共查询到20条相似文献,搜索用时 0 毫秒
1.
Guang-lin Xia Hai-yan LengNai-xin Xu Zhi-lin LiZhu Wu Jun-lin Du Xue-bin Yu 《International Journal of Hydrogen Energy》2011,36(12):7128-7135
Though LiBH4-MgH2 system exhibits an excellent hydrogen storage property, it still presents high decomposition temperature over 350 °C and sluggish hydrogen absorption/desorption kinetics. In order to improve the hydrogen storage properties, the influence of MoCl3 as an additive on the hydrogenation and dehydrogenation properties of LiBH4-MgH2 system is investigated. The reversible hydrogen storage performance is significantly improved, which leads to a capacity of about 7 wt.% hydrogen at 300 °C. XRD analysis reveals that the metallic Mo is formed by the reaction between LiBH4 and MoCl3, which is highly dispersed in the sample and results in improved dehydrogenation and hydrogenation performance of LiBH4-MgH2 system. From Kissinger plot, the activation energy for hydrogen desorption of LiBH4-MgH2 system with additive MoCl3 is estimated to be ∼43 kJ mol−1 H2, 10 kJ mol−1 lower than that for the pure LiBH4-MgH2 system indicating that the kinetics of LiBH4-MgH2 composite is significantly improved by the introduction of Mo. 相似文献
2.
Various LiBH4/carbon (graphite (G), purified single-walled carbon nanotubes (SWNTs) and activated carbon (AC)) composites were prepared by mechanical milling method and further examined with respect to their hydrogen storage properties. It was found that all the carbon additives can improve the H-exchange kinetics and H-capacity of LiBH4 to some extents. Compared with G, SWNTs and AC exhibited better promoting effect on the hydrogen storage properties of LiBH4. Based on combined property/phase/structure analysis results, the promoting effect of the carbon additives was largely attributed to their heterogeneous nucleation and micro-confinement effect on the reversible dehydrogenation of LiBH4. 相似文献
3.
F.C. Gennari 《Journal of power sources》2010,195(10):3266-3274
Mg50Ni-LiBH4 and Mg50Ni-LiBH4-CeCl3 composites have been prepared by short times of ball milling under argon atmosphere. Combination of HP-DSC and volumetric techniques show that Mg50Ni-LiBH4-CeCl3 composite not only uptakes hydrogen faster than Mg50Ni-LiBH4, but also releases hydrogen at a lower temperature (225 °C). The presence of CeCl3 has a catalytic role, but it does not modify the thermodynamic properties of the composite which corresponds to MgH2. Experimental studies on the hydriding/dehydriding mechanisms demonstrate that LiBH4 and Ni lead to the formation of MgNi3B2 in both composites. In addition, XRD/DSC analysis and thermodynamic calculations demonstrate that the addition of CeCl3 accounts for the enhancement of the hydrogen absorption/desorption kinetics through the interaction with LiBH4. The in situ formation and subsequent decomposition of Ce(BH4)3 provides a uniform distribution of nanosize CeB4 compound, which plays an important role in improving the kinetic properties of MgH2. 相似文献
4.
Improved reversible dehydrogenation of LiBH4–MgH2 composite by the synergistic effects of Al and MgO
In this paper, we report a novel method of improving the reversible dehydrogenation properties of the 2LiBH4–MgH2 composite. Our study found that mechanically milling with small amount of Al powder can markedly shorten or even eliminate the problematic incubation period that interrupts the dehydrogenation steps of the 2LiBH4–MgH2 composite. But the resulting composite showed serious kinetics degradation upon cycling. In an effort to solve this problem, we found that combined usage of small amounts of Al and MgO enabled the 2LiBH4–MgH2 composite to rapidly and reversibly deliver around 9 wt% hydrogen at 400 °C under 0.3 MPa H2, which compares favorably with the dehydrogenation performance of the composites with transition-metal additives. A combination of phase/microstructural analyses and series of control experiments has been conducted to gain insight into the promoting effects of Al and MgO. It was found that Al and MgO additives act as precursor and promoter for the formation of AlB2 heterogeneous nucleation sites, respectively. 相似文献
5.
Jae-Hag Lim Jae-Hyeok Shim Young-Su Lee Jin-Yoo Suh Young Whan Cho Joonho Lee 《International Journal of Hydrogen Energy》2010
Rehydrogenation behavior of 6LiBH4 + CaH2 composite with NbF5 has been studied between 350 and 500 °C after dehydrogenation at 450 °C. The composite exhibits the best rehydrogenation feature at 450 °C in terms of the overall rehydrogenation rate and the amount of absorbed hydrogen. It is found that about 9 wt% hydrogen is absorbed at 450 °C for 12 h. Up to 10 dehydrogenation–hydrogenation cycles have been carried out for the composite. It is demonstrated that 6LiBH4 + CaH2 with 15 wt% NbF5 maintains a reversible hydrogen storage capacity of about 6 wt% at 450 °C after a slight degradation between the 1st and 5th cycles. The addition of NbF5 seems to improve the cycle properties by retarding microstructural coarsening during cycles. 相似文献
6.
S.X. Zhao C.Y. Wang D.M. Liu Q.J. Tan Y.T. Li T.Z. Si 《International Journal of Hydrogen Energy》2018,43(10):5098-5103
The de-/rehydrogenation features of the 6LiBH4/SrF2 reactive hydride system have been systematically investigated. It was found that the thermal stability of LiBH4 can be reduced markedly by combining it with SrF2. Dehydrogenation of the 6LiBH4/SrF2 system proceeds via the 6LiBH4 + SrF2 → SrB6 + 2LiF + 4LiH + 10H2 reaction, which involves SrH2 as the intermediate product. The dehydrogenation enthalpy change was experimentally determined to be 52 kJ/mol H2 based on the P–C isotherm analysis. For rehydrogenation, LiBH4 and SrF2 were regenerated along with LiSrH3 at 450 °C under ~8 MPa hydrogen pressure; thus, approximately 5.2 wt% of hydrogen can be released during the second dehydrogenation process. 相似文献
7.
Leigang Li Jianmei Huang Meng Li Qian Li Liuzhang Ouyang Min Zhu Xuebin Yu 《International Journal of Hydrogen Energy》2013
Two new cobalt-based ammine borohydrides were prepared via ball milling of LiBH4 and CoCln·3NH3 (n = 3, 2) with molar ratios of 3:1 and 2:1, respectively. X-ray diffraction (XRD) results revealed the as-prepared composites having amorphous state. Thermogravimetric analysis-mass spectrometry (TG-MS) measurements showed that the two composites mainly release H2, concurrent with the evolution of a small amount of NH3. Further results showed that the excessive addition of LiBH4 can suppress the liberation of NH3, resulting in the release of H2 with a high purity (>99 mol.%). By combination with the temperature-programmed-desorption (TPD) results, the CoCl3·3NH3/4LiBH4 and CoCl2·3NH3/3LiBH4composites can release 7.3 wt.% (4.2 wt.% including LiCl) and 4.2 wt.% (2.0 wt.% including LiCl) pure hydrogen, respectively, in the temperature range of 25–300 °C. Isothermal dehydrogenation results reveal that CoCl3·3NH3/3LiBH4 shows favorable dehydrogenation rate at low temperatures, releasing about 5.2 wt.% (2.9 wt.% including LiCl) of hydrogen within 45 min at 80 °C. 相似文献
8.
Investigations of alternative renewable energy resources continue, with many studies concentrating on hydrogen storage. However, there are a few problems such as storage, transportation, delivery to the user and usage safely, to be addressed to facilitate commercialization and wide usage of the hydrogen. The absorbed form within the metal hydrides seems to be the best solution of this problem. Since Li is the lightest metal, it has the advantage as the stored amount of hydrogen mass ratio. LiBH4 production process was investigated using elemental Li, B and H2. Spex type ball milling with tungsten carbide, stainless steel and zirconia type vessels, was used to mix the different amount of Li and B under argon atmosphere. X-ray diffraction pattern demonstrated that the LiB was obtained. A system was designed to provide a hydrogen atmosphere of 60 bars to force hydrogen into the LiB structure. FTIR analysis strongly indicated the LiBH4 compound when the mol ratio of B/Li is 0.214. Thermal decomposition and heat flow experiments performed simultaneously with DSC and TGA techniques also indicate hydrogen-rich structure showing greater mass loss. One gram of lithium borohydride sample released 1423 ml of hydrogen with Ni catalyst while NiO caused 1972.94 ml of hydrogen gas desorption, equaling to 90% of the theoretical yield of commercial LiBH4. Indicating that, hydrogen of water can be obtained by either Ni or NiO catalysts. 相似文献
9.
To improve the hydrogen storage property of LiBH4, the LiBH4/Ca(AlH4)2 reactive systems with various ratios were constructed, and their de-/hydrogenation properties as well as the reaction mechanisms were investigated experimentally. It was found that the sample with the LiBH4 to Ca(AlH4)2 molar ratio of 6:1 exhibits the best comprehensive hydrogen storage properties, desorbing hydrogen completely (8.2 wt.%) within 35 min at 450 °C and reversibly absorbing 4.5 wt.% of hydrogen at 450 °C under a hydrogen pressure as low as 4.0 MPa. During the first dehydrogenation process of the LiBH4/Ca(AlH4)2 systems, the CaH2 and Al particles were in situ precipitated via the self-decomposition of Ca(AlH4)2, and then reacted with LiBH4 to form CaB6, AlB2 and LiH. Whereafter, the sample can cycle between LiBH4 + Ca(BH4)2 + Al in the hydrogenated state and CaB6 + AlB2 + LiH in the dehydrogenated state. 相似文献
10.
Here we report the first investigation of the dehydriding and re-hydriding properties of 2LiBH4 + MgH2 mixtures in the solid state. Such a study is made possible by high-energy ball milling of 2LiBH4 + MgH2 mixtures at liquid nitrogen temperature with the addition of graphite. The 2LiBH4 + MgH2 mixture ball milled under this condition exhibits a 5-fold increase in the released hydrogen at 265 °C when compared with ineffectively ball milled counterparts. Furthermore, both LiBH4 and MgH2 contribute to hydrogen release in the solid state. The isothermal dehydriding/re-hydriding cycles at 265 °C reveal that re-hydriding is dominated by re-hydriding of Mg. These unusual phenomena are explained based on the formation of nanocrystalline and amorphous phases, the increased defect concentration in crystalline compounds, and possible catalytic effects of Mg, MgH2 and LiBH4 on their dehydriding and re-hydriding properties. 相似文献
11.
Kyle Crosby 《Journal of power sources》2010,195(21):7380-1150
The hydriding process of the 2LiH + MgB2 mixture is controlled by outward diffusion of Mg and inward diffusion of Li and H within MgB2 crystals to form LiBH4. This study explores the feasibility of using transition metal dopants, such as Mn and V, to enhance the diffusion rate and thus the hydriding kinetics. It is found that Mn can indeed enhance the hydriding kinetics of the 2LiH + MgB2 mixture, while V does not. The major factor in enhancing the diffusion rate and thus the hydriding kinetics is related to the dopant's ability to induce the lattice distortion of MgB2 crystals. This study demonstrates that the kinetics of the diffusion controlled solid-state hydriding process can be improved by doping if the dopant is properly selected. 相似文献
12.
13.
C.W. James Jr.D.A. Tamburello K.S. BrinkmanJ.R. Gray B.J. HardyD.L. Anton 《International Journal of Hydrogen Energy》2011,36(3):2471-2477
It has been shown that the consequence of environmental exposure can be qualitatively predicted by modeling the heat generated as a result of environmental exposure of reactive hydrides along with heat loss associated with conduction and convection with the ambient surroundings. To this end, an idealized finite volume model was developed to represent the behavior of dispersed hydride from a breached system. Semi-empirical thermodynamic calculations and substantiating calorimetric experiments were performed in order to quantify the energy released, energy release rates and to quantify the reaction products resulting from water and air exposure of a lithium borohydride and magnesium hydride combination. The hydrides, LiBH4 and MgH2, were studied in a 2:1 “destabilized” mixture which has been demonstrated to be reversible. Liquid water hydrolysis reactions were performed in a Calvet calorimeter equipped with a mixing cell using pH-neutral water. Water vapor and gaseous oxygen reactivity measurements were performed at varying relative humidities and temperatures by modifying the calorimeter and utilizing a gas circulating flow cell apparatus. The results of these calorimetric measurements were used to develop quantitative kinetic expressions for hydrolysis and air oxidation in these systems. Thermodynamic parameters obtained from these tests were then incorporated into a computational fluid dynamics model to predict both the hydrogen generation rates and concentrations along with localized temperature distributions. The results of these numerical simulations can be used to predict ignition events and the resultant conclusions will be discussed. 相似文献
14.
LiBH4 is regarded as a promising hydrogen storage material due to its high hydrogen density. In this study, the dehydrogenation properties of LiBH4 were remarkably enhanced by doping hydrogenated Mg3RE compounds (RE denotes La, Ce, Nd rare earth metals), which are composed of nanostructured MgH2 and REH2+x (denoted as H − Mg3RE). For the LiBH4 + H − Mg3La mixture, the component LiBH4 desorbed 6 wt.% hydrogen even at a relatively low temperature of 340 °C, far lower than the desorption temperature of pure LiBH4 or the 2LiBH4 + MgH2 system. This kinetic improvement is attributed to the hydrogen exchange mechanism between the H − Mg3La and LiBH4, in the sense that the decomposition of MgH2 and LaH2+x catalyzed the dehydrogenation of LiBH4 through hydrogen exchange effect rather than mutual chemical reaction requiring higher temperature and hydrogen pressure. However, prior to fast hydrogen release, the hydrogen exchange effect suppressed the dehydriding of MgH2 and elevated its desorption temperature. It is expected to strengthen the hydrogen exchange effect by compositing the LiBH4 with other nanosized metal hydrides and to obtain better dehydrogenation properties. 相似文献
15.
Junhong Luo Hui Wu Wei Zhou Xiangdong Kang Zhanzhao Fang Ping Wang 《International Journal of Hydrogen Energy》2012
Mechanically milling ammonia borane and lithium borohydride in equivalent molar ratio results in the formation of a new complex, LiBH4·NH3BH3. Its structure was successfully determined using combined X-ray diffraction and first-principles calculations. LiBH4·NH3BH3 was carefully studied in terms of its decomposition behavior and reversible dehydrogenation property, particularly in comparison with the component phases. In parallel to the property examination, X-ray diffraction and Fourier transformation infrared spectroscopy techniques were employed to monitor the phase evolution and bonding structure changes in the reaction process. Our study found that LiBH4·NH3BH3 first disproportionates into (LiBH4)2·NH3BH3 and NH3BH3, and the resulting mixture exhibits a three-step decomposition behavior upon heating to 450 °C, totally yielding ∼15.7 wt% hydrogen. Interestingly, it was found that h-BN was formed at such a moderate temperature. And owing to the in situ formation of h-BN, LiBH4·NH3BH3 exhibits significantly improved reversible dehydrogenation properties in comparison with the LiBH4 phase. 相似文献
16.
Charles W. James Jr. Kyle S. BrinkmanJoshua R. Gray Jose A. Cortes-ConcepcionDonald L. Anton 《International Journal of Hydrogen Energy》2014
While the storage of hydrogen for portable and stationary applications is regarded as critical in bringing PEM fuel cells to commercial acceptance, little is known of the environmental exposure risks posed in utilizing condensed phase chemical storage options as in complex hydrides. It is thus important to understand the effect of environmental exposure of metal hydrides in the case of accident scenarios. Simulated tests were performed following the United Nations standards to test for flammability and water reactivity in air for a destabilized lithium borohydride and magnesium hydride system in a 2 to 1 molar ratio respectively. It was determined that the mixture acted similarly to the parent, lithium borohydride, but at slower rate of reaction seen in magnesium hydride. To quantify environmental exposure kinetics, isothermal calorimetry was utilized to measure the enthalpy of reaction as a function of exposure time to dry and humid air, and liquid water. The reaction with liquid water was found to increase the heat flow significantly during exposure compared to exposure in dry or humid air environments. Calorimetric results showed the maximum normalized heat flow of the fully charged material was 6 mW/mg under liquid phase hydrolysis; and 14 mW/mg for the fully discharged material also occurring under liquid phase hydrolysis conditions. 相似文献
17.
This study discusses results of an experimental program to determine dust cloud combustion characteristics of 2LiBH4 + MgH2 binary system in air. The determined parameters of hydrided and partially-dehydrided states of this system include: maximum deflagration pressure rise (PMAX), maximum rate of pressure rise (dP/dt)MAX, minimum ignition temperature (TC), minimum explosible concentration (MEC), minimum ignition energy (MIE), and explosion severity index (KSt). Impact of dust particle size on the measured parameters is evaluated for the partially-dehydrided state. For dust of same mean particle size, results show the hydrided state to be more explosible in air compared to its partially-dehydrided state. Moreover, MIE of the partially-dehydrided mixture is identified in the test with lowest ignition delay time (IDT) and highest dust cloud concentration (DC). Taguchi's mixed-levels design of experiments (DoE) methodology is employed to calculate dust's MIE response surface as a function of DC and IDT. The one-at-a-time effect and interaction effect between DC and IDT on dust MIE are determined. The core insights of this contribution are useful for quantifying risks in mobile and stationary H2 storage applications, informing H2 safety standards, and augmenting property databases of H2 storage materials. 相似文献
18.
Density functional theory calculations of an interaction of LiBH4 represented by n = 2−6 and 12 formula units nanoclusters with models of activated carbon and porous silica show that on both non-defective substrates only physisorption is observed for all cluster sizes. The binding energies are low, reaching up to −43 kJ/mol for smallest clusters. The charge transfer between LiBH4 and the support is not observed. On defective graphene (LiBH4)2 may adsorbed dissociatively. Hydrogens detached from BH4 groups saturates under-coordinated C atoms while the binding between BH3 moiety and underlying C atoms restores sp3-hybridization in the BH4 group. The dissociative adsorption of LiBH4 clusters leads to the retrieval of the three-fold coordination of the C atoms, the subsequent (LiBH4)2 physisorps with the differential heat of adsorption not exceeding −46 kJ/mol. The present calculations indicate that chemical interaction between matrix and lithium borohydride, leading to a destabilization of LiBH4, takes place until substrate's defects remain unsaturated. 相似文献
19.
Chuan Liu Shengli Zhang Peng Wang Shiping Huang Huiping Tian 《International Journal of Hydrogen Energy》2013
Confinement effect on the structural, electronic and thermodynamic properties of LiBH4 is investigated by density functional theory. The thermodynamically and dynamically stable confinement structure is testified to be γ-LiBH4@C31Ti according to the adsorption energy and vibrational frequency calculations. The tridentate structure formed by [BH4]− and Li+ in the unconfined LiBH4 changes into bidentate structure in γ-LiBH4@C31Ti. We observe that both the occupied and unoccupied states of H 1s, B 2s, B 2p, Li 2s, and Li 2p orbitals in the partial DOSs of γ-LiBH4@C31Ti shift to high energy level and the splits of DOS peaks occur at the states of H 1s, B 2p, and Li 2p orbitals. Different from the first-step decomposition reaction of LiBH4, the one for γ-LiBH4@C31Ti changes into 2LiBH4@C31Ti → 2LiH + 2B@C31Ti + 3H2. Moreover, the reaction enthalpy for the first-step decomposition reaction of γ-LiBH4@C31Ti decreases to 5.864 eV, which is smaller than that (17.204 eV) of LiBH4. According to the hydrogen removal energy calculations, we observe that the confinement effects make the removal of the first and second hydrogen atoms in γ-LiBH4@C31Ti easy. 相似文献
20.
Huaqin Kou Ge Sang Yuanlin Zhou Xiaoying Wang Zhiyong Huang Wenhua Luo Lixin Chen Xuezhang Xiao Guiying Yang Changwen Hu 《International Journal of Hydrogen Energy》2014
In this work, the hydriding–dehydriding properties of the LiBH4–NbF5 mixtures were investigated. It was found that the dehydrogenation and reversibility properties of LiBH4 were significantly improved by NbF5. Temperature-programed dehydrogenation (TPD) showed that 5LiBH4–NbF5 sample started releasing hydrogen from as low as 60 °C, and 4 wt.% hydrogen could be obtained below 255 °C. Meanwhile, ∼7 wt.% H2 could be reached at 400 °C in 20LiBH4–NbF5 sample, whereas pristine LiBH4 only released ∼0.7 wt.% H2. In addition, reversibility measurement demonstrated that over 4.4 wt.% H2 could still be released even during the fifth dehydrogenation in 20LiBH4–NbF5 sample. The experimental results suggested that a new borohydride possibly formed during ball milling the LiBH4–NbF5 mixtures might be the source of the active effect of NbF5 on LiBH4. 相似文献