Organometallically prepared AlH3 and as-received Al powders were mixed with MgH2 to improve the dehydriding and rehydriding properties of MgH2. Thermal analysis shows that the onset dehydriding temperature of MgH2 is reduced by 55 °C (or 25 °C) when mixed with AlH3 (or Al). The destabilization of MgH2 is attributed to the formation of Mg–Al alloys through the reaction between MgH2 and Al. Isothermal dehydriding measurements demonstrate that AlH3 and Al both improve the dehydriding kinetic of MgH2 to some extent, and it only takes 44 min for MgH2 + AlH3 (5.4 h for MgH2 + Al) to release 60% of the hydrogen of MgH2 at 300 °C, but 8.6 h are required for as-milled MgH2. The apparent activation energy for the dehydriding of MgH2 is reduced from 174.6 kJ mol−1 for as-milled MgH2 to 154.8 and 138.1 kJ mol−1 for MgH2 mixed with Al and AlH3 respectively; this is responsible for the improvement in the dehydriding kinetics of MgH2. Despite this, AlH3 is better in destabilizing MgH2 than the as-received Al for the fact that Al* formed in situ from the decomposition of AlH3 is oxide-free on the particle surfaces, which effectively increases the chemical activity of Al*. Furthermore, the brittleness of AlH3 makes it easier to mix MgH2 with AlH3, which would result in uniform distributions of Mg and Al and shortening of the diffusion length. Concerning the reversibility, at 300 °C and 5 MPa H2 and MgH2 are fully recovered in the dehydrided MgH2 + Al, and MgH2 + AlH3 samples after rehydriding for 10 h. The rehydriding kinetic of MgH2 is significantly enhanced for the dehydrided MgH2 + AlH3, but not in the case of the MgH2 + Al.

Li3AlH6 and LiNH2 at a 1:3 molar ratio were mechanically milled to yield a Li–Al–N–H composite. The hydrogen storage properties of the composite were studied using thermogravimetry, differential scanning calorimetry, mass spectrometry, and X-ray diffraction. Addition of LiNH2 lowered the decomposition temperature of Li3AlH6. The Li–Al–N–H composite began to release hydrogen at around 110 °C, which was 90 °C lower than the initial desorption temperature of Li3AlH6. About 7.46 wt% of hydrogen was released from the composite after heating from room temperature to 500 °C. A total hydrogen desorption capacity of 8.15 wt% was obtained after accounting for hydrogen released in the ball-milling process. The resulting dehydrogenated composite absorbed 3.56 wt% of hydrogen at 400 °C under a hydrogen pressure of 110 bar. The hydrogen absorption capacity and kinetic properties of the Li–Al–N–H composite significantly improved when CeF3 was added to the composite. A maximum hydrogen absorption capacity of 4.8 wt% was reached when the composite was doped with 2 mol% CeF3.

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.%.

Organometallically prepared AlH3 and as-received Al powders were mixed with MgH2 to improve the dehydriding and rehydriding properties of MgH2. Thermal analysis shows that the onset dehydriding temperature of MgH2 is reduced by 55 °C (or 25 °C) when mixed with AlH3 (or Al). The destabilization of MgH2 is attributed to the formation of Mg–Al alloys through the reaction between MgH2 and Al. Isothermal dehydriding measurements demonstrate that AlH3 and Al both improve the dehydriding kinetic of MgH2 to some extent, and it only takes 44 min for MgH2 + AlH3 (5.4 h for MgH2 + Al) to release 60% of the hydrogen of MgH2 at 300 °C, but 8.6 h are required for as-milled MgH2. The apparent activation energy for the dehydriding of MgH2 is reduced from 174.6 kJ mol−1 for as-milled MgH2 to 154.8 and 138.1 kJ mol−1 for MgH2 mixed with Al and AlH3 respectively; this is responsible for the improvement in the dehydriding kinetics of MgH2. Despite this, AlH3 is better in destabilizing MgH2 than the as-received Al for the fact that Al* formed in situ from the decomposition of AlH3 is oxide-free on the particle surfaces, which effectively increases the chemical activity of Al*. Furthermore, the brittleness of AlH3 makes it easier to mix MgH2 with AlH3, which would result in uniform distributions of Mg and Al and shortening of the diffusion length. Concerning the reversibility, at 300 °C and 5 MPa H2 and MgH2 are fully recovered in the dehydrided MgH2 + Al, and MgH2 + AlH3 samples after rehydriding for 10 h. The rehydriding kinetic of MgH2 is significantly enhanced for the dehydrided MgH2 + AlH3, but not in the case of the MgH2 + Al.