NiPt Nanocatalysts Supported on Boron and Nitrogen Co-Doped Graphene for Superior Hydrazine Dehydrogenation and Methanol Oxidation

Article abstract of DOI:10.1002/cctc.201501405

Boron and nitrogen co-doped graphene (BNG) with negligible covalent boron-nitride (BN) bonding, and high boron and pyridinic nitrogen contents has been synthesized by a two-step method using boron-carbon-nitride (BCN) as the boron and nitrogen sources. The use of the BCN precursor is the key for preparing BNG, while annealing reduced graphene oxide, urea, and boric acid in a one-step method results in separated domains of larger amounts of covalent BN in the graphene networks (s-BNG). The resulting BNGs are further used to anchor NiPt nanoparticles (NPs) with good dispersion. Consequently, Ni₃Pt₇/BNG-1000 exhibits the highest catalytic activity toward hydrazine dehydrogenation at room temperature, with the turnover frequency of 199.4 h^-1. Furthermore, as evidence of its multifunctionality, Ni₃Pt₇/BNG-1000 is further employed for electrocatalytic methanol oxidation.

Full text of DOI:10.1002/cctc.201501405

DOI: 10.1002/cctc.201501405
Full Papers
NiPt Nanocatalysts Supported on Boron and Nitrogen Co-
Doped Graphene for Superior Hydrazine Dehydrogenation
and Methanol Oxidation
[a]
[a]
[a]
[a, b, c]
[a]
Xiaoqiong Du, Cheng Du, Ping Cai,* Wei Luo,*
and Gongzhen Cheng
Boron and nitrogen co-doped graphene (BNG) with negligible
covalent boron–nitride (BN) bonding, and high boron and pyri-
dinic nitrogen contents has been synthesized by a two-step
method using boron–carbon–nitride (BCN) as the boron and
nitrogen sources. The use of the BCN precursor is the key for
preparing BNG, while annealing reduced graphene oxide, urea,
and boric acid in a one-step method results in separated do-
mains of larger amounts of covalent BN in the graphene net-
works (s-BNG). The resulting BNGs are further used to anchor
NiPt nanoparticles (NPs) with good dispersion. Consequently,
Ni Pt /BNG-1000 exhibits the highest catalytic activity toward
3
7
hydrazine dehydrogenation at room temperature, with the
À1
turnover frequency of 199.4 h . Furthermore, as evidence of
its multifunctionality, Ni Pt /BNG-1000 is further employed for
3
7
electrocatalytic methanol oxidation.
Introduction
Anchoring metal nanoparticles (NPs) with good dispersion and
enhanced catalytic performance on carbon-based materials has
effect, it is necessary to develop an effective strategy for the
[
4]
synthesis of B,N co-doped graphene (BNG) with no/low BN.
[1]
recently attracted great attention. Compared with metal
oxides, they are chemical and physical versatile. However, the
With the continuous depletion of fossil fuels, increasing ef-
forts have been made to explore recyclable and pollution-free
2
[5]
abundant free-flowing p electrons in sp carbon materials,
power sources. Hydrogen, producing water as the only by-
such as graphene, are too inert to be used directly for anchor-
ing metal NPs. Thus, the distinct interaction between graphene
and metal NPs is defectively tight. To tailor the electronic struc-
ture and chemical properties of graphene, heteroatoms have
been used as dopants for graphene. For example, the carbon
p electrons in N-doped graphene can be activated by conju-
product, has been considered as a globally accepted clean
fuel. However, the safe and efficient storage of hydrogen is still
[
6]
the key issue for the “hydrogen economy”. Currently, liquid-
phase chemical storage materials that do not involve any solid
byproducts, have attracted a great deal of attention because
of their easy handling and the merits of using the existing
[2]
[7]
gating with the lone pair electrons from N. Furthermore, the
lone pair electrons in pyridinic N and pyrrolic N are able to co-
ordinate metal NPs with empty orbitals, forming catalytic
liquid-based fuel distribution infrastructure. Among them, hy-
drous hydrazine (H N ·H O) has the advantages of high hydro-
4
2
2
gen content (8.0 wt%), easy recharging, and the production of
nitrogen as the only byproduct through the reaction in Equa-
tion (1), which makes it one of the most compelling candidates
[3]
active sites and good durability. From another aspect, the
carbon p electrons could also be activated by doping with
boron, which has low electronegativity and a vacant orbital.
However, the formation of covalent boron–nitride (BN) during
synthesis, which may significantly decrease the catalytic activi-
ty, should be avoided. Therefore, based on the synergistic
[
8]
for practical application. Ammonia, which is toxic to fuel cell
catalysts, could be released through the reaction in Equa-
[
9]
tion (2), so should be avoided.
H NNH ðIÞ ! N ðgÞ þ 2 H ðgÞ
ð1Þ
ð2Þ
2
2
2
2
[
a] X. Du, C. Du, Prof. P. Cai, Prof. W. Luo, Prof. G. Cheng
College of Chemistry and Molecular Science
Wuhan University
3 H NNH ðIÞ ! N ðgÞ þ 4 NH ðgÞ
2
2
2
3
To this end, a number of nanocatalysts have been developed
recently and it has been found that their catalytic activities are
highly dependent on the dispersion of the active metal nano-
particles (NPs) and the synergistic effects between metal NPs
and supporting materials. For example, Hur and co-workers re-
ported hollow nickel-coated silica microspheres containing
rhodium NPs (Rh/Ni@SiO ) with 99.4% H selectivity and turn-
Wuhan, Hubei 430072 (P.R. China)
E-mail: wluo@whu.edu.cn
[
b] Prof. W. Luo
Key Laboratory of Advanced Energy
Materials Chemistry, Ministry of Education
Nankai University
Tianjin 300071 (P.R. China)
2
2
[
c] Prof. W. Luo
Suzhou Institute of Wuhan University
Suzhou, Jiangsu 215123 (P.R. China)
À1
[10]
over frequency (TOF) of 66 h at room temperature. Zhang
and co-workers reported Al O -supported NiIr NPs with 99%
2
3
À1
[11]
H selectivity and a TOF of 12.4 h at 303 K. Yan and co-
Supporting Information for this article can be found under http://
dx.doi.org/10.1002/cctc.201501405.
2
workers reported a Ni/La O catalyst containing low content
2
3
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À1
[12]
PtRh NPs with a TOF of 45.9 h at 298 K, and Ce O -support-
2
3
À1
[13]
ed NiPt with a TOF of 28.1 h at 298 K. Xu and co-workers
reported dendrimer-encapsulated NiPt NPs with a TOF of
À1
[14]
2
40 h at 343 K. Zhang and co-workers reported graphene-
À1
[15]
supported RhNi NPs with a TOF of 65.1 h at 298 K. Very re-
cently, our group reported the nanoscale metal–organic frame-
À1
work (MIL-101) immobilized RhNi NPs with a TOF of 344 h at
3
23 K, and nitrogen-doped porous-carbon-supported RhNi NPs
À1
[16]
with a TOF value of 156 h at 323 K. Although these en-
couraging results have been achieved, the kinetic properties
under moderate conditions, especially at room temperature,
are still very sluggish. Therefore, the development of highly H2-
selective and efficient catalysts for the dehydrogenation of hy-
drazine at room temperature is highly desirable and crucial for
its practical application.
Scheme 1. Schematic of the preparation of BCN (Line 1), BNG (Line 2), and s-
BNG (Line 3).
On the other hand, direct methanol fuel cells (DMFCs) have
gained great attention in terms of providing portable power
Figure S1a (in the Supporting Information) shows the
powder X-ray diffraction (XRD) patterns of BNG-800, BNG-900,
BNG-1000, and s-BNG-1000, in which the strong diffraction
peak at 26.58 can be attributed to the (002) lattice plane of
graphite. The diffraction peaks around 42.78, 55.78, and 77.68
correspond to the (100), (004), and (110) reflections of graph-
[17]
sources and for energy technology development. Although
Pt-based catalysts exhibit excellent electrochemical activity for
methanol oxidation, their high cost and poor tolerance to CO
[
18]
poisoning have hampered their practical applications. It has
been recently revealed that Pt-based catalysts anchored on N-
doped graphene can homogeneously disperse metal NPs and
accelerate the destruction of the absorbed CO, and thus in-
[
21]
ite, respectively. The Raman spectra of BNG-800, BNG-900,
BNG-1000, and s-BNG-1000 are shown in Figure S1b. The D
[19]
À1
crease their catalytic activity.
However, direct growth of
band and the G band are located around 1330 cm and
À1
metal NPs on BNG and boosting their catalytic activities, to the
best of our knowledge, has been rarely reported. Therefore, it
is imperative to study the synergistic effect of BNG as a sup-
porting material for Pt-based nanocatalysts to further increase
their electrocatalytic performance and CO tolerance.
1580 cm , respectively. The G band arises from the bond
2
stretching of all sp bonded pairs, including CÀC, BÀC, NÀC,
3
and BÀN, whereas the D band is associated with the sp defect
[
22]
sites.
It can be observed from Figure S1b that the I /I ratios of
D
G
Herein, for the first time, we report a two-step strategy for
the synthesis of B,N co-doped graphene with high boron and
nitrogen content, and low covalent BN ratios. The BNGs are
further used as supporting materials for anchoring NiPt NPs.
Thanks to the synergistic effect between boron and nitrogen,
the NiPt NPs supported on BNG prepared through a two-step
annealing method at 10008C, with the highest boron and pyri-
dinic N contents, and the lowest covalent boron–nitride (BN)
ratios, exhibit superior catalytic activity toward hydrazine dehy-
drogenation and methanol oxidation.
BNG decrease from 1.24 to 1.16 as the annealing temperature
increases from 800 to 10008C. This may be due to the im-
proved graphitic degree of the BNG caused by the reduction
effect and “self-repairing” of the graphene layer at higher an-
nealing temperature. Conversely, the ratio of ID/IG increased
from s-BNG-1000 to BNG-1000 owing to the introduction of
[
23]
defects by isolated B,N co-doping. This result is further con-
firmed by the X-ray photoelectron spectroscopy (XPS) analysis.
As shown in Figures S2a and S3a (in the Supporting Infor-
mation), the XPS survey scans indicate that the BCN precursor
and BNG-1000 are composed of C, O, N, and B elements; how-
ever, covalent BN is dominant in the BCN precursor. The pre-
dominant asymmetric C1s peak of BNG-1000, shown in Fig-
ure S3b, implies the existence of CÀN (286.0 eV) or CÀB
Results and Discussion
As illustrated in Scheme 1, to prepare BNG, boron–carbon–ni-
tride (BCN) was first synthesized by annealing boric acid and
[
21,24]
(283.5 eV) bonds in the graphitic network.
The N1s spectra
[20]
urea at 8008C in an Ar atmosphere (Line 1). Then, in a typical
synthesis of BNG, the same amount of pre-synthesized BCN
and reduced graphene oxide (rGO) was annealed at 800, 900,
or 10008C in an Ar atmosphere (Line 2) to give BNG-800, BNG-
can generally be further deconvoluted into five primary peaks
(Figure S3c), which correspond to pyridinic N (398.7 eV), pyrrol-
ic N (399.8 eV), graphitic N (400.9 eV), NÀO (402.5 eV), and NÀB
[
25]
(397.8 eV). The high-resolution B1s peak in Figure S3d can
be divided into two peaks at 191.3, 192.7 eV, arising from the
9
00, and BNG-1000, respectively. The BCN is decomposed to
[
26]
afford N and B sources, and we find it is essential to use the
pre-synthesized BCN as the N and B source to obtain the iso-
lated B,N co-doped graphene with low amounts of covalent
BN. For comparison, the mixture of urea, boric acid, and rGO is
also annealed at 10008C in Ar, which results in separated do-
mains of larger amounts of covalent BN in the graphene net-
work, and is denoted as s-BNG-1000 (Line 3).
BÀN, BC and BC O bonds.
3
2
As shown in Figure 1a and Figures S3–S6 (in the Supporting
Information), while increasing carbonization temperature from
800 to 10008C, the total B and N contents are increased ac-
cordingly. From Figure 1b,c, it can be seen that in BNG-1000
both the N1s and B1s bands show the presence of a large
amount of CÀB and CÀN bonding, whereas the BÀN bonding
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Figure 1. a) Bar chart atomic percentages of the elements present in sample composites obtained by using XPS. b) The content of the five types of nitrogen.
c) The content of the two types of boron. d) Schematic of the possible bonding configurations for B and N atoms in BNG.
is negligible. Moreover, BNG-1000 exhibits the highest pyridinic
N content and boron content, which may result in the highest
catalytic performance (see below). However, s-BNG-1000, syn-
thesized by annealing rGO, urea, and boric acid, as shown in
Figure 1b and Figure S6, contains a much higher covalent BN
content. These results further highlight the key fact of using
pre-synthesized BCN as the B and N source for preparing iso-
lated, higher pyridinic N and boron containing B,N co-doped
graphene.
domly compacted and stacked together, showing many meso-
pores in the nanosheets, which may be formed by urea de-
composition. This morphology may accelerate B and N doping
into graphene during the pyrolysis process. Figure 2 shows the
SEM image and corresponding energy-dispersive X-ray (EDX)
mapping of BNG-1000. A homogenous distribution of boron
and nitrogen emerged at the same positions, where carbon
was also detected, further indicating that boron and nitrogen
are successfully doped on the graphene sheets.
The Brunauer–Emmett–Teller (BET) specific surface area of
The B,N co-doped graphenes were further used as support-
ing materials to anchor NiPt NPs for more applications. Fig-
ure S9 (in the Supporting Information) shows the catalytic ac-
the obtained samples were studied by N adsorption/desorp-
2
tion isotherms at 77 K (Figure S7 in the Supporting Informa-
2
À1
tion). The specific surface area of BNG-1000 is 151.27 m g ,
2
À1
which is slightly higher than that of BNG-800 (122.235 m g ),
2
À1
2
À1
BNG-900 (112.518 m g ), and s-BNG-1000 (133.056 m g ) as
shown in Table S1 (in the Supporting Information).
The morphology of BNG-1000 was further characterized by
transmission electron microscopy (TEM). As displayed in Fig-
ure S8a and S8b (in the Supporting Information), BNG-1000
presents transparent wrinkled ultrathin nanosheets of a large
size, which should provide more active sites and increase the
specific surface area of sample. However, s-BNG-1000 displays
more wrinkled graphene layers and shows clear aggregation,
as shown in Figure S8c and S8d. Furthermore, the morpholo-
gies of the B,N precursor BCN were also characterized by TEM.
As shown in Figure S8e and S8 f, the BCN nanosheets are ran-
Figure 2. a) SEM image of BNG-1000 and b) the distribution of B, N, C, and O
elements.
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tivity of NiPt/BNG-1000 with different compositions toward de-
hydrogenation of hydrous hydrazine in alkaline solution (0.5m
NaOH) at 258C. Among all the bimetallic NiPt/BNG-1000 sam-
ples investigated, Ni Pt /BNG-1000 exhibits the highest catalyt-
prepared catalysts were estimated from the integrated charge
of the hydrogen adsorption/desorption region (from À0.2 to
1.1 V) in 0.5m H SO solution, as shown in Figure 4a. It is
2
4
2
À1
found that the ECSA is 176.8 m g for Ni Pt /BNG-1000, which
3
7
3
7
À1
2
À1
ic activity, with the TOF value of 199.4 h at room tempera-
ture, which is among the highest reported values (Table S2 in
the Supporting Information). Furthermore, the mass spectros-
copy of the gas released over Ni Pt /BNG-1000 further indi-
is much higher than that of Ni Pt /s-BNG-1000 (99.7 m g )
3 7
2
À1
and Pt/C (40.3 m g ). In Figure 4b, Ni Pt /BNG-1000, Ni Pt /s-
3
7
3
7
BNG-1000, and commercial Pt/C catalyst decorated electrodes
are used to investigate the electrocatalytic activities toward
methanol oxidation by cyclic voltammetry (CV) in 0.5m
3
7
cates 100% H selectivity (Figure S10 in the Supporting Infor-
2
À1
mation). To study the effects of different supporting materials
on the catalytic performances of the as-synthesized Ni Pt cata-
H SO +0.5m CH OH solution at a scan rate 50 mVs . Clearly,
2
4
3
the forward peaks of current density are in the order of Ni Pt /
3
7
3
7
lysts, Ni Pt NPs supported on various BNGs, including BNG-
BNG-1000>Pt/C>Ni Pt /s-BNG-1000, suggesting that the
3 7
3
7
8
00, BNG-900, and s-BNG-1000 were synthesized, and their cat-
Ni Pt /BNG-1000 catalyst has a higher catalytic activity toward
3 7
alytic performances toward dehydrogenation of hydrous hy-
drazine at 258C in alkaline solution (0.5m NaOH) are displayed
in Figure 3a. Ni Pt /BNG-1000 exhibits the highest catalytic
the electro-oxidation of methanol in acidic solution. The maxi-
À1
mum current of Ni Pt /BNG-1000 is about 359.8 mAmg Pt,
3
7
À1
which is much higher than that of Pt/C (200.2 mAmg Pt) and
3
7
À1
performance, whereas Ni Pt /s-BNG-1000 exhibits the lowest
Ni Pt /s-BNG-1000 (155.6 mAmg Pt). These results further
3
7
3
7
catalytic activity, highlighting the isolated doping of B and N in
facilitating the catalytic activity. As shown in Figure 3b, com-
pared with rGO, BCN, and the physical mixture of rGO and
BCN, the BNG-1000-supported Ni Pt NPs exhibit the highest
highlight the synergistic effect of B,N co-doping in facilitating
their catalytic performance.
As shown in Figure 5a, for all the catalysts tested, the cur-
rent density decreased with time, which could be due to the
formation of adsorbed CO and other intermediate species
during the methanol oxidation reaction. However, Ni Pt /BNG-
3
7
catalytic activity, revealing the synergistic effect between NiPt
NPs and B,N co-doped graphene.
3
7
To obtain the Arrhenius activation energy (E ), the decompo-
1000 exhibits higher stability toward methanol oxidation in
acidic solution than the Ni Pt /s-BNG-1000 and commercial Pt/
a
sition of hydrazine catalyzed by the Ni Pt /BNG-1000 catalyst
3
7
3
7
at different temperatures from 258C to 508C were also carried
out (Figure S11a in the Supporting Information). The values of
the rate constant, k, at different temperatures were calculated
from the slopes of the linear parts of each plot. From the Ar-
C catalysts. Moreover, as shown in Figure 5b, a CO stripping
experiment was conducted in 0.5m HClO solution, and the
4
onset potential for the CO oxidation on the Ni Pt /BNG-1000,
3
7
Ni Pt /s-BNG-1000, and commercial Pt/C catalysts were deter-
3
7
rhenius plot of ln k versus 1/T for the catalyst, E is determined
mined as 190 mV, 220 mV, and 320 mV, respectively. Clearly,
Ni Pt /BNG-1000 is negatively shifted by 30 mV and 130 mV in
a
À1
2
to be 28.4 kJmol with an R value of 0.99 (Figure S11b),
which is lower than most of the reported values (Table S2).
Inspired by their high catalytic performance towards dehy-
drogenation of hydrous hydrazine, the catalytic activities
toward the methanol oxidation reaction (MOR) were also
tested. The electrochemical surface activity (ECSA) of the as-
3
7
comparison with Ni Pt /s-BNG-1000 and commercial Pt/C cata-
3
7
lysts, respectively, indicating the adsorbed CO is more easily
oxidized on the Ni Pt /BNG-1000 catalyst. Thus, Ni Pt /BNG-
3
7
3
7
1000 possesses the highest MOR activity as a result of its high
CO tolerance.
Figure 3. a) Time course plots for hydrogen generation by the decomposition of hydrazine in aqueous NaOH solution (0.5m) by Ni
00, Ni Pt /s-BNG-1000, and Ni Pt /BNG-1000. b) Decomposition of hydrazine in aqueous NaOH solution (0.5m) by Ni Pt /rGO, Ni Pt
mixture of rGO and BCN (denoted as rGO+BCN) at 258C (metal/N
3
Pt
7
/BNG-800, Ni Pt
3
7
/BNG-
9
3
7
3
7
3
7
3
7
/BCN, and Ni
3
Pt /physical
7
2
H
4
·H
2
O=0.05)
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Figure 4. a) Cyclic voltammetry curves for Ni
CH OH.
3
Pt
7
/BNG-1000, Ni
3
Pt
7
/s-BNG-1000, and commercial Pt/C in 0.5m H
2
SO
4
2 4
solution and b) in 0.5m H SO +0.5m
3
Figure 5. a) Chronoamperometric curves of Ni
3
Pt
7
/BNG-1000, Ni
3
Pt
7
/s-BNG-1000, and commercial Pt/C catalysts in 0.5m H
2
SO
4
+0.5m CH
3
OH solution at 0.5 V
solution at the
À1
and the scan rate of 50 mVs . b) CO stripping curves for Ni
3
Pt
7
/BNG-1000, Ni
3
Pt /s-BNG-1000, and commercial Pt/C catalysts in 0.5m HClO
7
4
À1
scan rate of 20 mVs
.
To study the crystalline structures of the NiPt NPs with differ- Conclusions
ent compositions supported on BNG-1000, XRD was carried
out. As shown in Figure S12 (in the Supporting Information),
the diffraction peaks of all the NiPt NPs shift to higher angles
when the Ni content is increased, which may be caused by the
lattice compression effect of Ni, and further indicates the for-
mation of NiPt alloy. The morphology of Ni Pt /BNG-1000 was
We have developed a facile two-step method for the synthesis
of boron and nitrogen co-doped graphene. The use of the
BCN precursor is essential for preparing BNGs with high boron
content, high pyridinic N content, and low covalent BN ratio,
whereas annealing rGO, urea, and boric acid in one-step results
in separated domains of larger amounts of covalent BN in the
graphene network (s-BNG). The BNGs were further used as
supporting materials to anchor well-dispersed NiPt NPs.
Thanks to the synergistic effect of the separated B and N
doping, high boron and pyridinic N content, the BNG-1000-
supported NiPt nanocatalyst exhibits the highest catalytic ac-
tivity toward dehydrogenation of alkaline solutions of hydra-
3
7
further characterized by TEM. As shown in Figure S13 (in the
Supporting Information), the NiPt NPs are well-dispersed on
BNG-1000. The XPS spectra of Ni Pt /BNG-1000 (Figure S14 in
3
7
the Supporting Information) show the characteristic signals for
Ni and Pt, indicating the co-existence of both metals. The sig-
nals of the Pt4f7/2 and Pt4f5/2 peaks with binding energies of
0
7
1.4 and 74.7 eV correspond to Pt , and the signals of the
À1
Ni2p3/2 and Ni2p1/2 peaks with binding energies of 852.7 and
zine with a TOF value of 199.4 h at room temperature, which
0
8
70.2 eV correspond to Ni . The formation of oxidized Ni most
is among the highest reported values. As evidence of its multi-
functionality, NiPt/BNG-1000 was further employed for electro-
catalytic methanol oxidation, in which it exhibits superior cata-
likely occurs during the sample preparation process for the
[
27]
XPS measurements.
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lytic activity and high CO tolerance. The development of boron
and nitrogen co-doped graphene with high boron and pyridin-
ic nitrogen content and negligible covalent BN bonding as
supporting materials to anchor metal NPs and thus boost their
catalytic activity and stability may open up a new avenue for
preparing other synergistic heteroatom-doped graphene-sup-
ported metal NPs for more applications.
varied from 25 to 508C to obtain the activation energy (E ) (metal/
a
N H ·H O=0.05).
2
4
2
Preparation of the NiPt/BNG catalyst for the methanol
oxidation reaction
The NiPt/BNG catalyst was synthesized by the same method as the
NiPt/BNG catalyst for hydrous hydrazine decomposition. After re-
duction by NaBH , the catalyst was collected by centrifugation at
4
9
800 rpm for 6 min, followed by washing with deionized water
Experimental Section
and ethanol, and drying under vacuum at room temperature.
Synthesis of reduced graphene oxide (rGO)
[28]
GO was prepared according to the classical Hummers method.
In the synthesis of rGO, GO powder (1.0 g) was dispersed in
000 mL ultrapure water, and hydrous hydrazine (10 mL) was
added to the solution. Then, the mixture was heated to reflux for
8 h with continuous stirring. After cooling to the room tempera-
ture, the solid precipitate was collected by vacuum filtration. The
product was washed by water and ethanol and dried under
vacuum at 508C.
Physical characterizations
Powder X-ray diffraction (XRD) patterns were measured by
a Bruker D8-Advance X-ray diffractometer using a CuKa radiation
source (l=0.154178 nm) with a velocity of 10 degmin . Raman
spectroscopy was performed with a laser micro-Raman spectrome-
ter (Renishaw inVia, Renishaw, 532 nm excitation wavelength). The
morphologies and sizes of the samples were observed by using
a Tecnai G20 U-Twin transmission electron microscope (TEM) at an
acceleration voltage of 200 kV. X-ray photoelectron spectroscopy
(XPS) measurements were performed with a Thermo Fischer ESCA-
LAB 250Xi spectrophotometer. The characterization of BET surface
1
À1
1
Synthesis of boron–carbon–nitride (BCN) and boron and
nitrogen co-doped graphene (BNG)
data, which was based on N adsorption/desorption isotherms at
2
Boric acid (1.0295 g) and urea (6.0 g) were dissolved in 30 mL ultra-
pure water at room temperature, and then the mixture was dried
by using a rotary evaporator. After that, the mixture was placed in
a quartz tube furnace, followed by calcining at 8008C for 1 h at
7
7 K and controlled by liquid nitrogen, was measured by using
a Quantachrome NOVA 4200e. The SEM images and element map-
ping were obtained with a Zeiss Sigma electron microscope
equipped with an energy dispersive X-ray detector (EDX). MS of
the generated gases were collected by using an Ametek Dycor
mass spectrometer under an Ar atmosphere.
À1
a heating rate of 58Cmin under Ar. The product was collected
when the furnace temperature was below 608C and denoted as
BCN. The doping process was carried out by annealing the mixed
rGO and BCN with a mass ratio of 1:1 at 800, 900, or 10008C for
2
1
h in Ar to form BNG (denoted as BNG-800, BNG-900, and BNG-
000). As a control experiment, s-BNG-1000 was prepared by ther-
Electrochemical tests
Electrochemical measurements were conducted on an electro-
chemical workstation (CHI 630E, CH Instruments, Inc., Shanghai,
China). The NiPt/BNG catalyst ink was prepared by ultrasonically
dispersing the catalyst powder (5.0 mg) in 1 mL of 0.05wt% Nafion
ethanol solution, which was sonicated for about 45 min to form
a homogeneous ink solution. The glassy carbon (GC) working elec-
trode with 5 mm diameter was polished with 500 nm alumina sus-
pensions to a mirror finish before the experiment. The catalyst dis-
persion (5 mL) was coated on the GC with a micropipette and al-
lowed to dry in air. A standard three-electrode electrochemical
mally annealing the mixture of rGO (50 mg), boric acid (110 mg),
and urea (640 mg) under the same conditions.
Preparation of NiPt/BNG catalyst for hydrous hydrazine
decomposition
In a typical experiment, BNG (10 mg) was dispersed in 3 mL water
in a two-necked round-bottom flask. Ultrasonication was required
to get a uniform dispersion. Potassium chloroplatinate solution
À1
(
0
0.7 mL, 0.1 molL
)
and nickel chloride solution (0.3 mL,
system equipped with gas (N ) flow system was employed. The
2
À1
.1 molL ) were added to the flask. The resulting mixture was
NiPt/BNG-loaded GC was used as the working electrode, a platinum
foil was used as the counter electrode, and a saturated calomel
electrode (SCE) was used as the reference electrode.
then reduced by 4 mL aqueous solution containing NaBH4
75.8 mg) and NaOH (200 mg) with vigorous stirring at 258C. The
(
process of hydrous hydrazine decomposition was as follows: one
neck of the flask was connected to a gas burette to monitor the
volume of the gas evolution, and the other was used for the intro-
duction of hydrazine monohydrate (0.1 mL, 1.96 mmol). A water
bath was used to control the temperature of the reaction solution
Acknowledgements
This work was financially supported by the National Natural Sci-
ence Foundation of China (21201134, 21571145), the Natural Sci-
ence Foundation of Jiangsu Province (BK20130370), the Creative
Research Groups of Hubei Province (2014CFA007) and the Large-
scale Instrument and Equipment Sharing Foundation of Wuhan
University.
(
258C). The gas released during the reaction was passed through
HCl solution (1.0m) before it was measured volumetrically. The se-
lectivity of the H generation (X) can be calculated by using Equa-
2
tion (3):
X ¼ ð3 lÀ1Þ=8 ½l ¼ nðH þ N Þ=nðH NNH ފ
ð3Þ
2
2
2
2
To optimize the reaction conditions for catalytic dehydrogenation
of hydrazine, the molar ratio of Ni/Pt was varied between 1:9, 3:7,
Keywords: boron–nitrogen doping · hydrazine · hydrogen
storage · methanol oxidation
5
:5, 7:3, and 9:1 in different reaction trials. The temperatures were
ChemCatChem 2016, 8, 1410 – 1416
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1415
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Published online on March 1, 2016
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim