New platinum-cobalt nanocatlysts for fuel cells greatly enhance activity and stability and cut costs
A research team at the Energy Materials Center at Cornell (EMC2) is developing platinum-cobalt nanoparticles with a platinum enriched shell that show improved catalytic activity for the oxygen reduction reaction in fuel-cell applications. The new class of Pt–Co nanocatalysts—composed of ordered Pt3Co intermetallic cores with a 2–3 atomic-layer-thick platinum shell—exhibited a more than 200% increase in mass activity and a more than 300% increase in specific activity when compared with the disordered Pt3Co alloy nanoparticles as well as Pt/C.
The new material could reduce the cost by a factor of five, according to Héctor Abruña, the E.M. Chamot Professor of Chemistry and Chemical Biology, senior author of a paper describing the work published in the journal Nature Materials. The mass activity for the oxygen reduction reaction is the highest among the Pt–Co systems reported in the literature under similar testing conditions, the authors noted. These ordered nanoparticles provide a new direction for catalyst performance optimization for next-generation fuel cells, they suggested.
Stability tests showed a minimal loss of activity after 5,000 potential cycles and the ordered core–shell structure was maintained virtually intact, as established by atomic-scale elemental mapping. The researchers attributed the high activity and stability are attributed to the Pt-rich shell and the stable intermetallic Pt3Co core arrangement.
Previously, the Cornell research team created nanoparticles of a palladium-cobalt alloy coated with a thin layer of platinum that worked like pure platinum at lower cost. Forming the catalyst as nanoparticlesprovides more surface area to react with the fuel.
Deli Wang, a post-doctoral researcher in Abruña's group, devised a new chemical process to manufacture nanoparticles of a platinum-cobalt alloy that included an annealing step in which the randomly distributed atoms in the alloy form an orderly crystal structure. Platinum atoms layered onto these particles line up with the lattice and are pushed closer together than they would be in pure platinum, with the resulting strain enhancing the catalytic activity.
The Energy Materials Center at Cornell is an Energy Frontier Research Center funded by the US Department of Energy.
Deli Wang, Huolin L. Xin, Robert Hovden, Hongsen Wang, Yingchao Yu, David A. Muller, Francis J. DiSalvo & Héctor D. Abruña (2012) Structurally ordered intermetallic platinum–cobalt core–shell nanoparticles with enhanced activity and stability as oxygen reduction . Nature Materials doi: 10.1038/nmat3458