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PEM Fuel Cells
The
essay below outlines the technology and history of proton
exchange membrane, or PEM, fuel cells. 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:
PEM Fuel Cell Technology
Proton exchange
membrane (PEM) fuel cells work with a polymer electrolyte
in the form of a thin, permeable sheet. This membrane is small
and light, and it works at low temperatures (about 80 degrees
C, or about 175 degrees F). Other electrolytes require temperatures
as high as 1,000 degrees C.
GE's Russell
Hodgdon shows a polymer electrolyte in 1965 |
To speed the
reaction a platinum catalyst is used on both sides of the
membrane. Hydrogen atoms are stripped of their electrons,
or "ionized," at the anode, and the positively charged protons
diffuse through one side of the porous membrane and migrate
toward the cathode. The electrons pass from the anode to the
cathode through an exterior circuit and provide electric power
along the way. At the cathode, the electrons, hydrogen protons
and oxygen from the air combine to form water. For this fuel
cell to work, the proton exchange membrane electrolyte must
allow hydrogen protons to pass through but prohibit the passage
of electrons and heavier gases.
Efficiency for a PEM cell reaches about 40 to 50 percent.
An external reformer is required to convert fuels such as
methanol or gasoline to hydrogen. Currently, demonstration
units of 50 kilowatt (kw) capacity are operating and units
producing up to 250 kw are under development.
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PEM
Fuel Cell History
PEM technology
was invented at General Electric in the early 1960s, through
the work of Thomas Grubb and Leonard Niedrach. GE announced
an initial success in mid-1960 when the company developed
a small fuel cell for a program with the U.S. Navy's Bureau
of Ships (Electronics Division) and the U.S. Army Signal Corps.
The unit was fueled by hydrogen generated by mixing water
and lithium hydride. This fuel mixture was contained in disposable
canisters that could be easily supplied to personnel in the
field. The cell was compact and portable, but its platinum
catalysts were expensive.
Thomas
Grubb and Leonard Niedrach of General Electric (Schenectady)
run a fan with a small diesel powered PEM fuel cell
in April 1963 |
PEM technology served as part of NASA's Project Gemini
in the early days of the U.S. piloted space program. Batteries
had provided spacecraft power in earlier Project Mercury
missions, but the lunar flights envisioned for Project Apollo
required a longer duration power source. Gemini's main objective
was to test equipment and procedures for Apollo, and missions
lasting up to 14 days included operational tests of fuel
cells. GE's PEM cells were selected, but the model PB2 cell
encountered repeated technical difficulties, including internal
cell contamination and leakage of oxygen through the membrane.
Geminis 1 through 4 flew with batteries instead.
GE redesigned their PEM cell, and the new model P3, despite
malfunctions and poor performance on Gemini 5, served adequately
for the remaining Gemini flights. Project Apollo mission
planners, however, chose to use alkali fuel cells for both
the command and lunar modules, as did designers of the Space
Shuttle a decade later.
Technicians
inspect a PEM fuel cell in the Gemini 7 spacecraft,
1965 |
GE continued working on PEM cells and in the mid-1970s
developed PEM water electrolysis technology for undersea
life support, leading to the US Navy Oxygen Generating Plant.
The British Royal Navy adopted this technology in early
1980s for their submarine fleet. Other groups also began
looking at PEM cells. In the late 1980s and early 1990s,
Los Alamos National Lab and Texas A&M University experimented
with ways to reduce the amount of platinum required for
PEM cells.
Recently PEM developers added the weatherproofing material
Gore-Tex to their cells to strengthen the electrolyte.
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PEM
Fuel Cell Applications
A Ballard
fuel cell powers a laptop computer.
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PEM cells may
have a mixed record in space, but several companies have been
testing the cells in more down-to-earth vehicles. In 1995,
Ballard Systems tested PEM cells in buses in Vancouver and
Chicago and later in experimental vehicles made by DaimlerChrysler.
PEM cells have also supplied power to unmanned blimps called
aerostats and to sonobuoys, which are nautical buoys that
generate and receive sonar signals.
Early in 2000, AeroVironment selected PEM technology to
provide nighttime power for its solar-powered Helios
long-duration aircraft. The goal was to make an unpiloted
aircraft that could fly continuously for up to six months
by using photovoltaic panels during the day to run electric
motors and electrolyze water. At night, the fuel cell was
to run the motors by converting the hydrogen and oxygen
back into water. Several test flights were made with and
without a fuel cell from 2001 to 2003.
The Helios
research aircraft takes to the air. |
Automotive research
has taken on new urgency as air quality regulations grow steadily
stricter, particularly in California. Energy Partners and
the U. S. Department of Energy's Office of Advanced Automotive
Technologies provided two 20 kw fuel cell stacks to Virginia
Tech and Texas Tech universities to evaluate performance in
hybrid electric cars. Major automakers like Ford and Volkswagen
are also testing PEM vehicles.
Since the mid-1980s, PEM development has included stationary
power applications. In 1989, Ballard Systems introduced
a 5 kw hydrogen and air PEM stack. Two years later, GPU
and Ballard began operating a 250 kw plant at Crane Naval
Air Station in Indiana.
Avista
Laboratory's 7.5KW PEM residential fuel cell power plant.
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One of the more publicized demonstrations has been Plug
Power's PEM unit in Albany, New York, which began powering
a home in June 1998. Promoted by the company as the "first
permanent home installation," the 5 kw power plant helped
the company to make significant partnerships with both GE
and Detroit Edison. These partners had hoped to market a
residential fuel cell during 2002, however those plans have
been postponed.
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©2004
Smithsonian Institution
(Copyright Statement)
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