A fleeting glimpse of the dual roles of SiB4 in promoting the hydrogen storage performance of LiBH4

Article abstract of DOI:10.1039/c8dt04720k

In this study, the positive effects and dual roles of SiB₄ on the dehydrogenation and rehydrogenation performance of the LiBH₄-SiB₄ system are reported. Characterizations were performed through temperature programmed desorption mass spectrometry (TPD-MS), isothermal kinetics measurements, and XRD and FTIR analyses. For the hydrogen desorption from LiBH₄, SiB₄ played the role of a catalyst to kinetically facilitate the structural destabilization of LiBH₄ and its intermediate phase Li₂B₁₂H₁₂. Accordingly, a dehydrogenation capacity of 2.24 at. H/f.u. LiBH₄ (close to 10.3 wt% H) was attained at a relative temperature of 350 °C. For hydrogen absorption to generate LiBH₄, SiB₄ was unexpectedly found to act as a reactant to thermodynamically improve the rehydrogenation process by reacting with LiH under moderate conditions of 10 MPa H₂ and 400 °C, and a superior reversible capacity of 2.16 at. H/f.u. LiBH₄ was achieved. These experimental results remind us to take into account the explicit role(s) of the employed components during the dehydrogenation and rehydrogenation reactions when designing a desirable LiBH₄-based system.

Full text of DOI:10.1039/c8dt04720k

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A fleeting glimpse of the dual roles of SiB in
4
promoting the hydrogen storage performance
Cite this: DOI: 10.1039/c8dt04720k
of LiBH4
a
a
a
b,c
Weitong Cai, * Yuanzheng Yang, Pingjun Tao, Liuzhang Ouyang,
b,c
d
Hui Wang and Xusheng Yang
*
In this study, the positive effects and dual roles of SiB
formance of the LiBH –SiB
programmed desorption mass spectrometry (TPD-MS), isothermal kinetics measurements, and XRD and
FTIR analyses. For the hydrogen desorption from LiBH , SiB played the role of a catalyst to kinetically
facilitate the structural destabilization of LiBH and its intermediate phase Li 12. Accordingly, a dehy-
drogenation capacity of 2.24 at. H/f.u. LiBH (close to 10.3 wt% H) was attained at a relative temperature
of 350 °C. For hydrogen absorption to generate LiBH , SiB was unexpectedly found to act as a reactant
4
on the dehydrogenation and rehydrogenation per-
4
4
system are reported. Characterizations were performed through temperature
4
4
4
2 12
B H
4
4
4
to thermodynamically improve the rehydrogenation process by reacting with LiH under moderate con-
ditions of 10 MPa H and 400 °C, and a superior reversible capacity of 2.16 at. H/f.u. LiBH was achieved.
Received 29th November 2018,
Accepted 13th December 2018
2
4
These experimental results remind us to take into account the explicit role(s) of the employed com-
DOI: 10.1039/c8dt04720k
ponents during the dehydrogenation and rehydrogenation reactions when designing a desirable LiBH
4
-
rsc.li/dalton
based system.
order to accelerate the practical progress of HSMs, particularly
complex hydrides having extremely high capacity of over
1
. Introduction
7
Solid-state hydrogen storage technology is particularly promis- 10 wt% H.
ing for on-demand large-scale hydrogen application, such as
As a typical example, lithium borohydride (LiBH ) is a
4
hydrogen energy vehicles and portable energy-storage equip- promising candidate that is employed to create novel HSMs
1
ment. Along these lines, physical methods using MOFs, with favorable dehydrogenation and/or rehydrogenation per-
COFs, carbon, etc., and chemical means employing light- formance guided by fundamental mechanisms as the following.
weight materials such as Mg-based alloys, chemical hydrides,
(i) Synthesizing derivatives via chemically combining
complex hydrides, etc. have been developed to efficiently store counterparts.
2
–4
substantial amounts of hydrogen.
Unfortunately, the per-
These LiBH -based derivatives feature high hydrogen
4
formance of these chemicals and their derivatives are still far capacity and low dehydrogenation temperatures with rapid
from the technical requirements for onboard hydrogen storage kinetics. However, the irreversibility resulting from difficulty in
5
,6
systems. Moreover, a limited understanding of the funda- reconstructing these compounds needs to be addressed.
mental principles lying behind the interaction between Enlightened by a theoretical prediction that the higher electro-
n+
+
p
materials and hydrogen stalls the accessibility of desired negativities x of metal cations (M ) substituting Li cations
8
,9
hydrogen storage materials (HSMs). Hence, researchers have could result in lower dehydrogenation temperatures, various
made great efforts to push forward the scientific knowledge in novel substituted compounds with a general formula of
x 4 y
LiM (BH ) have been developed and their flexible structural
properties and modifiable dehydrogenation performances
1
0–14
a
have been reported.
For instance, LiZn (BH ) and
2 4 5
School of Materials and Energy, Guangdong University of Technology, Guangzhou,
10006, China. E-mail: mewtcai@gdut.edu.cn
5
b
LiAl(BH quickly decomposed at 127 °C and 67 °C, respect-
4 4
)
10,15
Anion substitution of H− by F or of [BH4] by Cl
−
−
−
School of Materials Science and Engineering, South China University of Technology,
Guangzhou 510640, China
ively.
was also predicted to have capability towards adjustable
c
Guangdong Provincial Key Laboratory of Advanced Energy Storage Materials,
16,17
thermodynamic performance.
Stemming from the idea
South China University of Technology, Guangzhou, 510640, China
d
that hydridic H− interacting with protonic H would advance
+
Department of Industrial and Systems Engineering, The Hong Kong Polytechnic
University, Hung Hom, Kowloon, Hong Kong, China. E-mail: xsyang@polyu.edu.hk
the hydrogen storage performance, ammoniated LiBH4
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(
LiBH
4 3 4 4 2 2
·nNH ), hydrazine-assisted LiBH (LiBH ·nNH NH ) and
2
. Experimental section
ammonia borane-assisted LiBH4 (LiBH ·nNH BH ) were then
experimentally demonstrated to be remarkable HSMs.
4
3
3
1
8–20
Commercial LiBH
4
(≥95%, Sigma Aldrich), SiB
4
(Sigma
Taking LiBH ·nNH as an example, when n = 1, 4/3 and 2, Aldrich) and LiH (Chemical Reagent Co., Tianjin) were used
4
3
1
5.3 wt%, 17.8 wt% and 14.3 wt% hydrogen was released from directly as raw materials. Later, SiB was milled to a size of less
4
2
1
the corresponding derivative at 250 °C, respectively.
than 500 nm by a ball milling machinery (QM-3SP2, Nanjing
(ii) Establishing destabilization systems through physical Nanda Instrument Plant) under the conditions of a ball-to-
mixing with other components. powder ratio of 40 : 1, a rotation speed of 90 rpm and a milling
These systems have the main virtues of remarkable reversi- time of 70 hours. LiH was also milled with a ball-to-powder
bility and fast dehydrogenation rate. However, a major obstacle ratio of 40 : 1, a rotation speed of 1000 rpm and a milling time
for these systems right now is the high dehydrogenation temp- of 2 hours. Systems of LiBH –SiB with a molar ratio of 1 : 0.3
4
4
erature that demands further improvement. Inspired by a strat- and LiH–SiB
4
with a molar ratio of 4 : 1 were subsequently
egy involving reactive hydride composites (RHCs) having milled under the conditions of a ball-to-powder ratio of 120 : 1,
2
2
alternative dehydrogenation pathways, intensive attention a rotation speed of 600 rpm and a milling time of 1 hour. The
was directed to selecting suitable binary or ternary compounds samples were sealed in a stainless steel vessel with hardened
4
and employing them to form new LiBH -based destabilization stainless steel balls under 1 bar argon gas protection.
systems. Experimental trials on materials such as metal
The gaseous species released from the samples were
metal halides detected via temperature programmed desorption mass spec-
metal chalco- trometry (TPD-MS, Hiden Qic20) with a heating range was
2
3–25
hydrides (e.g., MgH
e.g., NdF , SrF , TiF
genides (e.g., Fe O , TiO , SiO , CoS, and MoS),
2
, CaH
2
, YH
3 2
, and LaH ),
2
6–29
(
5
2
3
, LaCl
3
, and CeCl
3
),
30–33
−1
and from 50 °C to 700 °C at a rate of 4 °C min with an argon
3
4
2
2
1
chemical/complex hydrides (e.g., LiNH
2
, Mg(NH
2
)
2
, NaBH
4
,
purge rate of 60 mL min− . The dehydrogenation kinetics was
3
4–41
KBH
4
, and Ca(BH
4
)
2
)
had been reported. In particular, a determined by a Sievert-type apparatus (PCTPro 2000, Setaram)
synergetic effect of destabilization/catalysis or destabilization/ at 350 °C under static vacuum. Rehydrogenation of LiBH –SiB
4
4
nanoconfinement using other effective materials was further and LiH–SiB
4
systems were executed by the same apparatus
employed to promote the hydrogen storage performance of under the conditions of a hydrogen pressure of 10 MPa and a
4
2–47
these new systems.
nanostructured LiBH
attained in 1 hour at 350 °C without degradation over 25 X-ray diffractometer) with Cu Kα radiation and tube para-
For instance, for a graphene-wrapped temperature of 250 °C or 400 °C. The phase analysis was per-
4
–MgH system, 8.9 wt% hydrogen was formed by X-ray diffraction measurement (XRD, Philips X’Pert
2
2
3
cycles, which was drastically superior to that of 1.8 wt% meters of V = 40 kV, I = 40 mA. The samples were covered with
hydrogen production in 4 hours at 450 °C over 10 cycles for a 3 M film prior to measurement, and its background signal
4
8
the bulk LiBH
4
–MgH
2
system.
was subtracted in each XRD pattern. The bond vibration of the
Although establishing LiBH -based HSMs with favorable phases was detected by a Fourier transform-infrared spectro-
4
performance is admittedly important, exposing the mecha- meter (FTIR, Vector 33; Bruker), and the signals were recorded
nism behind the dehydrogenation and rehydrogenation beha- from 32 scans between 4000 cm− and 400 cm with a 4 cm
1
−1
−1
viors of these systems is also vital to guide the design of novel resolution. The background signal was subtracted from the
HSMs. Recently, intensive attention has paid to the catalytic sample spectra. Before testing, the samples were mixed with
efficiency of boron-based compounds, such as h-BN, NiB, anhydrous KBr to form pressed pellets. A glove-box filled with
NbB , TiB , and CoNiB, for tuning the hydrogen storage per- highly pure Ar gas (99.999%) was used to handle the samples,
2
2
4
9–52
formance of HSMs.
In our previous study, an insight into and the H
2
O and O
2
level in this box were kept below 3 ppm to
in particular.
the linear relationship between the catalytic efficiency and the avoid the contamination of LiBH
4
5
3
cation electronegativity of MgB /TiB /FeB/SiB was reported.
2
2
4
4
However, the real role of SiB was still uncertain due to the
coexistence of dehydrogenated products of B or intermediate
phase Li B H , which can serve as boron sources for the
3
. Results and discussion
2
12 12
3.1 Catalytic role of SiB on dehydrogenation of LiBH
4
4
rehydrogenation of the LiBH
4 4
–SiB system. Accordingly, the
revisited system was investigated in this study, and the dual Fig. 1 exhibits the dehydrogenation behavior of the LiBH
4
–SiB
4
roles of SiB in the dehydrogenation and rehydrogenation pro- system together with LiBH for comparison. As revealed by the
4
4
cesses of LiBH
4
were found. This finding implied that a more TPD-MS results, LiBH
4
started to release hydrogen at its
preferable hydrogen storage performance could be achieved in melting point of 280 °C and sluggishly reached a dehydrogena-
9
LiBH -based materials, particularly comprising higher stoi- tion peak at 439 °C, similarly to the reported result. After
4
6 4 4
chiometry of B, such as SiB . To be specific, higher the content introducing SiB into LiBH , dehydrogenation was initiated at
of B in the component, higher would be the preservation of 201 °C and a broadened plateau between 307 °C and 437 °C
the catalyst for dehydrogenation, and lower would be the was clearly observed. This result demonstrates that the dehy-
depletion of the reactant for rehydrogenation. Thus, a superior drogenation of LiBH
4
took place at its solid state, which
balance can be achieved via this boron-designed approach to should be ascribed to the enhanced interaction between SiB
4
advance efficient designs of LiBH -based HSMs.
and LiBH . It noteworthy that the volcano-like dehydrogena-
4
4
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capacity of 2.16 at. H/f.u. LiBH
4
(close to 9.9 wt% H) when it
was rehydrogenated at a moderate condition of 10 MPa and
00 °C H . This system outperforms the direct rehydrogenation
of LiBH from its dehydrogenated products of LiH and B (15.5
MPa and 600 °C).
4
2
4
5
4
Fig. 2 shows the XRD patterns and FTIR spectra of the
investigated samples, and mainly reveals the dehydrogenation
mechanism under the LiBH –SiB system. As revealed by the
4
4
4 4
XRD patterns, only the diffraction peaks from LiBH and SiB
are clearly observed in the curve (c), thus indicating that the
milled LiBH –SiB system comprises these two crystalline com-
4
4
ponents. The significantly reduced diffraction intensity and
broadened peak of milled LiBH and SiB , in contrast to that
4
4
of the raw samples in curve (a) and (b) respectively, indicated
the reduction of their grain size resulting from the severe
Fig. 1 TPD-MS (left) and isothermal kinetics at 350 °C (right) of LiBH
4
4 4
milling effect. This concludes that the LiBH –SiB system was
st
nd
(
a), LiBH
genation (c). Dehydrogenation of LiBH
assistance of SiB , as indicated by the faster kinetics.
4
–SiB
4
system for the 1 dehydrogenation (b) and 2 dehydro-
a physical mixture of LiBH and SiB .
4
4
4
was greatly promoted with the
As seen from curve (d), the diffraction peak intensity of
dehydrogenated LiBH was almost unchanged compared with
that of raw LiBH , accordingly demonstrating that few LiBH
4
4
4
4
molecules underwent dehydrogenation. This observation is in
tion behavior shows faster kinetics indicated by a sharper line with its dehydrogenation behavior, as shown in Fig. 1.
slope of the profile in contrast to that of pure LiBH . It is also Moreover, the LiH phase was observed, as indicated by its
4
noticeable that these enhanced kinetics happen only at a point high-intensity diffraction peak, and elemental B derived from
4
near the melting point of LiBH , therefore demonstrating that LiBH4 should be in the amorphous state, resulting in the
the molten state of LiBH significantly intensifies the dehydro- absence of its diffraction peak. This finding is in good agree-
4
5
4,55
genation process with the assistance of SiB
whether SiB was used, the dehydrogenation of both the system was subjected to dehydrogenation, the diffraction
systems ended at around 550 °C and pure hydrogen without peaks of LiBH4 with significantly lower intensity became
4
. Irrespective of ment with other reported studies.
4 4
After the LiBH –SiB
4
the by-product diborane (B
2
H
6
) was acquired.
almost invisible, as shown in curve (e). It also can be seen that
As for the isothermal dehydrogenation behavior, LiBH
4
dis- the diffraction intensity of SiB4 was retained and any other
played a slow dehydrogenation kinetics and released only diffraction peaks from boron-containing phases were absent.
about 0.50 at. H/f.u. LiBH (close to 2.7 wt% H) within This result indicates that SiB did not react with LiBH to form
hours. In contrast, faster dehydrogenation kinetics and other crystalline phases. Hereafter, it should be noted that the
4
4
4
6
higher capacity of 2.24 at. H/f.u. LiBH (close to 10.3 wt% H) LiH and B phases in the dehydrogenated LiBH –SiB system
4
4
4
with a continuously rising trend were achieved in the LiBH
4
–
should have an amorphous structure, and accordingly gives
4 4
SiB system. This result certainly indicates that SiB had a posi- rise to the disappearance of their diffraction peaks in the XRD
tive influence on promoting the dehydrogenation of LiBH4. pattern. Furthermore, the FTIR spectrum of the LiBH –SiB
4
4
4 4
Significantly, the LiBH –SiB system had a superior reversible system (curve (e)) revealed that only the characteristic B–H
Fig. 2 XRD patterns (left) and FTIR spectra (right) of LiBH
SiB system after dehydrogenation (e) and LiBH –SiB system after rehydrogenation (f). SiB
genation of LiBH
4 4 4 4 4 4
(a), SiB (b), LiBH –SiB system after milling (c), LiBH after dehydrogenation (d), LiBH –
4
4
4
4
played the role of a catalyst to facilitate the dehydro-
4
.
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vibrations from the residual LiBH
1
4
with bending modes at
125 cm− and stretching modes at 2291/2223/2382 cm−1 and
1
a B–H bond vibration from amorphous Li
2
2
B
12
H
12 located at
474 cm− are clearly detected. According to the phase ana-
lysis, it was found that SiB played the role of a catalyst to kine-
1
56
4
4
tically facilitate the dehydrogenation of LiBH . Combining the
aforementioned phase analysis with the dehydrogenation be-
havior for the release of 2.24 at. H/f.u. LiBH at 6 hours and
4
having an increasing trend of capacity versus time as shown in
Fig. 1, the possible catalytic reaction for the dehydrogenation
of the LiBH –SiB system is proposed in reaction (1a) and (1b).
4
4
It is believed that SiB
4
could catalyze the hydrogen liberation
from LiBH
4
and Li B H12 simultaneously.
2 12
SiB4
LiBH4 !1=12 Li2B12H12 þ5=6 LiH þ13=12 H2
ð1aÞ
ð1bÞ
2
:16 at: H=f:u: LiBH4
Fig. 3 FTIR spectra of LiBH
50 °C (b) and 400 °C (c). LiBH
system hydrogenated at moderate conditions.
4
(a), LiH–SiB
4
systems hydrogenated at
SiB4
2
4 4
was unexpectedly found in the LiH–SiB
Li2B12H12 !2LiH þ12B þ5H2
3
:00 at: H=f:u: LiBH4
3
.2 Reactant role of SiB on rehydrogenation of LiBH4
4
under moderate conditions, and the higher temperature
could further enhance the formation of the [BH4] unit of
−
As shown in Fig. 1, the superior reversibility of the LiBH –SiB
4
4
system leads us to investigate the rehydrogenation of LiBH
With the coexistence of B, Li 12, and SiB
sources, three types of rehydrogenation reactions possibly took Li B H in small quantities only when the hydrogenation
4
.
LiBH . Moreover, the weak vibration peak located at
4
1
2
B
12
H
4
serving as boron 2474 cm− disclosed the formation of the intermediate phase
2
12 12
place during the rehydrogenation process of the LiBH
system. B reacted with LiH and H to generate LiBH
Li B H reacted with LiH and H to produce LiBH , and SiB
4
–SiB
4
treatment was executed at 400 °C. This result proves that the
formation of LiBH4 was prior to that of Li B H in the
2
4
,
2
12 12
2
12 12
2
4
4
hydrogenating LiH–SiB4 system. Li B H was suspected to
2 12 12
2 4
2 6
probably reacted with LiH and H to form LiBH . As reported be produced from the reaction between LiBH4 and B H
in previous studies, elemental B necessitates extremely harsh where B H possibly originated from the combination of H
2
6
5
9,60
conditions of 15.5 MPa and 600 °C to combine with LiH and atoms from H and B atoms from SiB .
Accordingly, the
due to the chemical inertness of above experimental results certainly indicate that SiB played
2
4
consequently form LiBH
4
4
5
5,57
B.
tated the conditions of 100 MPa and 500 °C to be rehydroge- and it is plausible to conclude that the superior reversibility
nated into LiBH because of its high thermal stability and low of the LiBH –SiB system originated from the contribution of
chemical reactivity, thus causing a high reaction kinetic the above-mentioned reaction.
2 12
4
Moreover, the intermediate phase Li B H12 necessi- the role of a reactant in this hydrogenating LiH–SiB system,
4
4
4
5
8
barrier. Therefore, it seems that these two reactions did not
occur in our study, where the applied rehydrogenation para-
meters were 10 MPa and 400 °C. Thus, the superior reversible
performance of the LiBH –SiB system should not be attribu-
SiB4 þ4LiH þ6H2 !4LiBH4 þSi
ð2Þ
To further figure out the possibility of this declaration, the
4
4
ted to the direct rehydrogenation of B and/or Li
reacting with LiH. In this case, SiB
2
B
12
H
12 by quantity calculation in the hydrogenation reactions was per-
4
4
is speculated to play an formed. It was assumed that 1 mol LiBH was completely
important role to facilitate the rehydrogenation of LiBH , and heated into LiH and B, which was a combination of reactions
4
it consequently stimulates us to determine its explicit effect. (1a) and (1b). In this occasion, the available capacity of
Subsequently, controlled experiments were performed via 10.3 wt% H resulted in a yield of 0.75 mol LiH. This result
hydrogenating the LiH–SiB system.
indicated that 0.19 mol SiB4 is required to generate LiBH4
system was subjected to a hydrogenation con- according to reaction (2). In fact, in the experimental design of
dition of 10 MPa and 250 °C or 400 °C. The corresponding the LiBH –SiB system, the component molar ratio was
results via FTIR spectroscopy are shown in Fig. 3. It is surpris- LiBH : SiB = 1 : 0.3. Due to 0.19 mol being less than 0.3 mol,
4
The LiH–SiB
4
4
4
4
4
−
1
4
ing that the B–H bending mode at 1125 cm and stretching it was reasonable to conclude that the quantity of SiB was
modes at 2291/2223/2382 cm , which are in good agreement sufficient for the occurrence of reaction (2) in the rehydrogena-
with that of LiBH , were clearly detected, and their vibration tion process of the LiBH –SiB system, and the consumption
−
1
4
4
4
peak intensity increased along with the increase in hydrogen- of SiB
ation temperature. This demonstrates that the B state in the Fig. 2, the diffraction peak intensity of SiB
4
was calculated to be 63%. In addition, as shown in
was reduced after
SiB was easily changed by chemically reacting with H atoms the system’s rehydrogenation (curve f) in contrast to that for
4
4
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Table 1 The quantity calculations for the hydrogenation reactions
SiB4
a
Hydrogenation reactions
LiBH4 !LiH þB þ3=2 H2
4 2 4
SiB + 4LiH + 6H → 4LiBH + Si
Available capacity of H
Resultant quantity of LiH
Reactant quantity of SiB
Theoretical value of SiB
2
10.3 wt%
0.75 mol
—
0.3 mol
—
—
0.75 mol
0.19 mol
—
63%
58%
4
4
Consumption ratio of SiB
4
According to reaction
According to XRD
—
a
4
It was assumed that 1 mol LiBH completely dehydrogenated into LiH and B, which is a combination of reactions (1a) and (1b).
4 4
Fig. 4 Sketch of the hypothetical dehydrogenation (a) and rehydrogenation (b) mechanisms of the LiBH –SiB system.
4
the dehydrogenated SiB (curve e). According to these XRD pat- genated products B and LiH under moderate rehydrogenation
terns, 58% SiB was estimated to be spent in the rehydroge- conditions of this study.
4
nated sample. Table 1 summarized the calculation analysis in
those two hydrogenation reactions. The fact that the calculated
value of 63% was quite close to the actual value of 58%
assures us that SiB did react with LiH to form LiBH under
4. Conclusion
4
4
the applied rehydrogenation conditions and accordingly, a In this study, the effect of SiB on the dehydrogenation and rehy-
4
superior reversibility of LiBH
slight capacity reduction.
4
–SiB
4
was achieved with only a drogenation performance of LiBH4 was investigated and the
corresponding mechanism was proposed. With the assistance of
Combining the aforementioned analysis, we attempted to SiB , hydrogen emission from LiBH was drastically promoted.
4
4
elucidate the catalysis mechanism of SiB
4
for the dehydro- Therefore, a capacity of 2.24 at. H/f.u. LiBH4 (close to
genation and rehydrogenation processes of LiBH –SiB , as 10.3 wt% H) was achieved, which was better than that of 0.50 at.
4
4
sketched in Fig. 4. For the dehydrogenation catalyzed by SiB
4
,
H/f.u. LiBH (close to 2.7 wt% H) for pristine LiBH . After rehy-
4 4
the catalysis mechanism is explained by the non-compen- drogenation treatment under moderate conditions of 10 MPa H2
sated electronic structure of SiB4 in which the electron was and 400 °C, superior reversibility of 2.16 at. H/f.u. LiBH was
4
transferred from B to Si, making B electron-deficient and Si attained. During these two processes, SiB4 was found to act
electron-enriched. Thus, the electron-enriched Si sites struc- differently. It played the role of a catalyst to facilitate the dehy-
turally destabilized LiBH4 and the intermediate phase drogenation of LiBH , possibly originating from its non-compen-
4
Li
viding sufficient electrons to [BH
and then produce the dehydrogenated products LiH and B.
With regard to the rehydrogenation, SiB was a reactant and acted as a reactant to generate LiBH by reacting with LiH and
cooperated with LiH and hydrogen to generate LiBH
2 12
B H12 to release substantial amounts of hydrogen via pro- sated structure effect. The electron-enriched Si active sites trans-
−
−
anions, ferred electrons to the [BH4]− and [B H ] units and led to
−
4
]
and [B12
H
12
]
12 12
8
destabilization of the structure. As for the rehydrogenation, SiB4
4
4
4
with a hydrogen owing to the higher reactive nature of SiB than that of
4
−
1
calculated reaction enthalpy change of −65 kJ mol H . It is elemental B. These experimental results assert that during the
2
well known that the enthalpy change of rehydrogenating B dehydrogenation and rehydrogenation reaction processes, the
−
1
and LiH into LiBH
which was quite close to our value. Therefore, the experi- based hydrogen storage materials could change, which would
mental result indicates that SiB was more reactive than certainly influence the hydrogen storage behavior of LiBH4.
elemental B to react with LiH and form LiBH . This should
result from a different boron state with a high chemical
activity for SiB compared with that of B, leading to a reduced
reaction activation energy. In other words, the formation of
LiBH from SiB and LiH was prior to that from its dehydro- There are no conflicts of interest to declare.
4
was reported to be −67 kJ mol
H
2
,
roles of the components adopted in the design of new LiBH4-
6
1
4
4
4
Conflicts of interest
4
4
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F. Besenbacher, J. Skibsted and T. R. Jensen, Structural
studies of lithium zinc borohydride by neutron powder
diffraction, Raman and NMR spectroscopy, J. Alloys
Compd., 2011, 509, S698–S704.
Acknowledgements
This study was supported by the National Natural Science
Foundation of China (grant number: 21805046), the Public
Welfare Research and Capacity Building Project of Guangdong 12 X. B. Xiao, W. Y. Yu and B. Y. Tang, First-principles study of
grant number: 2015A010105028), the Open Fund of the double-cation alkali metal borohydride LiK(BH4)2,
Guangdong Provincial Key Laboratory of Advanced Energy J. Phys.: Condens. Matter, 2008, 20(44), 445210.
Storage Materials, the Project of “One-Hundred Young 13 M. Paskevicius, L. H. Jepsen, P. Schouwink, R. Cerny,
(
a
Talents” of Guangdong University of Technology (grant
number: 220413551), and the PolyU Departmental General
Research Grant (grant number: G-UADK).
D. B. Ravnsbaek, Y. Filinchuk, M. Dornheim,
F. Besenbacherf and T. R. Jensen, Metal borohydrides and
derivatives - synthesis, structure and properties, Chem. Soc.
Rev., 2017, 46(5), 1565–1634.
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4 J. S. Hummelshoj, D. D. Landis, J. Voss, T. Jiang, A. Tekin,
N. Bork, M. Dulak, J. J. Mortensen, L. Adamska,
J. Andersin, et al., Density functional theory based screen-
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