Pocket sockets: tiny fuel cells for portable electronics have arrived, almost - Industry Overview

Science News, Sept 7, 2002 by Peter Weiss

At Germany's weeklong Hannover Fair last April, a camcorder monitored the crowds visiting the energy-exhibits section of the giant technology trade show. The device had no battery nor was it plugged into the wall. Instead, the palmsize camera got its power from a prototype fuel cell that transformed hydrogen gas and oxygen into water and electricity. The unusually compact fuel cell was "pretty reliable," though not dependable enough to keep the camera running continuously, says Christopher Hebling of the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany, the alternative-energy laboratory that built the fuel cell.

In the same vast exhibit hall were examples of much larger fuel cells for cars, homes, and even factories (SN: 11/19/93,p. 314). Despite growing interest in such alternative energy sources, the introduction of fuel cells in those realms remains an uphill battle. Although clean and efficient, these systems, which have been under development for decades, remain expensive.

On the other hand, say technology analysts, if reliable fuel cells as small as the one in the camcorder--and smaller--could be mass-produced, consumers would snap them up. Users of cell phones, laptop computers, and other portable electronics are frustrated with having to recharge batteries every few hours, says Atakan Ozbek of Allied Business Intelligence in Oyster Bay, N.Y.

Fuel cells as small as a few centimeters across--known as micro fuel cells--could last 10 or more hours and be refueled in seconds, their promoters say. For personal electronics, "people ... desperately need the product," says Robert K. Lifton of New York City-based fuel cell developer Medis Technologies.

Ozbek expects sales of the little power plants to reach 200 million units per year by 2008, at a price of $30 to $50 apiece.

That potential market is stimulating a broad range of efforts to develop micro fuel cells. Furthest along are so-called direct-methanol fuel cells, which have evolved from research funded by the Defense Advanced Research Projects Agency in the late 1980s and early 1990s. Today, several developers of these fuel cells are promising to roll out their first products--most likely, battery chargers--within the next year or so.

Nevertheless, direct-methanol fuel cells remain rife with problems ranging from getting flooded to drying out, and they produce uneven electrical output. "It's a complicated system," says Shimshon Gottesfeld of MTI MicroFuel Cells in Albany, N.Y.

Keenly aware of such shortcomings, many researchers are pursuing alternatives--some with surprising features. These include butane fuel cells with components that get scorching hot and a fuel cell that runs on an ingredient found in honey and beer.

GIVE IT SOME JUICE Today's typical fuel cell, which can be as a big as a house, contains multiple electricity-generating units that are stacked like pancakes. Each of those units consists of two flat, metallic electrodes that sandwich a layer of electrolyte. The electrolyte layer, which can be liquid or solid, acts as a membrane allowing ions but not electrons to pass. This creates a voltage.

Although superficially similar to a battery, a fuel cell gets its energy in a different way. In a battery, chemical reactions produce current and consume the electrodes. In a fuel cell, however, chemical reactions consume fuel that comes from outside the cell, and the electrodes act only as catalysts for those reactions.

In general, fuel cells take in hydrogen and oxygen and convert them into water and electricity. However, sometimes the hydrogen is generated directly within the cell from another fuel, such as methanol.

At one electrode, the anode, molecules of hydrogen gas break down into electrons and positively charged hydrogen ions. Those ions--protons--then migrate through the electrolyte to the other electrode, the cathode.

Meanwhile back at the anode, the electrons from the hydrogen flow out of the fuel cell, where they serve as usable electric current that eventually returns to the cathode. There, oxygen combines with the hydrogen ions and electrons to create water and heat. Both electrodes incorporate precious-metal catalysts that spur the power-generating reactions.

The first fuel cell, made in 1839, used the liquid electrolyte sulfuric acid, and many modern fuel cells still have liquid electrolytes--usually held in a spongelike matrix. However, for some fuel cells, particularly the small ones, developers rely on solid, damp electrolytes. The most common one is known as a polymer-electrolyte membrane or proton-exchange membrane, both names conveniently boiling down to the acronym PEM.

Most current PEM fuel cells run on pure hydrogen, but the gas requires bulky storage canisters ill-suited handheld appliances. To make a direct-methanol PEM cell, however, developers beefed up the catalysts in the electrodes to promote more-complex reactions, notably the combination of methanol and water to form carbon dioxide and the hydrogen needed to drive the cell.