碳纳米管储氢性能的计算机模拟

采用巨正则蒙特卡罗(GCMC Grand Canonical Monte Carlo)方法^[11],系统地研究了锯齿(Zigzag)型单壁碳纳米管(SWNT-Single Walled Carbon Nanotubes)的储氢性能,得到了管径和管长与储氢能力的关系曲线,给出了氢在碳纳米管中的分布,并对碳纳米管储氢能力的表征提出了建设性意见.     

碳硼富勒烯衍生物C18B2M(M=Li,Ti, Fe)的储氢性能计算研究

本文使用密度泛函理论(density functional theory, DFT)中的广义梯度近似(generalized gradient approximation, GGA)研究了经碱金属原子Li、过渡金属原子Ti和Fe原子修饰的富勒烯C₁₈B₂M(M=Li, Ti, Fe)的储氢性能. 研究发现, C₁₈B₂由于B的替代掺杂, 比C₂₀对金属原子具有更高的结合能. 由平均吸附能分析可知: C₁₈B₂Li对H₂的吸附能力较弱, C₁₈B₂Fe对H₂的吸附能力过强, 而C₁₈B₂Ti对H₂的平均吸附能介于0.45-0.59 eV 之间, 介于物理吸附和化学吸附之间 (0.2-0.6 eV), 因此可以实现常温下的可逆储氢. C₁₈B₂M(M=Li, Ti, Fe)能够吸附的H₂数目最多分别为4, 6和4. 由储氢机理分析可知: C₁₈B₂Li主要通过碱金属离子激发的静电场来吸附H₂, 而C₁₈B₂Ti和C₁₈B₂Fe主要通过金属原子与H₂之间的Kubas作用来吸附H₂. 由于C₁₈B₂Ti既有较大的储氢数目, 又可以实现可逆储氢, 因此有望开发成新型纳米储氢材料.     

氢分子在Na2Al6团簇上的吸附和解离性能

氢的物理和化学吸附是氢存储的基本形式，而H₂分子的解离能垒是决定可逆储氢动力学性能的重要因素.纳米团簇是研究材料储氢性能的重要物质层次，研究氢与Na-Al团簇的相互作用性质能够了解纳米尺度的Na-Al氢化物的储氢性能.本文利用密度泛函理论，计算研究了H₂分子在较小的合金团簇Na₂Al₆上的吸附与解离性能.结果表明H₂分子在Na₂Al₆团簇上是弱的物理吸附，但很容易发生解离.氢分子的解离能垒很低，解离可以在环境温度下发生，纳米结构的Na₂Al₆团簇具有良好的化学储氢性能.     

掺硼水吸附碳纳米管电子场发射性能的第一性原理研究

运用第一性原理研究了掺硼碳纳米管(BCNT)顶端吸附水分子后的电子场发射性能.结果表明：掺B及吸附H₂O的碳纳米管(BCNT+H₂O)端部形成电子聚集的原子尺度微区,其电子态密度(DOS)在费米能级(E_f)附近有很大提高.根据计算的电子DOS,HOMO/LUMO及Mulliken电荷分布等可知BCNT+H₂O比CNT+H₂O有更好的场发射性能. 关键词： 掺硼碳纳米管 吸附 密度泛函理论 电子场发射     

微孔对单壁纳米碳管储氢性能的影响

用巨正则蒙特卡罗分子模拟方法研究了单壁纳米碳管中的微孔即单壁纳米碳管基本孔-内管腔和管间孔对单壁纳米碳管储氢性能的影响.与低温下氮气吸附实验结果的比较发现单壁纳米碳管的内管腔是吸附的主要位置.分析单壁纳米碳管内管腔中吸附势的叠加和利用效率，发现管径为2nm左右时单壁纳米碳管内管腔的储氢容量最高.当单壁纳米碳管阵列的管间距增加时，单壁纳米碳管的管间孔也会成为有效的氢吸附位. 关键词： Monte Carlo方法 单壁纳米碳管 储氢 微孔     

Rb原子修饰缺陷h-BN单层储氢性能的第一性原理研究

基于密度泛函理论框架下的第一性原理计算方法,系统的研究了碱金属Rb原子修饰具有空位缺陷h-BN单层体系的储氢性能.发现Rb原子可稳定吸附在h-BN单层的B单空位缺陷(V_B)上,且Rb原子间无团簇倾向,单个Rb原子最多可稳定吸附5个H₂分子,H₂分子平均吸附能在0.18-0.21 eV范围内.电子结构分析表明H2分子主要通过极化机制和轨道杂化作用吸附在Rb修饰的缺陷h-BN单层体系上.Rb双侧修饰缺陷h-BN单层体系的理论储氢质量比可以达到5.0 wt%.基于范特霍夫方程和从头算分子动力学(AIMD)模拟对储氢体系的热力学稳定性进行了进一步的研究.     

Li修饰的C$lt;sub$gt;6$lt;/sub$gt;分子对H$lt;sub$gt;2$lt;/sub$gt;O的吸附研究

采用密度泛函理论中的广义梯度近似研究C₆Li吸附H₂O分子并将之进行分解的催化过程. 几何优化发现：Li原子最稳定的吸附位置是位于C 原子顶位上方. 研究表明,第一个H₂O 分子吸附在C₆Li上需要克服1.77 eV的能量势垒,然后分解为H和OH且与Li原子成键. 当吸附第二个H₂O分子时,第二个H₂O分子需要克服1.2 eV的能量势垒分解为H和OH,其中H与Li原子上的H原子结合成H₂,OH则替代Li 原子上的H结合在Li原子上. 因此C₆Li 可以作为催化剂将H₂O分子进行分解得到H₂. 分析可知：C₆Li主要是通过Li原子与H₂O之间形成的偶极矩作用来吸附H₂O 分子,与C₆₀Li₁₂ 的储氢机制类似. 研究结果可为储氢材料的制备提供一个新的思路. 关键词： 6')" href="#">C₆ Li 2O')" href="#">H₂O 密度泛函理论     

结构与尺寸对碳纳米管物理吸附储氢的影响

采用巨正则蒙特卡罗方法,在298K和10MPa下,系统地研究了碳纳米管及其阵列的物理吸附储氢量与单壁管的管径、多壁管的层间距和管层数、单壁管阵列的管间距和排列方式的关系.发现单壁管的管径等于6nm时,管内的储氢密度达到最大;多壁管的层间距由034nm增大至061或088nm时,物理吸附储氢量明显增大;单壁管阵列的管间距等于17nm时,其管外间隙处的储氢密度达到最大,且方阵阵列优于三角阵列;当单壁管阵列的管间距大于06nm时,其管外的储氢密度均大于管内的储氢密度.指出合理地选择单壁管的管径、多壁管的层间距、单壁管阵列的管间距和排列方式,可以有效地提高碳纳米管及其阵列的物理吸附储氢量,并给出了相应的理论解释.     

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     

高比表面积金属有机骨架材料(PCN-61,PCN-66)储氢性能研究

应用巨正则蒙特卡洛方法,研究了PCN-61和PCN-66两类金属有机骨架材料的储氢性能;采用Horvath-Kawazoe(HK)微孔分析方法,分析了两类金属有机骨架材料的孔径分布.研究结果表明:在低温77 K,120个大气压条件下,PCN-61和PCN-66的质量储氢密度可达6.2%和7.0%.低压吸附阶段,两种材料的储氢性能差别不大,随着压力的增加,由于PCN-66具有更多大于8的孔径,因此在增压吸附过程中PCN-66表现出了更好的吸附能力.     

Preparation and hydrogen storage of activated rayon-based carbon fibers with high specific surface area

Activated carbon fibers were prepared from rayon-based carbon fibers by two step activations with steam and KOH treatments. Hydrogen storage properties of the activated rayon-based carbon fibers with high specific surface area and micropore volume have been investigated. SEM, XRD and Brunauer-Emmett-Teller (BET) were used to characterize the samples. The adsorption performance and porous structure were investigated by nitrogen adsorption isotherm at 77 K on the base of BET and density functional theory (DFT). The BET specific surface area and micropore volume of the activated rayon-based carbon fibers were 3144 m²/g and 0.744 m³/g, respectively. Hydrogen storage properties of the samples were measured at 77 and 298 K with pressure-composition isotherm (PCT) measuring system based on the volumetric method. The capacities of hydrogen storage of the activated rayon-based carbon fibers were 7.01 and 1.46 wt% at 77 and 298 K at 4 MPa, respectively. Possible mechanisms for hydrogen storage in the activated rayon-based carbon fibers are discussed.     

Li and Na Co-decorated carbon nitride nanotubes as promising new hydrogen storage media

The capacity of Li and Na co-decorated carbon nitride nanotube (CNNT) for hydrogen storage is studied using first-principles density functional theory. The results show that with two H₂ molecules attached to per Li and four H₂ molecules per Na the Li and Na co-decorated CNNT gains a gravimetric density of H₂ as high as 9.09 wt% via electrostatic interaction without the clustering of the deposited metal atoms (at T=0 K). The average adsorption energy of hydrogen molecule is in the range of 0.09-0.22 eV/H₂, which is suitable for practical hydrogen storage at ambient temperatures.     

碳气凝胶储氢性能的理论研究

采用基于Metropolis蒙特卡罗和Reverse蒙特卡罗的杂化逆向蒙特卡罗方法,构建碳气凝胶的微孔结构模型,根据碳气凝胶的介孔尺寸构建介孔模型.设计不同形状、不同孔径的介孔模型,使用巨正则蒙特卡罗方法详细模拟在298 K和77 K下的储氢量.结果显示,在77 K时,所设计的碳气凝胶的储氢量几乎是室温下的4倍.在77 K,100 bar时,储氢量最高可达到11.12 wt%和45.68 g·L^-1.     

Monte Carlo simulation of hydrogen physisorption in K-doped single walled carbon nanotube array

Properties of hydrogen physisorption in K-doped single walled carbon nanotube array (SWCNTA) are investigated in detail by grand canonical Monte Carlo simulation. The optimization of hydrogen storage capacity at 293 K and 10 MPa as a function of K-doping schemes, K atoms’ doped-sites, and SWCNTA configuration is discussed.     

Hydrogen storage in multi-wall carbon nanotubes using samples up to 85 g

Hydrogen storage in carbon nanotubes (CNTs) is investigated at ambient temperature and pressures of 0–12 MPa, using 35–85 g multi-wall carbon nanotube (MWNT) samples that were synthesized in a nano-agglomerate fluidized bed reactor. The volume of hydrogen gas released by the CNTs was measured by a volumetric flow meter. The capability of H₂ storage in the CNT samples of mass of up to 85 g can be obtained with a precision of 0.01 wt.%. MWNTs with average diameters ranging from 10–30 nm and were pretreated using nitric acid or a sodium hydroxide solution wash and a high temperature treatment. The influence of the hydrogen pressure, hydrogen storage time and treatment method were studied. All data show that the amount of hydrogen released by the MWNTs at room temperature is no more than 0.30 wt.%, while hydrogen released by MWNT at 77 K can reach 2.27 wt.%. PACS 61.46.+w; 68.43.-h; 84.60.Ve     

氢在碳纳米纤维中的低温吸附储存特性

利用容积法测量了77K下氢在一种碳纳米纤维上的吸附等温线。采用分子模拟的方法模拟了77K下氢分子在平板状碳纳米纤维中的吸附,碳纳米纤维的石墨层层间距分别为0.335nm、0.6nm、0.9nm以及1.5nm。模拟结果表明:石墨层层间距为0.335nm的碳纳米纤维在77K下吸附储氢密度很难达到DOE的能量密度标准;当板间距为0.9nm时,系统吸附储氢的重量密度和体积密度均能达到最大,且在77K、1MPa下,能达到DOE的能量密度标准。     

氢在A、X及ZSM-5型沸石上的高压物理吸附

采用常规体积吸附装置测定了77、195、293K和7MPa的条件下氢在A、X及ZSM-5沸石上的吸附特性和吸附容量．所有的氢吸附等温线基本符合Ⅰ型等温线,但在77K,压力为2-5MPa的等温线上观察到了超临界高压吸附所特有的最大吸附量．从等温线确定了等量吸附热并讨论了其影响因素．根据骨架结构和所含阳离子类型的差异,各种沸石表现出不同的氢吸附量．其中NaX沸石在77K/4MPa下的重量储氢分数为2．55％,是该实验中所测得的最高吸附量．CaA、NaX和ZSM-5沸石的氢吸附量与其比表面积成正比,这与沸石中的可用空穴容积有关．然而NaA和KA沸石不存在这种线性关系．实验中还观察到,NaA与KA沸石间出现氢吸附量的临界值是由KA沸石中较大的阳离子堵塞效应引起的．该实验将吸附质分了的动力学直径与沸石主晶孔的有效直径之比用于判断物理吸附中的堵塞效应．     

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.     

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.     

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.