Wendy Mao at Los Alamos National Laboratory in New Mexico and colleagues bombarded ice with X-rays for around 6 hours at extremely high pressures comparable to those at which diamond forms. To their surprise, the water molecules broke down into separate oxygen and hydrogen molecules, which then recombined to form a brownish, stable alloy (Science, vol 314, p 636).

"This is a novel material, uniquely different from water," says David Mao, a team member at the Carnegie Institution in Washington DC. "It is very energetic, but stable and does not react back to form water when kept at high pressure."

Once synthesised, the alloy can be stored for over 120 days at temperatures up to 400 °C when kept at high pressure. The team is now characterising the properties of the alloy and Mao suggests that the material could be used as a way of storing and transporting hydrogen for use in fuel cells.

Hydrogen is widely touted as a fuel of the future but questions remain over how it can be stored and transported safely and cheaply. It is expensive to liquefy and the gas damages metal containers and pipes.
From issue 2576 of New Scientist magazine, 04 November 2006, page 16

If you think we know all there is to know about water, think again. Scientists claim they have created a totally new alloy of hydrogen and oxygen molecules by splitting water.

It takes high-energy X-rays and an extremely high pressure, but the end result is a solid mixture of H2 and 02 that has never been identified before, they say. The discovery could change our understanding of the complex chemistry of water.

The new alloy is "a highly energetic material", says Wendy Mao at Los Alamos National Laboratory, US, who led the research. "It may help us find a way of storing energy."

Mao’s team subjected water to a pressure 170,000 times greater than atmospheric pressure at sea level. Then they bombarded it with X-rays, causing the water molecules to split and reform into a previously unknown crystalline solid made of H2 molecules and 02 molecules.
Just right

The phenomenon has been missed by hundreds of previous experiments, researchers say, because it only happens after several hours of exposure to 10-kiloelectronvolt-X-rays. "We managed to hit on just the right level of X-ray energy input," says team member Russell Hemley, at the Carnegie Institution’s geophysical laboratory in Washington DC, US.

"Any higher, and the radiation tends to pass right through the sample. Any lower, and the radiation is largely absorbed by the diamonds in our pressure apparatus," he explains.

After making several nanograms (10-9 of a gram) of the new alloy, researchers tested its properties by subjecting it to a range of temperatures and pressures, and further bombardment by X-rays and laser radiation. As long as it remained under a pressure 10,000 times greater than at sea level, it was "surprisingly stable", they say.
Fresh avenues

Under pressure, water is known to form 15 different types of ice, with a variety of crystal structures. But in all of them hydrogen and oxygen atoms remain bound to each other.

The discovery that molecules of oxygen and hydrogen can form an alloy opens up fresh avenues of research, including new possibilities for studying molecular interactions between oxygen and hydrogen, the researchers say.

"The existence of this new alloy is very interesting but not hugely surprising," says Sean McWhinnie, at the Royal Society of Chemistry in London, UK.

"Given high enough pressures, even hydrogen will behave as a metal. All, the other heavier elements in hydrogen's group of the periodic table are metals," she points out.