Slow Heterogeneous Charge Transfer Kinetics for the ClO₂^-/ClO₂Redox Couple at Platinum, Gold, and Carbon Electrodes. Evidence for Nonadiabatic Electron Transfer

Abstract

Chlorite (ClO2 -) is one of the few simple aqueous anions that forms a stable product on one-electron oxidation. The heterogeneous charge transfer rate constants at E° = 0.700 V vs SCE for the ClO2 -/ClO2 redox couple have been measured at Au, Pt, and glassy carbon electrodes in aqueous KNO3 solutions using rotating disk and ac voltammetry techniques between 10 and 30 °C. At 25 °C in 1.0 M KNO3 and pH = 7, the standard heterogeneous rate constants k el were measured as 0.015 ± 0.001 cm/s and 0.014 ± 0.003 cm/s, respectively, at Au and reduced Pt electrodes. The transfer coefficient α on gold was measured to be 0.50 ± 0.01 using ac voltammetry. The heterogeneous rate constants obtained with the use of a glassy carbon electrode were slower (0.0079 ± 0.001 cm/s at 25 °C). The measured activation free energy for electron transfer at a gold electrode was 25 ± 3.3 kJ/mol with a preexponential factor of 310(+900/−230) cm/s. Heterogeneous rate constants of experiments performed in D2O solvent were only slightly slower than those measured in H2O, indicating that the redox couple does not exhibit differential hydrogen bonding. Digital simulation of cyclic voltammograms, with k el determined from the ac voltammetry and rotating disk techniques, gave good agreement with experiment. Marcus theory was applied to understand the unexpected slow heterogeneous kinetics for this simple redox couple. Additionally, the preexponential factor in the semiclassical expression describing heterogeneous electron transfer was examined. The slow electron transfer process is primarily attributed to a small preexponential factor that may arise from a high degree of nonadiabaticity in the electron transfer process.

Development of an automated on-line electrochemical chlorite ion sensor

“…Substituting 50 mM chlorate or perchlorate ions for chlorite ion could not be distinguished from the deionized water background. In the conventional cell (Figure 2 top), the peak separation, 98 mV, and the anodic-to-cathodic peak current ratio, 1.04, agreed with a previous report of general reversibility (11), including the absence of a coupled chemical reaction on the time scale of the experiment. The Pt working electrode was treated by evolution of H 2 at -2.0 V to reduce any oxide of Pt in that the reduction of chlorite was demonstrated to be sensitive to the condition of the Pt surface (11).…”

“…They reported a log[i/(i d – i)] vs. E plot showing a straight line with a slope of about 60 mV, which is consistent with a reversible, one-electron transfer reaction. The most thorough investigation of the electrochemistry of chlorite ion was performed by Sinkaset and Trogler using rotating disc and ac voltammetry to measure the heterogeneous rate constant (k el ) (11). The reported cyclic voltammogram of chlorite ion had a ΔE p of ~70 mV and an anodic-to-cathodic peak current ratio of ca.…”

A Miniaturized Carbon Black‐based Electrochemical Sensor for Chlorine Dioxide Detection in Swimming Pool Water

“…As depicted in Figure , an oxidation and reduction peak at around 0.6 V vs Ag/AgCl pseudoreference was observed in presence of ClO 2 using both bare and CB‐SPE. In agreement with the literature , this couple of the peaks is ascribed to the redox reaction of chlorine dioxide/chlorite ion: …”

Kinetic parameters for anodic oxidation of hypochlorite ion on Pt and Pt oxide electrodes in alkaline solution

“…The polished electrode was pretreated in an electrolytic solution by anodic or cathodic controlled electrolysis by bubbling N 2 gas for 15 min. The controlled electrolysis for 30 s at the anode and the cathode was +1.4 and −1.0 V, respectively [14,22,23]. The GC electrode was pretreated in a supporting electrolyte by a cyclic potential sweep for 15 min at the rate of 50 mV s −1 in the potential window range [4,20].…”

“…On the other hand, in (ii), there are many proposed methods for the electrode pretreatment: pulse [19], sweep [4,20], and laser ablation in recent years [21]. In particular, the reports on the platinum electrode, which formed an oxide film electrochemically [14,22] and as a result had a reduced surface area [23], are very interesting. Therefore, we believe that both kinetic knowledge and the understanding of the effect of the lattice oxygen on surface oxide are important for elucidating the electrode reactions.…”