Dynamic instabilities and mechanism of the electrochemical oxidation of thiosulfate

The electrochemical oxidation of thiosulfate is revealed to have two distinct oscillatory regimes in both linear potential and galvanic voltammograms, where various nonlinear behaviors such as period-2, mixed-mode and quasi-periodic oscillations, and chaos are observed under potentiostatic or galvanostatic conditions. Electrochemical impedance spectroscopy and iR compensation characterization indicate that, depending on the operating conditions, the system could be either a strictly potentiostatic oscillator or an S-shaped negative differential resistance oscillator. Chronoamperometry measurements reveal that the first oscillatory process involves a single-electron transfer, whereas within the second oscillatory regime the average number of electrons transferred is around 3.8. Measurements with capillary electrophoresis and chemical methods illustrate that the oxidation products include S2O6(2-), S4O6(2-), S5O6(2-), S3O6(2-), and SO4(2-).