Alkaline electrolytes, fuel cell development

Alkaline fuel cell (AFC) working at 80 °C with concentrated potassium hydroxide as electrolyte, conducting by the OH anion. This kind of fuel cell, developed by IFC (USA), is now used in space shuttles. 

Normally, the C02 present in the atmosphere poisons the electrodes of alkaline fuel cells—one reason why transportation fuel cell developers have been concentrating on PEM-type fuel cells in the 1990s, since they are largely immune to the problem. Kordesch neatly solved that particular difficulty by installing a soda-lime air scrubber, which removed at least half of the air s C02 content of 0.03 percent. Additionally, his cell s alkaline (KOH) electrolyte absorbed some C02, reducing contamination even more. (Kordesch says the electrolyte could be easily changed when it had taken up too much C02.)... 

In the laboratories of the agricultural equipment manufacturers Allis-Chalmers, a new version of fuel cell with immobilized alkaline electrolyte solution was developed. The company reequipped one of its tractors to electric traction with an electric motor powered by four batteries consisting of 252 alkaline fuel cells each. The traction was strong enough for a load of 3000 pounds. This tractor was a successful demonstration exhibited on different agricultural fairs in the United States. 

Electrochemical Impedance Studies of AFC Cathodes. A review of the state of the art of alkaline fuel cell is given by McLean et al. [2002]. The electrolyte in AFC is a concentrated KOH solution, 25-50 wt% when operated at 120°C or below and in older AFC systems, operated at 250°C a 85 w/o KOH solution was used. The AFC was first fuel cell developed to technical maturity, based on the fundamental research of Bacon [1952] and has been employed extensively in the NASA space programs Apollo program (1960-1965) and space shuttle program (since 1981). 

This chapter reviews a new type of solid electrolyte low-temperature fuel cell, the alkaline membrane fuel cell. The principles and main components of this fuel cell technology are described, with a major focus on the electrocatalysts for both electrodes. Finally, the latest published results on operation of the first developed alkaline membrane fuel cells are reviewed. 

PoyntraiSD,ZengR,KizewskiJ,OngAL, Varcoe JR (2012) Development of alkaline exchange ionomcax for use in alkaline polymer electrolyte fuel cells. ECS Trans 50(2) 2067-2073... 

From the early stage of the fuel cell development, several types have been developed. A polymer electrolyte fuel cell (PEFC or PEMFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), and an alkaline fuel cell (AFC) are the fuel cells which use... 

Alkaline electrolytes played an important role in the beginning of fuel cell development, due to its less stringent requirements for electrocatalysts. An aqueous solution of NaOH or KOH at higher concentration is absorbed in a matrix, formerly asbestos, today a composite material of an oxide and a polymer binder. The electrochemistry of the respective HOR and ORR can be written the following way ... 

Recent developments in AAEMs have opened up the possibiUty of an alkaline analog of the acidic solid polymer electrolyte fuel cell. This could utilize the benefits of the alkaline cathode kinetics and at the same time eradicate the disadvantages of using an aqueous electrolyte. As the AAEM is also a polymer electrolyte membrane (sometimes abbreviated as PEM), some clarity in abbreviations is required. In this chapter, PEM refers only to the proton exchange membrane fuel cells (acidic), AAEM refers to the anion exchange membrane H2/O2 fuel cells, and AFC exclusively refers to the aqueous electrolyte alkaline H2/O2 fuel cells. Anion exchange membranes are also employed in alkaline direct alcohol fuel cells, discussion of which will refer to them as ADMFC/ADEFC (methanol/ ethanol). 

Yanagi, H Watanabe, S Sadasue, K Isomura, T Inoue, H., and Fukuta, K. (2009) Improved performance of alkaline membrane fuel cells based on newly developed electrolyte materials. ECS Meeting Abstracts, 902, 341-341. 

As it can be seen, low-temperature and high-temperature fuel cells can be distinguished. Low-temperature fuel cells are the Alkaline Fuel Cell (AFC), the Polymer Electrolyte Fuel Cell (PEMFC), and the Phosphoric Acid Fuel Cell (PAFC). The high-temperature fuel cells operate in the temperatures region from 500 to 1000 °C two different types have been developed the Molten Carbonate Fuel Cell (MCFC) and the Solid Oxide Fuel Cell (SOFC). They have the ability of using methane as fuel and thus present high inherent generation efficiency (45-60 % for common fuels such as natural gas, 90 % with heat recovery [3]). 

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