P-3 電気化学反応の電荷移動過程における超音波の照射効果(ポスターセッション)
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概要
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Investigations show that continuous ultrasound irradiation produces enhanced mass transport in electrochemical systems. No detailed work, however, has been undertaken in the evaluation of the effect of ultrasound on homogeneous electron transfer reactions in the electrode / solution interface because the electrochemical reactions always associate with the diffusion controlled processes. Electrochemical AC impedance spectroscopy is useful to study the kinetics at the interfaces and to distinguish between the various mechanisms which regulate the charge transfer based on a Randles equivalent circuit of electrolytic cell. The impedance experiment results in the present study indicated that there are two frequency regions, as at high and low, which can be used to distinguish the change in faradic impedance (charge transfer resistance) from the Cole-Cole plot for electrochemical reactions. In a stationary solution, a straight line was observed at low frequencies corresponding to the linear diffusion process electrochemical species, known as the Warburg impedance. This component, however, was disappeared under the ultrasound irradiation, and a semi-circle related to the faradic charge-transfer behavior was observed in spectrum. This phenomenon indicated that stronger ultrasound perturbations produced a limited thin diffusion layer so that the bulk concentration and surface concentration of electrochemical species did not differ appreciably. As a result, the Warburg element was omitted from the Randles equivalent circuit. As the width of the semi-circle giving the rate constant in the the heterogeneous charge-transfer process, AC impedance provided the necessary information in heterogeneous electron transfer rate constants for electroactive species during sonication. The charge transfer processes of an reversible electrochemical system (1 mM Fe(CN)_6^<3-> in 0.1 M KCl), a quasi- reversible system (1 mM Fe(CN)_6^<3-> + SDS in 0.1 M KCl) and an irreversible system (1 mM ascorbic acid in 0.1 M KCl) were examined with the proposed method. Ultrasound provided little effect on the reversible electrochemical system, but greatly enhanced the charge transfer rate constant for irreversible reaction in the process of electrochemical oxidation of ascorbic acid.
- 日本ソノケミストリー学会の論文
- 2004-11-11