Hydrogen permeation measurements of 1.5-10 mu m thick Pd/Ag23 wt% membranes before and after thermal treatments at 300 degrees C in air (both sides) or in the temperature range 300-450 degrees C in N-2 (feed side) and Ar (permeate side) were performed. Accompanying changes in surface topography and chemical composition were subsequently investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth pro. ling. For a 2 mu m thick membrane, the surface roughness increased for all annealing temperatures applied, while a temperature of 450 degrees C was required for an increase in roughness of both membrane surfaces to occur for the 5 mu m membrane. The thickest membrane, of 10 mu m, showed changed surface roughness on one side of the membrane only and a slight decrease in hydrogen permeance after all heat treatments in N-2/Ar. X-ray photoelectron spectroscopy investigations performed after treatment and subsequent permeation measurements revealed segregation of silver to the membrane surfaces for all annealing temperatures applied. In comparison, heat treatment at 300 degrees C in air resulted in significantly increased hydrogen permeance accompanied by increasing surface roughness. Upon exposure to oxygen, Pd segregates to the surface to form a 2-3 nm thick oxide layer (PdO), with more complex segregation behavior after subsequent reduction and permeance measurements in pure hydrogen. The available permeance data for the Pd/Ag23 wt% membranes after heat treatment in air at 300 degrees C is found to depend linearly on the inverse membrane thickness, implying bulk limited hydrogen permeation for thicknesses down to 1.5-2.0 mu m. (C) 2010 Elsevier B. V. All rights reserved.