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-delta (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 1.00 mm. 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 1.00 mm thick symmetric membranes indicated that a moderate improvement of the overall performance was achieved due to asymmetric architecture. The oxygen fluxes through membrane with 170 mu m thick dense and porous layers with thicknesses of 1.05 mm and 100 mu m at 1173 K were found to be similar to 1.5-1.8 times higher than those for a 1.00 mm 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. (C) 2011 Elsevier B.V. All rights reserved.