Disk electrodes reaction with

Shigehara K, Oyama N, Anson FC (1981) Evaluation of rate constants for redox selfexchange reactions fi om electrochemical measurements with rotating-disk electrodes coated with polyelectrolydes. Inorg Chem 20 518-522... 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. 

The values of that can be realized experimentally vary between 5 X 10 " cm/s (natural convection) and 2 X 10 cm/s (rotating-disk electrode at/= 10,000 rpm). Therefore, reactions for which 10 cm/s will remain reversible whatever the stirring intensity. Such reactions are called completely reversible ( very fast ). Reactions with 10 cm/s will always be irreversible and are called completely irreversible ( very slow ). In the region of intermediate values of the constant, the character of the reaction will depend on stirring conditions. With other values of a and of ratios idfJid,on the boundaries between the various regions of electrode operation will shift slightly, but the overall picture of the phenomena remains the same. 

Figure 8.12 Relationships between the catalytic properties and electronic structure of Pt3M alloys correlation between the specific activity for the oxygen reduction reaction measured experimentally by a rotating disk electrode on Pt3M surfaces in 0.1 M HCIO4 at 333 K and 1600 lev/min versus the li-band center position for (a) Pt-skin and (b) Pt-skeleton surfaces. (Reprinted with permission from Stamenkovic et al. [2007b]. Copyright 2007. Nature Pubhshing Group.)...

We consider the investigation of two consecutive electron-transfer reactions with a ring-disc electrode under stationary conditions. A species A reacts in two steps on the disk electrode first to an intermediate B which reacts further to the product C. The intermediate is transported to the ring, where the potential has been chosen such that it reants bank to A. The overall scheme is ... 

The absence of dimer radical cation formation by diphenyl selenide under the pulse radiolysis conditions is in contrast to bimolecular reactions believed to occur under electrochemical conditions/ In these experiments, a rotating disk electrode was used in combination with commutative voltammetry under anhydrous conditions. The results led to the conclusion that reversible one-electron oxidation is followed by disproportionation, then reaction of the resulting dication with diphenyl selenide or an external nucleophile, with the likely intermediacy of the dimer dication (Fig. 33). As expected, the dihydroxy selenane is formed when water is present. Based on the kinetics of the electrochemical reaction, the authors believe the diselenide dication, not the radical cation, to be the intermediate that reacts with the nucleophile. 

A precondition for an appropriate decision in the planning of a preparative electroorganic synthesis is sufficient information about the electrochemical reaction. As far as possible, knowledge about the influence of parameters such as temperature, solvent, pH value, and stirring rate should be included. Electroanalytical standard methods to acquire such data have been discussed in Chapter 1 cyclovoltammetry as an especially valuable tool and its combination with the rotating disk electrode method for additional knowledge. At... 

Figure 2.21 shows the dependence of dimensionless net peak currents of ferrocene and ferricyanide on the sphericity parameter (note that A0p = AT], andy = p)-The SWV experiments were performed at three different gold inlaid disk electrodes (ro = 30, 12.5 and 5 pm) and the freqnencies were changed over the range from 20 to 2000 Hz [26]. For ferrocene the relationship between AT], and p is linear A Fp = 0.88 + 0.74p. This indicates that the electrode reaction of ferrocene is elec-trochemically reversible regardless of the frequency and the electrode radius over the range examined. For ferricyanide the dependence of AT], on p appears in sequences. Each seqnence corresponds to a particular value of the parameter The results obtained with the same freqnency, but at different microelectrodes, are cormected with thin, broken lines. The difference in the responses of these... 

Additives can be consumed at the cathode by incorporation into the deposit and/or by electrochemical reaction at the cathode or anode. Consumption of coumarin in the deposition of nickel from a Watts-type solution has been studied extensively. Thus, in this section we discuss the consumption of coumarin, which is used as a leveler and partial brightener. In a series of papers (33, 36), Rogers and Taylor, described the effects of coumarin on the electrodeposition of nickel. They found that the coumarin concentration decreases linearly with time at —960 mV (versus SCE and 485 to 223 rpm at a rotating-disk electrode, for plating times of 8 to 75 min. A rotating-disk electrode was used to achieve a uniform and known rate of transport of additive to the cathode. Rogers and Taylor found that the rate of coumarin consumption is a function of coumarin bulk concentration. Figure 10.16 shows that the rate of consumption... 

Frumkin and Nekrassow then applied Levich s equation to an analysis of intermediate production when the intermediate could leave the electrode surface, with the possibility of reacting again at the ring or leaving for the bulk. Damjanovic et aL developed the Ivanov and Levich equation to include a term, x, the ratio of the velocity of the two parallel reactions (A) and (B), thus increasing the helpful information obtained by using the equation. Damjanovic et al. s equation for the ratio of disk current to ring current is... 

Are Rotating Disk with Ring Electrodes Still Useful in the Twenty-first Century When the rotating disk electrode was first used, it was the 1960s since that time, many new methods for measuring electrode reactions (above all, spectroscopic ones, e.g., those in Section 7.5.15), have been invented. Furthermore, microelectrodes have made it possible, in effect, to reduce 5 by as much as 1000 times compared with that in a still solution, so that one of the uses of the rotating disk... 

Other Unusual Electrode Shapes. Various modifications of the rotating disk electrode are described in the literature. For example, the rotating disk electrode with ring sometimes suffers from bubbles that collect in the cotter and make it difficult to determine the fraction of the disk available for electrode reactions. One remedy is to use a cone-shaped electrode the ring is on the side of the cote and the disk at the tip. Bubbles don t like tips and skelter. 

Assume that the reaction ox + c <=> red at the planar electrode is diffusion controlled. Sketch and correlate the concentration profiles Cox =f(x), where x is the distance from the electrode surface to the bulk of the solution, with the shape of the current-potential curve for electrolysis carried out at (a) a stationary disk electrode and (b) a rotating disk electrode. Support your explanation by the equations. (Skompska)... 

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