Effect of Operating Temperature on Sulfur Distribution and Performance Degradation of Porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δElectrode

The effect of low concentrations of SO2 (0.01 ppm) in air on the degradation of a porous La0.6Sr0.4Co0.2Fe0.8O3 (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-of-magnitude agreement with the features obtained using SEM-EDX.