A new type of catalyst could lead to fuel cells that use a fifth of the platinum they use now. The new material, developed by researchers at the University of Houston, Technical University of Berlin in Germany, and the Department of Energy’s SLAC National Accelerator Laboratory in Menlo Park, CA, consists of nanoparticles with cores made of a copper-platinum alloy and an outer shell that is mostly platinum. The material is up to five times as efficient as regular platinum.
Platinum and platinum alloys are the most efficient catalysts for speeding up chemical reactions in hydrogen fuel cells. Platinum is the only metal that can withstand the acidic conditions inside such a cell, but it is expensive, and this has limited the broad, large-scale applications of fuel cells. Furthermore, about 90 percent of the world’s platinum supply comes from just two countries–South Africa and Russia.
The new material already meets the U.S. Department of Energy’s 2015 target for platinum catalysts: producing at least 0.44 amperes of electric current per milligram of platinum. It produces up to 0.49 amps per milligram of platinum, and the researchers believe it should be possible to increase the material’s catalytic activity even more. “If we could get another factor of two [improvement in catalytic activity], we think that the cost of platinum in these fuel cells would make the technology more practical,” says SLAC physicist Anders Nilsson.
“This is excellent work that should enable us to use less platinum in fuel cells,” says Jean-Pol Dodelet, a professor of energy, materials, and telecommunications at the Institut National de la Recherche Scientifique (INRS) in Quebec.
At the anode of a conventional proton exchange membrane (PEM) fuel cell, the catalyst splits hydrogen into hydrogen ions and electrons, with the latter flowing out of the cell to create current. At the cathode, oxygen molecules combine with electrons and hydrogen ions to form water. This reaction is sluggish and speeding it up requires 10 times as much platinum as is used at the anode. “If you’re trying to replace platinum, it is more important to replace the platinum at the cathode,” says Dodelet.
Peter Strasser, a chemical engineering professor at both the University of Houston and the Technical University of Berlin, started working on a new type of catalyst in 2005, depositing nanoparticles of a copper-platinum alloy onto carbon supports. When a cyclic alternating current is applied to the material, the copper separates from the surface region, giving the nanoparticles a platinum-rich outer layer.