Scientists have devised a new way for storing hydrogen, a breakthrough that could pave the way for new hydrogen technologies.

Researchers at the Carnegie Institution have found that high pressure can be used to make a unique hydrogen-storage material. They found that the normally unreactive, noble gas xenon combines with molecular hydrogen (H2) under pressure to form a previously unknown solid with unusual bonding chemistry. It’s the first time these elements have been combined to form a stable compound.

Xenon has some intriguing properties: it’s used as an anesthesia, it can preserve biological tissues and is also used in lighting. It’s also a noble gas, which means that it doesn’t typically react with other elements.

“Elements change their configuration when placed under pressure, sort of like passengers readjusting themselves as the elevator becomes full,” said Maddury Somayazulu, a research scientist at Carnegie’s Geophysical Laboratory and lead author of the study. “We subjected a series of gas mixtures of xenon in combination with hydrogen to high pressures in a diamond anvil cell. At about 41,000 times the pressure at sea level (1 atmosphere), the atoms became arranged in a lattice structure dominated by hydrogen, but interspersed with layers of loosely bonded xenon pairs. When we increased pressure, like tuning a radio, the distances between the xenon pairs changed — the distances contracted to those observed in dense metallic xenon.”

By using imaging technology to look at the xenon part of the structure, the researchers realised the interaction of xenon with the surrounding hydrogen was responsible for the unusual stability and the continuous change in xenon-xenon distances as pressure was adjusted from 41,000 to 255,000 atmospheres.

“We were taken off guard by both the structure and stability of this material,” said Przemek Dera, the lead crystallographer for the research. As electron density from the xenon atoms spreads towards the surrounding hydrogen molecules, it seems to stabilise the compound and the xenon pairs.

“Xenon is too heavy and expensive to be practical for use in hydrogen-storage applications,” said Somayazulu. “But by understanding how it works in this situation, researchers can come up with lighter substitutes.”

“It’s very exciting to come up with new hydrogen-rich compounds, not just for our interest in simple molecular systems, but because such discoveries can be the foundation for important new technologies,” said Russell Hemley, director of the Geophysical Laboratory and a co-author of the study. “This hydrogen-rich solid represents a new pathway to forming novel hydrogen storage compounds and the new pressure-induced chemistry opens the possibility of synthesising new energetic materials.”

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