Effect of interfacial free energy on hydriding reaction of Mg–Ni thin films

The Mg2.9Ni film with preferential orientated nanocrystalline structure was obtained by magnetron sputtering. The hydrogen storage properties and microstructure were investigated by pressure-composition-isotherms measurement, x-ray diffraction and transmission electron microscopy. A reversible hydrogen storage content of about 4.45mass% at 497K has been obtained. The preferential orientation of the deposited film was destroyed after only one hydrogenation/dehydrogenation cycle. Both experiment and simplified calculation results proved that the hydrogenation/dehydrogenation reaction temperature decreases due to the extra interfacial free energy stored in the boundary, which demonstrate that Mg based hydride can be substantially destabilized by inducing nanocrystalline structure.