4 January 2024
Nothing works without them: catalysts have a major role to play for the energy transition, for instance for the production of green hydrogen. Using tiny nanoparticles significantly accelerates the reactions taking place in energy converters. The so called metal exsolution offers a way to fabricate such nanoparticles in a direct and very controlled way. Scientists from Forschungszentrum Jülich have now provided a detailed understanding of the processes taking place during this relatively new procedure in the journal Nature Materials, opening new pathways for the development of high-performance catalysts and smart functional materials.
Efficient catalysts are essential for the production of green hydrogen using renewable power from solar or wind generators. Such materials facilitate the chemical reactions that split water molecules into hydrogen and oxygen, thus avoiding substantial energy losses during hydrogen production.
The performance of a catalyst is largely determined by its surface properties. These determined whether water molecules “like“ to adsorb to the surface, disassociate into its constituents or react with other substances. The resulting products, for instance, hydrogen or chemical precursors for synthetic fuels, can be used to chemically store renewable energy and improve sector coupling.
The relevant electrochemical interface, where the catalyst surface is in contact with reactants such as water, is extremely thin and must be designed with care. Metal exsolution is a solid-state reaction where metallic nanoparticles segregate from a functional oxide, which enables tailored design of catalyst particles on an atomic level. Using this method, nanoscaled building blocks of various material classes can be combined to three-dimensional structures with high precision. This approach therefore offers promising possibilities for the development of catalysts based on abundant metals, eliminating the need for expensive and hard to come by noble metals.
Metals exsolution permits precise control of nanoparticle size, density and distribution on the surface of a functional oxide. With this self-sustained method, the metallic nanoparticles form complex structures in conjunction with the functional oxide. The process is driven by a heat treatment of a reducible metal oxide dispersed throughout a functional material. Metal ions diffuse to the surface of the oxide, where they are chemically reduced at elevated temperatures to form nanosized catalysts.
To date, the complex reactions taking place during this process are described in an inconsistent manner necessitating different explanatory approaches. A mechanistic breakthrough was recently achieved at Forschungszentrum Jülich, enabled by the synergy of expertise of the Institute of Energy- and Climate Research (IEK-1) and Peter Grünberg Institute (PGI-7). In the framework of a collaborative doctoral project funded directly by the board of directors, the research teams around energy researcher Dr. Christian Lenser (IEK-1) and materials physicist Dr. Felix Gunkel (PGI-7), in collaboration with Charles University in Prague, where able to elucidate fundamental processes during the formation of the nanoparticles. Lead author and laureate of the prestigious Jülicher Exzellenzpreis Dr. Moritz L. Weber was able to develop and experimentally verify a model that illustrates how the properties of the nanoparticles depend on the electrostatic interaction with the underlying functional material.
The article published in Nature Materials represents a significant improvement in the understanding and degree of control of nanoparticles in catalysts specifically in high-temperature fuel and electrolysis cells, which deliver the highest efficiencies among such devices. These results provide a new and improved understanding of the reaction dynamics and, through control of the surface properties, pave the way for the development of catalysts on the basis of perovksites – an important material class used as versatile materials in research on nanoelectronic, spintronics and further energy technologies.
Weber, M.L., Šmíd, B., Breuer, U. et al.
Space charge governs the kinetics of metal exsolution
Nature Materials (2024), DOI: 10.1038/s41563-023-01743-6
