L.Z. Ouyang

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.

Hydrogen storage properties of preferentially orientated Mg-Ni multilayer film prepared by magnetron sputtering

Mg-Ni multi-layer thin film was deposited on (001) Si wafer by magnetron sputtering with dual-target. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis reveal that the microstructure of the Mg-Ni multilayer thin film is composed of fine-crystalline Ni layer and crystalline [001] Mg layer. Hydrogenation process of the films were carried out by using the automatic gas reaction controller. The films undergone hydrogenation for different time were analyzed by XRD. The results show that hydrogenation properties of Mg with different preferential orientations are different. (002) diffraction peak of Mg disappears in compensating the appearing of the peaks of Mg2NiH4 and MgH2 in hydrogenation at 533 K, while the (101) peak still remains. The result reveals that the Mg film with (001) preferential orientation absorbs hydrogen at certain temperature easier than that of the Mg film with (101) orientation. This phenomenon can be explained in the view point of the energy change for the nucleation and growth of hydride in different crystal plane.

Effect of Ni on Mg based hydrogen storage alloy Mg3Nd

Abstract Magnesium-neodymium based alloys were prepared by induction melting in an alumina crucible under protection of pure argon atmosphere. XRD patterns show that the as-melted Mg-Nd and Mg 3 NdNi 0.1 diffraction peaks can be excellently indexed with DO 3 structure (BiF 3 type, space group Fm 3 m ). The lattice constant of Mg 3 Nd phase is 0.7390 nm, which is determined by XRD analysis using Cohens extrapolation method. The reversible hydrogen storage capacity reaches 1.95wt.% for Mg 3 Nd and 2.68wt.% for Mg 3 NdNi 0.1 . The desorption of hydrogen takes place at 291 °C for Mg 3 Nd and at 250 °C for Mg 3 NdNi 0.1 . The alloys could absorb hydrogen at room temperature with rapid hydriding and dehydriding kinetics after only one cycle. The enthalpy (Δ H ) and entropy (Δ S ) of Mg 3 Nd-H dehydriding reaction were −68.2 kJ.mol −1 H 2 and −0.121 kJ.(K.mol) −1 H 2 determined by using vant Hoff plot according to the pressurecomposition-isotherms (P-C-I) curve measured at different temperatures. Hydrogen absorption kinetic property of Mg 3 NdNi 0.1 alloy was also measured at room temperature.