LES PILES A HYDROGENE FONT LE PLEIN

'Soap' May Make Clean Fuel-cell Cars Feasible
Eric C. Evarts - Special Correspondent of The Christian Science Monitor
DETROIT - Space-age fuel cells that could eliminate auto emissions look as if they're just over the horizon.

Résumé:     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 fuels.
    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 stations needed
    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.