Transition-metal Nanoclusters Research Articles

A Theoretical Benchmark of the Geometric and Optical Properties for 3d Transition Metal Nanoclusters via Density Functional Theory.

Understanding structure-property relationships in atomically precise metal nanoclusters is vital in finding selective and tunable catalysts. In this study, density functional theory (DFT) was used to benchmark seven exchange correlation functionals at different basis sets for 17 atomically precise nanoclusters against experimentally determined geometries, band gaps, and optical gaps. The set contains both monometallic and bimetallic clusters that possess at least two types of 3d transition metals (specifically, Cu, Ni, Fe, or Co). The benchmark highlights that PBE0 is a good functional to use regardless of the basis set, and Minnesota functionals do well with respect to specific metals. Further, while long-range corrected functionals overestimate band and optical gaps, they model absorption features better than the other considered functionals. The study additionally looks at the photoinduced hydrogen evolution reaction (HER) and the CO2 reduction mechanism on nanoclusters reported from the literature.

Cage doping of Ti, Zr, and Hf-based 13-atom nanoclusters: two sides of the same coin.

Transition metal nanoclusters can exhibit unique and tunable properties which result not only from their chemical composition but also from their atomic packing and quantized electronic structures. Here, we introduce a promising family of bimetallic TM@Ti12, TM@Zr12, and TM@Hf12 nanoclusters with icosahedral geometry, where TM represents an atom from groups 3 to 12. Density functional theory calculations show that their stability can be explained with familiar concepts of metal cluster electronic and atomic shell structures. The magnetic properties of these quasispherical clusters are entirely consistent with superatom electronic shells and Hund's rules, and can be tuned by the choice of the TM dopant. The computed cluster atomization energies were analyzed in terms of the elements' cohesive energy, Ecoh, and contributions from geometric distortion, Edis, surface energy, Es, and ionic bonding, Ei. Some clusters have anomalous stability relative to Ecoh + Edis + Es + Ei. We attribute this to superatomic character associated with a favorable atomic and electronic shell structure. This raises the possibility of designing stable superatoms and materials with tailored electronic and magnetic properties.

On-surface growth of transition-metal cobalt nanoclusters using a 2D crown-ether array

We report an on-surface growth of transition-metal nanoclusters using a 2D self-assembled monolayer (SAM) crown ether ring molecular array prepared on Cu(111).

Blocking Metal Nanocluster Growth through Ligand Coordination and Subsequent Polymerization: The Case of Ruthenium Nanoclusters as Robust Hydrogen Evolution Electrocatalysts.

Metal nanoclusters providing maximized atomic surface exposure offer outstanding hydrogen evolutionactivities but their stability is compromised as they are prone to grow and agglomerate. Herein, a possibility of blocking metal ion diffusion at the core of cluster growth and aggregation to produce highly active Ru nanoclusters supported on an N, S co-doped carbon matrix (Ru/NSC) is demonstrated. To stabilize the nanocluster dispersion, Ru species are initially coordinated through multiple Ru─N bonds with N-rich 4'-(4-aminophenyl)-2,2:6',2''-terpyridine (TPY-NH2) ligands that are subsequently polymerized using a Schiff base. After the pyrolysis of the hybrid composite, highly dispersed ultrafine Ru nanoclusters with an average size of 1.55nm are obtained. The optimized Ru/NSC displays minimal overpotentials and high turnover frequencies, as well as robust durability both in alkaline and acidic electrolytes. Besides, outstanding mass activities of 3.85Amg-1 Ru at 50mV, i.e., 16fold higher than 20wt.% Pt/C are reached. Density functional theory calculations rationalize the outstanding performance by revealing that the low d-band center of Ru/NSC allows the desorption of *H intermediates, thereby enhancing the alkaline HER activity. Overall, this work provides a feasible approach to engineering cost-effective and robust electrocatalysts based on carbon-supported transition metal nanoclusters for future energy technologies.

First-Principles Investigation of Size Effects on Cohesive Energies of Transition-Metal Nanoclusters.

The cohesive energy of transition-metal nanoparticles is crucial to understanding their stability and fundamental properties, which are essential for developing new technologies and applications in fields such as catalysis, electronics, energy storage, and biomedical engineering. In this study, we systematically investigate the size-dependent cohesive energies of all the 3d, 4d, and 5d transition-metal nanoclusters (small nanoparticles) based on a plane-wave-based method within general gradient approximation using first-principles density functional theory calculations. Our results show that the cohesive energies of nanoclusters decrease with decreasing size due to the increased surface-to-volume ratio and quantum confinement effects. A comparison of nanoclusters with different geometries reveals that the cohesive energy decreases as the number of nanocluster layers decreases. Notably, monolayer nanoclusters exhibit the lowest cohesive energies. We also find that the size-dependent cohesive energy trends are different for different transition metals, with some metals exhibiting stronger size effects than others. Our findings provide insights into the fundamental properties of transition-metal nanoclusters and have potential implications for their applications in various fields, such as catalysis, electronics, and biomedical engineering.

Engineering of TiN (N = 1 – 15) nanoclusters by doping osmium impurity

Bimetallic transition metal nanoclusters have attracted significant attention in recent years due to their wide range of applications such as heterogeneous catalysts, electrochemistry and alloy design. However many studies were reported on pure transition metal nanoclusters and bimetallic of late transition metal nanoclusters. In this study the density functional theory (DFT) with PBEsol exchange correlation functional was employed to investigate the structural and electronic properties of TiN-1Os (N = 2-16) nanoclusters. The calculations showed that osmium impurity mostly prefers to be encapsulated by titanium nanoclusters. The binding energies gradually decrease with the cluster size N. The Os dopant was found to enhance the binding energy of titanium nanoclusters. The relative stability or second order energies showed that Ti6Os and Ti12Os clusters are the most stable. Interestingly, osmium dopant converted the nanocluster with 13 atoms to be the most stable. Furthermore, the dissociation energy or first order energies showed an excellent correlation with the relative stability trend. The HOMO-LUMO revealed the lowest energy gap at Ti12Os (N = 13) which correlates well with the predicted binding energy, relative stability and dissociation energy.

Electrocatalytic reduction of CO2 on size-selected nanoclusters of first-row transition metal nanoclusters: a comprehensive mechanistic investigation.

Recycling CO2 back to fuels offers an ideal solution to control anthropogenic global CO2 emissions as well as providing a sustainable green solution to alternative energy resources from a cheap and earth-abundant carbon source. Size-selected nanoclusters open a novel area in catalysis as these atomically precise nanoclusters possess unique electronic and catalytic properties different from larger nanoparticles and traditional bulk catalysts. In this work, we have investigated the ability of first-row transition metal nanoclusters (Sc-Cu) of varying sizes (3 to 10 atoms) for CO2 electroreduction (CO2RR). Employing computational hydrogen model (CHE), we have performed detailed analyzes on various CO2RR electrocatalytic reaction pathways on all nanocluster surfaces. We have identified a general trend of decreasing adsorption energies while moving across the periodic table from Sc to Cu. Moreover, we have found a general preference for CHO* mediated pathways over COH* mediated pathways for methane formation. The CHO* mediated pathways prefer the reaction route via CHO* → CH2O* → CH2OH* → CH2* → CH3* → CH4 + * on most of the nanocluster surfaces. In addition, we have established that methanol formation is greatly disfavored on all nanocluster surfaces, and the release of CO and HCOOH is greatly suppressed on all nanoclusters. We have identified several nanoclusters as potential nanocluster-based electrocatalysts for CO2RR for methane formation with relatively lower limiting potential values below 0.50 V. CO2 electroreduction versus hydrogen evolution reaction (HER) competition was also evaluated on various nanoclusters, and we identified a number of nanoclusters (Ti6, V5, V6, Mn4, Mn7, Mn10, Fe4, Fe8, Fe10, Ni4, and Cu5) that can suppress the formation of HER over CO2RR. We have also established a linear scaling relationship between the adsorption free energies of various CO2RR adsorbates to the adsorption free energies of CO2*, O*, and C* adsorbates. We have found that scaling free energy relationships that exit on heterogeneous catalysts such as the correlation between the adsorption energies of AHx with the adsorption energies of atom A (A = C, N, O, S, etc.) often breaks on nanocluster surfaces, especially for adsorbates with more than one binding motifs.

Improved properties of 3d transition metal nanoclusters deposited on defective hexagonal boron nitride quantum dots

Density functional theory calculations were used to investigate the stability and reactivity of icosahedral Fe 13 , Co 13 , Ni 13 , and Cu 13 nanoclusters deposited on pristine and defective hexagonal boron nitride quantum dots (h-BNQDs). The defective h-BNQDs were studied with a N vacancy (h-BN V QDs) and a B vacancy (h-B V NQDs). The binding energy between the Fe 13 , Co 13 , Ni 13 , and Cu 13 nanoclusters and pristine and defective h-BNQDs indicates that the stability of the Fe 13 , Co 13 , Ni 13 , and Cu 13 nanoclusters deposited on defective h-BNQDs is higher than those deposited on pristine h-BNQDs. Therefore, defective h-BNQDs are better support material for these nanoclusters. Typically, it is observed that the charge is transferred from metal nanoclusters to pristine and defective h-BNQDs. On the reactivity of the metal nanoclusters deposited on pristine and defective h-BNQDs, the nanoclusters/h-BNQDs composites exhibit similar HOMO–LUMO gaps than bare nanoclusters. Consequently, the formation of nanoclusters/h-BNQDs composites is a good strategy to improve the reactivity of h-BNQDs. 3 d transition metal nanoclusters deposited on defective hexagonal boron nitride quantum dots

CO2 Adsorption over 3d Transition-Metal Nanoclusters Supported on Pyridinic N3-Doped Graphene: A DFT Investigation.

CO2 adsorption on bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on pyridinic N3-doped graphene (PNG) was investigated by employing the density functional theory. First, the interaction of Co13 and Cu13 with PNG was analyzed by spin densities, interaction energies, charge transfers, and HUMO-LUMO gaps. According to the interaction energies, the Co13 nanocluster was adsorbed more efficiently than Cu13 on the PNG. The charge transfer indicated that the Co13 nanocluster donated more charges to the PNG nanoflake than the Cu13 nanocluster. The HUMO-LUMO gap calculations showed that the PNG improved the chemical reactivity of both Co13 and Cu13 nanoclusters. When the CO2 was adsorbed on the bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on the PNG, it experienced a bond elongation and angle bending in both systems. In addition, the charge transfer from the nanoclusters to the CO2 molecule was observed. This study proved that Co13/PNG and Cu13/PNG composites are adequate candidates for CO2 adsorption and activation.

The effect of doping with pt impurity on ti clusters: a density functional theory study

Transition metal nanoclusters have been greatly investigated in various areas such as catalysis, energy conversion and sensing due to their unique chemical, optical, structural, and electronic properties. Doping monometallic clusters with other metals offer the opportunity to enhance these properties. Extensive work has been done on late transition metal clusters i.e., noble and platinum metals. However, less work has been done on titanium metal clusters. The structural properties of TiN-1Pt (N = 2 – 16) clusters have been investigated using the density functional theory method with the PBEsol exchange-correlation functional. Our results showed that the binding energies for both systems decrease with cluster size N. The Ti12Pt cluster was found to be more enhanced in comparison with pure Ti revealed by the binding energy, relative stability and dissociation energy. Furthermore, binding, relative stability and dissociation energies were found to be enhanced as compared to the energies for Ti monometallic clusters.

Catalytic Ability Comparison of Five Transition Metal Clusters (Zn, Cu, Fe, Ni, and Ru) for Heat‐Induced Graphene Etching by Ab Initio Molecular Dynamics Simulations

AbstractGraphene can be widely utilized as a substrate to support various transition metal (TM) nanoclusters or nanoparticles for surfaced‐supported catalysis, such as electrocatalysis or photovoltaics. The subtle interactions between TM and graphene carbon atoms are expected to be crucial in TM–graphene nanocomposites to affect their growth morphologies and final functionalities. Here, the morphology evolution and catalytic ability of five ultrafine TM (Zn, Cu, Fe, Ni, and Ru) clusters with 48 atoms on graphene etching are investigated by using ab initio molecular dynamics (AIMD) simulations. It is found that three factors, i.e., TM cluster type, operation temperature, and graphene edge type, play important roles in the catalytic behaviors of TM clusters for heat‐induced graphene etching. The results are helpful in locating the catalytic performance of TM clusters in graphene cutting and ensuring stability of TM–graphene nanocomposites in device applications.

Ab initio screening of Pt-based transition-metal nanoalloys using descriptors derived from the adsorption and activation of CO2.

In this study, we report an ab initio screening, based on density functional theory calculations, of Pt-based transition-metal nanoalloys using physicochemical descriptors derived from the adsorption and activation of CO2 on 55-atom nanoclusters, namely, PtnTM55-n, with n = 0, 13, 42, 55, TM = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Au. From the adsorption on the unary and binary nanoclusters, at the chemisorption regime (bent CO2), we identified a linear correlation between the interaction energy and charge transfer from the nanoclusters towards CO2 and the bent CO2 angle; moreover, the interaction energy is enhanced for larger values of the molecular charge and angle. The alloying of Cu55, Ag55, and Au55 with Pt provides a path to change the CO2 adsorption from physisorption (linear, non-activated) to chemisorption (enhanced interaction energies, bent, activated), while the strong interaction energy of CO2 with Os55, Ru55, and Fe55 can be decreased by alloying with Pt using different structural configurations, i.e., the trends are similar for core-shell and segregated structures. Thus, based on our results and analyses, we can select different combinations of PtnTM55-n nanoalloys to yield the desired interaction strength and magnitude of the charge transfer towards the activated anionic CO2, which can help in the design of nanocatalysts for CO2 activation or different chemical reactions in which charge transfer plays a crucial role.

Metal nanoparticles encapsulated within charge tunable porous coordination cages for hydrogen generation reaction

Metal nanoparticles (M NPs) sometimes suffer from low stability and high aggregation, reducing their reactivity during catalytic cycles. In order to obtain stable and ultrafine noble metal (Ru/Rh/Pd) and first-row transition-metal (Co/Ni/Cu) nanoclusters, several porous coordination cages (PCCs) were applied to confine the nanoparticles within their cavities. Because of the electrostatic attraction, metal cations were only encapsulated by PCC-2a with a highly negatively charged cavity. By in situ reduction, M NPs were synthesized within the cavity of PCC-2a to form stable, ultrafine, and highly active catalyst composite. Through characterization by high resolution transmission electron microscope, the synthesized M NPs were found in face-cubic-centered single crystal form, which were rarely reported. In contrast, cages with only 6- negative charges (PCC-2b) or 12+ positive charges (PCC-3) were unable to obtain high crystalline, ultra-small M NPs, resulting in aggregation and large particle size. Finally, the M NPs@PCC catalysts exhibit different activities in methanolysis and hydrolysis of ammonium borane.

A theoretical indicator of transition-metal nanoclusters applied in the carbon nanotube nucleation process: a DFT study.

Knowledge about the appropriate indicators to point out the best components in a catalytic process is a basic prerequisite for obtaining insights into optimized reactions as, for example, in the chemical vapour deposition method, which enables the growth of carbon nanotubes. In this work, we report a density functional theory study of 13-atom transition-metal nanoclusters interacting with (5,0) zigzag and (3,3) armchair carbon nanotube fragments, considering all transition-metal species from the periodic table as possible candidates for the chemical vapour deposition method. The icosahedral configuration was found to be a good model to simulate the seed of nucleation in the case of the short carbon nanotube fragments that are initially formed during the growth process. From full geometric optimizations, without any constraints, we found that the energetic and structural nanocluster properties change as a function of the occupation of the bonding and anti-bonding d-states. The center of gravity of the occupied d-states for nanoclusters is found to be a good indicator to reveal the best candidates for the interaction with the carbon nanotubes, namely, Sc-Cu, Y-Nb, Pd, Lu, Hf, and Pt. The interaction between all transition-metal nanoclusters with both armchair and zigzag segments is favorable in terms of the adhesion energy, where the adhesion is larger for systems with smaller occupation of the d-states. The bond strength is more pronounced for systems with zigzag fragments than those with armchair fragments, which is confirmed by the smaller average bond length between the metal atoms of the nanocluster and the C atoms of the zigzag segment. Our prediction about the best 13-atom transition-metal candidates is reinforced by the linear relationship between the adhesion energy and the center of gravity of the occupied d-states. Thus, the adhesion energy presents increased intensity for the interaction between carbon nanotube fragments and nanoclusters in relation to the smaller occupation of the d-states. Consequently, our model is able to provide a good descriptor for indicating the best 13-atom transition-metal candidates in the chemical vapour deposition process.

Identification of optimally stable nanocluster geometries via mathematical optimization and density-functional theory

A novel methodology combining mathematical optimization with DFT calculations is developed to determine highly cohesive transition metal nanoclusters.

Long-Life Room-Temperature Sodium-Sulfur Batteries by Virtue of Transition-Metal-Nanocluster-Sulfur Interactions.

Room-temperature sodium-sulfur (RT-Na/S) batteries hold significant promise for large-scale application because of low cost of both sodium and sulfur. However, the dissolution of polysulfides into the electrolyte limits practical application. Now, the design and testing of a new class of sulfur hosts as transition-metal (Fe, Cu, and Ni) nanoclusters (ca. 1.2 nm) wreathed on hollow carbon nanospheres (S@M-HC) for RT-Na/S batteries is reported. A chemical couple between the metal nanoclusters and sulfur is hypothesized to assist in immobilization of sulfur and to enhance conductivity and activity. S@Fe-HC exhibited an unprecedented reversible capacity of 394 mAh g-1 despite 1000 cycles at 100 mA g-1 , together with a rate capability of 220 mAh g-1 at a high current density of 5 A g-1 . DFT calculations underscore that these metal nanoclusters serve as electrocatalysts to rapidly reduce Na2 S4 into short-chain sulfides and thereby obviate the shuttle effect.

Formation of a Highly Reactive Cobalt Nanocluster Crystal within a Highly Negatively Charged Porous Coordination Cage

Earth-abundant first-row transition-metal nanoclusters (NCs) have been extensively investigated as catalysts. However, their catalytic activity is relatively low compared with noble metal NCs. Enhanced catalytic activity of cobalt NCs can be achieved by encapsulating Co NCs in soluble porous coordination cages (PCCs). Two cages, PCC-2a and 2b, possess almost identical cavity in shape and size, while PCC-2a has five times more net charges than PCC-2b. Co2+ cations were accumulated in PCC-2a and reduced to ultra-small Co NCs in situ, while for PCC-2b, only bulky Co particles were formed. As a result, Co NCs@PCC-2a accomplished the highest catalytic activity in the hydrolysis of ammonium borane among all the first-row transition-metals NCs. Based on these results, it is envisioned that confining in the charged porous coordination cage could be a novel route for the synthesis of ultra-small NCs with extraordinary properties.

σ-Holes on Transition Metal Nanoclusters and Their Influence on the Local Lewis Acidity

Understanding the molecular interaction behavior of transition metal nanoclusters lies at the heart of their efficient use in, e.g., heterogeneous catalysis, medical therapy and solar energy harvesting. For this purpose, we have evaluated the applicability of the surface electrostatic potential [VS(r)] and the local surface electron attachment energy [ES(r)] properties for characterizing the local Lewis acidity of a series of low-energy TM13 transition metal nanoclusters (TM = Au, Cu, Ru, Rh, Pd, Ir, Pt, Co), including also Pt7Cu6. The clusters have been studied using hybrid Kohn–Sham density functional theory (DFT) calculations. The VS(r) and ES(r), evaluated at 0.001 a.u. isodensity contours, are used to analyze the interactions with H2O. We find that the maxima of VS(r), σ-holes, are either localized or diffuse. This is rationalized in terms of the nanocluster geometry and occupation of the clusters’s, p and d valence orbitals. Our findings motivate a new scheme for characterizing σ-holes as σs (diffuse), σp (localized) or σd (localized) depending on their electronic origin. The positions of the maxima in VS(r) (and minima in ES(r)) are found to coincide with O-down adsorption sites of H2O, whereas minima in VS(r) leads to H-down adsorption. Linear relationships between VS,max (and ES,min) and H2O interaction energies are further discussed.

Core–Shell versus Other Structures in Binary Cu38–nMn Nanoclusters (M = Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au; n = 1, 2, and 6): Theoretical Insight into Determining Factors

DFT calculations of binary transition-metal nanoclusters Cu38–nMn (M = Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au; n = 1, 2, and 6) clearly show that a core–shell structure Cu32M6(core) with M in the core is stable for M = Ru, Rh, Os, and Ir but unstable for M = Pd, Ag, Pt, and Au. These results are consistent with the segregation energies evaluated for Cu37M. Electron population is more accumulated on the core M atoms in Cu38–nMn(core) (M = Ru, Rh, Os, and Ir) than on the core Cu atoms in Cu38. Such electron accumulation substantially occurs for M = Ru, Rh, Os, and Ir because the d orbitals of these transition metals are not fully occupied. A linear relationship was first found between the segregation energy and the increase in the d-orbital population of the core atom, indicating that the electron accumulation at the Mn core is one of the important factors for the segregation energy and the stabilization of the core–shell structure; in other words, a core–shell structure with M atom(s) in the core is stable whe...

Preparation and optical properties of colloidal Ag0 nanoclusters from reduction of solution ionomer Ag-carboxylate ionic aggregates activated by swelling of covalently attached chain segments

Small colloidal Ag0 nanoclusters successfully were prepared from solution reaction of CH3COOAg with a copolymer acid, poly(methyl methacrylate-ran-methacrylic acid) (MMA–MAA), in a methanol-containing solvent at room temperature in the dark in the absence of a typical chemical reductant. Tentatively mechanistically, slow PMMA-ionomerisation of the Ag+ ions produces intramolecular –COO−–Ag+ aggregate cross-links in the solution, which, upon swelling of the chain segments covalently bound to them, are activated by the resultant elastic forces to dissociate instantaneously at the O–Ag coordination bonds to give bare (i.e. uncoordinated), highly oxidative Ag+ ions, which are subject to reduction by the active α-H atoms of the solvent methanol to make Ag0 nanoclusters supported by the re-formed MMA–MAA; the MMA–MAA acid-copolymer, without itself undergoing any permanent chemical change, serves as a mechanical-activator or, say, catalyst for the mechanochemical reduction of CH3COOAg. This novel, facile approach may universally be extended to fabricate other transition-metal nanoclusters deposited in diverse polymeric matrices.