Chromium Poisoning of LSM/YSZ and LSCF/CGO Composite Cathodes

An electrochemical study of SOFC cathode degradation, due to poisoning by chromium oxide vapours, was performed applying 3-electrode set-ups. The cathode materials comprised LSM/YSZ and LSCF/CGO composites, whereas the electrolyte material was 8YSZ. The degradation of the cathode performance was investigated as a function of time under a current load of 0.2 or 0.4 A cm(-2) and in the presence of Cr2O3 at 850 and 750 degrees C in air, dry or water saturated at room temperature, and compared to that of non-Cr exposed reference specimens tested under, otherwise, the same conditions. This involved continuous logging of the DC current, and the voltage between the reference electrode and the working electrode in the 3-electrode set-up combined with frequent AC impedance measurements under current load which would allow the deduction of the cathode polarisation resistance (R-p). The duration of the tests ranged from 300 to 2,970 h. Both LSM/YSZ and LSCF/CGO cathodes were sensitive to chromium poisoning; LSCF/CGO cathodes to a lesser extent than LSM/YSZ. Humid air aggravated the degradation of the cathode performance. Post-mortem electron microscopic investigations revealed several Cr-containing compounds filling up the microstructure of the cathodes.