Current oscillations during iodide oxidation at a gold rotating disk electrode

Oscillations in the electrode current were observed during the potentiostatic oxidation of iodide at a gold rotating disk electrode. In a 0.10 M KI solution, the oscillations were periodic, with a peak-to-peak amplitude equal to 70% of the peak current and a frequency of approximately 2 Hz. The oscillations continued for longer than 10 min, at which point the experiment was discontinued. Periodic oscillations in current were observed only for a narrow range of applied potentials, from 1.08 to 1.13 V vs. SCE in 0.10 M Kl. At lower concentrations of KI, the oscillations were less periodic, had a smaller amplitude, and were sustained for shorter times (about 30-60 s for 20 mM KI). No oscillations were observed for concentrations less than about 5 mM. Maximum and minimum current values were measured from the oscillating currents observed at various rotation rates, and the resulting linear plots of inverse current ra. inverse square root of rotation rate gave ii values of 1.28 and 0.24, respectively. Based on these results, a mechanism is discussed that involves the periodic formation and dissolution of a thick I?(s) film. The presence of this film decreases the rate of oxidation of iodide to iodine, thus yielding an apparent n value of less than one. (C) 1999 The Electrochemical Society. S0013-4651 (98)06-075-3. All rights reserved.