CHICAGO (Reuters) - Pellets made out of aluminum and gallium can produce pure hydrogen when water is poured on them, offering a possible alternative to gasoline-powered engines, U.S. scientists say.

A worker walks between stacks of high purity aluminum ingots at the RUSAL aluminum smelter in the Siberian city of Krasnoyarsk April 4, 2007. Pellets made out of aluminum and gallium can produce pure hydrogen when water is poured on them, offering a possible alternative to gasoline-powered engines, U.S. scientists say. REUTERS/Ilya Naymushin

Hydrogen is seen as the ultimate in clean fuels, especially for powering cars, because it emits only water when burned. U.S. President George W. Bush has proclaimed hydrogen to be the fuel of the future, but researchers have not yet found the most efficient way to produce and store hydrogen.

The metal compound pellets may offer a way, said Jerry Woodall, an engineering professor at Purdue University in Indiana who invented the system.

“The hydrogen is generated on demand, so you only produce as much as you need when you need it,” Woodall said in a statement. He said the hydrogen would not have to be stored or transported, taking care of two stumbling blocks to generating hydrogen.

For now, the Purdue scientists think the system could be used for smaller engines like lawn mowers and chain saws. But they think it would work for cars and trucks as well, either as a replacement for gasoline or as a means of powering hydrogen fuel cells.

“It is one of the more feasible ideas out there,” Jay Gore, an engineering professor and interim director of the Energy Center at Purdue’s Discovery Park, said in a telephone interview on Thursday. “It’s a very simple idea but had not been done before.”

On its own, aluminum will not react with water because it forms a protective skin when exposed to oxygen. Adding gallium keeps the film from forming, allowing the aluminum to react with oxygen in the water.

This reaction splits the oxygen and hydrogen contained in water, releasing hydrogen in the process.

“I was cleaning a crucible containing liquid alloys of gallium and aluminum,” Woodall said. “When I added water to this alloy -- talk about a discovery -- there was a violent poof.”

What is left over is aluminum oxide and gallium. In the engine, the byproduct of burning hydrogen is water.

“No toxic fumes are produced,” Woodall said.

“When and if fuel cells become economically viable, our method would compete with gasoline at $3 per gallon even if aluminum costs more than a dollar per pound.”

Recycling the aluminum oxide byproduct and developing a lower grade of gallium could bring down costs, making the system more affordable, Woodall said.

The Purdue Research Foundation holds title to the primary patent, which has been filed with the U.S. Patent and Trademark Office. An Indiana startup company, AlGalCo LLC., has received a license for the exclusive right to commercialize the process.