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 change in the Ag3d level. A new valence band in the binding energy region of 7-9 eV corresponding to the interaction between H 1s and Pd4d appears on a hydrogen permeated membrane surface. Quantitative XPS analysis reveals that Pd segregates at the membrane surface toward the high hydrogen pressure side while Ag segregation occurs at the surface on the 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. It is concluded that hydrogen chemisorption induces palladium segregation on the Pd-Ag membrane surface.