In a recent Nature Chemistry paper, the researchers reveal the mechanism that makes this catalyst more active than regular platinum. By studying how x-ray beams are scattered by the new catalyst, they discovered that the distance between the platinum atoms that are left on the surface of the nanoparticles is less than the distance in pure platinum nanoparticles. A good catalyst should be able to split up oxygen molecules into atoms but should not bind too strongly with the free atoms; the shorter distance between platinum atoms in the new material makes it a more effective catalyst because it binds even more weakly with the oxygen atoms.
There are alternatives to using platinum as a catalyst. Dodelet and his group have worked with General Motors to develop a promising iron-based catalyst that they are now working to commercialize. Meanwhile, low-cost carbon nanotube catalysts and nickel catalysts are in the works for alkaline fuel-cell chemistries.
Platinum-free catalysts have advantages other than their low cost, says Liming Dai, a materials engineering professor at the University of Dayton, in Ohio, who is working on carbon nanotube catalysts. Platinum nanoparticles tend to lose their catalytic efficiency by aggregating into larger particles over time or when carbon monoxide sticks to their surface. Carbon nanotubes are more robust in the long-term, Dai says.
“This is interesting work and an important advance because the mechanism could be applied to other catalysts,” Dai says of the new platinum catalyst. “It would be interesting to check out the long-term stability and carbon monoxide [surface] poisoning effect for this kind of core-shell catalyst.”
Strasser agrees that the new catalyst will need further testing. However, the larger size of the core-shell particles makes them intrinsically more stable than pure platinum, he says. The choice of this metal also makes a difference. “We are confident that alternative non-platinum metals in the core, like cobalt or nickel, will solve the stability problem while maintaining the activity advantage of the core-shell structure,” Strasser says.
The new material has also been tested in working fuel cells, which could be a crucial market advantage. “Most of these other catalysts were measured in electrochemical measurements,” he says. “They have potential for use in the future, but this [new catalyst] is something we have that you can put in real fuel cells today.”