A.C. impedance study of rate constants for two-phase electron-transfer reactions

Abstract

The a.c. impedance technique has been used for the measurement of electron-transfer rate constants between organic and inorganic redox couples at the water/1,2-dichloroethane interface. The organic compounds studied were lutetium diphthalocyanine, bis(pyridine)(meso-tetraphenylporphyrinato)ruthenium(II) and 7,7,8,8-tetra-cyanoquinodimethane; Fe(CN)^3–/4–₆ was in all cases the aqueous redox couple. Electron-transfer rate constants were calculated using recent theoretical developments based on a continuum media model. It is concluded that Marcus theory can be used to predict the rate constants for two-phase reactions. Potential-dependent transfer coefficients have been found and it is shown that the origin of this effect is ionic adsorption in the form of interfacial ion pairing.