Voltammetric behavior

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.)... 

Figure 64. Voltammetric behavior simulated for increasing scan rates (10 to 50 mV s-1), when the cathodic potential of departure was -2500 mV, the anodic limit 300 mV, and the temperature 25°C. (Reprinted from T. F. Otero, H.-J. Grande, and J. Rodriguez, J. Phys. Chem. 101, 8525,1997, Figs. 3-11, 13. Copyright 1997. Reproduced with permission from the American Chemical Society.)...

The observed complexity of the Se(IV) electrochemistry due to adsorption layers, formation of surface compounds, coupled chemical reactions, lack of electroactivity of reduction products, and other interrelated factors has been discussed extensively. Zuman and Somer [31] have provided a thorough literature-based review with almost 170 references on the complex polarographic and voltammetric behavior of Se(-i-IV) (selenous acid), including the acid-base properties, salt and complex formation, chemical reduction and reaction with organic and inorganic... 

Zuman P, Somer G (2000) Polarographic and voltammetric behavior of selenous acid and its use in analysis. Talanta 51 645-665... 

Recently, a eutectic mixture of choline chloride and urea (commercially known as Reline) was used as a medium from which CdS, as well as CdSe and ZnS, thin films were electrodeposited for the first time [53]. Reline is a conductive room-temperature ionic liquid (RTIL) with a wide electrochemical window. The voltammetric behavior of the Reline-Cd(II)-sulfur system was investigated, while CdS thin films were deposited at constant potential and characterized by photocurrent and electrolyte electroabsorbance spectroscopies. 

Fig. 4.7 Voltammetric behavior of a Au(lll) electrode immersed in 1 mM Se02 in 0.100 M HCIO4 supporting electrolyte. The five major cathodic waves corresponding to Se deposition are labeled C1-C5, respectively. The scan rate was 0.100 V s. (Reprinted from [82], Copyright 2009, with permission from Elsevier)...

The qualitative voltammetric behavior of methanol oxidation on Pt is very similar to that of formic acid. The voltammetry for the oxidation of methanol on Pt single crystals shows a clear hysteresis between the positive- and negative-going scans due to the accumulation of the poisoning intermediate at low potentials and its oxidation above 0.7 V (vs. RHE) [Lamy et al., 1982]. Additionally, the reaction is also very sensitive to the surface stmcture. The order in the activity of the different low index planes of Pt follows the same order than that observed for formic acid. Thus, the Pt(l 11) electrode has the lowest catalytic activity and the smallest hysteresis, indicating that both paths of the reaction are slow, whereas the Pt( 100) electrode displays a much higher catalytic activity and a fast poisoning reaction. As before, the activity of the Pt(l 10) electrode depends on the pretreatment of the surface (Fig. 6.17). 

At higher potentials, positive of the Hupd OHad exchange, the C Vs of the Pt island-modified Ru(OOOl) surface closely resemble those of the ft-fiee Ru(OOOl) electrode, except for the lower currents/charges in the characteristic features. This simply reflects the fact that at these potentials, the surface reactivity is dominated by the electrochemical properties of the remaining exposed Ru surface. As already mentioned, the Pt monolayer islands themselves contribute only little to the voltammetric behavior, which is due to the weak bonding and hence low adsorbate coverages on these islands. 

We shall consider the voltammetric behavior of a base at the 0/W interface. In the discussion stated above it is assumed that the transfer process of drugs at the 0/W interface is of reversible nature (see the assumptions 1-6 above). With increasing pH of the W phase, particularly in basic solutions, however, the rate of protonation in the W phase, that is, B(W) - - H+(W) = BH+(W) should rapidly decrease, resulting in decreasing of the current associated with the transfer of BH+ ion across the O/W interface. This has actually... 

Studies of the linear sweep and cyclic voltammetric behavior of N-methyl-ated xanthines 35 -37> reveals that they undergo electrochemical oxidation over a fairly wide pH range at the PGE (Table 1). All but three of the xanthines studied show just a single voltammetric oxidation peak, although it is prob-... 

M. Borsari and H.A. Azab, Voltammetric behavior of bovine erythrocyte superoxide dismutase. Bioelectrochem. Bioenerg. 27, 229-233 (1992). 

The electrochemistry of Ti2+ in 66.7 m/o AlCl3-NaCl has been investigated wherein the electroactive Ti2+ was prepared by the oxidation of Ti metal with liquid A1C13 [176, 185] and by the electrochemical dissolution of titanium metal [120, 177], The authors of both studies concluded that Ti2+ may be oxidized stepwise to Ti3+ and Ti4+ and that both processes are reversible at platinum and tungsten electrodes. However, anomalous voltammetric behavior at high Ti2+ concentrations (greater than 50 mmol L ) suggests the formation of polymeric Ti2+ species in the melt. The reduction of Ti2+ to the metal was not observed at potentials more positive than that required for aluminum deposition. 

Electrochemical detection is sensitive and selective, and it gives useful information about polyphenolic compounds in addition to spectra obtained by photodiode array detectors. Differences in electrochemically active substituents on analogous structures can lead to characteristic differences in their voltammetric behavior. Because the response profile across several cell potentials is representative of the voltammetric properties of a compound, useful qualitative information can be obtained using electrochemical detection (Aaby and others 2004). 

To favor the coupling reaction, the competing side reaction of the radical cation with nucleophiles must be suppressed by the use of a medium of low nucleophilicity. The solvent of choice is dichloromethane. Especially in elec-troanalytic studies, neutral alumina is frequently added to suppress hydroxy-lation of the radical cation [162]. The reversible cyclic voltammetric behavior of radical cations is also enhanced in mixtures of methylene dichloride, triflu-oroacetic acid, and trifluoroacetic anhydride (TFAn) with TBABF4 as supporting electrolyte. With acetonitrile as solvent... 

The voltammetric behavior of pyrite at pH= 8.8 (see Fig. 3.8) shows that an anodic current commenced at about -0.25 V to give an anodic peak at about 0 V. On the reverse scan a cathodic current that appeared at the same potential could be presumed to represent the reduction of the initial oxidation products. According to the reaction (3-9), the formation of sulphur would be expected to occur at -0.26 V for the HS concentration of 10" mol/L at pH = 8.8 which is consistent with an anodic current that begins to occur. 

Thin-film ideal or Nemstian behavior is the starting point to explain the voltammetric behavior of polyelectrolyte-modified electrodes. This condition is fulfilled when (i) the timescale of the experiment is slower than the characteristic timescale for charge transport (fjD pp, with Ithe film thickness) in the film, that is all redox within the film are in electrochemical equibbrium at any time, (ii) the activity of redox sites is equal to their concentration and (iii) all couples have the same redox potential. For these conditions, anodic and cathodic current-potential waves are mirror images (zero peak splitting) and current is proportional to the scan rate [121]. Under this regime, there exists an analytical expression for the current-potential curve ... 

Kv = j reflecting the influence of the kinetics of the surface and volume follow-up chemical reaction, respectively. Figure 2.78 depicts the variation of the dimensionless net peak current with kv, for a variety of adsorption strengths of the redox couple, obtained by simulations of the mechanism (2.177). Instead of decreasing, the enlarges by accelerating the volume chemical reaction. The increase of AWp is a consequence of the enhancement of the reverse component of the response. Beside the pecuhar variation of A Fp, the peak potential shifts in a positive direction with a slope of = 2.303. Accordingly, the overall voltammetric behavior is... 

The effect of the volume and the surface catalytic reaction is sketched in Figs. 2.80 and 2.81, respectively. Obviously, the voltammetric behavior of the mechanism (2.188) is substantially different compared to the simple catalytic reaction described in Sect. 2.4.4. In the current mechanism, the effect of the volume catalytic reaction is remarkably different to the surface catalytic reaction, revealing that SWV can discriminate between the volume and the surface follow-up chemical reactions. The extremely high maxima shown in Fig. 2.81 correspond to the exhaustive reuse of the electroactive material adsorbed on the electrode surface, as a consequence of the synchronization of the surface catalytic reaction rate, adsorption equilibria, mass transfer rate of the electroactive species, and duration of the SW potential pulses. These results clearly reveal how powerful square-wave voltammetry is for analytical purposes when a moderate adsorption is combined with a catalytic regeneration of the electroactive material. This is also illustrated by a comparative analysis of the mechanism (2.188) with the simple surface catalytic reaction (Sect. 2.5.3) and the simple catalytic reaction of a dissolved redox couple (Sect. 2.4.4), given in Fig. 2.82. 

The electrochemistry of oxo-bridged manganese complexes in aqueous solution is characterized by coupled electron and proton-transfer reactions. The cyclic voltammetric behavior of [Mn2 02(phen)4] + in aqueous pH 4.5 phosphate buffer is illustrated in Fig. 12 [97]. It is of interest to compare this result with that obtained for the same complex dissolved in CH3CN (Fig. 9). Two one-electron reactions are observed in each case. However, these correspond to Mn(IV,IV) Mn(IV,III) and Mn(IV,III) Mn(III,III) reductions in the nonaqueous solvent and to Mn(IV,III) Mn(III,III) and Mn(III,III) Mn(III,II) reductions in... 

Effect of Adsorption and Surface Structure on the Voltammetric Behavior of Platinum Electrodes... 

Considering these results it was an important task to reconsider some questions connected with the technique of platiniza-tion, examining whether the method of platinization has some influence on the voltammetric behavior of the platinized surfaces. In [220], attempts were made to demonstrate that the voltammetric behavior of the platinized system could depend on the experimental conditions of the deposition carried out by a simple gal-vanostatic method. 

It follows from a comparison of Fig. 5(b) and (c) with Fig. 6(b) and (c) that the electrocatalytic reduction of NOs" ions depends strongly on structural factors, reflected by the voltammetric behavior in pure FI2SO4 solution. This observation is in accordance with earlier findings [173, 233, 234] that (100) crystal faces have an excellent catalytic activity toward the reduction of N03 ions compared with the other low index planes. 

Such effect of small cations on the voltammetric behaviors of a-[SiMoi204o]" and a-[PMoi204o] in acetone and acetonitrile was investigated recently [37]. For the o -[SiMoi204o]" complex, the presence of Li+ or Na" " caused the one-electron wave to be converted into a two-electron wave at ca. 0.3 V more positive than the first one-electron wave. In the presence of Li+ or Na+, the a-[PMoi204o] complex underwent a two-electron reduction at the same potential as the original first one-electron wave in CH3COCH3, whereas it exhibited only successive... 

Evidence for an Influence of the Dissymmetry on the Voltammetric Behavior of PWig Comparison with P2Wi8... 

Voltammetric behavior in trace determination of cadmium at a calixarene modified screen-printed carbon paste electrode was investigated [405]. 

The solid-state electrochemical formation of bilayer electrode structures of different hexacyanoferrates was studied, and a theoretical model was proposed for cyclic voltammetric behavior of the transformation of PB into cadmium hexacyanoferrates [411]. 

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