Reference electrodes configuration

Conventional reference electrodes consist of a solid reversible electrode and an aqueous electrolyte solution. To measure the individual contributions from the anode and the cathode of a PEM fuel cell, the electrolyte solution of the reference electrode must either be in direct contact with one side of the solid proton exchange membrane or be located in a separate compartment with electrical contact between the reference electrode and the solid membrane by means of a salt bridge [66], As a result, two different types of reference electrode configurations are employed for the study of fuel cells internal and external. 

The external type of reference electrode is connected to the membrane via a liquid electrolyte bridge, such as a sulphuric acid solution, as shown in Figure 5.45. Compared with the internal reference electrode configuration, the external type is easier to use in a normal PEM fuel cell set-up because it needs minimal modifications. However, attention must also be paid to ensure that the liquid electrolyte has good contact with the membrane and does not flow into the cell. Furthermore, the use of a liquid electrolyte in an acid bridge can induce non-uniform hydration and a proton concentration gradient in the membrane, therefore interfering with the fuel cell electrodes. 

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 6-20 Configuration of a penicillin sensor based on an microarray electrode coated with a pH-responsive polypyrrole. Vq = gate voltage VD = drain voltage ID = drain current PS = potentiostat CE and RE = counter and reference electrodes, respectively. (Reproduced with permission from reference 76.)... 

While there are no problems in the definition of the configuration leading to 0, difficulties are encountered in the procedure to reproduce the electrochemical situation. In fact, Eq. (17) has meaning only if the M/S interface has exactly the same structure during the measurement of E (relative to a reference electrode-electrochemical configuration) as well as during the measurement of 0. ... 

SXS measurements. (A) Single-crystal disk electrode, (B) Pt counter electrode, (C) Ag/AgCl reference electrode, (D) Mylar window, (E) electrolyte solution, (F) inlet for electrolyte solution, (G) outlet for electrolyte solution, (H) cell body, (1) micrometer, (J) electrode holder, (K) outer chamber, (b) Cell configuration for electrochemical measurement, (c) Cell configuration for SXRD measurement. (From Kondo et al., 2002, with permission from Elsevier.)... 

One barrel-tip contains the organic membrane phase and an internal reference electrode the other constitutes a second reference electrode. A four-barrel configuration with a 1-pm tip in which three barrels are liquid membrane electrodes for Na, Ca and and the fourth is a reference electrode has been reported Some representative applications of ion-selective electrodes for intracellular measurements are shown in Table 3. 

Fig. 10. Half wave potentials (at a rotating platinum electrode) vs. d-electron configuration for Et2dtc complexes. The E1/2 values depend upon solvent and reference electrode used (see text), but this is a minor effect as compared with the influence of the d-electron configuration.

FIG. 3 (a) Block schematic of the typical instrumentation for SECM with an amperometric UME tip. The tip position may be controlled with various micropositioners, as outlined in the text. The tip potential is applied, with respect to a reference electrode, using a potential programmer, and the current is measured with a simple amplifier device. The tip position may be viewed using a video microscope, (b) Schematic of the submarine UME configuration, which facilitates interfacial electrochemical measurements when the phase containing the UME is more dense than the second phase. In this case, the glass capillary is attached to suitable micropositioners and electrical contact is made via the insulated copper wire shown. 

Cu, In, Ga, and Se are codeposited from the solution at room temperature in a three-electrode cell configuration, where the reference electrode is a platinum pseudo-reference, the counter electrode is platinum gauze, and the working electrode is the substrate. The substrates typically used are glass, DC-sputtered with about 1 pm of Mo. In all experiments, the applied potential is -1.0V versus the Pt pseudo-reference electrode. The corresponding current density range for the deposition is 5 to 7 mA/cm2. 

The counter electrode is the current carrying electrode and it must be inert and larger in dimension. Platinum wire or foil is the most common counter electrode. For work with micro- or ultramicroelectrode where the maximum current demand is of the order of few microamperes, the counter electrode is not necessary. At very low current, a two-electrode system with the reference electrode can function as the current-carrying electrode with very little change in the composition of the reference electrode. Many commercial glucose sensors and on-chip microcells have such electrode configuration. 

In situ eiectrolysis-EPR methods usually employ a wire or grid electrode contained in a conventional flat or tube EPR cell. The constraints on the geometric configuration are such that secondary and reference electrodes are usually remote from the generating electrode, which often leads to problems in the control of the potential nevertheless it is a valuable technique for recording spectra of EPR active intermediates. These and related spectroelectrochemical techniques have been reviewed by Robinson.5... 

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