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | Ball milled (LiAlH 4 + 5 wt.% n-Fe) slowly self-discharges up to ∼5 wt.% H 2 during storage at room temperature (RT), 40 and 80 °C. Fully dehydrogenated (LiAlH 4 + 5 wt.% n-Fe) has been partially rehydrogenated up to 0.5 wt.% H 2 under 100 bar/160°C/24 h. However, the rehydrogenation parameters are not optimized yet. | _ |
!492 | NaBH 4 is considered as a promising candidate material for solid-state hydrogen storage due to its high hydrogen content of 10.6 wt %. However, its practical use is hampered by its high thermodynamic stability and slow H-exchange kinetics. In the present work, the effects of Ti-based additives, including Ti, TiH 2, and TiF 3, on the dehydrogenation and rehydrogenation of NaBH 4 (NaH+B) were investigated. It was revealed that all of the titanium-based additives were effective in improving the hydrogen desorption and absorption reactions of NaBH 4, and, among them, TiF 3 possessed the highest catalytic activity. The whole dehydrogenation process for the NaBH 4-0.05TiF 3 sample can be regarded as a two-step process: (i) a preferential reaction (3NaBH 4 + TiF 3 → 3NaF + TiB 2 + B + 6H 2) occurring at around 300 °C, and (ii) the formation of Ti- and F-containing species catalyze the dehydrogenation of the remaining NaBH 4. It was also indicated that the F anion can substitute for anionic H in NaH to form NaF 1-xH x in the case of NaH-B-0.05TiF 3 during the hydrogenation process. Therefore, the observed promotion effect of TiF 3 on the reversible dehydrogenation of NaBH 4 should be understood as arising from the combined effects of active Ti- and F-containing species. Also, FTIR spectroscopy confirmed the presence of amorphous Na 2B 12H 12, in both the dehydrogenated and the rehydrogenated states, which may play a role in the partial dehydrogenation and reversibility observed in NaBH 4 with and without catalyst doping. © 2011 American Chemical Society. | NaBH 4 is considered as a promising candidate material for solid-state hydrogen storage due to its high hydrogen content of 10.6 wt %. It was revealed that all of the titanium-based additives were effective in improving the hydrogen desorption and absorption reactions of NaBH 4, and, among them, TiF 3 possessed the highest catalytic activity. | _ |
!493 | A Mg-Zr thin film is prepared on a glass substrate by co-sputtering of Mg and Zr targets and in situ sputtering of a thin Pd overlayer. The structural and optical properties of Mg-Zr and Mg-Zr-H thin film are investigated induced by hydrogen absorption and/or desorption at room temperature. Optical transmission and reflection data indicated that Mg-Zr-H thin film is the color-neutral in the visible range with chromaticity coordinates of x = 0.3566 and y = 0.3430. The formation of the ternary hydride Mg 0.82Zr 0.18H 2 is confirmed in an Mg-rich Mg-Zr solid solution thin film in the hydride state. The hydrogen insertion and extraction occurs in fcc lattice structure. Because the volume change according to hydrogenation and dehydrogenation, the switching durability is much better than that of the switchable mirror using Mg-Ni alloy. © 2011 Elsevier B.V. All rights reserved. | Optical transmission and reflection data indicated that Mg-Zr-H thin film is the color-neutral in the visible range with chromaticity coordinates of x = 0.3566 and y = 0.3430. The hydrogen insertion and extraction occurs in fcc lattice structure. | _ |
!494 | The motorcycle plays an important role in the life for the people of Taiwan. However, the motorcycles' emissions are the main moving air pollution sources. Therefore, it's important to develop more efficient combustion technology in order to save energy and reduce air pollution. In this paper, a novel technology of hydrogen-gasoline compound fuel is developed. Hydrogen gas is released from solid state hydrogen storage tank and then mixed with the incoming gasoline. The intake valve in manifold sucks the hydrogen-gasoline compound fuel into the cylinder for combustion. A series of performance test is conducted by motorcycle chassis dynamometers. The results reveal that this technology can increase the power and torque, and decrease fuel consumption per kilo-power due to promote combustion efficiency. In addition, the hydrogen has greater heat value, so the oil temperature and sparkplug temperature increase. This technique can reduce CO and HC, but increase CO2 and NOx. The engine performance is improved at rarefied hydrogen-gasoline compound fuel. Therefore, the engine performance with M.J. #98 is better than that with M.J. #110. This technique can achieve energy saving and environment-friendly purpose. Copyright © 2012, IGI Global. | In this paper, a novel technology of hydrogen-gasoline compound fuel is developed. A series of performance test is conducted by motorcycle chassis dynamometers. | _ |
!495 | A comprehensive study of the decomposition behavior of as received and mechanically (ball) milled LiAlH4 has been carried out using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and volumetric hydrogen desorption in a Sieverts-type apparatus. Alfa Aesar LiAlH4 powder investigated in this work has the average particle size of 9.9 ± 5.2 μm as compared to 50-150 μm for Sigma-Aldrich LiAlH4 investigated by Ares et al. [9]. High energy ball milling reduced the particle size of the present LiAlH4 to 2.8 ± 2.3 μm. In general, comparing the results of our microstructural studies with those reported by Ares et al. [9] it is clear that the morphology, microstructure and chemistry of LiAlH4 can be very dissimilar depending on the supplier from which LiAlH4 powder was purchased. We do not observe a partial decomposition of LiAlH4 during milling up to 5 h under high energy impact mode. The observed melting of LiAlH4 in a DSC test is a very volatile event where the liquid LiAlH4 starts foaming and flowing out of the alumina crucible. After completion of solidification and desorption at temperatures above melting the powder resembles a lava rock. A thermal sectioning in DSC tests at pre-determined temperatures and subsequent XRD studies show that LiAlH4 starts decomposing into Li 3AlH6 immediately after melting. Li3AlH 6 seems to be already solidified before it starts decomposing in the next stage. All volumetric desorption curves at the 120-300 °C range clearly exhibit a two-stage desorption process, Stage I and II. As received LiAlH 4 is able, in a fully solid state, to desorb at 120 °C under pressure of 0.1 MPa H2 (atmospheric) as much as 7.1 wt.%H2 within ∼259,000 s (∼72 h), i.e. ∼93% of the purity-corrected H 2 content from the reactions in Stage I (LiAlH4(s) → (1/3)Li3AlH6(s) + (2/3)Al(s) + H2) and Stage II ((1/3)Li3AlH6(s) → LiH + (1/3)Al + 0.5H 2). The apparent activation energy for Stage I and II for unmilled LiAlH4 is equal to ∼111 and ∼100 kJ/mol, respectively. For the ball milled LiAlH4 the apparent activation energy for Stage I and II is slightly lower ∼92.5 and ∼92 kJ/mol, respectively. The water absorption up to 11.7% due to exposure to air for 1 h does not change in any drastic way the hydrogen desorption rate of ball milled LiAlH4 in Stage I. Flammability tests show that the ball milled LiAlH4 powder does not self-ignite on contact with air but can only be ignited by scraping the cylinder walls with a metal tool and then the powder burns with an open flame. © 2010 Elsevier B.V. All rights reserved. | We do not observe a partial decomposition of LiAlH4 during milling up to 5 h under high energy impact mode. A thermal sectioning in DSC tests at pre-determined temperatures and subsequent XRD studies show that LiAlH4 starts decomposing into Li 3AlH6 immediately after melting. | _ |
!496 | Multiple reaction mixtures with different composition ratios of MCl 3-LiBH 4 (M = La, Gd) were studied by mechano-chemical synthesis, yielding two new bimetallic borohydride chlorides, LiM(BH 4) 3Cl (M = La, Gd). The Gd-containing phase was obtained only after annealing the ball-milled mixture. Additionally, a solvent extracted sample of Gd(BH 4) 3 was studied to gain insight into the transformation from Gd(BH 4) 3 to LiGd(BH 4) 3Cl. The novel compounds were investigated using in situ synchrotron radiation powder X-ray diffraction, thermal analysis combined with mass spectroscopy, Sieverts measurements, Fourier transform infrared spectroscopy, and electrochemical impedance spectroscopy. The two new compounds, LiLa(BH 4) 3Cl and LiGd(BH 4) 3Cl, have high lithium ion conductivities of 2.3 ×10 -4 and 3.5 ×10 -4 S•cm -1 (T = 20 °C) and high hydrogen densities of ρ m = 5.36 and 4.95 wt % H 2, and both compounds crystallize in the cubic crystal system (space group I-43m) with unit cell parameter a = 11.7955(1) and a = 11.5627(1) Å, respectively. The structures contain isolated tetranuclear anionic clusters [M 4Cl 4(BH 4) 12] 4- with distorted cubane M 4Cl 4 cores M = La or Gd. Each lanthanide atom coordinates three chloride ions and three borohydride groups, thus completing the coordination environment to an octahedron. The Li + ions are disordered on 2/3 of the 12d Wyckoff site, which agrees well with the very high lithium ion conductivities. The conductivity is purely ionic, as electronic conductivities were measured to only 1.4 ×10 -8 and 9 ×10 -8 S•cm -1 at T = 20 °C for LiLa(BH 4) 3Cl and LiGd(BH 4) 3Cl, respectively. In situ synchrotron radiation powder X-ray diffraction (SR-PXD) reveals that the decomposition products at 300 °C consist of LaB 6/LaH 2 or GdB 4/GdH 2 and LiCl. The size of the rare-earth metal atom is shown to be crucial for the formation and stability of the borohydride phases in MCl 3-LiBH 4 systems. © 2012 American Chemical Society. | Multiple reaction mixtures with different composition ratios of MCl 3-LiBH 4 (M = La, Gd) were studied by mechano-chemical synthesis, yielding two new bimetallic borohydride chlorides, LiM(BH 4) 3Cl (M = La, Gd). In situ synchrotron radiation powder X-ray diffraction (SR-PXD) reveals that the decomposition products at 300 °C consist of LaB 6/LaH 2 or GdB 4/GdH 2 and LiCl. | _ |
!497 | The rapidly depleting petroleum feed stocks and increasing green house gas emissions around the world has necessitated a search for alternative renewable energy sources. Hydrogen with molecular weight of 2.016 g/mol and high chemical energy per mass equal to 142 MJ/kg has clearly emerged as an alternative to hydrocarbon fuels. Means for safe and cost effective storage are needed for widespread usage of hydrogen as a fuel. Chemical storage is the one of the safer ways to store hydrogen compared to compressed and liquefied hydrogen. It involves storing hydrogen in chemical bonds in molecules and materials where an on-board reaction is used to release hydrogen. Ammonia-borane, (AB, H 3N·BH3) with a potential capacity of 19.6 wt% is considered a very promising solid state hydrogen storage material. It is thermally stable at ambient temperatures. There are two major routes for the generation of H2 from AB: catalytic hydrolysis/alcoholysis and catalytic thermal decomposition. There has been a flurry of research activity on the generation of H2 from AB recently. The present review deals with an overview of our efforts in developing cost-effective nanocatalysts for hydrogen generation from ammonia borane in protic solvents. | The rapidly depleting petroleum feed stocks and increasing green house gas emissions around the world has necessitated a search for alternative renewable energy sources. The present review deals with an overview of our efforts in developing cost-effective nanocatalysts for hydrogen generation from ammonia borane in protic solvents. | _ |
!498 | This paper discusses the results of an experimental program carried out to determine dust cloud deflagration parameters of selected solid-state hydrogen storage materials, including complex metal hydrides (sodium alanate and lithium borohydride/magnesium hydride mixture), chemical hydrides (alane and ammonia borane) and activated carbon (Maxsorb, AX-21). The measured parameters include maximum deflagration pressure rise, maximum rate of pressure rise, minimum ignition temperature, minimum ignition energy and minimum explosible concentration. The calculated explosion indexes include volume-normalized maximum rate of pressure rise (KSt), explosion severity (ES) and ignition sensitivity (IS). The deflagration parameters of Pittsburgh seam coal dust and Lycopodium spores (reference materials) are also measured. The results show that activated carbon is the safest hydrogen storage media among the examined materials. Ammonia borane is unsafe to use because of the high explosibility of its dust. The core insights of this contribution are useful for quantifying the risks associated with use of these materials for on-board systems in light-duty fuel cell-powered vehicles and for supporting the development of hydrogen safety codes and standards. These insights are also critical for designing adequate safety features such as explosion relief venting and isolation devices and for supplementing missing data in materials safety data sheets. © 2012 Elsevier Ltd. | The deflagration parameters of Pittsburgh seam coal dust and Lycopodium spores (reference materials) are also measured. These insights are also critical for designing adequate safety features such as explosion relief venting and isolation devices and for supplementing missing data in materials safety data sheets. | _ |
!499 | Hydrogen interaction of porphyrin hetero-pairs has been studied by differential scanning calorimetry (DSC). Aggregates were prepared by spontaneous aggregation of water soluble anionic porphyrins meso-tetra(4-carboxyphenyl) porphine (TCPP) and meso-tetra(4-sulfonatophenyl)porphine (TPPS) with cationic meso-tetra-p-trimethylaminophenyl porphine tetrachloride (TAP). Aggregate formation in solution was investigated via UV-visible spectroscopy at different pH ranges. At neutral to basic conditions, porphyrin pairs formed partially soluble hetero H-aggregates and at low pH, soluble homo J-aggregates was formed. H-aggregates were isolated by centrifuging and freeze-drying. The obtained solids were studied by X-ray powder diffraction. Thermal stability of dry aggregates was determined by thermogravimetric analysis. The TCPP-TAP hetero aggregates exhibited hydrogen uptake between 80 °C and 250 °C. The amount of hydrogen absorbed by the sample corresponds to 0.29% by weight, indicating a potential use of such materials as a solid state hydrogen storage medium. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. | Hydrogen interaction of porphyrin hetero-pairs has been studied by differential scanning calorimetry (DSC). Aggregate formation in solution was investigated via UV-visible spectroscopy at different pH ranges. | _ |
!500 | The onboard hydrogen storage is the main challenge to achieve a hydrogen-based economy. The most promising way is the solid-state storage, and the best candidates as storage media are currently considered the complex hydrides. In the present work we review recent results obtained by anelastic spectroscopy studies on these materials. © 2009 Elsevier B.V. All rights reserved. | The onboard hydrogen storage is the main challenge to achieve a hydrogen-based economy. In the present work we review recent results obtained by anelastic spectroscopy studies on these materials. | _ |