The effect of SO 2 content in air on degradation of a La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF6428) cathode for solid oxide fuel cells was investigated at T = 1073 K for 24 h by setting the concentration of SO 2 to 0.1, 1, 10, and 100 ppm. The degradation of the LSCF6428 cathode became more significant with increasing SO 2 concentrations due to the increase of cathode polarization resistance. The SrSO 4 formation was confirmed after exposing to SO 2 from 0.1 to 100 ppm and became even harsh with increasing SO 2 concentrations. The reaction sequence can be interpreted from thermodynamic considerations using chemical potential diagrams and chemical equilibrium calculations.

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Effect of water vapor on the sulfur poisoning of LSCF6428 cathode were investigated by comparison in performance and impedance spectroscopy of LSCF6428/10GDC cells, which were tested at 1073 K (800 o C) for 100 h under two conditions: (a) 1 ppm SO 2 with dry air and (b) 1 ppm SO 2 with 1.2% humidified air. Results of performance degradation revealed that degradation speed is accelerated about 10 times in the presence of water vapor. Detailed SEM analyses show that the amount of formed SrSO 4 during the same operation time is much larger in the humidified air atmosphere.