Electronic Design

Alternative Fuel Cells Gain Efficiency

With rising gas prices and dwindling resources, alternative energy may be the key to transportation's future. Current fuel-cell technology has its merits, but it also has several flaws that must be resolved before it gains widespread acceptance and use. Fortunately, researchers at the California Institute of Technology in Pasadena have developed an alternative to this alternative.

Fuel cells convert chemical energy directly into electrical energy. Compared to a typical combustion engine, fuel cells are pollution-free and silent. Polymer electrolyte fuel cells are commonly used in today's prototype fuel-cell cars. But these electrolytes must be humidified for the cell to function. Also, these cells operate over a limited temperature range. They're permeable as well. Consequently, polymer electrolyte fuel cells require many auxiliary components, and they're less efficient than other types of fuel cells.

Sossina M. Haile, an assistant professor of materials science at Caltech, has developed a solution. Instead of using a hydrated polymer, her fuel cell is based on a so-called "solid acid." Solid acids are chemical compounds such as potassium hydrogen sulfate. Their properties lie between those of normal acids like sulfuric acid and normal salts like potassium sulfate. They conduct electricity at similar values to polymers. They don't need to be hydrated, either, and they can function up to 250°C. And, solid acids typically are inexpensive and easy to manufacture.

Scientists haven't investigated solid acids as fuel-cell electrolytes because they dissolve in water and lose their shape at even slightly elevated temperatures. Haile and her students solved these problems by operating the fuel cell at a temperature above the boiling point of water. They also used a solid acid, CsHSO4, that isn't very prone to shape changes.

Next, the researchers hope to reduce the electrolyte thickness and improve the catalyst performance. Most importantly, they have to prevent the reactions that can occur with prolonged exposure to hydrogen. Despite these challenges, the researchers believe their solid-acid fuel cells have potential.

"The system simplifications that come about by operating under dry and mildly heated conditions are tremendous," Haile says. "While there is a good deal of development work that needs to be done before solid-acid-based fuel cells can be commercially viable, the potential payoff is enormous."

For details, go to www.caltech.edu.

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