DFT study of hydrogen storage in Pd-decorated C60 fullerene

Hydrogen storage reactions on Pd-doped C₆₀ fullerene are investigated by using the state-of-the-art density functional theory calculations. The Pd atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to four hydrogen molecules with average adsorption energies of 0.61, 0.45, 0.32, and 0.21 eV per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.8 wt%. While the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 1 are outside the department of energy (DOE) domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 2–4 are inside this domain. While the interaction of 1H₂ with Pd + C₆₀ is irreversible at 459 K, the interaction of 2H₂ with Pd + C₆₀ is reversible at 529 K. The hydrogen storage of the irreversible 1H₂ + Pd–C₆₀ and reversible 2H₂ + Pd–C₆₀ interactions are characterised in terms of densities of states, infrared, Raman, and proton magnetic resonance spectra, electrophilicity, and statistical thermodynamic stability.     

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C₆₀ fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C₆₀ fullerene, and can bind up to four hydrogen molecules with average adsorption energies of ?0.85, ?0.83, ?0.58, and ?0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 3, 4) are inside this window. The irreversible 2H₂ + NiC₆₀ and reversible 3H₂ + NiC₆₀ interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.     

Molecular hydrogen storage in Al-doped bulk graphite with wider layer distances

Molecular hydrogen storage at room temperature in Al-doped bulk graphite with wider layer distances was studied using density functional theory calculation. Hydrogen storage capacity of 3.48 wt% or volume density of 51 kg/m³ was predicted at T=300 K and P=0.1 GPa with adsorption energy E_b=?0.264 eV/H₂. This is close to the target of volume density 62 kg/m³ and satisfies the requirement of immobilization hydrogen with binding strength of 0.2–0.7 eV/H₂ at ambient temperature and modest pressure for commercial applications specified by the U.S. Department of Energy.     

Hydrogen storage in Li-doped fullerene-intercalated hexagonal boron nitrogen layers

New materials for hydrogen storage of Li-doped fullerene (C₂₀, C₂₈, C₃₆, C₅₀, C₆₀, C₇₀)-intercalated hexagonal boron nitrogen (h-BN) frameworks were designed by using density functional theory (DFT) calculations. First-principles molecular dynamics (MD) simulations showed that the structures of the C _n -BN (n = 20, 28, 36, 50, 60, and 70) frameworks were stable at room temperature. The interlayer distance of the h-BN layers was expanded to 9.96–13.59 Å by the intercalated fullerenes. The hydrogen storage capacities of these three-dimensional (3D) frameworks were studied using grand canonical Monte Carlo (GCMC) simulations. The GCMC results revealed that at 77 K and 100 bar (10 MPa), the C₅₀-BN framework exhibited the highest gravimetric hydrogen uptake of 6.86 wt% and volumetric hydrogen uptake of 58.01 g/L. Thus, the hydrogen uptake of the Li-doped C _n -intercalated h-BN frameworks was nearly double that of the non-doped framework at room temperature. Furthermore, the isosteric heats of adsorption were in the range of 10–21 kJ/mol, values that are suitable for adsorbing/desorbing the hydrogen molecules at room temperature. At 193 K (–80 °C) and 100 bar for the Li-doped C₅₀-BN framework, the gravimetric and volumetric uptakes of H₂ reached 3.72 wt% and 30.08 g/L, respectively.     

The density functional study of the stabilities,bond characters,static linear polarisabilities,and aromaticities of the ’in-out’ isomerism Hn-60@CnH60（n=70,72,74）

This paper uses the density functional theory to analyse the stabilities,bond characters,static linear polarisabilities,and aromaticities of the ’in-out’ isomerism H n-60 @C n H 60 (n=70,72,74).The binding energies,C-H bond energies,and energy gaps explore that the ’in-out’ isometric perhydrogenation of C n (n=70,72,74) can remarkably improve the stabilities.The static linear polarisabilies of H n-60 @C n H 60 (n=70,72,74) are indeed relative to their shapes,while they show almost nonaromatic character.This study can suggest that the ’in-out’ isometric perhydrogenation of fullerenes could lead to the invention of entirely novel potential hydrogen storage nanomaterials.     

Hydrogen adsorption on N-decorated single wall carbon nanotubes

Using density functional theory and molecular dynamics we found that N-decorated single walled (8,0) carbon nanotubes are potential high capacity hydrogen storage media. This system could store up to 6.0 wt% hydrogen at 300 K and ambient pressure, with average adsorption energy of −80 meV/(H₂). Nitrogen coverage was C₈N.     

Hydrogenation of carbon fragments after femtosecond laser ablation of solid C60

We have observed several kinds of hydrocarbon cations after the nanosecond and the femtosecond laser ablation (nsLA and fsLA) of solid C₆₀. The observation indicates that the carbon fragments produced just after laser ablation of the C₆₀ molecule react with the hydrogen atoms and ions coexisting in the ablation plume. In the case of fsLA, clear dependence of the product hydrocarbon species on the ablation laser power has been observed although the dependence is not clearly observed in nsLA. The production of C_nH₅⁺ (n = 8, 10, and 12) is only observed in fsLA suggesting the unique nature of the transient carbon fragments produced by fsLA.     

Enhancement of H2 adsorption on a boron-doped carbon system for hydrogen storage

We study the adsorption of the molecular hydrogen on boron-doped polypyrrole ((–C₄BH₃)_n) using first-principles density functional calculations. We find that the binding energy of H₂ molecules is slightly reduced to 0.39 eV/H₂ from 0.51 eV/H₂ as the number of adsorbed H₂ molecules increases. This is in sharp contrast to the case of boron-doped fullerenes where the binding energy is drastically reduced as the number of adsorbed H₂ molecules increases. We find that the enhancement of H₂ adsorption is due to a local charge transfer by H₂ adsorption in the B-doped polypyrrole as opposed to a delocalized charge transfer in the B-doped fullerenes. Our finding shows that B-doped carbon systems could be utilized for room temperature hydrogen storage.     

Hydrogen adsorption and storage of Ca-decorated graphene with topological defects: A first-principles study

As a candidate for hydrogen storage medium, geometric stability and hydrogen capacity of Ca-decorated graphene with topological defects are investigated using the first-principle based on density functional theory (DFT), specifically for the experimentally realizable single carbon vacancy (SV), 585 double carbon vacancy (585 DCV) and 555–777 double carbon vacancy (555–777 DCV) defects. It is found that Ca atom can be stabilized on above defective graphenes since Ca׳s binding energy on vacancy defect is much larger than its cohesive energy. Up to six H₂ molecules can stably bind to a Ca atom on defective graphene with the average adsorption energies of 0.17–0.39 eV/H₂. The hybridization of the Ca-3d orbitals with H₂-σorbitals and the electrostatic interaction between the Ca cation and the induced H₂ dipole both contribute to the H₂ molecules binding. Double-side Ca-decorated graphene with 585 DCV and 555–777 DCV defects can theoretically reach a gravimetric capacity of 5.2 wt% hydrogen, indicating that Ca-decorated defective graphene can be used as a promising material for high density hydrogen storage.     

Hydrogen storage of beryllium adsorbed on graphene doping with boron: First-principles calculations

Based on density-functional theory, we find that B-doped graphene significantly enhances the Be adsorption energy and prevent Be atoms from clustering. The complex of Be adsorbed on B-doped graphene can serve as a high-capacity hydrogen storage medium: the hydrogen storage capacity (HSC) can reach up to 15.1 wt% with average adsorption energy ?0.298 eV/H₂ for double-sided adsorption. It has exceeded the target specified by US Department of Energy with HSC of 9 wt% and a binding energy of ?0.2 to ?0.6 eV/H₂ at near-ambient conditions. By analyzing the projected electronic density of states of the adsorbed system, we show that the high HSC is due to the change of electron distribution of H₂ molecules and a graphene system decorated with B and Be atoms.     

High hydrogen-storage capacity of B-adsorbed graphene: First-principles calculation

Based on density functional calculations, boron-adsorbed graphene has  been found to be a kind of hydrogen-storage medium. B-adsorbed graphene has excellent hydrogen-storage capacity: when the B atoms are adsorbed on one side, the hydrogen-storage capacity is up to 10.10 wt% and when the adsorption is on both sides the capacity is up to 16.95 wt%. In each of these two cases, the hydrogen-storage capacity exceeds 6 wt%, surpassing the target of US Department of Energy (DOE). The calculated adsorption energy of H₂ molecules is ?0.209 eV/H₂ and ?0.208 eV/H₂ for single-side and both-sides B-adsorbed graphene, respectively, which is within the range ?0.2 to ?0.6 eV/H₂ and indicates that hydrogenous storage can be recycled in near ambient conditions. By analyzing the electron density distribution of the adsorbed system, we have found that the high hydrogen-storage capacity was due to the change of electron distribution of H₂ molecules and graphene by adsorbed B atoms.     

Synthesis of vanadium-doped palladium nanoparticles for hydrogen storage materials

Palladium–vanadium (Pd/V) alloy nanoparticles stabilized with n-pentyl isocyanide were prepared as new hydrogen storage materials by a facile polyol-based synthetic route with tetraethylene glycol and NaOH at 250 °C. The size distribution of the nanoparticles thus obtained featured two peaks at 4.0 ± 1.1 and 1.4 ± 0.3 nm in diameter, which were the mixture of Pd/V alloy and Pd nanoparticles. The ratio between the number of Pd/V and that of Pd nanoparticles was 51:49, and the Pd:V ratio of the overall product was 9:1 in wt%, indicating that the 4.0 nm Pd/V nanoparticles were composed of 81% Pd and 19% V. The inclusion of vanadium caused the increase in the d-spacing and thus expansion of lattice constant. A rapid increase in hydrogen content at low H₂ pressures was observed for the Pd/V nanoparticles, and a 0.47 wt% H₂ adsorption capacity was achieved under a H₂ pressure of 10 MPa at 303 K. Hydrogen storage performances of Pd/V alloy nanoparticles was superior compared with Pd nanoparticles.     

CORAL: QSPR models for solubility of [C60] and [C70] fullerene derivatives

Quantitative structure–property relationships (QSPRs) between the molecular structure of [C₆₀] and [C₇₀] fullerene derivatives and their solubility in chlorobenzene (mg/mL) have been established by means of CORAL (CORrelations And Logic) freeware. The CORAL models are based on representation of the molecular structure by simplified molecular input line entry system (SMILES). Three random splits into the training and the external validation sets have been examined. The ranges of statistical characteristics of these models are as follows: n = 18, r ² = 0.748–0.815, s = 15.1 –17.5 (mg/mL), F = 47–71 (training set); n = 9, r ² = 0.806–0.936, s = 12.5–17.5 (mg/mL), F = 29–103 (validation set).     

Conventional and inverse magnetocaloric effects,and critical behaviors in Ni43Mn46Sn8In3 alloy

A systematic study of the conventional and inverse magnetocaloric effects, and critical behaviors in an alloy ingot of Ni₄₃Mn₄₆Sn₈In₃ has been performed. Our results reveal the sample exhibiting structural and magnetic phase transitions at temperatures T_C^M = 166 K (T_C of the martensitic phase), T_M–A = 260 K (the martensitic-to-austenitic phase transformation) and T_C^A = 296 K (T_C of the austenitic phase). The large values of refrigerant capacity (RC) around T_M–A and T_C^A are found to be RC_M–A = 172.6 and RC_A = 155.9 J kg⁻¹, respectively, under an applied field change of 30 kOe. Our critical analyses near the T_C^M and T_C^A reveal that a coexistence of the long- and short-range ferromagnetic order in the martensitic phase, while the long-range ferromagnetic order exists in the austenitic phase. Interestingly, at around T_C^A, the maximum magnetic entropy change (|ΔS_max|) versus magnetic field H obeys a power law, |ΔS_max| = a·Hⁿ, where the exponent n is found to be about 0.66.     

First principles study of small cobalt clusters encapsulated in C60 and C82 spherical nanocages

Structural, electronic and magnetic properties of the small Co_n clusters (n = 2-7) endohedrally doped in C₆₀ (Ih) and C₈₂ (C2v) fullerenes were investigated using ab initio calculations based on the density functional theory. It is found that the encapsulated Co_n clusters inside C₆₀ and C₈₂ cages are energetically favorable except for Co₇@C₆₀. The encapsulation does not change significantly the structure of the enclosed clusters, but the magnetic moment of the clusters reduces due to a stronger Co-C hybridization for the larger clusters.     

Hydrogen storage in boron nitride and carbon clusters studied by molecular orbital calculations

Possibility of hydrogen gas storage in carbon (C) and boron nitride (BN) clusters was investigated by molecular orbital calculations. Chemisorption calculation was carried out for C₆₀, B₂₄N₂₄ and B₃₆N₃₆ with changing position of hydrogen atom to compare the bonding energy at carbon, nitrogen and boron, tetragonal and hexagonal rings. Chemisorption calculation of hydrogen for BN clusters showed that hydrogen bondings with nitrogen atoms and tetragonal rings were the most stable. Stability of H₂ molecules inside BN and C clusters was also investigated by molecular orbital calculations. C and BN clusters showed possibility of hydrogen storage of 6.5 and 4.9 wt%, respectively.     

Stoichiometrically controlled direct solid-state synthesis of C60H2

The direct solid-state synthesis of C₆₀H₂ has been demonstrated by controlling the amount of hydrogen introduced into the reaction with C₆₀. Palladium hydride has been used as the source of hydrogen. The main product 1,2-C₆₀ is the isomer predicted to have the lowest energy of the possible 23 isomers; in addition, small amounts of the thermodynamically most stable isomer of C₆₀H₄, 1,2,3,4-C₆₀H₄, have also been obtained.     

Giant fullerenes formed on C60 films irradiated with electrons field-emitted from scanning tunneling microscope tips

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C₆₀ films grown on Si(1 1 1)-(7 × 7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C_60n (n = 2-4) expected from the simple fusion of C₆₀ molecules. It was proposed that electronic excitations of C₆₀ molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects.     

Internal evaluation of impregnation treatment of waterlogged wood; relation between concentration of internal materials and relaxation time using magnetic resonance imaging

The purpose of this study is to clarify the degree of impregnation resulting from treatment of internal waterlogged wood samples using MRI. On a 1.5 T MR scanner, T₁ and T₂ measurements were performed using inversion recovery and spin-echo sequences, respectively. The samples were cut waterlogged pieces of wood treated with various impregnation techniques which were divided into different concentrations of trehalose (C₁₂H₂₂O₁₁) and polyethylene glycol (PEG; HO-(C₂H₄O)_n-H) solutions. Then these samples underwent impregnation treatment every two weeks. From the results, we found that the slope of the T₁-concentration curve using linear fitting showed the value of the internal area for PEG to be higher than the external area; internal, − 2.73 ms/wt% (R² = 0.880); external, − 1.50 ms/wt% (R² = 0.887). Furthermore, the slope of the T₁-concentration curve using linear fitting showed the values for trehalose to have almost no difference when comparing the internal and the external areas; internal, − 2.79 ms/wt% (R² = 0.759); external, − 3.02 ms/wt% (R² = 0.795). However, the slope of the T₂-concentration curve using linear fitting for PEG showed that there was only a slight change between the internal and the external areas; internal, 0.26 ms/wt% (R² = 0.642); external, 0.18 ms/wt% (R² = 0.920). The slope of the T₂-concentration curve did not show a change in linear relationship between the internal and the external areas; internal, 0.06 ms/wt% (R² = 0.175); external, − 0.14 ms/wt% (R² = 0.043). In conclusion, using visualization of relaxation time T₁, it is possible to obtain more detail information noninvasively concerning the state of impregnation treatment of internal waterlogged wood.     

The oxidation of fullerenes (C<Subscript>60</Subscript>, C<Subscript>70</Subscript>) with various oxidants under ultrasonication

The reaction of C₆₀, under ultrasonication, with various oxidants, such as 3-chloroperoxy benzoic acid (Fluka 99%), 4-methyl morpholine N-oxide (Aldrich 97%), chromium (VI) oxide (Aldrich 99.9%), and the oxone® monopersulfate compound, causes the oxidation of fullerenes at room temperature. The FAB-MS spectra and HPLC profile confirmed that the products of fullerene oxidation were [C₆₀(O)_n] (n=1～3 or n=1). C₇₀ also reacted, under ultrasonication, with various oxidants, but the reaction rate of C₇₀ was lower than that of C₆₀.