Electrode three-phase

Bouchard, G., Galland, A., Garrupt, P. A., Gulaboski, R., Mirceski, V., Scholz, F., Girault, H. H. Standard partition coefficients of anionic drugs in the n-octanol/water system determined by voltammetry at three-phase electrodes. Phys. Chem. Chem. Phys. 2003, 5, 3748-3751. 

Three-Phase Electrodes and Their Application to Measnre the Energy of Ion Transfer Across Liqnid-Liqnid Interface... 

Three-phase electrodes have been constracted in two major configurations. Most frequently, it consists of a paraffin-impregnated graphite electrode (GE) modified with a macroscopic droplet of a water immiscible organic solvent (O) (e.g., nitroben-... 

Fig. 4.2 Scheme of a part of the three-phase electrode consisting of pyrolytic graphite electrode modified with an uneven thin film of an organic solvent covering partly the electrode surface and containing a neutral redox probe... 

Figure 4.3 shows a representative voltarmnogram recorded at a three-phase electrode with a droplet configuration consisting of DMFC as a redox probe and nitrobenzene as the organic solvent. The oxidation of DMFC to decamethyUerrocenium cation... 

The application of three-phase electrodes for determining the energy of ion transfer is based on precise measurements of the formal potential of reaction (4.1). The latter is defined as [4,5] ... 

Fig. 4.3 Forward (7f), backward (4) and net (/net) components of the voltammetric response recorded at a three-phase electrode with a droplet configuration consisting of a paraffin impregnated electrode and a nitrobenzene solution of DMFC at 0.1 mol/L concentration. The electrode is immersed in 1 mol/L aqueous solution containing SCN anions. The other experimental conditions are / = 100 Hz, = 50 mV, and AE = 0.15 mV (reprint from [7] with permission)...

Equation (4.2) predicts a linear dependence of Efvs. A with a slope 1, and a linear dependence between Ef vs. log(o ) with a slope 2.303. These two dependencies can serve as diagnostic criteria to identify the electrochemical mechanism (4.1). Figure 4.4a shows the effect of different anions on the position of the net peak recorded at the three-phase electrode with a droplet configuration, where DMFC is the redox probe and nitrobenzene is the organic solvent. Figure 4.4b shows the linear variation of the net peak potential with A, with a slope close to 1. Recalling that the net peak potential of a reversible reaction is equivalent to the formal potential of the electrochemical reaction (Sect. 2.1.1), the results in Fig. 4.4 confirm the validity and applicability of Eq. (4.2). 

The three-phase electrode with a thin-film configuration (Fig. 4.2) has been mainly used in combination with nitrobenzene as an organic solvent and lutetium bis(tetra-i-butylphthalocyaninato) complexes as a redoxprobe (LBPC) [21,23]. Figure 4.5 depicts a typical voltammogram recorded with this redox probe in contact with 0.1 mol/L aqueous solution of KNO3. LBPC can be both oxidized and re-... 

PCM and C" " are the cations exchanged between the PCM and the electrolyte solution. In Eq. (I), three different phases are indicated, phase I being the metal that conducts the electrons to or away from the PCM, phase II being the solid PCM, and phase III being the electrolyte solution. The three phases constitute the essential feature of a so-called three-phase electrode as it is schematically depicted in Fig. 3. 

Fig. 3 Situation at a three-phase electrode where a phase II possessing redox center is in close contact with phase I that can provide or take away electrons, and with phase III that can exchange ions with phase II.

This nine (3 x 3) electrode dot device comprises a four-layer printed circuit board [100,101]. The first layer has a nine-phase electrode dot matrix. The entire electrode dot matrix consists of multiple 3x3 units. Each electrode has a hole in its center for connection to the electric circuits of the layers below. These layers were connected to external terminals. Sequential voltages were applied to the three-phase electrode columns and lines. 

Three-phase electrodes — Electrodes at which three phases are involved in the electrochemical reaction. See - three-phase boundary. 

Independent of the nature of the respective solid electroactive crystal, it is a main feature of these systems that the electron transfer takes place at the three-phase boundary microcrystal electrode electrolyte, and the (frequently even electrochemically reversible) electron transfer is accompanied by the transfer of cations or anions between the microcrystal and the electrolyte phase, in order to maintain electroneutrality. This situation of a three-phase electrode, where the immobilized electroactive solid phase is simultaneously in contact with an electron-conducting phase (e.g., a metal or graphite) and also with an electrolyte solution phase, is illustrated in Figure 6.1. 

Figure 6.1 Scheme of the simultaneous electron and ion transfer at a three-phase electrode. 

Figure 6.2 Possible pathways of the charge transfer reactions and the charge transport processes proceeding at a three-phase electrode consisting of an electrochemically active Phase II, and electrolyte solution (Phase III), and an electron conductor (Phase I). The electron flux shows the direction in which electrons can be transferred across the interface I/II and...

In an experimentally focused publication, the behavior of a three-phase electrode tvith a rather well-defined three-phase boundary has been studied [27]. For this, white elemental phosphorus was oxidized at a graphite electrode that was partly embedded in the solid phosphorus, and partly immersed in an aqueous electrolyte solution (see Figure 6.6c). 

The charge movement can be treated diffusion-like as electron hopping with coupled solution phase ion motion, contributing to the effective diffusion coefficient [34] (as in the studies cited for the general treatment of a three-phase electrode in Section 6.3.1). 

At the conditions of long-term stationary electrolysis, the intermediate valency titanium compounds are deposited at the electrode surface forming a three-phase electrode/film/metal system, which is also very commrMi in high-temperature melts. Due to the presence of mobile anion, the reduction of the film s substances to Ti metal... 

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