Cathodes fabrication

A schematic view of the cold cathode fabrication process is shown in Fig. 10.18. The cold cathode is fabricated by low pressure chemical vapor deposition (LPCVD) of 1.5 pm of non-doped polysilicon on a silicon wafer or a metallized glass substrate. The topmost micrometer of polysilicon is then anodized (10 mA cnT2, 30 s) in ethanoic HF under illumination. This results in a porous layer with inclusions of larger silicon crystallites, due to faster pore formation along grain boundaries. After anodization the porous layer is oxidized (700 °C, 60 min) and a semi-transparent (10 nm) gold film is deposited as a top electrode. 

For the cathode, a mixture of strontium-doped lanthanum manganite (LSM) proved most suitable, and as the slurry spray process was not scalable to larger modules and production volumes, the screen printing process was chosen for the cathode fabrication [76]. 

Armstrong, T.J. Rich, J.G. Anode-supported solid oxide fuel-cells with Lao.6Sro.4Co03 5-Zro.84Yo.i602-5 composite cathodes fabricated by an infiltration method. J. Electrochem. Soc. 153 (2006), PP.A515-A520. 

Wang, Y, Zhang, H., Chen, FL. Xia, C.R. Electrochemical characteristics of nano-stmctured PrBaCo205+x cathodes fabricated with ion impregnation process. J. Power Sources 203 (2012), pp. 34-41. 

Due to the low solubility of oxygen in water, the mass transfer of oxygen at the cathode can severely affect the cell performance. Therefore, it is desirable to develop an air-breathing cathode for oxygen reduction. The air-breathing cathode is also called a gas diffusion electrode (GDE), which is widely used in fuel cell technology. The details of air-breathing cathode fabrication can be found in previous literature. 

To demonstrate the previously described BP as a good candidate for direct bioelectrocatalysis, in 2011 Hussein et al. immobilized MCOs on a BP electrode via physisorption [35]. MCOs are often apphed as oxygen reduction catalysts in BFCs [5,40,46-52]. By using BP as an electrode material, DET from the conductive surface to the T1 redox site is achieved and ehminates the need for mediators, thus simplifying design [53,54]. Compared with MCO-coated CNT aggregates, BP cathodes fabricated in this manner exhibited superior performance when normalized to the average mass of the CNT and BP electrodes, respectively [55]. 

The cell head is fabricated from a 2.54-cm steel plate and has separate compartments for fluorine and hydrogen. The oudet-gas manifolds, hydrogen fluoride feed and purge lines, and electrical connections are on top of the head. The gas separation skirt is made of Monel. An insulating gasket maintains the seal between the tank and the head. The anode assembly consists of 32 carbon blades bolted onto a copper bar, each of which contains three copper conductor posts. The cathode assembly consists of three vertical, 0.6-cm parallel steep plates. The plates surround the anode assembly and are supported by three steel posts which also serve as conductors. 

Anthracite. Anthracite is preferred to other forms of coal (qv) in the manufacture of carbon products because of its high carbon-to-hydrogen ratio, its low volatile content, and its more ordered stmcture. It is commonly added to carbon mixes used for fabricating metallurgical carbon products to improve specific properties and reduce cost. Anthracite is used in mix compositions for producing carbon electrodes, stmctural brick, blocks for cathodes in aluminum manufacture, and in carbon blocks and brick used for blast furnace linings. 

Fire Refining. The impurities in bhster copper obtained from converters must be reduced before the bUster can be fabricated or cast into anodes to be electrolyticaHy refined. High sulfur and oxygen levels result in excessive gas evolution during casting and uneven anode surfaces. Such anodes result in low current efficiencies and uneven cathode deposits with excessive impurities. Fite refining is essential whether the copper is to be marketed directly or electrorefined. 

The tank house is divided into commercial and stripper sections. In the latter, one-day deposits are prepared by electrorefining anode copper onto oiled copper, stainless steel, or titanium blanks. These copper sheets are stripped from the blanks and fabricated into starter sheets for the commercial sections as starting cathodes. After 9—15 days, depending on the tank house, hill-term cathodes are pulled and washed and either sent to the casting department or sold direcdy. 

The cast grids are made into battery anode and cathode plates by the application of a lead oxide paste of 70 percent lead oxide (PbO) and 30 percent metallic lead. Lead ingots are tumbled in a ball mill with airproducing lead oxide and fine lead dust (referred to as leady oxide ). Leady oxide particulates are entrained in the mill exhaust air, which is treated sequentially by a cyclone separator and fabric filter. The used fabric filter bags are shipped to a RCRA-permitled commercially operated ha2ardous waste landfill located in Colorado. The leady oxide production process does not produce wastewater. 

Conceptually elegant, the SOFC nonetheless contains inherently expensive materials, such as an electrolyte made from zirconium dioxide stabilized with yttrium oxide, a strontium-doped lanthanum man-gaiiite cathode, and a nickel-doped stabilized zirconia anode. Moreover, no low-cost fabrication methods have yet been devised. 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

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