New Innovation from MIT researchers to
boost efficiency of fuel cells
MIT research team led by Associate Professor of Mechanical
Engineering and Materials Science and Engineering Yang Shao-Horn,
have found a new way of powering fuel cells, which uses
methanol instead of hydrogen as its fuel and is considered
a potential replacement for batteries in homes, cars, portable
electronic devices such as cellphones and laptop computers.
The fuel cells eliminating emissions of greenhouse gases
and other pollutants has been outweighed by their high cost,
and researchers have been trying to find ways to make the
devices less expensive.
Since these electrodes are made up of platinum, increasing
their efficiency means that much less of the expensive metal
is needed to produce a given amount of power.
The key to the boost in efficiency, the team found, is
to change the surface texture of the material. By creating
tiny stair-steps to the surface instead of leaving it smooth,
the electrode's ability to catalyze oxidation of the fuel
and thus produce electric current was approximately doubled
in experiments, and the researchers believe that further
development of these surface structures could end up producing
far greater increases, yielding more electric current for
a given amount of platinum.
Their results are reported Oct. 13 in the Journal of the
American Chemical Society. The paper's eight authors include
chemical engineering graduate student Seung Woo Lee and
mechanical engineering postdoctoral researcher Shuo Chen,
along with Shao-Horn and other researchers at MIT, the Japan
Institute of Science and Technology, and Brookhaven National
"One of our research focuses is to develop active
and stable catalysts," Shao-Horn says, and this new
work is a significant step toward "figuring out how
the surface atomic structure can enhance the activity of
the catalyst" in direct methanol fuel cells.
In their experiments, the team used platinum nanoparticles
deposited on the surface of multi-wall carbon nanotubes.
Lee says that many people have been experimenting with the
use of platinum nanoparticles for fuel cells, but the results
of the particle size effect on the activity so far have
been contradictory and controversial. "Some people
see the activity increase, some people see a decrease"
in activity as the particle size decreases. "There
has been a controversy about how size affects activity."
The new work shows that the key factor is not the size
of the particles, but the details of their surface structure.
"We show the details of surface steps presented on
nanoparticles, and relate the amount of surface steps to
the activity." Chen says. By producing a surface with
multiple steps on it, the team doubled the activity of the
electrode, and the team members are now working on creating
surfaces with even more steps to try to increase the activity
further. Theoretically, they say, it should be possible
to enhance the activity by orders of magnitude.
This study looked at the enhancement of oxidation, but
the other side of a fuel cell undergoes oxygen reduction.
Does the addition of steps to the surface also enhance the
oxygen reduction? "We need to find why it does, or
why it doesn't," Shao-Horn says. The researchers expect
to have answers to that question in the next few months.