Electrode cyclic voltammetry

Cyclic voltammetry provides a simple method for investigating the reversibility of an electrode reaction (table Bl.28.1). The reversibility of a reaction closely depends upon the rate of electron transfer being sufficiently high to maintain the surface concentrations close to those demanded by the electrode potential through the Nemst equation. Therefore, when the scan rate is increased, a reversible reaction may be transfomied to an irreversible one if the rate of electron transfer is slow. For a reversible reaction at a planar electrode, the peak current density, fp, is given by... 

Flavin adenine dinucleotide (FAD) has been electropolymerized using cyclic voltammetry. Cyclic voltammograms of poly (FAD) modified electrode were demonstrated dramatic anodic current increasing when the electrolyte solution contained NADH compare with the absence of pyridine nucleotide. 

Emission spectra have been recorded for four aryl-substituted isoindoles rmder conditions of electrochemical stimulation. Electrochemiluminescence, which was easily visible in daylight, was measured at a concentration of 2-10 mM of emitter in V jV-dimethylformamide with platinum electrodes. Emission spectra due to electrochemi-luminescence and to fluorescence were found to be identical, and quantum yields for fluorescence were obtained by irradiation with a calibrated Hght source. Values are given in Table X. As with peak potentials determined by cyclic voltammetry, the results of luminescence studies are interpreted in terms of radical ion intermediates. ... 

Cyclic Voltammetry measurement of the current or current density as a function of the electrode potential by application of one or more potential sweep cycles. 

For PPV-imine and PPV-ether the oxidation potential, measured by cyclic voltammetry using Ag/AgCl as a reference are ,M.=0.8 eV and 0.92 eV, respectively. By adopting the values 4.6 eV and 4.8 eV for the work functions of a Ag/AgCl and an 1TO electrode, respectively, one arrives at zero field injection barriers of 0.4 and 0.55 eV. These values represent lower bounds because cyclic voltammetry is carried out in polar solvents in which the stabilization cncigy of radical ions exceeds that in a polymer film, where only electronic polarization takes place. E x values for LPPP and PPPV are not available but in theory they should exceed those of PPV-imine and PPV-ether. 

FIGURE 2-21 EQCM (a) and cyclic voltammetry (b) profiles at an ion exchanger-coated electrode in the presence of 6 x 10 3 M Ru(NH3)6C16. (Reproduced with permission from reference 65.)... 

Another spectroscopic technique, high-resolution electron energy loss spectroscopy (HREELS), has been used by Wagner and Moylan211 in combination with cyclic voltammetry to estimate ffs0of a Pt(lll) electrode from the reaction of H30+ formation. 

The electrical double layer at an Ag electrode chemically polished in H20 + NaCN24 was studied using impedance and cyclic voltammetry.375... 

The electrical double-layer structure at Au(l 11), Au(110), Au(100), and Au(210) faces and at a pc-Au electrode has been studied in 5 x 10 3 and 1 x 10-2 M LiC104 solutions in DMSO by cyclic voltammetry and impedance methods.477 The electrodes were cleaned by heating in a flame ... 

The surface electrochemistry of Pt single-crystal electrodes has been exhaustively studied using cyclic voltammetry.100 186 188 197 209 412 753-756,771,-773,779-788,794-796 qq g technique has been proved to be highly... 

The electrochemistry of a polymer-modified electrode is determined by a combination of thermodynamics and the kinetics of charge-transfer and transport processes. Thermodynamic aspects are highlighted by cyclic voltammetry, while kinetic aspects are best studied by other methods. These methods will be introduced here, with the emphasis on how they are used to measure the rates of electron and ion transport in conducting polymer films. Charge transport in electroactive films in general has recently been reviewed elsewhere.9,11... 

Figure 10. Cyclic voltammetry (top) and in situ electronic resistance (bottom) of poly(3-methylthiophene) from parallel-band electrode [Fig. 9(A)] experiments in S02(1) containing 0.1 M Bu4NPF6.37 (Reprinted with permission from J. Am. Chem. Soc. 112, 7869-7879, 1990. Copyright 1990, American Chemical Society.)...

The kinetics of charge transfer between metallic electrodes and conducting polymer films have proved to be difficult to investigate, and little reliable data exist. Charge-transfer limitations have been claimed in cyclic voltammetry, and Butler-Volmer kinetics have been used in a number of... 

J. Yi, A. Kaloyannis, and C.G. Vayenas, High Temperature cyclic voltammetry of Pt electrodes in solid electrolyte cells, Electrochim. Acta 38(17), 2533-2539 (1993). 

In the majority of examples in the Uterature, the desired product is obtained by applying a single fixed potential. It is also possible, however, to programme the electrode potential to change in a pre-determined manner, and this is commonly done in studies of reaction intermediates and the kinetics of electrode processes. Thus, cyclic voltammetry (Adams,... 

Such effects are observed inter alia when a metal is electrochemically deposited on a foreign substrate (e.g. Pb on graphite), a process which requires an additional nucleation overpotential. Thus, in cyclic voltammetry metal is deposited during the reverse scan on an identical metallic surface at thermodynamically favourable potentials, i.e. at positive values relative to the nucleation overpotential. This generates the typical trace-crossing in the current-voltage curve. Hence, Pletcher et al. also view the trace-crossing as proof of the start of the nucleation process of the polymer film, especially as it appears only in experiments with freshly polished electrodes. But this is about as far as we can go with cyclic voltammetry alone. It must be complemented by other techniques the potential step methods and optical spectroscopy have proved suitable. 

For the in situ characterization of modified electrodes, the method of choice is electrochemical analysis by cyclic voltammetry, ac voltammetry, chronoamperometry or chronocoulometry, or rotating disk voltametry. Cyclic voltammograms are easy to interpret from a qualitative point of view (Fig, 1). The other methods are less direct but they can yield quantitative data more readily. 

Electrochemical oxidation of the group-IIB metal can generate metal-metal bonds analogously to the manner described in 8.3.3.4. For example, cyclic voltammetry with Hg electrodes shows that M(CO)2dpam (M = Cr, Mo) reacts to form Hg—M bonds in two stages ... 

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