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 SrCrO4, which was presumably synthesized by the reaction of Cr2O3 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. (C) 2004 Elsevier B.V. All rights reserved.