Oxygen separation by mixed conductive perovskite-type oxides

Mixed ionic-electronic conductors are materials which conduct both oxide ions and electronic charge carriers (electron and/or hole) simultaneously. Perovskite-type oxides (ABO₃) with valence-variable cations and oxide ion vacancies such as La_1-xSr_xCo_1-yFe _yO_3-δ (LSCFs) are representative and most intensively studied mixed conductors. LSCFs and their relatives desorb and absorb a large amount of oxygen reversibly from and into the crystal lattice without changing their fundamental crystal structures. By full use of the reversible oxygen sorption-desorption and mixed conductive properties, oxygen separation from, for example, air with 100% selectivity is possible at temperatures above 300 °C. High temperature oxygen separation is very important technology to recover waste heat from high-temperature facilities and can contribute the improvement of energy efficiencies. Oxygen separation is also a key technology for oxy-fuel combustion, because its exhaust consists, in principle, of H₂O and CO₂ which is ready for CCS (Carbon dioxide Capture and Storage). In this review article, two types of oxygen separation technologies by using mixed ionic-electronic conductors are outlined; membrane separation at high temperature range (usually above 800 °C) and temperature/pressure swing separation at medium to high temperature range (for example, 300-800 7deg;C). After describing basic aspects of mixed conductive perovskite-type oxides, current research status and future challenges will be reviewed.