What is a Fuel Cell?

In the effort to cut auto pollution, hybrids and battery cars are a step forward, assuming anybody will buy them. But they're far from perfect: Hybrids burn gasoline, making air pollution. Batteries run down, and even though battery cars are called "zero emissions" vehicles, they generally just move the pollution rather than eliminate it.

On the horizon, however, is a car where "zero emissions" meets truth-in-advertising. Bye-bye catalytic converters and associated pollution-control gadgetry. In fact, so long to pollution entirely. In fuel-cell cars running on hydrogen, the waste products amount to water and heat.

The fuel cell, furthermore, is a new kind of engine -- one without moving parts! Even if fuel cells burn alcohol or gasoline, they will be far more efficient than today's internal combustion engines, and will produce less carbon dioxide, the primary culprit in global warming.

Fuel cells have been producing power since the start of the space age. But bulky, expensive and relatively weak, the cells seemed unlikely to find a place under the hood of Detroit's finest.

Then, in the 1980s, Canadian engineer Geoffrey Ballard began tinkering with fuel cells in search of a cleaner way to move people and goods. Among the several possible varieties, Ballard selected the proton-exchange membrane, a technology that operates at low temperature and starts up quickly, making it suitable for a machine that would replace the ol' Buick Roadmaster.

Like batteries, fuel cells make electricity from chemical reactions. But while batteries have a limited supply of chemical energy, fuel cells get chemical energy from the fuel, so they drive until the tank runs dry.

Hydrogen is fed to the anode, and oxygen or air enters through the cathode. The catalyst splits the hydrogen into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte.

Like a battery, a fuel cell has a cathode, with a positive charge, and an anode, with a negative charge. The cell uses a catalyst -- often platinum -- to dissociate some electrons from atoms. These liberated electrons become the electric current that leaves the cell to do useful work.

In Ballard cells, the anode and cathode are separated by a polymer membrane that acts as an electrolyte -- a substance that allows electrons to flow. As hydrogen enters the anode, it is broken into protons and electrons by the catalyst. The liberated electrons flow as a current through the external circuit to electric motors powering the wheels. The protons pass through the membrane to the cathode and combine with oxygen from air and electrons returning from the external circuit. If hydrogen is the fuel, the waste products are simply water and heat.

When Ballard began, only bulky cells could produce a reasonable amount of power, so he began imprinting tiny channels on the membranes, allowing the fuel to move through thin cells that could be pancaked into a stack hefty enough to power a bus.

Ballard's inventions dramatically raised the power density -- the amount of power available from a given volume of cells. As power density rose, Ballard began testing cells in various vehicles

By the late 1990s, Ballard was attracting attention from the big wheels in the auto biz: Daimler Benz (now DaimlerChrysler) started testing cells in its cars and wound up buying part of Ballard.

In 1999, Daimler claimed that the New Electric Car 4, a compact Mercedes, would go 90 miles per hour and get almost 280 miles on a tank of liquid hydrogen (not counting stops for traffic tickets...). The liquid hydrogen fuel was stored in a large thermos in the trunk; the fuel cells were stashed beneath the floor.

While Daimler and Ford Motor Co. plan to sell fuel-cell cars in the 2004 model year, fuel cells don't need to go anywhere to be helpful: Several manufacturers are building stationary fuel cell stacks to power homes and businesses. In these stacks, the waste heat could warm water or air, increasing overall efficiency.

Burn what?
As fuel cells approach the market, a key decision concerns fuel. Most of today's cells oxidize hydrogen, which is a clear winner in environmental terms, since the oxidation process produces dihydrogen oxide, AKA water.

However, carbon-bearing fuels, including gasoline and methane, also contain lots of hydrogen. In August, 2000, General Motors and ExxonMobil, eager to maintain its future market, announced a technology to extract hydrogen from gasoline.

Despite the environmental drawback -- the cell would produce the greenhouse gas carbon dioxide -- the gasoline supply is in place, while a new infrastructure would be needed to supply hydrogen.

Ultimately, the best solution, from an environmental point of view, would involve finding a way to generate hydrogen from renewable energy. Toward that end, Iceland, which has the highest per-capita oil imports, is talking about establishing a "hydrogen economy."

Iceland is awash in renewable energy, and it plans to use geothermally heated water from the many volcanoes to drive the separation of water into oxygen and hydrogen to power fuel cells in buses and the nation's large fishing fleet.

Whether powered by hydrogen or gasoline, the move toward fuel cells seems real. In August, Erhard Schubert, co-director of GM's Global Alternative Propulsion Center, told the Cleveland Plain Dealer , "If we want future generations to enjoy the same kind of mobility we have become accustomed to, the fuel cell is now the only viable option in light of our planet's limited fossil fuel energy resources."