Self-Restoring of the Active Surface in the Hydrogen Sponge LaNi5

Photoemission studies combined with measurements of the magnetic susceptibility show that La segregates to the surface of La${\mathrm{Ni}}_5$ in the presence of ${\mathrm{O}}_2$ or ${\mathrm{H}}_2$O, and the Ni precipitations are formed during hydrogenation. This represents a self-restoring mechanism of the active surface, since the highly reactive La removes the oxygen and keeps the Ni metallic. Dissociative adsorption of ${\mathrm{H}}_2$ may then occur at the Ni atoms.