Hydrogen storage and structure variation in Mg/Pd multi-layer film

The hydrogen storage properties of the as-deposited Mg/Pd multi-layer films by magnetron sputtering have been studied in this work. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis revealed that the Mg/Pd multi-layer film was composed of fine-crystalline Pd layers and columnar crystalline Mg layers. The cycle hydrogenation and dehydrogenation of the film were performed at different temperatures (305 K, 373 K and 323 K). The film absorbed and desorbed about 2.6 wt.% hydrogen at a low temperature of 373 K, which is close to the theoretical hydrogen absorption value of 2.8 wt.% for Mg6Pd. When lowering to 323 K, the film can still absorb–desorb about 2.5 wt.% of hydrogen. During hydrogenation–dehydrogenation, Mg6Pd formed first, followed by MgH2 and Mg5Pd2. After desorption there were only Mg6Pd and Mg5Pd2 phases identified in the film, showing complete dehydrogenation of the thin film at 323 K. It is believed that additional interfacial free energy in the thin film and the catalytic effect of Pd, can be accounted for the low temperature hydrogen absorption–desorption cycles.