The role of supporting electrolyte in heterogeneous electron transfer

The effects of supporting electrolyte on the kinetics of the elementary step of electron transfer are considered as unavoidable interplay of interfacial phenomena and ionic equilibria in solution. For the former, the problems to separate contributions of electrostatic electrode-reactant interactions and specific adsorption are addressed, and various aspects of the traditional Frumkin correction (psi-prime effect) are discussed. The construction of corrected Tafel plots is shown to be a procedure containing the internal contradiction resulting in an uncertainty. This uncertainty can be eliminated by combining the principles of traditional analysis of the double layer effects with physical theory instead of phenomenological approaches. Specific manifestations of parallel electron transfer to an ensemble of reacting species are presented in the context of mean reactant charge in solution bulk. The approach to account for non-spherical shape and inhomogeneous charge distribution in reacting species is considered in terms of molecular psi-prime effect. Finally, some comments are given on analogy of double layer effects at metal/solution interface and interfacial phenomena specific for more complex and highly relevant electrochemical systems.