September 1, 2005
UPTON, NY -- As part of ongoing research to make
hydrogen a mainstream source of clean, renewable
energy, scientists from the U.S. Department of Energy's
Brookhaven National Laboratory have determined how
titanium atoms help hydrogen atoms attach to an aluminum
surface. Their study isolates the role of titanium,
which is used as a catalyst in the crucial first
step to trap hydrogen within a particular class of
hydrogen-storage materials. The work may also help
identify and develop similar hydrogen-storage systems.
To be a mainstream source of fuel, hydrogen must
be stored safely and efficiently. Conventional high-pressure
storage tanks can be dangerous and are too big and
heavy for certain applications, such as hydrogen-based
fuel cells in automobiles. Hydrogen-storage materials,
however, incorporate hydrogen safely and compactly,
and temporarily hold large quantities of it that
can be recovered easily under safe, controlled conditions.
"A hydrogen-storage material must be able to store
hydrogen quickly under 'normal' conditions -- that
is, without very high temperatures and pressures," said
Chaudhuri. "In tiny amounts, an appropriate catalyst,
such as titanium, can speed up the reaction and make
the hydrogen-storage process suitable for practical
applications. Our study has helped us better understand
the role of these catalysts."
Through this research, Chaudhuri and his collaborator,
Brookhaven chemist James Muckerman, hope to improve
the performance of sodium alanate, a hydrogen-storage
material composed of sodium and aluminum hydride.
Sodium alanate, known as a "complex metal hydride," expels
hydrogen gas (the fuel) and aluminum when heated,
leaving a mixture of sodium hydride and metallic
aluminum. But because neither aluminum nor sodium
hydride absorb hydrogen well, putting the hydrogen
back in -- to reform sodium alanate and allow reuse
of the material -- becomes difficult.
"We found that aluminum absorbs significantly more
hydrogen -- and does so more quickly and at lower
temperatures -- when a small number of titanium atoms
are incorporated into its surface," Chaudhuri said.
Chaudhuri and Muckerman created a computer model
that provides a plausible mechanism of the reaction.
Their model agrees with an experimental x-ray absorption
study of sodium alanate, performed at the National
Synchrotron Light Source, a facility at Brookhaven
that produces x-ray, ultraviolet, and infrared light
Chaudhuri and Muckerman's collaborators at Brookhaven
used x-rays to "see" and thus calculate how the titanium
atoms subtly changed the atomic-level structure of
the aluminum, resulting in a more hydrogen-absorbent
surface. Results from these two studies agree on
the role of titanium atoms on an aluminum surface
and mechanisms of subsequent steps in hydrogen capture.
In the future, Chaudhuri and Muckerman's group plans
to study the subsequent steps in the sodium alanate
hydrogen-storage process, in which aluminum and hydrogen
react with sodium hydride to reform the starting
This research was funded by the Office of Basic
Energy Sciences within the U.S. Department of Energy's
Office of Science.
Mgrdichian , (631) 344-8191 or Mona
S. Rowe , (631) 344-5056