Cathode contact cells

The cell for this process is unlike the cell for the electrolysis of aluminum which is made of carbon and also acts as the cathode. The cell for the fused-salt electrolysis is made of high temperature refractory oxide material because molten manganese readily dissolves carbon. The anode, like that for aluminum, is made of carbon. Cathode contact is made by water-cooled iron bars that are buried in the wall near the hearth of the refractory oxide cell. 

Lead is oxidized to lead sulfate at the anode, and lead dioxide is reduced to lead sulfate at the cathode. The cell doesn t need to have separate anode and cathode compartments because the oxidizing and reducing agents are both solids (Pb02 and Pb) that are kept from coming in contact by the presence of insulating spacers between the grids. 

The cell consists of a commercially available four-necked, 500-mL, round-bottomed flask equipped with a 34/45 standard-taper joint electrode assembly (Note 1), a 24/40 standard-taper joint purge and vent assembly, a mercury pool cathode (Note 2), a cathode contact (Note 3), a magnetic stirring bar (Note 4), and thermometer (inserted in a 10/18 standard-taper joint neck). The two platinum anodes of the electrode assembly (Note 1) are positioned in a horizontal plane ca. 1 cm above (Note 4) the mercury (Cathode) surface. 

Alumina electrolysis cells consist of a rectangular steel shell lined with a 25-35 cm layer of baked and rammed dense carbon, which provides both chemical resistance and the cathode contact with the electrolyte via steel bus bars imbedded in the carbon. Normal lining life is 4—6 years, after which it is replaced as large preformed slabs. Once a reduction pot has been started the bulk of the cathode current to the carbon lining is via the pool of newly formed molten aluminum in the bottom of the cell (Fig. 12.2). 

Cathodes have an effective depositions surface area of 1.67 m and there are 33 cathodes in a cell. A knife switch type is used for the cathode contacts. This type allows the cathode header bar to come in contact with both the clip and the equipotential bar, resulting in a wide contact area. With a self-weight contact type, the contact resistance is increased because the weight of the cathode is light at the initial stage of electrolysis. To minimize this disadvantage, the knife switch type has been consistently in use to the present time. 

What is the cell potential of a concentration cell that contains two hydrogen electrodes if the cathode contacts a solution with pH = 7.8 and the anode contacts a solution with [H+] = 0.05 M ... 

A dry cell, so named because it has no fluid component, consists of a zinc container (the anode) in contact with manganese dioxide and an electrolyte (Figure 19.6). The electrolyte consists of ammonium chloride and zinc chloride in water, to which starch is added to thicken the solution to a paste so that it is less likely to leak. A carbon rod, immersed in the electrolyte in the center of the cell, serves as the cathode. The cell reactions are ... 

The principle is shown in Figure 5.5. The electrolyte is KOH solution, with a fuel, such as hydrazine, or ammonia, mixed with it. The fuel anode is along the lines discussed in Section 5.4.4, with a platinum catalyst. The fuel is also fully in contact with the cathode. This makes the fuel crossover problem discussed in Section 3.5 very severe. However, in this case, it does not matter greatly, as the cathode catalyst is not platinum, and so the rate of reaction of the fuel on the cathode is very low. There is thus only one seal that could leak, a very low-pressure joint around the cathode. The cell is refuelled simply by adding more fuel to the electrolyte. A possible variation is to put a membrane across the electrolyte region and only provide fuel below the membrane - a suitably chosen membrane will stop the fuel from reaching the air cathode. 

There are three common lithium anode configurations Li(Si) alloy, LiAl alloy, and Li metal in metal matrix, Li(M), where the matrix is usually iron powder. With the difference that the alloy anodes remain solids and the lithium in the Li(Fe) mix is molten in an activated cell, all three anodes participate in the cell reaction similarly. All may be used with the same FeS2 cathode and the same electrolytes. These electrolytes may be the basic LiCl-KCl eutectic electrolyte, LiCl-LiBr-LiF electrolyte for best ionic conductivity, or a lower-melting-point electrolyte such as LiBr-KBr-LiF for extended activated life. Since the FeS2 is a good electronic conductor, the electrolyte layer is necessary in order to prevent direct anode-to-cathode contact and cell short-circuiting. When molten, the electrolyte between the anode and the cathode is held in place by capillary action through the use of a chemically compatible (inert) binder material. MgO is the preferred material for this application. °... 

Moreover, phosphonium halides can be used as an interfacial n-dopant to improve the electrical properties of cathode contacts. Perovskite solar cells incorporating organic halides as processing additives and interfacial modifiers show significant device performance improvement. 

Fig. 1 Cross section of a standard cell (1) anode channel (2) cathode channel (3) cooling channel (4) gas-diffusion layer (5) membrane (6) cathode contact area (7) anode contact area (8) hydrogen diffusion length at the channel (9) hydrogen diffusion length at the contact area (10) oxygen diffusion length at the channel (11) oxygen diffusion length at the contact areas (12) water diffusion length at the channel (13) water diffusion length at the contact areas...

Fig. 6 Cross section of a cell with a porous gas distribution structure (1) anode channel (2) cathode channel (3) cooling channel (4) gas-diffusion layer (5) membrane (6) cathode contact area (7) anode contact area...

Fig. 2.5 Cr poisoning for different combinations of electrolyte and electrode, measured with a cathode half-cell in contact with a plate of INCONEL 600 by Matsuzaki and Yasuda [18]...

Basu, R.N., Tietz, F., Teller, O., Wessel, E., Buchkremer, H.P and Stover, D. (2003), LaNio.6Feo.4O3 as a cathode contact material for solid oxide fuel cells, J. Solid State Electrochem., 7,416-420. 

Corrosion problems are particularly important when two metals are in contact. The more reactive metal becomes the cathode of the cell and goes into solution when the cell is activated by an electrolyte. A typical cell is shown in Figure 13.7. When the metal in contact with iron is more reactive than iron itself, the iron is protected from corrosion. This is important when mechanical strength... 

Caustic Soda. Diaphragm cell caustic is commercially purified by the DH process or the ammonia extraction method offered by PPG and OxyTech (see Fig. 38), essentially involving Hquid—Hquid extraction to reduce the salt and sodium chlorate content (86). Thus 50% caustic comes in contact with ammonia in a countercurrent fashion at 60°C and up to 2500 kPa (25 atm) pressure, the Hquid NH absorbing salt, chlorate, carbonate, water, and some caustic. The overflow from the reactor is stripped of NH, which is then concentrated and returned to the extraction process. The product, about 62% NaOH and devoid of impurities, is stripped free of NH, which is concentrated and recirculated. MetaUic impurities can be reduced to low concentrations by electrolysis employing porous cathodes. The caustic is then freed of Fe, Ni, Pb, and Cu ions, which are deposited on the cathode. 

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