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

Chronocoulometry and a thermodynamic analysis of charge density data were u sed to describe chloride adsorption at the Pt(111) electrode surface. The G ibbs excess, the Gibbs energy of adsorption, the number of electrons flowin g to the interface per adsorbed chloride ion at a constant potential (elect rosorption valency) and at constant chloride concentration (reciprocal of t he Esin-Markov coefficient) were determined. Chloride forms a chemisorption bond with platinum. The charge numbers at constant potential and at consta nt chloride concentration are close to unity. This result suggests that the polarity of the chemisorption bond is very small. The highest packing dens ity of chloride determined by the thermodynamic method corresponds to 0.43 ML. This number agrees well with coverage determined in recent surface X-ra y scattering experiments [1]. Adsorption of chloride at Pt(111) is potentia l and pH dependent. We have demonstrated that at negative potentials, co-ad sorption 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.