Electrodes nickel

When nickel hydroxide is oxidized at the nickel electrode in alkaline storage batteries the black trivalent gelatinous nickel hydroxide oxide [12026-04-9], Ni(0H)0, is formed. In nickel battery technology, nickel hydroxide oxide is known as the nickel active mass (see Batteries, secondary cells). Nickel hydroxide nitrate [56171-41-6], Ni(0H)N02, and nickel chloride hydroxide [25965-88-2], NiCl(OH), are frequently mentioned as intermediates for the production of nickel powder in aqueous solution. The binding energies for these compounds have been studied (55). 

There are many methods of fabricating the electrodes for these cell systems. The eadiest commercially successhil developments used nickel hydroxide [12054-48-7] Ni(OH)2, positive electrodes. These electrodes are commonly called nickel electrodes, disregarding the actual chemical composition. Alkaline cells using the copper oxide—2inc couple preceeded nickel batteries but the CuO system never functioned well as a secondary battery. It was, however, commercially available for many years as a primary battery (see BatterieS-PRIMARY cells). 

The other type of nickel electrode involves constmctions in which the active material is deposited in situ. This includes the sintered-type electrode in which nickel hydroxide is chemically or electrochemically deposited in the pores of a 80—90% porous sintered nickel substrate that may also contain a reinforcing grid. 

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. 

Some y-NiOOH has been shown to be formed in sintered nickel electrodes (38), and changes in water and KOH concentration during the cycling of nickel electrodes has been studied (12,39—41). Although there is some disagreement on the movement of water, KOH is adsorbed on the nickel electrode when the cell is charged and desorbed from the electrode when the cell is discharged. 

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 ... 

Tubular Cells. Although the tubular nickel electrode invented by Edison is ahnost always combined with an iron negatwe electrode, a small quantity of cells is produced in wliich nickel in the tubular fomi is used with a pocket cadniium electrode. Tliis type of cell construction is used for low operating temperature environments, where iron electrodes do not perfomi well or where charging current must be limited. 

Eor the negative electrolyte, cadmium nitrate solution (density 1.8 g/mL) is used in the procedure described above. Because a small (3 —4 g/L) amount of free nitric acid is desirable in the impregnation solution, the addition of a corrosion inhibitor prevents excessive contamination of the solution with nickel from the sintered mass (see Corrosion and corrosion inhibitorsCorrosion and corrosion control). In most appHcations for sintered nickel electrodes the optimum positive electrode performance is achieved when one-third to one-half of the pore volume is filled with active material. The negative electrode optimum has one-half of its pore volume filled with active material. 

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. 

Siatered nickel electrodes used in nickel iron ceUs are usually thicker than those used in Ni/Cd ceUs. These result in high energy density ceUs, because very high discharge rates are usually not required. 

Cell Construction. Nickel—2iac batteries are housed ia molded plastic cell jars of styrene, SAN, or ABS material for maximum weight savings. Nickel electrodes can be of the siatered or pocket type, however, these types are not cost effective and several different types of plastic-bonded nickel electrodes (78—80) have been developed. 

However, the generation and migration of water in the half-ceU reactions must be considered in the cell design. At the nickel electrode ... 

The overcharge reactions for the cell are the same as for nickel—cadmium and nickel—hydrogen cells. The oxygen generated on the nickel electrode at the end of charge and overcharge finds its way to the anode and reacts to form water in the Ni—H2 case and Cd(OH)2 in the Ni—Cd case. 

Electrolysis of acidified water using platinum electrodes is a convenient source of hydrogen (and oxygen) and, on a larger scale, very pure hydrogen (>99.95%) can be obtained from the electrolysis of warm aqueous solutions of barium hydroxide between nickel electrodes. The method is expensive but becomes economical... 

Fig. 2.33 Potential difference Kbetween a redox electrode and a nickel electrode immersed in an alkali chloride melt 700°C, argon atmosphere ...

This reaction, like that between Zn and Cu2+, can serve as a source of electrical energy in a voltaic cell The cell is similar to that shown in Figure 18.2 except that, in the anode compartment, a nickel electrode is surrounded by a solution of a nickel(II) salt, such as NiCl2 or NiS04. The cell notation is Ni Ni2+ Cu2+ Cu. 

For many years, sintered-nickel electrodes have been used as the positive electrodes for sealed-type nickel-cadmium batteries. With an increase in the demand for high energy density, this type of elec-... 

Nickel-metal hydride batteries contain a nickel electrode similar to that used in nickel-cadmium batteries as the positive... 

The reaction of hydrogen at the nickel electrode determines the rate of selfdischarge in nickel-hydrogen batteries. 

After a constant potential step beyond the pitting potential is applied to a nickel electrode in NaCl solution, the current transient shown in Fig. 39 is observed. The J vs. 1/VT plot according to Eq. (104) is shown in Fig. 40. From the linear portion corresponding to Eq. (104), the slope of the plot can be described as a function of the surface coverage 6 of the passive film in the following... 

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