Improving the chemical stability of oxygen permeable SrFeO3 − δ perovskite in CO2 by niobium doping

• Structure and oxygen permeability of SrFeO3 − δ severely degraded in CO2.
• CO2 tolerance of SrFeO3 − δ was greatly improved by Nb doping.
• No reaction or flux degradation was found for 30% Nb-doped sample at 800 °C.
• Enhanced CO2 tolerance was related with metal–oxygen bonding.

Among mixed-conducting perovskite oxides, SrFeO3 − δ shows very good oxygen permeability, but it suffers degradation in the presence of CO2. In this work, we investigated the effects of Nb doping on the structure and oxygen permeability of SrFe1 − xNbxO3 − δ (x = 0–0.30). For SrFeO3 − δ, significant absorption of and reaction with CO2 led to structural degradation as well as rapid deterioration of the oxygen permeation flux at 800 °C. However, the reaction became much less pronounced and the decrease of the flux was much smaller with Nb doping (x = 0.05–0.20). Most importantly, almost no reaction and no decrease in the oxygen flux were observed even at the relatively low temperature of 800 °C as the Nb doping was increased to 0.3. The improvement of the CO2 resistance with Nb doping was discussed in terms of the increased metal–oxygen bonding in the perovskite.