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Hydrogen Atoms Manipulated Below Palladium Crystal Surface: Implications for H2 Storage, Fuel Cells, Catalytic Reactions

5 December 2005

For the first time, scientists have manipulated hydrogen atoms into stable sites beneath the surface of a palladium crystal, creating a structure predicted to be important in metal catalysts, in hydrogen storage and in fuel cells.

The research, led by Paul S. Weiss at Penn State, will be published in the Dec. 13 issue of the journal Proceedings of the National Academy of Science.

Observations of the effects of the resulting subsurface hydrides (hydrogen atoms with a partial negative charge) confirmed the existence of the stable sites, which had been predicted—and thought to have critical roles in hydrogen storage, metal embrittlement, fuel cells, and catalytic reactions—but previously had neither been deliberately assembled nor directly observed.

After moving absorbed hydrogen atoms to just below the crystal surface, the researchers were able to observe how the presence of the hydride in specific sites within a metal crystal affects the chemical, physical and electronic properties of the metal.

Understanding these effects could advance efforts to improve chemical reactions involving metal catalysts. In addition, the subsurface hydride may provide a model material for application in hydrogen storage and fuel cells. The ability to prepare the subsurface hydride provides an important research tool for these applications.

The researchers carried out the experiments in a low-temperature scanning tunneling microscope (STM) under ultrahigh vacuum by exposing the crystal to a hydrogen atmosphere. They removed excess hydrogen from the surface by cycles of exposure to heat and oxygen. After the surface had been cleaned, the researchers were able to use electrons from the STM tip to move hydrogen atoms that had been absorbed into the bulk metal up into the stable subsurface sites.

As the hydride formed underneath the surface of the material, Weiss and his team observed that the surface of the crystal distorted, the positive charge of palladium atoms above them increased, and interactions occurred with hydrogen atoms on the surface of the palladium crystal.

One of the most interesting aspects of the research was the ability to move atoms beneath the surface. The observation of the effects of the populated sites, such as surface distortion, confirmed the existence of the stable sites and the theoretical predictions of the physical and electrical properties of the hydrides.

Years ago, Weiss was the first on an IBM team to manipulate xenon atoms on a metal surface. His coworkers later moved atoms to spell out their corporate logo. By extending the ability to manipulate atoms beyond the surface of a material, this research is expected to advance the understanding and control of important chemical reactions in a variety of commercial applications. In addition, this ability has potential as a model system of a technologically important material.

This research was funded by the Air Force Office of Scientific Research, with additional support from the Army Research Office, the National Science Foundation and the Office of Naval Research.

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December 5, 2005 in Hydrogen, Nanotech, Research | Permalink | Comments (0) | TrackBack (0)

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