Electrodes cadmium

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. 

The chemistry, electrochemistry, and crystal stmcture of the cadmium electrode is much simpler than that of the nickel electrode. The overall reaction is generally recognized as ... 

Tlierefore, tlie cadmium electrode is being electrically charged and chemically discharged at tlie same rate. 

Other Cells. Other methods to fabricate nickel—cadmium cell electrodes include those for the button cell, used for calculators and other electronic de dces. Tliis cell, the construction of which is illustrated in Figure is commonly made using a pressed powder nickel electrode mixed with graphite that is similar to a pocket electrode. Tlie cadmium electrode is made in a similar manner. Tlie active material, graphite blends for the nickel electrode, are ahnost the same as that used for pocket electrodes, ie, 18% graphite. 

Anodization is facilitated at alkaline pH by the stability of low oxidation state chalcogen species (e.g., Te ) in this range. Thus, intended corrosion of a cadmium electrode in telluride environment may lead to the formation of CdTe ... 

An interesting idea has been to prepare the photosensitive electrode on site having the liquid play the dual role of a medium for anodic film growth on a metal electrode and a potential-determining redox electrolyte in the electrochemical solar cell. Such integration of the preparation process with PEC realization was demonstrated initially by Miller and Heller [86], who showed that photosensitive sulfide layers could be grown on bismuth and cadmium electrodes in solutions of sodium polysulfide and then used in situ as photoanodes driving the... 

Nowadays, such hydride electrodes are used widely to make alkaline storage batteries which in their design are similar to Ni-Cd batteries but exhibit a considerably higher capacity than these. These two types of storage battery are interchangeable, since the potential of the hydride electrode is similar to that of the cadmium electrode. The metal alloys used to prepare the hydride electrodes are multicomponent alloys, usually with a high content of rare-earth elements. These cadmium-free batteries are regarded as environmentally preferable. 

In 1899, the nickel-cadmium battery, the first alkaline battery, was invented by a Swedish scientist named Waldmar Jungner. The special feature of this battery was its potential to be recharged. In construction, nickel and cadmium electrodes in a potassium hydroxide solution, it was the first battery to use an alkaline electrolyte. This battery was commercialized in Sweden in 1910 and reached the Unites States in 1946. The first models were robust and had significantly better energy density than lead-acid batteries, but nevertheless, their wide use was limited because of the high costs. 

Cadmium dichromate, molecular formula, properties, and uses, 6 56 It Cadmium dihydrogen phosphate, 4 514 Cadmium diphosphide, 4 510 Cadmium electrodes, 3 408 standard potential, 3 413t Cadmium electroplating, 24 749 Cadmium ethylenediamine hydroxide, solvent for cotton, 8 21 Cadmium fluoride, 4 512 physical properties of, 4 508t Cadmium fluoroborate, 4 511 Cadmium fluoroborate hexahydrate,... 

The above galvanic cell is constructed with a cadmium electrode in a 1.0 M Cd(N03)2 solution in the left compartment, and a silver electrode in a 1.0 M AgN03 solution in the right compartment. The salt bridge contains a KN03 solution. The cell voltage is positive. 

One half-cell of a galvanic cell has a nickel electrode in a 1 mol/L nickel(II) chloride solution. The other half-cell has a cadmium electrode in a 1 mol/L cadmium chloride solution. 

A nicad cell has a cadmium electrode and another electrode that contains nickel(lll) oxyhydroxide, NiO(OH). When the cell is discharging, cadmium is the anode. When the cell is recharging, cadmium is the cathode. The electrolyte is a base, sodium hydroxide or potassium hydroxide. 

Figure 9—4 shows the polarization curves observed for the transfer reaction of cadmium ions (Cd Cd ) at a metallic cadmium electrode in a sulfuric acid solution. It has been proposed in the literature that the transfer of cadmium ions is a single elemental step involving divalent cadmium ions [Conway-Bockris, 1968]. The Tafel constant, a, obtained from the observed polarization curves in Fig. 9-4 agrees well with that derived for a single transfer step of divalent ions the Tafel constant is = (1- P) 1 in the anodic transfer and is a = z p = 1 in the cathodic transfer. 

Fig. 9-4. Anodic and cathodic polarization curves measured for transfer of divalent cadmium ions (dissolution-deposition) at a metallic cadmium electrode in a sulfate solution (0.005MCd + 0.4MS04 ) i (i )= anodic (cathodic) reaction current a = Tafel constant (transfer coefficient). [From Lorenz, 1954.]...

The nickel foil and a cadmium electrode were immersed in a stirred solution which was 0.5 M in CdSOj and 1 M in NHj Cl. Cadmium and nickel electrodes were shorted through an ammeter. This resulted in a rapidly decaying current which stabilized at about... 

Structural aspects of electrochemical adsorption of inorganic ions and neutral organic molecules and water dipoles on quasi-perfect cadmium electrode were also studied [19]. 

The structural and electrochemical characteristics of cadmium electrodes with nickel introduced in metallic state into the active material of the electrode by electroless plating were studied [213]. The specific role played by hetero phase interactions between nickel and cadmium in the mechanism of the Cd electrode activation was substantiated experimentally. 

The cadmium electrodeposition on the solid cadmium electrode from the sulfate medium was investigated [217]. The following kinetic parameters were obtained cathodic transfer coefficient a = 0.65, exchange current density Iq = 3.41 mA cm , and standard rate constant kg = 8.98 X 10 cm s . The electrochemical deposition of cadmium is a complex process due to the coexistence of the adsorption and nucleation process involving Cd(II) species in the adsorbed state. 

The blocking effect of ben2yl and substituted ben2yl alcohol additives on the electrodeposition of cadmium [220] and stabilization of cadmium electrode properties [221] were studied voltammetrically. 

The cadmium electrodeposition on the cadmium electrode from water-ethanol [222, 223], water-DMSO [224], and water-acetonitrile mixtures [225-229] was studied intensively. It was found that promotion of Cd(II) electrodeposition [222] was caused by the formation of unstable solvates of Cd(II) ions with adsorbed alcohol molecules or by interaction with adsorbed perchlorate anions. In the presence of 1 anions, the formation of activated Cd(II)-I complex in adsorbed layer accelerated the electrode reaction [223]. 

A method was proposed for electrolytic cadmium refining in molten CdCl2 using electrolyzer with bipolar cadmium electrode [235]. The results demonstrated that high-purity Cd could be obtained in a single electrolysis cycle. 

The electrochemical behavior of the cadmium electrodes in alkaline solutions was intensively studied [313-318]. It was suggested [314-318] that during anodic dissolution of the Cd electrode in alkaline solutions, a passive layer consisting of Cd(OH)2 and CdO is formed, and Cd(II) soluble species are also generated. The composition of the anodically formed layer on cadmium in alkaline solution was dependent on the electrolyte cation [319]. In 1 M NaOH and KOH solutions, both / -Cd(OH)2 and y-Cd(OH)2 were formed, while in 1 M LiOH, /J-Cd(OH)2 was the only product. 

The sintered electrode constructions are gradually replaced with structures of higher capacity as, for example, felted nickel fibril or foam structures [350-352]. An open nickel foam structure can be obtained by vapor deposition of nickel from nickel carbonyl into a bed of urethane foam and then burning off the polymer. The porosity increases from 80% typical for sinter electrodes and reaches 90-95% for felted or foam structures. Application of polymer bonded cadmium electrodes significantly reduces environmentally dangerous dusting during cell production [350]. 

Schmuld and coworkers [422] have studied initial stages of Cd electrodeposition on the Au(lll) surface from H2SO4 solutions. The results have shown that in such solutions (Cd(II) in H2SO4), the Au(lll) surface starts to reconstruct at potentials around 850 mV versus bulk formal potential of cadmium electrode. Nucle-ation of Cd started in the potential range 350-300 mV as the formation of separated islands of monoatomic height. Further, cathodic polarization led to the formation of strings and finally to the cadmium layer... 

---