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"This new class of compounds offers a possible
alternative route for technologically useful hydrogen storage," said
Russell Hemley, Senior Staff Scientist at the Geophysical Laboratory
of the Carnegie Institution of Washington. The findings also could
help explain how hydrogen becomes incorporated in growing planetary
bodies, he said.
The father-daughter team synthesized compounds made
of hydrogen and water, hydrogen and methane, and hydrogen and octane
in a diamond-anvil cell, which researchers often use to simulate the
high pressures found far beneath Earth's surface.
The hydrogen-water experiments produced the best
results. "The hydrogen-water system has already yielded three
compounds so far, with more likely to be found," said Wendy Mao, a
graduate student in Geophysical Sciences at the University of Chicago.
The compound that holds the most promise for
hydrogen storage, called a hydrogen clathrate hydrate, was synthesized
at pressures between 20,000 and 30,000 atmospheres and temperatures of
minus 207 degrees Fahrenheit. More importantly, the compound remains
stable at atmospheric pressure and a temperature of minus 320 degrees
Fahrenheit, the temperature at which liquid nitrogen boils.
"We thought that would be economically very
feasible. Liquid nitrogen is easy and cheap to make," Wendy Mao said.
The hydrogen in a clathrate can be released when
heated to 207 degrees Fahrenheit. The clathrate's environmentally
friendly byproduct: water.
David Mao noted that while petroleum-based fuels
will eventually run out, the supply of hydrogen is limitless. "Hydrogen
is the most abundant element in the universe," said David Mao, a
Visiting Scientist in Geophysical Sciences at the University of
Chicago. If the new method of storing hydrogen fuel works as expected,
"that's going to change everyone's life in a big way," he said.
The Maos have applied for a patent on their
hydrogen clathrate synthesis technique, but one problem still remains:
how to make the clathrates in quantities sufficient to power a car. "We've
only made them in very small amounts in diamond-anvil cells," Wendy
Mao said. The Carnegie Institution's Hemley noted that the clathrates
can be produced in gas pressure devices as well as diamond-anvil cells.
In the realm of planetary science, the study helps
explain how some of Jupiter's moons could have incorporated hydrogen
during their formation. Scientists once thought that the moons were
incapable of retaining hydrogen during their formation. Now it appears
that Callisto, Ganymede and especially Europa contain large quantities
of water ice, which would require the presence of hydrogen. The
hydrogen clathrates that the Maos synthesized in the laboratory could
have formed naturally under the temperature and pressure conditions
expected to prevail inside these Jovian moons, Wendy Mao said. |
