Sulfur poisoning of SOFC cathodes

In order to examine degradation of solid oxide fuel cell (SOFC) cathodes due to a trace of SO_x in air, sulfur poisoning of SOFC cathodes was investigated in an accelerated mode using SO₂-concentrated air at T = 1073 K. Two different cathode materials, Sm_0.5Sr _0.5CoO₃ (SSC) and (La_0.85Sr_0.15) _0.95MnO₃ (LSM), were fired on button-type La _0.8Sr_0.2Ga_0.8Mg_0.15Co _0.05O_3-δ electrolytes. SO₂-concentrated air (98 ppm SO₂-air mixture) was selected as the source of sulfur in order to accelerate degradations due to sulfur poisoning. By exposure to SO ₂, the performance of SSC cathode rapidly declined, because both ohmic and polarization resistances increased. The performance of the LSM cathode slightly decreased after exposure to SO₂, and the performance recovered by interrupting the feed of SO₂. Secondary phases such as strontium sulfate were formed on SSC cathode after exposing SO₂ and were not clearly detected on LSM cathode. The LSM cathode was more stable in SO₂ concentrated air than the SSC cathode. This can be explained by the difference in the activity of strontium oxide in LSM and SSC.