氢在碳纳米材料中吸附的实验研究

按照容积法的原理建立了用于氢气吸附储存研究的吸附等温线测量的实验装置，从实验和理论的角度分析了本实验装置的精度和误差，用实验的方法验证了理想气体状态方程、RK状态方程以及MBWR方程描述实际气体的适用性。本文还测量了经三种不同后处理方式所得到的碳纳米纤维在298K下的吸附等温线，实验结果低于Rzepka的分子模拟计算结果。实验证明，利用MBWR方程描述实际气体和实验结果符合最好，本实验装置适合用于准确确定氢在碳纳米材料中的吸附储存量。     

碳纳米管的球磨处理及其对储氢性能的影响

采用电子显微镜分析技术研究了碳纳米管经过不同时间和不同方式机械球磨处理后其微观组织和结构的变化，并探讨了球磨对碳纳米管储氢性能的影响。研究结果表明，机械球磨可以截断碳管，碳管长度从原来的微米级降到几十到几百纳米；同时碳管端口打开，缺陷增多，表面积增大。在球磨的碳管中加入纳米级MgO，可使球磨效果更显著。球磨2h处理的碳纳米管的储氢量是未球磨碳纳米管储氢量的2倍以上，达到0.44wt％。而加入MgO球磨1h后，其储氢量达到0．81wt％。     

甲烷受控扩散火焰合成碳纳米管的实验研究

燃烧火焰法是合成碳纳米管的新方法，具有设备简单、容易实现等优点。以硝酸镍为催化剂，在甲烷-空气受控扩散火焰中合成了多壁碳纳米管，燃烧产物中还发现了碳纳米颗粒、碳纳米纤维和碳黑。实验结果表明，随着采样高度的增加，所合成的无定形多壁碳纳米管和富勒烯状碳纳米颗粒逐渐转变为石墨化程度较高的竹节形多壁碳纳米管和洋葱状碳纳米颗粒。分析表明，火焰温度、甲烷裂解产物以及催化剂种类等因素影响碳纳米管的形态和结构。     

活性炭纤维吸附汞的量子化学研究

构建四碳环模型结构作为活性炭纤维的基本模型框架,采用量子化学密度泛函理论B3LYP方法在lanl2dz基组水平上研究了活性炭纤维表面对汞的微观吸附机理,讨论了该簇模型在羰基、内酯、羧基和酚羟基官能团下对汞的吸附作用.结果表明:与单纯的活性炭纤维相比,羰基、内酯、羧基官能团的存在能够促进对单质汞的吸附,使其更倾向于化学吸附;而酚羟基对汞的吸附起不到促进作用.试验结果与理论计算结果一致,表明量子化学的理论计算是研究汞吸附机理的一种有效方法.     

氢在单壁碳纳米管中吸附的计算机模拟

采用巨正则系综蒙特卡罗(Grand Canonical Ensemble Monte Carlo，GCEMC)方法模拟了不同结构参数(管径和管间距)的单壁碳纳米管在不同操作工况(温度和压力)下的吸附储氢性能。由计算结果发现，在不同管间距的情况下，不同的管径对吸附性能的影响不同：在管间距较小的情况下，吸附储氢重量百分比和体积百分比均随管径的增大而增大；在管间距较大的情况下，吸附储氢的体积百分比却随管径的增大而减小。在不同的操作工况下，存在一个最优的管间距，能使吸附储氢的体积百分比达到最大值。通过模拟，得到77K下最接近DOE能量密度标准的碳纳米管结构参数和操作工况。     

不同直径多壁碳纳米管对其储氢性能的影响

研究了不同直径的多壁碳纳米管对其吸附储氢的影响。其中的碳纳米管以Fe/SiO2粉状物作催化剂分别在600、700、800℃下用化学沉积法制备。结果发现,碳纳米管粗样品储氢量很少,而纯化后的样品的储氢量有了明显的提高。同时碳纳米管的储氢量与其直径存有一定的比例关系,这表明碳纳米管的直径对储氢量产生很大的影响。     

活性炭吸附储存H2的研究

通过几种储氢方式的对比,论证了以活性炭作为吸附剂储存H_2的可行性;着重阐述了影响H_2吸附储存的因素,即活性炭的比表面积、活性炭的微孔容积和活性炭表面含氧官能团对H_2吸附储存量的重要影响。综述了活性炭吸附储存H_2的研究,同时概括了H_2吸附储存的理论研究并展望今后发展及研究的方向。     

多壁碳纳米管吸附储氢性能的研究

采用容量法研究温度在273～300K范围内,压力升高到10MPa时多壁碳纳米管的吸附储氢性能.采用SEM、 TEM和低温N2吸附对碳纳米管的微观结构进行表征.结果发现,在相同压力下吸附量随温度的增加而降低,表明碳纳米管的吸附主要是物理吸附.采用Clausius-Clapeyron方程解析了氢气在碳纳米管上的等量吸附热,平均值为9.1kJ/mol.     

燃料电池车车载储氢系统的技术发展与应用现状

综述了燃料电池车车载储氢系统技术，包括高压氢、液氢、金属氢化物、低温吸附、纳米碳管高压吸附以及液体有机氢化物等的研究进展及其车载应用现状。参照燃料电池车对车载储氢系统单位重量储氢密度与体积储氢密度的目标要求，对目前已应用和处于研发阶段的一些储氢技术的性能指标和存在问题进行了分析讨论。同时对目前该领域的若干新的研究报道，如超高压轻质复合容器、混合储氢容器、b.c．c．储氢合金、超级活性碳和“浆液”双相储氢等，也作了简要介绍。     

活性炭在低温下的平衡储氢特性分析

基于格子理论建立通用吸附等温方程,从吸附氢分子间作用能随表面遮盖率、温度的变化中比较活性炭在低温区域储氢行为的异同.应用文献中的拟合公式计算氢在活性炭上的吸附数据,通过通用吸附等温方程的线性化确定氢在活性炭上与最大吸附容量对应的最大表面密度.引入维里吸附方程,结合第二维里吸附系数和亨利定律计算吸附层内氢分子受到的壁面吸附势,并由平衡态的能量分析确定氢分子间作用能.结果表明,氢分子在活性炭吸附表面的最大密度小于液氢表面密度且随温度升高而减小,氢分子间作用能在较大比表面积和微孔容积的活性炭中随表面遮盖率和温度的变化更为剧烈,须根据氢分子特性设计活性炭以提高其储氢性能.     

Investigation of hydrogen storage capacity of various carbon materials

Hydrogen storage capacity of various carbon materials, including activated carbon (AC), single-walled carbon nanohorn, single-walled carbon nanotubes, and graphitic carbon nanofibers, was investigated at 303 and 77 K, respectively. The results showed that hydrogen storage capacity of carbon materials was less than 1 wt% at 303 K, and a super activated carbon, Maxsorb, had the highest capacity (0.67 wt%). By lowering adsorption temperature to 77 K, hydrogen storage capacity of carbon materials increased significantly and Maxsorb could store a large amount of hydrogen (5.7 wt%) at a relatively low pressure of 3 MPa. Hydrogen storage capacity of carbon materials was proportional to their specific surface area and the volume of micropores, and the narrow micropores was preferred to adsorption of hydrogen, indicating that all carbon materials adsorbed hydrogen gas through physical adsorption on the surface.     

Modification of single wall carbon nanotubes (SWNT) for hydrogen storage

Due to unique structural, mechanical and electrical properties of single wall carbon nanotubes, SWNTs, they have been proposed as promising hydrogen storage materials especially in automotive industries. This research deals with investing of CNT’s and some activated carbons hydrogen storage capacity. The CNT’s were prepared through natural gas decomposition at a temperature of 900?C over cobalt-molybdenum nanoparticles supported by nanoporous magnesium oxide (Co–Mo/MgO) during a chemical vapor deposition (CVD) process. The effects of purity of CNT (80–95%wt.) on hydrogen storage were investigated here. The results showed an improvement in the hydrogen adsorption capacity with increasing the purity of CNT’s. Maximum adsorption capacity was 0.8%wt. in case of CNT’s with 95% purity and it may be raised up with some purification to 1%wt. which was far less than the target specified by DOE (6.5%wt.). Also some activated carbons were manufactured and the results compared to CNTs. There were no considerable H₂-storage for carbon nanotubes and activated carbons at room-temperature due to insufficient binding between H₂ molecules carbon nanostructures. Therefore, hydrogen must be adsorbed via interaction of atomic hydrogen with the storage environment in order to achieve DOE target, because the H atoms have a very stronger interaction with carbon nanostructures.     

Carbon materials for H2 storage

In this work a series of carbons with different structural and textural properties were characterised and evaluated for their application in hydrogen storage. The materials used were different types of commercial carbons: carbon fibers, carbon cloths, nanotubes, superactivated carbons, and synthetic carbons (carbon nanospheres and carbon xerogels). Their textural properties (i.e., surface area, pore size distribution, etc.) were related to their hydrogen adsorption capacities. These H₂ storage capacities were evaluated by various methods (i.e., volumetric and gravimetric) at different temperatures and pressures. The differences between both methods at various operating conditions were evaluated and related to the textural properties of the carbon-based adsorbents. The results showed that temperature has a greater influence on the storage capacity of carbons than pressure. Furthermore, hydrogen storage capacity seems to be proportional to surface area, especially at 77 K. The micropore size distribution and the presence of narrow micropores also notably influence the H₂ storage capacity of carbons. In contrast, morphological or structural characteristics have no influence on gravimetric storage capacity. If synthetic materials are used, the textural properties of carbon materials can be tailored for hydrogen storage. However, a larger pore volume would be needed in order to increase storage capacity. It seems very difficult approach to attain the DOE and EU targets only by physical adsorption on carbon materials. Chemical modification of carbons would seem to be a promising alternative approach in order to increase the capacities.     

A study on the hydrogen storage capacity of Ni-plated porous carbon nanofibers

In this study, we prepared highly porous carbon-nanofiber-supported nickel nanoparticles as a promising material for hydrogen storage. The porous carbons were activated at 1050 °C, and the nickel nanoparticles were loaded by an electroless metal-plating method. The textural properties of the porous carbon nanofibers were analyzed using N₂/77 K adsorption isotherms. The hydrogen storage capacity of the carbons was evaluated at 298 K and 100 bar. It was found that the amount of hydrogen stored was enhanced by increasing nickel content, showing 2.2 wt.% in the PCNF-Ni-40 sample (5.1 wt.% and 6.4% of nickel content and dispersion rate, respectively) owing to the effects of the spill-over of hydrogen molecules onto the metal–carbon interfaces. This result clearly indicates that the presence of highly dispersed nickel particles can enhance high-capacity hydrogen storage.     

Activated carbon synthesis from tangerine peel and its use in hydrogen storage

Activated carbon samples were synthesized by chemical and physical activations of tangerine peel. The activated carbons were characterized via using Fourier Transform Infrared-Attenuated Total Reflectance spectroscopy (FTIR-ATR), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET), Differential Thermal Analysis-Thermogravimetry (DTA/TG) techniques. It was found that the activated carbon samples were porous, and their surface areas were increased by treating with the various concentrations of ZnCl₂ and KOH. After the formation of activated carbons, they turned into a structure that was formed from carbon atoms, and their residual amounts decreased. In addition, the hydrogen storage capacities of the activated carbon samples were measured in different pressures at 77 and 298 K using the Hiden IMI PSI instrument. The results, confirmed that the hydrogen storage capacities of the activated carbons were higher at the cryogenic temperatures, and higher hydrogen storage capacity were observed by the increasing concentrations of activation agents in the synthesized activated carbons. The activated carbons synthesized by ZnCl₂ had higher hydrogen storage capacity than those by KOH.     

Helical confinement effects on hydrogen storage in double-walled carbon nanotubes

Molecular configurations are some of the important factors that strongly affect the hydrogen adsorption in carbon nanotubes (CNTs). A Quantum Molecular dynamics simulations are performed to study the adsorption isotherm of torsional double-walled carbon nanotubes (DWCNTs) filled with hydrogen molecules. The considered key factors that affect the hydrogen storage responses of the DWCNTs are the adsorption energy and the surface tension effect. Our simulated results show that 2-sided effect is observed and kinetic diameter of H₂ molecules is shortened approximately 4.11% under helical confinement. The results further reveal that the amounts of hydrogen storage wt% are computed at 77 K and found to be 1.77 wt% and 3.92 wt% for pristine and twisted-DWCNTs, respectively. Finally, it is shown that the adsorption heat, which reflects surface property, is twisted dependent.     

A study on optimal pore range for high pressure hydrogen storage behaviors by porous hard carbon materials prepared from a polymeric precursor

In this study, activated polymer-based hard carbons were prepared using various steam activation conditions in order to enhance their hydrogen storage ability. The structural characteristics of the activated carbons were observed by X-ray diffraction and Raman spectroscopy. The N₂ adsorption isotherm characteristics at 77 K were confirmed by Brunauer-Emmett-Teller, Barrett-Joyner-Halenda and non-local density functional theory equations. The hydrogen storage behaviours of the activated carbons at 298 K and 10 MPa were studied using a Pressure-Composition-Temperature apparatus. From the results, specific surface areas and total pore volume of the activated carbons were determined to be 1680–2320 m²/g and 0.78–1.39 cm³/g, respectively. It was also observed that various pore size distributions were found to be dependent on the functions of activation time. In the observed result, the hydrogen adsorption of APHS-9-4 increased about 30% more than that of as-prepared hard carbon. This indicates that hydrogen storage capacity could be a function not only of specific surface area or total pore volume, but also of micropore volume fraction in the range of 0.63–0.78 nm of adsorbents.     

Hydrogen storage in hybrid nanostructured carbon/palladium materials: Influence of particle size and surface chemistry

Hydrogen adsorption on porous materials is one of the possible methods proposed for hydrogen storage for transport applications. One way for increasing adsorption at room temperature is the inclusion of metal nanoparticles to increase hydrogen–surface interactions. In this study, ordered mesoporous carbon materials were synthesized by replication of nanostructured mesoporous SBA-15 silica. The combination of different carbon precursors allowed to tailor the textural, structural and chemical properties of the materials. These carbons were used for the synthesis of hybrid nanostructured carbon/palladium materials with different sizes of metal nanoparticles. The hydrogen sorption isotherms were measured at 77 K and 298 K between 0.1 and 8 MPa. Hydrogen storage capacities strongly correlate with the textural properties of the carbon at 77 K. At room temperature, Pd nanoparticles enhance hydrogen storage capacity by reversible formation of hydride PdH_x and through the spillover mechanism. The hydrogen uptake depends on the combined influences of metal particle size and of carbon chemical properties. Carbons obtained from sucrose precursors lead to the hybrid materials with the highest storage capacities since they exhibits a large microporous volume and a high density of oxygenated surface groups.     

Copper-doped activated carbon from amorphous cellulose for hydrogen,methane and carbon dioxide storage

The transition away from fossil fuel and ultimately to a carbon-neutral energy sector requires new storage materials for hydrogen and methane as well as new solutions for carbon capture and storage. Among the investigated adsorbents, activated carbons are considered especially promising because they have a high specific surface area, are lightweight, thermally and chemically stable, and easy to produce. Moreover, their porosity can be tuned and they can be produced from inexpensive and environmentally friendly raw materials. This study reports on the development and characterization of activated carbons synthesized starting from amorphous cellulose with and without the inclusion of copper nanoparticles. The aim was to investigate how the presence of different concentrations of metal nanoparticles affects porosity and gas storage properties. Therefore, the research work focused on synthesis and characterization of physical and chemical properties of pristine and metal-doped activated carbons materials and on further investigation to analyze their hydrogen, methane and carbon dioxide adsorption capacity. For an optimized Cu content the microporosity is improved, resulting in a specific surface area increase of 25%, which leads to a H₂ uptake (at 77 K) higher than the theoretical value predicted by the Chahine Rule. For CH₄, the storage capacity is improved by the addition of Cu but less importantly because the size of the molecule hampers easy access of the smaller pores. For CO₂ a 26% increase in adsorption capacity compared to pure activated carbon was achieved, which translated with an absolute value of over 48 wt% at 298 K and 15 bar of pressure.