Ferrocyanide redox

Quinn et al. studied ET at micro-ITIES supported by micropipettes or microholes [16]. The studied systems involved ferri/ferrocyanide redox couple in aqueous phase and ferrocene, dimethylferrocene, or TCNQ in either DCE or o-nitrophenyl octyl ether. Sigmoidal, steady-state voltammograms were obtained for ET at the water-DCE interface supported at a micropipette. The semilogarithmic plot of E versus log[(/(j — /)//] was... 

Later measurements by Fouad and Gouda (F5), who used the ferri-ferrocyanide redox reaction, yielded a much lower coefficient in the free-convection correlation, Eq. (29a). However, uncertainty about the interfacial composition in free convection (S9a) may be responsible for the discrepancy observed in the results obtained with the redox system. Taylor and Hanratty (Tib) showed that the data of Fouad and Gouda could be... 

Figure 28.6 The current-potential response of an n-CdS/ferri/ferrocyanide cell under chopped irradiation in (488 nm, 40 mW/cm2). The ferri/ferrocyanide redox potential is marked in the diagram. Note that even when a dark cathodic current is present (solid line), a photocurrent is observed (spikes).

The Surface Potential arising from the Interaction between the Surface "States" and the Redox Couples in the Solution. When the ferricyanide/ferrocyanide redox couple is present in a 0.1 N NaOH solution, the dark cathodic current of the n-GaP (111)-face sets out at —1.1 V (SCE), showing that an electron transfer occurs... 

It is, however, to be pointed out that this simplified picture constitutes at the utmost a rough approximation to the real situation. In fact, a close examination of reorganization energies, derived from different series of experimental data shows large differences between X values of various ions and even between those concerning the same ionic species. Thus, for instance, the values of X mentioned in the literature for the ferricyanide/ferrocyanide redox couple vary from 0.4 to about 1.2... 

There have been fewer studies in electrochemistry where the flow is known but the boundary-layer approach is inapplicable. One example has been recently analyzed and compared with experiment. In this case, mass transfer to a line electrode or an array of line electrodes in the presence of an oscillatory shear flow was treated. A finite-volume approach was used for the numerical analysis and a ferri/ferrocyanide redox couple was used to measure the mass-transfer rate. The studies show that boundary-... 

Based on these ideas, Cunnane et al. [88] compared the oxidation of tin diphthalo-cyanine [Sn(PC)2] in the DCE phase by aqueous ferri/ferrocyanide redox couple under external polarization and in ideally nonpolarizable conditions. Good correlation for the formal redox potential measured in each case was observed. One of the main conclusions of this work is that the role of PT catalysts can be simply associated with polarization of the two-phase system, resulting in an enhancement of the interfacial concentration of the... 

Typical Applications EPR spectra were obtained for both the interfacial reduction of 7,7,8,8,-tetracyanoquinodi-methane (TCNQ) and oxidation of tetrathi-afulvalene (TTF), when dissolved in DCE by the aqueous phase ferri/ferrocyanide redox couple, following the application of a potential difference directly to the liquid I liquid interface. Previous work [111, 112] suggested that a charge-transfer process occurs at the liquid liquid interface, due to the heterogeneous reduction of TCNQ by the aqueous couple,... 

Case study 5.2 Ferri/ferrocyanide redox system... 

There are a number of systems that can be used to determine a limiting current density but in the authors opinion the ferri-ferrocyanide redox system dissolved in aqueous alkali (the latter stabilizes the complex ion and... 

Figure 1.21 Cyclic voltammograms of ferri/ferrocyanide redox couple on a bare Pt electrode surface.

Four rotation speeds are considered for the study of the ferri/ferrocyanide redox reaction 300, 1000, 1500 and 2000 rpm. Figure 4.a presents a comparison between the mean experimental voltammogram at 2000 rpm and the modeled voltammogram, calculated with the best-fit-parameters, and the 95% confidence interval 2cr, with cr the standard deviation of the current in the set of experimental curves. The difference between the experimental and the modeled curve (Figure 4.b) lies in the 95% confidence band. This means that the model is able to describe the experiments appropiately. 

The analytical modeling utilized for the RDE configuration is applied to the IRDE reactor. The experimental procedure described in section 4.1 is used for the LSV experiments of the ferri/ferrocyanide redox reaction on the IRDE. Eq. 29 is fitted to the mean polarization curves, obtained at 300, 1000 and 1500 rpm. The mean polarization curve is calculated from 11 independently recorded polarization curves. The 95 % confidence intervals of kox, k ed arid Oiox obtained at 300,1000 and 1500 rpm perfectly overlap (not shown). This means that the values of the charge transfer parameters, kox, and aox, are independent of the rotation speed, as expected theoretically. The calculated weighted mean values of the model parameters for charge transfer, kox, and Xox, are respectively 1.03E-08 m/s 1.31E-09 m/s, 9.12E-01 1.25E-01 m/s and 5.39E-01 7.06E-03. 

The redox potentials were determined by a chemical titration of the reaction center in tris-LDAO buffer at pH 7.8 with a potassium ferricyanide/ferrocyanide redox couple. The state of oxidation of the special pair was monitored by optical absorption spectroscopy. At most 70% reversibility to the original reduced state of the special pair was achieved with potassium ferrocyanide. At that point the solutions were so dilute that the concentration of the special pair could not be measured with sufficient accuracy. 

A typical outer-sphere charge-transfer reaction is the ferricyanide-ferrocyanide redox couple... 

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