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.

Sulfur poisoning behavior of La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF6428) cathode was investigated at T = 1073 K (800 °C) under 0.1 ppm of SO2‐air mixture gas; the amount of supplied SO2 was controlled by changing the flow rate. Two stages of the performance degradation were found: a rapid degradation at the early stage and a subsequent monotonic degradation. The elemental distributions of SrSO4 showed a strong correlation between the electrochemically active sites and SrSO4 reaction sites in the vicinity of the LSCF6428/10GDC interfaces. Considerations were made to attribute the first and the second stages of performance degradation to the SO2 adsorption and the SrSO4 formation, respectively. The SO2 adsorption mechanism was discussed in terms of the high concentration of oxide ion vacancies in the electrochemically active region under the cathodic polarization condition.

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Attempts have been made to simulate numerically the conductivity degradation of solid oxide fuel cell (SOFC) YSZ electrolyte; physicochemical model has been constructed on the basis of experimental conductivities of Pt/1%NiO-doped YSZ/Pt cells under OCV condition. The temperature effect was extracted from the time constant for degradation caused by one thermal activation process (namely Y-diffusion), whereas the oxygen potential effect was determined by those Raman peak ratios between the tetragonal and the cubic phases which linearly change in relation to the conductivity. The electrical properties of the YSZ electrolyte before and after the transformation are taken into account. The time constant is directly correlated with Y-diffusion with proper critical diffusion length (∼10 nm), while the Y-diffusion can be enhanced on the reduction of NiO; this gives rise to the oxygen potential dependence. The most important objective of simulating the conductivity degradation is to reproduce the oxygen potential profile shift on transformation. Detailed comparison between experimental and simulation results reveal that the shift of oxygen potential profile, therefore, the conductivity profile change inside the YSZ electrolyte can well account for the Raman spectra profile. This also reveals that with decreasing temperature, there appear other kinetic factors of weakening or diminishing enhancing effects by NiO reduction. This may be important in interpreting the ohmic losses in real stacks, because there are differences in time constant or in magnitude of degradation between the pellets and those industrial stacks in which transformation was confirmed by Raman spectroscopy.