engleski

A comparative study of the anion transfer kinetics across water|nitrobenzene interface by means of electrochemical impedance spectroscopy and square-wave voltammetry at thin organic film-modified electrodes

Kinetics of the transfer of a series of hydrophilic monovalent anions across the water|nitrobenzene (W|NB) interface has been studied by means of thin organic film-modified electrodes in combination with electrochemical impedance spectroscopy and square-wave voltammetry. The studied ions are: Cl-, Br-, I-, ClO4-, NO3-, SCN- and CH3COO-. The electrode assembly comprises of a graphite electrode (GE) covered with a thin nitrobenzene film containing a neutral strongly hydrophobic redox probe (decamethylferrocene or lutetium bis(tetra-tert-butylphthalocyaninato)) and an organic supporting electrolyte. The modified electrode is immersed in an aqueous solution containing a supporting electrolyte and transferring ions, and used in a conventional three-electrode configuration. Upon oxidation of the redox probe, the overall electrochemical process proceeds as an electron-ion charge transfer reaction coupling the electron transfer at the GE|NB interface and compensating ion transfer across the W|NB interface. The rate of the ion transfer across the W|NB interface is the limiting step in the kinetics of the overall coupled electron-ion transfer reaction. Moreover, the transferring ion that is initially present in the aqueous phase only at a concentration lower than the redox probe, controls the mass transfer regime in the overall reaction. A rate equation describing the kinetics of the ion transfer valid for the conditions at thin organic film-modified electrodes is derived. Kinetic data measured with two electrochemical techniques are in very good agreement.

ion transfer kinetics; electrochemical impedance spectroscopy; square-wave voltammetry; liquid|liquid interface; quasireversible maximum

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