Influence of sulfur impurities on the stability of La_0.6Sr _0.4Co_0.2Fe_0.8O₃ cathode for solid oxide fuel cells

The initial degradation of a La_0.6Sr_0.4Fe _0.8Co_0.2O₃ (LSCF) cathode for solid oxide fuel cells (SOFCs) was investigated. Degradation of the cathodic performance at 973 K was accelerated by decreasing the oxygen partial pressure from 20 to 10% due to the reduction of Fe^{3 +} in LSCF. Sulfur contamination (1513 and 752 ppm) in the LSCF powder significantly increased the IR loss of the cathode within the initial few hours of SOFC operation. Impedance and conductivity measurements suggested that the increase in IR loss could be explained by the decrease in the electrical conductivity of LSCF due to the phase separation of Sr^{2 +} from lattice or surface segregation of Sr, and the formation of SrSO₄. Sintering of the LSCF powder electrode was enhanced at the Sr enriched part and the diffusion overpotential was significantly increased after degradation for 24 h. Therefore, sulfur impurities in the LSCF powder have a negative influence on the stability of cathode during the initial period of SOFC operation.