Hydrogen storage in hydrofullerides

Highly reduced fullerenes containing nearly 5 wt.% of dihydrogen can be synthesized using readily available reagents. Hydrides prepared from C₆₀ by dissolving metal reductions give complex mixtures of unstable isomers of C₆₀H₃₆. High temperature syntheses using transfer hydrogenation reagents such as dihydroanthracene provide mainly two stable isomers of C₆₀H₃₆ that have been characterized spectroscopically. Dihydrogen can be removed thermally from these materials at 500 °C. The experimentally determined activation energy for the thermal removal of dihydrogen from C₆₀H₂ is 61.4 kcal/mol. This value is in good agreement with the value determined computationally for a multi step radical reaction. The 92 kcal/mol barrier determined computationally for the concerted loss of dihydrogen reflects the symmetry-imposed barrier to dehydrogenation. PACS 81.05.Tp; 82.30.Cf; 82.56.Ub     

Creating nanostars with buckyballs

We report creating superradiant quantum nanoplasmas (nanostars) by impacting buckyballs at hypervelocities (v>100 km/s) in an innovative tabletop apparatus. The nanostars are estimated to have ～10 TPa transient pressures and convert ～35% of impact energy into soft-X-ray energy. The ultrahigh-efficiency conversion is proposed to result from Dicke Superradiance of Metastable Innershell Molecular State, originally discovered by the author and his colleagues in 1994. The usage of buckyballs and successful orders-of-magnitude scaling down of the apparatus size and complexity establish an innovative tabletop method for generating, studying, and utilizing matter in planetary or stellar interiors and open doors to numerous unprecedented applications.     

Hydrogen storage in sonicated carbon materials

The hydrogen storage in purified single-wall carbon nanotubes (SWNTs), graphite and diamond powder was investigated at room temperature and ambient pressure. The samples were sonicated in 5 M HNO₃ for various periods of time using an ultrasonic probe of the alloy Ti-6Al-4V. The goal of this treatment was to open the carbon nanotubes. The maximum value of overall hydrogen storage was found to be 1.5 wt %, as determined by thermal desorption spectroscopy. The storage capacity increases with sonication time. The sonication treatment introduces particles of the Ti alloy into the samples, as shown by X-ray diffraction, transmission electron microscopy, and chemical analysis. All of the hydrogen uptake can be explained by the assumption that the hydrogen is only stored in the Ti-alloy particles. The presence of Ti-alloy particles does not allow the determination of whether a small amount of hydrogen possibly is stored in the SWNTs themselves, and the fraction of nanotubes opened by the sonication treatment is unknown. Received: 18 December 2000 / Accepted: 18 December 2000 / Published online: 9 February 2001     

钴修饰氮化铝纳米管的储氢性能

本文采用密度泛函理论中的广义梯度近似系统地研究了钴原子修饰的(5,5)单壁氮化铝纳米管(SWANNT)的几何结构、电子性质以及储氢性能.研究结果表明:钴原子倾向于以顶位的形式吸附于(5,5) SWANNT表面N原子上.在钴原子周围可以吸附4个完整的H分子,平均吸附能为0.624 e V,表明钴原子修饰的SWANNT材料有望在温和环境中实现对H分子的快速吸附和脱附.     

Hydrogen storage using physisorption – materials demands

A survey is presented of the storage capacities of a large number of different adsorbents for hydrogen at 77 K and 1 bar. Results are evaluated to examine the feasibility and perspectives of transportable and reversible storage systems based on physisorption of hydrogen on adsorbents. It is concluded that microporousadsorbents, e.g. zeolites and activated carbons, display appreciable sorption capacities. Based on their micropore volume (∼1 ml/g) carbon-based sorbents display the largest adsorption, viz. 238 ml (STP)/g, at the prevailing conditions. Optimization of sorbent and adsorption conditions is expected to lead to adsorption of ∼560 ml (STP)/g, close to targets set for mobile applications. Received: 9 January 2001 / Accepted: 27 January 2001 / Published online: 23 March 2001     

储氢材料与金属氢化物-镍电池

储氢合金是金属氢化物-镍电池的关键材料，文中简要评述了稀土镍系合金、Laves相系合金、镁基合金、钒基固溶体和纳米管材料作为储氢电极材料的研究进展与目前存在问题，并简要介绍了动力金属氢化物-镍电池的开发动态。     

纳米多孔碳气凝胶的储氢性能

以间苯二酚和甲醛为原料,采用溶胶-凝胶工艺,结合高温碳化和溶剂替换常压干燥技术,制备了碳气凝胶。通过改变间苯二酚与碳酸钠的物质的量比和反应物间苯二酚与甲醛的质量分数,实现对碳气凝胶孔洞结构的控制。制备了钯掺杂碳气凝胶。以透射电镜、X射线衍射谱证实了钯元素以纳米单质颗粒形式存在于碳气凝胶的骨架结构中。对掺杂碳气凝胶进行了活化工艺的后处理,成功提高了比表面积有2倍之多,获得了比表面积为1 273 m2/g的钯掺杂碳气凝胶。氢吸附性能研究结果表明：最优活化工艺所得的碳气凝胶样品（3 212 m2/g）在92 K,3.5 MPa条件下的饱和储氢质量分数为3%,此样品在303 K,3.2 MPa时的储氢质量分数为0.84%。对钯掺杂碳气凝胶的常温（303 K）氢吸附测试表明,掺杂后碳气凝胶的总储氢质量分数下降了,但单位比表面积的储氢质量分数提高了。     

纳米多孔碳气凝胶的储氢性能

 以间苯二酚和甲醛为原料,采用溶胶-凝胶工艺,结合高温碳化和溶剂替换常压干燥技术,制备了碳气凝胶。通过改变间苯二酚与碳酸钠的物质的量比和反应物间苯二酚与甲醛的质量分数,实现对碳气凝胶孔洞结构的控制。制备了钯掺杂碳气凝胶。以透射电镜、X射线衍射谱证实了钯元素以纳米单质颗粒形式存在于碳气凝胶的骨架结构中。对掺杂碳气凝胶进行了活化工艺的后处理,成功提高了比表面积有2倍之多,获得了比表面积为1 273 m²/g的钯掺杂碳气凝胶。氢吸附性能研究结果表明：最优活化工艺所得的碳气凝胶样品（3 212 m²/g）在92 K,3.5 MPa条件下的饱和储氢质量分数为3%,此样品在303 K,3.2 MPa时的储氢质量分数为0.84%。对钯掺杂碳气凝胶的常温（303 K）氢吸附测试表明,掺杂后碳气凝胶的总储氢质量分数下降了,但单位比表面积的储氢质量分数提高了。     

Hydrogen storage by physisorption: beyond carbon

Hydrogen storage using physisorption requires higher desorption temperatures than those possible using conventional adsorbents such as carbon. Using computational design, we predict that several materials have extremely strong physisorption interactions with hydrogen, including 12 kJ/mol heat of adsorption for hydrogen on some sites. Experimental adsorption isotherms on one of the materials, boron oxide, confirm the calculations, and large coverage is observed at temperatures as high as the boiling point of methane, 115 K. Since these materials have sp²-like bonding, they should be amenable to the rich variety of chemical manipulations that have been used with carbon.     

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.     

Hydrogen for novel materials and devices

We start by recalling some of the properties of hydrogen and present a summary of the phenomena caused by the reversible hydrogen sorption by metals and various forms of condensed carbon, at the surface and into the bulk, using molecular hydrogen gas, hydrogen plasma and electrochemically sorbed hydrogen. We then describe the use of hydrogen to modify the surface and bulk properties of various materials with a focus on applications and devices: electronic and optic phase transitions of thin films and related energy devices, surface polishing and cleaning, decrepitation and amorphization of intermetallics, growth of carbon nanostructures and electron emission from diamond-like and graphitic carbon, longrange perturbation of the electron distribution of graphitic structures by hydrogen defects, and the consequences for potential nanoelectronics. Received: 8 November 2000 / Accepted: 20 November 2000 / Published online: 9 February 2001     

La内嵌 graphene/MoS2层的储氢性能研究

运用密度泛函理论研究了La内嵌graphene/MoS₂层的储氢性能.由于La的内嵌graphene/MoS₂异质结的层间距被拉大.详细研究了氢气分子在La内嵌的graphene/MoS₂结构上的吸附行为.结果表明,一个La原子最多可以吸附六个氢气分子,采用GGA/PBE泛函计算得到氢气分子的平均吸附能为0.198 eV.合适的吸附能使得设计材料能够在温和条件下实现可逆存储.重要的是,La原子能够分散地内嵌在graphene/MoS₂异质结中,这将为氢气分子提供更多吸附位.研究表明理论上预测La内嵌graphene/MoS₂材料是一种潜在的储氢材料.     

真空热处理碳纳米管的储氢性能研究

研究了真空热处理对多壁碳纳米管(MWNTs)电化学储氢性能的影响.采用化学气相沉积法(CVD)制备碳纳米管，碳纳米管与LaNi₅储氢合金按质量比1∶10混合，制作成CNTs-LaNi₅电极.电解池采用三电极体系，6mol/L KOH为电解液，Ni(OH)₂为正极，Hg/HgO为参比电极.实验结果表明，在相同的充放电条件下，850℃时CNTs-LaNi₅电极的储氢性能最好，克容量最大为503.6mAh/g，相应的平台电压高达1.18V.从500—850℃随着温度升高，放电量有较大幅度的增加，但到950℃时放电量反而下降.由此可见，碳纳米管的热处理温度对碳纳米管的电化学储氢性能有着较大的影响. 关键词： 碳纳米管(CNTs) 储氢性能 5合金')" href="#">LaNi₅合金 化学气相沉积法(CVD法)     

Fullerene-like Si60C60 nanocage: Hydrogen storage capacity

For investigating the hydrogen storage capacity of the Si₆₀C₆₀ nanocage, we have performed first principle density functional theory calculations with van der waals corrections. According to the force and energy minimization of the complex structures of nH₂@Si₆₀C₆₀, we have found that the systems with n = 1 to 70 are energetically favorable. We also found that the most stable nH₂@Si₆₀C₆₀ system is related to the systems with n close to 50 which make it possible to reach 4.2 wt% of hydrogen storage. Although it is found that the nH₂@Si₆₀C₆₀ system remains stable up to n = 70 and 5.8 wt%. The NPT molecular dynamic investigation at different pressures (0–30 atm) and also different temperatures (300–1800 K) were carried out on the optimized stable system with maximum capacity of encapsulating H₂ molecules (70H₂@Si₆₀C₆₀).     

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.     

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.     

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.     

Li修饰的C24团簇的储氢性能

利用密度泛函理论研究了Li原子修饰的C₂₄团簇的储氢性能. Li原子在C₂₄团簇表面的最佳结合位是五元环. Li原子与C₂₄团簇之间的作用强于Li原子之间的相互作用, 能阻止它们在团簇表面发生聚集. 当Li原子结合到C₂₄表面时, 它们向C原子转移电子后带正电荷. 当氢分子接近这些Li原子时, 在电场作用下发生极化, 通过静电相互作用吸附在Li原子周围. 在Li修饰的C₂₄复合物中, 每个Li原子能吸附两到三个氢分子, 平均吸附能处于0.08到0.13 eV/H₂范围内. C₂₄Li₆能吸附12个氢分子, 储氢密度达到6.8 wt%.     

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.     

Hydrogen storage using carbon adsorbents: past, present and future

Interest in hydrogen as a fuel has grown dramatically since 1990, and many advances in hydrogen production and utilization technologies have been made. However, hydrogen storage technologies must be significantly advanced if a hydrogen based energy system, particularly in the transportation sector, is to be established. Hydrogen can be made available on-board vehicles in containers of compressed or liquefied H₂, in metal hydrides, via chemical storage or by gas-on-solid adsorption. Although each method possesses desirable characteristics, no approach satisfies all of the efficiency, size, weight, cost and safety requirements for transportation or utility use. Gas-on-solid adsorption is an inherently safe and potentially high energy density hydrogen storage method that could be extremely energy efficient. Consequently, the hydrogen storage properties of high surface area “activated” carbons have been extensively studied. However, activated carbons are ineffective in storing hydrogen because only a small fraction of the pores in the typically wide pore-size distribution are small enough to interact strongly with hydrogen molecules at room temperatures and moderate pressures. Recently, many new carbon nanostructured absorbents have been produced including graphite nanofibers and carbon multi-wall and single-wall nanotubes. The following review provides a brief history of the hydrogen adsorption studies on activated carbons and comments on the recent experimental and theoretical investigations of the hydrogen adsorption properties of the new nanostructured carbon materials. Received: 16 October 2000 / Accepted: 15 November 2000 / Published online: 9 February 2001