Solid, Man, Solid?
ECD could make fuel cells safe and practical.
by Paul A. Eisenstein
Imagine having to haul around an oil refinery everywhere you go just to get your car to run.
That?s the challenge facing automotive engineers as they struggle to bring a viable fuel
cell-powered car to market later this decade.
The fuel cell itself is a surprisingly simple device. Pump in hydrogen on one side, oxygen on
the other, and the gases combine to form water vapor?and energy that can be used to run
an electric motor. While the fuel cell itself is looking increasingly attractive as the "green"
alternative to the Internal Combustion Engine, it?s not likely to see widespread use unless
and until engineers can find a practical way to store or produce a steady stream of
hydrogen gas to feed the fuel cell.
Storing hydrogen in liquid form is impractical, since that means cooling it to nearly
absolute zero. Storing it as a compressed gas isn?t much better, since it would be
difficult?and potentially dangerous?to carry enough to provide much range. So until
now, the onboard reformer has seemed the only practical alternative.
A reformer is basically an onboard chemical plant that converts gasoline or methanol
into gaseous hydrogen. It?s a complex and costly process that would take up a lot of
vehicle space. And it?s still not certain the technology will work on the road as well as it
does in the lab.
But a fourth form of storage suddenly is emerging as a viable alternative ? and if it
proves practical, it could make the fuel cell a reality before the decade is out.
Power out of powder
The small glass jar sitting on Bob Stempel?s desk doesn?t look like much, certainly not
the breakthrough the auto industry has been looking for. It contains a dull gray powder,
a finely ground mix of nickel, chromium and vanadium combined to form a compound
called a metal hydride. But under the right conditions, the mixture acts almost like a
hydrogen magnet. Pump in gaseous hydrogen, and it binds to the hydride mixture.
Heat it, and the gas separates, so it can be pumped out to feed a fuel cell.
"Essentially, we contain the hydrogen as a solid," explains Stempel, the chairman of
Troy, MI-based Energy Conversion Devices.
While ECD isn?t the first to come up with hydride storage, it appears to have
developed a formula that makes the process practical. ECD?s hydride mixture absorbs
7 percent of its weight in hydrogen gas. In a given space, that means it can hold three
times more hydrogen than in compressed gas form, and 50 percent more than in liquid
form. Fill a container the size of today?s typical gas tank with this hydride, and you could
hold enough hydrogen to double the range of a conventional, gasoline-powered car.
General Motors? prototype Precept is an example of a hydride-fueled vehicle.
Introduced at the North American International Auto Show, last January, it is a
five-passenger midsize sedan "that could deliver (the equivalent of) better than 100
miles per gallon fuel economy performance, just over nine seconds 0-60 mph
acceleration, and 500 miles range," said Byron McCormick, co-executive director of
GM?s Global Alternative Propulsion Center. "And all of this with no compromises in
driving safety, crashworthiness and safe refueling."
Solid storage appears to minimize the dangers of fire or explosion inherent in gaseous
or liquid hydrogen storage. Hydrides would also, obviously, eliminate the need for an
onboard reformer. And that would significantly lower vehicle cost. That doesn?t mean
hydride storage comes cheap.
"For this to be practical, we would have to keep the cost to $1500" for the entire fuel
storage system, estimated Stempel. A former chairman of General Motors Corp., he
joined ECD several years ago to help the research firm commercialize its technology.
Size still matters
Hydride storage alone won?t make the fuel cell viable. Researchers are still working to
reduce the size and cost of the fuel cell itself, but breakthroughs are coming at a steady
pace. Another challenge would be to come up with a fuel infrastructure. While it?s not
difficult to produce hydrogen, there?s currently no easy way to get it to the pump.
One possibility would be to place reformers at service stations. Given an efficient
method of storing hydrogen onboard a car, it would be more practical and cost
effective to convert gasoline, natural gas or methanol into hydrogen at a fixed location.
Hydrides could provide another alternative, according to Stempel. Hydrogen could be
produced at regional refineries, then shipped to service stations on fuel tankers filled
with hydrides.
ECD is reportedly negotiating with a major oil company that would like to use its
hydrides to ship hydrogen from Iceland, where large quantities of the gas are already
being produced.
According to Stempel, ECD is discussing several other possible applications for its
solid hydrogen storage. One would permit the use of fuel cells for home power
generation. Another would store the gas for use in portable camping stoves and
lanterns. A third potential customer is developing a miniature fuel cell for powering
laptop computers. With hydride storage, Stempel claims the system would be able to
run almost indefinitely.
While the solid hydrogen storage system has been working well in the lab, real world
testing should begin in the coming year.
[March 13, 2000] |
