Uphill diffusion effects during hydrogen permeation in palladium-cerium alloy membranes

Uphill diffusion effects of hydrogen during permeation processes in Pd-Ce alloy membranes with 3, 6, 9 and 12.5 at.% Ce have been investigated at 303 K by an electrochemical permeation method, Uphill diffusion effects in the lower Ce content alloys with 3 and 6 at,% Ce would seem Likely to be associated with lattice volume differences occurring across (alpha + beta)/beta and (alpha + beta)/alpha interfaces during absorption and desorption of hydrogen, respectively. In the cases of the 9 and 12.5 at,% Ce content alloys, the uphill non-Fickian diffusion behaviour would seem more attributable to more homogeneous lattice strain gradients also self-created by the ''diffusion-elastic'' lattice expansion effects of the permeating hydrogen, Effects have not been observed in the case of the fully annealed Pd-12.5 at.% Ce, corresponding to a Pd7Ce ordered structure, This may be associated with decreases in creations of overall hydrogen concentration gradients necessary to induce the lattice strain gradients required for operations of uphill diffusion, Observations have been related to changes in the forms of p-c relationships with increasing Ce content and to the relatively larger diffusivity of hydrogen in the higher Ce content alloys, especially in ordered Pd7Ce, where the larger hydrogen diffusivity could counterbalance opposite effects of decreases in bulk modulus with Ce content.