Design of a Nanometric AlTi Additive for MgB2-Based Reactive Hydride Composites with Superior Kinetic Properties

A thorough investigation of the effect of nano TiAl alloy formation on the hydrogen storage properties of the Reactive Hydride Composite systems 2LiBH4+MgH2/2LiH+MgB2 (Li-RHC) is presented. The additive 3TiCl3.AlCl3 was used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ~ 5 wt. % of 3TiCl3.AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and to a reversible hydrogen storage capacity of 9.5 wt.%. The properties of the material doped with 3TiCl3.AlCl3 additive were directly compared with those of the material doped with TiCl3 (the best additive known to date for the Li-RHC). The results clearly show that the material containing 3TiCl3.AlCl3 possess hydrogen storage properties superior to those of the material containing TiCl3. The formation of nanosized AlTi alloys was unveiled by HR-TEM technique. The most frequently observed TiAl phase is hexagonal AlTi3. This phase appears to act in a twofold manner: first, it promotes the nucleation of MgB2 upon dehydrogenation; and second it suppresses the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling.