Zusammensetzung und Struktur von nanoporösem Au entlegiert aus AuAg und AuCu
Zusammenfassung der Projektergebnisse
The project aimed at the characterization of NPG samples obtained by corrosion of AuAg, AuCu and AuAgCu alloys by electron microscopy. It was intended to contribute to the understanding of the high catalytic activity of NPG and to the development of a reproducible sample preparation protocol. Regarding the objectives, several questions were answered. We contributed to the reproducibility of NPG samples dealloyed from AuCu alloys by identifying reasons for only partial corrosion. For this purpose, we investigated the chemical composition and the crystal structure in partially dealloyed NPG-Cu and NPG-Ag and identified the formation of Cu-oxides, different crystal phases in the master alloy and the formation of a Au-rich layer at the interface between porous material and uncorroded master alloy as the major reasons to be avoided for a reproducible sample preparation. The structure and chemical composition of alloy nanoparticles before and after dealloying was investigated. This was done by analysis of sample series in which the preparation protocols for alloy particle formation and particle dealloying were varied. In a sample with different particle structures the threedimensional structure of the particles was measured by STEM tomography. A correlation between content of residual Ag left in the particles after dealloying and particle structure was found. The tortuosity of the particles was determined in order to find the effective elongation of paths through the porous medium for atoms or molecules in catalysis applications. Results were correlated with PFG NMR diffusion measurements and contributed to the identification of bottlenecks in catalysis. Three-dimensional measurements of atom positions for measurements of strain and the determination of low-coordinated surface atoms as intended were not possible because the microscope which was required for the measurements was delivered too late. For this reason, another method for measurement of strain in planes perpendicular to the electron beam direction was investigated and further improved. The influence of lens aberrations on measurement of strain was determined and a method for the minimization of this influence was developed. The precision of the measurement was improved by using condenser apertures with a dedicated shape. In another work the accuracy of the method at interfaces between regions with different strain was enhanced. Initially, it was intended to investigate the morphology of NPG powder which was decorated with Cu by UPD. As the sample preparation process turned out to be challenging for the NPG powder, we did not arrive at investigating the samples with Cu UPD. However, we were able to show that the structure of NPG powder is unaltered compared to the structure of bulk NPG. For this reason, electrochemical results obtained with NPG powder electrodes are representative for bulk NPG. Concluding, we addressed all objectives of the proposal and investigated them as intended if possible. Objectives that were not possible to investigate primarily due to the delayed delivery of the new microscope are not answered yet, but alternative research heading towards a similar direction was performed. Results were published in ten peer-reviewed articles, two further publications are in preparation. Findings were presented further on national and international conferences.
Projektbezogene Publikationen (Auswahl)
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Nanoporous gold dealloyed from AuAg and AuCu: Comparison of structure and chemical composition. Materialia, 2(c(2018, 10)), 131-137.
Mahr, Christoph; Schowalter, Marco; Mitterbauer, Christoph; Lackmann, Anastasia; Fitzek, Lisa; Mehrtens, Thorsten; Wittstock, Arne & Rosenauer, Andreas
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Electron Bessel beam diffraction for precise and accurate nanoscale strain mapping. Applied Physics Letters, 114(24).
Guzzinati, Giulio; Ghielens, Wannes; Mahr, Christoph; Béché, Armand; Rosenauer, Andreas; Calders, Toon & Verbeeck, Jo
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Influence of distortions of recorded diffraction patterns on strain analysis by nano-beam electron diffraction. Ultramicroscopy, 196(c(2019, 1)), 74-82.
Mahr, Christoph; Müller-Caspary, Knut; Ritz, Robert; Simson, Martin; Grieb, Tim; Schowalter, Marco; Krause, Florian F.; Lackmann, Anastasia; Soltau, Heike; Wittstock, Arne & Rosenauer, Andreas
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Accurate measurement of strain at interfaces in 4D-STEM: A comparison of various methods. Ultramicroscopy, 221(c(2021, 2)), 113196.
Mahr, Christoph; Müller-Caspary, Knut; Grieb, Tim; Krause, Florian F.; Schowalter, Marco & Rosenauer, Andreas
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Quantitative 3D Characterization of Nanoporous Gold Nanoparticles by Transmission Electron Microscopy. Microscopy and Microanalysis, 27(4), 678-686.
Mahr, Christoph; Dworzak, Alexandra; Schowalter, Marco; Oezaslan, Mehtap & Rosenauer, Andreas
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Investigation of the dealloying front in partially corroded alloys. Materials Research Letters, 10(12), 824-831.
Mahr, Christoph; Tapia Burgos, Jorge Adrian; Schowalter, Marco; Wittstock, Arne & Rosenauer, Andreas
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New Perspectives for Evaluating the Mass Transport in Porous Catalysts and Unfolding Macro- and Microkinetics. Catalysis Letters, 153(11), 3405-3422.
Wild, Stefan; Mahr, Christoph; Rosenauer, Andreas; Risse, Thomas; Vasenkov, Sergey & Bäumer, Marcus
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Promoting Effect of the Residual Silver on the Electrocatalytic Oxidation of Methanol and Its Intermediates on Nanoporous Gold. ACS Catalysis, 12(8), 4415-4429.
Silva Olaya, Alex Ricardo; Kühling, Franziska; Mahr, Christoph; Zandersons, Birthe; Rosenauer, Andreas; Weissmüller, Jörg & Wittstock, Gunther
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Towards the interpretation of a shift of the central beam in nano-beam electron diffraction as a change in mean inner potential. Ultramicroscopy, 236(c(2022, 6)), 113503.
Mahr, Christoph; Grieb, Tim; Krause, Florian F.; Schowalter, Marco & Rosenauer, Andreas
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Nanoporous Gold: From Structure Evolution to Functional Properties in Catalysis and Electrochemistry. Chemical Reviews, 123(10), 6716-6792.
Wittstock, Gunther; Bäumer, Marcus; Dononelli, Wilke; Klüner, Thorsten; Lührs, Lukas; Mahr, Christoph; Moskaleva, Lyudmila V.; Oezaslan, Mehtap; Risse, Thomas; Rosenauer, Andreas; Staubitz, Anne; Weissmüller, Jörg & Wittstock, Arne
