Engineering the Mg-Mg₂Ni eutectic transformation to produce improved hydrogen storage alloys

The technique of trace element doping to modify the solidification mechanism of faceted/non-faceted eutectics has been applied to the Mg-Mg₂Ni alloy system. It is demonstrated that the micro- and nano-structure of cast hypoeutectic Mg-Mg₂Ni alloys can be varied by trace additions of Na, Ca or Eu to the liquid prior to solidification. As a result, the reversible hydrogen absorption capability was in excess of 90% of the theoretical value of 6.8 wt.% under the absorption parameters of 350 °C and 1 MPa for 24 min and subsequent desorption at 0.2 MPa for 24 min after activation. The hydrogen absorption kinetics have been dramatically improved under realistic industrial conditions, and show no sign of reduced capacity over 200 cycles. This processing route results in a non-pyrophoric material that may be produced in large quantities at comparatively low cost.