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Hot deformation behavior of a Fe3Al Ta alloy in the B2 order regime
Get PDFIn the present work, the hot deformation behavior and the corresponding microstructure evolution of an Fe 25Al 1.5Ta at. alloy in the B2 phase field were investigated. Uniaxial compression tests were carried out in a strain rate range from 0.0013 s amp; 8722;1 to 1 s amp; 8722;1 and in a temperature range from 800 C to 850 C, where an ordered B2 FeAl matrix phase along with a C14 Fe, Al 2Ta Laves phase was confirmed by X ray diffraction. A dynamic material model was applied to predict the safe and damaging processing windows. The underlying flow softening mechanisms were characterized using scanning electron microscopy and electron backscatter diffraction. The flow stress strain curves mostly showed a broad maximum followed by a slight decrease in stress until a steady stress was reached. The optimum processing window for the studied alloy was located at 850 C 0.0013 s amp; 8722;1, where the e amp; 64259;ciency of power dissipation amp; 951; and strain rate sensitivity m reached 50 and 0.25, respectively. The processing map also showed a domain of amp; 64258;ow instability, resulting from cracking, in the range of lower temperatures and higher strain rates 800 C 1 s amp; 8722;1 . The microstructural analyses confirmed a combination of dynamic recovery DRV and dynamic recrystallization DRX over the entire range of deformation conditions tested. The current study reveals a well suited parameter range to achieve a high degree of hot deformability in Fe Al alloys at significantly lower temperatures than those typically used. This may contribute to optimizing the thermomechanical processing of Fe Al alloys and reducing energy consumption in industrial forging operation
In situ nanoscale mapping of electrical and catalytic properties
Get PDFBy enabling the conversion of sustainably derived electrical energy into chemical energy, electrocatalytic reactions are vital for closing the anthropogenic carbon cycle. A wide array of electrocatalytic reactions have gained extensive attention, including hydrogen evolution HER , oxygen evolution OER , and CO2 electroreduction CO2RR . However, progress in enhancing catalyst activity, selectivity, and stability is impeded by the lack of fundamental insight. Under reaction conditions, multi step electron transfer and elementary catalytic processes convolute, influenced by the applied potential that affects the electrostatic potential of electrons through charging of the electric double layer EDL and or the chemical potential of the electrocatalysts. This complexity presents challenges in interpreting catalytic mechanisms, especially for non metallic catalysts, where both chemical and electrostatic potentials are altered by the applied voltage. For semiconducting catalysts in electrolytes, it remains a key challenge to resolve how the conduction band and the Fermi level shift, the potential drops across semiconductor electrolyte interfaces, and electron transfer pathways correlate with catalytic rates [1 3]. While conventional electrochemical techniques can only provide ensemble information, thus neglecting the spatial heterogeneity in the electronic structure and catalytic sites of electrode materials, differentiation of potential distributions between non metallic catalysts and the electric double layer EDL relies largely on theoretical calculation
Halide perovskite solar photovoltaics
No full textTechnological progress in photovoltaic PV technologies provides hope that a comprehensive and desperately needed decarbonization of the energy sector is possible. Commercially successful PV technologies based predominantly on silicon wafer technology are reliable and cost effective, but remain capital and carbon intensive. In this context, emerging PV technologies, such as metal halide perovskites MHPs , could further catalyze the energy transition by providing technological opportunities for even lower cost, mass producible, high efficiency solar cells with a significantly reduced carbon footprint. This themed issue of MRS Bulletin on Halide perovskite solar photovoltaics summarizes the current state of the art, challenges, and opportunities of perovskite photovoltaics with contributions and perspectives from six expert teams worldwide. The topics covered provide a status update on perovskite PV, remaining hurdles to their deployment, and challenges to realizing the potential of this technology to impact climate goals. Articles in this collection address scalability of perovskite PV and prospects for industrial manufacturing; perovskite PV as an add on technology on top of commercial silicon PV; environmental and sustainability considerations; and durability and reliability considerations. Further considerations include prospects of automation, coupled to artificial intelligence and machine learning, for accelerating material based solutions to these outstanding challenges including the possibilities of discovering new absorber and device component materials to enable success and ultimately deployment of these next generation PV
Monolithic Two Terminal Tandem Solar Cells Using Sb2S3 and Solution Processed PbS Quantum Dots Achieving an Open Circuit Potential beyond 1.1 V
No full textMultijunction solar cells have the prospect of a greater theoretical efficiency limit than single junction solar cells by minimizing the transmissive and thermalization losses a single absorber material has. In solar cell applications, Sb2S3 is considered an attractive absorber due to its elemental abundance, stability, and high absorption coefficient in the visible range of the solar spectrum, yet with a band gap of 1.7 eV, it is transmissive for near IR and IR photons. Using it as the top cell the cell where light is first incident in a two terminal tandem architecture in combination with a bottom cell the cell where light arrives second of PbS quantum dots QDs , which have an adjustable band gap suitable for absorbing longer wavelengths, is a promising approach to harvest the solar spectrum more effectively. In this work, these two subcells are monolithically fabricated and connected in series by a poly 3,4 ethylene dioxythiophene polystyrene sulfonate PEDOT PSS ZnO tunnel junction as the recombination layer. We explore the surface morphology of ZnO QD films with different spin coating conditions, which serve as the PbS QD cell s electron transport material. Furthermore, we examine the differences in photogenerated current upon varying the PbS QD absorber layer thickness and the electrical and optical characteristics of the tandem with respect to the stand alone reference cells. This tandem architecture demonstrates an extended spectral response into the IR with an open circuit potential exceeding 1.1 V and a power conversion efficiency of 5.6 , which is greater than that of each single junction cel
One pot synthesis of iron doped ceria catalysts for tandem carbon dioxide hydrogenation
Get PDFWe report on the one pot synthesis of inexpensive and abundant CeO2 and 1.5, 4.5, and 9 mol Fe doped ceria Ce1 amp; 8722;xFexO2 amp; 8722; amp; 948; systems and their catalytic activity for tandem CO2 hydrogenation. XAFS and XRD demonstrate that oxygen vacancies are generated via two mechanisms firstly, by the substitution of Ce4 by Fe3 in the lattice and the subsequent loss of oxygen anions. Secondly, by the partial reduction of Ce4 to Ce3 , which is enhanced by the presence of Fe. All the samples tested show high activity for CO2 hydrogenation and the production of CO, CH4, and light C2 C4 alkanes and alkenes, with the 9 mol Fe doped CeO2 showing the best performance in terms of CO2 reaction rate and product selectivity. During reaction, Fe exsolves seggregates from the ceria, resulting in particles decorating the surface of the catalyst and increasing the reaction rates of CO2. This system is composed of two functionalities, the oxygen vacancy and the Fe, whose close vicinity results in a high selectivity toward CO and CH4 detrimental to the more valuable hydrocarbons. A rather complex interplay between the two functionalities, their interface, and the particle size of the catalysts exists for this tandem reaction network on this catalytic system and deserves further studie
Ultrathin Two dimensional Layered Composite Carbosilicates from in situ Unzipped Carbon Nanotubes and Exfoliated Bulk Silica
No full textA key task in today s inorganic synthetic chemistry is to develop effective reactions, routes, and associated techniques aiming to create new functional materials with specifically desired multilevel structures and properties. Herein, we report an ultrathin two dimensional layered composite of graphene ribbon and silicate via a simple and scalable one pot reaction, which leads to the creation of a novel carbon metal silicate hybrid family carbosilicate. The graphene ribbon is in situ formed by unzipping carbon nanotubes, while the ultrathin silicate is in situ obtained from bulk silica or commercial glass; transition metals Fe or Ni oxidized by water act as bridging agent, covalently bonding the two structures. The unprecedented structure combines the superior properties of the silicate and the nanocarbon, which triggers some specific novel properties. All processes during synthesis are complementary to each other. The associated synergistic chemistry could stimulate the discovery of a large class of more interesting, functionalized structures and material
Synthesis and structural characterization of new macrocyclic inhibitors of the Zika virus NS2B NS3 protease
No full textThree new series of macrocyclic active site directed inhibitors of the Zika virus ZIKV NS2B NS3 protease were synthesized. First, attempts were made to replace the basic P3 lysine residue of our previously described inhibitors with uncharged and more hydrophobic residues. This provided numerous compounds with inhibition constants between 30 and 50 amp; 8201;nM. A stronger reduction of the inhibitory potency was observed when the P2 lysine was replaced by neutral residues, all of these inhibitors possess Ki values gt;1 amp; 8201; M. However, it is possible to replace the P2 lysine with the less basic 3 aminomethylphenylalanine, which provides a similarly potent inhibitor of the ZIKV protease Ki amp; 8201; amp; 8201;2.69 amp; 8201;nM . Crystal structure investigations showed that the P2 benzylamine structure forms comparable interactions with the protease as lysine. Twelve additional structures of these inhibitors in complex with the protease were determined, which explain many, but not all, SAR data obtained in this study. All individual modifications in the P2 or P3 position resulted in inhibitors with low antiviral efficacy in cell culture. Therefore, a third inhibitor series with combined modifications was synthesized; all of them contain a more hydrophobic d cyclohexylalanine in the linker segment. At a concentration of 40 amp; 8201; M, two of these compounds possess similar antiviral potency as ribavirin at 100 amp; 8201; M. Due to their reliable crystallization in complex with the ZIKV protease, these cyclic compounds are very well suited for a rational structure based development of improved inhibitor
Multifunctional Modification of the Buried Interface in Mixed Tin Lead Perovskite Solar Cells
No full textMixed tin lead perovskite solar cells can reach band gaps as low as 1.2 amp; 8197;eV, offering high theoretical efficiency and serving as base materials for all perovskite tandem solar cells. However, instability and high defect densities at the interfaces, particularly the buried surface, have limited performance improvements. In this work, we present the modification of the bottom perovskite interface with multifunctional hydroxylamine salts. These salts can effectively coordinate the different perovskite components, having critical influences in regulating the crystallization process and passivating defects of varying nature. The surface modification reduced traps at the interface and prevented the formation of excessive lead iodide, enhancing the quality of the films. The modified devices presented fill factors reaching 81 amp; 8201; and efficiencies of up to 23.8 amp; 8201; . The unencapsulated modified devices maintained over 95 amp; 8201; of their initial efficiency after 2000 amp; 8197;h of shelf storag
Organic Thin Films Enable Retaining the Oxidation State of Copper Catalysts during CO2 Electroreduction
Get PDFA key challenge in electrocatalysis remains controlling a catalyst s structural, chemical, and electrical properties under reaction conditions. While organic coatings showed promise for enhancing the selectivity and stability of catalysts for CO2 electroreduction CO2RR , their impact on the chemical state of underlying metal electrodes has remained unclear. In this study, we show that organic thin films on polycrystalline copper Cu enable retaining Cu species at reducing potentials down to amp; 8722;1.0 V vs RHE, as evidenced by operando Raman and quasi in situ X ray photoelectron spectroscopy. In situ electrochemical atomic force microscopy revealed the integrity of the porous organic film and nearly unaltered Cu electrode morphology. While the pristine thin film enhances the CO2 to ethylene conversion, the addition of organic modifiers into electrolytes gives rise to improved CO2RR performance stability. Our findings showcase hybrid metal organic systems as a versatile approach to control, beyond morphology and local environment, the oxidation states of catalysts and energy conversion material
Structure based mapping of the histone binding pocket of KDM4D using functionalized tetrazole and pyridine core compounds
Get PDFKDM4 histone demethylases became an exciting target for inhibitor development as the evidence linking them directly to tumorigenesis mounts. In this study, we set out to better understand the binding cavity using an X ray crystallographic approach to provide a detailed landscape of possible interactions within the under investigated region of KDM4. Our design strategy was based on utilizing known KDM binding motifs, such as nicotinic acid and tetrazolylhydrazides, as core motifs that we decided to enrich with flexible tails to map the distal histone binding site. The resulting X ray structures of the novel compounds bound to KDM4D, a representative of the KDM4 family, revealed the interaction pattern with distal residues in the histone binding site. The most prominent protein rearrangement detected upon ligand binding is the loop movement that blocks the accessibility to the histone binding site. Apart from providing new sites that potential inhibitors can target, the novel compounds may prove helpful in exploring the capacity of ligands to bind in sites distal to the cofactor binding site of other KDMs or 2 oxoglutarate 2OG dependent oxygenases. The case study proves that combining a strong small binding motif with flexible tails to probe the binding pocket will facilitate lead discovery in classical drug discovery campaigns, given the ease of accessing X ray quality crystal