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On the basis of the electrochemical and spectroelectrochemical behavior of thin films of TTF over a glassy carbon electrode in iodide media, a new, more complete mechanism for the electrode processes involved is proposed. The voltammetric and chronoamperometric results for the films can be explained in light of a recently developed nucleation-growth model involving a layer-by-layer mechanism. Also, their in situ UV-vis spectral data expand the available knowledge about the overall mechanism and the nature of the compound formed over the glassy carbon electrode.

On the basis of the electrochemical results obtained for thin films of 7,7,8,8- tetracyanoquinodimethane (TCNQ) on a glassy carbon electrode, the reduction and oxidation of the [TCNQ](0/)(-) couple in KCl aqueous media occurs via a mechanism involving layer-by-layer nucleation and growth. In situ recorded UV-visible spectroelectrochemical data allow two different crystal structures for the oxidized form of TCNQ to be discriminated.

The formation of condensed phases by salts of heptyl viologen cation radical on mercury electrode in aqueous media under potentiostatic conditions is explained in light of a new mathematical model based on a desorption-nucleation mechanism. This initially assumes the nucleation process to be governed by the desorption of molecules previously adsorbed on the electrode surface. The potential subsequent incorporation of adsorbed molecules into the condensed 2D phase via surface reorientation (a reorientation-nucleation mechanism) is considered. The proposed model was successfully applied to the 2D nucleation of heptyl viologen in the presence of both strongly (bromide) and weakly (sulfate) adsorbed anions on a mercury electrode surface.

In aqueous media, heptyl viologen (HV2+) is reduced via a one-electron transfer to its cation radical (HV•+), the salt of which forms a two-dimensional (2D) phase on a mercury electrode. In this work, we studied the influence of temperature, the reagent concentration, and the type of anion present in the medium on the formation of this 2D phase. The critical temperature for the phase transition was found to be 80−85 °C. The experimental value obtained for the surface area occupied by the heptyl viologen molecule below 30 °C is about 70 A2; accordingly, the molecules must arrange themselves at an angle with the electrode surface. The anion concentration in a chloride medium was found to exert no appreciable effect on the 2D phase; on the other hand, increasing bromide ion concentrations in the medium shifted the nucleation peak to increasingly more negative potentials.

Methyl viologen (MV 2+ ) gives a very narrow, sharp, tailless reversible peak by cyclic voltammetry at a mercury electrode. The peak arises from the one-electron reduction of the molecule to its cation radical (MV .+ ), which forms a two-dimensional (2D) phase over the electrode. In this work, we tested various analytical criteria in order to validate this assignation and fit the voltammetric peak numerically to the theoretical model developed for this purpose. The formation of the two-dimensional condensed phase of MV .+ over mercury was found to depend on temperature. Like three-dimensional phases, 2D phases are not formed above a given, critical temperature. Thus, the voltammetric peak disappeared abruptly above 67 o C, which can therefore be adopted as the critical temperature for the 2D phase of methyl viologen