Electrode: auxiliary glass

Figure 9.3 Stationary solution voltammetry cells, (a) Platinum wire loop auxiliary electrode, (b) reference electrode or reference electrode probe tip, (c) carbon paste working electrode, (d) graphite auxiliary electrode, (e) dropping mercury electrode, (0 platinum wire contact to mercury pool working electrode, (g) nitrogen gas inlet tube, (h) magnetic stirrer, (i) mercury pool working electrode, (j) glass frit isolation barrier.

Fig. 25. Single graphite fiber EC detector orKnechtei ai (1984). (A)Cell inlet, (B) capillary column, (C) graphite fiber inserted into capillary, (D) epoxy, (E) wo ng electrode sheath (glass tube), (F) mercury electrical contact, (G) O ring, (H) outer cell body (glass tubeX and (I) Ag/AgCI tefeience/auxiliary eketrode.

Figure 12.2 The electrochemical cell has a 25 p-m Teflon spacer sandwiched between the electrode and a window (Cap2 or Mgp2) to provide an electrolyte layer of known and controlled thickness. Working, reference, and auxiliary electrodes are indicated. Construction materials are glass and Teflon.

In principle, the auxiliary electrode can be of any material since its electrochemical reactivity does not affect the behaviour of the working electrode, which is our prime concern. To ensure that this is the case, the auxiliary electrode must be positioned in such a way that its activity does not generate electroactive substances that can reach the working electrode and interfere with the process under study. For this reason, in some techniques the auxiliary electrode is placed in a separate compartment, by means of sintered glass separators, from the working electrode. 

The auxiliary electrode, which is normally a mercury pool, must be positioned in a compartment separate from the working electrode. Such a separation compromises the desired symmetric disposition of the electrodes. Normally, the compartments of a macroelectrolysis cell are separated by sintered glass frits, such that the catholyte and the anolyte are not mixed. In fact, if the working electrode is involved, for example, in a cathodic process, the auxiliary electrode will act as an anode. This implies that the auxiliary electrode will produce oxidized material (by anodic decomposition of the solvent itself, of the supporting electrolyte, of mercury-contaminated products or of electroactive residues diffused at the auxiliary electrode) that may subsequently be reduced at the working electrode, contaminating and falsifying the primary process. 

Fig. 9.3. The electrolyte dropping electrode REj, RE2 - reference electrodes CE2 - auxilliary electrode 1 - aqueous phase formed by dropping of the electrode 2 - nitrobenzene phase 3 - Teflon capillary 4 - sintered glass. The arrow denotes the connection to the reservoir with the aqueous electrolyte and the auxiliary electrode CEi. (After Samecefai. [20].)...

The cell for rotating electrodes, Fig. 7, is usually cylindrical and surrounded by a water jacket for thermostatting purposes, but as long as the cell walls are more than 1 cm or so from the rotating assembly, there are usually no cell edge effects. The auxiliary electrode is very often contained in a separate compartment behind a glass frit in order to avoid contamination problems. A Luggin capillary, where required, can be positioned in various ways unless it is more than 0.5 cm from the electrode, it must be placed under the centre of the disc in order to avoid a non-equipotential surface this can cause some problems with disturbance of the fluid flow. 

Figure 9.8 Experimental arrangement for use of thin-layer electrode constructed with glass or quartz plates. W, Working electrode R, reference electrode A, auxiliary electrode a, inert-gas inlet.

Figure 9.9 Assembly of sandwich-type optically transparent thin-layer electrochemical cell, a, Glass or quartz plates b, adhesive Teflon tape spacers c, minigrid working electrode d, metal thin-film working electrode, which may be used in place of (c) e, platinum wire auxiliary electrode f, silver-silver chloride reference electrode g, sample solution h, sample cup. [Adapted with permission from T.P. DeAngelis and W.R. Heineman, J. Chem. Educ. 53 594 (1976), Copyright 1976 American Chemical Society.]...

Figure 11.8 Cell for use of thin-film electrodes. A, Aluminum retaining plate B, OTE C, copper foil D, O-ring E, Lucite body F, glass salt bridge for reference electrode G, Hamilton valves H, auxiliary electrode I, quartz disk. [From Ref. 89, with permission. Copyright 1972 American Chemical Society.]...

Figure 17.11 Transmission spectroelectrochemistry cell designed for use with room-temperature haloaluminate melts and other moisture-reactive, corrosive liquids, (a) Auxiliary electrode and reference electrode compartments, (b) quartz cuvette containing the RVC-OTE, (c) brass clamping screw, (d) passageway between the separator and OTE compartment, (e) fritted glass separator, (f) A1 plate, (g) lower cell body (Teflon), (h) upper cell body (Teflon). This cell is normally used inside a glove box and is optically accessed with fiber optic waveguides. [From E. H. Ward and C. L. Hussey, Anal. Chem. 59 213 (1987), with permission.]...

Broadly, the sensor contains, apart from the glassy-carbon working electrode, a reference electrode, a counter electrode, a temperature sensor and a pH glass electrode with associated reference electrode. As to the auxiliary sensor and electrodes, in the experiments on a laboratory scale, described in the previous chapters, types commonly used in research were employed. Here these need to be replaced by types which satisfy the above-mentioned requirements, which are discussed in the next section. 

EG G PAR (USA), Model 273 A, Potentiostat/Galvanostat volt-ammetric analyzer controlled by PC equipped with a data acquisition and treatment software to record the signal generated in the electrochemical cell for DPY measurements. A 25 mL glass cell at 25°C with the carbon paste biosensor, Ag/AgCl (3.0 mol L-1 KC1) reference electrode, and a platinum wire as auxiliary electrode to perform the volt-ammetric measurements. 

Auxiliary Electrode Chamber (fritted glass tube)... 

If a cell divider is necessary (mostly important for cathode processes), a piece of glass tubing with a glass frit of medium porosity at one end is inserted into the beaker and serves as the auxiliary electrode compartment. For more elaborate designs (Figs. 7—9) the reader should consult the references given above and recent articles 86-87>366c). 

Ohmic drop in three-electrode circuits. In modem coulometry and voltammetry the use of a potentiostat and a three-electrode configuration is the routine practice. The three electrodes are usually called the working, reference, and counter (or auxiliary) electrodes (see Figure 5.2). The cell current passes between the working electrode immersed in the test solution and the counter electrode, which may be in the test solution but is usually isolated from it by a single- or double-junction glass frit. 

In process of intercalation a three-electrode glass cell from a chemically and thermic stable glass consisting (see Fig. 2b) from an electrode of comparison (AgCl), working and auxiliary (platinum wire) electrodes were used. Investigated... 

Scanning electrochemical microscopy seeks to overcome the lack of sensitivity and selectivity of the probe tip in STM and AFM to the substrate identity and chemical composition. It does this by using both tip and substrate as independent working electrodes in an electrochemical cell, which therefore also includes auxiliary and reference electrodes. The tip is a metal microelectrode with only the tip active (usually a metal wire in a glass sheath). At large distances from the substrate, in an electrolyte solution containing an electroactive species the mass-transport-limited current is therefore... 

Recently a low-cost, high efficiency (about 12 per cent in diffuse daylight) photovoltaic cell based on dye-sensitized colloidal titanium oxide films with a conducting glass auxiliary electrode was described71. 

The vacuum-tube diode, invented by Fleming24 in 1904 [2,3], works because of the relative geometrical shapes of the two concentric electrodes, the cathode and the anode. It consists of a cylindrical glass enclosure that is partially evacuated, bonded, and sealed to a metal base. It contains an inner metallic thin-wire "cathode" (negative electrode, consisting of W, oxide-covered W, or a Th-W alloy), placed along the cylinder axis. This cathode is electrically heated to 900 K or above, using an auxiliary filament circuit, typically driven by a 6.3-V power supply, to foster thermoionic emission of electrons from the cathode. This cathode is cylindrically surrounded by a metallic outer electrode, the anode or "positive electrode" or "plate," which is a hollow metallic cylinder, whose axis coincides with that of the cathode. The... 

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