Cyclic voltammetry scanning curve

Fig. 12.13 Optical photograph of (a) a commercial cotton T-shirt (b) a piece of ACT and (c) a piece of ACT under folding condition, showing its highly flexible nature (d) and (e) SEM images of cotton T-shirt textile and ACT, and insets are SEM images of individual cellulose fibre and activated carbon fibre, respectively. Scale bars, 1 mm (d) 2 pm (inset of (d)) 1 mm (e) and 5 pm (inset of (e)) (f) cyclic voltammetry (CV) curves of ACT at different scan rates in 1M aqueous NUjSO solution (g) specific capacitances at different scan rates of ACT derived from CV curves (h) CV curves of MnO /ACT hybrid composite at different scan rates in 1M aqueous Na SO solution (i) comparative CV curves of ACT and MnO /ACT hybrid composite at a scan rate of 2mVs .

Fig. 7.8 Cyclic voltammetry (CV) curves and crossover (CO) curves of NSAP-2.5 and Nafion-112 MEAs. Temperature 30°C, anode and cathode N, cathode Pt loading 0.3 mg/cm, scan rates CV at 30 mVs" and CO at 4 mVs ...

One of the most problematic issues, still to be fully resolved, is the dependence of the degree of oxidation on potential, as measured most commonly by cyclic voltammetry at low scan rates. There is currently no accepted model to describe the shape of the curve and the hysteresis between anodic and cathodic scans. The debate over whether the charge has a significant component due to a polymer/solution double layer is still not fully resolved. 

Such effects are observed inter alia when a metal is electrochemically deposited on a foreign substrate (e.g. Pb on graphite), a process which requires an additional nucleation overpotential. Thus, in cyclic voltammetry metal is deposited during the reverse scan on an identical metallic surface at thermodynamically favourable potentials, i.e. at positive values relative to the nucleation overpotential. This generates the typical trace-crossing in the current-voltage curve. Hence, Pletcher et al. also view the trace-crossing as proof of the start of the nucleation process of the polymer film, especially as it appears only in experiments with freshly polished electrodes. But this is about as far as we can go with cyclic voltammetry alone. It must be complemented by other techniques the potential step methods and optical spectroscopy have proved suitable. 

Figure 6.8 S-shaped polarization curve observed in the CO oxidation model (for the exact model parameters, see Koperetal. [2001]). The thin line shows the cyclic voltammetry observed at a low scan rate of 2 mV/ s.

Figure 16.9 Comparison of cyclic voltammetry in a CO-saturated electrolyte (0.5 M HCIO4) of Au supported on carbon (solid curves) and titania (dashed curves) for four different particle sizes (indicated). The measurements were made at a temperature of 298K and a scan rate of 50mV s ...

Fig. 4. Voltammograms in 0.1M Eti+NClOi+ZCH CNj rT = 1.2X1 O 8 mol/cm. Curve As Cyclic voltammetry of Pt/poly-Co -NI TPP at 20 mv/s = 200pA/cm. Curve B Four-electrode voltammetry of Pt/poly-Co( -NHi(,)TPP/Au sandwich electrode with E u = 0.0 Vj Ep scanned negatively at 5 mV/s = 400pA/cm. Curve Ci Surface profilometry of a poly-Co(o-NH2)TPP film on Sn02/glassj Tt = 7.6X10 9 mol/cm. (Reproduced from Ref. 6. Copyright 1987 American Chemical Society.)...

Figure 3.6 Reflect vity-potential curve (top) and corresponding cu r rent-poten tial c y clic volta m -mograms (bottom) for a platinum electrode in 1.0M H2S04. The reflectivity curve was taken at 546 nm using S-poiarised light at a 701 angle of incidence. The potential limits for both the reflectivity and cyclic voltammetry experiments were + 0.535 V and —0.006 V vs. NHF, and the scan rate was 26.46 Vs-1. From Bewick and Tuxford (1973).

In cyclic voltammetry, the current-potential curves are completely irreversible whatever the scan rate, since the electron transfer/bond-breaking reaction is itself totally irreversible. In most cases, dissociative electron transfers are followed by immediate reduction of R, as discussed in Section 2.6, giving rise to a two-electron stoichiometry. The rate-determining step remains the first dissociative electron transfer, which allows one to derive its kinetic characteristics from the cyclic voltammetric response, ignoring the second transfer step aside from the doubling of the current. 

Fig. 12.11 A schematic view for constructingmultilayerfilms on substrate, (b) Photographs of multilayer films of ITO/(PDDA/PSS-GS/PDDA/Mn02)n, n = 0, 5,10, and 15 for A, B, C, and D, respectively, (c) Cyclic voltammetry curves of ITO/(PDDA/PSS-GS/PDDA/MnO2)10 electrode at different scan rates, (d) Charge-discharge behavior of an ITO/(PDDA/PSS-GS/PDDA/MnO2)10 electrode at different current densities.

Pyrrhotite is one of many sulphides which display collectorless flotation resulting from the formation of sulphur on the mineral surface (Hamilton and Woods, 1981 Heyes and Trahar, 1984 Hodgson and Agar, 1984). The anodic scan section of cyclic voltammetry for pyrrhotite electrode in pH = 2.2, 4.7, 7.0, 8.8, 11, 12.1, 12.7 buffer solutions respectively, is presented in Fig. 2.23. The cyclic voltammograms curve at pH = 8.8 is also presented in Fig. 2.23. It can be seen from Fig. 2.23 that anodic current peak emerges at about -0.1—0 V when pH < 11. As pH increases, the peak moves to the left. This peak may correspond to the following reactions ... 

Cyclic voltammetry is a powerful tool for following mechanisms since varying the scan rate v is equivalent to varying the time-scale of observation, t. In order to obtain the rate constant k of the homogeneous C reaction, the CV is obtained as a function of the scan rate, with k of the reaction then being determined from working curves calculated from theoretical principles. 

In this equation, aua represents the product of the coefficient of electron transfer (a) by the number of electrons (na) involved in the rate-determining step, n the total number of electrons involved in the electrochemical reaction, k the heterogeneous electrochemical rate constant at the zero potential, D the coefficient of diffusion of the electroactive species, and c the concentration of the same in the bulk of the solution. The initial potential is E/ and G represents a numerical constant. This equation predicts a linear variation of the logarithm of the current. In/, on the applied potential, E, which can easily be compared with experimental current-potential curves in linear potential scan and cyclic voltammetries. This type of dependence between current and potential does not apply to electron transfer processes with coupled chemical reactions [186]. In several cases, however, linear In/ vs. E plots can be approached in the rising portion of voltammetric curves for the solid-state electron transfer processes involving species immobilized on the electrode surface [131, 187-191], reductive/oxidative dissolution of metallic deposits [79], and reductive/oxidative dissolution of insulating compounds [147,148]. Thus, linear potential scan voltammograms for surface-confined electroactive species verify [79]... 

The cyclic voltammetry behavior of the Cu(II) rotaxane, 4(5)2+ (Fig. 14.8b), is very different from that of 4, t l +. The potential sweep for the measurement was started at - 0.9 V, a potential at which no electron transfer should occur, regardless of the nature of the surrounding of the central Cu(II) center (penta- or tetracoordinate). Curve i shows two cathodic peaks a very small one, located at + 0.53 V, followed by an intense one at —0.13V. Only one anodic peak at 0.59 V appears during the reverse sweep. If a second scan ii follows immediately the first one i, the intensity of the cathodic peak at 0.53 V increases noticeably. The main cathodic peak at —0.15 V is characteristic of pentacoordinate Cu(II). Thus, in 4(5)2+ prepared from the free rotaxane by metalation with Cu(II) ions, the central metal is coordinated to the terdentate terpyridine of the wheel and to the bidentate dpp of the axle. On the other hand, the irreversibility of this peak means that the pentacoordinate Cu(I) species formed in the diffusion layer when sweeping cathodically is transformed very rapidly and in any case before the electrode potential becomes again more anodic than the potential of the pentacoordinate Cu2 + /Cu+ redox system. The irreversible character of the wave at —0.15 V and the appearance of an anodic peak at the value of + 0.53 V indicate that the transient species, formed by reduction of 4(5)2 +, has undergone a complete reorganization, which leads to a tetracoordinate copper rotaxane. The second scan ii, which follows immediately the first one i, confirms this assertion. 

Fig. 6.9. Cyclic voltammetry of three platinum electrodes in clean 0.1 M HCI04 solution (broken curves) and in the same solution containing 1.0 mM of H2S04 (solid curves), (a) Pt(100), (b) Pt(poly), and (c) Pt(110). Scan rate 50 mV s 1. (Reprinted from Y-E. Sung, A. Thomas, M. Gamboa-Aldeco, K. Franaszczuk and A. Wieckowski, J. Electroanal. Chem. 378 131 copyright, 1994, Fig. 13, with permission of Elsevier Science.)...

Cyclic voltammetry is often abbreviated CV. In this method, the potential is linearly scanned forward from ) to E2 and then backward from E2 to E), giving a triangular potential cycle (Fig. 5.18). Figure 5.21 shows some examples of cyclic voltammo-grams for the process Ox+ne Red, where only Ox is in the solution. Curve 1... 

On the contrary, the radical cation of anthracene is unstable. Under normal volt-ammetric conditions, the radical cation, AH +, formed at the potential of the first oxidation step, undergoes a series of reactions (chemical -> electrochemical -> chemical -> ) to form polymerized species. This occurs because the dimer, tri-mer, etc., formed from AH +, are easier to oxidize than AH. As a result, the first oxidation wave of anthracene is irreversible and its voltammetric peak current corresponds to that of a process of several electrons (Fig. 8.20(a)). However, if fast-scan cyclic voltammetry (FSCV) at an ultramicroelectrode (UME) is used, the effect of the follow-up reactions is removed and a reversible one-electron CV curve can be obtained (Fig. 8.20(b)) [64], By this method, the half-life of the radical cat-... 

First, the electrochemical behaviour of the substrate material, which is platinum, was investigated as a function of applied potential by cyclic voltammetry. For that, the potential was swept in positive direction from -0.5 V vs. AglAgCl to a first vertex potential of 0.9V vs. AglAgCl, followed by a scan in reversed direction to a second vertex potential of -0.8 V and back to -0.5 V vs. AglAgCl. The curves obtained in solutions of different pH values are shown in Fig. 6.5. Similarly shaped curves were obtained by variation of... 

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. 

The kind of voltammetry described in Sect. 4.2. is of the single-sweep type, ie., only one current-potential sweep is recorded, normally at a fairly low scan rate (0.1-0.5 V/min), or by taking points manually. Cyclic voltammetry is a very useful extension of the voltammetric technique. In this method, the potential is varied in a cyclic fashion, in most cases by a linear increase in electrode potential with time in either direction, followed by a reversal of the scan direction and a linear decrease of potential with time at the same scan rate (triangular wave voltammetry). The resulting current-voltage curve is recorded on an XY-recorder,... 

Figure 4.11 Effect of SAM formation on the cyclic voltammetry of ferrocenylmethyltrimethylam-monium on a polycrystalline gold electrode the supporting electrolyte is 0.5 M H2SO4, with a scan rate of 0.1 V s-1. Curve (a) is the reversible cyclic voltammogram obtained on bare gold, while curves (b)-(d) are obtained on the same electrode with different monolayers (for details see text). The symbols represent theoretical fits to a microarray electrode model. Reprinted with permission from H.O. Finklea, D.A. Snider, J. Fedyk, E. Sabatani, Y. Gafni and I. Rubinstein, Langmuir, 9,3660 (1993). Copyright (1993) American Chemical Society...

Fig. 11.1. Cyclic Voltammetry on Pt electrodes in 1.0 M H2S04. Voltage scan rate, vs = 100 mV s-1. Variation of potential of positive scan reversal basic curve curve in the presence of 11WEPN. Voltages of scan reversal UH (1) 1.4 V, (2) 1.6 V, (3) 1.7 V. Shown is the sixth cycle after starting the experimental sequence. Freshly prepared Pt electrode for the first sequence was at the most positive potential of scan reversal. T = 20 °C, N2 purging. (Reprinted from B. Wermeckes and F. Beck, Electrochim. >4cfa30 1491, copyright 1985, with permission from Elsevier Science.)...

The EQCM has been most commonly used simultaneously to quasisteady state techniques like slow scan cyclic voltammetry. In this way mass changes during electrolysis can be obtained from A/(Am/.4) vs. potential curves, while A/(AmA4) vs. charge density curves allow evaluation of the number of Faraday exchanged per mole of electro-active species by use of Faraday s law of electrolysis. 

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