L’utilisation des combustibles fossiles (énergies non renouvelables) est responsable de l’augmentation de la concentration en gaz à effet de serre dans l’atmosphère. Parmi les solutions de remplacement envisagées, l’hydrogène apparaît comme le vecteur énergétique le plus séduisant. Son stockage dans des intermétalliques permet d’obtenir des capacités massiques et volumiques (e.g. 140 g/L) supérieures à celles obtenues en voie liquide ou sous pression (respectivement 71 et 40 g/L). Nous avons élaboré des composés à base de Mg et de terres rares (e.g. Y, Ce et Gd) dérivant des phases de Laves cubiques AB2. Leurs propriétés physico-chimiques ont été étudiées (hydruration, électrochimie, magnétisme, …). Les conditions de sorption (P et T) se sont révélées particulièrement favorables (i.e. absorption à température ambiante et pression atmosphérique). Par ailleurs, afin d’améliorer la cinétique de sorption du magnésium métallique, les composés précédemment élaborés ont été utilisés comme catalyseurs. Ainsi, GdMgNi4 a été co-broyé avec du magnésium et les vitesses d’absorption et de désorption du composite sont supérieures à celles obtenues pour les composites Mg+Ni ou Mg+V qui sont des références. Une approche théorique (DFT) a permis de modéliser la structure électronique des composés ternaires (i.e. TRMgNi4) et ainsi de prédire ou de confirmer les résultats expérimentaux. Enfin nous avons étudié de nouveaux intermétalliques riches en terre rare (TR4MgNi) dont les capacités d’absorption en hydrogène sont élevées (2H/M). / The use of fossil fuels (non-renewable energy) is responsible for increasing the concentration of greenhouse gases in the atmosphere. Among the considered alternatives, hydrogen is seen as the most attractive energy vector. The storage in intermetallics makes it possible to obtain mass and volume capacities (e.g. 140 g/L) higher than those obtained by liquid form or under pressure (respectively 71 and 40 g/L). We have synthesised Mg and Rare Earth based compounds (RE = Y, Ce and Gd), derived from the cubic Laves phases AB2. Their physical and chemical properties have been studied (hydrogenation, electrochemistry, magnetism, ...). The conditions of sorption (P and T) are particularly favorable (i.e. absorption at room temperature and atmospheric pressure). Besides, to improve the sorption kinetics of metallic magnesium, the compounds developed previously were used as catalysts. Thus, GdMgNi4 was milled with magnesium and the speeds of absorption and desorption of the mixture are found higher than those obtained for the composites Mg+Ni or Mg+V, which are reference systems. A theoretical approach (DFT) was used to model the electronic structure of the ternary compounds (i.e. REMgNi4) and thus to predict or confirm the experimental results. Finally we have studied new intermetallics rich in rare earth (RE4MgNi) whose hydrogen absorption capacities are high (2H/M).

Philosophiae Doctor - PhD / Magnesium hydride has long been regarded as a promising candidate for lightweight hydrogen storage applications, owing to reasonably high theoretical capacity (7.6 wt. %). It is burdened by slow absorption/desorption kinetics which has been the target for improvement of many research groups over the years. Nanostructured MgH2 prepared by high energy reactive ball milling (HRBM) of Mg under hydrogen atmosphere with the addition of V or Ti results in modified MgH2 that demonstrates superior hydrogenation/dehydrogenation kinetics without a crippling compromise in storage capacity. Mg – FeV nanocomposites prepared via ball milling of Mg and FeV raw materials demonstrated up to 96.4% of the theoretical storage capacity and comparable kinetics to Mg - V prepared via the same method using pure refined V (which is far costlier than FeV). In both cases, the hydrogenation/dehydrogenation kinetics was much improved than pure Mg alone, as evidenced by faster hydrogenation times. In terms of cyclic stability, Mg – 10FeV demonstrated improvement over pure Mg with final absorption and desorption capacities of 4.93 ± 0.02 wt. % and 4.82 ± 0.02 wt. % respectively over 30 cycles. When compared against Mg – V, Mg – FeV showed slightly inferior improvements, attributed to incomplete hydrogenation of V in the presence of Fe. However, they share similar crystalline BCC, BCT – V2H and FCC - VH phases with the size of less than 10 nm and demonstrated the same behaviour at high temperatures; at temperatures approaching 400 °C, particle sintering became an issue for both nanocomposites resulting in a drop in absorption capacity even in the first cycle. The further inclusion of carbonaceous species showed several effects, one of which was an improvement in hydrogen uptake speed as well as kinetics for the addition of 5 wt. % activated carbon. For the sample with 5 wt. % graphite, the appearance of an initial incubation period of up to 60 minutes was noted, presumably corresponding to the duration of time when the carbon was sheared and crushed before hydrogenation commences.

Thesis advisor: Shih-Yuan Liu / This dissertation describes progress in the field of polycyclic boron- nitrogen-containing systems, especially for potential application in organic-based optoelectronic devices and hydrogen storage materials. The replacement of a BN unit for a CC unit organic compounds (BN/CC isosterism) can have a profound effect on the electronic structure and even function of a given molecular topology without changing its physical structure very much. Direct comparison between a BN-containing molecule and its direct all-carbon analogue is crucial to establishing the origin of these differences. The synthesis and optoelectronic characterization of boron- nitrogen-containing analogues of naphthalene, anthracene, and tetracene are disclosed. Also examined herein is the aromatic Claisen rearrangement applied to an azaboryl allyl ether. Finally, the chemistry of saturated BN heterocycles, including an iridium-catalyzed transfer dehydrogenation method for synthesizing BN-fused azaborines. Also disclosed is the actual application of these cyclic amine-boranes in supplying hydrogen for a proton exchange membrane (PEM) fuel cell. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

<p>In a time of global environmental problems due to overuse of fossil fuels, and a subsequent depletion of the supplies, hydrogen is considered as one of the most important renewable future fuels for use in clean energy systems with zero greenhouse-gas emission. Hydrogen storage is the main issue that needs to be solved before the technology can be implemented into key areas such as transport. The high energy density, good stability and reversibility of metal hydrides make them appealing as hydrogen storage materials. In this thesis research on synthesis and hydrogen absorption properties for intermetallic compounds based on scandium and aluminium is reported. The compounds were synthesized by arc melting or induction melting and exposed to hydrogen in a high pressure furnace. Desorption investigations were performed by thermal desorption spectroscopy. The samples were analyzed by x-ray powder diffraction and electron microscopy. ScAlNi, crystallizing in the MgZn2-type structure (space group: P63/mmc; a = 5.1434(1) Å, c = 8.1820(2) Å), was found to absorb hydrogen by two different mechanisms at different temperature regions. At ~120 °C hydrogen was absorbed by solid solution formation with estimated compositions up to ScAlNiH0.5. At ~500 °C hydrogen was absorbed by disproportionation of ScAlNi into ScH2 and AlNi. The reaction was found to be fully reversible due to destabilization effects which lowered the decomposition temperature of ScH2 by ~460 °C.</p>

First principles computation can be used to investigate an design materials in ways that can not be achieved with experimental means. We show how computations can be used to rapidly capture the essential physics that determines the useful properties in different applications. Some applications for predicting crystal structure, thermodynamic and kinetic properties, and phase stability are discussed. This first principles tool set will be demonstrated with applications from rechargeable batteries and hydrogen storage materials. / Singapore-MIT Alliance (SMA)

In a time of global environmental problems due to overuse of fossil fuels, and a subsequent depletion of the supplies, hydrogen is considered as one of the most important renewable future fuels for use in clean energy systems with zero greenhouse-gas emission. Hydrogen storage is the main issue that needs to be solved before the technology can be implemented into key areas such as transport. The high energy density, good stability and reversibility of metal hydrides make them appealing as hydrogen storage materials. In this thesis research on synthesis and hydrogen absorption properties for intermetallic compounds based on scandium and aluminium is reported. The compounds were synthesized by arc melting or induction melting and exposed to hydrogen in a high pressure furnace. Desorption investigations were performed by thermal desorption spectroscopy. The samples were analyzed by x-ray powder diffraction and electron microscopy. ScAlNi, crystallizing in the MgZn2-type structure (space group: P63/mmc; a = 5.1434(1) Å, c = 8.1820(2) Å), was found to absorb hydrogen by two different mechanisms at different temperature regions. At ~120 °C hydrogen was absorbed by solid solution formation with estimated compositions up to ScAlNiH0.5. At ~500 °C hydrogen was absorbed by disproportionation of ScAlNi into ScH2 and AlNi. The reaction was found to be fully reversible due to destabilization effects which lowered the decomposition temperature of ScH2 by ~460 °C.

Hydrogen storage has been identified as a primary bottleneck in the large-scale implementation of a hydrogen-based economy. Many research efforts are underway to both improve the capacity of existing hydrogen storage systems and develop new systems. One promising area of research is hydrogen physi-sorbed into carbonbased structures such as nanotubes and graphene. Two novel systems consisting of a phthalocyanine salt with a large cation were studied. Ab initio, density functional theory, and molecular dynamics simulations of tetramethylammonium lithium phthalocyanine (TMA-LiPc) and trimethyl-(2-trimethylazaniumylethyl) azanium phthalocyanine (TMA2-Pc) were undertaken to estimate the H2 gas-solid adsorption uptake (wt/wt) as a function of pressure and temperature. For TMA-LiPc, the maximum H2 binding energy was approximately 0.9 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.49 Å ranged from 2.1% to 6.0% (wt/wt) at 300 K, 2.5% to 6.5% at 273K, 3.3% to 7.2% at 236K, 5.2% to 8.6% at 177K, and 10.4% to 11.7% at 77K. At ILD 10 Å H2 adsorption was about 1.5% (wt/wt) higher at all points. For TMA2-Pc, the maximum H2 binding energy was approximately 1.3 kcal/mol for an isolated system and 1.2 kcal/mol for a crystal. H2 adsorption at the optimal inter-layer distance of 8.12 Å ranged from 0.5% to 2.6% (wt/wt) at 300 K, 0.6% to 2.8% at 273K, 0.8% to 3.2% at 236K, 1.4% to 3.9% at 177K, and 4.5% to 6.0% at 77K. At ILD 10 Å H2 adsorption ranged from about 0.1% (wt/wt) at 40 bar to 0.5% higher at 250 bar. The behavior of H2 adsorption for both TMA-LiPc and TMA2-Pc were compared. The adsorbed H2 probability density was compared to pair correlation function data and surfaces of constant binding energy. Regions of relatively high H2 density appear to correlate well with the binding energy, but the total adsorption does not, indicating that the adsorption is driven by factors other than binding energetics. Lithium ion transport in TMA2-Pc was also investigated for suitability as an electrolyte medium for use in lithium ion battery systems.

The primary goal of this research concerns the synthesis of organic ligands in an effort to create metal-organic porous materials for the storage of gas molecules for alternative energy applications as well as other applications such as catalysis, molecular sensing, selective gas adsorption and separation. Initially, the focus of this work was on the synthesis of metal-organic polyhedra, yet the research has to date not progressed past the synthesis of ligands and the theoretical polyhedron that may form. Further efforts to obtain polyhedra from these ligands need to be explored. Concurrently, the search for a metal-organic framework that hopefully breaks the record for methane adsorption at low pressure and standard temperature was undertaken. A framework, PCN-80, was synthesized based off a newly synthesized extended bianthracene derivative, yet was unstable to the atmosphere. Hydrogen and methane adsorption capacities have been evaluated by molecular simulations; these adsorption isotherms indicated a gravimetric hydrogen uptake of 9.59 weight percent and a volumetric uptake of methane of 78.47 g/L. Following the synthesis of PCN-80, a comparison study involving the effect of the stepwise growth of the number of aromatic rings in the ligand of a MOF was pursued; the number of aromatic rings in the ligand was varied from one to eight while still maintaining a linear, ditopic moiety. The synthesis of another bianthracene-based ligand was used to complete the series of ligands and PCN-81, a two-dimensional framework with no noticeable porosity as evident by the simulated hydrogen uptake of 0.68 weight percent, was synthesized. All of these MOFs were synthesized from zinc salts to reduce the number of variables. No clear relationship was established in terms of the number of aromatic rings present in the ligand and the hydrogen adsorption capacity. However, it was confirmed that the density and hydrogen uptake in weight percent are inversely proportional. Further work needs to be done to determine what advantages are offered by these novel frameworks containing extended bianthracene derivatives. For example, with the highly fluorescent nature of the ligands from which they are composed, both PCN-80 and PCN-81 should be studied for the potential use in the application of fluorescent materials.

No description available.

A need was identified to test multi–layer vacuum super insulation (MLVSI) used in cryogenic applications for hydrogen storage. The study focuses on the application of commercially available MLVSI to a locally patented liquid hydrogen cryogenic storage system. This led to an investigation of different types of multi–layer vacuum insulation configurations, as well as further research on tank inlet coupling configurations. It includes the manufacturing of a liquid nitrogen testing cryostat to be able to test and evaluate the system performance. The first set of tests was based on the development of an inlet coupling configuration to limit heat transfer through the inner tank inlet, of a double cryogenic tank system in order to reduce gas boil–off. The couplings were manufactured in the form of a bellow to handle cryogenic vacuum levels, while ensuring low heat transfer rates between inner and outer tanks. It was found that various coupling designs can be considered to limit gas boil–off. The second set of tests was conducted on a specific MLVSI configuration to determine its effectiveness to insulate the spherical header surface of a typical hydrogen storage vessel. The installation procedure, to limit heat transfer and boil–off due to edge effects in this configuration was investigated. It was found that insulation–overlap–edge effects will always have an impact on insulation performance when a spherical header of a storage vessel is insulated, due to its specific geometry. A time efficient way to install MLVSI on such a spherical header is presented and evaluated. Further investigations were carried out by combining findings into one single system to determine the performance of an optimised insulated cryogenic system. It was found that copper plate discs installed between the vanes of a bellowed inlet/outlet nozzle is the most promising to limit heat transfer to the cryogenic fluid. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012.