Optimisation of MmNi5-xSnxMmNi5-xSnx (Mm=LaMm=La, Ce, Nd and Pr, 0.27<x<0.50.27<x<0.5) compositions as hydrogen storage materials

In the frame of the development of a hydrogen production and storage unit to supply a 40 kW stationary fuel cell, a metal hydride storage tank was chosen according to its reliability and high energetic efficiency. For this purpose, the AB5-type system MmNi5-xSnxMmNi5-xSnx (Mm stands for mischmetal) has been investigated. Hydrogen absorption and desorption plateau pressures were adapted to the working range by adjusting the tin content. The structural and thermodynamic properties of the metal hydrides have been analyzed. Stoichiometry (B/AB/A ratio) and composition have been adjusted to obtain single phase compounds with maximum hydrogenation capacity. Reversible storage capacity was optimized by lanthanum enrichment of the mischmetal. Finally, a study of the kinetics and of the defects created during cycling was made.