ITIES charge transfer kinetics

Recent fundamental improvements in experimental methods for studying the structure and kinetics at ITIES, on the one hand, and theoretical developments in describing the double layer structure and charge transfer kinetics - the contributions mainly from the field of statistical mechanics - on the other hand, have provided us with factual and conceptual means of elucidating dynamic aspects at ITIES. 

Charge Transfer Kinetics at Water-Organic Solvent Phase Boundaries 2.3.2 Inner Layer and Potential Profile Across the ITIES... 

Progress in experimental and theoretical studies of the mechanistic and dynamic aspects of charge transfer at the ITIES is developing swiftly. The present reviews is therefore deemed to be a status report concerning the charge transfer kinetics at the ITIES, rather than a systematic presentation of the subject. 

On the one hand, the thermodynamic realities of the ITIES, e.g., electrocapillarity and standard ion transfer potential, have been well established. On the other hand, our knowledge of charge transfer kinetics is less solid. Although traditional macroscopic concepts appear to be applicable at least as a first approximation, there is still a rift between macroscopic views and microscopic understanding. 

These spectroscopic and theoretical developments have stimulated the recent advances on electron-transfer dynamics at ITIES. In addition to the correlation between structure and dynamics of charge transfer, fundamental problems in connection with the energetics of ET reactions remain to be fully addressed. We shall consider these problems primarily before discussing kinetic aspects in full detail. 

Potential differences at the interface between two immiscible electrolyte solutions (ITIES) are typical Galvani potential differences and cannot be measured directly. However, their existence follows from the properties of the electrical double layer at the ITIES (Section 4.5.3) and from the kinetics of charge transfer across the ITIES (Section 5.3.2). By means of potential differences at the ITIES or at the aqueous electrolyte-solid electrolyte phase boundary (Eq. 3.1.23), the phenomena occurring at the membranes of ion-selective electrodes (Section 6.3) can be explained. 

The primary purpose of this review is to summarize comprehensively advances in the study of this kinetic aspect of charge transfer across ITIES since 1981, when Koryta and Vanysek gave a timely review at that early stage of the development of electrochemistry at ITIES. Reviews [5-14] and monographs [15, 16] are available of other aspects of the electrochemistry at ITIES, e.g., ion transfer facilitated by ionophores, applications to analytical purposes or to liquid extraction, and instrumentation. In a recent review on charge transfer across ITIES, Girault [14] addressed key issues regarding the mechanism of ion transfer the dependence of the rate constant of ion transfer on the applied potential, the presence of an activation barrier, the double layer correction, the effect of solvent viscosity, theoretical treatments, etc. Since the author s [14] opinions differ in several respects from ours, we have tried to review this subject as systematically and critically as possible. 

The nonideality of both polarized ITIES and nonpolarized ITIES, the latter of which is usually employed as a reference ITIES to define the potential of the organic phase, often poses experimental difficulty in obtaining reliable kinetic parameters of charge transfer and double layer capacitance. It is worth considering in depth the degree of ideality of both ITIES before dealing with the kinetics of charge transfer at ITIES. 

Kinetics of Charge-Transfer Reactions at the Nano-ITIES.557... 

The concentration of the transferred ion in organic solution inside the pore can become much higher than its concentration in the bulk aqueous phase [15]. (This is likely to happen if r <5c d.) In this case, the transferred ion may react with an oppositely charged ion from the supporting electrolyte to form a precipitate that can plug the microhole. This may be one of the reasons why steady-state measurements at the microhole-supported ITIES are typically not very accurate and reproducible [16]. Another problem with microhole voltammetry is that the exact location of the interface within the hole is unknown. The uncertainty of and 4, values affects the reliability of the evaluation of the formal transfer potential from Eq. (5). The latter value is essential for the quantitative analysis of IT kinetics [17]. Because of the above problems no quantitative kinetic measurements employing microhole ITIES have been reported to date and the theory for kinetically controlled CT reactions has yet to be developed. 

The kinetics of ion transfer across ITIES is closely linked to the double-layer structure. The concentration of the ion transferred in each phase close to the plane dividing the both phases is related to the concentration outside the space charge region by the Boltzmann formula, for example, for the aqueous phase (cf. [9])... 

More recently, this topic has been revisited by Daikhin and Urbakh [88] who presented a kinetic description of ionic surfactant transfer across an ITIES that includes the charging of the interface, adsorption, and transfer as well as characteristics of the electrical circuit. This model showed that the irregular current oscillations are due to a dynamic instability induced by the interplay between the potential-dependent adsorption and direct transfer across the interface. In particular, this model showed that current anomalies occur in a potential range close to the standard ion-transfer potential. 

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