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 N₂gaseous impurities using in situ synchrotron XRD. We find that a N₂content as low as 0.5 mol.% can completely inhibit the hydriding of pure Mg₂Ni whereas the Na-modified equivalent remains relatively unaffected even at N₂concentrations 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 N₂while leaving metallic Ni available for H₂adsorption/dissociation. The results are important in designing Mg–Ni alloys with tailored properties that are suitable for use in hydrogen storage/purification/separation applications.