The Transient Behavior of Graphite-Silver Iodide and Platinum-Silver Iodide Interfaces in a Solid-State System

The electrochemical characteristics of the interface formed by solid silver iodide in contact with either platinum or graphite have been studied by linear sweep voltammetry, chronopotentiometry, and the potential and current step techniques. The results indicate that the graphite-silver iodide interface exhibits pure double-layer behavior over the potential range of 0.03 to +0.46V (vs. Ag/AgI), with no frequency dispersion effects observed up to approximately 1 MHz. In contrast, pure double-layer behavior could not be isolated for the platinum-silver iodide case under the same conditions. It is suggested that, for cathodic potentials, this is due to the rapid discharge of silver atoms onto the platinum surface at subunit activity, and at anodic potentials to liberation of iodine. Comparison of the two electrode systems in terms of recent ideas concerning molten salt double-layer behavior indicates that in both of these systems, the double layer is essentially determined by the structure of solid Agl. The graphite interface behaves very much in an ideally polarized manner while the platinum interface behaves very much as an ideally reversible system because of the rapid faradaic reactions prevalent throughout the entire accessible potential range.