An overview of progress in Mg-based hydrogen storage films

Mg-based hydrogen storage materials are considered to be one of the most promising solid-state hydrogen storage materials due to their large hydrogen storage capacity and low cost. However, slow hydrogen absorption/desorption rate and excessive hydrogen absorption/desorption temperature limit the application of Mg-based hydrogen storage materials.The present paper reviews the advances in the research of Mg-based hydrogen storage film in recent years, including the advantage of the film, the function theory of fabricating method and its functional theory, and the influencing factors in the technological process. The research status worldwide is introduced in detail. By comparing pure Mg, Pd-caped Mg, nonpalladium capped Mg, and Mg alloy hydrogen storage films, an ideal tendency for producing Mg-based film is pointed out,for example, looking for a cheap metal element to replace the high-priced Pd, compositing Mg film with other hydrogen storage alloy of catalytic elements, and so on.     

Titanium-functional group complexes for high-capacity hydrogen storage materials

Using first-principles density-functional electronic structure calculations, we propose functionalized organic molecules decorated with titanium atoms as high-capacity hydrogen storage materials. We study six kinds of functional groups which form complexes with Ti atoms and find that each complex is capable of binding up to six H₂ molecules. Among such complexes, Ti-decorated ethane-1,2-diol can store H₂’s with the maximum gravimetric density of 13 wt% and, under ambient conditions, a practically usable capacity of 5.5 wt%. We also present various forms of storage materials which are obtained by modifying well-known nanomaterials using Ti-functional group complexes.     

Modified carbon nanostructures as materials for hydrogen storage

Within the framework of ab initio simulation, a number of modifications of well-known carbon nanostructures are proposed, which could form the basis for designing materials with high adsorptivity for molecular hydrogen.     

Synthesis of vanadium-doped palladium nanoparticles for hydrogen storage materials

Palladium–vanadium (Pd/V) alloy nanoparticles stabilized with n-pentyl isocyanide were prepared as new hydrogen storage materials by a facile polyol-based synthetic route with tetraethylene glycol and NaOH at 250 °C. The size distribution of the nanoparticles thus obtained featured two peaks at 4.0 ± 1.1 and 1.4 ± 0.3 nm in diameter, which were the mixture of Pd/V alloy and Pd nanoparticles. The ratio between the number of Pd/V and that of Pd nanoparticles was 51:49, and the Pd:V ratio of the overall product was 9:1 in wt%, indicating that the 4.0 nm Pd/V nanoparticles were composed of 81% Pd and 19% V. The inclusion of vanadium caused the increase in the d-spacing and thus expansion of lattice constant. A rapid increase in hydrogen content at low H₂ pressures was observed for the Pd/V nanoparticles, and a 0.47 wt% H₂ adsorption capacity was achieved under a H₂ pressure of 10 MPa at 303 K. Hydrogen storage performances of Pd/V alloy nanoparticles was superior compared with Pd nanoparticles.     

Transition metal-metal oxide hybrids as versatile materials for hydrogen storage

Metal atom located on metal oxide (MMO) is a promising material with various applications such as hydrogen storage. As one of the metal oxides, niobium oxide (NbO) presents fascinating properties that make it a possibly applicable in MMOs. Here, we investigated the feasibility of transition metal-NbO hybrids as MMO materials for application in the hydrogen storage technology. In this respect, the hydrogen adsorption of transition metals (Fe, Ni, Cu, Pd, Ag, and Pt) decorated on the NbO nanocluster has been explored using density functional theory calculations. We found that the adsorption energy of the H₂ molecule on the NbO adsorbent is remarkably increased by locating the transition metals on the NbO metal oxide. Our results reveal that the transition metals decorated on the NbO nanocluster can act as active sites for hydrogen adsorption. Among the studied transition metals, Pt shows the highest hydrogen capacity up to 6.52 wt%.     

Exploring the possibility of GaPNTs as new materials for hydrogen storage

The possibility of hydrogen storage in gallium phosphate nanotubes (GaPNTs) as a high-capacity hydrogen storage media is studied by employing ab-initio density functional theory (DFT) calculations with a van der Waals (VdW) correction. The binding energy, the distance of the adsorbed hydrogen molecules and the charge transfer were particularly calculated. The obtained results indicate that hydrogenation of the GaPNTs is sensitive to the curvatures and chiralities of the nanotubes. It is found that the binding energy of hydrogen physisorption on GaP nanotubes is higher that on carbon nanotubes. These results are useful in the search for a proper media for hydrogen storage at ambient conditions.     

Metal-decorated defective BN nanosheets as hydrogen storage materials

Density functional theory computations were performed to investigate hydrogen adsorption in metaldecorated defective BN nanosheets. The binding energies of Ca and Sc on pristine BN nanosheets are much lower than the corresponding cohesive energies of the bulk metals; however, B vacancies in BN nanosheets enhance the binding of Ca and Sc atoms dramatically and avoid the clustering of the metal atoms on the surface of BN nanosheets. Ca and Sc strongly bind to defective BN nanosheets due to charge transfer between metal atoms and BN nanosheets. Sc-decorated BN nanosheets with B vacancies demonstrate promising hydrogen adsorption performances with a hydrogen adsorption energy of ?0.19～ ?0.35 eV/H₂.     

新型轻质储氢材料的第一性原理原子尺度设计

综述了近几年涌现出的一批新型轻质储氢材料,包括：碳纳米管、金属有机框架多孔材料、Al/B系复杂氢化物、金属-氮-氢系、金属有机复合物等,对其中采用第一性原理研究所取得的成果和最新的进展做了介绍,并结合实验结果做了应用分析.总结了各轻质储氢材料关联,为各种储氢材料设计之间提供了可以相互借鉴的方法,以便发展新的研究思路. 关键词： 储氢材料 第一性原理 从头算 密度泛函理论     

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     

Towards the mechanism of electrochemical hydrogen storage in nanostructured carbon materials

The mechanism of electrochemical hydrogen storage in a nanostructured carbon electrode using the electrodecomposition of KOH and H₂SO₄ aqueous solutions has been investigated by means of galvanostatic and voltammetry techniques. The role of charging the electrical double layer is carefully considered during the process of hydrogen insertion and deinsertion into carbon, i.e. electroreduction and electrooxidation, respectively. Once the electrode potential becomes lower than the equilibrium potential, hydrogen in the zero oxidation state is formed by the reduction of water in alkaline solution or the reduction of hydronium ions H₃O⁺ in acidic medium. In the next step, hydrogen is physically adsorbed (H_ad) onto the carbon surface and diffuses into the bulk of the carbon material with an efficiency which depends on the type of electrolyte. A higher amount of hydrogen is stored using the KOH medium, and the galvanostatic oxidation shows a well-defined plateau around -0.5 V vs. Normal Hydrogen Electrode (NHE). Due to the high overvoltage value in KOH (=0.55 V), the recombination steps of H_ad leading to molecular hydrogen evolution through the chemical (Tafel) or electrochemical (Heyrovsky) reactions are less favoured than in an H₂SO₄ medium (=0.32 V). Hence, a meaningful sorption of hydrogen is observed only in the basic electrolyte which shows a reversible capacity of 350 mAh/g (i.e. 1.3 wt.%) with a good electrical efficiency. Such performance demonstrates that nanostructured activated carbons might be a promising alternative to metallic alloys for electrochemical hydrogen storage. PACS 82.45.Yz; 81.05.Uw; 82.30.Rs; 82.45.Hk; 82.45.Fk; 81.05.Rm     

Progress in improving thermodynamics and kinetics of new hydrogen storage materials

Hydrogen storage material has been much developed recently because of its potential for proton exchange membrane (PEM) fuel cell applications. A successful solid-state reversible storage material should meet the requirements of high storage capacity, suitable thermodynamic properties, and fast adsorption and desorption kinetics. Complex hydrides, including boron hydride and alanate, ammonia borane, metal organic frameworks (MOFs), covalent organic frameworks (COFs) and zeolitic imidazolate frameworks (ZIFs), are remarkable hydrogen storage materials because of their advantages of high energy density and safety. This feature article focuses mainly on the thermodynamics and kinetics of these hydrogen storage materials in the past few years.     

Electronic properties of hydrogen storage materials with photon-in/photon-out soft-X-ray spectroscopy

The applications of resonant soft X-ray emission spectroscopy on a variety of carbon systems have yielded characteristic fingerprints. With high-resolution monochromatized synchrotron radiation excitation, resonant inelastic X-ray scattering has emerged as a new source of information about electronic structure and excitation dynamics. Photon-in/photon-out soft-X-ray spectroscopy is used to study the electronic properties of fundamental materials, nanostructure, and complex hydrides and will offer potential in-depth understanding of chemisorption and/or physisorption mechanisms of hydrogen adsorption/desorption capacity and kinetics.     

New alkali doped pillared carbon materials designed to achieve practical reversible hydrogen storage for transportation

We propose a new generation of materials to maximize reversible H2 storage at room temperature and modest pressures (<20 bars). We test these materials using grand canonical Monte Carlo simulations with a first-principles-derived force field and find that the Li pillared graphene sheet system can take up 6.5 mass% of H2 (a density of 62.9 kg/m(3) at 20 bars and room temperature. This satisfies the DOE (Department of Energy) target of hydrogen-storage materials for transportation. We also suggest ways to synthesize these systems. In addition we show that Li-doped pillared single-wall nanotubes can lead to a hydrogen-storage capacity of 6.0 mass% and 61.7 kg/m(3) at 50 bars and room temperature storage, which is close to the DOE target.     

基于密度泛函理论解读不同高密度储氢材料释氢能力

采用基于密度泛函理论的第一原理平面波赝势方法,研究了MgH₂, LiBH₄,LiNH₂,NaAlH₄几种高密度储氢材料及其合金的释氢及影响机理.结果表明:高密储氢材料MgH₂,LiBH₄,LiNH₂,NaAlH₄都比较稳定,释氢温度都很高,合金化可以降低它们的稳定性,但系统稳定性不是决定高密度储氢材料释氢性质的关键因素;带隙的宽窄基本可以表征储氢材料成键的强弱,能隙越宽,键断开越难,释氢温度就越高;LiNH₂价带顶成键峰主要由Li—N成键贡献,N—H键构成较低的峰,使得LiNH₂储氢材料的带隙虽很窄释氢温度却较高,且放氢过程中有氨气放出;合金化使得几种高密度储氢材料的带隙变窄,费米能级进入导带,从而使它们的释氢性能大大改善;电荷布居分析发现LiBH₄中B—H键最强,LiNH₂中H—N键最弱,因此LiNH₂中H相对容易放出.合金化后,各储氢材料中X—H键强度都有所降低,且LiMgNH₂中N—H键强度最低,因此从降低释氢温度角度,发展LiNH₂储氢材料最为有利. 关键词： 储氢材料 第一原理 释氢能力     

钒基固溶体储氢材料弹性性质第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法,计算了（59Cr-41Ti）_100－xV_x（x=5,15,30,60,80,100）六种钒基储氢合金的晶格常数、弹性性质和电子态密度,计算结果与实验值符合较好.发现当x=60时的钒基合金具有较好弹性性质,杨氏模量为14930 GPa,切变模量为5442 GPa及体弹模量为19396 GPa.结合实验循环性能分析认为在吸放氢过程中合金已经发生塑性变形,弹性 关键词： 钒基固溶体 储氢合金材料 密度泛函理论 弹性性质     

Use of non-aqueous electrochemical cells to investigate air- and water-sensitive hydrogen storage materials

Electrochemical methods have been used to study hydrogen in vanadium, titanium and three binary magnesium alloy systems. These materials are all sensitive to air and/or water, which prohibits the use of aqueous electrolytes. The measurements have involved the use of alkali halide and lower temperature organic-anion molten salts saturated with an alkali hydride so that they conduct charge by the transport of hydride ions, rather than protons. Alkali metals, or their alloys, can be used as indirect reference electrodes for hydrogen in these electrolytes.     

Development of metal borohydrides for hydrogen storage

A metal borohydride M(BH₄)_n is a potential candidate for hydrogen storage materials because of its high gravimetric hydrogen density. The important research issues for M(BH₄)_n are to control the thermodynamic stability and to achieve the faster reaction kinetics. To clarify the thermodynamic stability, M(BH₄)_n (M=Mg, Ca∼Mn, Zn, Al, Y, Zr and Hf; n=2-4) were synthesized by mechanical milling and its thermal desorption properties were investigated. The hydrogen desorption temperature T_d of M(BH₄)_n decreases with increasing Pauling's electronegativities χ_P of M. Because Mn, Zn, and Al borohydrides (χ_P?1.5) desorb borane, they are too unstable for hydrogen storage applications. The enthalpy changes of desorption reaction ΔH_des can be estimated by using our predicted heat of formation of M(BH₄)_n ΔH_boro and reported data for decomposed products ΔH_prod, which are useful indicators for searching M(BH₄)_n with appropriate stability for hydrogen storage material. In the latter case, microwave processing was adopted for achieving fast reaction kinetics. Among metal borohydrides, LiBH₄ was rapidly heated above 380 K by microwave irradiation, 13.7 mass% of hydrogen was desorbed by microwave irradiation. The composites of LiBH₄ with B or C desorbed hydrogen within 3 min. Microwave heating aids in realizing faster kinetics of the hydrogen desorption reaction.