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.     

Hydrogen storage properties of MgH<Subscript>2</Subscript> co-catalyzed by LaH<Subscript>3</Subscript> 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, under 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.     

Effect of CeH_(2.29) on the microstructures and hydrogen properties of LiBH_4-Mg_2NiH_4 composites

A composite of LiBH4-Mg2NiH4 doped with 10wt% CeH2.29 was prepared by ball milling followed by dynamic interspace vacuum treatment at 573 K. The introduction of CeH2.29 caused a transformation in the morphology of Mg from complex spongy and lamellar to uniformly spongy, resulting in refined particle size and abundant H diffusion pathways. This LiBH4-Mg2NiH4 + 10wt% CeH2.29 composite exhibited excellent hydrogen storage properties. The starting temperature of rapid H absorption decreased to 375 K in the doped composite from 452 K for the unmodified material, and the onset decomposition temperature of its hydride was reduced from 536 K to 517 K. In addition, the time required for a hydrogen release of 1.5wt%(at 598 K) was 87s less than that of the un-doped composite.     

Mg+10%TiFe1-xCrx(x=0,0.3)复相合金的储氢特性

采用高能机械球磨法制备了Mg 10%TiFe1-xCrx(x=0,0.3)复相储氢合金,对比研究了球磨复相合金和球磨纯镁的微结构与储氢性能.研究结果表明:在纯Mg中添加质量分数为10%的TiFe1-xCrx(x=0,0.3)进行复合球磨,可以明显提高其吸放氢性能;在相同温度条件下,x=0.3的含铬复相合金具有最佳的吸放氢性能,其中在613 K下的吸氢容量(氢的质量分数)为7.14%,放氢容量(氢的质量分数)为6.91%;在493～573 K的较低温度下,含铬复相合金表现出更好的放氢动力学性能.通过XRD、SEM、EDS分析研究表明,TiFe1-xCrx(x=0,0.3)合金粉以细小颗粒的形式分散镶嵌在镁粉基体上成为催化活性点,改善了体系的吸放氢性能.     

Mg2Ni+x0.5 wt% V2O5+y0.5 wt Ni(x,y=0,1)复合体系的贮氢和电化学性能研究

用球磨方法制备Mg2Ni x0.5 wt%V2O5 y0.5 wt Ni(x,y=0,1)复合贮氢合金,并进行气态吸放氢变温动力学与电化学充放电实验.结果表明,x,y=1时体系的气态吸放氢和放电容量效果最好,多元复合的放电容量超过单一化合物的放电容量的总和.     

Hydrogen storage and low-temperature electrochemical performances of A2B7 type La-Mg-Ni-Co-Al-Mo alloys

The effect of Mo-addition on hydrogen storage and low-temperature electrochemical performances of La-Mg-Ni-Co-Al alloys is investigated. The alloys were synthetized via vacuum induction melting followed by annealing treatment at 1123 K for 8 h. The major phases in the annealed alloys are consisted of (La, Mg)2Ni7, (La, Mg)5Ni19 and LaNi5 phases. Mo-addition facilitates phase transformation of LaNi5 into (La, Mg)2Ni7 and (La, Mg)5Ni19 phases. Hydrogen absorption/desorption PCI curves indicates that the hydrogen storage capacity of the alloy increases remarkably with the addition of Mo. Furthermore, the La0.75Mg0.25Ni3.05Co0.2Al0.05Mo0.2 alloy shows excellent hydriding/dehydriding kinetics with a higher capacity, requiring only 100 s to reach its saturated hydrogen capacity of 1.58 wt% at low temperature of 303 K, and releasing 1.57 wt% hydrogen within 400 s at 338 K. Electrochemical experiments manifest that the Mo-added alloy electrode has perfect activation properties and the maximum discharge capacity. The low-temperature dischargeability shows that the La0.75Mg0.25Ni3.05Co0.2Al0.05Mo0.2 alloy exhibits the excellent low-temperature discharge performance, and the maximum discharge capacity is improved from 231.0 to 334.6 mAh/g at 253 K. The HRD property of the alloy electrode is enhanced, suggesting that Mo enhances the kinetic ability at low-temperature.     

Reversible hydrogenation of AB2-type Zr–Mg–Ni–V based hydrogen storage alloys

The development of hydrogen energy is hindered by the lack of high-efficiency hydrogen storage materials. To explore new high-capacity hydrogen storage alloys, reversible hydrogen storage in AB₂-type alloy is realized by using A or B-side elemental substitution. The substitution of small atomic-radius element Zr and Mg on A-side of YNi₂ and partial substitution of large atomic-radius element V on B-side of YNi₂ alloy was investigated in this study. The obtained ZrMgNi₄, ZrMgNi₃V, and ZrMgNi₂V₂ alloys remained single Laves phase structure at as-annealed, hydrogenated and dehydrogenated states, indicating that the hydrogen-induced amorphization and disproportionation was eliminated. From ZrMgNi₄ to ZrMgNi₂V₂ with the increase of the degree of vanadium substitution, the reversible hydrogen storage capacity increased from 0.6 ?wt% (0.35H/M) to 1.8 ?wt% (1.0H/M), meanwhile the lattice stability gradually increased. The ZrMgNi₂V₂ alloy could absorb 1.8 ?wt% hydrogen in about 2 ?h ?at 300 ?K under 4 ?MPa H₂ pressure and reversibly desorb the absorbed hydrogen in approximately 30 ?min ?at 473 ?K without complicated activation process. The prominent properties of ZrMgNi₂V₂ elucidate its high potential for hydrogen storage application.     

笼型Li6Si5团簇的结构和储氢性能研究

利用密度泛函M06方法,在6-311+G(d, p)基组水平上对Si_5和Li修饰的Si_5团簇的几何结构和电子性质及储氢性能进行理论计算研究.结果表明, Si_5团簇最低能量构型为笼型结构,纯Si_5团簇不能有效吸附氢分子. Li原子的引入显著改善了Si_5团簇的储氢能力.以六个Li原子穴位修饰Si_5团簇为载体,每个Li原子周围可以有效吸附三个氢分子,其氢分子的平均吸附能为2.395 kcal/mol,储氢密度可达16.617 wt%.合适的吸附能和较高储氢密度表明Li修饰Si_5团簇有望成为理想的储氢材料.     

SiLi5+团簇的结构及储氢性能理论研究

SiLi_5~+团簇由于具有高稳定特性,并且SiLi_5~+可以最多有效绑定15个氢分子,其理论质量储氢密度达到了32.3 wt%.在B3LYP理论水平上,氢分子与SiLi_5~+相互作用过程中的平均氢吸附能在1.36～2.62 kcal·mol~(-1)之间,从平均氢吸附能看,此系统满足可逆吸氢反应的热力学要求,可以作为理想储氢材料的候选物.     

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.     

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。     

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.     

无机骨架和哌嗪客体构成的有机-无机杂化物的合成和结构研究

利用常温水溶液合成方法,采用过渡金属钴离子为桥连原子制得1种具有三维无机骨架结构的化合物(Hpip)2[{Co(H2O)4}4(H2W12O42)].10H2O(pip=piperazine).采用元素分析、红外光谱、热重分析和X射线单晶衍射技术对化合物进行了表征.晶体结构分析表明:[H2W12O42]10-为8齿配体,它的8个端氧原子与8个Co2+进行了配位,钴离子桥连2个[H2W12O42]10-阴离子,形成3D无机骨架;哌嗪分子和结晶水作为客体填充在孔道中,客体与骨架之间存在着大量的氢键.     

MgH2-X(X=Si,Ge,Sn,Pb)体系解氢能力的第一原理计算

采用基于密度泛函理论的第一原理赝势平面波方法,研究了MgH2-X(X=Si,Ge,Sn,Pb)合金化体系的能量、几何与电子结构.负形成热的计算发现:合金化元素X在镁氢化合物(MgH2)中少量固溶时,体系相结构稳定性变差,预示着解氢能力得到改善.电子态密度(DOS)与电子密度的进一步分析发现:镁氢化合物X合金化后,X与其周围的H原子相互作用不明显,而Mg-H之间的成键作用减弱.体系Ge合金化解氢能力增强的理论计算与实验结果一致,预测Si,Sn,Pb少量固溶于MgH2能提高体系的解氢能力.     

Crystallite growth characteristics of Mg during hydrogen desorption of MgH_2

MgH_2 is one of promising hydrogen storage materials,but Mg crystallites grow up very fast during hydrogen desorption,leading to the degradation of hydrogen storage properties.Therefore the growth behavior and mechanism of Mg crystallites during hydrogen desorption of nanocrystalline MgH_2 were investigated in this work.It was found that the transformation from MgH_2 to Mg occurred by the surface-controlled‘nucleation and growth' mechanism.After the instantaneous nucleation of Mg at free surfaces of MgH_2 particles,Mg crystallites grew through three stages,namely one-dimensional,then two-dimensional and finally one-dimensional growths.In the second stage,Mg crystallites grew quickly as compared with other stages.After complete hydrogen desorption,the average Mg crystallite size in MgH_2-10 wt% Pr_3 Al_(11) sample was smaller than that in pure MgH_2 sample due to the presence of Pr_3 Al_(11).     

Synergic catalytic effect of Ti hydride and Nb nanoparticles for improving hydrogenation and dehydrogenation kinetics of Mg-based nanocomposite

The Mg-9.3 wt% (TiH1.971-TiH)?0.7 wt% Nb nanocomposite has been synthesized by hydrogen plasma-metal reaction (HPMR) approach to enhance the hydrogen sorption kinetics of Mg at moderate temperatures by providing nanosizing effect of increasing H “diffusion channels” and adding transition metallic catalysts. The Mg nanoparticles (NPs) were in hexagonal shape range from 50 to 350 nm and the average size of the NPs was 177 nm. The small spherical TiH1.971, TiH and Nb NPs of about 25 nm uniformly decorated on the surface of the big Mg NPs. The Mg-TiH1.971-TiH-Nb nanocomposite could quickly absorb 5.6 wt% H2 within 5 min at 573 K and 4.5 wt% H2 within 5 min at 523 K, whereas the pure Mg prepared by HPMR could only absorb 4 and 1.5 wt% H2 at the same temperatures. TiH1.971, TiH and Nb NPs transformed into TiH2 and NbH during hydrogenation and recovered after dehydrogenation process. The apparent activation energies of the nanocomposite for hydrogenation and dehydrogenation were 45.0 and 50.7 kJ mol?1, which are much smaller than those of pure Mg NPs, 123.8 and 127.7 kJ mol?1. The improved sorption kinetics of the Mg-based nanocomposite at moderate temperatures and the small activation energy can be interpreted by the nanostructure of Mg and the synergic catalytic effects of Ti hydrides and Nb NPs.     

Cost-effective integrated strategy for the fabrication of hard-magnet barium hexaferrite powders from low-grade barite ore

Ultrafine barium hexaferrite (BaFe₁₂O₁₉) powders were synthesized from the metallurgical extracts of low-grade Egyptian barite ore via a co-precipitation route. Hydrometallurgical treatment of barite ore was systematically studied to achieve the maximum dissolution efficiency of Fe (~99.7%) under the optimum conditions. The hexaferrite precursors were obtained by the co-precipitation of BaS produced by the reduction of barite ore with carbon at 1273 K and then dissolved in diluted HCl and FeCl₃ solution at pH 10 using NaOH as a base; the product was then annealed at 1273 K in an open atmosphere. The effect of Fe3+/Ba2+ molar ratio and the addition of hydrogen peroxide (H₂O₂) on the phase structure, crystallite size, morphology, and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. Single-phase BaFe₁₂O₁₉ powder was obtained at an Fe3+/Ba2+ molar ratio of 8.00. The formed powders exhibited a hexagonal platelet-like structure. Good maximum magnetization (48.3 A·m2·kg–1) was achieved in the material prepared at an Fe3+/Ba2+ molar ratio of 8.0 in the presence of 5% H₂O₂ as an oxidizer and at 1273 K because of the formation of a uniform, hexagonal-shaped structure.     

Wet spinning of PVA composite fibers with a large fraction of multi-walled carbon nanotubes

PVA composites fibers with a large fraction of multi-walled carbon nanotubes modified by both covalent and non-covalent functionalization were produced by a wet-spinning process.Model XQ-1 tensile tester,thermogravimetric analysis,scanning electron microscopy,differential scanning calorimetry,and wide-angle X-ray diffraction were used to characterize the properties of PVA/MWNT composite fibers.The TGA results suggested that MWNTs content in composite fibers were ranged from 5.3 wt%to 27.6 wt%.The mechanical properties of PVA/MWNT composite fibers were obviously superior to pure PVA fiber.The Young's modulus of composite fibers enhanced with increasing the content of MWNTs,and it rised gradually from 6.7 GPa for the pure PVA fiber to 12.8 GPa for the composite fibers with 27.6 wt%MWNTs.Meanwhile,the tensile strength increased gradually from 0.39 GPa for the pure PVA fiber to 0.74 GPa for the composite fibers with 14.4 wt%MWNTs.Nevertheless,the tensile strength of the composite fibers decreased as the MWNTs content up to 27.6 wt%.SEM results indicated that the MWNTs homogeneously dispersed in the composite fibers,however some agglomerates also existed when the content of MWNTs reached27.6 wt%.DSC results proved strong interfacial interaction between MWNTs and PVA chain,which benefited composite fibers in the efficient stress-transfer.WXAD characterization showed that the orientation of PVA molecules declined from 94.1%to 90.9%with the increasing of MWNTs content.The good dispersibility of MWNTs throughout PVA matrix and efficient stress-transfer between MWNTs and PVA matrix may contributed to significant enhancement in the mechanical properties.     

GeLi62+团簇的结构及储氢性能研究

利用密度泛函B3LYP理论在6-311+G(d,p)基组水平上研究四价锗负离子经过6个一价锂正离子修饰后的结构和电子特征,并计算了H2分子在其表面的吸附行为,进而研究其储氢性能。结果表明,由6个Li离子修饰锗离子形成GeLi_6~(2+)团簇结构具有较高的动力学稳定性。GeLi_6~(2+)团簇表面最多能够有效吸附18个氢分子,其质量密度为24.10wt%。H2分子与GeLi_6~(2+)团簇的相互作用能量范围为2.14～4.004k Cal.mol-1。储氢性能研究表明GeLi_6~(2+)团簇在储氢领域有望具有良好的应用前景。     

新型储氢复合材料Mg/MWNTs的氢化性能

采用催化反应球磨方法,研制成复合材料Mg-MWNTs(w=5%,20%).利用储放氢实验装置,测试了Mg/MWNTs吸放氢动力学性能.研究发现,复合材料Mg-MWNTs(w=5%,20%)在298 K和2.0 MPa氢压时最大储氢量都很低;在373 K、473 K和553 K温度时,Mg-5%(w)MWNTs的最大储氢量分别为5.34%、5.89% 和6.08%;而Mg-20%(w) MWNTs只有2.11%、2.68% 和2.75%.与其它储氢复合材料相比,复合材料Mg-5%(w)MWNTs在保持较好的最大储氢量基础上,具有很好的吸放氢动力学性能.