Oxygen permeation in SrCo_0.8Fe_0.2O_3-δ membranes with porous electrodes

Measurements of oxygen flux, in the temperature range, 770-870°C on planar membranes of SrCo_0.8Fe_0.2O_3-δ, consisting of a dense discs ∼0.1 cm thick modified by coating with porous layers on both sides, yielded an enhancement in the oxygen flux, η≈2, compared to the uncoated membrane. When only one side of the disc was coated with the porous layer on the high pressure side of the membrane then η≈1.2, while when the modified side was on the low pressure side then η≈1.4. The observed values of η were explained by a model of diffusion-reaction transport in mixed ionic electronic conductor membranes with porous electrodes, extended to the case of finite thickness of the dense layer. From a fit of the model to the experimental data, values of the surface exchange coefficient, k_i0, and ambipolar oxygen ion-electron hole pair diffusion coefficient, D_a, were deduced. At 870°C, k_i0 = 2.5 × 10^-4 cm/s and D_a = 5 × 10^-6 cm²/s.