New class of catalysts for energy conversion

The research team describes their uncommon electrocatalytic working principles as well as their potential for systematic application in the journal ACS Energy Letters from 17. April 2019.

Material libraries for electrocatalysis research

The material class of high entropy alloys features 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," explains 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. "Very limited research has as yet been conducted into the usage of such materials in electrocatalysis," says Ludwig.

Manipulating individual reaction stages

This is expected to change in the near future. The researchers have postulated that the unique interactions of different neighbouring 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," says Tobias Löffler, PhD researcher at the Center for Electrochemical Sciences at the RUB Chair of Analytical Chemistry. "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."

Foundation for ongoing research

In order 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," supposes Professor Wolfgang Schuhmann, Chair of Analytical Chemistry at RUB.

Visualisation in 3D

The characterisation of catalyst nanoparticles, too, is conducive to research. "In order to gain an indication of how, exactly, the activity is affected by the structure, high-resolution visualisation of the catalyst surface on the atomic level is a helpful tool, preferably in 3D," says Professor Christina Scheu from Max-Planck-Institut für Eisenforschung in Düsseldorf. Researchers have already demonstrated that this is an attainable goal -- if not yet applied to this class of catalysts.

The question if such catalysts will facilitate the transition to sustainable energy management remains to be answered. "With our studies, we intend to lay the foundation for ongoing research in this field," conclude the authors.

Funding

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.