Rotating disk voltammetry

Town, J. L. MacLaren, F. Dewald, H. D. Rotating Disk Voltammetry Experiment, /. Chem. Educ. 1991, 68, 352-354. 

In situ electron transport measurements on conducting polymers are commonly made by using a pair of parallel-band electrodes bridged by the polymer [Fig. 9(A)].141142 Other dual-electrode techniques in which the polymer film is sandwiched between two electrodes [Fig. 9(B)],139,140 rotating-disk voltammetry [Fig. 9(C)],60,143 impedance spectroscopy,144,145 chronoamperometry,146 and chronopotentiometry147 have also been used. 

Rotating-disk voltammetry has a practical range of about 10 "9 to 10"4 S cm-1 and is particularly useful for investigating the conductivity of very... 

Figure 11. Cyclic votammetry (top) and in situ electronic conductivity from rotating-disk voltammetry [ , Fig. 9(C)] and sandwich electrode voltammetry [ , Fig. 9(B)] for poly(3-methylthiophene) in acetonitrile containing 0.1 M BU4CIO4.60 (Reprinted from J. Ochmanska and P. G. Pickup, In situ conductivity of poly-(3-methylthiophene) and (3-methylthiophene)x,-[Ru(2,2 -bipyridine)2 (3- pyrrol-l-ylmethyl pyridine)2]2+ copolymers, J. Electroanal. Chem. 297, 211-224, 1991, with kind permission from Elsevier Sciences S.A.)...

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

Rotating-disk voltammetry is the most appropriate and most commonly employed method for studying mediation. In most systems that have been studied, there has been little penetration of the substrate in solution into the polymer film. This can be demonstrated most easily if the polymer film is nonconductive at the formal potential of the substrate. Then the absence of a redox wave close to this potential for an electrode coated with a very thin film provides excellent evidence that the substrate does not penetrate the film significantly.143 For cases where the film is conductive at the formal potential of the substrate, more subtle argu-... 

Responses, electrochemical, during polymer formation, 400 Rotating disk voltammetry diagrammated, 569 in electrochemical polymer formation, 580... 

Appropriate electroanalytical procedures to verify the one or other case have been given in the references of this section. The main techniques are cyclic voltammetry, chronoamperometry, chronocoulometry, and rotating disk voltammetry. The last one appears to be best suited since constant mass transport in the film is a very important feature as outlined aixive Table 2 gives examples for... 

As the field of electrochemical kinetics may be relatively unfamiliar to some readers, it is important to realize that the rate of an electrochemical process is the current. In transient techniques such as cyclic and pulse voltammetry, the current typically consists of a nonfaradaic component derived from capacitive charging of the ionic medium near the electrode and a faradaic component that corresponds to electron transfer between the electrode and the reactant. In a steady-state technique such as rotating-disk voltammetry the current is purely faradaic. The faradaic current is often limited by the rate of diffusion of the reactant to the electrode, but it is also possible that electron transfer between the electrode and the molecules at the surface is the slow step. In this latter case one can define the rate constant as ... 

Ru" (0)(N40)]"+ oxidizes a variety of organic substrates such as alcohols, alkenes, THE, and saturated hydrocarbons. " In all cases [Ru (0)(N40)] " is reduced to [Ru (N40)(0H2)] ". The C— H deuterium isotope effects for the oxidation of cyclohexane, tetrahydrofuran, 2-propanol, and benzyl alcohol are 5.3, 6.0, 5.3, and 5.9 respectively, indicating the importance of C— H cleavage in the transitions state. For the oxidation of alcohols, a linear correlation is observed between log(rate constant) and the ionization potential of the alcohols. [Ru (0)(N40)] is also able to function as an electrocatalyst for the oxidation of alcohols. Using rotating disk voltammetry, the rate constant for the oxidation of benzyl alcohol by [Ru (0)(N40)] is found to be The Ru electrocatalyst remains active when immobilized inside Nafion films. 

Within these broad categories two principal classes may be distinguished, depending on whether current or voltage is the controlled parameter. The individuals in each class are often described by an operational nomenclature consisting of an independent-variable part followed by a dependent-variable part (i.e., volt-ammetry, chrono-potentiometry) with some system-specific modifiers (i.e., rotating disk voltammetry). Unfortunately, the whims of history have left the electrochemical nomenclature in a rather confused state. The operational approach has been only partially adopted but seems to be gaining popularity. 

MFEs are also useful in hydrodynamic techniques, such as rotating-disk voltammetry (Chap. 3) and electrochemical detection for liquid chromatogra-... 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

We initially employed coupled SERS-rotating disk voltammetry (RDV) to examine the irreversible reductions of Co(NH3)63, ... 

The osmium-containing polymers can also be used for the mediated reduction of N02 to produce NO+ [96]. Rotating-disk voltammetry shows that for... 

Figures 5.4 and 5.5 summarize results of a recent study of P. versicolor laccase electrochemistry based on cyclic and rotating disk voltammetry [60]. Figure 5.4 shows unequivocally that this laccase is voltammetrically active and gives a kinetically controlled, unpromoted four-electron peak at edge-plane pyrolytic graphite. Electrochemical reduction of 02 catalyzed by an immobilized laccase monolayer is close to reversible, and unrestricted by mass transport. The electrocatalysis follows, moreover, a Michaelis-Menten pattern (Fig. 5.5). Finally, there is a characteristic bell-shaped functional pH-profile with a pronounced maximum at pH 3.1.

Rotating disk voltammetry is widely used for studying catalytic processes. For a reversible -electron transfer process controlled by mass transport in solution, the limiting current, Ziim (pA), recorded in a linear potential scan voltammogram varies with the rotation rate, co (sec" ), following the Levich equation (Bard and Faulkner, 2001) ... 

This equation corresponds to the Lineweaver-Burk kinetic equation (Lyons et al., 1992, 1994) and can be transformed into an equation giving the dependence of kinetic currents, 4, on the concentration of substrate in the solution bulk. Values of /), at different concentrations of substrate can be determined from the limiting, steady-state currents, tht.i, obtained, for instance, as plateau currents in rotating disk voltammetry, using Equation (3.6). For the case of thin films with a surface concentration of catalytic centers (rnol/crn ) over an electrode of area A, one can write ... 

Two reversible one electron processes are observed for oxidation and reduction of Ir(OEP)(C8Hi3) >. These occur at 0.68 V and - 1.79 V vs. SCE in THF, 0.1 M TBAP. The wave at 0.68 V was shown by rotating disk voltammetry to be an oxidation while the wave at —1.79 V was shown to be a reduction. The oxidation is reversible on both cyclic voltammetric and bulk electrolysis time scales (1-5 min) and was shown to involve the abstraction of an electron from the bound axial ligand. 

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