Casting was used to develop new Mg–Ni based hydrogen storage alloys having improved hydrogen sorption properties. A nanostructured eutectic Mg–Mg2Ni was formed upon solidification which introduced a large area of interfaces along which hydrogen diffusion could occur with high diffusivity. After a few cycles of hydrogenation and dehydrogenation, an ultrafine porous structure formed in the eutectic Mg–Mg2Ni and some cracks developed along the interface between the eutectic and the α-Mg matrix. This indicates that hydrogen atoms introduced into the alloys preferentially migrate along the interfaces in the nanostructured eutectic which enables effective short-range diffusion of hydrogen. Furthermore, transition metals such as Nb, Ti and V in the range 240–560ppm were added directly to molten Mg-10wt%Ni alloys and were found to form intermetallic compounds with Ni during solidification. The alloys could store 5.6 to 6.3wt% hydrogen at 350C and 2MPa. Transition metal-rich intermetallics distributed homogeneously in the cast alloys appeared to play a key role in accelerating the nucleation of Mg from MgH2 upon dehydrogenation. This leads to a significant improvement in the hydrogen desorption kinetics.

The Effect of Transition Metals on Hydrogen Migration and Catalysis in Cast Mg–Ni Alloys. Y.H.Cho, S.Aminorroaya, H.K.Liu, A.K.Dahle: International Journal of Hydrogen Energy, 2011, 36[8], 4984-92