Oxide electrodes powders

Application of composite electrodes in the arc discharge process is a well-known route to metallofullerenes [1], To prepare electrodes, a graphite rod is used to be coaxially drilled, stuffed with mixture of metal oxide, graphite powder and thermosetting resin then annealed under vacuum at ca. 2000°C. Such procedure seems to be laborious whereas the yield of metallofullerenes is low [2]. To increase the yield, composite electrodes structure was varied [2] and new equipment was... 

Metal-oxide electrodes cannot be used for investigations of the acid-base properties of strong oxidants and reducing agents because of the chemical reactions of the melt with the constructional electrode material in the former case, and with the metal-oxide powder in the latter case. 

Other Semiconductors.—Kennedy et alf have continued to study FcjOj photoelectrodes, and their most recent work shows that high efficiencies are obtained with Si-doped sintered electrodes. Dare-Edwards et alf have characterized lithium-doped NiO in some detail but, as expected, the very low carrier mobility in this material makes it quite unsuitable for solar energy conversion. Gissler has investigated trigonal Se films, and Davidson and Willsher have given further details of the properties of HgS powder photoanodes. Derivatized tin-oxide electrodes have been prepared by Fox et al.f and Janzen et al. have successfully attached the photosynthetic reaction centre molecule isolated from Rhodopseudomones sphaeroides to tin oxide (see also Section 2). 

Zinc electrodes can also be manufactured by the plastic-bonded method, similar to that of the nickel electrode described above. The zinc oxide dry powder, PTFE binder and other additives are blended with an organic solvent and then the mixture is passed through a calendaring process similar to that in Fig. 31.1. The PTFE fibriUates into a nano-structured three-dimensional fiber matrix. This electrode structure for the calcium zincate electrode is shown in Fig. 31.3 for a freshly prepared electrode. The active materials are locked into the electrode structural matrix which helps to reduce the tendency towards shape change and dendritic growth. 

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). 

For the production of lamp-filament wire, aluminum, potassium, and siHcon dopants are added to the blue oxide. Some dopants are trapped in the tungsten particles upon reduction. Excess dopants are then removed by washing the powder in hydroflouric acid. Eor welding electrodes and some other appHcations, thorium nitrate is added to the blue oxide. After reduction, the thorium is present as a finely dispersed thorium oxide. 

A critical issue is the stabiUty of the hydride electrode in the cell environment. A number of hydride formulations have been developed. Table 5 shows hydride materials that are now the focus of attention. Most of these are Misch metal hydrides containing additions of cobalt, aluminum, or manganese. The hydrides are prepared by making melts of the formulations and then grinding to fine powers. The electrodes are prepared by pasting and or pressing the powders into metal screens or felt. The additives are reported to retard the formation of passive oxide films on the hydrides. 

Example. The Pechini method for fuel cell electrode preparation. La, Ba, Mn niU ates - - CgHgO — citrate complex - - C2FI6O2 — gel. Metal nitrates are complexed with citric acid, and then heated with ethylene glycol to form a transparent gel. This is then heated to 600 K to decompose the organic content and then to temperatures between 1000 and 1300K to produce tire oxide powder. The oxide materials prepared from the liquid metal-organic procedures usually have a more uniform particle size, and under the best circumstances, this can be less than one micron. Hence these particles are much more easily sintered at lower temperatures than for the powders produced by tire other methods. 

The production of the active material for positive and negative electrodes starts with the same substance, a mixture of lead oxide (PbO) and metallic lead called gray oxide or lead dust. It is a fine powder that contains 20-30 wt.% of lead (Pb). The size of the primary particles is in the range of 1-10 /an. Larger agglomerates are usually formed. 

Perhaps the first practical application of carbonaceous materials in batteries was demonstrated in 1868 by Georges Le-clanche in cells that bear his name [20]. Coarsely ground MnO, was mixed with an equal volume of retort carbon to form the positive electrode. Carbonaceous powdered materials such as acetylene black and graphite are commonly used to enhance the conductivity of electrodes in alkaline batteries. The particle morphology plays a significant role, particularly when carbon blacks are used in batteries as an electrode additive to enhance the electronic conductivity. One of the most common carbon blacks which is used as an additive to enhance the electronic conductivity of electrodes that contain metal oxides is acetylene black. A detailed discussion on the desirable properties of acetylene black in Leclanche cells is provided by Bregazzi [21], A suitable carbon for this application should have characteristics that include (i) low resistivity in the presence of the electrolyte and active electrode material, (ii) absorption and retention of a significant... 

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