Electrochemical Oxidation Behavior of Iodide on Platinum Electrode in Acid Solution

The oxidation behavior of iodide ion on platinum electrode in sulfuric acid media was investigated by the technique of cyclic voltammetry. The electrochemical performance showed that the electrochemical reaction of 2I--2e→ I2 occurred when the potential scanning range lowered than 0.6 V(vs Hg/Hg2SO4). The obtained cyclic voltammograms were affected by the formation of iodine film and triiodide species. The whole reaction performance is consistent with electrochemical-chemical (E-C) model. Iodine film can be formed during electrochemical oxidation process and dissolved by chemical reaction of I2+I-葑I3-. When the electrode was polarized to over 0.6 V(vs Hg/Hg2SO4), high-valent iodine- containing compounds could be formed by I-+3H2O→IO3- +6H++6e, not by iodine which was the product of anodic oxidation. Two reduction peaks occurred during reverse cathodic potential scanning and they could be assigned to the reduction of iodine film and triiodide ion in the solution, respectively. The anodic oxidation of iodide ion is controlled by the liquid-phase diffusion process of iodide ion when there is no iodine film formed on the electrode. However, when iodine film is formed on the electrode, solid-phase diffusion process of iodide ion through the iodine film would become the rate determining step. In addition, the acidity of the solution would affect the process of anodic oxidation of iodide ion seriously. The onset potential and peak potential corresponding to the anodic current in linear sweep voltammetry are shifted to lower direction with the increase of acid concentration.