Degradation Mechanism of SOFC Cathodes under CrO₃ and SO₂ Impurity Exposures

The effects of Cr-and S-impurities on the cathode performances were examined at the mixed ionic-electronic conducting La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathode. Under exposures to CrO₃ and SO₂, the cathode performance decreased drastically by forming SrCrO₄ and SrSO₄ at the LSCF grain surfaces and electrochemical active sites. The main degradation factors of LSCF cathode was the decrease of surface reaction rates by the impurities. The Sr-diffusion and depletion in the LSCF structures can affect the cathode performance degradation. Relatively large amounts of Sr were depleted in the LSCF grains under CrO₃ exposures by forming a thick SrCrO₄ at the Pt-mesh/LSCF cathode interfaces, while small amounts of Sr-depletion in the LSCF grains under SO₂ exposures.