Monitoring Ag−Cr Interactions in SOFC Cathodes Using Raman Spectroscopy

Due to its excellent conductivity and catalytic activity toward oxygen reduction, silver has been used as cathode (or electrocatalyst), current collector, or electrical contact in low-temperature solid oxide fuel cells (SOFCs). Here we report our findings on the contamination of silver or a silver-containing cathode from the chromium oxide layer found on a Cr-containing interconnect. Silver wire was attached to a patterned La0.8Sr0.2MnO3 cathode deposited onto a yttrium oxide-stabilized zirconium oxide substrate. The samples were placed inside a temperature- and atmosphere-controlled sample chamber filled with Cr-containing vapor. Raman spectra collected in situ from the sample surface revealed the formation of silver chromate, Ag2CrO4, on the silver surface at temperatures as low as 500 °C. At 625 °C, the Ag2CrO4 was found to have vaporized and deposited across the LSM surface. In light of this contamination, special attention should be given to the selection of a metallic interconnect layer for an SOFC system that uses silver or a silver-containing cathode. Further, the use of in situ Raman spectroscopy as a powerful tool for probing and mapping new phase formation on electrode surfaces under fuel cell operating conditions is demonstrated.