stores more hydrogen
Technology Research News
Hydrogen is the most abundant element in
the universe, and when it is burned its only byproduct is water. One reason
the world isn't running on hydrogen fuel is that it's hard to store.
Researchers from the National University of Singapore have made an accidental
discovery that brings the promise of clean hydrogen energy a big step
The challenges to using hydrogen as a fuel include finding a hydrogen
storage system that is reasonably small and light, and finding a way to
release the stored fuel quickly enough when it is needed.
The researchers have found a material that can store and quickly release
large amounts of hydrogen. Lithium nitride can store 11.4 percent of its
own weight in hydrogen, which is 50 percent more than magnesium hydride,
the previous best hydrogen storage material. Other metal hydrides generally
store only 2 to 4 percent of their weight.
The new material is not ready for practical applications because the temperature
required to release the hydrogen is too high, but it points the way to
a practical hydrogen storage material, according to Ping Chen, a senior
research fellow at the National University of Singapore. "We think the
main application might be... on-board hydrogen storage," he said.
The researchers discovered the material accidentally, according to Chen.
"In the last three years we continuously pursued the task of storing hydrogen
in lithium-carbon," he said. In the course of that work, the researchers
treated lithium-carbon with nitrogen, and found that hydrogen absorption
increased. When they studied the material, they found that lithium nitride
was the substance responsible for the increased uptake.
Lithium nitride absorbs hydrogen when it is exposed to hydrogen that is
under pressure. The chemistry involves one lithium nitride molecule combining
with four hydrogen atoms to form lithium amide and lithium hydride. Reducing
the pressure reverses the process. "Under low hydrogen pressure, lithium
amide and [lithium] hydride react with each other and give out hydrogen
gas," said Chen.
The current drawback to the researchers' material is that in order for
the hydrogen to be released at one atmosphere of pressure, the storage
material has to be heated to 270 degrees Celsius. It will release hydrogen
at lower temperatures, but only at pressures below one atmosphere, which
is the pressure of Earth's atmosphere at sea level. The researchers' next
step is to find a way to release the hydrogen at a usable pressure and
The work is "the first to establish that alkali metal nitrides are worthy
of serious consideration as viable hydrogen storage materials," said Craig
Jensen, a professor of chemistry at the University of Hawaii at Manoa.
Although the thermodynamic parameters of the system render it impractical,
"the paydirt reported by the authors is rich enough that it should attract
a rush of prospectors into this area to search for the elusive hydrogen
storage material that will open the door to the hydrogen era," Jensen
The researchers are working on improving the hydrogen storage performance
of their system through both mechanical and chemical modifications, said
They are investigating the hydrogen storage potential of related nitrides
and imides in order to find one with better temperature attributes, said
Chen. New species, or forms of nitrides, imides and metal-nitride-hydrogen
composites are emerging continuously, he said. "With abundant chemical
information and well-developed synthetic and characteristic techniques,
we believe there is huge scope for development of materials [that will
work at a] practical temperature."
Another technical challenge to making a practical onboard hydrogen storage
system is making sure the storage material is chemically stable, said
Chen. The researchers' current prototype is sensitive to moisture, oxygen,
carbon dioxide and other common substances, which makes strict conditions
necessary for practical operation, he said.
It will take five to ten years to develop a practical metal nitride or
imide hydrogen storage material, he said.
Chen's research colleagues were Zhitao Xiong, Jizhong Luo, Jianyi Lin
and Kuang Lee Tan. They published the research in the November 21, 2002
issue of the journal Nature. The research was funded by the Singapore
Agency for Science, Technology and Research.
Timeline: 5-10 years
TRN Categories: Energy; Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Interaction of Hydrogen
with Metal Nitrides Imides," Nature, November 21, 2002.
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