Noble metal-free catalyst system as active as platinum

Affordable high-performance catalysts have come within reach.

Noble metal-free catalyst system as active as platinum
The team Tobias Löffler, Alan Savan, Alfred Ludwig, and Wolfgang Schuhmann (from the left) in the laboratory RUB, Kramer©

The industry has been traditionally deploying platinum alloys as catalysts for oxygen reduction, which is for example essential in fuel cells or metal-air batteries. Expensive and rare, that metal imposes strict restrictions on manufacture. Researchers at Ruhr-Universität Bochum (RUB) and Max-Planck-Institut für Eisenforschung have discovered an alloy made up of five elements that is noble metal-free and as active as platinum. They published their paper in the journal Advanced Energy Materials on October 21, 2018.

New neighbors form active centers
The catalytic properties of non-noble elements and their alloys are usually rather poor. To the researchers’ surprise, one alloy made up of five almost equally balanced components offers much better properties. This is because of the so-called high entropy effect. It causes multinary alloys to maintain a simple crystal structure.

“Through the interaction of different neighboring elements, new active centers are formed that present entirely new properties and are therefore no longer bound to the limited properties of the individual elements,” explains Tobias Löffler, Ph.D. student at the RUB Chair of Analytical Chemistry – Center for Electrochemical Sciences headed by Professor Wolfgang Schuhmann. “Our research has demonstrated that this alloy might be relevant for catalysis.”

Generating alloy nanoparticle libraries
Searching for an alternative to platinum, researchers at the RUB Chair of Materials for Microtechnology headed by Professor Alfred Ludwig deployed a special method to generate an alloy nanoparticle library of five source elements. Their atoms blend in plasma and form nanoparticles in a substrate of an ionic liquid. The liquid is placed in small cavities on a carrier.

If the nanoparticles are located in the vicinity of the respective atom source, the percentage of atoms from that source is higher in the respective particle. In the center of the carrier, all five elements are present in more or less equal quantities. “This combinatorial process enables us to precisely control the composition of the alloy nanoparticles anywhere in the material library,” says Alfred Ludwig.

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