Silver chloride reference probe

In order to use the pH electrode described above, two half-cells (probes) are needed—the pH electrode itself and a reference electrode, either the SCE or the silver-silver chloride electrode—and two connections are made to the pH meter. An alternative is combination pH electrode. This electrode incorporates both the reference probe and pH probe into a single probe and is usually made of epoxy plastic. It is by far the most popular electrode today for measuring pH. The reference portion is a silver-silver chloride reference. A drawing and a photograph of the combination pH electrode is given in Figure 14.7. 

Figure 9.4 Reference electrodes and reference electrode probe. (A) Silver-silver chloride reference electrode, (B) calomel reference electrode, (C) reference electrode probe, a, Silver wire, ca. 22 gauge b, reference electrode filling solution, saturated or known concentration of KC1 c, silver chloride electrochemically precipitated on silver wire by anodization d, reference electrode junction e, Pt/glass seal f, mercury g, calomel h, electrochemical cell body wall i, working electrode surface.

Figure 23-12 is a schematic showing details of a gassensing probe for carbon dtoxidc. The heart of the probe is a thin, porous membrane, which is easily replaceable, This membrane separates the analyte solution from an internal solution containing sodium bicarbonate and sodium chloride, A pH-sensilive glass electrode having a flat membrane is held in position so that a very thin film of the internal solution is sandwiched between it and the gas-permeable membrane. A silver-silver chloride reference electrode is also located in the internal solution. It is the pi I of the film of liquid adjacent to the gla.ss electrode that provides a measure of the carbon dioxide content of the analyte. solution on the other side of the membrane,... 

Fig. 10.31 Portable reference electrode probe, (a) Surveys of electrode potential distribution on ships hulls, submerged offshore pipelines, oilrigs, platforms, jetties and docks are often carried out by manual diver-held probes, (b) These battery-powered devices usually incorporate a tip spike, a silver/silver chloride reference electrode and a digital voltmeter (dvm) within a tough, insulated and sealed pistol. The shroud surrounding the electrode element defines the sensing area. These probes are used to depths of approximately 300 m and are capable of measuring to a precision of 1 mV. Rechargeable Ni-Cd batteries are used. Sharpened tips may be used to penetrate coatings. (Courtesy Corrintec (UK) Ltd.)...

There are two procedures for doing this. The first makes use of a metal probe coated with an emitter such as polonium or Am (around 1 mCi) and placed above the surface. The resulting air ionization makes the gap between the probe and the liquid sufficiently conducting that the potential difference can be measured by means of a high-impedance dc voltmeter that serves as a null indicator in a standard potentiometer circuit. A submerged reference electrode may be a silver-silver chloride electrode. One generally compares the potential of the film-covered surface with that of the film-free one [83, 84]. 

In addition to their use as reference electrodes in routine potentiometric measurements, electrodes of the second kind with a saturated KC1 (or, in some cases, with sodium chloride or, preferentially, formate) solution as electrolyte have important applications as potential probes. If an electric current passes through the electrolyte solution or the two electrolyte solutions are separated by an electrochemical membrane (see Section 6.1), then it becomes important to determine the electrical potential difference between two points in the solution (e.g. between the solution on both sides of the membrane). Two silver chloride or saturated calomel electrodes are placed in the test system so that the tips of the liquid bridges lie at the required points in the system. The value of the electrical potential difference between the two points is equal to that between the two probes. Similar potential probes on a microscale are used in electrophysiology (the tips of the salt bridges are usually several micrometres in size). They are termed micropipettes (Fig. 3.8D.)... 

A few types of reference electrodes are used for potential mapping, mainly silver/ silver chloride (Ag/AgCl) or copper/copper sulfate (CSE). They differ in their standard potential, which is the potential difference to the standard hydrogen electrode (SHE). Standard potentials of these reference electrodes are given in Table 16.1, together with some other types used as embedded probes in concrete (Chapter 17). 

The most common probe is the embeddable half cell, A number of formulations are used but the most popular is the silver/silver chloride cell (Figure 6,20). Mercury/mercury oxide, lead/lead oxide and other formulations are also commercially available as well as carbon, coated titanium and lead. These last three are relative rather than absolute references, This means that they may stay stable over a few hours for a potential decay measurement, but the absolute values of the potential measured cannot be relied upon. 

General Electrochemical Setup. Catalytic studies to probe formic acid electrooxidation efficiencies are commonly not performed in a complex fuel cell, but using a three-electrode electrochemical cell at room temperature, consisting of a working (catalyst of interest), a counter (Pt mesh), and a reference electrode. Potentials are typically referenced against an RHE, saturated calomel electrode (SCE), or sUver/silver chloride (Ag/AgCl). 

Yang et al. (2010) developed an EIS technique to characterize a DMFC under various operating conditions. A silver/silver chloride electrode was used as an external reference electrode to probe the anode and cathode during fuel cell operation. The external reference was sensitive to the anode and cathode as current was passed in the working DMFC. The impedance spectra and DMFC polarization curves were investigated systematically as a function of air and methanol flow rates, methanol concentration, temperature, and current density. Water flooding in the cathode was also examined. 

Taylor et al. conducted LEIS in a mapping mode to characterize the spatial variation in the admittance associated with various types of intentionally formed defects on organically coated metal surfaces (135). The LEIS probe used in these experiments consisted of chloridized silver wires to form Ag AgCl reference electrodes. Excitation frequencies between 100 and 1000 Hz were used for mapping admittance. The precise frequency used was selected to maximize the admittances differences observed. Admittance mapping resolved differences due to millimeter-sized defects associated with adsorbed machine oil, underfilm NaCl... 

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