Cyclic voltammetry counter electrode

A standard method to determine capacitance is cyclic voltammetry. One electrode, made of the material of interest (with know surface area A) and a counter electrode, are introduced into the electrolyte solution. A reference electrode can be used in addition. Then a triangular potential is applied and the electric current is measured. From the current, the capacitance can be calculated. 

Figure 2.15 Schematic representation of the equipment necessary to perform linear sweep voltammetry LSV) or cyclic voltammetry CV). WFG waveform generator, P potentiostat, CR chart recorder, EC electrochemical cell, WE working electrode, CE counter electrode, RE...

The ohmic drop effect we are discussing deals only with the Ru portion ofthe cell resistance (Figure 1.5c). Indeed, the action of the potentiostat makes the working electrode potential independent not only of the possible shift of the counter electrode potential as the current varies, but also independent of the ohmic drop in the Rc portion of the cell resistance. In the case of cyclic voltammetry, the equation above becomes... 

Cyclic voltammetry experiments were controlled using a Powerlab 4/20 interface and PAR model 362 scanning potentiostat with EChem software (v 1.5.2, ADlnstruments) and were carried out using a 1 mm diameter vitreous carbon working electrode, platinum counter electrode, and 2 mm silver wire reference electrode. The potential of the reference electrode was determined using the ferrocenium/ ferrocene (Fc+/Fc) couple, and all potentials are quoted relative to the SCE reference electrode. Against this reference, the Fc /Fc couple occrus at 0.38 V in acetonitrile and 0.53 V in THF [30, 31]. 

A cell for cyclic voltammetry (CV) employs three electrodes, a working microelectrode, a counter electrode, and a reference electrode the current flows between the two former, and the potential of the working electrode is determined by measuring the potential difference between that and the reference electrode. 

The regenerated ionic liquid phase was investigated dectrochemically to determine its quality. Cyclic voltammetry was performed using a rotating platinum disk electrode (500 rpm), a platinum counter electrode and a platinum wire as (quasi ) reference electrode placed closed to the rotating disk. 

Platinum, glasslike carbon, and tungsten are often used as inert working electrodes for the fundamental electrochemical studies in the ionic liquids. For such transient electrochemical techniques as cyclic voltammetry, chronoamperometry, and chronopotentiometry, it is safer to use the working electrode with a small active area. This is because most of the ionic liquids will have low conductivity, and this often causes the ohmic drop in the measured potentials by the current flowing between the working and counter electrode. Microelectrodes may be useful for the electrochemical measurements in the case of handling low conductive media. 

Figure 3. Schematic of simple cell setup for cyclic voltammetry (taken from ref. 8 with permission). W.E. = working electrode, C.E. = counter electrode, and R.E. = reference electrode.

The Au layer - which is a prerequisite for surface-plasmon optics - can be used simultaneously as the working electrode in a regular three-electrode electrochemical set-up (also shown in Fig. 3a) with the reference and the counter electrode being immersed in the flow-cell attached to the Au coated substrate. In this way, various electrochemical techniques, e.g., cyclic voltammetry or impedance spec-... 

Another popular mode for transmission experiments involves a thin-layer system (9, 10, 13, 18) like that shown in Figure 17.1.2. The working electrode is sealed into a chamber (e.g., between two microscope slides spaced perhaps 0.05-0.5 mm apart) containing the electroactive species in solution. The chamber is filled by capillarity, and the solution within it contacts additional solution in a larger container, which also holds the reference and counter electrodes. The electrolytic characteristics of the cell are naturally similar to those of the conventional thin-layer systems discussed in Section 11.7. One can do cyclic voltammetry, bulk electrolysis, and coulometry in the ordinary way, but there is also a facility for obtaining absorption spectra of species in the cell. 

For the electrochemical measurements, the copper-2% zinc alloy was mounted into epoxy (Buehler epoxide resin) by curing at room temperature for about 10 h. The finished metal surface had 1 cm2 exposed. The reference electrode probe and both high-density graphite counter electrodes were also positioned into the beaker. The working electrodes were immersed in the solutions for up to 0.5 h prior to the cyclic voltammetry for monitoring the open circuit potential. 

The theme of photosensitizing semiconductor electrodes introduced in Section 57.3.2.5(iii) may be developed with an example from ruthenium-bipyridyl chemistry. The sequence (40) is well known. The effectiveness of the photosensitization should be increased by the covalent attachment of the tris(bipyridyl)ruthenium(II) entity to the semiconductor surface, for example to Sn02- This has been achieved using the versatile halosilane chemistry shown in equation (41). The counter anion was PFg . Cyclic voltammetry showed that the behaviour of the systems Sn02/aqueous [Ru(bipy)3]2 and Sn02(film)/electrolyte were very similar but with a +0.05 V shift in E°. The coated electrode gives a photocurrent with a red shift of 10 nm which is twice as large as for the non-coated electrode. Unfortunately the current falls off due to promotion of the hydrolysis of the film. 

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