Abstract
Hydrogen oxidation reaction (HOR) kinetics were measured at films of high-surface-area platinum/Vulcan carbon (Pt/VC) exposed to aqueous solutions of mercaptopropionic acid (MPA), a water-soluble organosulfur compound, using rotating disk voltammetry. Results were fitted to a recently developed dual-pathway kinetics model. At all levels of sulfur coverage (0-96% of a monolayer of MPA), the potential-independent Tafel-Volmer pathway, or two-site HOR pathway, seems largely unaffected. Decreases in current at low overpotentials are accounted for entirely by loss in surface area of the electrode due to site occlusion by the adsorbed organosulfur. Rates for the single site, potential-dependent Heyrovsky-Volmer pathway decrease by a factor of 10 after the initial MPA exposure (50% of a monolayer), indicating an electronic effect of sulfur on the potential-dependent Heyrovsky reaction.
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