Supporting electrolyte voltammetric

Fig. 4.7 Voltammetric behavior of a Au(lll) electrode immersed in 1 mM Se02 in 0.100 M HCIO4 supporting electrolyte. The five major cathodic waves corresponding to Se deposition are labeled C1-C5, respectively. The scan rate was 0.100 V s. (Reprinted from [82], Copyright 2009, with permission from Elsevier)...

Heterogeneous ET reactions at polarizable liquid-liquid interfaces have been mainly approached from current potential relationships. In this respect, a rather important issue is to minimize the contribution of ion-transfer reactions to the current responses associated with the ET step. This requirement has been recognized by several authors [43,62,67-72]. Firstly, reactants and products should remain in their respective phases within the potential range where the ET process takes place. In addition to redox stability, the supporting electrolytes should also provide an appropriate potential window for the redox reaction. According to Eqs. (2) and (3), the redox potentials of the species involved in the ET should match in a way that the formal electron-transfer potential occurs within the potential window established by the transfer of the ionic species present at the liquid-liquid junction. The results shown in Figs. 1 and 2 provide an example of voltammetric ET responses when the above conditions are fulfilled. A difference of approximately 150 mV is observed between Ao et A" (.+. ... 

In the second category, SECMIT has been used to probe the relative permeability of oxygen between water and DCE or NB, with no supporting electrolyte present in any phase. Under the conditions employed, direct voltammetric measurements in the organic phase would be impractical due to the high solution resistivity (DCE or NB) or limitations of the solvent window available (NB). Figure 24 shows the steady-state current for the... 

In 1985, Sullivan et al. reported a voltammetric study on (Bipy)Re[CO]3Cl in acetonitrile with tetrabutylammonium hexafluorophosphate (TBAHFP) as the supporting electrolyte. 

Electrochemical studies of the behaviour of [100] (5 X 10 4 mol dm-3 in dichloromethane solution containing 0.1 mol dm-3 [NBu"]BF4 as supporting electrolyte) have been carried out using cyclic and square-wave voltammetric techniques. The receptor itself undergoes two quasi-reversible oxidations at Epi = +350 mV and Ep2 = +450 mV referenced to Ag/Ag+. Rotating disk... 

Table 1 Typical tabulation of cyclic voltammetric data. [Fe(f-C5H )2)] solution (1.0 X 10 3 mol dm 3) in CH2CI2. Supporting electrolyte [NBu4][PF6] (0.2 mol dm 3). Platinum disc electrode radius = 1 mm. Potential values are referred to SCE...

Figure 18 Cyclic voltammetric responses at different temperatures of ferrocene in a 16 17 1 chloroethane tetrahydrofuran 2-methyl-tetrahydrofuran solution containing LiBF4 (0.6 mol dm 3) as supporting electrolyte, (a) Platinum electrode (b) Tl 1223 ( Tl0.sPbo.s Sr2Ca2Cu306). Scan rate 0.025 V s. Potential values are referred to a pseudo-reference silver wire...

The situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

To favor the coupling reaction, the competing side reaction of the radical cation with nucleophiles must be suppressed by the use of a medium of low nucleophilicity. The solvent of choice is dichloromethane. Especially in elec-troanalytic studies, neutral alumina is frequently added to suppress hydroxy-lation of the radical cation [162]. The reversible cyclic voltammetric behavior of radical cations is also enhanced in mixtures of methylene dichloride, triflu-oroacetic acid, and trifluoroacetic anhydride (TFAn) with TBABF4 as supporting electrolyte. With acetonitrile as solvent... 

As indicated above, all of the experimental data reported thus far were obtained at low concentrations of both supporting electrolyte (mM) and electroactive species (pM). This was done because we have observed an interesting effect of supporting electrolyte concentration on the shape of the voltammetric waves observed at the NEEs [25]. We have found that the reversibility of the voltammetric waves for all couples investigated to... 

Examination of the behaviour of a dilute solution of the substrate at a small electrode is a preliminary step towards electrochemical transformation of an organic compound. The electrode potential is swept in a linear fashion and the current recorded. This experiment shows the potential range where the substrate is electroactive and information about the mechanism of the electrochemical process can be deduced from the shape of the voltammetric response curve [44]. Substrate concentrations of the order of 10 molar are used with electrodes of area 0.2 cm or less and a supporting electrolyte concentration around 0.1 molar. As the electrode potential is swept through the electroactive region, a current response of the order of microamperes is seen. The response rises and eventually reaches a maximum value. At such low substrate concentration, the rate of the surface electron transfer process eventually becomes limited by the rate of diffusion of substrate towards the electrode. The counter electrode is placed in the same reaction vessel. At these low concentrations, products formed at the counter electrode do not interfere with the working electrode process. The potential of the working electrode is controlled relative to a reference electrode. For most work, even in aprotic solvents, the reference electrode is the aqueous saturated calomel electrode. Quoted reaction potentials then include the liquid junction potential. A reference electrode, which uses the same solvent as the main electrochemical cell, is used when mechanistic conclusions are to be drawn from the experimental results. 

Fig. 28 Reductive electrochemistry data for (72). Cyclic voltammetric curves for a 0.1-mM CH2CI2 solution of (72) at 100 mV s , glassy carbon as a working electrode, Pt-mesh as a counter electrode, and a Ag wire as a quasi-reference electrode, T = 25 °C, TBAPFs (0.1 M) was used as supporting electrolyte.

U(III) species and a second three-electron reduction to give U(0) metal. The first reduction, U(IV)/U(III) couple, is elec-trochemically and chemically irreversible except in hexamethylphosphoramide at 298 K where the authors report full chemical reversibility on the voltammetric timescale. The second reduction process is electrochemically irreversible in all solvents and only in dimethylsulfone at 400 K was an anodic return wave associated with uranium metal stripping noted. Electrodeposition of uranium metal as small dendrites from CS2UCI6 starting material was achieved from molten dimethylsulfone at 400 K with 0.1 M LiCl as supporting electrolyte at a platinum cathode. The deposits of uranium and the absence of U CI3, UCI4, UO2, and UO3 were determined by X-ray diffraction. Faradaic yield was low at 17.8%, but the yield can be increased (55.7%) through use of a mercury pool cathode. 

In this work it was also shown that [C4CiIm][PFJ is suitable for extraction-voltammetric determination of phenols without back-extraction or adding a support electrolyte. 

However, the same workers performed a series of interesting voltammetric measurements [182] on dibutylmethylamine (DBMA), fluorinated dibutyl-methylamine (F-DBMA), HF-phase (protonated and unprotonated) in acetonitrile, with (Bu)4NBF4 as supporting electrolyte, both on platinum and nickel anodes. Their results are set out in the table below. 

The supporting electrolytes influence polarographic and voltammetric measurements in the manners as described below ... 

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