Interaction of hydrogen molecules on Ni-doped single-walled carbon nanotube

Adsorption of hydrogen molecules on an Ni-doped (8,0) single-walled carbon nanotube (SWNT) is investigated by using first-principles density functional calculations. The result shows that a single Ni atom adsorbed on the bridge site of the tube could cannot dissociate the H₂, however it can chemisorb three H₂ at most, with the average binding energy per H₂ suitable for the hydrogen storage at the room temperature. More H₂ would physisorb around an Ni atom weakly. As for the SWNT with an Ni dimer adsorbed, we find that when the H₂ approaches the Ni--Ni bond, it dissociates without overcoming any barrier and makes bonds with Ni atom.     

Li原子修饰笼型Si6团簇的结构和储氢性能

利用杂化密度泛函B3LYP方法, 在6-311+G(d, p)基组水平上对Si6和Li修饰的Si6团簇的几何结构和电子性质及储氢性能进行模拟计算和理论研究. 结果表明, Si6团簇最低能量构型为笼型结构, 纯Si6团簇不能有效吸附氢分子. Li原子的引入显著改善了Si6团簇的储氢能力. 以两个Li原子端位修饰Si6团簇为载体, 其氢分子的平均吸附能为1.692~2.755 kcal/mol, 每个Li原子周围可以有效吸附五个氢分子, 储氢密度可达9.952wt%. 合适的吸附能和较高储氢密度表明Li修饰Si6团簇有望成为理想的储氢材料.     

Density functional theory study of hydrogen storage on Ni-doped C59X (X = B,N) heterofullerene

ABSTRACT

Hydrogen storage reactions on Ni ? C₅₉X(X = B, N) heterofullerene are investigated by using the state-of-the-art density functional theory calculations. The Ni atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to five hydrogen molecules with average adsorption energies of (?0.94, ?0.48, ?0.33, ?0.25 and ?0.20 eV) per hydrogen molecule for Ni ? C₅₉B, while (?1.20, ?0.60, ?0.41, ?0.28 and ?0.23 eV) per hydrogen molecule for Ni ? C₅₉N. With no metal clustering, the system gravimetric capacities are expected to be as large as 10.87 and 10.85 wt % for 5H₂NiC₅₉B?and 5H₂NiC₅₉N, respectively. While the desorption activation barriers of the complexes 1H₂ + C₅₉X?(X = B, N)?are outside the Department of Energy domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH₂ + C₅₉X(X = B, N)(n = 2 ? 5) are inside this domain. The hydrogen storage of the irreversible 1H₂ + NiC₅₉X?(X = B, N) and reversible 2H₂ + NiC₅₉X?(X = B, N) interactions is characterised in terms of density of states and projected densities of states, pairwise and non-pairwise additivity, infrared, Raman, electrophilicity and molecular electrostatic potentials.     

Li原子修饰笼型Si_6团簇的结构和储氢性能

利用杂化密度泛函B3LYP方法,在6-311+G(d,p)基组水平上对Si_6和Li修饰的Si_6团簇的几何结构和电子性质及储氢性能进行模拟计算和理论研究.结果表明,Si_6团簇最低能量构型为笼型结构,纯Si_6团簇不能有效吸附氢分子.Li原子的引入显著改善了Si_6团簇的储氢能力.以两个Li原子端位修饰Si_6团簇为载体,其氢分子的平均吸附能为1.692~2.755 kcal/mol,每个Li原子周围可以有效吸附五个氢分子,储氢密度可达9.952 wt%.合适的吸附能和较高储氢密度表明Li修饰Si_6团簇有望成为理想的储氢材料.     

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.     

钇覆盖Si@Al12团簇的贮氢性能

利用密度泛函理论系统地研究了Y_mSi@Al₁₂ (m=1—3)团簇及其贮氢性质. 结果表明, 在所研究的尺度范围内, 钇原子未在Si@Al₁₂团簇上团聚; 每个钇原子按18电子规则吸附氢分子, 其中Y₃Si@Al₁₂团簇可以吸附16个完整氢分子, 贮氢质量分数为5.0 %, 平均吸附能处于0.324—0.527 eV之间, 较为理想的吸附能说明在室温条件下吸氢和脱氢是可行的.     

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.     

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 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.     

Tripyrrylmethane based 2D porous structure for hydrogen storage

The key to hydrogen storage is to design new materials with light mass, large surface and rich adsorption sites. Based on the recent experimental success in synthesizing tripyrrylmethane, we have explored Ti-tripyrrylmethane based 2D porous structure for hydrogen storage using density functional theory. We have found that the structure is stable, and the exposed Ti sites can bind three hydrogen molecules with an average binding energy of 0.175 eV/H₂, which lies in the energy window for storage and release of hydrogen in room temperature and at the ambient pressure.     

Hydration effect on the electronic transport properties of oligomeric phenylene ethynylene molecular junctions

A first-principles computational method based on the hybrid density functional theory is developed to simulate the electronic transport properties of oligomeric phenylene ethynylene molecular junctions with H₂O molecules accumulated in the vicinity as recently reported by Na {\it et al.} [\wx{Nanotechnology}{18} 424001 (2007)]. The numerical results show that the hydrogen bonds between the oxygen atoms of the oligomeric phenylene ethynylene molecule and H₂O molecules result in the localisation of the molecular orbitals and lead to the lower transition peaks. The H₂O molecular chains accumulated in the vicinity of the molecular junction can not only change the electronic structure of the molecular junctions, but also open additional electronic transport pathways. The obvious influence of H₂O molecules on the electronic structure of the molecular junction and its electronic transport properties is thus demonstrated.     

Computational investigation of hydrogen storage on B5V3

Based on density functional theory method with 6-311+G(d,p) basis set, the structures, stability and hydrogen storage capacity of B₅V₃ have been theoretically investigated. It is found that a maximum of seven hydrogen molecules can be adsorbed on B₅V₃ with gravimetric uptake capacity of 6.39 wt%. The uptake capacity exceeds the target set by the US Department of Energy for vehicular application. Moreover, the average adsorption energy of B₅V₃ 01 (7H₂) is 0.60 eV/H₂ in the desirable range of reversible hydrogen storage. The kinetic stability of H₂ adsorbed on B₅V₃ 01 is confirmed by using gap between highest occupied molecular orbital (HOMO)and the lowest unoccupied molecular orbital (LUMO). The gap value of B₅V₃ 01 (7H₂) is 2.81 eV, which indicates the compound with high stability. In addition, the thermochemistry calculation (Gibbs free energy corrected adsorption energy) is used to analyse if the adsorption is favourable or not at different temperatures. It can be found that the Gibbs corrected adsorption energy of B₅V₃ 01 (7H₂) is still positive at 400 K at 1 atm. It means that the adsorption of seven hydrogen molecules on B₅V₃ 01 is energetically favourable in a fairly wide temperature range. All the results show that B₅V₃ 01 can be considered as a promising material for hydrogen storage.     

三明治结构graphene-2Li-graphene的储氢性能

本文使用密度泛函理论中的广义梯度近似对扩展三明治结构graphene-2Li-graphene的几何结构、电子性质和储氢性能进行计算研究.计算得知:位于单层石墨烯中六元环面心位上方的单个Li原子与基底之间的结合能最大(1.19 eV),但小于固体Li的实验内聚能(1.63 eV),然而,在双层石墨烯之间的单个Li原子与基底的结合能增加到3.41 eV,远大于固体Li的实验内聚能,因此位于双层石墨烯之间的多个Li原子不会成簇,有利于进一步储氢.扩展三明治结构graphene-2Li-graphene中每个Li原子最多可以吸附3个H_2分子,储氢密度高达10.20 wt.%,超过美国能源部制定的5.5 wt.%的目标.该体系对1—3个H_2分子的平均吸附能分别为0.37,0.17和0.12 eV,介于物理吸附和化学吸附(0.1—0.8 eV)之间,因此该体系可以实现常温常压下对H_2的可逆吸附.通过对态密度分析可知,每个Li原子主要通过电场极化作用吸附多个H_2分子.动力学和巨配分函数计算表明graphene-2Li-graphene结构对H_2分子具有良好的可逆吸附性能.该研究可以为开发良好的储氢材料提供一个好的研究思路,为实验工作提供理论依据.     

碱金属修饰的多孔石墨烯的储氢性能

基于第一性原理深入研究了碱金属原子(Li,Na,K)修饰的多孔石墨烯(PG)体系的储氢性能,并且通过从头算分子动力学模拟了温度对Li-PG吸附的H2分子稳定性的影响.研究结果表明,PG结构的碳环中心是碱金属原子最稳定的吸附位置,PG单胞最多可以吸附4个碱金属原子,Li原子被束缚最强,金属原子间无团聚的倾向;H2分子通过极化机制吸附在碱金属修饰的PG结构上,每个金属原子周围最多可以稳定地吸附3个H2分子;Li-PG对H2分子的吸附最强(平均吸附能为-0.246 eV/H2),Na-PG对H2分子的吸附较弱(平均吸附能为-0.129 eV/H2),K-PG对H2分子的吸附最弱(平均吸附能为-0.056 eV/H2),不适合用做储氢材料;在不考虑外界压强且温度为300 K的情况下,Li-PG结构可稳定地吸附9个H2分子,储氢量为9.25 wt.%;在400 K时,有7个吸附H2分子脱离Li-PG的束缚,在600-700 K的范围内,吸附H2分子全部脱离了Li-PG体系的束缚.     

A theoretical study of hydrogen adsorption on Li, Be, Na, and Mg atoms attached to aromatic hydrocarbons

The binding energy of a hydrogen molecule on metal atoms (Li, Be, Na, and Mg) attached to aromatic hydrocarbon molecules (benzene and anthracene) was calculated using an ab initio molecular orbital method at the MP2(FC)/cc-pVTZ level with basis set superposition error (BSSE) correction. The energy tended to become more negative as the metal atom had a more positive charge and a smaller radius. The energies of Li₂C₆H₆-H₂, Li₂C₁₄H₁₀-H₂, Na₂C₁₄H₁₀-H₂, and MgC₁₄H₁₀-H₂ were −2.7 to −2.2, −4.0 to −3.1, −2.8 to −0.3, and −1.3 kcal/mol, respectively. Most of these energies were more negative than those on the hydrocarbons without metal atoms (ca. −1 kcal/mol). Analyzing the Lennard–Jones type potential with the parameters determined by the MP2 calculations, it was found that these energies mainly consisted of the induction force caused by the positive charge of the metal atom and the dispersion force from the nearest C₆-ring. The energy of BeC₁₄H₁₀-H₂ was more negative (−8.6 kcal/mol) than of the other complexes. The hydrogen molecule in this complex had a comparatively longer H–H distance and a more positive H₂ charge than the others. These data suggest that the hydrogen adsorption on this complex involves a charge transfer process in addition to physisorption interactions. The hydrogen binding energies in some Li₂C₁₄H₁₀-H₂ systems (∼−4.0 kcal/mol) and BeC₁₄H₁₀-H₂ are promising to operate hydrogen storage/release at ambient temperature with moderate pressure.     

Complexation of hydrogen by lithium: structures,energies and vibrational spectra of Li+ (H2) n (n = 1–4), Li-H(H2) m and Li-H + (H2) m (m = 1–3)

The interaction of metals with hydrogen is of importance in several areas of technology. Lithium-hydrogen complexes are particularly amenable to theoretical study. Although no stable compound of the Li atom and H₂ has been found, a weak dative interaction forms between the σ bond of H₂ and the positively charged Li atom for Li⁺, Li-H⁺, and Li-H. At least four H₂ molecules can be complexed by Li⁺, and three by Li-H⁺ and Li-H. The presence of the Li ion does not substantially weaken the H₂ bond, nor is the energy of dissociation affected; however, the Li ion does form stable complexes with the dissociated H atoms.     

Electronic structure and decomposition pathways of monoammoniate of lithium borohydride Li(NH3)BH4: A first-principles investigation

The monoammoniate of lithium borohydride (Li(NH₃)BH₄) is a potential candidate for hydrogen storage owing to its high hydrogen capacity (18 wt%). In this work, electronic structure, bonding characters, and decomposition pathways of Li(NH₃)BH₄ are investigated from first-principles calculations. We find that NH₃ molecules are covalently attached to Li atoms through N atoms and the ionization of Li atoms plays an essential role in stabilizing the compound. A general correlation between the stability of X(NH₃)BH₄ (X=H,Li,Na,K) and the electronegativities of $X$ atoms is established. The thermal stability of X(NH₃)BH₄ could be modulated by manipulating the cation electronegativities. Free energy computations indicate that Li(NH₃)BH₄→LiBH₄+NH₃ is the most likely thermal decomposition route.     

Probing the paramagnetic interactions between the unpaired electronic spins of carbon atoms and the nuclear spins of hydrogen molecules with Raman spectroscopy

Carbon materials typically have a high density of unpaired electronic spins but the exact nature of the defect sites that give rise to their magnetic properties are not yet well understood. In this work, the paramagnetic interactions between the unpaired electronic spins of carbon atoms and the nuclear spins of hydrogen molecules were probed with Raman spectroscopy by monitoring the relative population of H₂ rotational states. For H₂, the symmetries of nuclear spin and rotational wave functions are correlated. Because of the weak interactions between H₂ nuclear spins, the transitions between odd and even rotational states are normally hindered. The magnetic field generated by unpaired electronic spins relaxes the selection rules and promotes transitions between H₂ rotational levels of different symmetry. This affects the rotational levels' relaxation kinetics toward equilibrium and makes H₂ molecules useful to study unpaired electrons in paramagnetic materials. It is suggested that simultaneous electron paramagnetic resonance and Raman measurements on carbon materials interacting with hydrogen molecules could result in a better understanding of the nature of paramagnetic defects in carbon materials, which could have a substantial impact on Li‐ion batteries or for understanding the graphene electronic properties. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction between nanobuds and hydrogen molecules: A first-principles study

Hydrogen storage materials are crucial for the wide application of hydrogen in fuel cells. In this Letter, the interaction between hydrogen molecules and nanobuds has been studied using the Dmol3 package. The results show that the adsorption energies of hydrogen molecules onto nanobuds range from 0.069 eV to 0.115 eV, and that the adsorption energies are not sensitive to the nanobuds' structures but closely related to the number of carbon atoms around H₂ molecules. The energy barrier of a hydrogen molecule entering C176 is 2.38 eV. Each C176 nanobud can accommodate four H₂ molecules. The stress existing in nanobuds induces alterative charge distribution, which can improve the hydrogen storage performance of nanobuds to a certain extent.