Improved Sinterability and Performance of Lanthanum Ferrite SOFC Cathodes
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 750 C 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 1400 C ({approx}250 C 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 ?1000 C. The current cathode of choice, La0.8Sr0.2FeO3-? (LSF-20), has an optimized (in terms of adherence and microstructure) sintering temperature of {approx}1150 C. 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 <1000 C in an attempt to avoid the LSF-YSZ reaction. Modifications must be subtle in nature since high cation dopant levels can result in the formation of poorly conducting zirconate phases, typically observed with manganites and cobaltites. A composition that appears somewhat promising is a slightly A-site deficient lanthanum ferrite with a marginal amount of Cu dopant on the B-site, (La0.8Sr0.2)0.98Fe0.98Cu0.02O3-?. This composition can be sintered onto YSZ at 950 C, and to date has indicated power densities of 1.3-1.8 W/cm2 at 750 C and 0.7V ({approx}1.5-2.0 times greater than the performance exhibited for a cell with an LSF-20 cathode and ceria interlayer). Other transition metal dopants and degrees of non-stoichiometry are also under investigation.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 885209
- Report Number(s):
- PNNL-SA-39233; AA2530000
- Country of Publication:
- United States
- Language:
- English
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