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

Ming Li,Wen Xu,John Druce,Vin R Dhanak,Leanne A H Jones,Matthew J Rosseinsky,J Felix Shin,Tatsumi Ishihara,Helena Téllez,Marco Zanella,John A Kilner,Dingyue Hu,John B Claridge,Hripsime Gasparyan,Michael J Pitcher,Luke M Daniels,Hongjun Niu

doi:10.1002/adma.201905200

Abstract

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σo ) and electronic conductivity (σe ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σe but inadequate σo . It has been a long-standing challenge to develop MIECs with both high σo and stability under device operation conditions. For example, the well-known perovskite oxide Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF) exhibits exceptional σo and electrocatalytic activity. The reactivity of BSCF with CO2 , however, limits its use in practical applications. Here, the perovskite oxide Bi0.15 Sr0.85 Co0.8 Fe0.2 O3- δ (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σo 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.

Highlights

Mixed ionic–electronic conductors (MIECs) that display high oxide ion conoxygen, or in a mixture of oxygen balanced with recycled flue gas, producing a ductivity and electronic conductivity constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes
The MIEC membranes can provide pure oxygen with a reduced energy penalty and cost compared to conventional cryogenic air separa
Mixed ionic–electronic conductors (MIECs) that combine the ture, in which oxygen ions migrate through the so-called saddle required intrinsic transport properties of high oxide ion con- point defined between two A-site ions and a B-site ion.[11]

Summary

As polished

Less Sr than the bulk (Figure 3b), consistent with the Bi surface enrichment observed with LEIS in Bi-based pyrochlores.[29]. The more electropositive character of Bi3+ versus Ba2+ and Sr2+ decreases the basicity of the oxide anions in BiSCF below that in the alkaline-only A site BSCF where the ionic character of the A O bond is higher, and reduces reactivity with Lewis acidic CO2 This effect is amplified at the surface due to the locally increased Bi content. The work demonstrates an approach to achieve synergic tuning of the bulk and surface properties of a complex perovskite oxide mixed ionic–electronic conductor to couple high anion mobility with enhanced chemical stability. During these processes the roughness of the membrane surface can increase, which increases the surface exchange kinetics, and JO2 returns to be above the initial value.[50]. BiSCF cathodes are about one order of magnitude lower than the typical values of LSCF[51–53] and are comparable to those of BSCF without interfacial/microstructural optimization,[49]

Experimental Section

Findings

Conflict of Interest