Silver–chromium oxide interactions in SOFC environments

Interactions between silver and chromium oxide were investigated during SOFC-relevant extended exposures pertaining to secondary phase formation and associated electrical contact degradation. In one case, Ag or Ag2O and Cr2O3 powders were mixed, pressed into pellets and thermally treated in air at 700 °C, 800 °C and 900 °C for up to 1000 h. X-ray diffraction revealed AgCrO2 and trace Cr2O3 in the specimens treated at 700 °C and 800 °C; however, Cr2O3, Ag and only trace amounts of AgCrO2 were detected at 900 °C. In another case, silver contact paste was used in area specific resistance (ASR) measurements of ferritic stainless steel (FSS), with and without (Co,Mn)3O4 coatings, in 800 °C air for greater than 1500 h. A distinct reaction layer, having AgCrO2 stoichiometry, was observed to form between the Cr-containing corrosion-products on the uncoated FSS and the silver contact paste yielding a 500% increase in ASR over 1500 h. No significant chemical interactions and ASR losses were observed with the (Co,Mn)3O4 coated FSS at this interface. Analyses and implications of the observed interactions of Cr2O3 and Ag within SOFC cathode environments are presented and discussed.