Oxygen permeation through fluorite-type bismuth-yttrium-copper oxide membranes

Dense Bi(1.5-x)Y_0.5Cu(x)O(3-δ) membranes in fluorite phase (δ phase) with different Cu(O) concentration (x = 0.005-0.015) and thickness (1-3 mm) were prepared from corresponding powders synthesized by the Citrate method. Oxygen permeation through these membranes was studied using a high-temperature permeation system to examine the oxygen transport mechanism of the membranes. The oxygen permeation fluxes through these membranes (2 mm thick) at 800°C are in the range (5.0-9.2) x 10^-9 mol/cm²s at P'(O₂) of 0.21 atm and P'(O₂) of 5 x 10^-4 - 1 x 10^-3 atm. The permeation flux is inversely proportional to the membrane thickness, indicating bulk diffusion being the rate-limiting step. The driving force for the oxygen permeation through the membranes is (P'(O₂)(-1/4) - P'(O₂)(1/4)). The activation energy for oxygen permeation is 136, 113 and 80 kJ/mol for the membranes with 0.25, 0.5, and 0.75 mol% CuO concentration, respectively.