Exploring phase stability in multinary intermetallic nanoparticles and films by comparative sputtering in ionic liquids and on solid substrates, and analysis by advanced transmission electron microscopy and electrochemical measurements

• Applicants: Professor Dr.-Ing. Alfred Ludwig; Professorin Dr. Christina Scheu
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 320295168

This project builds up on the results of its predecessor project “Exploring Multinary Nanoparticles by Combinatorial Sputtering into Ionic Liquids and Advanced Transmission Electron Microscopy” (DFG projects LU1175/23-1 and SCHE 634/21-1) with the aim to further enhance the knowledge about multinary nanoparticles synthesized by (co-)sputtering into ionic liquids in comparison to thin films grown on solid substrates employing the same sputter deposition chamber and parameters. Special emphasis is laid on multinary intermetallic (Fe-Co-Ni)(Pt,Pd) systems in their equilibrium ordered crystal structure in comparison to their non-equilibrium solid solution counterparts with the same chemical composition as this offers unique opportunities to understand the influence of order/disorder on electrochemical performance and stability. By the application of versatile sputter techniques like high-power impulse magnetron sputtering new capabilities of influencing the nanoparticle formation and their phase constitution, crystal structures and composition might become possible in comparison to direct current sputtering used in the predecessor project which appeared to be limited to bulk-miscible elements. We also want to explore whether we can obtain the same crystal structure and composition of the nanoparticles and thin films which, with direct current sputtering, was not possible. The nanoparticles typically adopted the equilibrium crystal structure and composition according to the bulk phase diagram while the thin films grew with a non-equilibrium structure and required annealing to reach the equilibrium state. The advantage of achieving comparable structure and composition for nanoparticles and thin films is immense as screening via material libraries is easier for thin films. The main focus is laid on the synthesis of multinary (Fe-Co-Ni)(Pt,Pd) intermetallic systems with high catalytic activity for the oxygen reduction reaction or hydrogen evolution reaction and stability during electrochemical load. Besides the composition, the crystal structure (solid solution versus ordered phases) and the crystallinity itself (amorphous versus short range order versus crystalline) are most likely tuneable when applying high-power impulse magnetron sputtering and by annealing treatments. The most active systems will be investigated in depth using advanced aberration corrected high-resolution scanning transmission electron microscopy, including various high-resolution imaging techniques, tomography, energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. In addition, the most interesting nanoparticles will be extracted from the ionic liquid and be studied at identical location with scanning transmission electron microscopy before and after several thousand cyclic voltammetry measurements to investigate their (in-)stability and identify at the atomic scale reasons for example for dissolution.

• DFG Programme: Research Grants