Two-electrode setup

In potentiometry, a two-electrode setup is used and is given schematically in Fig. 1.3. This setup consists of a working and a reference electrode, and it is the aim of this method to measure equilibrium conditions at the surface of the working electrode. Under equilibrium, the Nernst equation is valid  

The requirements that need to be met when performing measurement with current flowing through the electrochemical cell will be explained in section 1.6. 

The potential of the equilibrium between Ag and Ag+ in the neighbourhood of the Ag wire surface is given by the Nernst equation, keeping in mind that the activity of a solid (metallic silver) is equal to 1  

However, this equilibrium is not obtained in practice because the Ag+ ions form immediately the sparingly soluble AgCI with the chloride ions in solution. Therefore the potential given in Equation 1.10 will be dependent of the presence of CT ions. The unknown parameter is the activity of Ag+, but this parameter can be calculated through the solubility constant, Ksp  

Substitution of Equationl.il in Equationl.10 results in the following equation  

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Voltammetric experiments without external solution were carried out using a 0-pipette with one barrel filled with an aqueous solution and the second barrel filled with organic phase. In a two-electrode setup, voltage was applied between Ag/AgCl and Ag/AgTPBCl reference electrodes inserted in two barrels. 

Equivalent electrical circuit for a two-electrode setup with planar electrodes. (WE working electrode CE/RE counter electrode and reference electrode, respectively, being fulfilled by one single electrode.)... 

The equivalent electrical circuit in the case of a three-electrode setup is given in Fig. 2.9. Working and counter electrode are identical as for a two-electrode setup, while the reference electrode, as a non-current conducting electrode, only has the role of potential reference and therefore does not contribute to the impedance. However, the position of the Haber-Luggin capillary determines the contribution of Re and Rcomp to Ra given by the following equation ... 

Figure 1. Typical H-cell for electrolysis using two-electrode setup (reference electrode can be inserted into working compartment for potentiostatic control).

The electropolymerization of thiophene-derivatives was conducted in a glove box using a two-electrode setup equipped with a Cu-mesh as counter electrode. The electrolyte used was the ionic liquid [BMIM][TFSI], which was deoxygenated by bubbling with nitrogen for 40 min and dried overnight with molecular sieves prior to use, containing 0.2M of either 2,2 -bithiophene or 3-methylthiophene [40]. Electrosynthesis was conducted under potentiostatic conditions at 3.2-3.4 V and 3.6-3.7 V for bi- and methylthiophene, respectively. Thereafter, the films were successively rinsed in [EMIM][BF4] and DI water, dried, and freed from their templated by dissolution in pure diethyl ether or a 2 1 mixture of diethyl ether and hexane. 

The hypothesis example above is very general and the testability could be improved by making it more specific, such as Transthoracic bioimpedance is lower when measured by gel electrodes than measured by textile electrodes using a two-electrode setup if this is the relevant setup we want to test. It is easier to test this hypothesis because it implies only one certain type of measurement, and reduces the chance of an inconclusive result. A... 

Using a two-electrode setup with transparent ITO electrodes, the authors observed that the poly(3,4-ethyl-dioxythiophene)(PEDOT) growth commensurate with the domains of the LC template and the polymer thickness was found to vary with the LC director orientation. The results indicate that the anisotropic LC environment mediates polymerization, especially becanse the polymer growth is faster in cores aligned normal to the snbstrate, that is parallel to the electric field. Later on, the same group determined that in these LLC conditions, electropolymerized PEDOT exhibits anisotropic absorption and conductivity. 

However, sometimes, it is difficult to identify each electrode process through EIS measurements with a two-electrode setup, and thus, it is important to use the three-electrode setup (Fig. 8.4b) to verify their identity and/or their magnitude... 

In a three-electrode setup, a separate reference electrode is used, and the EIS measurements are performed for the working electrode with respect to the reference electrode. For example, to measure resistances from all anode processes, the anode would be selected as the working electrode, the reference electrode would be placed close to the anode, and the cathode would be used as the counter electrode. In this case, the impedance measured includes the resistance from all processes occurring at the anode, as well as the Ohmic loss that occurs between the anode and the reference electrode. The latter can also be used to perform i-R correction for CV measurements, which is an important step to interpret CV data accurately, especially when these resistances are large. Similarly, to obtain the cathode resistances, the cathode would be selected as the working electrode. While the three-electrode setup for EIS measurements has been used to support data primarily from two-electrode setups in MXC research, there have recently been a few studies published where the three-electrode setup is used to understand microbial electron transfer processes, both at the anode and at the cathode, at a fundamental level, in further detail [22, 23], We believe that this represents one of the most promising applications of EIS. 

We do, however, want to point out an application of the two-electrode setup that has not yet been used extensively in MXC research. We believe that EIS can be a simple tool to rapidly quantify the resistances from various membranes that are used in MXCs. As MXCs involve ionic solutions apart from the membrane, unlike in PEM fuel cells, traditional methods for measuring membrane conductivity... 

EC analysis is an essential tool to evaluate the performance of porous electrode systems. Many options are available for what current or voltage signals to apply in EC analysis, and for what experimental system to test. The experimental system is often one of the following two options. The first option is to test a single porous electrode in combination with a counter- and a reference electrode ( three electrode setup ). The other option is to test two porous electrodes as one another s counter electrode. The use of a reference electrode is not obligatory in this second option, and solely the cell voltage difference between the two electrodes is externally controlled or measured ( two electrode setup ). This second option resembles actual CDI operation (likewise for supercapacitors), and we will, therefore, discuss this EC analysis method in this chapter. 

The electrochemical route for the synthesis of metal nanomaterials foresees the electrochemical oxidation-reduction of metal complexes accomplished in a simple two- [76] or three- [77] electrode t3 e cell. The electrodes are immersed in an electrolytic solution basically composed of soft-templating molecules which operate in the reaction domain both as shape-inducing reagents stabilizing and delineating the nanoparticles shape and size and furthermore as supporting electrol3 e [76, 78, 79]. A two-electrode setup is sketched in Fig. 10.3a. 

Figure 10.3 [a] Two-electrode setup for solution-phase nanocrystal syn-... 

With these reservations in mind, the results of the experiment described above are shown in Fig. 20. Panel A shows pore current-time traces for 12 subsequent electrodeposition steps, each with a duration of 20 s. At the early stages, each trace is dominated by capacitive recharging of the device, which is also reproduced by the three-electrode impedance model discussed above [48]. With each step, more Pt is deposited and the pore current decreases, cf. Fig. 20 C. Finally, panel D displays the ion current/Vbias trace in 0.1 M KCl, i.e. in a conventional two-electrode setup. Essentially no... 

Ion-selective electrodes (ISEs) are measured under zero current conditions in a two-electrode setup, see Fig. 9.2. The indicator electrode (ion-selective electrode) is treated as the cathode, while the reference electrode acts as the anode. 

If the counter electrode is replaced by a reference electrode in the two-electrode setup for amperometric measurements, polarization of the RE is avoided (Fig. 18.14). Thus, the applied potential becomes better controllable. 

Fig. 18.14 Two-electrode setup for potential control using a working and a reference electrode...

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