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Alkali Fuel Cells
The essay below outlines the technology and history of alkali fuel cells as currently understood
by the project team. If you have artifacts,
photos, documents, or other materials that would help to improve our understanding of these devices
be sure to respond to the questionnaire:
Alkali Fuel Cell Technology
Alkali fuel cells operate on
compressed hydrogen and oxygen and generally use a solution of potassium hydroxide in
water as their electrolyte. Operating temperatures
inside alkali cells are around 150 to 200 degrees C (about 300 to 400 degrees F).
A U.S. Army soldier demonstrates an alkali fuel cell. |
In these cells, hydroxyl ions (OH-) migrate from the cathode to the anode. At the
anode, hydrogen gas reacts with the OH- ions to produce water and release electrons.
Electrons generated at the anode supply electrical power to an external circuit then
return to the cathode. There the electrons react with oxygen and water to produce more
hydroxyl ions that diffuse into the electrolyte.
Alkali fuel cells operate at efficiencies up to 70 percent and, like other fuel
cells,
create little pollution. Because they produce potable water in addition to
electricity, they have been a logical choice for spacecraft. A major drawback,
however, is that alkali cells need very pure hydrogen or an unwanted chemical
reaction forms a solid carbonate that interferes with chemical reactions inside the
cell. Since most methods of generating hydrogen from other fuels produce some carbon
dioxide, this need for pure hydrogen has slowed work on alkali fuel cells in recent
years. Another drawback has been the need for large amounts of a costly platinum catalyst to speed up the reaction. Researchers have worked to reduce the amount of platinum needed, and have eliminated the metal entirely from some designs.
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Alkali Fuel Cell History
Francis Thomas Bacon (1904-1992) of Britain began experimenting
with alkali electrolytes in the late 1930s, settling on potassium hydroxide
(or KOH) instead of using the acid electrolytes known since Grove's early discoveries.
KOH performed as well as acid electrolytes and was not as corrosive to the electrodes.
Bacon's cell also used porous "gas-diffusion electrodes" rather than solid electrodes as
Grove had used. Gas-diffusion electrodes increased the surface area in which the
reaction between the electrode, the electrolyte and the fuel occurs. Also, Bacon used
pressurized gases to keep the electrolyte from "flooding" the tiny pores in the electrodes.
Over the course of the following twenty years, Bacon made enough progress with the alkali cell to
present large scale demonstrations.
One of the first of these demonstrations consisted of a 1959 Allis-Chalmers farm
tractor powered by a stack of 1,008 cells. With 15,000 watts of power, the
tractor generated enough power to pull a weight of about 3,000 pounds. (The tractor was later donated to the
Smithsonian.) Allis-Chalmers maintained a research
program for some years, building a fuel cell powered golf cart, submersible, and fork
lift. The U.S. Air Force also participated in this program.
Union Carbide's Karl Kordesch rides
his alkali fuel cell motorcycle in 1967.
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Union Carbide also experimented with alkali cells in the late 1950s
and 1960s. Building on the work done in the 1930s by researchers G. W. Heise and
E. A. Schumacher, Karl Kordesch and his colleagues designed alkali cells
with carbon gas-diffusion electrodes. They demonstrated a fuel-cell-powered mobile radar set for the
U.S. Army, a fuel-cell-powered motorbike (see photo), and drew up plans for an
undersea base that would run on fuel cells. About the same time, Eduard Justi of Germany
designed gas-diffusion electrodes using nickel sponge on a carbonyl nickel matrix.
In the early 1960s, aircraft engine manufacturer Pratt & Whitney licensed the
Bacon
patents and won the National Aeronautics and Space Administration (NASA) contract
to power the Apollo spacecraft with alkali cells. Its successes notwithstanding,
alkali technology has challenges ahead. Current alkali fuel cells still demand very
pure hydrogen and expensive platinum catalysts, and other kinds of fuel cells are
mounting stiffer competition.
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Alkali Fuel Cell Applications
NASA selected alkali fuel cells for the Space Shuttle fleet, as well as the Apollo program, mainly because of power generating
efficiencies that approach 70 percent. Alkali cells also provide
drinking water for the astronauts. The cells are expensive -- perhaps too
expensive for commercial applications -- but
several companies are examining ways to reduce costs and improve
the cells' versatility. Most of these alkali fuel cells are being designed for
transport applications.
A Pratt & Whitney alkali fuel cell being assembled for an Apollo spacecraft, 1964
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In July 1998,
the Zero Emission Vehicle Company (ZEVCO) launched its first prototype taxi in London, England. The taxi uses a 5,000-watt alkali fuel
cell that produces no noxious fumes and much less noise
than traditional internal combustion taxis. (The company reports one inquiry from
an English police agency looking for a "stealth" cruiser that would allow them to
sneak up on criminals.) The ZEVCO cells
reportedly use cobalt catalysts instead of platinum reducing the high
cost. The company has also introduced a series of other
commercial vehicles including delivery vans, airport tow-tugs, and an associated
company is demonstrating fuel-cell-powered boats.
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©2009 Smithsonian Institution
(Copyright Statement)
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