Lightweight chemical hydride materials have been promoted as potential hydrogen storage materials due to their high gravimetric and volumetric capacities. However, their commercial applicability is limited by the high temperatures required for dehydrogenation (decomposition) and the high temperatures and pressures required for direct hydrogen reversibility. Understanding the decomposition and reversibility in reversible lightweight hydride systems, such as LiNH2/LiH and LiBH4 is crucial if we are to improve their functional properties. In both materials the ability to store and release hydrogen must be related to structure and the ability of ions to travel through the bulk materials, and both have been shown to be fast ion conductors. However, direct hydrogen absorption/desorption reversibility is significantly more facile for the LiNH2/Li2NH system than for any tetrahydroborate.To investigate the synthesis, structure, ionic conductivity and decomposition of these lightweight hydride systems we have utilised a variety of characterization techniques including;X-ray Synchrotron and neutron diffraction to probe the structure during dehydrogenation and rehydrogenation,Thermogravimetric analysis with simultaneous mass spectroscopy to probe decomposition and to investigate mechanism,Simultaneous thermogravimetric analysis and neutron diffraction to dynamically probe decomposition, rehydrogenation and hydrogen cyclingHere we will examine experimental data on the decomposition of amides and tetrahydroborate materials together with a number of chemical and theoretical models that include inorganic energy scales, ionic radius, structure and chemical electronegativity to develop an understanding of decomposition processes and provide an explanation for the difference in hydrogenation/dehydrogenation behaviour in amides and tetrahydroborates.

Understanding decomposition of tetrahydroborate and amide complex chemical hydrides

245th National Meeting (2013)

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