Abstract
The kinetics of the hydrogen oxidation reaction (HOR) were measured at high surface-area platinum/Vulcan carbon (Pt/VC) films before and after exposure to aqueous solutions of either sodium sulfide or mercaptopropionic acid (MPA, ) using rotating disk electrode (RDE) voltammetry. At 45–90% blocking of surface Pt atoms by inorganic sulfur, sulfur appears to adsorb as oligomerized sulfur . Current–potential RDE data for the HOR at -exposed Pt/VC films were fitted to a recently developed dual-pathway kinetics model. At a submonolayer coverage of surface Pt atoms, the exchange current densities for the potential-independent Tafel–Volmer pathway, or two-site HOR pathway, decrease by about –50-fold compared to electrochemically cleaned Pt/VC films. Exchange current densities for the single-site, potential-dependent Heyrovsky–Volmer pathway decrease by comparable factors at the same levels of sulfur exposure. The potential-range constant γ increases in the presence of adsorbed . The exposure of Pt/VC to aqueous solutions of MPA, an organosulfur species, results in similarly diminished HOR exchange current densities at Pt/VC, as observed for exposure, but yields higher values of γ. The model is sufficiently sensitive to delineate the effects of different catalyst poisons on HOR kinetics at carbon-supported nanoscopic Pt.
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