Dense perovskite-type ceramic membranes made from mixed oxygen ionic-electronic conductors (MIEC) have received much attention due to the high selectivity for oxygen separation. Using an MIEC membrane system for the pure oxygen supply benefits an oxy-fuel power plant with a significant increase in the efficiency, compared with the conventional route by cryogenic air separation. For such application, membranes with sufficient long-term stability under the desired working conditions, that is, in atmospheres containing aggressive gases like CO₂ and H₂O etc., and at temperatures typically above 700 °C, are crucial. Some perovskite-type membranes with high oxygen permeability have recently been shown to be susceptible to the presence of these aggressive gases.

In order to better understand how the presence of CO₂ affects the performance of the perovskite oxides and to explore strategy for development of CO₂-resistant materials, BaCo_0.8-xFe_xNb_0.2O_3-δ (x=0.2-0.8) perovskite membranes were prepared and their oxygen permeability and stability in CO₂ were investigated. The oxygen permeation fluxes were measured with pure CO₂ as sweep gas and compared with those measured with Ar. Degradation in the oxygen fluxes was observed when CO₂ was used. The stability of the materials was also examined by a series of CO₂ annealing experiments under various conditions and the results of the (micro-)structural analyses for the annealed samples will be presented. The behaviour of the membranes in CO₂ is linked with the B-site cation composition of the perovskites.

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1. The Role of Gas-Solid Interfaces in Oxygen Permeable Dense Ceramic Membranes