Fuel cell alkali

In a simple version of a fuel cell, a fuel such as hydrogen gas is passed over a platinum electrode, oxygen is passed over the other, similar electrode, and the electrolyte is aqueous potassium hydroxide. A porous membrane separates the two electrode compartments. Many varieties of fuel cells are possible, and in some the electrolyte is a solid polymer membrane or a ceramic (see Section 14.22). Three of the most promising fuel cells are the alkali fuel cell, the phosphoric acid fuel cell, and the methanol fuel cell. 

The hydrogen-oxygen cell used in the space shuttle is called an alkali fuel cell, because it has an alkaline electrolyte ... 

Although its cost prohibits its use in many applications, the alkali fuel cell is the primary fuel cell used in the aerospace industry. 

Alkali fuel cells containing KOH and platinum- and gold-coated electrodes were developed for the space program, but these are too expensive for down-to-earth vehicles. In addition, these cells require pure oxygen rather than CO2 -containing air. 

Two new technologies have reduced the cost of alkali fuel cells to the point where a European company markets taxis that use them. One is the use of CO2 scrubbers to purify the air supply, making it possible to use atmospheric O2 rather than purified oxygen. The other is the development of ultrathin films of platinum so that a tiny mass of this expensive metal can provide the catalytic surface area needed for efficient fuel-cell operation. 

For example, the electrolyte of alkali fuel cells is a solution of potassium hydroxide (an alkaline, which has a high pH). Solid oxide fuel cells use compoimds of metal oxides as electrolytes. (Fuel cell names are generally... 

Although its expense prohibits its use in many applications, the alkali fuel cell is the primary fuel cell used in the aerospace industry, because it has a very high power density (see Box 12.1). One problem is the reaction of the alkali electrolyte with the carbon dioxide in air to form potassium carbonate, which clogs the openings in the electrode gauze. 

Alkali fuel cell (AFC) 80-90 Potash lye Hydrogen 50-65 Transport, space flight, shipping... 

Galvanic cells designed for continuous reaction -> Require a continuous supply of reactants Alkali-fuel cell — used in the space shuttle... 

Davtjan has dealt with solid oxide, molten carbonate, and alkali fuel cells. Since that the laboratory under Davtjan has developed as follows ... 

Figure 2. The Davtjan s 200 W hydrogen-oxygen alkali fuel cell stock.

Current research is centred on making compact cells of high efficiency. They are described in terms of the electrolyte that is used. The principle types are alkali fuel cells, described above, with aqueous KOH as electrolyte, MCFCs (molten carbonate fuel cells), with a molten alkali metal or alkaline earth carbonate electrolyte, PAFCs (phosphoric acid fuel cells), PEMs (proton exchange membranes), using a solid polymer electrolyte that conducts ions, and SOFCs, (solid oxide fuel cells), with solid electrolytes that allow oxide ion, 0 , transport The... 

Fuel cells can be classified by the kind of electrolyte, there are Alkali fuel cells (AFCs), Polymer electrolyte fuel cells (PEFCs), Phosphoric acid fuel cells (PAFCs), Molten carbonate fuel cells (MCFCs) and Solid oxide fuel cells (SOFCs). 

Water is produced at the cathode, whereas in the alkali fuel cell, it is produced at the anode. At present, a 200 kW PAFC costs about 3000 per kW. The leading manufacturer is International Fuel Cells (Toshiba/United Technologies). 

Hydroxide Exchange Membrane Alkali Fuel Cells (HEMFCs)... 

The manufacturing process can be done using modified paper-making machines, at quite low cost. Such electrodes are not just used in fuel cells but are also used in metal/air batteries, for which the cathode reaction is much the same as for an alkali fuel cell. For example, the same electrode can be used as the cathode in a zinc air battery (e.g. for hearing aids), an aluminium/air battery (e.g. for telecommunications reserve power), and an alkaline electrolyte fuel cell. The carbon-supported catalyst is of the same structure as that shown in Figure 4.6 in the previous chapter. However, the catalyst will not always be platinum. For example, manganese can be used for the cathode in metal air batteries and fuel cells. 

The reactions at the MH electrode (eqs. 10-11) are the same as for the hydrogen diflusion electrode using platinum-containing carbon in an alkali fuel cell. Usually, the reaction... 

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