单壁碳纳米管低温及常温下储氢行为的模拟计算研究

采用巨正则系综蒙特卡罗方法, 通过含有此方法模块的GULP软件, 系统地研究了扶手椅式单壁碳纳米管在低温和常温下的储氢性能, 给出了5种半径的扶手椅管在液氮温度(77 K)和常温(280 K)下的吸附等温线, 同一管径在不同温度不同压强下氢分子在碳纳米管中的分布构型图等. 对77 K和280 K下不同压强不同管径的碳纳米管储氢能力做了较为全面的对比分析, 最后根据模拟计算的结果, 对碳纳米管储氢能力的强化提出了一些建设性意见.     

多壁碳纳米管储氢的物理吸附特性

采用巨正则蒙特卡罗方法 ,模拟常温、1 0MPa下氢在扶手椅型多壁壁碳纳米管中的物理吸附过程 .氢分子之间、氢分子与碳原子之间的相互作用采用Lennard Jones势能模型 .研究了双壁碳纳米管外 (内 )径固定而内 (外 )径改变时的物理吸附储氢情况 ,发现氢分子主要储存在双壁碳纳米管的管壁附近 ,当双壁碳纳米管的内外管壁间距由 0 .34nm增大到 0 .6 1或 0 .88nm时可有效增加物理吸附储氢量 ,并给出了相应的理论解释 .在此基础上 ,计算了管壁间距为 0 .34、0 .6 1和 0 .88nm时的三壁碳纳米管的物理吸附储氢量 ,并与相同条件下单壁和双壁碳纳米管的物理吸附储氢量作了比较 ,发现多壁碳纳米管的物理吸附储氢量随碳管层数的增加而减小 .     

单壁BN纳米管和碳纳米管物理吸附储氢性能的理论对比研究

采用巨正则蒙特卡罗方法(GCMC)研究了单壁氮化硼纳米管(SWBNNTs)和单壁碳纳米管(SWCNTs)的物理吸附储氢性能,主要对比研究了纳米管的管径、温度和手性对二者物理吸附储氢量的影响. 研究结果表明：在低温下,SWBNNTs的物理吸附储氢性能优于相应的SWCNTs;但是随着温度的升高,二者的物理吸附储氢性能差别越来越小,在常温下,SWBNNTs不具备有比SWCNTs更强的物理吸附储氢性能,而是和相同条件下的SWCNTs相差不大,只是在高压下的物理吸附储氢量稍稍大于SWCNTs,并给出了合理的理论解释 关键词： 巨正则蒙特卡罗方法(GCMC) 单壁氮化硼纳米管(SWBNNTs) 单壁碳纳米管(SWCNTs) 储氢     

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)     

H2的自由扩散和吸附状态的对比研究

运用巨正则Monte Carlo方法, 模拟了H₂在自由扩散状态下及碳纳米管吸附状态下的分布, 对H₂的自由扩散和吸附状态进行了对比研究. 研究表明: 77 K和2 MPa下, (30, 30)扶手椅型碳纳米管质量储氢密度为3.74%, 77 K和10 MPa下, 质量储氢密度为7.4%. 吸附状态的H₂分子主要汇聚在碳纳米管内外两个壁面. 关键词： 储氢 碳纳米管 巨正则Monte Carlo     

BC3复合纳米管的储氢性能研究

采用巨正则蒙特卡罗方法(GCMC)研究了BC3复合纳米管的物理吸附储氢性能,获得了该纳米管在不同温度和压强下的吸附等温线,及其在不同条件下的物理储氢吸附量,并和相应的碳纳米管进行了对比研究.结果表明,BC3纳米管在所有条件下的储氢性能均优于相应的碳纳米管,因而它是一种比碳纳米管更强的氢存储介质,并从纳米管和H2分子以及H2分子和H2分子之间的平均总相互作用能的分布情况等因素出发解释了这两种纳米管有不同储氢行为的原因.     

碳纳米管在储氢上的应用

氢能是一种理想的能源载体,而经济有效的储氢手段是氢能实现规模应用急需解决的关键问题之一。碳纳米管在存储氢气上表现出来的独特性质,使其最有希望成为一种新的高效的储氢材料。从实验、理论研究两个方面总结了前人在碳纳米管储氢上的研究成果,并对碳纳米管储氢吸附方式,吸附量影响因素等方面做出分析。最后指出为实现碳纳米管储氢大规模应用仍需做的一些基础性研究工作。     

单壁碳纳米管储氢的第一原理分子动力学模拟

本文用第一性原理平面波赝势方法模拟研究了手性单壁碳纳米管与氢分子的相互作用,考察了碳纳米管直径对储氢性能的影响.对单壁碳纳米管储氢的模拟结果表明:(1)物理吸附时,H2可以吸附在空腔内,也可以吸附在管与管之间的空隙中,纳米管内部的氢吸附力均高于管外,而“完好无损”的H2分子不能够穿过管壁而进入管内.(2)化学吸附时,碳纳米管对氢的吸附首先出现在管的边缘附近,碳纳米管局部会发生形变,SWCNTs的张力会随C-H键的增加而增大,系统不稳定.(3)随着直径的增加,纳米管内、外的氢吸附力差异减小.     

单壁碳纳米管储氢的第一原理分子动力学模拟

本文用第一性原理平面波赝势方法模拟研究了手性单壁碳纳米管与氢分子的相互作用,考察了碳纳米管直径对储氢性能的影响。对单壁碳纳米管储氢的模拟结果表明: (1)物理吸附时,H2可以吸附在空腔内,也可以吸附在管与管之间的空隙中,纳米管内部的氢吸附力均高于管外,而“完好无损”的H2分子不能够穿过管壁而进入管内。(2)化学吸附时,碳纳米管对氢的吸附首先出现在管的边缘附近,碳纳米管局部会发生形变,SWCNTs的张力会随C-H键的增加而增大,系统不稳定。（3）随着直径的增加,纳米管内、外的氢吸附力差异减小。     

纳米储氢材料的研究进展

储氢材料的纳米化为新型储氢材料的研究提供了新的研究方向和思路,本文详细介绍了纳米储氢材料性能提高的机理,综述了纳米碳纳米管储氢材料、镁基纳米储氢材料以及复合纳米储氢材料的最新研究进展,并对储氢材料纳米化的广阔前景进行了展望。     

Hydrogenation of single-walled carbon nanotubes

Towards the development of a useful mechanism for hydrogen storage, we have studied the hydrogenation of single-walled carbon nanotubes with atomic hydrogen using core-level photoelectron spectroscopy and x-ray absorption spectroscopy. We find that atomic hydrogen creates C-H bonds with the carbon atoms in the nanotube walls, and such C-H bonds can be completely broken by heating to 600 degrees C. We demonstrate approximately 65 +/- 15 at % hydrogenation of carbon atoms in the single-walled carbon nanotubes, which is equivalent to 5.1 +/- 1.2 wt % hydrogen capacity. We also show that the hydrogenation is a reversible process.     

Hydrogen storage in BC3 composite single-walled nanotube:a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory(DFT) and grand canonical Monte Carlo simulations(GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC 3 nanotubes and carbon nanotubes.The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes.Furthermore,the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions.The present results have shown that with both computational methods,the hydrogen storage capacity of BC 3 nanotubes is superior to that of carbon nanotubes.The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.     

First-principle study of interaction of molecular hydrogen with BC<Subscript>3</Subscript> composite single-walled nanotube

The physisorption of molecular hydrogen in BC₃ composite single-walled nanotube, investigated using density functional theory, was compared with single-walled carbon nanotube. Both external and internal adsorption sites of these two nanotubes have been studied with the hydrogen molecular axis oriented parallel to the nanotube wall. The calculated results show that: ([see full textsee full text]) the physisorption energies of a H₂ molecule are larger for BC₃(8,0) composite nanotube than for C(8,0) nanotube at all adsorption sites examined. ([see full textsee full text]) For these two nanotubes, the physisorption energies are larger for hydrogen bound inside the nanotubes than for adsorption outside the nanotubes. The different behavior between these two nanotubes is explained by the contour plots of electron density and charge-density difference of them. The present computations suggest that BC₃ nanotube may be a better candidate for hydrogen storage than carbon nanotube.     

Effect of hydrogenation on the spectra of electronic and vibrational transitions in single-walled carbon nanotubes

Single-walled carbon nanotubes containing 5.4 wt% H are prepared under a hydrogen pressure of 50 kbar at the temperature T = 500°C. Analysis of the optical transmission spectra has revealed that the hydrogenation of single-walled carbon nanotubes brings about suppression of high-frequency conduction provided by free charge carriers in the nanotubes, the disappearance of interband electronic transitions, and the appearance of an absorption line at 2845 cm^?1 corresponding to stretching vibrations of the C-H bonds. The removal of hydrogen from hydrogenated single-walled carbon nanotubes owing to vacuum annealing at a temperature of 500°C is accompanied by a linear decrease in the intensity of this line as the hydrogen content in the system decreases. This phenomenon indicates that the greater part of the hydrogen atoms in single-walled carbon nanotubes are covalently bonded to the carbon atoms.     

Review of theoretical calculations of hydrogen storage in carbon-based materials

In this paper we review the existing theoretical literature on hydrogen storage in single-walled nanotubes and carbon nanofibers. The reported calculations indicate a hydrogen uptake smaller than some of the more optimistic experimental results. Furthermore the calculations suggest that a variety of complex chemical processes could accompany hydrogen storage and release. Received: 24 August 2000 / Accepted: 15 November 2000 / Published online: 9 February 2001     

Immobilization of redox mediators on functionalized carbon nanotube: A material for chemical sensor fabrication and amperometric determination of hydrogen peroxide

Chemical functionalization of single-walled carbon nanotubes with redox mediators, namely, toluidine blue and thionin have been carried out and the performance of graphite electrode modified with functionalized carbon nanotubes is described. Mechanical immobilization of functionalized single-walled nanotube (SWNT) on graphite electrode was achieved by gently rubbing the electrode surface on carbon nanotubes supported on a glass slide. The electrochemical behaviour of the modified electrodes was investigated by cyclic voltammetry. The SWNT-modified electrodes showed excellent electrocatalytic effect for the reduction of hydrogen peroxide. A decrease in overvoltage was observed as well as an enhanced peak current compared to a bare graphite electrode for the reduction of hydrogen peroxide. The catalytic current was found to be directly proportional to the amount of hydrogen peroxide taken.     

NMR spectroscopy of hydrogen adsorption on single-walled carbon nanotubes after exposure to high pressure

Hydrogen storage properties of single-walled carbon nanotubes (CNTs) after exposure to a pressure of 14.3 MPa are studied by (1)H nuclear magnetic resonance spectroscopy. The nanotubes were carefully pre-characterized using inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM), and Raman spectroscopy. We have shown previously that at ambient temperature in the pressure range from 0 to 1.5 MPa, hydrogen adsorption is fast and reversible and must be described as physisorption. However, exposure to a much higher pressure (14.3 MPa) of hydrogen leads to slower desorption kinetics where longer exposure causes greater hydrogen uptake. Our data suggest that interstitial sites and the tube interior may be identified as these strong adsorption sites.