Mediated Electron Transfer at Redox Active Monolayers

A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. We describe theoretically the time dependent chronoamperometric response expected for a redox active monolayer in the absence of a substrate in solution, and subsequently extend the analysis to consider the reaction of a solution phase substrate mediated by surface immobilized redox groups. This is accomplished via a Laplace transform based solution of the Fick diffusion equation for the substrate transport to the monolayer surface coupled with the development of a suitable flux matching condition at the monolayer/solution interface . The latter procedure enables the development of an analytical expression for the transient current response in terms of well established mathematical special functions. We have shown that kinetic information may be readily extracted from the developed expressions for the current response as a function of time. In the present paper we assume that the reaction between mediator and substrate is of a simple outer sphere bimolecular type.