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Helmholtz Earth & Environment DataHub
No full textThe digital ecosystem of the Helmholtz Earth & Environment DataHub features fully automatic ingestion technologies for time series data, joint data interfaces, such as the OGC SensorThings API, a joint metadata schema and powerful clients, such as the Earth Data Portal
13CFLUX — Third-generation high-performance engine for isotopically (non)stationary 13C metabolic flux analysis
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Functional Materials, Degradation Phenomena, and Operating Parameters for CO2 Electrolysis
No full textInvestigation of 2D materials using low energy electron microscopy (LEEM)
No full textLow-energy electron microscopy (LEEM) is a versatile and powerful surface science tool for imaging, structural analysis and the study of kinetic surface processes such as molecular island growth, thin film growth and surface reconstruction. It uses electrons with kinetic energies below a few hundred electronvolts, often below 10 eV. In this thesis, LEEM serves as the main technique to support our research efforts in fabricating 30◦-twisted bilayer graphene (TBG) and in studying the deposition and degradation behavior of a cyclic, tire-shaped molecules on a metal crystal. The first two topics of this thesis build on previous work from our group that demonstrated the epitaxial growth of unconventionally oriented monolayer graphene on a 6H-SiC(0001) substrate. In the first topic, LEEM and other investigation methods were used to characterize the morphology and electronic properties of such unconventionally oriented monolayer graphene. The effect of the preparation temperature on the resulting graphene sample was highlighted. In the second topic, we achieved and studied bilayer stacking and twist configurations of graphene by hydrogen intercalation of the carbon buffer layer, an intrinsic component between the epitaxial graphene and the SiC substrate. Hydrogen atoms were successfully introduced to decouple the buffer layer from the substrate. The buffer layer was transformed into a true graphene layer with distinct π-band properties. This intercalation process was carried out in a stepwise manner, with LEEM being used to study each step. The deintercalation process was monitored in situ and in real time. This provided deeper insights into the mechanisms of hydrogen intercalation and deintercalation. In the third topic of the thesis, the deposition behavior of a carbon-based cyclic aromatic molecule, [6]-cycloparaphenylenes, is investigated using LEEM in addition to pristine 2D graphene layers. Interestingly, our observations contradict previous results obtained by scanning tunneling microscopy. This provides new insights into the deposition behavior of this type of molecules on surfaces
Numerical simulations of colliding rings using PEPC-DVH, the 3D extension of Diffused Vortex Hydrodynamics
No full textA three-dimensional extension of the Diffused Vortex Hydrodynamics (DVH), called PEPC-DVH, was a recently developed as a frontend to the open-source code PEPC, the Pretty Efficient Parallel Coulomb solver [1]. DVH is a vortex particle method developed in-house in a 2D framework and widely validated [2], whereas the PEPC engine for multi-body interaction is based on a parallel Barnes–Hut tree code [3]. The time integration is carried out using the Chorin decomposition: an inviscid advection is followed by a steady diffusion. A superposition of elementary heat equation solutions in a cubic support is performed during the diffusion step. This redistribution avoids excessive clustering or rarefaction of vortex particles, providing robustness and high accuracy to the method. The new PEPC-DVH code was used to simulate free vorticity dynamics. In particular, the collision of two identical viscous vortex rings, starting in a side-by-side configuration, is investigated. The Reynolds number considered, calculated as the ring circulation over the viscosity, spans from 577 to 1153, in agreement with the numerical simulations of Kida et al. [4]. Differently from the literature, where a spectral method was adopted for simulations with about 250,000 grid points, the exploitation of vortex method abilities allow us to follow the rings interaction at high resolution and to preserve the whole vortex wake. A final amount of about 150 Millions of vortices was used for achieving the same final time considered in literature. Bridging and second reconnection are correctly captured and comparisons are offered in terms of vorticity fields and global quantities, like the time evolution of the circulation around the vortex core. Heuristic convergence measurements were also performed, by considering the conservation of prime integrals and the energy–enstrophy balance. Finally, a new algorithm for a multi-resolution strategy, embedded in PEPC-DVH, is introduced. The multi-resolution is obtained by means of a multi-layered distribution of vorticity, which guarantees higher resolution where particles at higher vorticity are found. Low vorticity particles are interpolated on a sparser grid-level, maintaining the same global circulation and ensuring compliance with Kelvin's circulation theorem. This strategy functions similarly to an Automatic Mesh Refinement (AMR) algorithm but eliminates the complexity of constructing a hash table as required in that approach
Anode catalyst layer composition for PEM Electrolysis: An in-depth electrochemical analysis
No full textProton exchange membrane (PEM) water electrolysis is a technology for large-scale hydrogen production.[1,2] The oxygen evolution reaction (OER) at the membrane electrode assembly (MEA) is the rate determining step dominating the overall cell performance. The choice of the OER catalyst and deposition procedure significantly affect the reaction kinetics, chemical stability and electronic conductivity.[3] To maintain a high and long-term consistent cell performance, manufacturing and performance control of the MEA is indispensable.Electrochemical analysis is a powerful tool for MEA evaluation providing information about catalytic activity, kinetics and electrochemically active surface area (ECSA). In addition, scanning electrochemical microscopy and eddy current measurements give insights into the micro- and macroscopic homogeneity of catalyst layers and MEAs.[4,5]In this study, we clarify the significance of electronic conductivity focusing on Ir-based anodes of customized MEAs. The effect of catalyst material and loading on the in-plane MEA resistance, OER performance and ECSA was investigated.Funding: This work was financially supported by the Bundesministerium für Bildung und Forschung (BMBF): Wasserstoff - Leitprojekt H2Giga, Teilvorhaben DERIEL (project number 03HY122C), SEGIWA (project number 03HY121B).[1] A. S. Aricò et al (2013) Appl. Electrochem. 43 107, DOI 10.1007/s10800-012-0490-5[2] T. Wang et al (2022) Carbon Neutr. 1 21, DOI 0.1007/s43979-022-00022-8[3] S. Mo et al (2023) Electrochem. Energy Rev. 6 28, DOI 0.1007/s41918-023-00190-w[4] D. Polcari et al (2016) Chem. Rev. 116 13234, DOI 10.1021/acs.chemrev.6b00067[5] G. Belkacem et al (2024) 24 1629, DOI 10.3390/s2405162
