Cadmium oxide electrodes

Almost all the methods described for the nickel electrode have been used to fabricate cadmium electrodes. However, because cadmium, cadmium oxide [1306-19-0], CdO, and cadmium hydroxide [21041-95-2], Cd(OH)2, are more electrically conductive than the nickel hydroxides, it is possible to make simple pressed cadmium electrodes using less substrate (see Cadmium and cadmium alloys Cadmium compounds). These are commonly used in button cells. 

Oxygen evolution occurs on nickel oxide electrodes throughout charge, on overcharge, and on standby. It is the anodic process in the self-discharge reaction of the positive electrode in nickel-cadmium cells. Early work in the field has been reviewed [9], No significant new work has been reported in recent years. 

In alkaline solutions, sometimes the cadmium-cadmium oxide RE is used its design is the same as that of the silver-silver chloride RE (a thin layer of cadmium oxide is formed on the surface of metallic cadmium). This electrode is quite simple to make and manipulate, but its potential is not very stable E = +0.013 V. 

Photopotential as a fimction of wave length of photons for zinc oxide and cadmium selenide electrodes in aqueous solutions X. = photon wave length. [From Williams, I960.]... 

Cadmium oxide is used in storage battery electrodes. Its solution, mixed with sodium cyanide, is used in electroplating baths. Other uses are in PVC heat stabilizers as an additive to nitrile rubbers and plastics to improve heat resistance and in ceramic glazes and phosphors. 

However, it is recognized that slightly soluble intermediates such as CdO(OH) and Cd(OH)3 are involved. Cadmium does not corrode since its equilibrium potential is more positive than that of hydrogen in the same solution. The active material in pocket plate cells consists of metallic cadmium, with up to 25% of iron and small quantities of nickel and graphite to prevent agglomeration. Two methods of preparation are used. One involves the electrochemical co-reduction of a solution of cadmium and iron sulphate in the other, dry mixtures of cadmium oxide or hydroxide and Fe304 or iron powder are used. In some methods of pocket plate manufacture, the electrode material is pressed into pellets or briquettes before being inserted into the pockets, and various waxes or oils may be used to facilitate this process. 

In pocket plate cells, the active materials are a mixture of finely powdered metallic iron and Fe304. The preparation of this mixture varies from manufacturer to manufacturer, but generally involves a final process in which controlled air oxidation of iron powder or reduction of Fe304 with hydrogen is used to form the appropriate composition. Additives such as cadmium, cadmium oxide or graphite are commonly included to improve the capacity retention and electronic conductance. The performance of the electrode is improved by the addition of up to 0.5% of FeS the mechanism of the sulphide involvement is not well understood. If sulphide is lost by oxidation after prolonged use, small amounts of soluble sulphide may be added to the electrolyte,... 

New, high-density nickel oxide electrode materials, coupled with nonwoven nickel-fiber current collectors, have significantly improved the performance of the nickel electrode even in the nickel-cadmium cells [5j. The alloys used to form hydride, which capture and release hydrogen in volumes up to nearly a thousand times their own, include rare-earth/nickel alloys (generally based on LaNis and called AB5)... 

Nickel oxide electrodes constitute the positive plates of several storage systems (among which nickel-zinc, nickel cadmium, nickel metal-hydride, sodium-nickel chloride) [16]. In recent years, the high-specific energy and specific power of Ni-Zn systems has increased the interest in their use for electric vehicles with respect to the past years, when their application was essentially limited by a short cycle life. 

Of course, one of the most common uses for nickel is coinmaking, specifically, the five-cent coin. The nickel coin is an alloy made of copper and nickel. Another important and common use for this metal is the nickel-cadmium battery, which contains a nickel-oxide electrode. This battery is rechargeable, making it ideal for calculators, computers, and other small electrical appliances. 

Finally, the conversion of the primary metal into the product and the form which are actually utilized in the battery system should be considered. For example, the electrode materials in lead acid batteries are normally cast lead or lead-alloy grids. The materials utilized in NiCd batteries are cadmium oxide and high surface area nickel foams or meshes. Technically, all of these factors should be considered to produce a detailed life cycle analysis. However, again, these differences are generally quite small compared to the principal variables - composition, performance and spent battery disposal option. 

Until the 50 s, companies showed little interest in recovering the cadmium, which was not considered hazardous and the negative electrodes available weighed very little. Moreover, putting complete nickel-cadmium batteries in the furnace to produce nickel-based ferroalloys posed absolutely no problem. The cadmium was vaporised on the surface, where it burned to produce cadmium oxide, which was usually released into the environment. At best, some of the dust was picked up by relatively efficient filters, in the case of zinc, lead and other forms of dust. 

In the USA, BIG RIVER ZINC developed a process designed to produce cadmium oxide directly from pocket-plate negative electrodes. It discontinued this process when the price of cadmium fell very sharply in 1991/1992. 

A more recent design that has shown significantly improved performance characteristics is the plastic-bonded or pressed-plate electrode. This new development of electrode materials in industrial batteries is a spin-off from the development of electrode materials for use in aircraft and sealed portable consumer batteries. In the plastic-bonded plate, which is mainly used in the cadmium electrode, the active material cadmium oxide is mixed with a plastic powder, normally PTFE, and a solvent to produce a paste. The paste is isotropic and the materials are manufactured at the final density for the active material. As a result, dust problems are eliminated during manufacturing. The paste is extruded, rolled, or pasted onto a center current collector normally made of nickel-plated perforated steel. The plate stmcture is welded to nickel-plated steel tabs. 

Most silver-cadmium cells contain cadmium electrodes that are manufactured by pressed-power or pasting techniques. Although other methods have been used, such as impregnating nickel plaque with cadrnium salts, as is done for nickel-cadmium cells, the most common method in silver-cadmium cells is to press or paste a mixture of cadmium oxide or cadmium hydroxide with a binder onto a silver or nickel grid. These processes are similar to those used for the pressed and pasted zinc electrodes. 

Fatas, et al. (63), have also done a study on the electrodeposition of CdS from nonaqueous solutions, in this case on stainless steel and tin oxide. They studied two solvents DMSOandPC. Thesolutionswere0.19 M sulfur and 0.055 M cadmium chloride in DMSO, and PC saturated with sulfur, cadmium chloride and potassium chloride. The depositions were carried out at a constant current at 120°C. All voltages were referenced to a cadmium/cadmium chloride electrode. 

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