Fuel cells use chemical reactions to produce electricity from hydrogen fuel (some start with compounds such as methanol and then extract the hydrogen). Unlike batteries, which store a fixed amount of energy, fuel cells can produce power as long as they are supplied with fuel. Today, the world buys several hundred million dollars worth of fuel cells each year to provide power generation for utilities, buildings, spacecraft and industrial machinery. As the technology improves, fuel cells are predicted to overtake batteries in many applications, from backup power to mobile electronics.

And the fuel cell industry is chasing an even bigger target: the internal combustion engine. After a century of refinement, the engine in your car is still only 25% efficient-that is, only a quarter of the energy stored in its fuel is converted to useful work. Fuel cells, on the other hand, convert nearly fifty percent of their hydrogen fuel into electricity-with the potential for further improvement. And where the internal combustion engine coughs out a cloud of smog, hydrogen fuel cells produce only water.

But many challenges stand in the way of fuel cell cars, including how to increase cells’ durability, reduce their cost, and improve fuel storage. The greatest challenge may be to create an infrastructure to extract and deliver the hydrogen fuel. Last month, the Department of Energy announced a new effort to tackle these challenges with government and industry research into automotive fuel cells.

Fuel cells work by harnessing the chemical attraction between oxygen, which is taken from the air, and hydrogen, which is stored in a tank, to produce electricity. A catalyst pries apart hydrogen atoms into a positive ion and electron. The positive ions pass through a membrane to bond with the oxygen; the electron travels around the membrane and through a circuit, generating electrical current. On the other side of the membrane, the oxygen, hydrogen ions and electrons form water.

Because hydrogen is difficult to store and transport, some fuel cells are designed to use methanol or other hydrocarbon fuels, and work by extracting the hydrogen. But these designs aren’t as efficient, and they emit carbon dioxide as well as water.

In Technology Review

In November 2000, TR contributor Peter Fairley mapped the road to fuel cell cars in ”Fill ‘er Up with Hydrogen.” He discussed current efforts by carmakers, their alliances with fuel cell suppliers, and the challenges they face.

In April 2001, two TR stories documented fuel cell breakthroughs: the first, the Prototype ”Fuel Cells Clean Up,” highlighted a fuel-cell-powered vacuum cleaner; the second, “Building a Better Fuel Cell” by technologyreview.com staff editor Alan Leo, detailed efforts at Caltech to improve on fuel cell membranes.

In March 2001, Fairley returned to the subject of fuel cells in “Power to the People,” a look at fuel cells and a new generation of distributed generators called microturbines. As backup systems in many commercial buildings today, these technologies appeal to customers who need power that is resistant both to failure and to fluctuation.

But big installations are only part of the fuel-cell story, reports TR contributor David Voss in November 2001’s “A Fuel Cell in Your Phone.” Companies are racing to shrink fuel cells for mobile electronics, and several partnerships have already developed prototype fuel-cell phones.

In January 2002’s “Fuel Cells vs. the Grid,” TR contributor David Freedman examined the fuel cell’s potential to compete with the power grid. Backup power, he writes, will be fuel cells’ killer app–paving the way for longer term advances such as the fuel cell car.

Which brings us back to the Energy Department’s announcement last month that it would boost research into automotive fuel cells. The initiative, called FreedomCAR, will support fuel cell projects at government labs, and encourage research by the Big Three automakers. In January’s “FreedomCAR: Will It Drive?” technologyreview.com’s Leo asks the experts what the plan will mean for auto research.

Powerful History

In 1839, Welsh chemist William Grove took a step backwards. It was well known that adding electricity to water would separate its component elements, oxygen and hydrogen-a process known as electrolysis. By the same logic, Grove figured, there must be a way to reverse the process: to join oxygen and hydrogen to produce water and electricity. His experiment worked, and the fuel cell was born. But fuel cells sat on the shelf for more than 100 years, little more than a laboratory curiosity.

That changed in the 1960s, when the U.S. space program needed a renewable power source for its Gemini spacecraft. It turned to a new fuel-cell technology, the proton exchange membrane, which dramatically increased the amount of energy captured from the hydrogen-oxygen reaction.

Today, that technology is vying to be the next great power revolution: clean, decentralized energy, powered by hydrogen.