Comparative analysis of the hydriding kinetics of LaNi5, La0.8Nd0.2Ni5 and La0.7Ce0.3Ni5 compounds

In two-phase domains, the plateau pressure of hydride forming materials (such as intermetallic compounds or IMCs) depends markedly on the operating temperature (Van't Hoff relationships). Therefore, for practical applications, it is necessary to select hydrogen storage materials by considering the thermal environment of the hydride tank. The thermodynamic properties (absorption and desorption pressure plateaux) of IMCs can be adjusted to some extend by chemical alloying with foreign metals and substitution on different crystallographic sites. In this paper, we report on the hydriding kinetics of substituted AB5 compounds. Isotherms have been measured at different temperatures on LaxNd1−xNi5 (x ≈ 0.2) and LaxCe1−xNi5 (x ≈ 0.3) compounds. Pneumato-chemical impedance spectroscopy has been used to analyze the hydriding kinetics and to determine microscopic rate parameters associated with surface dissociation of molecular hydrogen, diffusion-controlled transport of atomic hydrogen to bulk regions and hydride formation. Results have been compared to those measured on LaNi5 and the interest of using such substituted compounds for application in auxiliary power units is discussed.