The layered double hydroxides (LDH) represent a broad class of inorganic lamellar compounds with a high versatility in composition and large range of technological applications (1). We have studied the NiCuAl LDH where the charge of the trivalent ions ($Al^{3+}$) is compensated by carbonate anions in the inter-layer space (2). The coprecipitation method has been employed for the LDH...
Metal thin films deposited on different substrates have been studied for many applications ranging from electrical contact to electrocatalysis (1,2). This work, part of the CatLab project, focuses on the development of novel catalysts based on thin-film technology. Catalysts and reference materials were produced by the Helmholtz-Zentrum Berlin (HZB) via sputtering (Poster-AC 4.4). Pd is a...
To intensify long-term renewable energy storage and conversion and furthermore make an energy-efficient conversion of renewable hydrogen and $CO_2$ to synthetic fuels and basic chemicals, within the framework of CatLab, this project deals with the targeted synthesis of active centres by reducing conventional 3D catalyst materials to two dimensions. 2D thin-film catalysts for hydrogenation and...
In the CatLab project, thin closed metal films ( 10 nm) are deposited on a homogeneous support material. In this way, the support material can influence the properties of the metal catalyst in a designed manner despite not being directly exposed to the reaction gas mixture. Such a sample configuration allows to reduce the complexity of the catalyst – support perimeter region and simplifies...
Coking has been known to be unavoidable in various catalytic reactions, e.g. non-oxidative propane dehydrogenation (PDH), which enforces the need for removal of carbon deposits in regeneration processes (1). This is typically achieved by air oxidation at temperatures between 600 °C and 700 °C (2). In the case of Pt-based catalysts, oxidative treatments at such high temperatures lead to...
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 analyses the influence of process parameters on the reaction rate to...
Modelling of dielectric interfaces remains one of the central challenges in computational chemistry. Liquid-liquid and liquid-gas interfaces have so far received relatively little attention, compared to solid-liquid and solid-gas. We present a new method for efficient simulations of large organic adsorbates at liquid-liquid and liquid-gas interfaces. The adsorbate is treated on the...
Here we report on concepts and activities of the AC department in data management and automation.
We apply the idea of the FAIR principle$^1$ and seek to establish the basis for the application of data analysis and data mining methods.
This requires reliable, reproducible data sets with high diversity. To generate such data, handbooks are used in the research in which the characterisation of...
INTRODUCTION: Conventional Mass Spectrometry (MS) techniques detect gas-phase ions based on their mass-to-charge ratio (m/z), whereas Ion Mobility-MS instruments additionally separate ions according to their size and shape. This orthogonal technique is particularly adapted for challenging samples such as glycoconjugates, which often present multiple isomers due to their inherent complex...
Operando analysis has shown that the working structure of heterogeneous catalysts is a consequence of chemical potential gradients and kinetic stabilization. Combining time-resolved transmission electron microscopy (TEM), time-resolved scanning electron microscopy (SEM), selected area electron diffraction (SAED) and online conversion detection with quadrupole mass spectrometry (QMS), we are...
One of the most relevant parameters to create a dense, cold, and stable ensemble of molecules is to create them in a controllable manner. In most of the cases, molecules XY that will be further cooled down appear as a product of a reaction between an ablated metal, X, in a given atmosphere enriched with a Y-donor gas, AY$_n$, i.e., AY$_n$+X$\rightarrow$XY + AY$_{n-1}$. However, and...
Lipids are essential for all forms of life. They constitute the scaffold of every cell membrane, act as hormones, secondary messengers, and energy storage for times of famine. The functional diversity of lipids goes hand in hand with a huge structural diversity and heterogeneity. One major challenge in the analysis of lipids is the existence of isomers – molecules with different structures...
Rapid deactivation presently limits a widespread use of high-temperature solid oxide cells (SOCs) as otherwise highly efficient chemical energy converters. With deactivation triggered by the ongoing conversion reactions, an atomic-scale understanding of the active triple-phase boundary between electrolyte, electrode, and gas phase is essential to increase cell performance.
Here, a...
Cyclic voltammograms (CVs) are one of the most studied experiments in electrochemistry. Recently, we showed that the inclusion of applied potential effects in density-functional theory (DFT) calculations within an implicit solvent model affects the simulated thermodynamic cyclic voltammograms. In particular, a consistent grand canonical description alters the CV's shape due to classical...
Machine-learning interatomic potentials like Gaussian Approximation Potentials (GAPs) constitute a powerful class of surrogate models to computationally involved first-principles calculations.[1] At similar predictive quality but significantly reduced cost, they could leverage otherwise barely tractable extensive sampling as in global surface structure determination (SSD).[2] This efficiency...
The combination of modern machine learning (ML) approaches with high-quality data from quantum mechanical (QM) calculations can yield models with an unrivalled accuracy/cost ratio. However, such methods are ultimately limited by the computational effort required to produce the reference data. In particular, reference calculations for periodic systems with many atoms can become prohibitively...
The kinetic Monte Carlo (kMC) method is, without question, the physically most sound approach for simulating chemical kinetics on heterogeneous catalysts. Unlike prevalent approaches which employ some kind of physical approximation, it essentially is a numerical method and allows estimating turnover frequencies or coverages with a tunable accuracy, given a reaction mechanism and corresponding...
Graphene (Gr) is a two-dimensional allotrope of carbon which has been demonstrated as a highly attractive material for many high technology applications. Current large-scale synthesis strategies are, however, costly and usually yield a defect-rich product, void of its outstanding properties. Recently, rapid and high-quality synthesis of Gr has been discovered on liquid Cu. Compared to its...
One promising strategy for better utilizing renewable energy from intermittent sources such as wind and solar is to use it to convert simple molecules (N$_2$, CO$_2$, H$_2$O) found in our environment into useful products such as NH$_3$, H$_2$, and hydrocarbons. The electrochemical reduction of CO$_2$ (CO$_2$RR) is a particularly appealing approach because it not only recycles CO$_2$ back into...
Catalysts have the ability of improving the kinetics of a given chemical reaction by providing alternative reaction paths with lower activation energies, thus affecting the selectivity of a chemical reaction.$^1$ Their activity, selectivity, and lifetime strongly depend on their morphology, substrate, chemical composition, and oxidation state.$^2$ Particularly, bimetallic nanoparticles (NPs)...
Does electrochemistry at stepped and kinked single-crystal surfaces differ significantly from that at ideal low-index surfaces? Intuitively, in a classical electrostatic picture we expect a potential-induced excess surface charge to accumulate on protruding sites. In this picture, the high local surface curvature causes strong inhomogeneous electrical fields, that then could significantly...
In situ information on surface structure and morphology is of utmost importance in order to understand and influence the electrode activity and selectivity in electrocatalysis [1]. Progress in prominent electrochemical processes like CO$_{2}$ electroreduction hinges on such knowledge [2]. Electrochemical scanning probe microscopies (EC-SPMs), including EC-AFM [3] and EC-STM [4], can provide...
A nano-scale complexion encapsulating solid-state electrolyte Li$_{(1+x)}$Al$_{(x)}$Ti$_{(2-x)}$(PO$_{4}$)$_{3}$ (LATP) grains is identified which functions as a protective layer suppressing Li dendrite formation [1]. Hence, the ceramic LATP electrolyte shows an increased stability against electrochemical decomposition, despite the measured bulk electronic conductivity exceeding a recently...
Carbocations are important intermediates in many chemical reactions, however, due to their short lifetimes, they also are frequently elusive species that cannot be observed in the condensed phase. This short lifetime is usually given by their high chemical reactivity. Isolating carbocations in the gas phase, on the other hand, offers the opportunity to study their structures and properties....
Cobalt oxides are promising, non-precious catalysts for the anodic oxygen evolution reaction (OER) of alkaline water electrolysis. To promote a rational catalyst design, fundamental knowledge is required and topic of investigations. In this regard, it has been shown that as-prepared structurally-different CoO$_{x}$(OH)$_{y}$ materials unify towards an octahedral CoO$_{6}$ coordination with di...
Recent years have seen an explosion of work related to machine-learning (ML) models trained on electronic structure data. To push the boundaries of what can be done with physics-based ML, we have explored how ML can be directly incorporated into electronic structure calculations. This dispenses of the separation between electronic structure theory as a mere data generation device on one hand,...
Transport of energetic electrons through gases and dense media is invariably determined by electron scattering. In photoemission experiments, the influence of scattering can be avoided in gas-phase experiments by choosing a sufficiently dilute target, but inelastic scattering becomes noticeable as soon as atomic or molecular clusters are considered. In solids and liquids, inelastic scattering...
Despite being used as anode material in commercial Li-ion batteries for decades, lithium-graphite intercalation compounds (Li-GICs) are still not sufficiently understood at the atomistic level. This is, in part, due to meso-scale domain ordering and non-equilibrium phenomena, which cannot be extensively investigated by density functional theory (DFT) due to computational cost. Therefore, we...
Compound materials, such as transition-metal (TM) carbides, are anticipated to be effective electrocatalysts for the carbon dioxide reduction reaction (CO2RR) to useful chemicals. This expectation has been nurtured by density functional theory (DFT) based studies [1]. The latter predict the mixture of catalytically active sites in compound materials to break adsorption energy...
A strategy for the re-use of carbon dioxide is to convert it into a platform chemical, from which valuable products can be prepared. In particular, from all the possible products, light olefins (C2=, C3=) are of great interest as important synthesis building blocks. In the frame of the CatVIC (Catalytic Valorization of Industrial Carbon) project, our goal is to investigate the direct...
Silver catalyzes two large-scale partial oxidation reactions. At temperatures of 220-280 °C silver catalyzes to the conversion of ethylene and oxygen gas into ethylene oxide with epoxide selectivity in excess 90% being achievable. In the range of 500-650 °C silver becomes active in both the direct catalytic oxidation of methanol to formaldehyde under and methanol dehydrogenation. Near ambient...
The physicochemical properties of life-essential molecules such as carbohydrates, amino acids, and DNA arise from a series of complex intramolecular and intermolecular interactions within aqueous cellular environments. Knowledge of the aqueous-phase electronic structure of these important biomolecules is indispensable to understand structure–function relationships, chemical activity, and...
The unique physical and chemical properties of interfaces are governed by a finite depth that describes the transition from the topmost atomic layer to the properties of the bulk material. Understanding the physical nature of interfaces thus requires detailed insight into the different structures, chemical compositions, and physical processes that form this interfacial region. Such insight has...
Electrochemical reduction of CO$_{2}$ (CO$_{2}$RR) is an attractive technology to turn undesired CO$_{2}$ back into the carbon cycle driven by renewable energy and a suitable catalyst. Cu$_{2}$O nanocubes have been shown to be a promising catalyst by converting CO$_{2}$ into various C$_{2+}$ hydrocarbons.$^1$ Thus, an essential challenge is to control the selectivity toward particular...
The industrial and societal transformation towards carbon neutrality requires the development of mitigating strategies to significantly reduce the greenhouse gas emissions. In this framework, CO$_2$ electroreduction (CO$_2$RR) is an elegant and promising approach to convert excess electrical energy and store it in the chemical bonds of multicarbon (C$_{2+}$) products such as alcohols and...
Heterogeneous catalysis is strongly influenced by surface features of the respective catalysts, such as the presence, amount and nature of defects, the electronic structure and compositional variations. Here, we present an in-depth look at the surfaces of cobalt-based spinel and perovskite oxides as catalysts for the oxidation of carbon monoxide (CO) and the selective oxidation of 2-propanol....
Photoelectron Circular Dichroism (PECD) is a method of chiral discrimination, which can aid in our fundamental understanding of electron dynamics and holds promise for future analytical techniques of chiral compounds. In PECD, ionization of a non-racemic sample by circularly polarized light results in a forward-backward asymmetry of the photoelectron angular distribution. This technique has...
Computational modeling and the simulation of catalytic processes, in particular of reactions like water electrolysis to produce hydrogen and CO or CO$_2$ hydrogenation to produce alkanes or higher oxygenates, have become key ingredients in developing new catalytic materials for the sustainable generation of synthetic fuels. The calculation of relevant quantities such as adsorption enthalpies...
Electrochemical CO$_2$ reduction reaction (CO$_2$RR) converts CO$_2$ into value-added chemicals and fuels, and is an attractive pathway for closing the carbon cycle [1]. Copper based nanocatalysts are commonly used for CO$_2$RR due to their unique ability to convert CO$_2$ into more complex hydrocarbons, but the distribution of reaction products is hard to control [2]. A commonly used strategy...
Fundamental studies of reaction kinetics and operando spectroscopy are crucial for understanding the mechanism of selective oxidation of alkanes on oxide catalysts. Due to their versatile composition, exceptional redox properties and high thermal stability, perovskites with the general formula $ABO_3$ are the ideal platform for studying reaction rates and selectivity as a function of catalyst...
Electrochemical CO$_2$ reduction reaction (CO$_2$RR) over Cu based catalysts is a promising process to produce useful chemicals and fuels, but suffers from low energy efficiency and product selectivity. Among various strategy to enhance the product selectivity of CO$_2$RR, applying periodic oxidative potentials (i.e., the pulsed electrolysis) during the CO$_2$RR have been shown to be an...
Interfacial water is known to exhibit significantly slower relaxation times than bulk water, which complicates the convergence of molecular dynamics sampling but also justifies the frequent use of static interfacial water in atomistic simulations. Typical use cases for the latter are e.g. the computation of solvation energies or reaction barriers at interfaces. However, detailed knowledge...
For CO$_{2}$ electroreduction (CO$_{2}$RR), copper (Cu) is unique due to its ability to produce hydrocarbons and alcohols with a significant faradaic efficiency. This ability is ascribed to the unique binding of Cu with CO$_{2}$ and subsequent CO-like reduction intermediates.$^1$ Interestingly, there still exists debate about the location of these sites leading to the observed activity and/or...
Electrochemical energy conversion driven by renewable energy is a cost-effective, environmentally friendly route to convert undesired substances (such as CO$_2$) into valuable chemicals and fuels, but a suitable catalyst is needed. Here, due to their unique ability to convert CO$_2$ into more complex hydrocarbons, particularly attractive are Cu-based catalysts [1]. A challenge for the...
Surface diffusion and chemical reactions on surfaces are important fundamental processes in catalysis. To fully understand these processes at the atomic scale, real time and real space observations are crucial. Since the first experimental evidence for surface diffusion 100 years ago [1], a variety of methods evolved to study atomic processes on well-defined surfaces. The prominent approach of...
The oxygen evolution reaction (OER) plays a decisive role in many alternative energy schemes as it supplies the protons and also the electrons required for converting renewable electricity into chemical fuels. Electrocatalysts accelerate the reaction by facilitating both the required electron transfer and the formation as well as rupture of chemical bonds. This involvement in fundamentally...
In recent years NiO has come into focus as a low-cost, efficient material in the Oxygen Evolution Reaction (OER) via electrochemical water splitting. However, the detailed mechanism of the electrochemically induced reaction is not yet fully understood.[1] Hence, three types of experiments were performed. Firstly, as a model catalyst, NiOx thin films were put in contact with oxygen and...
Electron attachment by closed-shell species presents an interesting fundamental question: If an electron cannot be accommodated by an open valence, what attractive forces must be at play to allow for electron binding? Such attractive forces are non-valence interactions, which include electron attraction by a molecule’s dipole or quadrupole moment, polarizability, or electron correlation. Often...
The electrolysis of water is a promising method to store renewable electricity generated by solar and wind power. The efficiency of water splitting, however, is limited by the sluggish half-reaction of anodic oxygen evolution (OER), which has, in turn, led to immense interest in finding better and more cost-effective catalysts$^{1}$. Electrocatalysts based on nickel oxides/hydroxides$^{2-4}$...
Against the background of dwindling fossil fuel resources and the threats of climate change, sustainable and environmentally friendly production processes for fuels and chemical feedstock become all the more important. Methanol, a liquid fuel of high energy density, may pave the way to sustainable society [1]. It can be produced from green H$_2$ generated via electrochemical water-splitting...
The interaction of complex solids with intense light pulses can induce novel emergent phenomena far from equilibrium. Prominent examples include optical enhancement of the critical temperature in certain superconductors and photo-stabilization of metastable states. A common theme in materials featuring exotic out-of-equilibrium behavior is the formation of charge density waves (CDWs), i.e., a...
