Effect of chemisorbed sulfur on the electrochemical hydrogen adsorption and recombination reactions on Pt (111)

Abstract

The effect of preadsorbed sulfur on the cathodic hydrogen adsorption and recombination reactions was quantitatively studied on a platinum (111) surface in acid aqueous medium. The sulfur coverage was measured by a radiotracer technique. In the presence of sulfur the rate of the overall hydrogen evolution reaction (HER) is strongly lowered. This effect is attributed to a poisoning by sulfur of the sites of adsorption of hydrogen. The weakly bonded hydrogen species involved in the HER is not adsorbed in the same sites as the strongly bonded hydrogen species adsorbed at underpotential. Different poisoning effects by sulfur are observed on the two kinds of sites. The measurements are well fitted by a model in which one isolated sulfur atom blocks three adsorption sites of weakly bonded hydrogen.