Different oxides used as diffusion barriers in composite hydrogen permeable membranes

Composite Pd–Ag membranes supported on modified porous stainless steel substrates were prepared by sequential electroless plating. To improve the stability of the Pd–Ag alloy, two different intermediate layers of α-Fe2O3 and γ-Al2O3 oxides were employed as diffusion barriers. A new activation method was also investigated which consisted in the impregnation of a layer of Pd supported γ-Al2O3 to generate palladium seeds. The membranes were studied by XRD, Auger depth profiling, SEM and EPMA. They were tested in a gas permeation system to determine the hydrogen permeability and selectivity. The Pd–Ag/PSS membranes had a good thermal resistance. The membranes prepared with alumina diffusion barriers exhibited lower ideal selectivity than the Pd–Ag/α-Fe2O3/PSS. However, the former membranes had two times higher hydrogen permeability. The Auger depth profiles did not show the presence of Fe in the Pd–Ag film, indicating that the γ-Al2O3 layer effectively blocked the intermetallic diffusion.