ON THE THEORY OF ELECTROCHEMICAL AND CHEMICAL ELECTRON TRANSFER PROCESSES

Kinetic studies of simple electron transfer systems in solution and at electrodes have revealed a number of interesting and simplifying features. The chemical reactions also represent one of the very few cases in kinetics where it has been possible to make reasonable calculations of the absolute rate constant without introducing adjustable parameters or arbitrary assumptions. Because of their comparative simplicity, these processes also serve as a useful kinetic tool for investigating ion–solvent–electrode interactions.In the present paper the writer's recent theoretical investigations are summarized and used to interpret data obtained from both solution and electrode studies. Various phenomena are discussed in the light of this theory and several predictions of behavior are made. The topics considered include effects of changing the overpotential or the standard free energy of reaction, the ionic structure, temperature, salt concentration, solvent, and electrode material. Both the parallelism between chemical and electrochemical transfers and the role played by the electrostatic image in the latter case are discussed. A classification of reactants is employed throughout, based in part on differences in the theoretical treatment.