Effect of electrolytes on the electrochemical behaviour of 11-(ferrocenylcarbonyloxy)undecanethiol SAMs on gold disk electrodes

The interfacial electrochemistry of mixed monolayers formed by self-assembly from a dilute dodecanethiol-11-(ferrocenylcarbonyloxy)undecanethiol (FcSH) ethanolic solution at pre-treated Au electrodes is reported. The effect of different electrolytes on the interaction among electrochemical products, the interfacial capacitance and the heterogeneous electron transfer rate constant (k(0)), using fast cyclic voltammetry and chronoamperometry, are examined. The anions have a strong influence on the kinetic and thermodynamic parameters of the interfacial redox reaction through the formation of ion pairs with the oxidized ferrocenium. The ion-pairing capability of various anions with immobilized ferrocenium is compared through evaluation of an effective formation constant. The electrolyte cation is shown to affect the thermodynamics of the ferrocene-ferrocenium electrochemical reaction, with cations of lower mobility shifting the apparent formal potential to more positive potentials, which is explained for the first time with the electric force by means of Debye-Huckel theory. A linear relationship between the apparent formal potential of the ferrocene redox couple in self-assembled monolayers and cation mobility and concentration was observed.