Oxygen permeation through tape-cast asymmetric all-La0.6Sr0.4Co0.2Fe0.8O3−δ membranes

Abstract

One of the most promising materials for oxygen separation amongst ceramic oxygen transport membranes (OTMs) is La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) due to its relatively high oxygen permeability combined with high stability. In this work, asymmetric thin-film LSCF membranes supported over a porous LSCF support were manufactured by inverse sequential tape casting. Moreover, surface activation was accomplished by depositing a porous LSCF activation layer in order to promote oxygen evolution reaction, i.e. O2− to O2 oxidation, in the permeate membrane side. In this case, the porous layer allows the surface area available for oxygen activation to be enlarged. Both the manufacturing of the asymmetric thin-film membranes and the surface activation are described in detail. A thorough study of the oxygen permeation is presented for disk-shaped 30µm thick LSCF-supported membranes considering the following operating parameters: temperature (1000–600°C), sweep flow rate (300–750mlmin−1 argon) and oxygen partial pressure in the feed (0.21–1atm). High permeation fluxes were achieved, e.g., 11.87mlmin−1cm−2 at 1000°C and 300mlmin−1 argon sweep when using pure oxygen as feed. A change in the apparent activation energy at about 850ºC was related to a reversible structural change in the perovskite symmetry (cubic↔rhombohedral), as revealed by XRD measurements. Furthermore, the application of an activation layer allowed the permeation process to be improved, especially at low temperatures, i.e. below 800°C. Specifically, an improvement of up to about 300% at 600°C is observed upon application of the activation layer. The activated membrane reached a flux of 13.3mlmin−1cm−2 at 1000°C under an O2/Ar gradient. Additional permeation tests using CO2-rich sweep gas demonstrated the good stability and performance of these LSCF asymmetric membranes at 900 and 1000ºC.