Development of an Mg-Based Alloy with High Hydriding and Dehydriding Rates and Large Hydrogen Storage Capacity by Adding TaF5.

A sample with a composition of 95 wt% Mg + 5 wt% TaF5 (named Mg-5TaF5) was prepared by reactive mechanical grinding. The activation of Mg-5TaF5 was not necessary, and Mg-5TaF5 had an effective hydrogen storage capacity (the quantity of hydrogen absorbed for 60 min) larger than 5 wt%. At the first cycle (n = 1), the sample absorbed 4.50 wt% H for 10 min and 5.06 wt% H for 60 min at 593 K under 12 bar H2. At n = 1, the sample desorbed 1.58 wt% H for 10 min and 4.93 wt% H for 60 min at 593 K under 1.0 bar H2. The Mg-5TaF5 sample dehydrided at n = 3 contained MgF2 and Ta2H. The hydriding-dehydriding cycling of the sample, which forms MgF2 and Ta2H by reaction with hydrogen, is considered to produce defects on the surface of and inside the Mg particles, to create clean surfaces, and to reduce the particle size of Mg, due to the repetition of expansion with hydrogen absorption and contraction with hydrogen release. Mg-5TaF5 had a higher hydriding rate and a higher dehydriding rate after an incubation period and greater quantities of hydrogen absorbed and desorbed for 60 min than Mg-10TaF5, Mg-10MnO, or Mg-10Fe2O3.