Modified electrodes cyclic voltammetry

Electrochemical Techniques. Cyclic Voltammetry (CV) was performed on most of the poly(3-methylthiophene) anion sensor electrodes. Cyclic voltammetry provided the electrochemical characterization and evaluation of the post treatment of the modified electrodes. The potential of the platinum electrodes (Model MF-1012, BAS Inc.), with or without modifying film of poly(3-methylthiophene) was controlled relative to an Ag/AgCl reference electrode (BioanaJytical Systems Inc., West Lafayette, IN). The auxiliaiy electrode was a platinum flag electrode or in the case of the FIA experiments a stainless steel block electrode (BAS, West Lafayette, IN). 

Electron microscopy and spectroscopic techniques are employed to identify the structural characteristics of the modified surface. Cyclic voltammetry is largely used to define the electrochemical behaviours of the sensor and to elucidate mechanistic aspects of the electrode reaction. A.C. voltammetry has also been applied . As both spectroscopic and electrochemical results are often required to obtain valuable information, the use of spectroelectrochemical methods may be very useful2 -28 ... 

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. 

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... 

If the film is nonconductive, the ion must diffuse to the electrode surface before it can be oxidized or reduced, or electrons must diffuse (hop) through the film by self-exchange, as in regular ionomer-modified electrodes.9 Cyclic voltammograms have the characteristic shape for diffusion control, and peak currents are proportional to the square root of the scan speed, as seen for species in solution. This is illustrated in Fig. 21 (A) for [Fe(CN)6]3 /4 in polypyrrole with a pyridinium substituent at the 1-position.243 This N-substituted polypyrrole does not become conductive until potentials significantly above the formal potential of the [Fe(CN)6]3"/4 couple. In contrast, a similar polymer with a pyridinium substituent at the 3-position is conductive at this potential. The polymer can therefore mediate electron transport to and from the immobilized ions, and their voltammetry becomes characteristic of thin-layer electrochemistry [Fig. 21(B)], with sharp symmetrical peaks that increase linearly with increasing scan speed. 

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. 

The redox potentials of the ITO electrodes modified with CgoN -MePH clusters were measured by cyclic voltammetry and differential pulse voltammetry in the absence and presence of magnetic processing. 

In the cyclic voltammetry, the oxidation peaks of PH were clearly observed in positive scans for all the modified electrodes. In contrast, reduction peaks of Cgo were clearly observed in the absence of magnetic processing but not in the presence of magnetic processing. 

Figure 3.96 The effect of increasing time of exposure (as indicated) of a gold electrode once-modified with SSBipy to thiophenol on the cyclic voltammetry of horse heart cytochrome t (0.4mM). 20 mM sodium phosphate/0.1 M NaCI04 pH 7.0. Scan rate 20mVs l. From Hill...

M.F.S. Teixeira, A. Segnini, F.C. Moraes, L.H. Marcolino, O. Fatibello, and E.T.G. Cavalheiro, Determination of vitamin B-6 (pyridoxine) in pharmaceutical preparations by cyclic voltammetry at a copper(II) hexacyanoferrate(III) modified carbon paste electrode. J. Brazilian Chem. Soc. 14, 316-321... 

The first CNT-modified electrode was reported by Britto et al. in 1996 to study the oxidation of dopamine [16]. The CNT-composite electrode was constructed with bro-moform as the binder. The cyclic voltammetry showed a high degree of reversibility in the redox reaction of dopamine (see Fig. 15.3). Valentini and Rubianes have reported another type of CNT paste electrode by mixing CNTs with mineral oil. This kind of electrode shows excellent electrocatalytic activity toward many materials such as dopamine, ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid [39], hydrogen peroxide, and NADH [7], Wang and Musameh have fabricated the CNT/Teflon composite electrodes with attractive electrochemical performance, based on the dispersion of CNTs within a Teflon binder. It has been demonstrated that the electrocatalytic properties of CNTs are not impaired by their association with the Teflon binder [15]. 

Preparation and Electrochemical Behavior of Macroelectrodes Modified with Polv(I). The electrochemical behavior of 2 was investigated in CH3CN/0.I 1 [11-BU4N]PF via cyclic voltammetry at a Pt electrode. 

Nanocarbons can also be deposited onto surfaces via electrochemistry, such as electrophoretic deposition described earlier. A method for one-step electrochemical layer-by-layer deposition of GO and PANI has been reported by Chen et al. [199]. A solution of GO and aniline was prepared and deposited onto a working electrode via cyclic voltammetry. GO was reduced on the surface when a potential of approx. -1 V (vs. SCE) was applied compared to the polymerization of aniline which occurred at approx. 0.7 V (vs. SCE). Repeated continuous scans between -1.4 to 9 V (vs. SCE) resulted in layer by layer deposition [199]. A slightly modified method has been reported by Li et al. who demonstrated a general method for electrochemical RGO hybridization by first reducing GO onto glassy carbon, copper, Ni foam, or graphene paper to form a porous RGO coating [223]. The porous RGO coated electrode could then be transferred to another electrolyte solution for electrochemical deposition, PANI hybridization was shown as an example [223]. 

Reduction potentials of the S. obliqms His59 Ru(NH3)5-modified protein have been determined by cyclic voltammetry using as electrode the oxidized surface obtained by polishing the edge plane of pyrolytic graphite [137]. The modified protein responds well at the electrode, whereas the native protein requires multi-eharged cations, e.g. Mg or [Cr(NH3)g] as mediators to give satisfactory reversibility. Separate reduction potentials at 1=0.10 M(NaCl) for native S. obliquus plastocyanin (389 mV) and [Ru(NH3)5 (imidazole)]... 

When the characteristic time for charge diffusion is lower than the experiment timescale, not all the redox sites in the film can be oxidized/reduced. From experiments performed under these conditions, an apparent diffusion coefficient for charge propagation, 13app> can be obtained. In early work choroamperometry and chronocoulometry were used to measure D pp for both electrostatically [131,225] and covalently bound ]132,133] redox couples. Laviron showed that similar information can be obtained from cyclic voltammetry experiments by recording the peak potential and current as a function of the potential scan rate [134, 135]. Electrochemical impedance spectroscopy (EIS) has also been employed to probe charge transport in polymer and polyelectrolyte-modified electrodes [71, 73,131,136-138]. The methods... 

Figure 3.15 (a) Cyclic voltammetry of SWNT-modified electrodes where the tubes were cut for 2 h and either randomly dispersed or vertically aligned. CVs are recorded relative to an Ag/AgCI reference electrode in 1 mM l<3Fe(CN)6 in a background electrolyte of 0.05 M KH2PO4 and 0.05 M KCI at pH 7.0 at lOOmV/s. The y-axis shows the current normalized to the anodic peak... 

Chen and coworkers were the first to describe the electrochemical behavior of PB NPs [41]. They prepared solutions of PB NPs by reaction of Fe(III) with Fe(CN)6 in the presence of H2O2, giving 30-50-nm diameter NPs. These were then immobilized at cysteine-modified Au electrodes with pendant amine groups by prolonged (10 h) exposure of the modified electrode to a solution of the NPs. This produced a monolayer of immobilized NPs that was subsequently examined using cyclic voltammetry. Interestingly, they observed two redox processes near 0.25 V vs. 

A Chemically mediated spectroelectrochemical titration B Cyclic voltammetry at a 3-mercaptopropionic acid-modified Au electrode C Chemically mediated coulometric titration. 

The electrodes modified by hexacyano-ferrates compounds were also used as voltammetric sensors [409-412]. The cadmium hexacyanoferrate-based composite ion-sensitive electrode for voltammetry was explored by Scholz and coworkers [409]. The potential of such electrode depends linearly on the logarithm of concentration of alkali and alkaline-earth metals ions in the solutions. Bo and fin have studied [410] Prussian blue (PB)/Pt modified electrode in GdGh electrolyte by cyclic voltammetry and in situ Fourier transform IR spectroscopy (FTIR) spectro-electrochemistry. Cadmium hexacyanofer-rates were formed on a PB film. 

Apart from the above techniques, the electromodulated reflectance spectroscopy combined with cyclic voltammetry has been utilized by Gaigalas et al. [14] in the investigations of electron transfer between the 2Fe-2S protein putidaredoxin and either bare or bekanamycin-modified Ag electrode. Of the two models considered, the free diffusion model, as compared to the adsorbed layer model, exhibited better concordance with the experimental data. After modification of the Ag electrode with bekanamycin, it exhibited only a small increase in the observed redox reaction... 

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