Potential waveform, cyclic voltammetry

Equation (6.96) can be applied to any sequence of constant potential pulses and so to any voltammetric technique. In the particular case of cyclic voltammetry, the waveform is given by Eq. (5.1) and the current takes the form... 

Before discussing the voltammogram obtained with the triangular waveform of figure 16.3, which is simply a plot of the observed current intensity versus the applied potential, it is useful to describe some experimental details of a cyclic voltammetry experiment [335-337] and to recall some basic theory of dynamic electrochemistry [180,332], A typical cell (figure 16.4) consists of... 

Figure 16.3 A potential waveform in cyclic voltammetry. F°(R/R ) is the standard electrode potential of the half-reaction under examination.

In cyclic voltammetry, we apply the triangular waveform in Figure 17-22 to the working electrode. After the application of a linear voltage ramp between times t0 and f, (typically a few seconds), the ramp is reversed to bring the potential back to its initial value at time t2. The cycle may be repeated many times. 

Stripping is the most sensitive form of voltammetry. In anodic stripping polarography, analyte is concentrated into a single drop of mercury by reduction at a fixed voltage for a fixed time. The potential is then made more positive, and current is measured as analyte is reoxidized. In cyclic voltammetry, a triangular waveform is applied, and cathodic and anodic processes are observed in succession. Microelectrodes fit into small places and their low current allows them to be used in resistive, nonaqueous media. Their low capacitance... 

As an alternative to a stepwise variation with time, a continuously changing potential may be imposed. Though other possibilities have been used [42, 43], a linearly changing potential—time waveform, known as a potential ramp [Fig. 17(a)], is the most common. The technique has many names, including linear sweep voltammetry [44]. If the direction of the ramp is reversed [Fig. 17(b)], the technique is often termed cyclic voltammetry (see Chap. 3), though this name is more appropriately applied after sufficient ramp reversals [Fig. 17(c)] have caused the experiment to become periodic. 

Sinusoidal voltammetry (SV) is an EC detection technique that is very similar to fast-scan cyclic voltammetry, differing only in the use of a large-amplitude sine wave as the excitation waveform and analysis performed in the frequency domain. Selectivity is then improved by using not only the applied potential window but also the frequency spectrum generated [28]. Brazill s group has performed a comparison between both constant potential amperometry and sinusoidal voltammetry [98]. 

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... 

If the potential is inverted at a given value (inversion or final potential) until the initial potential is reached again, the two above techniques are denoted Cyclic Staircase Voltammetry (CSCV) and Cyclic Voltammetry (CV), respectively (see Scheme 5.3). The potential waveform in CV can be written as a continuous function of time... 

Cyclic Voltammetry is the most widely used technique for acquiring qualitative information about electrochemical processes and it has also proved to be very useful for the study of ion transfer across bulk, supported, or polymer composite membranes [63]. The expression for the current in CV can be obtained from Eq. (5.105) by considering the potential waveform given in (5.1),... 

By inserting the solutions proposed in Eq. (6.189) and condition (6.175) in Eq. (6.185), recurrent expressions for coefficients 8lp) and are deduced [68] and by inserting these expressions into (6.191) the current is calculated. These expressions allow us to obtain limiting cases like the reversible and irreversible ones which have a discrete character which makes them applicable to any multipulse technique by simply changing the potential time waveform, including the continuous limit of Cyclic Voltammetry. Moreover, they are independent of the kinetic formalist considered for the process. 

Figure 6 Potential waveforms for linear sweep (LSV (a) and cyclic voltammetry (CV) (b) displaying potential versus time including the initial and final potentials, and a typical hnear sweep voltammogram and cyclic voltammogram plotting current versus potential...

Voltammetry in unstirred solution where the predominant mode of mass transport is limited to diffusion is one of the most useful techniques for the study of electrochemical reactions [l-5,8-l 1]. Most often, a triangular potential-time waveform with equal positive and negative slopes is used, and usually also the initial potential (Einitiai) and final potential (Efinai) are the same as illustrated in Fig. 1(a). This has given rise to the term cyclic voltammetry (CV). However, sometimes the voltage sweep is continued to include one or more additional E-t half-cycles or includes more complicated sawtooth-like waveforms to meet special needs. 

In cyclic voltammetry (CV), Ihe current response of a small stationary electrode in an unstirred solution is excited by a triangular voltage waveform, such as that shown in Figure 25-2.L In this example, the potential is ftrst varied linearly from -K).8 V to -0,15 V versus an SCH. When the extreme of -0,15 V is reached. Ihc scan direction is reversed, and the potential is returned to its original value of -l O.S V. The scan rate in cither direction is 50 mV/s. This excitation cycle is often repeated several times. The voltage extrema at which... 

Fig. 2.1. The waveform of the potential applied during a typical cyclic voltammetry experiment. In this case the initial potential, Ei, is 0.5 V, the vertex potential, E-o, is —0.5 V, and the scan rate, v, is 0.1 V s. ...

In this article, the potential waveform employed to run cyclic voltammetry experiments is first described. The current—voltage waveforms for both reversible and irreversible redox reactions are then presented with an emphasis on the various parameters of... 

The triangular potential waveform employed in cyclic voltammetry is shown in Figure 1. Typically, the potential is ramped linearly from an initial potential, Ej, to the switching potential, Emax- The direction of the potential sweep is then reversed and scanning continues until E ,in is reached. The potential sweep may be terminated at the end of the first cycle or it may continue for an arbitrary number of cycles. The primary experimental parameters are the initial potential, the switching potentials, and the potential sweep rate. Typical sweep rates for cyclic voltammetry, employing electrodes of conventional sizes (e.g.. 

Figure 1 Triangular potential waveform employed in cyclic voltammetry. E ax and i are the switching potentials is the switching time E, is the initial potential.

Figure 1 Potential waveforms for linear sweep (A), and cyclic (B) voltammetry and the resulting voltammograms.

Linear sweep voltammetry and cyclic voltammetry [23-25] Potential-time waveforms employed for potential sweep measurements are shown in Figs. 4 and 5a. Linear sweep voltammetry involves sweeping potential between two limited values Ej and E2 at a controlled sweep rate v. A more useful method is cyclic voltammetry in which the potential sweep is reversed usually at the same sweep rate on reaching... 

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