Lighter Materials for Hydrogen Storage

Rosalind Davies
PhD student in the group of Dr Paul Anderson

Vehicles powered by hydrogen release only water at point of use, and are therefore preferable to petrol or diesel vehicles as pollution levels are reduced. Currently, one of the main obstacles to using hydrogen to power a vehicle is the on-board storage of the hydrogen. Lithium amide (LiNH2) combined with lithium hydride (LiH) is a promising hydrogen storage system, releasing up to 6.5 weight percent of hydrogen. However, the system currently requires high temperatures to release the stored hydrogen. Addition of halide ions, such as chloride (Cl−), forms amide halides that show a reduction in the temperature of hydrogen release. However, the addition of halides also increases the weight of the system, which is not favourable for mobile or vehicular applications. The aim of this research was to lower the chloride level without increasing the desorption temperature. A new phase with half the amide: chloride ratio was synthesised and characterised. The lower chloride phase maintained the improvement in hydrogen cycling properties when compared to the original amide chloride. The illustration shows the crystal structures of both the phases calculated from synchrotron X-ray diffraction data and how the theoretical weight percent of hydrogen that can be stored in the system varies between them.