Oxygen dissolution in polycrystalline palladium at O2 pressures of 0.1 to 100 Pa

Abstract

Oxygen dissolution in polycrystalline palladium Pd(poly) at O2 pressures (\(P_{O_2 } \)) of 0.1 to 100 Pa and a temperature of 600 K has been investigated by temperature-programmed desorption. The dissolution process under these conditions includes O2 chemisorption on the oxide film surface, the insertion of Oads atoms under the oxide layer, and their diffusion into the subsurface layers of palladium. During chemisorption, a structure ensuring that the Oads coverage of the surface increases with increasing \(P_{O_2 } \) forms on the surface of the oxide film. This is favorable for Oads penetration through the oxide film and increases the amount of absorbed oxygen. The Oads coverage of the surface calculated via the Langmuir equation at an O2 desorption activation energy of Edes = 125 kJ/mol correlates with the number of absorbed oxygen monolayers (n). At n ≥ 1, oxygen absorption by Pd(poly) is due to the diffusion of O atoms in the palladium lattice. After the accumulation of 14–18 oxygen monolayers in the subsurface layers of palladium, oxygen absorption practically stops depending on \(P_{O_2 } \). Thus, the acceleration of oxygen dissolution in palladium is due to the formation of the surface oxide film and the increase in the Oads coverage of this film, which facilitates the insertion of Oads atoms into the subsurface layers of palladium.