LaNi5-xAlx is a versatile alloy system for metal hydride applications

Abstract

METAL alloys which reversibly absorb and desorb hydrogen are being used or considered for a variety of energy applications1,2. Alloys of general composition AB5 are prime candidates because of their good hydrogen absorption/desorption kinetics and large hydrogen storage capacity. The LaNi5–H2 system, in particular, has been extensively investigated. In many applications, however, materials are required whose plateau pressures are different from those of LaNi5H6,7. The desorption pressure of LaNi5H6,7 may be modified by substitutions either of La or Ni with other elements. Previous work3 has shown that 20% substitutions of Ni by a variety of transition metals can lower plateau pressures by a factor of ∼4. We report here that Al can substitute for Ni in LaNi5 with dramatic results in lowering decomposition pressures without impairing the kinetics or the hydrogen carrying capacities. The important new result is that Al substitutions allow a wide range of decomposition pressure to be spanned in continuous fashion. In the range 0–20% Al, the plateau pressures of the LaNi5–LaNi4 Al hydride system are reduced by a factor of ∼ 300.