NH3 and H2S Contamination

The presence of H2S in the air at the cathode side severely degrades fuel cell performance. Mohtadi et al. [35] found that in the presence of 200 ppm, at a cell voltage of 0.68 V, the current density decreased sharply from around 500 mA/cm to less than 150 mA/cm in under 10 hours. After 60 hours of neat air flushing, the current density was only recovered to 170 mA/cm, indicating that H2S poisoning is almost un-recoverable [35]. 

Similar to the mechanism at the anode, the mechanism of the H2S poisoning effect is assigned to strong sulfur adsorption on Pt, blocking oxygen adsorption sites  

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