Cyclic voltammetry current function values

TABLE 3.2 Current Function Values for Cyclic Voltammetry of Reversible Processes (o = 0.5)6... 

FIGURE 1.17. Cyclic voltammetry of slow electron transfer involving immobilized reactants and obeying a Butler Volmer law. Normalized current-potential curves as a function of the kinetic parameter (the number on each curve is the value of log A ) for a. — 0.5. Insert irreversible dimensionless response (applies whatever the value of a). 

Using, for example, cyclic voltammetry, the cathodic peak current (normalized to its value in the absence of RX) is a function of the competition parameter, pc = ke2/(ke2 + kin), as detailed in Section 2.2.6 under the heading Deactivation of the Mediator. The competition parameter can be varied using a series of more and more reducing redox catalysts so as eventually to reach the bimolecular diffusion limit. km is about constant in a series of aromatic anion radicals and lower than the bimolecular diffusion limit. Plotting the ratio pc = keij k,n + km) as a function of the standard potential of the catalysts yields a polarogram of the radical whose half-wave potential provides the potential where ke2 = kin, and therefore the value of... 

The term voltammetry refers to measurements of the current as a function of the potential. In linear sweep and cyclic voltammetry, the potential steps used in CA and DPSCA are replaced by linear potential sweeps between the potential values. A triangular potentialtime waveform with equal positive and negative slopes is most often used (Fig. 6.8). If only the first half-cycle of the potential-time program is used, the method is referred to as linear sweep voltammetry (LSV) when both half-cycles are used, it is cyclic voltammetry (CV). The rate by which the potential varies with time is called the voltage sweep (or scan) rate, v, and the potential at which the direction of the voltage sweep is reversed is usually referred to... 

In the cyclic mode of SWV, two scans can be analyzed in an anologous way to Cyclic Voltammetry. In Fig. 7.61, the Cyclic SWV curves (7.61a) of the catalytic process given in (7.XI) for different values of A at planar electrodes have been plotted, together with the evolution of the peak currents (7.61b) and peak potentials (7.61c) of the first (1) and second (2) scans toward cathodic and anodic potentials, respectively, as a function of logA. 

In most cases the current is plotted as a function of potential on an X-Y recorder or on a plotter. This becomes particularly useful when the potential is swept forward and backward between two fixed values, a technique referred to as cyclic voltammetry. In this way the current measured at a particular potential on the anodic sweep can readily be... 

Therefore the electrochemical response with porous electrodes prepared from powdered active carbons is much increased over that obtained when solid electrodes are used. Cyclic voltammetry used with PACE is a sensitive tool for investigating surface chemistry and solid-electrolyte solution interface phenomena. The large electrochemically active surface area enhances double layer charging currents, which tend to obscure faradic current features. For small sweep rates the CV results confirmed the presence of electroactive oxygen functional groups on the active carbon surface. With peak potentials linearly dependent on the pH of aqueous electrolyte solutions and the Nernst slope close to the theoretical value, it seems that equal numbers of electrons and protons are transferred. 

Cyclic Voltammetry. In this method, the potential of the working electrode is varied linearly with time from an initial potential of E to a final value of f, and then reversed from Ef to E at the same rate, as shown in Fig. 4.3.15. The resulting current is measured as a function of time or potential. This scheme can be used as a single sweep or a multisweep, as used in cyclic voltaimnetry. The potential range is generally selected to suit the reaction under study. 

Cyclic voltammetry of spinach plastocyanin portrays an interesting view of how these factors affect its ability to transfer electrons. It was observed [99] that the eonditions required to promote electrochemistry at a PGE electrode were broadly similar to those pertaining to the photosynthetic electron-transport system. For a solution of the protein (oxidized or reduced) at low ionic strength, well-defined diffusion-controlled voltammetric waves were observed upon addition of Mg " or by acidification to pH 4. The peak-current response as a function of these variables is shown in Fig. 12. At pH 7 (3 °C), E was found to be 375 mV, in good agreement with the potentiometric value reported by Katoh and co-workers [156]. The electrode reaction was found to be essentially reversible at pH 4. Whilst this appears at first to be in conflict with the evidence for plastocyanin being inactive at this pH, closer consideration shows that this is a consistent result. The corresponding electrode reaction may be written as in Eqs. (11)-(12)... 

PAMAM dendrimers functionalized with bis (terpyridyl) cobalt(II) dend-n-[Co(tpy)2], G1 and 3 with n = 8 and 32, respectively), similar to those functionalized with dend-n-[Ru tpy)2], have been synthesized and characterized by the same group [86]. In TBAH/AN solution, when the potential was scanned between +0.60 and —1.20 V versus Ag/AgCl, the dendrimers showed two redox couples with formal potential values of +0.30 and -0.75 V versus Ag/AgCl, which correspond to the Co(II/III) and Co(I/II) processes, respectively (Fig. 9b). Interestingly, when cyclic voltammetry was performed immediately after the immersion of a Pt electrode into a solution containing dend- -[Co(tpy)2], the peak current of the Co(I/II) redox process initially appeared to be the same as that of Co(II/III) (Fig. 9a). However,... 

The uncertainty does not stem only from the way the data are interpreted. It also depends heavily on the experimental method employed to obtain these data. In Fig. 17 we show an example of data obtained during the deposition of Ag on An, in both the upd and the opd regions, measured galvanostatically j = constant) and by cyclic voltammetry at different scan rates. The cathodic parts of the CV curves were used to construct the plot of A/ as a function of the charge passed. In measurements conducted under galvanostatic conditions, all values of the frequency shift were above the calculated line, as shown also in Fig. 16, practically independent of the applied current density. The response always had the same shape a delay until a few atomic layers have been deposited, followed by a line having the theoretical slope, but shifted upwards (i.e., to higher frequencies). Cyclic voltammetry leads... 

The potential-time waveforms used for sweep measurements are shown in Fig. 6.1. The simplest of these techniques is linear sweep voltammetry (LSV), and this involves sweeping the electrode potential between limits Ei and E2 at a known sweep rate, v, before halting the potential sweep. A generally more useful (and consequently more widely applied) technique is cyclic voltammetry (CV). In this case the waveform is initially the same as in LSV, but on reaching the potential E2 the sweep is reversed (usually at the same scan rate) rather than terminated. On again reaching the initial potential, Ei, there are several possibilities. The potential sweep may be halted, again reversed, or alternatively continued further to a value 3. In both LSV and CV experiments the cell current is recorded as a function of the applied potential (it should be noted, however, that the potential axis is also a time axis). The sweep rates used in... 

The first example [15] shows how cyclic voltammetry may be used to demonstrate the rapid isomerisation of the anion radical of diethylmaleate (DEM). Fig. 6.17 shows the voltammograms for DEM and diethylfumarate (DEF), the CIS and trans isomers respecively. The reduction of DEF shows a well formed reduction peak, Ep = —1.41 V vs SCE, and a coupled anodic peak above 0.1 Vs the curve has all the properties of a reversible le process. Below this scan rate, there is evidence for a slow chemical reaction, and more detailed investigations showed this to be dimerisation. The reduction peak for DEM, below 5 Vs is much broader, Ep = —1.61V, with no anodic peak corresponding to the reverse process. There is, however, an anodic peak at —1.35 V which is the same potential required for the oxidation of DEF. Also on the second and subsequent cycles a new reduction peak is seen to grow at —1.41V. On increasing the potential scan rate above 50Vs a small anodic peak is seen where the oxidation of DEM is expected and the anodic peak at —1.35 V becomes relatively smaller (i.e. when corrected for scan rate effects). Finally, the current functions, for the main reduction peaks for DEF and DEM are almost independent of v and correspond to reasonable values for a reversible and irreversible le reduction... 

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