Development of a Mg-based hydrogen-storage material by addition of Ni and NbF5 via milling under hydrogen. (21st September 2015) - Kwak, Young Jun
Abstract Milling under hydrogen was used to prepare samples with a composition of 80 wt% Mg + 14 wt% Ni + 6 wt% NbF5 (named 80Mg + 14Ni + 6NbF5). 80Mg + 14Ni + 6NbF5 had a large effective storage capacity of hydrogen of approximately 5.6 wt% H. The activation of 80Mg + 14Ni + 6NbF5 was done after one storing-releasing cycle. At n = 2 at 593 K, 80Mg + 14Ni + 6NbF5 stored 3.92 and 5.57 wt% H after 2.5 and 60 min, respectively, under 12 bar H2, and released 2.34 and 4.81 wt% H after 10 and 60 min, respectively, under 1.0 bar H2. The following reaction happened during milling under hydrogen and at the early storing-releasing cycles: 14Mg + Ni + 4NbF5 + 7H2 → MgH2 + Mg2NiH4 + Mg + 10MgF2 + 4NbH2. At a fairly low temperature of 423 K, the sample stored 0.28, 0.34, and 0.57 wt% H after 5, 10, and 60 min, respectively. The initial storing rate of 80Mg + 14Ni + 6NbF5 increased as the temperature rose from the room temperature to 573 K since the effect of thermal activation is predominant, and fell as the temperature rose from 573 K to 623 K since the effect of decrease in the driving force for storing reaction is predominant.