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 Ag 2O and Cr 2O 3 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 AgCrO 2 and trace Cr 2O 3 in the specimens treated at 700 °C and 800 °C; however, Cr 2O 3, Ag and only trace amounts of AgCrO 2 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) 3O 4 coatings, in 800 °C air for greater than 1500 h. A distinct reaction layer, having AgCrO 2 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) 3O 4 coated FSS at this interface. Analyses and implications of the observed interactions of Cr 2O 3 and Ag within SOFC cathode environments are presented and discussed.