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1.
The composites of (NaBH4+2Mg(OH)2) and (LiBH4+2Mg(OH)2) without and with nanometric Ni (n-Ni) added as a potential catalyst were synthesized by high energy ball milling. The ball milled NaBH4-based composite desorbs hydrogen in one exothermic reaction in contrast to its LiBH4-based counterpart which dehydrogenates in two reactions: an exothermic and endothermic. The NaBH4-based composite starts desorbing hydrogen at 240 °C. Its ball milled LiBH4-based counterpart starts desorbing at 200 °C. The latter initially desorbs hydrogen rapidly but then the rate of desorption suddenly decelerates. The estimated apparent activation energy for the NaBH4-based composite without and with n-Ni is equal to 152 ± 2.2 and 157 ± 0.9 kJ/mol, respectively. In contrast, the apparent activation energy for the initial rapid dehydrogenation for the LiBH4-based composite is very low being equal to 47 ± 2 and 38 ± 9 kJ/mol for the composite without and with the n-Ni additive, respectively. XRD phase studies after volumetric isothermal dehydrogenation tests show the presence of NaBO2 and MgO for the NaBH4-based composite. For the LiBH4-based composite phases such as MgO, Li3BO3, MgB2, MgB6 are the products of the first exothermic reaction which has a theoretical H2 capacity of 8.1 wt.%. However, for reasons which are not quite clear, the first reaction never goes to full completion even at 300 °C desorbing ∼4.5 wt.% H2 at this temperature. The products of the second endothermic reaction for the LiBH4-based composite are MgO, MgB6, B and LiMgBO3 and the reaction has a theoretical H2 capacity of 2.26 wt.%. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4-and LiBH4-based composites is rather negligible. The n-Ni additive may not be the optimal catalyst for these hydride composite systems although more tests are required since only one n-Ni content was examined. 相似文献
2.
The hydrolysis of sodium-borohydride (SBH) to produce hydrogen has been studied at various temperatures using salts of nickel (II) or iron (III) as catalyst. Excess of water has been added to a mixture of solid SBH and catalyst to start hydrolysis reaction and the evolved hydrogen measured as a function of time. After a sudden peak a constant hydrogen flow was observed when Ni is used as catalyst. The activation energy has been evaluated from the dependence of the reaction time and of the hydrogen flow on the inverse of temperature. If Ni is substituted by a Fe based catalyst, after the initial increase, a different shape is observed in the hydrogen flow: it reaches a maximum and then monotonously decrease to zero. The different shape has been related to the different activity of the catalyst. The reaction activation energy was evaluated to be 73 KJ/mol. 相似文献
3.
Mei-qiang Fan Shu LiuWen-qiang Sun Yong FeiHua Pan Chun-Ju LvDa Chen Kang-Ying Shu 《International Journal of Hydrogen Energy》2011,36(24):15673-15680
On-demand hydrogen generation from solid-state Al/NaBH4 hydrolysis activated by Li-NiCl2 additives are elaborated in the present paper. Hydrogen generation amount and rate can be regulated by changing Al/NaBH4 weight ratio, Li and NiCl2 amount, hydrolytic temperature, etc. The optimized Al−10 wt.% Li−15 wt.% NiCl2/NaBH4 mixture (weight ratio of 1:1) yields 1778 ml hydrogen/1 g mixture with 100% efficiency within 50 min at 323 K. The improved hydrolytic performance comes from the effect of Li-NiCl2 additives, which decrease aluminum particle size in the milling process and produce the catalytic promoter BNi2/Al(OH)3 in the hydrolytic process. Compared with the conventional reaction of Al and NaBH4 in water, there is an interaction of Al/NaBH4 hydrolysis which improves the hydrolytic kinetics of Al/NaBH4 via the catalytic effect of hydrolysis by-products Al(OH)3, BNi2, and NaBO2. The Al/NaBH4 mixture may be applied as a portable hydrogen generation material. Our experimental data lay a foundation for designing practical hydrogen generators. 相似文献
4.
A high-activity Al(OH)3 suspension is prepared by the reaction of Al with water using an ultrasonic procedure. The above Al(OH)3 suspension could considerably promote the Al-water reaction and hydrogen-generation under ambient condition. This Al(OH)3 suspension has a good stability in air and its activity increases with decreasing the particle sizes of Al powder to prepare it. The mechanism analyses reveal that the Al(OH)3 particles in ultrasonically prepared Al(OH)3 suspensions are very fine, which could effectively dissociate water molecules and promote the hydration of the passive oxide film on Al particle surfaces, speeding up the Al-water reaction. As the present Al(OH)3 suspension is chemically neutral and there is no special treatment for Al powder, the present method provides a viable way to generate hydrogen for portable application. 相似文献
5.
A process to produce hydrogen from polyethylene [–CH2–]n (PE) is developed by milling with Ca(OH)2 and Ni(OH)2 followed by heating the milled product. Characterizations by a set of analytical methods of X-ray diffraction (XRD), infrared spectroscopy (FT-IR), thermogravimetry–mass spectroscopy (TG/MS) and gas chromatography (GC) were performed on the milled and heated samples to monitor the process. It has been observed that addition of nickel hydroxide as well as increases in milling time and rotational speed of the mill is beneficial to the gas generation, mainly composed of H2 and CH4, CO, CO2. Gaseous compositions from the milled samples vary depending on the added molar ratio of calcium hydroxide. H2 emission occurs between 400 and 500 °C, and H2 concentration of 95% is obtained from the mixture of PE/Ca(OH)2/Ni(OH)2 (C:Ca:Ni = 6:14:1) sample, and the concentrations of CO and CO2 remain below 0.5%. The process offers a novel approach to treat waste plastic by transforming it into hydrogen. 相似文献
6.
The effects of surface coating of Y(OH)3 on the electrochemical performance of spherical Ni(OH)2 were studied by cyclic voltammetry (CV) with soft-embedded electrode (SE-E). The coating was performed by chemical surface precipitation under different conditions. The structure, morphology, chemical composition and electrochemical properties of two different samples with surface coating of Y(OH)3 were characterized and compared. The results show that a two-step oxidation process exists in the oxidation procedure of spherical Ni(OH)2 corresponding to the formation of Ni(III) and Ni(IV), respectively. The conversion of Ni(III) to Ni(IV) is regarded as a side reaction in which Ni(IV) species is not stable. The presence of Y(OH)3 on the particle surface can restrain the side reactions, especially the formation of Ni(IV). The application of coated Ni(OH)2 to sealed Ni–MH batteries yielded a charge acceptance of about 88% at 60 °C. The results manifest that the high-temperature performance of Ni(OH)2 electrode is related to the distribution of the adding elements in surface oxide layer of Ni(OH)2, the sample with dense and porous coating surface, larger relative surface content and higher utilization ratio of yttrium is more effective. 相似文献
7.
Yanjing Yang Mingxia Gao Yongfeng Liu Jianhui Wang Jian Gu Hongge Pan Zhengxiao Guo 《International Journal of Hydrogen Energy》2012
A two-step ball-milling method has been provided to synthesize Mg(BH4)2 using NaBH4 and MgCl2 as starting materials. The method offers high yield and high purity (96%) of the compound. The as-synthesized Mg(BH4)2 is then combined with LiAlH4 by ball-milling in order to form new multi-hydride systems with high hydrogen storage properties. The structure, the dehydrogenation and the reversibility of the combined systems are studied. Analyses show that a metathesis reaction takes place between Mg(BH4)2 and LiAlH4 during milling, forming Mg(AlH4)2 and LiBH4. Mg(BH4)2 is excessive and remains in the ball-milled product when the molar ratio of Mg(BH4)2 to LiAlH4 is over 0.5. The onset dehydrogenation temperature of the combined systems is lowered to ca. 120 °C, which is much lower than that of either Mg(BH4)2 or LiAlH4. The dehydrogenation capacities of the combined systems below 300 °C are all higher than that of both Mg(BH4)2 and LiAlH4. The combined systems are reversible for hydrogen storage at moderate hydrogenation condition, and rapid hydrogenation occurred within the initial 30 min. Moreover, the remained Mg(BH4)2 in the combined systems is found also partially reversible. The mechanism of the enhancement of the hydrogen storage properties and the dehydrogenation/hydrogenation process of the combined systems were discussed. 相似文献
8.
Juner Chen Yao ZhangZhitao Xiong Guotao WuHailiang Chu Teng HePing Chen 《International Journal of Hydrogen Energy》2012
Co-based catalyst can significantly improve the dehydrogenation kinetics of the eutectic composite of LiBH4–Mg(BH4)2 (1/1 M ratio). The onset hydrogen desorption temperature of the composite is at about 155 °C, which is ca. 245, 110 or 27 °C lower than that of LiBH4, Mg(BH4)2 or pristine LiBH4–Mg(BH4)2, respectively. Upon holding the samples at 270 °C, the Co catalyzed composite can release hydrogen at a rate 1.6 times faster than that of the pristine one. Electron Paramagnetic Resonance (EPR) characterization evidenced that Co was in a reduced state of Co+ which may serve as the functional species in catalyzing the dehydrogenation of the composite. 相似文献
9.
Yuepeng Pang Yongfeng LiuXin Zhang Mingxia GaoHongge Pan 《International Journal of Hydrogen Energy》2013
A significant decrease in the dehydrogenation temperature of Mg(AlH4)2 was achieved by low-energy ball milling with TiF4. Approximately 8.0 wt% of hydrogen was released from the Mg(AlH4)2-0.025TiF4 sample with an on-set temperature of 40 °C, which represents a decrease of 75 °C relative to pristine Mg(AlH4)2. In contrast to the three-step reaction for pristine Mg(AlH4)2, hydrogen desorption from the TiF4-doped sample involves a two-step process because the Ti-based species participates in the dehydrogenation reaction. The presence of TiF4 alters the nucleation and growth of the dehydrogenation product, significantly decreasing the activation energy barrier of the first step in the dehydrogenation of Mg(AlH4)2. Further hydrogenation measurements revealed that the presence of the Ti-based species was also advantageous for hydrogen uptake, as the on-set hydrogenation temperature was only 100 °C for the dehydrogenated TiF4-doped sample, compared with 130 °C for the additive-free sample. 相似文献
10.
Saisai Chen Jin Liu Yongfei Xu Zhen Li Tai Wang Jiong Xu Zhuo Wang 《International Journal of Hydrogen Energy》2018,43(32):15370-15377
Metal organic frameworks (MOF) are a type of nanoporous materials with large specific surface area, which are especially suitable for gas separation and storage. In this work, we report a new approach of crosslinking UiO-66-(OH)2 to enhance its hydrogen storage capacity. UiO-66-(OH)2 was synthesized using hafnium tetrachloride (HfCl4) and 2, 5-dihydroxyterephthalic acid (DTPA) through a canonical modulated hydrothermal method (MHT), followed by a post-synthesis modification, which is to form a crosslinking structure inside the porous structure of UiO-66-(OH)2. During the modification process, the phenolic hydroxyl groups on the UiO-66-(OH)2 reacted with methanal, and HCl aqueous solution and triethylamine served as catalyst (the products denoted as UiO-66-H and UiO-66-T, respectively). Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), 13C nuclear magnetic resonance spectroscopy (13C NMR) proved that the crosslinking was formed. The BET specific surface area and the average adsorption pore size of UiO-66-H and UiO-66-T significantly increased after modification. The hydrogen storage capacity of UiO-66-H reached a maximum of 3.37 wt% (16.87 mmol/g) at 77 K, 2 MPa. Hydrogen adsorption enthalpy of UiO-66-T was 0.986 kJ/mol, which was higher than that of UiO-66-(OH)2 (0.695 kJ/mol). This work shows that UiO-66-(OH)2 is a promising candidate for potential application in high-performance hydrogen storage. 相似文献
11.
Sandra Kurko Annalisa Aurora Daniele Mirabile Gattia Vittoria Contini Amelia Montone Željka Rašković-Lovre Jasmina Grbović Novaković 《International Journal of Hydrogen Energy》2013
The hydrogen sorption properties of magnesium hydride–sodium borohydride composites prepared by means of high-energy ball milling under Ar atmosphere were investigated. Mutual influence of milling time and the content of NaBH4 were studied. Microstructural and morphological analyses were carried out using X-ray Diffraction (XRD), laser scattering measurements and Scanning Electron Microscopy (SEM), while kinetic analysis and cycling were performed in a Sievert's volumetric apparatus. It has been shown that low content of NaBH4 and short milling time are beneficial for hydrogen sorption kinetics. 相似文献
12.
13.
Jianjun Jiang Jia WeiHaiyan Leng Qian LiKuo-Chih Chou 《International Journal of Hydrogen Energy》2013
The various Mg–B–Al–H systems composed of Mg(BH4)2 and different Al-sources (metallic Al, LiAlH4 and its decomposition products) have been investigated as potential hydrogen storage materials. The role of Al was studied on the dehydrogenation and the rehydrogenation of the systems. The results indicate that the different Al-sources exhibit a similar improving effect on the dehydrogenation properties of Mg(BH4)2. Taking the Mg(BH4)2 + LiAlH4 system as an example, at first LiAlH4 rapidly decomposes into LiH and Al, then Mg(BH4)2 decomposes into MgH2 and B, finally the MgH2 reacts with Al, LiH and B, which forms Mg3Al2 and MgAlB4. The system starts to desorb H2 at 140 °C and desorbs 3.6 wt.% H2 below 300 °C, while individual Mg(BH4)2 starts to desorb H2 at 250 °C and desorbs only 1.3 wt.% H2 below 300 °C. The isothermal desorption kinetics of the Mg–B–Al–H systems is about 40% faster than that of Mg(BH4)2 at the hydrogen desorption ratio of 90%. In addition, the Mg–B–Al–H systems show partial reversibility at moderate temperature and pressure. For Al-added system, the product of rehydrogenation is MgH2, while for LiAlH4-added system the product is composed of LiBH4 and MgH2. 相似文献
14.
Rohit R. Shahi Himanshu RaghubanshiM.A. Shaz O.N. Srivastava 《International Journal of Hydrogen Energy》2013
The effect of different carbon nanostructures specifically carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the improvement of the de/re-hydrogenation characteristics of a Mg(NH2)2/LiH mixture have been studied. Amongst CNTs and CNFs, the improvement in the hydrogenation properties for the Mg(NH2)2/LiH mixture is higher when CNFs are used as a catalyst. Investigations are also focused on the deployment of two different types of CNF (a) CNF1 (synthesized using a ZrFe2 catalyst) and (b) CNF2 (synthesized using a LaNi5 catalyst). The results show that CNF2 is better. The maximum decomposition temperature for the pristine Mg(NH2)2/LiH mixture is found to be ∼250 °C, which is reduced to ∼180 and ∼150 °C for the sample mixed with 4 wt% of multi-walled carbon nanotubes (MWCNTs) and CNF2 respectively. The activation energy for the dehydrogenation reaction is found to be 74 and 68 kJ mol−1 for the samples mixed with MWCNT and CNF2 respectively, whereas the activation energy for the dehydrogenation reaction of the pristine Mg(NH2)2/LiH mixture is 97 kJ mol−1. The catalytic activity and the de/re-hydrogenation characteristics of the Mg(NH2)2/LiH mixture mixed with different carbon nanostructures are described and discussed. 相似文献
15.
Rohit R. Shahi Himanshu Raghubanshi M.A. ShazO.N. Srivastava 《International Journal of Hydrogen Energy》2012
The effect of carbon nanofibres (CNFs) on the de/re-hydrogenation characteristics of 1:2 magnesium amide (Mg(NH2)2) and lithium hydride (LiH) mixture is investigated. It is found that the desorption as well as absorption characteristic of the 1:2 Mg(NH2)2/LiH mixture is improved with admixing of different shaped (planar and helical) CNFs separately. The different shaped CNFs were synthesized through catalytic decomposition of acetylene gas over LaNi5 alloy. The synthesized CNFs contain Ni-metal nano particles. Among two different types of nanofibres namely planar carbon nanofibres (PCNFs) and helical carbon nanofibres (HCNFs), the later was found to act as a better catalyst. The decomposition temperature of the pristine Mg(NH2)2/LiH mixture is ∼250 °C, reduced to 150 and 140 °C for the PCNF and HCNF admixed Mg(NH2)2/LiH mixture respectively. The activation energy for dehydrogenation reaction was found to ∼97.2 kJ/mol, which is further reduced to ∼67 and ∼65 kJ/mol for the PCNF and HCNF admixed Mg(NH2)2/LiH mixture respectively. The lowering of decomposition temperature and enhancement in desorption kinetics, with admixing of different shaped CNFs are described and discussed. 相似文献
16.
Yongfeng Liu Yuepeng PangXin Zhang Yifan ZhouMingxia Gao Hongge Pan 《International Journal of Hydrogen Energy》2012
Mg(AlH4)2 submicron rods with 96.1% purity have been successfully synthesized in a modified mechanochemical reaction process followed by Soxhlet extraction. ∼9.0 wt% of hydrogen is released from the as-prepared Mg(AlH4)2 at 125–440 °C through a stepwise reaction. Upon dehydriding, Mg(AlH4)2 decomposes first to generate MgH2 and Al. Subsequently, the newly produced MgH2 reacts with Al to form a Al0.9Mg0.1 solid solution. Finally, further reaction between the Al0.9Mg0.1 solid solution and the remaining MgH2 gives rise to the formation of Al3Mg2. The first step dehydrogenation is a diffusion-controlled reaction with an apparent activation energy of ∼123.0 kJ/mol. Therefore, increasing the mobility of the species involved in Mg(AlH4)2 will be very helpful for improving its dehydrogenation kinetics. 相似文献
17.
Zhihong Yuan Shichang Li Junchao Liu Xianggang Kong Tao Gao 《International Journal of Hydrogen Energy》2018,43(29):13639-13648
Density functional theory (DFT) with optPBE-vdW functional is used to simulate the structural, electronic, dynamical and thermodynamic properties of Ca10(PO4)6(OH)2(Ca-HA) and Sr10(PO4)6(OH)2(Sr-HA). The calculated structural properties within optPBE-vdW functional is found to yield better agreement with the experimental results, which indirectly suggests the important role of weak hydrogen bond in this crystal. The calculated electronic properties indicate that Ca-HA and Sr-HA are insulator materials with indirect band gap of 5.52 eV and 5.10 eV, respectively. The detailed dynamical properties of two apatites are obtained by the linear-response approach. With replacement of Ca by Sr, the librational mode of OH group decreases from 612 cm?1 to 569 cm?1, the stretching mode of OH group increases from 3614.5 cm?1–3649.9 cm?1, which is consistent with the experimental results. Finally, some phonon related thermodynamic properties, such as Helmholtz free energy F, internal energy E, entropy S and heat capacity CV of Sr-HA and Ca-HA are studied according to the phonon calculations within the harmonic approximation. The present calculation results of two apatites with optPBE-vdW functional are in good agreement with the existing experimental. 相似文献
18.
Borohydrides such as Mg(BH4)2 and Ca(BH4)2 continue to attract attention as potential hydrogen storage materials because of their high hydrogen content. In this study the desorption kinetics of Mg(BH4)2, Ca(BH4)2 and a 5Mg(BH4)2/Ca(BH4)2 mixture of the two were compared in the two-phase region at the same temperature and at a constant pressure thermodynamic driving force. The rate of hydrogen desorption from the two-phase region in the 5Mg(BH4)2/Ca(BH4)2 mixture was faster than that from either of the constituents. This indicated that Ca(BH4)2 was able to serve as a destabilizing agent for Mg(BH4)2. The results also showed that the desorption rates from the two-phase region were much faster than those from the single phase region. Modeling studies showed that the rate of hydrogen release from Mg(BH4)2, during the first 80% of the reaction, is diffusion controlled while in Ca(BH4)2 the reaction rate is phase boundary controlled. In the mixture the rate appears to be under the mixed control of both processes. 相似文献
19.
S. Garroni C. Milanese A. Girella A. Marini G. Mulas E. Menéndez C. Pistidda M. Dornheim S. Suriñach M.D. Baró 《International Journal of Hydrogen Energy》2010
The sorption properties of NaBH4/MH2 (M = Mg, Ti) powder systems prepared by high-energy ball milling have been thoroughly investigated. Concerning the systems containing MgH2, the 2:1 and 1:2 molar compositions have been studied and both lead to a multi-step desorption pathway, where the formation of MgB2 confirms the destabilization of NaBH4 induced by the presence of MgH2. A noticeable kinetic enhancement is achieved for the MgH2-rich system (composition 1:2) if compared with the NaBH4-rich system (composition 2:1). Even though full re-absorption is obtained for neither of the two compositions, fast kinetics is achieved. During absorption, the unsuspected formation of the perovskite-type hydride NaMgH3 is detected and it is showed that this ternary phase contributes to reduce the gravimetric capacity of the systems. Conversely, in the 2NaBH4/TiH2 system, there is no formation of the intermetallic compound TiB2. Furthermore, a decrease in the sorption kinetics is found in comparison with the systems based on MgH2. 相似文献
20.
Yongfeng Liu Ni Jian Zhuanghe Ren Jianjiang Hu Fang Du Mingxia Gao Hongge Pan 《International Journal of Hydrogen Energy》2018,43(30):13981-13989
A novel dual-cation/anion complex hydride (Li2Mg(BH4)2(NH2)2), which contains a theoretical hydrogen capacity of 12.1 wt%, is successfully synthesized for the first time by ball milling a mixture consisting of MgBH4NH2 and Li2BH4NH2. The prepared Li2Mg(BH4)2(NH2)2 crystallizes in a triclinic structure, and the [NH2] and [BH4] groups remain intact within the structure. Upon heating, the prepared Li2Mg(BH4)2(NH2)2 decomposes to release approximately 8.7 wt% hydrogen in a three-step reaction at 100–450 °C. In addition, a small amount of ammonia is evolved during the first and second thermal decomposition steps as a side product. This ammonia is responsible for the lower experimental dehydrogenation amount compared to the theoretical hydrogen capacity. The XRD and FTIR results reveal that Li2Mg(BH4)2(NH2)2 first decomposes to LiMgBN2, LiBH4, BN, LiH and MgBNH8 at 100–250 °C, and then, the newly formed MgBNH8 reacts with LiH to form Mg, LiBH4 and BN at 250–340 °C. Finally, the decomposition of LiBH4 releases hydrogen and generates LiH and B at 340–450 °C. 相似文献