04/19/2001 07:00:00

Scientists achieve breakthrough in fuel-cell technology

Embargoed for Release at 11 a.m. PST, Wednesday, April 18, 2001

PASADENA, Calif.—Gasoline averaging $3 per gallon? Oil drilling in an Alaskan wildlife reserve? A need to relax air quality standards? It seems the long-term future of fossil fuels is bleak. One promising solution scientists have been studying is fuel cells, but they've had limitations too. Now, in the April 19 issue of the science journal Nature, the California Institute of Technology's Sossina M. Haile reports on a new type of fuel cell that may resolve these problems.

Unlike the engines in our cars, where a fuel is burned and expanding gases do the work, a fuel cell converts chemical energy directly into electrical energy. Fuel cells are pollution free, and silent. The most common type now being developed for portable power—the type used in today's fuel-cell-powered prototype cars—is a polymer electrolyte fuel cell. An electrolyte is a chemical that can conduct electricity, and is at the heart of the fuel cell. Polymer electrolytes must be humidified in order for the fuel cell to function, can only operate over a limited temperature range, and are permeable. As a consequence, polymer electrolyte fuel cell systems require many auxiliary components and are less efficient than other types of fuel cells.

Haile, an assistant professor of materials science, has taken a completely different tack, developing an alternative type of fuel cell that is not a hydrated polymer, but is instead based on a so-called "solid acid." Solid acids are chemical compounds, such as KHSO4 (potassium hydrogen sulfate). Their properties are intermediate between those of a normal acid, such as H2SO4 (sulfuric acid), and a normal salt, such as K2SO4 (potassium sulfate). Solid acids can conduct electricity at similar values to polymers, they don't need to be hydrated, and they can function at high temperatures, up to 250 degrees Centigrade. Solid acids are also typically inexpensive compounds that are easy to manufacture.

But until now such solid acids have not been examined as fuel-cell electrolytes because they dissolve in water and can lose their shape at even slightly elevated temperatures. To solve these problems, Haile and her graduate students Dane Boysen, Calum Chisholm and Ryan Merle, operated the fuel cell at a temperature above the boiling point of water, and used a solid acid, CsHSO4, that is not very prone to shape changes.

The next challenge, says Haile, is to reduce the electrolyte thickness, improve the catalyst performance, and, most importantly, prevent the reactions that can occur upon prolonged exposure to hydrogen. Still, she says, solid acid fuel cells are a promising development.

"The system simplifications that come about (in comparison to polymer electrolyte fuel cells) by operating under essentially dry and mildly heated conditions are tremendous. While there is a great deal of development work that needs to be done before solid acid based fuel cells can be commercially viable, the potential payoff is enormous."

The Department of Energy, as part of its promotion of energy-efficient science research, recently awarded Haile an estimated $400,000 to continue her research in fuel cells. She also recently received the J.B. Wagner Award of the Electrochemical Society (High Temperature Materials Division). She is the recipient of the 2001 Coble Award from the American Ceramics Society, and was awarded the 1997 TMS Robert Lansing Hardy Award. Haile has received the National Science Foundation's National Young Investigator Award (1994–99), Humboldt Fellowship (1992–93), Fulbright Fellowship (1991–92), and AT&T Cooperative Research Fellowship (1986–92).