Oxygen transport properties of tubular Ce_0.9Gd_0.1O_1.95-La_0.6Sr_0.4FeO_3−d composite asymmetric oxygen permeation membranes supported on magnesium oxide

The oxygen permeation through dense Ce_0.9Gd_0.1O_1.95-La_0.6Sr_0.4FeO₃−d  dual-phase composite asymmetric membranes supported on a porous MgO tube was studied. The membranes were prepared by thermoplastic extrusion, dip coating, co-sintering and infiltration of a catalyst. Oxygen permeation measurements and electrical conductivity characterization of the membrane were performed as a function of temperature and oxygen partial pressure. The oxygen flux through the membrane in a H₂/air gradient at 850 °C reached 15 N ml cm⁻² min⁻¹. The measured oxygen flux was in good agreement with the theoretically estimated one, taking into account the transport properties of the composite, surface exchange losses, gas diffusion and gas conversion in the MgO support. The performance of the membrane was limited by the surface exchange for the operation in N₂/air, CO₂/air and H₂/air at low temperatures and most probably by the porosity of the MgO support for the operation in H2/air at 850 °C. The stability tests of the membrane in CO₂/air and H₂/air configurations revealed that an initial degradation of the oxygen flux occurs and it is followed by a relatively stable performance. Post-mortem analysis of the membrane after 900 h of operation did not reveal any significant microstructural degradation of the membrane layer.