Fabrication of Cathodes

In general, cathodes are made by powder processing routes. Cathode material powders are either made by solid state reaction of constituent oxides or high surface area powders are precipitated from nitrate and other solutions as a gel product, which is dried, calcined and comminuted to give crystalline particles in the 1-10 pm size range. 

Physical processes have also been used to make cathodes. For example, vacuum plasma spraying has been tried for fabricating entire anode/electrolyte/ cathode assembly [75], In this approach, cathode layers are deposited onto a porous metallic felt substrate. 

499-503 see also N. Sakai, K. Yamaji, H. Negishi, T. Horita, Y.-P. Xiong and H. Yokokawa, in Solid Oxide Fuel Cells VII, eds. H. Yokokawa and S. C. Singhal, The Electrochemical Society Proceedings. Pennington. NJ, PV 2001-16.2001. pp. 511-520. 

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Fluorinated carbon, CFX, where x is between 0 and 1.3, is prepared by the direct fluorination of carbon at high temperatures [108]. Many varieties of fluorinated carbon can be prepared depending on the type of carbon used in the process (e.g. graphite, petroleum coke, carbon black, etc.) and the level of fluorination (i. e. the value of ). Fluorinated carbons, such as those manufactured by Allied-Signal (Accufluor ), Central Glass Co. (Cefbon ) and Daikin, are used for the fabrication of cathodes in lithium anode batteries and as solid lubricants [109]. 

Fuel cell performance of the composite LSM-YSZ/YSZ/Ni-YSZ cell was investigated using forming gas (10 vol% H2 in N2) as the fuel (Figure 3-25). The results showed that a maximum power density of about 0.26 W cm2 as obtained at a temperature of 850°C. The temperature dependence of the area specific resistances of the asymmetrical cell is shown in Figure 3-26. The electrode overpotential was estimated to 0.3 Q cm2 at 800°C, which is the total of anode and cathode overpotential. It appeared that about half of the overpotential originated from the anode, because the cathode overpotential determined from the symmetrical cell test was found to be about 0.14 Q cm2 at 800°C. The performance of the cell was mainly limited by the electrolyte resistance. The decrease in the electrolyte thickness would decrease electrolyte resistance. It can be concluded that the net shape technology can be successfully applied for the fabrication of cathode and anode electrodes. 

Duquette, J., Basu, R.N., Deng, X., Zhitomirsky, I. and Petrie, A. (2005), Fabrication of cathode supported SOFC by colloidal processing. Ninth International Symposium on Solid Oxide Fuel Cells (SOFC-IX), Eds. S.C. Singhal and J. Mizusaki, pp. 482-488. The Electrochemical Soc., Inc., Pennington, NJ, USA. 

The ordn uses for polypropylene are varied. It is used in the fabrication of personnel body armor (Refs 6 7) in slurry-type expls for the demolition of concrete structures (Ref 11) as a microporous hydrazine-air (cathode) separator in fuel cells (Ref 9) as a propint binder matl, particularly in caseless ammo, (Refs 5 8) and as a candidate to act as a proplnt aging inhibitor for the 155mm RAP round (Ref 10) Refs 1) Beil 1, 196, (82), [167], 677 and (725) 2) A.V. Topchiev V.A. Krentsel,... 

The cathodic approach has been investigated actively as a method for the production of thin film CdS, in particular for the fabrication of heterojunction cells. Photoactive CdS films could be grown in alkaline NH3/NH4Cl-buffered aqueous solutions containing thiosulfate as sulfur source and complexed Cd (EDTA+NH3), on Ti substrates [41]. The electroreduction of thiosulfate was considered to proceed as... 

Aqueous cathodic electrodeposition has been shown to offer a low-cost route for the fabrication of large surface n-CdS/p-CdTe solar cells. In a typical procedure, CdTe films, 1-2 xm thick, are electrodeposited from common acidic tellurite bath over a thin window layer of a CdS-coated substrate under potential-controlled conditions. The as-deposited CdTe films are stoichiometric, exhibit strong preferential (111) orientation, and have n-type conductivity (doping density typically... 

Now let us consider a model for a SC device that comprises two electrodes (anode and cathode), each of them being electrically connected to a current collector fabricated of A1 foil. Let two of such collectors have a certain thickness of SAi- As an electrode material, an activated carbon powder is considered below. Anode and cathode are interposed with a separator of thickness Ss. The electrodes and separator are impregnated with electrolyte. In this paper we mostly focus on the optimization of SC performance by varying the electrode thickness, while some other effects will briefly be considered in the next section. 

In this chapter the technological development in cathode materials, particularly the advances being made in the material s composition, fabrication, microstructure optimization, electrocatalytic activity, and stability of perovskite-based cathodes will be reviewed. The emphasis will be on the defect structure, conductivity, thermal expansion coefficient, and electrocatalytic activity of the extensively studied man-ganite-, cobaltite-, and ferrite-based perovskites. Alterative mixed ionic and electronic conducting perovskite-related oxides are discussed in relation to their potential application as cathodes for ITSOFCs. The interfacial reaction and compatibility of the perovskite-based cathode materials with electrolyte and metallic interconnect is also examined. Finally the degradation and performance stability of cathodes under SOFC operating conditions are described. 

In addition to the use of composite anodes and cathodes, another commonly used approach to increase the total reaction surface area in SOFC electrodes is to manipulate the particle size distribution of the feedstock materials used to produce the electrodes to create a finer structure in the resulting electrode after consolidation. Various powder production and processing methods have been examined to manipulate the feedstock particle size distribution for the fabrication of SOFCs and their effects on fuel cell performance have also been studied. The effects of other process parameters, such as sintering temperature, on the final microstructural size features in the electrodes have also been examined extensively. 

G.E. Jabbour, S.E. Shaheen, M.M. Morrell, B. Kippelen, N.R. Armstrong, andN. Peyghambarian, Aluminum composite cathodes a new method for the fabrication of efficient and bright organic light-emitting devices, Opt. Photon. News, 10 (4), 24, 1999. 

As noted in section 3.1. the fabrication of cells in which the cathode and anode are separated by a conformal thin-film electrolyte, perhaps a few tens of nanometers in thickness, is on the near horizon. Thus, it is interesting to consider potential phenomena. not normally considered in battery design, that... 

In the case of SOFCs, a large volume of work shows that for many SOFC electrodes, overall performance scales with the ID geometric length of this three-phase boundary. As such, the TBP concept and electrode performance models based on it have proven to be some of the most useful phenomenological concepts for guiding design and fabrication of SOFC cathodes, particularly the microstructure. 

While high temperatures do not severely limit fabrication of Ni—YSZ cermets, they can impact the way in which other composite electrodes are made. This is well-known for cathodes, where the most commonly used material is a composite of YSZ and Sr-doped LaMnOs (LSM). The primary reason for using LSM, rather than materials such as Sr-doped LaFeOs (LSF) or LaCoOs (LSC) that exhibit a better performance, is that LSM—YSZ mixtures can be... 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

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