Electrochemical Impedance Spectroscopy Analysis on SO2 Contamination in PEMFCs

Electrochemical impedance spectroscopy (EIS) was applied to analyze the effects of 2 ppm SO₂ on the electrochemical reactions in PEMFCs cathode during the two-stage performance degradation. An equivalent electrical circuit model (ECM) was used to fit the resistances of the fuel cell reactions. The extracted parameters of the oxygen reduction reaction (ORR) suggested that during the first poisoning stage, the SO₂ adsorption increased the charge transfer resistance of the ORR and caused the initial degradation in cell performance. During the second poisoning stage, SO₂ adsorption might assist in shifting the ORR from the "direct four electron pathway" to the "series two electron pathway", which may have resulted in the subsequent degradation in cell performance.