Axel Groß

Understanding CO2 activation on ceria is central to elucidating elementary steps in catalytic CO2 conversion, yet direct vibrational identification of carbonate species on well-defined ceria single crystals has remained elusive. Here, we use polarization-resolved infrared reflection–absorption spectroscopy to identify surface carbonates formed upon CO2 adsorption on oxidized CeO2(110), with surface quality confirmed using CO as a probe molecule and X-ray photoelectron spectroscopy. Alongside molecularly physisorbed CO2, we observe bands at 1510 and 1280 cm–1 that we assign to a monodentate carbonate on the stoichiometric surface; their distinct polarization dependence matches the adsorption geometry predicted by density functional theory, giving direct experimental validation of the proposed structure. Additional bands at 1570 and 1610 cm–1, absent from the ideal-surface picture, are tentatively assigned to carbonates at defective sites such as step edges or oxygen vacancies. By establishing definitive, structurally validated vibrational fingerprints for CO2 activation on a single-crystal ceria surface, this work provides an essential molecular-level reference for interpreting infrared spectra of ceria-based powder catalysts.

The conversion of carbon dioxide into useful or environmentally benign chemicals is currently of great interest to reduce greenhouse gas emissions. Yet in spite of numerous efforts effective CO2 conversion still presents a considerable challenge. One of the most promising catalysts for CO2 conversion to hydrocarbons is copper. In this computational study based on density functional theory we have addressed bimetallic PbCu catalysts to elucidate whether there are synergistic catalytic effects through the alloying of Cu with Pb, as suggested experimentally. Using a well-established descriptor for the catalytic activity based on hydrogen and CO adsorption energies, we analyzed the potential catalytic activity of PbCu surface alloys on copper. The computational results confirm that through a combination of strain and ligand effects these surface alloys can act as favorable catalysts for valuable hydrocarbons.

At electrochemical interfaces, alkali-metal and alkaline-earth metal cations are usually described as solvated species that nonspecifically adsorb, whereas specifically adsorbed anions interact more directly with metal electrodes. However, the mode of cation-surface interaction remains poorly defined at the atomic scale because experiments typically measure averaged interfacial responses. Distinguishing hydration modulated polarization from localized ion-surface coupling therefore requires access to both the atomic structure and the redistribution of electronic charge. Using density functional theory molecular dynamics, we reexamine this distinction for hydrated K+, Na+, Ca2+, oand Mg2+ at Pt(111), Au(111), and Ag(111) metal-water interfaces. Charge neutral, symmetric 3 × 3 cells containing one cation and five to seven water molecules at each interface allow for the study of compact, ion-rich layer configurations, rather than dilute electrolytes or electrodes maintained at an applied potential. Within the sampled compact layer configurations, structural sampling and charge density difference analysis indicate that cation adsorption spans a continuum of interfacial responses, ranging from diffuse, hydration modulated polarization to localized, compact layer coupling. Divalent cations exhibit the most persistent direct contact, and the selected divalent configurations show localized electronic redistribution, while monovalent cations are more sensitive to water coverage and substrate identity. Even predominantly non-contact cations can remain electronically relevant by polarizing the interfacial water layer and metal surface. These results suggest that cation adsorption within the compact interfacial region requires a local, structure dependent description that goes beyond simple specific or nonspecific classifications.

The direct conversion of solar energy to produce useful chemical products such as molecular hydrogen is one of the ultimate goals of photocatalysis. Photochemical molecular devices enable such a process cost-efficiently while offering additional benefits like repairability. We present here a full mechanism for the complete photo-induced catalytic hydrogen evolution reaction by combining a Ru-containing photocenter and a Pt-based catalytically active center in one molecular device. State-of-the-art quantum-chemical calculations shed light on the interplay between light-driven electron transfer processes and activation of protons as substrates. They reveal an induction process and the crucial role of the formation of unpaired electronic states corresponding to a doublet and subsequent higher spin multiplicities. Furthermore, the study indicates that sacrificial donors not only provide electrons but also act as a proton regulator in combination with the bridging ligand acting as a base. Based on the mechanistic understanding derived from the detailed atomistic calculations, our study provides design principles for operative photochemical molecular devices. Thus, our results that are validated through the comparison with experimental spectroscopic data are expected to alter the perspective on elementary concepts of artificial photosynthesis.

High-throughput computational studies can significantly aid in the identification of crystalline battery materials with improved properties. Here, we present a density functional theory (DFT)-based numerical study addressing the stability of crystalline materials for chloride ion batteries under operating conditions using a grand canonical approach. Cl-ion batteries have emerged at the science stage as a possible energy storage technology promising enhanced energy density based on safe and environmentally benign chemistries. Although significant progress has been achieved in this field recently, the discovery of potential materials is only in its infancy. In the present work, we computationally address the materials class of chloride perovskites for the development of chloride-ion battery materials. Here, 18 782 intercalation configurations for 205 different compounds are evaluated employing a state-of-the-art machine-learning interatomic potential and periodic DFT calculations. For the analysis, focus is put on the comprehensive investigation with grand canonical diagrams. As this method inclusively covers the thermodynamic relations between the pristine compounds, its intercalation configurations, and possible conversion products under varying electrochemical conditions, we believe this approach is of great aid in the theoretical description and identification of potential materials. Our investigation resulted in the proposal of 23 solid electrolyte materials for further investigation. Six compounds exhibit reversible Cl intercalation/deintercalation, i.e., they are, in principle, suitable as cathode materials; however, reversible cycling should only be possible in a rather narrow potential window.

ZUSAMMENFASSUNG: Bei heterogenen Katalysatoren wird häufig angenommen, dass es unter Reaktionsbedingungen zu erheblichen chemischen und morphologischen Änderungen kommt. Es ist jedoch schwierig, Informationen über den Zustand einer Katalysatoroberfläche bei den üblicherweise angewandten hohen Drücken zu gewinnen. Für den in der industriellen Fischer‐Tropsch‐Synthese verwendeten Co‐Katalysator besteht die weitverbreitete Auffassung, dass es auf der Oberfläche zu einer kohlenstoffinduzierten Aufrauung kommt, die für die Aktivität wesentlich ist. Wir haben diese Vorstellung überprüft, indem wir die Reaktion an einer Co(0001)‐Oberfläche mit einer als Opferschicht dienenden Carbidschicht durchgeführt haben. In‐situ‐Rastertunnelmikroskopie‐Experimente bei ∼1 bar Synthesegas und 473 K zeigen jedoch, dass die vorhergesagte Aufrauung der Oberfläche bei erhöhter C‐Bedeckung nicht auftritt. Stattdessen bildet sich eine besondere kohlenstoffinduzierte Rekonstruktion aus dreieckigen partiellen Stapelfehlern, bei denen die Linien zwischen den Stapelfehlern mit C‐Atomen besetzt sind. Laut Dichtefunktionaltheorie‐Rechnungen ist die Rekonstruktion stabiler als der aufgeraute Zustand. Für die Bildungsrate der gaschromatographisch nachweisbaren C ₁ ‐ bis C ₄ ‐Reaktionsprodukte wurde kein Einfluss der Rekonstruktion beobachtet. Dieser Befund passt zu der Vorstellung, dass die Aktivität hauptsächlich durch die Dichte der atomaren Stufen bestimmt wird, die unverändert bleibt. Die Ergebnisse können die Vorstellungen über die Co‐Partikel des industriellen Katalysators auf eine neue Grundlage stellen.

Heterogeneous catalysts are often assumed to undergo substantial chemical and morphological changes under reaction conditions. However, obtaining information on the state of a catalyst surface at the usually applied high pressures is difficult. For the Co catalyst used in the industrial Fischer–Tropsch synthesis, a widely held view is that the surface experiences a carbon‐induced roughening that is essential for its activity. We have tested this idea by performing the reaction on a Co(0001) surface with a sacrificial carbide layer. In situ scanning tunneling microscopy experiments at ∼1 bar synthesis gas and 473 K show that, at the increased C coverage, the surface does not undergo the predicted roughening. Instead, a unique carbon‐induced reconstruction forms, consisting of triangular partial stacking faults in which C atoms occupy the fault lines. Density functional theory calculations reveal that the reconstruction is more stable than the roughened state. For the detectable range of C ₁ to C ₄ reaction products, gas chromatography shows no effect of the reconstruction, consistent with the view that the activity is primarily determined by the density of atomic steps, which remains unchanged. These findings can serve as a new basis for describing the Co particles of the industrial catalyst.

High-throughput computational studies can significantly aid in the identification of crystalline battery materials with improved properties. Here we present a density functional theory-based numerical study addressing the stability of crystalline materials for chloride ion batteries under operating conditions using a grand canonical approach. Cl ion batteries have emerged at the science stage as a potential energy storage technology promising enhanced energy density based on safe and environmentally benign chemistries. Although significant progress has been achieved in this field recently, the discovery of potential materials is only in its infancy. In the present work, we computationally address the materials class of chloride perovskites for the development of new chloride ion battery materials. 18782 intercalation configurations for each of a total of 205 different compounds are evaluated employing a state-of-the-art machine learning interatomic potential and periodic density functional theory calculations. For the analysis, a particular focus is put on the comprehensive investigation with grand canonical diagrams. As this method inclusively covers the thermodynamic relations between the pristine compounds, its intercalation configurations, and potential conversion products under varying electrochemical conditions, we believe this approach is of great aid in the theoretical description and identification of potential materials. Our investigation resulted in the proposal of 23 solid electrolyte materials for further investigation. Six compounds exhibit reversible Cl intercalation/deintercalation, i.e. they are in principle suitable as cathode materials, however, the reversible cycling should only be possible in a rather narrow potential window.

Hard carbon is one of the most promising anode materials for post-Li-ion batteries; however, the relationship between the precursor material and performance is still hardly understood.