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1.
Study on the synergistic catalytic effect of the SrTiO3 and Ni on the improvement of the hydrogen storage properties of the MgH2 system has been carried out. The composites have been prepared using ball milling method and comparisons on the hydrogen storage properties of the MgH2 – Ni and MgH2 – SrTiO3 composites have been presented. The MgH2 – 10 wt% SrTiO3 – 5 wt% Ni composite is found to has a decomposition temperature of 260 °C with a total decomposition capacity of 6 wt% of hydrogen. The composite is able to absorb 6.1 wt% of hydrogen in 1.3 min (320 °C, 27 atm of hydrogen). At 150 °C, the composite is able to absorb 2.9 wt% of hydrogen in 10 min under the pressure of 27 atm of hydrogen. The composite has successfully released 6.1 wt% of hydrogen in 13.1 min with a total dehydrogenation of 6.6 wt% of hydrogen (320 °C). The apparent activation energy, Ea, for decomposition of SrTiO3-doped MgH2 reduced from 109.0 kJ/mol to 98.6 kJ/mol after the addition of 5 wt% Ni. The formation of Mg2Ni and Mg2NiH4 as the active species help to boost the performance of the hydrogen storage properties of the MgH2 system. Observation of the scanning electron microscopy images suggested the catalytic role of the SrTiO3 additive is based on the modification of composite microstructure. 相似文献
2.
In this study, the hydrogen storage properties of MgH2 with the addition of K2TiF6 were investigated for the first time. The temperature-programmed desorption results showed that the addition of 10 wt% K2TiF6 to the MgH2 exhibited a lower onset desorption temperature of 245 °C, which was a decrease of about 105 °C and 205 °C compared with the as-milled and as-received MgH2, respectively. The dehydrogenation and rehydrogenation kinetics of 10 wt% K2TiF6-doped MgH2 were also significantly improved compared to the un-doped MgH2. The results of the Arrhenius plot showed that the activation energy for the hydrogen desorption of MgH2 was reduced from 164 kJ/mol to 132 kJ/mol after the addition of 10 wt% K2TiF6. Meanwhile, the X-ray diffraction analysis showed the formation of a new phase of potassium hydride and titanium hydride together with magnesium fluoride and titanium in the doped MgH2 after the dehydrogenation and rehydrogenation process. It is reasonable to conclude that the K2TiF6 additive doped with MgH2 played a catalytic role through the formation of active species of KH, TiH2, MgF2 and Ti during the ball milling or heating process. It is therefore proposed that this newly developed product works as a real catalyst for improving the hydrogen sorption properties of MgH2. 相似文献
3.
The hydrogen desorption properties of Magnesium Hydride (MgH2) ball milled with cassiterite (SnO2) have been investigated by X-ray powder diffraction and thermal analysis. Milling of pure MgH2 leads to a reduction of the desorption temperature (up to 60 K) and of the activation energy, but also to a reduction of the quantity of desorbed hydrogen, referred to the total MgH2 present, from 7.8 down to 4.4 wt%. SnO2 addition preserves the beneficial effects of grinding on the desorption kinetics and limits the decrease of desorbed hydrogen. Best tradeoff – activation energy lowered from 175 to 148 kJ/mol and desorbed hydrogen, referred to the total MgH2 present, lowered from 7.8 to 6.8 wt% – was obtained by co-milling MgH2 with 20 wt% SnO2. 相似文献
4.
A bi-component catalyst TiB2/GNSs (GNSs is the abbreviation of graphene nanosheets) is synthesized by a solid-state method. Microstructural characterizations based on SEM (scanning electron microscopy), TEM (transmission electron microscopy) and N2 physisorption show that the size of TiB2/GNSs catalyst is at nanoscale (20–30 nm) with a surface area of 84.69 m2 g−1. The TiB2/GNSs nanoparticles ball milled with MgH2 and exhibit enhanced catalytic effects on the dehydrogenation properties of MgH2 compares to TiB2 and GNSs individually. DSC (differential scanning calorimetry) measurements confirm that the peak desorption temperature of MgH2-5 wt%TiB2/GNSs composites can be lowered more than 44 °C than the pure as-milled MgH2. And the dehydrogenation kinetics of TiB2/GNSs-doped MgH2 is severalfold acceleration compares to the pure as-milled MgH2. It is proposed that the TiB2/GNSs nanoparticles could significantly enhance the intimate interface between TiB2/GNSs and hydride, therefore, provide more active “catalytic sites” and H “diffusion channels” to reduce the dehydrogenation temperature and improve the dehydrogenation kinetics of MgH2. The synergistic effect of nano-GNSs and TiB2 nanoparticles contributes to the highly efficient for dehydrogenation of MgH2-5wt%TiB2/GNSs composites. 相似文献
5.
M.S. Yahya N.N. Sulaiman N.S. Mustafa F.A. Halim Yap M. Ismail 《International Journal of Hydrogen Energy》2018,43(31):14532-14540
The catalytic effects of K2NbF7 on the hydrogen storage properties of MgH2 have been studied for the first time. MgH2 + 5 wt% K2NbF7 has reduced the onset dehydrogenation temperature to 255 °C, which is 75 °C lower than the as-milled MgH2. For the rehydrogenation kinetic, at 150 °C, MgH2 + 5 wt% K2NbF7 absorbs 4.7 wt% of hydrogen in 30 min whereas the as-milled MgH2 only absorbs 0.7 wt% of hydrogen under similar condition. For the dehydrogenation kinetic, at 320 °C, the MgH2 + 5 wt% K2NbF7 is able to release 5.2 wt% of hydrogen in 5.6 min as compared to 0.3 wt% by the as-milled MgH2 under similar condition. Comparatively, the Ea value of MgH2 + 5 wt% K2NbF7 is 96.3 kJ/mol, which is 39 kJ/mol lower compared to the as-milled MgH2. The MgF2, the KH and the Nb that are found after the heating process are believed to be the active species that have improved the system properties. It is concluded that the K2NbF7 is a good catalyst to improve the hydrogen storage properties of MgH2. 相似文献
6.
MgH2 with 10 wt.% Ti0.4Mn0.22Cr0.1V0.28 alloy (termed the BCC alloy for its body centred cubic structure) and 5 wt.% carbon nanotubes (CNTs) were prepared by planetary ball milling, and its hydrogen storage properties were compared with those of the pure MgH2 and the binary mixture of MgH2 and the BCC alloy. The sample with CNTs showed considerable improvement in hydrogen sorption properties. Its temperature of desorption was 125 °C lower than for the pure sample and 59 °C lower than for the binary mixture. In addition, the gravimetric capacity of the ternary sample was 6 wt.% at 300 °C and 5.6 wt.% at 250 °C, and it absorbed 90% of this amount at 150 s and 516 s at 300 °C and 250 °C, respectively. It can be hypothesised from the results that the BCC alloy assists the dissociation of hydrogen molecules into hydrogen atoms and also promotes hydrogen pumping into the Mg/BCC interfaces, while the CNTs facilitate access of H-atoms into the interior of Mg grains. 相似文献
7.
Eki J. Setijadi Cyrille Boyer Kondo-Francois Aguey-Zinsou 《International Journal of Hydrogen Energy》2013
Magnesium hydride (MgH2) with a range of morphologies has been synthesized via a simple hydrogenolysis route involving the decomposition of di-n-butylmagnesium. As the synthetic medium evolved from an inert atmosphere of argon to hydrogen pressure, the morphology shifted from rod like to small particles (25–170 nm). In cyclohexane, a solvent relative inert toward magnesium, smaller particles (15–50 nm) were formed. However in diethyl ether, which is more reactive toward magnesium, flakes organized in large microstructures were obtained. Remarkably in all cases β-MgH2 was readily obtained with some residual carbon contamination. Hydrogen release from these structures occurred at a relatively low temperature (300 °C), with desorption kinetics faster or equivalent to that of ball milled magnesium. In particular, hydrogen desorption from the smallest particles of MgH2 produced via the hydrogenolysis of di-n-butylmagnesium under hydrogen pressure or cyclohexane was impressive with the full desorption achieved in less than 10 min without any catalyst. These remarkable hydrogen storage properties are believed to result from an appropriate stabilization of the nanoparticles generated. 相似文献
8.
A. Ranjbar Z.P. Guo X.B. Yu D. Attard A. Calka H.K. Liu 《International Journal of Hydrogen Energy》2009,34(17):7263
In this work, MgH2–SiC–Ni was prepared by magneto-mechanical milling in hydrogen atmosphere. Scanning electron microscope mapping images showed a homogeneous dispersion of both Ni and SiC among MgH2 particles. Based on the differential scanning calorimetry traces, the temperature of desorption is reduced by doping MgH2 with SiC and Ni. Hydrogen absorption/desorption behaviour of the samples was investigated by Sievert's method at 300 °C, and the results showed that both capacity and kinetics were improved by adding SiC and Ni. The hydrogen desorption kinetic investigation indicated that for pure MgH2, the rate-determining step is surface controlled and recombination, while for the MgH2–SiC–Ni sample it is controlled as described by the Johnson–Mehl–Avrami 3D model (JMA 3D). 相似文献
9.
N.A. Sazelee N.H. Idris M.F. Md Din N.S. Mustafa N.A. Ali M.S. Yahya F.A. Halim Yap N.N. Sulaiman M. Ismail 《International Journal of Hydrogen Energy》2018,43(45):20853-20860
Previous studies have shown that ferrites give a positive effect in improving the hydrogen sorption properties of magnesium hydride (MgH2). In this study, another ferrite, i.e., BaFe12O19, has been successfully synthesised via the solid state method, and it was milled with MgH2 to enhance the sorption kinetics. The result showed that the MgH2 + 10 wt% BaFe12O19 sample started to release hydrogen at about 270 °C which is about 70 °C lower than the as-milled MgH2. The doped sample was able to absorb hydrogen for 4.3 wt% in 10 min at 150 °C, while as-milled MgH2 only absorbed 3.5 wt% of hydrogen under similar conditions. The desorption kinetic results showed that the doped sample released about 3.5 wt% of hydrogen in 15 min at 320 °C, while the as-milled MgH2 only released about 1.5 wt% of hydrogen. From the Kissinger plot, the apparent activation energy of the BaFe12O19-doped MgH2 sample was 115 kJ/mol which was lower than the milled MgH2 (141 kJ/mol). Further analyses demonstrated that MgO, Fe and Ba or Ba-containing contribute to the improvement by serving as active species, thus enhancing the MgH2 for hydrogen storage. 相似文献
10.
G. Urretavizcaya V. FusterF.J. Castro 《International Journal of Hydrogen Energy》2011,36(9):5411-5417
Hydrogen absorption and desorption properties of ball milled Mg and Mg/graphite materials were analyzed by high pressure differential scanning calorimetry. The influence on hydrogen sorption kinetics of different graphite distribution, oxygen poisoning and magnesium sintering was studied. The Mg/graphite mixture with graphite distributed in the bulk showed better kinetics than the material with graphite located on the surface and Mg without additive. The effect of sintering and oxygen poisoning was a progressive storage capacity loss, due to a kinetic limitation in the case of sintering, and due to irreversible magnesium oxidation in the case of poisoning. The mixtures with graphite exhibited more resistance toward oxygen contamination, particularly in the case where graphite was primarily located on the surface compared to the material with graphite well dispersed in the bulk. 相似文献
11.
Pavel Rizo-Acosta Fermín Cuevas Michel Latroche 《International Journal of Hydrogen Energy》2018,43(34):16774-16781
Magnesium hydride is extensively examined as a hydrogen store due to its high hydrogen content and low cost. However, high thermodynamic stability and sluggish kinetics hinder its practical application. To overcome this last drawback, different Ti amounts (y = 0, 0.025, 0.05, 0.1, 0.2 and 0.3) were added to magnesium to form (1-y)MgH2+yTiH2 nanocomposites (NC) by reactive ball milling under hydrogen gas. Thermodynamic stability of the MgH2 phase in NCs was determined using a manometric Sieverts rig. Reversible hydrogen capacity and reaction kinetics were determined at 573 K over 20 sorption cycles under a limited reaction time of 15 min. On increasing Ti amount, reaction kinetics are enhanced both in absorption and desorption leading to a higher reversibility for hydrogen storage with the MgH2 phase. However, titanium increases the molar weight of NCs and forms irreversible titanium hydride. The highest reversible capacity (4.9 wt% H) was obtained for the lowest here studied TiH2 content (y = 0.025). 相似文献
12.
《International Journal of Hydrogen Energy》2019,44(55):29196-29202
The influences of Nb-containing oxides and ternary compound in hydrogen sorption performance were investigated. As faster desorption kinetic and lower activation energy were reported by addition of a ternary compound catalyst such as K2NiF6, the influence of KNbO3 on hydrogen storage properties of MgH2 has been investigated for the first time. The MgH2 - KNbO3 composite desorbed 3.9 wt% of hydrogen within 10 min, while MgH2 and MgH2-Nb₂O₅ composites desorbed 0.66 wt% and 3.2 wt% respectively under similar condition. For MgH2 with other Nb-contained catalysts such as Nb, NbO and Nb₂O3, the desorption rate was almost the same as the one registered for as-milled MgH2. The analysis of differential scanning calorimetry (DSC) showed that MgH2-KNbO3 composite started to release hydrogen at ∼335 °C which is 50 °C lower compared to as-milled MgH2 without any additives. The activation energy for the hydrogen desorption was estimated to be about 104 ± 6.8 kJ mol−1 for this material, while for the as-milled MgH2 was about 165 ± 2.0 kJ mol−1. It is believed that Nb-ternary oxide catalyst (KNbO3) showed a good catalytic effect and enhance the sorption kinetics of MgH2. 相似文献
13.
Chunyu Zhu Haruya Hayashi Itoko Saita Tomohiro Akiyama 《International Journal of Hydrogen Energy》2009,34(17):7283
This paper describes the direct synthesis of magnesium hydride (MgH2) nanofibers by hydriding chemical vapor deposition (HCVD), in which the effect of hydrogen pressure on the production rate, the composition and the shape of products obtained were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). The XRD patterns showed that the main product in each case was MgH2; in particular, the products formed at 2, 3 and 4 MPa were highly pure. In contrast, at a hydrogen pressure of 1 MPa, unhydrided Mg was deposited along with MgH2. The SEM images also revealed orientation of the as-deposited products; higher pressures of 3 and 4 MPa caused the formation of straight and curved nanofibers, and lower ones of 1 and 2 MPa, highly curved nanofibers and nanorods with a few straight nanofibers. With pressurizing hydrogen, not only the BET specific surface areas of the products but also the production rate increased. The results also appealed that HCVD could control the shape/size of MgH2 nanofibers by changing the pressure via only a single operation. 相似文献
14.
The objective of the present work is the comparative study of the behaviour of the Nb- and Ti-based additives in the MgH2 single hydride and the MgH2 + 2LiBH4 reactive hydride composite. The selected additives have been previously demonstrated to significantly improve the sorption reaction kinetics in the corresponding materials. X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-Ray Photoelectron Spectroscopy (XPS) and Electron Microscopy (TEM) analysis were carried out for the milled and cycled samples in absence or presence of the additives. It has been shown that although the evolution of the oxidation state for both Nb- and Ti-species are similar in both systems, the Nb additive is performing its activity at the surface while the Ti active species migrate to the bulk. The Nb-based additive is forming pathways that facilitate the diffusion of hydrogen through the diffusion barriers both in desorption and absorption. For the Ti-based additive in the reactive hydride composite, the active species are working in the bulk, enhancing the heterogeneous nucleation of MgB2 phases during desorption and producing a distinct grain refinement that favours both sorption kinetics. The results are discussed in regards to possible kinetic models for both systems. 相似文献
15.
In the present work, the hydrogen storage properties of MgH2-X wt.% FeCl3 (X = 5, 10, 15 and 20) are investigated experimentally. It is found that the MgH2 + 10 wt.% FeCl3 sample exhibits the best comprehensive hydrogen storage properties, in terms of the onset dehydrogenation temperature, the hydrogen amounts de/reabsorbed as well as the relative de/rehydrogenation rates. The onset dehydrogenation temperature of the 10 wt.% FeCl3-doped MgH2 sample is reduced by about 90 °C compared to the as-milled MgH2, and the sorption kinetics measurements indicate that the FeCl3-doped sample displays an average dehydrogenation rate 5–6 times faster than that of the undoped MgH2 sample. Higher levels of doping introduce negative effects, such as lower capacity and slower absorption/desorption rates compared to samples with lower FeCl3 doping levels. The apparent activation energy for hydrogen desorption is decreased from 166 kJ•mol−1 for as-milled MgH2 to 130 kJ•mol−1 by the addition of 10 wt.% FeCl3. It is believed that the improvement of the MgH2 sorption properties in the MgH2/FeCl3 composite is due to the catalytic effects of the in-situ generated Fe species and MgCl2 that are formed during the heating process. 相似文献
16.
The influence of multiple additions of two oxides, Cr2O3 and Nb2O5, as additives on the hydrogen sorption kinetics of MgH2 after milling was investigated. We found that the desorption kinetics of MgH2 were improved more by multiple oxide addition than by single addition. Even for the milled MgH2 micrometric size powders, the high hydrogen capacity with fast kinetics were achieved for the powders after addition of 0.2 mol% Cr2O3 + 1 mol% Nb2O5. For this composition, the hydride desorbed about 5 wt.% hydrogen within 20 min and absorbed about 6 wt.% in 5 min at 300 °C. Furthermore, the desorption temperature was decreased by 100 °C, compared to MgH2 without any oxide addition, and the activation energy for the hydrogen desorption was estimated to be about 185 kJ mol−1, while that for MgH2 without oxide was about 206 kJ mol−1. 相似文献
17.
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
18.
In this paper, we present a new route for recycling waste Mg with the production of MgH2 nanofiber, which is a promising candidate for energy storage and conversion used in Li-ion batteries and H2 storing technologies. Highly pure MgH2 nanofibers were successfully manufactured from Mg-alloy swarfs (AM60B and AZ91D) via the hydriding chemical vapor deposition (HCVD) process. The possibility of recycling all types of Mg scraps using the HCVD process was demonstrated, which requires only a pretreatment of obtaining a dried raw material. The HCVD method shows many advantages over other methods in the synthesis of MgH2: it can produce MgH2 at low cost using waste Mg as the raw material, requires less energy, offers a high-purity product, and enables control over the growth of nanosized structures. 相似文献
19.
The present study compares the dehydrogenation kinetics of (2LiNH2+MgH2) and (LiNH2+LiH) systems and their vulnerabilities to the NH3 emission problem. The (2LiNH2+MgH2) and (LiNH2+LiH) mixtures with different degrees of mechanical activation are investigated in order to evaluate the effect of mechanical activation on the dehydrogenation kinetics and NH3 emission rate. The activation energy for dehydrogenation, the phase changes at different stages of dehydrogenation, and the level of NH3 emission during the dehydrogenation process are studied. It is found that the (2LiNH2+MgH2) mixture has a higher rate for hydrogen release, slower rate for approaching a certain percentage of its equilibrium pressure, higher activation energy, and more NH3 emission than the (LiNH2+LiH) mixture. On the basis of the phenomena observed, the reaction mechanism for the dehydrogenation of the (2LiNH2+MgH2) system has been proposed for the first time. Approaches for further improving the hydrogen storage behavior of the (2LiNH2+MgH2) system are discussed in light of the newly proposed reaction mechanism. 相似文献
20.
I.E. MalkaM. Pisarek T. Czujko J. Bystrzycki 《International Journal of Hydrogen Energy》2011,36(20):12909-12917
Magnesium hydride with 7 wt.% of various metal halide additives (ZrF4, TaF5, NbF5 and TiCl3) were ball milled, and the influence of these dopants on the kinetics of absorption and desorption was studied. The pressure-composition-temperature isotherms (P-C-T) measured by Sieverts’ apparatus did not show thermodynamic changes in the studied materials. Moreover, XPS studies demonstrated that the metal halides used in this study (except ZrF4) took part in the partial and full disproportionation reactions directly after milling and the first desorption/absorption cycle. The catalytic effect of metal halides on the Mg hydrogenation/dehydrogenation process was caused by the formation of pure transition metal and/or the MgF2 phase, which led to the influence of two simultaneous factors on the sorption properties of the MgH2. 相似文献