Relationship between electrochemical properties of SOFC cathode and composition of oxide layer formed on metallic interconnects

A Cr-poisoning of SOFC cathode was studied using half-cells with alloy separators of various Cr-content. The surfaces of the oxide layer formed on the alloys were observed using energy dispersion X-ray analysis, and the precipitation of Cr at the interface between YSZ electrolyte and the cathode was studied using electron probe micro analysis. All the Cr-containing alloys were found to promote cathode degradation. However, the time dependencies of overvoltage in half-cell tests were different from one another in three kinds of alloy materials. We found that the reason of the difference was in relation to the Cr₂O₃ and the MnCr₂O₄ in the oxide layer formed on the alloy surface. Tests of single-cell stacks were also performed with these alloy separators. The degradation of stack voltage was large for all the stacks, and that was consistent with the half-cell tests. The reason for the large degradation was found to be a formation of SrCrO ₄, which was presumably synthesized by the reaction of Cr ₂O₃ in the oxide layer on the alloy and Sr diffused from the cathode. Therefore, it is necessary to develop a component in which the alloy does not contact the cathode directly.