Expressions for the complex impedance and admittance of a streaming mercury electrode in the presence of either an irreversible or a reversible redox system are derived. An irreversible redox couple gives rise to complex plane diagrams identical with those formerly derived for other electrodes (part I part 111 2). However, complex plane diagrams characteristic for the streaming mercury electrode occur in the case of a reversible redox system. Methods for obtaining information from the diagrams are indicated. The application of streaming mercury electrodes for the determination of kinetic parameters of electrode reactions does not seem very attractive.
Methods for evaluating the effective length of the streaming mercury electrodes according to Heyrovsky and Schwabe have been indicated. At open circuit the charging of the double layer causes changes of concentration at the electrode surface. Only at the former type of electrode do these give rise to a shift of the electrode potential.
The applied electrodesAmong the types of streaming mercury electrodes proposed in the literature 1-6, those according to Heyrovsky and Schwabe (indicated by Heyrovskyand Schwabe-electrode, respectively) have been chosen to test the theory developed in part XI1 ' . This verification requires a preceding detailed investigation of the electrodes, the more so as their properties so far have been poorly defined 8. This paper is concerned with the effective length and the charging mechanism of the double layer at both types of electrodes.The measuring circuit used was identical with that formerly described by one of us 9. The cells used, however, w&e entirely different as well as the auxiliary components to ensure a proper functioning of the streaming mercury electrodes.The Heyrovsky-electrode ( fig. 1) comprises a jet of mercury directed upwards through the bulk of the electrolyte solution. The operating area is limited by the capillary orifice and the liquid surface, which is coned up around the jet. Under the conditions satisfied here, the cone passes into a Abstracted from A. B. IJzermans, Thesis, State University of Utrecht, 1965.
Abstract-A theory is presented of the complex behaviour of the streaming zinc amalgam electrode in a Zns+ solution. It is assumed that the Znp+/Zn+ and the Zn+/Zn(Hg) electrode reactions occur at potentials where at the dropping amalgam electrode the Zna+-resp. Zn-concentration at the electrode surface is virtually zero as a consequence of the Zn*+/Zn(Hg) electrode reaction. At the streaming amalgam electrode the Zn*+/Zn(Hg) reaction behaves more irreversibly owing to the increased mass transfer. Consequently the surface concentration of Zns+ resp. Zn is fmite in the neighbourhood of the standard potential of the redox couple Zn'+/Zn+ resp. Zn+/Zn(H@, this giving rise to additional peaks in the ac polarogram.With a view to the fact that the one-electron-transfer reactions appear to be more reversible than the two-electron-transfer reaction, it can be expected that similar ac polarograms will be obtained for the dropping electrode, if the electrode processes are forced to behave more irreversibly eg by the addition of a surface-active substance. Experiments confirming this idea are described. Vu que les transferts d'un Gctron paraisse& &tre plus rkversibles que le transfert de deux Electrons, on peut s'attendre g des polarogrammes du courant alternatif similaires pour l'blectrode ti gouttes, si on rend le comportement des reactions electrochimiques plus irreversible par addition d'une substance qui est absorb&e il la surface de l%lectrode. On d&it quelques experiences pour confirmer cette thborie.
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