Modification of the hydrogenation properties of LaNi5 upon Ni substitution by Rh, Ir, Pt or Au

The hydrogenation properties of the LaNi5−xMx (M = Rh, Ir, Au) compounds have been studied. The Ni substitution has several consequences: pressure plateau splitting and increase of plateau pressure. This latter observation disagrees with the general rule that a cell volume increase of the alloy should result in a plateau pressure lowering. In order to elucidate the origin of this anomalous behaviour, DFT calculations have been performed on both LaNi5−xRhx and LaNi5−xPtx intermetallic compounds, which, according to the present and previous experimental work, present a similar anomaly. We discuss our results in light of the models proposed in the literature. We conclude that, in the case of a Ni substitution by 4d or 5d elements, the size effect alone fails in predicting the hydrogen absorption properties while the rule of reverse stability is obeyed.

► Hydrogen absorption properties of LaNi5−xMx intermetallic compounds (M = Rh, Ir, Au). ► Stability of LaNi5−xMx (M = Rh, Pt) intermetallics and hydrides using ab initio calculations. ► Influence of the substituting elements (geometric, thermodynamic and electronic) on the hydride stability.