Ammonia borane composites for solid state hydrogen storage and calcium-ammonia solutions in graphite Atahl Nathanson This thesis is in accordance with the requirements of the University College London for the degree of Engineering Doctorate February 2014 I Ammonia borane composites for solid state hydrogen storage and calcium-ammonia solutions in graphite Submitted for the degree of Doctor of Engineering February 2014 Abstract The dual problems of worlds growing population, increasing energy demand and global warming, necessitate an alternative to fossil fuels. Hydrogen is plentiful and has a high energy density but storage in high pressure tanks is complex and presents safety concerns. Ammonia borane (AB) is one of the most promising solid state hydrogen storage materials due to its high releasable hydrogen content (13.1 wt%), stability in air, and low toxicity. On heating, however, pure AB releases hydrogen only after long nucleation times and is accompanied by the liberation of gaseous impurities including borazine and ammonia; additionally, extensive material expansion and foaming occurs. AB composites with polyethylene oxide, polystyrene and imogolite have been synthesized. It is concluded that the decomposition of AB is best ameliorated by providing access to functional groups that catalyse alternative dehydrogenation routes. Lowering the onset of hydrogen loss to below the melting temperature limits the overall foam and expansion. The two dimensional confined motion of liquid ammonia in a multi staged ternary calcium ammonia graphite intercalation compound was studied with respect to temperature. Hopping diffusion at 300K gives way to rotation below 100K. The dynamics of this confined calcium ammonia solution are observed as similar to the three dimensional counterpart. II I, Atahl Nathanson confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis III Acknowledgements Firstly, a thank you to my supervisors Stephen Bennington and Neal Skipper for their guidance, support and the enthusiasm expressed for my scientific endeavours. Both provided distinct and valuable roles in allowing me to experience both academia and industry. The team at Cella Energy, Arthur (Thank you for being an invaluable mentor and friend.), Zeynep (Thanks for all the great food, help with experiments and political awareness.), Stephen (All that wardrobe advice and unfortunately I still wear shorts with tights.), Tom (We didn’t get shot!), Dave, Joe, Lucile, Marie, Lindsey (Tango till dawn with me?), Gemma (I’ve still got that duck!), Anna and Matt (Many thanks, soon we will all be published authors!) and Kevin (Thank you for starting for my ill car – it’s now in mechanical heaven.). Now all those at Isis: Tati (where would we be without your bus? Thank you for all those hours spent waiting for me at the side of the road), Aziz (keep up the music), Jordi (Who will throw things at me now?), Rowen, Bruno, Konstantin, Davide, Rob, Giovanni, Sev, Roberto (Thank you, I will come to Milan…soon…very soon!), Vicky (Thank you for all your help and patience.), Ruth (Thanks for Robbie and all the fabulous gossip.), Ivan (Thanks for all those great coffees and cakes.) and Joe (Keep peddling.). Thank you to the F10 crew for support during my write up. Emily, so handy with the hanky and the prep talks, thank you. Christian, Dave, Paddy, Radhika and Stephen, thanks for the help, lunches and letting me play my atrocious football. I’m building a team over in Chemistry so prepare yourselves! Hello and thanks also to the EngD group Nic, Nuru, Will, Szymon, Clyde, Marcus, Isaac, Liz, Jay and Kathrine, unfortunately dl-poly didn’t make the final cut this time. Thank you Chris for making the calcium and lithium graphite samples. Spencer and Jaqueline, without your guidance through Modes the neutron data would still be very raw. Derek, many thanks for all the science advices! Arthur, gracias for the Sketchup electrospinning picture. My three keen work experience students Bouyan, Ben and Hannah. Thank you for coming and being, well, so keen! Jaqueline (Thank you for your help, you’re always in my heart.), Jake (Thanks for tolerating my general madness.) and Eloise (your good wishes are always so well timed). Thank you to all my proof readers; Steve, Neal, Mum, Christian, Joe, Tim and Rhiain. So to my family, Mum, Dad, Phil, Rhiain, Brighid and Lucien. Thank you for believing in me and making me feel intelligent. Sarah, Gemma, Jade, Parry, Isaac and Suki, you rock my world, IV thanks for letting me live in your home. And last but not least thanks to Robbie my feline bed warmer. V Contents 1 An introduction to hydrogen storage and graphite intercalation compounds ............ 1 Hydrogen....................................................................................................................... 1 Fossil fuels and global warming ........................................................................... 1 A hydrogen economy ............................................................................................ 1 Hydrogen storage targets for vehicles ........................................................................... 4 Current hydrogen storage methods for vehicles............................................................ 4 Storing hydrogen as a gas or liquid ....................................................................... 7 Clathrates .............................................................................................................. 7 Physisorbed hydrogen storage .............................................................................. 8 Chemisorbed hydrogen storage ............................................................................. 9 Alkali metal ammonia graphite intercalation compounds .......................................... 12 2 Materials introduction .............................................................................................. 15 Ammonia borane ......................................................................................................... 15 Structure .............................................................................................................. 15 Ammonia borane synthesis and regeneration ..................................................... 17 The reaction pathway of the dehydrogenation of ammonia borane .................... 17 Modifying the dehydration properties of ammonia borane – literature study ............. 20 Ammonia borane in water ................................................................................... 20 Ammonia borane in alternative solvents ............................................................. 20 Ammonia borane in ionic liquids ........................................................................ 21 Ammonia borane in acidic conditions................................................................. 22 Zeolites and metal organic frameworks .............................................................. 23 Carbon ................................................................................................................. 23 Metal catalysts and ammonia borane .................................................................. 24 Ammonia borane in the presence of polymers .................................................... 24 Materials used and project aims .................................................................................. 25 Polymers ............................................................................................................. 25 VI Clays ................................................................................................................... 27 Graphite intercalation compounds .............................................................................. 30 3 Experimental methods ............................................................................................. 32 Making samples .......................................................................................................... 32 Electrospinning ................................................................................................... 32 Spinning parameters ............................................................................................ 39 Freeze drying ...................................................................................................... 41 Dry mixing .......................................................................................................... 41 A vapour transport method for intercalation into graphite .......................................... 42 Analysing samples ...................................................................................................... 42 Scanning electron microscopy ............................................................................ 42 Fourier transform infrared spectroscopy ............................................................. 44 Foam tests ........................................................................................................... 45 Thermogravimetric analysis and differential scanning calorimetry .................... 45 Mass spectrometry .............................................................................................. 47 X-ray diffraction ................................................................................................. 53 Nuclear magnetic resonance spectroscopy .........................................................