Nanoparticulate Pt-catalyzed hydrogenation of Yb films: Towards hydrides with higher hydrogen compositions

It is more difficult to synthesize beta-phase ytterbium trihydride (beta-YbH3-delta) under moderate conditions than other rare-earth metal trihydrides because it requires a valence change from a fully occupied 4f shell (4f(14)) in Yb2+ to an unclosed shell (4f(13)) in Yb3+. We synthesized beta-YbH3-delta at ambient pressure through hydrogenation of a Yb film capped with platinum (Pt) nanoparticle (NP) catalysts. In addition, Pt NP capping enabled us to synthesize alpha-phase Yb dihydride (alpha-YbH2 +/-delta) at room temperature. The difficulty of trihydrogenating Yb to beta-YbH3-delta is explained by kinetic analyses based on temperature and time dependences of molar fractions of alpha-YbH2 +/-delta and beta-YbH3-delta. Pt NP capping can be used to synthesize other hydrogen-rich rare-earth metal hydrides under ambient pressure and lower temperatures.