An investigation on the reaction mechanism of LiAlH4–MgH2 hydrogen storage system

The mechanism and hydrogen absorption/desorption properties of LiAlH4 + xMgH2 (where x = 1, 2.5, and 4) composites have been investigated. With the combination of MgH2 and LiAlH4 by mechanical grinding, initial decomposition temperatures of the mixtures can be reduced by about 50 °C. Mechanical grinding treatment makes MgH2 react with LiAlH4 to release a certain amount of hydrogen. The final resultants of the composites after thermal decomposition contain Al12Mg17. Intermetallic Al12Mg17 hydrogenated into Al2Mg3, MgH2 and Al firstly, intermediate Al2Mg3 then transforms into MgH2 and Al in the subsequent hydriding process. Hydrogenation of intermediate Al2Mg3 is supposed to occur synchronously to that of Al12Mg17, therefore demarcation of the two hydrogenation processes is ambiguous. Al12Mg17 can be totally recovered by complete dehydriding. Formation of Al12Mg17 alters the reaction pathway of LiAlH4 + xMgH2 (where x = 1, 2.5, and 4) systems and improves their thermodynamic properties. The dehydrogenation process of LiAlH4 + xMgH2 (x = 1, 2.5, and 4) composites contain two stages, their maximum desorption capacity reaches 7.46 wt.%.