Cohesive Energy Of Metals Research Articles

First-principles thermodynamics study of CO/OH induced disintegration of precious metal nanoparticles on TiO2(110)

Revealing the fundamental mechanisms governing reactant-induced disintegration of supported metal nanoparticles and their dependences on the metal component and reactant species is vital for improving the stability of supported metal nanocatalysts and single-atom catalysts. Here we use first-principles based disintegration thermodynamics to study the CO- and OH- induced disintegration of Ag, Cu, Au, Ni, Pt, Rh, Ru, and Ir nanoparticles into metal-reactant complexes (M(CO)n, M(OH)n, n=1 and 2) on the pristine and bridge oxygen vacancy site of TiO2(110). It was found that CO has a stronger interaction with these considered transition metals compared to OH, resulting in lower formation energy and a larger promotion effect on the disintegration of nanoparticles (NPs). The corresponding reactant adsorption energy shows a linear dependence on the metal cohesive energy, and metals with higher cohesive energies tend to have higher atomic stability due to their stronger binding with reactant and support. Further disintegration free energy calculations of NPs into metal-reactant complexes indicate only CO-induced disintegration of Ni, Rh, Ru, and Ir nanoparticles is thermodynamically feasible. These results provide a deeper understanding of reactant-induced disintegration of metal nanoparticles into thermodynamically stable metal single-atom catalysts.

Periodicity in the Electrochemical Dissolution of Transition Metals.

Extensive research efforts are currently dedicated to the search for new electrocatalyst materials in which expensive and rare noble metals are replaced with cheaper and more abundant transition metals. Recently, numerous alloys, oxides, and composites with such metals have been identified as highly active electrocatalysts through the use of high‐throughput screening methods with the help of activity descriptors. Up to this point, stability has lacked such descriptors. Hence, we elucidate the role of intrinsic metal/oxide properties on the corrosion behavior of representative 3d, 4d, and 5d transition metals. Electrochemical dissolution of nine transition metals is quantified using online inductively coupled plasma mass spectrometry (ICP‐MS). Based on the obtained dissolution data in alkaline and acidic media, we establish clear periodic correlations between the amount of dissolved metal, the cohesive energy of the metal atoms (E coh), and the energy of oxygen adsorption on the metal (ΔH O,ads). Such correlations can support the knowledge‐driven search for more stable electrocatalysts.

Search for encapsulation of platinum, silver, and gold at the surface of graphite

This work provides a platform to predict metal encapsulation atop the surface of graphite. The authors show a linear scaling between the optimal encapsulation temperature and the metal's cohesive energy; and use density functional theory to validate their experiments.

Graphene pillared with hybrid fullerene and nanotube as a novel 3D framework for hydrogen storage: A DFT and GCMC study

A new-type 3D pillared graphene framework with hybrid fullerene and nanotube pillars (PGF-hFN) has been created depended on density functional theory (DFT) and first-principles molecular dynamics simulations (MD). It is proved to have excellent thermal structural stability. The average adsorption energy of Li is 2.77 eV much higher than the metal cohesive energy excluding lithium aggregation problem. From DFT calculations, for Li-decorated B-doped PGF-hFN, the hydrogen gravimetric density (HGD) is as high as 12.92 wt% and the according volumetric uptake is 96.4 g/L with an average adsorption energy of 0.195 eV per H2. Further grand canonical Monte Carlo (GCMC) simulations predict 7.2 wt% in excess HGD and 53.8 g/L in excess volumetric hydrogen density at near ambient temperature (233 K) and 100 bars with the ideal adsorption enthalpy which have exceeded the 2020 the U.S. Department of Energy (DOE) ultimate target for mobile applications. Our multiscale theoretical simulations indicate this new pillared structure should be a promising carrier accessible for sorption of hydrogen molecules.

Calculation of the Surface Energy of Metals: Agreement of the Thermodynamic Vacancy Model with the First-Principles Theory

The thermodynamic vacancy model (TVM) of surface energy (SE) leads to the formula of the linear dependence of the minimum SE value of the low-index fcc (111) and bcc (110) faces on half of the vacancy formation energy or the 1/6 part of the cohesive energy of metals. Comparison of the numerical values of SE calculated by the TVM method with those calculated by the DFT method for the same faces shows negative deviations of the latter (from 2 to 17%). Using the values of these deviations, the surface energy relaxation of metals was calculated with a maximum value for Au and Pt and a minimum value for Ag and Pd.

DFT Study on Planar (CaO) n Rings (n = 1–5) and Their Hydrogen Storage Behavior: Ca–O Versus Mg–O Clusters

In this work, the results of DFT-based calculations on the structures, stabilities, vibrational, electronic, and hydrogen storage behavior of (CaO) n rings are presented and discussed systematically. The equilibrium ring structures of Ca–O clusters for n = 2–5 are found to be stable. Vibrational frequencies and IR intensities further support the enhanced stability with an increase in the size of Ca–O clusters. The HOMO–LUMO surfaces and their derived parameters are used to explain the electronic properties of the titled systems. For efficient hydrogen storage, metals especially, the transition metals with large cohesive energy (CE) suffer from the problem of cohesion as it is expected that the adsorption energies of metal decorated absorbents should be larger than the CEs of metal. In order to avoid this, hydrogen adsorbed directly on the absorbents is preferred. Due to relatively smaller CEs of the s-block metals, hydrogen adsorbs directly on the cluster which indeed solves the problem of cohesion. The hydrogen storage capacity of (CaO) n clusters, considering hydrogen adsorption on (CaO)4 and (CaO)5 rings is studied. The outcomes appear to give meaningful and satisfactory results. Thus the present work is expected to lead further the applications of small clusters for easy, efficient, and eco-friendly hydrogen storage.

Dy uniform film morphologies on graphene studied with SPA-LEED and STM

The use of graphene for microelectronics and spintronic applications requires strategies for metals to wet graphene and to grow layer-by-layer. This is especially important when metals will be used as electrical contacts or as spin filters. Extensive work in the literature so far has shown that this is very challenging, since practically all metals grow 3D, with multi-height islands forming easily. Reasons for the 3D morphology are the much weaker metal carbon bond when compared to the metal cohesive energy and the role of Coulomb repulsion of the poorly screened charges at the metal graphene interface. We employed the complementary techniques of SPA-LEED and STM to study the growth of Dy on graphene. It was found that under kinetic limitations it is possible to fully cover graphene with a bilayer Dy film, by growing well below room temperature in stepwise deposition experiments. The Dy film, however, is amorphous but ways to crystallize it within the 2D morphology are possible, since long range order improves at higher growth temperature.

A computational study of Na behavior on graphene

We present the first ab initio and molecular dynamics study of Na adsorption and diffusion on ideal graphene that considers Na–Na interaction and dispersion forces. From density functional theory (DFT) calculations using the generalized gradient approximation (GGA), the binding energy (vs. the vacuum reference state) of −0.75eV is higher than the cohesive energy of Na metal (EcohDFT=−1.07 eV). The binding energy approaches the Na metal cohesive energy (EcohDFT−D=−1.21 eV) when dispersion correction is included (DFT-D), with Eb=−1.14eV. Both DFT and DFT-D predict that the increase of Na concentration on graphene results in formation of Na complexes. This is evidenced by smaller Bader charge on Na atoms of Na dimer, 0.55e (0.48e for DFT) compared to 0.86e (for both DFT and DFT-D) for the single atom adsorption as well as by the formation of a NaNa bond identified by analysis of the electron density. These results suggest that ideal graphene is not a promising anode material for Na-ion batteries. Analysis of diffusion pathways for a Na dimer shows that the dimer remains stable during the diffusion, and computed migration barriers are significantly lower for the dimer than that for the single atom diffusion. This indicates that Na–Na interaction should be taken into account during the analysis of Na transport on graphene. Finally, we show that the typical defects (vacancy and divacancy) induce significant strengthening of the NaC interaction. In particular, the largest change to the interaction is computed for vacancy-defected graphene, where the found lowest binding energy (vs. the metal reference state) is about 1.15eV (1.21eV for DFT) lower than that for ideal graphene.

Comparative computational study of the energetics of Li, Na, and Mg storage in amorphous and crystalline silicon

To assess the potential of amorphous Si (a-Si) as an anode for Li, Na, and Mg-ion batteries, the energetics of Li, Na, and Mg atoms in a-Si are computed from first-principles and compared to those in crystalline Si (c-Si). It is shown that Si preamorphization increases the average anode voltage and slightly reduces the volume expansion of the anode during the insertion of the metal atoms. Analysis of computed formation energies of Li, Na, and Mg defects in a-Si and c-Si suggests that the insertion energetics of single atoms into a-Si are thermodynamically more favorable. For instance, the lowest defect formation energies of Li, Na, and Mg defects in a-Si are respectively 0.43, 1.42, and 1.52eV lower compared to those in c-Si. Moreover, the defect formation energies of Li, Na, and Mg defects (vs. vacuum reference states) in a-Si are comparable with the metal cohesive energies and consequently the insertion of the metal atoms might be possible with appropriate control of charging process. This is in contrast to c-Si, where the storage of Na and Mg atoms is limited due to high energy cost of Na and Mg insertion into c-Si.

Transition Metal Decorated Graphyne: An Efficient Catalyst for Oxygen Reduction Reaction

The sluggish kinetics of oxygen reduction reaction at the cathode of the fuel cell is found to be one of the limiting factors in fuel cell technology. The conventional platinum based catalysts make the fuel cell more expensive because of its limited availability and high cost. In the present study, we have explored transition metal decorated graphyne as an alternate catalyst for oxygen reduction. The metal (Fe, Co, and Ni) binding energies over the graphyne surface are found to be higher than the corresponding metal cohesive energies. Iron and cobalt decorated graphyne are found to be more reactive toward oxygen adsorption, whereas the nickel decorated system is inactive. In acid medium, both iron and cobalt decorated systems are observed to follow a more efficient four electron reduction path. In alkaline medium, the reduction on iron decorated system is through a four electron reduction path, while in cobalt system it is through a two-electron reduction path with the formation of hydroperoxide anion. Th...

Transition Metal Decorated Porphyrin-like Porous Fullerene: Promising Materials for Molecular Hydrogen Adsorption

Transition metal decorated carbon materials like fullerenes and nanotubes have been studied extensively for hydrogen adsorption applications. However, the weaker metal binding energy makes these materials unsuitable for making a stable hydrogen storage material. Here, using ab initio based density functional theory (DFT) calculations, we have studied the hydrogen adsorption in transition metal doped porphyrin-like porous fullerene, C24N24. This porous fullerene is generated through truncated doping of 24 carbon atoms by 24 nitrogen atoms, and the resulting fullerene contains six N4 cavities with a cavity diameter of 3.708 A. These N4 cavities are found to bind with transition metal atoms (Sc, Ti, and V) very strongly, and the binding energies are found to be considerably larger than (nearly double) the corresponding metal cohesive energies. These transition metal sites are found to adsorb molecular hydrogen through well-known Kubas-type interactions. The calculated adsorption energies of molecular hydroge...

Ordering and segregation in isolated Au–Pd icosahedral nanoclusters and nanowires and the consequences of their encapsulation inside carbon nanotubes

Metropolis Monte Carlo sampling in the semi-grand canonical ensemble with empirical potentials is used to predict equilibrium ordered structures and segregation properties of small icosahedral Au–Pd nanoclusters and helical nanowire segments over the whole range of compositions at low temperatures. The cases of free-standing clusters and wires are compared with the same systems encapsulated in carbon nanotubes.A number of chemically ordered structures and segregation states are identified and found to be consistent with the same interplay between size mismatch, mixing enthalpy and surface energies of elemental metals which determines the thermodynamic equilibrium of binary metal alloys. Encapsulation has the effect of modifying the surface energies of nanoclusters and wires, with considerable consequences on their thermodynamic states, although the metal–graphite interaction strength is low as compared with the metal cohesive energy and the carbon–carbon binding energy.

Tuning the Metal Binding Energy and Hydrogen Storage in Alkali Metal Decorated MOF-5 Through Boron Doping: A Theoretical Investigation

Using ab initio quantum chemical calculations, we explore the possibility of improving the light metal binding energy as well as the hydrogen adsorption energy in MOF-5 so that the clustering problem at high concentration can be overcome. To mimic the linking group (C6H4(COO)22–) in MOF-5, we have considered the simple benzene ring. Because the binding energy of light metals (Li, Na, and Mg) to benzene is poor, we have modified the carbon ring by substituting two carbon atoms with two boron atoms. The metal ion (atom) interaction with C4B2H62– (C4B2H6) is found to be very strong, and the interaction energies are extremely high as compared with the metal cohesive energies. Metal sites in these complexes are found to have partial ionic (positive) character and are shown to adsorb molecular hydrogen with reasonably good adsorption enthalpies. We have also studied the extended periodic system of lithium as well as sodium-decorated modified MOF-5 and their hydrogenated counterparts. In the case of lithium-deco...

Deposition of metal clusters on single-layer graphene/Ru(0001): Factors that govern cluster growth

Fabrication of nanoclusters on a substrate is of great interest in studies of model catalysts. The key factors that govern the growth and distribution of metal on graphene have been studied by scanning tunneling microscopy (STM) based on different behaviors of five transition metals, namely Pt, Rh, Pd, Co, and Au supported on the template of a graphene moiré pattern formed on Ru(0001). Our experimental findings show that Pt and Rh form finely dispersed small clusters located at fcc sites on graphene while Pd and Co form large clusters at similar coverages. These results, coupled with previous findings that Ir forms the best finely dispersed clusters, suggest that both metal–carbon (M–C) bond strength and metal cohesive energies play significant roles in the cluster formation process and that the M–C bond strength is the most important factor that affects the morphology of clusters at the initial stages of growth. Furthermore, experimental results show Au behaves differently and forms a single-layer film on graphene, indicating other factors such as the effect of substrate metals and lattice match should also be considered. In addition, the effect of annealing Rh on graphene has been studied and its high thermal stability is rationalized in terms of a strong interaction between Rh and graphene as well as sintering via Ostwald ripening.

An in situ STM study on the long-range surface restructuring of Au(1 1 1) in a non-chloroaluminumated ionic liquid

We report an in situ STM study of a potential-dependent long-range surface restructuring of Au(1 1 1) electrode in neat 1-butyl-3-methylimidazolium tetrafluoroborates (BMIBF 4) ionic liquid. Au(1 1 1) undergoes a significant long-range surface restructuring upon cathodic excursion to −1.0 V vs. Pt quasi-reference. The restructuring involves the formation of tiny pits, which then develops into a stable worm-like network with an average width of the network grids ∼2 nm. Electrochemical annealing occurs at the cathodic limit with the presence of a reduction product of cation BMI +. A smooth surface is recovered with the appearance of the typical (√3 × 22) reconstruction of Au(1 1 1). The surface restructuring is reestablished upon anodic excursion to −1.3 V after the adsorbed reduction product is oxidized. The long-range surface restructuring phenomenon is tentatively explained as a result of partial charge transfer to the weakly adsorbed BMI +, which reduces the metal–metal cohesive energy. In addition, the synergetic effect of the counter anion BF 4 − may also be involved. The results provide a knowledge of Au(1 1 1) electrode behavior in the neat ionic liquid and are beneficial to understanding in situ STM results involving surface morphological changes in such a media.

Adsorption energy and spin state of first-row transition metals adsorbed on MgO(100)

Slab and cluster model spin-polarized calculations have been carried out to study various properties of isolated first-row transition metal atoms adsorbed on the anionic sites of the regular MgO(100) surface. The calculated adsorption energies follow the trend of the metal cohesive energies, indicating that the changes in the metal-support and metal-metal interactions along the series are dominated by atomic properties. In all cases, except for Ni at the generalized gradient approximation level, the number of unpaired electron is maintained as in the isolated metal atom. The energy required to change the atomic state from high to low spin has been computed using the PW91 and B3LYP density-functional-theory-based methods. PW91 fails to predict the proper ground state of V and Ni, but the results for the isolated and adsorbed atom are consistent within the method. B3LYP properly predicts the ground state of all first-row transition atom the high- to low-spin transition considered is comparable to experiment. In all cases, the interaction with the surface results in a reduced high- to low-spin transition energy.

Topology of the Electron Density and Cohesive Energy of the Face-Centered Cubic Transition Metals

The topology of the electron density for face-centered cubic transition metals (β-Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) was studied. All of the electron density critical points in the unit cell w...

First-principles step- and kink-formation energies on Cu(111)

In rough agreement with experimental values derived from Cu island shapes vs. temperature, ab-initio calculations yield formation energies of 0.27 and 0.26 eV/ step-edge-atom for (100)- and (111)-micro facet steps on Cu(lll), and 0.09 and 0.12 eV per kink in those steps. Comparison to ab-initio results for Al and Pt shows that as a rule, the average formation energy of straight steps on a close-packed metal surface equals -7% of the metal's cohesive energy.

Deposition and Surface Dynamic of Metals Studied by the Embedded-Atom Molecular Dynamics Method

Abstract The embedded atom method (EAM) was used to simulate the dynamics of deposition of supported metal clusters on fcc transition metals and the dynamic behavior of surfaces. The formation of metal clusters was observed before deposition and the geometries, stabilities and dynamics of a series of metal clusters were discussed as obtained by EAM and compared with first-principle calculations. The calculations indicate that the structure of a cluster in the vapor phase is governed by its zero kelvin stability. We find that if the cluster forms in the vapor phase, it is difficult to get epitaxial growth since the metal cohesive energy is large and the chester can not be broken by thermal motions. The effect of impurities on the deposition is also discussed. The anharmonicity, roughening and reconstruction of surface were also investigated. Three-body interactions were found to he important to understand these phenomena

Some general aspects of hydrogen chemisorption on metal surfaces

Chemisorption of hydrogen on metal surfaces requires the dissociation of the H 2 molecule in the first place; this process has been experimentally investigated and theoretically described in terms of multi-dimensional potential energy diagrams. The adsorption of atomic hydrogen is frequently accompanied by displacements of the metal surface atoms leading to phenomena such as layer relaxation or surface reconstruction. Especially surface reconstruction may be regarded as a precursor stage for a progressive chemical attack of the hydrogen atoms also on the bulk metal, leading to the occupation of so-called “subsurface” sites, to bulk diffusion and, finally, to hydride compound formation. All these processes depend sensitively on the crystallographic structure of the surface, and some examples for H on Rh, Co and Pd surfaces will demonstrate the general correlation between the hydrogen surface concentration and the metal's cohesive energy, surface crystallography, and its tendency to reconstruct.