Enhancement of oxygen permeation through La0.6Sr0.4Co0.2Fe0.8O3-δ hollow fibre membranes by surface modifications

La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) mixed conducting hollow fibre membranes were prepared via the combined phase inversion and sintering technique. A porous layer of silver or LSCF perovskite was coated on the outside surface of the hollow fibres to improve the surface exchange kinetics. Oxygen permeation fluxes through both the modified and the unmodified LSCF hollow fibre membranes were measured under air/He gradients at different temperatures. The oxygen permeation process through the unmodified LSCF hollow fibre membranes is mainly controlled by the oxygen dissociation on the membrane surface exposed to feed gas of air. After surface modifications, the oxygen permeation fluxes can be improved from the original values of 0.01-0.81 mL standard temperature and pressure (STP) cm(-2) min(-1) in the unmodified hollow fibre membrane to 0.08-1.85 mLcm(-2) min(-1) in the Ag-coated membrane and to 0.05-1.48 mLcm(-2) min(-1) in the porous LSCF-modified membrane, respectively, in the temperature range of 700-1000 degrees C. The maximum enhancements for the Ag-coated and the porous LSCF-modified membranes are achieved at 800 degrees C to be 17.8 and 9.3 times the original flux, respectively. Due to the surface modifications, the operating temperature to achieve anticipated oxygen permeation fluxes of commercial interest can be reduced noticeably. (C) 2008 Elsevier B.V. All rights reserved.