Mg17Al12-hydride （abbreviated as MAH） was selected as a destabilization agent to improve de/rehydrogenation properties of LiBH4. 58LiBH4＋Mg17Al12-hydride composite was prepared by ball-milling. It is found that the dehydrogenation of ball-milled LiBH4/MAH composite presents a two-step reaction for hydrogen release. The composite starts desorbing hydrogen at about 300 ℃ and yields 9.8%of hydrogen （mass fraction） below 500 ℃. By adding MAH, the dehydrogenation kinetics of LiBH4 is improved and the dehydrogenation temperature of LiBH4 is also lowered by 20 ℃. High rehydriding capacity of 8.3% was obtained for the dehydrogenated composite in the first cycle at 450 ℃. The XRD analysis shows the formation of MgB2 and AlB2 in the dehydrogenation process, which reduces the thermodynamics stability of LiBH4 system and is beneficial to the reversible hydrogen storage behaviors of LiBH4/MAH composite.
NaAlH4 complex hydrides doped with lanthanon hydrides were prepared by hydrogenation of the ball-milled NaH/Al＋ xrnol.% RE-H composites （RE=La, Ce; x=2, 4, 6） using Nail and A1 powder as raw materials. The influence of lanthanon hydride catalysts on the hydriding and dehydriding behaviors of the as-synthesized composites were investigated. It was found that the com- posite doped with 2 mol.% LaH3.01 displayed the highest hydrogen absorption capacity of 4.78 wt.% mad desorption capacity of 4.66 wt.%, respectively. Moreover, the composite doped with 6 mol% CEH2.51 showed the best hydriding/dehydriding reaction kinetics. The proposed catalytic mechanism for reversible hydrogen storage properties of the composite was attributed to the presence of active LaH3.01 and CeH2.51 particles, which were scattering on the surface of Nail and A1 particles, acting as the catalytic active sites for hydrogen diffusion and playing an important catalytic role in the improved hydriding/dehydriding reaction.
Mg2FeH6 doped with and without Ti and its alloys (TiMn2, TiAl) were prepared combing ball milling and heat treatment. The effects of these additives on the dehydrogenation performance of Mg2FeH6 were studied systematically. The results show that all additives have favor influence on improving the hydrogen desorption property of Mg2FeH6. Especially, TiMn2 exhibits prominent effect on enhancing the dehydrogenation kinetics of Mg2FeH6. Moreover, the activation energy of TiMn2-doped Mg2FeH6 calculated by Kissinger equation is 94.87 kJ/mol, which is 28 kJ/mol lower than that of the undoped Mg2FeH6. The cycling tests suggest that the improved dehydrogenation kinetics of Mg2FeH6 doped by TiMn2 can maintain in the second cycle.
