SURFACE SEGREGATION OF PD-AG MEMBRANES UPON HYDROGEN PERMEATION

Pd-Ag membranes are permeable to hydrogen. Hydrogen treatment results in a small chemical shift (+/-0.1-0.2 eV) of Pd3d core level but no ch ange in the Ag3d level. A new valence band in the binding energy regio n of 7-9 eV corresponding to the interaction between H 1s and Pd4d app ears on a hydrogen permeated membrane surface. Quantitative XPS analys is reveals that Pd segregates at the membrane surface toward the high hydrogen pressure side while Ag segregation occurs at the surface on t he low hydrogen pressure side after hydrogen permeation. Both surface segregations are explained based on an MTCIP-1A (modern thermodynamic calculation of interface properties - first approximation) approach. I t is concluded that hydrogen chemisorption induces palladium segregati on on the Pd-Ag membrane surface.