A.J. Bard, L.R. Faulkner - Electrochemical methods - Fundamentals and Applications (794273), страница 102
Текст из файла (страница 102)
Since the ac voltammogram shows a response only in the potential regionswhere such transition takes place, we can expect the cyclic ac voltammogram to showsplit peaks that are largely aligned with the forward and reverse dc voltammetricpeaks. The standard potential E will lie between them. Some traces are shown in Figure 10.5.7.Evidently there is a crossover potential, Eco, where both scans yield the same response. This potential can be rigorously shown to lie atа1 -а(10.5.28)regardless of the details of dc polarization (26). It serves as a convenient source for theevaluation of a. The amplitude and the phase angle of the ac response at Eco are totallyindependent of the dc process.
In this respect Eco is a unique potential, and it may be themost convenient point for evaluating k° by a plot of cot ф vs. col/2. One can also derivek° from the separation of forward and reverse peaks in the ac voltammogram (26, 27).Figure 10.5.8 is a display of an actual cyclic ac voltammogram for ferric acetylacetonate, Fe(acac)3, in acetone containing 0.1 M tetraethylammonium perchlorate. Since thissystem is very nearly reversible to the dc process, the peak splitting is quite small, buteasily detectable. The convenience of the waveform for quantitative work is also readilyapparent.400 • Chapter 10. Techniques Based on Concepts of Impedance1.201.00•|о0.80j§0.60a§0.40CO1 0.200.400.200.00E6c-EV2-0.20(volts)-0.400.00-0.20-0.40o3 0.30 -0.20 -0.10 -0.400.20£ d c - £ 1 / 2 (volts)0.20 -$0.10 -0.40Figure 10.5.7 Predicted cyclic acvoltammograms for systems withnon-nernstian dc behavior, (a) k° =4.4 X 10~3<b>Текст обрезан, так как является слишком большим</b>.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
