Voltammetry of lodine(I) Chloride, Iodine, and lodate at Rotated Platinum Disk and Ring-Disk Electrodes

The voltammetry of I, l₂, l⁻, and IO₃⁻ has been studied using platinum-ring disk electrodes. The l⁺/l₂ (in acid chloride medium) and l₂/l⁻ systems are reversible and the diffusion coefficients (× 10⁵, cm²/sec) of these species are: ICl −1.16, l₂ −1.05 and l⁻ −1.72 at 25°C, µ = 0.5. The oxidation of l⁻ to ICl is rapidly inhibited by the formation of a film of the electrode surface, while the oxidation of l⁻ to l₂ is not. During a large scale electrolysis of an l~ solution, in ClO₄⁻ medium, l₂ is the first product and then l₂ is irreversibly oxidized to IO₃⁻. Using a ring-disk electrode it was demonstrated that oxidation of I⁻ to IO₃⁻ at a platinum electrode becomes significant at potentials more positive than +1.15 V vs. SCE in 0.1M HCIO₄ (+0.4M NaCIO₄). IO₈⁻ is reduced to I⁻ at a platinum electrode in acid chloride medium via a catalytic process. I⁻ formed by the highly irreversible reduction of IO₃⁻ reacts with IO₃⁻ to form I₂, which is then electroreduced to I⁻.