Chronocoulometric studies of chloride adsorption at the Pt(111) electrode surface

Chronocoulometry and a thermodynamic analysis of charge density data were used to describe chloride adsorption at the Pt(111) electrode surface. The Gibbs excess, the Gibbs energy of adsorption, the number of electrons flowing to the interface per adsorbed chloride ion at a constant potential (electrosorption valency) and at constant chloride concentration (reciprocal of the Esin-Markov coefficient) were determined. Chloride forms a chemisorption bond with platinum. The charge numbers at constant potential and at constant chloride concentration are close to unity. This result suggests that the polarity of the chemisorption bond is very small. The highest packing density of chloride determined by the thermodynamic method corresponds to 0.43 ML. This number agrees well with coverage determined in recent surface X-ray scattering experiments [1]. Adsorption of chloride at Pt(111) is potential and pH dependent. We have demonstrated that at negative potentials, co-adsorption of Cl and hydrogen atoms has a synergistic character. In contrast the adsorption of chloride and OH at positive potentials has a competitive nature. (C) 2000 Elsevier Science B.V. All rights reserved.