Koutecky-Levich analysis

Due to the formation of an intermediate complex, this type of reaction mechanism was described as being analogous to Michaelis-Menten kinetics [39]. A common error made when examining the behaviour of systems of this type is to use the Koutecky-Levich equation to analyse the rotation speed-dependence of the current. This is incorrect because the Koutecky-Levich analysis is only applicable to surface reactions obeying strictly first-order kinetics. Applying the Koutecky-Levich analysis to situations where the surface kinetics are non-linear, as in this case, leads to erroneous values for the rate constants. Below, we present the correct treatment for this problem based on an extension of a model originally developed by Albery et al. [42]... 

As an alternative to EHD measurements, the presence of a surface film of constant thickness can be detected using Koutecky-Levich analysis. From equation (10.32),... 

Vandeputte et al. [122] used both of these equations to derive more accurate values of the constants than could be obtained from the Koutecky-Levich analysis alone, and hence derived rate constants for the predissociation of the thiosulfate complex involved in the electrodeposition of silver from thiosulfate solutions. 

While the voltammograms can be quantitatively analyzed to yield permeant transport parameters - for example, via numerical simulations - we have instead utilized rotating disk electrode (RDE) voltammetry for this purpose. Sequential solution and film transport problems are generally well described by a variant of the Koutecky-Levich analysis [11]. This analysis represents the series process Idnetically as a reciprocal sum of pure solution-phase convection/dilFusion (cd) and pure film permeation (p) rates or fluxes. Since detection is electrochemical, the fluxes can be written in terms of currents, where ilim is the observed overall, mass-transport limited, current [12] ... 

FIGURE 2.25. Koutecky-Levich analysis of the first unmediated oxidation wave in Fig. 2.24. The linear regression line and the 98% confidence lines are also illustrated. 

Then the film exerts only diffusion and partition effects, which is what we assumed when we determined is by analyzing the first wave. Examining Eqn. 89 we see that the Koutecky-Levich intercept is given by (M/ ) . Hence if is is known, then i can be determined. The Koutecky-Levich analysis of the second wave is illustrated in Fig. 2.27. A good plot is... 

Hence we obtain a value for from the Koutecky-Levich analysis of the first wave. 

The fact that catechol oxidation occurs via a Michaelis-Menten mechanism is confirmed by obtaining the RDE response for a range of catechol concentrations and subsequently subjecting the data to a Koutecky-Levich analysis [see (Fig. 2.36(a)]. The Koutecky-Levich intercept 7/cz, is then obtained and a Lineweaver-Burk analysis applied, which predicts that //fi, varies in an inverse manner with bulk substrate concentration according to... 

Masa J, Batchelor-McAuley C, Schuhmann W, Compton RG (2014) Koutecky-Levich analysis applied to nanoparticle modified rotating disk electrodes electrocatalysis or misinterpretation. Nano Res 7(l) 71-78... 

The voltammetry of [(L)Cu ] " is similar at pH 1 and 10 (Figure 4.23). ° Under Ar, the Cu couple is positively shifted from 0.23 V at pH 1 to 0.49 V at pH 10, which corresponds to a shift of 30 mV per pH unit. ° The onset of O2 reduction at pH 10 is at 0.77 V, which is 240 mV more positively shifted as compared to the value at pH l. ° The ring current also shows that H2O2 is formed at potentials between the onset and the diffusion-limited current. The Koutecky-Levich analysis of the dependence of the rotation rate on the reduction current also shows that 3.9 e were transferred at this pH, ° indicating nearly four-electron reduction of O2. This is consistent with the results in the homogeneous system vide supra). 

As may have been predicted, however, both these materials were found to follow a similar mechanistic pathway to that of Co-Co4, that is, a chemical step was rate determining, as judged by the bent Levich plots. A more detailed kinetic analysis based on the Koutecky-Levich intercepts was in this instance complicated by the mixed reaction pathway. 

As discussed in Figure 5.5, Koutecky—Levich theory can be used to analyze the current—potential curves, and the equations used for this analysis are Equations (5.23) and (5.24). To obtain the ORR exchange current density (i°), the electron-transfer... 

FIGURE 2.36. (a) Koutecky-Levich plots for catechol oxidation in 0.2 M H2SO4 at the metal oxide/ionomer composite electrode as a function of catechol concentration, (b) Lineweaver-Burk analysis of data in Fig. 2.36(a). 

Typical examples discussed below can help us gain a better understanding of the application of RDEs. Jiang et al. [44] studied the ORR at a rotating disk electrode with multiple small potential steps. Figure 21.6 shows a serial of current-potential curves for the ORR at a HT-FeTPP/CoTPP/PG rotating disk electrode in an 02-saturated 0.5 M sulfuric acid electrolyte. With increasing rotation rate, the catalytic current increases. The kinetic analysis of the ORR at the catalyst coated RDE can be carried out by the Koutecky-Levich equation ... 

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