Hydrogen-evolution and -oxidation on Ag(111) covered by Pt

Physical vapour deposited Pt on Ag(111) forms inhomogeneous films, leaving access to the Ag(111) surface, as proven by electroreflectance. The overpotential of the hydrogen evolution reaction at Ag(111) by water splitting in neutral perchlorate and sulphate electrolytes and by H3O+ discharge in acidic perchlorate and sulphate electrolytes is considerably reduced by the Pt coverage, but does not vanish. The transfer coefficient for water splitting is more than 50% lower than for H3O+ discharge. In H-2-saturated neutral electrolytes, the potential gap between hydrogen evolution by water splitting and H-2-oxidation decreases with the increasing number of Pt monolayers. In acidic electrolytes, this gap does not exist. Here, the absolute current densities of W-reduction and H-2-oxidation grow with the number of Pt monolayers. In the neutral electrolytes, sulphate strongly inhibits the H-2-oxidation (by a factor of about 25 with respect to perchlorate). (c) 2005 Elsevier B.V. All rights reserved.