Effect of impurity N2 concentration on the hydriding kinetics of Na-doped Mg-Ni alloys

Here, we report on the hydriding behaviour of various Mg-Ni alloys in the presence of N2 gaseous impurities using in situ synchrotron XRD. We find that a N2 content as low as 0.5 mol.% can completely inhibit the hydriding of pure Mg2Ni whereas the Na-modified equivalent remains relatively unaffected even at N2 concentrations of up to 5 mol.%. The activated hypoeutectic Mg-Ni alloy demonstrates excellent hydriding kinetics compared to the as-cast counterpart under 1 mol.% of N2. Surface analysis shows it is the electropositive nature of a Na-modified Mg-Ni surface that facilitates selective adsorption of N2 while leaving metallic Ni available for H2 adsorption/dissociation. The results are important in designing Mg-Ni alloys with tailored properties that are suitable for use in hydrogen storage/purification/separation applications.