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 °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 (Rp). 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.