Alkaline fuel cells orbiter

Typical polarization curves for alkaline fuel cells are shown in Fig, 27-63, It is apparent that the all aline fuel cell can operate at about 0,9 and 5()() rnA/cnr current density. This corresponds to an energy conversion efficiency of about 60 percent IIII, The space shuttle orbiter powder module consists of three separate units, each measuring 0,35 by 0,38 by I rn (14 by 15 by 40 in), weighing 119 kg (262 lb), and generating 15 kW of powder. The powder density is about 100 W/L and the specific powder, 100 W/kg,... 

The application of gold as an electrocatalytic component within the fuel cell itself has to date been limited primarily to the historical use of a gold-platinum electrocatalyst for oxygen reduction in the Space Shuttle/Orbiter alkaline fuel cells (AFC)88 and the recent use of gold for borohydride oxidation in the direct borohydride alkaline fuel cell (DBAFC).89,90 Electrocatalysts with lower cost, improved carbon monoxide tolerance and higher... 

Alkaline Fuel Cell The electrolyte for NASA s space shuttle orbiter fuel cell is 35 percent potassium hydroxide. The cell operates between 353 and 363 K (176 and 194°F) at 0.4 MPa (59 psia) on hydrogen and oxygen. The electrodes contain platinum-palladium and platinum-gold alloy powder catalysts bonded with polytetrafluoro-ethylene (PTFE) latex and supported on gold-plated nickel screens for current collection and gas distribution. A variety of materials, including asbestos and potassium titanate, are used to form a micro-porous separator that retains the electrolyte between the electrodes. The cell structural materials, bipolar plates, and external housing are usually nickel, plated to resist corrosion. The complete orbiter fuel cell power plant is shown in Fig. 27-62. 

Fuel cells have the longest record of application in space exploration. Since the Gemini missions of NASA, fuel cells have been an indispensable technology in matmed space travel. The fuel cell systems used in the NASA space shuttles are based on alkaline fuel cells from UTC. Each orbiter has three systems of 7kWe each, which produce all electric power on board and provide potable water. These systems are hydrogen and oxygen fueled. 

The Alkaline Fuel Cell (AFC) was one of the first modern fuel cells to be developed, beginning in 1960. The application at that time was to provide on-board electric power for the Apollo space vehicle. Desirable attributes of the AFC include excellent performance compared to other candidate fuel cells due to its active O2 electrode kinetics and flexibility to use a wide range of electro-catalysts. The AFC continues to be used it now provides on-board power for the Space Shuttle Orbiter with cells manufactured by UTC Fuel Cells. 

This mobile electrolyte system was used by Bacon in his historic alkaline fuel cells of the 1950s and in the Apollo mission fuel cells. It is almost universally used in terrestrial systems, but the Shuttle Orbiter vehicles use a static electrolyte, as described in the next section. 

While there remains some interest in alkaline fuel cells (AFCs) for commercial applications, notably by Zetek as a range extender for battery-powered vehicles, this is at a low level compared with that for PEMFC systems. Modified anode and cathode catalysts have now been developed that supersede the high concentrations of Pt and Pt/Au used in the space Orbiter vehicle. However, there is no consensus on whether precious or base metals are the preferred system. The choice depends on the balance between the required performance and acceptable cost. With increasing interest in the use of hydrogen for fuel cell powered vehicles, interest in the AFC system may increase. On the other hand, it is reported that the new fuel cells for the space shuttle Orbitor vehicles will be PEMFC in preference to the established AFC [12]. 

Space—Fuel cells continue to be used in the U.S. Space Program, providing power on the space orbiters. Although this proven technology is of the alkaline type, NASA announced plans to use PEM fuel cells in the future. 

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