Linear voltammetric sweeps

Linear voltammetric sweeps (a) Pb—2.0 wt% Sb and (b) Pb—12 wt% Sb electrodes performed after 16 h of potentiostatic polarization at +0.6 V in 0.5 M H2SO4 solution. Dashed lines show the voltammograms of a pure Pb electrode [49]. Left ordinate current density for Pb—Sb electrodes. Right ordinate current density for the pure Pb electrode. 

The Application of FTIR Spectrometers In essence, the routine use of FTIR spectrometers has meant that in situ infrared spectroscopic studies requiring high sensitivity, such as the study of adsorbed species, were no longer limited to the fast, reversible electrochemical systems dictated by lock-in detection techniques infrared spectra could be collected during a slow linear voltammetric sweep, during a series of potential steps to higher... 

Cyclic voltammetry belongs to the category of voltammetric techniques based on a linear potential sweep chronoamperometric technique. It certainly constitutes the most useful technique for a preliminary determination of the redox properties of a given species. 

The potential-time relation for voltammetric measurements is presented in Figure 3.2. With linear-sweep voltammetry, the potential is linearly increased between potentials Ex and E2. Cyclic voltammetry is an extension of linear-sweep voltammetry with the voltage scan reversed after the current maximum (peak) of the reduction process has been passed. The voltage is scanned negatively beyond the peak and then reversed in a linear positive sweep. Such a... 

A steady state is independent of the details of the experiment used in attaining it. Thus, under conditions where a steady state is attained, e.g., under convective conditions in an - electrochemical cell, the application of a constant current leads to a constant potential and similarly the application of a constant potential leads to the same constant current. Voltammetric steady states are most commonly reached using linear potential sweeps (or ramps) in a single or cyclic direction at a UME or RDE. A sigmoidally shaped current (l)-potential (E) voltammogram (i.e., a steady-state voltammogram) is recorded in the method known as steady-state voltammetry as shown in the Figure. Characteristics of the... 

As has been shown in section 2.1.2, the design of the electrochemical cell used in this research was significantly different from conventional voltammetric cells . This was necessitated by the requirements of compatibility with the UHV-transfer system . A sketch of the cyclic voltammetry system is shown in Fig. 2.7. The linear potential sweep and the current measurements were supplied by a RDE 3 Potentiostat (Pine... 

By proper treatment of the linear potential sweep data, the voltammetric i-E (or i-t) curves can be transformed into forms, closely resembling the steady-state voltammetric curves, which are frequently more convenient for further data processing. This transformation makes use of the convolution principle, (A.1.21), and has been facilitated by the availability of digital computers for the processing and acquisition of data. The solution of the diffusion equation for semi-infinite linear diffusion conditions and for species O initially present at a concentration Cq yields, for any electrochemical technique, the following expression (see equations 6.2.4 to 6.2.6) ... 

T. R. Mueller and R. N. Adams (see R. N. Adams, Electrochemistry at Solid Electrodes, Marcel Dekker, New York, 1969, p. 128) suggested that by measurement of ip/v for a nemstian linear potential sweep voltammetric curve, and by carrying out a potential step experiment in the same solution at the same electrode to obtain the limiting value of it, the n value of an electrode reaction can be determined without the need to know A, C, or Dq. Demonstrate that this is the case. Why would this method be unsuitable for irreversible reactions ... 

Similar results were reported by Fan et al. in their voltammetric studies of nitrite reduction by Hb contained in DNA film electrodes at pH 4. These films showed well-defined Fe V couple at —0.36 V SCE, Eq. (4.26), and upon addition of nitrite two new cathodic peaks were observed. Also, when the lower scan potential was limited to —0.5 V, the Fe / peak current decreased linearly due to formation of stable Hb-Fe NO complex, as previously seen for Mb. Pre-electrolysis followed by linear scan voltammetric sweeps showed that at H-0.3 V the predominant species is met-Hb, at —0.5 V the Hb-NO complex is the predominates species, and at —0.9 V the Hb-Fe predominates, apparently due to NO depletion in the electroactive layer. 

Gold and mercury electrodes display ideally polarizable behavior in a broad range of electrode potentials. Under these conditions, the metal solution interface behaves as a capacitor. The capacity of the electrode decreases when organic molecules are present at the interface [28,29]. The measurement of the electrode capacity provides a convenient tool to study the spreading of an insoluble mono-layer onto a metal electrode surface. The capacity may be measured by applying a linear voltage sweep to the electrode and recording the voltammetric current (CV-cyclic... 

The rate of oxygen reduction on the oxide-free Pt surface is limited by the mass transport of dissolved oxygen to the electrode surface. The dependence of the oxygen reduction on the scan rate, v, was examined. Figure 31 shows the linear potential sweep voltammetric i-E curves for a Pt/diamond composite electrode in 02-saturated 0.1 M HCIO4 [125]. The peak current, ip, increases linearly with when the scan rate is varied from 50 to 400 v/s, indicative of a semi-infinite linear diffusion-controlled process. However, ip rather approaches a proportionality with v at scan rates higher than 400 v/s. This is expected as the reaction shifts from being mass transport limited to control by the surface adsorption process. 

Further data illustrating the electrocatalytic behavior are contained in Figure 7. Figure 7 contrasts the concentration dependence of the first and second wave reduction currents at different voltammetric sweep rates. For (ox) (s-r) reduction, the plots of ip vs FeMoco concentrations are linear and display the sweep rate dependence expected for a diffusion-controlled electrode reaction. Plots of ip vs concentration for (s-r) (red) reduction are likewise linear, but display almost no dependence on sweep rate. Such behavior corresponds to Equations (7) and (8) operating under full catalytic conditions with the sweep-rate in-pendent current depending linearly on catalyst (FeMoco) concentration according to the relationship... 

Explain clearly the reason for the peaked response of linear sweep voltammetric experiments involving a planar macrodisk electrode and a quiescent solution. 

Differential pulse voltammetry provides greater voltammetric resolution than simple linear sweep voltammetry. However, again, a longer analysis time results from the more sophisticated potential waveform. At scan rates faster than 50 mV/sec the improved resolution is lost. Because it takes longer to scan the same potential window than by linear sweep, an even longer relaxation time between scans is required for differential pulse voltammetry. 

The Model 384B (see Fig. 5.10) offers nine voltammetric techniques square-wave voltammetry, differential-pulse polarography (DPP), normal-pulse polar-ography (NPP), sampled DC polarography, square-wave stripping voltammetry, differential pulse stripping, DC stripping, linear sweep voltammetry (LSV) and cyclic staircase voltammetry. 

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-... 

In linear sweep voltammetric techniques the applied electrode potential is varied from an initial value E to a final value f at a constant scan rate v (single sweep voltammetry). Once the value is reached the direction of the scan can be reversed, maintaining the same scan rate v, and the potential brought back to the initial value (cyclic voltammetry). In the two cases the form of the potential-time impulse can be represented as shown in Figure 1. 

Fig. 5 Linear sweep and cyclic voltammetry (a) dotted lines five profiles respectively at various typical excitation signal (b) current response times, increasing time shown by arrows] for a and concentration profiles [(c) forward scan cyclic voltammetric experiment.

Figure 6.5 Potential is varied at a constant rate of dE/dt during voltammetric techniques such as polarography, linear sweep voltammetry and cyclic voltammetry. The scan rate v is always cited as a positive number.

Linear kinetic behaviour according to the Tafel equation indicates a linear free energy relationship between activation energy and driving force for the reaction and the value of a is defined by Equation 1.11. Methods based on polarography or linear sweep voltammetr) are available for the determination of a in the electron... 

The voltammetric response of an electrodeposited film of 2 in CH2CI2 with 0.1 M TBAH is shown in Figure 6 as a representative example. A well-defined, symmetrical oxidation-reduction wave is observed, which is characteristic of surface-immobilized reversible redox couples, with the expected linear relationship of peak current with potential sweep rate A formal potential value of =+0.42... 

For the pseudo-capacity of adsorbed intermediates and for double-layer charging, cyclic voltammetric currents increase linearly with the sweep rate. For diffusion-controlled currents, the variation of the current increases with the square root of the sweep rate. 

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