| Based on the review of the progress in the metal aluminium hydrides for hydrogen storage, the Li-Mg-Al-H complex system was selected as the research object in this work. By means of XRD, FTIR, TPD and hydrogen desorption measurements, the following three contents were investigated:the preparation, hydrogen desorption properties and mechanisms of LiMg(AlH4)3, and the effects of various catalysts on the hydrogen storage performance of LiMg(AlH4)3, and the hydrogen storage performances of the Li3AlH6/MgH2 system.LiMg(AlH4)3 was synthesized by ball-milling the mixture of LiAlH4 and MgCl2 at a molar ratio of 3:1. XRD and FTIR measurements demonstrated that the LiAlH4 and MgCl2 definitely converted to LiMg(AlH4)3 and LiCl after 4 h of ball-milling.～8.78 wt% of hydrogen was released from LiMg(AlH4)3 at 96-280℃through a three-step reaction. The kinetic investigations showed the apparent activation energy was about 94.6 kJ/mol for the first step hydrogen desorption reaction of LiMg(AlH4)3. It is found that the first-step hydrogen desorption can be explained by an increasing nucleation and diffusion controlled growth. However, only about 1.5 wt% of hydrogen was recharged into the dehydrogenated LiMg(AlH4)3, which mainly comes from the hydrogenation of Al3Mg2.To reduce the dehydorgantion temperature of LiMg(AlH4)3, various Ti-based catalysts (TiF3, TiF4, TiO2 and TiSi2) were introduced as catalysts. It is found that the onset temperature of the first-step desorption of LiMg(AlH4)3 with 5wt% TiF3 decreased to 68℃, a～28℃reduction compared to the pristine sample. XRD examinations revealed that the addition of TiF3 neither changed the structures of the post-milled samples nor affected the pathway of the dehydrogeantion reaction of LiMg(AlH4)3. It is therefore believed that TiF3 is an effective catalyst for the dehydrogenation of LiMg(AlH4)3, The apparent activation energy of LiMg(AlH4)3 with 5 wt% TiF3 was calculated to be around 69.1 kJ/mol, a 25.5 kJ/mol reduction with respect to the pristine LiMg(AlH4)3 sample. Further investigation on the desorption kinetics of LiMg(AlH4)3 showed that the first-step desorption of the 5 wt% TiF3-doped sample was converted to a site-saturation nucleation and diffusion controlled growth reaction. The added TiF3 could serve as the nuclei sites for the dehydrogenated products of LiMg(AlH4)3, which is responsible for the improvement of the desorption kinetics. However the hydrogenation performances of the LiMg(AlH4)3 maintained almost unchanged, only 1.4 wt% hydrogen could be reversibly absorbed.In addition, the hydrogen desorption/absorption behaviors of the Li3AlH6/MgH2 complex system were systematically investigated. It is found that the dehydrogenation temperatures were obviously decreased by mixing with Li3AlH6, which can be attributed to the presence of Al after the dehydrogenation of Li3AlH6 since the Al can reacts with MgH2 to form Al12Mg17. Moreover, investigations on the catalytic modification revealed that the TiF4-doped Li3AlH6-MgH2 (1:1) sample began to dehydrogenate at 100℃. A 50℃reduction was achieved on the onset desorption temperature relative to the pristine sample. Further analyses showed that the apparent activation energy of the first-step desorption of TiF4-doped Li3AlH6-MgH2 (1:1) was 112 kJ/mol, which was 32 kJ/mol lower than that of the undoped sample. JMA equation analyses revealed the first-step desorption of TiF4-doped Li3AlH6-MgH2 sample was a site-saturation nucleation and a diffusion controlled growth reaction. The doped TiF4 is likely to work as the nucleation center, which decreases the apparent activation energy of the Li3AlH6-MgH2 sample, and consequently improving the dehydrogenation kinetics.
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