Researchers from Chalmers University of Technology and Technical University of Denmark have shown that thin alloy films of single-target co-sputtered platinum-yttrium exhibit up to 7x higher specific activity (13.4 ± 0.4 mA cm−2) for the oxygen reduction reaction (ORR) in fuel cells than polycrystalline platinum, and up to one order of magnitude higher mass activity (3.5 ± 0.3 A mg−1) than platinum nanoparticles.
These nanoalloys have the highest reported ORR activity for an as-deposited material—i.e., without any additional chemical or thermal treatment. The films also show an improvement in stability over the same materials in nanoparticulate form. In a paper published in the journal Advanced Materials Interfaces, the researchers suggest that their results open new possibilities for the preparation of platinum-rare earth metal alloy catalysts in commercial devices.
Physical characterization shows that the thin films form a platinum overlayer supported on an underlying alloy. The high activity is likely related to compressive strain in that overlayer, the researchers suggest. In addition to enabling a significant reduction in the need for platinum in fuel cells, the technology is also well suited for mass production as sputtering can be used to mass-produce the nanoalloy materials.
With our method, only one tenth as much platinum is needed for the most demanding reactions. This can reduce the amount of platinum required for a fuel cell by about 70%. Hopefully, this will allow fuel cells to replace fossil fuels and also be a complement to battery-powered cars.—Björn Wickman, researcher at the Department of Physics at Chalmers
If this level of efficiency is possible to achieve in a fuel cell, the amount of required platinum would be comparable to what is used in an ordinary car catalytic converter.
The catalysts in today’s fuel cells require large amounts of platinum, which is one of the world’s most expensive metals. Previous research has shown that it is possible to mix platinum with other metals, such as yttrium, to reduce the amount of platinum in a fuel cell. However, no one has yet managed to create alloys with these metals in nanoparticle form in a manner that can be used for large-scale production. The major problem has been that yttrium oxidizes instead of forming an alloy with the platinum.
The researchers solved the problem by combining the metals in a vacuum chamber using a technique called sputtering. The result is a nanometer-thin film of the new alloy that allows mass-produced platinum and yttrium fuel cell catalysts.
To use the new material, today’s fuel cells need to change slightly, but doing so creates incredible opportunities.
N. Lindahl, E. Zamburlini, L. Feng, H. Grönbeck, M. Escudero-Escribano, I. E. L. Stephens, I. Chorkendorff, C. Langhammer, B. Wickman (2017) “High Specific and Mass Activity for the Oxygen Reduction Reaction for Thin Film Catalysts of Sputtered Pt3Y” Adv. Mater. Interfaces doi: 10.1002/admi.201700311