Effect of SrFe12O19 nanopowder on the hydrogen sorption properties of MgH2

Article abstract of DOI:10.1039/c6ra22291a

In this study, the effects of different amounts (5, 10, 15, 20 and 50 wt%) of an SrFe₁₂O₁₉ nanopowder, doped into MgH₂ and prepared by the ball milling method, were investigated with the aim of improving hydrogen storage p

Full text of DOI:10.1039/c6ra22291a

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Effect of SrFe12O19 nanopowder on the hydrogen sorption properties of MgH2
N. S. Mustafa, N. N. Itam Sulaiman, M. Ismail*
School of Ocean Engineering, Universiti Malaysia Terengganu, 21030 Kuala Terengganu,
Malaysia
*Corresponding author. Tel: +609-6683487; Fax: +609-6683991
E-mail address: mohammadismail@umt.edu.my
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Abstract
In this study, the effects of different contents (5, 10, 15, 20 and 50 wt.%) of an SrFe12O19
nanopowder, doped into MgH2 and prepared by the ball milling method, were investigated with
the aim of improving hydrogen storage properties. The results indicated that 10 wt.% SrFe12O19
showed the best performance, compared with un-doped MgH2, in terms of the onset
dehydrogenation temperature. The desorption temperature of MgH2 + 10 wt.% SrFe12O19
decreased to about 270 °C compared to the 350 °C and 420 °C for as-milled and as-received
MgH2, respectively. The de/rehydrogenation kinetics of MgH2 also improved after doping with
SrFe12O19. Increasing the doping amount of SrFe12O19 to 15, 20 and 50 wt.% initiated negative
effects, such as lower capacity and slower sorption rates. From the Kissinger plot differential
scanning calorimetry, the apparent activation energy was 133.31 kJ/mol for as-milled MgH2 and
114.22 kJ/mol for MgH2 + 10 wt.% SrFe12O19, indicating that SrFe12O19 addition decreased the
activation energy for hydrogen desorption of MgH2. From the X-ray diffraction results, it is
believed that the formation of a new phases of Fe, MgFe2O4 and SrO during the dehydrogenation
process might be responsible for the catalytic effects which further enhanced the hydrogen
storage properties of MgH2.
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1. Introduction
Being environmentally-friendly, numerous efforts have been made to realize the potential of
hydrogen as a major energy carrier, in both mobile and stationary applications.1 However,
hydrogen storage is still a major problem and three main approaches currently exist, high
pressure, cryogenics and chemical compounds, which reversibly release H2 upon heating (solid-
state storage). Storing hydrogen in a solid state offers several benefits over compressed and
liquid forms, particularly in terms of safety, cost and high volumetric and gravimetric density.2
Various types of material have been proposed and are currently under investigation. Among
them MgH2 has been a research hotspot due to its large gravimetric density (7.6 wt.%), superior
reversibility and low cost.3, 4
Nevertheless, its high temperature of hydrogen release (> 400 °C) and slow rehydration
and dehydration kinetics are two main problems that limit the use of MgH2 as a hydrogen storage
material in practical applications.5 In an attempt to improve the hydrogen storage properties of
MgH2, a lot of studies have been performed. One of the strategies is the addition of a catalyst.
Various catalysts have been doped into MgH2 via ball milling, such as metals,6-10 metal oxides,11-
15 metal halides,16-23 carbon-based materials,24, 25 and alloys.26-28 To date, metal oxides, especially
the ternary oxide known as ferrite, have attracted attention because of the role they play in
enhancing the hydrogen storage properties of materials.
In a previous report by Wan et al.,29 the dehydrogenation performance of MgH2 was
significantly improved after doping with NiFe2O4 nanoparticles. Meanwhile, Li et al.30 also
reported that addition of MnFe2O4 nanoparticles significantly enhanced the dehydrogenation
properties of MgH2. Furthermore, in a study by Zhang et al.31 on the dehydrogenation
mechanism of ball milled MgH2 doped with ferrite nanoparticles (CoFe2O4, ZnFe2O4, MnFe2O4
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and Mn0.5Zn0.5Fe2O4), the result indicated that all ferrites can significantly reduce the desorption
temperature of MgH2, and that CoFe2O4 showed the best catalytic performance of the ferrites.
Shang et al.32 also found that addition of 7 mol% CoFe2O4 enhanced the hydrogen storage
properties of MgH2 by reducing the onset desorption temperature to 160 °C, 200 °C lower than
as-milled MgH2.
Although some ferrites have a positive effect on the hydrogen storage properties of MgH2,
they still do not fulfil the requirements for practical application as suitable hydrogen storage
materials. Therefore, it is important to find other types of catalyst that can improve the hydrogen
storage properties of MgH2. Therefore, in this study another type of ferrite, SrFe12O19, was
selected as a catalyst for MgH2. There is no existing research into the effect of SrFe12O19
nanoparticles on MgH2 properties. A recent study suggests that improvement in the hydrogen
storage properties of MgH2 doped with 7 mol% NiFe2O4 is related to in situ formed intermetallic
Fe7Ni3 and (Fe,Ni) phases from the reaction between NiFe2O4 and MgH2 during the desorption
process, and that these phases act as a real catalyst.29 So, it can be speculated that SrFe12O19
reacts with MgH2 during the desorption process to form a new active species.
In this work, MgH2 was mixed with SrFe12O19 to improve its hydrogen storage properties.
The aim was to combine the in situ active species factors and thus enhance the de/hydrogenation
properties of MgH2. The hydrogen storage properties and reaction pathways of MgH2 were
investigated using Sievert-type pressure-composition-temperature (PCT) apparatus, differential
scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM).
The possible mechanism behind the catalytic effect of SrFe12O19 on MgH2 is also discussed.
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2.
Experimental Details
2.1 Preparation of samples
The starting maetrials, MgH2 (98% purity), SrFe12O19 were purchased from Sigma-Aldrich and
were used as received. All handling of the powder, including weighing and loading, was
performed in an argon atmosphere using an MBraun Unilab glovebox to prevent from humidity
and oxidation. The MgH2 powder was ball milled with different wt.% of SrFe12O19 (5, 10, 15, 20
and 50 wt.%) in a planetary ball mill (NQM-0.4) for 1 h, by milling for 15 min, resting for 2 min
and then milling for another 15 min. This process was conducted in 3 cycles in a different
direction at a rotation speed of 400 rpm using hardened stainless steel vials and stainless steel
balls. The ratio of the weight of the balls to the weight of the powder was 40:1.
2.2 Characterizations of sample
For the temperature-programmed desorption (TPD) and the rehydrogenation and
dehydrogenation kinetic measurements, about 100 mg of the sample was loaded into a sample
vessel in the glovebox. The experiments were performed in a Sievert-type PCT apparatus
(Advanced Material Corporation). For the TPD experiment, all the samples were heated in a
vacuum chamber and the amount of desorbed hydrogen was measured to determine the lowest
o
decomposition temperature. The heating rate for the TPD experiment was 5 C/min and the
samples were heated from 25 oC to 450 oC. The de/rehydrogenation kinetics measurements were
conducted at the desired temperature with initial hydrogen pressures of 1.0 atm and 30 atm,
respectively.
The phase structures of the samples before and after desorption as well as after
rehydrogenation were performed using a Rigaku MiniFlex X-ray diffractometer with Cu Kα
radiation. θ-2θ scans were carried out over diffraction angles from 20° to 80° at a speed of 2.00
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°/min. All the samples were prepared in the glovebox in order to minimise the oxidation of the
sample. To avoid exposure to the air during the measurement, the sample was spread uniformly
on the sample holder and covered with scotch tape and sealed in plastic wrap.
Differential scanning calorimetry (DSC) analysis of the dehydrogenation process was
carried out on a Mettler Toledo TGA/DSC 1. About 2–6 mg of sample was loaded into an
alumina crucible in the glove box. The crucible was then placed in a sealed glass bottle in order
to prevent oxidation during transportation from the glove box to the DSC apparatus. An empty
alumina crucible was used as the reference material. The samples were heated from room
temperature to desire temperature under an argon flow of 50 ml/min, and different heating rates
were used. The microstructures of the samples were characterized by using a scanning electron
microscope (SEM; JEOL JSM-6360LA) by setting the samples on carbon tape and then coating
them with gold spray under a vacuum
3. Results and Discussion
3.1 Dehydrogenation temperature
Fig. 1 shows the TPD patterns for the dehydrogenation of as-received MgH2, as-milled
MgH2, MgH2 + 5 wt.% SrFe12O19, MgH2 + 10 wt.% SrFe12O19, MgH2 + 15 wt.% SrFe12O19,
MgH2 + 20 wt.% SrFe12O19 and MgH2 + 50 wt.% SrFe12O19. The as-received MgH2 started to
release hydrogen at about 420 °C, with a total dehydrogenation capacity of 7.42 wt.% H2 by
450 °C. After milling, the onset desorption temperature of MgH2 was reduced to about 350 °C
with the total capacity of hydrogen desorbed about 6.68 wt.%, indicating that the milling process
also influences the onset desorption temperature of MgH2, as reported by Huot et al.33 It is
obvious that after doping with different percentages of SrFe12O19 the onset desorption
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temperature of MgH2 dramatically reduced compared with that as-milled and as-received. With 5
wt.% SrFe12O19 the onset desorption temperature initiated at about 300 °C, but the addition of 10
wt.% caused a reduction to 270 °C. By increasing the doping amount of SrFe12O19 to 15 and 20
wt.%, the desorption temperature reduced to about 285 °C for both samples. Meanwhile, by
increasing the additive amount to 50 wt.%, hydrogen started to desorb at about 300 °C but with a
reduction in released hydrogen content. It can be speculated that when the desorption capacity of
the samples with 20 and 50 wt.% SrFe12O19 dropped slightly to about 4.7 wt.%, this was due to
the excessive catalytic effect of added amounts of SrFe12O19.
3.2 De/rehydrogenation kinetics
Isothermal dehydrogenation kinetic curves for the as-milled MgH2 and MgH2 doped with
5, 10, 15, 20 and 50 wt.% SrFe12O19 were studied at a constant temperature of 320 °C under 1
atm pressure, as shown in Fig. 2. The results show that the samples doped with 5 and 10 wt.%
SrFe12O19 released 2.8 and 4.3 wt.% hydrogen, respectively, within 15 min. Meanwhile, for the
samples doped with 15 and 20 wt.% SrFe12O19, the capacity of hydrogen released was about 2.1
wt.% for both samples over the same time period. By increasing the SrFe12O19 content to 50
wt.%, the amount of hydrogen released reduced to 1.9 wt.% in 15 min and about 3.1 wt.% after
60 min. In contrast, only 0.2 wt.% hydrogen was released from as-milled sample at this
temperature in 15 min. It can be seen that the addition of SrFe12O19 improved the
dehydrogenation kinetics of MgH2 and that samples doped with 10 wt.% SrFe12O19 showed the
fastest desorption.
In order to investigate the reversibility of the samples, isothermal rehydrogenation
kinetics for as-milled MgH2 and doped-MgH2 were measured at a constant temperature of
320°C, under a 30 atm H2 pressure, as shown in Fig. 3. It is obvious that the MgH2 doped with 5
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and 10 wt.% SrFe12O19 had better rehydrogenation kinetics than undoped MgH2. The samples
doped with 5 and 10 wt.% SrFe12O19 absorbed approximately 4.6 and 4.8 wt.% hydrogen,
respectively, within 1 h, while the hydrogen absorbed by the as-milled MgH2 was about 4.2 wt.%
under the same conditions. However, the samples of MgH2 doped with 15 and 20 wt.%
SrFe12O19 showed slow rehydrogenation kinetics compared with MgH2, with only 3.6 wt.% and
3.1 wt.% hydrogen absorbed within 1 h, respectively. When the amount of SrFe12O19 was
increased to 50 wt.%, the sample only absorbed about 2.8 wt.% hydrogen at 1 h, i.e. a slower
absorption rate than as-milled MgH2 and MgH2 doped with 15 and 20 wt.% SrFe12O19. The
decreasing hydrogen capacity and slower rehydrogenation kinetics in the 15, 20 and 50 wt.%
samples was due to a superfluous catalytic effect brought about by the relatively large amount of
added SrFe12O19, blocking the diffusion path of hydrogen to some extent, and thereby reducing
the reaction between Mg and hydrogen.34 This same phenomenon was reported in our previous
3
paper . These results indicate that the addition of a minimum amount of SrFe12O19 can also
improve the rehydrogenation kinetics of MgH2.
Therefore, the results of the onset decomposition temperature reduction and hydrogen
sorption kinetics, show that 10 wt.% SrFe12O19 is optimum for enhancement of MgH2 hydrogen
storage properties. Thus, this sample was chosen for further analysis to determine exactly how
this catalyst affects MgH2 properties.
3.3 Differential Scanning Calorimetry
Fig. 4 presents the thermal properties of as-received MgH2, as-milled MgH2 and MgH2 +
10 wt.% SrFe12O19, identified by DSC at heating rate of 20°C/min within a temperature range of
25–500°C and under an argon flow of 50 ml/min. The DSC curves of all samples display only a
single strong endothermic peak which corresponds to the decomposition of MgH2. The DSC
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curve of as-received MgH2 shows the peak temperature at approximately 458.4°C. Meanwhile,
the hydrogen desorption temperature of the as-milled MgH2 and MgH2 + 10 wt.% SrFe12O19
show the peak of the DSC curves shifted to the lower temperatures compared with as-received
MgH2. The DSC curves for the as-milled MgH2 and MgH2 + 10 wt.% SrFe12O19 samples had
strong endothermic peaks at 426.7°C and 409.5°C, which decreased by approximately 31.7°C
and 48.9°C, respectively. The reduction of the peak temperature in the DSC results indicate that
the dehydrogenation properties of MgH2 were significantly enhanced by adding SrFe12O19.
However, the onset desorption temperature of the samples from the DSC results were slightly
higher than from TPD. These phenomena may be due to the different atmospheres and heating
rates used in the two types of measurements as explained in our previous paper.35-38
In order to determine the effects of SrFe12O19 addition on the activation energy of MgH2,
Kissinger analysis39 was used according to the following equation:
2
/Tp ] = -EA/RTp + A
ln[β
(1)
where
β
is the heating rate, Tp is the peak temperature in the DSC curve, R is the gas constant,
and A is a linear constant. Thus, the activation energy, EA, could be obtained from the slope in a
2
/Tp ] versus 1000/Tp. The DSC traces at different heating rates for as-received MgH2,
plot of ln[
β
as-milled MgH2 and MgH2 + 10 wt. % SrFe12O19 used for calculation of the activation energy,
EA, are shown in Fig. 5.
From the Kissinger plot of the DSC data, Fig. 6, the apparent activation energy for the as-
received MgH2 and as-milled MgH2 was found to be 183.0 kJ/mol and 133.3 kJ/mol,
respectively. Meanwhile, the apparent activation energy for MgH2 + 10 wt. % SrFe12O19 was
114.2 kJ/mol, significantly lower by comparison than the other samples which were reduced by
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68.8 and 19.1 kJ/mol, respectively. This result indicates that the apparent activation energy is
reduced after doping with SrFe12O19 and thus the dehydrogenation behaviour of MgH2 improves.
3.4 Scanning Electron Microscope
Fig. 7 shows the morphologies of the as-received MgH2, as-received SrFe12O19, as-milled
MgH2 and as-milled MgH2 + 10 wt.% SrFe12O19. The SEM images show that the as-received
MgH2 particles had an angular shape, with an average particle size larger than 100 µm.
Meanwhile, the particle size of the as-received SrFe12O19 was smaller than 5 µm. In addition, the
MgH2 particle size drastically reduced after ball milling for 1 h. However, the particle size was
not homogenous and some agglomeration existed. By comparison, the MgH2 sample doped with
10 wt.% SrFe12O19 had a smaller particle size and appeared to have less agglomeration. It has
been reported that reduction in particle agglomeration and growth results in improvement of the
hydrogen storage properties of light metal hydrides 40. Meanwhile, a smaller particle size helps to
improve hydrogen absorption and desorption, as it reduces the diffusion length and offers a
larger particle surface.34, 41 Hence, it can be speculated that the hydrogen storage properties of
MgH2 are improved after adding the SrFe12O19 due to a reduction in particle size and less
agglomeration.
3.5 X-ray diffraction
To investigate the catalyst effect on the improvement of MgH2, Fig. 8 represents the
XRD pattern of as-milled MgH2 + 10 wt.% SrFe12O19 after 1 h ball milling, after
dehydrogenation at 450 °C and after rehydrogenation at 320 °C under 30 atm. The result shows
that after 1 h ball milling, Fig. 8 (a), in addition to the MgH2 peaks, a few peaks corresponding to
the SrFe12O19 phase exist. After dehydrogenation at 450 °C, Fig. 8 (b), there was a distinct Mg
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peak, indicating that the dehydrogenation of MgH2 was complete. The transformation of MgH2
to Mg is represented by the following equation:
MgH2 → Mg + H2
(2)
Meanwhile, new diffraction peaks of MgO, MgFe2O4 and Fe were detected after the
dehydrogenation process, indicating that MgH2 and SrFe12O19 may have reacted. For the
rehydrogenated sample, Fig. 8 (c), it can be seen that the Mg peak was largely transformed into
MgH2. The peaks of MgFe2O4 and Fe, with a small amount of MgO, were still present after the
rehydrogenation process.
In order to investigate the phase structure in more detail, a sample of MgH2 doped with
50 wt.% SrFe12O19 was prepared, as only slight MgFe2O4 and Fe peaks were detected and no Sr-
containing phase appeared in the XRD phase composition of the 10 wt.% SrFe12O19. Fig. 9
shows the XRD patterns of MgH2 doped with 50 wt.% SrFe12O19 after 1 h ball milling, after
dehydrogenation at 450 °C, and after rehydrogenation at 320 °C. The results indicate that after 1
h ball milling, the peak intensity of MgH2 and SrFe12O19 gradually enhanced after increasing the
amount of SrFe12O19 to 50 wt.%, Fig. 9 (a), compared to the MgH2 + 10 wt.% SrFe12O19 sample.
After dehydrogenated at 450 °C, the diffraction peaks of Mg slightly decline and those of the Fe,
MgFe2O4 and MgO phases are more discernible, while a new phase of SrO appears due to the
higher SrFe12O19 concentration. The MgH2 + 10 wt.% SrFe12O19 sample shows no Sr-containing
species. Meanwhile, after rehydrogenated at 320 °C, the Fe, MgFe2O4 and SrO diffraction peaks
remain unchanged and the Mg peak is largely transformed to MgH2. MgO is still observed,
probably due to oxygen contamination during sample preparation. From this result, it can be
assumed that MgH2 reacts with SrFe12O19 during the heating process forming Fe, MgFe2O4 and
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SrO phases, and this reaction becomes more acute with increasing SrFe12O19. The reaction
between MgH2 and 50 wt.% SrFe12O19 may be postulated as the following equation:
9MgH2 + 2SrFe12O19 → 9MgFe2O4 + 2SrO + 6Fe + 9H2
(3)
The standard state free energy of reaction, ꢀG°, can be calculated from the standard state free
energies using the equation below:
ꢀG° =
ꢀG°fproducts
∑
−
ꢀG°freactants
∑
(4)
The values of standard Gibbs free energy, ꢀG°f, of MgH2, SrFe12O19, MgFe2O4 and SrO are
−35.98, −5015.88, −1317.12 and −562.41 kJ/mol, respectively, have been obtained from the
literature.42 Thus, by using eqn (4), the total change, ꢀG, associated with the reaction in equation
(3) will be −2623.34 kJ/mol of MgH2. The possibility of the reaction stated in eqn (3) is proven
by the results obtained from the thermodynamic potentials.
Based on the above analyses, the improvement in hydrogen storage properties acquired in
this study may be attributed to a few factors. First, the reduction in particle size after ball milling
and addition of a catalyst may contribute to a high density of surface defects and more grain
boundaries. It is believed that a large number of defects introduces a large number of nucleation
sites at the surface of MgH2 and provides hydrogen diffusion channels for dehydrogenation.30
Second, the new active species of Fe, MgFe2O4, and SrO, formed after de/rehydrogenation,
might act as real catalysts for improving the hydrogen sorption properties of MgH2 as they can
create surface activation and form a large number of nucleation sites at the surface of the MgH2
matrix.41 The in situ Fe particles, with a higher peak intensity than the MgFe2O4 and SrO species
as shown in the XRD pattern, may play an important role as it has been reported that Fe is one of
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the good catalysts for improvement in MgH2 hydrogen storage properties.43, 44 Bassetti et al.45
reported that proper combination of Fe and MgH2 leads to a significant increase in the desorption
kinetics of MgH2 where almost the whole H content is released in less than 1000 seconds at 300
°C. Meanwhile, previous studies also discuss transition metal catalysts such as Fe, Ni, Co and Pd
that play an important role in enhancing MgH2 hydrogen storage properties.46-48 In addition,
MgFe2O4 and SrO may also have an extra catalytic effect on MgH2. Previous studies have shown
that MgH2 with metal oxide addition gives as good or even faster hydrogenation kinetics than
their metallic counterpart.12, 49, 50 So, the catalytic effect of Fe may further combine with the
catalytic functions of MgFe2O4 and SrO to generate a synergetic catalytic effect. Thus, it is
reasonable to conclude that these newly developed products act as real catalysts and doping with
SrFe12O19 can result in significant improvement in MgH2 desorption properties.
4. Conclusion
The effects of different contents (5, 10, 15, 20 and 50 wt.%) of an SrFe12O19 additive on the
hydrogen storage properties of MgH2, prepared by the ball milling method, were investigated for
the first time. It was found that the hydrogen sorption properties of MgH2 improved significantly
after SrFe12O19 addition, and that compared with un-doped MgH2, 10 wt.% SrFe12O19 resulted in
optimum performance in terms of onset dehydrogenation temperature and de/rehydrogenation
kinetics. The onset desorption temperature of MgH2 + 10 wt.% SrFe12O19 was reduced to 270 °C,
decreasing by about 80 °C and 150 °C for as-milled and as-received MgH2, respectively. The
isothermal dehydrogenation kinetics show that a 10 wt.% SrFe12O19 doped sample can release
4.3 wt.% H2 in 15 min, whereas as-milled MgH2 can only release 0.2 wt.% within the same time.
Regarding rehydrogenation kinetics, the sample doped with 10 wt.% SrFe12O19 absorbed
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approximately 4.8 wt.% hydrogen within 1 h at 320 °C, while the hydrogen absorbed by the as-
milled MgH2 was about 4.3 wt.% under the same conditions. From the Kissinger plot of DSC,
the apparent activation energies for as-received MgH2 and as-milled MgH2 were 183 kJ/mol and
133.31 kJ/mol, respectively. This reduced to 114.22 kJ/ mol for MgH2 + 10 wt.% SrFe12O19,
indicating that SrFe12O19 addition decreased the activation energy for hydrogen desorption of
MgH2. In addition, particle size reduction and less agglomeration may help improve the
hydrogen sorption properties of MgH2. From the XRD results, it is believed that the formation of
a new species of Fe, MgFe2O4 and SrO during ball milling or the de/rehydrogenation process
might actually be responsible for the catalytic effects and thus, further enhanced the hydrogen
storage properties of the MgH2. It can be concluded that SrFe12O19 is one of the promising
additives for MgH2 as it tends to reduce the onset desorption temperature and significantly
improves the kinetic performance.
Acknowledgements
The authors thanks the Universiti Malaysia Terengganu for providing the facilities to carry out
this project. The author also acknowledges the Malaysian Government for the financial support
through the Fundamental Research Grant Scheme (VOT 59362). N. S. Mustafa and N. N Itam
Sulaiman are grateful to the Malaysian Ministry of Education for a MyBrain15 scholarship.
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References
1.
2.
3.
4.
L. Mai, X. Tian, X. Xu, L. Chang and L. Xu, Chem. Rev., 2014, 114, 11828-11862.
L. Schlapbach and A. Züttel, Nature, 2001, 414, 353-358.
M. Ismail, Int. J. Hydrogen Energy, 2014, 39, 2567-2574.
B. Sakintuna, F. Lamari-Darkrim and M. Hirscher, Int. J. Hydrogen Energy, 2007, 32,
1121-1140.
5.
6.
G. Principi, F. Agresti, A. Maddalena and S. Lo Russo, Energy, 2009, 34, 2087-2091.
H. Gasan, O. N. Celik, N. Aydinbeyli and Y. M. Yaman, Int. J. Hydrogen Energy, 2012,
37, 1912-1918.
7.
A. Ranjbar, Z. P. Guo, X. B. Yu, D. Attard, A. Calka and H. K. Liu, Int. J. Hydrogen
Energy, 2009, 34, 7263-7268.
8.
L. E. A. Berlouis, P. Honnor, P. J. Hall, S. Morris and S. B. Dodd, J. Mater. Science,
2006, 41, 6403-6408.
9.
L. Z. Ouyang, X. S. Yang, M. Zhu, J. W. Liu, H. W. Dong, D. L. Sun, J. Zou and X. D.
Yao, J. Phys. Chem. C, 2014, 118, 7808-7820.
10.
V. Koteski, J. Belosevic-Cavor, K. Batalovic, J. Radakovic and A. Umicevic, RSC Adv.,
2015, 5, 34894-34899.
11.
12.
13.
N. Juahir, N. S. Mustafa, A. Sinin and M. Ismail, RSC Adv., 2015, 5, 60983-60989.
K. S. Jung, E. Y. Lee and K. S. Lee, J. Alloys Compd., 2006, 421, 179-184.
V. V. Bhat, A. Rougier, L. Aymard, G. A. Nazri and J. M. Tarascon, J. Alloys Compd.,
2008, 460, 507-512.
14.
15.
16.
17.
A. Patah, A. Takasaki and J. S. Szmyd, Int. J. Hydrogen Energy, 2009, 34, 3032-3037.
B.-H. Chen, Y.-S. Chuang and C. o.-K. Chen, J. Alloys Compd., 2016, 655, 21-27.
M. Ismail, Energy, 2015, 79, 177-182.
M. Ismail, N. S. Mustafa, N. Juahir and F. A. H. Yap, Mater. Chem. Phys., 2016, 170,
77-82.
15

RSC Advances
Page 16 of 24
View Article Online
DOI: 10.1039/C6RA22291A
18.
V. V. Bhat, A. Rougier, L. Aymard, X. Darok, G. Nazri and J. M. Tarascon, J. Power
Sources, 2006, 159, 107-110.
19.
20.
I. E. Malka, T. Czujko and J. Bystrzycki, Int. J. Hydrogen Energy, 2010, 35, 1706-1712.
I. E. Malka, M. Pisarek, T. Czujko and J. Bystrzycki, Int. J. Hydrogen Energy, 2011, 36,
12909-12917.
21.
L. Z. Ouyang, Z. J. Cao, H. Wang, J. W. Liu, D. L. Sun, Q. A. Zhang and M. Zhu, J.
Alloys Compd., 2014, 586, 113-117.
22.
23.
24.
N. S. Mustafa and M. Ismail, Int. J. Hydrogen Energy, 2014, 39, 15563-15569.
F. A. Halim Yap, N. S. Mustafa and M. Ismail, RSC Adv., 2015, 5, 9255-9260.
A. Ranjbar, M. Ismail, Z. P. Guo, X. B. Yu and H. K. Liu, Int. J. Hydrogen Energy, 2010,
35, 7821-7826.
25.
26.
27.
28.
29.
30.
31.
32.
33.
M. Lototskyy, J. M. Sibanyoni, R. V. Denys, M. Williams, B. G. Pollet and V. A. Yartys,
Carbon, 2013, 57, 146-160.
X. B. Yu, Y. H. Guo, H. Yang, Z. Wu, D. M. Grant and G. S. Walker, J. Phys. Chem. C,
2009, 113, 5324-5328.
X. B. Yu, Y. H. Guo, Z. X. Yang, Z. P. Guo, H. K. Liu and S. X. Dou, Scripta Mater.,
2009, 61, 469-472.
X. B. Yu, Z. X. Yang, H. K. Liu, D. M. Grant and G. S. Walker, Int. J. Hydrogen Energy,
2010, 35, 6338-6344.
Q. Wan, P. Li, J. Shan, F. Zhai, Z. Li and X. Qu, J. Phys. Chem. C, 2015, 119, 2925-
2934.
P. Li, Q. Wan, Z. Li, F. Zhai, Y. Li, L. Cui, X. Qu and A. A. Volinsky, J. Power Sources,
2013, 239, 201-206.
J. Zhang, J. Shan, P. Li, F. Zhai, Q. Wan, Z. Liu and X. Qu, J. Alloys Compd., 2015, 643,
174-180.
J. Shan, P. Li, Q. Wan, F. Zhai, J. Zhang, Z. Li, Z. Liu, A. A. Volinsky and X. Qu, J.
Power Sources, 2014, 268, 778-786.
J. Huot, G. Liang, S. Boily, A. Van Neste and R. Schulz, J. Alloys Compd., 1999, 293-
295, 495-500.
16

Page 17 of 24
RSC Advances
View Article Online
DOI: 10.1039/C6RA22291A
34.
35.
36.
37.
A. Ranjbar, Z. P. Guo, X. B. Yu, D. Wexler, A. Calka, C. J. Kim and H. K. Liu, Mater.
Chem. Phys., 2009, 114, 168-172.
M. Ismail, Y. Zhao, X. B. Yu and S. X. Dou, Int. J. Hydrogen Energy, 2010, 35, 2361-
2367.
M. Ismail, Y. Zhao, X. B. Yu, A. Ranjbar and S. X. Dou, Int. J. Hydrogen Energy, 2011,
36, 3593-3599.
M. Ismail, Y. Zhao, X. B. Yu, I. P. Nevirkovets and S. X. Dou, Int. J. Hydrogen Energy,
2011, 36, 8327-8334.
38.
39.
40.
41.
M. Ismail, Y. Zhao, X. B. Yu and S. X. Dou, Int. J. Electroactive Mater., 2013, 1, 13-22.
H. E. Kissinger, Anal. Chem., 1957, 29, 1702-1706.
M. Ismail, N. Juahir and N. S. Mustafa, J. Phys. Chem. C, 2014, 118, 18878-18883.
F. Zhai, P. Li, A. Sun, S. Wu, Q. Wan, W. Zhang, Y. Li, L. Cui and X. Qu, J. Phys.
Chem. C, 2012, 116, 11939-11945.
42.
43.
http://www.drjez.com/uco/.../StandardThermodynamicValues.
S. Deledda, A. Borissova, C. Poinsignon, W. J. Botta, M. Dornheim and T. Klassen,
Phys. Chem. Chem. Phys., 2005, 404-406, 409-412.
44.
45.
A. Montone, A. Aurora, D. M. Gattia and M. V. Antisari, Catalysts, 2012, 2, 400-411.
A. Bassetti, E. Bonetti, L. Pasquini, A. Montone, J. Grbovic and M. Vittori Antisari, Eur.
Phys. J. B, 2005, 43, 19-27.
46.
J.-l. Bobet, E. Akiba, Y. Nakamura and B. Darriet, Int. J. Hydrogen Energy, 2000, 25,
987-996.
47.
48.
49.
50.
N. Hanada, T. Ichikawa and H. Fujii, J. Phys. Chem. B, 2005, 109, 7188-7194.
N. N. Sulaiman, N. S. Mustafa and M. Ismail, Dalton Trans., 2016, 45, 7085-7093.
G. Barkhordarian, T. Klassen and R. Bormann, Scripta Mater., 2003, 49, 213-217.
Gupta R, Agresti F, Russo SL, Maddalena A, Palade P and P. G, J. Alloys Compd., 2008,
450, 310-313.
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Figure captions
Fig. 1 TPD patterns for the dehydrogenation of the as-received MgH2, as-milled MgH2 and
MgH2 doped with 5 wt. % , 10 wt. % , 15 wt. % , 20 wt. % and 50 wt. % SrFe12O19.
Fig. 2 Isothermal dehydrogenation kinetic of the as-milled MgH2 and MgH2 doped with 5 wt.%,
10 wt.% , 15 wt.%, 20 wt. % and 50 wt. % SrFe12O19 at 320 °C.
Fig. 3 Isothermal rehydrogenation kinetic of the as-milled MgH2 and MgH2 doped with 5 wt.%,
10 wt.% , 15 wt.%, 20 wt. % and 50 wt. % SrFe12O19 at 320 °C under 30 atm.
Fig. 4 DSC traces of as-received MgH2, as-milled MgH2 and MgH2 + 10 wt. % SrFe12O19
(heating rate: 20 °C/min; argon flow: 50 mL/min).
Fig. 5 DSC traces at different heating rates for as-received MgH2, as-milled MgH2, and MgH2 +
10 wt. % SrFe12O19.
Fig. 6 Kissinger plot of dehydrogenation for as-received MgH2, as-milled MgH2, and MgH2 +
10 wt. % SrFe12O19.
Fig. 7 SEM images of as-received MgH2, as-received SrFe12O19, as-milled MgH2 and MgH2+ 10
wt.% SrFe12O19.
Fig. 8 X-ray diffraction patterns of MgH2+ 10 wt.% SrFe12O19 (a) after 1 h ball milling, (b) after
dehydrogenation at 450 °C , and (c) after rehydrogenation at 320 °C.
Fig. 9 X-ray diffraction patterns of MgH2+ 50 wt.% SrFe12O19 (a) after 1 h ball milling, (b) after
dehydrogenation at 450 °C , and (c) after rehydrogenation at 320 °C.
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Figures
Figure 1
Figure 2
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Figure 3
Figure 4
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Figure 5
Figure 6
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Figure 7
Figure 8
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Figure 9
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Graphical Table of Contents (GTOC)
The desorption temperature of MgH2 + 10 wt.% SrFe12O19 decreased to about 270°C
compared to the 350°C and 420°C for as-milled and as-received MgH2, respectively. The
activation energy calculated by Kissinger analysis for hydrogen desorption decreased to
114.2 kJ/mol after Fe2O3 was added compared with the un-doped 4MgH2-Li3AlH6 composite,
which was 133.3 kJ/mol.