TY - JOUR A1 - Wahl, S. A1 - El-Refaei, S. M. A1 - de Oliveira Guilherme Buzanich, Ana A1 - Amsalem, P. A1 - Lee, K.-S. A1 - Koch, N. A1 - Doublet, M.-L. A1 - Pinna, N. T1 - Zn0.35Co0.65O – A Stable and highly active oxygen evolution catalyst formed by zinc leaching and tetrahedral coordinated cobalt in wurtzite structure JF - Advanced Energy Materials N2 - To arrive to sustainable hydrogen-based energy solutions, the understanding of water-splitting catalysts plays the most crucial role. Herein, state-of-the-art hypotheses are combined on electrocatalytic active metal sites toward the oxygen evolution reaction (OER) to develop a highly efficient catalyst based on Earth-abundant cobalt and zinc oxides. The precursor catalyst Zn0.35Co0.65O is synthesized via a fast microwaveassisted approach at low temperatures. Subsequently, it transforms in situ from the wurtzite structure to the layered γ-Co(O)OH, while most of its zinc leaches out. This material shows outstanding catalytic Performance and stability toward the OER in 1 m KOH (overpotential at 10 mA cm−2 ηinitial = 306 mV, η98 h = 318 mV). By comparing the electrochemical results and ex situ analyses to today’s literature, clear structureactivity correlations are able to be identified. The findings suggest that coordinately unsaturated cobalt octahedra on the surface are indeed the active centers for the OER. KW - Oxygen Evolution Catalyst KW - XAFS KW - Oxygen evolution reaction (OER) KW - Cobalt and zinc oxides PY - 2019 DO - https://doi.org/10.1002/aenm.201900328 SN - 1614-6832 SN - 1614-6840 VL - 9 IS - 20 SP - 1900328,1 EP - 10 PB - WILEY-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-48200 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Baer, Wolfram A1 - Breidung, Marc A1 - Wossidlo, Peter A1 - Wahl, Ken A1 - Gerwien, Peter A1 - Zerbst, Uwe A1 - Madia, Mauro A1 - Küppers, M. ED - Zimmermann, Martina T1 - Gezielte Werkstoffprüfung zur fail-safe-Bauteilauslegung am Beispiel eines Achsschenkels T2 - Werkstoffprüfung 2022 Werkstoffe und Bauteile auf dem Prüfstand, Prüftechnik – Kennwertermittlung – Schadensvermeidung N2 - Bei der Auslegung von Achsschenkeln für Nutzfahrzeuge wird für den Überlastfall ein fail-safe-Kriterium (kontrolliertes Versagen) als Basisphilosophie angesetzt. Gefordert wird, dass sich der Achsschenkel auch unter Akzeptanz begrenzten Risswachstums hinreichend elastisch-plastisch verformen kann, ohne dass es zum Bruch kommt. Der Fahrer soll anschließend anhand der bleibenden Verformungen bemerken können, dass mit seinem Fahrzeug etwas nicht in Ordnung ist. Eine Voraussetzung für dieses Bauteilverhalten ist eine hinreichende Bruchzähigkeit des Werkstoffs. Diese, wie auch die Rissspitzenbeanspruchung, müssen ermittelt werden, um den bruchmechanischen Sicherheitsnachweis führen zu können. Zur Ermittlung der mechanisch-technologischen und bruchmechanischen Werkstoffeigenschaften wurde ein Prüfkonzept entwickelt, bei dem die Proben an der potenziell kritischen Stelle direkt aus den geschmiedeten Achsschenkeln entnommen werden. Die experimentelle Werkstoffcharakterisierung bildet dann die Beanspruchungsbedingungen beim Überlastereignis ab. Im Rahmen der Produktion stehen jedoch nur Kerbschlagarbeitswerte zur Verfügung und aufwändige bruchmechanische Versuche sollen vermieden werden. Deshalb wurde eine Korrelation zur Abschätzung der vorhandenen Bruchzähigkeit aus der Kerbschlagarbeit herangezogen. Es ergibt sich eine Ergebnismatrix, die die Einflussgrößen Versagenswahrscheinlichkeit, Temperatur und Bruchzähigkeit verknüpft. Abschließend wird ein erster Vergleich der abgeschätzten mit den experimentell ermittelten Bruchzähigkeitswerten gezogen. Dieser weist aus, dass die abgeschätzten Werte geringfügig konservativ sind. T2 - 40. Vortrags- und Diskussionstagung Werkstoffprüfung 2022 CY - Dresden, Germany DA - 27.10.2022 KW - Kerbschlagarbeit KW - Achsschenkel KW - Fail-safe KW - Bruchmechanische Auslegung KW - Korrelation PY - 2022 SP - 1 EP - 6 PB - DGM - Deutsche Gesellschaft für Materialkunde e.V. CY - Sankt Augustin AN - OPUS4-56152 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ye, S. A1 - Loll, B. A1 - Berger, A. A1 - Mülow, Ulrike A1 - Alings, C. A1 - Wahl, M. A1 - Koksch, B. T1 - Fluorine teams up with water to restore inhibitor activity to mutant BPTI JF - Chemical Science N2 - Introducing fluorine into molecules has a wide range of effects on their physicochemical properties, often desirable but in most cases unpredictable. The fluorine atom imparts the C–F bond with low polarizability and high polarity, and significantly affects the behavior of neighboring functional groups, in a covalent or noncovalent manner. Here, we report that fluorine, present in the form of a single fluoroalkyl amino acid side chain in the P1 position of the well-characterized serine-protease inhibitor BPTI, can fully restore inhibitor activity to a mutant that contains the corresponding hydrocarbon side chain at the same site. High resolution crystal structures were obtained for four BPTI variants in complex with bovine b-trypsin, revealing changes in the stoichiometry and dynamics of water molecules in the S1 subsite. These results demonstrate that the introduction of fluorine into a protein environment can result in “chemical complementation” that has a significantly favorable impact on protein–protein interactions. KW - serine-protease inhibitor KW - crystal structures KW - Peptide synthesis PY - 2015 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-358987 DO - https://doi.org/10.1039/C4SC03227F IS - 9 SP - 5246 EP - 5254 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-35898 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wahl, S. A1 - El-Refaei, S. M. A1 - Amsalem, P. A1 - de Oliveira Guilherme Buzanich, Ana A1 - Koch, N. A1 - Pinna, N. T1 - Operando diffuse reflectance UV-vis spectroelectrochemistry for investigating oxygen evolution electrocatalysts JF - Catalysis Science & Technology N2 - The characterization of the active structure of water-splitting catalysts is crucial to evolve to a sustainable energy future based on hydrogen. Such information can only be obtained by operando methods. We present a diffuse reflectance UV-vis (DRUV) spectroelectrochemical study that allows tracking the changes of solid oxygen evolution catalysts under working conditions. The versatility of our approach is demonstrated on two cobalt-containing catalysts, Zn0.35Co0.65O and CoAl2O4. The changes the catalysts undergo during the oxygen evolution reaction can be tracked by probing the electronic structure using UV-vis spectroscopy. These findings are compared to ex situ analyses, which support the assignments of the structures stabilized under different potentials. Thus, structure–activity correlations can be proposed, and deeper insights into the catalytically active structures can be obtained. KW - EXAFS PY - 2020 DO - https://doi.org/10.1039/c9cy02329a VL - 10 IS - 2 SP - 517 EP - 528 PB - Royal Society of Chemistry AN - OPUS4-50468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Radunz, Sebastian A1 - Schavkan, A. A1 - Wahl, Sebastian A1 - Würth, Christian A1 - Tschiche, H. R. A1 - Krumrey, M. A1 - Resch-Genger, Ute T1 - Evolution of Size and Optical Properties of Upconverting Nanoparticles during High-Temperature Synthesis JF - Journal of physical chemistry C N2 - We investigated the growth of β-phase NaYF4:Yb3+,Er3+ upconversion nanoparticles synthesized by the thermal decomposition method using a combination of in situ and offline analytical methods for determining the application-relevant optical properties, size, crystal phase, and chemical composition. This included in situ steady state luminescence in combination with offline time-resolved luminescence spectroscopy as well as small-angle X-ray scattering (SAXS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and inductively coupled Plasma optical emission spectrometry (ICP-OES). For assessing the suitability of our optical monitoring approach, the in situ-collected spectroscopic data, which reveal the luminescence evolution during nanocrystal synthesis, were compared to measurements done after cooling of the reaction mixture of the as-synthesized particles. The excellent correlation of the in situ and time-resolved upconversion luminescence with the nanoparticle sizes determined during the course of the reaction provides important insights into the various stages of nanoparticle growth. This study highlights the capability of in situ luminescence monitoring to control the efficiency of UCNP synthesis, particularly the reaction times at elevated temperatures and the particle quality in terms of size, shape, and crystal structure, as well as luminescence lifetime and upconversion quantum yield. KW - Rare earth nanoparticles KW - Upconversion KW - TEM KW - SAXS PY - 2018 UR - https://pubs.acs.org/doi/pdf/10.1021/acs.jpcc.8b09819 DO - https://doi.org/10.1021/acs.jpcc.8b09819 VL - 50 IS - 122 SP - 28958 EP - 28967 PB - American Chemical Society CY - Washington, DC AN - OPUS4-47169 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -