Role of intermetallics in hydrogen storage materials

Many intermetallics such as AB₅, AB₂, A₂B show the excellent hydrogen absorbing properties. Specially, LaNi₅ compound has been extensively studied for the negative electrode of Ni-MH batteries. In today's use for the negative electrode of Ni-MH batteries, alloys must be single phase. But it is well known that it is difficult to make non-stoichiometric LaNi₅ alloys as single phase because of its limited solid-solution range. The present study describes the rapid quenching effects on the solid-solution range of La(Ni, M)_x (x = 3-5) alloys prepared by melt spinning in discussing their hydrogen absorption properties. It is found that the single phase with CaCu₅ crystal structure extends to LaNi_4.65 compositional alloys. For fuel cell automobile, the alloys with high content of hydrogen must be developed. Strong candidates for this will be Vanadium based BCC alloys, which would be hard to be activated. Since it is well known that the Laves phases undergo easy activation treatment, it may be possible that the BCC phases will be easily activated if the alloys contain such Laves phases. The present study also found that Zr addition is effective on forming Laves phase as grain boundary phases in BCC phases in V-Ti-Zr-Ni alloys, and on improving the hydrogen absorbing properties. The study will be also extended to future hydrogen absorbing alloys with high capacity.