Fundamental Research for Analysis of Electrode Reactions Involving Adsorption of Electroactive Species

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Redox-electrode reactions of adsorbed electroactive species on the electrode surface have been statistical mechanically treated using two-dimensional quasi-crystalline lattice model and taking into account the interactions among adsorbed species and coordination numbers. Theoretical current-potential curves have been obtained for potential sweep voltammetry and AC voltammetry for one electron transfer step. Furthermore, the theoretical treatment has been extended to two step one-electron transfer reactions. In order to establish a method of analysis of electrode processes of adsorbed species, it is required to have a suitable model system which can be regarded as a prototype. It has been found that some viologen dications adsorb on mercury electrode even in the +2 state and that the adsorbed species in a monolayer exhibits a pair of sharp spike-like waves which may be attributed to the redox-electrode reaction of the adsorbed species involving a phase transition of the adsorbed layer. These waves show very good reproducibility and it is concluded that the viologen-mercury systems can be regarded as a model system. The adsorption and the electrochemical behavior of the viologens has been studied in detail. Simulation of experimental current-potential curves using the derived theoretical results has been tried, taking into consideration the kinetic parameters of electrode processes and interaction energies among adsorbed species. Although a completely satisfactory agreement between the experimental and theoretical curves has not been obtained so far, it has been confirmed that the theoretical results obtained here can be applied to the analysis of current-potential curves can can explain some involved shapes of such curves.