Polylithiated (OLi2) functionalized graphane as a potential hydrogen storage material

Hydrogen storage capacity, stability, bonding mechanism and the electronic structure of polylithiated molecules (OLi2) functionalized graphane (CH) has been studied by means of first principle density functional theory (DFT). Molecular dynamics (MD) have confirmed the stability, while Bader charge analysis describe the bonding mechanism of OLi2 with CH. The binding energy of OLi2 on CH sheet has been found to be large enough to ensure its uniform distribution without any clustering. It has been found that each OLi2 unit can adsorb up to six H2 molecules resulting into a storage capacity of 12.90 wt% with adsorption energies within the range of practical H2 storage application.Comment: 11 pages, 4 figures, 1 table, Phys. Chem. Chem. Phys. (submitted

A model study of effect of M = Li<SUP>+</SUP>, Na<SUP>+</SUP>, Be<SUP>2+</SUP>, Mg<SUP>2+</SUP>, and Al<SUP>3+</SUP> ion decoration on hydrogen adsorption of metal-organic framework-5

The effect of light metal ion decoration of the organic linker in metal-organic framework MOF-5 on its hydrogen adsorption with respect to its hydrogen binding energy (&#916;B.E.) and gravimetric storage capacity is examined theoretically by employing models of the form MC6H6:nH2 where M = Li+, Na+, Be2+, Mg2+, and Al3+. A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out. Our results show that the interaction energy (&#916;E) of the metal ion M with the benzene ring, &#916;B.E., and charge transfer (Qtrans) from the metal to benzene ring exhibit the same increasing order: Na+ &lt; Li+ &lt; Mg2+ &lt; Be2+ &lt; Al3+. Organic linker decoration with the above metal ions strengthened H2-MOF-5 interactions relative to its pure state. However, amongst these ions only Mg2+ ion resulted in &#916;B.E. magnitudes that were optimal for allowing room temperature hydrogen storage applications of MOF-5. A much higher gravimetric storage capacity (6.15 wt.% H2) is also predicted for Mg2+-decorated MOF-5 as compared to both pure MOF-5 and Li+-decorated MOF-5

Improvement in hydrogen desorption from β- and γ-MgH2 upon transition-metal doping

A thorough study of the structural, electronic, and hydrogen-desorption properties of β- and γ-MgH2 phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125% in both the hydrides. This insertion of TMs causes a variation in the cell volumes of β- and γ-MgH2. The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both β- and γ-MgH2 and cause destabilization by weakening the Mg-H bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from β- and γ-MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis

Improvement in Hydrogen Desorption from β- And γ-MgH2 upon Transition-Metal Doping

A thorough study of the structural, electronic, and hydrogendesorption properties of β- and γ-MgH2 phases substituted by selected transition metals (TMs) is performed through firstprinciples calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125% in both the hydrides. This insertion of TMs causes a variation in the cell volumes of β- and γ-MgH2 . The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formationenergy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both β- and γ-MgH2 and cause destabilization by weakening the Mg-H bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from band g MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis

Improvement in the hydrogen desorption from MgH2 upon transition metals doping : A hybrid density functional calculations

This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM's. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.

Strain in Catalysis: Rationalizing Material, Adsorbate, and Site Susceptibilities to Biaxial Lattice Strain

The binding strengths of reaction intermediates on a surface are often the principal descriptors of the effectiveness of heterogeneous catalysts. Although strain is a well-known theoretical strategy to modify binding strengths, and experimental methods have been introduced to directly induce strain, there is comparatively little systematic understanding of the binding energy susceptibilities of different adsorbates, materials, and surface sites to strain. In this work, we employ electronic structure calculations to develop such a systematic understanding. We utilize density functional theory calculations with 10 simple reaction intermediates adsorbed on four binding sites of five metal fcc(111) surfaces under an in-plane biaxial strain of ±2.0%. The responsiveness to strain is quantified using a single parameter named strain susceptibility, which we define as the slope of the adsorption energy versus strain. Typical values for this slope are in the tens of meV per unit percent strain. Based on these calculations, several general trends are identified. First, the material susceptibility order is found to be (Au, Pt) > Pd > (Ag, Cu), which we show can be correlated with the relative changes in d-band widths with strain. Second, binding sites with a higher degree of coordination to the adsorbate tend to exhibit a higher strain susceptibility. Third, adsorbates having higher valency tend to exhibit larger susceptibilities, and among adsorbates having the same valency, N- and O-containing adsorbates exhibit similar susceptibilities, but both show higher susceptibilities than that of C-containing adsorbates. The resulting changes in binding energy are compared to the linear scaling relations of adsorption and are found not to follow the published slopes, but rather to scale more closely with coordination number. This analysis can help to make predictions of which reactions are likely to respond favorably to strain and which catalysts may exhibit enhanced activity. Finally, an eigenforce model is used to rationalize the strain trends. The model-predicted susceptibilities show decent agreement with values by electronic structure calculations, differing by a mean absolute error of 0.013 eV/% for a variety of adsorption systems

Strain and doping effects on the energetics of hydrogen desorption from the MgH

On the basis of first-principles calculations we have systematically investigated the energetics of hydrogen desorption from the MgH2 (001) surface. Based on total energy and electronic structure calculations, two modes namely strain and doping of selected dopants (Al, Si, Ti) and the combined effect of both on the dehydrogenation energies (ΔH) of MgH2 (001) systems have been analyzed. The maximum improvement in ΔH has been obtained with the combined effect of doping and strain. Among all the dopants, Al gives the lowest value of ΔH when the system Al-MgH2 is subjected to a 7.5% biaxial symmetric strain whereas the Si-MgH2 systems show the least improvement in ΔH. The doping of Ti on MgH2 (001) is also very beneficial even without strain. The reduction in ΔH is caused by the charge localization on the metal atoms, destabilization and the weakening of metal-hydrogen bonds

Atomically precise and monolayer protected iridium clusters in solution

The first atomically precise and monolayer protected iridium cluster in solution, Ir-9(PET)(6) (PET - 2-phenyethanethiol) was synthesized via a solid state method. The absence of a plasmonic band at similar to 350 nm, expected in the UV/Vis spectra for spherical Ir particles of 10 nm size indicated that the synthesized cluster is smaller than this dimension. Small angle X-ray scattering (SAXS) showed that the cluster has a particle size of similar to 2 nm in solution which was confirmed by transmission electron microscopy (TEM). The blue emission of the cluster is much weaker than many noble metal clusters investigated so far. X-ray photoelectron spectroscopy (XPS) measurements showed that all Ir atoms of the cluster are close to the zero oxidation state. The characteristic S-H vibrational peak of PET at 2560 cm(-1) was absent in the FT-IR spectrum of the cluster indicating RS-Ir bond formation. The molecular formula of the cluster, Ir-9(PET)(6) was assigned based on the most significant peak at m/z 2553 in the matrix assisted laser desorption ionization mass spectrum (MALDI MS), measured at the threshold laser intensity. Density functional theory calculations on small Ir@SCH3 and Ir@PET clusters and comparison of the predictions with the IR and H-1-NMR spectra of Ir-9(PET)(6) suggested that the PET ligands have two distinct structural arrangements and are likely to be present as bridging thiolates -(Ir-SR-Ir)-and singly attached thiolates -(Ir-SR)