In order to improve the hydrogen storage capacity and the activation property of the $MmNi_{4.5}Al_{0.5}$ alloy, the multiphase alloy systems are prepared by adding the excess Zr in $MmNi_{4.5}Al_{0.5}$ alloy.
It is estimated from the x-ray diffaction pattern and the energy dispersive x-ray analysis that the 2nd phases in $MmNi_{4.5}Al_{0.5}Zr_x$ alloys have the basic composition of $ZrNi_3$, β-Zr.
Among the 2nd phases observed from the above experiments, the main 2nd phase is $ZrNi_3$, which has the excellent catalytic effect on the hydrogen dissociation.
As the Zr contents increase the activation property of the $MmNi_{4.5}Al_{0.5}Zr_x$ is improved due to the excellent catalytic effect on the hydrogen dissociation of $ZrNi_3$ phase.
The hydrogen storage capacity shows maxima at x=0.05 in $MmNi_{4.5}Al_{0.5}Zr_x$ (x=0.0 - 0.2) alloys. As the Zr contents exceeds 0.05, the hydrogen storage capacity decrease because amount of the 2nd phases which do not form a hydride ($ZrNi_3$) or absorb irreversibly hydrogen (β-Zr) increase with Zr contents in $MmNi_{4.5}Zr_x$ alloys. As the Zr contents increase the plateau pressure decrease, sloping of the plateau pressure increase.
The $MmNi_{4.5}Al_{0.5}Zr_{0.05}$ alloy, which shows the maximum storage capacity and the strong resistance to pressure cycling, is considered as a proper alloy for hydrogen storage.
