Hydrogen permeation and diffusion of metallic composite membranes

We have investigated hydrogen permeation of Pd/V–15Ni/Pd and Pd–25Ag/V–15Ni/Pd–25Ag alloy composite membranes with about 40-μm and 1-mm thickness in the temperature range of 423–673 K. Hydrogen permeation of Pd–25Ag/V–15Ni/Pd composite membranes with about 40-μm thickness was also examined. There were two directions for the hydrogen permeation of Pd–25Ag/V–15Ni/Pd composite membranes. Higher permeation flux was obtained in the Pd–25Ag/V–15Ni/Pd composite membrane when the Pd–25Ag overlayer was at the upstream side and the Pd overlayer was at the downstream side. Overall hydrogen diffusion coefficients of the composite membranes were independent of the permeation pressure and overlayer, while hydrogen permeation flux had strong dependence on the overlayer composition and sequence. Membrane thickness and overlayer had profound effects on hydrogen permeation of composite membranes. The overlayer effects were discussed.