Accelerated Degradation of SOFC Cathodes by Cr Vapors

摘要

Among the degradation factors of SOFCs, Cr poisoning is one ofthe important issues for long-term operation. Pre-oxidized Cr metalwas used to generate Cr vapors to accelerate Cr poisoning atcathodes. Cathodic polarization currents decrease with time due todeposition of Cr at electrochemical active sites. The concentrationlevels of Cr in the porous cathodes (La_(0.8)Sr_(0.2)MnO_3 (LSM)) andLa_(0.8)Sr_(0.2)FeO_3 (LSF)) were determined by secondary ion massspectrometry (SIMS). The concentration level of Cr changes from100 to 2000 ppm depending on cathode materials and analyzedareas. For LSM cathode, a maximum of Cr concentration wasobserved at the LSM/electrolyte interface, while no condensationwas observed at the LSF/electrolyte interface. The concentration ofCr deposited in the LSF cathode is estimated to be about 21-25%of the supplied Cr and is about 1.8 times higher than theconcentration of Cr atoms in the LSM. The electrochemicalperformance of LSF is relatively high compared with that of LSM.