Three electrode configuration

When the two phases have the same chemical composition, the chemical potentials are equal, and then AV — f — cf 2, which was already pointed out in Section 2.1. In our case both leads are made of the same material, platinum so the measured electrode potential, 

Generally, when two phases are in electronic equilibrium, eoifa — fa) = Hi — ji 2- In our case, the wire I is in equilibrium with the metal M, the latter is in equilibrium with the redox couple, and the platinum electrode II is in equilibrium with the reference couple (index ref ). 

Since the redox couple and the reference system experience the same inner potential fa0i, we have  

In the preceding derivation we presumed that equilibrium prevails, so that the Fermi levels of the metal and of the redox couple are equal. This equilibrium can be disturbed by the application of an external electrode potential / fa, which lowers the electronic energies in the metal, and in particular the Fermi level, by an amount — eo 7, where r) — (f — fa is called the overpotential (see Fig. 2.4). Thus the application of an overpotential leads to a difference —eor] in the Fermi levels of the metal and the solution. However, as the equilibrium is 

Standard electrodes potentials can be found in A. J. Bard, R. Parsons, and J. Jordan (eds.), Standard Potentials in Aqueous Solutions, Dekker, New York, 1985. 

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The solution to reference electrode instabiUty is the introduction of a third or auxiUary electrode. This particular electrode is intended to carry whatever current is required to keep the potential difference between the working and reference electrodes at a specified value, and virtually all potentiostats (instmments designed specifically for electrochemistry) have this three-electrode configuration. Its use is illustrated in Figure 3. 

Figure 2.3 Electrochemical cell with a three-electrode configuration.

The opposite conclusion was reported by Lin et al., who used a three-electrode configuration to study the electrode polarization of the MCMB anode and LiCo02 cathode under galvanostatic conditions. They found that in all cases the polarization at the MCMB anode surface far outweighs that at the cathode to such an extent that the potential profile... 

An approach similar to this avoids the use of a comparative nohle metal electrode and neglects overpotential losses at the electrodes. In this method, the potential applied at the hydrogen (or oxygen) electrode (in a three electrode configuration) is compared with the potential generated at an ideal fuel cell anode (or cathode). In the case of a n-type semiconductor photoanode ... 

The indicator or working electrode is given first then, after a solidus or virgule ("/") or On a second line, the reference electrode. In three-electrode configurations the nature of the auxiliary or counter electrode Is given in column 13-... 

This column is also used to give the identity of the auxiliary or counter electrode when a three-electrode configuration was used, and to indicate whether the indicator or working electrode was subjected to chemical, mechanical, or electrolytic pretreatment. 

A simple flow-through system that permits the constant flow of lead solution in 0.1 M HC1 was also used. The electrochemical cell used permitted the integration of the same three-electrode configuration as in the batch measurements. The detection limit was similar to batch measurements. The stability of the system for 16 runs of a 500 ppb lead solution showed a 4% RSD. 

C.A. Galan-Vidal, J. Munoz, C. Dominguez and S. Alegret, Glucose biosensor strip in a three electrode configuration based on composite and biocomposite materials applied by planar thick film technology, Sens. Actuators B Chem., 52 (1998) 257-263. 

To minimize errors in voltammetric work, the three-electrode configuration (Figure 5.2b) is commonly used. The cell current flows between the working electrode and the counter or auxiliary electrode, while the potential of the working electrode is measured with respect to the reference electrode using a high-impedance measuring device. This avoids internal polarization of the reference electrode and compensates for the major portion of the iR drop in the cell. 

Ohmic drop in three-electrode circuits. In modem coulometry and voltammetry the use of a potentiostat and a three-electrode configuration is the routine practice. The three electrodes are usually called the working, reference, and counter (or auxiliary) electrodes (see Figure 5.2). The cell current passes between the working electrode immersed in the test solution and the counter electrode, which may be in the test solution but is usually isolated from it by a single- or double-junction glass frit. 

The experiments were performed in batch mode with stirring. The sensor was placed in 20.00 mL of buffer in a three electrode configuration. The potential was applied (+150 mV vs SCE) and the response was allowed to reach baseline. The required amount of analyte was added to measure the response to electroactive interferents and to generate a glucose calibration curve. 

To operate an RRDE, one needs a four-electrode potentiostat, often referred to also as a "double" potentiostat. Now, we started this book with a simple two-electrode cell, then went on to the three-electrode configuration. How does the fourth electrode fit into this scheme The... 

Measurements of the photocurrent-voltage (/-F) and photovoltage properties describe the energy conversion properties of dye-sensitized photoelectrochemical cells and are probably the best fundamental method for their evaluation. This data can be acquired in a two- or three-electrode configuration. Figure 8 shows sche-... 

A plot of the photocurrent quantum yield versus excitation wavelength is termed the photoaction or photocurrent action spectrum. These spectra are obtained at short-circuit in a two-electrode arrangement or with an external bias in a three-electrode configuration. The photocurrent quantum yield is defined as the number of electrons measured in the external circuit divided by the number of absorbed photons. It is experimentally difficult to calculate the number of absorbed photons and corrections for scattered or transmitted light often appear to be fudge factors that increase the uncertainty of the absolute photocurrent yield. Therefore, the incident photocurrent yield is often reported which represents a lower limit of the true photocurrent quantum yield. 

The electrochemical sensing system was set up in a cylindrical quartz cell equipped with a standard three-electrode configuration and controlled by an electrochemical workstation (CHI 660C, CH Instruments Co., Ltd. USA). Both bare Ti02/Ti and functional GOD-Ti02/Ti nanotube array were used as the working electrodes with an effective reaction area of 2.0 cm2. A standard Hg/Hg2Cl2 saturated calomel electrode (SCE) was used as a reference electrode and Pt foil was used as a counter electrode. Standard calibration curve (responsive current... 

Electrochemical cells employed to carry out voltammet-ric or amperometric measurements can involve either a two or three electrode configuration. In the two electrode mode, the external voltage is applied between the working and a reference electrode, and the current monitored. Since the current must also pass through the reference electrode, such current flow can potentially alter the surface concentration of electroactive species that poises the actual half-cell potential of the reference electrode, changing its value by a concentration polarization process. For example, if an Ag/AgCl reference electrode were used in a cell in which a reduction reaction for the analyte occurs at the working electrode, then an oxidation reaction would take place at the surface of the reference electrode ... 

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