Hydrogen adsorption and storage on porous materials

The development of safe and efficient methods of hydrogen storage is a prerequisite for the use of hydrogen with fuel cells for transport applications. In this paper, results available for adsorption of hydrogen on porous materials, ranging from activated carbons to metal organic framework materials, are discussed. The results indicate that up to 5 and 7.5 wt% of hydrogen can be stored on porous carbon and metal organic framework materials, respectively, at 77 K. The amounts of hydrogen adsorbed on porous materials at ambient temperatures and high pressures are much lower (0.5 wt%). The strong temperature dependence of hydrogen physisorption on porous materials is a limitation in the application of this method for hydrogen storage in addition to storage capacity requirements.     

三氢化铝应用于燃料电池的研究进展

三氢化铝（AlH₃）具有储氢量大、质量轻、释氢温度较低、产物洁净等优势,是应用于燃料电池的理想储氢材料,但因其合成成本较高、室温条件下难以再生,目前尚未大规模应用。本文从燃料电池对储氢材料的要求出发,介绍了AlH₃的基本性质、合成再生方法及其释氢性能与改进方法,简述了基于AlH₃的储氢装置及系统、车载储氢和便携式电源等应用的国内外研究现状,提出今后研究工作应集中在降低释氢温度、调控释氢速率、提高释氢率、设计高效储氢系统及开发低成本制备和再生工艺。     

金属氢化物应用最新研究进展

综述了金属氢化物(MH)的应用技术，包括MH在氢的储存运输、氢汽车、热泵、热一机械能转换、氢的分离与精制、电池和催化等方面的应用。存在贮氢能力低、对气体杂质高度敏感、初始活化困难等问题。今后应开发可逆氢容量大、价格性能比合适、寿命长的新型MH。     

基于金属氢化物固态氢源的氢燃料电池动力系统特性的研究

以基于金属氢化物的固态储氢技术,与质子交换膜燃料电池(PEMFC)耦合,搭建了基于金属氢化物固态氢源的氢燃料电池动力系统试验台,测试了吸氢压力、放氢温度、氢流量等关键操作参数对氢燃料电池动力系统性能的影响。结果表明,当吸氢压力大于等于0.60 MPa时,固态储氢反应器放氢流量稳定的时间最长可达4500 s以上。当放氢温度大于60℃时,储氢反应器能完全释放氢气,且放氢时间基本相同。放氢流量越小,氢燃料电池动力系统稳定工作的时间越长。     

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。     

Study of sorption/desorption of water and organic vapors on poly(ethylene maleate)‐based sensor‐coating materials using an automated gravimetric analyzer

Hydrophobic comonomers bisphenol‐A and hexafluorobisphenol‐A were incorporated as diol components in the sensor‐coating material poly(ethylene maleate) (PEM), resulting in modified polymers, HCPEM and HFPEM, respectively. To assess the suitability of these polymers as sensor interfaces, the sorption/desorption isotherms and kinetics of water and a range of volatile organic vapors were obtained over the entire relative pressure range of 0.1 to 1.0, using an automated intelligent gravimetric sorption analyzer. The extent and rate of sorption of organic vapors were higher in the modified polymers compared to those of the parent polymer. Sorption hysteresis was observed at high relative pressures, especially with water and other hydrogen‐bonded polar organic vapors. Polarizable vapors like toluene and benzene were sorbed more than nonpolarizable cyclohexane vapors. The sorption results were interpreted in terms of semiempirical models based on concepts of thermodynamic interaction parameter, partition coefficient, and linear solvation energy relationship. The study reveals the potential of sorption/desorption isotherms and kinetics in characterizing the sorption properties of coating materials that are used as an interface in acoustic wave sensors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1760–1767, 2003     

Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters

Multi-walled carbon nanotubes (MWNTs) with different mean outer diameters in the range of 13-53 nm, synthesized by the catalytic decomposition of hydrocarbons using a floating catalyst method, were purified and pretreated with the same procedure for volumetric hydrogen adsorption/desorption measurements. It was found that the hydrogen storage capacity of the purified and pretreated MWNTs was proportional to their diameter, and that hydrogen in all types of MWNTs measured could not be completely desorbed at room temperature and ambient pressure. A possible mechanism for the above behavior was proposed based on the results of cryogenic nitrogen adsorption analysis and high-resolution transmission electron microscopy observations. It was considered that small “carbon islands” might be the main hydrogen adsorption site in MWNTs. The effects of metal catalyst as well as an etched cavity on the surface of MWNTs on the hydrogen adsorption/desorption of MWNTs were also discussed.     

Hydrogen storage on nickel catalysts supported on amorphous activated carbon

We have studied the hydrogen storage at room temperature and high pressure on nickel catalysts impregnated on an amorphous commercial activated carbon. The catalysts were studied by means of the BET method, XRD, metal surface area and temperature programmed desorption. It was shown that the catalysts could store significant amounts of hydrogen at room temperature and high pressure (up to 0.53% at 30 bars against 0.1% for the activated carbon). Various factors influencing the level of hydrogen uptake were examined and discussed. The hydrogen spillover would be the driving force for the hydrogen storage. Two mechanisms of hydrogen uptake are proposed.     

Hydrogen storage in carbon nanotubes revisited

The reported hydrogen uptake of carbon nanotubes (CNTs) has been the subject of much controversy. We have measured the hydrogen uptake capacity of different types of CNTs using a volumetric measurement setup specifically-designed for CNTs. It was found that under a pressure of ∼12 MPa and at room temperature, the hydrogen storage capacity of the CNTs is less than 1.7 wt.%, which is far below the benchmark set for on-board hydrogen storage systems by the US Department of Energy. These results suggest that it is no longer worth investigating hydrogen uptake in pure CNTs for on-board applications. However, our recent research indicates that CNTs can be an effective additive to some other hydrogen storage materials to improve their kinetics.     

Fatgiue behavior of metal matrix nanocomposites

Light-weight high-strength composites (particularly with aluminum and magnesium base alloys) have principal applications in a wide variety of fields ranging from automotive and aerospace structures to medical and energy applications wherein the materials undergo both static and dynamic (fatigue) loading conditions. Conventional metal matrix composites (MMCs), i.e. those filled by micro-sized reinforcements, have usually poor ductility and insufficient mechanical performance made them, therefore, unreliable to be used in some critical applications. Instead, those composites strengthened by nano-sized reinforcing agents, namely metal matrix nano-composites (MMNCs), have newly been developed in order to boost the mechanical properties. The current paper aims to study the fatigue behavior of the MMCs with a particular attention on recent investigations made on MMNCs. It is believed that the materials selection, microstructural features, manufacturing and processing parameters, etc. have a dominant influence on the fatigue response of MMNCs.     

The electrochemical impedance of metal hydride electrodes

The electrochemical impedance responses for different laboratory type metal hydride electrodes were successfully modeled and fitted to experimental data for AB₅ type hydrogen storage alloys as well as one MgNi type electrode. The models fitted the experimental data remarkably well. Several AC equivalent circuits have been proposed in the literature. The experimental data, however, could not always be satisfactorily approximated. The approximation model presented here exhibits smooth fit to the experimental results for all frequencies in the whole range from 10 kHz to 0.1 mHz. Equivalent circuits, explaining the experimental impedances in a wide frequency range for electrodes of hydride forming materials mixed with copper powder, were obtained. Both charge transfer and spherical diffusion of hydrogen in the particles are important sub processes that govern the total rate of the electrochemical hydrogen absorption/desorption reaction. To approximate the experimental data, equations describing the current distribution in porous electrodes were needed. Indications of one or more parallel reduction/oxidation processes competing with the electrochemical hydrogen absorption/desorption reaction were observed. The impedance analysis was found to be an efficient method for characterizing metal hydride electrodes in situ.     

Unique hydrogen adsorption properties of graphene

Graphene showed an unusually high hydrogen storage capacity as well as a unique, slow hydrogen adsorption process compared with a variety of carbon materials (carbon nanotubes, activated carbons, mesoporous carbons, templated carbons, and metal organic frameworks). Catalytic dissociation of hydrogen on graphene is observed for the first time. The hydrogen dissociation rate on graphene is also significantly faster than the adsorption rate. This leads to the conclusion that the most active sites on graphene for hydrogen dissociation are not the only sites where the enhanced adsorption occurs. The mechanistic differences in adsorption on graphene when compared with the other carbons are further demonstrated by differences in temperature‐programed desorption results and heats of adsorption. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

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).     

一类新型镁材料——镁基金属有机骨架材料

镁基金属有机骨架材料（Mg-MOFs）是近年来逐渐受到关注的一类新型功能材料,其种类与结构多样化,使其在很多领域中展现出了潜在的应用价值,为镁资源的开发利用开拓了一个新的领域。本文从Mg-MOFs的种类、特点、制备方法、应用以及稳定性5个方面展开论述。详细阐述了Mg-MOFs在催化、药物缓释、光学材料、气体储存、气体吸附和分离等方面的应用,着重介绍了Mg-MOFs的储氢能力和对二氧化碳的吸附能力及对不同混合物的选择分离能力。提出了今后Mg-MOFs的研究重点：优化Mg-MOFs的制备条件,降低制备难度及成本;选择新的配体源及溶剂,开发具有结构稳定、高比表面积、功能多样的Mg-MOFs,扩大其在气体吸附与选择性分离方向的应用;将Mg-MOFs应用于复合材料中,拓宽其应用范围。     

Atypical hydrogen uptake on chemically-activated, ultramicroporous carbon

Hydrogen adsorption on ultramicroporous carbon was investigated at near-ambient temperatures using volumetric and gravimetric methods. The results showed that the main process, physisorption, is accompanied by a slow process of different nature, that causes slow uptake at high pressures and hysteresis on desorption. The combined result is unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt.% at 25 °C and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17-20 kJ/mol) is higher than usually reported for carbon materials; the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption induced by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.     

Kinetics of CO2 Adsorption/Desorption of Polyethyleneimine‐Mesoporous Silica

The kinetics of adsorption of CO₂ on solid sorbents based on polyethyleneimine/mesoporous silica (PEI/MPS) was studied by following the mass gain during CO₂ flow. Linear (PEI‐423) and branched (PEI‐10k) polymers were studied. The solid sorbents were synthesized by impregnating the PEI into MPS foam. The kinetics of adsorption was fitted with a double‐exponential model. In contrast, the desorption process obeyed first‐order kinetics. The activation energy of desorption of PEI‐423 was lower than that of PEI‐10k, presumably because the branched polymer required more energy to expose its nitrogen to CO₂. To increase the CO₂ sorption capacity, the MPS was treated with nonionic surfactant materials prior to impregnation with PEI. This also lowered the maximum sorption temperature and desorption activation energies.     

化学储氢研究进展

氢气作为一种高效、清洁的能量载体,被视为21世纪最具发展潜力的能源。氢的储存是氢能规模化应用的关键,相比于物理储氢,化学储氢更加高效安全。常用的化学储氢方式主要有金属氢化物、配位氢化物、有机液体氢化物等。本文综述了上述3种主要储氢方式的研究进展并指出存在的问题。金属氢化物中,如新近发现的多相R-Mg-Ni系储氢合金储氢量较高,价格低廉,但其仍存在过于稳定、加/脱氢动力学性能差等问题;配位氢化物含有丰富的轻金属元素,储氢密度较高,但存在可逆循环性能差的问题,限制了其应用;液体有机物储氢量高,还可以同汽油一样在常温常压下运输,且环己烷、苯等液体有机储氢介质均为工业上可以大规模生产的化学品,如果能开发出高稳定性、高转化率和高选择性的脱氢催化剂,将大幅度推动氢能规模化应用。     

新型储氢材料研究进展

氢能作为一种环保可再生的新型能源,生产技术逐渐走向成熟,成本大幅度下降,将迎来快速发展的机遇期。氢能被广泛利用的关键在于是否能够实现高效储存。本文重点讨论了四类新型储氢材料,即金属络合氢化物储氢材料、碳纳米管储氢材料、沸石以及新型沸石类材料、有机液态储氢材料。文章指出：金属络合氢化物储氢材料储存压力低但循环稳定性差;碳纳米管储氢材料已经有很长的发展历史,安全性高且易脱氢,然而目前对其储氢机理认识不够成熟;沸石以及新型沸石类材料价格低廉,但是对反应条件的要求高;有机液态储氢材料被认为是大规模储存和运输的可行选择,然而昂贵的成本和苛刻的反应条件限制了其发展。文章指出后续需要改进并开发具有较高存储容量和具有经济价值的储氢材料。     

基于金属氢化物的热能-机械能转换系统的研究进展

金属氢化物是近年来在节能方面应用较为广泛的一种高性能材料.简述了热能-机械能转换系统的工作原理以及其具体的应用方式,如热机、氢压缩机和太阳能水泵等,存在合金储氢量低、易中毒、反应床传热传质性能不佳及整体效率低下等主要问题,并对氢化物热能-机械能转换系统进行了展望.     

Hydrogen Storage in Metal-Organic Frameworks

Recent decades have witnessed the explosive emergence of metal organic frameworks (MOFs) as functional ultrahigh surface area materials. Categorized as an intriguing class of hybrid materials, MOFs exhibit infinite crystalline lattices with inorganic vertices and molecular-scale organic linkers. Fortunately, the large internal surface areas and overall pore volumes, adjustable pore sizes, ultralow densities, and tunable framework–adsorbate interaction by ligand functionalization and metal choice, enable MOFs to be promising materials for wide applications. In particular, these remarkable properties render MOFs potential hydrogen storage materials. By virtue of their exceptionally high surface areas, unparalleled tenability and structural diversity, MOFs have become a hotspot of research within the scientific community. This paper reviews the different methods used for the synthesis of MOFs, the relationship between structural features and hydrogen adsorption, the strategies for hydrogen uptake improvement as well as the molecular simulation.