Air electrode supported

The tubular design is probably the best-known design. It has been developed by Westinghouse (now Siemens Power generation) [8]. The first concept that was pursued by Westinghouse consisted of an air electrode supported fuel cell tube. In earlier days the tubes were made from calcium-stabilized zirconia on which the active cell components were sprayed. Nowadays this porous supported tube (PST) is replaced by a doped lanthanum manganite (LaMn) air electrode tube (AES) that increases the power density by about 35 %. The LaMn tubes are extruded and sintered and serve as the air electrode. The other cell components are deposited on this construction by plasma spraying. 

The CHP-100 kWe SOFC Field Unit (Siemens Power Generation-Stationary Fuel Cells) is the first to utilize the commercial prototype air electrode supported cells (22 mm diameter, 150... 

Siemens Westinghouse, in conjunction with Ontario Hydro Technologies, tested air electrode supported (AES) cells at pressures up to 15 atmospheres on both hydrogen and natural gas (42). Figure 7-14 illustrates the performance at various pressures ... 

Figure 8,12 Comparison of the voltage-current characteristics of the thick-wall PST, the thin-wall PST, and the air electrode-supported tubularcellsatlOOO°C[25].

In addition to eliminating the porous support tube, the active length of the cells was continually increased to Increase the power output per cell a greater cell power output decreases the number of cells required in a given power size generator and thus improves power plant economics. The active length (the length of the interconnection) was Increased from 30 cm for pre-1986 thick-wall PST cells to 150 cm for today s commercial prototype air electrode-supported cells. Additionally, the diameter of the cells has been... 

Phosphoric Acid Fuel Cell In this type of fuel cell, the electrolyte is 93 to 98 percent phosphoric acid contained in a matrix of silicon carbide. The electrodes consist of finely divided platinum or platinum alloys supported on carbon black and bonded with PTFE latex. The latter provides enough hydrophobicity to the electrodes to prevent flooding of the structure by the electrolyte. The carbon support of the air electrode is specially formulated for oxidation resistance at 473 K (392°F) in air and positive potentials. 

Air diffusion electrodes In fuel cells and in air-breathing batteries, a mesoporous carbon electrode is made up of two layers an outer layer composed of carbon powder and a hydrophobic (nonwettable) binder, typically PTFE. This enables the access of gas to the inner layer, where the binder is selected to be both a hydrophilic (wettable) and an ion-conducting ionomer, to support (rather than impair if the binder was nonconducting) the ionic conductivity of the porous electrode. The catalyst particles are dispersed in-between the carbon particles. Thus, a very tortuous interface between the two layers is formed. The reacting gas approaches this interface, forming three phase points of contact providing a high active surface area. See also - air electrode. 

G. Schiavon, G. Zotti, R. Toniolo and G. Bontempelli, Amperometric monitoring of sulfur dioxide in liquid and air samples of low conductivity by electrodes supported on ion-exchange membranes, Analyst, 1991, 116, 797-801. 

A recent paper by Reiser et al. [42] suggests, however, that transient conditions or localized fuel starvation can induce local potentials on the air electrode significantly higher than IV and thereby induee eorrosion of the carbon supports that results in permanent loss of eleetroehemieally aetive area. The mechanism they describe suggests that the highly conductive bipolar plates of the fuel cell allow for sufficient redistribution of current in the plane of the current collectors and that all regions of the cell experience the same potential difference. 

A reversible lithium-air system was first implemented on a laboratory scale in 1996. In this cell, the gel-polymer electrolyte was pressed between lithium foil on the one side and an air electrode on the other. (Later, usual liquid electrolyte in a porous, for example, glass fabric, separator was often used in lithium-air batteries). The whole cell was sealed into a plastic container ( coffee bag ) and small holes were made in the container wall adjacent to the air electrode to supply air under discharge and remove oxygen under charging. The air electrode was made of a mixture of particles of polymer electrolyte and carbon black with the catalyst supported on its surface (cobalt phthalocyanine). 

The air electrode operation is largely determined by the catalyst. In the above first version of the lithium-air battery, the catalyst was pyrolyzed cobalt phthalocya-nine. Later, manganese dioxide applied on a carbon support became the most popular catalyst. As a rule, carbon black is treated by a solution containing potassium permanganate and a bivalent manganese salt to obtain the catalytically active material of the positive electrode. Because of the disproportionation reaction. 

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