One-step uniform growth of magnesium hydride nanoparticles on graphene

A simple solvent-free method to synthesize MgH2 nanoparticles (MgH2 NPs) uniformly grown on graphene nanosheets (GNs) has been reported in this paper. Based on the formation of MgH2 by di-n-butylmagnesium ((C4H9)2Mg) thermal decomposition under hydrogen pressure, the GNs were added as matrix to hinder the agglomeration and growing of MgH2 NPs. The fabricated MgH2/GNs nanocomposites, in which MgH2 NPs were homogenously growing in the graphene matrix, have been synthesized by the favorable adsorption energy between (C4H9)2Mg and GNs. Resulting from the one-step solvent-free route, the generated MgH2 NPs shows high hydrogen capacity and steady hydriding and dehydriding properties, without the interference of the synthetic medium. At the same time, the size of the fabricated MgH2 NPs can be controlled by adjusting the mass ratio of MgH2 to graphene, the various hydrogen pressure and temperature. Attributed to smaller size effect, well uniform distribution of high density MgH2 NPs, and the agglomeration blocking ability of graphene, the MgH2/GNs-40 wt% exhibits the favorite hydrogen storage performance.     

Hydrogen storage properties of MgH2 co-catalyzed by LaH3 and NbH

To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH2 + 10wt%LaH3 + 10wt%NbH was prepared by a mechanical milling method. The composite exhibited favorable hydrogen desorption properties, releasing 0.67wt% H2 within 20 min at 548 K, which was ascribed to the co-catalytic effect of LaH3 and NbH upon dehydriding of MgH2. By contrast, pure MgH2, an MgH2 + 20wt%LaH3 composite, and an MgH2 + 20wt%NbH composite only released 0.1wt%, 0.28wt%, and 0.57wt% H2, respectively, un-der the same conditions. Analyses by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping demonstrated that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH2 + 10wt%LaH3 + 10wt%NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH2. The introduction of LaH3 and NbH was beneficial to the hydrogen storage performance of MgH2.     

Significantly enhanced hydrogen desorption properties of Mg(AlH4)2 nanoparticles synthesized using solvent free strategy

Mg(AlH_4)_2 nanoparticles with a particle size less than 10 nm have been successfully synthesized by mechanochemical method using LiAlH_4 and MgCl_2 as raw materials together with Li Cl buffering additive. In comparison to Mg(AlH_4)_2 microparticles, Mg(AlH_4)_2 nanoparticles exhibit a faster hydrogen desorption kinetics and lower desorption temperature. The hydrogen desorption temperatures of the first and second dehydrogenation steps are 80 and 220 °C for the Mg(AlH_4)_2 nanoparticles, which are about 65 and 60 °C, respectively, lower than those of Mg(AlH_4)_2 microparticles. The decomposition activation energy is reduced from 135 k J/mol for Mg(AlH_4)_2 microparticles to 105.3 k J/mol for Mg(AlH_4)_2 nanoparticles. It is proposed that the shortened diffusion distance and enhanced diffusivity of Mg(AlH_4)_2/MgH_2 nanoparticles provide an energy destabilization for lowering the dehydrogenation temperature, and thus being the key factor for promoting the hydrogen desorption kinetics. More importantly, it is demonstrated that the dehydrided nano MgH_2 hydride with a particle size below 10 nm can be formed after rehydrogenation process, resulting in the good cycling hydrogen desorption performance of nano MgH_2.     

MgH2基态分子结构与势能函数

用从头算CCSD（T）方法和aug-cc-pVTZ基函数对MgH2分子的结构进行优化,得到其平衡几何构型和谐振频率．根据原子分子反应静力学原理得到可能的电子状态和基态分子的离解极限．并用多体展式理论导出MgH2基态分子的解析势能函数．     

镁基固态储氢材料研究进展

 镁基储氢材料具有储氢量高、镁资源丰富以及成本低廉等优点,被认为是极具应用前景的一类固态储氢材料。利用镁基储氢材料供氢主要有热分解放氢和水解产氢2种途径。MgH₂的热分解放氢焓值高（75 kJ/mol H₂）,造成其放氢温度较高、动力学差; MgH₂的水解过程中,由于常温水解产物Mg（OH）₂逐渐包裹在MgH₂表面,阻隔了MgH₂与水的接触,从而导致水解产氢效率较低。近年来,大量研究工作聚焦于改善MgH₂的热解/水解供氢性能及实际应用,已经取得了大量成果。针对目前国内外镁基固态储氢材料的研发,总结了材料/结构改性、反应条件对镁基储氢材料的热解/水解性能的影响,重点阐述了固态镁基储氢材料组成成分-微观结构-储放氢性能之间的关系,并对镁基储氢系统及实际应用场景进行了归纳。未来通过镁基固态储运氢技术的发展,将实现氢气的高安全、高效及大规模储运,助力中国氢能产业的发展。     

Cs-Mg-H合金的形成能力与成键机制研究

采用基于密度泛函理论第一性原理的Vienna Ab initio Simulation Package (VASP)软件研究了CsMgH₃, Cs₄Mg₃H₁₀和Cs₂MgH₄氢化物的晶体结构、反应焓和电子结构. 结果表明 CsMgH₃, Cs₄Mg₃H₁₀和Cs₂MgH₄都能直接由单质Cs和Mg在H₂中反应生成, 其中Cs₄Mg₃H₁₀的形成能力最强; 态密度和电荷密度的分析与讨论表明了Mg和H的成键机制为离子键伴随着显著的共价键.     

Hydrogen absorption-desorption cycle decay mechanism of palladium nanoparticle decorated nitrogen doped graphene

As a hydrogen storage material, palladium nanoparticle decorated nitrogen doped graphene (Pd/N-rGO) has drawn much attention owing to its high absorption capacity at moderate conditions. However, its hydrogen absorption-desorption cycle performance, which is essential for their practical application, has been rarely studied. In this paper, a simple and convenient high temperature thermal reduction method was used to synthesize nitrogen-doped graphene decorated with Pd nanoparticles (Pd/N-rGO). Taken it as a representative, the hydrogen absorption-desorption cycle performance of Pd/N-rGO was investigated. The results showed that after three cycles the hydrogen storage capacity dropped from 2.9 ​wt% to 0.8 ​wt% at 25 ​°C and 4 ​MPa pressure. It was found that the palladium nanoparticles shed from Pd/N-RGO sheet after cycle performance test, and then agglomerated. These phenomena will weaken the hydrogen spillover effect, leading to the decrease of hydrogen storage capacity. Meanwhile, decreased defects reduce the hydrogen absorption sites, which will thus deteriorate the hydrogen storage capacity.     

纯Ti(BH_4)_3·5NH_3的制备及储氢性能

氨合硼氢化钛是一类放氢温度适宜的高容量储氢材料,但已报道的通过球磨法制备的氨合硼氢化钛通常含有质量分数42%以上的LiCl杂质,降低了体系总含氢量的同时也为氨合硼氢化钛本征放氢性能的表征带来了困难.因此,纯氨合硼氢化钛的制备和性能表征十分必要.本文以钛酸四异丙酯、乙硼烷、四氢呋喃和NH_3为初始原料,通过先制备前驱体Ti(BH_4)_3·2THF,然后再氨化的二步反应首次成功合成纯Ti(BH_4)_3·5NH_3,并对前驱体和氨合硼氢化钛的组成、结构和放氢性能进行系统地研究.结果表明,前驱体Ti(BH_4)_3·2THF属于斜方晶系,Pbcn空间群,且在室温下能稳定存在,是制备氨合硼氢化钛的良好前驱体;纯Ti(BH_4)_3·5NH_3具有良好的放氢性能,于75℃开始放氢,至200℃释放质量分数约10%的氢气.     

Recent advances in improving performances of the lightweight complex hydrides Li-Mg-N-H system

A brief review of state-of-the art advances in improving performances of the lightweight complex hydrides Li-Mg-N-H system is reported. Among the hydrogen storage materials, Li-Mg-N-H combination systems are regarded as one of the most potential candidates for the vehicular applications owing to their high hydrogen storage capacity (>5 wt% H) and a more appropriate thermodynamic properties of hydrogen absorption and desorption. In the Li-Mg-N-H systems, tremendous efforts have been devoted to improving the hydrogen storage properties by adjusting composition, revealing reaction mechanisms, adding catalysts and refining the microstructures, etc. During the studies, different mechanisms, such as the coordinated two-molecule or multimolecule reaction mechanism and the ammonia-mediated mechanism, are proposed and applied under some certain conditions. Catalysis and nanosizing are very effective in enhancing the kinetic properties and thermodynamic destabilization of Li-Mg-N-H systems. Due to nano effects, the space-confinement and nanoconfinement seems to be more effective for improving the hydrogen storage performance, and it is great significant to develop hydrogen storage materials by studying the nanoconfined effects on the Li-Mg-N-H systems.     

镁基储氢材料的研究进展

从镁基储氢材料体系入手,综述了该体系的研究情况及近期进展．对镁基储氢材料进行了合理的分类,将其分为单质镁储氢材料、镁基储氢合金和镁基储氢复合材料．并结合各类镁基储氢材料的国内外研究状况,指出要改善镁基储氢材料的储氢性能,必须走多元合金化的路线并在学习有关理论的基础上,采用优化合金成分与新的合成方法来进一步提高材料的储氢性能．     

Improvement in hydrogen storage performance of Mg by mechanical grinding with molten salt etching Ti3C2Clx

Mg-based materials are currently a hot research topic as hydrogen storage materials due to their considerable theoretical hydrogen storage capacity. However, the kinetic performance of hydrogen absorption and desorption of Mg is too slow and requires high temperature, which seriously hinders the application of this material. MXene is a new type of two-dimensional material with significant role in improving thermodynamics and kinetics. In this experiment, a two-dimensional layered MXene containing Cl functional group was prepared by molten salt etching using the Ti-containing MAX phase as the raw material. Then different ratios of Ti₃C₂Cl_x were uniformly dispersed onto the surface of Mg by high energy ball milling. The samples were characterized by hydrogen absorption and desorption kinetics, SEM, XRD, XPS, and DSC to investigate the effect of Ti₃C₂Cl_x on the hydrogen absorption and desorption performance of Mg. The onset hydrogen absorption temperature can be reduced to room temperature and the hydrogen release temperature is reduced by 200 ​°C by doping Ti₃C₂Cl_x. And there is also 5.4 ​wt% hydrogen storage in the isothermal hydrogen absorption test at 400 ​°C. The results of DSC demonstrate that the E_a of Mg+15 ​wt% Ti₃C₂Cl_x was reduced by 12.6% compared to pristine Mg. The ΔH is almost invariable. The results of XPS show that the presence of multivalent Ti promotes electron transfer and thus improves the conversion between Mg²⁺/Mg and H⁻/H. This study provides a guideline for further improving the hydrogen absorption and desorption performance of Mg-based hydrogen storage materials.     

稀土金属La吸附掺杂BN纳米管储氢性能的第一性原理研究

本文采用基于密度泛函理论的第一性原理方法研究了稀土金属La吸附掺杂对单壁BN纳米管储氢性能的影响.通过分析计算结果得到,稀土金属La可以稳定吸附到BN纳米管上,每个La原子最多可以吸附六个氢气分子,系统的储氢量能达到4.50wt%,平均结合能为0.223eV.根据态密度图分析可知,由于La的5d、6s轨道与BN纳米管中B、N原子的2p轨道发生杂化,使得La原子与其周围的原子发生了电荷转移,带正电的La原子将会极化吸附在其周围的氢气分子,使得更多的氢气分子聚集在其周围.本文的研究对于实验上合成高性能的BN纳米管储氢材料具有一定的指导意义.     

微晶碳在镁基复合储氢材料中的作用

为了提高金属镁的放氢动力学性能,将无烟煤经脱灰并碳化后制得的微晶碳添加到镁粉中,用氢气反应球磨法一步制得高性能镁碳复合储氢材料。用X射线衍射和红外光谱对微晶碳的结构进行了表征,用透射电镜、引射线能谱、粉末X射线衍射对储氢材料的结构进行了测试,用差示扫描量热分析和P—C-T分析对材料的储氢性能进行了研究。结果表明,微晶碳具有类石墨晶体结构,对镁有良好的助磨作用,并与镁有协同吸氢和放氢作用。镁粉中添加40％微晶碳,球磨2h的粒度即可达到30-50nm,储氢材料的初始放氢温度可低至227.4℃,储氢密度可达6.7％。     

Synchrotron radiation X-ray powder diffraction techniques applied in hydrogen storage materials——A review

Synchrotron radiation is an advanced collimated light source with high intensity. It has particular advantages in structural characterization of materials on the atomic or molecular scale. Synchrotron radiation X-ray powder diffraction (SR-XRPD) has been successfully exploited to various areas of hydrogen storage materials. In the paper, we will give a brief introduction on hydrogen storage materials, X-ray powder diffraction (XRPD), and synchrotron radiation light source. The applications of ex situ and in situ time-resolved SR-XRPD in hydrogen storage materials, are reviewed in detail. Future trends and proposals in the applications of the advanced XRPD techniques in hydrogen storage materials are also discussed.     

Current Research Progress in Magnesium Borohydride for Hydrogen Storage (A review)

Hydrogen storage in solid-state materials is believed to be a most promising hydrogen-storage technology for high efficiency, low risk and low cost. Mg(BH₄)₂ is regarded as one of most potential materials in hydrogen storage areas in view of its high hydrogen capacities (14.9 ​wt% and 145–147 ​kg ​cm⁻³). However, the drawbacks of Mg(BH₄)₂ including high desorption temperatures (about 250 ​°C–580 ​°C), sluggish kinetics, and poor reversibility make it difficult to be used for onboard hydrogen storage of fuel cell vehicles. A lot of researches on improving the dehydrogenation reaction thermodynamics and kinetics have been done, mainly including: additives or catalysts doping, nanoconfining Mg(BH₄)₂ in nanoporous hosts, forming reactive hydrides systems, multi-cation/anion composites or other derivatives of Mg(BH₄)₂. Some favorable results have been obtained. This review provides an overview of current research progress in magnesium borohydride, including: synthesis methods, crystal structures, decomposition behaviors, as well as emphasized performance improvements for hydrogen storage.     

Hydrogen storage performance of LaNi3.95Al0.75Co0.3 alloy with different preparation methods

Rare-earth AB₅-type La–Ni–Al hydrogen storage alloys are widely studied due to their extensive application potentials in hydrogen isotope storage, hydrogen isotope isolation and hydrogen compressors, etc. Good hydriding/dehydriding kinetics, easily activation, high reversibility are important factors for their practical application. However, their overall hydrogen storage performance, especially plateau pressure and hydrogen absorption/desorption durability need to be further optimized. In this study, the microstructures and the hydrogen storage properties of as-cast, annealed, and melt-spun LaNi_3.95Al_0.75Co_0.3 alloys were investigated. The experimental results of XRD and SEM showed that all alloys contained a pure CaCu₅ type hexagonal structure LaNi₄Al phase. The cell volume increased in an order of annealed ?> ?melt-spun ?> ?as-cast, resulting in a lower hydrogen absorption/desorption plateau pressure and a more stable hydride phase. The hydrogen storage capacity of three alloys was almost the same. The slope factor of the annealed and melt-spun alloys is smaller than the as-cast alloy, indicating that heat-treatment process can make the alloys more uniform. For the cycle stability of the alloys, the hydrogen absorption rate of the annealed alloy and melt-spun alloy was much faster than that of the as-cast alloy after 500 cycles. The melt-spun alloy showed high pulverization resistance during hydrogen absorption/desorption, and exhibited an excellent cycling retention of 99% after 500 cycles, suggesting that melt-spinning process can enhance the cycle stability and improve the cycle life of the alloy.     

Li原子修饰缺陷蓝磷单层储氢性能的第一性原理研究

本文基于第一性原理计算,系统地研究了碱金属Li原子修饰缺陷蓝磷单层体系的储氢性能. 研究结果表明,双空位缺陷DV2的引入可以有效增强Li原子与蓝磷单层间的相互作用,能够有效阻止单层表面Li团簇的形成. 单个Li原子可以稳定吸附3个H2分子,H2分子平均吸附能为0.248 eV/H2. 电子结构分析表明,H2分子主要通过极化机制和轨道杂化作用吸附在Li修饰的缺陷蓝磷单层体系上. 此外,本文还研究了温度和压强对Li/DV2体系储氢性能的影响. 结果表明,在室温和低压条件下,H2分子可以稳定吸附在Li/DV2体系表面,从而实现室温条件下的可逆储氢.     

BLim1/2+(m=6、7)团簇的结构及储氢性能的研究

为开发新型储氢材料提供更为丰富的理论基础,采用B3LYP泛函在6-311++G(d,p)基组水平上对BLi₆⁺超碱团簇和BLi₇²⁺超碱土团簇的稳定性结构、电荷分布等方面进行理论研究,进而研究团簇的储氢性能。结果表明：两个离子团簇均比它们所对应的中性团簇均具有较高的动力学稳定性。两个离子团簇中的每个Li原子同时有效吸附2个氢分子,BLi₆⁺团簇中氢分子在团簇表面平均吸附能为0.969~2.162kCal/mol,储氢质量分数达31.56wt%。而BLi₇⁺团簇中氢分子在团簇表面平均吸附能为1.764~3.714kCal/mol,储氢质量分数达32.21wt%。它们的储氢性能表明BLi₆⁺团簇和BLi₇²⁺团簇均有望成为良好的储氢媒介。     

湿法球磨结合表面改性制备贮氢合金粉

研究湿法球磨结合KBH4表面改性一步处理法对AB5型贮氢合金晶体结构和电化学性能的影响，并比较此新方法和先湿法球磨制粉后表面处理两步法制备的贮氢合金粉的电化学性能。研究结果表明：采用此新方法能显著提高贮氢合金的综合性能；当KBHt的浓度为0．08mol／L时，利用此法制得合金粉的晶体主相仍为LaNi5相，出现Al2Os杂相；其电化学容量变化不大；达到最大容量的活化次数从12降低到5；放电中值电压从1．22V升高到1．28V；倍率为2C的放电效率从79．0%提高到86．1％，容量保持率S200从74％提高到86％。     

液相有机氢载体的催化研究与应用

氢能清洁高效、能量密度高，是理想的能源载体，也是公认的未来能源发展方向之一。氢气的存储是氢能利用的关键环节，目前仍没有完美适配所有场景的储氢材料，储氢技术的选择势必要以使用场景为导向。液相有机氢载体（liquid organic hydrogen carriers，LOHCs）作为一种液相储氢材料，在运输方面具有独特的应用优势。本文介绍了常见的液相有机储氢材料，重点探讨了适用于运输工具（车、船、航空器等）的LOHCs，综述其加氢/脱氢的催化研究进展、应用技术难点，并展望了其应用前景。