Double layer effects on the enthalpy of activation of heterogeneous electron transfer reactions

Abstract

The contributions to the experimental enthalpy of activation due to temperature variation in the double layer effect and the pre-exponential factor of the rate constant are considered in detail for heterogeneous electron transfer reactions. It is shown that the magnitude of the double layer correction depends significantly on the electrical variable held constant when the temperature is varied. Correction of real enthalpies of activation, the quantity most often reported, requires a knowledge of the temperature dependence of the standard potential, and of the electrode charge density and the differential capacity at the standard potential. Data in the literature for the enthalpies of activation for simple one electron redox reactions involving organic molecules and triply charged metal ions are reviewed and the double layer effects analyzed. It is emphasized that the simplest way to determine the enthalpy of activation corrected for double layer effects is by examining the temperature dependence of the double layer corrected rate constant.