Theories of electrode kinetics

The present lecture consists of two parts. In the first, a comparison is made of theory and experiment for simple electron transfer reactions in solution and at electrodes, reactions for which no bonds are broken of formed. The main part of the lecture is concerned with electrode reactions involving the breaking and forming of chemical bonds and principally with the hydronium ion discharge reaction, H_3O(+) + M(e) yields H_2O + H-M(ads.). The treatment of this reaction has been the subject of some controversy (cf. 1965 Faraday Discussions on Proton Transfer and more recent literature). To provide further insight, a more dynamical theory of this elementary step for general potential energy surfaces is described. It is then shown how, depending on the nature of the potential energy surface, the theory leads to various approaches in the literature. For example, depending on the surface, the system may or may not for dynamical reasons be able to reach sufficiently easily the saddle-point region or, again, Franck-Condon solvation effects may or may not contribute to the rate. There is a clear need for the application of recent theoretical methods of electronic structure to determine the essential features of the potential energy surface