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Gizatullin, Bulat; Mattea, Carlos; Stapf, Siegfried
Radicals on the silica surface: probes for studying dynamics by means of fast field cycling relaxometry and dynamic nuclear polarization. - In: Magnetic resonance letters, ISSN 2772-5162, Bd. 3 (2023), 3, S. 256-265

Determining the dynamics of adsorbed liquids on nanoporous materials is crucial for a detailed understanding of interactions and processes on the solid-liquid interface in many materials and porous systems. Knowledge of the influence of the presence of paramagnetic species on the surface or within the porous matrices is essential for fundamental studies and industrial processes such as catalysts. Magnetic resonance methods, such as electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and dynamic nuclear polarization (DNP), are powerful tools to address these questions and to quantify dynamics, electron-nuclear interaction features and their relation to the physical-chemical parameters of the system. This paper presents an NMR study of the dynamics of polar and nonpolar adsorbed liquids, represented by water, n-decane, deuterated water and nonane-d20, on the native silica surface as well as silica modified with vanadyl porphyrins. The analysis of the frequency dependence of the nuclear spin-lattice relaxation time is carried out by separating the intra- and intermolecular contributions, which were analyzed using reorientations mediated by translational displacements (RMTD) and force-free-hard-sphere (FFHS) models, respectively.



https://doi.org/10.1016/j.mrl.2023.03.006
Zhang, Chenglin; Yan, Chengzhan; Jin, Rui; Hao, Jinhui; Xing, Zihao; Zhang, Peng; Wu, Yuhan; Li, Longhua; Zhao, Huaping; Wang, Shun; Shi, Weidong; Lei, Yong
Weak interaction between cations and anions in electrolyte enabling fast dual-ion storage for potassium-ion hybrid capacitors. - In: Advanced functional materials, ISSN 1616-3028, Bd. 33 (2023), 52, 2304086, S. 1-10

Identifying an effective electrolyte is a primary challenge for hybrid ion capacitors, due to the intricacy of dual-ion storage. Here, this study demonstrates that the electrochemical behavior of graphite oxide in ether-solvent electrolyte outperforms those in ester-solvent electrolytes for the cathode of potassium-ion hybrid capacitor. The experimental and theoretical assessments verify that the anion and cation are isolated effectively in dimethyl ether, endowing a weaker interaction between cations and anions compared to that of ester-solvent electrolytes, which facilitates the dual-ion diffusion and thus enhances the electrochemical performance. This result provides a rational strategy to realize high-rate cations and anions storage on the carbon cathode. Furthermore, a new low-cost and high-performance capacitor prototype, modified graphite oxide (MGO) cathode versus pristine graphite (PG) in ether-solvent electrolyte (MGOǁDMEǁPG), is proposed. It exhibits a high energy density of 150 Wh kg^−1cathode at a high power density of 21443 W kg^−1cathode (calculation based on total mass: 60 Wh kg^−1 at 8577 W kg^−1).



https://doi.org/10.1002/adfm.202304086
Dreßler, Christian; Hänseroth, Jonas; Sebastiani, Daniel
Coexistence of cationic and anionic phosphate moieties in solids: unusual but not impossible. - In: The journal of physical chemistry letters, ISSN 1948-7185, Bd. 14 (2023), 32, S. 7249-7255

Phosphoric acid is commonly known either as a neutral molecule or as an anion (phosphate). We theoretically confirm by ab initio molecular dynamics simulations (AIMD) that a cationic form H4PO4+ coexists with the anionic form H2PO4- in the same salt. This paradoxical situation is achieved by partial substitution of Cs+ by H4PO4+ in CsH2PO4. Thus, HnPO4 acts simultaneously as both the positive and the negative ion of the salt. We analyze the dynamical protonation pattern within the unusual hydrogen bond network that is established between the ions. Our AIMD simulations show that a conventional assignment of protonation states of the phosphate groups is not meaningful. Instead, a better description of the protonation situation is achieved by an efficiently fractional assignment of the strongly hydrogen-bonded protons to both its nearest and next-nearest oxygen neighbors.



https://doi.org/10.1021/acs.jpclett.3c01521
Flecken, Franziska; Knapp, Anna; Grell, Toni; Dreßler, Christian; Hanf, Schirin
Acute bite angle POP- and PSP-type ligands and their trinuclear copper(I) complexes: synthesis and photo-luminescence properties. - In: Inorganic chemistry, ISSN 1520-510X, Bd. 62 (2023), 32, S. 13038-13049

In the current work, the rational synthesis of trinuclear copper complexes, incorporating acute bite angle POP- and PSP-type ligands, is reported. The in situ formation of POP (Ph2P–O–PPh2) or PSP (Ph2P–S–PPh2) ligands in the presence of a copper(I) precursor gave access to various trinuclear copper complexes of the form [Cu3(μ3-Hal)2(μ-PXP)3]PF6 [X = O; Hal = Cl (1), Br (2), I (3) and X = S; Hal = Cl (5), Br (6), I (7)]. Related iodide-containing complexes and clusters, such as [Cu4(μ3-I)4(Ph2PI)4] (4) and [Cu3(μ3-I)2(μ-I)(μ-PSP)2] (8), could also be obtained via the variation of the reaction stoichiometry. The investigation of the photo-optical properties by photo-luminescence spectroscopy has demonstrated that the phosphorescence in the visible region can be switched off through the mere change of the heteroatom in the ligand backbone (POP vs PSP ligand scaffold). Theoretical studies have been conducted to complement the experimental photo-optical data with detailed insights into the occurring electronic transitions. Consequently, this systematic study paves the way for tuning the photo-optical properties of transition metal complexes in a more rational way.



https://doi.org/10.1021/acs.inorgchem.3c01865
Omidian, Maryam; Schulte, Stefan; Néel, Nicolas; Kröger, Jörg
Scanning tunneling spectroscopy of lithium-decorated graphene. - In: Annalen der Physik, ISSN 1521-3889, Bd. 535 (2023), 11, 2300249, S. 1-8

Lithium decoration of graphene on SiC(0001) is achieved in a surface science approach by intercalation and adsorption of the alkali metal. Spectroscopy of the differential conductance with a scanning tunneling microscope at the Li-decorated graphene surfaces does not give rise to a pairing gap at the Fermi energy, which may be expected because of the previously predicted superconducting phase [Profeta et al., Nat. Phys. 2012, 8, 131]. Rather, pronounced gaps in the spectroscopic data of intercalated samples reflect the excitation of graphene phonons. Rationales that possibly explain this discrepancy between experimental findings and theoretical predictions are suggested.



https://doi.org/10.1002/andp.202300249
Ran, Yan; Ren, Jie; Yang, Zhi Chao; Zhao, Huaping; Wang, Yude; Lei, Yong
The 3D flower-like MnV12O31&hahog;10H2O as a high-capacity and long-lifespan cathode material for aqueous zinc-ion batteries. - In: Small structures, ISSN 2688-4062, Bd. 4 (2023), 11, 2300136, S. 1-11

Selecting the right cathode material is a key component to achieving high-energy and long-lifespan aqueous zinc-ion batteries (AZIBs); however, the development of cathode materials still faces serious challenges due to the high polarization of Zn2+. In this work, MnV12O31&hahog;10H2O (MnVO) synthesized via a one-step hydrothermal method is proposed as a promising cathode material for AZIBs. Because the stable layered structure and hieratical morphology of MnVO provide a large layer space for rapid ion transports, this material exhibits high specific capacity (433 mAh g−1 at 0.1 A g−1), an outstanding long-term cyclability (5000 cycles at a current density of 3 A g−1), and an excellent energy density (454.65 Wh kg−1). To illustrate the intercalation mechanism, ex situ X-Ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy are adopted, uncovering an H+/Zn2+ dual-cation co-intercalation processes. In addition, density-functional theory calculation analysis shows that MnVO has a delocalized electron cloud and the diffusion energy barrier of Zn2+ in MnVO is low, which promotes the Zn2+ transport and consequently improves the reversibility of the battery upon deep cycling. The key and enlightening insights are provided in the results for designing high-performance vanadium-oxide-based cathode materials for AZIBs.



https://doi.org/10.1002/sstr.202300136
Stapf, Siegfried; Siebert, Niklas; Spalek, Timo; Hartmann, Vincent; Gizatullin, Bulat; Mattea, Carlos
Binary fluids in mesoporous materials: phase separation studied by NMR relaxation and diffusion. - In: Magnetic resonance letters, ISSN 2772-5162, Bd. 3 (2023), 2, S. 108-117

Relaxation and diffusion measurements were carried out on single and binary liquids filling the pore space of controlled porous glass Vycor with an average pore size of about 4 nm. The dispersion of the longitudinal relaxation time T1 is discussed as a means to identify liquid-surface interaction based on existing models developed for metal-free glass surfaces. In addition, the change of T1 and T2 with respect to their bulk values is discussed, in particular T2 serves as a probe for the strength of molecular interactions. As the native glass surface is polar and contains a large amount of hydroxyl groups, a pronounced interaction of polar and protic adsorbate liquids is expected; however, the T1 dispersion, and the corresponding reduction of T2, are also observed for non-polar liquids such as alkanes and cyclohexane. Deuterated liquids are employed for simplifying data analysis in binary systems, but also for separating the respective contributions of intra- and intermolecular interactions to the overall relaxation rate. Despite the lack of paramagnetic impurities in the glass material, 1H and 2H relaxation dispersions of equivalent molecules are frequently found to differ from each other, suggesting intermolecular relaxation mechanisms for the 1H nuclei. The variation of the T1 dispersion when comparing single and binary systems gives clear evidence for the preferential adsorption of one of the two liquids, suggesting complete phase separation in several cases. Measurement of the apparent tortuosity by self-diffusion experiments supports the concept of a local variation of sample composition within the porespace.



https://doi.org/10.1016/j.mrl.2023.03.002
Selzer, Silas A.; Bauer, Fabian; Bohm, Sebastian; Runge, Erich; Bretschneider, Peter
Physics-guided machine learning techniques for improving temperature calculations of high-voltage transmission lines. - In: Die Energiewende beschleunigen, (2023), S. 353-360

The calculation of the temperature of high-voltage transmission lines is usually done by the commercially used standard models, the CIGRE Standard No. 601 and the IEEE Standard No. 738. These turn out to be prone to errors in application. Based on data analysis, new models based on machine learning techniques and their combination with physics-based models, called physics-guided machine learning techniques, were developed and compared with the results of the established physical models and measurement results. The improved models achieve a reduction of the mean absolute estimation error as well as a significant reduction of the values that deviate more than 5 K from the measured conductor temperature. Also, the mean underestimation of the conductor temperature was changed into an applicationtechnically unproblematic overestimation by the transition from the best standard to the best data-scientific model. The optimization of the models could be achieved by eliminating the incorrect determination of the physical parameters, a compensation of the conservative estimation of the physical effects as well as the consideration of the neglected thermal components of the heat balance. The investigations are based on measured data of the conductor temperature and electrical quantities from the grid area of 50Hertz Transmission GmbH.



Köster, Felix; Patel, Dhruvit; Wikner, Alexander; Jaurigue, Lina; Lüdge, Kathy
Data-informed reservoir computing for efficient time-series prediction. - In: Chaos, ISSN 1089-7682, Bd. 33 (2023), 7, 073109, S. 073109-1-073109-11

We propose a new approach to dynamical system forecasting called data-informed-reservoir computing (DI-RC) that, while solely being based on data, yields increased accuracy, reduced computational cost, and mitigates tedious hyper-parameter optimization of the reservoir computer (RC). Our DI-RC approach is based on the recently proposed hybrid setup where a knowledge-based model is combined with a machine learning prediction system, but it replaces the knowledge-based component by a data-driven model discovery technique. As a result, our approach can be chosen when a suitable knowledge-based model is not available. We demonstrate our approach using a delay-based RC as the machine learning component in conjunction with sparse identification of nonlinear dynamical systems for the data-driven model component. We test the performance on two example systems: the Lorenz system and the Kuramoto-Sivashinsky system. Our results indicate that our proposed technique can yield an improvement in the time-series forecasting capabilities compared with both approaches applied individually, while remaining computationally cheap. The benefit of our proposed approach, compared with pure RC, is most pronounced when the reservoir parameters are not optimized, thereby reducing the need for hyperparameter optimization.



https://doi.org/10.1063/5.0152311
Phi, Hai Binh; Bohm, Sebastian; Runge, Erich; Dittrich, Lars; Strehle, Steffen
3D passive microfluidic valves in silicon and glass using grayscale lithography and reactive ion etching transfer. - In: Microfluidics and nanofluidics, ISSN 1613-4990, Bd. 27 (2023), 8, 55, S. 1-12

A fabrication strategy for high-efficiency passive three-dimensional microfluidic valves with no mechanical parts fabricated in silicon and glass substrates is presented. 3D diffuser-nozzle valve structures were produced and characterized in their added value in comparison to conventional diffuser-nozzle valve designs with rectangular cross sections. A grayscale lithography approach for 3D photoresist structuring combined with a proportional transfer by reactive ion etching allowed to transfer 3D resist valve designs with high precision into the targeted substrate material. The efficiency with respect to the rectification characteristics or so-called diodicity of the studied valve designs is defined as the ratio of the pressure drops in backward and forward flow directions. The studied valve designs were characterized experimentally as well as numerically based on finite element simulations with overall matching results that demonstrate a significantly improved flow rectification of the 3D valves compared to the corresponding conventional structure. Our novel 3D valve structures show, for instance, even without systematic optimization a measured diodicity of up to 1.5 at low flow rates of only about 10 μl/s.



https://doi.org/10.1007/s10404-023-02663-2