Adsorption energy and isotherms of ions at the electrode

A general approach to the theory of ionic adsorption at the mercury electrode (mobile adsorption) is given. An explicit expression of the excess free energy of adsorption is derived on the basis of the method of cluster expansion as indicated by Buff and Stillinger provided that the following assumptions are made: (1) pure electrostatic coupling between diffuse layer ions and adions, (2) adsorbed solvent effects defined in terms of a local dielectric constant. At low ionic coverage of the electrode surface a simplified version of the adsorption isotherm is suggested. In this case a hard-core model is used to describe steric effects between adions, and a model of distribution at the surface is further assumed that serves to bring out, respectively, the cavity field effect, the atmosphere effect, and reordering of particles upon adsorption. The resulting isotherm of adsorption is then compared to experimental data concerning chloride adsorption. At large coverages the hexagonal lattice approximation for ionic adsorption is shortly discussed.SCOPUS: ar.j