Electrode pocket-type

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. 

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. 

The nickel-based systems include the flowing systems nickel—iron (Ni/Fe), nickel—cadmium (NiCd), nickel—metal hydrides (NiMH), nickel—hydrogen (Ni/ H2), and nickel—zinc (Ni/Zn). All nickel systems are based on the use of a nickel oxide active material (undergoing one valence change from charge to discharge or vice versa). The electrodes can be pocket type, sintered type, fibrous type, foam type, pasted type, or plastic roll-bonded type. All systems use an alkaline electrolyte, KOH. 

Pocket-type cadmium electrodes are made by a procedure similar to that described for the positive electrode. Because cadmium active material is more dense Ilian nickel active material, and because cadmium has a 2+ valence, cadmium electrodes, when fabricated to equal thicknesses, have almost twice the working capacity of the nickel electrode. 

In the older versions of Ni-Cd storage cells and in the Ni-Fe cells pocket-type electrodes were used. In this version the pressed active mass of the electrodes are... 

The electrodes of the nickel-cadmium secondary battery are classified into pocket type, sintered type, and pasted type according to those manufacturing methods. Moreover, the batteries... 

The positive active material of a pocket-type electrode consists of nickel hydroxide powder by which cobalt hydroxide was coprecipitated, and is obtained from those mixed sulfate by a neutralizing method. Graphite powder is mixed as a conductor. The addition of cobalt is performed for increasing the capacity of the positive active material. Cadmium hydroxide which is a negative active material is manufactured by a coprecipitation method or a dry-mixing method. Moreover, iron powder is usually mixed with negative active material of a pocket type electrode for the increase in capacity. Graphite powder and/or nickel flake is mixed as a conductor. 

The electrochemically active material of the nickel electrode is nickel hydroxide. This material is an amorphous colloid and is only semiconductive at best. It must be supported and contained by a structural component which provides mechanical support, conductivity and current collection for the electrode. Standard types of nickel electrodes can be used in the nickel-zinc system. They can be classified by the type of electrode substrate used and by the method of preparation. These electrodes consist of two basic types, sintered and nonsin-tered. Each type has different advantages and disadvantages and may be selected based on the application. Other types of nickel electrodes, such as pocket plate, are generally not in common use. 

Types T and TP These are storage batteries with pocket-type electrodes. The series T storage batteries, from 65 to 1250 Ah, have a nickel-plated sheet steel case and are delivered in open wooden crates (from 65 to 380 Ah) and as single cells (from 450 to 1250 Ah). The 10-315 Ah storage batteries, series TP, have a transparent plastic cell case, which makes it possible to control the electrolyte level from outside. They are available as compact blocks, portable... 

Types HK and HKP Discharge data on types T and TP are given in Table 51.60. Types HK and HKP are storage batteries with pocket-type electrodes. The series HK storage batteries from 73 to 1390Ah have... 

Cell construction is mainly confined to two types, using either pocket plate electrodes (vented cells) or sintered , bonded or fibre plate electrodes (vented and sealed cells). In the former, the active materials are retained within pockets of finely perforated nickel-plated sheet steel which are interlocked to form a plate. Positive and negative plates are then interleaved with insulating spacers placed between them. In sintered plate electrodes, a porous sintered nickel mass is formed and the active materials are distributed within the pores. In sintered plate vented cells, cellulose or other membrane materials are used in combination with a woven nylon separator. In sealed or recombining cells, special nylon separators are used which permit rapid oxygen diffusion through the electrolyte layer. 

Figure 4-6. (A) A close-up view of the active site of yeast cytochrome c peroxidase showing the residues in the distal pocket at which hydrogen peroxide is reduced to water. Overlaid on the structure of the wild type enzyme are the positions of residues in the W51F mutant (tryptophan is replaced by phenylalanine). (B) Voltammograms of a film of wild type CcP on a PGE electrode, obtained in the absence and presence of H2O2 at ice temperature, pH 5.0. The electrode is rotating at 200 rpm, but the catalytic current in this case continues to increase as the rotation rate is increased therefore under these conditions the electrocatalysis is diffusion controlled and few facts are revealed about the enzyme s chemistry. For the W51F mutant, the signal due to the reversible two-electron couple and the catalytic wave are both shifted >100 mV more positive in potential compared to the wild-type enzyme. Reproduced from ref. 46 and 47 with permission.

Another type of battery is the mercuiy batteiy often formerly used in pocket calculators. The mercuiy battery has a zinc electrode while mercuiy oxide HgO are oxidised in the basic environment consisting of typically KOH and Zn(OH)2. The figure below shows the set-up of the mercuiy diy cell batteiy. 

Many enzymes use redox centers to store and transfer electrons during catalysis. These redox centers can be composed of metals such as iron or cobalt, or organic cofactors such as quinones, amino acid radicals, or flavins. In order to fully appreciate the catalytic mechanisms of these enzymes, it is often necessary to determine the free energy required to reduce or oxidize their protein redox centers. This is called the redox potential. The measurement of enzyme redox potentials can be performed by either direct or indirect electrochemical methods. The type of electrochemistry suitable for a particular protein system is simply dictated by the accessibility of its redox center to the electrode surface. Because most reactions catalyzed by enzymes occur within hydrophobic pockets of the protein, the redox sites are often far from the surface of the protein. Unless an electron transfer path exists from the protein surface to the redox center, it is not feasible to use direct electrochemistry to measure the redox potential. Since only a few enzymes (most notably certain heme-containing enzymes) have such electron transferring paths and... 

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