Potential use of some metal clusters as hydrogen storage materials—a conceptual DFT approach (original) (raw)

Aromatic Clusters as Potential Hydrogen Storage Materials

Frontiers in Energy Research, 2021

The scientific community is engrossed in the thought of a probable solution to the future energy crisis keeping in mind a better environment-friendly alternative. Although there are many such alternatives, the green hydrogen energy has occupied most of the brilliant minds due to its abundance and numerous production resources. For the advancement of hydrogen economy, Government agencies are funding pertinent research projects. There is an avalanche of molecular systems which are studied by several chemists for storing atomic and molecular hydrogens. The present review on molecular hydrogen storage focuses on all-metal and nonmetal aromatic clusters. In addition to the effect of aromaticity on hydrogen trapping potential of different molecular moieties, the importance of using the conceptual density functional theory based reactivity descriptors is also highlighted. Investigations from our group have been revealing the fact that several aromatic metal clusters, metal doped nonmetal c...

Theoretical studies of the effect of hydrogen–hydrogen interactions on the structural and dynamical properties of metal/hydrogen clusters

The Journal of Chemical Physics, 1998

Using a combination of ground state, equilibrium, and dynamical Monte Carlo methods, we examine the role of hydrogen-hydrogen interactions on selected structural and time-dependent properties of hydrogen containing metal clusters. Equilibrium simulations include studies of the classical and quantum-mechanical geometries and energetics for embedded atom potential models of both the ground states and low-lying structural isomers of Ni n H 2 and Pd n H 2 clusters (4рn р9). In addition to these time-independent investigations, we utilize dynamical path integral methods to characterize the effects of hydrogen-hydrogen interactions on the hydrogen vibrational lineshapes in these systems.

Bonding, aromaticity and reactivity patterns in some all-metal and non-metal clusters

2009

Several sandwich-like metal clusters have been studied at the B3LYP/6-311 + G* level of theory. Bonding and reactivity have been analysed through various geometrical parameters and conceptual density functional theory based global reactivity descriptors. Aromaticity patterns have been understood in terms of the associated nucleus independent chemical shift values. Possibility of bond-stretch isomerism in some doped clusters is explored. Preferable sites for electrophilic and nucleophilic attacks have been identified using different local reactivity descriptors.

Theoretical study of structure and stability of h+x (h2)n clusters

Chemical Physics Letters, 1981

Structural parameters, energies, and spectroscopic characteristics of two series of layerwise hydrogenated aluminum clusters Al 44 H n (n = 27-44) and Al 89 H т (т = 15, 24, 39, and 63) have been calculated by the density functional theory method. It has been shown that increasing number of H atoms in both series entails rapid enhancement of structural distortions up to cooperative rearrangements accompanied by a change in the shape and composition of the surface layer and internal core of the cluster. At the end of the first series Al 44 H n , several surface atoms migrate to the outer sphere of the cage to form valence-unsaturated "outer-surface" AlH n and Al 2 H n moieties, which can be active sites at the stages of deeper hydrogenation. Simultaneously, the inner core [Al] 5 disintegrates, and its atoms are introduced into the surface layer. A family of "inverted" Al 42 H 42 isomers with the hollow [Al 42 ] cage has been localized; the isomers contain the endohedral AlH 4 group and "inner" Al−H bonds with their hydrogen end directed to the center of the inner cavity. At the end of the second series, five alanate groups AlH 4 and two Al 3 H 2 fragments bonded to the surface through hydrogen bridges are formed in the outer sphere of the cluster. The results are of interest for DFT modeling of hydrogenation of nanosized aluminum clusters at the molecular level.

Toward analyzing some neutral and cationic boron-lithium clusters (B x Li y x = 2-6; y = 1, 2) as effective hydrogen storage materials: A conceptual density functional study

International Journal of Quantum Chemistry, 2011

The ability of neutral and cationic B x Li y (x ¼ 2-6; y ¼ 1, 2) systems as effective hydrogen-trapping materials are investigated at the MP2 level of theory using the 6-311þG(d, p) basis set. The different conceptual DFT-based global and local reactivity descriptors and the associated electronic structure principles provide invaluable insights toward assessing the utility of the boron-lithium clusters in trapping molecular hydrogen. A consistent thermodynamic spontaneity of the allied H 2-binding reactions along with a favorable decrease in the average dissociative chemisorption energies invokes the plausible usage of these cluster motifs for hydrogen loading in practice.

Theoretical study on the structure and stability of hydrogen-ion clusters Hn+ and Hn− (n = 3, 5, 7, 9, 11, 13)

Chemical Physics, 1983

Ab initio SCF and CI calculations have been carried out for H,' and Hi (n = X5.7.9. 11. 13) clusters with 1 double-zeta plus polarization basis set. The stabilization energy of negative ion clusters H,-is ver?_ small (less than 1 kcal) and their existence is critical. The structural difference between positive-and negative-ion clusters are discussed in terms of the bonding ability involved. While H, + is a charge-transfer complex. the stability of Hi comes mainly from the ion-induced-dipole attractions. The electron correlation effect on the structure and stability of these ion clusters is also discussed.

H 2 Adsorption on 3d Transition Metal Clusters: A Combined Infrared Spectroscopy and Density Functional Study

The Journal of Physical Chemistry A, 2008

The adsorption of H 2 on a series of gas-phase transition metal (scandium, vanadium, iron, cobalt, and nickel) clusters containing up to 20 metal atoms is studied using IR-multiple photon dissociation spectroscopy complemented with density functional theory based calculations. Comparison of the experimental and calculated spectra gives information on hydrogen-bonding geometries. The adsorption of H 2 is found to be exclusively dissociative on Sc n O + , V n + , Fe n + , and Co n + , and both atomic and molecularly chemisorbed hydrogen is present in Ni n H m + complexes. It is shown that hydrogen adsorption geometries depend on the elemental composition as well as on the cluster size and that the adsorption sites are different for clusters and extended surfaces. In contrast to what is observed for extended metal surfaces, where hydrogen has a preference for high coordination sites, hydrogen can be both 2-or 3-fold coordinated to cationic metal clusters.

Density Functional Methods for Fast Screening of Metal-Organic Frameworks for Hydrogen Storage

Classical density functional theory (DFT) has been routinely used for the characterization of pore size distribution and specific surface area of porous materials by gas physisorption. However, its application to large-scale screening of materials for gas storage has been largely unexplored because it is commonly believed that the DFT calculations are applicable only to one-dimensional systems and highly sensitive to the approximations introduced in the free-energy functionals. In this work, we have investigated four representative versions of nonlocal density functionals for predicting H 2 adsorption using both the slit pore model and a large library of metal−organic frameworks (MOFs) under a broad range of temperatures and pressures. The four versions of DFT share a common functional from the modified fundamental measure theory to account for the molecular excluded volume effects while differing in their approximations to represent the intermolecular attractions, viz., meanfield approximation, two versions of weighted-density approximations (WDA), and the quadratic functional expansion method. We have tested these functionals by extensive comparison with Monte Carlo simulation data for H 2 adsorption at conditions of practical interest. Overall all four versions of DFT are reasonably accurate in comparison with the simulation results. While the density expansion method performs rather well at the DOE target condition for hydrogen storage, the WDA methods are found most accurate at low temperature, a condition typically used in materials characterization. In addition to rapid prediction of the adsorption isotherms, DFT is able to generate molecular density profiles revealing microscopic details such as favorable adsorption sites. From a computational perspective, the DFT calculation is at least 1 order of magnitude faster than conventional simulation methods, promising for large-scale screening of nanostructured materials for gas storage. 5374−5385 temperature and pressure of hydrogen gas in the bulk are fixed at T = 243 K and P = 100 bar, respectively. The DFT functionals are (a) WDA-Y, (b) WDA-L, (c) FMSA, (d) MFA, and (e) WDA-Y with FMSA EOS. Color code: Blue, top 300 from excess CH 4 adsorption in weight category; Red, top 300 from excess CH 4 adsorption in volume category; Purple, top 300 from void fraction category; Teal, top 300 from surface area category.

Binding energy, structure, and vibrational spectra of (HCl) and (HF) clusters by density functional theory

The Journal of chemical …, 2003

We are reporting density functional theory results for the binding energies, structures, and vibrational spectra of (H-Cl)(2-6) and (H-F)(2-10) clusters. The performance of different functionals has been investigated. The properties of HF clusters predicted by hybrid functionals are in good agreement with experimental information. The HCl dimer binding energy DeltaE(e) is underestimated by hybrid functionals. The Perdew and Wang exchange and correlation functional (PW91) result for DeltaE(e) is -9.6 kJ mol(-1), in very good agreement with experiment (-9.5 kJ mol(-1)). However, PW91 overestimates binding energies of larger clusters. Hydrogen bonding cooperativity depends on the cluster size n but reaches a limit for moderately sized clusters (n=8 for HF). The average shift to low frequencies (Deltanu) of the X-H (X=Cl,F) stretching vibration relative to the monomer is in good agreement with experimental data for HF clusters in solid neon. However, some discrepancies with experimental results for HCl clusters were observed. The behavior of Deltanu as a function of the cluster size provides an interesting illustration of hydrogen-bond cooperative effects on the vibrational spectrum. The representation of the electronic density difference shows the rearrangement of the electronic density induced by hydrogen bonding in the clusters and supports the view that hydrogen-bond cooperativity is related to electronic sharing and delocalization.