酸性介质中碘离子在铂电极上的电化学氧化行为

采用循环伏安法研究了酸性介质中碘离子在铂电极上不同电位区间, 不同酸度下的电化学反应行为. 结果表明, 当极化电位较低(小于0.6 V(vs Hg/Hg2SO4))时, 碘离子在铂电极上发生2I--2e→I2电氧化反应, 反应产物通过I2+I-=I-3被进一步溶解, 整个反应属于E-C(electrochemical-chemical)模式. 电氧化过程中可以形成碘膜, 其也可以被碘离子溶解. 当极化电位升高至0.6 V(vs Hg/Hg2SO4)或以上时, 碘离子会直接电氧化为高价态碘化合物, I-+3H2O→IO-3+6H++6e, 而析出的碘膜并不发生再氧化反应; 在电化学还原过程中, 出现了两个还原峰, 分别对应于I2、I-3的还原反应; 在无碘膜时, 碘离子电氧化过程受溶液中碘离子的液相扩散步骤控制; 碘膜形成后, 主要受碘膜中碘离子的固相扩散控制; 酸度对于碘离子的电化学氧化过程有很大的影响, 其线性极化曲线的起峰电位及电流峰值电位均随酸浓度升高而负移.

Electrochemical Oxidation Behavior of Iodide on Platinum Electrode in Acid Solution

The oxidation behavior of iodide ion on platinumelectrode 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 filmcan be formed during electrochemical oxidation process and dissolved by chemical reaction of I2+I-=I-3 . When the electrode was polarized to over 0.6 V(vs Hg/Hg2SO4), high-valent iodine-containing compounds could be formed by I-+3H2O→IO-3+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.