Solution cyclic voltammograms

Polypyrrole Film Formation in Glucose Oxidase Enzyme Solution. Cyclic voltammograms recorded in the GOD and pyrrole solution showed an anodic peak current (E = 1.08 V), which suggested the polymerization of pyrrole in the above solution. However, the polymerization potential moved toward the more positive direction compared to the polymerization potential of PPy doped with Cl ( pa < 1.0 V). This is due to the fact that the polymerization is more difficult to take place in enzyme solution than in Cl solution because the enzyme solution is a much weaker electrolyte than NaCl it may also be due to the less conductive nature of the PPy-GOD film as compared to that of the PPy-Cl film. The polymerization current level was much lower in the enzyme solution than in the Cl solution because of the poor charge-transport property of the enzyme protein molecules. It was found that the constant current method was more suitable than the controlled potential method for making the PPy-GOD film on the GC electrode. 

Figure 2. (A) Solution cyclic voltammogram of 0.35 mM 1 in 0.1 MTEATFA solution of CH2CI2. Scan rate = 100 mV/s. Au electrode area = 0.24 cn. (B) Simultaneous mass changes as recorded by the QCE.

Figure 4. Cyclic voltammograms of Pt-poly disk electrode and Pt/C catalysts (40 wt.% Pt, Alfa Aesar), recorded at 50 mV s in de-aeiated 0.1 mol dm HCIO4 solution. Cyclic voltammograms are normalized by real surface area of Pt assessed by investigating hydrogen underpotential deposition.

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. 

Figure 9 shows the first and second cycle of a cyclic voltammogram of a 0.2 molal (mol kg"1) solution of lithium bis[2,2 biphenyldiolato(2-)-0,0 ]borate in PC at a stainless steel electrode. The sweep covers the potential range from open circuit potential ER versus a lithium reference electrode up to 4500 mV versus Li and back to ER. The first cycle shows... 

FIGURE 2-7 Repetitive cyclic voltammograms for 1 x 10 6 m riboflavin in a 1 niM sodium hydroxide solution. (Reproduced with permission from reference 10.)... 

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. 

When cyclic voltammograms of an electrode partially or completely covered with an adsorbate in contact with an electrolyte solution are recorded, various characteristic features of the obtained voltammogram can be used to deduce the amount of adsorbed material. This procedure can be repeated at various concentrations of the species to be adsorbed in the solution. From the obtained relationship between... 

Fig. 2. Cyclic voltammograms over supported Pt (40wt.%) catalysts in H2SO4 solution at 298K (scan rate = 20mV/s).

Figure 7. Cyclic voltammogram of 7% w/w FePc dispersed on Vulcan XC-72 carbon. The specimen was prepared by mixing the carbon with an FePc solution In pyridine and subsequently removing the solvent by boiling It off. The sample was then heat treated at 300°C In flowing He to remove coordinated pyridine. The cyclic voltammogram was obtained with the material In the form of a thin porous coating In 1 M NaOH at 25 C. Sweep rate 5 mV s (19).

Figure 12. Cyclic voltammograms of direct methanol oxidation catalyzed by the porous Pt nanoparticle membrane and as-made Pt nanoparticles. The reaction solution was made of an aqueous mixture containing O.IMHCIO4 and 0.125 M methanol. (Reprinted with permission from Ref [31], 2005, Wiley-VCH.)...

Figure 7.5 Cyclic voltammogram of a Pt(775) electrode in 0.5 M H2SO4 solution and a hard sphere model of this surface. Sweep rate 50 mV/s. In the hard sphere model, four atoms forming the (110) step site have been identified in black.

Figure 8.9 Polarization curves for a PtSn/C catalyst recorded by a rotating disk electrode in 0.5 M H2SO4 saturated with either pure hydrogen, a H2/2% CO mixture, and pure CO (the arrow points to the onset of CO oxidation) at 60 °C with 1 mV/s and 2500 rev/min the dashed curve is the cyclic voltammogram (in arbitrary units) in an argon-purged solution at 60 °C with 50 mV/s. (Reprinted with permission from Aienz etal. [2005]. Copyright 2005. Elsevier.)...

Figure 17.14 Cyclic voltammograms recorded at 1 V s at a PGE RDE rotating at 2500 rev min ) modified by adsorption of a submonolayer film of [NiEe]-hydrogenase from the purple photosynthetic sulfur bacterium Allochromatium vinosum in buffered aqueous solution at pH 7.0 under an atmosphere of H2 (1 bar). Reprinted with permission from Leger et al., 2002. Copyright (2002) American Chemical Society.

FIG. 4 Cyclic voltammogram of the ion transfer between the aqueous solution inside a 15 mm-radius pipette and the external DCE solution of TEA+ (60/xM). (Reprinted with permission from Ref. 18a. Copyright 1990 Elsevier Science S.A.)... 

FIG. 5 Cyclic voltammograms of [Fe(CN)6] redox couple on bare (solid line), DNA-modified (heavy line), and HEDS-modified Au electrodes (dotted line). Electrol5de solution, aqueous each 5 mM of K4[Fe(CN)g] and K3[Fe(CN)g] containing 10 mM KCl scan rate 25 mV s temperature, 25°C electrode area, 0.02 cm (geometrical). 

As mentioned above, the distribution of the various species in the two adjacent phases changes during a potential sweep which induces the transfer of an ion I across the interface when the potential approaches its standard transfer potential. This flux of charges across the interface leads to a measurable current which is recorded as a function of the applied potential. Such curves are called voltammograms and a typical example for the transfer of pilocarpine [229] is shown in Fig. 6, illustrating that cyclic voltammograms produced by reversible ion transfer reactions are similar to those obtained for electron transfer reactions at a metal-electrolyte solution interface. 

FIG. 6 Typical cyclic voltammogram obtained for the transfer of pilocarpine hydrochloride at the water-DCE interface. The organic phase contains 0.01 M tetrabutylammonium tetrakis(4-chloro-phenyl)borate, the aqueous solution is 0.01 M HCl + 0.2 mM pilocarpine hydrochloride, and the sweep rate is fixed at 10, 25, 75, 100, and 150mV/s. (Reprinted from Ref. 229.)... 

Cyclic voltammograms of solutions of the pyrrole monomers also show a dependence on the anion present in the electrolyte and can show multiple peaks with Epa values ranging from + 1.0 to + 1.3 V in acetonitrile [57,279]) (+ 0.8 to + 1.1 V vs. 

---