Characterization of Pd–Ag membranes after exposure to hydrogen flux at high temperatures

Pd–Ag films were deposited by sequential electroless plating on porous stainless steel tubes. Two different intermediate layers of α-Fe2O3 and γ-Al2O3 oxides were employed as diffusion barriers to modify the stainless steel porous size and to avoid the intermetallic diffusion of Fe and Ni through the Pd–Ag layer. The membranes were tested in a gas permeation system to determine the hydrogen permeability and selectivity at temperatures between 673 and 923 K. After the high temperature treatments, they were characterized by XRD, XPS, SEM, AFM and EPMA. The Pd–Ag/PSS membranes had a good thermal resistance. After annealing at 923 K, the Auger depth profiles did not show the presence of Fe in the Pd–Ag/γ-Al2O3 membranes. However, iron was detected in the surface layer after long-term hydrogen permeation measurements at temperatures between 673 and 923 K, indicating that the γ-Al2O3 layer did not completely block the intermetallic diffusion under these severe conditions.