Epitaxial Core-Shell Oxide Nanoparticles: First-Principles Evidence for Increased Activity and Stability of Rutile Catalysts for Acidic Oxygen Evolution

Using first-principles density-functional theory calculations combined with ab initio thermodynamics, we introduce a design protocol for RuO2-based core-shell catalysts which exhibit enhanced stability and activity under oxygen evolution reaction (OER) operating conditions. Due to their high activity and favorable stability in acidic electrolytes, Ir and Ru oxides are primary catalysts for the oxygen evolution reaction (OER) in proton-exchange membrane (PEM) electrolyzers. For a future large-scale application, core-shell nanoparticles are an appealing route to minimize the demand for these precious oxides. Here, we employ first-principles density-functional theory (DFT) and ab initio thermodynamics to assess the feasibility of encapsulating a cheap rutile-structured TiO2 core with coherent, monolayer-thin IrO2 or RuO2 films. Resulting from a strong directional dependence of adhesion and strain, a wetting tendency is only obtained for some low-index facets under typical gas-phase synthesis conditions. Thermodynamic stability in particular of lattice-matched RuO2 films is instead indicated for more oxidizing conditions. Intriguingly, the calculations also predict an enhanced activity and stability of such epitaxial RuO2/TiO2 core-shell particles under OER operation

A model-free sparse approximation approach to robust formal reaction kinetics

Accurate and transferable models of reaction kinetics are of key importance for chemical reactors on both laboratory and industrial scale. Usually, setting up such models requires a detailed mechanistic understanding of the reaction process and its interplay with the reactor setup. We present a data driven approach which analyzes the influence of process parameters on the reaction rate to identify locally approximated effective rate laws without prior knowledge and assumptions. The algorithm we propose determines relevant model terms from a polynomial ansatz employing well established statistical methods. For the optimization of the model parameters special emphasize is put on the robustness of the results by taking not only the quality of the fit but also the distribution of errors into account in a multi-objective optimization. We demonstrate the flexibility of this approach based on artificial kinetic data sets from microkinetic models. This way, we show that the kinetics of both the classical HBr reaction and a prototypical catalytic cycle are automatically reproduced. Further, combining our approach with experimental screening designs we illustrate how to efficiently explore kinetic regimes by using the example of the catalytic oxidation of CO

Fulminant Cerebral Malaria in a Swiss Patient

Abstract : Malaria remains the most important parasitic disease worldwide. Falciparum malaria is a medical emergency and requires immediate diagnosis and treatment. Cerebral malaria is a rapidly progressive, potentially fatal complication of Plasmodium falciparum infection. This case, including post-mortem observations, histology, and laboratory diagnosis, emphasizes the necessity of appropriate advice regarding malaria prophylaxis before travel to an endemic area. Malaria should always be considered in the differential diagnosis of patients presenting with fever and/or nonspecific flu-like symptoms after traveling to endemic countrie

Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet

The electronic structure of the single molecule magnet system M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission spectroscopy, and density functional calculations. There is good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 eV and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron atom, giving a high spin state molecule with a total S=5 effective spin for the case of M = Fe.Comment: Fig.2 replaced as it will appear in J. Chem. Phy

Data-Efficient Iterative Training of Gaussian Approximation Potentials: Application to Surface Structure Determination of Rutile IrO₂ and RuO₂

Machine-learning interatomic potentials like Gaussian Approximation Potentials (GAPs) constitute a powerful class of surrogate models to computationally involved first-principles calculations. At similar predictive quality but significantly reduced cost, they could leverage otherwise barely tractable extensive sampling as in global surface structure determination (SSD). This efficiency is jeopardized though, if an a priori unknown structural and chemical search space as in SSD requires an excessive number of first-principles data for the GAP training.To this end, we present a general and data-efficient iterative training protocol that blends the creation of new training data with the actual surface exploration process. Demonstrating this protocol with the SSD of low-index facets of rutile IrO2 and RuO2 , the involved simulated annealing on the basis of the refining GAP identifies a number of unknown terminations even in the restricted sub-space of (1×1) surface unit-cells. Especially in an O-poor environment, some of these, then metal-rich terminations, are thermodynamically most stable and are reminiscent of complexions as discussed for complex ceramic materials

On the Role of Long-Range Electrostatics in Machine-Learned Interatomic Potentials for Complex Battery Materials

Modeling complex energy materials such as solid-state electrolytes (SSEs) realistically at the atomistic level strains the capabilities of state-of-the-art theoretical approaches. On one hand, the system sizes and simulation time scales required are prohibitive for first-principles methods such as the density functional theory. On the other hand, parameterizations for empirical potentials are often not available, and these potentials may ultimately lack the desired predictive accuracy. Fortunately, modern machine learning (ML) potentials are increasingly able to bridge this gap, promising first-principles accuracy at a much reduced computational cost. However, the local nature of these ML potentials typically means that long-range contributions arising, for example, from electrostatic interactions are neglected. Clearly, such interactions can be large in polar materials such as electrolytes, however. Herein, we investigate the effect that the locality assumption of ML potentials has on lithium mobility and defect formation energies in the SSE Li7P3S11. We find that neglecting long-range electrostatics is unproblematic for the description of lithium transport in the isotropic bulk. In contrast, (field-dependent) defect formation energies are only adequately captured by a hybrid potential combining ML and a physical model of electrostatic interactions. Broader implications for ML-based modeling of energy materials are discussed

Challenges of the LHC Computing Grid by the CMS experiment

This document summarises the status of the existing grid infrastructure and functionality for the high-energy physics experiment CMS and the expertise in operation attained during the so-called ”Computing, Software and Analysis Challenge” performed in 2006 (CSA06). This report is especially focused on the role of the participating computing centres in Germany located at Karlsruhe, Hamburg and Aachen

Effects on performance, carcass and meat quality of replacing maize silage and concentrate by grass silage and corn-cob mix in the diet of growing bulls

Grass silage is barely used in intensive beef production, but it is unclear if its lower energy supply compared to maize-silage feeding really impairs growth performance. Diets with 100, 300, 500 or 750 g grass silage/kg dry matter replacing maize silage and concentrate were tested with or without dried corn-cob mix (CCM). Performance, carcass and meat quality were studied in 30 Limousin-sired bulls. Feeding grass silage, CCM, and concentrate in a ratio of 500:300:200 allowed to maintain a similar animal performance, carcass and meat quality compared to a conventional maize silage/concentrate diet. Increasing the dietary grass silage proportion to 750 g/kg decreased the shear force of the meat. The proportion of n–3 fatty acids in intramuscular fat increased with dietary grass silage proportion. Consequently, a strategic combination of grass silage with energyrich forages may facilitate grassland-based feeding strategies in intensive beef production with favourable meat fatty acid profiles and a performance comparable to that with maize-silage based diets

Time-reversal symmetry breaking in superconducting low-carrier-density quasi-skutterudite Lu3Os4Ge13

The complex structure of the Remeika phases, the intriguing quantum states they display, and their low carrier concentrations are a strong motivation to study the nature of their superconducting phases. In this work, the microscopic properties of the superconducting phase of single-crystalline Lu$_3$Os$_4$Ge$_{13}$ are investigated by muon-spin relaxation and rotation ($\mu$SR) measurements. The zero-field $\mu$SR data reveal the presence of spontaneous static or quasi-static magnetic fields in the superconducting state, breaking time-reversal symmetry; the associated internal magnetic field scale is found to be exceptionally large ($\approx$ 0.18~mT). Furthermore, transverse-field $\mu$SR measurements in the vortex state of Lu$_3$Os$_4$Ge$_{13}$ imply a complex gap function with significantly different strengths on different parts of the Fermi surface. While our measurements do not completely determine the order parameter, they strongly indicate that electron-electron interactions are essential to stabilizing pairing in the system, thus, demonstrating its unconventional nature.Comment: 7 pages, 2 figure