PROCESSING AND HYDROGEN DESORPTION PROPERTIES OF NOVEL LITHIUM BOROHYDRIDE (LIBH4)-BASED HYDROGEN STORAGE MATERIALS

PhDThe primary aim of this project was the development of an inorganic Lithium borohydride (LiBH4)-based material for effective use in hydrogen storage. The objective was to find a material which would desorb a minimum of 5 wt.% H2 under mild conditions. To do so, LiBH4 has been investigated and the possibility to destabilise it so that it could release a maximum of its hydrogen content without losing boron, which is a requirement for reversible hydrogen storage. Why LiBH4? Lithium borohydride has one of the greatest hydrogen content (18.5 wt.%) among hydride materials. Nevertheless, the compound is very stable, hence the desorption temperature is too high for practical considerations. Hopefully, some interesting results have been reported by previous studies and opened the way for possible improvement mainly in terms of lowering the desorption temperature. The impact of chemical additions such as transition metal chlorides and ammonium chloride (NH4Cl) to its thermostability has been assessed. NH4Cl has a number of advantages compared to transition metal chlorides since it contains hydrogen, is less heavy and is a precursor to ammonia borane (NH3BH3), another promising material for solid-state hydrogen storage applications. Mass spectrometry and thermal analysis of mixtures of LiBH4 and NH4Cl indicate that contrary to the results obtained with the addition of transition metal chlorides where a significant amount of B2H6 escapes from the mixture upon heating, sole release of hydrogen may be obtained. Moreover, the onset hydrogen desorption may be as low as 65ºC for (LiBH4 + NH4Cl) mixtures, similarly to the one observed for (2LiBH4 + ZnCl2) mixtures. In the case of NH4Cl-added mixtures, the proportion of H2 released is much higher, around 2 wt.% at this temperature. Also, sole release of up to 6 wt. % hydrogen may be achieved at temperatures as low as 150ºC, which is a huge improvement compared to pure LiBH4, transition metal chlorides added mixtures and even NH3BH3. This whole study shows the clear potential for using B-N-H compounds as highcapacity hydrogen storage applications.UK-SHEC and EPSR