Processing and oxygen permeation studies of asymmetric multilayer Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ membranes

The oxygen transport studies of dense Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O₃₋δ (BSCF) ceramic membranes, prepared via glycine–nitrate route, demonstrated that the permeation rate is predominantly controlled by surface exchange kinetics when the membrane thickness is smaller than 1.00mm. In order to improve oxygen exchange, an asymmetric membrane concept including two porous and one dense layer was implemented. The amount of graphite as a pore-forming additive, powder compaction and sintering conditions were optimized to produce three-layer membranes having appropriate mechanical strength and microstructure. Comparison of the data on oxygen permeation through three-layer and dense 1.00mm thick symmetric membranes indicated that a moderate improvement of the overall performance was achieved due to asymmetric architecture. The oxygen fluxes through membrane with 170μm thick dense and porous layers with thicknesses of 1.05mm and 100μm at 1173K were found to be ∼1.5–1.8 times higher than those for a 1.00mm thick symmetric membrane. The variation of oxygen flux changes with pressure and the values of the activation energies for oxygen permeation suggest significant gas diffusion limitations in the porous layers, whilst the role of other factors is still significant. Microstructure of the porous layers requires further optimization for successful application of the oxygen exchange catalysts.