Enhancement of Hydrogen Storage Characteristics of Mg by Addition of Nickel and Niobium (V) Fluoride via Mechanical Alloying

A specimen with a composition of 80 wt% Mg+14 wt% Ni+6 wt% NbF5 (termed Mg-Ni-NbF5) was prepared by mechanical alloying. Its hydrogen absorption and release characteristics were then examined. Mg2NiH4 was formed by a reaction of Mg with nickel and hydrogen during mechanical alloying and hydrogen absorption-release cycling. The particles after hydrogen absorption-release cycling became smaller than those after mechanical alloying owing to the expansion and contraction of the particles upon cycling. The cycled Mg-Ni-NbF5 had a fairly high hydrogen absorption rate and a large hydrogen storage capacity, with an effective hydrogen storage capacity close to 5.6 wt% at 593 K. The cycled Mg-Ni-NbF5 absorbed 5.58 wt% H in 12 bar H2 and released 4.81 wt% H in 1.0 bar H2 at 573 K for 60 min. At 593 K, the cycled specimen absorbed 4.53 wt% H for 5 min, 5.27 wt% H for 10 min, 5.50 wt% H for 25 min, and 5.58 wt% H for 60 min in 12 bar H2, and released 1.28 wt% H for 5 min, 2.26 wt% H for 10 min, 4.13 wt% H for 30 min, and 4.81 wt% H for 60 min in 1.0 bar H2.