Precious-metal-free nanocatalysts for highly efficient hydrogen production from hydrous hydrazine

Article abstract of DOI:10.1002/adfm.201401731

Hydrous hydrazine (H₂NNH₂·H₂O) has generally been considered a promising hydrogen storage carrier because of inherent advantages such as its high hydrogen content and easy recharging as a liquid. Unfortunately, the decomposition of hydrous hydrazine to H₂ is terribly sluggish and/or not entirely favored - a competing decomposition to ammonia may be preferred. This has been the case using noble-metal catalysts and using non-precious-metal-based catalysts, even at elevated temperatures. To overcome this challenge, non-precious-metal-based Cu@Fe₅Ni₅ core@shell nanocatalysts are prepared using an in situ seeding-growth approach. Unexpectedly, the catalyst exerts 100% H 2 selectivity and excellent activity and stability toward the complete decomposition of hydrous hydrazine, which is due to the synergistic effect of the core@shell structure. These promising results will certainly promote the effective application of hydrous hydrazine as a potential hydrogen storage material.

Full text of DOI:10.1002/adfm.201401731

www.afm-journal.de
www.MaterialsViews.com
Precious-Metal-Free Nanocatalysts for Highly Efficient
Hydrogen Production from Hydrous Hydrazine
Jun Wang, Yang Li, and Yu Zhang*
Hydrous hydrazine (H NNH ·H O) has generally been considered a prom-
ising hydrogen storage carrier because of inherent advantages such as its
high hydrogen content and easy recharging as a liquid. Unfortunately, the
ammonia-producing reaction: 3H NNH
2 2
2
2
2
[
5]
→
4NH3 + N2.
The development of
highly H -selective (as opposed to NH -
2
3
selective) and highly efficient catalysts,
especially based on non-precious and
abundant metals, is of crucial importance
for the effective application of hydrazine.
To this end, Xu and co-workers devel-
oped a series of bimetallic nanocatalysts
decomposition of hydrous hydrazine to H is terribly sluggish and/or not
2
entirely favored—a competing decomposition to ammonia may be preferred.
This has been the case using noble-metal catalysts and using non-precious-
metal-based catalysts, even at elevated temperatures. To overcome this
challenge, non-precious-metal-based Cu@Fe Ni core@shell nanocatalysts
5
5
(
NCs) by alloying Ni with another noble
are prepared using an in situ seeding-growth approach. Unexpectedly, the
[
6]
metal, such as Rh, Pt and Ir; 100%
H2 selectivity (i.e., over the ammonia-
producing decomposition) has already
been successfully achieved. Thereafter,
our group further improved the reaction
kinetics via a synergistic effect of the gra-
phene support, the RhNi nanoparticles
catalyst exerts 100% H selectivity and excellent activity and stability toward
2
the complete decomposition of hydrous hydrazine, which is due to the
synergistic effect of the core@shell structure. These promising results will
certainly promote the effective application of hydrous hydrazine as a potential
hydrogen storage material.
[
7]
(
NPs), and the use of NaOH. Neverthe-
less, the incorporation of noble metals to
nickel greatly increases the cost of catalysts. In a subsequent
study, Xu and co-workers synthesized FeNi alloy NCs for they
complete and hydrogen-selective decomposition of N H ·H O
1
. Introduction
Hydrogen is generally proposed to be an important energy
vector for facing the ever-increasing levels of the energy crisis
and of environmental pollution due to its high energy density
and efficiency with low environmental load.[1,2] However, even
after several decades of intensive exploration, hydrogen storage
is still one of the most challenging barriers that impede the
implementation of the hydrogen-based economy.[ Hydrous
hydrazine (N H ·H O) is considered a promising liquid-
2
4
2
[
8]
in the presence of NaOH at 70 °C. In addition, very recently
highly dispersed Ni/Al O NCs derived from Ni-Al hydrotal-
2
3
cite reported by Zhang and co-workers revealed 93% H selec-
2
[
9]
tivity for the catalytic decomposition of N H ·H O at 30 °C.
2
4
2
Although these encouraging results have been achieved, the
improvements are still far from satisfying. For example, the cat-
alytic kinetics of the FeNi alloy NCs is still terribly sluggish even
at a relatively high reaction temperature. As for the Ni/Al O
2]
2
4
2
hydrogen storage material due to its high content of hydrogen
2
3
[
3]
(8.0 wt%) and its ability for CO-free H production. Hydra-
NCs, the small amount of impurity (NH ) not only reduces the
2
3
zine is usually used as a propellant for some special applica-
tions, such as unmanned space vehicles and submarine power
sources.[ However, to maximize the efficacy of hydrazine as a
hydrogen storage material, one must follow the desired reac-
tion pathway: H NNH → N + 2H , and avoid the unwanted
yield of H , but it also poisons current fuel-cell devices, thus
2
requiring a sophisticated post-treatment for separation. Con-
sequently, the development of highly hydrogen-selective and
efficient precious-metal-free catalysts in order to significantly
enhance the kinetic properties under mild conditions remains
challenging, but it is crucial for promoting the application of
hydrous hydrazine as a hydrogen storage material.
4]
2
2
2
2
J. Wang
Herein, the successful synthesis of core@shell NCs (Cu@
Fe Ni ), which do not contain any precious metals, is reported.
University of Chinese Academy of Sciences
Beijing 100049, P. R. China
5
5
They exhibit 100% H selectivity and high activity for the com-
2
Y. Li, Prof. Y. Zhang
plete decomposition of N H ·H O under ambient conditions,
Key Laboratory of Bio-inspired Smart Interfacial Science
and Technology of Ministry of Education
School of Chemistry and Environment
Beihang University
Beijing, 100191, P. R. China
E-mail: jade@buaa.edu.cn
2
4
2
which is due to the electronic coupling between the core and
[10]
shell metals. Moreover, in light of this synergistic structural
and electronic effect, much higher catalytic efficiency can be
obtained by replacing Cu with a noble metal for the core. The use
of core can significantly reduce the limitations involving reaction
temperature for the complete conversion of N H ·H O to H .
DOI: 10.1002/adfm.201401731
2
4
2
2
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201401731
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
1

www.afm-journal.de
www.MaterialsViews.com
2
. Results and Discussion
particle sizes of Cu@Fe5Ni5 and CuFe5Ni5 are ≈8.5 and
≈
7.6 nm, respectively (SI: Figure S2c,d). The TEM image of
The synthesis of Cu@Fe Ni NCs follows an in-situ seeding-
growth approach as reported previously.
synthetic process can be achieved simply by introducing
ammonia borane (NH BH ), as a weak reducing agent, into an
aqueous solution containing Cu(NO ) , FeSO , and NiCl with
a molar ratio of 0.02:0.1:0.1 in the presence of polyvinylpyrro-
lidone (PVP) as a capping agent. The core Cu NPs are able to
form first due to the high reduction potential of Cu . Subse-
quently, the in-situ generated Cu NPs catalytically reduce Fe
and Ni , which cannot be directly reduced by NH BH . As a
Cu@Fe Ni NPs (Figure 1a) clearly reveals that a distinct con-
5
5
5 5
[
11]
Briefly, the whole
trast between the core and shell sections can be observed. The
high-resolution TEM (HRTEM) image (Figure 1b) shows that
the core is in crystalline state with a d spacing of 0.209 nm,
which can be assigned to the {111} plane of Cu. Meanwhile,
no lattice fringes are observed in the shell, indicating its amor-
phous state. These are also consistent with the corresponding
selected-area electron diffraction (SAED) patterns (Figure 1b
inset), in which the crystalline nature of metallic Cu is revealed.
The energy dispersive spectroscopy (EDS) profile (Figure 1c)
illustrates the presence of Cu, Fe, and Ni with an atomic ratio
of 9.57:44.53:45.90, which was also confirmed by inductively
coupled plasma atomic emission spectroscopy (ICP-AES;
1:4.76:4.83), corresponding to the specified atomic ratio and
indirectly confirming that both Fe2+ and Ni can be catalyti-
cally reduced by Cu NPs with NH BH to form the FeNi shell.
3
3
3
2
4
2
2+
2+
2
+
3
3
result, the successive growth of Fe and Ni on the surface of
the Cu NPs leads to the formation of Cu@Fe Ni core@shell
5
5
NPs. The formation process is observable by the gradual color
evolution of the solution (see Supporting Information (SI):
Figure S1). In order to reveal the improved catalytic activity
derived from the synergistic effect of the core@shell structure
for N H ·H O dehydrogenation, CuFe Ni alloy NCs were also
2+
3
3
We then analyzed the X-ray diffraction pattern (XRD) of the
2
4
2
5
5
prepared for comparison using a relatively stronger reducing
agent (NaBH4).
Cu@Fe Ni5 NCs (Figure 1d). The prominent diffraction
5
peaks with the 2θ values of 43.29°, 50.43°, and 74.13° can be
indexed to diffractions of the (111), (200), and (220) planes of
Cu, respectively (powder diffraction file, PDF #04–0836). Dif-
fraction peaks of Fe or Ni were not present, indicating the
amorphous state of the FeNi shell, which is consistent with
the results obtained from HRTEM. In contrast, changing the
reducing agent (NH BH ) to conventional NaBH resulted only
Transmission electron microscopy (TEM) was used to charac-
terize the two as-prepared NCs, and the images confirm the suc-
cess in obtaining the core@shell nanostructure via the in-situ
seeding-growth approach. The two NCs are both composed of
aggregated NPs with roughly spherical shape (SI: Figure S2a,b).
Statistical analyses based on 100 NPs revealed that the average
3
3
4
Figure 1. a) TEM image, b) HRTEM image (inset: SAED pattern), c) EDS profile, and d) XRD pattern of as-synthesized Cu@Fe Ni NCs.
5
5
2
wileyonlinelibrary.com
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201401731

www.afm-journal.de
www.MaterialsViews.com
Figure 2. a) Time-course plots for the decomposition of N H ·H O toward H over the Cu@Fe Ni and CuFe Ni NCs in the presence of NaOH at
2
4
2
2
5
5
5
5
7
0 °C; n represents the number of moles, so n(H + N )/n(N H ) is the ratio of the moles of the desired decomposition products to that of hydrazine.
2 2 2 4
b) Mass spectral profile of released gases over Cu@Fe Ni NCs under an argon atmosphere.
5
5
in the formation of CuFe Ni alloy NPs, as proved by the fact
that intraparticular boundaries within a single particle are not
observed with HRTEM (SI: Figure S3).
catalyst surface, resulting in the degraded catalytic perfor-
mance. In contrast, for Cu@Fe Ni NCs, the introduction of a
5
5
5
5
Cu core does not affect the combined effect of Fe and Ni, but Cu
acts as an electron donor for the catalyst surface allowing easier
The catalytic reactions were carried out by introducing
N H ·H O into the reaction flask containing a catalyst sus-
[
10]
activation of N H . To verify these results, a surface analysis
2
4
2
2
4
pension at 70 °C in the presence of NaOH. The alkalinity is
of the Cu@Fe Ni NCs was performed by X-ray photoelectron
5 5
+
not not only able to convert N H5 to N H in aqueous solu-
spectroscopy (XPS). The coexistence of the characteristic peaks
for Fe 2p and Ni 2p was observed (SI: Figure S5), indicating the
lack of segregation. The absence of Cu 2p signals is ascribed
to the formation of the Cu@Fe Ni core@shell structure. Com-
2
2
4
tion and to accelerate the rate-determining deprotonation step
*
(
N H →N H )—thus promoting reaction kinetics, but it is
2 4 2 3
also responsible for restraining the generation of the basic by-
product NH , increasing the H selectivity of the N H ·H O
5
5
pared to the standard peaks of Fe and Ni, both of the peaks for
Fe 2p3/2 and Ni 2p3/2 shift to lower binding energies by ∼0.4
and ≈0.7 eV, respectively, indicating increased electron density
in the FeNi surface as a result of the electron-donating effects
of Cu. We propose that the synergistic effect between the Cu
core and FeNi shell contributes to the high catalytic activity.
Inspired by the electron-donating role of the Cu core, in order
to further tune and improve the catalytic performance, a series
3
2
2
4
2
[7,8]
decomposition.
Hence, the addition of NaOH is beneficial
for maximally enhancing the catalytic efficacy of the catalysts.
Figure 2a shows the catalytic activities of the Cu@Fe Ni and
5
5
CuFe Ni NCs based on the volume of generated gases. Encour-
5
5
agingly, the Cu@Fe Ni NCs exhibit superior catalytic activity
5
5
and H selectivity—complete release of 3 equivalents of gas
2
only takes 60 min at 70 °C. The generated gases were identi-
fied by mass spectrometry (MS; Figure 2b) to be H and N .
of M@Fe Ni
(M = Ir, Pt, Pd, Cu, or Ru) NCs with various
2
2
x
(10-x)
To further eliminate the presence of NH , the generated gases
Fe/Ni molar ratios were prepared via the in-situ seeding-growth
approach, and their catalytic performance for the decomposition
of N H ·H O were investigated and compared (Figure 3 and SI:
3
are also characterized by gas chromatography (SI: Figure S4),
which reveals a H :N ratio of 2.0, in agreement with the volu-
2
2
2
4
2
metric observations, confirming the complete conversion of
N H to H and N . In contrast, for the CuFe Ni NCs, only
Figure S6). As shown in Figure 3, when the shell is composed of
both Fe and Ni (regardless of what the core composition is), the
2
4
2
2
5
5
2.3 equivalents of gas was generated— even after 125 min
H selectivity increases as the Fe/Ni molar ratio increases—with
2
under the same reaction conditions. It has been reported that
the exception of Cu@Fe Ni . In contrast, all of the as-synthe-
9
1
FeNi alloy NCs exhibit 100% H selectivity with a total reac-
sized NCs containing a pure Fe shell did not exhibit any activity
toward N H ·H O decomposition, which is in agreement with
a previous report. On the other hand, when Ir, Pt, Pd, or Cu
was employed as the core and the Fe/Ni molar ratio of the shell
2
tion time of 190 min.[ The much superior catalytic activity of
8]
2
4
2
[8]
Cu@Fe Ni relative to CuFe Ni and FeNi NCs highlights the
5
5
5
5
significant activity promotion of Cu@Fe Ni5 NCs by intro-
5
ducing a catalytically inactive Cu core, which is derived from
the synergistic structural and electronic effects of the metals
was either high or low, i.e., not near 5:5, 100% H selectivity
2
was favored. Comparing the activities of M@Fe Ni , the per-
5
5
(
via the so-called strain and ligand effects).
As is known to all, the interactions between chemical reac-
formance of NCs with noble-metal cores are almost superior to
that of NCs with a Cu core (SI: Figure S6). Interestingly, among
tants and the catalyst surface control the activity and efficiency.
Precise modification of the catalyst surface at the atomic level
and consequently merging the intermetallic electronic interac-
the investigated M@Fe Ni
mance is exhibited by the Pt@Fe Ni NC, of which a release of
3 equivalents of gas takes only 7 min. However, improved cata-
NCs, the highest catalytic perfor-
x
(10-x)
9
1
tions is an important pathway for obtaining optimized catalytic
lytic performance is not observed for the Ru@Fe Ni
which should be explained by further work.
From the viewpoint of practical application, obtaining 100%
H2 selectivity at decreased temperature is of critical impor-
tance. To this end, we tested the catalytic performance of the
NCs,
x
(10-x)
performance.[
10b–f]
The alloying of Fe and Ni is essential for
[8]
complete dehydrogenation of N H . Therefore, for CuFe Ni5
2
4
5
NCs, incorporating a third metal component, Cu, with FeNi
disturbs the electronic interaction between Fe and Ni on the
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201401731
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
3

www.afm-journal.de
www.MaterialsViews.com
(
Figure 4b). Additionally, when 1.5 equivalents of gas is released
with the Cu@Fe Ni and Pt@Fe Ni NCs, the activation ener-
5
5
5
5
gies were calculated to be 79.2 and 51.2 KJ/mol, respectively.
To investigate the influence of the core content, Cu @
2
Fe Ni and Pt @Fe Ni NCs were also prepared and applied
5
5
0.5
5
5
for the catalytic decomposition of N H ·H O. It is found that
2
4
2
the activity increases/decreases with the increase/decrease in
the amount of the core (SI: Figure S7). In addition, the con-
tinuous tests of the catalytic activity revealed good stability of
Cu@Fe Ni NCs (SI: Figure S8).
5
5
3
. Conclusion
In summary, non-precious-metal-based Cu@Fe Ni core@shell
5
5
NCs, prepared via an in-situ seeding-growth approach, not only
exhibit good catalytic performance for N H ·H O dehydrogena-
2
4
2
tion at 70 °C, but they also show 100% H selectivity at even
2
lower temperature, highlighting the synergistic effect of core@
shell structure. These encouraging findings are certainly helpful
for the long-term endeavors in optimizing and enhancing the
catalytic efficacy of low-cost catalysts for developing N H ·H O
2
4
2
Figure 3. Hydrogen selectivity of the catalytic decomposition of N H ·H O
2
4
2
as a viable on-board hydrogen storage material.
using the as-prepared M@Fe Ni
NCs in the presence of NaOH at
x
(10-x)
7
0 °C (M = Ir, Pt, Pd, Cu and Ru; x = 0, 1, 3, 5, 7, 9, and 10).
4
. Experimental Section
Cu@Fe Ni NCs at different temperatures (Figure 4a). When
5
5
Catalyst Preparation: The synthesis of Cu@Fe Ni5 NCs follows an
5
the reaction temperature is decreased to 50 °C, N H ·H O
2
4
2
in-situ seeding-growth approach. Briefly, Cu(NO ) ·3H O (0.02 mmol),
NiCl ·6H O (0.1 mmol), FeSO ·7H O (0.1 mmol), and PVP (100 mg)
3
2
2
can still be completely converted to H in a reaction time of
2
2 2 4 2
2
50 min. However, upon further decreasing the reaction tem-
were dispersed in 6 mL of H O to obtain a transparent solution.
2
perature to 30 °C, 2.1 equivalents of gas can be released from
Afterwards, the black suspension was obtained by adding an aqueous
solution (4 mL) containing NH BH3 (15 mg) with vigorous shaking.
N H ·H O after 21.5 h. Considering the fact that the FeNi
3
2
4
2
The synthesis of CuFe Ni5 alloy NCs using NaBH4 (20 mg) instead of
5
alloy NCs only exhibited 100% H selectivity at 70 °C and are
2
NH BH as the reducing agent, followed a similar process as that for the
inactive at 25 °C,[ we can reasonably conclude that the intro-
duction of a Cu core for FeNi active components can effec-
tively reduce the activation energy for the catalytic decompo-
sition of N H ·H O, highlighting the synergistic effect of the
8]
3
3
Cu@Fe Ni NCs. For the synthesis of M@Fe Ni NCs (M = Ir, Pt, Pd,
5
5
x
(10-x)
Cu or Ru; x = 0, 1, 3, 5, 7, 9 or 10), the amount of M was fixed to be
.02 mmol whereas the total amount of Fe and Ni was fixed to be 0.2 mmol.
A similar process for the Cu@Fe Ni NCs was used. For the synthesis of
0
2
4
2
5
5
core@shell structure again. It should be noted that achieving
00% H selectivity from the N H ·H O decomposition at even
lower temperature at the cost of decreased activity is extremely
worthy from the viewpoint of practical use. Moreover, for Pt@
Cu2@Fe5Ni5 and Pt0.5@Fe5Ni5 NCs, 0.04 mmol of Cu(NO3)2·3H2O and
.01 mmol of H PtCl were used, respectively. Likewise, a similar synthesis
0
1
2
6
2
2
4
2
as for that of the Cu@Fe Ni5 NCs was adopted. NOTE: The complete
5
absence of gas evolution from the solution should be verified before
carrying out the tests of the catalytic decomposition of N H ·H O.
2
4
2
Fe Ni NCs, 100% H selectivity is obtained with a reaction
5
5
2
Characterization: Powder XRD measurements were performed
on a Bruker D8 Focus Powder X-ray diffractometer using Cu Kα
time of 11 min at 70 °C, 31 min at 50 °C, and 98 min at 30 °C
Figure 4. Time-course plots for the decomposition of N H ·H O toward H catalyzed by the Cu@Fe Ni (a) and Pt@Fe Ni (b) NCs in the presence
2
4
2
2
5
5
5
5
of NaOH at different temperatures.
4
wileyonlinelibrary.com
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201401731

www.afm-journal.de
www.MaterialsViews.com
λ = 0.15405 nm) radiation (40 kV, 40 mA). TEM was performed using
(
[1] a) L. Schlapbach, A. Zuttel, Nature 2001, 414, 353; b) P. Chen,
Z. Xiong, J. Luo, J. Lin, K. L. Tan, Nature 2002, 420, 302;
c) W. Grochala, P. P. Edwards, Chem. Rev. 2004, 104, 1283.
[2] a) J. Graetz, Chem. Soc. Rev. 2009, 38, 73; b) A. W. C. Van de Berg,
C. O. Areán, Chem. Commun. 2008, 668; c) U. Eberle, M. Felderhoff,
F. Schuth, Angew. Chem. Int. Ed. 2009, 48, 6608; d) J. Sculley,
D. Q. Yuan, H. C. Zhou, Energy Environ. Sci. 2011, 4, 2721.
3] a) E. W. Schmidt, Hydrazine and its Derivatives: Preparation, Prop-
erties, Applications, 2nd ed., John Wiley & Sons, New York 1984;
b) R. R. Schrock, T. E. Glassman, M. G. Vale, M. Kol, J. Am. Chem.
Soc. 1993, 115, 1760; c) S. H. Wu, D. H. Chen, J. Colloid Interface
Sci. 2003, 259, 282.
4] X. Chen, T. Zhang, P. Ying, M. Zheng, W. Wu, L. Xia, T. Li, X. Wang,
C. Li, Chem. Commun. 2002, 288.
5] a) X. Chen, T. Zhang, M. Zheng, Z. Wu, W. Wu, C. Li, J. Catal. 2004,
24, 473; b) D. G. Tong, X. L. Zeng, W. Chu, D. Wang, P. Wu, Mater.
Res. Bull. 2010, 45, 442; c) S. K. Singh, X. B. Zhang, Q. Xu, J. Am.
Chem. Soc. 2009, 131, 9894.
a FEI Tecnai G2 S-Twin instrument with a field-emission gun operating
at 200 kV. Mass spectrometry analysis of the generated gases was
performed using an Ominstar-Thermostar GSD 320 system (Pfeiffer
Vacuum) mass spectrometer, wherein argon gas was chosen as the
carrying gas. A Techcomp GC7900 gas chromatograph (GC) with
a thermal conductivity detector (TCD) was used to analyze the gas
products generated from the hydrous hydrazine decomposition. ICP-AES
measurements were performed on a TJA (Thermo Jarrell Ash) Atomscan
Advantage instrument. XPS measurements were performed on an
ESCALAB 250 photoelectron spectrometer.
[
Catalytic Decomposition of N H ·H O : Catalytic reactions were
2
4
2
carried out using a two-necked round-bottom flask with one of the flask
openings connected to a gas burette and the other for the introduction
of N H ·H O. The catalytic decomposition reaction of N H ·H O
[
2
4
2
2
4
2
[
for the release of hydrogen (along with nitrogen) was initiated by
shaking the mixture of 2 mmol of N H ·H O, which was introduced
2
2
4
2
via a pressure-equalization funnel, and the aqueous suspension of the
catalyst prepared as described above in the presence of NaOH (0.1 M).
The reaction temperature was kept constant at a specified reaction
temperature using a water bath. The gases released during the reaction
were passed through a condenser and a trap containing 1.0 M sulfuric
acid to ensure the absorption of ammonia, if produced, of which the
volume was monitored using the gas burette. To prepare the samples for
mass spectral analysis and gas chromatography of the released gases,
an acid trap was not used. An illustration of the apparatus for the tests
of the catalytic reaction is shown in the SI (Scheme S1).
[6] a) S. K. Singh, Q. Xu, J. Am. Chem. Soc. 2009, 131, 18032;
b) S. K. Singh, Q. Xu, Inorg. Chem. 2010, 49, 6148; c) S. K. Singh,
Q. Xu, Chem. Commun. 2010, 46, 6545; d) S. K. Singh, Z. H. Lu,
Q. Xu, Eur. J. Inorg. Chem. 2011, 2232.
[7] J. Wang, X. B. Zhang, Z. L. Wang, L. M. Wang, Y. Zhang, Energy
Environ. Sci. 2012, 5, 6885.
[
8] S. K. Singh, A. K. Singh, K. Aranishi, Q. Xu, J. Am. Chem. Soc. 2011,
33, 19638.
1
[
9] L. He, Y. Huang, A. Wang, X. Wang, X. Chen, J. J. Delgado, T. Zhang,
Angew. Chem. Int. Ed. 2012, 51, 6191.
[
10] a) R. Ghosh Chaudhuri, S. Paria, Chem. Rev. 2012, 112, 2373;
b) D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu,
A. F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight,
G. J. Hutchings, Science 2006, 311, 362; c) S. Alayoglu, A. U. Nilekar,
M. Mavrikakis, B. Eichhorn, Nat. Mater. 2008, 7, 333; d) P. Strasser,
S. Koh, T. Anniyev, J. Greeley, K. More, C. F. Yu, Z. C. Liu, S. Kaya,
D. Nordlund, H. Ogasawara, M. F. Toney, A. Nilsson, Nat. Chem.
Supporting Information
Supporting Information is available free of charge from the Wiley Online
Library or from the author.
Acknowledgment
2
010, 2, 454; e) K. Tedsree, T. Li, S. Jones, C. W. A. Chan, K. M. K. Yu,
P. A. J. Bagot, E. A. Marquis, G. D. W. Smith, S. C. E. Tsang, Nat.
Nanotechnol. 2011, 6, 302; f) C. J. Serpell, J. Cookson, D. Ozkaya, P.
D. Beer, Nat. Chem. 2011, 3, 478.
This work was financially supported by the fundamental research funds
for the central universities, the National Natural Science Foundation of
China (Grant No. 51372007 and 213001014).
[
11] a) J. M. Yan, X. B. Zhang, T. Akita, M. Haruta, Q. Xu, J. Am. Chem.
Soc. 2010, 132, 5326; b) H. L. Jiang, T. Akita, Q. Xu, Chem. Commun.
2011, 47, 10999; c) H. L. Wang, J. M. Yan, Z. L. Wang, Q. Jiang, Int.
J. Hydrogen Energy 2012, 37, 10229.
Received: May 29, 2014
Revised: July 10, 2014
Published online:
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201401731
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
5