The intensity of current fuel cell development
programs was confirmed by successes reported by
authors of 27 technical papers presented at the
41st Power Sources Conference that was held in
June in Philadelphia, Pennsylvania. Around 600
people attended and 44 companies exhibited their
products. A total of 147 presentations were made
there. In the text that follows we review the
important developments that were described in
fuel cell related papers at this conference. We
first note the slow development of fuel cells
in the past, and then cite the sudden and important
new need for developing fuel cells, based on new
electrochemistry, and the consequent recent successes
that resulted from intense development effort
that was supported by many agencies.
Sir William Grove, the father of fuel cell development,
started working on fuel cells in 1839, using his
own money and contributed platinum. Subsequent
development progressed slowly. In 1939 Allis Chalmers
built a fuel cell powered tractor, which was exhibited
at farm fairs and ended in the Smithsonian Institution’s
museum. In 1967 a fuel cell energy-conversion
efficiency of 45% was being achieved. The Electric
Power Research Institute of the U.S. Department
of Energy and several utilities in 1983 supported
the development of a 4.8MW fuel cell power plant
that was installed by Consolidated Edison at a
station on Manhattan Island. The sponsors spent
$22.5 million on its development. The project
was eventually abandoned because it could not
compete with combined-cycle steam power plants
that can now convert fuel energy to electric power
with 60% efficiency.
The need for electric power in a manned space
flight to the moon created a development program
for a power source in which compressed hydrogen
and oxygen in tanks supplied fuel and oxidizer
to fuel cells. These cells that contained precious-metal
catalysts successfully fulfilled mission power
requirements. However, these fuel cells were so
costly that they could not compete with other
sources of earth-surface power.
Military Need for Fuel Cell Power
Motivates Research and Development
Newly available technology in communications
and sensing has produced weapons that can be commanded
to go after a moving target and can even be redirected
after they are launched. The launched weapon can
sense targets from their optical or thermal radiation,
or even from their acoustic sound emissions. For
example, the exact location of a soldier acknowledging
a telephoned command can be precisely detected
from his hand-held wireless telephone’s electromagnetic
emission. An engine that powers his radar and
radio can be detected from either its acoustic
noise or the thermal radiation from its exhaust
gases. A missile can carry a sensor that guides
it to the engine to destroy the engine and nearby
personnel.
For soldiers this new environment has produced
a requirement for quiet and reliable power sources
that don’t need a truck for towing them to
the moving battlefront. Batteries are available,
but a soldier may have to perform battle-related
tasks other than keeping his battery charged.
Furthermore, a 120V 60Hz outlet may not be available
at his battle position for plugging in the battery
charger he carries on his back.
The bandwidth requirements of new lightweight
electronic apparatus demand more power than lightweight
batteries can supply. Therefore, fuel cell technology
is being developed to provide a power source for
the individual soldier, sensors, communication
equipment, and other U.S. Army applications.
A fuel cell power source that gets its energy
from a commonly available military fuel is the
obvious power source for the soldier, command
posts, and even military vehicles. This need has
resulted in an intense research program that has
utilized government laboratories, university research
laboratories, and the research-and-development
facilities in companies in the United States and
in other nations around the world. This intense
research, plus non-military development, produced
16 of the 27 fuel cell related papers that were
presented at the 41st Power Sources Conference.
Hydrogen Production with Reformers
and PEM Cells
Fuel cells can be a convenient source of electric
power for soldier-carried equipment as well as
other needs of military activity in remote regions.
Carrying hydrogen gas for fuel cells is not practical,
so hydrogen needs to be extracted from petroleum
fuels by reformers that also release non-hydrogen
gases. These gases must be separated from the
hydrogen produced by the reformer. The efficient
proton-membrane (PEM) fuel cell deteriorates when
supplied impure hydrogen.
Mukund Karannjikar summarized the advantages and
problems in fueling PEM cells with hydrogen from
petroleum reformers (1). The hydrogen extracted
from the hydrogen-containing liquid by heating
it over catalysts produces a hydrogen gas that
contains vapors and gases that can quickly end
the useful life of the membrane in the PEM cell.
Figure 1 shows the filters and absorbers that
extract the contaminants from the produced hydrogen
that is then delivered to the PEM fuel cell. PEM
fuel cells that can be scaled down to small size
without sacrificing performance are suitable for
applications ranging from microwatts to hundreds
of kilowatts. Their noise level is low, in comparison
to engines. They release pure water as a byproduct,
and can be refueled rather than recharged or discarded.
PEM fuel cells are preferred in applications like
mobile power generation units, man-portable power
generators, and on-board power generation for
vehicle propulsion.
The steps in producing pure hydrogen from JP4
fuel are outlined in Figure 1. The liquid fuel
is boiled to produce a vapor that is split into
its chemical components, and compressed. The first
reactor is the steam reformer for JP8 fuel. The
reformer’s output flows into a post reformer.
Then after H2S removal the reformate flows into
high-temperature water-gas shift and low-temperature
water-shift reactors, followed by preferential
oxidation of CO in a reactor. The reformate then
flows through a carbon dioxide removal absorption
tower that has continuous circulation of alkaline
absorbent. The reformate finally flows through
a fuel filter to remove trace quantities of all
gases other than hydrogen before entering the
fuel cell.
The steam reforming of JP8 at 900°C and atmospheric
pressure over the commercial catalyst gives reformate
with a composition of 60 to 65% H2, 18 to 22%
of CO2, 8 to 12% of CO, 5 to 12% of C1-C3, and
around 60 parts per million of H2S. Post reformation
reduces the light hydrocarbons to below detection
limits.
PEM fuel cells require pure hydrogen fuel, and
hydrocarbon reforming is the best way of extracting
hydrogen from methane, methanol, ethanol, gasoline,
and diesel fuel. Diesel and JP8 have advantages
over other fuels in their high energy density,
safe handling, and logistics.
Karanjikar concluded that with additional process
integration, mainly energy, the fuel processor
can become an attractive means of hydrogen generation.
Factors in Overall Efficiency
Power plant performance is measured in terms
of heat rate, expressed as the higher value of
the fuel consumed in generating 1kWh of electric
power of electricity (2). A 100% efficient fuel
cell would need only 3412Btu of fuel per kWh generated.
The best U.S. steam plant in 1983 had a heat rate
of 8987 Btu per kWh. The United Technology 4.8MW
fuel cell power plant built for Tokyo Electric
at that time had a heat rate of 9600Btu per kWh.
The year 2001 Mitsubishi Industries model MPCP(M501H)
combined-cycle electric power plant delivers 403,000kW
with a heat rate of 5689Btu per kWh, with an efficiency
of 60% (3).
The energy released when hydrogen and oxygen combine
in combustion is 1.48 volts if water is the output
of the fuel cell, and 1.23 volts if it is steam.
Neither voltage can be achieved because of the
irreversibility of the electrode process, activation
polarization, and concentration or activity gradient
in the electrodes.
Power on Demand Fuel Cell Systems
A soldier in today’s battle environment
must have a quickly available and dependable source
of electric power for needs ranging from communication
with his commander to launching a rocket that
demolishes a missile that is headed to his location.
Shailesh Shah described a new “Hydrogen on
Demand” technology that enables fuel cartridges
for both battery replacement and battery charging
applications from 20 to 300 watts(4).
The main barrier to the implementation of hydrogen
fuel cell technology for portable power applications
is the lack of a practical method of storing hydrogen
in a small container. Compressed hydrogen is practical
for small devices only if it is stored at a pressure
like 10,000 pounds per square inch (psi). Hydrogen
from compressed gas is dry, and it can dry out
PEM fuel cell membranes unless it is wetted. Metal
hydrides are inefficient in terms of weight, and
require unique recharging facilities. On-board
reforming of methanol requires a reactor that
operates at over 200°F, plus a power supply.
On the other hand, chemical hydrides, which release
hydrogen when wetted with water, have significant
advantages. An example reaction is:
NaBH4
+ 2H2O --> catalyst
--> NaBO2 + 4H2
This hydrogen source has the following advantages:
• Regulating the contact
of the SBH fuel solution with the catalyst controls
hydrogen generation.
• The hydrogen is humidified and free from
catalyst poisons like CO and S that are associated
with hydrogen produced from hydrocarbons or methanol
reformation.
• The cost of energy with a PEM/HODTM system
is 20% of the cost of energy from alkaline batteries.
• The reaction is exothermic and therefore
requires no parasitic energy to produce hydrogen.
In contrast, methanol reformation consumes almost
30% of the stored methanol to provide the energy
to make hydrogen.
Millennium Cell Inc. has demonstrated the potentialities
of the Hydrogen on Demand technology with a prototype
that is similar to the system that they are developing
for a 30-watt 72-hour mission with an energy density,
including a fuel cell, of over 450Wh/kg. Development
of dry sodium borohydride fuel technology will
enable the cartridge to deliver 1100Wh/Kg if on-site
water is used. The demonstration prototype ran
on a hydrogen supply pressure of 5 to 10psig,
and supported a 20W load.
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