A RE-FORMULATION OF THE WAGNER AND TRAUD ADDITIVITY PRINCIPLE - CATALYTIC AND ELECTROCHEMICAL EXPERIMENTS WITH IODIDE MODIFIED SURFACES

Adsorption of iodide on reduced platinum electrodes has been shown to increase the rate of reduction of Fe3+ ions and to inhibit the reduction of oxygen. As a result, platinum was found to catalyse the Fe3+ + I- reaction to a greater extent than predicted from the simple Wagner and Traud additivity principle while, contrary to initial expectation, platinum and gold did not catalyse the O2 + I- reaction at all. However, these facts were quite consistent with the additivity postulate when use was made of current-potential curves for Fe3+ reduction, and for oxygen reduction, measured in the presence of small concentrations of iodide ion. It follows that the current-potential curve of a mixture of couples can be obtained by algebraically adding the current-potential curves of the couples present provided the latter curves have been determined in circumstances which correspond to those in the mixture.