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Metallated Derivatives of Ammonia Borane with a View to Their Potential As Hydrogen Storage Materials

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Metallated Derivatives of Ammonia Borane with a View to Their Potential As Hydrogen Storage Materials Metallated Derivatives of Ammonia Borane with a view to their potential as Hydrogen Storage Materials by Ian C. Evans Supervisor: Dr Paul A. Anderson A thesis submitted to the University of Birmingham for the Degree of Doctor of Philosophy The School of Chemistry College of Engineering and Physical Sciences The University of Birmingham February 2011 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Ammonia borane, NH3BH3, has attracted growing interest in recent years in the field of hydrogen storage due to its high gravimetric hydrogen content. In this study the reaction of NH3BH3 with various metal hydrides was investigated. The reactions with hydrides of lithium and sodium required a molar ratio of 1:2 in favour of NH3BH3 and + − the reaction products were characterised as [Li(NH3)] [BH3NH2BH3] and + − 11 23 [Na] [BH3NH2BH3] , respectively, through solid state B and Na MAS NMR and Raman spectroscopy. The reaction of CaH2 with NH3BH3 required a reaction stoichiometry of 1:4 and this reaction proceeded through a different reaction mechanism, forming Ca(BH4)2·2NH3. The crystal structures of Ca(BH4)2·2NH3 and Ca(BH4)2·NH3 were determined by powder diffraction methods and the reaction pathway investigated through solid state 11B MAS NMR spectroscopy. The thermal desorption properties of these hydrogen rich materials were investigated and hydrogen was released from all the materials. However, under certain conditions ammonia was the major gaseous desorption product from Ca(BH4)2·2NH3 and was + − observed as a minor product from the decomposition of [Li(NH3)] [BH3NH2BH3] . + − Ammonia was also released during the synthesis of [Na] [BH3NH2BH3] , but the decomposition of this material was free from ammonia release. Ramped thermal + − + − desorption studies of [Na] [BH3NH2BH3] and [Li(NH3)] [BH3NH2BH3] to 350°C resulted in weight losses due to hydrogen desorption of 7.5 wt% and 12.5 wt%, respectively. Heating Ca(BH4)2·2NH3 to 350°C resulted in a total weight loss of 27.5 wt%, which was predominantly due to NH3 desorption. Powder XRD and solid state 11B MAS NMR spectroscopy were employed to identify the solid decomposition products and decomposition pathways were proposed. Metal borohydrides were identified in all cases as well as polymeric products possessing B–N chains. Acknowledgements Well the nightmare of writing a thesis has finally come to an end and for that I am exceptionally grateful. It has been a long and painful journey and I could not have got to the end without the support of so many people. Firstly, I would like to thank my supervisor, Paul, who has been eternally patient and helpful for the last few years as well as for our many football chats when we probably should have been discussing things a little more closely related to my PhD. I‘d like to thank the members of the Anderson group, past and present, for the last few years, with a special mention going to Dr Phil Chater for kindly synchronising his departure from the group with my submission day, as well as for all his help over the years with all things chemistry. Probably should mention the other group members to avoid an earful, so Alvaro, Matt, Alex, Dave, Tom C and Ivan, you have all been in the group. Thanks to the rest of Floor 5 for the fun and laughs while I‘ve been there. In Mat & Met Dan, Allan and Big Dave have been nice enough to let me use their equipment and help me out when things have not gone to plan. Tom Partridge at the University of Warwick is due a mention for the countless hours he spent collecting and interpreting NMR spectra, as well as John Hanna. I am also thankful for having a fantastic set of mates, who I haven‘t really seen for the last 12 months, but that‘s about to change with some big nights out planned, starting today! So Bails, Evo, Jeff, Lairddog and Ugs, congratulations you have all made it in. And I have to mention the mighty Bournville Village and Village C football clubs for giving me a distraction from my thesis over the last year and keeping me sane. I‘m sure some silverware is just around the corner! Too many others to mention, but Nic, Ad and Deb are in for some brilliant times over the years. Finally, and most importantly, thanks to my parents and grandparents, without their love and support I could never have achieved everything that I have in life. i Contents 1. Introduction 1 1.1. The Current World Energy System 1 1.2. Hydrogen 1 1.3. Hydrogen Production 2 1.3.1. From Fossil Fuels 3 1.3.2. Electrolysis 4 1.3.3. Thermal Production 5 1.3.4. Biomass 5 1.4. Hydrogen as a Fuel 6 1.4.1. Hydrogen Internal Combustion Engine 6 1.4.2. Fuel Cells 7 1.5. Batteries 9 1.6. Hydrogen Storage 10 1.6.1. Storing Hydrogen as a Gas 11 1.6.2. Liquid Hydrogen Storage 12 1.6.3. Solid State Hydrogen Storage 12 1.6.4. Physisorption 13 1.6.5. Metallic Hydrides 14 1.6.6. Complex Hydrides 16 1.6.6.1. Alanates 17 1.6.6.2. Borohydrides 17 1.6.6.3. Amides 19 1.6.6.4. Mixed Amide Borohydrides 22 1.6.7. Hydrogen Storage Targets 22 1.6.8. Thermodynamics of Hydrogen Storage 24 1.7. Ammonia Borane 26 1.7.1. Synthesis 26 1.7.2. Structure 28 CONTENTS ii 1.7.3. Decomposition 33 1.7.4. As a Hydrogen Storage Material 39 1.8. Aims 41 1.9. References 42 2. Experimental 51 2.1. Crystallography 51 2.1.1. Crystal Systems and Unit Cells 51 2.1.2. Lattices 52 2.1.3. Lattice Planes and Miller Indices 53 2.1.4. Crystal Structures 54 2.2. X-Ray Diffraction 54 2.2.1. Generation of X-Rays 54 2.2.2. Bragg‘s Law 55 2.2.3. Powder Diffraction 56 2.2.4. Laboratory X-Ray Diffraction 59 2.3. Rietveld Analysis 59 2.4. Mass Spectrometry 62 2.5. Temperature Programmed Desorption 63 2.6. Intelligent Gravimetric Analysis 67 2.7. Thermogravimetric Analysis 67 2.8. Solid State Nuclear Magnetic Resonance Spectrometry 68 2.9. Raman Spectroscopy 74 2.10. References 76 3. The Thermal Decomposition of Ammonia Borane 77 3.1. Introduction 77 3.2. Experimental 77 3.3. Powder X-Ray Diffraction 78 3.4. Thermal Desorption Studies 80 3.5. Raman Spectroscopy 84 3.6. Solid State 11B MAS NMR Spectroscopy 96 CONTENTS iii 3.7. Conclusion 103 3.8. References 104 4. The Reaction of Sodium Hydride with Ammonia Borane 107 4.1. Introduction 107 4.2. Experimental 107 4.3. Powder X-Ray Diffraction 108 4.3.1. Discussion 114 4.3.2. Indexing 118 4.3.2.1. Impurities 127 4.3.2.2. Refined Lattice Constants 129 4.4. Thermal Desorption Studies 132 4.4.1. NaNH2BH3 132 4.4.2. NaH + NH3BH3 135 4.4.3. NaH + 2NH3BH3 138 4.4.4. Alternative Thermal Desorption Studies 147 + − 4.4.5. Na [BH3(NH2)BH3] Phase 151 4.4.5.1. TPD–MS 151 4.4.5.2. IGA–MS 152 4.4.5.3. Discussion 153 4.5. Solid State 11B MAS NMR Spectroscopy 155 4.5.1. NaH + NH3BH3 Reaction 156 4.5.2. NaH + 2NH3BH3 Reaction 161 4.6. Solid State 23Na MAS NMR Spectroscopy 172 4.7. Raman Spectroscopy 176 4.7.1. NaNH2BH3 176 + − 4.7.2. Na [BH3NH2BH3] 185 4.8. Overall Discussion and Conclusion 189 4.8.1. The NaH + NH3BH3 Reaction Pathway 189 4.8.2. The NaH + 2NH3BH3 Reaction Pathway 192 4.8.3. Potential as Hydrogen Storage Materials 194 4.9. References 196 CONTENTS iv 5. The Reaction of Lithium Hydride with Ammonia Borane 200 5.1. Introduction 200 5.2. Experimental 200 5.3. Powder X-Ray Diffraction 201 5.3.1. Indexing 208 5.3.2. Discussion 212 5.4. Thermal Desorption Studies 219 5.4.1. TPD Study of LiNH2BH3 219 5.4.2. TPD Study of LiH + 2NH3BH3 Reaction Mixture, Heated to 350°C at a rate of 2°C min−1 221 5.4.3. TPD Study of LiH + 2NH3BH3 Reaction Mixture, Heated to 60°C at a rate of 0.1°C min−1 224 5.4.4. TPD–MS Study of the Tetragonal Phase 226 5.4.5. IGA–MS Study of the Tetragonal Phase 228 5.4.6. Comparison of H2 desorption from the LiH + 2NH3BH3 reaction mixture + − and [Li(NH3)] [BH3NH2BH3] to NH3BH3 233 5.5. Solid State 11B MAS NMR Spectroscopy 234 5.6. Raman Spectroscopy 242 5.7. Overall Discussion and Conclusion 246 5.7.1. The LiH + 2NH3BH3 Reaction Pathway 246 5.7.2. Potential as a Hydrogen Storage Material 248 5.8. References 249 6. The Reaction of Calcium Hydride with Ammonia Borane 252 6.1. Introduction 252 6.2. Experimental 252 6.3. Powder X-Ray Diffraction 253 6.4.
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