Les batteries Ni-MH sont utilisées dans diverses applications, aussi bien stationnaires (panneaux solaires) que mobiles (véhicules hybrides). La matière active des électrodes négatives des batteries actuellement commercialisées est un alliage intermétallique de type AB5 (A = terres rares, B = métaux de transition). La demande croissante en énergie nécessite d'améliorer la capacité massique de ces accumulateurs. Pour cette raison, nous étudions de nouveaux matériaux d'électrode de type ABy (y = 3,5 ou 3,8). La structure d'empilement particulière de ces alliages composés d'unités [AB5] et [A2B4] leur confère une capacité plus importante. L'unité [A2B4] est en effet capable d'absorber davantage d'hydrogène que l'unité [AB5]. Cependant, sa stabilité au cyclage lui fait défaut. Dans cette thèse nous avons, dans un premier temps, mené une étude sur les composés binaires de type ANi3,5 et ANi3,8 (A Æ Gd, Sm ou Y) puis nous avons étudié l'évolution des propriétés thermodynamiques, électrochimiques et de corrosion et après substitutions successives de la terre rare (ou yttrium) par du magnésium puis du lanthane / Ni-MH batteries are used in both stationary (solar panels) and mobile (hybrid vehicles) applications. The active material of negative electrodes currently on the market is an AB5-type alloy (A = rare earth, B = transition metal). The continuously increasing demand for energy requires improving the mass capacity of these batteries. For this reason, we study new type of electrode materials ABy (y Æ 3.5 or 3.8). The particular stacking structure of these alloys composed of [AB5] and [A2B4] units give them more capacity. Indeed, [A2B4] unit is able to absorb more hydrogen than [AB5] unit. However, stability in cycling is lowered. In this phD work we have, at first, conducted a study of binary compounds type ANi 3.5 and ANi3.8 (A = Gd, Sm ou Y), then we studied the evolution of the thermodynamic properties, electrochemical and corrosion after successive substitutions of the rare earth (or yttrium) with magnesium and lanthanum

Depuis une quinzaine d’années, les matériaux poreux de type Metal Organic Frameworks (MOFs) offrent de nouvelles perspectives dans le cadre du stockage d’hydrogène par adsorption. Ces matériaux possèdent une structure et un réseau de pores particulièrement bien adaptés à l’adsorption des gaz. Ainsi, le téréphtalate de Chrome (III) (MIL-101(Cr)), composé chimiquement très stable, possède une grande capacité de stockage de l’hydrogène, du dioxyde de carbone et du méthane. Afin de renforcer sa capacité de stockage d’hydrogène, un dopage au charbon actif (AC) du matériau a été envisagé. Les synthèses des matériaux dopés et non-dopés ont été réalisées et, pour cela, différents agents minéralisants (acide fluorhydrique, acide acétique et acétate de sodium) ont été testés. Les matériaux synthétisés furent caractérisés par diffraction des rayons X (DRX), par microscopie électronique à balayage (MEB), par analyses thermogravimétriques (ATG) et par adsorption d’azote à 77K. Les capacités de stockage d’hydrogène de ces matériaux à 77 K et 100 bar ont été évaluées par mesures des isothermes d’adsorption d’hydrogène, réalisées par méthodes volumétrique et gravimétrique. Les résultats obtenus par ces deux méthodes sont en parfait accord et le matériau composite affiche une capacité d’adsorption de 13.5 wt%, qui est supérieure à celle du matériau non dopé (8.2 wt% dans les même conditions expérimentales). Les cinétiques d’adsorption ont été mesurées à 77 K par méthode volumétrique. Les résultats obtenus ont été comparés au modèle de la force motrice linéaire, Linear Driving Force (LDF). Un modèle de diffusion dépendant de la température a été développé afin de tenir compte des variations de températures qui se produisent durant le processus d’adsorption. / Since the last 15 years, the porous solids such as Metal-Organic Frameworks (MOFs) have opened new perspectives for the development of adsorbents for hydrogen storage. The structure and the pore networks of these materials are especially adapted to the adsorption of gases. The chromium (III) terephthalate-based MIL-101(Cr) is a very stable material which exhibits good adsorption uptakes for hydrogen (H2), carbon dioxide (CO2) and methane (CH4).In this study, syntheses were carried out by different ways and several mineralizing agents such as hydrofluoric acid (HF), acetic acid (CH3COOH) and sodium acetate (CH3COONa) have been tested. Moreover, Activated Carbon (AC) has been introduced in the framework to create an AC incorporated composite material with an enhanced specific surface area. Conventional techniques such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and nitrogen (N2) adsorption isotherms at 77 K were used for materials characterizations.In the aim to evaluate hydrogen storage capacities of these materials, hydrogen adsorption isotherms were measured at 77 K via both volumetric and gravimetric methods, and the obtained results are in good agreement. A hydrogen uptake value of 13.5 wt% has been measured at 77 K and 100 bar for the composite material which shows a great improvement of hydrogen capacity compared to the pristine MIL-101(Cr) (8.2 wt%).Finally, hydrogen adsorption kinetics has been measured at 77 K using volumetric method. The obtained results were compared to the Linear Driving Force (LDF) and a temperature dependent diffusion model was also considered to take into account the temperature variations which occur during the adsorption process.

Nanoporous metal represents a particular form of a metal, which combines the characteristics of metals, such as good thermal and electrical conductivity, catalytic activity with the materials properties characteristic of nanoporosity, which include high surface area, low density, large number of pores, etc. Nanoporous metals have applications in various fields such as catalysis, hydrogen storage, electrochemical sensing, membranes, SERS, and supercapacitors. The three dimensional porous structures offer high specific surface area and large pore volumes, which enhance substrate diffusion within the porous structures and provide a large number of surface active sites for catalytic applications. However, synthesis of nanoporous metal based on conventional approach (template assisted synthesis and dealloying) suffers from scalability issue, specific for few metals, additional synthetic steps etc. Challenges still remain in this field to fabricate three dimensional porous metals where pores are interconnected (bicontinuous). Recently, development of the synthesis of nanoporous metal got a thrust by the advent of the concept of assembly of nanoparticles in either an ex-situ or in an in-situ manner. Objectives 1. Establish the synthetic strategy of metal nanosponge formation by capping agent dissolution method (ex-situ assembly) 2. Explore the catalytic activity of these metal nanosponges towards 4-nitrophenol reduction and alkene hydrogenation reactions 3. Elucidate the mechanism of formation of metal nanosponge in solution state (kinetic in-situ assembly of nanoparticles) using ammonia borane as a reducing agent in water under different conditions 4. Investigate the hydrogen storage properties and catalytic arene hydrogenation activities of metal nanosponges 5. Synthesis of bismuth oxide nanosponge using bismuth nanosponge as a template. Study of the photocatalytic dye degradation behavior using bismuth oxide nanosponge under visible light irradiation Significant results Synthesis of metal nanosponges was carried out using capping agent dissolution method wherein addition of water to M@BNHx polymer gives metal nanosponges. The B-H bond of BNHx polymer is unstable in the presence of water and gets hydrolyzed to give hydrogen gas bubbles which act as dynamic templates for the formation of metal nanosponges. The pristine nature of the surface of these metal nanosponges was elucidated by several analytical techniques. The catalytic activity of these metal nanosponges (Ag, Au, Pd, Pt, and Cu) was demonstrated using 4-nitrophenol reduction reaction in the presence of sodium borohydride as a reducing agent. Iridium nanosponge was obtained by capping agent dissolution method from Ir@BNHx polymer. Mesoporous high surface area iridium nanosponge was found to be an active catalyst for alkene hydrogenation reaction, whereas Ir@BNHx polymer does not exhibit any catalytic activity under similar reaction conditions. The effects of temperature, solvent, substrate to catalyst ratio, and pressure on catalyst activity were established using styrene as a substrate. The thermal stability (up to 300 oC) and robustness over several cycles were demonstrated for the iridium nanosponge. Several alkenes (linear alkene, cycloalkane, and conjugated alkene) were successfully hydrogenated using iridium nanosponge at room temperature and 4 bar hydrogen pressure. Generality of the synthetic procedure was explored by using different iridium precursors which gave iridium nanosponges exhibiting similar catalytic activity. Silver, gold, palladium, platinum, and copper nanosponges have been synthesized by chemical reduction method (in-situ kinetic assembly of nanoparticles) using ammonia borane as a reducing agent in water as a solvent. The effect of variables (metal salt to amine borane ratio, concentration of the reactants, solvent, temperature, and reducing agent) were thoroughly investigated using the silver system as a model. In the absence of a capping agent, metal salt reduction was carried out using amine borane which forms nanoparticles. In a high dielectric solvent, the colloidal particles attach together to form agglomerates. During the course of the reaction, hydrogen gas bubbles were generated which produce pores within the agglomerates leading to the formation of three dimensional nanosponge structures. Finally, the hydrogen storage properties (pressure composition isotherm and sorption kinetics) of these metal nanosponges were investigated under different conditions. These metal nanosponges exhibit reasonable, reversible storage characteristics: Ag (3 wt%), Pd (5.5 wt%), Pt (6 wt%), and Cu (2.5 wt%). Phase selective ruthenium nanosponge was synthesized using chemical reduction method. It was found that amine borane as a reducing agent for certain ruthenium precursors results in the hcp phase of ruthenium whereas, reduction using sodium borohydride affords fcc phase of ruthenium. Hcp and fcc phases of ruthenium were established using electron and X-ray diffraction methods. Surface characterization technique showed the pristine nature of ruthenium nanosponge. Both hcp and fcc ruthenium nanosponges were employed as catalysts for hydrogenation of benzene; it was found that hcp ruthenium is more active than fcc ruthenium for benzene hydrogenation to cyclohexane. Substrate to catalyst ratio, temperature, hydrogen pressure, and solvent effect were thoroughly investigated using benzene as a model substrate. It was found that hcp ruthenium nanosponge is capable of hydrogenating a variety of alkyl substituted benzenes under ambient conditions. The catalyst was found to be active over several cycles without any loss in its activity. Phosphine was used as a catalyst poison and hot filtration test was performed separately to show the true heterogeneous nature of the active catalyst. Hydrogen storage experiments were performed to understand the interaction of hydrogen with different phases of ruthenium. Bismuth nanosponge was synthesized using chemical reduction method. Synthesis of different polymorphs of bismuth oxide nanosponges (tetragonal, monoclinic and body centered cubic) were carried out by calcination of bismuth nanosponge at different temperature (300 oC, 500 oC, and 800 oC). The phase purity of bismuth oxide nanosponges were established using X-ray and electron diffraction method. It was found that surface area decreases with increasing the calcination temperature. Tetragonal bismuth oxide (300 oC annealed sample) nanosponge shows the highest photocatalytic activity as compared to other polymorphs. Mechanistic investigation suggests that hole and hydroxyl radical are responsible for dye degradation. Recyclability study demonstrated the formation of bismuth oxycarbonate which leads to a drop in catalytic activity. However, the tetragonal phase of bismuth oxide with high catalytic activity could be regenerated upon annealing at 300 oC for 3 h.

Fossil fuels constitute a significant fraction of the world’s energy demand. The burning of fossil fuels emits huge amounts of carbon dioxide into the atmosphere. Therefore, the limited availability of fossil fuel resources and the environmental impact of their use require a change to alternative energy sources or carriers (such as hydrogen) in the foreseeable future. The development of methods to mitigate carbon dioxide emission into the atmosphere is equally important. Hence, extensive research has been carried out on the development of cost-effective technologies for carbon dioxide capture and techniques to establish hydrogen economy. Hydrogen is a clean energy fuel with a very high specific energy content of about 120MJ/kg and an energy density of 10Wh/kg. However, its potential is limited by the lack of environment-friendly production methods and a suitable storage medium. Conventional hydrogen production methods such as Steam-methane-reformation and Coal-gasification were modified by the inclusion of NaOH. The modified methods are thermodynamically more favorable and can be regarded as near-zero emission production routes. Further, suitable catalysts were employed to accelerate the proposed NaOH-assisted reactions and a relation between reaction yield and catalyst size has been established. A 1:1:1 molar mixture of LiAlH4, NaNH2 and MgH2 were investigated as a potential hydrogen storage medium. The hydrogen desorption mechanism was explored using in-situ XRD and Raman Spectroscopy. Mesoporous metal oxides were assessed for CO2 capture at both power and non-power sectors. A 96.96% of mesoporous MgO (325 mesh size, surface area = 95.08 ± 1.5 m2/g) was converted to MgCO3 at 350°C and 10 bars CO2. But the absorption capacity of 1h ball milled zinc oxide was low, 0.198 gCO2 /gZnO at 75°C and 10 bars CO2. Interestingly, 57% mass conversion of Fe and Fe3O4 mixture to FeCO3 was observed at 200°C and 10 bars CO2. MgO, ZnO and Fe3O4 could be completely regenerated at 550°C, 250°C and 350°C respectively. Furthermore, the possible retrofit of MgO and a mixture of Fe and Fe3O4 to a 300 MWe coal-fired power plant and iron making industry were also evaluated.

Orientadores: Munir Salomão Skaf, Vitor Rafael Coluci / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T20:42:42Z (GMT). No. of bitstreams: 1 Faro_TatianaMellodaCosta_D.pdf: 8054394 bytes, checksum: ce0d79df42ce453ffc39b51bf0ad1094 (MD5) Previous issue date: 2015 / Resumo: Atualmente, a economia mundial depende do uso de combustíveis fósseis para a geração de energia. Esse modelo apresenta problemas ambientais graves, uma vez que o petróleo é um material não-renovável e muito poluente. O gás hidrogênio apresenta-se como uma alternativa promissora para substituir os combustíveis utilizados atualmente devido a um conjunto de características positivas: ele é atóxico, tem uma alta densidade energética gravimétrica e gera apenas água como produto de sua combustão. Apesar de tais vantagens, ele ainda não é utilizado comercialmente em larga escala. O maior empecilho tecnológico para que o hidrogênio possa substituir os combustíveis fósseis está no seu armazenamento. Existem diversas propostas para armazenar o hidrogênio, como tanques contendo o hidrogênio nas formas de gás pressurizado ou de líquido, além de sistemas sólidos que permitam a sua adsorção. Todavia, nenhum sistema construído até então foi capaz de armazenar o hidrogênio de forma tão barata, segura e eficaz quanto seria necessário. Nanoestruturas de carbono são vistas como uma boa alternativa para construir dispositivos de armazenamento de hidrogênio baseados na fisissorção. Os nanopapiros de carbono, formados por folhas de grafeno enroladas no formato de um papiro, são considerados particularmente promissores para armazenar o hidrogênio, uma vez que possuem uma alta área superficial, extremidades abertas e distâncias intercamadas facilmente controláveis. Na primeira etapa deste trabalho, realizamos simulações de Dinâmica Molecular (MD) para estudar a dinâmica e a estabilidade de diversos nanopapiros em função de alguns dos seus parâmetros estruturais. Posteriormente, aplicamos o método de Monte Carlo Grand-Canônico (GCMC) para estudar o processo de adsorção de hidrogênio em nanopapiros selecionados, de forma a caracterizar quantitativamente e qualitativamente as fases adsorvidas / Abstract: Presently, the world economy depends on the use of fossil fuels to generate energy. This model presents serious environmental problems, since petroleum is a non-renewable and very pollutant material. Hydrogen gas presents itself as a promising alternative to substitute the fuels currently used due to a few positive characteristics: it is non-toxic, possesses a high gravimetric energetic density and only generates water as a combustion byproduct. In spite of all these advantages, hydrogen still isn't used commercially in a large scale. The biggest technological drawback for hydrogen to substitute fossil fuels is in its storage. There are many proposed ways to store hydrogen, such as tanks containing highly pressurized or liquid hydrogen, or solid systems that allow its adsorption. However, no system built up to the date had been able to store hydrogen as cheap, safe and efficiently as necessary. Carbon nanostructures are seen as a good alternative to build hydrogen storage devices based on physisorption. Carbon nanoscrolls, formed by graphene sheets scrolled in a papirus-like shape, are considered as particularly promising adsorption materials, since they possess a high surface area, open edges and easily controllable interlayer distances. In the first step of this work, we made Molecular Dynamics (MD) simulations to study the dynamics and the stability of several nanoscrolls as a function of their structural parameters. Subsequently, we used the Grand-Canonical Monte Carlo (GCMC) method to study the hydrogen adsorption process in selected nanoscrolls, as to characterize the adsorbed phases quantitatively and qualitatively / Doutorado / Físico-Química / Doutora em Ciências

The present study focuses on the development of Al-based systems and their examination as a medium for reversible hydrogen uptake. The first part of this thesis is dedicated to the chemistry and properties of Al-N-based materials. The synthesis, characterization, and detailed thermal decomposition studies of several aminoalanes have been described. As a result, single-crystal X-ray diffraction analyses revealed two new crystal structures of piperidinoalanes. The perspective approach employing activated aluminum and piperidine for reversible hydrogen uptake has been established. The second part of this work was focused on the modification of the properties of NaAlH4-based systems in order to generate the material with the high dissociation pressure suitable for high-pressure tank technologies. Considerable progress has been achieved in improving the hydrogen sorption properties by adding the extra aluminum powder to the Ti-catalysed NaAlH4-based system. Thus, the present study contributes to the understanding of the hydrogen sorption behavior of Al-based systems with perspectives being applicable to other related materials.:DECLARATION ACKNOWLEDGEMENTS DEFINITIONS AND ABBREVIATIONS ABSTRACT CONTENTS LIST OF TABLES LIST OF FIGURES MOTIVATION AND GOALS 1 INTRODUCTION 1.1 The prospects for hydrogen-based energy systems 1.2 Requirements for the hydrogen storage system 1.3 An overview of hydrogen storage strategies 1.4 Complex hydrides as a promising hydrogen storage materials 1.4.1 Metal borohydride systems 1.4.2 Alanate-based systems 1.4.3 Nitrogen-containing complex hydrides 1.5 Summary 2 GENERAL CHARACTERIZATION METHODS 2.1 X-ray crystallography 2.1.1 X-ray powder diffraction (XRPD) 2.1.2 Single-crystal structure analysis 2.2 Thermal analysis 2.3 Quantitative chemical analysis 2.3.1 Elemental analysis 2.3.2 Inductively coupled plasma optical emission spectrometry (ICP-OES) 2.4 Nuclear magnetic resonance spectroscopy (NMR) 3 LIQUID-STATE HYDROGEN STORAGE 3.1 State of the art 3.1.1 Liquid-state hydrogen storage materials 3.1.2 Al-N-based compounds as potential materials for hydrogen storage 3.1.3 Summary 3.2 Materials preparation and experimental details 3.2.1 Chemicals and sample handling 3.2.2 Synthesis of aminoalane in diethyl ether solution with aluminum hydride 3.2.3 Preparation of activated aluminum 3.2.4 Direct hydrogenation of activated aluminum supported by amine 3.3 Results and discussion 3.3.1 Is the solid-state hydrogen storage in aminoalanes possible? 3.3.2 Optimization of the direct hydrogenation of activated aluminum supported by amine 3.3.2.1 Synthesis and characterization of triethylenediamine alane complex 3.3.2.2 Synthesis of aminoalanes via direct hydrogenation of activated aluminum and N-heterocyclic amine 3.3.3 Investigation of piperidinoalanes for reversible hydrogen uptake 3.3.3.1 Crystal structure determination of piperidinoalanes 3.3.3.2 Influence of the initial reaction parameters on the piperidinoalane formation 3.3.3.3 Reversible hydrogenation in piperidinoalane system 3.3.4 Conclusions 4 SOLID-STATE HYDROGEN STORAGE 4.1 State of the art 4.1.1 Thermodynamic tuning of the hydrides 4.1.2 Features of the sodium alanate system 4.1.3 Catalytic enhancement of reversible hydrogenation in sodium alanate 4.1.4 The relevance of the Al-TM species in doped sodium alanate 4.1.5 Summary 4.2 Materials preparation and experimental details 4.2.1 Chemicals and purification procedure 4.2.2 Activation procedure of sodium alanate via mechanochemical treatment 4.2.3 Pressure-composition-isotherm measurements with a Sieverts-apparatus 4.2.4 High-pressure differential scanning calorimetry investigation of sodium alanate samples 4.3 Results and discussion 4.3.1 Tailoring the properties of sodium alanate-based system with the help of Ti-additive 4.3.2 Influence of the aluminum addition on the sorption behavior of Ti-doped sodium alanate 4.3.3 High-pressure DSC study of hydrogen sorption properties of doped sodium alanate system 4.3.4 Conclusions 5 SUMMARY AND CONCLUSIONS RECOMMENDATIONS AND OUTLOOK REFERENCES SUPPORTING INFORMATION Appendix A Appendix B Appendix C Publications

Dans le cadre de la recherche de vecteurs d'énergie “propres”, le borazane et ses dérivés amine-boranes sont devenus des candidats intéressants en tant que matériaux de stockage de l'hydrogène en raison de leur pourcentage massique relativement élevé en hydrogène (19,6% pour borazane) et de la réversibilité potentielle de la réaction de déshydrogénation. Pour des applications réelles, le contrôle des réactions se produisant à la température ambiante est fondamental. Dans ce contexte, la compréhension du processus de la déshydrogénation/déshydrocouplage catalytique de l'amine-borane apparaît comme un élément important. Dans cette thèse, les catalyseurs de types métallocènes du Groupe IV (Cp2M, M = Ti, Zr et Hf) sont étudiés en détail. Le déshydrocouplage de HMe2N·BH3 catalysé par le titanocène a été étudié à la fois expérimentalement et théoriquement mais aucun accord n'avait été atteint auparavant. Dans ce travail, les caractérisations systématiques des interactions 3-centre 2-électron M···H-B impliquées dans les intermédiaires réactionnels ont été réalisées avec des approches topologiques QTAIM et ELF. Par la suite, des mécanismes réactionnels détaillés ont été étudiés. Les résultats théoriques ont démontré que la méthode DFT corrigée avec la dispersion (DFT-D) étaient nécessaire et suffisantes pour une description énergétique correcte des chemins réactionnels. Mon travail a également permis l'identification d'un complexe de van der Waals jouant un rôle clé dans le mécanisme réactionnel en accord avec les observations expérimentales. / With the increasing demand of clean energy carriers, ammonia borane and its related amine-borane compounds have emerged as attractive candidates for hydrogen storage materials due to their relatively high weight percentage of available hydrogen (19.6% for ammonia borane) as well as the potential reversibility for the hydrogen release reactions. Actual applications would benefit from controlled reactions occurring close to room-temperature. In this context, catalytic dehydrogenation/dehydrocoupling of amine-borane appears as a promising solution. In this thesis the Group IV metallocene (Cp2M, M = Ti, Zr and Hf) are mainly discussed. The dehydrocoupling of HMe2N·BH3 catalyzed by titanocene was investigated both experimentally and theoretically but no agreement were reached. In this work, systematic characterization of M···H-B 3-center 2-electron interactions involved in reaction intermediates were carried out with QTAIM and ELF topological approaches. Afterwards, detailed mechanisms were further studied. Computational results have demonstrated that the dispersion corrected DFT (DFT-D) method was indispensable for a correct enegetic prediction for reaction pathways. The identification of a van der Waals complexe also plays a central role for a reaction mechanism with good agreement with experimental observations.

Le développement de l’hydrogène en tant que nouveau vecteur d’énergie demande de pouvoir le stocker à grande échelle, dans des conditions d’encombrement, de coût énergétique et de sécurité acceptables. Le stockage sous forme solide dans des hydrures métalliques réversibles, constitue une solution particulièrement sûre et intéressante pour des applications dans le secteur des transports. Parmi de nombreux matériaux possibles, le système Mg/MgH2, constitue l’un des meilleurs candidats : abondant, bon marché, capacité de stockage réversible et élevée (7,6 % H2 en masse). Son utilisation à l’échelle industrielle est néanmoins limitée par les cinétiques de sorption très lentes et la stabilité thermodynamique importante (enthalpie de formation élevée) nécessitant des températures de fonctionnement supérieure à 300 °C. Ce projet vise au développement de composites à base de MgH2 et d’additifs avec des propriétés de stockage améliorées. L’originalité des travaux menés repose sur le type d’additifs choisi, les complexes de métaux de transition (centre métallique : Ni et Ru, ligands organiques : phosphines). En effet, ces derniers ne sont pour le moment que très peu utilisés dans la littérature. L’objectif de ce travail de thèse est donc d’explorer leur potentiel et leur efficacité pour améliorer les propriétés de stockage du système Mg/MgH2. Différents composites "MgH2 + complexe" ont été préparés par broyage et imprégnation et les cinétiques de sorption des systèmes obtenus ainsi que leurs paramètres thermodynamiques ont été déterminés par analyse thermique (DTP, DSC, PCT). Enfin, de nombreuses techniques de caractérisation physico-chimiques (DRX, RMN, XPS, MEB, MET) ont été utilisées afin de comprendre les phénomènes se déroulant lors de l’hydrogénation et la déshydrogénation des composites préparés. Le meilleur système « MgH2 + complexe » préparé durant ce travail (MgH2 dopé avec 20 % du complexe NiHCl(PCy3)2) est capable d’absorber 6 % en masse d’H2 à 100 °C en 30 min et de libérer son hydrogène sous vide à 200 °C. Les énergies d’activation apparentes et enthalpies de formation de ce composite sont respectivement de 22 et –65 kJ/mol H2 pour l’hydrogénation (contre 200 et –74,7 kJ/mol H2 pour du Mg commercial) et de 127 et 63 kJ/mol H2 pour la déshydrogénation (contre 239 et 74,7 kJ/mol H2 pour du MgH2 commercial) / Although hydrogen is widely recognized as a promising energy carrier, its widespread adoption as alternative to fossil fuels depends critically on the ability to store hydrogen at adequate densities, cost and security. Application devices are far from a valuable technology, and fundamental research is still required. In this regard, solid-state systems present the advantage of denser and safer hydrogen storage. Among them, Mg/MgH2 is considered as a highly promising material in terms of reversibility, cost, gravimetric and volumetric capacity. However, high thermodynamic stability (high formation enthalpy) and slow hydrogen sorption kinetics limits its practical applications.This project aims to develop Mg/MgH2-based systems with improved hydrogen storage properties thanks to the use of additives. The originality of this work is brought by the kind of additive chosen, transition metal complexes (Ni and Ru based, with phosphine ligands). Indeed, they are, for now, only very little used in the literature. The objective of this work is therefore to study their potential and their efficiency to improve the hydrogen storage properties of the Mg/MgH2 system. Different “MgH2 + complex” composites were prepared by ball milling and impregnation method and the sorption kinetics and thermodynamic parameters of the formed systems were studied by TPD, DSC and PCT analyses. Finally, XRD, NMR, XPS, SEM and TEM techniques were used to understand the phenomena taking place during the hydrogenation and the dehydrogenation of the prepared composites.The best “MgH2 + complex” system prepared during this work (MgH2 doped with 20 wt% of NiHCl(PCy3)2 complex) is able to absorb 6 wt% of H2 at 100 °C in 30 min, and to release the stored hydrogen at 200 °C under vacuum. The apparent activation energies and the formation enthalpies of the composite are respectively of 22 and –65 kJ/mol H2 for the hydrogenation reaction (against 200 and –74,7 kJ/mol H2 for commercial Mg) and of 127 and 63 kJ/mol H2 for dehydrogenation (against 239 and 74,7 kJ/mol H2 for commercial MgH2).

A magnetic functionalization of microcrystalline MOF particles was realized using magnetic iron oxide particles. Such magnetic MOFs can be separated using a static magnetic field after use in catalytic processes and heated by an external alternating magnetic field to trigger desorption of encaged drug molecules. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Im Rahmen dieser Arbeit wurden neuartige, gemischte Tetrahydridoborate (Borhydride), die für die Wasserstoffspeicherung im Festkörper für die mobile Anwendung geeignet sein könnten, synthetisiert und vollständig charakterisiert. Entscheidende Materialanforderungen für die Kombination mit einer Tieftemperaturbrennstoffzelle sind die hohe Wasserstoffspeicherkapazität von min. 6 m% bei einer Wasserstoffdesorption unterhalb von 100°C. Um beide dieser Hauptkriterien zu erfüllen, wurden Li-Al- und Na-Al-Borhydrid entsprechend dem Konzept von Nakamori u.a. ausgewählt. Beide Borhydride desorbieren unterhalb von 100°C, wobei das synthetisierte Li-Al-Borhydrid aufgrund des hohen Wasserstoffgehalts (17,2 m% H2) die vielversprechendsten Eigenschaften zeigte. Beide Systeme wurden mittels Pulverdiffraktometrie am Synchrotron hinsichtlich Ihrer Struktur aufgeklärt, wobei die Struktur der einzelnen komplexen Ionen anhand von Schwingungsspektroskopie (Infrarot-, Ramanspektroskopie) ebenfalls bestätigt werden konnte. Mit Hilfe verschiedener kombinierter Desorptionsanalysen war es möglich den Zersetzungspfad, insbesondere die Bildung instabiler Desorptionsprodukte, aufzuklären. So erfolgt die Zersetzung des Li-Al-Borhydrids über die Bildung von Lithiumborhydrid in der Festphase, das mittels in-situ Ramanspektroskopie in einer speziellen Ramanzelle beobachtet werden konnte. Die Infrarotspektroskopie des Desorptionsgases zeigte zunächst die Freisetzung von Aluminiumborhydrid, dass wiederrum Diboran und Wasserstoff desorbiert. Weiterhin wurden verschiedene Möglichkeiten verfolgt, wie der Zusatz von Kohlenstoff oder das Nanoconfinement von Lithiumalanat, um den Zersetzungsweg hinsichtlich ausschließlicher Wasserstofffreisetzung zu modifizieren und somit Reversibilität zu ermöglichen. Es konnte jedoch kein reversibles System mit hoher gravimetrischer Wasserstoffspeicherdichte und Desorption unterhalb von 100°C erzeugt werden. / Aim of the work was the synthesis and characterisation of novel mixed tetrahydroborates (borohydrides) for solid state hydrogen storage suitable for mobile applications. The combination with a PEM fuel cell requires a material with at least 6 wt% hydrogen combined with hydrogen desorption below 100°C. To fulfill both criteria, Li-Al- und Na-Al-borohydride were selected according to Nakamori’s concept. Both mixed borohydrides desorb well below 100°C whereas the mixed Li-Al-borohydride showed the most promising properties due to its high gravimetric hydrogen content (17.2 wt% H2). The crystal structures were examined by powder diffraction with a synchrotron source. The symmetry of the containing complex cations and anions was confirmed with vibrational spectroscopy (infrared, raman spectroscopy). The desorption pathway was clarified using a variety of combined thermal analysis techniques. Especially the desorption of unstable products of the most promising Li-Al-borohydride was possible via spectroscopy. Hence the desorption of Li-Al-borohydride leads to the formation of lithium borohydride in the solid state which was monitored via in-situ raman spectroscopy in a special raman cell. Infrared spectroscopy of the desorbed gas showed the initial desorption of aluminium borohydride which desorbs diborane and hydrogen in the following. Different options were examined in order to modify this desorption pathway by carbon addition or nanoconfinement of lithium alanate. However, none of the materials showed high hydrogen content combined with exclusive hydrogen desorption below 100°C and reversibility.