Theoretical analysis of the local electric double layer effect by Monte Carlo simulation

Abstract

The detail of the potential profile of the electrical double layer at the solid/liquid interface is usually not discussed because the potential difference between the electrode and the bulk solution has great significance for the redox reaction and the charging of the electrode. In the case of the self-assembled monolayer of thiols with dissociative group terminals on Au(111) surface the charge density has a high value such as 0.74μC m-2. For this interface we found that the reaction rate of the redox species such as [Fe(CN)6 ]3-/4- in electrolyte solution is enhanced by the order of more than 105 even when the coverage of the dissociated terminals of ammonium group terminal is less than 1/100. By the use of the primitive model and the canonical Monte Carlo simulation the three-dimensional distribution of the potential was evaluated. With the combination of the Butler-Volmer-Frumkin theory and the potential profiles the reaction rate was numerically calculated. The calculated change in the reaction rate was in good agreement with the experimental results. From this theoretical analysis we had the conclusion that the enhancement of the redox reaction rate can be induced by the local electrical double layer effect around the dissociated group terminal.