Dependence of the Absolute Rate Constant of an Electrode
Process on the Metal Nature: Electroreduction
of the Cr(3+) Ethylenediamine Tetraacetate on Hg, Bi, and Cd
and Its Analysis in the Context of the Classical Approach

M. L. Khrushcheva, G. A. Tsirlina, and O. A. Petrii

Moscow State University, Vorob’evy gory, Moscow, 119899 Russia

Received October 9, 1996

Abstract—The electrochemical behavior of Cr(3+) ethylenediamine tetraacetate ([CrEDTA]^–) on Hg, Au(Hg),
Bi, and Cd electrodes is studied using the polarographic and rotating disk electrode techniques. The electrore-
duction of this complex in a buffer acetate solution (pH 6.2) on the metals under study is shown not to be com-
plicated by chemical or electrochemical side processes. The absence of specific adsorption of EDTA-containing
species on polycrystalline Cd is proved by the measurements of differential capacitance on electrodes with
renewable surface in Na₂H₂EDTA solutions. By comparing the experimental data in the framework of the clas-
sical theory of slow discharge, with due allowance for the reaction center localization at different distances from
the electrode surface, the rate constant of the ([CrEDTA]^–) electroreduction is found to vary in the Au(Hg) > Bi
> Cd sequence; the variation can be as large as 2.5 orders of magnitude. A conclusion is drawn that the reaction
studied is nonadiabatic, at least, on Cd.

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