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Enhancement of hydrogen storage properties in 4MgH2 Na3AlH6 composite catalyzed by TiF3
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Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3 F.A. Halim Yap, M.S. Yahya, M. Ismail* School of Ocean Engineering, University Malaysia Terengganu, 21030, Kuala Terengganu, Malaysia
article info
abstract
Article history:
In this work, we have investigated the hydrogen release and uptake pathways storage
Received 8 May 2017
properties of the MgH2eNa3AlH6 with a molar ratio of 4:1 and doped with 10 wt% of TiF3
Received in revised form
using a mechanical alloying method. The doped composite was found to have a significant
21 June 2017
reduction on the hydrogen release temperature compared to the un-doped composite
Accepted 2 July 2017
based on the temperature-programme-desorption result. The first stage of the onset
Available online xxx
desorption temperature of MgH2eNa3AlH6 was reduced from 170 C to 140 C with the
Keywords:
released hydrogen were observed for the 4MgH2eNa3AlH6-10 wt% TiF3 composite. The
addition of the TiF3 additive. Three dehydrogenation steps with a total of 5.3 wt% of Hydrogen energy
re/dehydrogenation kinetics of 4MgH2eNa3AlH6 system were significantly improved with
Hydrogen storage
the addition of TiF3. Kissinger analyses showed that the apparent activation energy, EA, of
Magnesium hydride
the 4MgH2eNa3AlH6 doped composite was 124 kJ/mol, 16 kJ/mol and 34 kJ/mol lower for
Sodium alanate
un-doped composite and the as-milled MgH2, respectively. It was believed that the enhancements of the MgH2eNa3AlH6 hydrogen storage properties with the addition of TiF3 were due to formation of the NaF, the AlF3 and the Al3Ti species. These species may played a synergetic catalytic role in improving the hydrogenation properties of the MgH2eNa3AlH6 system. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction In years, it is extensively acknowledged that hydrogen, as an energy carrier will become the fuel for most vehicles due to its benefits such as environmental friendly and high energy density. However, problems related to hydrogen storage have prohibited the commercialization of its application like renewable energy sources [1,2]. A lot of works have been focussed on the improvement of the hydrogen storage whether in gaseous state [3e5], cryogenic liquid state [6e8] or solid state [9e12]. Safety concerns, provision of spaces for storage [13,14] and energy efficiency [15] are among the factors why solid-state hydrogen storage has been considered as a
promising method compared to other conventional storage methods. Consequently researchers have shown an interest on the solid-state hydrogen storage materials especially light metal hydrides [16,17] and complex hydrides [18]. High hydrogen storage capacity is one of the reasons why this material has attracted researchers' attention. In addition, metal hydrides can store large amounts of hydrogen in a compact and safe ways [19]. However, metal hydrides such as MgH2 start to release hydrogen at high temperature [20,21] and complex hydrides such as Na3AlH6 suffer from slow rate of dehydrogenation kinetics [22]. These drawbacks are the major obstacles in the development of hydrogen energy applications. Therefore, studies are conducted to enhance the hydrogen
* Corresponding author. E-mail address: [email protected] (M. Ismail). http://dx.doi.org/10.1016/j.ijhydene.2017.07.012 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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storage properties of MgH2 and Na3AlH6 in order to meet the technical target given by the U.S. Department of Energy [23]. Several approaches have been used in improving the decomposition temperature and rate of kinetic such as adding with a catalyst [24e30], reducing the particles size by ball milling [31], and destabilizing the hydrides [32e35], and a ball-milling process assisted by dielectric-barrier discharge plasma for dual-tuning the thermodynamics and kinetics [36e38]. Among the approaches, the destabilization system has been considered as a promising solution to this problem. Many efforts were concentrated on combining metal with other metal hydrides such as NaBH4eMgH2 [39], LiBH4eMgH2 [40], MgH2eNaAlH4 [35], MgH2eLi3AlH6 [41], LiNH2eLi3AlH6 [42], and MgH2eNa3AlH6 [43]. In this context, reduction on the desorption temperature and improvement on the rate of sorption kinetics from our previous work [43] on the system of MgH2 destabilized with Na3AlH6 have motivated us to work further so that it can fulfil the requirement for the hydrogen energy application. As discussed in the previous work, the formation of the NaMgH3, Al and H2 from the reaction between MgH2 and Na3AlH6 help to reduce the dehydrogenation temperature of Na3AlH6 for about 55 C compared to the asmilled Na3AlH6. Meanwhile, at 275 C, the Al component destabilized the MgH2 to form the intermetallic compound (Mg17Al12) that led to the improvement of the MgH2 desorption temperature property. However, the finding still did not fulfil the requirement in a commercial field for the practical application. Therefore, further work has been carried out in order to enhance the hydrogenation properties of the MgH2e Na3AlH6 system with the addition of an additive. To the best of the authors' knowledge, there is no work has been reported on the understanding of the additive effects on MgH2eNa3AlH6 hydrogen storage properties. Therefore, it is interesting to explore the possible influence of an additive on the improvement of hydrogenation properties of the MgH2e Na3AlH6 system. To date, there is no reported literature on the improvement of the MgH2eNa3AlH6 system with TiF3 as the additive. Many literature have reported the effects of TiF3 on metal hydrides [44] and complex hydrides [45,46], where the formation of Ti and F anion played the catalytic roles that led to the enhancement of hydrogen storage performance. According to the work done by Juahir et al. [47], the Ti-containing and F-containing phases through the formations of NaF and Al3Ti active species had played a catalytic role in promoting the improvement of NaAlH4eMg(BH4)2 hydrogen storage properties. In addition, Mao et al. [46] proved that the Ticontaining species and the active function of the F anion had improved the hydrogenation properties of NaBH4. On the other hand, tremendous works by other researchers in improving the hydrogen storage properties of hydride materials catalyzed by the metal based-fluoride have been published. Recently, Mao et al. [48] found that the hydrogen storage performance of the NaAlH4 was improved after the addition of NbF5. DSC results indicate that the ball-milled NaAlH4e0.03NbF5 sample lowered the completion temperature for the first two steps dehydrogenation by 71 C compared to the pristine NaAlH4 sample. More recently, Wang et al. [49] found that the desorption temperature of the NaMgH3 was reduced for about 252 C with the addition of K2TiF6. Furthermore, catalysts made of metal based-chloride have
attracted researchers' attentions. Works done by Zhang et al. [50] showed that by introducing FeCl3 as a catalyst to the LiNH2e2LiH, the dehydrogenation kinetics of the system was improved. They stated that the temperature was reduced and the dehydrogenation activation energy was lowered from 102.45 kJ/mol to 87.52 kJ/mol. Hence, it is noteworthy to believe that upon heating, the TiF3 additive will react with the MgH2eNa3AlH6 composite by an in situ reactions to form active species that will enhance the hydrogen sorption properties of the MgH2eNa3AlH6 system. In this work, TiF3 was introduced to the MgH2eNa3AlH6 composite by ball milling method. The aim is to study the performance improvement on hydrogen storage properties of the MgH2eNa3AlH6 system. The hydrogen storage properties, the thermal analysis, the reaction mechanisms as well as the surface morphology of the MgH2eNa3AlH6eTiF3 were investigated in this study. A Sievert-type pressure-compositiontemperature (PCT) apparatus, differential a scanning calorimetry (DSC), a scanning electron microscopy (SEM) and an Xray diffraction (XRD) were used for the investigation. The possible mechanism of the composite supported by the results from the study was discussed.
Experimental Starting materials, MgH2 (hydrogen storage grade), NaAlH4 (hydrogen storage grade, 93% purity), NaH (dry, 95% purity) and TiF3 were purchased from Sigma Aldrich. All the materials were used directly without any further purification. All samples preparation for every analysis was performed in an argon filled glove box in order to prevent the samples from oxidation. The Na3AlH6 composite was synthesized through the mechanochemical reaction between the NaH and the NaAlH4 [51]. The mixture of NaH and NaAlH4, with a mole ratio of 2:1, was milled for 20 h in a planetary ball mill (NQM-0.4) with the ball to powder ratio (BPR) of 40:1 at a rotation speed of 400 rpm. The sample of MgH2 and Na3AlH6 composite with a molar ratio of 4:1 was prepared using similar method but with milling time of 1 h only. For comparison purposes, the pristine MgH2 and the Na3AlH6 were also prepared by 1 h of milling time. Temperature-programmed-desorption (TPD) and ab/ desorption kinetic experiments were conducted in a Sievertstype pressure-composition-temperature (PCT) apparatus (Advanced Materials Corporation). For each sample, about 80 mg was loaded into a sample vessel in a glove box. For the TPD experiment, all samples were heated from room temperature to 450 C with a heating rate of 5 C/min in a vacuum chamber so that the lowest decomposition temperature and the amount of hydrogen desorbed can be determined. Meanwhile the rehydriding and dehydriding kinetics were studied at 320 C under hydrogen pressures of 33 atm and 1 atm, respectively. Differential scanning calorimetry (DSC) measurement of the dehydrogenation process was conducted using a thermogravimetric analysis/differential scanning calorimeter (TGA/DSC) 1 from Mettler Toledo. Each sample with an amount of 5e10 mg was loaded into an alumina crucible in the glove box. The samples were heated from room temperature to 500 C under an argon flow of 50 ml/min, and different
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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heating rates were used. An empty alumina crucible was used as a reference. Samples for the scanning electron microscopy (SEM) were placed on a surface of carbon tape and were coated with gold under vacuum condition to avoid contact with air. The surface morphology of the samples was analysed by scanning electron microscope (SEM; JEOL JSM-6360LA). Meanwhile, the phase structure analysis of the samples after ball milling and after desorption temperature, as well as after rehydrogenation kinetics, were determined by X-ray diffraction (Rigaku MiniFlex X-ray diffractometer with Cu Ka radiation). The samples were scanned over diffraction angles of 20 e80 at a speed of 2.00 /min.
Results and discussions Mechanical synthesis of Na3AlH6 Fig. 1 displays the XRD pattern of the 2NaHeNaAlH4 mixture after milling for 20 h. As can been seen from the XRD spectra, only peaks of the Na3AlH6 can be detected, while peaks of the starting materials, the NaH and the NaAlH4 are absent. This result indicates that the solid-state reaction is completed between the components of the NaHeNaAlH4 (2:1) during the milling process, as represent in Eq. (1): 2NaH þ NaAlH4 /Na3 AlH6
(1)
The formation of the metastable b-Na3AlH6 phase is believed to happen during the milling process and the polymorphic transformation from Na3AlH6 to b-Na3AlH6 is partially occurred. This result is similar to other studies [51,52].
Dehydrogenation temperature The TPD performance of the as-milled MgH2, the as-milled Na3AlH6, the MgH2eNa3AlH6 and the MgH2eNa3AlH6eTiF3 composites are shown as in Fig. 2. From the graph, the as-
Fig. 2 e TPD curves of the as-milled MgH2, the as-milled Na3AlH6, the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6e TiF3 composites. (I, II and III phases refer to the first, second and third dehydrogenation stages, respectively).
milled MgH2 sample has started to release hydrogen at 350 C and has desorbed 7.4 wt% of hydrogen after 450 C. Meanwhile, the hydrogen has been released at the temperature of 230 C for the as-milled Na3AlH6 composite. As for the 4MgH2eNa3AlH6 composite, based on the results, three dehydrogenation stages have happened during the heating process. The stages are corresponding to the decomposition of the Na3AlH6 and the MgH2, with the onset desorption temperature has experienced a reduction as compared to the asprepared Na3AlH6 and the as-milled MgH2. As shown in the graph, the dehydrogenation process of the 4MgH2eNa3AlH6 composite has occurred in three stages. The first dehydrogenation process has started at the temperature of 170 C and has completed at 230 C with the capacity of 1.0 wt% of hydrogen. Meanwhile the second dehydrogenation process has taken place within the temperature of 270 Ce350 C and the third stage of the dehydrogenation has occurred at the temperature of 375 C with the capacity of 5.9 wt% of hydrogen in total. Moreover, after the addition of the TiF3 additive, the results show that the dehydrogenation process is still occurred in three stages. The onset desorption temperature at the first stage has been reduced for 30 C as compared to the un-doped MgH2eNa3AlH6 composite. The 4MgH2eNa3AlH6 doped with TiF3 has started to release hydrogen at 140 C with a capacity of 1.0 wt% of hydrogen. Meanwhile the dehydrogenation process for the second and third stages have occurred at 270 Ce355 C and 360 Ce400 C, respectively.
Sorption kinetics properties
Fig. 1 e XRD spectra of the 2NaHeNaAlH4 mixture after 20 h of milling.
In order to investigate the reversibility of the MgH2eNa3AlH6e TiF3 composite, the rehydrogenation of the dehydrogenated sample has been studied. The absorption kinetic of 4MgH2e Na3AlH6-10 wt% TiF3 composite is carried out at the temperature of 320 C and 33 atm of hydrogen. For comparison, the rehydrogenation kinetic of the un-doped 4MgH2eNa3AlH6 composite is also measured under the same parameters. As
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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displayed in Fig. 3, about 3.7 wt% of hydrogen has been absorbed by the 4MgH2eNa3AlH6-10 wt% TiF3 composite in 60 min. Meanwhile only 3.1 wt% of hydrogen has been absorbed by the 4MgH2eNa3AlH6 composite for the similar time period. Based on the result, it is reasonable to conclude that the doped composite has shown a better performance on the rehydrogenation kinetic compared to the un-doped composite. The TiF3 component has improves the hydrogen absorption property of the MgH2eNa3AlH6 system. In order to determine the dehydrogenation kinetic performance of the 4MgH2eNa3AlH6-10 wt% TiF3 composite, the dehydrogenation has been investigated at 320 C for 60 min. The desorption kinetic of the un-doped 4MgH2eNa3AlH6 composite has also been determined under similar condition as shown in Fig. 4. From the result, the un-doped 4MgH2e Na3AlH6 composite has desorbed 0.85 wt% of hydrogen within 60 min. The achieved desorption capacity is almost similar to our previous work [43] which was about 0.95 wt% in 60 min. Meanwhile, the 4MgH2eNa3AlH6-10 wt% TiF3 composite has released about 1.1 wt% of hydrogen for the same period. These two results exhibit that the TiF3 additive also plays an important role in improving the performance of the dehydrogenation kinetic of MgH2eNa3AlH6 system.
Fig. 4 e Isothermal dehydrogenation kinetics curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites at 320 C.
Differential scanning calorimetry Fig. 5 shows the DSC curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites. Based on the DSC traces of the 4MgH2eNa3AlH6 composite, two endothermic peaks at about 255 C and 390 C are observed. It is believed that the two endothermic DSC peaks are corresponding to the decomposition processes of the Na3AlH6 and the MgH2. Meanwhile, the characteristic peaks of the 4MgH2eNa3AlH610 wt% TiF3 composite also showed two endothermic peaks; which are at 240 C and 380 C. Based on the results obtained from the DSC analysis, the onset decomposition temperature is higher compared to the TPD results as in Fig. 2. The differences have happened due to different measurement conditions between the two methods. The DSC measurement has
Fig. 5 e DSC curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 samples at a heating rate of 20 C/min.
been conducted at a heating rate of 20 C/min under 1 atm of an argon flow, whereas the TPD measurement is carried out at 1 atm with 5 C/min of heating rate. These differences have caused different reading by the equipments as discussed in our previous paper [53]. In order to calculate the apparent activation energy of the MgH2, the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites, the Kissinger equation has been used and is presented as follows: h . i ln b T2p ¼ EA =RTp þ A
Fig. 3 e Isothermal rehydrogenation kinetic curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites at 320 C and 33 atm.
(2)
where b is the heating rate, Tp is the peak temperature in the DSC curve, R is the gas constant, and A is the linear constant. Thus, the apparent activation energy, EA, can be obtained from the slope in a plot of ln [b/T2p] versus 1000/Tp. The DSC traces for the as-milled MgH2, the 4MgH2eNa3AlH6 and the
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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4MgH2eNa3AlH6-10 wt% TiF3 composites at different heating rates were shown as in Fig. 6(a), (b) and (c), respectively. Based on the Kissinger plot in Fig. 7, the apparent activation energy for the as-milled MgH2 is found to be 158 kJ/mol. This result is closed to the result that has been published by other researchers with value of 160 kJ/mol [54]. Meanwhile, the apparent activation energy of the 4MgH2eNa3AlH6 composite has been reduced to 140 kJ/mol, 18 kJ/mol lesser compared to the as-milled MgH2. Furthermore, the addition of 10 wt% of the TiF3 on the 4MgH2eNa3AlH6, has reduced the apparent activation energy to 124 kJ/mol. The reduction of the apparent activation energy after the addition of TiF3 has suggested that the TiF3 additive also plays an important role in reducing the activation energy of the MgH2eNa3AlH6 system.
Surface morphology The scanning electron microscopy (SEM) images of the asreceived MgH2, the as-milled MgH2, the as-milled Na3AlH6, the as-received TiF3, the as-milled 4MgH2eNa3AlH6 and the as-milled 4MgH2eNa3AlH6-10 wt% TiF3 are shown as in Fig. 8. The SEM image of the as-received MgH2 (Fig. 8(a)) shows the particles with an angular shape that are larger than 50 mm. As for the 1 h of ball-milled MgH2, the particle sizes are reduced significantly and less homogenous as can been seen in Fig. 8 (b). On the other hand, the Na3AlH6 particles are agglomerated with coral-like shapes (Fig. 8(c)). Meanwhile, Fig. 8(d) represents the as-received TiF3 particles without further purification which are larger than 50 mm. Furthermore, the particle sizes of the ball-milled MgH2 with Na3AlH6 have decreased drastically as shown in Fig. 8 (e). It is also observed that the addition of TiF3 on the 4MgH2eNa3AlH6 composite
Fig. 7 e Kissinger's analysis of (a) the as-milled MgH2, (b) the 4MgH2eNa3AlH6 and (c) the 4MgH2eNa3AlH6-10 wt% TiF3.
(Fig. 8 (f)) has resulted in smaller particle sizes than the undoped 4MgH2eNa3AlH6 composite. The hydrogen sorption properties will be improved for smaller particle sizes as it lessens the diffusion length of the hydrogen and will increase the particle reactive surfaces [55].
X-ray diffraction analysis XRD measurements are carried out to clarify the dehydrogenation mechanism in every stage of the 4MgH2eNa3AlH6 composite. As shown in Fig. 9(a), the MgH2, the Na3AlH6 and
Fig. 6 e DSC traces of the (a) as-milled MgH2, (b) the 4MgH2eNa3AlH6 and (c) the 4MgH2eNa3AlH6-10 wt% TiF3 composites at different heating rates. Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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Fig. 8 e SEM images of (a) the as-received MgH2, (b) the as-milled MgH2, (c) the as-milled Na3AlH6, (d) the as-received TiF3, (e) the as-milled 4MgH2eNa3AlH6 and (f) the as-milled 4MgH2eNa3AlH6-10 wt% TiF3.
the metastable b-Na3AlH6 peaks are detected in the 4MgH2e Na3AlH6 composite after 1 h of ball-milling. After the first stage of dehydrogenation process at 230 C (Fig. 9(b)), new phases, the perovskite-type hydride NaMgH3 and the unreacted MgH2 are detected corresponding to the disappearance of Na3AlH6 phase after the heating process. In addition, few peaks of the Al clearly present in this stage. This result has agreed with the previous work [43], which the Na3AlH6 is believed to react with the MgH2 to form the NaMgH3 and the Al products. The decomposition process is shown as follows: Na3 AlH6 þ 3MgH2 /3NaMgH3 þ Al þ H2
(3)
In Fig. 9(c), the NaH phase is observed while the intermediate phase Mg17Al12 and the Mg have dominated the XRD spectra pattern for the dehydrogenated sample after heating to 375 C. In addition, the NaMgH3 and the MgH2 phases are
Fig. 9 e XRD patterns of the 4MgH2eNa3AlH6 composite after ball milling for 1 h (a), and after dehydrogenation at 230 C (b), 375 C and (c) at 450 C.
completely undetected. These findings have demonstrated that the dehydrogenation process at this stage is resulted from the self decomposition of the MgH2 (Eq. (4)). The reactions of the excessive MgH2 with the Al and the decomposition of NaMgH3 are shown as in Eqs (5) and (6): MgH2 /Mg þ H2
(4)
17MgH2 þ 12Al/Mg17 Al12 þ 17H2
(5)
NaMgH3 /NaH þ Mg þ H2
(6)
As the heating process is further increased to 450 C (Fig. 9 (d)), the Na peaks are discovered and can be concluded that the NaH component is completely decomposed as shown in Eq. (7): NaH/Na þ H2
(7)
XRD measurements are performed to further investigate the possible reaction of each dehydrogenation stages of MgH2eNa3AlH6 composite with the addition of 10 wt% of TiF3. Fig. 10 exhibits the XRD patterns of the 4MgH2eNa3AlH6-10 wt % TiF3 composite (a) after 1 h of ball milling, (b) after dehydrogenation at 200 C, (c) 360 C and (d) at 450 C. The MgH2 and the Na3AlH6 along with the metastable b-Na3AlH6 peaks are detected after 1 h of ball milling as seen in Fig. 10(a). The TiF3 peak is not detected from the XRD spectra due to small amount of the TiF3 additive. Meanwhile, after heating process at 200 C, besides the presence of the NaMgH3, the MgH2 and the Al species, new phases, the NaF, the AlF3 and the Al3Ti are identified from the XRD spectra (Fig. 10(b)). This result indicated that the Ti-containing and F-containing species are reacted with the Al and the Na components to form new species that acted as the active species. These new species are responsible on the improvement of desorption temperature of MgH2eNa3AlH6 system as shown in Fig. 2. The new phases also can be detected after being heated to 360 C (Fig. 10 (c)) and 450 C (Fig. 10 (d)).
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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Mg17 Al12 þ ð17 2yÞH2 /yMg2 Al3 þ ð17 2yÞMgH2 þð12 3yÞAl
Fig. 10 e XRD patterns of the 4MgH2eNa3AlH6-10 wt% TiF3 composite (a) after ball milling for 1 h, (b) after dehydrogenation at 200 C, (c) 360 C and (d) 450 C.
In order to determine the reaction mechanism of the rehydrogenation stage, XRD analyses are conducted on the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites. The analyses are conducted after the rehydrogenation process at 320 C under 33 atm of hydrogen pressure. From the XRD patterns, peaks of the MgH2, the NaMgH3, the Al3Mg2, the Al and the MgO can be discovered from the 4MgH2eNa3AlH6 composite (Fig. 11 (a)) and after the addition of TiF3 on the 4MgH2eNa3AlH6 composite (Fig. 11 (b)). In addition, peaks of the NaF, the AlF3 and the Al3Ti are recognized in the rehydrogenated sample of the doped composite (Fig. 11 (b)). These peaks are previously detected in the dehydrogenated sample of MgH2eNa3AlH6eTiF3 composite as shown in Fig. 10. Meanwhile, as displayed by the XRD spectra on the un-doped and the doped sample, the disappearance of Mg17Al12 and Mg phases after the rehydrogenation process has suggested that the MgH2 has been fully transformed as in Eq. (8):
(8)
According to the result, the formations of the NaF, the AlF3 and the Al3Ti during the heating process from the reaction of the MgH2eNa3AlH6 with the TiF3 have played an important role in the enhancement of the MgH2eNa3AlH6 destabilized system. As reported by Ivanov et al. [56], the NaF and the NaCl have been found to modify the magnesium particle surfaces. They discussed that the addition of NaF and NaCl with magnesium has led to the intercourse of magnesium particles and has increased the specific surface of the sample. Their discussion was supported by the SEM result where the particle sizes of the MgH2eNa3AlH6 was found to be smaller after the addition of the TiF3. Meanwhile, Kang et al. [57] found that the reversible hydrogenation of the NaAlH4 was improved after a long period of mechanical milling with the Al3Ti. Furthermore, Yuan et al. [58] studied the addition of AlF3 on the LiBH4 composite. The doped-LiBH4 started to release hydrogen at about 100 C, which was 80 C lower compared to the as-milled LiBH4. On the other hand, the formation of active species which has led to the improvement of hydrogen storage properties was also reported by Ouyang and his co-workers [59]. They claimed that the formation of CeH2.73 and Ni species from the hydrogenation of as-melt Mg80Ce18Ni2 alloy had showed an excellent hydrogen storage performance. With the presence of CeH2.73 and Ni, the nanocomposite started to release hydrogen at a lower desorption temperature with a capacity of more than 4.0 wt% of H2 and had higher kinetics rate. The nanocomposites also have long cycle life. In addition, the hydrogenation properties of Mg also could be improved by forming a composite structure as discussed by Zhu et al. [60]. They believe that the components that were combined with Mg can catalyze the hydrogenation reaction of Mg. Therefore, based on the literature discussed, it is reasonable to conclude that the TiF3 component in the MgH2eNa3AlH6eTiF3 composite plays a catalytic role through the formation of the NaF, the AlF3 and the Al3Ti catalytic species. These active species may acted as the active sites for the nucleation and growth of the dehydrogenation products thus enhanced the hydrogen storage properties of the MgH2eNa3AlH6.
Conclusion
Fig. 11 e XRD patterns after the rehydrogenation process at 320 C of (a) the 4MgH2eNa3AlH6 composite (a) and 4MgH2eNa3AlH6-10 wt% TiF3 composite (b).
In summary, the hydrogen storage properties of MgH2e Na3AlH6 system has been improved with the introduction of TiF3 additive. Based on the TPD results, the dehydrogenation process of 4MgH2eNa3AlH6-10 wt% TiF3 has involved three steps which is similar to the 4MgH2eNa3AlH6 composite. The onset desorption temperature of the TiF3 doped with 4MgH2e Na3AlH6 composite has been reduced to 140 C as compared to the un-doped composite (170 C) at the first stage. In addition, the re/desorption kinetics of MgH2eNa3AlH6 system have been improved with the addition of TiF3. Meanwhile, the presented Kissinger plot has shown that the apparent activation energy of the H-desorption of MgH2 in the 4MgH2e Na3AlH6 composite has been reduced for about 16 kJ/mol with the addition of 10 wt% of TiF3. Based on the result, it is
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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believed that these improvements are because of the formation of the NaF, the AlF3 and the Al3Ti catalytic species during the heating process. The formed active species have reinforced the interaction between MgH2 and Na3AlH6 and have further enhanced the MgH2eNa3AlH6 hydrogen storage properties.
[13] [14]
[15]
Acknowledgements [16]
This work was supported by Ministry of Higher Education Malaysia through the Fundamental Research Grant Scheme (FRGS 59362). The authors would like to acknowledge the Universiti Malaysia Terengganu for providing the facilities to run this project. F. A. Halim Yap would like to thank Universiti Malaysia Terengganu for his BUMT scholarship.
[17]
[18]
references [19] [1] Chen P, Zhu M. Recent progress in hydrogen storage. Mater Today 2008;11:36e43. [2] Satyapal S, Petrovic J, Read C, Thomas G, Ordaz G. The US department of energy's national hydrogen storage project: progress towards meeting hydrogen-powered vehicle requirements. Catal Today 2007;120:246e56. [3] Walker SB, Mukherjee U, Fowler M, Elkamel A. Benchmarking and selection of power-to-gas utilizing electrolytic hydrogen as an energy storage alternative. Int J Hydrogen Energy 2016;41:7717e31. [4] Bailera M, Kezibri N, Romeo LM, Espatolero S, Lisbona P, Bouallou C. Future applications of hydrogen production and CO2 utilization for energy storage: hybrid power to gasoxycombustion power plants. Int J Hydrogen Energy 2017;42:13625e32. [5] Peng DD, Fowler M, Elkamel A, Almansoori A, Walker SB. Enabling utility-scale electrical energy storage by a power-togas energy hub and underground storage of hydrogen and natural gas. J Nat Gas Sci Eng 2016;35(Part A):1180e99. [6] Eypasch M, Schimpe M, Kanwar A, Hartmann T, Herzog S, Frank T, et al. Model-based techno-economic evaluation of an electricity storage system based on liquid organic hydrogen carriers. Appl Energy 2017;185(Part 1):320e30. [7] Liu S-Y, Kundu P, Huang T-W, Chuang Y-J, Tseng F-G, Lu Y, et al. Quasi-2D liquid cell for high density hydrogen storage. Nano Energy 2017;31:218e24. [8] Zeng D-W, Xiao R, Zeng J-M, Zhang H-Y. Liquid foam assisted solegel synthesis of iron oxides for hydrogen storage via chemical looping. Int J Hydrogen Energy 2016;41:13923e33. [9] Callini E, Aguey-Zinsou K-F, Ahuja R, Ares JR, Bals S, Bili skov N, et al. Nanostructured materials for solid-state hydrogen storage: a review of the achievement of COST Action MP1103. Int J Hydrogen Energy 2016;41:14404e28. [10] Petit J-F, Miele P, Demirci UB. Ammonia borane H3N-BH3 for solid-state chemical hydrogen storage: different samples with different thermal behaviors. Int J Hydrogen Energy 2016;41:15462e70. [11] Lototskyy M, Yartys VA. Comparative analysis of the efficiencies of hydrogen storage systems utilising solid state H storage materials. J Alloy Compd 2015;645(Suppl. 1):S365e73. [12] Padmini M, Kiran SK, Lakshminarasimhan N, Sathish M, Elumalai P. High-performance solid-state hybrid energystorage device consisting of reduced graphene-oxide
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
anchored with NiMn-layered double hydroxide. Electrochim Acta 2017;236:359e70. Schlapbach L, Zu¨ttel A. Hydrogen-storage materials for mobile applications. Nature 2001;414:353e8. Liang C, Gao M, Pan H, Liu Y, Yan M. Effect of gas back pressure on hydrogen storage properties and crystal structures of Li2Mg(NH)2. Int J Hydrogen Energy 2014;39:17754e64. Murthy SS, Kumar EA. Advanced materials for solid state hydrogen storage:“Thermal engineering issues”. Appl Therm Eng 2014;72:176e89. Ouyang L, Tang J, Zhao Y, Wang H, Yao X, Liu J, et al. Express penetration of hydrogen on Mg(10ı3) along the close-packedplanes. Sci Rep 2015;5, 10776. Huang M, Ouyang L, Wang H, Liu J, Zhu M. Hydrogen generation by hydrolysis of MgH2 and enhanced kinetics performance of ammonium chloride introducing. Int J Hydrogen Energy 2015;40:6145e50. Ismail M, Zhao Y, Yu XB, Nevirkovets IP, Dou SX. Significantly improved dehydrogenation of LiAlH4 catalysed with TiO2 nanopowder. Int J Hydrogen Energy 2011;36:8327e34. Zuttel A. Materials for hydrogen storage. Mater Today 2003;6:24e33. Wang H, Zhang J, Liu JW, Ouyang LZ, Zhu M. Improving hydrogen storage properties of MgH2 by addition of alkali hydroxides. Int J Hydrogen Energy 2013;38:10932e8. Milosevic S, Milanovic I, Mamula BP, Dukic A, Rajnovic D, Pasquini L, et al. Hydrogen desorption properties of MgH2 catalysed with NaNH2. Int J Hydrogen Energy 2013;38:12223e9. Kiyobayashi T, Srinivasan SS, Sun D, Jensen CM. Kinetic study and determination of the enthalpies of activation of the dehydrogenation of titanium-and zirconium-doped NaAlH4 and Na3AlH6. J Phys Chem A 2003;107:7671e4. Jiang Z, Pan Q, Xu J, Fang T. Current situation and prospect of hydrogen storage technology with new organic liquid. Int J Hydrogen Energy 2014;39:17442e51. Yu XB, Yang ZX, Liu HK, Grant DM, Walker GS. The effect of a Ti-V-based BCC alloy as a catalyst on the hydrogen storage properties of MgH2. Int J Hydrogen Energy 2010;35:6338e44. Yu HZ, Dai JH, Song Y. Catalytic effect of Ti on dehydrogenation of Na3AlH6: a first principles investigation. Int J Hydrogen Energy 2015;40:11478e83. Halim Yap FA, Mustafa NS, Ismail M. A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2. RSC Adv 2015;5:9255e60. Mustafa NS, Ismail M. Hydrogen sorption improvement of MgH2 catalyzed by CeO2 nanopowder. J Alloy Compd 2017;695:2532e8. Mustafa NS, Sulaiman NN, Ismail M. Effect of SrFe12O19 nanopowder on the hydrogen sorption properties of MgH2. RSC Adv 2016;6:110004e10. Jalil Z, Rahwanto A, Mulana F, Mustanir. Desorption temperature characteristic of Mg-based hydrides catalyzed by nano-SiO2 prepared by high energy ball milling. Int J Technol 2016;7:1301e6. Sulaiman NN, Ismail M. Enhanced hydrogen storage properties of MgH2 co-catalyzed with K2NiF6 and CNTs. Dalton Trans 2016;45:19380e8. House SD, Vajo JJ, Ren C, Rockett AA, Robertson IM. Effect of ball-milling duration and dehydrogenation on the morphology, microstructure and catalyst dispersion in Nicatalyzed MgH2 hydrogen storage materials. Acta Mater 2015;86:55e68. Ismail M. The hydrogen storage properties of destabilized MgH2eAlH3 (2:1) system. Mater Today Proc 2016;3(Suppl. 1):S80e7.
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e9
[33] Liu DM, Huang WJ, Si TZ, Zhang QA. Hydrogen storage properties of LiBH4 destabilized by SrH2. J Alloy Compd 2013;551:8e11. [34] Ibikunle AA, Goudy AJ. Kinetics and modeling study of a Mg(BH4)2/Ca(BH4)2 destabilized system. Int J Hydrogen Energy 2012;37:12420e4. [35] Ismail M, Zhao Y, Yu XB, Mao JF, Dou SX. The hydrogen storage properties and reaction mechanism of the MgH2NaAlH4 composite system. Int J Hydrogen Energy 2011;36:9045e50. [36] Ouyang L, Cao Z, Wang H, Hu R, Zhu M. Application of dielectric barrier discharge plasma-assisted milling in energy storage materials e a review. J Alloy Compd 2017;691:422e35. [37] Ouyang LZ, Ye SY, Dong HW, Zhu M. Effect of interfacial free energy on hydriding reaction of MgeNi thin films. Appl Phys Lett 2007;90, 021917. [38] Ouyang LZ, Cao ZJ, Li LL, Wang H, Liu JW, Min D, et al. Enhanced high-rate discharge properties of La11.3Mg6.0Sm7.4Ni61.0Co7.2Al7.1 with added graphene synthesized by plasma milling. Int J Hydrogen Energy 2014;39:12765e72. [39] Mao JF, Yu XB, Guo ZP, Liu HK, Wu Z, Ni J. Enhanced hydrogen storage performances of NaBH4-MgH2 system. J Alloy Compd 2009;479:619e23. [40] Gosalawit-Utke R, Milanese C, Nielsen TK, Karimi F, Saldan I, Pranzas K, et al. Nanoconfined 2LiBH4-MgH2 for reversible hydrogen storages: reaction mechanisms, kinetics and thermodynamics. Int J Hydrogen Energy 2013;38:1932e42. [41] Liu S-S, Sun L-X, Zhang J, Zhang Y, Xu F, Xing Y-H, et al. Hydrogen storage properties of destabilized MgH2eLi3AlH6 system. Int J Hydrogen Energy 2010;35:8122e9. [42] Yang J, Wang X, Mao J, Chen L, Pan H, Li S, et al. Investigation on reversible hydrogen storage properties of Li3AlH6/2LiNH2 composite. J Alloy Compd 2010;494:58e61. [43] Ismail M, Zhao Y, Dou SX. An investigation on the hydrogen storage properties and reaction mechanism of the destabilized MgH2-Na3AlH6 (4:1) system. Int J Hydrogen Energy 2013;38:1478e83. [44] Ma LP, Wang P, Cheng HM. Improving hydrogen sorption kinetics of MgH2 by mechanical milling with TiF3. J Alloy Compd 2007;432:L1e4. [45] Kang X-D, Wang P, Cheng H-M. Advantage of TiF3 over TiCl3 as a dopant precursor to improve the thermodynamic property of Na3AlH6. Scr Mater 2007;56:361e4. [46] Mao J, Guo Z, Nevirkovets IP, Liu HK, Dou SX. Hydrogen de-/ absorption improvement of NaBH4 catalyzed by titaniumbased additives. J Phys Chem C 2011;116:1596e604.
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[47] Juahir N, Mustafa NS, Halim Yap FA, Ismail M. Study on the hydrogen storage properties and reaction mechanism of NaAlH4-Mg(BH4)2 (2:1) with and without TiF3 additive. Int J Hydrogen Energy 2015;40:7628e35. [48] Mao J, Guo Z, Liu H. Improved hydrogen sorption performance of NbF5-catalysed NaAlH4. Int J Hydrogen Energy 2011;36:14503e11. [49] Wang Z, Tao S, Deng J, Zhou H, Yao Q. Significant improvement in the dehydriding properties of perovskite hydrides, NaMgH3, by doping with K2TiF6. Int J Hydrogen Energy 2017;42:8554e9. [50] Zhang W, Wang H, Cao H, He T, Guo J, Wu G, et al. Effects of doping FeCl3 on hydrogen storage properties of Li-NH system. Prog Nat Sci Mater Int 2017;27:139e43. [51] Huot J, Boily S, Gu¨ther V, Schulz R. Synthesis of Na3AlH6 and Na2LiAlH6 by mechanical alloying. J Alloy Compd 1999;283:304e6. [52] Wang P, Kang X, Cheng H. Direct formation of Na3AlH6 by mechanical milling NaH∕ Al with TiF3. Appl Phys Lett 2005;87, 071911. [53] Ismail M, Halim Yap FA, Sulaiman NN, Ishak MHI. Hydrogen storage properties of a destabilized MgH2-Sn system with TiF3 addition. J Alloy Compd 2016;678:297e303. [54] Ouyang L, Cao Z, Wang H, Liu J, Sun D, Zhang Q, et al. Enhanced dehydriding thermodynamics and kinetics in Mg (In)eMgF2 composite directly synthesized by plasma milling. J Alloy Compd 2014;586:113e7. [55] Liang G. Synthesis and hydrogen storage properties of Mgbased alloys. J Alloy Compd 2004;370:123e8. [56] Ivanov E, Konstanchuk I, Bokhonov B, Boldyrev V. Comparative study of first hydriding of MgeNaF and MgeNaCl mechanical alloys. J Alloy Compd 2003;360:256e65. [57] Kang XD, Wang P, Song XP, Yao XD, Lu GQ, Cheng HM. Catalytic effect of Al3Ti on the reversible dehydrogenation of NaAlH4. J Alloy Compd 2006;424:365e9. [58] Yuan PP, Liu BH, Zhu HP, Pan WY, Li ZP. Destabilized dehydrogenation reaction of LiBH4 by AlF3. J Alloy Compd 2013;557:124e9. [59] Ouyang L, Yang X, Zhu M, Liu J, Dong H, Sun D, et al. Enhanced hydrogen storage kinetics and stability by synergistic effects of in situ formed CeH2. 73 and Ni in CeH2. 73-MgH2-Ni nanocomposites. J Phys Chem C 2014;118:7808e20. [60] Zhu M, Wang H, Ouyang LZ, Zeng M. Composite structure and hydrogen storage properties in Mg-base alloys. Int J Hydrogen Energy 2006;31:251e7.
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3 F.A. Halim Yap, M.S. Yahya, M. Ismail* School of Ocean Engineering, University Malaysia Terengganu, 21030, Kuala Terengganu, Malaysia
article info
abstract
Article history:
In this work, we have investigated the hydrogen release and uptake pathways storage
Received 8 May 2017
properties of the MgH2eNa3AlH6 with a molar ratio of 4:1 and doped with 10 wt% of TiF3
Received in revised form
using a mechanical alloying method. The doped composite was found to have a significant
21 June 2017
reduction on the hydrogen release temperature compared to the un-doped composite
Accepted 2 July 2017
based on the temperature-programme-desorption result. The first stage of the onset
Available online xxx
desorption temperature of MgH2eNa3AlH6 was reduced from 170 C to 140 C with the
Keywords:
released hydrogen were observed for the 4MgH2eNa3AlH6-10 wt% TiF3 composite. The
addition of the TiF3 additive. Three dehydrogenation steps with a total of 5.3 wt% of Hydrogen energy
re/dehydrogenation kinetics of 4MgH2eNa3AlH6 system were significantly improved with
Hydrogen storage
the addition of TiF3. Kissinger analyses showed that the apparent activation energy, EA, of
Magnesium hydride
the 4MgH2eNa3AlH6 doped composite was 124 kJ/mol, 16 kJ/mol and 34 kJ/mol lower for
Sodium alanate
un-doped composite and the as-milled MgH2, respectively. It was believed that the enhancements of the MgH2eNa3AlH6 hydrogen storage properties with the addition of TiF3 were due to formation of the NaF, the AlF3 and the Al3Ti species. These species may played a synergetic catalytic role in improving the hydrogenation properties of the MgH2eNa3AlH6 system. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction In years, it is extensively acknowledged that hydrogen, as an energy carrier will become the fuel for most vehicles due to its benefits such as environmental friendly and high energy density. However, problems related to hydrogen storage have prohibited the commercialization of its application like renewable energy sources [1,2]. A lot of works have been focussed on the improvement of the hydrogen storage whether in gaseous state [3e5], cryogenic liquid state [6e8] or solid state [9e12]. Safety concerns, provision of spaces for storage [13,14] and energy efficiency [15] are among the factors why solid-state hydrogen storage has been considered as a
promising method compared to other conventional storage methods. Consequently researchers have shown an interest on the solid-state hydrogen storage materials especially light metal hydrides [16,17] and complex hydrides [18]. High hydrogen storage capacity is one of the reasons why this material has attracted researchers' attention. In addition, metal hydrides can store large amounts of hydrogen in a compact and safe ways [19]. However, metal hydrides such as MgH2 start to release hydrogen at high temperature [20,21] and complex hydrides such as Na3AlH6 suffer from slow rate of dehydrogenation kinetics [22]. These drawbacks are the major obstacles in the development of hydrogen energy applications. Therefore, studies are conducted to enhance the hydrogen
* Corresponding author. E-mail address: [email protected] (M. Ismail). http://dx.doi.org/10.1016/j.ijhydene.2017.07.012 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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storage properties of MgH2 and Na3AlH6 in order to meet the technical target given by the U.S. Department of Energy [23]. Several approaches have been used in improving the decomposition temperature and rate of kinetic such as adding with a catalyst [24e30], reducing the particles size by ball milling [31], and destabilizing the hydrides [32e35], and a ball-milling process assisted by dielectric-barrier discharge plasma for dual-tuning the thermodynamics and kinetics [36e38]. Among the approaches, the destabilization system has been considered as a promising solution to this problem. Many efforts were concentrated on combining metal with other metal hydrides such as NaBH4eMgH2 [39], LiBH4eMgH2 [40], MgH2eNaAlH4 [35], MgH2eLi3AlH6 [41], LiNH2eLi3AlH6 [42], and MgH2eNa3AlH6 [43]. In this context, reduction on the desorption temperature and improvement on the rate of sorption kinetics from our previous work [43] on the system of MgH2 destabilized with Na3AlH6 have motivated us to work further so that it can fulfil the requirement for the hydrogen energy application. As discussed in the previous work, the formation of the NaMgH3, Al and H2 from the reaction between MgH2 and Na3AlH6 help to reduce the dehydrogenation temperature of Na3AlH6 for about 55 C compared to the asmilled Na3AlH6. Meanwhile, at 275 C, the Al component destabilized the MgH2 to form the intermetallic compound (Mg17Al12) that led to the improvement of the MgH2 desorption temperature property. However, the finding still did not fulfil the requirement in a commercial field for the practical application. Therefore, further work has been carried out in order to enhance the hydrogenation properties of the MgH2e Na3AlH6 system with the addition of an additive. To the best of the authors' knowledge, there is no work has been reported on the understanding of the additive effects on MgH2eNa3AlH6 hydrogen storage properties. Therefore, it is interesting to explore the possible influence of an additive on the improvement of hydrogenation properties of the MgH2e Na3AlH6 system. To date, there is no reported literature on the improvement of the MgH2eNa3AlH6 system with TiF3 as the additive. Many literature have reported the effects of TiF3 on metal hydrides [44] and complex hydrides [45,46], where the formation of Ti and F anion played the catalytic roles that led to the enhancement of hydrogen storage performance. According to the work done by Juahir et al. [47], the Ti-containing and F-containing phases through the formations of NaF and Al3Ti active species had played a catalytic role in promoting the improvement of NaAlH4eMg(BH4)2 hydrogen storage properties. In addition, Mao et al. [46] proved that the Ticontaining species and the active function of the F anion had improved the hydrogenation properties of NaBH4. On the other hand, tremendous works by other researchers in improving the hydrogen storage properties of hydride materials catalyzed by the metal based-fluoride have been published. Recently, Mao et al. [48] found that the hydrogen storage performance of the NaAlH4 was improved after the addition of NbF5. DSC results indicate that the ball-milled NaAlH4e0.03NbF5 sample lowered the completion temperature for the first two steps dehydrogenation by 71 C compared to the pristine NaAlH4 sample. More recently, Wang et al. [49] found that the desorption temperature of the NaMgH3 was reduced for about 252 C with the addition of K2TiF6. Furthermore, catalysts made of metal based-chloride have
attracted researchers' attentions. Works done by Zhang et al. [50] showed that by introducing FeCl3 as a catalyst to the LiNH2e2LiH, the dehydrogenation kinetics of the system was improved. They stated that the temperature was reduced and the dehydrogenation activation energy was lowered from 102.45 kJ/mol to 87.52 kJ/mol. Hence, it is noteworthy to believe that upon heating, the TiF3 additive will react with the MgH2eNa3AlH6 composite by an in situ reactions to form active species that will enhance the hydrogen sorption properties of the MgH2eNa3AlH6 system. In this work, TiF3 was introduced to the MgH2eNa3AlH6 composite by ball milling method. The aim is to study the performance improvement on hydrogen storage properties of the MgH2eNa3AlH6 system. The hydrogen storage properties, the thermal analysis, the reaction mechanisms as well as the surface morphology of the MgH2eNa3AlH6eTiF3 were investigated in this study. A Sievert-type pressure-compositiontemperature (PCT) apparatus, differential a scanning calorimetry (DSC), a scanning electron microscopy (SEM) and an Xray diffraction (XRD) were used for the investigation. The possible mechanism of the composite supported by the results from the study was discussed.
Experimental Starting materials, MgH2 (hydrogen storage grade), NaAlH4 (hydrogen storage grade, 93% purity), NaH (dry, 95% purity) and TiF3 were purchased from Sigma Aldrich. All the materials were used directly without any further purification. All samples preparation for every analysis was performed in an argon filled glove box in order to prevent the samples from oxidation. The Na3AlH6 composite was synthesized through the mechanochemical reaction between the NaH and the NaAlH4 [51]. The mixture of NaH and NaAlH4, with a mole ratio of 2:1, was milled for 20 h in a planetary ball mill (NQM-0.4) with the ball to powder ratio (BPR) of 40:1 at a rotation speed of 400 rpm. The sample of MgH2 and Na3AlH6 composite with a molar ratio of 4:1 was prepared using similar method but with milling time of 1 h only. For comparison purposes, the pristine MgH2 and the Na3AlH6 were also prepared by 1 h of milling time. Temperature-programmed-desorption (TPD) and ab/ desorption kinetic experiments were conducted in a Sievertstype pressure-composition-temperature (PCT) apparatus (Advanced Materials Corporation). For each sample, about 80 mg was loaded into a sample vessel in a glove box. For the TPD experiment, all samples were heated from room temperature to 450 C with a heating rate of 5 C/min in a vacuum chamber so that the lowest decomposition temperature and the amount of hydrogen desorbed can be determined. Meanwhile the rehydriding and dehydriding kinetics were studied at 320 C under hydrogen pressures of 33 atm and 1 atm, respectively. Differential scanning calorimetry (DSC) measurement of the dehydrogenation process was conducted using a thermogravimetric analysis/differential scanning calorimeter (TGA/DSC) 1 from Mettler Toledo. Each sample with an amount of 5e10 mg was loaded into an alumina crucible in the glove box. The samples were heated from room temperature to 500 C under an argon flow of 50 ml/min, and different
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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heating rates were used. An empty alumina crucible was used as a reference. Samples for the scanning electron microscopy (SEM) were placed on a surface of carbon tape and were coated with gold under vacuum condition to avoid contact with air. The surface morphology of the samples was analysed by scanning electron microscope (SEM; JEOL JSM-6360LA). Meanwhile, the phase structure analysis of the samples after ball milling and after desorption temperature, as well as after rehydrogenation kinetics, were determined by X-ray diffraction (Rigaku MiniFlex X-ray diffractometer with Cu Ka radiation). The samples were scanned over diffraction angles of 20 e80 at a speed of 2.00 /min.
Results and discussions Mechanical synthesis of Na3AlH6 Fig. 1 displays the XRD pattern of the 2NaHeNaAlH4 mixture after milling for 20 h. As can been seen from the XRD spectra, only peaks of the Na3AlH6 can be detected, while peaks of the starting materials, the NaH and the NaAlH4 are absent. This result indicates that the solid-state reaction is completed between the components of the NaHeNaAlH4 (2:1) during the milling process, as represent in Eq. (1): 2NaH þ NaAlH4 /Na3 AlH6
(1)
The formation of the metastable b-Na3AlH6 phase is believed to happen during the milling process and the polymorphic transformation from Na3AlH6 to b-Na3AlH6 is partially occurred. This result is similar to other studies [51,52].
Dehydrogenation temperature The TPD performance of the as-milled MgH2, the as-milled Na3AlH6, the MgH2eNa3AlH6 and the MgH2eNa3AlH6eTiF3 composites are shown as in Fig. 2. From the graph, the as-
Fig. 2 e TPD curves of the as-milled MgH2, the as-milled Na3AlH6, the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6e TiF3 composites. (I, II and III phases refer to the first, second and third dehydrogenation stages, respectively).
milled MgH2 sample has started to release hydrogen at 350 C and has desorbed 7.4 wt% of hydrogen after 450 C. Meanwhile, the hydrogen has been released at the temperature of 230 C for the as-milled Na3AlH6 composite. As for the 4MgH2eNa3AlH6 composite, based on the results, three dehydrogenation stages have happened during the heating process. The stages are corresponding to the decomposition of the Na3AlH6 and the MgH2, with the onset desorption temperature has experienced a reduction as compared to the asprepared Na3AlH6 and the as-milled MgH2. As shown in the graph, the dehydrogenation process of the 4MgH2eNa3AlH6 composite has occurred in three stages. The first dehydrogenation process has started at the temperature of 170 C and has completed at 230 C with the capacity of 1.0 wt% of hydrogen. Meanwhile the second dehydrogenation process has taken place within the temperature of 270 Ce350 C and the third stage of the dehydrogenation has occurred at the temperature of 375 C with the capacity of 5.9 wt% of hydrogen in total. Moreover, after the addition of the TiF3 additive, the results show that the dehydrogenation process is still occurred in three stages. The onset desorption temperature at the first stage has been reduced for 30 C as compared to the un-doped MgH2eNa3AlH6 composite. The 4MgH2eNa3AlH6 doped with TiF3 has started to release hydrogen at 140 C with a capacity of 1.0 wt% of hydrogen. Meanwhile the dehydrogenation process for the second and third stages have occurred at 270 Ce355 C and 360 Ce400 C, respectively.
Sorption kinetics properties
Fig. 1 e XRD spectra of the 2NaHeNaAlH4 mixture after 20 h of milling.
In order to investigate the reversibility of the MgH2eNa3AlH6e TiF3 composite, the rehydrogenation of the dehydrogenated sample has been studied. The absorption kinetic of 4MgH2e Na3AlH6-10 wt% TiF3 composite is carried out at the temperature of 320 C and 33 atm of hydrogen. For comparison, the rehydrogenation kinetic of the un-doped 4MgH2eNa3AlH6 composite is also measured under the same parameters. As
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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displayed in Fig. 3, about 3.7 wt% of hydrogen has been absorbed by the 4MgH2eNa3AlH6-10 wt% TiF3 composite in 60 min. Meanwhile only 3.1 wt% of hydrogen has been absorbed by the 4MgH2eNa3AlH6 composite for the similar time period. Based on the result, it is reasonable to conclude that the doped composite has shown a better performance on the rehydrogenation kinetic compared to the un-doped composite. The TiF3 component has improves the hydrogen absorption property of the MgH2eNa3AlH6 system. In order to determine the dehydrogenation kinetic performance of the 4MgH2eNa3AlH6-10 wt% TiF3 composite, the dehydrogenation has been investigated at 320 C for 60 min. The desorption kinetic of the un-doped 4MgH2eNa3AlH6 composite has also been determined under similar condition as shown in Fig. 4. From the result, the un-doped 4MgH2e Na3AlH6 composite has desorbed 0.85 wt% of hydrogen within 60 min. The achieved desorption capacity is almost similar to our previous work [43] which was about 0.95 wt% in 60 min. Meanwhile, the 4MgH2eNa3AlH6-10 wt% TiF3 composite has released about 1.1 wt% of hydrogen for the same period. These two results exhibit that the TiF3 additive also plays an important role in improving the performance of the dehydrogenation kinetic of MgH2eNa3AlH6 system.
Fig. 4 e Isothermal dehydrogenation kinetics curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites at 320 C.
Differential scanning calorimetry Fig. 5 shows the DSC curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites. Based on the DSC traces of the 4MgH2eNa3AlH6 composite, two endothermic peaks at about 255 C and 390 C are observed. It is believed that the two endothermic DSC peaks are corresponding to the decomposition processes of the Na3AlH6 and the MgH2. Meanwhile, the characteristic peaks of the 4MgH2eNa3AlH610 wt% TiF3 composite also showed two endothermic peaks; which are at 240 C and 380 C. Based on the results obtained from the DSC analysis, the onset decomposition temperature is higher compared to the TPD results as in Fig. 2. The differences have happened due to different measurement conditions between the two methods. The DSC measurement has
Fig. 5 e DSC curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 samples at a heating rate of 20 C/min.
been conducted at a heating rate of 20 C/min under 1 atm of an argon flow, whereas the TPD measurement is carried out at 1 atm with 5 C/min of heating rate. These differences have caused different reading by the equipments as discussed in our previous paper [53]. In order to calculate the apparent activation energy of the MgH2, the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites, the Kissinger equation has been used and is presented as follows: h . i ln b T2p ¼ EA =RTp þ A
Fig. 3 e Isothermal rehydrogenation kinetic curves of the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites at 320 C and 33 atm.
(2)
where b is the heating rate, Tp is the peak temperature in the DSC curve, R is the gas constant, and A is the linear constant. Thus, the apparent activation energy, EA, can be obtained from the slope in a plot of ln [b/T2p] versus 1000/Tp. The DSC traces for the as-milled MgH2, the 4MgH2eNa3AlH6 and the
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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4MgH2eNa3AlH6-10 wt% TiF3 composites at different heating rates were shown as in Fig. 6(a), (b) and (c), respectively. Based on the Kissinger plot in Fig. 7, the apparent activation energy for the as-milled MgH2 is found to be 158 kJ/mol. This result is closed to the result that has been published by other researchers with value of 160 kJ/mol [54]. Meanwhile, the apparent activation energy of the 4MgH2eNa3AlH6 composite has been reduced to 140 kJ/mol, 18 kJ/mol lesser compared to the as-milled MgH2. Furthermore, the addition of 10 wt% of the TiF3 on the 4MgH2eNa3AlH6, has reduced the apparent activation energy to 124 kJ/mol. The reduction of the apparent activation energy after the addition of TiF3 has suggested that the TiF3 additive also plays an important role in reducing the activation energy of the MgH2eNa3AlH6 system.
Surface morphology The scanning electron microscopy (SEM) images of the asreceived MgH2, the as-milled MgH2, the as-milled Na3AlH6, the as-received TiF3, the as-milled 4MgH2eNa3AlH6 and the as-milled 4MgH2eNa3AlH6-10 wt% TiF3 are shown as in Fig. 8. The SEM image of the as-received MgH2 (Fig. 8(a)) shows the particles with an angular shape that are larger than 50 mm. As for the 1 h of ball-milled MgH2, the particle sizes are reduced significantly and less homogenous as can been seen in Fig. 8 (b). On the other hand, the Na3AlH6 particles are agglomerated with coral-like shapes (Fig. 8(c)). Meanwhile, Fig. 8(d) represents the as-received TiF3 particles without further purification which are larger than 50 mm. Furthermore, the particle sizes of the ball-milled MgH2 with Na3AlH6 have decreased drastically as shown in Fig. 8 (e). It is also observed that the addition of TiF3 on the 4MgH2eNa3AlH6 composite
Fig. 7 e Kissinger's analysis of (a) the as-milled MgH2, (b) the 4MgH2eNa3AlH6 and (c) the 4MgH2eNa3AlH6-10 wt% TiF3.
(Fig. 8 (f)) has resulted in smaller particle sizes than the undoped 4MgH2eNa3AlH6 composite. The hydrogen sorption properties will be improved for smaller particle sizes as it lessens the diffusion length of the hydrogen and will increase the particle reactive surfaces [55].
X-ray diffraction analysis XRD measurements are carried out to clarify the dehydrogenation mechanism in every stage of the 4MgH2eNa3AlH6 composite. As shown in Fig. 9(a), the MgH2, the Na3AlH6 and
Fig. 6 e DSC traces of the (a) as-milled MgH2, (b) the 4MgH2eNa3AlH6 and (c) the 4MgH2eNa3AlH6-10 wt% TiF3 composites at different heating rates. Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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Fig. 8 e SEM images of (a) the as-received MgH2, (b) the as-milled MgH2, (c) the as-milled Na3AlH6, (d) the as-received TiF3, (e) the as-milled 4MgH2eNa3AlH6 and (f) the as-milled 4MgH2eNa3AlH6-10 wt% TiF3.
the metastable b-Na3AlH6 peaks are detected in the 4MgH2e Na3AlH6 composite after 1 h of ball-milling. After the first stage of dehydrogenation process at 230 C (Fig. 9(b)), new phases, the perovskite-type hydride NaMgH3 and the unreacted MgH2 are detected corresponding to the disappearance of Na3AlH6 phase after the heating process. In addition, few peaks of the Al clearly present in this stage. This result has agreed with the previous work [43], which the Na3AlH6 is believed to react with the MgH2 to form the NaMgH3 and the Al products. The decomposition process is shown as follows: Na3 AlH6 þ 3MgH2 /3NaMgH3 þ Al þ H2
(3)
In Fig. 9(c), the NaH phase is observed while the intermediate phase Mg17Al12 and the Mg have dominated the XRD spectra pattern for the dehydrogenated sample after heating to 375 C. In addition, the NaMgH3 and the MgH2 phases are
Fig. 9 e XRD patterns of the 4MgH2eNa3AlH6 composite after ball milling for 1 h (a), and after dehydrogenation at 230 C (b), 375 C and (c) at 450 C.
completely undetected. These findings have demonstrated that the dehydrogenation process at this stage is resulted from the self decomposition of the MgH2 (Eq. (4)). The reactions of the excessive MgH2 with the Al and the decomposition of NaMgH3 are shown as in Eqs (5) and (6): MgH2 /Mg þ H2
(4)
17MgH2 þ 12Al/Mg17 Al12 þ 17H2
(5)
NaMgH3 /NaH þ Mg þ H2
(6)
As the heating process is further increased to 450 C (Fig. 9 (d)), the Na peaks are discovered and can be concluded that the NaH component is completely decomposed as shown in Eq. (7): NaH/Na þ H2
(7)
XRD measurements are performed to further investigate the possible reaction of each dehydrogenation stages of MgH2eNa3AlH6 composite with the addition of 10 wt% of TiF3. Fig. 10 exhibits the XRD patterns of the 4MgH2eNa3AlH6-10 wt % TiF3 composite (a) after 1 h of ball milling, (b) after dehydrogenation at 200 C, (c) 360 C and (d) at 450 C. The MgH2 and the Na3AlH6 along with the metastable b-Na3AlH6 peaks are detected after 1 h of ball milling as seen in Fig. 10(a). The TiF3 peak is not detected from the XRD spectra due to small amount of the TiF3 additive. Meanwhile, after heating process at 200 C, besides the presence of the NaMgH3, the MgH2 and the Al species, new phases, the NaF, the AlF3 and the Al3Ti are identified from the XRD spectra (Fig. 10(b)). This result indicated that the Ti-containing and F-containing species are reacted with the Al and the Na components to form new species that acted as the active species. These new species are responsible on the improvement of desorption temperature of MgH2eNa3AlH6 system as shown in Fig. 2. The new phases also can be detected after being heated to 360 C (Fig. 10 (c)) and 450 C (Fig. 10 (d)).
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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Mg17 Al12 þ ð17 2yÞH2 /yMg2 Al3 þ ð17 2yÞMgH2 þð12 3yÞAl
Fig. 10 e XRD patterns of the 4MgH2eNa3AlH6-10 wt% TiF3 composite (a) after ball milling for 1 h, (b) after dehydrogenation at 200 C, (c) 360 C and (d) 450 C.
In order to determine the reaction mechanism of the rehydrogenation stage, XRD analyses are conducted on the 4MgH2eNa3AlH6 and the 4MgH2eNa3AlH6-10 wt% TiF3 composites. The analyses are conducted after the rehydrogenation process at 320 C under 33 atm of hydrogen pressure. From the XRD patterns, peaks of the MgH2, the NaMgH3, the Al3Mg2, the Al and the MgO can be discovered from the 4MgH2eNa3AlH6 composite (Fig. 11 (a)) and after the addition of TiF3 on the 4MgH2eNa3AlH6 composite (Fig. 11 (b)). In addition, peaks of the NaF, the AlF3 and the Al3Ti are recognized in the rehydrogenated sample of the doped composite (Fig. 11 (b)). These peaks are previously detected in the dehydrogenated sample of MgH2eNa3AlH6eTiF3 composite as shown in Fig. 10. Meanwhile, as displayed by the XRD spectra on the un-doped and the doped sample, the disappearance of Mg17Al12 and Mg phases after the rehydrogenation process has suggested that the MgH2 has been fully transformed as in Eq. (8):
(8)
According to the result, the formations of the NaF, the AlF3 and the Al3Ti during the heating process from the reaction of the MgH2eNa3AlH6 with the TiF3 have played an important role in the enhancement of the MgH2eNa3AlH6 destabilized system. As reported by Ivanov et al. [56], the NaF and the NaCl have been found to modify the magnesium particle surfaces. They discussed that the addition of NaF and NaCl with magnesium has led to the intercourse of magnesium particles and has increased the specific surface of the sample. Their discussion was supported by the SEM result where the particle sizes of the MgH2eNa3AlH6 was found to be smaller after the addition of the TiF3. Meanwhile, Kang et al. [57] found that the reversible hydrogenation of the NaAlH4 was improved after a long period of mechanical milling with the Al3Ti. Furthermore, Yuan et al. [58] studied the addition of AlF3 on the LiBH4 composite. The doped-LiBH4 started to release hydrogen at about 100 C, which was 80 C lower compared to the as-milled LiBH4. On the other hand, the formation of active species which has led to the improvement of hydrogen storage properties was also reported by Ouyang and his co-workers [59]. They claimed that the formation of CeH2.73 and Ni species from the hydrogenation of as-melt Mg80Ce18Ni2 alloy had showed an excellent hydrogen storage performance. With the presence of CeH2.73 and Ni, the nanocomposite started to release hydrogen at a lower desorption temperature with a capacity of more than 4.0 wt% of H2 and had higher kinetics rate. The nanocomposites also have long cycle life. In addition, the hydrogenation properties of Mg also could be improved by forming a composite structure as discussed by Zhu et al. [60]. They believe that the components that were combined with Mg can catalyze the hydrogenation reaction of Mg. Therefore, based on the literature discussed, it is reasonable to conclude that the TiF3 component in the MgH2eNa3AlH6eTiF3 composite plays a catalytic role through the formation of the NaF, the AlF3 and the Al3Ti catalytic species. These active species may acted as the active sites for the nucleation and growth of the dehydrogenation products thus enhanced the hydrogen storage properties of the MgH2eNa3AlH6.
Conclusion
Fig. 11 e XRD patterns after the rehydrogenation process at 320 C of (a) the 4MgH2eNa3AlH6 composite (a) and 4MgH2eNa3AlH6-10 wt% TiF3 composite (b).
In summary, the hydrogen storage properties of MgH2e Na3AlH6 system has been improved with the introduction of TiF3 additive. Based on the TPD results, the dehydrogenation process of 4MgH2eNa3AlH6-10 wt% TiF3 has involved three steps which is similar to the 4MgH2eNa3AlH6 composite. The onset desorption temperature of the TiF3 doped with 4MgH2e Na3AlH6 composite has been reduced to 140 C as compared to the un-doped composite (170 C) at the first stage. In addition, the re/desorption kinetics of MgH2eNa3AlH6 system have been improved with the addition of TiF3. Meanwhile, the presented Kissinger plot has shown that the apparent activation energy of the H-desorption of MgH2 in the 4MgH2e Na3AlH6 composite has been reduced for about 16 kJ/mol with the addition of 10 wt% of TiF3. Based on the result, it is
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
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believed that these improvements are because of the formation of the NaF, the AlF3 and the Al3Ti catalytic species during the heating process. The formed active species have reinforced the interaction between MgH2 and Na3AlH6 and have further enhanced the MgH2eNa3AlH6 hydrogen storage properties.
[13] [14]
[15]
Acknowledgements [16]
This work was supported by Ministry of Higher Education Malaysia through the Fundamental Research Grant Scheme (FRGS 59362). The authors would like to acknowledge the Universiti Malaysia Terengganu for providing the facilities to run this project. F. A. Halim Yap would like to thank Universiti Malaysia Terengganu for his BUMT scholarship.
[17]
[18]
references [19] [1] Chen P, Zhu M. Recent progress in hydrogen storage. Mater Today 2008;11:36e43. [2] Satyapal S, Petrovic J, Read C, Thomas G, Ordaz G. The US department of energy's national hydrogen storage project: progress towards meeting hydrogen-powered vehicle requirements. Catal Today 2007;120:246e56. [3] Walker SB, Mukherjee U, Fowler M, Elkamel A. Benchmarking and selection of power-to-gas utilizing electrolytic hydrogen as an energy storage alternative. Int J Hydrogen Energy 2016;41:7717e31. [4] Bailera M, Kezibri N, Romeo LM, Espatolero S, Lisbona P, Bouallou C. Future applications of hydrogen production and CO2 utilization for energy storage: hybrid power to gasoxycombustion power plants. Int J Hydrogen Energy 2017;42:13625e32. [5] Peng DD, Fowler M, Elkamel A, Almansoori A, Walker SB. Enabling utility-scale electrical energy storage by a power-togas energy hub and underground storage of hydrogen and natural gas. J Nat Gas Sci Eng 2016;35(Part A):1180e99. [6] Eypasch M, Schimpe M, Kanwar A, Hartmann T, Herzog S, Frank T, et al. Model-based techno-economic evaluation of an electricity storage system based on liquid organic hydrogen carriers. Appl Energy 2017;185(Part 1):320e30. [7] Liu S-Y, Kundu P, Huang T-W, Chuang Y-J, Tseng F-G, Lu Y, et al. Quasi-2D liquid cell for high density hydrogen storage. Nano Energy 2017;31:218e24. [8] Zeng D-W, Xiao R, Zeng J-M, Zhang H-Y. Liquid foam assisted solegel synthesis of iron oxides for hydrogen storage via chemical looping. Int J Hydrogen Energy 2016;41:13923e33. [9] Callini E, Aguey-Zinsou K-F, Ahuja R, Ares JR, Bals S, Bili skov N, et al. Nanostructured materials for solid-state hydrogen storage: a review of the achievement of COST Action MP1103. Int J Hydrogen Energy 2016;41:14404e28. [10] Petit J-F, Miele P, Demirci UB. Ammonia borane H3N-BH3 for solid-state chemical hydrogen storage: different samples with different thermal behaviors. Int J Hydrogen Energy 2016;41:15462e70. [11] Lototskyy M, Yartys VA. Comparative analysis of the efficiencies of hydrogen storage systems utilising solid state H storage materials. J Alloy Compd 2015;645(Suppl. 1):S365e73. [12] Padmini M, Kiran SK, Lakshminarasimhan N, Sathish M, Elumalai P. High-performance solid-state hybrid energystorage device consisting of reduced graphene-oxide
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
anchored with NiMn-layered double hydroxide. Electrochim Acta 2017;236:359e70. Schlapbach L, Zu¨ttel A. Hydrogen-storage materials for mobile applications. Nature 2001;414:353e8. Liang C, Gao M, Pan H, Liu Y, Yan M. Effect of gas back pressure on hydrogen storage properties and crystal structures of Li2Mg(NH)2. Int J Hydrogen Energy 2014;39:17754e64. Murthy SS, Kumar EA. Advanced materials for solid state hydrogen storage:“Thermal engineering issues”. Appl Therm Eng 2014;72:176e89. Ouyang L, Tang J, Zhao Y, Wang H, Yao X, Liu J, et al. Express penetration of hydrogen on Mg(10ı3) along the close-packedplanes. Sci Rep 2015;5, 10776. Huang M, Ouyang L, Wang H, Liu J, Zhu M. Hydrogen generation by hydrolysis of MgH2 and enhanced kinetics performance of ammonium chloride introducing. Int J Hydrogen Energy 2015;40:6145e50. Ismail M, Zhao Y, Yu XB, Nevirkovets IP, Dou SX. Significantly improved dehydrogenation of LiAlH4 catalysed with TiO2 nanopowder. Int J Hydrogen Energy 2011;36:8327e34. Zuttel A. Materials for hydrogen storage. Mater Today 2003;6:24e33. Wang H, Zhang J, Liu JW, Ouyang LZ, Zhu M. Improving hydrogen storage properties of MgH2 by addition of alkali hydroxides. Int J Hydrogen Energy 2013;38:10932e8. Milosevic S, Milanovic I, Mamula BP, Dukic A, Rajnovic D, Pasquini L, et al. Hydrogen desorption properties of MgH2 catalysed with NaNH2. Int J Hydrogen Energy 2013;38:12223e9. Kiyobayashi T, Srinivasan SS, Sun D, Jensen CM. Kinetic study and determination of the enthalpies of activation of the dehydrogenation of titanium-and zirconium-doped NaAlH4 and Na3AlH6. J Phys Chem A 2003;107:7671e4. Jiang Z, Pan Q, Xu J, Fang T. Current situation and prospect of hydrogen storage technology with new organic liquid. Int J Hydrogen Energy 2014;39:17442e51. Yu XB, Yang ZX, Liu HK, Grant DM, Walker GS. The effect of a Ti-V-based BCC alloy as a catalyst on the hydrogen storage properties of MgH2. Int J Hydrogen Energy 2010;35:6338e44. Yu HZ, Dai JH, Song Y. Catalytic effect of Ti on dehydrogenation of Na3AlH6: a first principles investigation. Int J Hydrogen Energy 2015;40:11478e83. Halim Yap FA, Mustafa NS, Ismail M. A study on the effects of K2ZrF6 as an additive on the microstructure and hydrogen storage properties of MgH2. RSC Adv 2015;5:9255e60. Mustafa NS, Ismail M. Hydrogen sorption improvement of MgH2 catalyzed by CeO2 nanopowder. J Alloy Compd 2017;695:2532e8. Mustafa NS, Sulaiman NN, Ismail M. Effect of SrFe12O19 nanopowder on the hydrogen sorption properties of MgH2. RSC Adv 2016;6:110004e10. Jalil Z, Rahwanto A, Mulana F, Mustanir. Desorption temperature characteristic of Mg-based hydrides catalyzed by nano-SiO2 prepared by high energy ball milling. Int J Technol 2016;7:1301e6. Sulaiman NN, Ismail M. Enhanced hydrogen storage properties of MgH2 co-catalyzed with K2NiF6 and CNTs. Dalton Trans 2016;45:19380e8. House SD, Vajo JJ, Ren C, Rockett AA, Robertson IM. Effect of ball-milling duration and dehydrogenation on the morphology, microstructure and catalyst dispersion in Nicatalyzed MgH2 hydrogen storage materials. Acta Mater 2015;86:55e68. Ismail M. The hydrogen storage properties of destabilized MgH2eAlH3 (2:1) system. Mater Today Proc 2016;3(Suppl. 1):S80e7.
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e9
[33] Liu DM, Huang WJ, Si TZ, Zhang QA. Hydrogen storage properties of LiBH4 destabilized by SrH2. J Alloy Compd 2013;551:8e11. [34] Ibikunle AA, Goudy AJ. Kinetics and modeling study of a Mg(BH4)2/Ca(BH4)2 destabilized system. Int J Hydrogen Energy 2012;37:12420e4. [35] Ismail M, Zhao Y, Yu XB, Mao JF, Dou SX. The hydrogen storage properties and reaction mechanism of the MgH2NaAlH4 composite system. Int J Hydrogen Energy 2011;36:9045e50. [36] Ouyang L, Cao Z, Wang H, Hu R, Zhu M. Application of dielectric barrier discharge plasma-assisted milling in energy storage materials e a review. J Alloy Compd 2017;691:422e35. [37] Ouyang LZ, Ye SY, Dong HW, Zhu M. Effect of interfacial free energy on hydriding reaction of MgeNi thin films. Appl Phys Lett 2007;90, 021917. [38] Ouyang LZ, Cao ZJ, Li LL, Wang H, Liu JW, Min D, et al. Enhanced high-rate discharge properties of La11.3Mg6.0Sm7.4Ni61.0Co7.2Al7.1 with added graphene synthesized by plasma milling. Int J Hydrogen Energy 2014;39:12765e72. [39] Mao JF, Yu XB, Guo ZP, Liu HK, Wu Z, Ni J. Enhanced hydrogen storage performances of NaBH4-MgH2 system. J Alloy Compd 2009;479:619e23. [40] Gosalawit-Utke R, Milanese C, Nielsen TK, Karimi F, Saldan I, Pranzas K, et al. Nanoconfined 2LiBH4-MgH2 for reversible hydrogen storages: reaction mechanisms, kinetics and thermodynamics. Int J Hydrogen Energy 2013;38:1932e42. [41] Liu S-S, Sun L-X, Zhang J, Zhang Y, Xu F, Xing Y-H, et al. Hydrogen storage properties of destabilized MgH2eLi3AlH6 system. Int J Hydrogen Energy 2010;35:8122e9. [42] Yang J, Wang X, Mao J, Chen L, Pan H, Li S, et al. Investigation on reversible hydrogen storage properties of Li3AlH6/2LiNH2 composite. J Alloy Compd 2010;494:58e61. [43] Ismail M, Zhao Y, Dou SX. An investigation on the hydrogen storage properties and reaction mechanism of the destabilized MgH2-Na3AlH6 (4:1) system. Int J Hydrogen Energy 2013;38:1478e83. [44] Ma LP, Wang P, Cheng HM. Improving hydrogen sorption kinetics of MgH2 by mechanical milling with TiF3. J Alloy Compd 2007;432:L1e4. [45] Kang X-D, Wang P, Cheng H-M. Advantage of TiF3 over TiCl3 as a dopant precursor to improve the thermodynamic property of Na3AlH6. Scr Mater 2007;56:361e4. [46] Mao J, Guo Z, Nevirkovets IP, Liu HK, Dou SX. Hydrogen de-/ absorption improvement of NaBH4 catalyzed by titaniumbased additives. J Phys Chem C 2011;116:1596e604.
9
[47] Juahir N, Mustafa NS, Halim Yap FA, Ismail M. Study on the hydrogen storage properties and reaction mechanism of NaAlH4-Mg(BH4)2 (2:1) with and without TiF3 additive. Int J Hydrogen Energy 2015;40:7628e35. [48] Mao J, Guo Z, Liu H. Improved hydrogen sorption performance of NbF5-catalysed NaAlH4. Int J Hydrogen Energy 2011;36:14503e11. [49] Wang Z, Tao S, Deng J, Zhou H, Yao Q. Significant improvement in the dehydriding properties of perovskite hydrides, NaMgH3, by doping with K2TiF6. Int J Hydrogen Energy 2017;42:8554e9. [50] Zhang W, Wang H, Cao H, He T, Guo J, Wu G, et al. Effects of doping FeCl3 on hydrogen storage properties of Li-NH system. Prog Nat Sci Mater Int 2017;27:139e43. [51] Huot J, Boily S, Gu¨ther V, Schulz R. Synthesis of Na3AlH6 and Na2LiAlH6 by mechanical alloying. J Alloy Compd 1999;283:304e6. [52] Wang P, Kang X, Cheng H. Direct formation of Na3AlH6 by mechanical milling NaH∕ Al with TiF3. Appl Phys Lett 2005;87, 071911. [53] Ismail M, Halim Yap FA, Sulaiman NN, Ishak MHI. Hydrogen storage properties of a destabilized MgH2-Sn system with TiF3 addition. J Alloy Compd 2016;678:297e303. [54] Ouyang L, Cao Z, Wang H, Liu J, Sun D, Zhang Q, et al. Enhanced dehydriding thermodynamics and kinetics in Mg (In)eMgF2 composite directly synthesized by plasma milling. J Alloy Compd 2014;586:113e7. [55] Liang G. Synthesis and hydrogen storage properties of Mgbased alloys. J Alloy Compd 2004;370:123e8. [56] Ivanov E, Konstanchuk I, Bokhonov B, Boldyrev V. Comparative study of first hydriding of MgeNaF and MgeNaCl mechanical alloys. J Alloy Compd 2003;360:256e65. [57] Kang XD, Wang P, Song XP, Yao XD, Lu GQ, Cheng HM. Catalytic effect of Al3Ti on the reversible dehydrogenation of NaAlH4. J Alloy Compd 2006;424:365e9. [58] Yuan PP, Liu BH, Zhu HP, Pan WY, Li ZP. Destabilized dehydrogenation reaction of LiBH4 by AlF3. J Alloy Compd 2013;557:124e9. [59] Ouyang L, Yang X, Zhu M, Liu J, Dong H, Sun D, et al. Enhanced hydrogen storage kinetics and stability by synergistic effects of in situ formed CeH2. 73 and Ni in CeH2. 73-MgH2-Ni nanocomposites. J Phys Chem C 2014;118:7808e20. [60] Zhu M, Wang H, Ouyang LZ, Zeng M. Composite structure and hydrogen storage properties in Mg-base alloys. Int J Hydrogen Energy 2006;31:251e7.
Please cite this article in press as: Halim Yap FA, et al., Enhancement of hydrogen storage properties in 4MgH2e Na3AlH6 composite catalyzed by TiF3, International Journal of Hydrogen Energy (2017), http://dx.doi.org/10.1016/j.ijhydene.2017.07.012