The catalysis mechanism of La hydrides on hydrogen storage properties of MgH_2 in MgH_2 + x wt.% LaH_3 (x = 0,10,20, and 30) composites

摘要

A systematic investigation was performed on the hydrogen storage properties of composites which were prepared by ball milling MgH_2 with different amounts of LaH_3 and the catalysis mechanism of La hydride on MgH_2 was reported in this paper. Pressure-Composition-Temperature (P-C-T) curves showed that the reversible hydrogen storage capacity of MgH_2 + 20 wt.% LaH_3 composite was 5.1 wt.% at 548 K, while the pure MgH_2 hardly released any H_2 under the same conditions. The addition of LaH_3 also significantly improved the hydriding/dehydriding kinetics, and led to the rate-controlling steps of MgH_2 becoming altered from a three-dimensional interfacial reaction to a one-dimensional diffusion process. The XRD pattern indicated that the LaH_3 phase partially transformed to LaH_(2.3) phase during the dehydriding process. TEM micrograph images revealed that the LaH_(2.3) phase was distributed homogeneously throughout the Mg phase and that the Mg crystals were coated with LaH_(2.3)crystals in the matrix. This microstructure exhibited an obvious volume contraction and resulted in a distinct strain of MgH_2 when the LaH_3 phase released H_2. DSC curves proved that the addition of LaH_3 could decrease the temperature at which the onset of the dehydrogenation of MgH_2 occurred by approximately 20.4 K.