Thermodynamic considerations on Cr poisoning in SOFC cathodes

Chromium poisoning has been considered with an emphasis on the thermodynamic stability of perovskite cathodes. Reactions of cathodes with chromium vapors are categorized mainly into (1) Cr substitution into perovskite B-sites, (2) SrCrO4 formation and (3) Cr2O3 or spinel (CrMn2O4) formation. These can be characterized in terms of the valence stability of transition metal tetravalent ions, which is also crucial in determining the cathode electrochemical reaction mechanism and in cathode-YSZ electrolyte chemical interaction. Observed chromium poisoning was compared with such thermodynamic features with aid of the consideration on the oxygen potential profile and related mass transfer caused by the electrical current.