Kinetic hindrance during the initial oxidation of Pd(100) at ambient pressures

TL;DR

This study investigates the initial oxidation process of Pd(100) surfaces under various pressures and temperatures, revealing a kinetic barrier that hinders bulk oxide formation even at elevated temperatures.

Contribution

It provides direct in-situ structural insights into oxidation phases and identifies a significant kinetic hindrance to PdO bulk oxide formation at ambient pressures.

Findings

Presence of a surface oxide or bulk PdO depending on conditions

Kinetic hindrance prevents bulk oxide formation at high temperatures

Structural analysis via SXRD elucidates oxidation phases

Abstract

The oxidation of the Pd(100) surface at oxygen pressures in the 10^-6 to 10^3 mbar 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 either observe a thin sqrt(5) x 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.