Impacts of Hydrogen Sulfide H2S

Similar to CO, H2S also strongly adsorbs on the Pt catalyst, competing for the active sites with hydrogen adsorption and hydrogen oxidation. In aqueous solutions containing H2S, the adsorption of H2S, HS , and occur through the following reactions [15, 16]  

The adsorption rate, coverage, and stability of H2S species are strongly affected by temperature [18]. It is known that the adsorbed H2S and SH are highly unstable on Pt, while the adsorbed S and H are the most stable intermediates on Pt [19]. The formation of the sulfide film on the platinum surface not only causes poisoning of the catalyst surface but also makes it impossible for the fuel cell to recover from contamination [17, 20, 21]. 

Studies show that the severity of the H2S poisoning depends not only on the concentration of H2S, as mentioned above, but also on current density and cell temperature. However, the H2S poisoning does not seem to be noticeably affected 

The effect of NH3 on the hydrogen oxidation reaction (HOR) has not been fully identified. Uribe et al. [25] reported that NH3 did not adsorb significantly on Pt surface sites, thus not affecting the HOR. But Halseid et al. [27] observed that the presence of NH3 shifted the potentials of the hydrogen adsorption process on a Pt surface in aqueous solutions. Clearly, more work is required to understand the effect of NH3 on the HOR. 

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