PNNL

Abstract

Strontium-doped lanthanum ferrite (LSF) materials have shown considerable promise as solid oxide fuel cell (SOFC) cathodes. When used in conjunction with an anode-supported yttria-stabilized zirconia (YSZ) electrolyte assembly, power densities of 0.7-0.9 W/cm2 at 750ºC and 0.7V can be achieved. However, this performance relies on the incorporation of a doped ceria interlayer between the YSZ electrolyte and LSF cathode. In the case of Sr-doped lanthanum manganites and cobaltites the ceria interlayer acts as a reaction barrier and prevents the formation of poorly conducting Sr- and La- zirconate phases. LSF, on the other hand, does not appear to react with YSZ to form the aforementioned zirconate phases even if reacted at 1400ºC (~250ºC above the typical firing temperature for LSF). Instead, when sintered in direct contact with YSZ, Zr4+ cations diffuse into the perovskite where they occupy B-site positions, and result in decreased electrical (and possibly ionic) conductivity of the cathode. As expected the Zr diffusion exhibits thermal dependence, and is typically observed at temperatures =1000ºC. The current cathode of choice, La0.8Sr0.2FeO3-? (LSF-20), has an optimized (in terms of adherence and microstructure) sintering temperature of ~1150ºC. Therefore, application of this cathode directly on YSZ results in the aforementioned LSF-YSZ interaction, and subsequently relatively poor performance. Hence, the need for the protective ceria interlayer. Recently, the authors have considered changes in the LSF-20 chemistry to facilitate enhanced cathode sintering