Effect of SO₂ Concentration on Degradation of Sm_0.5Sr_0.5CoO₃ Cathode

Abstract

A trace amount of SO2 in air is not a negligible factor on degradation of SOFC cathode. SO2 acts like Cr vapors which cause Cr-poisoning, and easily reacts with the strontium component in lanthanum-cobaltite based SOFC cathodes. Effects of SO2 concentration on degradation of an Sm0.5Sr0.5CoO3 (SSC) cathode were investigated in order to evaluate degradation of SSC cathode in an accelerated mode. Three different concentrations of SO2 (100 ppm, 1 ppm, and 5 ppb) were supplied to the cathode with air during cell tests at T = 1073 K Degradation of SSC cathode was accelerated with increasing SO2 concentration. In the thin SO2 conditions (1 ppm and 5 ppb SO2), SO2 in air was captured on the surface of the SSC cathode. SO2 reacted with the strontium component in the SSC cathode to form SrSO4. In the thick SO2 condition (100 ppm SO2), SO2 reacted with the strontium and samarium components. Too excess SO2 concentration in air was not suitable to examine cathode degradation in an accelerated mode because other degradation modes were appeared. One ppm - SO2 in air was applicable to accelerate the degradation of SSC cathode.