Kinetics of hydrogen absorption in the solid solution region for Laves phase Ho1−xMmxCo2 (x = 0, 0.2 and 0.4) alloys

Hydrogen diffusion in the solid solution is significant for the hydriding reaction kinetics of hydrogen storage materials. In this paper, Chou model was firstly used to investigate the kinetic mechanism of hydriding reaction in α phase (solid solution) region at the temperature ranging from 773 to 1073 K and the pressure range of 65-190 mbar for cubic Laves Ho1−xMmxCo2 (x = 0, 0.2 and 0.4, Mm = mischmetal) alloys. The results indicate that the hydrogen absorption kinetics in α phase region is controlled by hydrogen diffusion into the bulk. The activation energies calculated using Chou model with the least square method are in the range of 29.4-53.5 kJ/mol H2, which are close to the values reported in the original literature. Meanwhile, the characteristic absorption time can be used to characterize the reaction rate directly. In this way, influence of temperature, initial pressure and Mm concentration on the hydriding reaction kinetics was analyzed and discussed. It was found that the reaction rate can be accelerated with the increase of temperature, initial pressure and Mm concentration, and the diffusivity greatly depended on the Mm concentration.