Pure Clusters Research Articles

Boosting synergistic effects between PtGe nanoalloys and 2D materials for PEMFC applications

In the present work we have investigated the stability, CO poisoning tendency and HOR and ORR activities of small-sized monometallic Pt and bimetallic PtGe nanoclusters deposited on a series of 2D materials. By means of global minima search and mechanistic studies at the density functional theory (DFT) level with continuum implicit solvent, a screening of size, composition and support material has been carried out to obtain the optimal catalyst compositions that may boost the catalytic performance. Alloying and support effects work in two directions. On the one hand, the support increases the stability and modifies the electronic structure of the cluster via metal-support interaction. On the other hand, the cluster can change the electronic properties and catalytic activity of the support, which can be modulated with its size and composition. In addition, the 2D support assists pure Pt clusters in reducing the propensity to undergo CO poisoning, which can be further reduced by Ge alloying. This effect can be exploited to the point that the interaction with CO is not even favorable, as in Pt5Ge5/germanene, thus completely inhibiting the CO poisoning on the catalyst. Regarding the catalytic activities, all the catalysts studied in this work yield too high overpotentials for the ORR in acidic conditions, due to the presence of too oxophilic active sites which results in the overbinding of oxygenated species. However, the combination of Ge alloying and 2D support yield remarkable results in the HOR performance. The simultaneous tailoring of catalyst composition and support is demonstrated to be an effective strategy to successfully adjust the catalytic properties.

Reactive Gas Cluster Ion Beams for Enhanced Drug Analysis by Secondary Ion Mass Spectrometry.

In this study, we investigate the formation and composition of Gas Cluster Ion Beams (GCIBs) and their application in Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis. We focus on altering the carrier gas composition, leading to the formation of (Ar/CO2)n or (H2O)n GCIBs. Our results demonstrate that the addition of a reactive species (CO2) to water GCIBs significantly enhances the secondary ion yield of small pharmaceutical compounds in the positive ion mode. In negative ion mode, the addition of CO2 resulted in either a positive enhancement or no effect, depending on the sample. However, an excess of CO2 in the carrier gas leads to the formation of carbon dioxide clusters, resulting in reduced yields compared to that of water cluster beams. Cluster size also plays a crucial role in overall yields. In a simple two-drug system, CO2-doped water clusters prove effective in mitigating matrix effects in positive ion mode compared to pure water cluster, while in negative ion mode, this effect is limited. These clusters are also applied to the analysis of drugs in a biological matrix, leading to more quantitative measurements as shown by a better fitting calibration curve. Overall, the doping of water clusters with small amounts of a reactive gas demonstrates promising benefits for higher sensitivity, higher resolution molecular analysis, and imaging using ToF-SIMS. The effectiveness of these reactive cluster beams varies depending on the experimental parameters and sample type.

Nature of the Active Center for the Oxygen Reduction on Ag-Based Single-Atom Alloy Clusters.

The development of alternative alloy catalysts with high activity, surpassing platinum group metals, for the oxygen reduction reaction (ORR) is urgently needed in the field of electrocatalysis. The Ag-based single-atom alloy (AgSAA) cluster has been proposed as a promising catalyst for the ORR; however, enhancing its activity under operational conditions remains challenging due to limited insights into its actual active site. Here, we demonstrate that the operando formation of the MO x (OH) y complex serves as the key active site for catalyzing the ORR over AgSAA cluster catalysts, as revealed through comprehensive neural network potential molecular dynamics simulations combined with first-principles calculations. The volcano plot of the ORR over the MO x (OH) y complex addresses the gaps inherent in traditional metallic alloy models for pure AgSAA cluster catalysts in ORR catalysis. The appropriate orbital hybridization between OH and the dopant metal in the MO x (OH) y complexes indicated that the Ag54Co1, Ag54Pd1, and Ag54Au1 clusters are optimal AgSAA catalysts for the ORR. Our work underscores the significance of theoretical modeling considering the reaction atmosphere in uncovering the true active site for the ORR, which can be extended to other reaction systems for rational catalyst design.

Unveiling the effects of thallium and bismuth p-n doping on germanium-based clusters (n5 to n12) for applications in semiconductor materials

We report a computational investigation utilizing density functional theory (DFT) concerning the pure Gen, as well as their doped analogues (BiGen-1, TlGen-1) and p-n doped BiTlGen-2 clusters with n ranging from 5 to 12. To get a deeper insight in their properties, we focus on the size dependency of these Gen, BiGen-1, TlGen-1, and BiTlGen-2 clusters as well as their shape, relative stabilities, and thermochemical characteristics including binding energy, fragmentation energy, second-order energy difference, and HOMO-LUMO energy gaps. The systematic observations from the data of binding energies indicate that BiGen-1, TlGen-1 and BiTlGen-2 cluster have more structural and thermodynamic stability when compared with the pure Gen clusters. To validate the electronic characteristics of these clusters, additional energy gap-related parameters such as chemical hardness, vertical ionization potentials (VIP), and vertical electron affinities (VEA) are also computed. The doping seems to stabilize the Gen clusters and the highest stability has been achieved for BiGe7, TlGe9, and BiTlGe7 clusters as suggested by the combined effect of all these parameters.

Theoretical study of the reaction of organic peroxyl radicals with alkenes and their accretion products involved in the atmospheric nucleation

Organic peroxy radicals, including alkyl peroxy radicals (RO2) and acyl peroxy radicals (RC(O)O2), are crucial intermediates in the atmospheric photochemical reactions of volatile organic compounds and directly or indirectly affect the distribution of other species (e.g., HO2 radicals, NOx, OH radicals, and alkenes). However, the atmospheric reactions of organic peroxyl radicals with alkenes (RO2 + alkene reactions) are not fully understood. The present study used theoretical calculations to investigate the reaction mechanisms of various organic peroxy radicals with different alkenes, with the aim of clarifying the influence of molecular structure on RO2 + alkene and RC(O)O2 + alkene reactions. Furthermore, we investigated the nucleation mechanisms of the subsequent oxidation products. The results show that the reaction rate constants for RC(O)O2 + alkene reactions are 1–6 orders of magnitude higher than those for RO2 + alkene reactions. The addition products formed by organic peroxy radicals with alkenes not only undergo monomolecular reactions to generate epoxides, but also participate in O2 addition to yield the accretion products ROOR’. H2SO4 molecules synergistically interact with low-volatility ROOR’ to grow clusters up to the 1–2 nm scale, and the ROOR’ molecules can form pure organic clusters larger than 1 nm, even in the absence of H2SO4 molecules. Our study provides a new perspective on the formation of accretion products in the atmosphere and their involvement in new particle formation.

Study the structure, stability and CO2 adsorption of the ScVB5 cluster

A combination of genetic algorithm and density functional theory (GA-DFT) was used to calculate the minimum structures of ScVB5 clusters. The thirteen isomers of ScVB5 cluster were investigated at the level of PBE/def2-TZVPP, TPSSh/def2-TZVPP, and TPSSh/def2-QZVP levels. The relative energies, the structural geometry, ionization energy, affinity energy of neutral isomers were reported. The ScVB5 cluster can be formed by adding atom into smaller clusters. The proposed structure of ScVB5 cluster for CO2 treatment is a pentagonal bipyramid in the Cs symmetry with vanadium atom at one of the vertices and scandium atom in the base of bipyramid. The favor position for adsorp CO2 by the ScVB5 cluster were at around of Sc and V atoms. The dual transition metal-doped boron clusters can interact with CO2 molecules stronger than pure boron clusters.

Enantioselective Synthesis of Homochiral Hierarchical Nd8Fe3-Oxo Cluster from Racemic Nd9Fe2-Oxo Cluster.

Enantioselective synthesis of homochiral rare earth clusters is still a great challenge. In this work, we developed an efficient "cluster to cluster" approach, that is, a pair of enantiomerical R/S-{Nd8Fe3}-oxo clusters were successfully obtained from the presynthesized racemic {Nd9Fe2}-oxo cluster. R/S-hydrobenzoin ligands trigger the transformation of the pristine clusters by an SN2-like mechanism. Compared to the pristine cluster with an achiral core, the new cluster exhibits hierarchical chirality, from ligand chirality to interface chirality, then to helix chirality, and finally to supramolecular double helix chirality. The spectral experiments monitored the transformation and confirmed distinctly structure-related optical activity. The enantiomeric pure cluster also exhibits a potential asymmetric catalytic activity.

Ionization of small atmospheric acid–base clusters and its prospective role in seeding the growth of aqueous clusters

In the present study, we have examined the ionization of a set of small atmospheric acid–base clusters. The calculated ionization energy (IE) ranges from ∼660 kJ mol−1 to ∼1120 kJ mol−1, with clusters consisting of just the bases yielding the smallest IEs, while those of the acids yield the largest. For neutral clusters that form most readily, the IEs range from ∼790 kJ mol−1 to ∼880 kJ mol−1. These values are generally smaller than those of other chemicals with significant atmospheric presence. Thus, the radical cations of the acid–base clusters are not likely to ionize other atmospheric species. Charged atmospheric species have been hypothesized to facilitate the growth of large clusters. We have carried out a case study of the sequential hydration of an acid–base cluster and compared our results with previous studies of forming pure water clusters. The neutral acid–base cluster binds water more strongly than pure water clusters. Further strengthening of the binding can be seen for the radical cationic acid–base cluster. The resulting acid–base–water clusters may further represent a source of H3O+, which may proceed to facilitate cloud formation.

AMICO galaxy clusters in KiDS-DR3: Measuring the splashback radius from weak gravitational lensing

Context. Weak gravitational lensing offers a powerful method to investigate the projected matter density distribution within galaxy clusters, granting crucial insights into the broader landscape of dark matter on cluster scales. Aims. In this study, we make use of the large photometric galaxy cluster data set derived from the publicly available Third Data Release of the Kilo-Degree Survey, along with the associated shear signal. Our primary objective is to model the peculiar sharp transition in the cluster profile slope, that is what is commonly referred to as the splashback radius. The data set under scrutiny includes 6962 galaxy clusters, selected by AMICO (an optimised detection algorithm of galaxy clusters) on the KiDS-DR3 data, in the redshift range of 0.1 ≤ z ≤ 0.6, all observed at a signal-to-noise ratio greater than 3.5. Methods. Employing a comprehensive Bayesian analysis, we model the stacked excess surface mass density distribution of the clusters. We adopt a model from recent results on numerical simulations that capture the dynamics of both orbiting and infalling materials, separated by the region where the density profile slope undergoes a pronounced deepening. Results. We find that the adopted profile successfully characterizes the cluster masses, consistent with previous works, and models the deepening of the slope of the density profiles measured with weak-lensing data up to the outskirts. Moreover, we measure the splashback radius of galaxy clusters and show that its value is close to the radius within which the enclosed overdensity is 200 times the mean matter density of the Universe, while theoretical models predict a larger value consistent with a low accretion rate. This points to a potential bias of optically selected clusters preferentially characterized by a high density at small scales compared to a pure mass-selected cluster sample.

Adaptive Reaktion bei der Lösung von flexiblen Molekülen: Oligohydrate von 4‐Hydroxy‐2‐butanon

AbstractDurch Wasser hervorgerufene Strukturveränderungen spielen eine zentrale Rolle in der Chemie und Biologie, sind aber auf molekularer Ebene nach wie vor schwer vorherzusagen, zu messen und zu kontrollieren. Hier untersuchen wir in der Gasphase die größenabhängige Wasseraggregation am flexiblen Molekül 4‐Hydroxy‐2‐butanon und modellieren die Konformationsanpassungsfähigkeit flexibler Substrate an Wirtswassergerüste, sowie die Präferenzen für sequentielles Tröpfchenwachstum. Das Experiment wurde mittels breitbandiger Rotationsspektroskopie durchgeführt und mit quantenchemischen Berechnungen nachvollzogen. Experimentell wurden vom Di‐ bis zum Pentahydrat (4‐Hydroxy‐2‐butanon‐(H2O)n=2–5) zwei verschiedene Isomere beobachtet, einschließlich der 18O‐Isotopologen für die Di‐ und Trihydrate. Um Wassermoleküle effektiv unterzubringen, verändert sich interessanterweise das schwere Atomgerüst von 4‐Hydroxy‐2‐butanon in jedem beobachteten Isomer und entspricht nicht der stabilen Konformation des freien Monomers. Alle Solvate gehen von der Alkoholgruppe (Protonendonor) aus, behalten aber die Carbonylgruppe als sekundären Bindungspunkt bei. Die Wassergerüste ähneln stark denen in reinen Wasserclustern und balancieren zwischen der Fähigkeit von 4‐Hydroxy‐2‐butanon, die Orientierung und Position der Wassermoleküle zu steuern, und der Fähigkeit von Wasser, die Konformation des Monomers zu modulieren. Die vorliegende Arbeit liefert somit eine genaue molekulare Beschreibung, wie sich torsionsflexible Moleküle im Verlauf der fortschreitenden Solvatation dynamisch an Wasser anpassen.

Adaptive Response to Solvation in Flexible Molecules: Oligo Hydrates of 4-Hydroxy-2-butanone.

Structural changes induced by water play a pivotal role in chemistry and biology but remain challenging to predict, measure, and control at molecular level. Here we explore size-governed gas-phase water aggregation in the flexible molecule 4-hydroxy-2-butanone, modeling the conformational adaptability of flexible substrates to host water scaffolds and the preference for sequential droplet growth. The experiment was conducted using broadband rotational spectroscopy, rationalized with quantum chemical calculations. Two different isomers were observed experimentally from the di- to the pentahydrates (4-hydroxy-2-butanone-(H2O)n=2-5), including the 18O isotopologues for the di- and trihydrates. Interestingly, to accommodate water molecules effectively, the heavy atom skeleton of 4-hydroxy-2-butanone reshapes in every observed isomer and does not correspond to the stable conformer of the free monomer. All solvates initiate from the alcohol group (proton donor) but retain the carbonyl group as secondary binding point. The water scaffolds closely resemble those found in the pure water clusters, balancing between the capability of 4-hydroxy-2-butanone for steering the orientation and position of the water molecules and the ability of water to modulate the monomer's conformation. The present work thus provides an accurate molecular description on how torsionally flexible molecules dynamically adapt to water along progressing solvation.

Modulating the Hydrogenation Mechanism of Electrochemical CO2 Reduction Using Ruthenium Atomic Species on Bismuth

AbstractThe conversion of CO2 into formate through electrochemical methods is emerging as an elegant approach for industrial‐scale CO2 utilization in the near future. Although Bismuth (Bi)‐based materials have shown promise thank to their excellent selectivity, their limited reactivity remains a challenge. Herein, this study demonstrates a significant enhancement in the CO2‐to‐formate efficiency of Bi by incorporating ruthenium (Ru) atomic species. Ru single atom doped Bi exhibited a nearly twofold higher partial current density compared with pure Bi and Ru clusters doped Bi, while over 95% Faradaic efficiency (FE) is maintained. Through comprehensive investigations using a combined approach of electrochemical techniques, operando spectroscopy, and theoretical calculations, this study elucidates that the presence of Ru single atom promotes H2O dissociation and H* migration to Bi sites for CO2‐to‐formate conversion by significantly reducing the energy barrier via a H* spillover path. Besides, it is constructed Ru–Bi bridge sites for efficient CO2 hydrogenation via a non‐spillover path, which served as the major mechanism for CO2‐to‐formate conversion in Ru single atom doped Bi.

Structural evolution and electronic properties of the La-doped germanium clusters

The geometric structure, relative stability, and electronic properties of LaGe n − (n = 3–14) are systematically studied by density functional theory, and the results are compared with the experimental literature data. It is found that the structures of 10A-I, 11A-I, and 14A-I are clearly two-parted and have the potential to design molecular chains. Combined with the average binding energy and second-order differential energy analysis, it is speculated that LaGe 9 − is a magic number cluster. The density of states and natural population analysis indicate that electrons consistently transfer from the La atom to Ge atoms. Doped La atom increases the interaction with Ge atoms and improve the stability of pure germanium clusters. Interestingly, LaGe 9 − has a high transfer charge number, and its high stability can be further explained by the spherical jellium model. The investigation into LaGe 9 − magic number clusters offer valuable insights for the exploration of novel materials with superior stability and performance.

MB16 - (M=Sc, Y, La): Perfect Bowl-Like Boron Clusters.

The introduction of transition-metal doping has engendered a remarkable array of unprecedented boron motifs characterized by distinctive geometries and bonding, particularly those heretofore unobserved in pure boron clusters. In this study, we present a perfect (no defects) boron framework manifesting an inherently high-symmetry, bowl-like architecture, denoted as MB16 - (M=Sc, Y, La). In MB16 -, the B16 is coordinated to M atoms along the C5v-symmetry axis. The bowl-shaped MB16 - structure is predicted to be the lowest-energy structure with superior stability, owing to its concentric (2 π+10 π) dual π aromaticity. Notably, the C5v-symmetry bowl-like B16 - is profoundly stabilized through the doping of an M atom, facilitated by strong d-pπ interactions between M and boron motifs, in conjunction with additional electrostatic stabilization by an electron transfer from M to the boron motifs. This concerted interplay of covalent and electrostatic interactions between M and bowl-like B16 renders MB16 - a species of exceptional thermodynamic stability, thus making it a viable candidate for gas-phase experimental detection.

Structures of Ni-doped Bn (n = 1–13) clusters: A computational study

The structural and stability properties of Ni-doped boron clusters (NiBn with n = 1–13) are investigated by the SCG (systematic growth algorithm) method in combination with density functional theory (DFT) calculations. The results show that the Ni dopant adopt peripheral and top positions in the lowest-energy structures of NiBn clusters. Planar and quasi-planar structures are found for n = 3–6, 10 and 11 while three-dimensional for n = 7–8, 12 and 13. The NiBn clusters show slightly less binding energy compared to the pure Bn clusters. The relative stability of the clusters is rationalized through energetic parameters such as ionization potential, electron affinity, second order energy difference and HOMO–LUMO gap. The results show that NiB12 possess magic characteristics, supported by the energetic parameters and AdNDP bonding analyses.

Density functional theory study on the beryllium clusters doped with silicon atom

An all-electron calculation on BenSi (n = 1–12) clusters has been performed by using density functional theory with the generalized gradient approximation at the PW91 level. The results reveal that the lowest energy geometries of BenSi (n = 1–12) clusters may be generated by substituting a Si atom for one Be atom of the Ben+1 clusters. In addition, Si atom tends to occupy external locations of main Ben clusters and bonds with multiple Be atoms in the BenSi (n > 2) clusters. The average binding energy of BenSi clusters is higher than that of pure Ben+1 clusters, indicating that the doped of the Si atom enhances the cluster's binding force. Compared with pure Ben+1 clusters, the HOMO-LUMO GAP of Be7Si, Be8Si, and Be10Si clusters increase while the HLG of other BenSi clusters(n = 1–3,5,9,11,12) decreas. The vertical ionization potential and vertical electron affinities curves of clusters have the same general trend. The VIP of the cluster decreases gradually while the VEA increases gradually. The doping of the Si atom greatly influences the stability of pure Ben clusters, and the analysis of energy and electronic properties of BenSi clusters reveals that the Be3Si cluster is the magic number structure in the system.

SERS-Based Sensor Using Subnanometric Copper-Silver Mixed Clusters Ag(8-n)Cun (n = 0-8) for Pyridine: A DFT Study.

Surface-enhanced Raman spectroscopy (SERS) is a powerful Raman technique that provides high selectivity and sensitivity in analyzing the intermolecular interaction of a target compound adsorbed on the surface of a noble nanomaterial, i.e., silver, gold, or copper. Although copper presents a better SERS enhancement than gold and silver, its oxidation in the air is much easier than that of gold and silver. A mixed material between these metals may potentially improve the SERS signal enhancement in this context. In this work, we evaluated the SERS spectra of pyridine (Py) adsorbed on the copper-silver mixed clusters Ag(8-n)Cun (n = 0-8) using density functional theory (DFT) at the PBE functional. The cc-pVDZ-PP basis set was chosen for Ag and Cu, while the cc-pVDZ basis set was used for C, N, and H atoms. Geometrical and electronic structures of the mixed clusters and the Py adsorption configuration on these clusters were computed. The calculated SERS spectra then revealed the influence of the Ag/Cu mixing ratio on the SERS enhancement. As a result, the substituted copper atoms on the silver cluster turned out to be favorable adsorption sites for Py. Interestingly, when the number of Cu atoms increased from n = 0 (pure Ag8 cluster) to n = 5 (Ag3Cu5 cluster), the ring stretching peak (1590 cm-1) of Py significantly increased from 20 to 120 au and then saturated around this value despite increasing the Cu atom number to 8 (pure Cu8 cluster). This observation was extended for other ligands such as pyrazine and 3H-pyrrole. TD-DFT was then employed to clarify the chemical enhancement mechanism. The results obtained hopefully provide helpful information for the design of analytical sensors with lower costs.

Water Arrangements upon Interaction with a Rigid Solute: Multiconfigurational Fenchone-(H2O)4-7 Hydrates.

Insight into the arrangements of water molecules around solutes is important to understand how solvation proceeds and to build reliable models to describe water-solute interactions. We report the stepwise solvation of fenchone, a biogenic ketone, with 4-7 water molecules. Multiple hydrates were observed using broadband rotational spectroscopy, and the configurations of four fenchone-(H2O)4, three fenchone-(H2O)5, two fenchone-(H2O)6, and one fenchone-(H2O)7 complexes were characterized from the analysis of their rotational spectra in combination with quantum-chemical calculations. Interactions with fenchone deeply perturb water configurations compared with the pure water tetramer and pentamer. In two fenchone-(H2O)4 complexes, the water tetramer adopts completely new arrangements, and in fenchone-(H2O)5, the water pentamer is no longer close to being planar. The water hexamer interacts with fenchone as the least abundant book isomer, while the water heptamer adopts a distorted prism structure, which forms a water cube when including the fenchone oxygen in the hydrogen bonding network. Differences in hydrogen bonding networks compared with those of pure water clusters show the influence of fenchone's topology. Specifically, all observed hydrates except one show two water molecules binding to fenchone through each oxygen lone pair. The observation of several water arrangements for fenchone-(H2O)4-7 complexes highlights water adaptability and provides insight into the solvation process.

Decoration of atomic PdxAuy (1 ≤ x + y ≤ 4) clusters on polyaniline in electrochemical sensing of 1-propanol

Atomic PdxAuy (1 ≤ x + y ≤ 4) clusters are decorated on polyaniline to be used as the catalytic electrode in electrochemical sensors. The current responses in the oxidation of 1-propanol are used to reveal the catalytic activity. Effects of the size, decoration sequence, and composition of the atomic metal clusters decorated on the PANI on the catalytic activity are evaluated. Regarding the size, an odd-even size effect is observed in the atomic pure metal clusters, which the even-numbered pure metal clusters show a higher catalytic activity than the odd-numbered pure metal clusters. For the decoration sequence, the catalytic activity is high when the same metal is decorated in the first two cycles of the cyclic atomic electrodeposition process. For the composition effect, the atomic metal clusters show a high catalytic activity in the oxidation, in the region of second oxidation peak, when there are more Au in the atomic metal clusters.

Tailoring Titanium Carbide Clusters for New Materials: from Met-Cars to Carbon-Doped Superatoms.

Tailoring materials with prescribed properties and regular structures is a critical and challenging research topic. Early transition metals were found to form supermagic M8C12 metallocarbohedrenes (Met-Cars); however, stable metal carbides are not limited to this common stoichiometry. Utilizing self-developed deep-ultraviolet laser ionization mass spectrometry, here, we report a strategy to generate new titanium carbides by reacting pure Tin clusters with acetylene. Interestingly, two products corresponding to Ti17C2 and Ti19C10 exhibit superior abundances in addition to the Ti8C12 Met-Cars. Using global-minimum search, the structures of Ti17C2 and Ti19C10 are determined to be an ellipsoidal D4d and a rod-shaped D5h geometry, respectively, both with carbon-capped Ti4C moieties and superatomic features. We illustrate the electronic structures and bonding nature in these carbon-doped superatoms concerning their enhanced stability and local aromaticity, shedding light on a new class of metal-carbide nanomaterials with atomic precision.