A study on the hydriding-dehydriding kinetics of Mg1.9Al0.1Ni

The hydrogen absorption/desorption (A/D) kinetics of hydrogen storage alloys Mg1.9Al0.1Ni prepared by hydriding combustion synthesis in two-phase (α-β) region in the temperature range from 523 to 573 K have been investigated. The hydriding/dehydriding (H/D) reaction rate constants were extracted from the time-dependent A/D curves. The obtained hydrogen A/D kinetic curves were fitted using various rate equations to reveal the mechanism of the H/D processes. The relationships of rate constant with temperature were established. It was found that the three-dimensional diffusion process dominated the hydrogen A/D. The activation energies of Mg1.9Al0.1Ni are 52 ± 2 and 48 ± 1 kJ/mol H2 for the H/D processes smaller than that of Mg2Ni, which can be explained that the improvement of H/D reaction kinetics in Mg2Ni by using additive Al.