Shape of Voltammograms

The shape of a voltammogram is determined by several experimental factors, the most important of which are how the current is measured and whether convection is included as a means of mass transport. Despite an abundance of different voltam-metric techniques, several of which are discussed in this chapter, only three shapes are common for voltammograms (figure 11.33). 

In the voltammograms in figures 11.33a and 11.33b, the current is monitored as a function of the applied potential. Alternatively, the change in current following 

Concentration gradient for the analyte showing the effects of diffusion and convection as methods of mass transport. 

The interface between a positively or negatively charged electrode and the negatively or positively charged layer of solution in contact with the electrode. 

A current in an electrochemical cell due to the electrical double layer s formation. 

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The more densely packed reconstmcted surface has a higher work function and a more positive pzc than the unreconstructed one. During cyclic polarization, the shape of voltammograms changes markedly if the scan enters higher positive potentials. The current charge associated with the removal of the reconstruction must be accounted for in the electrochemical studies on reconstructing surfaces. 

The situation is more complicated in the case of 41 the shape of voltammograms recorded in the presence of lutidine depends not only on y but also on scan rates. Moreover, at a fast sweep rate, for example at 500 Vs-1, the number of electrons transferred is about 2, but it increases to the value of 2.5 at low sweep rates. The results seem to be in agreement with the following oxidation mechanism73 ... 

Fig. 1 Change in the shape of voltammograms recorded in 0.5 mol dm KOH for a series of SAM substrates prepared at varying times (indicated by line) of immersion of the Au substrates in 1 pmol dm undecanethiol in ethanol. Scan rate ...

Figure 1. Change in the shape of voltammograms of the FLINAK-KBF4 (0.594 m/o) melt with change in K2TaF7 concentration. T =710 C, scan rate 0.25 V s AAg=0.24 cm CK TaF, 2 -0.075 3 - 0.298 ...

Interaction of rhenium metal with KCl-K2ReCl6 and CsCl-Cs2ReCl6 melts at a concentration of (2-8) x 10" mol/cm causes a change in the shape of voltammograms. Peaks I and II increase in height, and peak 1 shifts into the anodic region, so that only peak II remains in the cathodic region. This points to the fact that, when the interaction proceeds via the reaction ... 

Figure 2-15 Zone diagram for he EC mechanism. Typical shapes of voltammograms...

Cathodic prewaves were discovered in reducing Cu(II)-glycine complexes [5]. Simulation procedures involving the determination of surface concentrations and the use of experimentally established kinetic parameters make it possible to obtain voltammograms that nicely coincide with experimental data (Figure 4.5). Analogous shapes of voltammograms were also observed for Sn(ll)-citrate solutions [6] (see Section 8.3.2). 

On the whole, the shape of voltammograms depends on various factors the composition of the solution, stability of complexes and protonated ligands, charge transfer mechanism and its kinetic parameters, and so on. Therefore, in a general case, the shape of voltammogram is rather difficult to forecast. 

Figure 9.42 Influence of an external resistance (indicated at the curves) on the shape of voltammograms. C(-y(n) = 0.09 M.

Comparing the voltammograms of markers mixture reduction (o-NP, o-NB, DNP) for different motor oils (Fig. 18.1) shows that the shape of voltammograms and the position of the peaks of markers reduction are depending on the nature of motor oil. 

For a series of CVs with fixed scan rate, but varied electrode surface temperature, shape of voltammograms changes from classical peak form (without heating) till complete sigmoidal shape (where the increased electrolysis current has driven the concentration profile thickness very fast to the boundary of the stagnant layer, this way generating a diffusion layer of constant thickness). 

Figure 7.23. Effect of the reversal potential on the shape of voltammograms recorded for C6o films in 0.05 M Cd(bpy)3(PF6)2 solution in acetonitrile (a) 30 nanomoles of Ceo on approx. 1 cm Pt flag electrode scan rate 50 mV/s 5 = 200 /rA. Cathodic reversal potential changed. (bHg) 16.6 nmol of Cgo on approx. 1 cm Pt flag electrode in the presence of 0.64 M bipyridine scan rate, 20 mV/s S=100/iA. Cathodic (bHf) and anodic (g) reversal potentials changed.

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