Detection of electroactive transient intermediates of electrochemical reactions by steady state and time-dependent techniques: Competition between heterogeneous electron transfer and homogeneous chemical reactions

Abstract

Detection of transient electroactive intermediates, such as σ-radicals, in electrochemical reactions by means of their reduction (or oxidation) wave in rotating disk electrode voltammetry and cyclic voltammetry is investigated in the framework of three frequently encountered reaction schemes. The effective reduction (or oxidation) potential of the transient intermediate depends upon the kinetics both of its heterogeneous reduction (or oxidation) and the chemical reactions it undergoes in the solution. Detection and kinetic characterization of the intermediate are possible when the effective reduction (or oxidation) potentials of the generating molecule and the intermediate itself are sufficiently separated. In this context, cyclic voltammetry possesses the diagnostic advantage that the reduction (or oxidation) peak of the intermediate is smaller than that of a stable product, and the smaller the intermediate peak, the larger the potential separation between the reduction (or oxidation) of the intermediate and that of the generating molecule.