Cyclic voltammetr

FIGURE 2-1 Potential-time excitation signal in cyclic voltammetric experiment. 

FIGURE 2-3 Concentration distribution of the oxidized and reduced forms of the redox couple at different times during a cyclic voltammetric experiment corresponding to the initial potential (a), to the formal potential of the couple during the forward and reversed scans (b, d), and to the achievement of a zero reactant surface concentration (c). 

The cyclic voltammogram is characterized by several important parameters. Four of these observables, the two peak currents and two peak potentials, provide the basis for the diagnostics developed by Nicholson and Shain (1) for analyzing the cyclic voltammetric response. 

Many anodic oxidations involve an ECE pathway. For example, the neurotransmitter epinephrine can be oxidized to its quinone, which proceeds via cyclization to leukoadrenochrome. The latter can rapidly undergo electron transfer to form adrenochrome (5). The electrochemical oxidation of aniline is another classical example of an ECE pathway (6). The cation radical thus formed rapidly undergoes a dimerization reaction to yield an easily oxidized p-aminodiphenylamine product. Another example (of industrial relevance) is the reductive coupling of activated olefins to yield a radical anion, which reacts with the parent olefin to give a reducible dimer (7). If the chemical step is very fast (in comparison to the electron-transfer process), the system will behave as an EE mechanism (of two successive charge-transfer steps). Table 2-1 summarizes common electrochemical mechanisms involving coupled chemical reactions. Powerful cyclic voltammetric computational simulators, exploring the behavior of virtually any user-specific mechanism, have... 

FIGURE 2-8 Ideal cyclic voltammetric behavior for a surface layer on an electrode. The surface coverage, FT can be obtained from the area under the peak. (Reproduced with permission from reference 11.)... 

Example 2-1 The reversible oxidation of dopamine (DA) is a two-electron process. A cyclic voltammetric anodic peak current of 2.2 pA is observed for a... 

A cyclic-voltammetric peak current of 12.5 pA was observed for the reversible reduction of a 1.5 mM lead solution using a 1.2 mm-diameter disk electrode and a 50 mV s 1 scan rate. Calculate the lead concentration that yields a peak current of 20.2 pA at 250 mV s 1. 

What is the reason for the gradual increase of the cathodic and anodic cyclic-voltammetric peak currents observed upon repetitive scanning ... 

How does the increase of the scan rate affect the ratio of peak currents (backward/forward) in a cyclic voltammetric experiment involving a redox process followed by a chemical reaction ... 

Explain clearly why and how a change of the scan rate affects the shape of the cyclic voltammetric response of an ultramicroelectrode. 

Cyclic voltammetric studies involving polymers, 558 and the nature of charge carriers, 561 and the nucleation loop, 557 of poly (3-methylthiophene), 564 and parallel-band electrodes, 570 Cyclic voltammograms as a function of scan rate, 559 involving polymerization, 559 with polyanaline, 566 of polypyrrole film, 581... 

One can then ask What is the rate at which the strongly bonded state is populated during the TPD and cyclic voltammetric experiments of Figures 5.2b and 5.2c The answer is clear It is the rate ofO2 supply to the catalyst, i.e. I/2F. 

T. Chao, K.J. Walsh, and P.S. Fedkiw, Cyclic voltammetric study of the electrochemical formation of platinum oxide in a Pt/yttria-stabilized zirconia cell, Solid State Ionics 47, 277-285 (1991). 

Figure 8.13. (a) Cyclic voltammetric investigation of the Ir02/YSZ interface (inset shows the circuit used to model the data)19 and (b) Effect of catalyst-electrode mass on the polarization resistance Rp and the double layer capacitance Cd.19 Scan rate 20 mV/s, T=380°C, pO2=20 kPa. 

Electrochemical measurements on polyaniline (PANI) produce a picture of the charge storage mechanism of conducting polymers which differs fundamentally from that obtained using PTh or PPy. In the cyclic voltammetric experiment one observes at least two reversible waves in the potential range between —0.2 and -)-1.23 V vs SCE. Above -1-1.0 V the charging current tends to zero. Capacitive currents and overoxidation effects, as with PPy and PTh, do not occur The striking... 

Such information can be obtained from cyclic voltammetric measme-ments. It is possible to determine the quantity of electricity involved in the adsorption of hydrogen, or for the electrooxidation of previously adsorbed CO, and then to estimate the real surface area and the roughness factor (y) of a R-C electrode. From the real surface area and the R loading, it is possible to estimate the specific surface area, S (in m g ), as follows ... 

Thomas S, Sung Y-E, Kim KS, Wieckowski A. 1996. Specific adsorption of abisulfate anion on a Pt(l 11) electrode. Ultrahigh vacuum spectroscopic and cyclic voltammetric study. J Phys Chem 100 11726-11735. 

Zhou W-P, Lewera A, Bagus PS, Wieckowski A. 2007. Electrochemical and electronic properties of platinum deposits on Ru(OOOl) Combined XPS and cyclic voltammetric study. J Phys ChemC 111 13490. 

The electrochemical cell for the polarographic measurements had a four-electrode configuration equipped with a microsyringe, and was connected to a computer-assisted data-acquisition system [7]. On the other hand, the cyclic voltammetric measurements that are also assisted by a computer data-acquisition system were carried out using a gel electrode that contains the aqueous phase [8]. The cell structure was as follows ... 

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