Forschungszentrum Jülich
  • Jülich, NRW, Germany
Recent publications
Indole has been proposed as a Liquid Organic Hydrogen Carrier (LOHC) component. Its hydrogenation leads to octahydro indole, which can subsequently release hydrogen again in an endothermic, catalytic dehydrogenation reaction. This reaction requires high temperatures due to limitations by the reaction equilibrium. It is therefore interesting to find derivatives of the carrier molecules with lower enthalpies of reaction, which corresponds to a higher equilibrium constant. In this study, methyl and phenyl substituted derivatives of indole have been examined. Vapor pressures and enthalpies of vaporisation/sublimation have been measured. The standard molar enthalpies of formation in the gas phase have been calculated using quantum chemistry. The liquid phase standard molar enthalpies of formation were derived and used for calculating reaction enthalpies. The results show that methylation lowers the enthalpy of reaction for dehydrogenation. The reduction is not very pronounced in case of single methylation (up to 3.1 kJ mol⁻¹/H2), but can be increased by manifold methylation (e.g. 4.6 kJ mol⁻¹/H2 in case of 2,3-dimethyl-H8-indole). Substitution of indole with a phenyl group leads to a corresponding hydrogenated counterpart, that can only be dehydrogenated partially under mild conditions. This is due to the fact that the reducing effect of the nitrogen atom on enthalpy of reaction is only effective in the indole system itself, while the cyclohexyl ring has similar dehydrogenation properties to homocyclic LOHCs.
Catalysis is inherently driven by the interaction of reactants, intermediates and formed products with the catalyst’s surface. In order to reach the desired transition state and to overcome the kinetic barrier, elevated temperatures or electrical potentials are employed to increase the rate of reaction. Despite immense efforts in the last decades, research in thermo- and electrocatalysis has often preceded in isolation, even for similar reactions. Conceptually, any heterogeneous surface process that involves changes in oxidation states, redox processes, adsorption of charged species (even as spectators) or heterolytic cleavage of small molecules should be thought of as having parallels with electrochemical processes occurring at electrified interfaces. Herein, we compare current trends in thermo- and electrocatalysis and elaborate on the commonalities and differences between both research fields, with a specific focus on the production of hydrogen peroxide as case study. We hope that interlinking both fields will be inspiring and thought-provoking, eventually creating synergies and leverage towards more efficient decentralized chemical conversion processes. Research in thermo- and electrocatalysis have often preceded in isolation, even for similar reactions. Here, the authors compare current trends in both fields and elaborate on the commonalities and differences with a specific focus on the production of hydrogen peroxide.
To realize future spintronic applications with magnetic skyrmions—topologically nontrivial swirling spin structures—it is essential to achieve efficient writing and deleting capabilities of these quasi-particles. Electric-field assisted nucleation and annihilation is a promising route, however, the understanding of the underlying microscopic mechanisms is still limited. Here, we show how the stability of individual magnetic skyrmions in an ultrathin transition-metal film can be controlled via external electric fields. We demonstrate based on density functional theory that it is important to consider the changes of all interactions with electric field, i.e., the pair-wise exchange, the Dzyaloshinskii–Moriya interaction, the magnetocrystalline anisotropy energy, and the higher-order exchange interactions. The energy barriers for electric-field assisted skyrmion writing and deleting obtained via atomistic spin simulations vary by up to a factor of three more than the variations of the interactions calculated from first-principles. This surprising effect originates from the electric-field dependent size of metastable skyrmions at a fixed magnetic field. The large changes in lifetimes allow the possibility of electric-field assisted thermally activated writing and deleting of skyrmions.
The pathological hallmark of neurodegenerative diseases is the formation of toxic oligomers by proteins such as alpha-synuclein (aSyn) or microtubule-associated protein tau (Tau). Consequently, such oligomers are promising biomarker candidates for diagnostics as well as drug development. However, measuring oligomers and other aggregates in human biofluids is still challenging as extreme sensitivity and specificity are required. We previously developed surface-based fluorescence intensity distribution analysis (sFIDA) featuring single-particle sensitivity and absolute specificity for aggregates. In this work, we measured aSyn and Tau aggregate concentrations of 237 cerebrospinal fluid (CSF) samples from five cohorts: Parkinson’s disease (PD), dementia with Lewy bodies (DLB), Alzheimer’s disease (AD), progressive supranuclear palsy (PSP), and a neurologically-normal control group. aSyn aggregate concentration discriminates PD and DLB patients from normal controls (sensitivity 73%, specificity 65%, area under the receiver operating curve (AUC) 0.68). Tau aggregates were significantly elevated in PSP patients compared to all other groups (sensitivity 87%, specificity 70%, AUC 0.76). Further, we found a tight correlation between aSyn and Tau aggregate titers among all patient cohorts (Pearson coefficient of correlation r = 0.81). Our results demonstrate that aSyn and Tau aggregate concentrations measured by sFIDA differentiate neurodegenerative disease diagnostic groups. Moreover, sFIDA-based Tau aggregate measurements might be particularly useful in distinguishing PSP from other parkinsonisms. Finally, our findings suggest that sFIDA can improve pre-clinical and clinical studies by identifying those individuals that will most likely respond to compounds designed to eliminate specific oligomers or to prevent their formation.
Quantum optimal control, a toolbox for devising and implementing the shapes of external fields that accomplish given tasks in the operation of a quantum device in the best way possible, has evolved into one of the cornerstones for enabling quantum technologies. The last few years have seen a rapid evolution and expansion of the field. We review here recent progress in our understanding of the controllability of open quantum systems and in the development and application of quantum control techniques to quantum technologies. We also address key challenges and sketch a roadmap for future developments.
Thermodynamic modelling is an effective approach to accelerate the development of novel materials such as V-based alloys. In the present work, the results of thermodynamic modelling of the ternary system V–Ti–B using the “CALculation of PHAse Diagrams” (CALPHAD) method are presented. The thermodynamic descriptions of the binary systems V–Ti, V–B, and Ti–B are based on available publications whereas thermodynamic parameters for the ternary system stem from the iterative approximation to the experimental investigations, which further serve for verifying the calculated phase diagram. Thus, eight different alloys in the compositional range of 10–40 at.% Ti and B were analyzed aiming at identifying the evolving phases. A set of thermodynamic parameters is proposed. The calculated isothermal phase diagram at 1673 K exhibits a high degree of agreement with the literature and experimental observations. In our further work, the thermodynamic data generated in this study will be useful to develop the quaternary V–Ti–Si–B system.
The present study reports on the existence of a new ternary phase, V8SiB4, in the V–Si–B system. The new phase was found in alloys heat-treated at 1400 °C for 100 h and 200 h within the Vss–V3Si–V5SiB2 phase field at 1600 °C. The crystal structure of V8SiB4 was determined by combining energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and density functional theory (DFT) calculations. To further examine the stability of V8SiB4, electronic density-of-states (EDOS), phononic density-of-states (PDOS), the chemical bonding and the elastic properties of V8SiB4 were calculated using DFT and compared with the properties of V5SiB2 (T2).
Replanting of mining soils is necessary for utilizing soil resources and increasing cultivated land areas. However, limited information exists on the long-term temporal trends of carbon accrual in agricultural systems containing carbonate-rich soil material. We examined changes in soil organic carbon (SOC), soil inorganic carbon (SIC), and total carbon (TC) stocks in an agricultural soil containing carbonate over a 62-year recultivation chronosequence. The most critical differences in the SOC, SIC, and TC stocks were observed in the 0–30 cm soil layer. The results revealed that the SOC stock increased rapidly during the first 10–20 years, but only slowly thereafter. The SIC stock decreased over 62-year from approximately 40 Mg C ha⁻¹ to 2 Mg C ha⁻¹. According to soil δ¹³CTC data, the SIC to TC ratio decreased from 83% (year 0) to 7% (year 62). Overall, the average sequestration rates were 0.30 Mg C ha⁻¹ y⁻¹ for SOC and −0.61 Mg C ha⁻¹ y⁻¹ for SIC over the 62 years after recultivation. Total carbon ultimately declined by approximately 19.5 Mg C ha⁻¹ in recultivated carbonate soils. Topsoil SOC model (Rothamsted Carbon Model) outputs predicted an equilibrium value of 38.6 Mg C ha⁻¹ after 197 years, which was less than the SIC stock lost in the first 70 years. Therefore, an overall TC increase in these carbonate-containing agricultural soils will only occur (i) during the initial rapid SOC sequestration accumulation phase (first 20 years of recultivation); and (ii) after the soils are fully decalcified (after ∼62 years), but when SOC still slowly increases before SOC stocks reached full equilibrium (after ∼197 years). However, compared with starting TC stocks, when we consider periods over a semicentennial and beyond, we will likely lose more TC than we gain in these recultivated agricultural soils if there are no additional TC sequestration measures.
The design and control of the solid electrolyte interphase (SEI) is essential for the implementation of rechargeable lithium metal based batteries and has been a major research theme of lithium metal electrodes for over 50 years. However, research on an as-defined SEI is challenging due to the inevitable presence of a native passivation layer (NPL), commonly contaminating an in situ formed SEI and its characteristics. Herein we present an original study on an uncontaminated SEI being an exclusive reaction product of lithium and a liquid aprotic electrolyte, highlighting the largely negative influence of the NPL on different SEI characteristics and functional additive evaluation. A preformed as-defined SEI (pSEI) was generated by an in-house designed advanced pre-treatment method, ensuring high reproducibility and exclusion of the NPL by cutting and pressing lithium metal in solution/electrolyte. The implementation of a pSEI allows for a systematic study and an unclouded comparison of the two common functional additives vinylene carbonate (VC) and fluoroethylene carbonate (FEC) in an equal molar setting. The introduction of an as-defined SEI allowed to clearly distinguish between enhancing influence on the SEI characteristics and full cell performance by FEC and the largely negative effect of VC on different SEI characteristics.
The challenges of the 21st century require resilient societies and a robust international regulatory framework [1]. The current disruptions to the global framework (most notably by the Covid-19 pandemic and the war on Ukraine) as well as the historic experiences especially of the Great Depression and the Lehman crisis (Annex II) elucidate the importance of the UN Sustainable Development Goals (SDGs) as a global regulatory framework. The SDGs provide new targets for resilient development. In this paper we set specific focus especially on SDG 17 “Partnerships for the Goals” and its aim of a free multilateral trading system (Annex I, SDG 17.10-17.12) for sustainable development [2]. Against this background the German Resilience Index was developed as a new measure for defining the resilience of the German society based on the SDGs including the explicit consideration of trade dynamics. The German Resilience Index (GRI) enables an analysis of the extent to which Germany has succeeded in building socio-economic-ecological resilience to defy the storms of globalization. The index is based on the German Sustainable Development Goals and the defined targets, considering also ethical values derived from the Universal Declaration of Human Responsibilities of the InterAction Council and trade relations as corner stones of resilient development. The analysis thus provides a first approach for systematically considering the impact of Germany’s intensive participation in globalization and the ethical values of the German Sustainability Strategy and its SDGs. The results are important for the political decision-making process and the political as well as social discourse about the future course of sustainable, and thus resilient, development in Germany.
The forest ecosystem plays a key role in mitigating global climate change through carbon sequestration in its biomass and soils to limit the rising atmospheric concentration of CO2. However, the combined overall interaction of climate and forest type on the quantities and forms of soil carbon (organic vs. inorganic) has not yet been sufficiently investigated. In this study, the contents of soil total carbon (STC), soil organic carbon (SOC) and soil inorganic carbon (SIC) were measured along the 4000 km North-South Transect of Eastern China. We sampled 252 soil samples (6 replicates for each site, 3 depths for each site) from four long-term ecosystem experimental stations in Dinghushan, Shennongjia, Beijing and Changbaishan, along the transect from south to north, including 14 different forest types. The contents of STC, SOC, and SIC in the upper 60 cm soil layer varied in different types of forest with 34–107 g C kg⁻¹, 31–104 g C kg⁻¹, and 1.5–8 g C kg⁻¹, respectively. The northern fir and birch forest, most notably in Changbaishan, had the highest STC and SOC contents. The higher SIC contents were found in the southern evergreen broad-leaved forests in Dinghushan and Shennongjia. The contents of STC, SOC and SIC differed significantly in terms of mean annual temperature (MAT), mean annual precipitation (MAP), forest type, and soil depth. In the upper 60 cm soil layer, the most significant correlations occurred between SOC (or STC) and MAT (R²SOC = −0.62, R²STC = −0.60) when compared with the correlation between SOC (or STC) and MAP (R²SOC = −0.45, R²STC = −0.45) or elevation (R²SOC = 0.48, R²STC = 0.48). The soil stratification ratio (SR) of STC and SOC were typically ∼2–3 in most forests and even reached 5– 7 in Changbaishan forest, indicating a well-functioning ecosystem overall. We concluded that on the near-continental scale (4000 km), forest soil carbon contents and forms (SOC, STC, SIC) were controlled most strongly by temperature (MAT). Therefore, an innovative selection of a specific forest type (fir or broad-leaved forest) within set temperature regimes can better contribute to maximizing soil carbon content and thus optimize its sequestration on the national to near-continental scale to mitigate climate change.
Passivation of semiconductor surfaces is crucial to reduce carrier recombination losses and thereby enhance the device performance of solar cells and other semiconductor devices. Thin-film stacks of phosphorus oxide (POx) and aluminum oxide (Al2O3) have recently been shown to provide excellent passivation of semiconductor surfaces, including crystalline silicon and indium phosphide, and can also be highly interesting for passivation of other semiconductor materials such as Ge and III-V semiconductors. On silicon, the excellent passivation is attributed to the combination of a high positive fixed charge and a very low interface defect density. On InP nanowires, application of the POx/Al2O3 stacks improves charge carrier lifetime threefold as compared to unpassivated nanowires. In this work, we review and summarize recent results obtained on POx/Al2O3 stacks for semiconductor surface passivation. Several topics are discussed, including the passivation performance on various semiconductor surfaces, the processing of the POx and Al2O3 layers, the role of the capping layer, and aspects related to device integration. The POx/Al2O3 stacks feature some unique properties, including an unusually high positive fixed charge density, a low interface defect density, and can be prepared over a wide deposition temperature range. These unique properties arise in part from the mixing process that occurs between the POx and Al2O3 layers, which upon post-deposition annealing leads to the formation of AlPO4. The surface passivation provided by POx/Al2O3 stacks is highly stable and the stack can be used to conformally coat high-aspect-ratio structures such as nanowires, showing their promise for use in semiconductor devices.
This Virtual Special Issue collects the results of six research projects conducted under the umbrella of the MODEX network. MODEX stands for Model Experiments and refers to the combination of qualitative and quantitative model comparisons, the latter based on a harmonized model application. While all projects focused on the comparison of energy system models, the experiments covered a broad range of different areas. Thus, the experiments address different model types, such as vehicle diffusion models, power system models, distribution grid models, and transmission grid models, but also different thematic scopes, such as policy instruments, decentralized flexibility, and sector coupling. In total, the projects involved 40 models. The experiments were based on a harmonization of models and data, which was realized to the degree possible and useful in the respective project context. Complementary to the harmonized model application, the methods and tools for the systematic comparison of energy system models were further developed within the MODEX projects. The results of the MODEX projects significantly expand the spectrum of systematic comparisons of energy system models. The added value compared to previous model experiments consists particularly in the profound characterization of the models involved, the consistent linking of model differences with outcome differences, and the transparent description of appropriate methods and challenges of comparing energy system models. Due to a high degree of transparency, the project findings can be used directly by developers and users of other models.
Cable fires in nuclear power plants have a significant probability to occur at any time in the course of a severe accident or may as well be the initiating event of a severe accident sequence. During the combustion process, enormous amounts of aerosols alongside specific combustion gases (e.g. CO, CO2) can be released. Both nature and amount of the cable fire products depend on the combustion conditions. The effect of cable fire products distributing inside the containment and getting in contact with the catalyst surfaces of passive auto-catalytic recombiners (PARs) is of vital interest for safety analyses, in order to assess the hydrogen mitigation efficiency under these conditions. The newly built REKO-Fire facility at Forschungszentrum Jülich combines a flow tube reactor for catalyst investigation with a steady-state tube furnace for the constant generation of cable fire products at varying combustion conditions. That way, simultaneous exposure of 5 × 5 cm² catalyst samples to cable fire products and hydrogen/air mixtures is possible, enabling to quantify the influence of gaseous and particulate components on the catalysts’ start-up behavior. The installation has been used in the present study to investigate the effect of cable fire products obtained from flame-retardant power cables under three different fire conditions on the start-up of two types of catalysts for hydrogen recombination. For well-ventilated cable fire, neither gaseous nor particulate (mainly soot) cable fire products seem to affect the onset of the catalytic H2 conversion for both Pt and Pd-based catalysts. In under-ventilated fire conditions, the Pt-based catalyst is significantly deactivated, while the only impairment for the Pd-based catalyst is observed at very low hydrogen concentrations. For cable fire products generated from oxidative pyrolysis, the overall picture is ambiguous. On the one side it is obvious that deactivation and start-up delay occur for both catalyst types. However, no clear conclusion can be taken from the experimental data concerning the effect of exposure time. The presence of carbon monoxide in the atmosphere as well as particulate depositions from cable pyrolysis seem to be the most relevant mechanisms for catalyst deactivation and deserve further investigation.
Miscanthus (ANDERSSON) is considered a promising perennial industrial crop for providing biomass in a growing bioeconomy. One approach to increasing the biodiversity-enhancing ecosystem services of Miscanthus is the co-cultivation of flower-rich native wild plant species (WPS), for example, the perennial WPS common tansy (Tanacetum vulgare L.) and mugwort (Artemisia vulgaris L.), as well as the biennial WPS wild teasel (Dipsacus fullonum L.) and yellow melilot (Melilotus officinalis L.). This study tested whether these selected WPS would be as suitable for combustion as Miscanthus, in this case the sterile hybrid Miscanthus x giganteus Greef et Deuter, allowing for a mixing of the biomasses. By doing so, no additional value chain (e.g. biogas production) would be necessary to economically exploit the diversification of the agricultural system for bioenergy production. Feedstock samples of Miscanthus and the four above-mentioned WPS from a field trial in southwest Germany were used to investigate the combustion characteristics as well as the higher heating value (HHV). It was found that all WPS exhibited better combustion properties than Miscanthus with respect to ash melting behavior at similar HHVs of 16.3–17.5 MJ kg⁻¹. From an admixture of >30% WPS to the Miscanthus biomass, a significant increase in the ash melting temperature by 20% from 1000 to 1200 °C was shown. Thus, the mixture of WPS and Miscanthus could potentially improve the combustion quality, leading to reduced costs in the incineration plant operation process. However, the reduced costs of incineration should be greater than the loss in productivity due to the lower biomass yields from the WPS. This is highly dependent on the particular site conditions and the establishment success of the WPS and needs to be investigated in long-term studies.
Fission products (FPs) released in the process of a severe loss of coolant accident can reach the containment – the last barrier against the leakage of radioactive isotopes to the surrounding environment – as airborne particles. Consequently, reliable assessment of a potential radiological source term requires in-depth knowledge of the aerosol behavior. The IN-EX facility at Forschungszentrum Jülich (FZJ, Germany) is built to study nuclear aerosol depletion behavior under accident scenarios by varying thermodynamic parameters (relative humidity, temperature and pressure). We performed a series of experiments using both, pure and mixed particles. The objective is to improve the understanding of aerosol depletion mechanisms and provide the latest data for optimization and validation of computational models for aerosol behavior. In the IN-EX experiments, SnO2 and CsI represent the insoluble and soluble particles released from the damaged core, respectively. In the case of mixed particles, in order to figure out the effect of varying mass composition on the aerosol behavior, we used the mass compositions of CsI and SnO2 in the ratio of 3:7 and 6:4 in this paper. In this work, we measured the mass concentration and size distribution, and derived the corresponding aerosol removal rate to analyze the data. During the experiments on CsI aerosols, we observed that the aerosol removal rate is accelerated by an increase in relative humidity, while relative humidity seems to have no effect on the depletion of SnO2 aerosol. Furthermore, pressure or temperature appears to have no significant effect on the depletion behavior both of SnO2 and CsI aerosols. Combining with the results of pure substances, we investigated the regularity of the depletion behavior of mixed aerosols. In general, SnO2 has the highest aerosol removal rate, while CsI has the lowest one. The removal rate of the mixture is between SnO2 and CsI. The components in the mixture with a high mass fraction determine the depletion behavior of this mixture. Particularly in the condensed state, we found almost no difference in the aerosol removal rate of either pure substances or mixtures.
Oxygen and proton transport properties of La5.4WO11.1-δ are investigated using electrical conductivity relaxation. Chemical diffusion coefficients and surface exchange coefficients of both hydrogen and oxygen presumed to govern conductivity relaxation are extracted from fitting the two-fold conductivity relaxation observed after hydration/dehydration steps at fixed oxygen partial pressure to the model equations. Surprisingly, the kinetic parameters obtained from fitting are found to depend on the magnitude of the current used in the measurements. A two-fold relaxation behavior with characteristics depending on the magnitude of the current is also observed after oxidation/reduction steps under dry conditions. Furthermore, at fixed temperature, oxygen and water partial pressures, the conductivity is found to exhibit relaxation behavior after a current step, while the apparent steady-state conductivity is found to depend on the applied current. The observations are attributed to the use of gold electrodes in the experiments and associated interfacial capacitances. It is obvious from this study that the use of partially ion-blocking electrodes in conductivity and conductivity relaxation measurements on mixed ionic-electronic conducting oxides with prevailing ionic conduction may lead to erroneous results and interpretations.
The increasing share of volatile renewable electricity production motivates demand response. Substantial potential for demand response is offered by flexible processes and their local multi-energy supply systems. Simultaneous optimization of their schedules can exploit the demand response potential, but leads to numerically challenging problems for nonlinear dynamic processes. In this paper, we propose to capture process dynamics using dynamic ramping constraints. In contrast to traditional static ramping constraints, dynamic ramping constraints are a function of the process state and can capture high-order dynamics. We derive dynamic ramping constraints rigorously for the case of single-input single-output processes that are exactly input-state linearizable. The resulting scheduling problem can be efficiently solved as a mixed-integer linear program. In a case study, we study two flexible reactors and a multi-energy system. The proper representation of process dynamics by dynamic ramping allows for faster transitions compared to static ramping constraints and thus higher economic benefits of demand response. The proposed dynamic ramping approach is sufficiently fast for application in online optimization.
Bone char (BC) is a promising P-recycling fertilizer but with rather low P-solubility, which can be increased by modifying the BC surface with elemental sulfur (BCplus), but effects on the soil P status have not been tested under field conditions yet. Hence, a long-time field experiment was started 2013 to track the fate of BC and BCplus P into different soil P pools compared to a control and triple superphosphate (TSP) treatment for severely P deficient (iSPTC-A) vs. sufficiently P fertilized (iSPTC-C) soil. The fingerprint of the recent land-use history (six years grassland prior arable land) was reflected by elevated labile-Po and NaOH-Po concentrations at the beginning of the experiment. However, after 3 years, labile Po concentrations converged and stabilized in both soils at a similar level. The formation of this new equilibrium of labile Po suggests that the rate of Po mineralization was, to some extent, controlled by the amount of available legacy P. After the first crop rotation, the effect of P fertilization on soil-P budgets and fractions were small and mostly insignificant. Only TSP increased the available-P pools in the soil. The other pools were not affected by treatments except stable-P increased significantly after BC application in iSPTC-A. The former laboratory results of higher P solubility of BCplus over BC could not be confirmed within the duration of the field trial. However, to prove that BC and BCplus are capable of maintaining adequate long-term crop P supply, the continuation of this unique field trial is highly recommended.
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Uli Schurr
  • Plant Sciences (IBG-2)
Andreas Wilden
  • Institute of Energy and Climate Research (IEK)
Martina Reske
  • Computational and Systems Neuroscience (INM-6)
Alexandros Katranidis
  • Institute of Biological Information Processing IBI-6
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Address
Leo-Brandt-Str., 52428, Jülich, NRW, Germany
Head of institution
Prof. Dr.-Ing. Wolfgang Marquardt (Chairman of the Board of Directors)
Website
www.fz-juelich.de/
Phone
02461 61 0