INMdok (Leibniz Institute for New Materials)
Not a member yet
931 research outputs found
Sort by
Nanoscale friction on MoS2/graphene heterostructures
Get PDFStacked hetero-structures of two-dimensional materials allow for a design of interactions with corresponding electronic and mechanical properties. We report structure, work function, and frictional properties of 1 to 4 layers of MoS2 grown by chemical vapor deposition on epitaxial graphene on SiC(0001). Experiments were performed by atomic force microscopy in ultra-high vacuum. Friction is dominated by adhesion which is mediated by a deformation of the layers to adapt the shape of the tip apex. Friction decreases with increasing number of MoS2 layers as the bending rigidity leads to less deformation. The dependence of friction on applied load and bias voltage can be attributed to variations in the atomic potential corrugation of the interface, which is enhanced by both load and applied bias. Minimal friction is obtained when work function differences are compensated
Self-Activation of Inorganic-Organic Hybrids Derived through Continuous Synthesis of Polyoxomolybdate and para-Phenylenediamine Enables Very High Lithium-Ion Storage Capacity
Get PDFInorganic-organic hybrid materials with redox-active components were prepared by an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD). A scalable and low-energy continuous wet chemical synthesis process, known as the microjet process, was used to prepare particles with large surface area in the submicrometer range with high purity and reproducibility on a large scale. Two different crystalline hybrid products were formed depending on the ratio of molybdate to organic ligand and pH. A ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1 resulted in the compound [C6H10N2]2[Mo8O26] ⋅ 6 H2O, while higher PPD ratios from 9 : 1 to 30 : 1 yielded a composition of [C6H9N2]4[NH4]2[Mo7O24] ⋅ 3 H2O. The electrochemical behavior of the two products was tested in a battery cell environment. Only the second of the two hybrid materials showed an exceptionally high capacity of 1084 mAh g−1 at 100 mA g−1 after 150 cycles. The maximum capacity was reached after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li2MoO4 and an additional in situ polymerization of PPD. The final hybrid material is a promising material for lithium-ion battery (LIB) applications
Unraveling the Electrochemical Mechanism in Tin Oxide/MXene Nanocomposites as Highly Reversible Negative Electrodes for Lithium-Ion Batteries
Get PDFLithium-ion batteries are constantly developing as the demands for power and energy storage increase. One promising approach to designing high-performance lithium-ion batteries is using conversion/alloying materials, such as SnO2. This class of materials does, in fact, present excellent performance and ease of preparation; however, it suffers from mechanical instabilities during cycling that impair its use. One way to overcome these problems is to prepare composites with bi-dimensional materials that stabilize them. Thus, over the past 10 years, two-dimensional materials with excellent transport properties (graphene, MXenes) have been developed that can be used synergistically with conversion materials to exploit both advantages. In this work, a 50/50 (by mass) SnO2/Ti3C2Tz nanocomposite is prepared and optimized as a negative electrode for lithium-ion batteries. The nanocomposite delivers over 500 mAh g−1 for 700 cycles at 0.1 A g−1 and demonstrates excellent rate capability, with 340 mAh g−1 at 8 A g−1. These results are due to the synergistic behavior of the two components of the nanocomposite, as demonstrated by ex situ chemical, structural, and morphological analyses. This knowledge allows, for the first time, to formulate a reaction mechanism with lithium-ions that provides partial reversibility of the conversion reaction with the formation of SnO
A Highly Active Cobalt Catalyst for the General and Selective Hydrogenation of Aromatic Heterocycles
Get PDFNanostructured earth abundant metal catalysts that mediate important chemical reactions with high efficiency and selectivity are of great interest. This study introduces a synthesis protocol for nanostructured earth abundant metal catalysts. Three components, an inexpensive metal precursor, an easy to synthesize N/C precursor, and a porous support material undergo pyrolysis to give the catalyst material in a simple, single synthesis step. By applying this catalyst synthesis, a highly active cobalt catalyst for the general and selective hydrogenation of aromatic heterocycles could be generated. The reaction is important with regard to organic synthesis and hydrogen storage. The mild reaction conditions observed for quinolines permit the selective hydrogenation of numerous classes of N-, O- and S-heterocyclic compounds such as: quinoxalines, pyridines, pyrroles, indoles, isoquinoline, aciridine amine, phenanthroline, benzofuranes, and benzothiophenes
Faradaic materials and processes for the electrochemical separation of alkali and alkaline earth metal ions
Get PDFAs industrial and agricultural activities expand along with a growing global population, numerous regions are experiencing shortages of water and essential metals. To address these challenges, electrochemical separation methods utilizing electroactive materials and interfaces offer an efficient and straightforward approach to water purification and targeted ion extraction. Although carbon-based materials have been extensively studied and have the advantages of stability and low cost, they suffer from low desalination capacity, particularly for high-salinity water, and low selectivity. This dissertation investigates the potential of Faradaic materials and processes for electrochemical ion/water separation, as well as ion/ion separation, with a focus on alkali and alkaline earth metal ions, which are vital for industrial development but challenging to separate. The study includes synthesizing several Faradaic materials to achieve high ion removal capacity in seawater desalination. This work also develops a strategy to exploit the nuanced differences of ion intercalation kinetics in 2D material to achieve specific ion separation. The study also examines the selectivity and stability of LiFePO4 and presents new ways to optimize its performance. Finally, the study establishes a novel electrochemical process based on redox flow batteries, which promises a more efficient and continuous extraction of lithium ions from seawater.Mitwachsender Weltbevölkerung, Industrie und Landwirtschaft werden zunehmend mehr Regionen einer Knappheit an Wasser und relevanten Elementen unterworfen. Entgegenwirkend bieten elektrochemische Trennverfahren unter Verwendung elektroaktiver Materialien und Grenzflächen einen effizienten und einfachen Ansatz zur Wasserreinigung und gezielten Ionenextraktion. Ausführlich untersuchte Kohlenstoffmaterialien welche Vorteile von Stabilität und niedrigen Kosten aufweisen, liefern nur eine geringe Selektivität und Entsalzungskapazität, insbesondere für Wasser mit hohem Salzgehalt. Diese Dissertation untersucht das Potenzial faraday‘scher Materialien und Prozesse für die elektrochemische Ionen/Wasser- sowie Ionen/Ionen-Trennung, mit einem Fokus auf Alkali- und Erdalkalimetallionen, die für die industrielle Entwicklung von entscheidender Bedeutung, aber schwierig zu trennen sind. Die Studie umfasst die Synthese faraday‘scher Materialien, um hohe Ionenentfernungskapazitäten im Kontext der Meerwasserentsalzung zu erreichen. Zudem wurde eine Strategie entwickelt, um die differenzierenden Unterschiede der Ioneninterkalationskinetik in 2D-Material für eine spezifische Ionentrennung auszunutzen. Die Studie untersucht auch die Selektivität und Stabilität von LiFePO4 und zeigt neue Möglichkeiten zur Optimierung seiner Leistung auf. Schließlich wird ein neuartiger elektrochemischer Prozess auf Basis von Redox-Flow-Batterien etabliert, der eine kontinuierlichere Extraktion von Lithium-Ionen aus Meerwasser verspricht
Continuous wet chemical synthesis of Mo(C,N,O)x as anode materials for Li-ion batteries†
Get PDFMolybdenum carbides, oxides, and mixed anionic carbide–nitride–oxides Mo(C,N,O)x are potential anode materials for lithium-ion batteries. Here we present the preparation of hybrid inorganic–organic precursors by a precipitation reaction of ammonium heptamolybdate ((NH4)6Mo7O24) with para-phenylenediamine in a continuous wet chemical process known as a microjet reactor. The mixing ratio of the two components has a crucial influence on the chemical composition of the obtained material. Pyrolysis of the precipitated precursor compounds preserved the size and morphology of the micro- to nanometer-sized starting materials. Changes in pyrolysis conditions such as temperature and time resulted in variations of the final compositions of the products, which consisted of mixtures of Mo(C,N,O)x, MoO2, Mo2C, Mo2N, and Mo. We optimized the reaction conditions to obtain carbide-rich phases. When evaluated as an anode material for application in lithium-ion battery half-cells, one of the optimized materials shows a remarkably high capacity of 933 mA h g−1 after 500 cycles. The maximum capacity is reached after an activation process caused by various conversion reactions with lithium
Effect of cation size of binary cation ionic liquid mixtures on capacitive energy storage
Get PDFIonic liquid mixtures show promise as electrolytes for supercapacitors with nanoporous electrodes. Herein, we investigate theoretically and with experiments how binary electrolytes comprising a common anion and two types of differently-sized cations affect capacitive energy storage. We find that such electrolytes can enhance the capacitance of single nanopores and nanoporous electrodes under potential differences negative relative to the potential of zero charge. For a two-electrode cell, however, they are beneficial only at low and intermediate cell voltages, while a neat ionic liquid performs better at higher voltages. We reveal subtle effects of how the distribution of pores accessible to different types of ions correlates with charge storage and suggest approaches to increase capacitance and stored energy density with ionic liquid mixtures
Thermo-Responsive Ultrafiltration Block Copolymer Membranes Based on Polystyrene-block-Poly(diethyl acrylamide)
Get PDFWithin the present work, a thermo-responsive ultrafiltration membrane is manufactured based on a polystyrene-block-poly(diethyl acrylamide) block copolymer (BCP). The poly(diethyl acrylamide) block segment features a lower critical solution temperature (LCST) in water, similar to the well-known poly(N-isopropylacrylamide), but having increased biocompatibility and without exhibiting a hysteresis of the thermally induced switching behavior. The BCP is synthesized via sequential “living” anionic polymerization protocols and analyzed by 1H-NMR spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The resulting morphology in the bulk state is investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) revealing the intended hexagonal cylindrical morphology. The BCPs form micelles in a binary mixture of tetrahydrofuran and dimethylformamide, where BCP composition and solvent affinities are discussed in light of the expected structure of these micelles and the resulting BCP membrane formation. The membranes are manufactured using the non-solvent induced phase separation (NIPS) process and are characterized via scanning electron microscopy (SEM) and water permeation measurements. The latter are carried out at room temperature and at 50 °C revealing up to a 23-fold increase of the permeance, when crossing the LCST of the poly(diethyl acrylamide) block segment in water
Best practice for electrochemical water desalination data generation and analysis
Get PDFElectrochemical desalination shows promise for ion-selective, energy-efficient water desalination. This work reviews performance metrics commonly used for electrochemical desalination. We provide a step-by-step guide on acquiring, processing, and calculating raw desalination data, emphasizing informative and reliable figures of merit. A typical experiment uses calibrated conductivity probes to relate measured conductivity to concentration. Using a standard electrochemical desalination cell with activated carbon electrodes, we demonstrate the calculation of desalination capacity, charge efficiency, energy consumption, and ion selectivity metrics. We address potential pitfalls in performance metric calculations, including leakage current (charge) considerations and aging of conductivity probes, which can lead to inaccurate results. The relationships between pH, temperature, and conductivity are explored, highlighting their influence on final concentrations. Finally, we provide a checklist for calculating performance metrics and planning electrochemical desalination tests to ensure accuracy and reliability. Additionally, we offer simplified spreadsheet tools to aid data processing, system design, estimations, and upscaling
A high-throughput 3D kinetic killing assay
Get PDFOur work presents a high-throughput kinetic killing assay in the 3D matrix using high-content imaging that is a robust and powerful cytotoxicity assay for evaluating the killing efficiency of immune killer cells or conducting drug screening under physiologically and pathologically relevant scenarios, particularly in the context of solid tumors