Electrode bridges

In situ electron transport measurements on conducting polymers are commonly made by using a pair of parallel-band electrodes bridged by the polymer [Fig. 9(A)].141142 Other dual-electrode techniques in which the polymer film is sandwiched between two electrodes [Fig. 9(B)],139,140 rotating-disk voltammetry [Fig. 9(C)],60,143 impedance spectroscopy,144,145 chronoamperometry,146 and chronopotentiometry147 have also been used. 

The thick-film design consists of four layers, to be separately screen printed and fired on a 1 in square alumina substrate (figure 14.9). Commercial formulations were used for electrodes, bridge trimming resistors, and passivation layers. The first attempted sensor layer was a commercial silver/palladium paste modified by the addition of palladium powder. Based on the performance of the first thick-film sensors, DuPont Electronics (Research Triangle Park, NC) specifically formulated a palladium-based thick-film paste for this application. 

Interdigitated electrodes, bridged by electroactive materials, can detect small changes in electrical conductance this assembly is frequently referred to as the chemiresistor. Selectivity is provided by utilization of different nanoscale materials. " Working at the nanoscale makes a useful range of resistive materials available. 

Lee, S. W., B. M. GaUanL H. R. Byon, P. T. Hammond, and Y. Shao-Hom. 2011. Nanostructured carbon-based electrodes Bridging the gap between thin-film lithium-ion batteries and electrochemical capacitors. Energy Environmental Science 4 1972-1985. 

Electrochemical Impedance Spectroscopy of Twin Working Electrodes Bridged with Conducting Polymer Layer, Electrochim. Acta 40, 1857-1862. 

Figure 5. Cell for electronic studies, (A) thermo-electric temperature block 5x7.5 cm, (B) silicone rubber gasket with centrally located 0.3 cm diam. window, (C) Perspex compartment 5x7.5x0.45 cm with 0.3 cm diam. window and 0.3 cm channel for introduction of reference electrode bridge-G, (D) silicone rubber gasket with 0.3 cm diam. window, (E) Perspex cover plate, (F) Pt counter-electrode, and (H) membrane plated Pt electrode.

Hill, P. L. and Schwan, H. P., 1968, Relative performance of different four-electrode bridges, Proc. 21st ACEMB, Houston, p. 19.7. 

The vacuum fuse is another example of the use of high-current vacuum arcs for current interruption and the protection of power circuits. Its design is similar to that of a triggered vaeuum gap with the fixed arcing electrodes bridged by a fuse element that conducts current under normal conditions. On the incident of a fault or other abnormal... 

Electrode reversible Standard reference Salt bridge... 

Standard Hydrogen Electrode The standard hydrogen electrode (SHE) is rarely used for routine analytical work, but is important because it is the reference electrode used to establish standard-state potentials for other half-reactions. The SHE consists of a Pt electrode immersed in a solution in which the hydrogen ion activity is 1.00 and in which H2 gas is bubbled at a pressure of 1 atm (Figure 11.7). A conventional salt bridge connects the SHE to the indicator half-cell. The shorthand notation for the standard hydrogen electrode is... 

The saturated calomel electrode (SCE), which is constructed using an aqueous solution saturated with KCl, has a potential at 25 °C of -hO.2444 V. A typical SCE is shown in Eigure 11.8 and consists of an inner tube, packed with a paste of Hg, HgiCli, and saturated KCl, situated within a second tube filled with a saturated solution of KCl. A small hole connects the two tubes, and an asbestos fiber serves as a salt bridge to the solution in which the SCE is immersed. The stopper in the outer tube may be removed when additional saturated KCl is needed. The shorthand notation for this cell is... 

A typical Ag/AgCl electrode is shown in figure 11.9 and consists of a silver wire, the end of which is coated with a thin film of AgCl. The wire is immersed in a solution that contains the desired concentration of KCl and that is saturated with AgCl. A porous plug serves as the salt bridge. The shorthand notation for the cell is... 

Reference Electrodes and Liquid Junctions. The electrical cincuit of the pH ceU is completed through a salt bridge that usually consists of a concentrated solution of potassium chloride [7447-40-7]. The solution makes contact at one end with the test solution and at the other with a reference electrode of constant potential. The Hquid junction is formed at the area of contact between the salt bridge and the test solution. The mercury—mercurous chloride electrode, the calomel electrode, provides a highly reproducible potential in the potassium chloride bridge solution and is the most widely used reference electrode. However, mercurous chloride is converted readily into mercuric ion and mercury when in contact with concentrated potassium chloride solutions above 80°C. This disproportionation reaction causes an unstable potential with calomel electrodes. Therefore, the silver—silver chloride electrode and the thallium amalgam—thallous chloride electrode often are preferred for measurements above 80°C. However, because silver chloride is relatively soluble in concentrated solutions of potassium chloride, the solution in the electrode chamber must be saturated with silver chloride. 

Carbon Electrodes. Carbon electrodes are rigid carbonaceous shapes deployed in electric furnaces. They are the final link in the chain of conductors from the energy source to the reaction zone of an electrically heated vessel. The gap bridged by the electrode is that between the contact plates that transmit current to the electrode and the discharge area at the arc end of the electrode. 

---