LaNi_5-xAl_x 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 applications^1,2. 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 LaNi₅H_6,7. The desorption pressure of LaNi₅H_6,7 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.