Oxygen permeation in symmetric and asymmetric La0.2Sr0.8Fe0.8Ta0.2O3−δ membranes

Abstract

La0.2Sr0.8Fe0.8Ta0.2O3-(LSFT) is a mixed ionic electronic conductor (MIEC) at elevated temperatures and as such a candidate material for applications both in syn-gas synthesis and as electrodes in solid oxide fuel cells (SOFC). This study addresses the variation in oxygen permeation rates for LSFT symmetric-and asymmetric-membranes at temperatures between 800 and 1000 o C with and without surface modification. The surface was strutured in two different scales, macro (porous LSFT-layer) and micro (acid etching). The asymmetric membranes showed a significant variation in permeation rate with surface treatment with increasing rate in the sequence from non-treated to macro-structured and finally micro structured, corresponding to oxygen permeation being controlled by surface exchange and gas diffusion. It was found that the permeation rate was sensitive to the gas sweep rate when H2-mixtures was introduced on the permeate side, which was rationalized by adsorption of H2O-molucules on the surface hampering the exchange of oxygen.

Oxygen semi-permeation properties of La1−xSrxFeO3−δ perovskite membranes under high oxygen gradient

“…Park et al 15 have reported a similar oxygen flux of 0.11 10 -2 ml.cm -2 .min -1 (8 10 -4 mol.m -2 .s -1 ) at 900°C with a La 0.6 Sr 0.4 Fe 0.8 Ti 0.2 O 3-δ dense membrane under an air/He gradient. Gurauskis et al 14 have reported a very high oxygen flux of 4.2 ml.cm -2 .min -1 (3.1 10 -2 mol.m -2 .s -1 ) at 900°C for a very thin (20 µm) dense La 0.2 Sr 0.8 Fe 0.8 Ta 0.2 O 3-δ membrane under an air/Ar-O 2 -H 2 gradient. However, La 1-x Sr x FeO 3-δ materials (LSF) have suitable mechanical properties and high electronic and ionic conductivities then, can therefore be used as dense membrane.…”

“…Indeed, the surface of BSCF and LSCF samples sintered at 1150°C shows a secondary phase exclusively located at grain boundary at the sample surface, which decreases the ionic and electronic conductivities of the membrane material 9 . Thus, the research is currently interesting in the development of more stable materials without cobalt, containing lanthanum and iron by substituting Fe with a judicious cation in the B site like Al 10 , Cr 11 , Ga 12 13 , Ta 14 , Ti 15 16 . For instance, the oxygen flux is about 0.12 10 -2 ml.cm -2 .min -1 (8.…”

Symmetric and asymmetric membranes based on La0.5Sr0.5Fe0.7Ga0.3O3-δ perovskite with high oxygen semipermeation flux performances and identification of the rate-determining step of oxygen transport

“…Although asymmetric membranes often show high semipermeation performances [27] [28] [29] [30], the rate-determining step of oxygen transport through the membrane is not clearly identified in the literature.…”

Improving the performance of oxygen transport membranes in simulated oxy-fuel power plant conditions by catalytic surface enhancement

“…It provides the driving force for the oxygen separation, allowing oxygen ion transport from the high oxygen partial pressure side to the low oxygen partial pressure side. Membranes based on single MIEC materials can achieve high oxygen fluxes [8][9][10][11][12][13][14][15][16][17][18], however most of the promising materials are not chemically stable under atmosphere containing CO2 and SO2 [11,[19][20][21][22][23][24][25], which is particularly required for oxy-fuel combustion applications. Dual-phase composites consisting of separated ionic and electronic conductor phases are a promising alternative approach to ensure high oxygen flux and chemical stability in realistic power plant conditions.…”