The coverage of a Pt anode in a proton exchange membrane fuel cell (PEMFC) by sulfur species resulting from exposure to 5 ppm H2S/H-2 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 degreesC. The rate constant for the H2S adsorption reaction on Pt at 50 degreesC was approximately 69% lower than at 90 degreesC. The Pt-sulfur species accounts for 90% of the Pt after 800 min (18 mumol of H2S) at 50 degreesC and 100% of the Pt after 600 min (13.5 mumol of H2S) at 90 degreesC. 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. (C) 2004 Elsevier B.V. All rights reserved.