Ferri/ferrocyanide redox couple

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... 

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,... 

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

Fig. 9 shows the titration results for the following samples chloroplast lamellae and TSF-1 particles, both measured at 820 nm, and the CPI complex measured at 820 as well as 703 nm. Each sample was titrated oxidatively (starting with 100 pM ferrocyanide and adding ferricyanide to a maximum concentra tion of 10 mM) and reductively (starting with 1-5 mM ferricyanide and adding ferrocyanide to a maximum concentration of 10 mM). The titration is a plot of the light-induced AA V5. the actual redox-potential of the medium or the ferri-/ferrocyanide ratio as shown in Fig. 9. The plot of the data points clearly show that the titration was completely reversible and that P700 was in redox equilibrium with the ferri-/ferro-cya-nide couple. The solid line is the theoretical Nernst curve for a one-electron transition and the data points agree well with the theoretical course. The titration curve for both the chloroplast lamellae and the TSF-1, as well as D144 (data not shown here), yielded an value of+492 mV.

FIG. 17 Reversal of the photocurrent sign upon replacing the electron donor DCMFc (a) by the electron acceptor TCNQ (b) in the presence of the porphyrin heterodimer ZnTMPyP-ZnTPPS at the water-DCE interface. The strong back electron-transfer features in the photoreduction of TCNQ were diminished upon addition of an equimolar ratio of ferri/ferrocyanide acting as supersensitizer in the aqueous phase (b). The mechanism of supersensitization is described in Fig. 11. From the potential relationship between these redox couples (Fig. 4), these phenomena can be regarded as interfacial photosynthetic processes as defined in Fig. 3(b). (Reprinted with permission from Ref. 87. Copyright 1999 American Chemical Society and from Ref. 166 with permission from Elsevier Science.)... 

Using the same approach as in analyzing chain (2), it would be of interest to trace how common is the coupling of the main redox reaction with the oxidation of membrane lipids. To this end, an investigation was made of the dark transmembrane potentials on bilayers formed from egg lecithin with cholesterol, modified by chlorophyll in the presence of such redox systems as ferri-ferrocyanide, NADP-ferrocyanide, NAD-ferrocyanide.103... 

That being said, Chang and coworkers [162,163] reported improved activity for Pt/TTO for the ORR and the ferri/ferrocyanide (FEFI) redox couple, Eq. (24.10). 

ET potential. This process involves the diffusion of four species, consequently, if the concentration of the reactants in both phases is similar, then rather large peak-to-peak separations could be observed [24]. In the particular case of Fig. 1, the redox couple in the aqueous phase is largely in excess with respect to the organic phase, therefore its concentration can be taken as constant and the ET rate is only controlled by the diffusion of tetracyanoquinodimethane (TCNQ). Under these conditions, commonly referred to as the constant composition approximation, the aqueous phase behaves as a solid electrode with the Fermi level defined by the electrochemical potential of the ferri/ferrocyanide couple. 

Anhydrous NiO has been studied in the form of mosaic crystals [(100) orientation] doped with 0.1%-10% Li. This material is ap-type semiconductor and hence cathodic processes such as O2 reduction would be expected to be inhibited. Examination of redox couples such as ferri-ferrocyanide with the rotating disk technique do indicate cathodic inhibition in acid solutions with the anode branch under combined kinetic and diffusion control. Differential capacitance measurements in acid solutions indicate that most of the electrode potential change occurs across the space charge region within the NiO (0.1% Li) at electrode potentials cathodic to 0.8 V vs. In... 

One simple way of characterization of CNT/MN4 electrodes using electrochemical techniques like cyclic or linear voltammetry is using a well-known redox probe, for example, the couple ferri/ferrocyanide, Fe(CN)6 /Fe(CN)6. The MWCNT-BPPG... 

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