Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2

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Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2 N.A. Sazelee a, N.H. Idris a, M.F. Md Din b, N.S. Mustafa a, N.A. Ali a, M.S. Yahya a, F.A. Halim Yap a, N.N. Sulaiman a, M. Ismail a,* a

School of Ocean Engineering, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Malaysia Department of Electrical and Electronic Engineering, Faculty of Engineering, National Defence University of Malaysia, Kem Sungai Besi, Kuala Lumpur, Malaysia

b

article info

abstract

Article history:

Previous studies have shown that ferrites give a positive effect in improving the hydrogen

Received 12 July 2018

sorption properties of magnesium hydride (MgH2). In this study, another ferrite, i.e.,

Received in revised form

BaFe12O19, has been successfully synthesised via the solid state method, and it was milled

27 August 2018

with MgH2 to enhance the sorption kinetics. The result showed that the MgH2 þ 10 wt%

Accepted 15 September 2018

BaFe12O19 sample started to release hydrogen at about 270  C which is about 70  C lower

Available online xxx

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

Keywords:

conditions. The desorption kinetic results showed that the doped sample released about

Hydrogen storage

3.5 wt% of hydrogen in 15 min at 320  C, while the as-milled MgH2 only released about

Solid-state storage

1.5 wt% of hydrogen. From the Kissinger plot, the apparent activation energy of the

Magnesium hydride

BaFe12O19-doped MgH2 sample was 115 kJ/mol which was lower than the milled MgH2

Barium iron oxide

(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. © 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Introduction Hydrogen is an energy carrier which is able to fully satisfy various requirements. The production of hydrogen via methods such as biomass and electrolysis are environmentalfriendly and can be handled quite easily, corresponding with the developments of new technologies for transportation and storage. Hydrogen gas is now considered to be the most promising fuel for various applications, e.g. fuel for transportation, stationary applications, reactants and scavengers [1]. Researches had also stated that hydrogen fuels have

attracted their attention since they are non-toxic, renewable and clean [2e4]. Due to all of these advantages, hydrogen fuels are deemed applicable for vehicular applications [5]. Although hydrogen has a bright future as an energy carrier, the problem with its storage is still the main obstacle [6]. Hydrogen can be stored as (i) liquid, (ii) compressed gas, and (iii) solid form [7]. Each of the options possesses attractive attributes for hydrogen storage. Among them, the solid state form has been considered as an ideal storage form due to safety considerations, high volumetric hydrogen capacity, and cost effectiveness [8].

* Corresponding author. E-mail address: [email protected] (M. Ismail). https://doi.org/10.1016/j.ijhydene.2018.09.125 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125

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An ultimate hydrogen storage should be low-cost, has high hydrogen storage capacity, uses a mild operation temperature, is easy to be used to absorb/desorb hydrogen, and also has a long life-span [9]. Metal hydride [10,11], complex hydride [12e17] and carbon materials [18,19] have been tested to fulfil the above requirements, but none of them had shown satisfactory performance. Previous study stated that metal hydrides especially MgH2 offer the possibility to store hydrogen by reasons of good reversibility, low-cost and high gravimetric hydrogen density [20,21]. However, MgH2 requires temperatures of 400  C and above to release hydrogen, and this is too high for practical on-board applications [14,22]. Besides that, the disadvantages of MgH2 are its high thermodynamics stability and slow sorption kinetics [23,24]. Hence, to overcome these disadvantages, a lot of works have been done to improve the hydrogen storage properties of MgH2 [25,26]. Several experiments also have been conducted to improve the drawbacks through the ball-milling of MgH2 using catalysts such as metal oxides, metal halides, metal hydrides, alloys and metals [27e37]. Recently, ternary oxides, especially ferrites have been a hotspot of research due to their role in improving the hydrogen storage properties of MgH2. As indicated by Wan et al. [38], hydrogen storage performance was improved when 7 mol% of NiFe2O4 was doped with MgH2. Onset desorption temperature of MgH2 reduced to 191  C after doped with NiFe2O4 compared with as-received MgH2 (441  C). Desorption activation energy of MgH2 þ 7 mol% of NiFe2O4 is 59.6 kJ/mol, decreased about 195.3 kJ/mol compared with as-received MgH2. The absorption kinetics displays that the MgH2 þ 7 mol% of NiFe2O4 sample could absorb 2.89 wt % of H2 within 3 h at 50  C, while as-milled MgH2 cannot absorb any amount of H2. The Fe7Ni3 and (Fe, Ni) phases existed during the dehydrogenation process, and could thus verify as a real catalyst. Mustafa et al. [39] also found that the hydrogen sorption properties of MgH2 had improved significantly after the addition of SrFe12O19. The onset temperature for as-milled MgH2 and MgH2 þ 10 wt% SrFe12O19 is 350  C and 270  C respectively. From Kissinger plot, the activation energy was 133.31 kJ/mol for as-milled MgH2 and 114.22 kJ/mol for MgH2 þ 10 wt% SrFe12O19. Regarding absorption kinetics, the doped samples show better absorption which is 4.8 wt% compared with as-milled (4.3 wt%) at 320  C. The reaction mechanism during the de/rehydrogenation process proved that the improved hydrogen storage properties of the ballmilled MgH2 with SrFe12O19 ascribe to the existence of SrO, Fe and MgFe2O4. Based on the result obtained, it is proved that the addition of SrFe12O19 improved hydrogen storage performance of MgH2. Meanwhile, Li et al. [40] analyzed that the activation energy of 7 mol% MnFe2O4-doped MgH2 sample is 64.55 kJ/mol which showed a 190.34 kJ/mol reduction compared to the as-received MgH2 sample. Besides that, onset desorption temperature for 7 mol% MnFe2O4-doped MgH2 is 300  C, 140  C lower, compared with as-received MgH2. Isothermal desorption kinetics shows the doped sample can release 5.05 wt% H2 in 1 h at 300  C, whereas as-received MgH2 only release 0.54 wt% H2 under the same condition. The new phases, Fe0.872O, Mg2MnO4 and Fe0.872O play an important role in reducing the activation energy, thus enhancing the hydrogen storage

properties of MgH2. As mentioned by Zhang et al. [41], the onset desorption temperature of ball-milled MgH2 (360  C) was dramatically reduced after the addition of a catalyst such as Mn0.5Zn0.5Fe2O4, ZnFe2O4, MnFe2O4 and CoFe2O4 nanoparticles. Onset desorption temperature for the doped sample (Mn0.5Zn0.5Fe2O4, ZnFe2O4, MnFe2O4 and CoFe2O4) are 260  C, 190  C, 280  C and 160  C respectively. The catalyst can easily absorb hydrogen atoms to fill its 3D orbits, thus improving the MgH2 properties. Based on the discussions above, it is proved that ternary oxide especially ferrites can improve hydrogen storage performance of MgH2. To explore more about the specific role of ternary oxides, especially ferrites in improving the hydrogen storage properties of MgH2, BaFe12O19 was chosen for this work. Wang et al. [42] reported the addition of BaTiO3 decreased the dehydriding activation energy of MgH2 from 116 kJ/mol to 108 kJ/mol. The temperature-programmed desorption results showed that with the addition of BaTiO3, the onset desorption temperature decrease to 270  C, which is 149  C lower than that as-received MgH2. As stated by Baricco et al. [43], the activation energy values for MgH2 þ BaRuO3 is 90 kJ/mol, which is lowered by 50 kJ/mol for as-received MgH2. Besides that, the previous study also stated that Ba is an effective promoter for Ru/C catalyst [44,45]. Furthermore, Song et al. [46] reported that the addition of metal oxide (e.g. Fe2O3) greatly increased the hydriding rate of Mg and slightly increased the dehydriding rate of MgH2. It can be concluded that as a catalyst, Fe is quite reactive. It is thus predicted to show better catalytic properties when ball-milled with MgH2 [47]. The results have suggested a specific investigation on the role of BaFe12O19 on hydrogen storage performance of MgH2. In this work, BaFe12O19 was synthesised via a simple solid state method. Up to this date, there are no researches that have been conducted to study the effects of BaFe12O19 on MgH2 for hydrogen storage. The main aim of this research is to investigate how the addition of the BaFe12O19 can enhance the hydrogen storage properties of MgH2.

Experimental parts The BaFe12O19 powder was synthesised by using a solid-state reaction. Specifically, 0.0958 g of Fe2O3 powders (<50 nm particle size; Sigma Aldrich), 0.0315 g Ba(OH)2.8H2O (98% pure; Sigma Aldrich) and 0.0637 g citric acid (99% pure; Sigma Aldrich) were grinded using agate mortar for 30 min and heated at 80  C for 6 h under vacuum. Then, the powder was annealed at 850  C for 1 h in air to obtain BaFe12O19. Next, 10 wt % BaFe12O19 and 500 mg MgH2 (95% pure; Sigma-Aldrich) were ball-milled using a planetary ball mill (NQM-0.4) at a rotating rate of 400 rpm for 1 h. The ratio of the weight of the balls to the weight of the powder was 40:1. All preparations were handled in a glove box with a high purity Argon atmosphere (MBraun Unilab). The de/rehydrogenation kinetics of the samples was measured using a Sieverts-type pressure-composition temperature (PCT) apparatus (Advanced Material Corporation). 100 mg of the sample was filled into the sample vessel and heated at a heating rate of 5  C/min from 25  C to 450  C.

Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125

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Measurements for de/rehydrogenation kinetics were accomplished at 1.0 atm and 33.0 hydrogen pressure. The phases of the samples were identified through X-ray diffraction (Rigaku MiniFlex X-ray diffractometer, Cu Ka radiation) from 20 to 80 at a speed of 2.00 /min. The morphology of the samples was observed using a scanning electron microscopy (SEM; JEOL JSM-6350LA). A Fourier transform infrared (FTIR) spectroscopy was performed using a Shimadzu IRTracer-100 at a range of 400e4000 cm1 with a resolution of 4 cm1. The Raman spectra were recorded from 100 to 1000 cm1 using a Renishaw Raman spectroscopy with a laser source at a wavelength of 532 nm.

Results and discussion The phase structure of the BaFe12O19 was confirmed before milling it with MgH2. The XRD pattern of the BaFe12O19 (Fig. 1(a)) can be indexed with the standard pattern for M-type hexagonal BaFe12O19 crystals (JCPDS card no.27-1029). The average crystallite size of the BaFe12O19 was approximately 0.663 nm, calculated using Scherrer's formula [48]: L ¼ Kl=b cos q

(1)

where L is the crystalline size, K is the constant (0.91), b is the full width at half maximum intensity of the XRD peak (in radians), l is the X-ray wavelength of Cu-Ka radiation (0.154 nm), and q is the angle of Bragg's diffraction. Fig. 1(b) shows the SEM images of pure BaFe12O19. The BaFe12O19 exhibited a porous structure with the pores' diameters ranging from 2 mm to 6 mm. The FTIR spectra as displayed in Fig. 1(c) show the typical bands appearing at 441 cm1 and 554 cm1, which can be assigned to the BaeO and FeeO bonds, respectively [49]. Furthermore, the strongest Raman band (Fig. 1(d)) at 682 cm1 can be ascribed to the symmetric stretching mode of the bipyramidal Fe(2)O5 group, which is a typical characteristic of the M-hexaferrite structure [50]. The Raman band at 179 cm1

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can be assigned to the whole spinel block [51]. There were no additional peaks or impurity peaks observed in the XRD pattern, FTIR and Raman spectra. Therefore, pure BaFe12O19 was successfully synthesised using the solid-state method. Fig. 2(a) exhibits the dehydrogenation behaviour of the asreceived MgH2, as-milled MgH2, and MgH2 þ 10 wt% of BaFe12O19 by using TPD. It is clear that the addition of BaFe12O19 had significantly improved the dehydriding of MgH2, resulting in the drastic reduction of the onset desorption temperature. The as-received MgH2 started to decompose at about 418  C, meanwhile the as-milled MgH2 started to decompose at 340  C with a total dehydrogenation capacity of 7.0 and 6.8 wt%, respectively. This shows that the ball-milling technique does affect the onset desorption temperature of MgH2. The addition of 10 wt% BaFe12O19 to MgH2 showed a decrease in temperature at about 270  C with a total of 6.0 wt% hydrogen released. The isothermal rehydrogenation kinetics (under 33.0 atm hydrogen pressure) of the samples at 150  C is shown in Fig. 2(b). It can be concluded that the MgH2 þ 10 wt% of BaFe12O19 has better hydrogen absorption compared to the asmilled MgH2. The hydrogen absorption capacity of MgH2 doped with 10 wt% of BaFe12O19 was about 4.3 wt% after 10 min, while the as-milled MgH2 only absorbed 3.5 wt% of hydrogen in the same period. Based on this result, it shows that the addition of BaFe12O19 improves the rehydrogenation kinetics of MgH2. The isothermal dehydrogenation kinetics for as-milled MgH2 and MgH2 þ 10 wt% of BaFe12O19 were evaluated at 320  C for 30 min as illustrated in Fig. 2(c). Obviously, the addition of BaFe12O19 significantly improved the dehydrogenation kinetics and faster desorption compared to the asmilled MgH2. MgH2 doped with BaFe12O19 released 3.4 wt% within 15 min, while the milled MgH2 released about 1.3 wt % in the same period. For the next 15 min, MgH2 þ 10 wt% of BaFe12O19 released about 4.2 wt%, compared to the asmilled MgH2, which only released 3.4 wt%. Hence, the

Fig. 1 e (a) XRD pattern, (b) SEM image, (c) FTIR spectra and (d) Raman spectra of BaFe12O19. Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125

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Fig. 2 e (a) TPD curves, (b) isothermal rehydrogenation kinetics at 150  C and under 33.0 atm and (c) isothermal dehydrogenation kinetics at 320  C and under 1.0 atm.

addition of BaFe12O19 helped to increase the dehydrogenation kinetics of MgH2. In order to investigate activation energy (EA), the dehydrogenation kinetics at 280, 300, 320 and 340  C were

accomplished for MgH2 with and without the additive, as shown in Fig. 3(a) and Fig. 3(b), respectively. The EA for both samples were determined using the Arrhenius equation, as described below [52]:

Fig. 3 e Isothermal dehydrogenation kinetics of (a) as milled MgH2 and (b) MgH2 þ 10 wt% BaFe12O19 at 280, 300, 320 and 340  C under 1.0 atm pressure and (c) Arrhenius plot of ln(k) vs. 1/T. Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125

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k ¼ k0 exp ðEA =RTÞ

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(2)

where R is the gas constant, T is the absolute temperature, k is the rate of dehydrogenation, k0 is a temperature independent coefficient, and EA is the apparent activation energy for hydride decomposition. The value of k was determined from the slope of dehydrogenation kinetic. Fig. 3(c) shows the Arrhenius plot for as-milled MgH2 and MgH2 doped with BaFe12O19. By carrying out the Arrhenius analysis, the EA obtained for as-milled MgH2 and MgH2 doped with BaFe12O19 were 141 kJ/mol and 115 kJ/mol, respectively, as shown in Fig. 4(c). The EA decreased about 26 kJ/mol when 10 wt% of BaFe12O19 was doped in MgH2. This shows that with the addition of 10 wt% of BaFe12O19 as an additive, the activation energy were decreased. The typical morphology of the samples is shown in Fig. 4. The as-received MgH2 pictured in Fig. 4(a) shows an angular shape with a size larger than 100 mm. After ball-milling (Fig. 4(b)), the powder's shape changed to be nearly spherical and agglomerated. It shows that the ball-milling process helps in reducing the size of the particles [53]. Meanwhile, Fig. 4(c) shows the MgH2 doped with BaFe12O19 which resulted in the reduction of particle size and less agglomeration. For instance, the hardness for MgH2 and BaFe12O19 were 0.58 GPa and 5.9 GPa respectively [54,55]. The hardness of the BaFe12O19 had thus broken the MgH2 particles. Therefore, smaller particle sizes will produce larger surface areas, thus improving the rate reaction for MgH2 [56,57]. To further explore the reaction and mechanism of MgH2 þ 10 wt% of BaFe12O19, the XRD analysis was used to analyse the phase structure of the sample. Fig. 5 shows the XRD patterns after ball-milling for 1 h, after dehydrogenation

Fig. 5 e XRD patterns of MgH2 þ 10 wt% BaFe12O19 (a) after ball milling for 1 h, (b) after dehydrogenation at 450  C and (c) after rehydrogenation at 150  C. at 450  C and after rehydrogenation at 150  C. After 1 h of milling, the only peaks present were MgH2 and BaFe12O19. No new compounds were shown in the XRD pattern as shown in Fig. 5(a). After dehydrogenation at 450  C (Fig. 5(b)), distinct Mg peaks were exposed, revealing that the dehydrogenation process had occurred completely. New peaks for MgO and Fe were also detected. Fig. 5(c) shows the XRD pattern after rehydrogenation at 150  C. The MgO and Fe diffraction peaks remain unchanged. At the same time, the peak for Mg still appears. This is because the rehydrogenation process had occurred at a low temperature. Besides that, the role of Ba or Ba containing also enhanced the hydrogen storage properties of MgH2. However, no Ba or Ba containing phase were detected

Fig. 4 e SEM images for (a) as received MgH2, (b) as milled MgH2 and (c) MgH2 þ 10 wt% BaFe12O19. Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125

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Fig. 6 e XRD patterns of MgH2 þ 20 wt% BaFe12O19 (a) after ball milling for 1 h, (b) after dehydrogenation of 450  C and (c) after rehydrogenation at 320  C.

by the XRD, suggesting that the Ba existed in an amorphous or well-dispersed state [58]. To illustrate MgH2's reaction with BaFe12O19 in more detail, a sample of MgH2 doped with 20 wt% BaFe12O19 was prepared as shown in Fig. 6. Fig. 6(a) displays the sample which was milled for 1 h to prove that the peak intensities of both MgH2 and BaFe12O19 have increased. After dehydrogenation at 450  C as in Fig. 6(b), the peaks of MgO and Fe are more obvious, meanwhile after rehydrogenation at 320  C as exhibited in Fig. 6(c), the peaks of MgO and Fe remained unchanged while the peak of Mg was transformed into MgH2. This indicates that the rehydrogenation process did occur completely at this temperature. The peak for Ba or Bacontaining still cannot be detected using XRD, even though the amount of BaFe12O19 has increased to 20 wt% as the samples were in the amorphous or well-dispersed state. From the XRD patterns, it is clearly shown that the MgH2 reacted with BaFe12O19 during the dehydrogenation process, forming MgO, Fe and Ba or Ba-containing phases. The reaction became more intense after the mass of BaFe12O19 was increased. The reaction between MgH2 doped with BaFe12O19 may be predicted as the following equation: 20MgH2 þBaFe12 O19 /Mg þ Ba þ 12Fe þ 19MgO þ 20H2

(3)

The standard state free energy of reaction, DG can be figured out using Eq. (4) [39]. DG ¼ SDGfproducts   SDGfreactants 

(4) DGf

of MgH2, The values of standard Gibbs free energy, BaFe12O19 and MgO are 35.9824 kJ/mol, 7246.688 kJ/mol and 569.024 kJ/mol, respectively as obtained from the literature [59]. Thus, the total energy DG related with the reaction in Eq. (4) is 2787.09 kJ/mol of MgH2. This confirms the possibility of the reaction in Eq. (3) from thermodynamic potentials. Based on the results obtained, the enhancement in MgH2 properties may be attributed to a few factors. The new active species of MgO, Fe and Ba or Ba-containing formed after dehydrogenation act as a real additive that enhance the performance of MgH2 for hydrogen storage. Aguey et al. [60] proved that MgO is justified in a concept called the “Process

Control Agent”. MgO allows for the reduction of agglomeration and cold welding. As a result, the hydrogen kinetics for MgH2 with MgO is higher compared to as-milled MgH2. Bassetti et al. [61] proved that the combination of MgH2 and Fe will improve the desorption kinetics of MgH2. Gopalsamy and Subramanian [62,63] proved that alkaline earth metals such as Mg2þ and Ca2þ can enhance hydrogen storage capacity. In this research, Mg2þ was doped adamantance adsorb 4H2 molecule with a binding energy of 32.19 kcal/mol. Besides that, the Admol(Ca2þ) can also bind a maximum of six H2 molecules, thus showing that the total binding value is 21.59 kcal/mol. Therefore, it was shown that the addition of new linkers increases the hydrogen storage capacity. From the study, it shows that the presence of alkaline group metals like Be2þ, Mg2þ, Ca2þ and Ba2þ can improve the hydrogen storage properties. It can be assumed that the formation of Ba or Bacontaining acts as the active species which improve the hydrogen storage properties since Ba is also included as an alkaline earth metal. Furthermore, the particle size was reduced after milling, and the addition of additive may be one of the factors that had enhanced the MgH2's properties. The dehydrogenation properties of MgH2 doped with 10 wt% BaFe12O19 had improved after the ball-milling due to the decrease in particle size. The decrease in particle size provided high surface defect density and achieved more boundaries. Other than that, the number of nucleation sites at the surface of the MgH2 matrix had also increased [40]. Zaluska et al. [64] also proved that the improvement in hydrogenation properties can be caused by the milling of MgH2 powder. The grain boundaries near the powder surface will allow hydrogen atoms to penetrate the material more easily, and the nucleation of the hydride may not be limited by the presence of the closest surface. Thus, it is reasonable to conclude that doping with BaFe12O19 will significantly enhance the performance of MgH2 for hydrogen storage.

Conclusion In this work, the effects of the addition of BaFe12O19 to the hydrogen storage properties of MgH2 were investigated. The onset desorption temperature of MgH2 þ 10 wt% BaFe12O19 was lowered to 270  C compared to the temperature used for as-milled MgH2 (340  C) and as-received MgH2 (418  C). The hydrogen absorption capacity for MgH2 doped BaFe12O19 is 4.3 wt% at 150  C for 10 min, which is higher compared to undoped MgH2 which had absorbed 3.5 wt% during the same period. Regarding dehydrogenation kinetics, it is obvious that MgH2 þ 10 wt% BaFe12O19 significantly improved the performance compared to the as-milled. Saturation of the dehydrogenation process for MgH2 þ 10 wt% BaFe12O19 can be achieved within 30 min with about 4.2 wt% of hydrogen release, meanwhile the as-milled MgH2 only released 3.4 wt% during the same time. The apparent activation energy of the as-milled MgH2 (141 kJ/mol) was reduced by about 26 kJ/mol after doped with BaFe12O19. In the meantime, the in-situ formation of MgO, Fe and Ba or Ba-containing had together facilitated the catalytic effects, hence improved the performance of MgH2 for hydrogen storage. In addition, doping with

Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125

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BaFe12O19 had obviously changed the microstructure of MgH2. Therefore, it can be concluded that BaFe12O19 can act as an additive in improving hydrogen storage properties of MgH2.

Acknowledgement The authors gratefully thanks to Universiti Malaysia Terengganu (UMT) for support the equipment and facilities. The authors also acknowledge the Research Management and Innovation Centre (RMIC), UMT for Talent and Publication Enhancement-Research Grant (TAPE-RG) (VOT 55134).

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Please cite this article in press as: Sazelee NA, et al., Synthesis of BaFe12O19 by solid state method and its effect on hydrogen storage properties of MgH2, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.09.125