Pure platinum alternative promises breakthrough in fuel cell technology
By Darren Quick
May 25, 2010
The most obvious obstacles for the widespread adoption of fuel cell technology are cost and performance. Although they promise benefits over internal combustion engines and batteries in terms of environmental impact, they are still fairly limited in use for these reasons. One of the most expensive elements used in most fuel cells is platinum, but now researchers have created a unique core and shell nanoparticle that uses far less platinum, yet performs more efficiently and lasts longer than commercially available pure-platinum catalysts at the cathode end of fuel cell reactions.
The oxygen reduction reaction that takes place at the fuel cell’s cathode creates water as its only waste and it is there that up to 40 percent of a fuel cell’s efficiency is lost. Platinum has been the catalyst of choice for this reaction for many researchers, but it is expensive, and the reaction causes it to break down over time. The core-shell nanoparticle developed by researchers at Brown University and Oak Ridge National Laboratory addresses both of these problems.
The team created a five-nanometer palladium (Pd) core and encircled it with a shell consisting of iron and platinum (FePt). The trick was in molding a shell that would retain its shape and require the smallest amount of platinum to pull off an efficient reaction. The team created the iron-platinum shell by decomposing iron pentacarbonyl and reducing platinum acetylacetonate to result in a shell that uses only 30 percent platinum. Although the researchers say they expect to be able to make thinner shells and use even less platinum.
The researchers demonstrated for the first time that they could consistently produce the unique core-shell structures. In laboratory tests, the palladium/iron-platinum nanoparticles generated 12 times more current than commercially available pure-platinum catalysts at the same catalyst weight. The output also remained consistent over 10,000 cycles, at least ten times longer than commercially available platinum models that begin to deteriorate after 1,000 cycles.
The team created iron-platinum shells that varied in width from one to three nanometers. In lab tests, the group found the one-nanometer shells performed best.
“This is a very good demonstration that catalysts with a core and a shell can be made readily in half-gram quantities in the lab, they’re active, and they last,” said Brown graduate student, Vismadeb Mazumder. “The next step is to scale them up for commercial use, and we are confident we’ll be able to do that.”
Mazumder and Shouheng Sun, professor of chemistry at Brown, are studying why the palladium core increases the catalytic abilities of iron platinum, although they think it has something to do with the transfer of electrons between the core and shell metals. To that end, they are trying to use a chemically more active metal than palladium as the core to confirm the transfer of electrons in the core-shell arrangement and its importance to the catalyst’s function.
The study detailing the researcher’s findings is published in the Journal of the American Chemical Society.