Boosting water oxidation through in situ electroconversion of manganese gallide: an intermetallic precursor approach

For the first time, the manganese gallide (MnGa4) served as an intermetallic precursor, which upon in situ electroconversion in alkaline media produced high‐performance and long‐term‐stable MnOx‐based electrocatalysts for water oxidation. Unexpectedly, its electrocorrosion (with the concomitant loss of Ga) leads simultaneously to three crystalline types of MnOx minerals with distinct structures and induced defects: birnessite δ‐MnO2, feitknechtite β‐MnOOH, and hausmannite α‐Mn3O4. The abundance and intrinsic stabilization of MnIII/MnIV active sites in the three MnOx phases explains the superior efficiency and durability of the system for electrocatalytic water oxidation. After electrophoretic deposition of the MnGa4 precursor on conductive nickel foam (NF), a low overpotential of 291 mV, comparable to that of precious‐metal‐based catalysts, could be achieved at a current density of 10 mA cm−2 with a durability of more than five days.DFG, 390540038, EXC 2008: UniSysCatTU Berlin, Open-Access-Mittel - 201

The medial entorhinal cortex is necessary for temporal organization of hippocampal neuronal activity.

The superficial layers of the medial entorhinal cortex (MEC) are a major input to the hippocampus. The high proportion of spatially modulated cells, including grid cells and border cells, in these layers suggests that MEC inputs are critical for the representation of space in the hippocampus. However, selective manipulations of the MEC do not completely abolish hippocampal spatial firing. To determine whether other hippocampal firing characteristics depend more critically on MEC inputs, we recorded from hippocampal CA1 cells in rats with MEC lesions. Theta phase precession was substantially disrupted, even during periods of stable spatial firing. Our findings indicate that MEC inputs to the hippocampus are required for the temporal organization of hippocampal firing patterns and suggest that cognitive functions that depend on precise neuronal sequences in the hippocampal theta cycle are particularly dependent on the MEC

Metadata Fields and Quality Criteria - XAS Reference Database under DAPHNE4NFDI

X-ray absorption spectroscopy is important to analyse solid materials, in particular amorphous materials, disordered or multicomponent materials. Due to its vast application in diverse fields XAS has become an essential tool for studying, e.g., catalytic reactions or battery materials to mention just a few. In the field of XAS, data are often evaluated by comparing them to previously measured or calculated reference spectra [1]. This sets the high requirements concerning both spectral quality and documentation of the measurements. Under DAPHNE4NFDI, we have been working on to set up a XAS reference database including raw and processed data with an interface developed for uploading and evaluating the data. In this context, defining metadata fields about an XAS experiments and documenting this information along with data is essential to make the measured data reusable by any researcher in a similar field and beyond. Another important aspect of a curated database is that users should be able to easily judge the quality and the usability of each data set by looking at the mentioned quality criteria. In the present work, we have discussed and highlighted the importance of metadata fields and quality criteria for the data to be uploaded at the XAS database

RefXAS: an open access database of X-ray absorption spectra

Under DAPHNE4NFDI, the X-ray absorption spectroscopy (XAS) reference database, RefXAS, has been set up. For this purpose, we developed a method to enable users to submit a raw dataset, with its associated metadata, via a dedi- cated website for inclusion in the database. Implementation of the database includes an upload of metadata to the scientific catalogue and an upload of files via object storage, with automated query capabilities through a web server and visualization of the data and files. Based on the mode of measurements, quality criteria have been formulated for the automated check of any uploaded data. In the present work, the significant metadata fields for reusability, as well as reproducibility of results (FAIR data principles), are discussed. Quality criteria for the data uploaded to the database have been formulated and assessed. Moreover, the usability and interoperability of available XAS data/file formats have been explored. The first version of the RefXAS database prototype is presented, which features a human verification procedure, currently being tested with a new user interface designed specifically for curators; a user-friendly landing page; a full list of datasets; advanced search capabilities; a streamlined upload process; and, finally, a server-side automatic authentication and (meta-) data storage via MongoDB, PostgreSQL and (data-) files via relevant APIs

X-ray absorption spectroscopy in the laboratory

In der vorliegenden Arbeit wird ein flexibler Laboraufbau für Röntgenabsorptionsspektroskopie vorgestellt, mit dem es möglich, ist verdünnte Proben mit hoher Effizienz zu messen und zu charakterisieren. Das Ziel ist, durch diesen Aufbau den möglichen Anwenderkreis aufgrund der höheren Verfügbarkeit einer Labormethode, im Gegensatz zur üblichen Verwendung ausschließlich an Synchrotronstrahlungsquellen, stark zu erweitern. Sowohl industrielle Prozesskontrolle, z. B. die Bestimmung von Speziesmischungsverhältnissen, als auch wissenschaftliche Anwendungen, z. B. die Charakterisierung des Oxidationszustandes und von Bindungslängen in der Katalyseforschung spielen als Motivation eine herausragende Rolle. Von einem Demonstrationsexperiment (Prinzip gezeigt von Legall et al. [67]) zu einem funktionierenden, effizienten Spektrometer für das Messen verdünnter Proben ist es ein weiter Weg. Die Schlüsselrollen für das hier präsentierte Spektrometer spielen dabei die verwendeten Optiken auf Grundlage von Graphit Mosaikkristallen (Highly Annealed Pyrolytic Graphite, HAPG) und die verwendete von Hámos Geometrie, wodurch sich dieser Ansatz von anderen aktuell vorhandenen und in der Entwicklung befindenden Spektrometern abhebt. Die insgesamt nötigen und in dieser Arbeit präsentierten Schritte beinhalten dabei Folgendes: Die grundlegende Geometrie kann aufgrund der verwendeten Optiken nicht frei gewählt werden und muss angepasst werden. Der Einfluss dieser Geometrie und der verwendeten Mosaikkristalle auf die Abbildungseigenschaften wurde verstanden und die mathematische Beschreibung in einen Algorithmus integriert, mit dem sich aus den Messbildern Spektren erzeugen lassen. Eine Energieachsenkalibrierung funktioniert dabei durch die Verwendung von Referenzproben und –spektren. Weiterhin sind im Rahmen dieser Arbeit die wichtigen spektroskopischen Größen wie spektrales Auflösungsvermögen, Raumwinkel und simultan messbarer Energiebereich bestimmt und deren Abhängigkeit von den verschiedenen Designparametern des Spektrometers untersucht worden. Dies ermöglicht zusammen mit eigens entwickelten Simulationswerkzeugen das Design optimierter Spektrometerlösungen. Weiterhin ist explizit die Probenpräparation als wichtiger Bestandteil der Messprozedur optimiert und der Einfluss von Inhomogenitäten auf das Spektrum untersucht und beschrieben worden. Die Leistungsfähigkeit und das Potential dieses optimierten Spektrometers wurden nicht nur an zwei Demonstrationsexperimenten, nämlich der Bestimmung von Speziesmischungsverhältnissen und von Bindungslängen, gezeigt, sondern auch explizit im Rahmen wissenschaftlicher Fragestellungen zur Bestimmung des Oxidationszustandes in der Katalyseforschung. Es ist also nun möglich Röntgenabsorptionsspektroskopie sowohl zur Bestimmung des Oxidationszustandes, als auch von Bindungslängen an verdünnten Proben im Labor zu betreiben. Als eines der großen Anwendungsfelder hat sich dabei die Katalyseforschung herauskristallisiert. Dafür werden innerhalb des nächsten Jahres zwei Spektrometer gebaut, die für die Bestimmung von Bindungslängen optimiert sind. Diese Spektrometer werden dann zum einen zum Max–Planck–Institut für chemische Energiekonversion in die Arbeitsgruppe von Prof. Serena DeBeer und zum anderen an den Exzellenzcluster Unifying Systems in Catalysis (UniSysCat) für Routineuntersuchungen transferiert. Dies betont noch einmal das Potential des hier erarbeiteten Spektrometers. Zusätzliche folgende Schritte sind das Erschließen weiterer Anwenderkreise und das Austesten auch der Grenzen der Methode in Hinblick auf die Quantifizierungsfähigkeiten.In the following thesis, a highly efficient laboratory setup for X–ray absorptions spectroscopy to measure and characterize diluted samples is presented. The goal is to extend the group of users compared to the usual synchrotron radiation–based spectrometers by offering a more accessible laboratory solution. Not only industrial processes, e. g. control by means of determination of mixture ratios of species, but also scientific research, e. g. the measurement of oxidation state and bonding distance in catalysis research, are key roles for the motivation of this work. It is a long way to go from a first proof of principle (shown by Legall et al. in 2009 [67]) to a working, highly efficient spectrometer for the measurement of also diluted samples. The key parts for the developed spectrometer are the used optics based on graphite mosaic crystals (Highly Annealed Pyrolytic Graphite, HAPG) and the von Hámos geometry. This contrasts to most of the other available laboratory spectrometers or those under development and the reason for the high efficiency. The necessary steps which are presented in this thesis are the following. The geometry cannot be chosen completely free due to the used mosaic crystals. The effect of both on the imaging properties is understood and the mathematical description is implemented in an algorithm to perform the transition from measured images to real spectra. An energy calibration is done by using reference samples and reference spectra. Additionally, spectroscopic properties as the spectral resolving power, the solid angle of detection and the simultaneously measurable spectral bandwidth are determined as well as their dependence on design parameters is understood. In combination with self–developed simulation tools, this allows to tailor optimized spectrometer solutions for various spectroscopic requirements. At last, the sample preparation is discussed as sample inhomogeneities have a major influence on the spectrum. These effects are measured as well as theoretically described. The performance and potential of this spectrometer is not only shown with two demonstration experiments, i.e. the determination of mixture ratios of different species and of bonding distances, but also in the frame of two independent projects in the frame of catalysis research. Here, the goal was the determination of the oxidation state at real world samples. From now on it is possible to perform X-ray absorption spectroscopy in the laboratory not only to determine oxidation states at diluted samples, but also bonding distances. Research in catalysis has proven to be one major field for future applications. For that purpose, two spectrometers optimized for the determination of bonding distances will be constructed and built. These spectrometers will then be transferred to first the research group of Prof. Serena DeBeer at the Max–Planck–Institute for chemical energy conversion and second to the excellence cluster Unifying Systems in Catalysis (UniSysCat) for routine investigations. This again highlights the potential of the spectrometer developed in this thesis. Additional steps will include the exploitation of further user groups and the optimization and testing of limits for using this method as a tool for quantitative analysis

XAFS spectroscopy by an X-ray tube based spectrometer using a novel type of HOPG mosaic crystal and optimized image processing

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.This paper presents recent achievements in laboratory based instrumentation for X-ray Absorption Fine Structure Spectroscopy (XAFS). The key component of the spectrometer is a HAPG mosaic crystal, which is employed in the von Hamos geometry. Due to the high efficiency of HAPG a low power micro focus X-ray tube can serve as an X-ray source. Besides a description of the spectrometer, the paper covers the treatment of the CCD images in detail. The latter is crucial in order to entirely exploit the potential of the HAPG (Highly Annealed Pyrolitic Graphite) spectrometer. One section is dedicated to applications. As a first kind of application, the concentrations of two different iron species in mixtures are determined. A second kind of typical usage of XAFS is the determination of bond lengths from the EXAFS. This XAFS application is demonstrated with metallic Ni as a reference material

Recent progress in the performance of HAPG based laboratory EXAFS and XANES spectrometers

New developments in the description and modeling of Highly Annealed Pyrolytic Graphite (HAPG) mosaic crystals have led to the possibility of designing optimized optical solutions for X-ray absorption fine structure (XAFS) spectroscopy. XAFS is a very versatile method that is usually divided into two sub methods: extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies, which need different experimental conditions concerning spectral resolving power, energetic bandwidth and number of detected photons. For facilitating XANES and EXAFS spectroscopies with laboratory- and von Hamos-based spectrometers, tailored optics were designed as well as optimized spectrometer components, i.e. an adequate microfocus X-ray source and a pixelated detector, were chosen. This is shown with a demonstration experiment on pure copper foil. In the XANES case a spectral resolving power of E/ΔE ≈ 4000 and an energy bandpass of around 300 eV were achieved with a measurement time of t = 7 min. For EXAFS, the tailored optic has an increased solid angle at moderate spectral resolving power in combination with a large energy bandpass of over 1 keV and a measurement time of t = 250 s for the given copper foil. These optimized solutions pave the way to perform XANES and EXAFS in the laboratory even for diluted samples with analyte concentrations of only a few weight percent or even less in a reasonable time frame of minutes to hours. Spectrometers, that already had an impact on research, especially catalysis research, therefore, made a huge leap in efficiency that prepares them to meet new challenges, not only as a standalone method, but also in combination with high-end synchrotron radiation facility-based XAFS experiments.TU Berlin, Open-Access-Mittel - 202

Laboratory based GIXRF and GEXRF spectrometers for multilayer structure investigations

This work reports laboratory angle resolved measurements with the goal of establishing laboratory techniques to obtain a more complete idea of the intralayer composition of multilayer samples. While X-ray reflectometry is a widely available technique for the characterization of multilayer samples, angle resolved XRF measurements (grazing emission/incidence X-ray fluorescence) are usually performed at synchrotron radiation facilities. With the development of efficient laboratory spectrometers and evaluation algorithms for angle resolved measurements, these methods become suited for routine measurements and screening. We present two laboratory spectrometers which make quantitative non-destructive elemental depth profiling feasible. For reasons of comparison a validation sample, a nickel–carbon multilayer sample, is measured with both setups and additional information on krypton contamination and its distribution is retrieved. Additionally, the first application for the characterization of multilayer structures with sub-nanometer layer thicknesses is shown.TU Berlin, Open-Access-Mittel - 201