An MIT-led research team used inelastic neutron
scattering to demonstrate that hydrogen atoms can diffuse to the
carbon surface of platinum-doped activated carbon at room
temperature
With hydrogen atoms consisting of just a single electron and
single proton, its gaseous form made up of two hydrogen atoms
can be hard to contain. Hydrogen storage, along with
hydrogen production and the lack of infrastructure, remains
a major stumbling block in efforts to usher in hydrogen as a
replacement for hydrocarbon-based fuels in cars, trucks and even
homes. But with the multiple advantages hydrogen offers,
developing hydrogen storage solutions has been the focus of a
great deal of research. Now an MIT-led research team has
demonstrated a method that could allow hydrogen to be stored
inexpensively at room temperature.
Hydrogen storage solutions fall into one of two technologies;
physical storage where compressed hydrogen gas is stored under
pressure or as a liquid; and chemical storage, where the
hydrogen is bonded with another material to form a hydride and
released through a chemical reaction.
Physical storage solutions are more established technologies
but offer significant problems when looking at using hydrogen to
fuel vehicles. Compressed hydrogen gas needs to be stored under
high pressure - current hydrogen fuel cell vehicles such as the
Mercedes-Benz F-Cell store hydrogen at 5,000 or 10,000 psi -
which requires heavy tanks that add to the weight of a vehicle.
Meanwhile, liquid hydrogen boils at -253°C (-423°F) so it needs
to be stored cryogenically with heavy insulation and actually
contains less hydrogen compared with the same volume of
gasoline.
Although they allow hydrogen to be stored at much lower
pressures, chemical storage solutions that bond hydrogen to a
highly porous, sponge-like material such as a metal hydride
generally require high temperatures to release their hydrogen
content because most metal hydrides bind with hydrogen very
strongly.
Previous research efforts have shown that a
Rhodium-based material could store hydrogen at room
temperature and would release the hydrogen when a small electric
current was applied. Now an MIT-led research team has
demonstrated that activated carbon can also store hydrogen under
similar conditions and can release the hydrogen by simply
releasing the pressure.
The activated carbon incorporates a platinum catalyst that
allows the hydrogen atoms to bond directly to the surface of
carbon particles and be released when needed. Because it allows
hydrogen to be stored at atmospheric pressure and room
temperature, storage tanks could be made much lighter, cheaper
and safer, thereby making them practical and economically viable
for hydrogen-powered cars, say the researchers.
To assess hydrogen's interaction with the activated carbon
storage material, the research team used a technique called
inelastic neutron scattering (INS). This method provided the
first evidence that a phenomenon called the "spillover effect"
was involved where, with platinum particles acting as a
catalyst, hydrogen atoms split off from their molecules and
diffuse through the carbon, where they bond with its surface.
Sow-Hsin Chen, MIT professor emeritus in the Department of
Nuclear Science and Engineering and senior author of a paper
describing the new method, says it should make it possible to
increase the storage capacity of the activated carbon material
by fine-tuning the size and concentrations of the particles of
platinum and carbon. The team also hopes to identify a catalyst
that isn't quite as expensive as platinum.
Once the storage system has been tuned to achieve the desired
capacity, Chen says it should be capable of storing hydrogen
under moderate pressure - possibly around 500 psi - and release
the gas on demand by simply releasing the pressure. This is
because when the hydrogen molecules are broken down into atoms
using the spillover effect, they bind with the activated carbon
with much less energy.
Chen led the research team, which included former MIT student
Yun Liu, now at the National Institute of Standards and
Technology and the University of Delaware; and researchers at
Taiwan's Institute of Nuclear Energy Research (including lead
author Cheng-Si Tsao, who was a visiting scientist at MIT for a
year working with Chen), National Tsinghua University in Taiwan
and Pennsylvania State University.
Their findings were reported in a paper published online in
the
Journal of Physical Chemistry Letters in August and is
scheduled to appear in an upcoming print issue.
Source:
MIT
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