La1 − xBaxCo0.2Fe0.8O3 − δ perovskites for application in intermediate temperature SOFCs

Abstract

Physicochemical properties of La1−xBaxCo0.2Fe0.8O3−δ (LBCF) oxides are presented in aspect of their possible application as cathode materials in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC). The obtained results show that the increase of concentration of Ba2+ leads to an increase of unit cell volume and to a decrease of crystal structure distortion, which is accompanied by an increase of the level of oxygen nonstoichiometry in the studied compounds. For samples with x≥0.6 cubic structure was observed, which is particularly worth noting for BaCo0.2Fe0.8O3−δ composition, as both BaCoO3−δ and BaFeO3−δ often, but depending on oxygen nonstoichiometry δ, adopt hexagonal-type structure. Electrical conductivity and Seebeck coefficient data of the materials are quite similar, comparing to La1−xSrxCo1−yFeyO3−δ oxides. For samples with barium content ≥0.6, at high temperatures, a clearly visible maximum on electrical conductivity dependence on temperature can be seen, which may be related to a significant increase of the oxygen nonstoichiometry. The highest conductivity in the intermediate temperature range (600–800°C) was observed for La0.6Ba0.4Co0.2Fe0.8O3−δ composition, however obtained values are significantly lower, comparing to strontium analog: La0.6Sr0.4Co0.2Fe0.8O3−δ. La0.6Ba0.4Co0.2Fe0.8O3−δ oxide was used as the cathode material in custom-made button-type IT-SOFCs, which properties were evaluated in 600–800°C temperature range. Additionally, chemical stability of that material in relation to Ce0.8Gd0.2O1.9 electrolyte was studied.