Iodine adsorption studies at platinum

Adsorption and desorption of iodine-containing species were studied using the electrochemical quartz crystal microbalance (EQCM), and the rotating ring-disk electrode (RRDE) techniques in 0.2 mol/dm³ sulfuric acid + 2 mmol/dm³ potassium iodide. The EQCM method showed that ca. 0.4 monolayer of iodine-containing species was adsorbed at the potential 0.2 V vs. SCE, with no concomitant faradaic process. At potentials on the limiting current region for th oxidation of iodide to iodine, one monolayer of adsorbed iodine was found using the EQCM technique. Charge and flux data obtained using the RRDE in the potential range 0.2 V to 0.8 V vs. SCE agree with the overall reaction sequence I^-_Soln + ?_ads = I_ads + ? + 2e^-, i.e., the charge passed at the disk was twice that required to account for the total adsorbed iodine formed from dissolved iodide ion. The assignment of the chemical identity of ?_ads to H^._ads is discussed in light of the previous literature dealing with the adsorption of iodine-containing species at platinum.