Effect of trace Na additions on the hydrogen absorption kinetics of Mg₂Ni

It is demonstrated that Na doping can significantly improve the hydriding performance of Mg2Ni under an isobaric-isothermal condition of 2 MPa H2 and 350 °C. This is achieved via an increase of the interphase grain boundary area and density of dislocations as compared to the Na-free material. Significant enrichment of Na⁺ cations on the alloys' surface coupled with the catalytic effect of metallic Ni are suggested to increase the hydrogen-metal bonding strength facilitating hydrogen adsorption/dissociation. The mechanisms of hydrogen absorption are discussed based on a nucleation and growth theory. Additionally, by means of in situ synchrotron powder x-ray diffraction, the transition of Mg2Ni into the stable Mg2NiH0.3 is observed in real-time.