Chemical and Physical Solutions for Hydrogen Storage

Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton‐exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high‐pressure and cryogenic‐liquid storage, adsorptive storage on high‐surface‐area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off‐board regeneration are both possible. Reforming of liquid hydrogen‐containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.     

储氢研究进展

氢能是21世纪主要的新能源之一。作为一种新型的清洁能源,氢的廉价制取、安全高效储存与输送及规模应用是当今研究的重点课题,而氢的储存是氢能应用的关键。储氢材料能可逆地大量吸放氢,在氢的储存与输送过程中是一种重要载体。本文综述了目前所采用或正在研究的主要储氢材料与技术,如高压气态储氢、低温液态储氢、金属氢化物储氢、化学氢化物储氢、吸附储氢、金属有机骨架储氢等,比较了各种储氢的优缺点,并指出其相关发展趋势。     

Strategies for the Improvement of the Hydrogen Storage Properties of Metal Hydride Materials

Metal hydrides are an important family of materials that can potentially be used for safe, efficient and reversible on‐board hydrogen storage. Light‐weight metal hydrides in particular have attracted intense interest due to their high hydrogen density. However, most of these hydrides have rather slow absorption kinetics, relatively high thermal stability, and/or problems with the reversibility of hydrogen absorption/desorption cycling. This paper discusses a number of different approaches for the improvement of the hydrogen storage properties of these materials, with emphasis on recent research on tuning the ionic mobility in mixed hydrides. This concept opens a promising pathway to accelerate hydrogenation kinetics, reduce the activation energy for hydrogen release, and minimize deleterious possible by‐products often associated with complex hydride systems.     

Tailoring Thermodynamics and Kinetics for Hydrogen Storage in Complex Hydrides towards Applications

Solid‐state hydrogen storage using various materials is expected to provide the ultimate solution for safe and efficient on‐board storage. Complex hydrides have attracted increasing attention over the past two decades due to their high gravimetric and volumetric hydrogen densities. In this account, we review studies from our lab on tailoring the thermodynamics and kinetics for hydrogen storage in complex hydrides, including metal alanates, borohydrides and amides. By changing the material composition and structure, developing feasible preparation methods, doping high‐performance catalysts, optimizing multifunctional additives, creating nanostructures and understanding the interaction mechanisms with hydrogen, the operating temperatures for hydrogen storage in metal amides, alanates and borohydrides are remarkably reduced. This temperature reduction is associated with enhanced reaction kinetics and improved reversibility. The examples discussed in this review are expected to provide new inspiration for the development of complex hydrides with high hydrogen capacity and appropriate thermodynamics and kinetics for hydrogen storage.

     

储氢研究进展

氢能是21世纪主要的新能源之一。作为一种新型的清洁能源,氢的廉价制取、安全高效储存与输送及规模应用是当今研究的重点课题,而氢的储存是氢能应用的关键。储氢材料能可逆地大量吸放氢,在氢的储存与输送过程中是一种重要载体。本文综述了目前所采用或正在研究的主要储氢材料与技术,如高压气态储氢、低温液态储氢、金属氢化物储氢、化学氢化物储氢、吸附储氢、金属有机骨架储氢等,比较了各种储氢的优缺点,并指出其相关发展趋势。     

Catalytic Synthesis of Organolithium and Organomagnesium Compounds and of Lithium and Magnesium Hydrides—Applications in Organic Synthesis and Hydrogen Storage

A recent development in homogeneous catalysis is the discovery of catalysts that are active for the lithiation of 1-alkenes to alkenyllithium compounds and lithium hydride as well as for the hydrogenation of lithium and magnesium under mild conditions. The catalytically prepared magnesium hydride is highly reactive and adds to 1-alkenes to give diorganomagnesium compounds and can also be used in the preparation of, for example, silane and “active” magnesium. The use of metal hydrides in hydrogen storage is discussed: hydrogenation/dehydrogenation experiments show that the catalytically prepared magnesium hydride (which can be doped with a second metal) can be used as a high-temperature hydrogen storage material.     

Li-Mg-N-H体系储氢材料的热力学和动力学调控

Mg（NH₂）₂-2LiH体系储氢材料具有较高的储氢容量和较适宜的热力学性能,并且其吸放氢过程完全可逆,是目前最有望实现大规模应用的固态储氢材料之一。然而,由于该体系在吸放氢过程中具有较高的动力学壁垒,导致其在200℃以上才能实现快速地吸放氢。因此,国际上对该体系储氢材料的研究主要集中在热力学和动力学的调控方面。本文从成分调变、纳米化和掺杂改性等方面,详细综述了Mg（NH₂）₂-2LiH体系储氢材料热力学和动力学调控的研究现状,并提出了其中存在的问题和相应对策,同时指出了将来的研究方向。     

The Role of Ionic Liquids in Hydrogen Storage

Ionic liquid (IL) based H₂ storage for H₂ generation from NH₃BH₃ derivatives is shown. These systems promote H₂ generation at low temperature, with good reaction rates and high total H₂ yields. The effects of ILs and the H₂ yield in correlation with the basicity, the cations of the ILs, and the role of carbenes are discussed. Furthermore, mechanistic findings on the dehydrogenation are described. IL material blends are competitive with conventional H₂ storage materials with experimental efficiencies of at least 6.5 wt % H₂.     

Boron‐Double‐Ring Sheet,Fullerene, and Nanotubes: Potential Hydrogen Storage Materials

Similar to carbon‐based graphene, fullerenes and carbon nanotubes, boron atoms can form sheets, fullerenes, and nanotubes. Here we investigate several of these novel boron structures all based on the boron double ring within the framework of density functional theory. The boron sheet is found to be metallic and flat in its ground state. The spherical boron cage containing 180 atoms is also stable and has I symmetry. Stable nanotubes are obtained by rolling up the boron sheet, and all are metallic. The hydrogen storage capacity of boron nanostructures is also explored, and it is found that Li‐decorated boron sheets and nanotubes are potential candidates for hydrogen storage. For Li‐decorated boron sheets, each Li atom can adsorb a maximum of 4 H₂ molecules with g_d=7.892 wt %. The hydrogen gravimetric density increases to g_d=12.309 wt % for the Li‐decorated (0,6) boron nanotube.     

Preparation and Catalytic Activity of a Novel Nanocrystalline ZrO2@C Composite for Hydrogen Storage in NaAlH4

Sodium alanate (NaAlH₄) has attracted intense interest as a prototypical high‐density hydrogen‐storage material. However, poor reversibility and slow kinetics limit its practical applications. Herein, a nanocrystalline ZrO₂@C catalyst was synthesized by using Uio‐66(Zr) as a precursor and furfuryl alcohol (FA) as a carbon source. The as‐synthesized ZrO₂@C exhibits good catalytic activity for the dehydrogenation and hydrogenation of NaAlH₄. The NaAlH₄‐7 wt % ZrO₂@C sample released hydrogen starting from 126 °C and reabsorbed it starting from 54 °C, and these temperatures are lower by 71 and 36 °C, respectively, relative to pristine NaAlH₄. At 160 °C, approximately 5.0 wt % of hydrogen was released from the NaAlH₄‐7 wt % ZrO₂@C sample within 250 min, and the dehydrogenation product reabsorbed approximately 4.9 wt % within 35 min at 140 °C and 100 bar of hydrogen. The catalytic function of the Zr‐based active species is believed to contribute to the significantly reduced operating temperatures and enhanced kinetics.     

贮氢材料及其应用研究进展

贮氢材料是一类新型高性能材料。本文对现有贮氢材料进行了合理的分类,对贮氢材料及其应用研究进展进行了综述。     

A Composite of Complex and Chemical Hydrides Yields the First Al‐Based Amidoborane with Improved Hydrogen Storage Properties

The first Al‐based amidoborane Na[Al(NH₂BH₃)₄] was obtained through a mechanochemical treatment of the NaAlH₄–4 AB (AB=NH₃BH₃) composite releasing 4.5 wt % of pure hydrogen. The same amidoborane was also produced upon heating the composite at 70 °C. The crystal structure of Na[Al(NH₂BH₃)₄], elucidated from synchrotron X‐ray powder diffraction and confirmed by DFT calculations, contains the previously unknown tetrahedral ion [Al(NH₂BH₃)₄]^?, with every NH₂BH₃^? ligand coordinated to aluminum through nitrogen atoms. Combination of complex and chemical hydrides in the same compound was possible due to both the lower stability of the Al?H bonds compared to the B?H ones in borohydride, and due to the strong Lewis acidity of Al³⁺. According to the thermogravimetric analysis–differential scanning calorimetry–mass spectrometry (TGA–DSC–MS) studies, Na[Al(NH₂BH₃)₄] releases in two steps 9 wt % of pure hydrogen. As a result of this decomposition, which was also supported by volumetric studies, the formation of NaBH₄ and amorphous product(s) of the surmised composition AlN₄B₃H_(0–3.6) were observed. Furthermore, volumetric experiments have also shown that the final residue can reversibly absorb about 27 % of the released hydrogen at 250 °C and p(H₂)=150 bar. Hydrogen re‐absorption does not regenerate neither Na[Al(NH₂BH₃)₄] nor starting materials, NaAlH₄ and AB, but rather occurs within amorphous product(s). Detailed studies of the latter one(s) can open an avenue for a new family of reversible hydrogen storage materials. Finally, the NaAlH₄–4 AB composite might become a starting point towards a new series of aluminum‐based tetraamidoboranes with improved hydrogen storage properties such as hydrogen storage density, hydrogen purity, and reversibility.     

MAlH4(M=Li,Na)储氢材料*

氢能是一种新型的清洁能源,有望替代碳经济,而氢的储存是氢能应用的关键。近年来,研究集中在具有储氢容量高和可逆性好等优点的固态储氢材料上。许多新型储氢材料不断出现,其中以MAlH₄(M=Li, Na)为代表的金属复合氢化物体系被认为是最有前景的储氢材料之一。本文综述了MAlH₄(M=Li, Na)作为可逆储氢材料的研究现状,主要从吸放氢反应、储氢性能、反应机理、理论计算和存在的问题等方面进行了讨论,并指出其相关发展趋势。     

Local Disorder in Hydrogen Storage Compounds: The Case of Lithium Amide/Imide

Amides and imides of alkali metals are a very promising class of materials for use as a hydrogen‐storage system, as they are able to store and release hydrogen via a chemical route at controllable temperatures and pressures. We critically revise the present picture of the atomic structure of the lightest member (LiNH₂/Li₂NH) by using a combined computational and experimental approach. Specifically, ab initio path integral molecular dynamics simulations and solid‐state ¹H NMR techniques are combined. The results show that the presently assumed local structure might be inconsistent or at least incomplete and needs considerable revision. In particular, the Li atoms turn out to be more mobile and more disordered than suggested by structural data obtained from X‐ray scattering. Also, the configuration of the hydrogen atoms, which is accessible via the NMR experiment and the corresponding first‐principles calculations, is different from the previously assumed data. The computed and experimentally observed ¹H NMR parameters are in very good mutual agreement and illustrate the unusual chemical environment of the hydrogen atoms in this system. Incorporating our results on the new lithium data, we show that the effect of nuclear quantum delocalization for the hydrogen atoms is considerably reduced compared to the perfect crystal structure.     

Improving Reproducibility in Hydrogen Storage Material Research

Research into new reversible hydrogen storage materials has the potential to help accelerate the transition to a hydrogen economy. The discovery of an efficient and cost-effective method of safely storing hydrogen would revolutionise its use as a sustainable energy carrier. Accurately measuring storage capacities – particularly of novel nanomaterials – has however proved challenging, and progress is being hindered by ongoing problems with reproducibility. Various metal and complex hydrides are being investigated, together with nanoporous adsorbents such as carbons, metal-organic frameworks and microporous organic polymers. The hydrogen storage properties of these materials are commonly determined using either the manometric (or Sieverts) technique or gravimetric methods, but both approaches are prone to significant error, if not performed with great care. Although commercial manometric and gravimetric instruments are widely available, they must be operated with an awareness of the limits of their applicability and the error sources inherent to the measurement techniques. This article therefore describes the measurement of hydrogen sorption and covers the required experimental procedures, aspects of troubleshooting and recommended reporting guidelines, with a view of helping improve reproducibility in experimental hydrogen storage material research.     

Boron: Its Role in Energy‐Related Processes and Applications

Boron's unique position in the Periodic Table, that is, at the apex of the line separating metals and nonmetals, makes it highly versatile in chemical reactions and applications. Contemporary demand for renewable and clean energy as well as energy‐efficient products has seen boron playing key roles in energy‐related research, such as 1) activating and synthesizing energy‐rich small molecules, 2) storing chemical and electrical energy, and 3) converting electrical energy into light. These applications are fundamentally associated with boron's unique characteristics, such as its electron‐deficiency and the availability of an unoccupied p orbital, which allow the formation of a myriad of compounds with a wide range of chemical and physical properties. For example, boron's ability to achieve a full octet of electrons with four covalent bonds and a negative charge has led to the synthesis of a wide variety of borate anions of high chemical and electrochemical stability—in particular, weakly coordinating anions. This Review summarizes recent advances in the study of boron compounds for energy‐related processes and applications.     

LaCo13基金属间化合物的磁性能和储氢性能

对LaCo13基金属间化合物在磁致冷材料和储氢材料领域中的应用进行了综述,总结了该系化合物的成相规律、替换元素对相稳定性的影响,讨论了近期的研究进展及存在的问题。作为磁致冷材料应用时,LaCo13基金属间化合物在室温具有巨大磁熵变,而作为储氢合金时该系化合物表现出优异的高温电化学容量。虽然在磁致冷和储氢材料领域尚未对LaCo13基金属间化合物进行实用开发,但作为新型绿色能源材料已经展示出良好的应用前景。