Efficient regeneration of sodium borohydride via ball milling dihydrate sodium metaborate with magnesium and magnesium silicide

Article abstract of DOI:10.1016/j.jallcom.2017.09.262

The application of NaBH₄ hydrolysis to hydrogen generation is currently obstructed by its regeneration. Finding a simple and low cost method to regenerate its hydrolysis byproduct is therefore important. Herein, the regeneration of NaBH₄ is obtained by reacting its direct hydrolysis byproduct, NaBO₂·2H₂O, with a mixture of Mg and Mg₂Si by ball milling. In this reaction, the reduced agents are only metal and intermetallic compounds, thus hydrogen in the regenerated NaBH₄ (H^δ?) derives solely from NaBO₂·2H₂O (H^δ+). The introduction of Mg₂Si increases the NaBH₄ regeneration yield to 86%, which is the highest regeneration yield reported for NaBH₄ until now. The reaction mechanism was also clarified for the first time.

Full text of DOI:10.1016/j.jallcom.2017.09.262

Journal of Alloys and Compounds 729 (2017) 1079e1085
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Efficient regeneration of sodium borohydride via ball milling
dihydrate sodium metaborate with magnesium and magnesium
silicide
a
a
a
,
b
,
*
a
a
Miaojun Huang , Hao Zhong , Liuzhang Ouyang
, Chenghong Peng , Xiaoke Zhu ,
a
c
,
**
a
Weiheng Zhu , Fang Fang
School of Materials Science and Engineering, Guangdong Provincial Key Laboratory of Advanced Energy Storage Materials, South China University of
Technology, Guangzhou, 510641, PR China
, Min Zhu
a
b
China-Australia Joint Laboratory for Energy & Environmental Materials, Key Laboratory of Fuel Cell Technology of Guangdong Province, Guangzhou,
5
10641, PR China
c
Department of Materials Science, Fudan University, Shanghai, 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2017
Received in revised form
The application of NaBH4 hydrolysis to hydrogen generation is currently obstructed by its regeneration.
Finding a simple and low cost method to regenerate its hydrolysis byproduct is therefore important.
Herein, the regeneration of NaBH
with a mixture of Mg and Mg Si by ball milling. In this reaction, the reduced agents are only metal and
intermetallic compounds, thus hydrogen in the regenerated NaBH derives solely from
4 2 2
is obtained by reacting its direct hydrolysis byproduct, NaBO $2H O,
14 September 2017
2
Accepted 23 September 2017
Available online 25 September 2017
dꢀ
4
(H
regeneration yield to 86%, which is
4
until now. The reaction mechanism was also clarified
)
þ
NaBO $2H Si increases the NaBH
2
2
O (Hd ). The introduction of Mg
2
4
the highest regeneration yield reported for NaBH
Keywords:
Sodium borohydride
Regeneration
for the first time.
©
2017 Elsevier B.V. All rights reserved.
Dihydrate sodium metaborate
Yield
Hydrolysis
1. Introduction
criteria of the US Department of Energy (DOE). Its hydrolysis occurs
via the following reaction (1a):
Hydrogen is an excellent alternative energy carrier, which could
satisfy the increasing demand for the efficient and clean energy
supply [1e5]. One of the most important challenges for the wide-
spread use of hydrogen is the development of safe and efficient
hydrogen storage materials [6e12].
NaBH
4
þ 4H
2
O / NaBO
2
$2H
2
O þ 4H
2
(1a)
On the other hand, the DOE discourages the on-board applica-
tion of NaBH hydrolysis, mainly because of the high cost of the
process and difficulty in conducting the regeneration [21].
Previous studies on NaBH regeneration focused mainly on the
dehydrated NaBO . Kojima et al. reported that NaBH can be re-
generated by annealing NaBO and MgH , achieving a 97% yield
[22]. Çakanyıldırım et al. also regenerated NaBH by annealing
NaBO and MgH and obtained a yield of about 92.33% [23];
Recently, Lang et al. regenerated NaBH by ball milling NaBO and
MgH with a yield of 89% [24]. However, it should be noted that the
raw material, MgH , is extremely expensive and could increase the
overall cost of the process. In addition to metal hydrides, Kojima
et al. also tried to regenerate NaBH by annealing elemental Mg and
NaBO under a H atmosphere, but only obtained a 10% yield [22].
Ou et al. reported that NaBH could be thermochemically
4
NaBH
4
is a potential candidate material for hydrogen storage
[13e19], due to its high gravimetric hydrogen storage capacity (up
4
to 10.8 wt%) and controllable hydrogen release at room tempera-
ture via hydrolysis. According to a previous study, the hydrogen
2
4
2
2
capacity of the solid NaBH
4
hydrolysis system (containing H
2
O,
4
NaBH and a catalyst) reaches about 7.3 wt% [20], which meets the
4
2
2
4
2
2
*
Corresponding author. School of Materials Science and Engineering, Guangdong
2
Provincial Key Laboratory of Advanced Energy Storage Materials, South China
University of Technology, Guangzhou, 510641, PR China.
4
** Corresponding author.
2
2
E-mail addresses: meouyang@scut.edu.cn (L. Ouyang), f_fang@fudan.edu.cn
(
F. Fang).
4
https://doi.org/10.1016/j.jallcom.2017.09.262
925-8388/© 2017 Elsevier B.V. All rights reserved.
0

1080
M. Huang et al. / Journal of Alloys and Compounds 729 (2017) 1079e1085
regenerated by a NaBO
was achieved at 611 C and 31 bar in a H
2
-Mg-H
2
system. A NaBH
atmosphere [25]. The
regeneration using Mg was also discussed
26]. Nonetheless, according to eq. (1a), the direct hydrolysis
4
yield of 90.04%
with argon, so as to remove oxygen and avoid moisture contact.
ꢁ
2
mechanism of NaBH
4
[
2.2. Synthesis of NaBH
4
byproduct is NaBO
2
$2H
2
O. And anhydrous NaBO
2
should be ob-
ꢁ
tained through annealing at 400 C [27]. In addition, the whole
regeneration process requires a high annealing temperature and
high hydrogen pressure [28], which entail high costs and compli-
cated technological solutions. It is therefore necessary to develop a
The stoichiometric Mg powders, Mg
NaBO $2H O powders were placed into a stainless steel reactor and
ball milled in a vibrational ball mill (QM-3C, Nanjing, China). The
mixture of Mg, Mg Si and NaBO $2H O (0.9:1.8:1 M ratio) was ball
milled at 1200 cycles per minute. Each sample was obtained by ball
milling of reactants (the mixture of Mg, Mg Si and
NaBO $2H O), which were loaded into the jar, with a ball to powder
2
Si powders and
2
2
2
2
2
simple NaBH
It was reported that the regeneration of NaBH
NaBO $2H O under a H atmosphere allows for a yield of 12.3% [29].
4
regeneration method.
4
using Mg and
1
g
2
2
2
2
2
2
On the other hand, elemental Mg has shown a remarkable reduc-
tion potential but with low reduction properties [21,28e35]. The
addition of Si to the system was found to significantly promote the
regeneration [22]. Si formed as a reaction byproduct can also be
reused as anodic material in Li ion batteries [36,37]. In this study,
ratio of 50:1 at ambient temperature. In each experiment, the
powders obtained were preserved and manipulated inside a glove
box under a high purity argon atmosphere with O
below 0.1 ppm.
2 2
and H O levels
the crystalline water contained in NaBO
hydrogen source for NaBH synthesis and low cost reducing agents,
Mg and Mg Si, were tested as reactants. The reaction was operated
via room temperature ball milling under argon atmosphere. The
2 2
$2H O was used as the
4
2.3. Purification and quantification of NaBH
4
2
The ball milling products were dissolved and extracted in eth-
ylenediamine. A syringe and syringe filter were used to separate the
extraction solution from formed oxides and remaining reactants
d
ꢀ
derives completely from the Hd
O of NaBO $2H O. Expensive
) and external hydrogen re-
sources (H ) are therefore not necessary in the regeneration pro-
þ
H
in the regenerated NaBH
4
initially present in the coordinate H
2
2
2
d
ꢀ
metal hydrides (such as H in MgH
2
4
that were undissolved. NaBH powders were produced by drying
0
the solution in the lyophilizer (Martin Christ, Alpha 1-2LD plus,
Osterode, Germany) and ethylenediamine was collected in the cold
trap of the freeze dryer. After removing the ethylenediamine,
d
ꢀ
cess. Furthermore, the H in MgH
NaBH , during the latter's regeneration, via the conventional re-
action of MgH with NaBO [22,23]. In this work, the Mg reacts with
NaBO $2H O to form small amounts of Mg(OH) , subsequently the
Mg further reacts with the intermediate Mg(OH) and forms MgH
2
was simply transferred to the
4
2
2
4
NaBH was obtained as a white powder, as clearly evidenced by
2
2
2
4
XRD (Fig. 2a). The yield of NaBH was determined by iodimetric
2
2
.
analysis.
d
þ
This is the key reaction of the process: the H in NaBO
2
$2H
2
O is
and
d
ꢀ
transformed to H in NaBH
MgH
4
via the intermediate Mg(OH)
2
2
in the above-mentioned reaction. Furthermore, recycling of
2.4. Hydrolysis of NaBH
4
the direct hydrolysis byproduct also simplifies NaBH
by avoiding the 400 C annealing process. To gain more information
on the unknown reaction mechanism, X-ray diffraction (XRD),
4
regeneration
ꢁ
The hydrolysis experiments were performed in a 10-mL tube
sealed by a silicon stopper. About 0.1 g of the purified NaBH were
hydrolyzed in 0.2 mL of distilled water using a 10 mL tube at room
temperature. The purified NaBH was transferred into the tube in a
glove box, the water was then injected into the reactor with a
needle placed directly toward the NaBH . The hydrolysis property
4
B
Fourier transform infrared spectroscopy (FTIR) and solid-state 11
magic angle spinning nuclear magnetic resonance (MAS NMR)
were used to identify the ball milling products. The study revealed
4
that NaBO
and the existence of Si contributes to the high NaBH
this work the NaBH regeneration process was simplified and the
cost was reduced [22,33].
2
$2H
2
O is more likely to react with Mg than with Mg
2
Si
4
4
yield. Thus, in
was detected by the system used in our previous studies [38]. The
hydrolysis curve was recorded by a computer via an electronic
4
scale. The commercial NaBH
method.
4
was also hydrolyzed with the same
2
. Experimental
2.1. Chemicals
2.5. Characterization
In this research, the reactant sodium metaborate tetrahydrate
The mechanism of sodium borohydride formation was
confirmed through XRD, FTIR and NMR analyses. The borohydride
yield was determined on the basis of hydrogen consumption and
iodimetric analysis [39]. XRD data of reactants and products were
collected on a Rigaku MiniFlex 300/600 X-ray diffractometer
(
(
NaBO
St. Louis, MO, USA). Mg powder (purity: 99.8%), magnesium sili-
Si, purityꢂ99.5%), H SO (98%), HCl (36%), sodium hy-
droxide (NaOH, purityꢂ99%), potassium iodate (KIO , AR-grade),
potassium iodide (KI, purityꢂ99%), sodium borohydride (NaBH
purityꢂ98%), starch indicator (purityꢂ99%) and sodium thiosulfate
Na , AR-grade) were obtained from Aladdin (Shanghai, China)
and used without further purification. Ethylenediamine
purityꢂ99%) was purchased from Sigma-Aldrich. Sodium
metaborate dehydrate (NaBO $2H O) was produced by heating
O for 12 h at 90 C. Mg, magnesium silicide, sodium
2 2
$4H O) (purity>99%) was purchased from Sigma-Aldrich
cide (Mg
2
2
4
3
4
,
(Tokyo, China) with Cu Ka radiation at 40 kV and 40 mA. Powder
samples were protected from air and moisture using liquid paraffin.
The chemical bonds in the ball milling products were identified
using a Nicolet IS50 Fourier transform infrared spectroscope (San
Jose, CA, USA) in the transmission mode. The tested samples were
pressed with anhydrous potassium bromide (KBr) powder, using a
sample to KBr ratio of 1: 99. NMR spectra were obtained using a
Bruker-AVANCE III HD 400 nuclear magnetic resonance spectro-
scope (Karlsruhe, Germany). For each set of NMR measurements,
1 mL of the ball-milled products was placed into a 5 mm NMR test
tube. The gas was collected by a gas-sampling bag in a glove box,
and then analyzed using Mass Spectrometry (Hiden, QC210).
(
2 2 3
S O
(
2
2
ꢁ
2 2
NaBO $4H
metaborate dihydrate and dehydrate sodium metaborate were
stored and handled in an argon-filled glove box (Mikrouna,
Shanghai, China) and equipped with a recirculation and regenera-
tion system. In the glove box, oxygen and water concentrations
were maintained below 1 ppm, and distilled water was purged

M. Huang et al. / Journal of Alloys and Compounds 729 (2017) 1079e1085
1081
NaBO
was confirmed by the peaks at 2
The presence of MgO was verified by the appearance of diffraction
2 2 4
∙2H O mixtures during ball milling. The formation of NaBH
ꢁ
ꢁ
ꢁ
ꢁ
q
¼ 28.9 , 41.4 , 49.0 and 51.3 .
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
peaks appearing at 36.9 , 42.8 , 62.2 , 74.5 and 78.4 . Si could be
ꢁ
identified by the peaks located at 28.8 . After 5 h, the XRD analysis
revealed the presence of Si, MgO and NaBH
NaBO $2H O reacted with Mg and Mg Si to generate NaBH
and Si according to the following reaction:
4
. It is suggested that
2
2
2
4
, MgO
NaBO
2
$2H
2
O þ 2Mg þ Mg
2
Si / 4MgO þ Si þ NaBH
4
(1b)
To obtain pure NaBH
4
, the ball milling products were separated
by dissolution, filtration and drying. The purified powder obtained
was characterized by XRD (Fig. 2a) and Fourier-transform infrared
spectroscopy (FTIR) (Fig. 2b). The apparent variations observed at
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
1
125 cm , 2225 cm , 2292 cm , 2386 cm in the FTIR spectra
were attributed to the B-H bond of NaBH [23,40], which was the
same as that of commercial NaBH (Fig. 2b). The XRD pattern in
Fig. 2a shows that the diffraction peaks of both the purified and
Fig. 1. XRD patterns of the products after ball milling the Mg, Mg
2
Si and NaBO
2
$2H
2
O
4
mixtures (0.9:1.8:1 M ratio) for different durations (5 h, 7.5 h, 10 h, 20 h).
4
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
commercial NaBH
0.0 , 66.0 and 68.0 , indicating the purified powder is NaBH
4
were located at 25.1 , 28.9 , 41.4 , 49.0 , 51.3 ,
3
. Results and discussion
ꢁ
ꢁ
ꢁ
6
4
.
To further characterize the purified product, its hydrolysis
properties were also studied. Purified NaBH (0.1 g) and commer-
cial NaBH (0.1 g) were reacted with 2 mL of 5% CoCl solution.
According to Liu et al. [41], CoCl can act as a catalyst during the
hydrolysis process. Fig. 2c shows that the purified NaBH exhibits
fast hydrogen generation kinetics, similarly to commercial NaBH
After hydrolysis, the byproduct was dried and characterized by
3
.1. Formation of NaBH
4
4
4
2
In order to investigate the influence of the duration of the ball
milling process on the product distribution, the process was carried
out for 5, 7.5, 10 and 20 h, using a mixture of Mg, Mg Si and
NaBO $2H O with a molar ratio of 0.9:1.8:1 under Ar atmosphere.
The obtained powder was stored in a glove box.
The ball milling products were identified by XRD (as shown in
Fig. 1). Fig. 1 displays the phase transformation of the Mg-Mg Si-
2
4
2
4
.
2
2
ꢁ
ꢁ
XRD. As shown in Fig. 2d, the weak peaks located at 22.0 , 24.5 ,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
2
5.2 , 30.7 , 33.2 , 34.9 , 39.2 , 39.7 , 44.9 , 50.4 belong to
2
Na ClB(OH) whereas the remaining peaks are relative to
2
4
,
Fig. 2. Characterization of the purified product (white powder) (a) XRD pattern, (b) FTIR spectra, (c) hydrolysis curve of the purified and commercial NaBH
4
, (d) XRD patterns of
NaBH hydrolysis byproduct and NaBO $2H O.
4
2
2

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M. Huang et al. / Journal of Alloys and Compounds 729 (2017) 1079e1085
Fig. 3. Reaction process of NaBH
1 h, 2 h, 4 h, 7.5 h), (b) FTIR patterns of the products after ball milling Mg, Mg
spectra of gas collected from the grinding jar after 2 h ball milling.
4
synthesis: (a) XRD patterns of the products after ball milling of Mg, Mg
2 2 2
Si and NaBO $2H O mixtures (0.9:1.8:1 M ratio) for different durations
(
2
Si and NaBO $2H O mixtures (0.9:1.8:1 M ratio) for different durations (1 h, 2 h, 4 h, 7.5 h), (c) Mass
2
2
NaBO
hydrolysis is NaBO
2
$2H
2
O, confirming that the main byproduct of the NaBH
$2H O.
4
agent system. Hydrogen was detected in both our previous study
[43] and the present work (Fig. 3c). Therefore, it is speculated that
2
2
dþ
Mg initially reacts with Mg(OH)
2 2
(H ) and generates MgO and H ;
d
ꢀ
it then reacts with H to form the intermediate MgH
2
2
(H ). In the
3.2. Mechanism of NaBH
4
formation
ꢀ
d
ꢀ
ꢀ
2
following step, the H in MgH (H ) is substituted by the OH
d
þ
d
þ
contained in NaB(OH)
4
(H ) forming Mg(OH)
reacts with the remaining Mg, and the re-
is consumed. The
transformation of (H ) to (H ) is realized in the reaction between
2 4
(H ) and NaBH
The products of the ball milling process were studied by XRD
analysis (Fig. 3a) with the aim of gaining insight into the reaction
mechanism. The diffraction peaks of MgO appeared after 1 h ball
d
ꢀ
(
H ). Finally, Mg(OH)
2
action cycle continues until the NaB(OH)
4
d
þ
d
ꢀ
milling, which means that the reaction of Mg, Mg
NaBO $2H O had already occurred. As the ball milling time was
prolonged to 2 h, the diffraction peaks of Mg completely dis-
appeared, while the peaks of Mg Si were still present. This result
suggests that NaBO $2H O preferentially reacts with Mg compared
to Mg Si.
According to the above statement, the whole process consists of
the reactions between Mg and NaBO $2H O and between Mg Si
and NaBO $2H O. It should be noted that NaBO $2H O can also be
written as NaB(OH) , which is more appropriate for its structure
42]. All the hydrogen contained in NaB(OH) is present in the form
of H , i.e. in the functional group of OH . With regards to the re-
2
Si with
Mg and the intermediate Mg(OH)
described as [43]:
2
. The whole reaction can be
2
2
2
2
2
2
MgH
þ NaB(OH)
Mg(OH)
þ 2Mg / 4MgO þ 2H
þ 2Mg / 2MgH
In the following steps of the process, Mg
/ 2Mg(OH)
þ NaBH
(2)
2
4
2
4
2
2
2
(3)
(4)
2
2
2
2
2
H
2
2
2
2
2
2
4
Si reacts with
2
[
4
2
2
NaBO $2H O to further generate NaBH4, which has been researched
d
þ
ꢀ
in our previous work [44]. As in our previous work [44], the XRD
diffraction peaks attributable to MgO and Si appeared after only 1 h
d
þ
action between Mg and NaBO
had shown that the peaks of MgO and Mg(OH)
after 10 min of ball milling, along with the decrease of Mg peaks. As
the ball milling time increased to 5 h, the intensity of the diffraction
peaks relative to Mg(OH)
able, while those of MgO became stronger [43]; however, the peaks
of Mg(OH)
study, probably because of its low content in the mixed reducing
2 2
$2H O (H ), our previous study [43]
d
þ
2
(H ) appeared
of milling, indicating that Mg
quickly; in addition, the Si-H bond appeared in the FTIR spectrum
44]. It could be speculated that Mg tends to bond with the O atom,
2 2
Si began to react with NaBO $2H O
2
[
d
þ
2
(H ) became weak and hardly observ-
pushing the H atom toward the Si and finally forming a special
intermediate (Mg, O, Si and H conjugated structure) in the reaction.
The Si-H bond may favor the breaking of the B-O bond and the
d
þ
2
(H ) did not appear in the ball milling process of this

M. Huang et al. / Journal of Alloys and Compounds 729 (2017) 1079e1085
1083
Fig. 4. XRD patterns of the products after ball milling Mg, Mg
0 h).
2 2 2
Si and NaBO $2H O mixtures in molar ratios of (a) 1.5:1.5:1 and (b) 2.5:1:1 for different durations (5 h, 7.5 h, 10 h,
2
formation of the B-H bond. The undetected Si-H in this work
Fig. 3b) may be the result of its low presence in the mixed reducing
3.3. Optimization of the yield of NaBH
4
(
agent system.
4 2
In order to study the yields of NaBH , Mg, Mg Si and
With regards to the transformation of the boron compound,
NaBO $2H O with ratios of 1.5:1.5:1 and 2.5:1:1, these mixtures
2
2
both of the previous works carried out on Mg
found that the intermediate product, [BH
during ball milling. Thus, it is speculated that the regeneration is
2
Si and Mg [44,45]
(OH) ] [44], appears
were also ball milled for 5 h, 7.5 h, 10 h and 20 h under the same
conditions. The XRD patterns of the products, shown in Fig. 4, were
similar to those obtained when working with the reacting mixture
in molar ratios of 0.9:1.8:1, which indicates that these compositions
ꢀ
3
ꢀ
ꢀ
ꢀ
actually a transformation process from [B(OH)
detail, the sequence of transformations is [B(OH)
4
]
]
to [BH
4
] . In
ꢀ
4
to [BH(OH)
] . However,
3
]
4
are also adequate to obtain the regeneration of NaBH .
ꢀ
ꢀ
ꢀ
to [BH
2
(OH)
2
]
to [BH
3
(OH)] and finally to [BH
4
After the purification of the ball-milled products, the yield of the
purified white powders was determined by iodimetric analysis (as
shown in Fig. 5). The products were first extracted by ethylenedi-
ꢀ
ꢀ
[BH(OH)
3
]
and [BH
2
(OH)
2
]
were not observed, probably as a
consequence of their short lifetime.
As shown in Fig. 3, the diffraction peaks of NaBH
4
appear after
amine, followed by filtration and drying. The NaBH
4
yield was
4
ball milling for 2 h, indicating the regeneration of NaBH .
calculated in accordance with the following equation (5):
2 2 2
Fig. 5. Product yield after ball milling Mg, Mg Si and NaBO $2H O mixtures in molar ratios of (a) 0.9:1.8:1 (b) 1.5:1.5:1 and (c) 2.5:1:1 for different durations (5 h, 7.5 h, 10 h, 20 h).

1084
M. Huang et al. / Journal of Alloys and Compounds 729 (2017) 1079e1085
discharge plasma-assisted milling in energy storage materialsea review,
obtain mass of NaBH4
theoretical mass of NaBH4
J. Alloys Compd. 691 (2017) 422e435.
[8] M.H. Huang, L.Z. Ouyang, J.S. Ye, J.W. Liu, X.D. Yao, H. Wang, H.Y. Shao, M. Zhu,
Hydrogen generation via hydrolysis of magnesium with seawater using Mo,
yieldðNaBH4Þ ¼
ꢃ 100%
(5)
2 3 2
MoO , MoO and MoS as catalysts, J. Mater. Chem. A. 5 (2017) 8566e8575.
9] A.A.C. Asselli, S.F. Santos, J. Huot, Hydrogen storage in filed magnesium,
The results are shown in Fig. 5.
For the purified NaBH obtained by ball milling the Mg, Mg
and NaBO $2H O mixtures (0.9:1.8:1 M ratio), the NaBH yields of
the products after milling for 5, 7.5, 10, 20 h were 59%, 66%, 76%,
[
4
2
Si
J. Alloys Compd. 687 (2016) 586e594.
[10] W.-C. Lu, S.-F. Ou, M.-H. Lin, M.-F. Wong, Hydrogen absorption/desorption
performance of MgAl alloys synthesized by reactive mechanical milling and
hydrogen pulverization, J. Alloys Compd. 682 (2016) 318e325.
2
2
4
6
2
7%, respectively (Fig. 5a). When the mixture was ball milled for
0 h, the yield decreased; at the same time, FeSi appeared. It was
[
4
11] D. Peng, Y. Li, Y. Liu, L. Zhang, H. Zhang, Z. Ding, S. Han, Effect of LiBH on
hydrogen storage properties of magnesium hydride-carbon composite,
J. Alloys Compd. 711 (2017) 104e110.
12] T. Yang, C.Y. Liang, X.H. Wang, H.S. Wang, Z.M. Yuan, F.X. Yin, Q. Li, Y.H. Zhang,
Effect of graphite (GR) content on microstructure and hydrogen storage
therefore supposed that Mg
deactivated the promoting function of Mg
may be due to the decomposition of NaBH
appearance of FeSi. For the ball milling products with a ratio of
.5:1.5:1, the NaBH4 yields after 5, 7.5, 10 and 20 h products were
2%, 75%, 73% and 66% (Fig. 5b). Fig. 5c shows that the yields of the
mixture of Mg, Mg Si and NaBO $2H O (2.5:1:1 M ratio) ball milled
for 5 h, 7.5 h, 10 h, 20 h were 61%, 63%, 82% and 86%, respectively.
The highest NaBH yield of this system was 86%. Compared to the
product yield obtained through the annealing process of Mg and
hydrated NaBO (12.3%), the corresponding value for the NaBH
2
Si was converted to FeSi, which
Si. The decreasing yield
along with the
[
2
properties of nanocrystalline Mg24
26 (2017) 498e506.
13] M.S. Yılmaz, A.K. Figen, S. Pi s¸ kin, Production of sodium metaborate tetrahy-
drate (NaB(OH) $ 2H O) using ultrasonic irradiation, Powder Technol. 215
(2012) 166e173.
14] W. Chen, L.Z. Ouyang, J.W. Liu, X.D. Yao, H. Wang, Z.W. Liu, M. Zhu, Hydrolysis
and regeneration of sodium borohydride (NaBH )eA combination of
hydrogen production and storage, J. Power Sources 359 (2017) 400e407.
3
Y eNieGR composites, J. Alloys Compd.
4
7
[
[
1
4
4
2
2
2
2
4
4
[15] M.C. Wang, L.Z. Ouyang, J.W. Liu, H. Wang, M. Zhu, Hydrogen generation from
sodium borohydride hydrolysis accelerated by zinc chloride without catalyst:
a kinetic study, J. Alloys Compd. 717 (2017) 48e54.
16] W. Chen, L.Z. Ouyang, J.W. Liu, X.D. Yao, H. Wang, Z.W. Liu, M. Zhu, Hydrolysis
and regeneration of sodium borohydride (NaBH4 ) e A combination of
hydrogen production and storage, J. Power Sources 359 (2017) 400e407.
2
4
[
process studied here is much higher. Furthermore, the present
work was carried out at room temperature, while the annealing
ꢁ
[17] H.A. Bandal, A.R. Jadhav, H. Kim, Cobalt impregnated magnetite-multiwalled
process was conducted at 600 C [29]. More importantly, the H in
carbon nanotube nanocomposite as magnetically separable efficient catalyst
for hydrogen generation by NaBH hydrolysis, J. Alloys Compd. 699 (2017)
4
1057e1067.
the regenerated NaBH
crystalline water in NaBO
4
comes completely from the sustainable
$2H O.
2
2
[
18] L.H. Ai, X.M. Liu, J. Jiang, Synthesis of loofah sponge carbon supported bime-
tallic silverecobalt nanoparticles with enhanced catalytic activity towards
hydrogen generation from sodium borohydride hydrolysis, J. Alloys Compd.
4
. Conclusions
625 (2015) 164e170.
[
19] M.H. Loghmani, A.F. Shojaei, Synthesis and characterization of CoeLaeZreB
quaternary amorphous nano alloy: kinetic study for hydrogen generation
from hydrolysis of sodium borohydride, J. Alloys Compd. 580 (2013) 61e66.
20] C.H. Liu, B.H. Chen, C.L. Hsueh, J.R. Ku, F.H. Tsau, Novel fabrication of solid-
In this paper, a new method was developed for the regeneration
of NaBH through ball milling of NaBO $2H O with Mg and Mg Si at
4
2
2
2
[
room temperature and under argon atmosphere, without the
introduction of additional hydrogen or hydrides. In this process, the
state NaBH
4
/Ru-based catalyst composites for hydrogen evolution using a
high-energy ball-milling process, J. Power Sources 195 (2010) 3887e3892.
d
þ
d
ꢀ
H
contained in NaBO
in NaBH , obtaining the highest regeneration yield reported until
now, equal to 86%. During the ball milling process, Mg reacts with
2
$2H
2
O is transformed into the H present
[21] U. Demirci, O. Akdim, P. Miele, Ten-year efforts and a no-go recommendation
for sodium borohydride for on-board automotive hydrogen storage, Int. J.
Hydrogen Energy 34 (2009) 2638e2645.
4
[
22] Y. Kojima, T. Haga, Recycling process of sodium metaborate to sodium boro-
NaBO
NaBO
2
$2H
$2H
2
O and forms NaBH
O.
4
, subsequently Mg
2
Si reacts with
hydride, Int. J. Hydrogen Energy 28 (2003) 989e993.
[23] Ç. Çakanyıldırım, M. Gürü, Processing of NaBH
milling and usage as hydrogen carrier, Renew. Energy 35 (2010) 1895e1899.
24] C.G. Lang, Y. Jia, J.W. Liu, H. Wang, L.Z. Ouyang, M. Zhu, X.D. Yao, NaBH
regeneration from NaBO by high-energy ball milling and its plausible
mechanism, Int. J. Hydrogen Energy 42 (2017) 13127e13135.
25] T.J. Ou, A. Giuliano, M. Panizza, A. Barbucci, G. Cerisola, Thermochemical
recycling of hydrolyzed NaBH . Part I: in-situ and ex-situ evaluations, Int. J.
4 2 2
from NaBO with MgH by ball
2
2
[
[
[
4
Acknowledgements
2
This work was supported by the Foundation for Innovative
Research Groups of the National Natural Science Foundation of
China (No. NSFC51621001), National Natural Science Foundation of
China Projects (Nos. 51431001 and 51771075) and by the Project
Supported by Natural Science Foundation of Guangdong Province
of China (2016A030312011 and 2014A030311004). Author Ouyang
also thanks Guangdong Province Universities and Colleges Pearl
River Scholar Funded Scheme (2014).
4
Hydrogen Energy 38 (2013) 15269e15274.
26] T. Kemmitt, G. Gainsford, Regeneration of sodium borohydride from sodium
metaborate, and isolation of intermediate compounds, Int. J. Hydrogen Energy
3
4 (2009) 5726e5731.
[27] A.K. Figen, S. Pi s¸ kin, Microwave assisted green chemistry approach of sodium
metaborate dihydrate (NaBO $2H O) synthesis and use as raw material for
sodium borohydride (NaBH ) thermochemical production, Int. J. Hydrogen
Energy 38 (2013) 3702e3709.
[28] K. Eom, E. Cho, M. Kim, S. Oh, S.-W. Nam, H. Kwon, Thermochemical pro-
duction of sodium borohydride from sodium metaborate in a scaled-up
reactor, Int. J. Hydrogen Energy 38 (2013) 2804e2809.
[29] B.H. Liu, Z.P. Li, J.K. Zhu, Sodium borohydride formation when Mg reacts with
hydrous sodium borates under hydrogen, J. Alloys Compd. 476 (2009)
L16eL20.
[30] D. Santos, C. Sequeira, Sodium borohydride as a fuel for the future, Renew.
Sustain. Energy Rev. 15 (2011) 3980e4001.
2
2
4
References
[1] M.L. Ma, L.Z. Ouyang, J.W. Liu, H. Wang, H.Y. Shao, M. Zhu, Air-stable hydrogen
generation materials and enhanced hydrolysis performance of MgH
2
-LiNH
2
composites, J. Power Sources 359 (2017) 427e434.
[
2] Z.J. Cao, L.Z. Ouyang, H. Wang, J.W. Liu, M. Felderhoff, M. Zhu, Reversible
hydrogen storage in yttrium aluminum hydride, J. Mater. Chem. A. 5 (2017)
[31] S.S. Muir, X.D. Yao, Progress in sodium borohydride as a hydrogen storage
material: development of hydrolysis catalysts and reaction systems, Int. J.
Hydrogen Energy 36 (2011) 5983e5997.
6042e6046.
[
[
3] L. Schlapbach, A. Züttel, Hydrogen-storage materials for mobile applications,
Nature 414 (2001) 353e358.
4] L. Wang, Z. Li, Y. Zhang, T. Zhang, G. Xie, Hydrogen generation from alkaline
[32] U.B. Demirci, The hydrogen cycle with the hydrolysis of sodium borohydride:
a statistical approach for highlighting the scientific/technical issues to prior-
itize in the field, Int. J. Hydrogen Energy 40 (2015) 2673e2691.
[33] C.L. Hsueh, C.H. Liu, B.H. Chen, C.Y. Chen, Y.C. Kuo, K.J. Hwang, J.R. Ku,
Regeneration of spent-NaBH back to NaBH by using high-energy ball mill-
4 4
ing, Int. J. Hydrogen Energy 34 (2009) 1717e1725.
[34] L.Z. Ouyang, H. Zhong, Z.M. Li, Z.J. Cao, H. Wang, J.W. Liu, X.K. Zhu, M. Zhu,
Low-cost method for sodium borohydride regeneration and the energy effi-
ciency of its hydrolysis and regeneration process, J. Power Sources 269 (2014)
768e772.
NaBH
4 2 3
solution using electroless-deposited CoeNieWeP/g-Al O as catalysts,
J. Alloys Compd. 702 (2017) 649e658.
[
5] N.M. Musyoka, J. Ren, H.W. Langmi, B.C. North, M. Mathe, D. Bessarabov,
Synthesis of rGO/Zr-MOF composite for hydrogen storage application, J. Alloys
Compd. 724 (2017) 450e455.
[
6] W. Luo, P.G. Campbell, L.N. Zakharov, S.-Y. Liu, A single-component liquid-
phase hydrogen storage material, J. Am. Chem. Soc. 133 (2011) 19326e19329.
7] L.Z. Ouyang, Z.J. Cao, H. Wang, R.Z. Hu, M. Zhu, Application of dielectric barrier
[
[35] T.J. Ou, M. Panizza, A. Barbucci, Thermochemical recycling of hydrolyzed

M. Huang et al. / Journal of Alloys and Compounds 729 (2017) 1079e1085
1085
NaBH
4
.
Part II: systematical study of parameters dependencies, Int. J.
[41] B.H. Liu, Z.P. Li, S. Suda, Solid sodium borohydride as a hydrogen source for
fuel cells, J. Alloys Compd. 468 (2009) 493e498.
Hydrogen Energy 38 (2013) 15940e15945.
[
[
[
36] Z.Y. Wu, L. Deng, J.T. Li, Q.S. Huang, Y.Q. Lu, J. Liu, T. Zhang, L. Huang, S.G. Sun,
Multiple hydrogel alginate binders for Si anodes of lithium-ion battery,
Electrochim. Acta 245 (2017) 371e378.
37] T. Matsumoto, K. Kimura, H. Nishihara, T. Kasukabe, T. Kyotani, H. Kobayashi,
Fabrication of Si nanopowder from Si swarf and application to high-capacity
and low cost Li-ion batteries, J. Alloys Compd. 720 (2017) 529e540.
38] L. Ouyang, M. Ma, M. Huang, R. Duan, H. Wang, L. Sun, M. Zhu, Enhanced
[42] J. Andrieux, U.B. Demirci, J. Hannauer, C. Gervais, C. Goutaudier, P. Miele,
Spontaneous hydrolysis of sodium borohydride in harsh conditions, Int. J.
Hydrogen Energy 36 (2011) 224e233.
[43] L.Z. Ouyang, W. Chen, J.W. Liu, M. Felderhoff, H. Wang, M. Zhu, Enhancing the
4
regeneration process of consumed NaBH for hydrogen storage, Adv. Energy
Mater. 1700299 (2017) 1e8.
[44] H. Zhong, L.Z. Ouyang, J.S. Ye, J.W. Liu, H. Wang, X.D. Yao, M. Zhu, An one-step
approach towards hydrogen production and storage through regeneration of
2
hydrogen generation properties of MgH -based hydrides by breaking the
magnesium hydroxide passivation layer, Energies 8 (2015) 4237e4252.
39] D. Lyttle, E. Jensen, W. Struck, Simple volumetric assay for sodium borohy-
dride, Anal. Chem. 24 (1952) 1843e1844.
40] V. D'Anna, A. Spyratou, M. Sharma, H. Hagemann, FT-IR spectra of inorganic
borohydrides, Spectrochim. Acta, Part A. 128 (2014) 902e906.
4
NaBH , Energy Storage Mater. 7 (2017) 222e228.
[
[
[45] A.M. Beaird, P. Li, H.S. Marsh, W. Al-Saidi, J.K. Johnson, M.A. Matthews,
C.T. Williams, Thermal dehydration and vibrational spectra of hydrated so-
dium metaborates, Ind. Eng. Chem. Res. 50 (2011) 7746e7752.