ELECTRODE POTENTIAL IN SUSPENSIONS INTERPRETED AS A MIXED POTENTIAL

Srečko F. Oman

Faculty of Chemistry and Chemical Technology, University of Ljubljana,

Aškerčeva 5, 1000 Ljubljana, Slovenia.

Abstract

A simple experimental method was developed and applied to establish and alter the mixed potential of a measurement electrode in a galvanic cell. The electrode, immersed simultaneously in two different contacting solutions forming a sharp boundary, alters its mixed potential when moved in regard to the boundary, because at the same time inhibition of the electrode reactions changes. Illustrative experiments were made with a Cu electrode in CuSO₄ solutions.

Using the same method the electrode potential behaved quite analogously when the electrode was dipped simultaneously in an equilibrium solution and in the sediment of a suspension composing a galvanic cell. This similarity allows interpretation of the potential of the electrode as the mixed potential when it is dipped in a suspension. By bringing the electrode into contact with charged particles, their double layers overlap and form sporadic contact regions, where the electrochemical potential of the potential determining ions is different from that in the surrounding equilibrium solution. Therefore two different electrochemical reactions can take place on the surface of the same electrode, which is the condition for the appearance of the mixed potential.

Keywords: mixed potential, double layer overlapping, suspension galvanic cells, suspension effect of the first kind, method for mixed potential establishment and change