@article{64182, abstract = {{Overcoming the slow kinetics of the oxygen evolution reaction at the anode is a key challenge for the production of hydrogen via electrolysis. This reaction operates at very positive potentials, where the electrocatalyst is exposed to highly oxidative conditions and prone to potential-dependent transformation of the near-surface region. While substantial evidence for such surface restructuring exists, its extent and relevance for the catalyst’s activity are unclear. We address this topic for the case of Co3O4, one of the best-known electrocatalysts exhibiting surface restructuring, by studies of epitaxial (111)-ordered electrodeposited films with combined operando X-ray surface diffraction and absorption spectroscopy, electrochemical impedance spectroscopy, and electrochemical measurements on rotating disk electrodes. Comparison of the as-prepared and annealed state of the same samples, which both are stable even under long-term oxygen evolution conditions, provides clear insight into the role of surface defects. Our results show that defect-free annealed Co3O4(111) surfaces are structurally stable over a wide potential range and hydroxylate via adsorption at surface oxygen and Co sites. Potential-induced surface restructuring of the Co3O4 lattice occurs only in the presence of surface defects, leading to the formation of the well-known nanometer-thick oxyhydroxide skin layer. The presence of this skin layer promotes oxygen evolution at low overpotentials but results in higher Tafel slopes. As a result, highly ordered Co3O4(111) surfaces are more active at high current densities than defective Co3O4 surfaces that undergo surface restructuring. These results highlight that strategies for catalyst surface defect engineering need to be application-oriented.}}, author = {{Scharf, Carl Hendric and Chandraraj, Alex and Dyk, Konrad and Stebner, Felix and Lepin, Sören and Tian, Jing and El Bergmi Byaz, Laila and Stettner, Jochim and Leppin, Christian and Kotova, Anastasiia and Reinke, Sebastian and Linnemann, Julia and Maroun, Fouad and Magnussen, Olaf M.}}, issn = {{2155-5435}}, journal = {{ACS Catalysis}}, keywords = {{electrocatalysis, oxygen evolution reaction, cobalt spinel, operando characterization}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Role of Defects in Reversible Surface Restructuring and Activity of Co3O4 Oxygen Evolution Electrocatalysts}}}, doi = {{10.1021/acscatal.5c08785}}, year = {{2026}}, } @inproceedings{63754, abstract = {{Data spaces are receiving an emerging interest in Information Systems Research and industry practice. They are central to many European research initiatives and shape the data economy in Industry 4.0. Generally, they aim to create secure environments for cross-organizational data management and sharing. Currently, there is considerable interest in developing new data spaces in Industry 4.0, also accelerated through regulatory changes. However, key questions about what precisely characterizes a data space in Industry 4.0 remain unresolved. Against this backdrop, we build a taxonomy of data spaces in the Industry 4.0 context. We identified nine distinctive dimensions and 40 corresponding characteristics among the 19 data spaces analyzed. The taxonomy enables clearer classification and nomenclature of data spaces in this context. This short paper will ignite planned further research on data spaces in Industry 4.0 and contribute to a conceptualization of a taxonomic theory for interested researchers.}}, author = {{Werth, Oliver and Koldewey, Christian and Uslar, Mathias and Zerbin, Julian}}, booktitle = {{Lecture Notes in Business Information Processing}}, isbn = {{9783032145178}}, issn = {{1865-1348}}, keywords = {{Industry 4.0, Taxonomy, Data spaces, Characterization}}, location = {{Stuttgart, Germany}}, publisher = {{Springer Nature Switzerland}}, title = {{{What Characterizes Data Spaces in Industry 4.0? Towards a Better Understanding}}}, doi = {{10.1007/978-3-032-14518-5_3}}, year = {{2026}}, } @article{61014, abstract = {{To obtain a more comprehensive understanding of the specific properties of complex-shaped technical aerosols—such as partially sintered aggregates formed in combustion processes or structured particles resulting from complex synthesis processes—it is essential to measure more than a single equivalent size. This study examines a novel method for determining a two-dimensional distribution of two distinct particle properties within the size range from 50nm to 1000nm: the Centrifugal Differential Mobility Analyzer (CDMA). The CDMA enables the simultaneous measurement of both mobility and Stokes equivalent diameters, providing a detailed two-dimensional particle property distribution. This, in turn, allows for the extraction of shape-related information, which is essential for characterizing particles in terms of their chemical composition, reactivity, and other physicochemical properties. This paper presents a detailed evaluation of a first CDMA prototype. First, CFD simulations of the flow field within the classifier are presented in order to assess and understand non-idealities arising from the exact geometry. Subsequently, the transfer function is evaluated by particle trajectory calculations based on the simulated flow field. It can be demonstrated that the simulated transfer functions agree quite well with transfer functions derived from streamlines of an ideal flow field, indicating that the non-idealities in the classifying region are almost negligible in their effect on the classification result. An experimental determination of the transfer function shows additional effects not covered by the previous simulations, like broadening by diffusion and losses due to diffusion and precipitation within the in- and outlet of the classifier. Finally, the determined transfer functions are used to determine the full two-dimensional distribution with regard to the mobility and Stokes equivalent diameter of real aerosols, like spherical particles and aggregates at different sintering stages, respectively.}}, author = {{Rüther, Torben Norbert and Gröne, Sebastian and Dechert, Christopher and Schmid, Hans-Joachim}}, issn = {{2674-0516}}, journal = {{Powders}}, keywords = {{centrifugal differential mobility analysis, 2D-measurement, particle characterization, moving reference frame CFD-simulation, transfer function}}, number = {{2}}, publisher = {{MDPI AG}}, title = {{{Centrifugal Differential Mobility Analysis—Validation and First Two-Dimensional Measurements}}}, doi = {{10.3390/powders4020011}}, volume = {{4}}, year = {{2025}}, } @article{61982, abstract = {{Doped Co3O4 nanoparticles are investigated via spectro-electrochemistry in the (pre-) oxygen evolution reaction (OER) regime by tracing the absorption signal of the Co3+ d–d transition under applied bias for getting insight into the catalysts activation and the formation of catalytically active phases. In the low potential regime up to 1.37 VRHE, a rise in the optical absorption signal of the [Co3+]oct d–d transition is observed and attributed to a structural change from [Co2+]tet to [Co3+]oct due to an electrochemically induced surface restructuring with water. For applied potentials higher than 1.37 VRHE an overall offset of the absorption spectra in the UV–vis range, equivalent to a darkening of the materials is detected. This is attributed to the formation of a CoOx(OH)y skin layer as supported by high-energy X-ray diffraction (HE-XRD) measurements. We found that the kinetics of the Co3+ states are heavily influenced by the type of dopant with V-doped Co3O4 exhibiting stable Co3+ states (>20 min) while the Mn-doped Co3O4 Co3+ states reduce within 36 s under reductive bias. We conclude that doping Co3O4 with transition metals affects the formation and potential-dependent thickness of the CoOx(OH)y skin layer as the catalytically active phase and the formation of long-time stable surface Co3+ states after activation in the first OER cycle.}}, author = {{Kampermann, L. and Klein, J. and Wagner, T. and Kotova, A. and Placke-Yan, C. and Yasar, A. and Jacobse, L. and Lasagna, S. and Leppin, Christian and Schulz, S. and Linnemann, Julia and Bergmann, A. and Roldan Cuenya, B. and Bacher, G.}}, issn = {{2155-5435}}, journal = {{ACS Catalysis}}, keywords = {{electrocatalysis, oxygen evolution reaction, cobalt spinel, operando characterization, spectroelectrochemistry}}, number = {{21}}, pages = {{18391--18403}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Operando Analysis of the Pre-OER Activation of Metal-Doped Co3O4 Nanoparticle Catalysts}}}, doi = {{10.1021/acscatal.5c03900}}, volume = {{15}}, year = {{2025}}, } @article{43441, abstract = {{This paper reveals the 3D character of the intermetallic layer at the aluminum–steel interface which pops up above the original sample surface during annealing. Popping out of the intermetallics was proven using atomic force microscopy. The phase expands out of the plane due to the exothermic formation of the Al5Fe2 phase and the feasibility of surface diffusion. Milling by a focused ion beam enabled the comparison of the chemical composition of the surface layer with the bulk interface, showing no difference. The growth direction is both towards aluminum and steel — the main diffusion flux is from aluminum towards steel, and the new intermetallic phase emerges at the steel side. The shortage of Al atoms causes a shift of the intermetallic as a whole towards aluminum.}}, author = {{Šlapáková, Michaela and Kihoulou, Barbora and Veselý, Jozef and Minárik, Peter and Fekete, Klaudia and Knapek, Michal and Králík, Rostislav and Grydin, Olexandr and Stolbchenko, Mykhailo and Schaper, Mirko}}, issn = {{0042-207X}}, journal = {{Vacuum}}, keywords = {{Al-steel clad, twin-roll casting, 3D characterization, atomic force microscopy, diffusion direction, surface growth}}, publisher = {{Elsevier BV}}, title = {{{3D-structure of intermetallic interface layer in Al–steel clad material}}}, doi = {{10.1016/j.vacuum.2023.112043}}, volume = {{212}}, year = {{2023}}, } @article{64045, abstract = {{Abstract In this work, we report on an improved cell assembly of cylindrical electrochemical cells for 23Na in-situ solid-state NMR (ssNMR) investigations. The cell set-up is suitable for using powder electrode materials. Reproducibility of our cell assembly is analyzed by preparing two cells containing hard carbon (HC) powder as working electrode and sodium metal as reference electrode. Electrochemical storage properties of HC powder electrode derived from carbonization of sustainable cellulose are studied by ssNMR. 23Na in-situ ssNMR monitors the sodiation/desodiation of a Na{\textbar}NaPF6{\textbar}HC cell (cell 1) over a period of 22?days, showing high cell stability. After the galvanostatic process, the HC powder material is investigated by high resolution 23Na ex-situ MAS NMR. The formation of ionic sodium species in different chemical environments is obtained. Subsequently, a second Na{\textbar}NaPF6{\textbar}HC cell (cell 2) is sodiated for 11?days achieving a capacity of 220?mAh/g. 23Na ex-situ MAS NMR measurements of the HC powder material extracted from this cell clearly indicate the presence of quasi-metallic sodium species next to ionic sodium species. This observation of quasi-metallic sodium species is discussed in terms of the achieved capacity of the cell as well as of side reactions of sodium in this electrode material.}}, author = {{Šić, Edina and Schutjajew, Konstantin and Haagen, Ulrich and Breitzke, Hergen and Oschatz, Martin and Buntkowsky, Gerd and Gutmann, Torsten}}, issn = {{1864-5631}}, journal = {{Chemsuschem}}, keywords = {{solid-state nmr, hard carbon, electrochemical cells, in-situ characterization, sodium}}, pages = {{e202301300}}, publisher = {{John Wiley & Sons, Ltd}}, title = {{{Electrochemical Sodium Storage in Hard Carbon Powder Electrodes Implemented in an Improved Cell Assembly: Insights from In-Situ and Ex-Situ Solid-State NMR}}}, doi = {{10.1002/cssc.202301300}}, volume = {{17}}, year = {{2023}}, } @article{63920, abstract = {{Coordinatively unsaturated sites (CUS) present a key feature of alumina based catalysts as they are believed to act as Lewis-acid sites in heterogeneously catalyzed reactions. In the present study, the direct observation of active species on a fluoride-doped aluminum oxide catalyst is demonstrated. This new fluoride-doped aluminum oxide exhibits strong Lewis-acid sites and superior catalytic activity as compared to gamma-Al2O3. To emphasize the labile state of Lewis-acid sites, two distinctive states of the catalysts surface are addressed using H-1-Al-27 cross polarization (CP) MAS NMR. On the one hand, the highly dehydrated and active state after calcination at 700 degrees C and on the other hand the rehydrated and catalytically inactive surface (produced by contact to air) are probed. These experiments revealed the presence of significant amounts of coordinatively unsaturated sites in the form of 4-and 5-fold coordinated Al-sites on the highly dehydrated surface. In contrast to this, the rehydrated sample exhibited a severely restructured surface caused by the chemisorption of H2O which is ’constituted in a manner that was proposed in earlier models for gamma-Al2O3 surfaces.}}, author = {{Ahrem, L. and Scholz, G. and Gutmann, Torsten and Calvo, B. and Buntkowsky, G. and Kemnitz, E.}}, issn = {{1932-7447}}, journal = {{Journal of Physical Chemistry C}}, keywords = {{al-27 nmr, characterization, Chemistry, cross-polarization, dynamic nuclear-polarization, eta-alumina, gamma-alumina, hydroxy fluorides, ions, Materials Science, pentacoordinated al3+, Science & Technology - Other Topics, solid-state nmr, spectroscopic, structural insights}}, number = {{22}}, pages = {{12206–12213}}, title = {{{Direct Observation of Coordinatively Unsaturated Sites on the Surface of a Fluoride-Doped Alumina Catalyst}}}, doi = {{10.1021/acs.jpcc.7b02535}}, volume = {{121}}, year = {{2017}}, } @article{6551, author = {{Bause, Fabian and Rautenberg, Jens and Feldmann, Nadine and Webersen, Manuel and Claes, Leander and Gravenkamp, Hauke and Henning, Bernd}}, journal = {{Measurement Science and Technology}}, keywords = {{material characterization, material parameters, acoustic waveguide, daming, ultrasonic transducer}}, number = {{10}}, title = {{{Ultrasonic transmission measurements in the characterization of viscoelasticity utilizing polymeric waveguides}}}, doi = {{10.1088/0957-0233/27/10/105601}}, volume = {{27}}, year = {{2016}}, }