Pd L₃edge 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 L 3 XANES measurements in both vacuum and in situ under hydrogen atmosphere were performed at room temperature on an ideally mixed Pd 0.8 Ag 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 L 3 edge white-line intensity.

Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction

“…Looking at the x-ray absorption near-edge spectra (XANES), we see that the normalized white-line (Pd L 3 -edge peak) intensity decreases with increased Ag loading. This clear decrease in white-line intensity is indicative of a net shift in electron density from Ag to Pd producing a decrease of 4 d -holes in Pd 32 , 33 , 35 , 36 . Moreover, the extended region features in Fig.…”

“…Although Pd XPS is complicated to interpret, the L 3 -edge XAS of Pd has been used effectively in the literature to elucidate the charge density within Ag-Pd alloys 23 , 32 , 33 . The small deviations from the single-particle-model for 4 d metals makes the use of the L 3 -edge quantitatively meaningful 34 .…”

Supported bimetallic AuPd clusters using activated Au25 clusters

“…6 for all the bimetallic AuPd samples studied. The most prominent feature of the Pd L 3 -edge is the white-line at 3173 eV, caused by excitation of electrons from the 2p to the 4d band [41]. samples.…”

Double-segregation effect inAgxPd1−x∕Ru(0001)thin film nanostructures

“…AgPd systems are of interest by diverse applications, often related to the ability of Pd to adsorb high amounts of H 2 , which, for instance, can be used to separate H 2 from a mixture of gases. 6 Ag and Pd have very small size mismatch ͑ϳ5%͒, and in the bulk they mix over the whole concentration interval. We use a theoretically consistent way of determining the internal structure for the four-monolayer ͑4-ML͒ film by employing Monte Carlo simulations with effective interatomic interactions calculated from first principles.…”