On the selection of the most probable mechanism of the Cd(II) reduction at mercury from 1 M KF solution

Abstract

A faradaic impedance study has been made of the reduction of Cd(II) ions from a 1 M KF base electrolyte at the DME. It could be shown that only the Cd(II) present in the solution and the end product, viz. Cd(Hg), are the diffusing partmles and that intermediates are present only at the interface. From the analysis of the impedance data it followed that at the interface the Cd(II) species is first subject to a heterogeneous chemical transfer and thereafter is reduced according to two discrete one-electron transfers, both obeying the Butler--Volmer equation. The kinetm parameters of the steps are reported. A number of other conceivable mechanisms were considered, but fortunately they all either could be defimtely ruled out or were found to be less acceptable.

A faradaic impedance study of the reduction of oxygen from aqueous alkaline solution at the dropping mercury electrode

“…The ac measurements were performed with the automatic Network Analyzer system described elsewhere [11 ]. This system measures the cell impedance in terms of amplitude and phase angle at a given set of frequencies and dc potentials.…”

“…It has been shown [11] that the slow response of the Network Analyzer to the time-dependent signal of the DME causes systematic errors in the measured amplitudes of ca 1.5%. These errors have been accounted for in the ultimate calculations.…”

Study of the CEE mechanism by voltammetry and chronoamperometry

“…The electrochemical reactions of bi-or polyvalent cations are usually more complicated than those of monovalent cations. Different mechanisms were proposed in the literature for the electrode reduction of metal cations, e.g., simple electron transfer process (2,3), stepwise electron transfer (4), disproportionation (5) or dimerization (6) of the intermediates, adsorption (6), CE or CEE mechanism (7)(8)(9)(10)(11)(12)(13).…”

“…(12) and Strujis et al (13) show that the electroreduction of Cd(I1) in concentrated aqueous solutions of perchlorates and fluorides involves a CEE mechanism with a heterogenous chemical reaction, probably a partial desolvation of the depolarizer at the electrode surface. Alternating current admittance and demodulation technique were applied to study those reactions.…”

“…Unfortunately the potential range available for the a.c. admittance technique is rather limited. Strujis et al (12) have presented kinetic data in the range of about 130 mV. Larger (-200 mV) potential range is available for the demodulation technique (13) but this method is, up to now, of limited use.…”