has long been considered a promising alternative to fossil fuels for powering
cars, trucks, and even homes. But one major obstacle has been finding
lightweight, robust, and inexpensive ways of storing the gas, whose atoms are
so tiny they can easily escape from many kinds of containers.
research by a team from the Massachusetts Institute of Technology (MIT) and
several other institutions analyzes the performance of a class of materials
considered a promising candidate for such storage: activated carbon that
incorporates a platinum catalyst, so hydrogen atoms can bond directly to the
surface of carbon particles and then be released when needed.
a storage system could avoid the cost and weight associated with conventional
hydrogen storage: Current approaches either liquefy the gas, requiring
energy-intensive systems and heavy insulation to maintain a temperature of
minus 423 F; or store it under high pressure, requiring powerful pumps and
robust tanks to withstand 5,000 to 10,000 lbs psi of pressure. Bonding the
hydrogen to a highly porous, sponge-like material such as a metal hydride or
activated carbon makes it possible to use ambient pressure and room temperature
in storage tanks that could be lighter, cheaper, and safer.
tricky part of designing such systems is finding a storage medium that bonds
the hydrogen atoms tightly enough so they don’t leak away, but not so tightly
that they can’t be released when needed. “You have to be able to pump the gas
in [at room temperature], and release it when you need it to burn,” explains
MIT’s Sow-Hsin Chen, senior author of a paper describing the new method.
a storage system could be key to making hydrogen-powered cars practical and
economically viable, and has been a key goal of the U.S. Department of Energy
(DoE). The hydrogen fuel could be made by splitting water; fuel cells would
then “burn” the fuel with no emissions at all except water vapor.
carbon has been proposed as a possible storage medium that could work by
bonding dissociated hydrogen atoms, but previously there was no good way of
analyzing the material’s behavior and optimizing its storage capability. Now,
such a method has been demonstrated by a team led by Chen, MIT professor
emeritus in the Department of Nuclear Science and Engineering; former student
Yun Liu SM ’03, PhD ’05, 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
team analyzed the activated carbon’s storage of hydrogen using a technique
called inelastic neutron scattering, which they say is uniquely capable of
determining whether the hydrogen in the sample exists as individual atoms or H2
molecules. This approach can also assess the gas’s interaction with the storage
this method, they were able to provide convincing evidence, for the first time,
that hydrogen moves into the material as a result of a phenomenon called the spillover
effect, in which atoms—thanks to the presence of platinum particles as a
catalyst—split off from their molecules and diffuse through the carbon, where
they bond to its surface. Other researchers had suspected the spillover effect
was involved, but had been unable to demonstrate that this was the case. “Although this concept had been proposed, there was a lot of debate about it in
the community,” Liu says.
new analysis method should make it possible to fine-tune the properties of the
activated carbon material to increase its storage capacity, Chen says. The key
is to find the optimum sizes and concentrations for the particles of platinum
and carbon, he adds. Ultimately, the researchers also hope to identify a
catalyst more abundant and less expensive than platinum.
storage system, once tuned to achieve the desired capacity, should be capable
of storing hydrogen under moderate pressure (possibly around 500 psi), then
releasing the gas on demand simply by releasing the pressure, Chen says. “When
you break the hydrogen molecules down to atoms” using the spillover effect, “it
binds with the material with much less binding energy, so you can pump it out
easily,” he says.