Cyclic reversible region

Cyclic Voltammetry for Monolayer Adsorption (a) Reversible region... 

Cholanic acid also possesses the ability of transporting cations across a lipophilic membrane but the selectivity is not observed because it contains no recognition sites for specific cations. In the basic region, monensin forms a lipophilic complex with Na+, which is the counter ion of the carboxylate, by taking a pseudo-cyclic structure based on the effective coordination of the polyether moiety. The lipophilic complex taken up in the liquid membrane is transferred to the active region by diffusion. In the acidic region, the sodium cation is released by the neutralization reaction. The cycle is completed by the reverse transport of the free carboxylic ionophore. 

While thick oxide formation on Ru occurs together with Oz evolution at a potential of 1.15 Vsce, the initial steps of oxide formation are expected to occur at more cathodic potentials of roughly 0.3 0.8 V [72]. Structures in the cyclic voltammogram in this potential region were attributed by Vucovik et al. [73] to hydroxide or oxide adsorption. These oxides are reversibly reduced at a potential of 0.1 V. The presence of a thin oxide layer on Ru at potentials cathodic of 1.15 V was demonstrated by... 

The compound formed is electroactive. The cyclic voltammogram of a Pt electrode in the carbamidc-NII4Cl melt exhibits a maximum (wave A) in the region of the zero value of potential on the reverse anodic sweep, which reflects the electrochemical reduction of the compound formed (Fig. 3). For... 

There seems to be no great difference in the free energy between acyclic triene and the cyclic diene. This is because of smaller strain in the six-membered ring as compared with the four-membered one. On the other hand in 6n electron system in electrocyclic process there is more efficient absorption in the near regions of u.v. spectrum. This is why under both thermal and photochemical conditions, the (1, 6) electrocyclic reactions are reversible. Side reactions are more frequent in reversible. Side reactions are more frequent in reversible transformations of trienes than in dienes. The dehydrogenation of cyclic dienes to aromatic compounds may also occur in the thermal process. On heating cyclohexadiene yields benzene and hydrogen. 

A cyclic voltammogram ofZn underpotential deposition on Pt(llO) in sulfuric acid solution is more reversible than that in perchlorie acid solution with respect to the change of potentials, as shown in Fig. 27. The was evaluated as about 1 V. Since Zn underpotential deposition in acidic solutions was observed in the adsorbed hydrogen region, the pH was increased to separate Zn underpotential deposition from the hydrogen adsorption region. At pH 4.6, Zn underpotential deposition was observed, as shown in Fig. 29. The different cyclic voltammogram appearances of Zn underpotential deposition on Pt(lll) at different pHs is discussed in Section n.4. 

Figure 6.19. Experimental cyclic voltammograms of carbon-supported high surface area nanoparticle electrocatalysts in deaerated perchloric acid electrolyte. Solid curve pure Pt dashed curve Pt5oCo5o alloy electrocatalyst. Inset blow up of the peak potential region of Pt—OH and Pt— formation. Scan rate 100 mV/s. Potentials are referenced with respect to the reversible hydrogen electrode potential (RHE).

As mentioned above, the characteristic feature of processes in this kinetic region is that the peak current ratio — z°x/Zped varies from about unity to zero. Thus, a procedure for studying the kinetics would be to record values of —/°x//ped at different sweep rates and compare these with a working curve for the proposed mechanism in a way analogous to that discussed for DPSCA above. However, a problem with this approach is the difficulty of defining a baseline for the reverse sweep (see below) and, for that reason, CV suffers from some limitations when used in quantitative work. This has led to the development of derivative cyclic voltammetry (DCV) [37]. 

Obviously, therefore there must be an intermediate case in which the kinetics of both the forward and reverse electron-transfer processes have to be taken account of. Such systems are described as being quasi-reversible and as would be expected, the scan rate can have a considerable effect on the nature of the cyclic voltammetry. At sufficiently slow scan rates, quasi-reversible processes appear to be fully reversible. However, as the scan rate is increased, the kinetics of the electron transfer are not fast enough to maintain (Nernstian) equilibrium. In the scan-rate region when the process is quasi-reversible, the following observations are made. 

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