'Soap' May Make Clean Fuel-cell Cars Feasible
Eric C. Evarts - Special Correspondent of The Christian Science
DETROIT - Space-age fuel cells that could eliminate auto emissions
look as if they're just over the horizon.
Lors d'un salon de l'automobile qui
vient de se tenir à Détroit, Daimler-Benz a présenté
une nouveau type de voiture à hydrogène.
Les piles à combustibles
se développent sans arrêt mais le stockage de l'hydrogène
reste une difficulté.
Sous forme gazeuse, son réservoir
prendrait la place de deux sièges plus le coffre. Sous forme liquide,
l'isolation thermique nécessaire ferait perdre les avantages de
la concentration. Quant à partir du méthane ou de l'essence
classique pour l'obtenir, cela ferait perdre une partie des bénéfices
(et ne nous sortirait pas du cycle pétrolier).
DaimlerChrysler a donc développé
une pile utilisant un produit chimique à base de bore, d'hydrogène
et de sodium. La seule émission au pot d'échappement reste
la vapeur d'eau mais la pile produit aussi du "borax", comme celui utilisé
dans les poudres à lessiver. Il serait possible (si l'industrie
chimique s'y met) de recycler ce borax pour refaire le combustible de base.
Gros avantages : gain de place
et pas de risque d'incendie...
The key, if automaker DaimlerChrysler
is right, is soap.
What's been holding back development of fuel-cell
cars - which consume only clean, abundant hydrogen and emit only steam
- is that the storage tanks such vehicles require are so big, there's hardly
room for passengers, let alone cargo.
But DaimlerChrysler may be onto something with,
in effect, a soap factory under the hood.
It involves simple borate - a chemical mined from
the ground and used as laundry detergent.
The company showed a running prototype minivan at
the North American International Auto Show in Detroit earlier this month
that demonstrates the viability of the "borax fuel cell."
The fuel cell runs on hydrogen taken from sodium
borohydride - a man-made chemical - in its "gas" tank. What's left is borax
soap in the tank. The only emission from the tailpipe is steam.
If this works, it could have ramifications far beyond
your driveway. Fuel cells - the power plants that provide heat and computing
power to spacecraft - are seen as the power source of the future because
they produce clean electricity from a virtually unlimited power source,
hydrogen, and produce no pollution other than steam. How fuel cells work
Fuel cells work by converting hydrogen and oxygen
into water and electricity. While there are several varieties, the leading
candidate for small consumer fuel cells are so-called proton exchange membrane
or PEM fuel cells. This variety divides two chambers on opposite sides
of a platinum-coated plastic membrane with microscopic holes just big enough
for a hydrogen proton to jump through.
An electric circuit - in this case driving the van's
motor - connects the two sides. Flip a switch - or step on the accelerator
- and electrons leap off the hydrogen molecules and zip around the circuit.
Meanwhile the positively charged hydrogen protons slip through the membrane,
and with the help of their reunited electrons, bond with the oxygen on
the other side to form water.
Since no combustion takes place, impurities in the
air (the oxygen side of the fuel cell) are left alone and don't form smog.
Fuel cells are coming down enough in price to be
competitive with electrical generators for midsize buildings. They are
expected to be cheap enough to power cars in the near future.
Cars, badly in need of a new power source to replace
the internal combustion engine, are likely to be the breakthrough application
that could catapult fuel cells into daily life.
"Hydrogen fuel-cell vehicles would be a breakthrough
on transportation as well as commercial and stationary [energy] efficiency."
says Michael Brylawski, vice president of Hypercar Inc., in Snowmass, Colo.,
a company that hopes to commercialize a hydrogen fuel-cell car. He says
they would usher in the renewable hydrogen economy, independent of fossil
He notes that a fuel-cell car could provide light
and heat for houses when parked in the garage at night: The car's fuel
cell could plug into the house to provide home electricity produced from
hydrogen in the car's tank.
Since fuel cells run directly on hydrogen, they
don't rely on fossil-fuel-burning power plants for energy, as battery-powered
electric cars (ultimately) do.
For energy efficiency, the borax fuel cell could
surpass all but gaseous hydrogen. Borate would have to be mined, hydrogen
produced from water or some other chemical (possibly by solar energy),
and sodium borohydride made in a factory.
All these processes use energy but promise to be
more efficient than a fuel cell powered by liquid hydrogen, says Thomas
Moore, vice president of future technology at DaimlerChrysler.
The bugaboo of automotive fuel cells so far has
been storing hydrogen on board - and having any room left for people in
the cars. In fact, the only commercially viable fuel-cell vehicles today
are city buses that have enough space for large hydrogen tanks on the roof.
Several are in use in Chicago and Vancouver, British Columbia. Filling
Besides, corner gas stations don't sell hydrogen.
So fuel-cell cars would need new or retrofitted hydrogen filling stations.
While hydrogen can be refined from water, no facilities
have the capacity to fuel America's 200 million-plus vehicle fleet.
Other running prototype fuel- cell cars so far have
used gaseous or liquid hydrogen, or an on-board chemical factory - a "reformer"
- to produce hydrogen.
All these technologies have their limits:
. Hydrogen gas has to be stored in giant, cylindrical,
pressurized tanks that take up the space of at least two seats and most
of the cargo area in a typical minivan. That's much larger than other storage
forms. In addition, gaseous hydrogen conjures mental images of the 1937
Hindenburg disaster in public perception. The Zeppelin airship burned and
crashed on landing in New Jersey. Public perception has long blamed the
volatile hydrogen lifting gas for the fire.
But more recent studies have cast doubt on hydrogen's
role in the disaster. Film images of the fire indicate that it was the
skin of the Hindenburg caught fire.
. Liquid hydrogen contains many more molecules in
a smaller tank and so could give a hydrogen vehicle the range of a gas-powered
car. But it evaporates into a gas at only a few degrees above absolute
zero - minus 460 degrees Fahrenheit. So the smaller fuel tank needs rampart-thick
insulation - more wasted space.
And "you use almost as much energy cooling the hydrogen
as it produces" in the fuel cell, says Mr. Moore. So it's not at all clear
that liquid hydrogen will ever be cost-effective.
. Reformers, which produce hydrogen from hydrogen-rich
methane or common gasoline, would solve many distribution problems. You
could fill up at your corner station. But the reformers produce pollution
much like today's engines (though less of it), and so negate a key advantage
of hydrogen. They take up almost as much room in the car as a gaseous hydrogen
tank, produce infernal heat, and take up to 30 minutes to warm up.
DaimlerChrysler's Natrium minivan solves several
problems: It stores hydrogen in a fifth the space of gaseous hydrogen;
it needn't be under pressure in a large cylindrical tank; it doesn't require
a large, hot, dirty reformer; and it is not flammable.
The spent fuel (soap) would be pumped back out of
the gas tank at fill-up time to be recycled into more sodium borohydride.
The idea is not technically new, but advancing catalytic-converter
technology has made the process space- and cost-efficient enough to fit
under the floor of a slightly raised minivan.
The van uses a catalyst to convert sodium borohydride
into borax, water, and hydrogen. A bladder in the fuel tank separates spent
borax from the fuel. The fuel cell makes electricity to drive the van via
an electric motor. Chemical partners wanted
What's missing is the infrastructure to convert
the spent borax solution back into sodium borohydride - and a pump to refuel
the van and recycle the borax. Today the van runs on industrial-grade sodium
borohydride and the nontoxic borax waste is simply dumped.
"We're showing this [prototype] to the public now
to try to interest chemical companies in developing facilities to rehydrogenate
the borax into sodium borohydride" says Moore.
In addition, the Bush administration's new Freedom
Car effort to push fuel-cell development will lend muscle to solving the
distribution and storage problems with hydrogen fuel - and could boost
the borax fuel cell in the process.
Daimler-Benz in Germany has led the way toward fuel-cell
cars since the 1980s. Now Chrysler, which had worked on its own fuel cells
in the United States government's Partnership for a New Generation of Vehicles,
has benefited from Daimler's research. Toyota and Honda have also displayed
running fuel-cell concept cars and promised to put them into production.
Building fuel-cell cars is one thing. But marketing
them to the public with no corner hydrogen stations is another.
Without government standards on fuels, these clean
cars from any continent will be sold only to commercial customers who can
provide their own refueling infrastructure.
Copyright 2002 The Christian Science Monitor. All