Hydrogen Storage Properties of a Ni and NbF5-added Mg Alloy

Samples with a composition of 80 wt% Mg-14 wt% Ni-6 wt% NbF5 (denoted as Mg-14Ni-6NbF(5)) were prepared by reactive mechanical grinding, and the hydriding and dehydriding properties of the specimens were then examined. The activation of Mg-14Ni-6NbF(5) was completed after two hydriding (under 12 bar H-2)-dehydriding (in vacuum) cycles. Mg-14Ni-6NbF(5) had a hydrogen storage capacity of about 5.5 wt% H. At the number of cycles n =2, the sample absorbed 4.93 wt% H for 5 min, 5.20 wt% H for 10 min, and 5.48 wt% H for 60 min at 573 K under 12 bar H-2, and desorbed 0.58 wt% H for 10 min, 1.52 wt% H for 30 min, and 2.47 wt% H for 60 min at 573 K under 1.0 bar H-2. The hydriding rate increased as the temperature increased from 423 K to 573 K since the effect of acceleration of thermally activated process predominates, and decreased from 573 K to 623 K since the effect of decrease in the driving force for the hydriding reaction predominates. NbF5 formed MgF2 and NbH2 by the reaction with Mg and hydrogen. Mg-14Ni-6NbF(5) exhibited a higher hydriding rate than both Mg-10NbF(5) and Mg-14Ni-6Fe(2)O(3).