The effect of diffusion direction on the permeation rate of hydrogen in palladium composite membranes

The experimentally measured hydrogen permeability of a composite Pd/porous stainless steel membrane was found to be influenced by the direction of permeation. For pure hydrogen, the direction from the stainless steel support to the metal film gave the higher hydrogen permeance. However, for a hydrogen/nitrogen mixture the opposite effect was obtained. Simulation results showed that while permeation from the support to the metal gave the expected Sieverts' law value of the pressure exponent of 0.5, that from the metal to the support gave a higher value for this exponent of approximately 0.66.