Heterogeneous Rates of Electron Transfer. Application of Cyclic Voltammetric Techniques to Irreversible Electrochemical Processes

Article abstract of DOI:10.1021/ja00534a036

The anodic peak potentials in the irreversible cyclic voltammograms of various homoleptic alkylmetals in acetonitrile show a striking linear correlation with their ionization potentials I_D determined in the gas phase.Application of various transient electrochemical techniques proves that the electrode process arises from a totally irreversible ECE sequence in which the peak potential is determined solely by the kinetics of heterogeneous electron transfer and diffusion-uncomplicated by any follow-up chemical reaction.As a result, the anodic peak potential E_p can be directly related to the activation free energy for electron transfer, and the correlation of E_P and I_D represents a linear free-energy relationship.The mechanism of heterogeneous electron transfer is described as an outer-sphere process, dependent only on the driving force for one-electron oxidation and independent of steric effects of the alkylmetal.The close relationship between the activated compexes for heterogeneous and homogeneous electron transfer is emphasized in a direct comparison of the electrochemical process with the oxidation of the same alkylmetals by a series of poly(pyridine)iron(III) complexes in solution.