Linear potential sweep techniques

Linear Potential Sweep Infra-Red Spectroscopy (LPSIRS) is a variation of EMIRS techniques where the absorbance at a particular wavenumber is monitored during a potential sweep. 

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. 

Many investigators have used different techniques to study the electrochemical behavior of different sulphide mineral electrodes in solutions of different compositions. Linear potential sweep voltammetry (LPSV), and cyclic voltammetry (CV) have been perhaps, used most extensively and applied successfully to the investigation of reactions of sulphide minerals with aqueous systems. These techniques have provided valuable information on the extent of oxidation as a function of potential for various solution conditions and have allowed the identity of the surface products to be deduced. 

Potential Sweep Method, In the transient techniques described above, a set of measurements of the potential for a given current or the current for a given potential is measured in order to construct the current-potential function, i = f(E). For example, the Tafel lines shown in Figure 6.20 were constructed from a set of galvanostatic transients of the type shown in Figure 6.18. In the potential sweep technique, i = f(E), curves are recorded directly in a single experiment. This is achieved by sweeping the potential with time. In linear sweep voltammetry, the potential of the test electrode is varied linearly with time (Fig. 6.23a). If the sweep rate is... 

Again, application of the principle to the simple potential-step method appears trivial or superfluous. However, it is of quite great important for other types of potential control, namely double potential step, cyclic potential step [73], and especially the linear potential sweep method [21, 22, 73]. In all these techniques, sets of data Jf ( ) /f (f) E can be obtained, thus enabling kt(E) to be determined from eqn. (100). For more details, the reader is referred to the quoted textbooks. 

The characterization of pure platinum catalysts and of Pt catalysts modified by lead was achieved in situ by linear potential sweep cyclic voltammetry. This technique allowed to measure the active platinum surface area in the absence and in the presence of deposited lead and to determine the surface fraction covered by lead adatoms (9-12). The adsorption stoichiometry of lead on platinum was also evaluated by electrochemical techniques and found to be equal to two (one lead atom covers two platinum atoms on the surface) (II). 

The technique of cyclic voltammetry or, more precisely, linear potential sweep chronoamperometry, is used routinely in aqueous electrochemistry to study the mechanisms of electrochemical reactions. Currently, cyclic voltammetry has become a very popular technique for initial electrochemical studies of new systems and has proven very useful in obtaining information about fairly complicated electrochemical reactions. There have been some reported applications of cyclic voltammetry for solid electrochemical systems. It is worth pointing out that, although the theory of cyclic voltammetry originally developed by Sevick, ° Randles, Delahay, ° and Srinivasan and Gileadi" and lucidly presented by Bard and Faulkner, is very well established and understood in aqueous electrochemistry, one must be cautious when applying this theory to solid electrolyte systems of the type described here, as some non-trivial refinements may be necessary. 

One could use the equation of chronopotentiometry under irreversible conditions (Eq. 5IK) to determine the transfer coefficient from a plot of E versus ln(x - t ), but again, the uncertainly in the determination of x makes this method less reliable than other similar techniques, such as the linear potential sweep method which will be discussed below. 

Linear potential sweep is a potentiostatic technique, in the sense that the potential is the externally controlled parameter. The potential is changed at a constant rate... 

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) ... 

The technique of controlled-potential cathodic deposition followed by anodic stripping with a linear potential sweep has been applied to the determinations of a number of metals (e.g., Bi, Cd, Cu, In, Pb, and Zn) either alone or in mixtures (Figure 11.8.5). An increase in sensitivity can be obtained by using pulse polarographic, square wave, or coulostatic stripping techniques. Other variants, such as stripping by a potential step, current step, or more elaborate programs (e.g., an anodic potential step for a short time followed by a cathodic sweep) have also been proposed (68-74). 

Since the forward reaction for a potential step to the limiting current region is unperturbed by the irreversible following reaction, no kinetic information can be obtained from the po-larographic diffusion current or the limiting chronoamperometric i-t curve. Some kinetic information is contained in the rising portion of the i-E wave and the shift of 1/2 with Wx- Since this behavior is similar to that found in linear potential sweep methods, these results will not be described separately. The reaction rate constant k can be obtained by reversal techniques (see Section 5.7) (32, 33). A convenient approach is the potential step method, where at = 0 the potential is stepped to a potential where Cq(x = 0) = 0, and at t = T it is stepped to a potential where Cr(x = 0) = 0. The equation for the ratio of (measured at time j.) to (measured at time Figure 5.7.3) is... 

Differential pulse voltammetry (DPV) is essentially an instrumental manipulation of chronoamperometry. It provides very high sensitivity because charging current is almost wholly eliminated. More important for CNS applications, it often helps to resolve oxidations which overlap in potential. The method combines linear potential sweep and square-wave techniques. The applied signal is shown in Fig. 16A and consists of short-duration square-wave pulses (<100 msec) with constant amplitude (typically 20 or 50 mV) and fixed repetition interval, superimposed on a slow linear potential scan. The Fapp waveform can be generated with a laboratory-built potentiostat, but most DPV work is done with a commercial pulse polarograph (see Appendix). The inset of Fig. 16A shows an enlargement of one pulse. The current is measured just before the pulse... 

The widespread use of large-amplitude relaxation techniques in the investigations of anodic organic oxidations, requires further comment on the value of these methods. Reinmuth divided these techniques into three classes based on the types of applications quantitative kinetic studies, qualitative kinetic studies, and analytical studies. We are not concerned here with the analytical applications. For studies in kinetics, controlled-potential techniques, particularly linear-potential scan, in either single sweep or in cycles, and to some extent chronopotentiometry, have been primarily employed. Chronopotentiometry has been successfully utilized in the study of transient reactions, e.g., the reaction of CO with platinum oxide or the reaction of oxalic acid with platinum oxide, and the study of simple charge-transfer reactions with linear diffusion (cf. Refs. 159-161). However, since the general application of chronopotentiometry is severely limited for the study of anodic organic oxidations, as commented previously, this technique will not be further discussed. The quantitative analysis of data obtained by linear potential scan techniques is complicated because the form of theoretical results even for the simplest cases, requires the use of computers and consequently very little quantitative kinetic information has been obtained. This... 

Linear potential sweep and cyclic voltammetry have been used extensively to examine the redox behavior of surface-deposited electroactive polymer films qualitatively. In this respect the technique can be classified as a form of electrochemical spectroscopy, since it delineates regons of redox activity, and provides an initial survey of overall electrochemical behavior of an electroactive polymer film as a function... 

In conclusion linear potential sweep and cyclic voltammetry can be used to obtain quantitative information on charge percolation in electroactive polymer films. However analysis is complex, and it may be preferable to use a simpler technique, such as potential or current step perturbation, to determine the transport parameters, as outlined in the preceding section. 

Linear sweep voltammetry (LSV) and cyclic voltammetry (CV) are the most commonly used potential sweep techniques. The perturbation signal of the working electrode (Figure 2.3) is based on a linear potential wave-form, where the potential E is changed with the time (t) in a linear fashion. The rate of potential change is known as the scan rate V (= dEldt), which typically varies between 1 mVs and 1 Vs [3,4]. 

In potential-sweep techniques, the current flowing at the WE/solution interface is monitored as a function of the potential applied to it. We consider three such volta-mmetric techniques linear sweep voltammetry (LSV), cyclic voltammetry (CV), and hydrodynamic voltammetry (Fig. 20.4). The voltammogram obtained in each case may be regarded as the electrochemical equivalent of a spectrum obtained in a spectrophotometric technique. Indeed, the term electrochemical spectroscopy has been applied to CV [56], and it is worth noting that the independent variable in both cases is related to energy—wavelength in the case of spectroscopy and potential in the case of CV. The potential is swept linearly at I V/s so that the potential at any time is (/) = E vt. 

The basic idea of this technique is that a linear potential sweep (of low rate) is applied to the disk electrode, while cyclic voltammograms (of a relatively high sweep rate) are measured at the ring. The results of such experiments can lead to the creation of a 3D map , which may reveal the electroactive intermediates or products that are formed in the electrode process(es) taking place on the disk. The applicability of the proposed technique is demonstrated here by considering the oxygen reduction process at the gold 0.5 mol dm sulphuric acid electrode as an illustrative model reaction. 

In addition to solid electrolyte potentiometry, the techniques of cyclic voltammetry" and linear potential sweep have also been used recently in solid electrolyte cells to investigate catalytic phenomena occurring on the gas-exposed electrode surfaces. The latter technique, in particular, is known in catalysis under the term potential-programmed reduction (PPR). With appropriate choice of the sweep rate and other operating parameters, both techniques can provide valuable kinetic" and thermodynamic information about catalytically active chemisorbed species and also about the NEMCA effect," as analyzed in detail in Section III. 

Figure 2 shows typical examples of UPD on single-crystal surfaces, that is, potentiodynamic mns obtained for the deposition of T1 on Ag(l 11) and Ag(lOO) single-crystal surfaces. The technique employed to get these results involves the application of a linear potential sweep to the working electrode, with the measurement of the resulting current /. This is usually referred to the electrode area, A, so the most commonly reported quantity is the current density i = If A. The latter can be written as... 

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