Energy Conversion Reports on Hydrogen Stored in a Solid For Fuel Cells
13 September 2000
Energy Conversion Devices Reports on Hydrogen Stored in a Solid For Fuel Cells: The Auto Industry's Game Changer
TROY, Mich., Sept. 13 Robert C. Stempel, chairman of
Energy Conversion Devices, Inc. (ECD) , has witnessed his share
of advanced automotive technology. During 34 years with General Motors,
including two years as chairman and CEO of the world's largest corporation,
Stempel personally fostered major advancements in pollution control, front-
wheel drive, electronic engine controls, occupant-safety systems, and electric
propulsion. So when Stempel heralds ECD's latest advancements in energy
storage as a "game changer," it's clear that he's touting something more
profound than the latest spill-proof cupholder.
Propulsion experts agree that cars in the near future will be
electrically-driven and fuel cell powered to satisfy the need for
environmentally-responsible transportation. A consensus is also forming -- in
both automobile industry and energy supply sectors -- that hydrogen will be
the ultimate fuel of the 21st century. Enter ECD's game-changer. "It's our
intention to lead the way to a hydrogen economy," said Stempel, "ECD's metal-
hydride storage systems offer a cost-effective, safe and efficient means of
transporting the energy necessary for vehicles of the future."
ECD's latest strides in metal-hydride technology build on pioneering work
begun in the 1960's by the company's co-founders, Stanford R. and Dr. Iris M.
Ovshinsky. During four decades of research, ECD has earned 350 U.S. and 800
foreign patents covering disordered and amorphous materials, their product
applications and manufacturing processes. Most recently (August 2000), the
American Chemical Society named Stan and Iris Ovshinsky as "Heroes of
Chemistry 2000" for creating clean and renewable energy technology, including
rechargeable batteries and hydrogen-fuel technology. The Ovonic Battery
Company was formed as an ECD subsidiary in 1982 to apply this expertise in the
nickel-metal hydride (NiMH) rechargeable batteries invented by the Ovshinskys.
Last year, 13 ECD licensees sold nine hundred million consumer NiMH batteries
for notebook computers, cell phones, and other portable electronic devices.
NiMH batteries are also the preferred power source for current electric and
hybrid vehicles.
Metal hydrides, formulated by the Ovshinskys and successive research
scientists, serve as the negative electrode (cathode) in a NiMH battery. The
Ovshinskys also surmised that metal hydrides could be developed to serve as a
storage medium so that hydrogen might eventually replace gasoline as an
automobile fuel. ECD's 1981 Annual Report speculated, "Hydrogen storage is
really the threshold problem. If it were possible to overcome the safety,
weight, and contamination difficulties associated with current hydrogen
storage, a major step forward would be taken."
ECD is now taking that step. Recent advancements in metal hydrides
facilitate storing sufficient hydrogen to power a fuel cell electric vehicle
several hundred miles. And, unlike every alternative method currently under
consideration for future cars-onboard reformation of hydrocarbon fuels to
hydrogen, high-pressure or cryogenic storage- carrying hydrogen as a solid in
a metal-hydride matrix is by far the safest approach. Stan Ovshinsky
explains, "The breakthrough Bob calls a 'game changer' is the quantity of
hydrogen that can be stored in our metal hydride. Until recently, the limit
was two or three grams of hydrogen per 100 grams of hydride. By using a high
percentage of magnesium with several other metals in our patented hydride
powders, ECD is capable of storing seven grams of hydrogen per 100 grams of
hydride (7 weight percent). We've also resolved the thermodynamic issues of
storing and releasing hydrogen from the metal hydride so a typical fill up
would require only three or four minutes."
ECD's Vice President of Advanced Materials Development, Dr. Rosa Young,
defines a metal hydride system as hydrogen gas, engineered metallic materials,
and the interface region between them. She says, "The metal alloys we have
formulated are in loose, dry-powder form. Hydrogen gas entering the storage
vessel absorbs onto the interface regions of this powder. H2 molecules
disassociate into individual hydrogen atoms and a metal hydride is formed when
these atoms arrange in a specific pattern with the metal atoms."
"Heat is also a factor. Removing heat drives the aforementioned
adsorption process. Adding heat reverses the chemical reaction and causes the
hydrogen atoms to reform as H2 molecules. The resulting pure hydrogen gas can
then be fed directly to a fuel cell which, in turn, produces the electrical
energy to power a car.
"The beauty of the metal hydride approach is that hydrogen atoms reside
very close together in the metal matrix. Even though the weight of the metal
matrix is substantially greater than the stored hydrogen, the energy storage
density is significantly higher than what's possible with gaseous or liquid
hydrogen."
In its natural form, hydrogen is bulky and can be dangerous. Storing it
at high pressures does raise the storage density, but it also exacerbates the
safety issue. At 5000 psi, it is possible to store 31 grams of hydrogen per
liter. Liquefying the gas at very low temperatures (-253 degrees C) can raise
the storage density to 71 grams per liter. Unfortunately, liquefaction is
energy intensive, requiring 10 kWh of electricity to liquefy each kilogram of
hydrogen. Also, exotic storage tanks are necessary to contain hydrogen in
either the compressed or the liquefied form.
"ECD has developed the superior alternative," says ECD's Senior Research
Scientist, Ned Stetson, "storing hydrogen as a safe, solid compound at low
pressure. We've achieved an energy density of 7 weight percent. That equates
to 103 grams of hydrogen per liter or 45 percent better than the liquid
approach and 230 percent better than the compressed alternative."
The safety of ECD metal hydride systems has been proven beyond a doubt in
tests conducted in cooperation with vehicle manufacturers. NiMH batteries
have run the gauntlet of drop trials, salt and fresh water submersion and
burning in gasoline without a problem. After destructive poking and prodding,
they've proven to be totally safe, a critically important attribute that
carries over intact to metal hydrides engineered for hydrogen storage.
Longevity is another strong point. Tests suggest that metal hydride systems
will provide more than 2000 refilling cycles with no performance degradation.
Two thousand cycles is equivalent to driving hundreds of thousands of miles in
a vehicle.
The Ovonic Solid Hydrogen Storage System(TM) can be packaged in any size
or shape to meet application requirements. To provide 300 miles of range in
an advanced fuel cell car, 6 kilograms of hydrogen storage capacity is needed.
Such a tank would occupy about 120 liters of space and weigh 120 kilograms.
These specifications include the refueling heat exchanger, a hydrogen fueled
catalytic burner to generate the heat necessary to quickly desorb the stored
fuel and high-efficiency insulation.
ECD is also exploring various potential applications beyond fuel cell
electric cars. One of the most interesting is providing clean hydrogen fuel
for conventional internal combustion engines. Another prospect is small
portable energy sources for home use. ECD is currently designing compact
canisters that can store hydrogen to operate lawn mowers, garden equipment, or
even the ubiquitous barbecue grille. Efforts are underway with developing
countries to update the high polluting two-stroke motorcycles with more
environmentally-friendly hydrogen stored in metal hydride fuel systems.
ECD already enjoys a dominant patent position in the metal hydride field
with 74 U.S. and 214 foreign patents applicable to hydrogen energy storage.
Last spring, Texaco provided a powerful vote of confidence in ECD and its
emerging technology by acquiring a 20 percent equity position in the firm.
Several joint ventures between Texaco and ECD are being formed to
commercialize ECD advanced technologies. The ECD-Texaco Energy Systems
liaison will be instrumental in developing both metal hydrides and the
infrastructure advancements needed to support a growing fleet of hydrogen-
powered automobiles. Notes Ovshinsky, "At ECD, we are dedicated to leading
the way toward a clean, renewable energy source for the future."