Article
pubs.acs.org/JPCC
Dehydrogenation Reaction Pathway of the LiBH4−MgH2 Composite
under Various Pressure Conditions
Kee-Bum Kim,†,‡ Jae-Hyeok Shim,*,† So-Hyun Park,† In-Suk Choi,† Kyu Hwan Oh,‡
and Young Whan Cho†
†
High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Republic of Korea
‡
S Supporting Information
*
ABSTRACT: This paper investigates dehydrogenation reaction behavior of the
LiBH4−MgH2 composite at 450 °C under various hydrogen and argon backpressure conditions. While the individual decompositions of LiBH4 and MgH2
simultaneously occur under 0.1 MPa H2, the dehydrogenation of MgH2 into Mg
first takes place and subsequent reaction between LiBH4 and Mg into LiH and
MgB2 after an incubation period under 0.5 MPa H2. Under 1 MPa H2, enhanced
dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H2
is obtained without the incubation period. However, the dehydrogenation reaction
is significantly suppressed under 2 MPa H2. The formation of Li2B12H12 as an
intermediate product during dehydrogenation seems to be responsible for the
incubation period. The degradation in hydrogen capacity during hydrogen sorption
cycles is not prevented with the dehydrogenation under 1 MPa H2, which
effectively suppresses the formation of Li2B12H12. The overall dehydrogenation
behavior under argon pressure conditions is similar to that at hydrogen pressure
conditions, except that under 2 MPa Ar.
■
INTRODUCTION
Lithium borohydride (LiBH4) has received much attention as a
promising solid-state hydrogen storage material owing to its
high gravimetric (18.5 wt % H2) and volumetric (121 kg H2/
m3) hydrogen storage capacities.1 However, its high reaction
temperature and slow kinetics for dehydrogenation should be
improved to be applied for on-board application.2,3 To improve
these drawbacks, extensive efforts have been carried out in the
past decade, and the concept of reactive hydride composite (or
destabilization) was devised as one of the efforts.4,5 In the
concept, the enthalpy change of hydrogen sorption reactions is
effectively reduced compared with pure LiBH4 owing to the
formation of thermodynamically stable metal borides instead of
free boron during dehydrogenation. Among the reactive
hydride composites, the LiBH4−MgH2 composite was first
proposed and has been most investigated so far due to its high
theoretical hydrogen storage capacity and relative low cost of
MgH2.6 The composite is expected to release 11.4 wt % H2
during dehydrogenation through the following reaction:
2LiBH4 + MgH2 → 2LiH + MgB2 + 4H 2
investigated the dependency of the reaction pathways on
hydrogen back-pressures. They found out that the application
of hydrogen back-pressure effectively suppresses the individual
decomposition of LiBH4 prior to a mutual dehydrogenation
reaction between LiBH4 and MgH2, and consequently the
suppression promotes the dehydrogenation through reaction 1.
Despite the positive role of hydrogen back-pressures in
dehydrogenation reaction of the LiBH4−MgH2 composite, it
has been found that the hydrogen desorption in the composite
progresses in two steps under 0.5−2.0 MPa H2.9,11,12 During
the dehydrogenation reaction, MgH2 is first decomposed into
Mg releasing ∼3 wt % H2, and then LiBH4 reacts with Mg into
LiH and MgB2 releasing ∼6 wt % H2. Moreover, obvious
kinetic retardation has been found between the two
dehydrogenation reactions exhibiting an incubation period as
long as 12 h.
Bösenberg et al.12 claimed that the kinetic retardation of the
second-step dehydrogenation reaction in the composite is
attributed to a lack of heterogeneous nucleation sites for the
formation of MgB2. They showed that the incubation for the
formation of MgB2 can be effectively reduced by the addition of
MgB2 or transition metal boride, which is believed to provide
heterogeneous nucleation sites of MgB2 with a small lattice
misfit. Also, there have been attempts to overcome the kinetic
(1)
Upon the dehydrogenation of the LiBH4−MgH2 composite,
it has been reported that the application of hydrogen backpressure plays an important role in the reaction pathway and
the formation of MgB2. Since Vajo et al.4 first found that the
application of 0.5 MPa of hydrogen enhances the formation of
MgB2 during the dehydrogenation of the composite, Nakagawa
et al.,7 Bösenberg et al.,8 Pinkerton et al.,9 and Yan et al.10
© 2015 American Chemical Society
Received: December 12, 2014
Revised: April 17, 2015
Published: April 17, 2015
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Article
The Journal of Physical Chemistry C
retardation of the composite using various additives.13−19
However, the one-step dehydrogenation according to reaction
1 has not been achieved, despite the kinetic enhancement in
these attempts. On the other hand, Yan et al.10 suggested that
the kinetic retardation is associated with the unexpected
formation of Li2B12H12 as an intermediate phase during the
dehydrogenation of the composite, which can block the contact
between LiBH4 and Mg. They found that the formation of
Li2B12H12 is effectively suppressed under hydrogen backpressure as high as 2 MPa. However, the kinetic enhancement
by the suppression of the Li2B12H12 formation was not
confirmed in their study. In spite of extensive research
concerning the dehydrogenation reaction pathway of the
composite, there has been very limited studies reporting the
reversibility of the composite without a catalytic additive due to
its poor dehydrogenation and rehydrogenation reaction
kinetics.19,20
In this study, we address the influence of hydrogen backpressure on the dehydrogenation reaction pathway of the
LiBH4−MgH2 composite with the purpose of confirming the
possibility of the one-step dehydrogenation reaction as well as
the kinetic enhancement under hydrogen back-pressures. Also,
the dehydrogenation behavior at various argon back-pressures
is analyzed in comparison with the hydrogen back-pressure
effect. Additionally, the hydrogen sorption cycle performance of
the composite is investigated up to 20 cycles.
quenched using liquid nitrogen during dehydrogenation before
XRD and Raman spectroscopy measurements. The whole
sample handlings were carried out inside an argon-filled
glovebox (mBraun, UniLab), where oxygen and water vapor
levels were kept below 0.1 ppm.
■
RESULTS AND DISCUSSION
Figure 1 shows the dehydrogenation profiles of the LiBH4−
MgH2 composite at 450 °C under static vacuum and various
■
Figure 1. Dehydrogenation profiles of the LiBH4−MgH2 composite
under (a) static vacuum and (b) 0.1, (c) 0.3, (d) 0.5, (e) 1.0, and (f)
2.0 MPa of hydrogen. The inset exhibits the reaction rate at the early
stage for 2 h. The symbols on each profile are not real data points but
a guide to improve readability.
EXPERIMENTAL PROCEDURE
Lithium borohydride (LiBH4 , Acros, 95% purity) and
magnesium hydride (MgH2, Alfa Aesar, 98% purity) were
used as raw materials without any purification. Three grams of
the LiBH4−MgH2 mixture with a 2:1 molar ratio was ballmilled using a Retsch PM200 planetary ball mill with 650 rpm
for 12 h. Thirteen 12.7 mm diameter and twenty-four 7.9 mm
diameter Cr-steel balls were employed together with a 140 mL
hardened steel bowl, sealed in argon atmosphere with a lid
having a Viton O-ring. The ball-to-powder weight ratio was
approximately 50:1.
A 0.3 g sample of the LiBH4−MgH2 composite was
dehydrogenated at 450 °C using a Sievert-type volumetric
apparatus with a 110 mL reactor. Dehydrogenations were
carried out at various hydrogen or argon back-pressure
conditions ranging from static vacuum to 2 MPa. The heating
rate was 30 °C/min in all the cases, and the pressure in the
reactor was monitored during dehydrogenation reaction.
Hydrogen sorption cycle test was carried out at 450 °C for 3
h under 1 and 8 MPa hydrogen for dehydrogenation and
hydrogenation, respectively. For cycle test, a compressed pellet
sample (5 mm in diameter) was used in order to avoid powder
scattering and to enhance heat transfer.21
XRD measurement was performed for dehydrogenated and
rehydrogenated samples using a Bruker D8 Advance X-ray
diffractometer with Cu Kα radiation. Also, Raman spectroscopy
was carried out using a Renishaw inVia Raman microscope with
a 532 nm YAG laser. For Raman spectroscopy analysis, the
reference peak positions of LiBH4,8,22−24 Li2B12H12,10,23−25 and
B25−27 were taken from the literature. In the case of MgB2, the
spectrum of commercial powder (Sigma-Aldrich, ≥99% purity)
was used. To prevent the samples from air exposure during the
XRD and Raman spectroscopy measurements, borosilicate
capillary tubes and specially designed alumina holders with a
cover glass were employed, respectively. To understand
dehydrogenation reaction pathway, some samples were
hydrogen pressure conditions. Under static vacuum, the
composite consistently releases about 8 wt % hydrogen within
2 h (Figure 1a). However, additional hydrogen release is rarely
achieved in subsequent 5 h, and the amount of released
hydrogen for 7 h fails to reach the theoretical hydrogen capacity
of the composite (11.4 wt %). Under 0.1 MPa hydrogen, the
final amount of released hydrogen for 7 h under 0.1 MPa
hydrogen increases to about 10 wt %, although the
dehydrogenation rate is very slightly retarded at the initial
stage (Figure 1b). The amount of released hydrogen continues
to increase under 0.3 and 0.5 MPa H2, although the amount
under 0.5 MPa is slightly larger than that under 0.3 MPa
(Figure 1c,d). However, the dehydrogenation behavior under
0.3 and 0.5 MPa is quite different from that under static
vacuum and 0.1 MPa, exhibiting a distinct two-stage reaction
behavior. In previous study,11 it has been believed that the first
and second reactions are the dehydrogenation of MgH2 into
Mg (∼2.8 wt % H2) and the reaction between LiBH4 and Mg
into LiH and MgB2 (∼7.2 wt % H2), respectively. Between the
two reactions, there is an incubation period, which lasts for
about 30 min. Interestingly, the incubation period clarifying the
two-step dehydrogenation reaction is eliminated with enhanced
dehydrogenation kinetics, when 1 MPa of hydrogen is applied
(Figure 1e). In addition, the composite releases the most
amount of hydrogen (11.3 wt %) under 1 MPa, which is close
to the theoretical hydrogen capacity. On the other hand, the
dehydrogenation reaction is significantly suppressed under 2
MPa, releasing only 5.0 wt % hydrogen for 7 h (Figure 1f).
XRD patterns of the products dehydrogenated under various
hydrogen pressure conditions are presented in Figure 2. Under
static vacuum and 0.1 MPa H2, Mg and LiH are observed as
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Figure 2. XRD patterns of the reaction products of the LiBH4−MgH2
composite dehydrogenated at (a) static vacuum and (b) 0.1, (c) 0.3,
(d) 0.5, (e) 1.0, and (f) 2.0 MPa of hydrogen.
main dehydrogenation products together with a small amount
of MgB2 (Figure 2a,b). The formation of Mg instead of MgB2
implies that the individual decomposition of MgH2 and LiBH4
occurs during the dehydrogenation, although the presence of B
is not confirmed in the patterns. On the other hand, MgB2 is
mainly found above 0.3 MPa, which is assumed to be formed
through reaction 1. Under 2 MPa H2, LiBH4 still remains
distinctly after the dehydrogenation for 7 h, although a small
amount of MgB2 and LiH is observed together with the sharp
Mg peaks (Figure 2f). The formation of a large amount of Mg
and the presence of LiBH4 indicate that the reaction between
Mg and LiBH4 is limited by a low thermodynamic driving force
because hydrogen pressure in the reactor approaches the
equilibrium pressure of the overall dehydrogenation reaction of
the composite at 450 °C, which is known to be 2.1 MPa.4 The
results in Figures 1 and 2 indicate that hydrogen back-pressure
above 0.3 MPa is essential for the dehydrogenation reaction of
the composite into LiH and MgB2 at 450 °C. Moreover, the
amount of formed MgB2 increases with the increase in the
amount of dehydrogenated hydrogen, as hydrogen backpressure increases up to 1 MPa. The dehydrogenation behavior
at 400 °C is similar to that at 450 °C (see Figures S1 and S2).
The disappearance of the incubation period under higher
hydrogen back-pressure is also observed for the dehydrogenation at 400 °C, although the kinetic enhancement is not
obvious (Figures S1). Also, the overall dehydrogenation
kinetics is significantly suppressed under 0.9 MPa H2,
approaching the equilibrium pressure of the composite (∼1.3
MPa).4
To analyze the change of reaction pathways of the composite
depending on hydrogen back-pressure, XRD and Raman
spectroscopy measurements of the samples obtained after
being quenched during dehydrogenation under 0.1, 0.5, and 1
MPa H2 were performed. For the dehydrogenation at 0.1 MPa,
small LiH and large Mg peaks are detected as dehydrogenation
products together with significantly reduced MgH2 peaks and a
small broad MgO peak at point 1 in Figure 3a, which is
presumed to form by oxygen source contained in relatively low
purity LiBH4 (∼95%). The formation of LiH indicates the
individual decomposition of LiBH 4 into LiH and B.
Accordingly, the result indicates that both MgH2 and LiBH4
are individually decomposed in the early stage of the
dehydrogenation. As shown Figure 3b, the result of Raman
Figure 3. (a) XRD patterns and (b) Raman spectrum of the LiBH4−
MgH2 composite during dehydrogenation at 450 °C under 0.1 MPa of
hydrogen.
spectroscopy shows that Li2B12H12 and B, which are not
detected by the XRD measurement due to their amorphous
feature, rapidly form through the individual decomposition
from LiBH4 in the early stage, as observed for the LiBH4−YH3
composite.28 At point 2 in Figure 3a, it is confirmed that
additional hydrogen desorption is attributed mainly to the
individual decomposition of LiBH4, considering the reduced
peak of LiBH4 compared with that at the point 1. MgB2, which
is observed at the final stage, seems to form by the reaction
between Mg and undecomposed LiBH4 during the individual
decompositions. MgB2 might form by a solid state reaction
between Mg and B, which is decomposed from the individual
decomposition of LiBH4. However, it was reported that the
reaction occurs above 600 °C due to strong B−B bonding of
intraicosahedron of α-B.26,29,30 Moreover, there is a low
possibility that MgB2 forms by a direct reaction between Mg
and Li2B12H12, considering that the crystal structure of
Li2B12H12 is similar to that of α-B.29
Figure 4 elucidates the reaction pathway of the composite
dehydrogenated under 0.5 MPa H2. At point 1 in Figure 4a,
which is close to the end of the first reaction in the two-step
reaction, large Mg peaks in the XRD pattern without the
presence of LiH and MgB2 shows that the only individual
decomposition of MgH2 occurs. LiBH4 is not likely to
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Figure 5. (a) XRD patterns and (b) Raman spectrum of 2LiBH4−
MgH2 composite during dehydrogenation reaction at 450 °C under
1.0 MPa of hydrogen.
Figure 4. (a) XRD patterns and (b) Raman spectra of the LiBH4−
MgH2 composite during dehydrogenation reaction at 450 °C under
0.5 MPa of hydrogen.
at point 2. However, it is noteworthy that a little peak of MgB2
is clearly detected at point 1, which is quite early compared
with the pattern of point 1 under 0.5 MPa (Figure 4a). The
formation of MgB2 at point 1 indicates that LiBH4 reacts with
Mg without an incubation period as soon as MgH2 decomposes
into Mg. There is no evidence that LiBH4 and MgH2 directly
react into LiH and MgB2. As shown in Figure 5b, the Raman
spectrum at point 1 under 1 MPa H2 exhibits a difference in
that the formation of Li2B12H12 is not observed, compared with
that at 0.5 MPa. This implies that the formation of Li2B12H12
might be responsible for the incubation period observed during
the dehydrogenation under 0.3 and 0.5 MPa H2 (Figure 1),
which is consistent with the findings observed for the LiBH4−
YH3 composite.28,31 Therefore, the enhancement in dehydrogenation kinetics under 1 MPa H2 observed in Figure 1 seems
to be associated with the suppression of the Li2B12H12
formation.
Figure 6 presents the dehydrogenation profiles of the
LiBH4−MgH2 composite at various argon back-pressure
conditions. The overall dehydrogenation behaviors under Ar
back-pressure is similar to that under hydrogen back-pressure,
individually decompose into LiH and B because 0.5 MPa H2 is
slightly higher than the equilibrium hydrogen pressure of its
decomposition reaction at 450 °C (∼0.46 MPa).3 It is found
that the MgB2 peaks start to form and grow after the incubation
period (points 2 and 3), indicating that LiBH4 reacts with Mg.
The Raman spectra before and after the incubation period
(points 1 and 2) during the dehydrogenation are compared in
Figure 4b. The main difference between the two spectra is that
the formation of Li2B12H12 is evident after the incubation
period. This indicates that a small amount of LiBH 4
decomposes into Li2B12H12 during the incubation period,
which is consistent with the slight increase of released hydrogen
during the incubation period.
The dehydrogenation reaction pathway under 1 MPa H2
slightly differs from that under 0.5 MPa. As shown in Figure 5a,
the composite releases hydrogen up to 11.3 wt % under 1 MPa
H2 without a distinct incubation period. It seems that the full
decomposition of MgH2 is almost achieved at point 1, and the
reaction between LiBH4 and Mg is subsequently under progress
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Figure 6. Dehydrogenation profiles of the LiBH4−MgH2 composite
under (a) 0.1, (b) 0.3, (c) 0.5, (d) 1.0, and (e) 2.0 MPa of argon. The
inset exhibits the reaction rate at the early stage for 2 h. The symbols
on each profile are not real data points but a guide to improve
readability.
Figure 7. Amount of hydrogen released from the LiBH4−MgH2
composite pressed during the cycle test.
exhibiting the two-step reaction feature under 0.3 and 0.5 MPa
Ar and the enhanced reaction kinetics with the increase in the
amount of released hydrogen under 1 MPa Ar, although the
amount of released hydrogen under Ar back-pressure is slightly
larger than that under hydrogen back-pressure at the same
pressure. One big difference from the dehydrogenation profiles
under hydrogen back-pressure conditions is that the dehydrogenation reaction under 2 MPa Ar is not much suppressed
releasing more than 9 wt % hydrogen compared with that
under 2 MPa H2, although the kinetics is retarded compared
with that under 1 MPa Ar. This is presumably because the
increase in Ar back-pressure does not reduce on a
thermodynamic driving force for the dehydrogenation reaction,
in contrast to hydrogen back-pressure. The XRD and Raman
measurements of the samples dehydrogenated under 0.1 and 1
MPa Ar show similar results to those under hydrogen backpressure, although they are not presented here.
The suppression of the Li2B12H12 formation under high
hydrogen back-pressure can be explained by thermodynamics.
According to Ohba et al.,29 the equilibrium hydrogen pressure
of the decomposition reaction of LiBH4 into LiH and Li2B12H12
at 450 °C is estimated to 0.9 MPa. Therefore, it is expected that
the application of higher than 1 MPa H2 will suppress the
formation of Li2B12H12. However, only with thermodynamics, it
cannot be explain why high Ar back-pressure is also effective in
suppressing the formation of Li2B12H12. In our previous study
of the LiBH4−YH3 composite,28,31 we proposed a hypothesis
that gas back-pressure kinetically suppresses the release of
diborane (B2H6) gas during the dehydrogenation of LiBH4,32
eventually forming Li2B12H12 by reacting with undecomposed
LiBH4.33 The similar mechanism seems to be true for the
LiBH4−MgH2 composite.
The amount of dehydrogenated hydrogen in the composite
at 450 °C during 21 cycles is presented in Figure 7. Up to the
15th cycle, the hydrogen capacity gradually decreases from 10.8
to 6.2 wt %. On the other hand, the capacity tends to be
maintained between 6 and 7 wt % after the 16th cycle. Figure 8
exhibits the dehydrogenation behaviors of the composite at
different cycles. It is found the dehydrogenation rate gradually
decreases with increasing cycle number. Moreover, the
composite is not fully dehydrogenated, being interrupted in 3
h before the saturation, after the fifth cycle. The dehydrogen-
Figure 8. Dehydrogenation profiles of the LiBH4−MgH2 composite
during the cycle test.
ation behaviors at the 17th and 21st cycles are similar,
indicating that the significant degradation of the dehydrogenation kinetics is not in progress after the 17th cycle. Thus, the
application of relatively high hydrogen back-pressure during
dehydrogenation is unlikely to play a positive role in enhancing
the cycle performance of the composite. There have been a
couple of studies on the cycle performance of the composite.
Xiao et al.17 and Jepsen et al.21 performed more than 15 cycles
of the composite with 5 mol % NbF5 and TiCl3, respectively, as
a catalytic additive. A significant decrease in hydrogen capacity
did not occur during their cycle tests, maintaining more than 8
wt %, although a slight degradation was observed in the results
of Jepsen et al.21 This is in contrast with the significant
degradation tendency observed in the early stage of our cycle
result. Therefore, there seems to be a positive role of a catalytic
additive in improving the cycle property of the composite. One
of the plausible explanations might be that these catalytic
additives retard microstructural coarsening in the composite
during the cycles. In addition, the cycle temperature in our
study (450 °C) higher than that in the works of Xiao et al.17
and Jepsen et al.21 (350−400 °C) is vulnerable to microstructural coarsening. Although Shao et al.20 and Mao et al.19
also investigated a few hydrogen sorption cycles of the
composite at 400 °C without a catalytic additive, however,
the number of cycles is too small to understand the overall
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cycle tendency. Hansen et al.34,35 investigated the cycle
performance of the LiBH4−MgH2−Al and LiBH4−Al composites with dehydrogenation pressure of vacuum and 0.5 MPa
H2. Although the application of hydrogen back-pressure was
effective in suppressing the formation of Li2B12H12, the initial
degradation was observed during the cycles at both pressure
conditions.
Figure 9 compares the XRD patterns of the samples after the
21st dehydrogenation and rehydrogenation. After the dehydro-
H2 for dehydrogenation and hydrogenation, respectively.
Although the dehydrogenation under 1 MPa H2 effectively
suppresses the formation of Li2B12H12, it fails to prevent the
degradation in hydrogen capacity during hydrogen sorption
cycles. The dehydrogenation behavior at argon pressure
conditions is similar to that at hydrogen pressure conditions,
except that the dehydrogenation under 2 MPa Ar is not much
suppressed.
■
ASSOCIATED CONTENT
S Supporting Information
*
Figure S1 presenting dehydrogenation profiles of the LiBH4−
MgH2 composite at 400 °C under 0.3, 0.6, and 0.9 MPa H2;
Figure S2 showing XRD patterns of the reaction products of
the LiBH4−MgH2 composite dehydrogenated at 400 °C under
0.3, 0.6, and 0.9 MPa. This material is available free of charge
via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected]; Ph +82-2-958-6760 (J.-H.S.).
Notes
The authors declare no competing financial interest.
■
■
ACKNOWLEDGMENTS
This study has been supported by the KIST Institutional
Program (Project No. 2E25322).
Figure 9. XRD patterns of the LiBH4−MgH2 composite after the 21st
(a) dehydrogenation and (b) rehydrogenation.
genation, a significant amount of LiBH4 and Mg is detected
together with LiH and MgB2 (Figure 9a), which indicates the
reaction between LiBH4 and Mg is uncompleted. As shown in
Figure 9b, Mg still remains after the rehydrogenation. The
degradation in cycle performance of the composite seems to
reflect these incomplete dehydrogenation and rehydrogenation
reactions. Longer diffusion distance due to gain coarsening
during cycles is presumed to be a main reason for the
uncompleted reactions according to microstructural analysis of
the composite.36 Consequently, the restriction of grain
coarsening during cycles seems to be crucial to achieve high
capacity hydrogen storage in the composite.
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■
CONCLUSIONS
The dehydrogenation reaction pathway and kinetics of the
LiBH4−MgH2 composite without a catalytic additive at 450 °C
have been investigated under various hydrogen and argon backpressure conditions. LiBH4 and MgH2 individually decompose
in the composite under 0.1 MPa H2, releasing about 10 wt %
H2 for 7 h. Under 0.5 MPa H2, MgH2 is first dehydrogenated
and subsequently LiBH4 reacts with Mg into LiH and MgB2
after an incubation period, which is as long as half an hour.
Although the similar reaction pathway seems to be effective
under 1 MPa H2, the incubation period disappears with
enhanced dehydrogenation kinetics compared with that at
lower hydrogen pressure conditions. The composite releases
about 11 wt % H2 under 0.5 and 1 MPa H2 for 2 h, which is
close to the theoretical hydrogen capacity of the composite.
The dehydrogenation reaction is significantly suppressed under
2 MPa H2, approaching thermodynamic equilibrium pressure.
Raman spectroscopy implies that the formation of Li2B12H12 as
an intermediate product during dehydrogenation is responsible
for the incubation period. Hydrogen sorption cycle of the
composite has been performed at 450 °C under 1 and 8 MPa
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DOI: 10.1021/jp5123757
J. Phys. Chem. C 2015, 119, 9714−9720