Bond formation in electrosorbates—II electrosorption and double layer properties in non-aqueous solvents

Abstract

According to the principles outlined in Part I, electrosorption valencies of various systems are summarized for non-aqueous solvents. γ/ z-values of ions adsorbed electrostatically can be taken as geometric factors, g, which characterize the relative penetration of the ions into the double layer. For different solvents, g increases with increasing double layer thickness, d, or decreasing minimum double layer capacity, C min. The partial charge transfer, −γ/ z, is discussed in dependence on the difference, |Δχ|, of the electronegativities of the metal and of the adsorbed substances. Corresponding to the analysis for water, γ/ z was plotted in dependence on |Δχ| for methanol and DMF as solvents. Complete charge transfer is observed in methanol for |Δχ| < 0·3, and electrostatic adsorption without charge transfer takes place for large |Δχ|-values. In the mean range of |Δχ|, eg in iodide systems, partial charge transfer takes place in all solvents. The influence of the solvation properties of the solvent on the partial charge transfer can be discussed qualitatively only. It is concluded that strong solvent-ion interaction facilitates the electrostatic adsorption, but increasing charge transfer is enhanced by a decreasing solvent-ion interaction, eg in case of anion adsorption from aprotic solvents.