Simulating coadsorption of surface active anions and organic molecules capable of forming two-dimensional condensed layers on the electrode

Within the framework of the Alekseev-Popov-Kolotyrkin model combined with a set of Frumkin isotherms, the adsorption of adamantanol (AdOH) molecules i s studied in the presence of a surface-inactive electrolyte and chloride io ns at the Hg/H2O interface. The position of points at the beginning and in the end of an equilibrium two-dimensional phase transition is shown to be d etermined by the equality of(a) surface tension and (b) calculated electrod e potentials. With these conditions fulfilled in the phase-transition regio n, the model of two parallel capacitors with a common diffuse layer (in the AdOH + NaF system) transforms into the classical model of two parallel cap acitors with two independent diffuse layers. Taking into account the latera l interaction between adsorbed chloride anions and AdOH molecules makes no difference to the two-dimensional phase transition potential at fixed adsor ption parameters. The effect of the diffuse layer on the position of two-di mensional phase transition potentials is analyzed.