Cyclic voltammetry scan rate

Figure 4.19 Cyclic voltammetry (scan rate = 0.1 V/s) of Ml (bold line) and M3 (thin line) in benzonitrile/0.1 M TBAPF6. With permission from the American Chemical Society, ref. 119.

Quasireversible at high cyclic voltammetry scan rates. 

Supporting Electrolyte Dc Polarography t - 1/2 DxlO =3 s Cyclic voltammetry, scan rate=40 mVs -Ep DxlO /,fc ... 

Scan rate, v In cyclic voltammetry, the rate at which the potential of the working electrode is varied, i.e. v = dE/dt). The value of v is always cited as positive. 

The time range of the electrochemical measurements has been decreased considerably by using more powerful -> potentiostats, circuitry, -> microelectrodes, etc. by pulse techniques, fast -> cyclic voltammetry, -> scanning electrochemical microscopy the 10-6-10-1° s range has become available [iv,v]. The electrochemical techniques have been combined with spectroscopic ones (see -> spectroelectrochemistry) which have successfully been applied for relaxation studies [vi]. For the study of the rate of heterogeneous -> electron transfer processes the ILIT (Indirect Laser Induced Temperature) method has been developed [vi]. It applies a small temperature perturbation, e.g., of 5 K, and the change of the open-circuit potential is followed during the relaxation period. By this method a response function of the order of 1-10 ns has been achieved. 

It is possible to control the thickness of the polyphenylene Aims by controlling (i) the time duration of the reaction, (ii) the concentration of the diazonium salts, or (iii) the potential(s) of the electrolysis or cyclic voltammetry. The flrst two methods apply to spontaneous and chanical grafting, while all the three apply to electrografting. Using these parameters, monolayers have been attached to PPF for microelectronic applications. For example, a film of 7 PF-N=N-QH,-N02 groups has been obtained by electrochemical reduction (one cyclic voltammetry scan between -t-0.4 V and 0 V/ Ag/Ag+, scan rate v = 0.2 V s ) of the corresponding diazonium salt. A thickness of... 

Cyclic voltammetry provides a simple method for investigating the reversibility of an electrode reaction (table Bl.28.1). The reversibility of a reaction closely depends upon the rate of electron transfer being sufficiently high to maintain the surface concentrations close to those demanded by the electrode potential through the Nemst equation. Therefore, when the scan rate is increased, a reversible reaction may be transfomied to an irreversible one if the rate of electron transfer is slow. For a reversible reaction at a planar electrode, the peak current density, fp, is given by... 

One of the most problematic issues, still to be fully resolved, is the dependence of the degree of oxidation on potential, as measured most commonly by cyclic voltammetry at low scan rates. There is currently no accepted model to describe the shape of the curve and the hysteresis between anodic and cathodic scans. The debate over whether the charge has a significant component due to a polymer/solution double layer is still not fully resolved. 

Figure 6.8 S-shaped polarization curve observed in the CO oxidation model (for the exact model parameters, see Koperetal. [2001]). The thin line shows the cyclic voltammetry observed at a low scan rate of 2 mV/ s.

Figure 6.9 Cyclic voltammetry of a Pt(llO) rotating disk electrode in a CO-saturated 0.1 M HCIO4 solution, (a) Influence of the voltage scan rate, (b) Influence of the disk rotation rate.

Figure 16.8 Pt/TiO c-catalyzed oxygen reduction potential, where 0.01 mA cm is reached during the negative scan in a cyclic voltammetry experiment (scan rate 20 mV s ) in oxygen-saturated 0.5 M HCIO4 at 25 °C. (See color insert.)...

Figure 16.9 Comparison of cyclic voltammetry in a CO-saturated electrolyte (0.5 M HCIO4) of Au supported on carbon (solid curves) and titania (dashed curves) for four different particle sizes (indicated). The measurements were made at a temperature of 298K and a scan rate of 50mV s ...

By varying the scan rate, this equation allows then the evaluation of the diffusion coefficient of the transferring ion. With the determination of the formal transfer potential of an ion and thus of its Gibbs energy of transfer by application of Eq. (10), this is the most important application of cyclic voltammetry. 

Figure 3.6 Reflect vity-potential curve (top) and corresponding cu r rent-poten tial c y clic volta m -mograms (bottom) for a platinum electrode in 1.0M H2S04. The reflectivity curve was taken at 546 nm using S-poiarised light at a 701 angle of incidence. The potential limits for both the reflectivity and cyclic voltammetry experiments were + 0.535 V and —0.006 V vs. NHF, and the scan rate was 26.46 Vs-1. From Bewick and Tuxford (1973).

The technique employed by Lamy and colleagues was rapid-scan cyclic voltammetry in extremely dry DMF. In order to try and increase the lifetime of the C02 species the experiments were performed in the presence of active alumina suspensions. Aylmer-Kelly et al1973 had calculated the rate constant for reaction of the radical with water as a fast 5.5dm1 niol 1 s 1 and it was also hoped that reducing the solvation of the radical by water would increase the coulombic repulsion between radicals and so reduce dimerisation). 

From the figure it can be seen that there is a pronounced anodic peak near 0.15 V vs. SCE that has also been observed in aqueous electrolyte. The current at this peak scales linearly with the scan rate, as expected for a surface-bound redox material (see section on cyclic voltammetry of adsorbed species). 

Figure 3.96 The effect of increasing time of exposure (as indicated) of a gold electrode once-modified with SSBipy to thiophenol on the cyclic voltammetry of horse heart cytochrome t (0.4mM). 20 mM sodium phosphate/0.1 M NaCI04 pH 7.0. Scan rate 20mVs l. From Hill...

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