Nano pyramids boost fuel cells

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 pyramids.

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).