Material design using molecular modeling for hydrogen storage

Using grand canonical Monte‐Carlo simulations, the adsorption capacities and isosteric heats of hydrogen on activated carbons, graphite nanofibers, and bundles of carbon nanotubes are estimated for identical thermodynamic states. These computations allow a systematic, meaningful, and unbiased comparison of the adsorption properties of hydrogen in such porous materials. The comparison shows that the hydrogen storage capacity can be optimized, but only to a limited extent, in adjusting the material pore sizes and functionalizing a part of the adsorption sites. Therefore, at room temperature and up to 70.0 MPa, for the three models of carbonaceous adsorbents, the hydrogen maximal excess adsorption is of the order of 2% of the adsorbent mass. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Hydrogen storage properties of B‐ and N‐doped microporous carbon

A B‐ and N‐doped microporous carbon has been synthesized via a substitution reaction. The obtained carbon exhibited much higher surface area than the previously reported B‐ and N‐doped carbon. The hydrogen storage measurements indicated that the B‐ and N‐doped microporous carbon had a 53% higher storage capacity than the carbon materials with similar surface areas. Furthermore, hydrogen storage via spillover was studied on Ru‐supported B‐ and N‐doped microporous carbon and a storage capacity of 1.2 wt % at 298 K and 10 MPa was obtained, showing an enhancement factor of 2.2. Ab initio molecular orbital calculations were also performed for the binding energies between the spiltover hydrogen atom and various sites on the doped carbon. The theoretical calculations can explain the experimental results well, which also shed light on the most favorable and possible sites with which the spiltover hydrogen atoms bind. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Hydrogen storage on chemically activated carbons and carbon nanomaterials at high pressures

Hydrogen adsorption measurements have been carried out at different temperatures (298 K and 77 K) and high pressure on a series of chemically activated carbons with a wide range of porosities and also on other types of carbon materials, such as activated carbon fibers, carbon nanotubes and carbon nanofibers. This paper provides a useful interpretation of hydrogen adsorption data according to the porosity of the materials and to the adsorption conditions, using the fundamentals of adsorption. At 298 K, the hydrogen adsorption capacity depends on both the micropore volume and the micropore size distribution. Values of hydrogen adsorption capacities at 298 K of 1.2 wt.% and 2.7 wt.% have been obtained at 20 MPa and 50 MPa, respectively, for a chemically activated carbon. At 77 K, hydrogen adsorption depends on the surface area and the total micropore volume of the activated carbon. Hydrogen adsorption capacity of 5.6 wt.% at 4 MPa and 77 K have been reached by a chemically activated carbon. The total hydrogen storage on the best activated carbon at 298 K is 16.7 g H₂/l and 37.2 g H₂/l at 20 MPa and 50 MPa, respectively (which correspond to 3.2 wt.% and 6.8 wt.%, excluding the tank weight) and 38.8 g H₂/l at 77 K and 4 MPa (8 wt.% excluding the tank weight).     

熔融盐斜温层混合蓄热单罐系统及其实验研究

经济型的蓄热系统设计对聚焦式太阳能热发电的市场竞争力影响效果非常明显,一个比较有效的方法就是采用斜温层蓄热。在斜温层蓄热单罐设计理念的基础上,提出了一种熔融盐斜温层混合蓄热单罐系统,该单罐的中段为斜温层显热蓄热,上部为高温壳管式相变换热器,下部为低温壳管式相变换热器。斜温层保障高低温熔融盐液在同一单罐内上下隔开,而高、低温壳管式相变换热器既增加了蓄热容量,又简化了熔融盐液的注入和出料结构。初步实验测定了该混合蓄热单罐系统的有效蓄热量,证实了其斜温层在放热与吸热循环运行中能稳定保持,并表明了该系统具有潜在的应用前景。     

Thermal effects in dynamic storage of hydrogen by adsorption

Thermal effects in dynamic hydrogen storage by adsorption at room temperature and high pressure are studied theoretically and experimentally. The system of adsorbate–adsorbent used was hydrogen in granular activated carbon. The theoretical analysis was based on heat- and mass-transfer modeling in a packed-bed adsorber, with particular emphasis on the thermal effects occurring during charge and discharge steps. The influence of gas flow rate and storage pressure (up to 15 MPa) on the total amount stored or delivered was investigated. Operating conditions were compatible with practical application for onboard vehicle storage. The experimental study was carried out in cylindrical 2-L reservoirs filled with granular activated carbon in which the bed temperature was measured at various positions. The temperature changes during both charge and discharge agreed well with the model predictions.     

镁基储氢材料在含能材料中的应用

根据化学结构不同将镁基储氢材料分为镁基储氢合金氢化物、氢化镁和镁基配位氢化物3类,分别介绍了3类镁基储氢材料在含能材料中应用的研究进展;分析了镁基储氢材料在含能材料中的应用前景和存在的问题;介绍了计算机模拟技术在研究镁基储氢材料对推进剂热分解影响中的应用情况。结果显示,镁基储氢材料能够通过促进含能材料的热分解过程提升其能量水平,同时其较高的热稳定性有利于改善含能材料组分的相容性和安定性。镁基储氢合金氢化物、氢化镁和镁基配位氢化物均可显著提高固体推进剂和炸药的应用性能。因此,镁基储氢材料在含能材料领域具有广阔的应用前景。附参考文献47篇。     

Intrinsic linear scaling of hydrogen storage capacity of carbon nanotubes with the specific surface area

The linear scaling of the gravimetric hydrogen storage capacity of single- and multi-walled carbon nanotubes (SWNTs and MWNTs) with the specific surface area is investigated at ambient temperature (298 K) and technically relevant pressures (0.9–1.6 MPa). All samples are found to adsorb hydrogen reversibly and their adsorption exhibits type-II BET isotherms according to the IUPAC classification. While there is strong sample-dependency on their pressure–composition isotherms, all of them follow the Henry's Law in the pressure range under consideration. A comparison of the observed slope of specific surface area versus gravimetric storage capacity with that of a theoretically predicted one using a hypothetical condensation model and that of chemically modified carbon nanotubes revealed that the hydrogen storage capacity depends on the accessibility of internal surfaces of nanostructured carbon. The linear scaling of hydrogen storage capacity with the respective specific surface area suggests that the hydrogen adsorption in carbon nanotubes depends on the specific surface area and is irrespective of the type of the nanotubes that is used.     

Concept,Design and Manufacture of a Prototype Hydrogen Storage Tank Based on Sodium Alanate

In the framework of the EC project STORHY (Hydrogen Storage for Automotive Applications), the prototype of a solid storage tank for hydrogen based on sodium alanate was developed. A storage tank containing 8 kg sodium alanate was designed and manufactured with the objective of fast refueling. To obtain the optimum design of the storage tank a simulation tool was developed and validated by experiments with a laboratory‐scale tubular reactor. Application of the simulation tool to different storage concepts and geometries yielded the final design. The chosen concept is modular, enabling simple scale‐up. This is the basis for the future development of fuel cell vehicle storage tanks containing 5 kg of hydrogen.     

On the methane adsorption capacity of activated carbons: in search of a correlation with adsorbent properties

BACKGROUND: There exists now a widely held view that the methane storage capacity on an activated carbon is not related to any of the routinely determined properties of the adsorbent, such as surface area or micropore volume. This has been confirmed and a correlation pursued with other physical and/or chemical properties of both commercially available carbons and those prepared in the laboratory. Textural characteristics (from nitrogen adsorption isotherms at 77 K) considered were BET‐equivalent specific surface area, DR micropore volume and Horvath–Kawazoe micropore size distribution. Chemical properties were evaluated using Fourier transform infrared (FTIR) spectroscopy, thermal programmed decomposition (TPD) and Boehm titrations. Both kinetic and equilibrium methane adsorption experiments were performed at 273 and 298 K and up to 3.5 MPa. RESULTS: Using phosphoric acid to activate peach stones together with additional thermal treatment enabled the production of activated carbons with 137 v/v methane adsorption capacity at 298 K. CONCLUSIONS: The presence of acidic surface functional groups has a detrimental influence on methane uptake, due to the chemical inertness of the adsorbate and/or to pore blockage of the adsorbent. Basic surface functional groups (pyrone), together with a desirable pore size distribution centered at ca 0.8 nm, are thought to be responsible for improved methane adsorption capacity on such activated carbons. Copyright © 2009 Society of Chemical Industry     

Feasibility of tailoring for high isosteric heat to improve effectiveness of hydrogen storage in carbons

The idea that increasing the enthalpy of adsorption increases the adsorptive capacity of carbon and makes it a better storage material for hydrogen is examined here considering the entire adsorption-desorption cycle. Structural modifications of carbon are examined to reveal the complex relationships between the enthalpy of adsorption, the pore volume, and the amount of hydrogen delivered over the course of a single cycle. The results provide an understanding of the connection between enthalpy and effective storage capacity in carbon materials and serve as a guide toward the search for an adsorbent which satisfies the DOE targets. Extensive GCMC simulations show that carbons having single graphene walls are optimal for hydrogen storage and that attempts to increase the enthalpy of adsorption either by increasing the wall thickness or by decreasing the pore size are detrimental to adsorptive capacity over a complete cycle from charging to exhaustion. It is found that carbon nanotubes display the same trend as slit pore carbons. The search for an adsorbent suitable for hydrogen storage should be aimed at the discovery of an entirely new high-capacity adsorbent with an enthalpy of adsorption of 15 kJ/mol, intermediate between that of carbon (4-6 kJ/mol) and metal hydrides (30-75 kJ/mol).     

Simulation on hydrogen storage properties of metal‐organic frameworks Cu‐BTC at 77–298 K

In recent years, many researchers have studied on the hydrogen storage properties of metal‐organic frameworks (MOFs) by grand canonical Monte Carlo (GCMC) simulation. At present, the GCMC studies of Cu‐BTC (BTC: benzene‐1,3,5‐tricarboxylate) which is a prototypical metal‐organic framework mainly adopt the classical force fields, the simulation temperatures are mainly focus on 298 and 77 K, and most researchers did not consider the effects of quantum effects at low temperature. Therefore, we used the quantum effects to correct the classical force fields and the force fields with more accurate simulation results were used to simulate the hydrogen adsorption performances of Cu‐BTC in the temperature range of 77–298 K and the pressure range of 1–8 MPa at each temperature. The results show that the effects of quantum effects on the hydrogen storage of Cu‐BTC cannot be neglected and the corrected Dreiding force field can simulate hydrogen adsorption performances of Cu‐BTC more accurately at low temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1383–1388, 2018     

等离子体法制备掺杂Ni碳材料的储氢性能

引言氢能是可再生的理想洁净能源,人类出于对环境的保护和化石燃料趋于短缺的考虑,太阳能和氢能的利用已是本世纪能源领域发展的必然趋势。特别是在燃料电池迅速发展并获得突破的今天,更安全、灵活和有效的氢能储藏技术的研究受到全球的广泛关注[1]。在吸附储氢材料中,碳质材料由于其质量轻、比表面积高和合适的结构引起了广泛的重视[2-10]。Yang等[11-12]发现在碳上掺杂过渡金属(Rh、Pt、     

Preparation of short carbon nanotubes by mechanical ball milling and their hydrogen adsorption behavior

Short multi-wall carbon nanotubes (MWNTs) with open tips were obtained by mechanical ball milling. The microstructure characteristics of MWNTs before and after ball milling were checked by transmission electron microscopy (TEM). The effect of ball milling on the hydrogen adsorption behavior of the MWNTs was studied. The hydrogen adsorption experiments were carried out at room temperature under a pressure of 8-9 MPa. The hydrogen adsorption capacity of carbon nanotubes milled for 10 h was 0.66 wt%, which was about six times that of MWNTs without milling. For the carbon nanotubes milled with MgO for 1 h, a hydrogen adsorption capacity of 0.69 wt% was obtained. The enhancement of hydrogen adsorption might result from the increase of defects and surface area of the MWNTs caused by ball milling.     

Activated carbon fibres and composites on its base for high performance hydrogen storage system

To obtain high hydrogen sorption capacity and reduce the time of the cycle (adsorption/desorption) in the gas storage system a new composite material (metal hydride particles on the activated carbon fibre matrix) was suggested. Different adsorbent materials such as activated carbon fibre “Busofit”, granular activated carbon and new composite sorbent (metal hydride La_0.5Ni₅Ce_0.5 particles on the activated carbon fibre “Busofit”) were tested. Effect of the carbon sorbent nature and metal hydride content is important to choose the optimal sorbent bed.In this paper, a thermally regulated storage system for hydrogen was numerically analyzed and experimentally validated. A two-dimensional transient model was used to analyze the influence of the thermal control on the operating characteristics of the flat sectional vessel. The evolution of the temperature, pressure and volumetric density of hydrogen inside the vessel during the charging/discharging is discussed. It was shown that heat pipe based thermal control of the process increase the efficiency of the hydrogen storage. Such vessels are interesting to be applied in fuel cells used for vehicle or dual-fuel engine car (hydrogen/gasoline, hydrogen/methane).     

Molecular Simulation of Adsorbed Natural Gas

Abstract

Adsorbed natural gas is being investigated as a substitute for gasoline. The most important factor in engineering studies is the maximum storage capacity of adsorbents for natural gas. Monte Carlo calculations were performed to simulate the adsorption of natural gas on activated carbon. Adsorption isotherms, storage capacities, and isosteric heats were determined from simulations and compared with experimental data. Simulations predict a maximum storage capacity of 244 V/V at 35 atm.     

化工系统消纳可再生能源的电-氢协调储能系统优化设计

针对可再生能源发电间歇性和波动性与化工过程系统氢气需求波动性协调匹配的问题，本文以电-氢储能系统总费用最小为目标，建立了可再生能源发电与化工生产中加氢系统耦合的电-氢协调储能系统优化设计模型，以确定电-氢协调储能系统的最优容量配置和功率调度方案。采用典型案例研究了可再生能源渗透率和电-氢储能系统构成对电-氢储能优化设计和运行特性的影响。研究表明：当化工系统的氢气需求全部由可再生能源发电制氢提供时，在系统中同时采用电池和氢气储罐储能可有效地降低系统的总费用；在该系统中，电池可用于平抑短期内发电侧和负荷侧的波动，氢气储罐可平衡发电侧和负荷侧长期的不匹配；随着可再生能源渗透率的增加，系统的总费用显著增大；为了维持外购氢气流率的稳定，系统中需要增加电解槽和储能系统的容量以解决发电侧和负荷侧的波动和不匹配问题。     

Structure and hydrogen adsorption properties of low density nanoporous carbons from simulations

We systematically model the hydrogen adsorption in nanoporous carbons over a wide range of carbon bulk densities (0.6–2.4 g/cm³) by using tight binding molecular dynamics simulations for the carbon structures and thermodynamics calculations of the hydrogen adsorption. The resulting structures are in good agreement with the experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated by comparisons of the microstructure at atomic level, pair distribution function, and pore size distribution. The hydrogen adsorption calculations in carbon structures demonstrate both a promising hydrogen storage capacity (excess uptake of 1.33 wt.% at 298 K and 5 MPa, for carbon structures at the lower range of densities) and a reasonable heat of adsorption (12–22 kJ/mol). This work demonstrates that increasing the heat of adsorption does not necessarily increase the hydrogen uptake. In fact, the available adsorption volume is as important as the isosteric heat of adsorption for hydrogen storage in nanoporous carbons.     

Solid‐state Materials and Methods for Hydrogen Storage: A Critical Review

Hydrogen is important as a new source of energy for automotive applications. It is clear that the key challenge in developing this technology is hydrogen storage. Current methods for hydrogen storage have yet to meet all the demands for on‐board applications. High‐pressure gas storage or liquefaction cannot fulfill the storage criteria required for on‐board storage. Solid‐state materials have shown potential advantages for hydrogen storage in comparison to other storage methods. In this article, the most popular solid‐state storage materials and methods including carbon based materials, metal hydrides, metal organic frameworks, hollow glass microspheres, capillary arrays, clathrate hydrates, metal nitrides and imides, doped polymer and zeolites, are critically reviewed. The survey shows that most of the materials available with high storage capacity have disadvantages associated with slow kinetics and those materials with fast kinetics have issues with low storage capacity. Most of the chemisorption‐based materials are very expensive and in some cases, the hydrogen absorption/desorption phenomena is irreversible. Furthermore, a very high temperature is required to release the adsorbed hydrogen. On the other hand, the main drawback in the case of physisorption‐based materials and methods is their lower capacity for hydrogen storage, especially under mild operating conditions. To accomplish the requisite goals, extensive research studies are still required to optimize the critical parameters of such systems, including the safety (to be improved), security (to be available for all), cost (to be lowered), storage capacity (to be increased), and the sorption‐desorption kinetics (to be improved).     

Optimisation of vertical axis wind turbine: CFD simulations and experimental measurements

A system for the conversion of kinetic energy of wind into thermal energy has been developed which can replace relatively expensive electro‐mechanical equipment. The system consists of a vertical axis wind turbine (VAWT) which is coupled with the shaft of a stirred vessel. In the present work, computational fluid dynamic (CFD) simulations have been performed for the flow generated in a stirred tank with disc turbine (DT). The predicted values of the mean axial, radial and tangential velocities along with the turbulent kinetic energy have been compared with those measured by laser Doppler anemometry (LDA). Good agreement was found between the CFD simulations and experimental results. Such a validated model was employed for the optimisation of drag‐based VAWT. An attempt has been made to increase the efficiency of turbine by optimising the shape and the number of blades. For this purpose, the combination of CFD and experiments has been used. The flows generated in a stirred tank and that generated by a wind turbine were simulated using commercial CFD software Fluent 6.2. A comparison has been made between the different configurations of wind turbines. Results show that a provision in blade twist enhances the efficiency of wind turbine. Also, a wind turbine with two blades has higher efficiency than the turbine with three blades. Based on the detailed CFD simulations, it is proposed that two bladed turbine with 30° twist shows maximum efficiency. © 2011 Canadian Society for Chemical Engineering     

STORAGE OF HYDROGEN ON CARBON MATERIALS: EXPERIMENTS AND ANALYSES

Superactivated carbon and carbon nanotubes are both considered potential hydrogen carriers. Adsorption isotherms of H₂ on activated carbon AX-21 and multi-wall carbon nanotubes were collected with a volumetric method for the temperature range of 77, 233-298 K and pressures up to 7 or 10 MPa. Based on the experimental data for 233-298 K, the limiting heats of adsorption of 7.6 and 1.8 kJ/mol were obtained for activated carbon and carbon nanotubes, respectively. The absolute adsorption was determined with a recently presented method, and the adsorption behavior of H₂ on carbon nanotubes was thus reasonably explained. A comparison was given for the storage capacities of compression alone and of filling powder or pellets of the two materials. It was concluded that adsorption of H₂ on carbon nanotubes is too weak to enhance storage, but activated carbon enhances storage capacity considerably. The weight percentage of hydrogen stored in carbon powder reaches 10.8% at 77 K and 6 MPa, including the quantity compressed in the void space, and 4.1 kg H₂ was stored in a 100-liter container filled with carbon pellets for the same condition.