Researchers at the University of Wisconsin-Madison and MIT have found that increasing the particle size of a fuel cell catalyst can decrease its degradation and therefore increase the useful lifetime of a fuel cell.
Current fuel cells use platinum and platinum alloys as a catalyst. While platinum can withstand the corrosive fuel cell environment, it is expensive and not very abundant. To maximize platinum use, researchers use catalysts made with platinum particles as small as two nanometers (approximately 10 atoms across). However, platinum catalysts this small degrade very quickly, resulting in short fuel cell lifetimes, or larger platinum loadings.
The US Department of Energy estimates that fuel cells must function for 5,000 hours, or approximately seven months of continuous use, to be practical for automotive energy solutions.
UW Madison materials science and engineering assistant professor Dane Morgan and Ph.D. student Edward Holby, working in collaboration with Professor Yang Shao-Horn from the Massachusetts Institute of Technology, developed a computational model that shows that if the particle size of a platinum catalyst is increased to four or five nanometers (approximately 20 atoms across), the level of degradation significantly decreases. This means the catalyst and the fuel cell as a whole can continue to function for much longer than if the particle size was only two or three nanometers.
The stability of bulk versus nanoparticle materials can be understood intuitively by thinking of cheese. When you leave a large chunk of cheese out and the edges get crusty, the surface is destroyed, but you can cut that off and there is still a lot of cheese inside that is good. But if you crumble the cheese into tiny pieces and leave it out, you destroy all of your cheese because a larger fraction of the cheese is at the surface.—Dane Morgan
Their modeling work is funded by 3M and the US Department of Energy. The research into the fundamental physics of particle size will be useful as scientists extend their platinum studies to exploring platinum alloys, which can reduce platinum consumption when used as fuel cell catalysts. Morgan is beginning to research models to study size effects on the stability of platinum alloys, such as copper-platinum and cobalt-platinum catalysts.
Fuel cells are just one of many energy technologies—solar, battery, etc.—with enormous potential to reduce our dependence on oil and our carbon emissions. Computer simulation offers a powerful tool to understand and develop new materials at the heart of these energy technologies.—Dane Morgan