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j.ijhydene.2018.07.180

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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
Available online at www.sciencedirect.com
ScienceDirect
journal homepage: www.elsevier.com/locate/he
Preparation and characterization of nanostructured
CoeMoeB thin film catalysts for the hydrolysis of
ammonia borane
Chao Li a,1, Wei Meng c,1, Guijuan Hu a, Yan Wang b,c,*, Zhongqiu Cao c,
Ke Zhang c
a
Light Industry College, Liaoning University, Shenyang 110036, PR China
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), Nankai University, Tianjin
300071, PR China
c
Institute of Catalysis for Energy and Environment, College of Chemistry and Chemical Engineering, Shenyang
Normal University, Shenyang 110034, PR China
b
article info
abstract
Article history:
Nanostructured CoeMoeB thin film catalysts were prepared via electroless plating method
Received 15 March 2018
on the foam sponge. The effect of depositional pH value on the hydrogen generation rate
Received in revised form
from the hydrolysis of ammonia borane was investigated. The results show that the
19 July 2018
hydrogen generation rate increases from 3890.9 to 5100.0 mL min1 g1
cat, when the pH value
Accepted 27 July 2018
increases from 10.5 to 11.0. However, the hydrogen generation rate reduces to 3945.5 and
Available online xxx
3242.3 mL min1 g1
cat, when the pH value further increases to 11.5 and 12.0, respectively.
Hence, it can be seen that the as-prepared CoeMoeB thin film catalyst (pH ¼ 11.0) exhibits
Keywords:
the highest hydrogen generation rate, which could be attributed to the smaller size and the
CoeMoeB thin film
synergistic effect of Co, Mo and B on the catalyst surface. Moreover, the activation energy of
Electroless plating
the catalytic hydrolysis reaction at 298 K was 41.7 kJ mol1. The value is lower than that of the
Ammonia borane
most of Niebased and Coebased catalysts, even some noble metal catalysts. After 5 cycles,
Hydrogen generation
the catalytic activity of the CoeMoeB thin film catalyst remains about 61.9% of its initial
Hydrolysis
value. Based on the SEM analysis, the reduction of the catalytic activity could be ascribed to
the agglomeration of the active substance and some impurity phase on the catalyst surface.
© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction
On-board hydrogen storage is a critical technical issue for the
large-scale utilization of hydrogen fuel cells for transportation.
With high gravimetric and volumetric hydrogen storage capacities, chemical hydrides such as Mg2FeH6, Mg2NiH4, LiAlH4,
NaBH4, NH3BH3, and MgH2 are considered attractive candidate
hydrogen storage materials [1e5]. Among them, ammonia
borane (NH3BH3) has been extensively investigated due to high
gravimetric hydrogen density (19.6 wt %) and good stability in
aqueous solution [6,7]. As shown in Eq. (1), the stored hydrogen
can be generated from the hydrolysis of NH3BH3 at ambient
conditions in the presence of appropriate catalysts [8e10].
* Corresponding author. Institute of Catalysis for Energy and Environment, College of Chemistry and Chemical Engineering, Shenyang
Normal University, Shenyang 110034, PR China.
E-mail address: wangyan@synu.edu.cn (Y. Wang).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.ijhydene.2018.07.180
0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
2
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
NH3 BH3 þ 2H2 O/NHþ
4 þ BO2 þ 3H2
(1)
To date, a range of research has been focused on the catalysts in the hydrolysis of NH3BH3. Significant developments
have been achieved for the heterogeneous catalytic dehydrogenation of NH3BH3 with metal catalysts. Some noble metalbased catalysts, such as Rh, Ir, Ru, Ni/Pt and Pt, have showed
remarkable catalytic activities [11e20]. However, considering
the high costs and poor abundance of the noble metals, it is
more attractive to develop an economical and earth-abundant
metal catalyst for the improvement of the hydrogen generation kinetics properties for NH3BH3 hydrolysis. Recent studies
indicate that a series of non-noble metal catalysts have been
widely studied in catalytic dehydrogenation of the hydrolysis
of NH3BH3, including Co [21e23], Ni [24], Fe [25], CoCu [26,27],
Co/geAl2O3/SiO2/C [28], CoeB [29], NieP [30] and CoeNieP/TiO2
[31]. Among them, CoeB is mostly considered as a good
candidate for catalyzed hydrolysis of NH3BH3 because of its
low-cost, but its catalytic activity need to be further improved.
For instance, Ke et al. [32] have revealed that the catalytic activity of CoeB catalysts can be enhanced by the modification of
Mo element. In addition, there are a few reports available in
literature on the catalytic performance of CoeMoeB catalysts
in NH3BH3 hydrolysis system [33].
Traditionally, Co-based catalysts have been mainly prepared by the chemical reduction method to obtain powder
samples. Nevertheless, powder catalysts have some disadvantages such as difficult to separate from the reaction system, and easily aggregate during the preparation and storage
process. Nowadays, several deposition technologies have
been used to obtain the thin film catalysts and solve abovementioned problems [2,31,34]. Owing to the advantages of
easier control and lower processing temperature, electroless
plating technology is applied as an efficient method to prepare
thin film catalysts [35e37]. During the process of electroless
plating, Cu sheet [38], Ni/Cu foam [3,37,39] and carbon cloth
[40] have been usually chosen as substrate materials. But so
far, it has rarely been reported that foam sponge is used as the
substrate of the catalyst for NH3BH3 hydrolysis.
In this work, a nanostructured CoeMoeB thin film catalyst
was prepared on the foam sponge by electroless plating at
ambient temperature. The effect of depositional pH value on
the particle size and the catalytic activity for the hydrolysis of
NH3BH3 was systematically investigated. The CoeMoeB thin
film catalysts with smaller particle size make them possess a
defect-rich structure, which contributes to improve catalytic
activity towards the hydrolysis of NH3BH3. Compared with
those conventional non-noble metal powder catalysts and
even noble metal catalysts, the aseprepared CoeMoeB thin
film catalyst shows a significant enhancement of the catalytic
activity for the hydrolysis of NH3BH3.
Experimental
Preparation of CoeMoeB thin film catalysts
The commercial foam sponge with a projected surface area of
4 4 cm2 was used as the supporting substrate. The electroless plating method was employed to fabricate the CoeMoeB
thin films. All of the reagents were purchased from Sinopharm Chemical Reagent Co., Ltd., except for NH3BH3 (97%
purity, Sigma Aldrich). Before plating, the tailored foam
sponge was first immersed into acidic eroded solution and hot
alkaline solution to remove the greasy dirt and other impurities according to our previously described process [41]. Then,
it was sensitized in the solution (1 g L1 SnCl2 þ 1 mL L1 HCl)
for 3 min, activated in the solution for 2 min, washed with
distilled water and absolute ethyl and dried in vacuum atmosphere at 298 K for 24 h. Finally, weigh above-pretreated
foam sponge to determine the weight of the bare foam
sponge (denoted as mfoam sponge). The electroless plating of the
CoeMoeB thin film catalysts was conducted in a typical solution and the composition of the bath solution is presented in
Table 1. The depositional pH value was adjusted to a series of
values, including 10.5, 11.0, 11.5 and 12.0. When the procedure
of electroless plating was over under the designed pH value,
the CoeMoeB/foam sponge was taken out from plating bath,
washed, dried and weighed (denoted as mCoeMoeB/foam sponge).
So the weight of the deposited CoeMoeB thin film catalyst
(denoted as mCoeMoeB thin film catalyst) was calculated with Eq.
(2)
mthin film CoeMoeB catalyst ¼ mCoeMoeB=foam sponge mfoam sponge
(2)
Catalyst characterization
The inductively coupled plasma-optical emission spectroscopy (ICP-OES, ICP-9000, Thermo Jarrell-ASH Corp) has been
carried out to determine the chemical atomic composition of
the as-prepared CoeMoeB thin film catalysts. The asprepared CoeMoeB thin film catalysts were characterized by
powder Xeray diffraction (XRD, Rigaku-Dmax 2500, Cu Ka
radiation, l ¼ 1.54178 A), scanning electron microscopy (SEM,
Hitachi Se4800), transmission electron microscopy (TEM,
HITACHI HT7700) and atomic force microscopy (AFM, Bruker
Dimension icon). X-ray photoelectron spectroscopy (XPS)
measurement was performed with a Kratos Axis Ultra DLD
multi-technique electron spectrometer.
Hydrogen generation testing
In a typical hydrogen generation experiment, 8 mL NH3BH3
aqueous solution (containing 40 mg NH3BH3) was placed into a
threeenecked roundebottom flask with a temperature control
device. Then, a certain amount of the CoeMoeB thin film
catalyst loaded on the foam sponge was completely dipped
into the solution without stirring. The volume of the released
Table 1 e Bath composition and electroless plating
conditions for the deposited CoeMoeB thin film catalysts.
Bath composition
CoCl2$6H2O
Na2MoO4$2H2O
NH2CH2COOH
NaBH4
Depositing temperature
pH
Depositing time
Electroless plating conditions
0.05 mol L1
0.05 mol L1
0.6 mol L1
0.6 mol L1
298 K
10.5, 11.0, 11.5, 12.0
5 min
Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
3
hydrogen (denoted as VmL) was monitored by the water
displacement method [42]. The hydrogen generation rate was
determined by the weight of CoeMoeB thin film catalyst
excluding the foam sponge and its unit is denoted as
mL$min1$g1
cat. To measure the activation energy of the hydrolysis reaction, the hydrogen generation temperature was
maintained to 298, 303, 308 and 313 K, respectively. After the
hydrolysis reaction was completed, the used CoeMoeB thin
film catalyst was separated from the hydrolysis solution,
washed with distilled water, and then reserved to reuse.
Results and discussion
Catalyst characterization
To determine the atomic chemical composition of the asprepared CoeMoeB thin film catalysts at different pH value,
the elemental analysis has been characterized by ICP-OES.
The results are shown in Table 2. It can be found that the
atomic ratio (Co/Mo) deposited at different pH values of 10.5,
11.0, 11.5 and 12.0 is 6.23, 28.64, 13.79 and 8.78, and the corresponding atomic ratio (Co/B) is 0.64, 1.68, 1.54 and 0.81,
respectively. It can be inferred that the atomic ratio (Co/Mo
and Co/B) is maximum at pH ¼ 11.0. The results imply that the
elemental chemical composition of the CoeMoeB catalyst is
€ ki-Arvela et al. [43] have reported
sensitive to the pH value. Ma
that pH value is very important in tuning the elemental
chemical composition of the as-prepared materials.
The XRD patterns of the CoeMoeB thin film catalysts
deposited on the foam sponge at different pH values are
shown in Fig. 1. For all the CoeMoeB thin film catalysts, the
peaks at 2q ¼ 29.4 , 36.2 , 47.7 and 48.6 can be indexed as
NiCx phase of the substrate foam sponge (JCPDS No. 45e0979).
Three small peaks at 2q ¼ 23.0 , 25.9 and 26.5 are assigned to
MoO3 (JCPDS No. 47e1081), which might be originated from
the catalyst preparation process as the following Eq. (3) [32].
An orthorhombic CoMo2B2 phase ascribed to the (020), (211)
and (202) plane are observed at 2q ¼ 39.5 , 43.2 and 64.5 ,
respectively. Furthermore, the three weak peaks at 2q ¼ 57.6 ,
60.9 and 66.2 can be assigned to orthorhombic CoB phase
(JCPDS No. 3e959). Especially, when the pH value is 10.5, small
peaks attributed to hexagonal cobalt phase are also found at
2q ¼ 44.8 and 47.5 , respectively.
BH4 þ 2MoO24- þ 6H2 O/BðOHÞ
4 þ 2MoO3 þ 4OH þ 4H2
(3)
The morphologies of the CoeMoeB thin film catalysts
deposited on foam sponge at different pH values are
Table 2 e Chemical composition of the different CoeMoe
B thin film catalysts analyzed by ICP.
ICP results
Co (wt. %)
Mo (wt. %)
B (wt. %)
Co/Mo (at. %)
Co/B (at. %)
pH
10.5
11.0
11.5
12.0
36.74
5.90
57.36
6.23
0.64
61.28
2.14
36.58
28.64
1.68
58.06
4.21
37.73
13.79
1.54
42.51
4.84
52.65
8.78
0.81
Fig. 1 e XRD diffraction patterns of the CoeMoeB thin film
catalysts deposited on foam sponge at different pH values:
(a) 10.5, (b) 11.0, (c) 11.5 and (d) 12.0, respectively.
characterized by typical scanning electron microscopy (SEM).
As can be seen from Fig. 2aed, the CoeMoeB thin film exhibit
nanoparticles with diverse particle size, which can be determined by the diagrams of the particle size distributions
(Fig. 2eeh). When the pH value is 10.5, the CoeMoeB nanoparticles with the average size of about 85.2 nm (Fig. 2e) are
well dispersed on the foam sponge. When the pH value is
increased to 11.0, the average size of the CoeMoeB nanoparticles is 84.3 nm (Fig. 2f). However, further increasing the pH
value from 11.5 to 12.0, the average size obviously increases
from 106.3 to 167.6 nm. By comparing the SEM images and
corresponding particle size distributions of the various Coe
MoeB nanoparticles, it can be clearly seen that the particle size
of the CoeMoeB thin film catalyst deposited at pH value of 11.0
is smallest. The CoeMoeB thin film catalyst prepared at
pH ¼ 11.0 is further investigated by TEM (Fig. 3). As shown in
the TEM micrograph (Fig. 3aeb), the obtained CoeMoeB sample is composed of dispersive particle with mean crystallite
size of about 43.1 nm (Fig. 3c). Eom et al. have reported that
catalysts with smaller particles can display higher catalytic
reactivity [44]. So it can be inferred that the difference in particle average size among the four CoeMoeB nanoparticles may
induce the difference in catalytic activities.
To further characterize the CoeMoeB thin film catalysts
deposited at different pH values, the atomic force microscopy
(AFM) images have been shown in three dimensions in
Fig. 4aed. In general, the surface topographies of the catalysts
are composed of cone-like or mountain-like structures, but
the crests or troughs in between the cones or mountains are
different with the change of the pH value. The distance of
peak and peak has been given out as shown in Fig. 4e. It is
calculated to be 4.635, 1.998, 4.020 and 4.426 nm for the asprepared catalysts deposited at the pH value of 10.5, 11.0,
11.5 and 12.0, respectively. Obviously, the distance of the Coe
MoeB thin film catalyst is declining with the increase of the
pH value from 10.5 to 11.0, but then increases with further
increasing the pH value from 11.5 to 12.0. When the pH value
is 11.0, the shortest distance is attained, which can provide
Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
4
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
Fig. 2 e SEM images and particle size distributions of the CoeMoeB thin film catalysts deposited on the foam sponge at
different pH values: (a, e) 10.5, (b, f) 11.0, (c, g) 11.5 and (d, h) 12.0, respectively.
Fig. 3 e TEM images (a, b) and crystallite size distributions (c) of the CoeMoeB thin film catalyst prepared at pH ¼ 11.0.
Fig. 4 e (aed) AFM images in three dimensions and (e) depth spectra of the CoeMoeB thin film catalysts deposited on the
foam sponge at different pH values: (a) 10.5, (b) 11.0, (c) 11.5 and (d) 12.0, respectively.
more active sites on the catalyst surface because of the more
defects induced, such as vacancies, dislocations, grain
boundaries, phase boundaries and so on. By further analyzing
the AFM images, the surface roughness of as-synthesized Coe
MoeB catalysts can be calculated to be 0.658, 4.16, 3.75 and
1.59 with increasing the pH value from 10.5 to 12.0, respectively. It can be seen that the surface roughness reaches the
largest value when the pH value is 11.0. Based on some relevant references reported [41,45e47], it can be inferred that the
larger the surface roughness, the more the number of the
Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
defects of angle, step, or edge and so on, which can provide
more active sites on the catalyst surface, and the characteristic is beneficial for catalytic reaction.
To obtain further insights into the surface electronic
interaction between the elemental atoms, X-ray photoelectron spectroscopy (XPS) are applied to the various nanostructured CoeMoeB thin film catalysts at the Co 2p, Mo 3d
and B 1s levels in Fig. 5. As shown in Fig. 5a, when the pH value
is 10.5, two primary peaks of Co 2p are observed with binding
energies at 777.4 and 780.7 eV corresponding to the metallic
(Co0) and oxidized (Co2þ) states, respectively. When the pH
value is further increased from 11.0 to 12.0, the peak standing
for metallic Co has absolutely disappeared, and the peak
assigned to the oxidized Co locates at 781.3 eV, which is
slightly shifted to a higher value as compared to that of the
CoeMoeB thin film catalyst deposited at the pH value of 10.5
(780.7 eV). It should be noted that the peak intensity assigned
to the oxidized Co (pH ¼ 11.0) is higher than that of other pH
values (pH ¼ 10.5, 11.5 and 12.0), which can supply more active
sites and is beneficial to enhancing the catalytic activity. In the
Mo 3d level (Fig. 5b), the peak at 232.1 eV confirms that the
molybdenum is basically in its Mo4þ state, and another peak at
235.1 eV can be attributed to Mo6þ (MoO3), which is consistent
with the result of XRD (Fig. 1). In addition, the peak intensity
assigned to Mo6þ (pH ¼ 11.0) is higher by comparing with the
catalysts deposited at other three pH values (pH ¼ 10.5, 11.5
and 12.0). As reported by Ke et al. [32], MoO3 can contribute to
generation of oxygen vacancies, which will facilitate the
dissociation of water. That is to say, it is able to accelerate the
hydrolysis of NH3BH3. In the B 1s level in Fig. 5c, it can be found
that boron species are differential with the difference of the
pH values. When the pH value is 10.5, there are two peaks at
187.4 and 191.4 eV, demonstrating that boron species are
assigned to alloying and oxidized boron, respectively. When
the pH value is increased to 11.0 and 11.5, the only peak at
191.9 and 191.7 eV can be observed, signifying that the boron
exists in oxidized states on the surface of CoeMoeB thin film
catalysts. Compared with the binding energies assigned
oxidized boron (pH ¼ 10.5), there is a positive shift (ca. 0.5 eV)
observed at pH ¼ 11.0. This shift indicates that partial electrons might be transferred to the Co or Mo. Such modified
electronic structures of Co, Mo and B in CoeMoeB thin film
catalysts will facilitate the catalytic activity of catalysts,
providing the electron required during the catalysis reaction.
5
Fig. 6 e Catalytic activity of the bare foam sponge and
nanostructured CoeMoeB thin film catalysts on the foam
sponge deposited at different pH values from 10.5 to 12.0
for hydrogen generation from the hydrolysis of NH3BH3.
However, further increasing the pH value to 12.0, the boron
specie is similar to that of the catalyst deposited at the pH
value of 10.5. Hence, by analyzing the XPS spectra, it can be
concluded that the catalytic performance might be affected by
the synergistic effect of Co, Mo and B on the catalyst surface.
Effect of depositional pH value in CoeMoeB bath
Fig. 6 shows the hydrogen generation kinetics from the hydrolysis of NH3BH3 catalyzed by the bare foam sponge and
nanostructured CoeMoeB thin film catalysts deposited on the
foam sponge at different pH values. As shown in Fig. 6, the
bare foam sponge has no any catalytic activity for hydrolysis
of NH3BH3. On the basis of the slope of the fitting line, the
hydrogen generation rate of the CoeMoeB thin film catalysts
deposited at different pH values of 10.5, 11.0, 11.5 and 12.0 is
3890.9, 5100.0, 3945.5 and 3242.3 mL min1 g1
cat, respectively.
Hence, it can be seen that the CoeMoeB thin film catalyst
deposited at the pH value of 11.0 manifests the highest
hydrogen generation rate, which can be attributed to the small
particle size of the CoeMoeB thin film catalyst (Fig. 2b and f)
Fig. 5 e XPS spectra of (a) Co 2p, (b) Mo 3d and (c) B 1s level for the CoeMoeB thin film catalysts deposited on the foam sponge
at different pH values from 10.5 to 12.0, respectively.
Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
6
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
and the synergistic effect of Co, Mo and B on the catalyst
surface (Fig. 5) [45e47].
Effect of solution temperature
T (K)
To get the activation energy (denoted as Ea) of the hydrogen
generation reaction from the hydrolysis of NH3BH3 catalyzed
by the as-obtained CoeMoeB thin film catalyst (pH ¼ 11.0), the
hydrolytic reactions at different temperatures from 298 to
313 K are carried out. Fig. 7a presents the temperaturedependent hydrogen generation properties of the CoeMoeB
thin film catalyst. With the increase of the solution temperature, it can be found that the hydrogen generation rate is
evidently increased. The hydrogen generation rate (denoted
as r) and rate constant (denoted as k) at different temperature
(denoted as T) can be determined according to the slope of the
fitting line (Fig. 7a) and the ideal gas state equation, as listed in
Table 3. The Arrhenius plot of lnk versus 1/T is given out in
Fig. 7b. The activation energy can be obtained in accordance to
the following Arrhenius equation [41].
lnk ¼ lnA Ea 1
$
R T
Table 3 e Hydrogen generation rates for the hydrolysis of
NH3BH3 catalyzed by CoeMoeB thin film catalyst
(pH ¼ 11.0) at different solution temperature.
(4)
where the parameter A and R represent the preeexponential
factor and the gas constant, respectively. The activation energy for the hydrolysis reaction of NH3BH3 solution catalyzed
by the CoeMoeB thin film catalyst is calculated to be
41.7 kJ mol1. The comparison of the Ea values among
different catalysts towards NH3BH3 hydrolysis is shown in
Table 4. From Table 4, it can be observed that the Ea value of
as-synthesized CoeMoeB thin film catalyst is higher than that
of some noble metal-based catalysts [11,48e50] and a few Ni,
Coebased catalysts [8,29,51e54], but is lower than most of the
reported Ea values [3,5,11,13,14,22,52,55e63], indicating the
superior catalytic performance of the CoeMoeB thin film
catalyst prepared on foam sponge in this work.
Reusability of the CoeMoeB thin film catalyst
It is well known that the reusability is an important factor
for the practical application of catalysts, Therefore, the
r
k
1/T (1/K)
1 1
(mL min1 g1
gcat)
cat) (mol min
298
303
308
313
5100.0
6500.0
9013.6
12145.5
0.2079
0.2606
0.3555
0.4790
0.00336
0.00330
0.00325
0.00319
lnk
1.5707
1.3448
1.0342
0.7360
Table 4 e Ea values for the hydrolysis of NH3BH3 solution
catalyzed by different catalysts.
Catalyst
Ag@Co/graphene
Rh/geAl2O3
Pt/geAl2O3
NieMo/graphene
Ru/geAl2O3
Co/PEIeGO
CoeB/C
Cu0.4@Fe0.1Ni0.5
Ni0.33@Pt0.67/C
CoeB/Si
Cu0.3@Fe0.1Co0.6
PtTi alloy
CoeMoeB/foam sponge
Au@AuCo/CNT
Rh/CeO2
Ni0.03Pt0.97 alloys
CoeB power
Co (0) nanoclusters
Ni3B/C
Ru (0) nanoclusters
Ni@heBN
CoeB
CoeP/Ni foam
NiAg
Zeolite-confined Cu
Co0.7Ni0.3/MCNT
Ni0.97Pt0.03 hollow spheres
Co/Ni foam
Co/geAl2O3
Ru/C
Ea (kJ mol1)
Ref.
20.0
21
21
21.8
23
28.2
29
32.9
33
34
38.8
39.4
41.7
41.9
43
43.7
44
46
46.3
47
47.3
47.5
48
51.5
51.8
52.1
57
59
62
76
[48]
[49]
[49]
[8]
[49]
[51]
[29]
[54]
[11]
[52]
[53]
[50]
This work
[56]
[55]
[14]
[52]
[22]
[57]
[13]
[5]
[10]
[3]
[58]
[61]
[59]
[62]
[60]
[11]
[63]
Fig. 7 e (a) Hydrogen generation volume as a function of reaction time measured at different solution temperature for the
hydrolysis of NH3BH3 solution catalyzed by the as-obtained CoeMoeB thin film catalyst (pH ¼ 11.0); (b) the corresponding
Arrhenius plot of ln k vs 1/T.
Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 8 ) 1 e9
7
Fig. 8 e (a) The histogram curves of the catalytic activity of hydrogen generation rate versus number of cycles for the asprepared CoeMoeB thin film catalyst (pH ¼ 11.0); SEM image of the as-prepared CoeMoeB thin film catalyst (pH ¼ 11.0)
before (b) and after 5 cycles (c), respectively.
reusability tests of the as-obtained CoeMoeB thin film catalyst (pH ¼ 11.0) are carried out for the hydrolysis of NH3BH3.
Fig. 8a shows the histogram curves of the catalytic activity of
hydrogen generation rate versus number of cycles for the asprepared CoeMoeB thin film catalyst (pH ¼ 11.0). Obviously,
the catalyst activity is decreased slightly during multi-cycle
tests, but the hydrogen generation rate still reaches
3159.1 mL min1 g1
cat after 5 cycles. Namely, the catalyst retains 61.9% of its initial catalytic activity in the hydrolysis of
NH3BH3 in the fifth run. Compared with the SEM image before
the cycling (Fig. 8b), the agglomeration phenomenon of particles is obvious and the particle size is larger after 5 cycles
(Fig. 8c) for the as-prepared CoeMoeB thin film catalyst, but
the active material is still loading on the supporting foam
sponge. Thus, we can infer that the attenuation of the catalytic activity may be due to the varieties of the catalyst
morphology as previously reported [57,64,65]. Furthermore,
some impurity phase on the catalyst surface might be introduced in the catalytic process. As reported by Chandra et al.
[12], attenuation effect of the increasing metaborate ion in the
course of reaction as shown in Eq. (1) should also be taken into
account.
Conclusions
In summary, we have prepared nanostructured CoeMoeB
thin film catalysts on the foam sponge by electroless plating at
room temperature. In order to study the effects of depositional
pH values on the particle size of the CoeMoeB thin film catalysts and the catalytic activities for NH3BH3 hydrolysis, pH
values were adjusted to 10.5, 11.0, 11.5 and 12.0, respectively.
The results showed that the difference in pH values caused
the difference in particle size among the four catalysts, and
ultimately induced the difference in catalytic activities. The
CoeMoeB thin film catalyst (pH ¼ 11.0) with smaller particle
size displayed high catalytic activity in the hydrolysis of
NH3BH3. The hydrogen generation rate is 5100.0 mL min1 g1
cat
at 298 K and the activation energy is 41.7 kJ mol1. This
enhanced catalytic activity may be due to the smaller particle
size and the synergistic effect of Co, Mo and B, providing more
active sites on the catalyst surface. Furthermore, the
hydrogen generation rate decreases gradually after 5 cycles,
about 61.9% of its initial value after 5 cycles, which indicated
that the CoeMoeB thin film catalyst was relatively stable in
hydrolysis of NH3BH3.
Acknowledgments
This work was financially supported by the fund of the National
Natural Science Foundation of China (51501118, 21606115,
51102125), Natural Science Foundation (20170540814, 201602679)
of Liaoning Province, Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education) (111 project, B12015),
the Innovation Talent Project of Chinese Universities of Liaoning
Province (LR2017008), the Science Foundation of Liaoning Province Department of Education (LYB201618), the Doctoral Science
Foundation of Liaoning Province (20170520130) and Shenyang
Municipal Science and Technology Projects (F16e205e1e17, 1776-1-00).
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Please cite this article in press as: Li C, et al., Preparation and characterization of nanostructured CoeMoeB thin film catalysts for the
hydrolysis of ammonia borane, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.07.180
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