Combined Cr and S poisoning behaviors of La1−xSrxMnO3±δ and La1−xSrxCo1−yFeyO3−δ cathodes in solid oxide fuel cells

[Display omitted] •The combined effect of airborne Cr and S species on air-electrodes was studied.•The combined Cr/S poisoning behavior of LSCF remains different from those of individual Cr/S poisonings.•The long-term exposure results in SrSO4 and Cr2O3 formation due to chemical reaction and electrochemical reduction, respectively.•The preferred interaction of SrO with SO2 allows Cr vapors to freely reach and deposit at the electrode/electrolyte interface. Although the individual effects of airborne Cr and S contaminants on SOFC cathode performance degradation have been extensively studied, the combined effects of Cr and S contaminants remain largely unexplored. Under the real SOFC operating condition where the Cr and S species coexist, their effects may compete, affecting the poisoning behavior. Our investigation reveals that the combined Cr and S poisoning behavior of LSCF remains different from those of individual Cr and S poisonings, while the combined poisoning mechanism of LSM is equivalent to the sum of those of individual Cr and S effects. For LSCF electrode, gaseous Cr species are deposited mainly at the LSCF/GDC interface by electrochemical reduction, rather than forming SrCrO4 on LSCF surfaces (as in the case of Cr-only poisoning), indicating no reaction between Cr vapors and SrO on the LSCF surface. Thermodynamic analysis demonstrates that the SrO on LSCF surface absorbs SO2 (g) and thereby loses the Cr-gettering effect, allowing Cr vapors to flow through LSCF and to reach the LSCF/GDC interface where the Cr deposition occurs. Unlike LSCF, LSM electrode shows cumulative effects of Cr and S, as Cr accumulation occurs at the triple-phase boundary and S absorption takes place at localized Sr-rich regions.