Over the past several years, advances in the design and fabrication of planar solid oxide fuel cells ͑SOFCs͒ have led to a steady reduction in the temperatures necessary for their operation. Consequently, it appears more realistic now to use low cost heatresistant alloys for interconnect components in the SOFC stack. However, no specific criteria or inclusive study are available as a reference to help select and evaluate suitable candidates from the hundreds of available heat-resistant alloy compositions, which overall demonstrate oxidation resistance at high temperatures. In this work, composition criteria have been proposed for the preselection of heat-resistant compositions, such as Ni-, Fe-, and Co-based superalloys, Cr-based alloys, and stainless steels. The proposed criteria have been employed to establish a database of heat-resistant alloys at Pacific Northwest National Laboratory, where a systematic approach has been initiated to evaluate and modify and/or develop alloys for SOFC interconnect applications. The preselected compositions are further evaluated by referring in-house studies and reference to published data. It appears that it would be difficult for traditional alloys to fully satisfy the materials requirements for long-term operation at temperatures higher than 700°C. However, the applicability can be improved via surface/bulk modification and by the implementation of novel stack designs.

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Perovskite compositions in the system La1M1Co1_8Fe8O3_, (M = Sr, Ba, Ca) exhibited high electronic and ionic conductivity. Substantial reversible weight loss was observed at elevated temperatures as the materials became increasingly oxygen deficient. Thisloss of lattice oxygen at high temperatures, which tended to increase with increasing acceptor content, resulted in a decrease in the electronic conductivity. In an oxygen partial pressure gradient, oxygen flux through dense sintered membranes of these materials was highly dependent on composition and increased with increasing temperature. The increase in oxygen flux with increasing temperature was attributed to increases in the mobility and concentration of lattice oxygen vacancies. The calculated ionic conductivities of some compositions exceeded that of yttriastabilized zirconia.

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