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Electronic and Structural Property Comparison of Iridium Based OER Nanocatalysts Enabled by Operando Ir L3 Edge X ray Absorption Spectroscopy
Get PDFIn this study, we investigate the electronic and structural behavior of a newly developed and of a commercially available Ir based oxygen evolution reaction OER catalyst under relevant conditions employing an operando Ir L3 edge X ray absorption near edge structure and extended X ray absorption fine structure approach. The newly developed Kopernikus P2X amorphous IrOx TiO2 catalyst is compared to the current commercial benchmark catalyst crystalline IrO2 TiO2, Umicore Elyst. Analysis of the redox behavior of the catalysts shows distinct electronic differences between the amorphous and crystalline oxides, with the former exhibiting significant reversible electronic transformations. Employing an equivalent charge transfer approach following Faraday s law of electrolysis, we study the behavior of the catalysts under equivalent OER conditions chronopotentiometric steps , as opposed to the conventional chronoamperometric approach. This enables the derivation of property amp; 8722;structure relationships under equivalent OER conditions for materials exhibiting distinctly different activities. The P2X IrOx TiO2 catalyst undergoes substantial electronic structure changes, with larger reduction in the Ir amp; 8722;O bond lengths compared to that of the commercial benchmark catalyst. The correlation between electronic states and local geometric information highlights diverse OER pathways, suggesting that the newly developed P2X IrOx TiO2 catalyst and the benchmark IrO2 TiO2 commercial catalyst follow mechanisms akin to those of amorphous iridium oxide am IrOx and rutile IrO2, respectively. These results shed light on the intrinsic activities of different iridium oxide based catalysts and provide crucial insights for enhancing their performances in proton exchange membrane water electrolyzer
Cellodextrin and beta D 1, 3 glucan phosphorylases as biocatalysts for novel glucan structure synthesis
No full textEnzymatic synthesis of polysaccharides is a relatively new field of science which combines innovative materials with the biological precision of enzymes. The publications presented in this thesis demonstrate that enzyme catalyzed reactions can be utilized to produce unique carbohydrate based materials. The work focuses on enzymatic synthesis of cellulose and amp; 946; 1,3 glucan with phosphorylase enzymes, aiming at the same to influence the structural properties of the produced polysaccharides for example by adjusting reaction conditions and performing the reactions with the enzyme s native and non native glycosyl acceptors. Publication 1 focuses on a recombinantly produced cellodextrin phosphorylase from Clostridium thermocellum bacteria and its application in in vitro cellulose synthesis. The most relevant findings of this work were that the length of the synthetic cellulose polymers as well as their structural properties of the cellulose fibrils that formed, could be influenced based on the initial concentration of the glycosyl acceptors. These results lead towards tailored cellulose materials that can be used in different applications. Utilizing similar methodology, in publication 2 we investigated amp; 946; 1,3 glucan synthesis with a recombinantly produced amp; 946; 1,3 glucan phosphorylase. When the synthesis reactions were carried out at certain temperatures, unique layered hexagonal particles were produced. These results improve our understanding on the structural behaviour of triple helical amp; 946; 1,3 glucans and broaden the range of enzymatically synthesizable carbohydrate based structures. Publication 3 broadens the scope of polysaccharide synthesis by utilizing chromophoric glycosyl acceptors as substrates for enzymatic synthesis reactions, which makes it possible to attach color molecules covalently to the structures that are formed as a product. This approach adds color molecules to the list of application areas for enzymatically synthesized materials and improves their attractability. Together, this research improves our understanding on the mechanisms of phosphorylase catalyzed polysaccharide synthesis and leads towards tailored biomaterials. The implications of this research are far reaching, and they have potential applications in smart materials, biocompatible and functional materials among other. This thesis highlights the broad potential of glycoside phosphorylases in biomaterial science and lays the groundwork for developing tailored carbohydrate based material
Mechanisms of enzyme adaptation to extreme environments The rational design of a thermophilic chorismate mutase
No full textExtremophiles, especially those living in high temperature environments, exhibit unique enzymatic mechanisms that allow survival under conditions detrimental to most life forms. Of particular interest is thermophiles, which are able to thrive at temperatures at which psychrophiles and mesophiles unfold and cease to function. The mechanisms by which these enzymes are able to overcome this temperature extreme are not yet well understood, leading to an increasing interest in studying how they function. Thermophiles have a multitude of applications under extreme conditions in industrial processes such as pharmaceuticals, waste management, and textiles, so a more complete understanding of these molecular mechanisms can lead to the development of novel enzymes for these purposes. This doctoral thesis focuses on exploring the molecular adaptations of the enzyme chorismate mutase CM . Chorismate mutases are found in bacteria and plants where they catalyze the conversion of chorismate to prephenate, an important precursor in the biosynthesis of aromatic amino acids. In this thesis, I characterize a new mesophilic chorismate mutase from B. pumilus, and a new thermophilic chorismate mutase from an unknown organism found from bioprospect soils in Antarctica. Using the thermophile as a guide, I attempt to mutate the mesophilic CM, inducing thermophilic behavior. The research in this thesis employs empirical valence bond EVB simulations to elucidate the molecular behavior of chorismate mutase. The methodology involves detailed computational modeling, to obtain accurate free energy estimates of the enzymatic reaction, emphasizing the enzyme s structural and functional adaptations to different environments. By conducting simulations across a range of temperatures, I am furthermore able to extract the enthalpic and entropic contributions to the activation free energy, providing insights into the molecular dynamics and stability mechanisms of chorismate mutase. This enables highlighting significant differences in enzyme behavior between normal and extreme environmental conditions. The findings contribute to a deeper understanding of enzyme adaptation mechanisms in extremophiles. The study also discusses the potential of EVB simulations as a powerful tool for exploring enzyme behavior in extremophiles, setting the stage for future research in this field. The thesis concludes by underscoring the importance of computational approaches in advancing our understanding of life under extreme conditions and their practical applications in industr
Advancing inorganic perovskite solar cells for application in tandem architectures
No full textSilicon perovskite tandem solar cells have remarkable power conversion efficiencies PCEs and can contribute to the rapid transition towards renewable energy sources. While inorganic perovskite solar cells show superior temperature stability as compared to organic inorganic perovskite solar cells, they have lower PCEs and lower open circuit voltages VOC , i.e. a higher voltage loss. In addition, a strong hysteresis in current density voltage measurements is common and results in a reduced stabilised power output. This thesis investigates the reasons for this and presents solutions for the higher voltage loss and hysteresis in inorganic perovskite solar cells. By conducting intensity dependent photoluminescence PL measurements on perovskite layers with and without each charge selective transport layer CTL , the contribution of each interface to the voltage loss could be quantified. This allowed for a targeted improvement of the limiting interface. For p i n CsPbI2Br perovskite solar cells, a lithium fluoride interlayer between the perovskite and the CTL C60 improved the energy level alignment and decreased the defect density at the interface. Even though the VOC was improved by 110mV, a strong mismatch between quasi Fermi level splitting QFLS and VOC remained. The perovskite C60 interface was also found to limit the efficiency of p i n DMAI CsPbI3 perovskite solar cells. A surface treatment of the perovskite layer using 1,4 butanediamine DAB improved this interface, removing the QFLS amp; 8722;e VOC mismatch. In combination with a passivation layer consisting of the fluorinated sodium molecule F Na, the limitation of the perovskite C60 interface could be overcome, and the VOC and fill factor could be substantially increased. These targeted improvements resulted in p i n DMAI CsPbI3 perovskite solar cells with a PCE of 20.05 . A comparative loss analysis showed that the voltage loss is almost as low as in state of the art triple cation perovskite solar cells, but the perovskite C60 interface needs further improvement. Measurements on CsPbI2Br and DMAI CsPbI3 perovskite solar cells revealed one order of magnitude higher ion densities and one to two orders of magnitude lower mobilities than in organic inorganic perovskite solar cells. Mobile ions were found to decrease the PCE, most likely by accumulating at the interfaces, screening the internal field and therefore increasing non radiative recombination. Even though the ion densities were similar, this decrease in PCE was lower in DMAI CsPbI3 perovskite solar cells as compared to CsPbI2Br perovskite solar cells. This suggests that the more effective interface passivation in DMAI CsPbI3 perovskite solar cells can decrease the non radiative recombination at the interface even at high ion densities, resulting in a lower hysteresis. These results addressed the main challenges for inorganic perovskite solar cells and presented new potential top cells for silicon perovskite tandem solar cell
Pseudo fermion functional renormalization group for spin models
Get PDFFor decades, frustrated quantum magnets have been a seed for scientific progress and innovation in condensed matter. As much as the numerical tools for low dimensional quantum magnetism have thrived and improved in recent years due to breakthroughs inspired by quantum information and quantum computation, higher dimensional quantum magnetism can be considered as the final frontier, where strong quantum entanglement, multiple ordering channels, and manifold ways of paramagnetism culminate. At the same time, efforts in crystal synthesis have induced a significant increase in the number of tangible frustrated magnets which are generically three dimensional in nature, creating an urgent need for quantitative theoretical modeling. We review the pseudo fermion PF and pseudo Majorana PM functional renormalization group FRG and their specific ability to address higher dimensional frustrated quantum magnetism. First developed more than a decade ago, the PFFRG interprets a Heisenberg model Hamiltonian in terms of Abrikosov pseudofermions, which is then treated in a diagrammatic resummation scheme formulated as a renormalization group flow of m particle pseudofermion vertices. The article reviews the state of the art of PFFRG and PMFRG and discusses their application to exemplary domains of frustrated magnetism, but most importantly, it makes the algorithmic and implementation details of these methods accessible to everyone. By thus lowering the entry barrier to their application, we hope that this review will contribute towards establishing PFFRG and PMFRG as the numerical methods for addressing frustrated quantum magnetism in higher spatial dimension
Molecular mechanisms and cellular functions of RNA methyltransferases targeting non coding RNAs
No full textBone strength and residual compressive stress in apatite crystals
No full textResidual stresses are omnipresent in composite materials, often arising during the fabrication process. Residual compressive stresses were recently observed to develop in collagen fibrils during the process of mineralization. They have in fact been reported in a range of bony materials spanning tooth dentin to mammalian and fish bones. Treatment by heat or by irradiation have shown that compressive residual stresses up to 100 MPa can be released in the mineral by inducing damage to the protein fibers. This mini review assembles some of the knowledge about residual stresses in bony nanocomposites and uses a composite model to argue that such stresses play a major role in enhancing the strength of bon
Solvent cavitation during ambient pressure drying of silica aerogels
No full textAmbient pressure drying of silica gels stands out as an economical and accessible process for producing monolithic silica aerogels. Gels experience significant deformations during drying due to the capillary pressure generated at the liquid vapor interface in submicron pores. Proper control of the gel properties and the drying rate is essential to enable reversible drying shrinkage without mechanical failure. Recent in operando microcomputed X ray tomography amp; 956;CT imaging revealed the kinetics of the phase composition during drying and spring back. However, to fully explain the underlying mechanisms, spatial resolution is required. Here we show evidence of evaporation by hexane cavitation during the ambient pressure drying of silylated silica gels by spatially resolved quantitative analysis of amp; 956;CT data supported by wide angle X ray scattering measurements. Cavitation consists of the rupture of the pore liquid put under tension by capillary pressure, creating vapor bubbles within the gels. We found the presence of a homogeneously distributed vapor air phase in the gels well ahead of the maximum shrinkage. The onset of this vapor air phase corresponded to a pore volume shrinkage of ca. 50 vol that was attributed to a critical stiffening of the silica skeleton enabling cavitation. Our results provide new aspects of the relation between the shape changes of silica gels during drying and the evaporation mechanisms. We conclude that stress release by cavitation may be at the origin of the resistance of the silica skeleton to drying stresses. This opens the path toward producing larger monolithic silica aerogels by fine tuning the drying conditions to exploit cavitatio
Embedding and cross sectioning as a sample preparation procedure for accurate and representative size and shape measurement of nanopowders
Get PDFReliable measurement of the size of polydisperse, complex shaped commercial nanopowders is a difficult but necessary task, e.g., for regulatory requirements and toxicity risk assessment. Suitable methods exist for the accurate characterization of the size of non aggregated, stabilized, spherical and monodisperse nanoparticles. In contrast, industrial nanoscale powders usually require dedicated sample preparation procedures developed for the analysis method of choice. These nano powders tend to agglomerate and or aggregate, a behavior which in combination with an innate broad particle size distribution and irregular shape often significantly alters the achievable accuracy of the measured size parameters. The present study systematically tests two commercially available nanoscale powders using different sample preparation methods for correlative analysis by scanning electron microscopy, dynamic light scattering, Brunauer Emmet Teller method and differential mobility analysis. One focus was set on the sample preparation by embedding nanoparticles in carbon based hot mounting resin. Literature on this topic is scarce and the accuracy of the data extracted from cross sections of these particles is unclearly stated. In this paper systematic simulations on the deviation of the size parameters of well defined series of nanoparticles with different shapes from the nominal value were carried out and the contributing factors are discusse