Electrode reaction rate elementary step, theory

Based on careful work on Fe(III)(C204)3 reduction, Sluyters considers that the potential dependence of a, observed with certain electrode processes, really arises from kinetic complications and that the transfer coefficient for the elementary step of charge transfer is constant at —0.5. However, the work of Hupp and Weaver on the Cr(OH2)6 system demonstrated a relation between the temperature and potential dependence of the rates, and showed that at overpotentials of ca. 0.7 — 0.9 V the potential dependence of rate arises extensively from the entropic factor (p. 133). It was also shown that the Marcus theory was able to predict a potential dependence of A5" " comparable to or > that of A// when the system has a large entropic asymmetry, i.e., a large net reaction entropy change. 

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