Voltage-sweep voltammetry

Another limitation of solid electrodes has been their complex diffusion-current response relative to time with slow-sweep voltammetry. The development of a capillary hanging-mercury-drop electrode (HMDE) by Kemula and Kublik,4,5 together with modem electronic instrumentation, allowed the principles of voltage-sweep voltammetry and cyclic voltammetry to be established. The success has been such that this has become one of the most important research tools for electrochemists concerned with the kinetics and mechanisms of electrochemical processes. These important contributions by Nicholson and Shain6 7 rely, as have all electrochemical kinetic developments, on the pioneering work by Eyring et al.8... 

Because of the dynamic nature of voltage-sweep voltammetry, irreversible... 

The solubility product of NiS was determined by linear voltage sweep voltammetry using a mercuric sulphide coated electrode (hanging mercury drop). The peak potential for the exchange reaction between the mercuric sulphide coated mercury electrode and Ni ions of a nickel perchlorate solution,... 

Linear sweep voltammetry at the dme. In linear sweep voltammetry (LSV) at the dme a continuously changing rapid voltage sweep (single or multiple) of the entire potential range to be covered is applied in one Hg drop. Originally the rapidity of the sweep (about 100 mV s 1) required the use of an oscilloscope,... 

One specific variant of the technique is known as direct current cyclic voltammetry (DCCV), in which the voltage sweep is over a limited range and a short time and is immediately reversed. The cycle is repeated many times and the pattern of current change is monitored. The technique uses relatively simple electrodes and is used to study redox reactions and there are a range of sophisticated variants of the technique. 

Linear sweep voltammetry, capacitance-voltage and automated admittance measurements have been applied to characterize the n-GaAs/room temperature molten salt interphase. Semiconductor crystal orientation is shown to be an important factor in the manner in which chemical interactions with the electrolyte can influence the surface potentials. For example, the flat-band shift for (100) orientation was (2.3RT/F)V per pCl" unit compared to 2(2.3RT/F)V per pCl" for (111) orientation. The manner in which these interactions may be used to optimize cell performance is discussed. The equivalent parallel conductance method has been used to identify the circuit elements for the non-illum-inated semi conductor/electrolyte interphase. The utility of this... 

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... 

Fig. 6.8 Typical cyclic voltammetry waveform corresponding to a voltage sweep rate (v) of 0.1 V s 1 initial — final = 0.5 V- nd Eswitch — —0.5 V.

A Gamry electrochemical measurements system and a Pine Bi-Potentiostat were used to study the experimental decomposition potential and current response to the applied voltage. The experimental variables were electrolyte flow rate and temperature. Linear sweep voltammetry (LSV) technique was the main method used to study the electrolytic processes. 

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... 

The techniques of voltage sweep and cyclic voltammetry provide the analytical and physicochemical capabilities of classical voltammetry and in addition provide the means for performing these measurements much more rapidly for a broader range of conditions. Cyclic voltammetry is particularly useful for the rapid assessment of thermodynamic reversibility, and for the evaluation of the stoichiometry for the electrode reaction. 

Implicit in the above is the notation that current-voltage curves measured at macroelectrodes for all but fast voltage scan rates are characterized by a mass transport limited current plateau rather than a current peak as in linear sweep voltammetry at a planar electrode of larger than micro dimensions. 

Figure 15.2 shows a typically observed current-voltage characteristic curve for PEC cells [4]. This curve was obtained by linear sweep voltammetry using a conventional electrochemical apparatus. The two major parameters used to estimate the PEC cell are as follows (1) the short-circuit photocurrent, which is denoted as... 

Parker, 1981c. Measured by derivative cyclic voltammetry in solvent containing Me4NBFi (0.05 M) at 18.5°C. vj refers to the voltage sweep rate at which the derivative peak ratio is equal to 0.500. 

Fig. 4 Cyclic voltammetry. (A) Voltage waveform showing the rapid forward and reverse voltage sweeps. (B) Typical cyclic voltammogram for completely reversible system.

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. 

The application of phase-selective SHAC voltammetry to organic systems has proved to be fruitful [147,148]. This method is capable of measuring even when the radical cation undergoes a moderately rapid reaction. Another approach for obtaining E° for the formation of reactive radical cations is the application of CV with voltage sweep rates in the kV s range [149-155]. 

The main SECM program is involved in acquiring data as a function of position. However, the SECM program is enhanced by the ability to perform voltammetry (i vs. E) or other time-based routines at a stationary electrode. A DAC on the ADC board can generate a voltage sweep or step. Alternately, a trigger pulse starts an external generator. 

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