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Li-rich layered oxides (LRLO) with specific energies beyond 900 Wh kg$^{−1}$ are one promising class of high-energy cathode materials. Their high Mn-content allows reducing both costs and the environmental footprint. In this work, Co-free Li$_{1.2}$Mn$_{0.6}$Ni$_{0.2}$O$_{2}$ was investigated. A simple water and acid treatment step followed by a thermal treatment was applied to the LRLO to reduce surface impurities and to establish an artificial cathode electrolyte interface. Samples treated at 300 °C show an improved cycling behavior with specific first cycle capacities of up to 272 mAh g$^{−1}$, whereas powders treated at 900 °C were electrochemically deactivated due to major structural changes of the active compounds. Surface sensitive analytical methods were used to characterize the structural and chemical changes compared to the bulk material. Online DEMS measurements were conducted to get a deeper understanding of the effect of the treatment strategy on O$_2$ and CO$_2$ evolution during electrochemical cycling.

Unravelling the mystery of Au/CeO2 catalysts! Challenged by the complex nature of Au/CeO2 catalysts, operando X-ray absorption spectroscopy in the near and extended Au LIII and Ce LIII energy edges is employed to decipher different aspects of the electronic and geometric features of Au NPs/clusters and CeO2 support. These results combined with findings from ex-situ XPS, in situ FTIR/Raman spectroscopy and temporal analysis of products (TAP) reactor, provide a more fundamental insight into the performance of these catalysts. The discovery of the activity of dispersed gold nanoparticles three decades ago paved the way for a new era in catalysis. The unusual behavior of these catalysts sparked many questions about their working mechanism. In particular, Au/CeO2 proved to be an efficient catalyst in several reactions such as CO oxidation, water gas shift, and CO2 reduction. Here, by employing findings from operando X-ray absorption spectroscopy at the near and extended Au and Ce LIII energy edges, we focus on the fundamental aspects of highly active Au/CeO2 catalysts, mainly in the CO oxidation for understanding their complex structure-reactivity relationship. These results were combined with findings from in situ diffuse reflectance FTIR and Raman spectroscopy, highlighting the changes of adlayer and ceria defects. For a comprehensive understanding, the spectroscopic findings will be supplemented by results of the dynamics of O2 activation obtained from Temporal Analysis of Products (TAP). Merging these results illuminates the complex relationship among the oxidation state, size of the Au nanoparticles, the redox properties of CeO2 support, and the dynamics of O2 activation., publishedVersion

The formation of the solid electrolyte interphase at the electrode-electrolyte interface is studied by X-ray photoelectron spectroscopy and dispersion-corrected density functional theory calculations. The interaction between an adsorbed ionic liquid, Li, and a Co3O4(111) thin-film model anode reveals bis(trifluoromethylsulfonyl)imide and 1-butyl-1-methylpyrrolidinium decomposition and lithiation of the cobalt oxide. In this work we aim towards the molecular understanding of the solid electrolyte interphase (SEI) formation at the electrode electrolyte interface (EEI). Herein, we investigated the interaction between the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI), Li and a Co3O4(111) thin film model anode grown on Ir(100) as a model study of the SEI formation in Li-ion batteries (LIBs). We employed mostly X-ray photoelectron spectroscopy (XPS) in combination with dispersion-corrected density functional theory calculations (DFT-D3). If the surface is pre-covered by BMP-TFSI species (model electrolyte), post-deposition of Li (Li+ ion shuttle) reveals thermodynamically favorable TFSI decomposition products such as LiCN, Li2NSO2CF3, LiF, Li2S, Li2O2, Li2O, but also kinetic products like Li2NCH3C4H9 or LiNCH3C4H9 of BMP. Simultaneously, Li adsorption and/or lithiation of Co3O4(111) to LinCo3O4 takes place due to insertion via step edges or defects; a partial transformation to CoO cannot be excluded. Formation of Co0 could not be observed in the experiment indicating that surface reaction products and inserted/adsorbed Li at the step edges may inhibit or slow down further Li diffusion into the bulk. This study provides detailed insights of the SEI formation at the EEI, which might be crucial for the improvement of future batteries., publishedVersion

Ru/Al2O3 ist ein au��erordentlich stabiler, aber weniger aktiver Katalysator f��r Methanisierungs-Reaktionen. Hier berichten wir ��ber einen neuartigen Ansatz, mit dem die Aktivit��t dieser Katalysatoren bei der Methanisierung von CO2 in CO2/H2-Gemischen erheblich gesteigert werden kann. Hochaktive und -stabile Ru/��-Al2O3-Katalysatoren wurden ��ber eine Hochtemperatur-Behandlung im reduktiven Reaktionsgasgemisch erhalten. Operando/In-situ-Spektroskopie und Rastertransmissionselektronenmikroskopie (STEM)-Abbildungen zeigen, dass die deutlich erh��hte Aktivit��t f��r die Methanisierung von CO bzw. CO2 mit einer Abflachung der Ru-Nanopartikel und der Bildung von stark basischen Pl��tzen auf dem hydroxylierten Aluminiumoxid einhergeht. Die erh��hte Aktivit��t der Katalysatoren um Faktoren von 5 (CO) bzw. 14 (CO2) f��hren wir auf eine aktivierte Modifikation der Tr��ger-Metall-Wechselwirkungen zur��ck, die durch eine reaktive Modifizierung der Al2O3-Oberfl��che im Reaktionsgas und eine erh��hte thermische Mobilit��t der Ru-Nanopartikel verursacht wird., publishedVersion

Angewandte Chemie / International edition 59, 2-10 (2020). doi:10.1002/anie.202007228, $Ru/Al_2O_3$ is a highly stable, but less active catalyst for methanation reactions. Here we report an effective approach to significantly improve its performance in the methanation of $CO_2/H_2$ mixtures. Highly active and stable $Ru/γ‐Al_{2}O_{3}$ catalysts were prepared by high-temperature treatment in the reductive reaction gas. Operando / in situ spectroscopy and STEM imaging reveals that the strongly improved activity, by factors of 5 and 14 for $CO$ and $CO_2$ methanation, goes along with a flattening of the Ru nanoparticles and the formation of highly basic hydroxylated alumina sites. We propose an activated modification of the metal-support interactions (MSIs) as origin of the increased activity, caused by reactive modification of the $Al_2O_3$ surface in the reductive atmosphere and increased thermal mobility of the Ru nanoparticles, allowing their transfer to modified surface sites. We suggest this as a general approach for the modification of alumina-supported noble metal catalysts in reactions involving reducing atmospheres., Published by Wiley-VCH, Weinheim

While being highly active for the CO oxidation reaction already at low temperatures, Au/CeO2 catalysts suffer from continuous deactivation with time on stream, with the activity and deactivation depending on the initial catalyst activation procedure. In previous X-ray absorption measurements at the Au LIII edge, which focused on changes in the electronic and geometric changes of Au, we found a modest increase of the Au particle size during reaction, with the Au nanoparticles (NPs) present in a dominantly metallic state during reaction, regardless of the pretreatment. Here we aim at expanding on these insights by examining the changes in electronic and chemical composition of the CeO2 support induced by different pretreatment procedures and during subsequent CO oxidation at 80 &deg, C, by following changes at the Ce LIII near edge region in time-resolved operando X-ray absorption measurements. The results indicate a strong dependence of the initial concentration of Ce3+ ions on the pretreatment, while during subsequent reaction this rapidly approaches a steady-state value which depends on the oxidative/reductive character of the reaction gas mixture, but is largely independent of the pretreatment. These results are discussed and related to earlier finding on the electronic properties of Au nanoparticles under identical reaction conditions.

Changes of the geometric and electronic structure of gold on Au/CeO2 catalysts induced by different pre-treatments (oxidative and reductive) and the CO oxidation reaction at 80°C have been determined by XANES and EXAFS. The results demonstrate that the active species during reaction is metallic Au, and that there is a reaction induced Au particle growth. This is true for each of the different pre-treatment procedures, although these result in significantly different Au particle sizes as well as different Au oxidation states. Correlations to the catalysts activity give a detailed insight into the origin of deactivation on Au/CeO2 under present reaction conditions, in particular on the role of the Au particle size during reaction

A continuously working arc cluster ion source was used to prepare mass-filtered Fe nanoparticles with a mean size of 6 to 10 nm. Their structure was determined by HRTEM. The nanoparticles were deposited into an Al matrix and additionally on a W(110) substrate for comparison. Within the matrix they maintain their spherical shape and do not show any magnetic anisotropic effect. For uncapped Fe nanoparticles on a tungsten surface, a flattening is observed by STM and the nanoparticles exhibit a distinct magnetic anisotropy with the easy magnetization axis being in the surface plane. Correlating both investigations we conclude that this observation is due to shape and interface-induced contributions to the magnetic anisotropy., publishedVersion

Der Ausgangspunkt dieser Arbeit ist die fundamentale Untersuchung der Unterschiede der elektrochemischen Zn-Abscheidung auf Au(111)- und Au(100)-Einkristallelektroden aus der ionischen Flüssigkeit N-Propyl-N-methylpiperidinium bis(trifluoromethylsulfonyl)imid. Zusätzlich sollen ein Aufbau zur eigenen Herstellung von Einkristallen mittels des Flammenschmelzverfahrens errichtet und damit Au(111)- und Au(100)-Einkristalloberflächen für elektrochemische Messungen präpariert werden. Für diese Arbeit ergeben sich somit folgende Fragestellungen: • Welche Erweiterungen müssen beim klassischen Flammenschmelzverfahren eingeführt werden um Au-Einkristalle in vergleichbarer Qualität zu kommerziellen Einkristallen herzustellen? Dieses Thema soll als „Proof-of-Concept“ zeigen, dass durch kleine Anpassungen am Flammenschmelzverfahren qualitativ gleich gute Au-Einkristalle erhalten werden können, wie es bereits für Pt-Einkristalle möglich ist. • Wie verhält sich eine Au(111)-Oberfläche im Vergleich zu einer Au(100)-Oberfläche in Kontakt mit der reinen ionischen Flüssigkeit, sowie bei der elektrochemischen Zn-Abscheidung aus dieser? Dieses Thema soll als Grundlage für die weitere Entwicklung von Zn-Luft-Batterien dienen und den Einfluss der Oberflächenorientierung auf die Zn-Ab-scheidung charakterisieren, um kompliziertere Elektroden besser verstehen zu können. • Können mit dem Flammenschmelzverfahren durch weitere Anpassungen zum ersten Mal auch Einkristalle aus unedlen Metallen hergestellt werden? Dieses Thema soll zukünftige Forschung auf monokristallinen Metallober flächen ermöglichen, die sonst nur schwer zugänglich sind. So sind beispielsweise für verschiedene Batterie-, Brennstoffzellen- und Katalysesyteme Cu oder Ni als Grundlagensystem deutlich interessanter als das zumeist verwendete Au.

Der Wandel in der ökologisch-politischen Agenda in den letzten Monaten hat deutlich gemacht, dass ein Wandel in der Energiegewinnung und -speicherung nötig ist. Um diesen Wandel zu beschleunigen sind neue Batterietechnologien nötig. Momentan sind Li-Ionen Batterien an der Spitze, in der Zukunft sind aber Batterien mit einer höheren Energiedichte nötig. Ein solcher Batterie-Typ sind Batterien die auf Metall-Anoden basieren, diese neigen aber dazu, die Lebensdauer verringernde, kristalline Gewächse, sogenannte "Dendriten", auszubilden. Die am meisten verbreiteten Erklärungsansätze für jenes Dendritwachstum konzentrieren sich auf die Elektrolyt Zusammensetzung und jene der Festkörper - Elektrolyt Grenzschicht. Kürzlich erfolgte Experimente zeigten aber, dass dem Dendritwachstum sogenanntes Nadelwachstum vorhergeht. Die Bildung jener Nadeln geschieht aber auch bei der physikalischen Gasphasenabscheidung von Lithium auf verschiedene Metallsubstrate.[1] Daher scheinen elektrolyt-unabhängige Faktoren für die Bildung jener Dendrit-Vorläufer verantwortlich zu sein. Die erwähnten Ergebnisse legen nahe, dass metall-inhärente Eigenschaften für die Tendenz zum Dendritwachstum eines Metalls verantwortlich sind. Eine Untersuchung der Festkörper- und Oberflächeneigenschaften führte jedoch zu keiner Korrelation. Ein Vergleich verschiedener Diffusionsprozesse an Oberflächenstrukturen sagt die experimentell beobachtete rauhe Oberflächenmorphologie von Lithium und die flache Morphologie von Magnesium voraus. Des Weiteren wurde für verschiedene Metalle eine Korrelation mit der Diffusionsbarriere an Stufenkanten hergestellt. Ein erster Ansatz zur Berücksichtigung der elektrochemischen Umgebung war das Modellieren einer elektrochemischen Doppelschicht mit Hilfe eines auf die Oberfläche gerichteten künstlichen elektrischen Feldes mit Feldstärken von bis zu 0.1 V / Å. Es zeigte sich, dass der Einfluss jenes Feldes auf die untersuchten Prozesse und innerhalb dieser Feldstärken vernachlässigbar gering ist. Die Zyklisierbarkeit von Magnesium Anoden in Verbindung mit Iod-haltigen Elektrolyten ist sehr gut. Bisher wurde angenommen, dass hierfür eine besonders gute Diffusivität der Magnesium Ionen durch das sich an der Magnesiumoberfläche bildende Magnesiumiodid verantwortlich ist. Da die relevanten Insertionsenergien und die Leerstellenbildungsenergien aber positiv und sehr hoch sind, ist eine Diffusion von Magnesium durch jenes Salz sehr unwahrscheinlich. [1] J. Steiger: "Mechanisms of Dendrite Growth in Lithium Metal Batteries", Diss., Karlsruher Institut für Technologie (KIT) (2015); DOI: 10.5445/IR/1000045310., Changes in ecological policies in the last few months have made it obvious, that a change in energy generation, and -storage is necessary. One crucial technology facilitating this change is battery technology. Currently, Li-ion batteries are dominant, however, in the future batteries with a higher energy density are necessary. One such battery type, that is currently being researched on, are batteries based on metal anodes. However, these batteries tend to grow crystalline growths called ’dendrites’, which drastically reduce the cyclability of such batteries. While the prevalent explanations for dendrite growth focus on the electrolyte composition, and consequently the solid-electrolyte interphase (SEI) composition, recent experimental investigations showed, that dendrite growth is preceded by needle-like precursors, which also grow via physical vapor deposition onto different metal foils.[1] Thus, electrolyte independent reasons seem to be responsible for the onset of the dendrite precursor growth. The mentioned findings suggest, that metal-inherent properties are responsible for the tendency of a metal to grow dendrites, or not. Investigations into bulkand surface properties of various metals did not yield a correlation with dendrite growth. A comparison of different diffusion processes at surface structures predicts the experimentally observed rough surface morphology of lithium, and the more flat one of magnesium. Additionally, for several investigated metals, a direct correlation was found with the downward across-step diffusion barrier. As a first approach to include the electrochemical environment in this work, an electrochemical double-layer (EDL) close to the metal surface was modeled by applying an artifical electric field with a strength of up to 0.1 V / Å onto the surface. It was found that for the investigated processes, and within this range, the effect of an electric field on diffusion barriers is neglectably small. Magnesium anodes with iodine-containing electrolytes posses a rather good cyclability. Up until now, an especially high diffusivity of the magnesium ions through magnesiumiodide, which forms on the magnesium surface, is presumed to be responsible. Another, rather suprising result of this thesis with respect to the above was, that the insertion energies of magnesium in magnesiumiodide, aswell as the vacancy formation energies of magnesiumiodide are positive and very large. Thus, a diffusion of magnesium through this salt is highly unlikely. [1] J. Steiger: "Mechanisms of Dendrite Growth in Lithium Metal Batteries", Diss., Karlsruher Institut für Technologie (KIT) (2015); DOI: 10.5445/IR/1000045310.

In electrochemistry, the atomistic structure at the solid-liquid interface has a strong influence on electrocatalytic reactions. Therefore it is of fundamental importance to understand surface properties like adsorbate structures at particular thermodynamic conditions e.g. pH, electrolyte-concentration and electrode potential first, before looking at any reaction at this interface. In this thesis I adressed the structure of various electrodes in a the presence of protons and anions, based on density functional theory calculations. Thereby I used different methods, e.g. the concept of the computational hydrogen electrode (CHE). This represents an efficient method to combine total energy calculations from density functional theory with thermodynamic properties of electrochemistry. I have extended these studies to analyze the co-adsorption of (bi)sulfate and hydrogen.