Researchers at Argonne National Laboratory have tested several cathodes on yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (CGO) electrolytes for use in solid oxide fuel cells (SOFCs). The Pr0.5Sr0.5CoO3 (PSC) and Gd0.5Sr0.5CoO3 (GSC) cathodes show the best performance on CGO, achieving an area-specific resistance (ASR) between 0.1 and 0.2 Omega.cm(2) at 650 degreesC. However, the desirable operating temperature for CGO is between 500 and 600 degreesC, where the ASRs remain very high. The cobalt-based materials in contact with the YSZ electrolyte exhibit severe reactions. To prevent these reactions, a dense interlayer of CGO has been added between the YSZ and the cobalt-based cathodes. The results for the PSC and GSC cathodes on the YSZ electrolyte protected by a CGO layer reveal ASR values between 0.1 and 0.2 Omega.cm(2) at 750degreesC and 0.3 Omega.cm(2) at 700 degreesC. Long-term testing of both PSC and GSC cathodes on YSZ electrolytes with CGO interlayers showed stable ASR values for 500 h at 800 degreesC. Thermal cycling between room temperature and 800 degreesC after long-term testing showed minimal degradation.