Mg-15 wt%Ni-5 wt%Fe2O3 (Mg155) was prepared by reactive mechanical grinding (RMG) Mg155 exhibited high hydriding and dehydriding rates even at the first cycle and its activation was completed after only two hydriding dehydriding cycles The activated Mg155 absorbed 5 06 and 5 38 wt% of hydrogen, respectively for 5 and 60 mm at 573 K under 12 bar H-2 It desorbed 1 50 and 5 28 wt% of hydrogen respectively for 5 and 60 mm at 573 K under 1 0 bar H-2 The initial hydrogen absorption rate decreased, but the hydrogen desorption rate increased rapidly with an increase in temperature from 563 K to 603 K The rate controlling step for the dehydriding reaction in a range from F similar or equal to 0 20 to F similar or equal to 0 75 is considered to be the chemical reaction at the Mg hydride/alpha solid solution interface The absorption and desorption PCT curves exhibited two plateaus at 573 K The hydrogen storage capacity of the activated Mg155 was about 6 43 wt% at 573 K (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved