Hydrogen absorption and desorption characteristics in the La0.5Ni1.5Mg17 prepared by hydriding combustion synthesis

The La0.5Ni1.5Mg17 alloy prepared by hydriding combustion synthesis (HCS) was investigated by an isovolumetric method and X-ray diffraction and this alloy has a large hydrogen storage capacity with good hydriding/dehydriding (H/D) kinetics. The kinetics of hydrogen absorption/desorption (A/D) in the two-phase (α-β) region has been studied between 523 and 573 K under approximately isobaric conditions and the experimental data were analyzed to find the kinetics mechanisms for both the H/D processes. It is shown that the rate-controlling step of the H/D processes is the diffusion of hydrogen, due to the good agreement between the experimental results and calculated curves using a simple new kinetic model. The activation energies are calculated to be 86.8 kJ/mol H2 for absorption and 84.9 kJ/mol H2 for desorption, which were much smaller than that of MgH2, and can be attributed to the La and Ni additions.