Dehydrogenation performance of NH3BH3 with Mg 2NiH4 addition

Article abstract of DOI:10.1016/j.tca.2011.06.006

The dehydrogenation performance of NH₃BH₃ destabilized by Mg₂NiH₄ was investigated. It was found that the onset dehydrogenation temperature was reduced, and no gaseous by-products were released during the whole decomposition process. This enhanced dehydrogenation performance could be attributed to the destabilization effect of Mg₂NiH₄. In comparison with the 2NH₃BH ₃/MgH₂ sample, the dehydrogenation behavior and destabilization mechanism are different. 4NH₃BH₃/Mg ₂NiH₄ composite exhibits a three-step decomposition feature. NH₃BH₃ and Mg₂NiH₄ decomposed separately. The destabilization effect of Mg₂NiH ₄ on the chemical bonds of NH₃BH₃ plays a crucial role in the enhanced dehydrogenation performance. Our results provide a new insight on destabilized dehydrogenation behavior of NH₃BH ₃ after metal hydrides addition.

Full text of DOI:10.1016/j.tca.2011.06.006

Thermochimica Acta 524 (2011) 23–28
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Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Dehydrogenation performance of NH BH with Mg NiH addition
3
3
2
4
a,∗
a
a
b
Baicheng Weng , Zhu Wu , Zhilin Li , Haiyan Leng
a
Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, PR China
Shanghai Key Laboratory of Modern Metallurgy & Materials Processing, Shanghai University, Shanghai 200072, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
3 3 2 4
The dehydrogenation performance of NH BH destabilized by Mg NiH was investigated. It was
Received 11 February 2011
Received in revised form 4 May 2011
Accepted 8 June 2011
found that the onset dehydrogenation temperature was reduced, and no gaseous by-products were
released during the whole decomposition process. This enhanced dehydrogenation performance could
be attributed to the destabilization effect of Mg2NiH4. In comparison with the 2NH3BH3/MgH2 sample,
the dehydrogenation behavior and destabilization mechanism are different. 4NH3BH3/Mg2NiH4 com-
posite exhibits a three-step decomposition feature. NH3BH3 and Mg2NiH4 decomposed separately. The
destabilization effect of Mg2NiH4 on the chemical bonds of NH3BH3 plays a crucial role in the enhanced
dehydrogenation performance. Our results provide a new insight on destabilized dehydrogenation behav-
ior of NH3BH3 after metal hydrides addition.
Available online 16 June 2011
Keywords:
Magnesium nickel hydride
Ammonia borane
Dehydrogenation
Hydrogen storage material
© 2011 Elsevier B.V. All rights reserved.
1
. Introduction
improvements on both the extent and rate of hydrogen release
from NH BH under mild conditions. Xiong et al. [9,10] substituted
3
3
Development of hydrogen storage materials is one of indispens-
one H atom in the NH3 group of NH BH3 with more electron-
3
able issues for hydrogen energy applications [1–3]. Although the
solid materials for hydrogen storage promise their storage capac-
ities which are much higher than those in other conventional
storage methods, so far only a few systems have been identified
which can potentially meet the international targets for mobile
hydrogen storage applications. Such candidates for the materials
donating elements LiH or NaH, by milling LiH or NaH with NH BH .
3
3
It was observed that more than 10 wt.% and 7 wt.% of hydrogen
desorbed from LiNH BH and NaNH BH , respectively, at around
2
3
2
3
◦
90 C. The release of detrimental gaseous impurities of borazine and
diborane were effectively depressed. Burrell and co-workers [11]
synthesized Ca(NH BH ) by reacting CaH2 with NH BH3 at the
2
3 2
3
include metal borohydrides (e.g. LiBH , Mg(BH ) , Ca(BH ) [4–7],
molar ratio of 1:2 in tetrahydrofuran (THF) solution. They found
4
4 2
4 2
◦
ammonia borane (NH BH ) and metal amidoboranes (LiNH BH ,
that Ca(NH BH ) started to release hydrogen at 80 C, and rapidly
3
3
2
3
2
3 2
◦
NaNH BH , Ca(NH BH ) , Sr(NH BH ) ), etc. [8–12].
dehydrogenated above 120 C. Thermolysis of metal amidoboranes
does not suffer from the induction period and concurrent genera-
tion of gaseous impurities present in the dehydrogenation process
of NH BH .
2
3
2
3 2
2
3 2
NH BH is a leading candidate for hydrogen storage applica-
3
3
tions as it possesses an intriguing hydrogen capacity of 19.6 wt.%
−3
based on weight and 160 kg m
on volume, respectively. 1 mol
3
3
NH BH can decompose to release more than 2 mol pure hydro-
gen gas (14 wt.%) below 160 C. The hydrogen release results in
Dehydrogenation properties of NH BH3 can be dramatically
improved by ball milling with MgH2 [13–15]. However, no solid-
3
3
3
◦
polymerization eventually to [NHBH]n [9–12]. However, the prac-
state reaction occurs between NH BH3 and MgH2 indicating that
3
tical application of NH BH3 is greatly restricted by the sluggish
dehydrogenation kinetics below 100 C, and concurrent release of
the effect of MgH is quite different from that of its analogues, LiH,
3
2
◦
NaH or CaH . Kang et al. [13] believed that the improvements could
2
detrimental gaseous by-products borazine (c-(NHBH) , m/z ∼80),
be attributed to the solid-state interaction of MgH with NH BH .
The interaction resulted in the formation of Mg–B–N–H intermedi-
ate complexes which were claimed by the authors to be the cause
3
2
3
3
monomeric aminoborane (BH NH , m/z ∼27) and diborane (B H ,
2
2
2
6
m/z ∼27).
Recently several approaches have been developed for promot-
ing hydrogen release from NH BH by ball milling alkali (or alkali
for thermodynamic improvements of NH BH . However, in the rel-
3 3
evant study by Wu et al. [14], they concluded that MgH2 did not
participate in the dehydrogenation process of NH BH , based on
3
3
earth metal) hydrides with NH BH , resulting in considerable
3
3
3
3
the identification of elemental Mg as the sole Mg-containing crys-
◦
talline phase in the post heated 2NH BH /MgH sample at 400 C.
3
3
2
∗ Corresponding author. Tel.: +8621 62511070; fax: +8621 32200534.
E-mail address: bcweng@mail.sim.ac.cn (B. Weng).
Kang and co-workers [15] further investigated the property and
the structure of 2NH3BH3/MgH2 sample and they claimed that
0
040-6031/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2011.06.006

2
4
B. Weng et al. / Thermochimica Acta 524 (2011) 23–28
unlike stated previously, only a fraction of MgH2 participated in
the dehydrogenation process of NH BH at early stage resulting in
3
3
the formation of Mg–B–N–H intermediate complexes.
In order to further understand the mechanism, particularly
the role of H atoms, we presented a strategy for enhancing the
dehydrogenation of NH BH by mechanical milling with Mg NiH .
3
3
2
4
Choosing Mg NiH as an additive is motivated by the recent find-
2
4
ings that the H atoms of Mg NiH4 show higher reactivity than
2
in MgH , and the bond energy of Mg–H is lower than that in
2
MgH2 [16–21]. The present study proves an enhancement on the
dehydrogenation performance of NH BH by replacing MgH with
3
3
2
Mg NiH . Through examining the structure, it is found that the
2
4
enhancement is mainly caused by the enhanced reactivity of H
atoms, and Mg Ni appears to maintain its phase stability in the
2
post heated sample.
2
. Experimental
Ammonia borane (NH BH , 97% purity), magnesium hydride
Fig. 1. XRD patterns of the Mg2NiH4 powder (a) and starting chemicals Ni powder
b) and MgH2 (c). The dashed line was added as a guide to the eye.
(
3
3
(
MgH , 95% purity) and nickel powder (Ni, 99% purity) were pur-
2
chased from Sigma–Aldrich. NH BH was purified by a sublimation
process before the following experiments [22,23]. All sample oper-
ations were carried out in an MBraun Labmaster 130 glove box
3
3
1:30 in an agate mortar and pestle and pressed into a pellet for anal-
ysis. Each spectrum was acquired after 64 scans with a resolution
−1
of 4 cm
.
maintained under argon atmosphere with <1 ppm O2 and H O
2
vapor. Mg NiH was synthesized as in reference [16], by ball milling
2
4
MgH2 with Ni powders in a molar ratio of 2:1 at 350 rpm for
00 h under hydrogen atmosphere with an initial pressure of 3 MPa,
3. Results and discussion
3
followed by three cycles of dehydrogenation and hydrogenation
at 350 C. Mechanical milling was carried out using a Fritsch
Fig. 1 shows the X-ray diffraction pattern of the as-prepared
◦
Mg NiH4 powder. The results indicate the disappearance of the
2
Pulverisette 6 planetary ball mill (PBM). The NH BH /Mg NiH
diffraction peaks of the starting chemicals, MgH and Ni. The reflec-
3
3
2
4
2
mixtures at molar ratio of 4:1 were mechanically milled under
inert argon (99.999%) atmosphere at 400 rpm for 2 h. The ther-
tions in the XRD pattern indicate that the lattice parameters are
a = 6.525 A˚ , b = 6.525 A˚ , c = 6.525 A˚ , which is in excellent agreement
mal decomposition behavior of the post-milled 4NH BH /Mg NiH
with the crystal structure of Mg NiH [16–21]. The results identify
3
3
2
4
2 4
and pristine NH BH3 samples were examined using a syn-
that the post-milled sample is Mg NiH with a high yield of up to
2 4
3
chronous thermogravimetry (TG)/differential scanning calorimetry
100%.
(
DSC)/mass spectroscopy (MS) (Netzsch STA449F3/Hiden HPR20),
Fig. 2 compares the thermal decomposition behaviors of pris-
tine NH BH and the post ball milled 4NH BH /Mg NiH mixture.
◦
in the temperature range from room temperature to 450 C at a
heating rate of 5 C min
3
3
3
3
2
4
◦
−1
under 1 atm argon with a purge rate
The TG-DSC plot of pristine NH BH decomposition shows a large
3 3
−1
of 30 mL min . The MS spectroscopy is interconnected with TG
through a capillary and the detection limit of the MS spectroscopy
is 5 ppb which is sufficient for getting accurate results due to the
high sensitivity of the used equipment. The dehydrogenation kinet-
ics of NH BH /Mg NiH mixtures were examined by a conventional
Sievert type P–C–T apparatus at 80, 120 and 240 C, respectively.
The dehydrogenation measurements at various isothermal temper-
ature were performed with an initial pressure of <100 Pa.
amount of weight loss of 60 wt.% occurred after the endother-
◦
mic melting peak at 107 C. The weight loss is greater than the
theoretical hydrogen content of 13 wt.%. The mass loss is consid-
erable high compared with the report in references [13,15,22],
which should be caused by the different experimental conditions
and sample preparation which could strongly affect the mass loss
3
3
2
4
◦
of NH BH3 decomposition. Moreover the large amount of weight
3
loss implies the concurrent release of gaseous impurities (borazine
X-ray diffraction (XRD) measurements were carried out by a
Rigaku D/max 2400 diffractometer using Cu/K␣ radiation. Samples
were sealed with a polyvinylchloride membrane to avoid oxidation
during the measurements. 11B magic-angle-spinning nuclear mag-
netic resonance (MAS-NMR) experiments were carried out at room
temperature on a Bruker Advance 300 NMR spectrometer (Bruker,
Germany) operating at 9.7 T on 128.3 MHz. Spectra were recorded
using a two-channel custom-built probe with a 3 mm ZrO2 rotor,
the magic-angle-spinning rate was set to 12 kHz to avoid the over-
lapping of spinning sidebands on other resonance lines. 300 scans
were taken for the samples. The 11B chemical shifts were referenced
((BHNH) ), m/z = 80; diborane (B H ), and monomeric aminobo-
3
2
6
rane (BH NH ) m/z = 27) [9–11,22,24,25]. In contrast, the TG-DSC
2
2
plot of 4NH BH /Mg NiH mixture decomposition shows that the
3
3
2
4
◦
onset decomposition temperature is below 75 C. Upon heating the
sample to 105 C, the most significant mass loss is observed. Fur-
◦
ther heating leads to a third decomposition step initiated at about
◦
220 C. The total weight loss observed for the 4NH BH /Mg NiH
3
3
2
4
◦
sample below 450 C is 8.4 wt.%. The weight loss is close to the the-
oretical hydrogen content of 8.5 wt.%, implying that the concurrent
generation of gaseous by-products might be inhibited.
Fig. 3 shows the MS characterization of the gaseous products
during thermolysis of pristine NH BH3 and 4NH BH /Mg NiH
to NaBH as −41 ppm. Raman spectra of the samples were recorded
4
3
3
3
2
4
using a Renishaw inVia plus spectrometer (Renishaw, UK) excited
by a 514 nm laser. Typically, in order to get intensified signals, each
sample was measured 20 times. Fourier Transform Infrared Spec-
troscopy (FTIR) spectra were recorded at room temperature on a
Bruker TENSOR 27 spectrometer (Bruker, Germany). The samples
were prepared in an Ar-filled glove box by grinding a small amount
of the samples with dry spectroscopic grad KBr at a mass ratio of
mixture. As shown in Fig. 3, during the thermolysis process of
pristine NH BH , two dehydrogenation peaks are observed at
3
3
◦
◦
114 C and 158 C, corresponding to the two decomposition steps
associated with the formation of solid residues polyaminoborane
(NH BH )n and polyiminoborane (NHBH)n, respectively [9–12].
2
2
In contrast, The MS spectrum of 4NH BH /Mg NiH decomposi-
3
3
2
4
◦
◦
◦
tion shows 3 hydrogen release peaks at 75 C, 110 C and 230 C,

B. Weng et al. / Thermochimica Acta 524 (2011) 23–28
25
Fig. 4. In situ MS characterizations of gaseous by-products release during the
thermolysis of pristine NH3BH3 (a) and 4NH3BH3/Mg2NiH4 mixture (b) ((borazine
(
(BHNH)3), m/z = 80; diborane (B2H6), and monomeric aminoborane (BH2NH2)
m/z = 27)).
◦
dehydrogenation rate at 80 C is even faster than that of pristine
◦
◦
NH BH3 at 100 C. The amount of hydrogen released at 80 C is
3
3
.3 wt.%, which is very close to the theoretical hydrogen capacity
of NH BH3 in the mixture decomposition to polyaminoborane
3
◦
(
[NH BH ]n) (3.4 wt.%). By raising the temperature to 120 C, the
2
2
sample totally release 6.9 wt.% hydrogen indicating that 3.6 wt.%
◦
hydrogen of NH BH3 is released at 120 C, which coincides with
3
the hydrogen capacity of [NH BH ]n decomposition to [NHBH]n.
2
2
◦
Up to 240 C, the sample releases 8.4 wt.% hydrogen indicating
that extra 1.5 wt.% hydrogen is released at 240 C which is in
◦
Fig. 2. DSC (a) and TG (b) profiles for dehydrogenation of pristine NH3BH3 (blue
lines) and the post ball milled 4NH3BH3/Mg2NiH4 mixture (red lines). (For interpre-
tation of the references to color in this figure legend, the reader is referred to the
web version of the article.)
good agreement with the hydrogen capacity of Mg2NiH4 addition
(1.7 wt.%).
Fig.
6
shows the XRD patterns of the post-milled
4
NH BH /Mg NiH sample at a series of dehydrogenation steps.
3
3
2
4
respectively. The result suggests that 4NH BH /Mg NiH exhibits
In comparison with the peak positions of Mg2NiH4 in the post
ball milled pattern (Fig. 6c), no apparent shifts during the initial
dehydrogenation steps (Fig. 6b), indicating that Mg2NiH4 remains
essentially unchanged. In addition, noting that at temperature
3
3
2
4
a three-step dehydrogenation feature.
The introduction of Mg NiH was found to reduce detrimental
2
4
gaseous impurities. As seen from the MS results of pristine NH BH3
3
◦
shown in Fig. 4, considerable amount of gaseous by-products
above 240 C, only Mg2Ni phase was detected in the relevant XRD
◦
(
borazine ((BHNH) ), m/z = 80; diborane (B H ), and monomeric
pattern, and the amount of hydrogen released at 240 C equivalent
3
2
6
aminoborane (BH NH ) m/z = 27) were released during the heat-
to the hydrogen capacity of Mg2NiH4 (Fig. 5), these results reveal
that Mg2NiH4 and NH3BH3 decomposed independently. Different
from 2NH3BH3/MgH2 [13,15], 4NH3BH3/Mg2NiH4 decomposition
does not involve the combination of Mg or Mg2Ni with B–N
2
2
ing process, especially in the second decomposition step, while for
NH BH /Mg NiH mixture, no gaseous by-products was detected
3
3
2
4
during the decomposition.
Fig.
5
presents the dehydrogenation kinetics of the
◦
4
NH BH /Mg NiH mixture at 80, 120 and 240 C, respectively. Its
3
3
2
4
◦
Fig. 3. In situ MS patterns of hydrogen release during the thermolysis of pristine
NH3BH3 (a) and 4NH3BH3/Mg2NiH4 mixture (b).
Fig. 5. Dehydrogenation kinetics of pristine NH3BH3 at 100
C
(b) and
◦ ◦ ◦
4NH3BH3/Mg2NiH4 mixture at 80 C (a), 120 C (c), and 240 C (d), respectively.

2
6
B. Weng et al. / Thermochimica Acta 524 (2011) 23–28
Fig. 6. XRD patterns of pristine NH3BH3 (a), Mg2NiH4 (b), 2 h post-milled
NH3BH3/Mg2NiH4 sample (c) and the XRD patterns of 4NH3BH3/Mg2NiH4 sam-
ple decomposition at 80 C (d), 110 C (e) and 240 C (f), respectively. The dashed
line was added as a guide to the eye.
Fig. 8. Raman spectra of post-milled pristine NH3BH3 (black line) and
4NH3BH3/Mg2NiH4 (red line). The dashed lines were added for guide of eyes. (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of the article.)
4
◦
◦
◦
structure forming Mg–B–N complexes and producing MgBNHx
residues in the solid products [13,15]. Its thermolysis route could
be hypothetically described using the following equations.
are identified in neat NH3BH3, in excellent agreement with the
literature results [13,29]. In comparison with neat NH3BH3, the
mechanically milled 4NH3BH3/Mg2NiH4 sample exhibits clearly
difference on the spectroscopic features. The intensities of B–H,
N–H, BH deformation and NH deformation vibration modes were
◦
0 C
5
NH BH −→ NH BH + H
(1)
(2)
(3)
3
3
2
2
2
3
3
◦
10 C
markedly reduced, and particularly, B–H BH3 deformation and NH3
1
NH BH −→ NHBH + H
−1
2
2
2
deformation vibration mode at 2376, 1186 and 1598 cm , respec-
◦
tively, are found to disappear in the milled 4NH BH /Mg NiH
2
20 C
3
3
2
4
Mg NiH −→ Mg Ni + 2H
2
4
2
2
sample; In addition, the B–N rocking model exhibit shifts to
−
1
new positions at 711, 796 and 840 cm , respectively. Mechani-
cal milling can only result in slight peak intensity changes through
changing the granular size [13]. The spectroscopic features changes
However, Fig. 6a shows that several peaks corresponding to
NH BH and Mg NiH disappear, implying that some subtle phys-
3
3
2
4
ical transformations occurred during the ball milling process.
Similar to MgH , addition of Mg NiH cannot substitute the H atom
2
2
4
in NH3 group of NH BH3 during milling process. But the disap-
3
pearance of several diffraction peaks suggests that NH BH3 and
3
Mg NiH become more amorphous during ball milling.
2
4
To further understand the potential physical transformations
during the milling process, 11B NMR characterizations of the post
ball milled mixture and post ball milled NH BH3 are compared
3
in Fig. 7. The peak of pristine NH BH3 do not show a single peak
3
morphology results from the splitting of the quartet pattern of
1
1
B resonance by three equivalent protons after being heated at
◦
11
6
0 C [26]. B NMR results show very different peak morpholo-
gies. These changes indicate the spin states changes among the N–B
and B–H chemical bonds [27,28]. The addition of Mg NiH leads to
2
4
destabilization of NH BH . This result is supported by the Raman
3
3
spectrometry studies of the post-milled 4NH BH /Mg NiH and
3
3
2
4
plain NH BH samples. As shown in Fig. 8, B–N stretches at 726,
3
3
−1
−1
7
83 and 798 cm , N–H stretches at 3177, 3253 and 3316 cm ,
−1
B–H stretches at 2282 and 2376 cm , BH deformation stretches at
3
−1
−1
1
186 cm and NH deformation stretches at 1375 and 1598 cm
3
Fig. 9. FTIR spectra of post-milled pristine NH3BH3 (red line) and
4NH3BH3/Mg2NiH4 (blue line). The dashed lines were added for guide of
eyes. (For interpretation of the references to color in this figure legend, the reader
is referred to the web version of the article.)
Fig. 7. 11B NMR patterns of the post ball milled NH3BH3 and 4NH3BH3/Mg2NiH4.

B. Weng et al. / Thermochimica Acta 524 (2011) 23–28
27
These results demonstrate that the interaction of NH BH3 and
3
Mg NiH4 result in subtle structure transformations among B–N,
2
N–H, B–H chemical bonds of NH BH . Noting that Mg Ni main-
3
3
2
tains its phase stability during the decomposition shown in XRD
patterns, these results demonstrate that the effect of the Mg NiH4
2
on NH BH3 is the destabilization effect. In the case of NH BH3
3
3
destabilized by MgH , Kang et al. [13,15] claimed that the improve-
2
ments resulted from Mg participating in the decomposition of
NH BH3 through the formation of Mg–B–N–H intermediate com-
3
plexes. However in our case, replacing MgH with Mg NiH results
2
2
4
in the destabilization of NH BH on B–N, B–H and N–H structures
3
3
which is believed to play a crucial role in the enhancement. In addi-
tion, the destabilization effect also affects Mg NiH which can well
2
4
◦
explain the decrease of onset temperature of Mg NiH from 300 C
2
4
◦
to 220 C [16–21].
Fig. 10 shows the difference of the thermal decomposition
behavior and hydrogen evolution performance for the 0 h, 1 h, 2 h
and 10 h ball milled 4NH BH /Mg NiH mixtures. For the mechan-
3
3
2
4
ically mixed mixture (0 h), the TG-MS spectrum is similar to that
◦
of pristine NH BH3 below 200 C. If the Mg NiH additive is not
3
2
4
taken into account, the weight loss of the mixture is the same
as that of pristine NH BH . The result shows that Mg NiH can-
3
3
2
4
not destabilize NH BH3 just via simple mechanical mix of the
3
composites. In contrast, the decomposition temperature of 1 h
◦
ball milled 4NH BH /Mg NiH is lowered to 90 C. The MS pro-
3
3
2
4
file of 4NH BH /Mg NiH shows hydrogen peaks shift to lower
3
3
2
4
temperature. As seen from the MS results of 1 h ball milled mix-
ture, no diborane was detected during the whole decomposition
process, but low boiling point by-product borazine was concur-
rently released during the second hydrogen release step of pristine
◦
4
NH BH /Mg NiH at 120 C. TG comparison reveals the amount
3
3
2
4
of weight loss of 10 h ball milled mixture is 8.4 wt.% which is the
same as 2 h ball milled mixture and lower than 1 h (18 wt.%) and
0
h (33 wt.%) ball milled mixtures. MS spectra of 2 h and 10 h ball
milled mixtures show that no gaseous byproducts were detected
during the whole decomposition process. The results confirm the
destabilization effect of Mg NiH4 on NH BH3 by ball milling, and
2
3
prove that the interaction between Mg NiH and NH BH accounts
2
4
3
3
for the enhanced dehydrogenation performance of NH BH .
3
3
4. Conclusions
The dehydrogenation performance of NH BH3 with Mg NiH4
3
2
addition was investigated. Our results show that the onset
dehydrogenation temperature is reduced, and no gaseous by-
products are released during the whole decomposition process.
4
NH BH /Mg NiH composite exhibits a three-step decomposi-
3 3 2 4
tion feature: NH BH3 first decomposes to form polyaminoborane
3
(
NH BH )n, and then forms polyiminoborane (NHBH)n at second
2 2
Fig. 10. TGA patterns (a) and MS spectra (b and c) of the 0 h, 1 h, 2 h and 10 h
ball milled 4NH3BH3/Mg2NiH4 mixture. ((borazine ((BHNH)3), m/z = 80; diborane
step, and the third step of hydrogen desorption is the decom-
position of Mg NiH . The weight losses in these three steps are
3
2
4
(
B2H6), and monomeric aminoborane (BH2NH2) m/z = 27)).
.3 wt.%, 3.4 wt.% and 1.5 wt.%, respectively. In comparison with the
NH BH /MgH sample, these improvements are more significant.
2
3
3
2
are ascribed to the bonding structure of NH BH3 changes in the
3
The enhanced dehydrogenation performance could be attributed
to the destabilization effect of Mg NiH . Our results provide a new
insight on destabilized dehydrogenation behavior of NH BH with
presence of Mg NiH .
2
4
2
4
In our further efforts to understand the effect of Mg NiH4
2
3
3
on NH BH , FTIR characterizations were carried out to identify
3
3
metal hydrides addition.
the changes of molecular vibrations of post-milled NH BH , and
3
3
4
NH BH /Mg NiH sample. As shown in Fig. 9, the symmetry
3 3 2 4
Acknowledgment
of N–H, B–N, BH3 deformation and NH3 deformation peaks are
obviously decreased. In addition, the 4NH BH /Mg NiH sample
3
3
2
4
This work was financially supported by National “863” High-
Tech. Research Programs of China (2007AA05Z102, 2008AA05Z102,
exhibits 3 clearly difference on the spectroscopic features. Firstly,
the symmetry B–H model at 2370 cm is markedly reduced. Sec-
−1
2
007AA05Z149), the National Natural Science Foundation of China
ondly, the intensity and intensity distribution of BH deformation
3
(
(
grant no. 21071149) and Shanghai Natural Science Foundations
11ZR1444300 and 095SKA1001).
and B–N vibration peaks are changed. Thirdly, NH3 deformation
peak disappeared.

2
8
B. Weng et al. / Thermochimica Acta 524 (2011) 23–28
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[
[
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[
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