The catalysis mechanism of La hydrides on hydrogen storage properties of MgH2 in MgH2 + x wt.% LaH3 (x = 0, 10, 20, and 30) composites

A systematic investigation was performed on the hydrogen storage properties of composites which were prepared by ball milling MgH2 with different amounts of LaH3 and the catalysis mechanism of La hydride on MgH2 was reported in this paper. Pressure-Composition-Temperature (P-C-T) curves showed that the reversible hydrogen storage capacity of MgH2 + 20 wt.% LaH3 composite was 5.1 wt.% at 548 K, while the pure MgH2 hardly released any H2 under the same conditions. The addition of LaH3 also significantly improved the hydriding/dehydriding kinetics, and led to the rate-controlling steps of MgH2 becoming altered from a three-dimensional interfacial reaction to a one-dimensional diffusion process. The XRD pattern indicated that the LaH3 phase partially transformed to LaH2.3 phase during the dehydriding process. TEM micrograph images revealed that the LaH2.3 phase was distributed homogeneously throughout the Mg phase and that the Mg crystals were coated with LaH2.3 crystals in the matrix. This microstructure exhibited an obvious volume contraction and resulted in a distinct strain of MgH2 when the LaH3 phase released H2. DSC curves proved that the addition of LaH3 could decrease the temperature at which the onset of the dehydrogenation of MgH2 occurred by approximately 20.4 K.