Potential Sweep and Cyclic Voltammetry

Linear potential sweep and cyclic voltammetry have been used extensively to examine the redox behavior of surface-deposited electroactive polymer films qualitatively. In this respect the technique can be classified as a form of electrochemical spectroscopy, since it delineates regons of redox activity, and provides an initial survey of overall electrochemical behavior of an electroactive polymer film as a function 

The peak width in the voltammetric profile conveys useful information about the electrochemistry of redox switching in an electroactive polymer film. Theory developed in Section 2.3, assuming an ideal situation of zero interredox center interaction, and sites in the layer at equilibrium with the potential applied at support electrode surface (which means that the site oxidation is Nemstian), predicts that the peak width at half height S has the following value  

Hence we see that considerable thermodynamic information is available from analyzing the shape of voltammetric current profiles. 

It is not always recognized that potential sweep voltammetry can be used to obtain quantitative information on charge percolation in polymer films. We now briefly indicate how apparent charge transport diffusion coefficients can be extracted by analyzing such voltammetric parameters as peak current, peak width, and peak potential as a function of scan rate. This analysis is diffusional in concept and perhaps best applied to polymer materials where redox conduction is the predominant mechanism of charge transport. 

The model we describe was developed in a comprehensive manner by Aoki and coworkers, who examined the situation where the redox transformation in the layer obeys the Nemst equation and the heterogeneous electron transfer kinetics at the support electrode/film interface become important. In the following analysis we concentrate on the former case. 

---

Linear potential sweep and cyclic voltammetry are at their best for qualitative studies of the reactions occurring in a certain range of potential. In Fig. 5L, for example, we see the cyclic voltammogram obtain on a mercury-drop electrode in a solution of p-nitrosophenol in acetate buffer. Starting at a potential of 0.3 V versus SCE, and sweeping in the cathodic direction, one observes the first reduction peak at about - 0.1 V. This potential corresponds to the reduction of... 

We conclude this section by noting that linear potential sweep and cyclic voltammetry are excellent qualitative tools in the study of electrode reactions. However, their value for obtaining quantitative information is rather limited. The best advice to the novice in the field is that cyclic voltammetry should always be the first experiment performed in a new system, but never the last. 

In conclusion linear potential sweep and cyclic voltammetry can be used to obtain quantitative information on charge percolation in electroactive polymer films. However analysis is complex, and it may be preferable to use a simpler technique, such as potential or current step perturbation, to determine the transport parameters, as outlined in the preceding section. 

Gueshi T, Tokuda K, Matsuda H (1979) Voltammetry at partially covered electrodes. Part n. Linear potential sweep and cyclic voltammetry. J Electroanal Chem 101 29-38... 

Potential step voltammetry (chronoamperometry) or normal pulse voltammetry (NPV) and potential sweep or cyclic voltammetry (CV) were employed for investigating drugs at the NB/W or DCE/W interface. A thin O-layer cell [15,16,23] was used to realize the partition equilibrium of neutral species (that is, B) at the O/W interface initially at t = 0 within a reasonably short time. All measurements were carried out at 25°C. Experimental details should be consulted in the references cited. 

The ylide is formed on electrochemical reduction of PPh3 at —2.77 V15 this is conclusively demonstrated by controlling the potential sweeps in cyclic voltammetry. With benzyltriphenylphosphonium nitrate, the above reaction scheme proceeds smoothly up to 2 F mol 1 when benzaldehyde and dicyano(fluoren-9-ylidene)methane are used in the reaction. 

Potential control or potential measurements are fundamental to electroanalytical studies, so the cells used are usually of the three-electrode type. A typical cell for electroanalytical work, such as linear sweep and cyclic voltammetry, is shown in Fig. 6.2. 

The term voltammetry refers to measurements of the current as a function of the potential. In linear sweep and cyclic voltammetry, the potential steps used in CA and DPSCA are replaced by linear potential sweeps between the potential values. A triangular potentialtime waveform with equal positive and negative slopes is most often used (Fig. 6.8). If only the first half-cycle of the potential-time program is used, the method is referred to as linear sweep voltammetry (LSV) when both half-cycles are used, it is cyclic voltammetry (CV). The rate by which the potential varies with time is called the voltage sweep (or scan) rate, v, and the potential at which the direction of the voltage sweep is reversed is usually referred to... 

Part IV is devoted to electrochemical methods. After an introduction to electrochemistry in Chapter 18, Chapter 19 describes the many uses of electrode potentials. Oxidation/reduction titrations are the subject of Chapter 20, while Chapter 21 presents the use of potentiometric methods to obtain concentrations of molecular and ionic species. Chapter 22 considers the bulk electrolytic methods of electrogravimetry and coulometry, while Chapter 23 discusses voltammetric methods including linear sweep and cyclic voltammetry, anodic stripping voltammetry, and polarography. 

Laviron55 has recently noted that linear potential sweep or cyclic voltammetry does not appear to be the best method to determine the diffusion coefficient D of species migrating through a layer of finite thickness since measurements are based on the shape of the curves, which in turn depend on the rate of electron exchange with the electrode and on the uncompensated ohmic drop in the film. It has been established that chronopotentiometric transition times or current-time curves obtained when the potential is stepped well beyond the reduction or oxidation potential are not influenced by these factors.55 An expression for the chronopotentiometric transition has been derived for thin layer cells.66 Laviron55 has shown that for a space distributed redox electrode of thickness L, the transition time (r) is given implicitly by an expression of the form... 

Fig. 2.9 Potential—time profiles used to perform linear sweep and cyclic voltammetry...

Nicholson and Shain revolutionized the voltammetric experiment with their elegant development and demonstration of linear-sweep and cyclic voltammetry. In their approach, the current-potential curve is presented as... 

Methods employing individual linear or triangular pulses (potential-sweep, triangular pulse and cyclic voltammetry, sometimes also called... 

---