Accession Number : ADA294508

Title :   Solvation Dynamics and the Structure in Electrolytes and Electrodes.

Descriptive Note : Rept. for 1 Jun 94-31 May 95,

Corporate Author : PUERTO RICO UNIV RIO PIEDRAS DEPT OF PHYSICS

Personal Author(s) : Blum, Lesser

PDF Url : ADA294508

Report Date : 31 MAY 1995

Pagination or Media Count : 21

Abstract : Phase transitions occurring during electrode processes have been studied using a model in - which the electrode is a planar wall with sticky adsorption sites. This model was used to explain the underpotential deposition (U PD) of copper on gold (111) in the presence of bisulfate ions. The model assumes that the bisulfate ions form a template for the adsorption of the first 2/3 of a monolayer of copper onto a honeycomb lattice. The centers of the hexagons that form the honeycomb are occupied by the bisulfate. In the absence of copper the bisulfate is desorbed as the electrode becomes more negatively charged, and for that reason the template 'melts' when the fraction of occupied sites drops below a certain critical value, which is estimated using the hard hexagon model of Baxter. We assume strong copper-bisulfate coadsorption, so that in the presence of a sufficiently large amount of Cu the template is reconstructed. Our model explains the qualitative features of the voltammogram, and makes definite predictions for the structures that should be observed. In previous work, we separated the problem as a second order phase transitions for the bisulfate, and a sequence of two first order phase transitions for the copper. The coupling of the copper and the bisulfate was treated in a simple mean field approximation. In the present work we go a step beyond this simple model: We introduce a model with individual couplings (copper-copper and copper-bisulphate), and use the method of cluster variation to solve approximately the complicated lattice problem in which the bisulphate excludes the first neighbors and the copper is always attractive. An approximate theory is constructed using the cluster variation method of Guggenheim and McGlashan

Descriptors :   *ELECTRODES, *ELECTROLYTES, COUPLING(INTERACTION), IONS, DYNAMICS, LAYERS, PHASE TRANSFORMATIONS, ADSORPTION, THEORY, SITES, VARIATIONS, CLUSTERING, COPPER, APPROXIMATION(MATHEMATICS), PLANAR STRUCTURES, WALLS, TRANSITIONS, MEAN, SULFATES, SOLVATION, GOLD, COUPLINGS.

Subject Categories : Electrical and Electronic Equipment

Distribution Statement : APPROVED FOR PUBLIC RELEASE