X-ray studies of Pd/Ag membranes for hydrogen separation

Abstract

The homogeneity of typical electrolessly plated Pd/Ag membranes for H2 separation was investigated with XAFS and XPS depth profiling. Next the crucial mixing of the separate Pd and Ag layers, obtained after the two sequential plating steps, was followed in situ with XRD. The results show that some low temperature alloying procedures found in the field are insufficient for obtaining a well-mixed Pd/Ag alloy membrane.The Pd/Ag-H XANES was determined for the first time. In contrast to the Pd-H and Pd/Ag systems, shifts in electron density from the Ag or H atoms to the Pd could not satisfactorily explain the observed XANES. Not only is the intensity of the whiteline higher than expected, the shape and the intensity of the anti-bonding Pd 4d H 1s feature have also significantly changed. Local geometry is expected to account for these deviations.