Normalisation scan rate

A series of conventional cyclic voltammograms obtained for a model system, the oxidation of 3.3 mM ferrocene in acetonitrile containing 0.1 M NBU4PF6 as supporting electrolyte at a 0.4-mm diameter platinum electrode, is shown in Fig. II. 1.9. The current scale has been normalised by dividing by the square through the square root of scan rate in order to compare data obtained at different scan rates. Data obtained from these cyclic voltammograms are summarised in Table II. 1.1. 

For the simulation of the cyclic voltammograms, an equilibrium constant K = 0.01 has been selected so that only a small amount of the intermediate B is present in the bulk solution. Thus, with fast scan rates, when little time for conversion of A to B is available, the voltammetric response associated with reduction of the small concentration of B is essentially hidden in the background. Only normalisation using the peak current shows the presence of the small voltammetric signal. The step-shaped characteristic of the oxidation response at high scan rates can be attributed to the potential independent rate constant kf = 2000 s limiting the rate. With sufficiently slow scan rate, the cyclic voltammogram becomes reversible, as expected for the case of a very fast pre-equilibrium. In this case, only the shift of the... 

The normalisation of the voltammograms with the square root of the scan rate allows the peak currents for the oxidation response to be compared as a function of the scan rate. It can be seen that the peak current increases considerably from the reversible one-electron process observed at high scan rate to the chemically irreversible two-electron process at slow scan rate. There are many chemical systems that can be described by the reaction scheme given in Eq. II. 1.26 [103]. Based on the discussion of the EC reaction it can be anticipated that the ErevCrevErev reaction scheme... 

Figure 7.4 depicts the simulated voltammetric response for the reduction of diethyl maleate (DEM) at three different scan rates. It should be highlighted that in order to allow direct comparison of the voltammograms, the current has been normalised with respect to the square root of the scan rate. DEM consists of a double bond where the ester groups are situated cis to each other. The stereoisomer of DEM is diethyl fumarate (DEF) where the ester groups are situated trans to each other, as shown in Fig. 7.5. The reduction potential for DEF is known to be less negative than that of DEM.

Fig. 7.4 The simulated cyclic voltammograms at various scan rates for the reduction of DEM at a macroelectrode. The current has been normalised with respect to the square root of scan rate.

Kg. 10 (a) TEM image of 40 nm long platinum nanowire with radius of 6 nm. (b) Oxygen reduction voltammetry in an oxygen saturated 0.1 M KOH solution observed at 4nm radius platinum disk and different length platinum nanowires (scan rate 10 mV s ). Current scale has been normalised with respect to the limiting current for each nanowire length. Reproduced from ref. 95 with permission from the American Chemical Society. 

Plot of the normalised peak current vs scan rate showing the transition from reversible ( diffusion only DO) to quasi-reversible (QR), and finally to irreversible (IR), charge transfer kinetics, c Plot of the peak-to-peak separation, A , as a function of scan rate... 

Three cases for this type of reaction sequence may be considered with (i) the simplest case - c,a+/a < c,b+/b related to the ErevCi ev process (vide supra), (ii) c,A+/A = c,B+/B> and (iii) - c,a+/a > c,b+/b, the case considered in Fig. II. 1.23. For this mechanistic scheme, a reversible voltammetric response for the A /A redox couple at - c,A+/A = V can be observed at sufficiently fast scan rates. Reducing the scan rate allows the chemical reaction step with k = 200 s" to compete with mass transport in the diffusion layer and the product B is detected on the reverse scan in the form of a B /B reduction process with -Ec,b+/b = -0.1 V. The normalisation of the voltammograms with the square root of the scan rate allows the peak currents for the oxidation response to be compared as a function of the scan rate. It can be seen that the peak current increases considerably from the reversible one-electron process observed at high scan rate to the chemically irre-... 

Fig. 3.17 Ferricyanide voltammetry Current (normalised to electrode radius) versus potential response for the graphene monolayer samples (Samples 1 and 2 1, monolayer contained no visible defects and its edges were completely masked—note however that although special attention was paid during the masking and preparation of samples in order to expose areas with the minimum number of defects, the authors acknowledge that to date it has not been possible to achieve a perfect, edge-fiee region 2, monolayer contains several holes of 10 pm diameter, hence some edge sites must be in contact with the electrolyte), a bilayer sample and the multilayer sample. Scan rate = 5 mVs concentration = 1 mM ferricyanide in 1 M KCl. Reprinted with permission from Ref. [30], Copyright 2011 American Chemical Society...

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