On the impedance of galvanic cells—XVII. The mechanism of the Zn2+/Zn(Hg) electrode reaction

Abstract

A theory is presented of the complex behaviour of the streaming zinc amalgam electrode in a Zn2+ solution. It is assumed that the Zn2+/Zn+ and the Zn+/Zn(Hg) electrode reactions occur at potentials where at the dropping amalgam electrode the Zn2+-resp. Zn-concentration at the electrode surface is virtually zero as a consequence of the Zn2+/Zn(Hg) electrode reaction. At the streaming amalgam electrode the Zn2+/Zn(Hg) reaction behaves more irreversibly owing to the increased mass transfer. Consequently the surface concentration of Zn2+ resp. Zn is finite in the neighbourhood of the standard potential of the redox couple Zn2+/Zn+ resp. Zn+/Zn(Hg), 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.