Waveform, reversible cyclic voltammogram

Figure 16.7 A reversible cyclic voltammogram obtained with the waveform shown in figure 16.3.

Fig. 5. Applied waveform for linear sweep voltammetry and cyclic voltammetry (a) and a reversible cyclic voltammogram (b).

Fig. 4 Cyclic voltammetry. (A) Voltage waveform showing the rapid forward and reverse voltage sweeps. (B) Typical cyclic voltammogram for completely reversible system.

Typical FFT a.c. cyclic voltammograms of Cr(CN)6 "/Cr(CN)6 " couple at HMDE in aqueous cyanide media. System 1.0 x 10"3 M Cr(CN)63- at Hg-1.0 M KCN, water interface, 25"C. Applied Pseudo-random, odd-harmonic a.c. waveform with 1.5 mV per frequency component, 32 total components superimposed on staircase d.c. scan (5 mV per step) with triangular envelope whose scan rate = 50 mV s-1. Measured Faradaic admittance magnitude at 1840.8 rad s-1 (A,C) and 7877 rad s"l (B,D) obtained on single measurement pass (30 other frequency components measured simultaneously, but not shown). (A,B) Raw data. (C,D) digitally filtered (smoothed) data. (+) Forward scan, ( ) reverse scan. Abscissa = potential vs. Ag/AgCl. 

In potential sweep methods, the current is recorded while the electrode potential is changed linearly with time between two values chosen as for potential step methods. The initial potential, E, is normally the one where there is no electrochemical activity and the final potential, 2, is the one where the reaction is mass transport controlled. In linear sweep voltammetry, the scan stops at E2, whereas in cyclic voltammetry, the sweep direction is reversed when the potential reaches 2 and the potential remmed to j. This constitutes one cycle of the cyclic voltammogram. Multiple cycles may be recorded, for example, to study film formation. Other waveforms are used to study the formation and kinetics of intermediates when studying coupled chemical reactions (Figure 11.4c). 

Figure 19.3 Charging current and selection of step potential for chronoamperometry. (a) Potential waveform applied to the electrode in chronoamperometry. At i = 0, the potential is stepped from the initial value to a constant value (b) Dependence of faradaic current (if) and charging current (ij on time for a planar macroelectrode, (c) Dependence of if and on time for a UME. (d) Cyclic voltammogram at a UME showing and selection of Ef and E. (e) Cyclic voltammogram of a reversible redox couple at a macroelectrode showing and Ey and selection of and 3,. (J) Cyclic voltammogram of a quasi-reversible redox couple at a macroelectrode showing and and selection of E and...

Figure 1. (Top) Waveform for linear-scan (solid line) and cyclic (dotted line) voltammograms. (Bottom) LSV and CV curves for reversible one-electron reduction of a Pd dithiolate complex.

Figure 10.5.8 is a display of an actual cyclic ac voltammogram for ferric acetylaceto-nate, Fe(acac)3, in acetone containing 0.1 M tetraethylammonium perchlorate. Since this system is very nearly reversible to the dc process, the peak splitting is quite small, but easily detectable. The convenience of the waveform for quantitative work is also readily apparent. 

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