Different oxides used as diffusion barriers in composite hydrogen permeable membranes

Abstract

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-Al 2O3 layer effectively blocked the intermetallic diffusion.