Kinetics rotating disk electrode voltammetry

Although cyclic voltammetry could fruitfully be applied to the kinetic analysis of these catalytic systems, it has mostly been investigated by means of rotating disk electrode voltammetry (Section 1.3.2). The simplest case is that of an irreversible catalytic reaction at a monolayer coating. The next section is devoted to the analysis of these systems by the two techniques. 

Burnette WB, Bailey MD, Kukoyi S, Blakely RD, Trowbridge CG, Justice JB, Jr. (1996) Human norepinephrine transporter kinetics using rotating disk electrode voltammetry. Anal Chem 68 2932-2938. 

Shuman and Michael [326,327] introduced a technique that has sufficient sensitivity for kinetic measurement at very dilute solutions. It combines anodic scanning voltammetry with the rotating-disk electrode and provides a method for measuring kinetic dissociation rates in situ, along with a method for distinguishing labile and non-labile complexes kinetically, consistent with the way they are defined. 

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. 

Cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) in a traditional tri-electrode cell are often employed in the study of the ORR kinetics and mechanisms on various catalysts in liquid electrolytes [27, 28]. As shown in Fig. 15.2, a tri-electrode cell contains a working electrode (WE), a reference electrode (RE), and a counter electrode (CE). The CE has much... 

Using cyclic voltammetry of Fe(CN)6 at a rotating disk electrode, Schlenoff provided evidence that decreases in Faradaic current due to the presence of P S S/poly(diallydimethylammonium chloride) occur because of slow movement of Fe(CN)6 through the film [37]. Peak currents are independent of potential suggesting that diffusion rather than kinetics is limiting current. This is in agreement... 

Miller, B., Bellavance, M., and Bruckenstein, S. (1971) Application of isosurface concentration voltammetry at a rotating disk electrode to simple electron transfer kinetics. /. Electrochem. Soc., 118 (7), 1082-1089. 

The rotating disk electrode is becoming one of the most powerful methods for studying both diffusion in electrolytic solutions and the kinetics of moderately fast electrode reaction because the hydrodynamics and the mass-transfer characteristics are well understood and the current density on the disk electrode is supposed to be uniform. Levich [179] solved the family of equations and provided an empirical relationship between diffusion limiting current (id) and rotation rate ( >) as shown in Eq. (9.42). In particular applications in fuel cells, the empirical relationship which is given by Levich was also used in linear scan voltammetry (LSV) experiment performed on a RDE to study the intrinsic kinetics of the catalyst [151,159,180-190]. However, it is more appropriate to continue the discussion later in detail in the LSV section. 

The main objective of this chapter is to show that transport processes can significantly contribute to the electrochemical kinetics measurements and therefore should be taken into account. Transport processes are based on hydrodynamics (fluid mechanics), which is described with mathematics of the vector analysis. Students should know what the terms vector, gradient, and divergence represent. Solutions of Pick s second law of diffnsion are given as examples of hydrodynamics coupled with electrochemical kinetics. The theory and use of the rotating disk electrode (RDE) are explained. Introdnction to cyclic voltammetry (CV) techniques is also given. 

Linear sweep voltammetry (LSV) in combination with a rotating disk electrode (RDE) is a widely used technique to study electrode kinetics. Different methods exist to extract the values of the process parameters from polarization curves. The Koutecky-Levich graphical method is frequently used to determine the mass transfer parameters (Diard et al., 1996) the slope of a plot of the inverse of the limiting current versus the inverse of the square root of the rotation speed of the rotating disk electrode is proportional to the diffusion coefficient. If more than one diffusing species is present, this method provides the mean diffusion coefficient of all species. The charge transfer current density is determined from the inverse of the intercept. In practical situations, however, the experimental observation of a limiting current... 

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 ... 

An interesting study [52] of the protonation kinetics and equilibrium of radical cations and dications of three carotenoid derivatives involved cyclic voltammetry, rotating-disk electrolysis, and in situ controlled-potential electrochemical generation of the radical cations. Controlled-potential electrolysis in the EPR cavity was used to identify the electrode reactions in the cyclic volt-ammograms at which radical ions were generated. The concentrations of the radicals were determined from the EPR amplitudes, and the buildup and decay were used to estimate lifetimes of the species. To accomplish the correlation between the cyclic voltammetry and the formation of radical species, the relative current from cyclic voltammetry and the normalized EPR signal amplitude were plotted against potential. Electron transfer rates and the reaction mechanisms, EE or ECE, were determined from the electrochemical measurements. This study shows how nicely the various measurement techniques complement each other. 

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. 

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 ... 

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