Effect of Na and Cooling Rate on the Activation of Mg–Ni Alloys for Hydrogen Storage

Abstract

In spite of favourable hydrogen storage properties such as low density, high theoretical capacity (7.6 wt% H/MgH2) and economics, commercial use of Mg-based alloys is not feasible due to long activation times, slow hydrogen sorption kinetics, and a high temperature for hydrogen release. Mg– Ni alloys have been considered promising materials for hydrogen storage systems as the Mg2Ni intermetallic phase enhances the kinetics of hydrogen absorption in Mg–Ni alloys through a catalytic effect. It has been suggested that the refinement of eutectic in Mg–Ni alloys can further improve hydrogen absorption kinetics and that this can be achieved through trace Na additions. However, the refinement of the eutectic can also be achieved by increasing the cooling rate during solidification. In this study we investigate the effect of cooling rate and Na additions to Mg–Ni alloys on hydrogen absorption kinetics. Our results indicate that Na additions improve the hydrogen absorption kinetics independent of eutectic refinement and that the effect of the latter is relatively small.