Electrodes three-electrode setup

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. 

Several variants of the biosensor in Scheme 5 have been proposed. One is a CPE containing at its tip a paste of graphite powder loaded with HRP and ferrocene ([Cp Fe(II) Cp]) mediator, which is further covered with a cellulose acetate film coated with Nafion. The biosensor is mounted on a FIA system in a three-electrode setup, as working electrode at a potential of 4-100 mV vs. SCSE and a Pt counterelectrode. The LOD (SNR 6) for H2O2 is 200 fmol (20 p,L injection of 10 nM solution), with linearity up to 25 In... 

Voltammetric methods in these methods, a potential is applied to the working electrode using a three-electrode setup (see section 1.6). The electrical current, resulting from charge transfer over the electrode-electrolyte interface, is measured and reveals information about the analyte that takes part in the charge transfer reaction. The potential applied can be constant (chronoamperometry, section2.5), varied linearly (cyclic voltammetry, section 2.3) or varied in other ways (Chapter 2). 

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 ... 

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

Finally, some practical questions such as the three-electrode setup, the influence of the ohmic drop, the RC time constant, and a short discussion on the nomenclature of the potential perturbations used in this techniques are addressed in Sects. 1.9 and 1.10. 

Returning to the three-electrode setup, it could seem that no ohmic drop would affect the measurement of the potential difference between the working and reference electrodes, since there is practically no current flow between both electrodes. However, this is not totally true. The reference electrode is located at a given distance from the working electrode surface, and, as a result of this separation, the potential difference measured contains a part of the ohmic drop in the solution which is called residual ohmic drop, IRU (with I being the current and Ru the uncompensated resistance). For more details concerning the minimization of the ohmic distortion of the current-potential response, see Sects. 1.8 and 5.4. 

In general, to compensate for larger IR drops, a three-electrode setup is used Most of the current I is passed between (i) the working electrode (WE) and (ii) an auxiliary electrode or counter electrode (CE), between which most of the IR drop will occur. The potential is monitored between WE and (iii) a reference electrode (RE), which draws very little current it is most often an NHE, or a standard calomel electrode (Hg Hg2Cl21KC1), or an Ag AgN03 electrode. A hopefully small fraction of the overall internal resistance, known as the "uncompensated" resistance Ru, will still be present between WE and RE the goal is to make Ru/R tolerably small. Figure 6.9 shows the symbols used for three-electrode electrochemical cells. 

H-cell — is a divided electrochemical cell, named after its similarity with letter H. It principally consists of two compartments, connected through a diaphragm. A modification or special H-type design is the -+ Lin-gane cell [i], developed for use with mercury electrodes within a three-electrode setup. Glass H-cells are commercially available, but may nevertheless be easily constructed in a laboratory, as shown in the figure [ii]. 

The electrodeposition of silver nanoparticles on 1.32 cm ITO substrates was performed in separate Teflon cells of 12 ml volume using a standard three electrode setup, as previously described for silver particles [29, 30]. The electrolyte used for the silver deposition contained 0.1 M KNO3, 0.1 M KCN, and 0.01 M AgNOs per liter. 

Fig.1 Electrochemical quartz crystal microbalance schematic of the three-electrode setup used for carrying out the electropolymerization/adsorption studies presented later in this chapter. This figure was reprinted with permission from [71]...

Experiments were carried out at room temperature on (lOO)-oriented p-Cdo.95Zno.05Te with a dopant density of 10 cm"3. Gold ohmic contacts were obtained at room temperature by electroless deposition. A classical three-electrode setup was used, with a p-Cdo.95Zno.05Te working electrode, a platinum counter electrode, and a saturated mercurous sulphate reference electrode (MSE = +0.64 V vs SHE). XPS surface analysis was carried out using a VG... 

Generally, just as in conventional solution voltammetric experiments, a three-electrode setup is to be preferred in order to avoid excessive voltage drops across the cell and undue potential shifts of the signals. 

The three-electrode setup in the Uqnid flow cell was constructed as follows the thin Cn film ( 300-nm thick) with 5 nm adhesive Cr layer was used as working electrode which was thermally deposited on the cell side of the SijN membrane (b in Fig. 5.19) a Pt wire and a Ag wire, inserted into the liquid flow cell through small holes on the sides of the PEEK body, were nsed as the counterelectrode and pseudoreference electrode, respectively (b and in Fig. 5.19). A VersaSTAT4 potentiostat (Princeton Applied Research) was used to manipulate the potential for electrochemical reactions. The in situ SXAS measuranents were recorded with the TPY mode nsing the channeltron detector under the controlled potentials (the TEY mode was not accessible in solntions). The thickness of the Cn film deposited on the SijN membrane was selected to ensure the transmission of both incident X-rays and the outgoing fluorescence photons. 

A polarization curve can be recorded with simple means such as a variable resistor box. A potentiostat equipped with a three-electrode setup and appropriate software is used for polarization curves, EIS, and current interrupt. 

Figure 8.4 Cell configurations to use for EIS measurements (a) two-elecirode setup that measures impedance for both working and counter electrodes, and the Ohmic resistance between them and (b) three-electrode setup that measures the impedance of the working electrode, and the Ohmic resistance between the working and the reference electrodes.

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 have investigated various experimental procedures to ensure the accurate application of EIS to MXCs. In the following sections, we discuss EIS experiments performed with biofilms of G. sulfurreducens grown on gold or graphite anodes of various geomefiies in several three-electrode setups. These experiments were... 

A potentiostat is a controlled electric power supply, which adjusts the potential drop across an active or passive dipole to a desired value. To do this, the device has to measure the actual potential drop and to force currents through the dipole, until actual value and desired value become equal. In electrochemical systems, the interest to keep the potential drop across a complete cell is limited to rare cases, e.g., charging or discharging of batteries. More interesting are kinetics of single electrodes, which means an electric control of the interface electrode/electrolyte. An additional device is needed to measure the electrolyte potential, the so-called reference electrode. As a result, a three-electrode setup is obtained (working, counter, and reference electrodes). Reference electrodes include at least one interface ionic conductor electronic conductor with an additional potential drop which must be taken into account. 

Mercury is deposited onto a Pt UME from a Hg2(N03)2 solution in a three-electrode setup and controlled by a potentiostat. A1 nun Pt wire serves as a counter electrode and a fritted... 

In each case, the sample was actuated in a three-electrode setup by linearly ramping the potential WE(PPy)-RE(Ag/AgCl) between 0 and — 1 V within 200 s. The potentials that are applied between PPy and CE differ significantly. In the case of a CE fabricated in silver, a full redox cycle could be obtained with WE-CE potentials between —0.5 and —1.2 V (compare the potentials for the oxidation and reduction peaks in current). In this case, the potentials can be kept below the threshold voltage for the occurrence of hydrolysis. Furthermore, the applied voltages do not need to be switched from positive to negative values, which simplifies required control electronics. 

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