Mechanism of the Hydrogen-Oxygen Reaction on Platinum Films from Surface Potential Measurements

The surface-potential changes that occur during the reaction of hydrogen and oxygen on an evaporated platinum film have been recorded by means of the static capacitor method. A sequence of reaction steps has been proposed for the reactions of hydrogen gas with an oxygen-adatom monolayer, and oxygen gas with a hydrogen-adatom layer. The chemisorption of water vapour, by both a clean film and one covered with an oxygen or hydrogen monolayer, has also been investigated. From separate measurements of the s.p. of monolayers of oxygen, hydrogen and water, that of a hydroxyl layer has been calculated; from these values and the measured uptakes of oxygen and hydrogen, the complete s.p. plots have been calculated with consistent agreement with the experimental values. The presence of groups of surface sites of different reactivity previously suggested is confirmed. Explanations for the lack of stoichiometry of the hydrogen titration results reported in the literature and for lack of agreement with infrared results on oxide-supported metal are outlined.