Hydrogen sorption properties of ball-milled Mg–C nanocomposites

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 5 ( 2 0 1 0 ) 1 0 3 9 6e1 0 4 0 3

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Hydrogen sorption properties of ball-milled MgeCnanocomposites

Tony Spassov*, Zlatina Zlatanova, Maya Spassova, Stanislava Todorova

Faculty of Chemistry, University of Sofia “St.Kl.Ohridski”, 1 James Bourchier str. 1164 Sofia, Bulgaria

a r t i c l e i n f o

Article history:

Received 27 May 2010

Received in revised form

19 July 2010

Accepted 22 July 2010

Available online 14 August 2010

Keywords:

MgeC nanocomposites

Microstructure

Hydriding/dehydriding

Hydrogen storage capacity

Hydriding kinetics

* Corresponding author.E-mail address: [email protected]

0360-3199/$ e see front matter ª 2010 Profedoi:10.1016/j.ijhydene.2010.07.123

a b s t r a c t

MgH2 75 at.%eC 25 at.% composites are synthesized by ball milling using different kinds of

carbon additives: carbon black (CB), nanodiamonds (ND) and amorphous carbon soot (AC).

X-ray diffraction analysis showed that the MgH2 phase in the as-obtained composite

powders is nanocrystalline (80e100 nm). The SEM observations revealed that the samples

consist of 5e15 mm MgH2 particles, surrounded and in some cases coated by carbon flakes.

The composite containing nanodiamonds revealed strong decrease of the MgH2 decom-

position temperature with more than 100 �C, compared to ball-milled pure MgH2. Impor-

tant issue of the present study is also the low temperature hydriding of the ball-milled

MgeC nanocomposites, investigated by high-pressure DSC. The process starts at about

200 �C for all materials studied, but the hydriding mechanism looks different for the

composites with different kinds of carbon additives. Whereas for Mgecarbon black it takes

place in a relatively narrow temperature range, expressed by a single exothermic peak

(200e300 �C) for the other two composites the hydriding is a multi-step process, featured by

two overlapped exothermic peaks for Mg-nanodiamonds and by two well separated

exothermic effects (at about 300 �C and 400 �C) for Mg-amorphous carbon soot. The

observed difference in the hydriding behavior of the MgeC composites is attributed to the

different kind of carbon component, which is supposed to play a catalytic role as well as

protects magnesium from oxidation. The incorporation of carbon into the MgH2 particles

results in the formation of high density of defects (dislocations and grain boundaries),

which is supposed to be among the most possible reasons for the decreased hydride

decomposition temperature. The MgeC nanocomposites show reproducible hydriding/

dehydriding behavior (thermodynamics and kinetics) during multiple cycling. Among the

composites in the present study “Mgecarbon black” reveals the best hydriding character-

istics e low temperature of hydriding in a relatively narrow temperature range by a single-

step reaction and relatively fast hydriding kinetics.

ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

1. Introduction of MgH2/Mg and carbon materials, incl. graphite, activated

The work on the effect of different kinds of carbon on the

hydrogen sorption of MgeC composites, prepared by ball

milling, has been intensive during the last years. The

hydriding and dehydriding properties of various composites

.bg (T. Spassov).ssor T. Nejat Veziroglu. P

carbon, carbon nanotubes (CNTs), multi-walled carbon

nanotubes (MWCNTs), carbon fibers were investigated [1e18].

The decrease in the MgH2 decomposition temperature is one

of the major consequences of the introduction of such carbon

materials. Lillo-Rodenas et al. [1] reported the best results for

ublished by Elsevier Ltd. All rights reserved.

mailto:[email protected]

http://www.elsevier.com/locate/he

http://dx.doi.org/10.1016/j.ijhydene.2010.07.123



30 40 50 60 70 80

a

b

c

Inte

nsity

2Θ

20 30 40 50 60 70 80

cb

a ...

.Mgβ MgH2

♦♦♦♦♦

♦

♦

♦

♦

♦♦

Inte

nsity

2Θ

a

b

Fig. 1 e XRD of (a) initial carbon materials (a-CB, b-ND, c-

AC) and (b) as-milled MgeC composites (a-MgH2eCB, b-

MgH2eND, c-MgH2eAC).

Table 1eAverage grain size of theMgH2eC composites in

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 5 ( 2 0 1 0 ) 1 0 3 9 6e1 0 4 0 3 10397

the MgH2 with CNTs and MWCNTs with metallic impurities.

They also found a clear relation between the MgH2 decom-

position temperature and its microstructure. The presence of

carbon was reported to prevent the MgH2 particle growth,

which, in turn, enhances its decomposition. Improvement of

H-sorption in ball-milled Mg/MgH2 using expanded natural

graphite (ENG) has been reported recently [2]. Although the

thermodynamic properties and intrinsic hydrogen sorption

kinetics were found to remain unchanged the ENG incorpo-

ration reduces the hydrogen permeability [2]. Rud et al. [3]

reported that the crystallite size in the ball-milled MgeC

nanocomposites is significantly reduced, as in the MgeC

nanomaterials composites it is smaller in comparison to the

Mgegraphite and MgeNiegraphite mixtures. The carbon

nanomaterials additions to Mg reduce the hydrogen sorption

temperature and essentially improve the hydrogen sorption

kinetics [3]. Prominent advantage of carbon additives com-

pared to non-carbon additions (e.g., boron nitride nanotubes

or asbestos) in improving the hydrogen capacity and hydrid-

ing/dehydriding kinetics of Mg was found by Wu et al. [4].

Among the various carbon additives purified single-walled

carbon nanotubes (SWNTs) were reported to exhibit the most

prominent “catalytic” effect on the hydriding of Mg. Under the

same conditions, hydrogen sorption rates of Mgecarbon

systems were found to be one order of magnitude higher than

that of pure Mg [4]. Montone et al. [5] reported that the pres-

ence of benzene in the milled MgeC blends induces a finer

powder particle size and results in a complete transformation

of the milled powder to the hydride by thermal reaction with

hydrogen gas. Imamura et al. have proposed the application of

Mgegraphite nanocomposites, produced by ball milling with

different organic additives (tetrahydrofuran, cyclohexane,

benzene) as new hydrogen storage materials [6e10]. They

reported about the possibility for the formation of new sites

for hydrogen storing other than those due to the magnesium,

able to store hydrogen reversibly [6].

Recent promising theoretical study of Kim et al. [19]

predicts the effect of the nanoparticle size on the thermody-

namics of hydrogen release from MgH2. The authors found

that for MgH2 particles below 10 nm the hydride phase is

thermodynamically destabilized, resulting in pronounced

lowering of the decomposition temperature [19].

High-pressure DSC (HPDSC) analysis was already applied

and was found to be a suitable method for studying the

decomposition of MgH2 as well as of magnesium hydriding

[20]. A possibility to make some conclusions on the magne-

sium hydriding/dehydriding mechanism based on isothermal

DSC measurements is demonstrated as well [20].

The aim of the present study is to compare the decompo-

sition temperature and enthalpy of MgH2 ball-milled with

different kinds of carbon as well as to study the hydriding and

dehydriding of the MgeC nanocomposites, applying for this

purpose HPDSC and Sievert’s type volumetric methods.

the as-milled and hydrided state.

sample d, nm as-milled d, nm after hydriding

MgH2 95 e

MgeCB 94 116

MgeND 84 116

MgeAC 101 114

2. Experimental details

The composites with a composition of MgH2 75 at.%eC 25 at.%

were synthesized by high-energy ball milling, by Fritsch

planetary equipment (Pulverisette 6), using stainless steel

vials and balls at weight ratio of ball to metal powders of 12:1.

The milling process was carried out for 10 h with 1 h of

continuous milling, followed by 15 min relaxation time.

Protective atmosphere of pure Ar (99.999%) was used and the

pressure within the vials was kept over 1 bar to preserve the

purity of the gas. Initial materials, used for the synthesis were

pure MgH2 (supplied by GKSS Research Center Geestacht

GmbH), carbon black (VULCAN XC72R, CABOT Corp.), deto-

nation generated nanodiamonds and carbon soot [21].

Microstructural information was obtained by XRD, using

Bruker D8 Advance diffractometer with CueKa radiation.




Morphology and particle size distribution were observed by

Scanning Electron Microscope JEOL 5510.

Possible phase transformations during annealing of the

as-milled materials and the hydriding/dehydriding processes

were studied by high-pressure differential scanning calorim-

etry (HPDSC), SETARAM Sensys Evo TG-DSC. The hydrogen

sorption behavior was investigated using Sievert’s type (PCT)

apparatus with samples from 150 to 200 mg.

3. Results and discussion

Fig. 1 presents the diffractograms of the initial carbon mate-

rials before milling and of the MgH2eC composites, produced

by milling for 10 h of MgH2 with different kinds of carbon:-

carbon black (CB), nanodiamonds (ND) and amorphous carbon

soot (AC). Except the nanodiamond, the other two kinds of

Fig. 2 e SEM micrographs of (a, b) MgH2eCB, (c, d) MgH2eND an

carbon used in the study are x-ray amorphous, as AC contains

tiny diffraction peaks of the diamond phase, Fig. 1a. From the

x-ray patterns of the composites it is obvious that the milling

results in MgH2 crystals size reduction, from about 95 nm to

different final size depending on the carbon additive, Table 1.

Formation of new phases due to the milling was not detected.

The morphology of the ball-milled powder composites is

shown in Fig. 2. On the micrographs particles with distinctly

different morphology and size can be detected. The compos-

ites contain larger particles of MgH2 (5e15 mm) and flakes of

carbon located around as well as on the surface of MgH2

particles. At larger magnification it is clearly seen that the

MgH2 particles are covered by very small carbon particles,

especially for the composite MgH2eND and MgH2eCB (Fig. 2).

To determine the temperature (Tdec) and enthalpy (DHdec)

of MgH2 decomposition as well as to study the hydriding and

dehydriding processes at different hydrogen pressure high-

d (e, f) MgH2eAC composites prepared by milling for 10 h.



100 200 300 400 500

MgH2-ND

MgH2-AC

MgH2-CB

MgH2

Hea

t flo

w, a

.u.

ex

o>

Temperature, oC

Fig. 3 e DSC plots under vacuum (0.1 bar and 5 K/min) for

the MgH2eC nanocomposites.

100 200 300 400 500

Mg

25 barMg-CB

Mg-ND

Mg-AC

Hea

t flo

w, a

.u.

ex

o>

Temperature, oC

Fig. 4 e High-pressure DSC plots (25 bar, 5 K/min) for the

MgeC composites.

.Mg

.β MgH2♦

MgOο

♦

♦♦


pressure DSC analyses with constant heating and cooling

rates were carried out. Fig. 3 shows the decomposition DSC

curves (under vacuum of 1.10�1 bar) for all MgH2eC nano-

composites and for the initial MgH2. A drastic decrease of Tdec

with about 100 �C was observed for the MgH2eND composite,

whereas for the other two composites Tdec does not change

noticeably. The improved dehydriding behavior of the as-

milled MgH2eND can be due to the finest particle and grain

size and better contact between the particles of different

phases leading to larger area of the MgH2 particle surface

protected against oxidation by the carbon. The DSC desorp-

tion peak of MgH2eND appears to be a little broader compared

to the endothermic peaks for the other composites. It is

necessary to be mentioned that the MgH2 decomposition

temperatures determined in the present study are lower than

those measured for similar MgeC composites [4e6]. The

enthalpies of the MgH2 decomposition obtained from the

endothermic DSC peaks are in the range of 1200e1500 J/g

composite, Table 2, as the largest value was obtained for

MgeCB.

When a pressure of 25 bar of hydrogen and a linear

temperature scan is applied to the decomposed composite

materials in the HPDSC, Fig. 4, they all reveal a broad

exothermic effect in the temperature range of 200e350 �C. TheMgeAC shows a second complex exothermic effect at higher

Table 2 e Enthalpies of MgH2 decomposition (DHdec) andMg hydriding (DHhydr) of ball-milled MgeC composites.

Composite DHdec [J/g](as-

milled)

DHhydr [J/g] DHdec [J/g](after

hydriding)low temp.hydriding

hightemp.

hydriding

MgeCB 1480 1240 1380 170 þ 1250

MgeND 1210 980 1195 160 þ 990

MgeAC 1290 990 1160 65 þ 1170

temperatures (350e425 �C). Comparing the other two

composites it can be seen that the exothermic peak for the

MgeCB is better shaped (consists of a single peak) and it is

shifted to lower temperature (200e300 �C). The observed

exothermic effects are associated with a hydriding process,

i.e., formation of MgH2, proved by XRD of samples annealed in

the HPDSC up to 300 �C under a hydrogen atmosphere of

25 bar, Fig. 5. For the composite MgeAC, where the main

hydriding occurs at higher temperatures (Fig. 4) diffraction

peaks of Mg can also be detected, i.e., the hydriding process is

not completed at 300 �C. The ball-milled nanocrystallineMgH2

after decomposition to pureMg does not showany exothermic

hydriding peak at these conditions (20e30 bar hydrogen

atmosphere and heating with 5 K/min up to 450 �C), Fig. 4.The enthalpy change due to the composites hydriding

(formation of MgH2) is different for the different materials

studied, as the maximum value of about 1240 J/g composite,

corresponds to MgH2eCB. All enthalpies of low temperature

20 30 40 50 60 70 80

. ♦♦♦..

cba

♦♦♦ο ο

♦

Inte

nsity

2Θ

Fig. 5 e XRD patterns of hydrided (up to 300 �C in DSC

under 25 bar hydrogen): a-MgeCB, b-MgeAC, c-MgeND.



100 200 300 400 500

Mg

Mg-CB

Mg-ND

Mg-AC

50 bar

Hea

t flo

w, a

.u.

ex

o>

Temperature, oC

400 300 200 100

cooling

Mg-CB

Mg-ND

Mg-AC

50 bar

Hea

t flo

w, a

.u.

ex

o>

Temperature, oC

a

b

Fig. 6 e HPDSC plots of MgeC composites at hydrogen

pressure of 50 bar with (a) heating rate 5 K/min and (b)

cooling rate of 5 K/min.


hydriding obtained from the exothermic DSC peaks are lower

than the enthalpies of the MgH2 decomposition of the corre-

sponding MgH2eC nanocomposite, determined from the DSC

analyses under vacuum of the as-milled powders. This result

ismost probably due to the incomplete MgeC hydriding at low

temperatures. In addition, it is necessary to be taken into

account, that at the lower rates of hydriding (at low temper-

atures) the enthalpies determined could be not very precise,

due to the broader and not so well defined DSC peaks. In both

DSC analyses (under vacuum and under hydrogen pressure),

however, we are considering the same process, but in opposite

directions (dehydriding of MgH2eC under vacuum and

hydriding of MgeC under hydrogen pressure). It is important

to be pointed out that the hydriding of Mg in the MgeC

nanocomposites in the present study takes place at substan-

tially lower temperatures (especially for MgeCB), compared to

the hydriding temperature of ball-milled nanocrystalline Mg

and of ball-milled Mg with other C additives [4].

Further annealing in the HPDSC under the same conditions

(25 bar H2 and 5 K/min heating rate) of the hydrided

composites leads to MgH2 decomposition, Fig. 4, expressed by

well shaped endothermic peaks, which appear at nearly the

same temperatures (450 �C) for all samples. For all nano-

composites the dehydriding under hydrogen pressure of

25 bar takes place with 2 endothermic peaks, first of which is

considerably smaller than the second one. The enthalpy of

dehydriding is practically equal to that of hydriding.

To study the effect of the hydrogen pressure on the

temperature and enthalpy of hydriding and dehydriding and

to try to separate the overlapping thermal effects of the

hydriding processes HPDSC analyses under a pressure of

50 bar H2 was realized with the same specimens, Fig. 6a. As

a result the same thermal effects were registered (exo- and

endo-) as those under 25 bar, as the overlapping effects of the

MgH2eAC composite were indeed better separated, allowing

more precise enthalpy determination. The shape of the

exothermic peaks, associated with the hydriding process, is

also slightly changed due to the increased pressure. The

exothermic peak of the MgH2eCB composite becomes sharper

and narrower; the two overlapping exothermic peaks of

MgeND are better distinguished at higher pressure and the

two exo- effects (the second of which consisting of 2 over-

lapped peaks) are also better separated. The enthalpy values

obtained coincide with those determined at 25 bar. The

observed difference in the hydriding behavior of the studied

MgeC nanocomposites can only be associated with the

different kinds of carbon component used (CB, ND, AC), which

is presumed to play a catalytic role as well as protects the Mg

surface from oxidation. The different kinds of carbon used to

produce the composites by ball milling reveal different ability

for magnesium hydride particles coating, seen by SEM, Fig. 2,

as well as show different stability of the contact between the

Mg and carbon particles.

When cooled down from 500 �C with 5 K/min under

hydrogen pressure (25 or 50 bar) the MgeC composites form

hydrides (MgH2) again at about 430 �C, Fig. 6b. It is interesting

that the high temperature hydriding reveals also two-peaks

process similar to the hydriding at low temperatures, but the

peaks are narrower and the peaks overlapping is stronger due

to the increased reaction rates. The enthalpies of the high

temperature hydriding are slightly higher than those deter-

mined at low temperatures and are close to the enthalpies of

MgH2 decomposition. Similar to the experiment at 25 bar at

higher pressure of 50 bar the MgH2 decomposition proceeds at

about 450 �C and during subsequent cooling a hydriding takes

place at about 430 �C.The composites, hydrided in a hydrogen gas atmosphere in

the HPDSC, were subjected to decomposition under vacuum

(1.10�1 bar), Fig. 7. Two well separated endothermic peaks

have been observed for all composites as well as after the

hydriding at both pressures (25 and 50 bar). The first small one

(H ¼ 70e170 J/g) at low temperatures (about 200 �C) and the

second, substantially larger (DH ¼ 950e1250 J/g) at tempera-

tures of about 300e400 �C. The main MgH2 decomposition

reaction for the nanocomposite MgH2eND takes place in the

same temperature range and with nearly the same enthalpy

compared to the as-milled material. For the other two com-

posites, however, the decomposition of the hydrided samples



100 200 300 400 500

MgH2-CB

MgH2-ND

MgH2-AC

Hea

t flo

w, a

.u.

ex

o>

Temperature, oC

Fig. 7 e Decomposition (0.1 bar) of the hydrided MgeC

composites during heating in DSC with 5 K/min.


(under hydrogen atmosphere of 25 bar) takes place at

substantially lower temperature (with 60e80 �C) compared to

the as-milled MgH2eC composites. Further hydriding and

dehydriding (2e3 times) of the composites reveal the same

temperatures and enthalpies of the processes, i.e., the nano-

composites show reversible hydriding/dehydriding behavior

during cycling. It is important to be pointed out that due to the

carbon additives the size of the MgH2 crystallites and particles

does not change markedly during multiple hydriding/dehy-

driding, which most probably results in improved hydrogen

sorption properties of the MgeC composites. Similar effect

was found by Lilo-Rodenas et al. [1] for MgH2 ball-milled with

CNTs.

With the aim to understand the origin of the low temper-

ature endothermic effect at about 200 �C XRD analysis of

annealed up to 250 �C (after the small endo-peak) MgH2eCB

composite has been performed, Fig. 8. It was found that this

thermal peak is due to MgH2 decomposition and formation of

β MgH2

♦

Mg.

... ♦♦♦♦

MgOο

♦

ο

♦

♦

♦

Inte

nsity

2Θ20 40 60 80

MgH2-CB partially decomposed

30 50 70

♦

ο

Fig. 8 e XRD of annealed up to 250 �C MgH2eCB composite.

Mg, as after this heat treatment the amount of the hydride

phase still dominates. It is important to be mentioned that

both decomposition reactions (low and high temperature)

affect the same magnesium hydride (b-MgH2), although the

temperature difference between them is more than 150 �C.Obviously, this result has to be associated with the effect of

carbon incorporation into the MgH2 particles, which creates

high density of MgH2/C phase boundaries, containing easy

accessible for hydrogen atoms sites. A possibility for forma-

tion of new hydrogen sites in similar composites was also

reported by Imamura et al. [6]. Judging from the measured

enthalpies of decomposition it can be concluded that the

amount of the weaker bounded hydrogen in MgeCB and

MgeND is about 13e18% of the total amount of hydrogen

stored asMgH2 and is only about 5% for theMgeAC composite.

Among the composites in the present studyMgeCB reveals

the best hydriding characteristics e low temperature of

hydriding in a relatively narrow temperature range

(200e300 �C) by a single-step reaction. Isothermal kinetic

curves of MgeCB hydriding at 250 and 300 �C are shown in

Fig. 9. At 300 �C the kinetics is relatively fast and complete.

6.0 wt.% hydriding was achieved for about 40 min with an

initial rate of 0.3 wt.%/min. When compared to the hydriding

kinetics of the pure nanocrystalline MgH2, reported in our

earlier study [22], it can be concluded that whereas the initial

hydrogenation rate for the MgeCB is similar, at higher

hydriding degrees the composite shows significantly

improved kinetics combined with notably higher hydrogen

capacity. The total capacity of the composites was determined

to be above 7.0 wt.% H2, which is a rather high value for this

material and most probably means that indeed new sites for

the hydrogen atoms have been created by milling MgH2 with

carbon additives. Important result is that the amount of these

new hydrogen sites corresponds to the fraction of the

hydrogen released at very low temperatures. Combining the

results from the PCT and HPDSC analyses enthalpies of MgeC

hydriding in the range 40e45 kJ/mol H2 could be determined. It

can be concluded, that most probably responsible for the

decreased MgH2 decomposition temperature and improved

hydriding/dehydriding kinetics of MgeC composites is the

0 10 20 30 40 50 60 70 80 900

1

2

3

4

5

6

7

8

wt.%

H2

time, min

250oC

300oC

25 bar

Fig. 9 e Isothermal kinetic curves (PCT) of MgeCB

hydriding.




formation of stable contacts between the carbon and Mg/

MgH2 particles and/or incorporation of carbon into the Mg/

MgH2 particles, resulting in a high density of phase bound-

aries, leading to protection of the magnesium surface from

oxidation and facilitating the diffusion of hydrogen into the

Mg grains. The high concentration of phase boundaries may

also have a favorable effect on the nucleation of Mg during the

decomposition of MgH2 and in this way to accelerate the

dehydriding process [23].

4. Conclusions

MgH2 75 at.%eC 25 at.% nanocomposites are synthesized by

ball milling in a planetary type mill using different kinds of

carbon additives: carbon black (CB), nanodiamonds (ND) and

amorphous carbon soot (AC). SEM observations reveal that

after 10 h of milling the samples consist of larger MgH2

particles (5e15 mm) surrounded by smaller carbon flakes.

Homogeneous distribution of small carbon particles deposited

on the MgH2 particles has been observed mostly for MgeCB

and MgeND composites. It was found that the crystallite and

particle size reduction, caused by the milling, depends on the

type of the carbon used for the composite production.

The composite containing nanodiamonds reveals strong

decrease of the MgH2 decomposition temperature with more

than 100 �C, compared to ball-milled MgH2. Another key issue

of this study is the low temperature hydriding of ball-milled

MgeC nanocomposites, investigated by high-pressure DSC.

The process starts at about 200 �C for all materials studied, but

the hydriding mechanism looks different for the composites

with different kinds of carbon additives.Whereas forMgeCB it

takes place in a relatively narrow temperature range,

expressed by a single exothermic peak (200e300 �C) for the

other two composites the hydriding is a multi-step process,

starting at about 200 �C. The observed difference in the

hydriding behavior of the present MgeC composites is

attributed to the different kinds of carbon component, which

is supposed to play a catalytic role as well as may protect

magnesium from oxidation. The incorporation of carbon into

the surface of the MgH2/Mg particles and thus the creation of

high density of phase boundaries leads to the formation of

new easy accessible for hydrogen atoms sites and enhances

the diffusion of hydrogen into the magnesium grains. The

MgeC nanocomposites thus prepared show fully reproducible

hydriding/dehydriding behavior (as thermodynamics and

kinetics) during multiple cycling. An interesting result is that

due to the carbon additives the size of the MgH2 nanocrystals

and particles does not change noticeably during repeated

hydriding/dehydriding, resulting in improved hydrogen

sorption properties of the MgeC composites. Among the

composites in the present study MgeCB reveals the best

hydriding characteristics e low temperature of hydriding in

a relatively narrow temperature range by a single-step reac-

tion and fast hydriding kinetics at relatively low temperatures

(<300 �C). Possible explanation of the improved dehydriding

behavior of this composite is the fine particle and grain size

and better contact between the carbon and MgH2/Mg particles

compared to the other two materials studied.

Acknowledgements

The work has been supported by the Bulgarian Scientific

Research Fund under grant DO 02-226/2008 and by Bulgarian

Scientific Research Fund under grant DO 02-82/2008, Project

“Union”.

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[2] Chaise A, de Rango P, Marty Ph, Fruchard D, Miraglia S,Olives R, et al. Enhancement of hydrogen sorption inmagnesium hydride using expanded natural graphite. IntJ Hydrogen Energy 2009;34:8589e96.

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Hydrogen sorption properties of ball-milled Mg–C nanocomposites

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