Electrochemistry of silver iodide. Double layer properties in the presence of adsorbed organic molecules

The surface charge on silver iodide suspended in a solution has been measured as a function of the potential of a cell consisting of a silver-silver iodide electrode, the solution under consideration, and a reference electrode. The influence of urea, n-propyl-, n-butyl-, isobutyl-, sec-butyl-, tert-butyl-, and n-amyl alcohol was investigated. Thermodynamic analysis shows that the surface excess of adsorbed alcohols if plotted as a function of the cell potential passes through a maximum. This maximum does not coincide with the zero point of charge. The results suggest that nalcohols adsorb with their hydrophobic part towards the silver iodide. These features are also encountered with the mercury system. Differences between the two systems are quantitative rather than qualitative, e.g., the Gibbs free energies of adsorption on silver iodide are about 25% less negative than the corresponding ones on mercury.