One way to improve fuel cells that generate
hydrogen on-the-fly is to increase the amount of surface area in a cell
that can host the necessary chemical reactions.
Researchers from Rutgers University have devised a way to make
iridium surfaces that are extremely finely textured. The surface is textured
with pyramids that range from 5 to 14 nanometers, or millionths of a millimeter,
on a side, which increases the available surface area of the metal. The
increased surface area speeds the catalytic reaction that breaks down
ammonia to extract hydrogen.
Storing pure hydrogen is difficult. One way around the hydrogen
storage problem is to make hydrogen with nitrogen at a fuel processing
plant to make ammonia, which is readily stored and transported. Cars could
use ammonia as fuel and use the researchers' textured catalyst to extract
hydrogen from ammonia within a fuel cell.
One plus of ammonia as a fuel is that it does not contain carbon,
which tends to clog fuel cells.
The researchers made the catalyst by heating atomically flat pieces
of iridium in oxygen, then exposing them to hydrogen to remove the oxygen.
The temperature and duration of the heating determines the size of the
The method could also be used for studying the effects of the
sizes of surface features like the pyramids on other types of chemistry,
according to the researchers.
It will be 5 to 10 years before the technology is ready to use
in practical applications, according to the researchers. The work appeared
in the March 28, 2005 issue of the the Journal of the American Chemical
Society (Decomposition of Ammonia and Hydrogen on Ir Surfaces: Structure
Sensitivity and Nanometer-Scale Size Effects).
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