Abstract: Nanocrystalline MgH₂ and MgH₂-based composites with 25%(mass fraction) of Al, Ca, or CaH₂ as an individual additive respectively were prepared by ball milling. The crystallite size and morphology of the as-milled powders were characterized and their hydrolysis behaviours were investigated in comparison with commercial polycrystalline MgH₂. The results show that the crystallite size of both MgH₂ and MgH₂-based composites is reduced to less than 13nm after milling for 15h. Due to its enhanced specific surface area and unique nanocrystalline structure, the as-milled MgH₂ shows much better hydrolysis kinetics than the commercial polycrystalline MgH₂, with the hydrolysed fraction upon hydrolysing for 70min enhances from 7.5% to about 25%. As compared with the as-milled MgH₂, the MgH₂-based composites with either CaH2 or Ca as an additive present further greatly improved hydrolysis kinetics, with the hydrolysed fraction for 80min achieving about 76% and 62% respectively. However, the addition of Al doesn’t show any positive effect on the improvement of the hydrolysis kinetics of MgH₂.

Key words:  ball milling; nanostructured material; MgH₂; chemical hydride; hydrogen generation by hydrolysis