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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 Ba0.5Sr0.5Co0.8Fe0.2O3−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 Bi0.15Sr0.85Co0.8Fe0.2O3−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.

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In this paper we examine the effect of partial substitution of Ga for Sc in the oxyanion (phosphate, sulfate) containing perovskites, Ba2Sc\(_2\)\(_-\)\(_x\)P\(_x\)O\(_5\)\(_+\)\(_x\) and Ba\(_2\)S\(_c\)\(_2\)\(_-\)\(_x\)S\(_x\)O\(_5\)\(_+\)3\(_x\)\(_/\)\(_2\) with the samples analysed through a combination of X-ray diffraction, TGA, Raman spectroscopy and conductivity measurements. The results demonstrate that in both cases, Ga can be incorporated in place of Sc up to 40%. In order to accommodate the increasing Ga content, a reduction in the oxyanion content is required. Thus for the highest Ga content sample achieved, only 10% oxyanion incorporation was achieved giving endmember compositions of Ba\(_2\)S\(_c\)Ga\(_0\)\(_.\)\(_8\)P\(_0\)\(_.\)\(_2\)O\(_5\)\(_.\)\(_2\) and Ba\(_2\)S\(_c\)Ga\(_0\)\(_.\)\(_8\)S\(_0\)\(_.\)\(_2\)O\(_5\)\(_.\)\(_3\) for phosphate and sulfate doping respectively. While the Ga doping was shown to significantly improve the stability of the systems towards CO\(_2\) containing atmospheres, conductivity measurements showed a reduction in the conductivity with increasing Ga content.

In the Solid Oxide Fuel Cell (SOFC) field, proton conducting perovskite electrolytes offer many potential benefits. However, an issue with these electrolytes is their stability at elevated temperatures in the presence of CO2. Recently we have reported enhanced oxide ion/proton conductivity in oxyanion (silicate, phosphate) doped Ba2In2O5, and in this paper we extend this work to examine the stability at elevated temperatures towards CO2. The results show improved CO2 stability compared to the undoped system, and moreover this can be further improved by co-doping on either the Ba site with La, or the In site with Zr. While this co-doping strategy does reduce the conductivity slightly, the greatly improved CO2 stability would suggest there is technological potential for these co-doped samples.

In this paper we report the successful incorporation of phosphate and sulphate groups into the ionic conductor, Ba2In2O5, with the samples analysed through a combination of X-ray diffraction, NMR, TGA, Raman spectroscopy and conductivity measurements. The results show that such oxyanion incorporation leads to a conversion from an ordered brownmillerite-type structure to a disordered perovskite-type, and hence increases the conductivity at temperatures < 800○C. In wet atmospheres, there is evidence for a significant enhancement of the conductivity through a protonic contribution.