A CO₂ -Tolerant Perovskite Oxide with High Oxide Ion and Electronic Conductivity

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σ_o ) and electronic conductivity (σ_e ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σ_e but inadequate σ_o . It has been a long-standing challenge to develop MIECs with both high σ_o and stability under device operation conditions. For example, the well-known perovskite oxide Ba_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_{3- δ} (BSCF) exhibits exceptional σ_o and electrocatalytic activity. The reactivity of BSCF with CO₂ , however, limits its use in practical applications. Here, the perovskite oxide Bi_0.15 Sr_0.85 Co_0.8 Fe_0.2 O_{3- δ} (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σ_o among the highest for known MIECs, but also high CO₂ tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO₂ . The combination of high oxide transport properties and CO₂ tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications.