Journal of Alloys and Compounds. 2018, V. 765, p. 635–643
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Recent investigations showed the formation of new amide-chloride phases between LiNH2 and AlCl3 after milling and/or heating under hydrogen pressure. These phases exhibited a key role in the improvement of the hydrogen storage properties of the LiNH2-LiH composite. In the present work, we studied the effects of Al and AlCl3 additives on the hydrogen storage behavior of the Li-Mg-N-H system. The dehydrogenation kinetics and the reaction pathway of Al and AlCl3 modified LiNH2-MgH2 composite were investigated through a combination of kinetic measurements and structural analyses. During the first cycle, the addition of Al catalytically accelerates the hydrogen release at 200 °C. In the subsequent cycles, the formation of a new phase of unknown nature is probably responsible for both increased equilibrium hydrogen pressure and decreased dehydrogenation rate. In contrast, AlCl3 additive reacts with LiNH2-MgH2 through the milling and continues during heating under hydrogen pressure. Addition of AlCl3 leads to the formation of two cubic structures identified in the Li-Al-N-H-Cl system, which improves dehydrogenation rate by modifying the thermodynamic stability of the material. This study evidences positive effect of cation and/or anion substitution on hydrogen storage properties of the Li-Mg-N-H system.