Alkaline fuel cells space applications

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 its excellent performance on hydrogen (H2) and oxygen (O2) compared to other candidate fuel cells due to its active O2 electrode kinetics and its flexibility to use a wide range of electrocatalysts, an attribute which provides development flexibility. 

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... 

Despite the intense activity [iii-x] of developing alkaline fuel cells on an industrial scale for vehicular and space applications, until a year ago none of the several types of fuel cells had reached the cost targets of systems for non-military or non-space applications. Practically all the commercially-marketed systems are mainly demonstrative. 

Alkaline fuel cells (AFCs) were the first type of fuel cell to be widely used in space exploration applications-for example, in NASA s Apollo and space shuttle flights. Figure 1.8 shows a schematic of an AFC stmcture. AFCs use H2 and 02 as fuel and oxidant, respectively. The electrolyte is a concentrated KOH solution absorbed into an asbestos matrix. The temperature for AFCs ranges from 100-250°C and the efficiency can be > 60%. OH ions are transported through the electrolyte from cathode to anode. The reactions are as follows ... 

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. 

Alkaline fuel cells (AFC) using aqueous KOH as electrolyte were the first type of fuel cells with practical applications at the beginning of the last century [9] but the formation of carbonate in the liquid electrolyte due to the CO2 contamination in the oxidant gas stream has limited its application to systems miming with pure oxygen, such as the fuel cells used by the NASA in the I960 Apollo space program, and currently used in the shuttle missions [10]. 

The high performance of the alkaline cell relative to phosphoric acid and other cells leads to the plausibility of developing the technology for terrestrial application. The leading developer of alkaline technology for space application, UTC Fuel Cells, investigated adaptating the... 

Alkaline fuel cells have been used the longest, since the 1960s by NASA for space shuttles. In fact, this application illustrates the utility of fuel cells. Hydrogen and oxygen gases are used to power the fuel cell, which powered the electrical components of the space shuttle. Water, the only byproduct of the reaction, was used as onboard drinking water for the crew. Although AFCs are the most inexpensive... 

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]. 

Alkaline fuel cell Solution of potassium hydroxide in water 60-250" CO2 High efficiency, low oxygen readuction reaction losses Must run on pure oxygen without CO2 contaminant Space applications with pure O2/H2 available... 

The fuel cell has already proved its usefulness in space technology and there are excellent prospects for its commerical application. Application on a large scale is not expected during the 20th century. The alkaline cell and the phosphoric acid cell are technically well developed, but from a commerical point of view it is questionable whether or not they will be of interest when other types reach technical maturity. The molten carbonate cell and the solid oxide cell seem to have the best prospects. For mobile application the solid polymer cell is a strong candidate. 

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