Increase in the Hydrogen-Sorption Rates and the Hydrogen-Storage Capacity of MgH2 by Adding a Small Proportion of Zn(BH4)2

Abstract

Abstract: In this work, Zn(BH4)2 was added to improve the hydrogen-storage properties of MgH2. A 99 wt% MgH2+1 wt% Zn(BH4)2 sample was prepared by milling in a planetary ball mill in a hydrogen atmosphere. The proportion of the added Zn(BH4)2 was small (1 wt%) in order to increase hydriding and dehydriding rates without reducing the hydrogen-storage capacity too much. Changes in the released hydrogen quantity, Hd, with temperature, T, for as-milled 99MgH2+1Zn(BH4)2 was obtained by heating the sample from room temperature to 683 K with a heating rate of 5 K/min under 1.0 bar of gas. Activation of the sample was not required. 99MgH2+1Zn(BH4)2 had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed in 60 min) of 4.83 wt% in the first cycle. The as-purchased MgH2 absorbed hydrogen slowly, absorbing 0.04 wt% H in 60 min. On the other hand, in the first cycle, 99MgH2+ 1Zn(BH4)2 absorbed 3.97 wt% H in 5 min, 4.49 wt% H in10 min, and 4.83 wt% H in 60 min at 593 K under 12 bar H2. (Received February 20, 2017; Accepted May 29, 2017)