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New class of catalysts for energy conversion: complex solid solution (CSS) nanoparticles

Researchers at Ruhr-Universität Bochum (RUB) and Max-Planck-Institut für Eisenforschung in Düsseldorf report on a new class of electrocatalysts that is theoretically suitable for universal use. These high entropy alloy nanoparticles are formed by mixing close to equal proportions of five or more elements, and may push the boundaries of traditional catalysts that have been unsurpassable for decades.

The research team describes the uncommon electrocatalytic working principles as well as the potential for systematic application in a paper in the journal ACS Energy Letters.


Complex solid solution (CSS) nanoparticles [also referred to as high-entropy alloys (HEA)] were recently discovered as efficient electrocatalysts for a variety of reactions. As one of many advantages, they exhibit the potential to replace noble-metal catalysts with multinary combinations of transition metals since they offer formation of new unique and tailorable active sites of multiple elements located next to each other.

—Löffler et al.

CSS or HEA materials feature physical properties that have considerable potential for numerous applications. In oxygen reduction, they have already reached the activity of a platinum catalyst.

At our department, we have unique methods at our disposal to manufacture these complex materials from five source elements in different compositions in form of thin film or nanoparticle libraries.

—Professor Alfred Ludwig from the Chair of Materials for Microtechnology at RUB

The atoms of the source elements blend in plasma and form nanoparticles in a substrate of ionic liquid. 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.

Although very limited research has as yet been conducted into the usage of such materials in electrocatalysis, said Ludwig, this is expected to change in the near future. The researchers have postulated that the unique interactions of different neighboring elements might pave the way for replacing noble metals with equivalent materials.

Our latest research has unearthed other unique characteristics, for example the fact that this class may also affect the interdependencies among individual reaction steps. Thus, it would contribute to solving one of the major problems of many energy conversion reactions, namely otherwise unavoidable great energy losses. The theoretical possibilities seem almost too good to be true.

—Tobias Löffler, PhD researcher at the Center for Electrochemical Sciences at the RUB Chair of Analytical Chemistry

To promote rapid progress, the team from Bochum and Düsseldorf has described its initial findings with the aim of interpreting first characteristic observations, outlining the challenges, and putting forward first guidelines—all of which are conducive to advancing research.

The complexity of the alloy is reflected in the research results, and many analyses will be necessary before one can assess its actual potential. Still, none of the findings to date precludes a breakthrough.

—Professor Wolfgang Schuhmann, Chair of Analytical Chemistry at RUB

The research was funded by the Federal Ministry of Education and Research in the Nemezu project (03SF0497B), by the German Research Foundation in the projects LU1175/23-1 and SCHE634/21-1, and through a Chemiefonds Fellowship by Fonds der chemischen Industrie.


  • Tobias Löffler, Alan Savan, Alba Garzón-Manjón, Michael Meischein, Christina Scheu, Alfred Ludwig, Wolfgang Schuhmann (2019) “Toward a paradigm shift in electrocatalysis using complex solid solution nanoparticles,” ACS Energy Letters doi: 10.1021/acsenergylett.9b00531


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