Kinetic Hindrance during the Initial Oxidation of Pd(100) at Ambient Pressures

Abstract

The oxidation of the Pd(100) surface at oxygen pressures in the ${10}^{-6}$ to ${10}^3\mathrm{m}\mathrm{b}\mathrm{a}\mathrm{r}$ range and temperatures up to 1000 K has been studied in situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the $(T,p)$ environmental conditions, we observe either a thin $(\sqrt{5}\times \sqrt{5})R27°$ surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K.