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Projekt Druckansicht

Nanoskalige Pt Legierungselektrokatalysatoren mit definierter Morphologie: Synthese, Electrochemische Analyse, und ex-situ/in-situ Transmissionselektronenmikroskopische (TEM) Studien

Fachliche Zuordnung Herstellung und Eigenschaften von Funktionsmaterialien
Physikalische Chemie von Festkörpern und Oberflächen, Materialcharakterisierung
Förderung Förderung von 2014 bis 2022
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 257727131
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

Developments in fuel cell technology are of great importance for future energy conversion and storage applications. Proton exchange membrane (PEM) fuel cells are attracting particular interest as clean power sources for mobile and stationary devices. A big obstacle that currently limits their performance is the sluggish oxygen reduction reaction (ORR) at fuel cell cathodes. Due to the exceptionally high ORR activity of the Pt3Ni (111) surface, (111)-faceted octahedral Pt-Ni nanoparticles have been considered the ultimate “dream electrocatalysts”. However, one major drawback in the application of octahedral Pt-Ni nanoparticles as ORR catalysts is the limited long-term stability. The goal of this DFG project was to overcome these drawbacks using new synthetic strategies, surface doping of the octahedral Pt-Ni particles with additional elements like Mo or Rh, as well as post-synthesis thermal-treatments for the purpose of improving the activity and stability of shaped Pt-Ni-alloy-based catalysts. A further aim was to gain deeper understanding in the structural evolutions during post-synthesis heat-treatment of multi-metallic surface-doped octahedral Pt-Ni nanoparticles. We combined state of the art atomic-scale structural and compositional analysis by aberration corrected analytical electron microscopy (ER-C, Heggen group) with advanced materials synthesis (TU-B, Strasser group) to ensure the high quality of the synthesized material. Furthermore, electrochemical activity and stability test (TU-B, Strasser group) were performed and closely linked with the atomic-scale microstructural investigation (ER-C, Heggen group) of the nanoparticle evolution and degradation during electrocatalysis. Methodologically, we have combined iterative synthesis (TU-B, Strasser group), electrochemical measurements (TU-B, Strasser group) and state-of-the-art ex-situ, identical-location (IL), in-situ, and operando analytical high-resolution scanning transmission electron microscopy (STEM) in combination with X-Ray spectroscopy (EDX) (ER-C, Heggen group). A new synthetic control strategy to obtain NPs with larger edge lengths (up to 14 nm) and higher Ni content was developed based on a robust yet tunable one-pot synthesis strategy. Surface Modoped monodisperse octahedral Pt-Ni nanoparticles and reference binary octahedral Pt-Ni nanoparticles were produced. Furthermore, a different synthesis strategy, using depressurization of a sealed pressure flask was developed and served as a new method to broaden the size window and also to control the atomic structure of the catalyst surface. The relationship between synthesis, particle size, composition, and catalytic ORR reactivity of ternary Mo-doped octahedral PtNi electrocatalysts was investigated. The addition of Mo in a one-step colloidal synthesis of octahedral PtNi nanocatalysts with high Ni-content promotes the shape stability during the potential sweeping as confirmed by post-mortem STEM-EDX analysis. The Ni-rich Mo-doped nanocrystals have a high residual activity, much higher compared to the original activity of the undoped Ni-rich octahedral PtNi catalyst. In addition, we have conducted a synthesis-structure-activity study of previously unexplored Nirich quaternary Mo- and Rh-doped Pt-Ni-alloy-based electrocatalysts. This catalyst family exhibited unusually high ORR performance and high electrochemical stability compared to a reference Ni-rich binary PtNi catalyst and also offers advantages over their ternary counterparts. Octahedral PtNi, PtNiMo and PtNiMoRh nanoparticles were furthermore investigated using in-situ electron microscopy in vacuum and under H2 atmosphere to track their morphological and compositional changes during thermal annealing. It was clearly shown that surface-doping with Mo or Mo/Rh improves morphological shape stability upon thermal treatment. The main goals of the project, to attain methodological and conceptual advances in the analysis and description of surface-doped octahedral shaped PtNi nanoparticles, in particular related to their synthesis, post-synthesis treatment, electrochemical test, combined with ex-and in-situ high resolution electron microscopy characterization were successfully reached. These results could facilitate the use of a new class of large, well defined, active and stable surface-doped and postsynthesis treated optimized catalysts for use in PEM fuel cell cathodes.

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