WILMINGTON, Del. (AP) _ DuPont said Thursday that it has formed a fuel-cell unit to capture a piece of the growing market for the clean-energy technology the chemical giant said it expects to be worth $10 billion by the end of the decade.

Fuel cells are battery-like devices that combine hydrogen and oxygen to produce electricity, heat and water. DuPont said it will focus on proton-exchange, or PEM, fuel cells, which are primarily used in portable and small stationary power generators and transportation applications.

DuPont said it will at first supply materials, including its Nafion membranes, which have been used in fuel cells for space travel for more than 35 years, and engineering polymers. DuPont said it later plans to supply fuel-cell system developers with other products, including PEM fuel cell stack components such as membrane electrode assemblies and conductive plates. DuPont said it also is involved in the development of direct methanol fuel cell technology.

``Increasing global energy requirements and the desire for new, alternative energy sources in many markets make fuel cells an exciting new growth opportunity for DuPont,'' says Richard J. Angiullo, vice president and general manager of DuPont Fluoroproducts.

``Fuel cells are a natural fit for DuPont technology and capabilities,'' Angiullo said. ``More than 50 percent of a PEM fuel cell stack _ the real transactional center of a fuel cell _ can be made from DuPont materials.''

DuPont said it also plans partnerships with other companies to improve the capabilities, availability and economic feasibility of fuel cell technology.