Generalized model of the surface layer for the case of adsorption of organic molecules on the electrode

Abstract

Summary An equation for the electrode charge in the presence of adsorbed organic molecules is suggested and analyzed; from this Frumkin's, Hansen's and Parsons' models, discussed earlier in the literature, can be derived under particular conditions. It follows from the comparison of the suggested equation with experimental data on the adsorption on mercury and bismuth electrodes of some aliphatic compounds with one functional group, that the behavior of these systems fits Frumkin's model better than those of Hansen's and Parsons'. The physical significance of the models mentioned has been reexamined with reference to the dependence of the ratios D/δ and μ/δ on the adsorbed amount Γ ( D —the dielectric constant of the surface layer, δ —its thickness and μ —the normal to the surface component of the dipole moment of the organic molecules). The better agreement with experimental data of the two parallel capacitors model is accounted for not only by a partial segregation of the adsorbate molecules from those of the solvent caused by the attractive interaction between organic molecules, but also by the increase of δ with rising Γ being compensated by an increase of μ due to a change in the orientation of organic dipoles (in the case of Frumkin's model μ/δ =const.).