Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles and Their Remarkable Catalytic Activity for Hydrogen Generation from Ammonia Borane Dehydrogenation

Article abstract of DOI:10.1007/s10562-018-2374-8

Abstract: The effective storage and generation of hydrogen at room temperature is an important issue in many areas, including alternative energy. In this work, NiCoB nanoalloys with high B contents, clean surfaces, and good dispersions are synthesized by an in-situ reduction method. The NiCoB catalyst with high B content exhibits significantly more excellent catalytic activity for hydrogen generation from the hydrolytic of ammonia borane than NiCoB catalyst with low B content. The remarkable catalytic performance is attributed to the strong electronic interaction between the incorporated B and the active metal sites of Co and Ni, the clean surface and good dispersion of the catalyst. Basically, the physical and catalytic properties of the catalyst take advantage of the selection of reductant used during the in-situ synthesis of the NiCoB nanoalloys. This work demonstrates that this facile synthetic method is a promising avenue for the rational design of various B incorporated metal catalysts for hydrogen energy exploitation, metal/air batteries, and electrochemical sensors.

Full text of DOI:10.1007/s10562-018-2374-8

Catalysis Letters
https://doi.org/10.1007/s10562-018-2374-8
Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles
and Their Remarkable Catalytic Activity for Hydrogen Generation
from Ammonia Borane Dehydrogenation
1
1
1
1
1
2
1
1
Hongli Wang · Dawei Gao · Liying Wang · Yue Chi · Minggang Wang · Yan Gu · Cong Wang · Zhankui Zhao
Received: 24 January 2018 / Accepted: 24 March 2018
©
Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
The effective storage and generation of hydrogen at room temperature is an important issue in many areas, including alterna-
tive energy. In this work, NiCoB nanoalloys with high B contents, clean surfaces, and good dispersions are synthesized by
an in-situ reduction method. The NiCoB catalyst with high B content exhibits significantly more excellent catalytic activity
for hydrogen generation from the hydrolytic of ammonia borane than NiCoB catalyst with low B content. The remarkable
catalytic performance is attributed to the strong electronic interaction between the incorporated B and the active metal sites
of Co and Ni, the clean surface and good dispersion of the catalyst. Basically, the physical and catalytic properties of the
catalyst take advantage of the selection of reductant used during the in-situ synthesis of the NiCoB nanoalloys. This work
demonstrates that this facile synthetic method is a promising avenue for the rational design of various B incorporated metal
catalysts for hydrogen energy exploitation, metal/air batteries, and electrochemical sensors.
Graphical Abstract
Keywords B incorporated nickel–cobalt alloy · In-situ reduction · Heterogeneous catalysis · Hydrogen generation ·
Ammonia borane
Extended author information available on the last page of the article
Vol.:(0
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H. Wang et al.
1
Introduction
the bonding structure is intrinsically different from its crys-
talline counterpart because of the covalent component of
its metal-metalloid bonds [29]. This property would result
in the occurrence of an electron effect between the metal
atoms and the B atoms, which may further promote their
catalytic performance [30]. Moreover, the incorporation of
B into transition metal catalyst can effectively enhance the
catalytic performance [31–34]. Therefore, the preparation
of amorphous CoB-based catalysts with different B contents
and a comparison of their catalytic performances for hydro-
gen generation from the hydrolysis of AB are both of great
interest.
Secure and efficient hydrogen storage and generation
remains one of the critical technical barriers to hydrogen
energy applications [1–3]. Currently, it is of great impor-
tance to the exploration of proper chemical hydrogen storage
materials that can release hydrogen through in-situ processes
under mild conditions for direct usage in fuel cells [4, 5].
Ammonia borane (NH BH , AB) has been widely regarded
3
3
as a promising candidate for chemical hydrogen storage
applications due to its high hydrogen content of 19.6 wt%,
nontoxicity, and high stability at room temperature [6, 7].
AB can release hydrogen through pyrolysis, solvolysis in
protic solvents (i.e., hydrolysis or methanolysis), and dehy-
drocoupling in nonprotic solvents [8–12]. Since pyrolysis
requires high temperatures [8], methanolysis and dehydro-
genation in organic liquids are not environmentally friendly
Non-noble metal NPs with ultrafine sizes have attracted
great interest because of their increased surface areas and the
adequate number of edge and corner atoms, which greatly
improve their catalytic performances. However, non-noble
metal NPs with ultrafine sizes are easily aggregated because
of their high surface energies and therefore lead to low cata-
lytic activities [35]. To avoid this aggregation, strong sur-
factants are usually employed to maintain minimization and
high dispersion of NPs [36]. However, an overly strong affili-
ation of surfactants to the NPs may decrease the number of
active sites on the surface of NPs, and thus cause the severe
deactivation of the NPs [37, 38]. In this sense, employing
weak surfactants to guarantee the clean surface and high
concentration of active sites of the NPs, while using weak
reductants to ensure the good dispersion of the NPs during
the slow nucleation process is an appropriate approach that
may effectively improve the catalytic performance of the
NPs.
[
11, 12], and the rates of hydrogen release of the above
methods are typically relatively low [13], the hydrolysis of
AB is considered to be the most promising process because
as much as 3 equiv. of hydrogen can be released from AB
with appropriate catalysts under mild conditions, according
to the equation below:
+
−
NH BH + 2H O → NH + BO2 + 3H2
3
3
2
4
In early research, noble metal nanoparticles (NPs), such
as Pt, Ru, and Pd, were the most widely investigated cata-
lysts for AB dehydrogenation systems due to their superior
catalytic performances [14–17]. However, the NPs’ limited
abundance and high cost restrict their practical applications
[
18]. Subsequently, transition metal catalysts, such as Fe,
In this study, amorphous CoNiB NPs possessing high B
contents (CoNiB-h) are successfully synthesized by a very
Co, and Ni, have been explored [19–21], and Co was com-
monly observed to exhibit higher catalytic activity than Fe
and Ni [22], though Co is relatively more scarce and higher
in cost than two others. To further improve the catalytic
activity and simultaneously minimize the cost of the cata-
lysts, combination Co with Fe (or Ni) has attracted much
attention [23–25]. Furthermore, nanomaterials containing
iron family elements usually possess good stability in cataly-
sis applications because of the easy magnetic separation,
which facilitates the recovery of such catalysts [26]. In this
sense, magnetic nanoalloys as catalysts are expected to own
the advantages of both nanoalloys and magnetic nanomateri-
als with better catalytic activities than their counterparts and
easy magnetic recovery.
facile in-situ reduction method employing AB and NaBH
4
as reductants. The resultant CoNiB-h catalyst without any
surfactants and supports exhibits uniform dispersion and
high activity for the hydrolysis dehydrogenation of AB at
298 K. The total turnover frequency (TOF) obtained by
Co Ni B-h is much higher than that of ex-situ prepared
0
.7 0.3
Co Ni B (Co Ni B-l), the latter exhibited obvious
0
.7
0.3
0.7
0.3
aggregation and possessed low content of B. It is interest-
ing that tuning the content of B and the dispersion of NPs
through the adoption of different synthesis methods leads to
remarkable enhancement of the activity for the hydrolytic
dehydrogenation of AB.
It has been reported that with their high concentration
of coordinative unsaturated sites and tunable compositions,
amorphous catalysts exhibit relatively unique physical and
chemical properties compared to crystalline materials [27].
As one of the most promising catalysts, an amorphous
metal-boron (B) alloy is applied as an advanced material for
petrochemical production, energy conversion and environ-
mental catalysis [28]. For amorphous metal-B alloy catalyst,
2 Experimental Details
2.1 Chemicals
Ammonia borane (NH BH , Aldrich, 90%), cobalt(II)
3
3
chloride hexahydrate(CoCl ·6H O, Sinopharm Chemical
2
2
Reagent Co., Ltd, >99%), nickel (II) chloride hexahydrate
1
3

Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles and Their Remarkable Catalytic…
(
NiCl ·6H O, Sinopharm Chemical Reagent Co., Ltd,
AB aqueous solution (0.16 M, 10 ml) was added to the flask to
regenerate hydrogen. The evolution of gas was monitored by
the gas burette. Such recycle experiments with Co Ni B-h
2
2
>
98%), iron (II) sulfate heptahydrate (FeSO ·7H O, Sinop-
4 2
harm Chemical Reagent Co., Ltd, >99%), hexadecyltrime-
thyl ammonium bromide (CTAB, Aladdin Chemistry Co.,
0
.7 0.3
was repeated 4 times under ambient atmosphere at room
temperature.
Ltd, >99%), and sodium borohydride (NaBH , Sinopharm
4
Chemical Reagent Co., Ltd, >96%) were used as received
without any purification.
2.3 Calculation Methods
2
.2 Synthesis and Catalytic Study
The turnover frequency (TOF) reported here was total TOF
values based on the measured mole number of metal contents
in catalysts, which was calculated from the equation as follow:
The CoNiB-h catalyst was prepared via an in-situ reduction
method using AB and NaBH as reductants. Typically, for
4
PatmV ∕RT
Co Ni B-h NPs, 10.8 mg of CoCl and 4.7 mg of NiCl
H
0
.7 0.3
2
2
2
TOF =
(1)
were dissolved in 10 ml of distilled water (with a conduc-
nmetal
t
−
1
tivity of 1 µS cm ). 55.0 mg of AB and 8.0 mg NaBH
4
were kept in a two-necked round-bottom flask. One neck was
connected to a gas burette, and the other was connected to a
pressure-equalization funnel to introduce 10 ml of aqueous
solution containing certain contents of CoCl and NiCl .
where TOF is the total turnover frequency, P is the atmos-
atm
pheric pressure, V is the volume of the generated H corre-
H2
2
sponding to the whole process of hydrolysis of AB, R is the
universal gas constant, T is the room temperature (298 K),
2
2
Once the aqueous solution was added to AB and NaBH
n
is the measured mole number of metal catalyst by ICP-
4
metal
under vigorously stirring, the black suspension appeared
OES, and t is the reaction time from the beginning of the AB
immediately, and the H generated at the meantime. The
hydrolysis reaction to the end.
2
reaction was completed until there was no more gas gener-
ated. The evolution of gas was monitored by using the gas
burette.
The relationship between the temperature and the hydrogen
generation rate (corresponding to 50% conversion) was fol-
lowed Arrhenius behavior. The Arrhenius’ reaction rate equa-
tion can be written as follows:
The CoNiB-l catalyst was prepared via an ex-situ reduc-
tion method using NaBH as a reductant. For Co Ni B-l,
4
0.7 0.3
ln k = ln A − E ∕RT
a
(2)
the preparation procedure is same as Co Ni B-h except
0
.7 0.3
where A is the reaction constant.
that using NaBH as a reductant. Once the metal NPs gener-
4
ated, the aqueous solution of AB was then introduced into
the above solution containing the as-prepared metal NPs to
start its catalytic hydrolysis reaction. The Co Ni B sta-
2.4 Characterization
0
.7 0.3
X-ray diffraction (XRD) was performed on a Rigaku
RINT-2000 X-ray diffractometer with Cu Kα radiation
bilized by CTAB was prepared by the similar method to
ex-situ reduction process, except mixed 20 mg CTAB with
(
λ=1.54056 Å). Transmission electron microscope (TEM,
1
0 ml aqueous solution of CoCl and NiCl . Furthermore,
2 2
Tecnai F20, Philips) and corresponding energy-dispersive
X-ray spectroscopy (EDS) were applied to analyze micro-
structures and compositions of the specimens. TEM and EDS
samples were prepared by depositing one or two droplets of the
nanoparticle suspensions onto the amorphous carbon-coated
copper grids, which were dried in an argon atmosphere. Induc-
tively coupled plasma-optical emission spectroscopy (ICP-
OES) measurements were performed on a Thermo Jarrell Ash
to exclude the impact of metal ions (which may be leached
from the catalyst) on the observed activity, the catalytic per-
2
+
2+
formance of Co and Ni salts in the presence of AB has
been applied, wherein only AB was employed as a reductant.
For comparison, Fe Co B-h NPs and Fe Ni B-h NPs
0.5
0.5
0.5 0.5
were also prepared by the same method as Co Ni B-h.
0
.7 0.3
CoNiB-h NPs with different Co and Ni compositions,
which labeled as Co Ni B-h, were also synthesized by a
x
1−x
(
TJA) Atomscan Advantage instrument. X-ray photoelectron
similar method shown above. The x value in Co Ni B-h
x
1−x
spectroscopy (XPS) spectra were acquired with an ESCAL-
ABMKLL (Vacuum Generators) spectrometer using Al Kα
X-rays (240 W).
was changed from 0 to 1.0 (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0).
2
+
2+
Notably, molar ratio of (Co +Ni ): AB was 0.04 for all
reactions.
To analyze activation energy of this reaction, a series
of experiments were carried out at different temperatures
(
298, 303, 308, and 313 K) with Co Ni B-h under ambi-
0.7 0.3
ent atmosphere.
To study the stability of the Co Ni B-h, after the first
0
.7 0.3
hydrogen generation reaction completed, another equivalent of
1
3

H. Wang et al.
3
Results and Discussion
Inductively coupled plasma-optical emission spectroscopy
(ICP-OES) furnished the accurate element analysis in the as-
3.1 Synthesis and Characterization
prepared Co0.7Ni0.3B-h and Co0.7Ni0.3B-l NPs. Through the
measured ppm values of Co, Ni, and B, the accurate molar
ratio of Co/Ni/B is determined to be 0.401:0.175:0.424
in Co0.7Ni0.3B-h, and 0.489:0.212:0.299 in Co0.7Ni0.3B-l
(Table 1). It is found that the B contents in the two samples
are quite different, revealing that the B content could be
regulated by different reduction methods.
The Co Ni B-h NPs were synthesized by a one-step in-
0
.7 0.3
2
+
situ reduction method at 298 K. Mixed metal ions of Co
2
+
and Ni were used as the metal precursors, and AB and
NaBH were added as the reducing agent. For compari-
4
son, Co Ni B-l NPs were prepared by the same method,
0
.7 0.3
except only NaBH was used as a reductant. This method is
According to previous reports, B atoms may serve as
electron donors to optimize the electronic structure of other
metal atoms for dehydrogenation reactions [28]. To inves-
tigate the effect of B on the electronic structure of Co and
Ni (the crucial active elements for the AB hydrolysis dehy-
drogenation reaction), X-ray photoelectron spectroscopy
(XPS) measurements were performed to identify the elec-
tronic states of Ni and Co in Co0.7Ni0.3B-h and Co0.7Ni0.3B-l
and the valence state of B in the Co0.7Ni0.3B-h sample
(Fig. 2). A thin oxidized layer formed during the exposure
of the sample to air in the XPS sample preparation process,
with binding energies for Ni 2p3/2 and 2p1/2 at 856.2 and
873.6 eV, respectively. Meanwhile, the binding energies for
Ni 2p3/2 and 2p1/2 at 852.1 eV and 869.5 eV, respectively,
4
referred to as the ex-situ reduction method. The as-prepared
NPs have been isolated from solutions by centrifugation for
characterization.
The phase structures and crystallinities of two samples
were first characterized by X-ray diffraction (XRD). As
shown in Fig. 1a, b, no peaks are observed in Co Ni B-h
0
.7 0.3
and Co Ni B-l, indicating that Co Ni B-h and
0
.7
0.3
0.7
0.3
Co Ni B-l are amorphous. After heat treating at 773 K
0
.7 0.3
for 3 h in argon, three obvious peaks are observed between
the (111) plane of face-centered cubic (fcc) Co (JCPDS:
1
5-0806) and the (111) plane of fcc Ni (JCPDS: 04-0850)
[
23, 39] (Fig. 1c, d). Thus, both samples are reasonably
deduced to be Co Ni B crystalline nanoalloys after
0
.7
0.3
0
annealing. Interestingly, compared to the Co Ni B-l
can be attributed to Ni . Notably, the Ni binding energies
0
.7
0.3
(
Fig. 1d), the diffraction peaks are slightly shifted to the
of Co0.7Ni0.3B-h are shifted negatively compared to those
of Co0.7Ni0.3B-l (Fig. 2a), and a similar electronic state is
present in the Co binding energies (Fig. 2b). After argon
etching, the surface oxidation layers of both specimens are
lower angles for Co Ni B-h (Fig. 1c). These slight expan-
0.7 0.3
sions of the CoNi lattice may be attributed to a certain
number of B atoms being incorporated into the inter-lattice
spaces of CoNi nanoalloy [34]. It should be noted that no
Co(Ni) B or Co(Ni) (BO ) were formed during the reduc-
0
0
removed, the Ni and Co binding energies in Co0.7Ni0.3B-h
are also shifted to the lower values compared with those in
Co0.7Ni0.3B-l (Fig. 2c, d). These shifts demonstrate that com-
pared to Co0.7Ni0.3B-l, more effective electrons transfer from
B to Ni (or Co) after a larger number of B atoms are incorpo-
rated into Co Ni B-h. Thus, it is reasonable to deduce that
2
3
3 2
tion reaction, even after the heat treatment of the samples
at 773 K for 3 h in argon according to the XRD patterns.
0.7 0.3
Co Ni B-h with electron-enriched active sites (Ni and Co
0.7 0.3
Co (JCPDS:15-0806)
(111)
sites) is favorable to the catalytic hydrolytic dehydrogena-
Ni (JCPDS:04-0850)
tion of AB [40]. In addition, the B element in Co Ni B-h
0
.7 0.3
is in the metallic and oxidized state before argon etching;
(d)
however, only a peak with a binding energy of 187.5 eV
0
corresponds to B was observed after argon sputtering for
(c)
5
min (Fig. 2e), which indicates that no boron oxides (BO )
x
or B ions existed in the as-prepared sample. Furthermore,
no oxygen and chlorine elements are found by XPS, cor-
responding to the sample is in an alloy state of CoNiB but
(b)
(a)
(200)
(220)
Table 1 The contents of Co, Ni and B in Co0.7Ni0.3B-h and
Co Ni B-l NPs
2
0
30
40
50
60
70
80
90
0.7 0.3
2
theta (degrees)
ppm (mg l−1
Samples
)
Measured value of Co:Ni:B
Co
Ni
B
Fig. 1 X-ray diffraction patterns of Co Ni B-h before (a) and
0
.7 0.3
after (c) heat treatment at 773 K for 3 h in argon atmosphere; and
Co0.7Ni0.3B-h 23.632 10.271 4.584 0.401:0.175:0.424
Co0.7Ni0.3B-l 28.818 12.443 3.232 0.489:0.212:0.299
Co Ni B-l before (b) and after (d) heat treatment at 773 K for 3 h
0.7 0.3
in argon atmosphere
1
3

Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles and Their Remarkable Catalytic…
x+
x+
Co 2p3/2 0
(
a)
0
(b)
Co 2p1/2 0
0
x+
Ni 2p
3/2
x+
Ni 2p3/2
Co 2p3/2
Ni 2p
Ni 2p1/2
1/2
Co 2p1/2
Co Ni B-h
0
.7
0.3
Co Ni B-h
0
.7
0.3
Co Ni B-l
Co Ni B-l
0.7 0.3
0
.7
0.3
880 875 870 865 860 855 850
810 805 800 795 790 785 780 775
Binding energy (eV)
Binding energy (eV)
0
0
Ni 2p
(d)
Co 2p
(
c)
3/2
3/2
0
Ni 2p
1/2
0
Co 2p
1/2
Co Ni B-h
0
.7
0.3
Co Ni B-h
0
.7
0.3
Co Ni B-l
0.7
0.3
Co Ni B-l
0.7
0.3
8
05 800 795 790 785 780 775 770
8
75
870
865
860
855
850
Binding energy (eV)
Binding energy (eV)
(
f)
3+
(
e)
B
O 1s
B 1s
0
B
5
44
540
536
532
528
Before Ar etching
After Ar etching
(g)
Cl 2p
1
96
194
192
190
188
186
2
10 208 206 204 202 200 198 196
Binding energy (eV)
Binding energy (eV)
Fig. 2 XPS spectra a before and c after argon etching of Ni 2p, b before and d after argon etching of Co 2p for Co0.7Ni0.3B-h and Co0.7Ni0.3B-l
NPs, e B 1s, f O 1s, g Cl 2p for Co Ni B-h NPs
0
.7 0.3
not in its oxides or chlorides state (Fig. 2f, g). On the basis
of the above arguments and XPS results, we suggest that an
effective electron effect should occur in Co Ni B-h, which
In addition to the different B contents of these two sam-
ples, the difference in their states of dispersion in the aque-
ous solution should be considered. The difference of disper-
sion between the two samples can be apparently observed
0.7 0.3
is contained with a high B content.
1
3

H. Wang et al.
by transmission electron microscopy (TEM) images. As
(SAED) patterns. As shown in Fig. 3, the Co Ni B-l
0
.7
0.3
shown in Fig. 3a, the Co Ni B-l NPs appear severely
and Co Ni B-h are both in an amorphous state, which is
0
.7
0.3
0.7 0.3
agglomerated. The dispersion of the Co Ni B-l NPs can
consistent with the XRD results. Moreover, the two typical
samples have similar particle sizes (less than 5 nm) (Fig. 3b,
c). The corresponding energy dispersive X-ray spectroscopy
(EDS) spectra confirm the rough atomic ratio of Co: Ni
0
.7 0.3
be improved by the introduction of strong surfactant [41].
This is confirmed by the fact that an analogous experi-
ment with a stronger surfactant, such as CTAB, resulted in
highly dispersed Co Ni B-l NPs (Fig. 3b). In contrast,
to be 65.10:34.90 for Co Ni B-h (Fig. 3d, trace 1) and
0
.7 0.3
0.7 0.3
the Co Ni B-h NPs are highly dispersed and the surface
71.20:28.80 for Co Ni B-l (Fig. 3d, trace 2), which is in
0
.7 0.3
0.7 0.3
of NPs is relatively clean (Fig. 3c). It can be reasonably
explained that NPs may have rapid nucleation and growth
when reduced by a strong reductant and thus may easily
agglomerate, despite the addition of a strong surfactant to
facilitate the dispersion of the NPs, long chain structure of
the surfactant causes the surfaces of the NPs to not be clean
good agreement with the ICP results.
3.2 Catalytic Activity and Activation Energy
The catalytic performances of Co Ni B-h and
0
.7
0.3
Co Ni B-l for H generation from the hydrolysis dehy-
0
.7
0.3
2
[
37, 38]. Therefore, employing a reductant with a moderate
drogenation of AB at 298 K under ambient atmosphere
are presented in Fig. 4. Both of the catalysts exhibit good
catalytic activities, this is attributed to the amorphous
structures of the two catalysts. It is generally known that
amorphous structures possess much more structure dis-
tortions and thus provide considerably higher concentra-
tions of surface reactive sites to elevate the activities of
nanocatalysts compared to the corresponding crystalline
counterparts [43, 44]. Interestingly, the Co Ni B-h
reducing ability to control the nucleation and growth rate
of the NPs while simultaneously using a weak surfactant to
disperse the NPs to guarantee their clean surfaces is of great
importance. AB, can not only serve as a weak reductant [42],
but also as an efficient weak surfactant with a mild affilia-
tion for stabilizing the NPs [19]. It is more appropriate as a
reductant than others for the synthesis of highly dispersed
surfactant-free amorphous CoNiB NPs in aqueous solution.
The crystal structures of the as-prepared samples were
further characterized by selected-area electron diffraction
0
.7
0.3
with high B content displays much higher catalytic activ-
ity than that of Co Ni B-l with low B content. With the
0
.7 0.3
Fig. 3 a TEM image for
Co Ni B-l NPs, TEM and
0.7 0.3
SAED (inset) images for b
Co Ni B-l NPs stabilized by
0.7 0.3
CTAB and c Co Ni B-h NPs,
0.7 0.3
d the corresponding EDS spec-
trum for (1) Co Ni B-h NPs
0.7 0.3
and (2) Co0 Ni B-l NPs
.7
0.3
1
3

Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles and Their Remarkable Catalytic…
1
1
1
40
20
00
to the hydrolysis reaction by providing the charges to pro-
mote the H atom separation from the catalyst surface [40].
It is worth mentioning that except the B contents of
Co Ni B-h and Co Ni B-l are different, the differ-
(
a)
(c)
(b)
0
.7
0.3
0.7
0.3
ence between their dispersion states in the aqueous solu-
tion should also be considered. As seen from Fig. 4a, b, the
Co Ni B-h exhibits a catalytic performance superior to
8
6
4
2
0
0
0
0
0
(a)
(b)
0
.7 0.3
(c)
that of the Co Ni B-l, which is ascribed to the good dis-
0.7 0.3
(d)
persion and clean surface of the Co Ni B-h. Although
0.7 0.3
the dispersion state of Co Ni B-l has been improved by
0
.7 0.3
(d)
the addition of a surfactant (Fig. 3b), the catalytic activ-
ity of the Co Ni B-l NPs stabilized by CTAB is still
0
5
10
15
20
25
0.7
0.3
inferior to that of the Co Ni B-h (Fig. 4a, c), which can
Time (min)
0.7 0.3
be explained as follows: the strong affiliation of the strong
surfactant to the surface of the NPs may decrease the num-
ber of active sites and thus cause severe deactivation of the
NPs in catalytic reactions [37, 38]. Thus, we conclude that
high B content, clean surface, and good dispersion play
the significant role in promoting the catalytic activities of
Fig. 4 Time-course plots for the hydrolysis of AB in the presence of
(
a) Co Ni B-h, (b) Co Ni B-l, (c) CTAB stabilized Co Ni B-l
0.7 0.3 0.7 0.3 0.7 0.3
2+ 2+
catalysts and (d) the mixed solution of Co and Ni salts in the
presence of AB at room temperature
Co Ni B-h, the AB releases its stoichiometric amount
nanocatalysts for H generation from hydrolytic dehydro-
0
.7
0.3
2
(
3.0 equiv.) of gases within only 3.5 min at 298 K, and
genation of AB, and the usage of AB as a mild reductant
has contributed to the preparation of amorphous CoNiB
catalyst with high B content, clean surface, and good dis-
persion. Moreover, to exclude the impact of metal ions on
the observed activity, the reaction which only employed
AB as reductant was performed. As a result, the metal
ions show no activity at all (Fig. 4d), which might due
to the fact that AB with weak reducing ability could
the total TOF is calculated (Eq. 1) to be 30.9 mol(H )·
2
−
1
− 1
mol(metal) ·min , which is comparable to most of the
reported non-noble metal catalysts for the hydrolysis of
AB to H at the same experimental conditions (Table 2)
2
[
10, 20, 45–55]. Whereas for the Co Ni B-l, a much
0
.7
0.3
longer time (18.5 min) is required to complete the same
reaction (Fig. 4b), and the total TOF is only 4.3 mol(H )·
2
−
1
− 1
2+
2+
mol(metal) ·min . This finding demonstrates that cata-
lysts with high B contents can exhibit superior catalytic
performance towards hydrogen generation reaction from
the AB hydrolysis dehydrogenation, which is attributed to
the electrons transfer from B to Ni (and Co) that provides
electron-enriched Ni (and Co) sites, thereby contributing
not reduce the Co and Ni salts within a short time.
Namely, without washing the catalysts during catalytic
tests, the potable leached metal ions are not responsible
for the observed catalytic activity. It should be noted that
the hydrogen evolution curves are consisted of two parts
(Fig. 4b, c). The fast one is contributed to the hydrolysis
Table 2 Activities in terms
of TOF values of different
nanocatalysts containing Co
or Ni tested for hydrogen
generation from hydrolysis of
AB aqueous solution
TOF (min−1
Catalyst
Temp. (K)
n catalyst/nAB
t (min)
)
Ref.
Cu0.2Co0.8/HPC
Cu@FeNi
298
298
298
298
298
293
298
298
298
298
298
298
298
298
298
0.158
0.040
0.100
0.040
0.040
0.034
0.500
0.090
0.036
0.020
0.033
0.020
0.020
0.100
0.050
3.5
12.0
3.5
7.5
7.8
4.5
4.0
5.8
3.5
3.0
5.8
3
6.3
8.2
[45]
[20]
[46]
[47]
[48]
[49]
[50]
[51]
This study
[52]
[53]
[52]
[54]
[55]
[10]
Cu0.3@Fe0.1Co0.6
Cu0.4@Co0.5Ni0.1
Cu0.1@Co0.45Ni0.45/graphene
Cu Co @MIL-101
10.5
14.0
15.46
19.6
20.9
30.8
30.9
44.3
45.0
51.7
53.6
58.8
66.7
3
7
Cu Ni @MIL-101
2
1
Cu0.5Co0.5/PDDA-HNT
Co0.7Ni0.3B-h
NiCo/MIL-101-U
Cu0.49Co0.51/C
CuCo/MIL-101-1-U
NiCo/ g-C N
2.6
1.5
0.9
3
4
Rh Ni @ZIF-8
1
5
85
Ni0.9Mo0.1/graphene
1
3

H. Wang et al.
of NaBH , which releases 18 mL gases (4.0 equiv.) [56],
catalyst for the hydrolytic dehydrogenation of AB can be
greatly improved by an in-situ reduction method.
4
and the slow one is contributed to the hydrolysis of AB,
which releases 107 mL gases (3.0 equiv.). However, this
phenomenon is not obviously observed in Fig. 4a. This is
because the rapid hydrogen generation from hydrolysis
of AB can occur when Co Ni B-h is used as a catalyst.
An investigation of the catalytic performance of
CoNiB-h nanocatalysts with various Co/Ni molar ratios
for AB hydrolysis at 298 K was also performed, and it
suggests that the catalytic performance of CoNiB-h cata-
lyst significantly depends on its composition (Fig. 6a).
Notably, without a Co addition (x = 0), NiB shows the
lowest catalytic activity, only giving a total TOF value
0
.7
0.3
To confirm that the in-situ NPs have higher catalytic
activities than that of ex-situ NPs, the non-noble metal Fe
was used as a substitute for Ni or Co to form FeCoB NPs and
FeNiB NPs. As expected, the catalytic performance of the
in-situ FeCoB NPs is notably better than that of the ex-situ
FeCoB NPs (Fig. 5a). A similar result can also be observed
when the AB hydrolysis reactions are catalyzed by FeNiB
NPs prepared by the different reduction methods (Fig. 5b).
These results demonstrate that the catalytic performance of
−
1
of 4.7 min . When the molar ratio of Co (x value) is
−
1
increased to 0.7, the TOF value increases to 30.9 min
.
Further increasing the Co molar ratio from 0.7 to 0.9, only
a slight enhancement in TOF can be obtained (Fig. 6b).
Even though when the molar ratio of Co reaches 1.0
(CoB), the reaction efficiency is only slightly superior
(
a)
(b)
1
1
1
40
20
00
140
120
100
80
(1)
(2)
(1)
(2)
8
6
4
2
0
0
0
0
0
60
40
(
(
1)
2)
(
(
1)
2)
20
0
0
5
10
15
20
25
30
0
5
10 15 20 25 30 35 40
Reaction time (min)
Reaction time (min)
Fig. 5 a Time-course plots for the hydrolysis of AB catalyzed
by (1) in-situ Fe Co B and (2) ex-situ Fe Co B catalysts; b
Fe Ni B and (2) ex-situ Fe0.5Ni0.5B catalysts at room temperature
0.5 0.5
under ambient atmosphere
0
.5
0.5
0.5
0.5
Time-course plots for the hydrolysis of AB catalyzed by (1) in-situ
(
a) 140
40
35
(b)
1
1
20
00
3
2
2
0
5
0
NiB-h
8
6
4
2
0
0
0
0
0
Ni Co B-h
0.9
0.1
Ni Co B-h
0
.7
0.3
Ni Co B-h
15
10
5
0
.5
0.5
Ni Co B-h
0
.3
0.7
Ni Co B-h
0
.1
0.9
CoB-h
0
0
2
4
6
8 10 12 14 16 18 20 22 24
0.0
0.2
0.4
0.6
0.8
1.0
Reaction time (min)
Co Ni B-h
x
1-x
Fig. 6 a Time-course plots for the hydrolysis of AB catalyzed by Co Ni1−xB-h NPs with different x values under ambient atmosphere at room
x
temperature, b The effect of Co/Ni molar ratios on the total TOF values
1
3

Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles and Their Remarkable Catalytic…
to the Co Ni B-h nanocatalyst. Compared to the NiB,
0
.7
0.3
st
nd
rd
th
1
20
1
2
3
the catalytic role of Co element in CoNiB-h nanoalloy
is synergistic with Ni, which can effectively adjust the
surface electronic states of nanocatalysts, especially with
the local strain on the surface and the number of effec-
tive atomic coordination, leading to a significant improve-
ment of AB hydrolysis [57]. Furthermore, considering the
lower abundance in the Earth’s crust and the correspond-
ing higher cost of Co compared with Ni, the Co Ni B-h
4
100
8
6
4
2
0
0
0
0
0
0
.7 0.3
nanocatalyst possesses the optimal comprehensive per-
formance. Therefore, the present molar ratio of Co: Ni
(
0.7:0.3) in the CoNiB-h system has been determined to
0
3
6
9
0 3 6 9
Reaction time (min)
0
3
6
9
0 4 8 12
be the most appropriate molar ratio for the hydrolysis of
AB.
Figure 7a presents the catalytic decomposition kinet-
ics profiles for hydrogen generation from the hydroly-
sis of AB at temperatures ranging from 298 to 313 K.
As expected, the catalytic activities elevated with the
increasing reaction temperature. The Arrhenius plot of
ln k vs. 1/T for Co Ni B-h is shown in Fig. 7b, from
Fig. 8 Recycle test of the Co Ni B-h nanocatalyst toward the
0.7 0.3
hydrolysis of AB (0.16 M, 10 ml) at room temperature
4 Conclusions
0
.7
0.3
which the activation energy (E ) is calculated (Eq. 2) to
Surfactant-free CoNiB NPs with different B contents have
been facilely synthesized through two different reduction
approaches. Compared to the ex-situ Co Ni B-l catalyst
a
−
1
be 32.3 kJ mol
.
The recycle stability of a catalyst is vital in practical
applications. As shown in Fig. 8, there is no apparent
deactivation after four runs for the Co Ni B-h cata-
0
.7 0.3
that has a low B content, the in-situ Co Ni B-h catalyst
0
.7 0.3
0
.7
0.3
possesses higher B content and better dispersion, and it
lyzed system, indicating that the Co Ni B-h catalyst
exhibits superior catalytic activity with a total TOF value
0
.7
0.3
−
1
has a good stability for AB hydrolytic dehydrogenation
reaction. Moreover, in this series of experiments, the
usage of magnetic nanomaterials containing iron family
elements (i.e., Fe, Ni, and Co) is advantageous to their
recyclability in catalysis applications due to the ease of
magnetic separation, especially in a liquid-phase reaction
of 30.9 min for hydrogen generation reaction from the
hydrolysis of AB. This remarkably improved catalytic per-
formance is attributed to the electron transfer between the
incorporated B and the active metal sites, clean surface and
good dispersion. Moreover, this convenient synthetic method
represents a promising step towards developing other B
incorporated metal catalysts for various applications.
[
58, 59].
(
a) 140
(b)
4
4
4
.6
.4
.2
1
1
20
00
8
6
4
2
0
0
0
0
0
32.3 kJ/mol
2
3
3
98 K
03 K
08 K
4.0
.8
3
313 K
0
1
2
3
4
0.00320 0.00325 0.00330 0.00335
-1
Reaction time (min)
1/T /K
Fig. 7 a Temperature effects on hydrogen generation rate catalyzed by Co0.7Ni0.3B-h NPs from AB hydrolysis and b ln k vs. 1/T plot obtained
from the data of Fig. 7a
1
3

H. Wang et al.
Acknowledgements This work was supported by National Natu-
27. Pei Y, Zhou G, Luan N, Zong B, Qiao M, Tao F (2012) Chem Soc
Rev 41:8140–8162
ral Science Foundation of China (51601018, 51608050, 51671035,
5
1605042); Jilin Province Science and Technology Development Pro-
28. Carenco S, Portehault D, Boissière C, Mézailles N, Sanchez C
(2013) Chem Rev 113:7981–8065
ject (20170520122JH, 20150520020JH); and Science and Technol-
ogy Research Project of the Education Department of Jilin Province
29. Greenwood N, Parish R, Thornton P (1966) Q Rev 20:441–464
30. He D, Zhang L, He D, Zhou G, Lin Y, Deng Z, Hong X, Wu Y,
Chen C, Li Y (2016) Nat Commun 7:12362
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3

Highly Dispersed Surfactant-Free Amorphous NiCoB Nanoparticles and Their Remarkable Catalytic…
Affiliations
1
1
1
1
1
2
1
1
Hongli Wang · Dawei Gao · Liying Wang · Yue Chi · Minggang Wang · Yan Gu · Cong Wang · Zhankui Zhao
2
*
*
Hongli Wang
Chongqing Key Laboratory of Extraordinary Bond
Engineering and Advanced Materials Technologies
wanghongli@ccut.edu.cn
(
EBEAM), Yangtze Normal University, Chongqing 408100,
Zhankui Zhao
China
zhaozk@ccut.edu.cn
1
Key Laboratory of Advanced Structural Materials, Ministry
of Education, College of Material Science and Engineering,
Changchun University of Technology, Changchun 130012,
China
1
3