Cyclic voltammetry auxiliary electrode

Cyclic voltammetry was conducted using a Powerlab ADI Potentiostat interfaced to a computer. A typical three electrode system was used for the analysis Ag/AgCl electrode (2.0 mm) as reference electrode Pt disc (2.0 mm) as working electrode and Pt rod (2.0 mm) as auxiliary electrode. The supporting electrolyte used was a TBAHP/acetonitrile electrolyte-solvent system. The instrument was preset using a Metrohm 693 VA Processor. Potential sweep rate was 200 mV/s using a scan range of-1,800 to 1,800 mV. 

For the electrochemical measurements reported herein, all cyclic voltammetry measurements are performed in CH2C12 with 0.1 M tetra-n-butylammonium tetrafluoroborate (Bu4NBF4) as supporting electrolyte, while measurements in CH3CN use 0.1 M tetra-ethylammonium perchlorate. Cyclic voltammetry measurements are performed in a three-electrode, one-compartment cell equipped with a Pt working electrode, a Pt auxiliary electrode, and a saturated sodium chloride calomel (SSCE) reference electrode. E1 2 = (Ep.a + Ep.c)/2 AEP = Ep,e - Ep,a-Ei/2 and AEP values are measured at 100 mV/sec. Ferrocene is used as a reference in the measurement of the electrochemical potentials. 

Apparatus Cyclic voltammetry and amperometric current-time curves were obtained with a Pine Instrument Inc., Model RDE4 bipotentiostat and Kipp Zonen BD 91 XYY recorder equipped with a time base module. All measurements were performed in a conventional single-compartment cell with a saturated calomel electrode as the reference electrode and a Pt mesh as the auxiliary electrode at room temperature. Chronoamperometry was made with EG G Princeton Applied Research potentiostat/galvanostat Model 273 equipped with Model 270 Electrochemical Analysis Software. 

Fig. 14.10. Transmembrane electron movement and redox reactions. Also shown schematically are electrodes and circuit diagram for cyclic voltammetry. WE, working electrode SCE, saturated calomel electrode AE, auxiliary electrode, p, and /7 are chemical and electrochemical potentials, respectively. Bulk concentrations of reduced (RED) and oxidized (OX) species on either side of the membrane as indicated by subscripts 1 and 2 interface concentrations are designated by a superscripts (Reprinted from H. T. Tien, Aspects of Membrane Chemistry,...

In cyclic voltammetry, both the oxidation and reduction of the metal complex (called the analyte from now on) will take place in one electrochemical cell. This cell houses the analyte solution as well as three electrodes, the working electrode, the auxiliary electrode and the reference electrode. Electron transfer to and from the metal complex takes place at the working electrode surface (Fig. A.2.2) and does so in response to an applied potential, /iapp, at the electrode surface. During the experiment, current develops at the surface as a result of the movement of analyte to and from the electrode as the system strives to maintain the appropriate concentration ratio (0, through electron transfer, as specified by the Nemst equation. 

The results of the studies of this process in different media are summarized in Table 6. When investigated by cyclic voltammetry, one usually starts with solutions that initially do not contain solvated electrons solvated electrons are then obtained during the cathodic sweep of potential. In other methods, the necessary bulk concentration of solvated electrons was attained by dissolving the alkali metal or by preliminary cathodic generation at an auxiliary electrode. 

Figure 6.6.5 Application of cyclic voltammetry to in vivo analysis in brain tissue, (a) Carbon paste working electrode, stainless steel auxiliary electrode (18-gauge cannula), Ag/AgCl reference electrode, and other apparatus for voltammetric measurements, (b) Cyclic voltammogram for ascorbic acid oxidation at C-paste electrode positioned in the caudate nucleus of an anesthetized rat. [From P. T. Kissinger, J. B. Hart, and R. N. Adams, Brain Res., 55, 20 (1973), with permission.]...

The relationship between electrode potential and current is determined by the electrochemical reaction taking place at the working electrode. Measurements are done usually in a three-electrode arrangement with a reference electrode to control the potential of the working electrode (typically no current is in practice allowed to flow through the reference electrode and its potential is constant) and a counter (auxiliary) electrode where a counterbalancing but not rate-deterrnmirig electrode process takes place. In cyclic voltammetry for a reversible electrode reaction, the cathodic, pc and anodic, pa peak potentials depend on the formal potential, E ... 

Thermodynamic cycles involving standard electrode potentials obtained by cyclic voltammetry have also been used to provide thermochemical information on organometallic compounds. This so-called electrochemical method leads to Gibbs energies of reaction in solution, from which bond dissociation enthalpies may be derived using a number of auxiliary data that are often estimated. For example, the derivation of a metal-hydrogen bond dissociation enthalpy in an L MH species requires (i) an estimate of the reduction potential of in the same solvent where the experiments were carried out (ii) an estimate of the solvation entropies of L MH, L M, and H and (iii) the knowledge of the pK of... 

FIGURE 4,3.16. Block diagram of the circuit for cyclic voltammetry. A Auxiliary electrode W Working electrode R Reference electrode. 

Determination of the energy levels is typically performed by electrochemistry, and cyclic voltammetry (CV) has been established as method of choice. The polymer is either dissolved in the supporting electrolyte or deposited on the working electrode. The measurements are usually performed with a three-electrode set-up that includes a working electrode, a reference electrode (for example Ag/AgCl), and a counter or auxiliary electrode. As electrolytes, acetonitrile (MeCN) or dichloromethane in the presence of conducting salts such as tetrabutyl-ammonium hexafluorophosphate (TBAPFe) are well-established. It is recommended to use ferrocene/ferrocenium (Fc/Fc" ) as external reference for each measurement to make electrochemical potentials comparable [31]. Detailed electrochemical characterization of P3HT films has been performed, for example, by Trznadel et al. [30] and Skompska et al. [32]. 

Cyclic voltammetry was carried out with a locally constructed low-current potentiostat and a waveform generator. All electrochemical measurements were carried out in a copper mesh Faraday cage. In vitro experiments were performed in a 30-mL glass bottle with three holes drilled in a plastic cap to accommodate the three electrode system. A sodium saturated calomel electrode (SSCE) served as the reference electrode and a platinum wire as the auxiliary electrode. 

The most common techniques that apply a constant and/or varying potential at an electrode surface, within a three-electrode system, measuring the resulting current intensity in an electrolytic solution are amperometry, cyclic voltammetry (CV), square wave voltammetry (SWV), and differential pulse voltammetry (DPV). These electro-analytical techniques evaluate the redox properties of a single compound or a mixture of compounds. The three-electrode system (Fig. 13.2) comprises an RE, a counter electrode (CE or auxiliary electrode) and a woiking electrode (WE). The RE contributes with a stable and known potential. 

---