Voltammetry, cyclic single sweep

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. 

In contrast to linear single sweep or cyclic voltammetry, which give non-symmetric peaks, DPV affords symmetric peaks which start from zero-current values and finish at zero-current values, see Figure 39. 

Staircase Voltammetry and Linear Sweep Voltammetry in Single and Cyclic Modes... 

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,... 

Both single-sweep and cyclic voltammetry can provide information about the approximate number of electrons transferred in each wave or peak. This is done by comparing the plateau or peak height with that of a known one- or two-electron transfer process under identical conditions (as an example, the oxidation of 9,10-diphenylanthracene to the cation radical is a commonly used reference reaction). 

Voltammetry with single and cyclic potential sweep was chosen as the electrochemical method of investigation. I - E curves were obtained with a PI-50-1 potentiostat in a polarization rate range of 0.005 -5- 0.1 V/s. Investigations were carried out in a temperature range of 500 850 °C and at a C02 pressure of 0.1 1.5 MPa. The temperature of the melt was maintained with accuracy to 2 °C. All... 

The use of a potential-step technique such as cyclic staircase voltammetry represents a simple alternative to Ichise s method (j0 of obtaining information on both adsorption and electron transfer kinetics. The current decay immediately after a step is primarily capacitive while current at later times is almost totally due to electron transfer reactions. Thus, by measuring the current at several times during each step and by changing the scan rate, information on both the kinetics of the electrode process and the differential capacity can be obtained with a single sweep. 

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. 

Non-Steady-State methods such as cyclic or single-sweep voltammetry are able to give both kinetic and (implicit) mechanistic information on organic electrode reactions in the following ways. 

Fig. 5.18 Potentiostatic methods (A) single-pulse method, (B), (C) double-pulse methods (B for an electrocrystallization study and C for the study of products of electrolysis during the first pulse), (D) potential-sweep voltammetry, (E) triangular pulse voltammetry, (F) a series of pulses for electrode preparation, (G) cyclic voltammetry (the last pulse is recorded), (H) d.c. polarography (the electrode potential during the drop-time is considered constant this fact is expressed by the step function of time—actually the potential increases continuously), (I) a.c. polarography and (J) pulse polarography...

Figure 1. Cyclic voltammetry for Pt single crystals in 0.05 M H2S0. Sweep rate 50 mV/s.

Electrochemical experiments on [Mo2Cl8]4 in 6 M HC1 have also been reported.24 In cyclic voltammetry studies a single oxidation peak is present at +0.5 V (vs. SCE), but except at high sweep rates (500mVs 1), the corresponding reduction peak is not observed. It is likely that [Mo2C18H]3 is formed in an irreversible step. 

A complete comprehension of Single Pulse electrochemical techniques is fundamental for the study of more complex techniques that will be analyzed in the following chapters. Hence, the concept of half-wave potential, for example, will be defined here and then characterized in all electrochemical techniques [1, 3, 8]. Moreover, when very small electrodes are used, a stationary current-potential response is reached. This is independent of the conditions of the system prior to each potential step and even of the way the current-potential was obtained (i.e., by means of a controlled potential technique or a controlled current one) [9, 10]. So, the stationary solutions deduced in this chapter for the current-potential curves for single potential step techniques are applicable to any multipotential step or sweep technique such as Staircase Voltammetry or Cyclic Voltammetry. Moreover, many of the functional dependences shown in this chapter for different diffusion fields are maintained in the following chapters when multipulse techniques are described if the superposition principle can be applied. 

This chapter offers a study of the application of the multipulse and sweep techniques Cyclic Staircase Voltammetry (CSCV) and Cyclic Voltammetry (CV) to the study of more complex electrode processes than single charge transfer reactions (electronic or ionic), which were addressed in Chap. 5. 

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... 

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