Koutecky-Levich plots potentials

The current-potential characteristics of a redox reaction can thus be measured in the following way An overpotential rj is applied, and the current is measured for various rotation rates in. From a Koutecky-Levich plot the corresponding kinetic current jk(rj) is extrapolated. This procedure is repeated for a series of overpotentials, and the dependence of jk on rj is determined. 

To learn that when the rate of electron transfer is slow, a useful approach is to construct Koutecky-Levich plots of (/(current) against l/Tafel plot from these mass-transport-limiting values of the current. 

Figure 9.3.7 Koutecky-Levich plots at potential where the rate of electron transfer is sufficiently slow to act as a limiting factor, and at E2, where electron transfer is rapid, for example, in the limiting-current region. The slope of both lines is (0.62nFACQDQ v ) ...

Figure 5.5 (A) Current-potential curves at different electrode rotating rates, recorded on a Pt disk electrode (0.196 cm ) using a potential scan rate of 5 mV s in Oa-saturated 0.5 M H2SO4 aqueous solution (B) the Levich plot (C) the Koutecky—Levich plots at different electrode potentials and (D) plot of E vs ln(/i<,o). The measurement was...

As an example. Figure 5.5 shows the current—potential curves at different electrode rotating rates (A), the corresponding Levich plot (B) and the Koutecky—Levich plots at different electrode potentials (C). Note that all the curves are located in the left side below the potential-axis rather than above the potential-axis. This is a traditional expression for the oxidant reduction, particularly for the ORR. 

From Figure 5.5(C), for Koutecky—Levich plots at different electrode potentials, all lines are almost parallel to each other, suggesting that they all have the similar values of... 

Figure 5.14 (A) Current-potential curves for ORR on a Fe-N/C-coated glassy carbon electrode. Recorded in 0.5 M H2SO4 solution at various electrode rotating rates as marked. Potential scan rate 5 mV s V Fe-N/C catalyst loading 0.10 mg cm and (B) Koutecky-Levich plots for the ORR on a Fe-N/C coated glassy carbon electrode. The current data were taken at 0.1 V (vs RHE) from (A). ...

Figure 5.15 Koutecky-Levich plots at different electrode potentials. The current-potential curves recorded on the Co-N-S/C catalyst-coated GC disk electrode (0.28 cm ) at different electrode rotation rates in 02-saturated 3.0 M KOH solution. Potential scan rate 25 mV s and catalyst loading 7.06 x 10 g cm ...

Actually, the disk curves in Figure 6.10 can be transformed into Koutecky—Levich plots at different potentials. The plots show a linear dependence at all potentials, as inserted in each figure. The linearity and the parallelism of these plots are usually taken to indicate first-order kinetics with respect to oxygen. The Koutecky—Levich slope in the insets for W2C/C is very close to the theoretical value of two-electron reaction, and other three are close to that of four-electron reaction, indicating that W2C/C can only catalyze a 2-electron-transfer ORR from O2 to peroxide, and Ag/C, Ag-W2C/C, and Pt/C can catalyze a 4-electron-transfer ORR from O2 to OH . 

Figure 7.9 (A) Cyclic voltammo-gratn of the basal plane graphite (BPG) coated by anthraquinone-carboxlyic-allyl ester (ACAE with a loading of 8.9 x 10 mol cm ) in N2 Saturated 0.1 M Na2S04 + 0.1 M CH3COOH/ CHaCOONa (pH = 5.8). Potential scan rate 100 mV s . (B) ORR current—potential curves of ACAE (1.0 X 10 " mol cm )-coated BPG electrode recorded in O2-saturated 0.1 M Na2S04 + 0.1 M CHaCOOH/CHaCOONa (pH = 5.6) at different electrode rotating rates as marked beside the curves. (C) Koutecky—Levich plot at electrode potential of 0.4 V vs SCE, data from (B). Reprinted with permission from Ref. 36.

Figure 7.14 (A) Current—potential curves for Co"HFPC adsorbed on a rotating graphite disk electrode at different rates of rotation as (marked on each curve), recorded in an air-saturated 0.1 M Na2S04 solution buffered to a pH 6. Temperature 20 °C. Potential scan rate 10 mV s (B) Koutecky—Levich plot, data from (B). The thinner solid line is calculated according to Levich theory for a 2-electron O2 reduction process. The thicker solid line and data points are the experimental data. Reprinted with permission from Ref. 47.

Figure 7.24 (A) Rotating-disk voltammograms of 20 wt% CoSe2/C nanocatalyst in O2- saturated 0.1 M KOH at 25 °C with a sweep rate of 5 mV s at different rotating rates from 400 rpm to 2500 rpm from top to bottom. (B) The corresponding Koutecky—Levich plots as a function of at four different potentials 0.1,0.4,0.6 and 0.65 V vs RHE. Catalyst mass loading is c.

I.OA/HCIO4. Previous studies indicated that the presence of perchlorate salts dehydrate the metallopolymer and make the morphology of the layer considerably more compact. Hence we may expect inhibited penetration of Fe " (aq) into the polymer matrix. Thus a decrease in permeation would decrease the reaction layer thickness and lead to a changeover in the kinetic zone from Lk to a surface type. Koutecky-Levich plots for this system are illustrated in Fig. 2.20. These are all linear, and they have the same slope as that observed for a bare electrode. However examining the dependence of k E on layer thickness L (see Fig. 2.21), we note that the reaction order is zero with respect to L. From the diagnostic scheme in Table 2.2 we see that the two possibilities are Sk or LSk. Both of these are surface cases. To distinguish between these two possibilities, we must as before examine the dependence of k E on mediator concentration ho- From Table 2.2 we see that for the Sk case a reaction order of 1/2 is expected, whereas for the LSk situation, the reaction order is unity. A typical Nemst-type plot obtained via potential step coulometry is illustrated in Fig. 2.22. In this case the plot deviates significantly from linearity then there are very reduced or very oxidized layers hence the thermodynamics of the Os(III/II) transformation in perchlorate media is rather complex. This... 

When the redox process is reversible, the shape of the wave should not depend on o). Hence, at any potential, the current should, like the limiting current, be proportional to If the shape of the curve depends on co, then the redox process is kinetically limited. In this case, one can measure the current at fixed potentials along the voltammogram and for each potential plot the inverse of the current vs. This is known as a Koutecky-Levich plot and follows the Koutecky-Levich equation ... 

Figure 21.7. Koutecky-Levich plot for oxygen reduction at a HT-FeTPP/CoTPP-coated rotating disk electrode in 02-saturated 0.5 M FI2SO4 solution. Catalyst loading 2.0 mg. The dashed line shows calculated results for the O2 4-electron reduction by diffusion process [44], (Reprinted from Electrochimica Acta, 45(24), Jiang R, Chu D, Multiple small potential steps at a rotating disk electrode and applications, 4025-30, 2000, with permission from Elsevier.)...

Figure 9.9. (a) j(E) polarization curves at different electrode rotation rates (S2) recorded on Pt(40wt%)/C catalyst prepared via a microwave-assisted polyol synthesis method in a 02-saturated 0.5M H2SO4 electrolyte. (T = 20°C, scan rate = 1 mVs ) (b) Koutecky-Levich plots determined from (a) at different potentials. 

In the present case, from the Koutecky-Levich plots in Fig. 9.9b, four electrons were exchanged over the whole considered potential range an exchange current... 

Again this is a Koutecky-Levich-type expression. A plot of T versus should be linear due to the k factor in Eqn. 22. However in this case the intercept depends on the value of the applied potential 0, since... 

Before the measurement of HOR activity, a pretreatment of the alloy electrode was carried out by potential sweeps (10 V s ) of 10 cycles between 0.05 and 1.20 V in N2-purged 0.1 M HCIO4. The cyclic voltammograms (CVs) at all the alloys resembled that of pure Pt. As described below, these alloy electrodes were electrochemically stabilized by the pretreatment. Hydrodynamic voltammograms for the HOR were then recorded in the potential range from 0 to 0.20 V with a sweep rate of 10 mV s in 0.1 M HCIO4 saturated with pure H2 or 100 ppm CO/H2 at room temperature. The kinetically controlled current 4 for the HOR at 0.02 V was determined from Levich-Koutecky plots [Bard and Faulkner, 1994]. 

Figure 3.6a depicts the linear scan voltammograms (LSVs) of the ORR on 20 % Pd/C without ethylene glycol at co = 400, 800, 1,200 and 1,600 rpm. The LSVs show a clear dependence of the ORR current densities with potential and rotation rate. The ORR on the Pd electrocatalyst seems to be under kinetic and mixed control in the potential scanned, not reaching a well defined limiting current. Levich-Koutecky plots 1/j vs. at different potentials corresponding to the experimen-... 

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