Variation with added material in the effects of reactive mechanical grinding and hydriding–dehydriding cycling on the hydrogen-storage properties of Mg

Samples Mg–14Ni–6Fe2O3, Mg–14Ni–3Fe2O3–3Ti, and Mg–14Ni–2Fe2O3–2Ti–2Fe were prepared by reactive mechanical grinding, and their hydrogen storage properties were examined. The activated Mg–14Ni–2Fe2O3–2Ti–2Fe had the highest hydriding rate, absorbing 4.14 wt% H for 5 min, and 4.27 wt% H for 10 min, and 4.42 wt% H for 60 min at 573 K under 12 bar H2. The activated Mg–14Ni–3Fe2O3–3Ti had the highest dehydriding rate, desorbing 3.81 wt% H for 20 min, 3.98 wt% H for 25 min, and 4.15 wt% H for 60 min. Mg–14Ni–6Fe2O3 dehydrided at n = 4 contained Mg, Mg2Ni, MgO, and Mg(OH)2. Mg(OH)2 is considered to be formed by the reactions of MgH2 or Mg with water vapor. The effects of reactive mechanical grinding and hydriding–dehydriding cycling are the creation of defects and cracks, and the reduction of Mg particle size. The addition of a larger amount of Ti and/or Fe has stronger effects of reactive mechanical grinding, whereas the addition of a larger amount of Fe2O3 has greater effects of hydriding–dehydriding cycling.