Reference electrodes construction

Fuel cell researchers have also investigated other reference electrodes, such as a pseudo-reference electrode constructed by inserting a micro-sized carbon filament between two polymer electrolyte membranes [73], The main advantage of pseudoreference electrodes is their easy implementation, although one disadvantage is that their DC potential is unknown. However, this DC potential may not be that critical because EIS measurements mainly rely on the AC perturbation signal from which the impedance is calculated. 

It can be seen from Fig. 7.4b that there is a significant effect on / when using an ionic liquid electrolyte as compared to aqueous or non-aqueous electrolytes. This is due to the difference in conductivities of ionic liquids when compared to aqueous or non-aqueous electrolytes. Consequently, electrochemical data measured in ionic liquid media will have an inherently higher level of IR issues. Thus, reference electrode construction and placement in order to minimise IR effects is critical when using IL electrolytes. 

The other stability test carried out by Gao et al. [68] was to add AgCl and KCl to a level of 10 wt% to the molten salt melt. These had insignilicant effect on the potential of the reference electrode. However, addition of small amounts of NaQ affected the potential of the reference electrode by 0.1522 V per decade. This is related to the changing concentration of Na, as well as Ca ", which indicates conduction of these ions through the membrane and a biuld up of a junctirm potential. Multiple reference electrodes constructed by the group [68] (by different workers) resulted in reference electrodes with potentials varying no more than 15 mV but typically with a variance smaller than 8 mV. 

Reference electrodes constructed similar to high-pressure pH sensors have been proposed, among them internal [209, 252-254] as well as external types [205, 255]. Cell design [257-260] suited for extreme conditions has been given, especially a wall-tube cell [259] (Fig. 3.9). 

The liquid junction potential calculated with this equation should not be used for very accurate applications. The conditions assumed in its derivation are never all fulfilled in practice. The main assumption, that the participating ions migrate exclusively according to the concentration gradients so that pure diffusion results, is seldom valid. This is true especially for the common reference electrode constructions in which convection of the electrolyte arises (this is desired for other reasons). In addition, in order to calculate the individual ion activities one needs the individual activity coefficients, and these are not accessible through experimental measurements (as shown in the Appendix). In practice, the analytical applications ofEMF measure-... 

Potentiometric electrochemical cells are constructed such that one of the half-cells provides a known reference potential, and the potential of the other half-cell indicates the analyte s concentration. By convention, the reference electrode is taken to be the anode thus, the shorthand notation for a potentiometric electrochemical cell is... 

When the potential of an electrode of the first kind responds to the potential of another ion that is in equilibrium with M"+, it is called an electrode of the second kind. Two common electrodes of the second kind are the calomel and silver/silver chloride reference electrodes. Electrodes of the second kind also can be based on complexation reactions. Eor example, an electrode for EDTA is constructed by coupling a Hg +/Hg electrode of the first kind to EDTA by taking advantage of its formation of a stable complex with Hg +. 

Figure 12-9 shows on and off potentials that were measured around the circumference of a flat-bottomed tank 100 m in diameter. These values, however, give no information on the tank/soil potentials at the center of the container or at points away from the edge of the tank. In new tank constructions, long-life reference electrodes are therefore installed in the center of the base where the most positive potentials are found [15]. 

The thermodynamic driving force behind the corrosion process can be related to the corrosion potential adopted by the metal while it is corroding. The corrosion potential is measured against a standard reference electrode. For seawater, the corrosion potentials of a number of constructional materials are shown in Table 53.1. The listing ranks metals in their thermodynamic ability to corrode. Corrosion rates are governed by additional factors as described above. 

If a controlled-potential determination is to be carried out, additional equipment will be required, namely an electronic voltmeter, a potentiostat and a reference electrode. The latter is most commonly a saturated calomel electrode, the construction of which is described in Chapter 14. 

The construction of these electrodes is exactly similar to that already described for the pH responsive glass electrode. They must of course be used in conjunction with a reference electrode and for this purpose a silver-silver chloride electrode is usually preferred. A double junction reference electrode is often used. The electrode response to the activity of the appropriate cation is given by the usual Nernst equation ... 

The H-type cell devised by Lingane and Laitinen and shown in Fig. 16.9 will be found satisfactory for many purposes a particular feature is the built-in reference electrode. Usually a saturated calomel electrode is employed, but if the presence of chloride ion is harmful a mercury(I) sulphate electrode (Hg/Hg2 S04 in potassium sulphate solution potential ca + 0.40 volts vs S.C.E.) may be used. It is usually designed to contain 10-50 mL of the sample solution in the left-hand compartment, but it can be constructed to accommodate a smaller volume down to 1 -2 mL. To avoid polarisation of the reference electrode the latter should be made of tubing at least 20 mm in diameter, but the dimensions of the solution compartment can be varied over wide limits. The compartments are separated by a cross-member filled with a 4 per cent agar-saturated potassium chloride gel, which is held in position by a medium-porosity sintered Pyrex glass disc (diameter at least 10 mm) placed as near the solution compartment as possible in order to facilitate de-aeration of the test solution. By clamping the cell so that the cross-member is vertical, the molten... 

Reference electrodes for non-aqueous solvents are always troublesome because the necessary salt bridge may add considerable errors by undefined junction potentials. Leakage of components of the reference compartment, water in particular, into the working electrode compartment is a further problem. Whenever electrochemical cells of very small dimensions have to be designed, the construction of a suitable reference electrode system may be very difficult. Thus, an ideal reference electrode would be a simple wire introduced into the test cell. The usefulness of redox modified electrodes as reference electrodes in this respect has been studied in some detail... 

Reference electrodes. There are two types of reference electrodes (see the scheme in Section 1.3.1) (a) those constructed as a reference type and (b) those used as a reference type both types fulfil the requirement of a constant reference potential by either being non-polarizable or becoming non-polarized during the measurememt. 

G. Valdes-Ramirez, G.A. Alvarez-Romero, C.A. Galan-Vidal, P.R. Hernandez-Rodrguez, and M.T. Ramrez-Silva, Composites a novel alternative to construct solid state Ag/AgCl reference electrodes. Sens. Actuators B. 110, 264-270 (2005). 

Measurement with the hydrogen electrode The SHE is the primary reference electrode, so other half-cell potentials are measured relative to its potential. In practice, if we wish to determine the value of E M then we construct a cell of the type... 

Even though the normal hydrogen electrode (NHE) is the best known and internationally accepted reference electrode, it is difficult to construct and handle, rendering it of little practical use. 

To try to separate the oxidation of adsorbate from that of bulk methanol, a droplet cell, shown in Fig. 3-2, was used. A working electrode, platiniun wire, is dipped into an electrolyte droplet on a capillary, which is then connected to the electrolyte reservoir. The top portion of the capillary was covered with Teflon FEP held by Teflon heat shrinking tube. The counter electrode, platinum wire, is in the capillary and its tip reaches just below the droplet. The reference electrode, R. H. E., is constructed between the reservoir and the droplet. 

In order to employ a reference electrode as part of an electroanalytical experiment, the analyst requires that potentials can be interconverted straightforwardly back and forth to the SHE scale. Consider the grid in Figure 3.5 which allows the interconversion of electrode potentials in aqueous systems (such a grid can be constructed quite easily). 

We will now look at the effects of Ej on thermodynamic calculations, and then decide on the various methods that can be used to minimize them. One of the most common reasons for performing a calculation with an electrochemical cell is to determine the concentration or activity of an ion. In order to carry out such a calculation, we would first construct a cell, and then, knowing the potential of the reference electrode, we would determine the half-cell potential, i.e. the electrode potential E of interest, and then apply the Nemst equation. 

To learn how to construct your own silver-silver chloride reference electrode, and learn how to test its quality with a simple test of its standard electrode potential C fgci Ag-... 

Macroelectrodes with solid membranes contain homogeneous [142] or heterogeneous [25] membranes. The construction of an ISE of this type with an internal reference electrode is shown in fig. 4.1. For good functioning of an ISE it is necessary that the membrane be completely sealed in the electrode body, with no cracks leading to short-circuiting between the external and internal solutions. Cements based on Teflon, PVC or epoxy resin are used (170). 

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