In situ formation of nanocrystalline MgH2 through room temperature hydrogenation

Nano-engineering is of particular interest in tailoring the hydrogen storage properties of magnesium hydride (MgH2). This work demonstrates in situ formation of nanocrystalline MgH2 by hydrogenation at room temperature. We investigated the effects of hydrogenation variables on the MgH2 nanostructure. The results showed a large amount of MgH2 nanocrystallites with sizes of 4–10 nm in the hydrogenated samples. The sample recharged at 298 K under 0.1 bar hydrogen showed MgH2 nanocrystallites with a mean size of 5.2 nm. The dehydrogenation kinetics of the sample hydrogenated at lower pressure are improved over samples hydrogenated at higher pressures. The in situ formation of nanocrystalline MgH2 can be achieved by deliberately engineering the nucleation and growth rate of MgH2. Hydrogenation pressure, temperature, and the defect density of the material are the critical parameters affecting the nucleation rate of MgH2. In addition to low temperature, hydrogenation under lower pressure can significantly slow the growth rate of MgH2 during hydrogenation. These findings provide a different strategy enabling in-process control over the nanostructure of MgH2.