Effect of Operating Temperature on Sulfur Distribution and Performance Degradation of Porous La0.6Sr0.4Co0.2Fe0.8O3−δ Electrode.

The effect of low concentrations of SO₂ (0.01 ppm) in air on the degradation of a porous La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) electrode was investigated as a function of operating temperature. At 1073 K, most of the introduced SO₂ became trapped as SrSO₄ in the vicinity of the air inlet, and consequently the degradation of cathode performance was not observed. At 973 K and 923 K, the SO₂ reached directly the electrochemically active region. Thus, the formed SrSO₄ caused a gradual decrease in cathode performance. These results suggest that sulfur poisoning behavior at 0.01 ppm SO₂ is mainly governed by two processes, the chemical reactions in the vicinity of air inlet and the electrochemically enhanced reactions in the active region; the former is strongly enhanced by temperature, whereas the latter additionally by the applied overpotential. SEM-EDX analysis confirmed the sulfur distribution was correlated to the degradation in the electrode performance. The concentration of SrSO₄ found near the triple-phase boundaries corresponded to the case where both the polarization and the ohmic resistances increased. Typical values for the effective reaction length essentially correlated with the k* and D* values obtained using the transmission line model. Results are in order-ofmagnitude agreement with the features obtained using SEM-EDX. [ABSTRACT FROM AUTHOR]