TEM studies of nanostructure in melt-spun Mg–Ni–La alloy manifesting enhanced hydrogen desorbing kinetics

The hydrogen storage properties of a magnesium-rich Mg–Ni–La alloy prepared by melt-spinning are significantly improved by nanostructure formation during crystallization and activation. It can absorb and desorb ∼5 wt% hydrogen at temperatures as low as 200 °C in moderate time periods. Transmission electron microscopic (TEM) studies on this alloy indicate that the nanostructure, consisting of LaH3 and Mg2NiH4 nano-particles dispersed homogeneously in MgH2 matrices after hydrogenation, is rather stable at temperatures below 300 °C but undergoes coarsening and segregation of these particles and matrices above ∼400 °C. These structural changes have been confirmed by electron energy-loss spectroscopic (EELS) imaging as well as high-resolution TEM techniques. A new EELS peak associated with a plasmon excitation in the MgH2 phase (H-plasmon) is found for the first time in this study. By imaging the H-plasmon peak, the hydrogen distribution in the alloy has been clearly visualized. We have succeeded in observing the hydrogen desorption process at ∼400 °C in-situ in the microscope using this EELS imaging technique.