Linear Sweep/Cyclic

Linear Sweep, Cyclic and Sqnare Wave Voltammetry (LSV, CV, SWV)... 

On the other hand, from the results of CTs, it is likely that the rate of the lithium insertion/desertion should be limited by the internal cell resistance during potential scanning as well, not by lithium diffusion in the electrode. In fact, it has been reported by a few authors " that the linear sweep/cyclic voltanunograms from the intercalation compounds were difficult to analyze under the diffusion control concept. In addition, the voltammetric results in a number of... 

The atypical features in the linear sweep/cyclic voltammograms include the asymmetry in shape between anodic and cathodic current peaks, and the abnormal dependence of peak current on potential scan rate. The cell-impedance controlled lithium transport concept is expected to provide a reasonable explanation of these atypical voltammetric responses, and give us a new insight into the lithium transport behavior during potential scanning. 

Similarly to the response at hydrodynamic electrodes, linear and cyclic potential sweeps for simple electrode reactions will yield steady-state voltammograms with forward and reverse scans retracing one another, provided the scan rate is slow enough to maintain the steady state [28, 35, 36, 37 and 38]. The limiting current will be detemiined by the slowest step in the overall process, but if the kinetics are fast, then the current will be under diffusion control and hence obey the above equation for a disc. The slope of the wave in the absence of IR drop will, once again, depend on the degree of reversibility of the electrode process. 

The Model 384B (see Fig. 5.10) offers nine voltammetric techniques square-wave voltammetry, differential-pulse polarography (DPP), normal-pulse polar-ography (NPP), sampled DC polarography, square-wave stripping voltammetry, differential pulse stripping, DC stripping, linear sweep voltammetry (LSV) and cyclic staircase voltammetry. 

Studies of the linear sweep and cyclic voltammetric behavior of N-methyl-ated xanthines 35 -37> reveals that they undergo electrochemical oxidation over a fairly wide pH range at the PGE (Table 1). All but three of the xanthines studied show just a single voltammetric oxidation peak, although it is prob-... 

Figure 2.15 Schematic representation of the equipment necessary to perform linear sweep voltammetry LSV) or cyclic voltammetry CV). WFG waveform generator, P potentiostat, CR chart recorder, EC electrochemical cell, WE working electrode, CE counter electrode, RE...

Figures 2.16(a) and (b) show the linear sweep voltammogram and cyclic voltammogram that would be expected from an electroactive adsorbed species assuming that ...

Thus, cyclic or linear sweep voltammetry can be used to indicate whether a reaction occurs, at what potential and may indicate, for reversible processes, the number of electrons taking part overall. In addition, for an irreversible reaction, the kinetic parameters na and (i can be obtained. However, LSV and CV are dynamic techniques and cannot give any information about the kinetics of a typical static electrochemical reaction at a given potential. This is possible in chronoamperometry and chronocoulometry over short periods by applying the Butler Volmer equations, i.e. while the reaction is still under diffusion control. However, after a very short time such factors as thermal... 

Except for very electron-rich donors that yield stable, persistent radical cations, the ox values are not generally available.64 Thus the cation radicals for most organic donors are too reactive to allow the measurement of their reversible oxidation potentials in either aqueous (or most organic) solvents by the standard techniques.65 This problem is partially alleviated by the measurement of the irreversible anodic peak potentials E that are readily obtained from the linear sweep or cyclic voltammograms (CV). Since the values of E contain contributions from kinetic terms, comparison with the values of the thermodynamic E is necessarily restricted to a series of structurally related donors,66 i.e.,... 

The redox characteristics, using linear sweep and cyclic voltammetry, of a series of (Z)-6-arylidene-2-phenyl-2,3-dihydrothiazolo[2,3-r][l,2,4]triazol-5(6//)-ones 155 (Figure 24) have been investigated in different dry solvents (acetonitrile, 1,2-dichloroethane, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO)) at platinum and gold electrodes. It was concluded that these compounds lose one electron forming the radical cation, which loses a proton to form the radical. The radical dimerizes to yield the bis-compound which is still electroactive and undergoes further oxidation in one irreversible two-electron process to form the diradical dication on the newly formed C-C bond <2001MI3>. 

Parker, V. D. Precision in Linear Sweep and Cyclic Voltammetry, in Electronalytical Chemistry, Bard, A. J., Ed., Marcel Dekker New York, 1985, Vol. 14. 

In linear sweep voltammetric techniques the applied electrode potential is varied from an initial value E to a final value f at a constant scan rate v (single sweep voltammetry). Once the value is reached the direction of the scan can be reversed, maintaining the same scan rate v, and the potential brought back to the initial value (cyclic voltammetry). In the two cases the form of the potential-time impulse can be represented as shown in Figure 1. 

Figure 1 Potential-time pulses in (a) linear sweep voltammetry (b) cyclic voltammetry. The slope of each line measures the potential scan rate...

Linear sweep and cyclic voltammetry (LSV and CV) are probably the most widely used techniques to investigate electrode reaction mechanisms. They are easy to apply experimentally, readily available in... 

Fig. 5 Linear sweep and cyclic voltammetry (a) dotted lines five profiles respectively at various typical excitation signal (b) current response times, increasing time shown by arrows] for a and concentration profiles [(c) forward scan cyclic voltammetric experiment.

Figure 6.5 Potential is varied at a constant rate of dE/dt during voltammetric techniques such as polarography, linear sweep voltammetry and cyclic voltammetry. The scan rate v is always cited as a positive number.

Linear-Sweep and Cyclic Voltammetry at Solid Electrodes... 

During cyclic voltammetry, the potential is similarly ramped from an initial potential E but, at the end of its linear sweep, the direction of the potential scan is reversed, usually stopping at the initial potential E (or it may commence an additional cycle). The potential at which the reverse occurs is known as the switch potential ( >.) Almost universally, the scan rate between E and Ex is the same as that between Ex and E. Values of the scan rates Vforwani and Ubackward are always written as positive numbers. 

Is cyclic voltammetry more useful than linear-sweep voltammetry ... 

Figure 6.15 Plot of peak current (/p) in a voltammogram (either linear-sweep or cyclic) against analyte concentration. The linear portion obeys the Randles-SevCik equation, while the horizontal plateau at low Ca aiyie values is usually caused by non-faradaic components of Ip, such as double-layer charging.

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