Oscillations in the Electro-Oxidation of Thiourea on Platinum Electrode Studied by On-Line HPLC

Abstract

The oscillations in the electro-oxidation of thiourea on platinum electrode in perchloric acid were studied by the cyclic voltammetry and potentiostatic method combined with on-line HPLC. The effects of different scanning speed, initial concentration of thiourea and sampling on the current oscillations of thiourea were investigated, results showed that: (1) the lower scanning speed and higher initial concentration of thiourea facilitated the oscillations; (2) the sampling increased the oscillation current and oxidation peak current; (3) the intermediates formamidine disulphide (TU22+) and formamidine sulphinic acid (TUO2) were detected at different potentials on the surface of platinum electrode and concentration of TU, TU22+ and TUO2 all exhibited oscillations in the potentiostatic eletrolysis. The existence of a closed feedback loop formed by a series of reactions leaded to electrochemical oscillations of thiourea. This paper provides a new perspective and method for the study of electrochemical oscillations.

Electrooxidation of Formamidine Disulfide Simultaneously Investigated by On‐Line High Performance Liquid Chromatography and Cyclic Voltammetry

“…A schematic diagram of this device can be found in a previous paper. [9] For HPLC analysis, the mobile phase consisted of a mixture of methanol, acetonitrile, and 0.01 M hydrochloric acid (6 : 26 : 68, vol%). All the electrochemical experiments were carried out with a VSP‐300 electrochemical station (BioLogic).…”

“…[2][3][4][5] A variety of studies have shown that abundant nonlinear dynamical phenomena occur in the TU oxidation process. [6][7][8][9] As an intermediate of such processes, the TU 2 2 + exhibits different valence changes and various products, including oxides and free radicals, as well as the occurrence of autocatalytic and hydrolysis reactions. [10][11] A. E. Bolzán et al applied voltammetry and rotating ringdisk electrode techniques to study electrochemical response of thiourea and formamidine disulphide on polycrystalline platinum electrode.…”

“…[ 2 , 3 , 4 , 5 ] A variety of studies have shown that abundant nonlinear dynamical phenomena occur in the TU oxidation process. [ 6 , 7 , 8 , 9 ] As an intermediate of such processes, the TU 2 2+ exhibits different valence changes and various products, including oxides and free radicals, as well as the occurrence of autocatalytic and hydrolysis reactions. [ 10 , 11 ]…”

“…The on‐line high‐performance liquid chromatography (HPLC) combined voltammetry technique provides a novel way to determine the electrode intermediates involved in electrochemical reactions at a given potential. [ 9 , 15 , 16 , 17 ] Now this method is typically used for online detection of the species and concentration changes on the electrode surface. As shown in Figure 1 , a micro‐sized sample collection tip (inner diameter of 0.3 mm) was fixed on the surface of the working electrode.…”

“…Moreover, the electrode products cannot be measured quantitatively. The on‐line high‐performance liquid chromatography (HPLC) combined voltammetry technique provides a novel way to determine the electrode intermediates involved in electrochemical reactions at a given potential [9,15–17] . Now this method is typically used for online detection of the species and concentration changes on the electrode surface.…”