The effects of halide modifiers on the sorption kinetics of the Li-Mg-N-H System

The effects of different transition metal halides (TiCl3, VCl3, ScCl3 and NiCl2) on the sorption properties of the 1:1 molar ratio of LiNH2 to MgH2 are investigated. The modified mixtures were found to contain LiNH2, MgH2 and LiCl. TGA results showed that the hydrogen desorption temperature was reduced with the modifier addition in this order: TiCl3 > ScCl3 > VCl3 > NiCl2. Ammonia release was not significantly reduced resulting in a weight loss greater than the theoretical hydrogen storage capacity of the material. The isothermal sorption kinetics of the modified systems showed little improvement after the first dehydrogenation cycle over the unmodified system but showed drastic improvement in rehydrogenation cycles. X-ray diffraction and Raman spectroscopy identified the cycled material to be composed of LiH, MgH2, Mg(NH2)2 and Mg3N2.

► LiNH2:MgH2 as milled and with halide modifier additions were cycled to measure the rates of dehydrogenation and rehydrogenation.
► Dehydrogenation data supported previous literature claims of a 3-step decomposition reaction pathway.
► Transition halide modifiers were added to enhance kinetics and reduce the ammonia release and found to be ineffective after two cycles.