Pd L3 edge XANES investigation of the electronic and geometric structure of Pd/Ag–H membranes

Abstract

The electronic and geometric structure of the Pd/Ag–H system, an important hydrogen membrane structure, has been studied with x-ray absorption spectroscopy. Palladium L₃ XANES measurements in both vacuum and in situ under hydrogen atmosphere were performed at room temperature on an ideally mixed Pd_0.8Ag_0.2 system obtained with bi-sputtering, and on a pure Pd system obtained with electroless plating. A model of fcc-Pd/Ag with the Ag atoms evenly distributed through the system and the hydrogen atoms placed in the octahedral holes was able to explain the observed XANES in great detail. FEFF calculations show that the Pd/Ag–H system generates an anti-bonding Pd–H band, in close agreement with the experimental results. In addition the calculations show that the hydrogen content of the system strongly influences the XANES, especially the intensity of the white-line and the anti-bonding peak. In contrast the influence of the Ag atoms is limited to relatively small changes in the white-line intensity. However change of the Ag distribution within the Pd/Ag fcc lattice from well-mixed to clustered was found to have a significant influence on the Pd L₃ edge white-line intensity.