Influence of different amounts of FeCl3 on decomposition and hydrogen sorption kinetics of MgH2

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Influence of different amounts of FeCl3 ondecomposition and hydrogen sorption kinetics ofMgH2

M. Ismail*

Department of Physical Sciences, Faculty of Science and Technology, Universiti Malaysia Terengganu,

21030 Kuala Terengganu, Malaysia

a r t i c l e i n f o

Article history:

Received 20 August 2013

Received in revised form

31 October 2013

Accepted 18 November 2013

Available online 6 January 2014

Keywords:

Magnesium hydride

Iron chloride

Catalytic effect

De/rehydrogenation

a b s t r a c t

In the present work, the hydrogen storage properties of MgH2-X wt.% FeCl3 (X ¼ 5, 10, 15

and 20) are investigated experimentally. It is found that the MgH2 þ 10 wt.% FeCl3 sample

exhibits the best comprehensive hydrogen storage properties, in terms of the onset

dehydrogenation temperature, the hydrogen amounts de/reabsorbed as well as the relative

de/rehydrogenation rates. The onset dehydrogenation temperature of the 10 wt.% FeCl3-

doped MgH2 sample is reduced by about 90 �C compared to the as-milled MgH2, and the

sorption kinetics measurements indicate that the FeCl3-doped sample displays an average

dehydrogenation rate 5e6 times faster than that of the undoped MgH2 sample. Higher

levels of doping introduce negative effects, such as lower capacity and slower absorption/

desorption rates compared to samples with lower FeCl3 doping levels. The apparent acti-

vation energy for hydrogen desorption is decreased from 166 kJ�mol�1 for as-milled MgH2

to 130 kJ�mol�1 by the addition of 10 wt.% FeCl3. It is believed that the improvement of the

MgH2 sorption properties in the MgH2/FeCl3 composite is due to the catalytic effects of the

in-situ generated Fe species and MgCl2 that are formed during the heating process.

Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction

Its large gravimetric density (7.6wt.%H2), abundant resources,

low cost and good reversibility are advantages of MgH2

compared with other metal hydrides or complex hydrides

such as LaNi5 [1] and LiAlH4 [2e5]. These advantages make

MgH2 an attractive material as a potential candidate for solid-

state hydrogen storage. Nevertheless, the high decomposition

temperature and slow desorption/absorption kinetics are two

problems that limit the use of MgH2 as a hydrogen storage

material. Many extensive efforts have been carried out to

overcome these problems, including the use of a catalyst [6,7],

mechanical treatment to produce nanocomposites [8e10] and

combination with other metal/complex hydrides (destabili-

sation systems) [11e20]. Among them, the introduction of

catalysts into MgH2 has produced a significant effect on the

hydrogen sorption properties of MgH2. Various catalysts have

been doped into MgH2 by mechanical milling such as metal

[21e27], metal oxide [28e36], metal halide [7,37e47], carbon

materials [48e55] and alloys [56e59].

Previous studies have shown that the addition of a

transition-metal compound on MgH2 significantly improved

the hydrogen sorption properties. This enhancement can be

* Tel.: þ609 6683336; fax: þ60 9 6694660.E-mail address: [email protected].

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associatedwith the catalytic role of transitionmetal cations to

the dissociation process of hydrogen molecules. Liang et al.

[23] reported that the added 5 wt.% transitionmetal (Ti, V, Mn,

Fe, Ni) improved the de/rehydrogenation kinetics of MgH2

compared to undopedMgH2. Meanwhile, the addition ofmetal

halides as catalysts significantly improved the hydrogen

storage properties of MgH2 [7,37,38]. Like the other additive

group, the real catalytic mechanism of metal halides on MgH2

is still an open question. Jin et al. [37] studied the effects of

NbF5 on the hydrogenation properties of MgH2 and concluded

that the actual catalyst was Nb hydride, not NbF5. It was

suggested that NbF5 melts during high-energy ball milling and

this promotes the formation of extremely fine, film-like Nb

hydride preferentially along the grain boundaries of nano-

crystalline MgH2 by a liquid/solid reaction and suppresses the

grain growth of MgH2 quite effectively. Ma et al. [41,42]

compared the catalytic effects of TiF3 and TiCl3, and found

that TiF3 showed a superior catalytic effect over TiCl3 in

improving the hydrogen sorption kinetics of MgH2, which was

attributed to the catalytic effects of the F anion. From com-

bined XPS examination and designed experiments, Ma et al.

suggested that a considerable amount of F participated in the

generation of a metastable active TieFeMg species. Recently,

Mao et al. [7] studied the catalytic effect of NiCl2 and CoCl2 on

the hydrogen sorption of MgH2 and suggested that besides the

catalytic effect of Mg2Ni and Mg2Co as a dehydrogenation

product, the chlorine-based product, MgCl2, may also play an

important role in improving the hydrogen sorption kinetic

properties of MgH2.

This paper introduces the use of FeCl3 to prepare an MgH2-

metal chloride system aiming at combining the functions of

both transition metal cations and chlorine anions. Different

amounts of MgH2 and FeCl3 were ball milled together to pre-

pare a set of MgH2/FeCl3 mixtures and their hydrogen storage

properties and reaction mechanisms were investigated by a

Sievert-type pressure-composition-temperature (PCT) appa-

ratus, differential scanning calorimetry (DSC) and X-ray

diffraction (XRD). The catalytic effect of FeCl3 on the hydrogen

sorption properties of MgH2 was investigated.

2. Experimental details

Pure MgH2 (hydrogen storage grade), FeCl3 (reagent grade,

97%) and MgCl2 (anhydrous, �98%) were purchased from

SigmaeAldrich. Iron powder (�200 mesh, 99þ% (metal basis))

were purchased from Alfa Aesar. All materials were used as

received with no further purification. The MgH2 and additives

were respectively loaded into a sealed stainless steel vial

together with hardened stainless steel balls in an argon at-

mosphere MBraun UNIlab glove box. The ratio of the weight of

the balls to the weight of the powder was 40:1. The samples

were then milled in a planetary ball mill (NQM-0.4) for 1 h, by

first milling for 0.5 h, resting for 6 min, and then milling for

another 0.5 h in a different direction at the rate of 400 rpm.

The experiments on de/rehydrogenation were performed

in a Sievert-type PCT apparatus (Advanced Materials Corpo-

ration). The sample was loaded into a sample vessel in the

glove box. For the temperature-programmed desorption (TPD)

measurements, all the samples were heated in a vacuum

chamber, and the amount of desorbed hydrogen was

measured to determine the lowest decomposition tempera-

ture. The heating rate for the TPD experiment was 5 �Cmin�1,

and samples were heated from room temperature to 450 �C.The de/rehydrogenation kinetics measurements were con-

ducted at the desired temperature with initial hydrogen

pressures of 0.1 MPa and 3.0 MPa, respectively.

XRD analysis was performed using a RigakuMiniFlex X-ray

diffractometer with Cu Ka radiation. q�2q scans were carried

out over diffraction angles from 20� to 80� with a speed of

2.00� min�1. Before the measurement, a small amount of

sample was spread uniformly on the sample holder, which

was wrapped with plastic wrap to prevent oxidation.

DSC analysis of the dehydrogenation process was carried

out on a Mettler Toledo thermogravimetric analysis/differ-

ential scanning calorimetry (TGA/DSC) 1. The 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 for reference.

The samples were heated from room temperature to 550 �Cunder an argon flow of 30 ml min�1, and different heating

rates were used.

3. Results and discussion

3.1. Dehydrogenation temperature

Fig. 1 presents the TPD performances of the as-received MgH2,

the as-milled MgH2, and the MgH2 doped with 5 wt.%, 10 wt.%,

15 wt.% and 20 wt.% FeCl3. From the TPD curves, it is clear that

raising the dopant percentage from 5 wt.% to 20 wt.% resulted

in a decrease of the onset desorption temperature compared

to the undopedMgH2. The as-received MgH2 started to release

hydrogen at about 410 �C, with a total dehydrogenation ca-

pacity of 7.0 wt.% H2 by 430 �C. After milling, the onset

desorption temperature of MgH2 was reduced to about 340 �C,indicating that the milling process also influenced the onset

Fig. 1 e TPD patterns for the dehydrogenation of as-

received MgH2, as-milled MgH2 and the MgH2 doped with

5 wt.%, 10 wt.%, 15 wt.% and 20 wt.% FeCl3.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 9 ( 2 0 1 4 ) 2 5 6 7e2 5 7 42568


desorption temperature of MgH2 [8,60]. The curve shows that

there was no reduction in the hydrogen desorption capacity of

MgH2 after milling. The addition of FeCl3 markedly improved

the onset desorption temperature for MgH2. All the samples

doped with FeCl3 started to decompose below 300 �C. For the5 wt.% doped sample, the dehydrogenation process was

initiated at 290 �C, which was a decrease in the desorption

onset of about 50 �C, with a total dehydrogenation capacity of

7.0 wt.% H2, which was the same as the hydrogen desorption

capacity of the as-received and as-milled MgH2. A further in-

crease of the additives up to 10 wt.% reduced the dehydroge-

nation temperatures to about 250 �C. The addition of 10 wt.%

FeCl3 caused decreases in the desorption onset of about 90 �C,but the amount of hydrogen released slightly dropped to about

6.5 wt.% H2. Further raising the doping amounts to 15 wt.%

and 20 wt.% reduced the desorption temperature to 245 �C but

at the cost of more loss of hydrogen release content. The

overall hydrogen release content was 6 wt.% H2. We assume

the reduction of hydrogen capacity in the 15 wt.% and 20 wt.%

added samples was due to the excessive catalytic effect

brought about by the relatively high level of the added FeCl3.

3.2. De/rehydrogenation kinetics

Isothermal desorption kinetics curves for the as-milled MgH2

and theMgH2 dopedwith 5 wt.%, 10 wt.%, 15 wt.% and 20 wt.%

FeCl3 samples were measured at 300 �C under 0.1 MPa pres-

sure. Fig. 2 shows that the samples doped with 5 wt.%,

10 wt.%, 15 wt.% and 20 wt.% FeCl3 released 5.06 wt.%,

5.75 wt.%, 4.77 wt.% and 4.06 wt.% hydrogen at 300 �C in

30 min under 0.1 MPa pressure, respectively. In contrast, the

undoped MgH2 sample desorbed just 0.88 wt.% hydrogen over

the same time. The doped samples showed a significant

improvement with respect to desorption kinetics. Fig. 3 shows

the isothermal absorption kinetics measurements for the as-

milled MgH2 and FeCl3-doped MgH2 samples. The samples

were soaked at a constant temperature of 300 �C and under

3.0 MPa hydrogen pressure. The hydrogen absorbed by the

5 wt.%, 10 wt.%, 15 wt.% and 20 wt.% FeCl3-doped MgH2

samples at 300 �C reached 4.65 wt.%, 5.21 wt.%, 4.74 wt.% and

4.02 wt.% hydrogen within 2 min. The as-milled MgH2 sample

absorbed 4.06 wt.% hydrogen over the same period. Analysis

of the isothermal de/absorption kinetics shows that a signifi-

cant improvement of MgH2 de/rehydrogenation kinetics can

be achieved by adding 10 wt.% FeCl3.

The result shows that the 10 wt.% doping amount can be

considered as the best compromise between the dehydroge-

nation temperature, isothermal de/absorption kinetics and

hydrogen yield, considering that a large amount of FeCl3 is

detrimental in terms of gravimetrical hydrogen density. Thus,

identification of the optimal 10wt.% amount of FeCl3 led to the

analysis of the FeCl3 mechanism and the catalytic effect in the

subsequent test.

In addition, to further analyse the hydrogen desorption

kinetics of the MgH2/FeCl3 composite, isothermal dehydroge-

nation measurements were performed at different

Fig. 2 e Isothermal desorption kinetics curves for as-milled

MgH2 and MgH2 doped with 5 wt.%, 10 wt.%, 15 wt.% and

20 wt.% FeCl3.

Fig. 3 e Isothermal absorption kinetics measurement of as-

milled MgH2 andMgH2 doped with 5 wt.%, 10 wt.%, 15 wt.%

and 20 wt.% FeCl3.

Fig. 4 e Isothermal dehydrogenation curves of as-milled

MgH2 and 10 wt.% FeCl3-doped MgH2 at 280 �C (a, d), 300 �C(b, e) and 320 �C (c, f).

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 en e r g y 3 9 ( 2 0 1 4 ) 2 5 6 7e2 5 7 4 2569


temperatures. Fig. 4 shows the isothermal dehydrogenation

curves of the as-milledMgH2 and 10wt.% FeCl3-dopedMgH2 at

280 �C, 300 �C and 320 �C, respectively. As expected, the

dehydrogenation rate was lower for the pureMgH2 (Fig. 4(c)) at

320 �C; however, the desorption kinetics increased dramati-

cally after the FeCl3 was added. The 10wt.% FeCl3-dopedMgH2

sample could release 5.45 wt.% hydrogen within 10 min at

320 �C (Fig. 4(f)); under the same temperature, only 0.33 wt.%

hydrogen was detected after 10 min for the pure MgH2, and

even after 30 min only 2.06 wt.% hydrogen release was ach-

ieved. Further investigation of the FeCl3-doped MgH2 sample

at lower temperatures revealed a similar result (Fig. 4(a)e(e)),

in which the 10 wt.% FeCl3-doped MgH2 sample exhibited

better dehydrogenation kinetics than the un-doped MgH2.

This kinetic enhancement is related to the energy barrier for

H2 release from MgH2. The activation energy for decomposi-

tion of the MgH2 has been reduced by adding FeCl3. To

calculate the activation energy of the as-milled MgH2 and

FeCl3-added MgH2, the Arrhenius equation was used as

follows:

k ¼ k0 expð � EA=RTÞ (1)

where k is the rate of dehydrogenation, k0 is a temperature-

independent coefficient, EA is the apparent activation energy

for hydride decomposition, R is the gas constant, and T is the

absolute temperature. As shown in Fig. 5, by plotting ln(k) vs.

1/T, the apparent activation energy, EA, for H2 release from the

as-milled MgH2 sample and the FeCl3-doped MgH2 sample,

can be identified. From the calculation, the apparent activa-

tion energy of dehydrogenation, EA, for the as-milled MgH2

was 166 kJ mol�1. This value was lowered by 36 kJ/mol after

adding 10 wt.% FeCl3 (EA w 130 kJ mol�1 for the FeCl3-added

MgH2). Owing to this lowering of the activation energy, the

decomposition of the MgH2 was improved significantly.

3.3. Differential scanning calorimetry

The thermal properties of the as-received and as-milled MgH2

and the FeCl3-doped MgH2 samples were further investigated

by DSC within the 30e550 �C temperature range (10 �C min�1

heating rate), as shown in Fig. 6. The DSC curve of as-received

MgH2 displayed only one strong endothermic peak at

approximately 440.79 �C, corresponding to the decomposition

of the MgH2. The hydrogen desorption temperature for the as-

milled MgH2 and MgH2 with added FeCl3 decreased by

approximately 55 �C and 145 �C compared to that for pure

MgH2. The DSC curves for the as-milled MgH2 and 10 wt.%

FeCl3-doped MgH2 samples had strong endothermic peaks at

424.62 �C and 353.35 �C, respectively. The notable reduction of

the peak temperature in the DSC results revealed that the

dehydrogenation properties of MgH2 were significantly

improved by adding FeCl3. However, it could be seen that the

onset decomposition temperatures of the samples in the DSC

were slightly higher than in the TPD (Fig. 1). These differences

may have resulted from the fact that the dehydrogenation

was conducted under different heating rates and there were

different heating atmospheres in the two types of

measurements.

To determine the enthalpy (DHdec) of MgH2 decomposition,

the DSC curves were analysed by STARe software. From the

integrated peak areas, the hydrogen desorption enthalpy was

obtained. For the as-milled MgH2, the hydrogen desorption

enthalpy can be calculated as 75.7 kJ mol�1 H2. This value is

almost the same as the theoretical value (76 kJmol�1 H2). After

the addition of FeCl3, the enthalpy of hydrogen desorption

fromMgH2was similar to that of undopedMgH2. These results

indicated that the additive investigated in this work acted as

catalysts, and did not change the thermodynamics of the

systems. This phenomenon is similar to Malka et al.’s report

on ZrF4, NbF5, TaF5, and TiCl3 doped MgH2 [44].

In order to compare the value of activation energy calcu-

lated by desorption kinetics analysis (Arrhenius plot, Fig. 5)

and DSC curve (Kissinger analysis) for hydrogen released from

MgH2, DSC traces for the as-received and as-milled MgH2 and

10 wt.% FeCl3-doped MgH2 composite at different heating

rates were measured as shown in Fig. 7(a)e(c). The activation

energy, EA, for the hydrogen desorption was obtained by per-

forming a Kissinger analysis [61], according to the following

equation:

Fig. 5 e Arrhenius plots of ln(k) vs. 1/T for as-milled MgH2

and MgH2 D 10 wt.% FeCl3.

Fig. 6 e DSC traces of as-received and as-milled MgH2 and

MgH2 D 10 wt.% FeCl3 (Heating rate: 10 �C minL1, argon

flow: 30 mlminL1).



ln�b=Tp2

� ¼ �EA=RTp þA (2)

where b 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, can be obtained from the slope

in a plot of ln[b/Tp2] versus 1000/Tp. Fig. 8 shows the Kissinger

plot of the dehydrogenation for the 10 wt.% FeCl3-doped MgH2

composite as compared with the as-received and as-milled

MgH2. The apparent activation energy, EA, estimated from

the Kissinger analysis for the 10 wt.% FeCl3-doped MgH2

compositewas found to be 130 kJmol�1, whichwas lower than

for the as-received and as-milled MgH2 (186 and 166 kJ mol�1,

respectively). The values obtained indicate that doping with

FeCl3 reduced the activation energy and thus improved the

dehydrogenation behaviour of MgH2. The activation energy

obtained from the Kissinger analysis was similar to that value

obtained from the Arrhenius plot. So, we systematically

proved that both the Kissinger analysis and Arrhenius plot

were appropriate methods to calculate the activation energy

of hydrogen releases from MgH2.

3.4. X-ray diffraction

In order to determine the phase structure of the doped

samples, XRD scans were performed on the 10 wt.% FeCl3-

doped MgH2 sample after milling, after dehydrogenation at

450 �C, and after rehydrogenation at 300 �C under 3.0 MPa

hydrogen pressure, as shown in Fig. 9. The results show

that neither FeCl3 nor any secondary FeCl-containing phase

was detected after milling, which was probably due to the

fact that the FeCl3 grains were too small to be detectable in

the MgH2 matrix by XRD, or because the FeCl-containing

phases may have existed in an amorphous state directly

after ball milling. In the dehydrogenation spectra, there

were distinct peaks of Mg, which indicates that the dehy-

drogenation of MgH2 was completed. A small amount of

MgO was also detected in the dehydrogenation spectra due

to slight oxygen contamination. In addition, some peaks of

the MgCl2 and Fe appeared after dehydrogenation,

Fig. 7 e DSC traces at different heating rates for (a) as-received MgH2, (b) as-milled MgH2, and (c) MgH2 D 10 wt.% FeCl3.

Fig. 8 e Kissinger plot of dehydrogenation for 10 wt.%

FeCl3-doped MgH2 composite compared with as-received

and as-milled MgH2.



suggesting that the reactions of MgH2 þ FeCl3 may have

occurred as follows:

3MgH2 þ 2FeCl3/3MgCl2 þ 2Feþ 3H2 (3)

The standard Gibbs free energy, DG�f of MgH2, MgCl2 and

FeCl3 are�35.98,�592.12 and�334.05 kJ/mol [62], respectively,

thus the total change DG associated with reaction (3) will be

�1000.31 kJ/mol of MgH2. This confirms the possibility of re-

action (3) from the thermodynamic potentials. For the rehy-

drogenated sample, it can be seen that Mg was largely

transformed into MgH2. The peaks of MgCl2 and Fe remained

unchanged, together with a small amount of MgO.

XRD examination of the dehydrogenated FeCl3-doped MgH2

samples identified the formation of MgCl2 and Fe, and this

product still remained after rehydrogenation. The formation of

MgCl2 and Fe encouraged us to speculate thatMgCl2 and Femay

have been acting as a real catalyst. Therefore, in order to

examine the effects of MgCl2 and Fe onMgH2, samples of MgH2

doped with 10 wt.% MgCl2, Fe and (MgCl2 þ Fe) were prepared,

as shown in Fig. 10. For comparison, the as-received and as-

milled MgH2 and the MgH2 þ 10 wt.% FeCl3 are also shown in

this figure. It is clear that the dehydrogenation kinetics of MgH2

were improved by doping with MgCl2 (Fe þ MgCl2), and Fe

compared to the as-milled MgH2, but their performance was

not as significant as that in the MgH2/FeCl3 composite. This

indicates that in-situ generated Fe species may have played an

important role and that the significantly improved dehydro-

genation performance of the MgH2/FeCl3 system was more

likely to be a synergistic effect. This phenomenon may have

arisen because, during the heating process, FeCl3 would react

with MgH2 as shown in reaction (3) and the subsequently

precipitated Fe particles might achievemuch higher dispersion

on theMgH2 surface andmore compact phase segregation than

the as-milled MgH2eFe. This would be likely to lead to

enhanced de/rehydrogenation kinetics.

From the results, we speculate that the formation of the

fresh and fine Fe particle resulted from the reaction of the

MgH2 and FeCl3 during the dehydrogenation processmay play

an important role in enhancement of MgH2 sorption, since it is

well known that Fe is a good catalyst for MgH2 [22,23]. The

presence of the fresh and fine Fe metal may interact with

hydrogen molecules, which may lead to the dissociation of

hydrogen molecules and the improvement of the desorption/

absorption rate. Apart from the speculated catalytic effects of

Fe species, the function of Cl� may also introduce an extra

catalytic effect on MgH2 sorption properties. Mao et al. [7] has

suggested that besides the catalytic effect of Mg2Ni andMg2Co

as a dehydrogenation product the chlorine-based product,

MgCl2, may also play an important role in improving the

hydrogen sorption kinetic properties of NiCl2 and CoCl2-doped

MgH2. As shown in Fig. 10, MgCl2 also has a positive influence

on the dehydrogenation behaviour of MgH2. These finely

dispersed dehydrogenated products may contribute to kinetic

desorption improvement by serving as the active sites for

nucleation and creation of the dehydrogenated product by

shortening the diffusion distance of the reaction ions. The

catalytic effect of MgCl2 may further combine with the cata-

lytic function of Fe species to generate a synergetic effect.

According to Malka et al. [44], the catalytic effect of a metal

halides on the hydrogen sorption of MgH2 could also be

simultaneously influenced by several factors, such as the

formation of MgF2 and the catalytic influence of transition

metal halides (with different levels ofmetal oxidation state) or

pure transitionmetals. In addition, reaction (3) could generate

clean surfaces (without MgO at MgH2 surface) and, subse-

quently, increase the surface reactivity and the decomposi-

tion reaction. However, further work is necessary to clarify

more details on the exact role of FeCl3 when added to MgH2.

4. Conclusion

The research reported in this paper systematically investi-

gated the catalytic effect of varying proportions of FeCl3 on the

hydrogen storage properties of MgH2 synthesised by ball

milling. We observed that the FeCl3 catalyst decreased the

dehydrogenation temperature and enhanced the sorption

Fig. 9 e X-ray diffraction patterns of FeCl3-doped MgH2 (a)

after milling, (b) after dehydrogenation, and (c) after

rehydrogenation.

Fig. 10 e TPD patterns for the dehydrogenation of as-

received and as-milled MgH2, and MgH2 doped with

10 wt.% MgCl2, Fe, (MgCl2 D Fe) and FeCl3.



kinetics of MgH2. The 10 wt.% FeCl3-doped MgH2 sample

exhibited optimal sorption performance, including the onset

dehydrogenation temperature, isothermal de/absorption ki-

netics, and the released hydrogen capacity. For example, the

dehydrogenation temperature of the 10 wt.% FeCl3-doped

MgH2 sample reduced by about 90 �C compared to the as-

milled MgH2, and the sorption kinetics measurements indi-

cated that the FeCl3-doped sample displayed an average

dehydrogenation rate that was 5e6 times faster than that of

the undoped MgH2 sample. The activation energy for

hydrogen desorption was also decreased from 166 kJ mol�1 for

the as-milled MgH2 to 130 kJ mol�1 by addition of 10 wt.%

FeCl3. However, heavy FeCl3 doping also introduced negative

effects, such as lower capacity and a decreased absorption/

desorption rate compared to the lightly doped sample. It is

believed that, upon heating, the fresh and fine Fe particle is in-

situ precipitated via the reaction of MgH2 and FeCl3, and this

may combine with the catalytic function of the MgCl2 species

to generate a synergetic effect, which in turn further improves

the hydrogen storage properties of MgH2.

Acknowledgements

The author is grateful to the University Malaysia Terengganu

for providing the facilities necessary to carry out this project.

The author also acknowledges the Malaysian Government for

financial support through the Research Acculturation Grant

Scheme (57087).

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Influence of different amounts of FeCl3 on decomposition and hydrogen sorption kinetics of MgH2

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