Electrode gauze

Although its expense prohibits its use in many applications, the alkali fuel cell is the primary fuel cell used in the aerospace industry, because it has a very high power density (see Box 12.1). One problem is the reaction of the alkali electrolyte with the carbon dioxide in air to form potassium carbonate, which clogs the openings in the electrode gauze. 

G.E., and M.P. are the dropping electrode, gauze electrode and mercury pool electrode respectively. A valve oscillator connected to points A and B supplied alternating current of adjustable frequency. The current passed by the dropping electrode flowed also through the variable resistance R and the variable capacity C (a set of standardised condensers). 

The properties of several representative liquid-based ion-selective electrodes are presented in Table 11.3. An electrode using a liquid reservoir can be stored in a dilute solution of analyte and needs no additional conditioning before use. The lifetime of an electrode with a PVC membrane, however, is proportional to its exposure to aqueous solutions. For this reason these electrodes are best stored by covering the membrane with a cap containing a small amount of wetted gauze to... 

Fig. 7. Section of disk-type cell where 1, is the cell cup 2, is the bottom insert 3, is the separator 4, is the negatwe electrode 5, is the positive electrode 6, is the nickel whe gauze 7, is the sealing washer 8, is the contact spring and 9, is the cell cover.

A fuel cell is simply a device with two electrodes and an electrolyte for extracting power from the oxidation of a fuel without combustion, converting the power released directly into electricity. The fuel is usually hydrogen. The principle of a fuel cell was first demonstrated by Sir William Grove in London in 1839 with sulphuric acid and platinum gauze as an electrocatalyst, and thereafter there were very occasional attempts to develop the principle, not all of which were based on sound scientific principles , as one commentator put it. 

The electrodes are made of platinum gauze as the open construction assists the circulation of the solution. It is possible to use one of the electrodes as stirrer for the solution, but special arrangements must then be made for connection of the electrolysis current to this electrode, and an independent glass-paddle stirrer or a magnetic stirrer offer a simple altemative.Typical electrodes are the Fischer type depicted in Fig. 12.4 a glass tube is slid into... 

The urease is incorporated into a polyacrylamide gel which is allowed to set on the bulb of the glass electrode and may be held in position by nylon gauze. Preferably, the urease can be chemically immobilised on to bovine serum albumin or even on to nylon. When the electrode is inserted into a solution containing urea, ammonium ions are produced, diffuse through the gel and cause a response by the ammonium ion probe ... 

Fig. 16. Small-scalo laboratory cell for preparative electrolysis. A, Pt gauze working electrode. B, Pt sheet secondary electrode. C, Reference electrode. D, Luggin capillary on a syringe barrel so that the position of the tip of the Luggin probe relative to the working electrode is readily adjustable. E, Glass sinter to separate anode and cathode compartments. F, Gas inlet to allow stirring with inert gas or the continuous introduction of reactant. G, Three-way tap where a boundary between the reference electrode and the working solutions may be formed.

The single cell thus fabricated was placed in a single chamber station as illustrated in Fig. 2. A humidified mixture of methane and oxygen was supplied to the station so that both electrode compartments were exposed to the same composition of methane and oxygen. For the measurement of the cell temperature, a thermocouple (TC) was placed approximately 4 mm away from the cathode site. For the evaluation of the fuel-cell performance, Ft wires and Inconel gauzes were used as the output terminals and electrical collectors, respectively. 

Enzyme electrodes. Guilbault52 was the first to introduce enzyme electrodes. The bulb of a glass electrode was covered with a homogeneous enzyme-containing gel-like layer (e.g., urease in polyacrylamide) and the layer was protected with nylon gauze or Cellophane foil when placed in a substrate solution (e.g., urea) an enzymatic conversion took place via diffusion of substrate into the enzymatic layer. 

In many instances electrogravimetry must be preceded by a separation between metals suitably this can be an electroseparation by means of constant-current electrolysis as previously described, but more attractively an electroseparation by means of controlled-potential electrolysis at a mercury pool or sometimes at an amalgamated Pt or brass gauze electrode. In this way one can either concentrate the metal of interest on the Hg or remove other metals from the solution alternatively, it can be a rougher separation, i.e., the concentration of a group of metals such as Fe, Ni, Co, Cu, Zn and Cd on the Hg whilst other metals such as alkali and alkaline earth metals, Be, Al, Ti and Zr remain in solution151. In all these procedures specific separation effects can be... 

The thermionic method is based on thermoemission of electrons in a diode. At elevated temperatures, metals emit electrons that are collected at a gauze electrode placed opposite the metal surface and charged to a high positive potential. C. W. Richardson has given the following relationship for the saturation current /s ... 

In principle, different reference electrodes may be used if the cell is provided with a separate compartment and a Luggin capillary. But if the flow cell technique is to be applied, it is more convenient to avoid the use of capillaries where the solution cannot be easily exchanged. Active bulk components could diffuse through the capillary and give rise to erroneous responses. A small palladium gauze charged with hydrogen directly immersed in the solution can be used as the reference electrode (PdH ) [18]. 

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. 

Indicator Electrodes Silver wire or Platinum wire or gauze plated with silver and sealed into... 

The working electrode generally consists of a cylindrical platinum gauze or a mercury pool thereby offering the largest surface area possible to the redox process. 

Figure 7 shows a typical electrolysis cell with a platinum gauze working electrode. Eventually the platinum gauze can be replaced by a mercury pool working electrode. The volume of solution contained in such a cell is about 30-50 ml. 

Figure 7 Typical cell for electrolysis with a working platinum gauze electrode...

Compounds 52, 53, 57, 58, and 69-72 were measured in 10% aqueous acetonitrile with 0.2 M BU4NBF4 as supporting electrolyte. All other compounds were measured in dichloromethane with 0.2 M BU4NBF4 as supporting electrolyte. A platinum electrode or a platinum gauze basket were the working electrode and all potentials are reported against the saturated calomel electrode (SCE) with a reference potential of 0.0 V. Values of for 57, 58, 70, 72, and 78 are actually values of E the reversible peak potential. All other values of are irreversible peak potentials. 

Another oxidative cyclization to afford a nitrogen heterocycle is illustrated in Scheme 12 [33]. This reaction was accomplished using a platinum gauze electrode at a controlled potential of -t-1.8 V versus Ag/AgCl. The reaction proceeded through the initial oxidation of the amide. Evidence... 

Anodic oxidation of enaminone 10 was performed at the platinum gauze electrode in methanol solution containing LiC104 in a divided cell at controlled potential. After passage of 1.2F/mol two major products 11 and 12 were isolated in 50 and 20% yields respectively (Scheme 12). Oxidation of the enaminone 10 is initiated by electron loss from the dimethylamino moiety to... 

The screen need not be of a specialized type, and could be a conventional fine-mesh gauze from a standard printing press. If the electrodes are small enough, we can also screen-print microelectrode systems. 

A significant step forward in our understanding of Pt was taken by Verkerk and Burgraff, who in 1983 analyzed the impedance of porous sputtered Pt (and Pt gauze) electrodes on YSZ and gadolinia-doped ceria (GDC). As shown in Figure 11, they used a Randles circuit to model the interfacial contributions to the impedance, allowing them to subtract from the data the contributions of uncompensated iR and... 

The difference between the two reactions of Scheme 2.9 may also be considered in terms of the complete electron transfer in both cases. If the a-nitrostilbene anion-radical and metallocomplex cation-radical are formed as short-lived intermediates, then the dimerization of the former becomes doubtful. The dimerization under electrochemical conditions may be a result of increased concentration of reactive anion-radicals near the electrode. This concentration is simply much higher in the electrochemical reaction because all of the stuff is being formed at the electrode, and therefore, there is more dimerization. Such a difference between electrode and chemical reactions should be kept in mind. In special experiments, only 2% of the anion-radical of a-nitrostilbene were prepared after interruption of controlled-potential electrolysis at a platinum gauze electrode. The kept potential was just past the cathodic peak. The electrolysis was performed in the well-stirred solution of trani -a-nitrostilbene in AN. Both processes developed in this case, namely, trans-to-cis conversion and dimerization (Kraiya et al. 2004). The partial electrolysis of a-nitrostilbene resulted in redox-catalyzed equilibration of the neutral isomers. 

Fig. 14. Scheme of the vidicon tube. (1) Scanning beam (cathode potential F = 0 volt) (2) gauze (3) dye film (4) transparent supporting electrode (potential +30 volt) (5) amplifier (6) galvanometer... 

The modified supported powder electrodes used in the experiments hitherto described on the anodic activity of CoTAA are out of the question for practical application in fuel cells, as they do not have sufficient mechanical stability and their ohmic resistance is very high (about 1—2 ohm). For these reasons, compact electrodes with CoTAA were prepared by pressing or rolling a mixture of CoTAA, activated carbon, polyethylene, and PTFE powders in a metal gauze. The electrodes prepared in this way show different activities depending on the composition and the sintering conditions. Electrodes prepared under optimal conditions can be loaded up to about 40 mA/cm2 at a potential of 350 mV at 70 °C in 3 M HCOOH, with relatively good catalyst utilization (about 5 A/g) and adequate stability. 

Outline of Pt gauze basket that surrounds electrode... 

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