Structure of the double layer and electrode processes. II. Effect of the nature of the electrode and application of the thallium-amalgam electrode

The influence of the nature of the electrode in electrochemical kinetics in the absence of specific electrode effects is interpreted on the basis of a change in the double layer structure. This double layer effect, which can be quite significant, should also be considered in kinetic correlations for processes with specific electrode effects. Application is made of the dropping thallium-amalgam electrode (up to 31% TI) for which the point of zero charge can be shifted continuously by as much as -0.4 volt with respect to this point for mercury. The following reductions are studied: bromate and iodate in alkaline solution, hexacyanochronaate(III) in cyanide medium, chromate in alkaline solution and tetracyano cadmium(II) in cyanide medium. Shifts of the Tafel line for bromate and variations of the exchange current density for hexacyanochromate(III) are interpreted quantitatively. Chromate waves for the dropping thallium amalgam electrode in supporting electrolyte of low concentration exhibit a pronounced minimum which is quantitatively discussed. The maximum in the tetracyano cadmium(II) waves is abscribed to a double layer effect in agreement with other investigators, and a quantitative study is attempted for the results obtained with the dropping mercury electrode.