The effect of temperature on the adsorption rate of hydrogen sulfide on Pt anodes in a PEMFC

The coverage of a Pt anode in a proton exchange membrane fuel cell (PEMFC) by sulfur species resulting from exposure to 5 ppm H2S/H2 is evaluated in situ by using cyclic voltammetry (CV). The coverage is shown to be a function of H2S dosage and temperature at 50, 70, and 90 °C. The rate constant for the H2S adsorption reaction on Pt at 50 °C was approximately 69% lower than at 90 °C. The Pt-sulfur species accounts for 90% of the Pt after 800 min (18 μmol of H2S) at 50 °C and 100% of the Pt after 600 min (13.5 μmol of H2S) at 90 °C. Shifts in the sulfur oxidation potential in cyclic voltammetry to higher values at lower temperatures were observed indicating that sulfur is more strongly adsorbed at lower temperatures. A value of the activation energy of hydrogen sulfide adsorption on Pt is shown to be 28.2 ± 5.5 kJ/mol.