Potential sweep, triangular cyclic

Methods employing individual linear or triangular pulses (potential-sweep, triangular pulse and cyclic voltammetry, sometimes also called... 

Potential sweep can be single or triangular, allowing cyclic VA... 

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...

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... 

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,... 

Third, consider a triangular cyclic potential sweep under reversible (Nerns-tian) conditions for a planar electrode (Fig. 6.10), to derive a cyclic voltam-mogram (Fig. 6.11) In the Nemst expression, Eq. (6.19.14) a time-dependent potential is added E(t) = E(0) — vt, whence... 

Figure 1.2.11 Current-time and current-potential plots resulting from a cyclic linear potential sweep (or triangular wave) applied to an RC circuit.

In cyclic voltammetry, which usually works with an unstirred electrode, the potential is varied with a typical sweep rate of 0.5-100 V/s. A triangular sweep is applied and the currents are in the range from femto- to milliamperes (lO -lO A). An oscilloscope or a fast X-Y recorder can sweep a cyclic voltam-... 

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.. 

A useful adjunct of linear potential sweep methods is called cyclic voltammetry. Rather than stopping an oxidative voltammogram at, say, + 0.8 V, the potential is reversed and scanned backward, i.e., a triangular wave potential is applied. The oxidation product formed is present at and close to the electrode surface. With fairly rapid potential sweeps (ca. >4 V/min) it is almost completely re-reduced back to the starting material on the reverse potential sweep. Figure 14B shows a typical cyclic voltammogram for a reversible system (solid line). The ratio of forward to reverse peak currents is unity. If, however, some rapid process removes the product(s), litde or no reverse current is obtained (dotted lines of Fig. 14B). This happens if the overall oxidation is totally irreversible, or fast chemical reactions intervene. We will also see later that a peculiar property of very small electrodes can eliminate most of the reverse current in a cyclic voltammogram. 

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. 

While it is possible to use a different scan rate (v ) on reversal (12), this is rarely done, and only the case of a symmetrical triangular wave is considered here. The theoretical treatment follows that of Section 6.2, except that (6.5.2) is used in the concentration-potential equation, rather than (6.2.1), for t > A. This sweep reversal method, called cyclic voltammetry, is extremely powerful and is among the most widely practiced of all electrochemical methods. 

Cyclic voltammetry is commonly used to study fuel cell electrodes and hydrogen crossover. In this technique, a linear sweep potential is applied to one electrode, while the other is held constant. The potential is cycled in a triangular wave pattern, while the current produced is monitored. The shape and magnitude of the current response provides useful quantitative and qualitative information regarding the amount of catalyst that is electro-chemically active, the double layer capacitance, hydrogen crossover, and the presence of oxide layers and contaminants. Wu et al. provide a description of this technique with example voltammograms [29]. 

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