TY - JOUR A1 - Grothausmann, R. A1 - Manke, I. A1 - Zehl, G. A1 - Dorbandt, I. A1 - Bogdanoff, P. A1 - Fiechter, S. A1 - Hentschel, Manfred P. A1 - Lange, Axel A1 - Kupsch, Andreas A1 - Hilger, A. T1 - Charakterisierung von Katalysatormaterialien für Brennstoffzellen mittels Elektronentomografie JF - MP materials testing N2 - Zur Optimierung moderner Katalysatoren für Brennstoffzellen werden diese elektronen-tomografisch charakterisiert. Die Elektronentomografie ermöglicht einzigartige Einblicke in die Nanometer-Strukturen der metallischen Katalysatorpartikel, die auf einem elektrisch leitenden, inerten Kohlenstoffträger abgeschieden werden. Die dreidimensional bildgebende Methode ermöglicht über qualitative Untersuchungen hinaus detaillierte quantitative Form- und Strukturanalysen der Katalysatormaterialien. So werden beispielsweise die Positionen der Katalysatorpartikel relativ zum Trägermaterial analysiert. Ihre Form und Einbettung in den Träger, welche die für die katalytische Reaktion maßgebliche "freie Oberfläche" definieren, werden bestimmt. Die Elektronentomografie ermöglicht somit quantitative Vergleiche zwischen verschiedenen Katalysatormaterialien und Herstellungsverfahren. Sie erweitert die Möglichkeiten der Korrelation gewünschter elektrochemischer Eigenschaften mit der Nanostruktur dieser Materialien und macht so weitere Optimierungen der Katalysatormaterialien möglich. KW - Computed tomography KW - Reconstruction algorithm KW - Electron tomography KW - Catalyst KW - Fuel cell PY - 2010 SN - 0025-5300 VL - 52 IS - 10 SP - 706 EP - 711 PB - Hanser CY - München AN - OPUS4-22072 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grothausmann, R. A1 - Zehl, G. A1 - Manke, I. A1 - Fiechter, S. A1 - Bogdanoff, P. A1 - Dorbandt, I. A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Schumacher, G. A1 - Banhart, J. T1 - Quantitative structural assessment of heterogeneous catalysts by electron tomography JF - Journal of the American chemical society N2 - We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells. KW - Electron tomography KW - Reconstruction algorithm KW - Catalyst KW - Fuel cell PY - 2011 DO - https://doi.org/10.1021/ja2032508 SN - 0002-7863 SN - 1520-5126 VL - 133 IS - 45 SP - 18161 EP - 18171 PB - American Chemical Society CY - Washington, DC AN - OPUS4-24833 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kupsch, Andreas A1 - Lange, Axel A1 - Hentschel, Manfred P. A1 - Manke, I. A1 - Kardjilov, N. A1 - Arlt, Tobias A1 - Grothausmann, R. T1 - Rekonstruktion limitierter CT-Messdatensätze von Brennstoffzellen mit Directt JF - MP materials testing N2 - Die Aufklärung spezifischer Fragestellungen zur Funktionalität von PEM(polymer electrolyte membrane)- und DMFC(Direct Methanol)-Brennstoffzellen bedarf der 3D-Abbildung der spezifischen Komponenten mit unterschiedlichen Strahlungsarten: des Wassergehalts in den Flow Fields mit Neutronen, der Katalysator-Alterung in der MEA (membrane electrode assembly) mit Synchrotronstrahlung und der freien (reaktiven) Katalysator-Oberfläche von Nano-Partikeln mit TEM-Elektronen-Tomografie. Diese Messungen im Bereich der mm- bis nm-Skala unterliegen dabei erheblichen Restriktionen: einer ortsabhängigen Verschmierung der Neutronenradiogramme, Manipulatorinstabilitäten der Synchrotronmessungen sowie einer Kombination von Limited-View-Datensätzen, wenigen Projektionswinkeln und teilweiser Nichtdurchstrahlbarkeit in der Elektronen-CT. Die Vorteile eines fortentwickelten Directt-Algorithmus für die Bewältigung dieser Randbedingungen gegenüber gefilterten Rückprojektionen werden aufgezeigt. KW - Computed tomography KW - Reconstruction algorithm KW - Electron tomography KW - Neutron tomography KW - Catalyst KW - Fuel cell PY - 2010 SN - 0025-5300 VL - 52 IS - 10 SP - 676 EP - 683 PB - Hanser CY - München AN - OPUS4-22070 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Manke, I. A1 - Hartnig, C. A1 - Kardjilov, N. A1 - Riesemeier, Heinrich A1 - Goebbels, Jürgen A1 - Kuhn, R. A1 - Krüger, P. A1 - Banhart, J. T1 - In situ synchrotron X-ray radiography investigations of water transport in PEM fuel cells JF - Fuel Cells N2 - Water transport in an operating PEM fuel cell was investigated with synchrotron X-ray radiography with a spatial resolution of 3 µm and a temporal resolution of 5 s. This method allows for the detection of water accumulations with less than 10 µm diameter. We demonstrate that synchrotron X-ray imaging can dramatically expand the possibilities of imaging with high spatial and time resolution, especially as a complement to neutron radiography. Water transport processes from the first appearance of small water accumulations in the gas diffusion layer to their transport into the channel system were analysed in situ. Correlations between local effects such as water formation and operating conditions of the whole system, e.g. power variations, were found. A recently described eruptive water transport mechanism is analysed in detail. KW - Fuel cell KW - Gas diffusion layer KW - Imaging KW - Synchrotron KW - X-ray radiography KW - Two-phase flow KW - Water transport PY - 2010 DO - https://doi.org/10.1002/fuce.200800123 SN - 1615-6846 SN - 1615-6854 VL - 10 IS - 1 SP - 26 EP - 34 PB - Wiley-VCH CY - Weinheim AN - OPUS4-22730 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Menga, D. A1 - Low, J. L. A1 - Li, Y.-S. A1 - Arcon, I. A1 - Koyutürk, B. A1 - Wagner, F. A1 - Ruiz-Zepeda, F. A1 - Gaberscek, M. A1 - Paulus, B. A1 - Fellinger, Tim-Patrick T1 - Resolving the Dilemma of Fe-N-C Catalysts by the Selective Synthesis of Tetrapyrrolic Active Sites via an Imprinting Strategy JF - Journal of the American Chemical Society N2 - Combining the abundance and inexpensiveness of their constituent elements with their atomic dispersion, atomically dispersed Fe−N−C catalysts represent the most promising alternative to precious-metal-based materials in proton Exchange membrane (PEM) fuel cells. Due to the high temperatures involved in their synthesis and the sensitivity of Fe ions toward carbothermal reduction, current synthetic methods are intrinsically limited in type and amount of the desired, catalytically active Fe−N4 sites, and high active site densities have been out of reach (dilemma of Fe−N−C catalysts). We herein identify a paradigm change in the synthesis of Fe−N−C catalysts arising from the developments of other M−N−C single-atom catalysts. Supported by DFT calculations we propose fundamental principles for the synthesis of M−N−C materials. We further exploit the proposed principles in a novel synthetic strategy to surpass the dilemma of Fe−N−C catalysts. The selective formation of tetrapyrrolic Zn−N4 sites in a tailor-made Zn−N−C material is utilized as an active-site imprint for the preparation of a corresponding Fe−N−C catalyst. By successive low- and high-temperature ion exchange reactions, we obtain a phase-pure Fe−N−C catalyst, with a high loading of atomically dispersed Fe (>3 wt %). Moreover, the catalyst is entirely composed of tetrapyrrolic Fe−N4 sites. The density of tetrapyrrolic Fe−N4 sites is more than six times as high as for previously reported tetrapyrrolic single-site Fe−N−C fuel cell catalysts. KW - Fe-N-C catalyst KW - Precious-group metal-free catalyst KW - Tetrapyrrolic active-site KW - Single-site catalyst KW - Fuel cell KW - Carbon materials PY - 2021 DO - https://doi.org/10.1021/jacs.1c04884 SN - 1520-5126 VL - 143 IS - 43 SP - 18010 EP - 18019 PB - American Chemical Society AN - OPUS4-53657 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Trogadas, P. A1 - Cho, J. I. S. A1 - Rasha, L. A1 - Lu, X. A1 - Kardjilov, N. A1 - Markötter, Henning A1 - Manke, I. A1 - Shearing, P. R. A1 - Brett, D. J. L. A1 - Coppens, M. O. T1 - A nature-inspired solution for water management in flow fields for electrochemical devices JF - Energy & Environmental Science N2 - A systematic, nature-inspired chemical engineering approach is employed to solve the issue of flooding in electrochemical devices. The mechanism of passive water transport utilized by lizards living in arid environments is leveraged to design flow-fields with a microchannel structure on their surface, through which capillary pressure rapidly removes the water generated in the electrochemical device. This water management strategy is implemented in proton exchange membrane fuel cells (PEMFCs) with a lunginspired flow-field, which ensures uniform distribution of reactants across the catalyst layer. Jointly, this nature-inspired approach results in flood-free, stable operation at 100% RH and a B60% increase in current (B1.9 A cm-2) and peak power density (B650 mW cm−2) compared to current PEMFCs with a flood-prone, serpentine flow-field (B0.8 A cm-2 and 280 mW cm-2, respectively). This significant advance allows for PEMFC operation at fully humidified conditions. KW - Neutron imaging KW - X-ray tomography KW - Fuel cell PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-596662 DO - https://doi.org/10.1039/d3ee03666a VL - 17 SP - 2007 EP - 2017 PB - Royal Society of Chemistry (RSC) AN - OPUS4-59666 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tötzke, C. A1 - Manke, I. A1 - Hartnig, C. A1 - Kuhn, R. A1 - Riesemeier, Heinrich A1 - Banhart, J. T1 - Investigation of carbon fiber gas diffusion layers by means of synchrotron X-ray tomography JF - ECS transactions N2 - The 3-dimensional spatial distribution of liquid water in different gas diffusion layer (GDL) materials was analyzed using synchrotron X-ray tomography. The capability of the method was demonstrated by virtually separating the GDL components in order to facilitate individual analysis of fiber material, liquid water and gas filled pore spaces. The influence of hydrophobic surface treatment on the water distribution in the GDL was illustrated by analyzing three GDL materials with different degrees of hydrophobicity. In the least hydrophobic sample, liquid water tends to form larger clusters which stretch out about several hundred µm inside the porous GDL. In contrast, only small water clusters were found in the strongly hydrophobic material with high Polytetrafluoroethylene (PTFE)-content as the liquid is partially pressed out of the GDL. Additionally, the influence of fiber orientation on the water distribution in the felt material was demonstrated. KW - Synchrotron X-ray tomography KW - Fuel cell KW - Gas diffusion layer (GDL) materials KW - Analysis of fiber material PY - 2011 DO - https://doi.org/10.1149/1.3635571 SN - 1938-6737 SN - 1938-5862 VL - 41 IS - 1 SP - 379 EP - 386 CY - Pennington, NJ, USA AN - OPUS4-25348 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Y. A1 - Lu, X. A1 - Cho, J.I.S. A1 - Rasha, L. A1 - Whiteley, M. A1 - Neville, T. P. A1 - Ziesche, R. A1 - Kardjilov, N. A1 - Markötter, Henning A1 - Manke, I. A1 - Zhang, X. A1 - Shearing, P. R. A1 - Brett, D. J. L. T1 - Multi-length scale characterization of compression on metal foam flow-field based fuel cells using X-ray computed tomography and neutron radiography JF - Energy Conversion and Management N2 - The mechanical compression of metal foam flow-field based polymer electrolyte fuel cells (PEFCs) is critical in determining the interfacial contact resistance with gas diffusion layers (GDLs), reactant flow and water management. The distinct scale between the pore structure of metal foams and the entire flow-field warrant a multilength scale characterization that combines ex-situ tests of compressed metal foam samples and in-operando analysis of operating PEFCs using X-ray computed tomography (CT) and neutron radiography. An optimal ‘medium’ compression was found to deliver a peak power density of 853 mW/cm². The X-ray CT data indicates that the compression process significantly decreases the mean pore size and narrows the pore size distribution of metal foams. Simulation results suggest compressing metal foam increases the pressure drop and gas velocity, improving the convective liquid water removal. This is in agreement with the neutron imaging results that demonstrates an increase in the mass of accumulated liquid water with minimum compression compared to the medium and maximum compression cases. The results show that a balance between Ohmic resistance, water removal capacity and parasitic power is imperative for the optimal performance of metal foam based PEFCs. KW - Fuel cell KW - Compression effect KW - Metal foam microstructure KW - Neutron radiography KW - X-ray CT PY - 2021 DO - https://doi.org/10.1016/j.enconman.2020.113785 VL - 239 SP - 10 EP - 113785 PB - Elsevier Ltd. AN - OPUS4-53842 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -