Ca and In co-doped BaFeO3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells

We report Ba(0.95)Ca(0.05)sFe(0.95)In(0.05)O(3-delta)(BCFI), a novel cobalt-free perovskite, as a promising cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). We synthesize this new material, and systematically characterize its lattice structure, thermal stability, chemical composition, electrical conductivity, and oxygen reduction reaction (ORR) activity. The cubic phase of BaFeO3-delta is stabilized by light isovalent and lower-valence substitution, i.e., 5% Ca2+ in the Ba2+ site and 5% In3+ in the Fe3+/Fe4+ site, in contrast with the typical approach of substituting elements of higher valence. Without resorting to co-doping strategy, the phase of BaFe0.95In0.05O3-delta (BFI) is rhombohedral, while Ba(0.95)Ca(0.05)sFeO(3-delta) (BCF) is a mixture of the cubic phase together with BaFe2O4 impurities. The structure of BCFI is cubic from room temperature up to 900 degrees C with a moderate thermal expansion coefficient of 23.2 x 10(-6) K. Thanks to the large oxygen vacancy concentration and fast oxygen mobility, BCFI exhibits a favorable ORR activity, i.e., we observe a polarization resistance as small as 0.038 Omega cm(2) at 700 degrees C. The significantly enhanced performance, compared with BR and BCF, is attributed to the presence of the cubic phase and the large oxygen vacancies brought by the isovalent substitution in the A-site and lower-valence doping in the B-site. (C) 2016 Elsevier B.V. All rights reserved.