Tunable aqueous phase synthesis and shape-dependent electrochemical properties of rhodium nanostructures

Article abstract of DOI:10.1021/ic100249t

Rhodium nanostructures with highly selective morphologies such as cubes, horned particles, dendrites, and network-shaped wires have been achieved through the synergetic effect of sodium lauryl sulfate (SLS) and halogen anions (F ^-, Cl^-, Br^-, I^-) in a green solvent, water. The effects of SLS and halogen anions were systematically investigated. The electrocatalytic performances of Rh nanostructures toward ethanol oxidation were tested. The results have shown that the rhodium nanostructures displayed shape-dependent properties, and the nanodendrites possessed the maximum catalytic activity.

Full text of DOI:10.1021/ic100249t

Inorg. Chem. 2010, 49, 5515–5521 5515
DOI: 10.1021/ic100249t
Tunable Aqueous Phase Synthesis and Shape-Dependent Electrochemical
Properties of Rhodium Nanostructures
Qiang Yuan,†,‡ Zhiyou Zhou,*,§ Jing Zhuang,† and Xun Wang*,†
†Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China, ‡Department of Chemistry,
§
Guizhou University, Guiyang, Guizhou province 550025, P. R. China, and Department of Chemistry, College of
Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China
Received February 6, 2010
Rhodium nanostructures with highly selective morphologies such as cubes, horned particles, dendrites, and network-
shaped wires have been achieved through the synergetic effect of sodium lauryl sulfate (SLS) and halogen anions
(F-, Cl-, Br-, I-) in a green solvent, water. The effects of SLS and halogen anions were systematically investigated.
The electrocatalytic performances of Rh nanostructures toward ethanol oxidation were tested. The results have shown
that the rhodium nanostructures displayed shape-dependent properties, and the nanodendrites possessed the
maximum catalytic activity.
Introduction
water still remains a challenge. In this paper, we demonstrate
rhodium as a case study in which the morphology of rhodium
nanocrystals can be harnessed in the aqueous phase through
the synergetic effect of SLS and different halogen anions while
maintaining other reaction conditions (Figure 1). Moreover,
the electrocatalytic activity of Rh nanostructures toward
ethanol oxidation exhibits shape-dependent properties.
Rhodium is a very important catalyst in many industrial
and lab applications. For example, rhodium is a well-known
catalyst for NOx reduction in three-way car catalysts,12 direct
ethanol fuel cells (DEFCs),13 oxidation of alcohols into
organic acids,14 hydrogenation/hydroformylation of unsatu-
rated hydrocarbon compounds,15 and in the petroleum refin-
ing process.16 On the other hand, the price of rhodium is very
high. Therefore, for the sake of maximum utilization of
rhodium, it is necessary to precisely control the size and
shape of rhodium crystals for exposing the maximumnumber
of atoms.
The synthesis of noble metal nanocrystals with controllable
morphologies (including dimension and shape) has received
increasing interest because of the nanocrystals’ intrinsic
shape- and size-dependent properties in many key fields such
as catalysis,1-6 biotechnology,7 magnetism,8 and optics.1,9
Noble metal nanocrystals with a variety of morphologies
including a sphere, polyhedron, plate, wire, dendrite, and so
forth have been synthesized by the bottom-up, solution-phase
methods. Meanwhile, up to now, the solution systems, which
were developed to control the crystal morphology of noble
metal, mainly focused on polyol, oil, and other organic
solvent systems.7,10,11 The morphology-controllable synthesis
of single noble metal nanocrystals in a “green” solvent such as
*To whom correspondence should be addressed. E-mail: zhouzy@
xmu.edu.cn (Z.Z.), wangxun@mail.tsinghua.edu.cn (X.W.).
(1) Xia, Y. N.; Xiong, Y. J.; Lim, B.; Skrabalak, S. E. Angew. Chem., Int.
Ed. 2009, 48, 60.
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Yang, P. D. Angew. Chem., Int. Ed. 2006, 46, 7824.
(3) Park, J. Y.; Zhang, Y. W.; Grass, M.; Zhang, T. F.; Somorjai, G. A.
Nano Lett. 2008, 8, 673.
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Int. Ed. 2008, 47, 3588.
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316, 732.
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J. Am. Chem. Soc. 2009, 131, 16350.
(7) Ferrando, R.; Jellinek, J.; Johnston, R. L. Chem. Rev. 2008, 108, 845.
(8) Cademartiri, L.; Ozin, G. Adv. Mater. 2009, 21, 1013.
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Angew. Chem., Int. Ed. 2009, 48, 3516.
For the above-mentioned reasons, much effort to synthe-
size monodispersed, well-defined rhodium nanostructures
withhigh selectivity has been expendedin the solution system.
However, limited success has been achieved for controlling
the morphology of rhodium compared to other noble metals
(Ag, Au, Pd, and Pt). In 2005, Tilley and co-workers first
(12) Gandhi, H. S.; Graham, G. W.; McCabe, R. W. J. Catal. 2003, 216,
433.
(13) Kowal, A.; Li, S. M.; Sasaki, K.; Vukmirovic, M. B.; Zhang, J.;
Marinkovic, N. S.; Liu, P.; Frenkel, A. I.; Adzic, R. R. Nat. Mater. 2009, 8,
325.
(14) Fujita, M.; Hiyama, T. Org. Synth. Coll. 1993, 8, 16.
(15) Park, K. H.; Jang, K.; Kim, H. J.; Son, S. U. Angew. Chem., Int. Ed.
2007, 46, 1152.
(10) Dumestre, F.; Chaudret, B.; Amiens, C.; Renaud, P.; Fejes, P.
Science 2004, 303, 821.
(11) Huang, X.; Zhang, H.; Guo, C.; Zhou, Z.; Zheng, N. Angew. Chem.,
Int. Ed. 2009, 48, 4808.
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hedron Lett. 2006, 47, 969.
r
2010 American Chemical Society
Published on Web 05/25/2010
pubs.acs.org/IC

5516 Inorganic Chemistry, Vol. 49, No. 12, 2010
Yuan et al.
Characterizations. The size and morphology of the nano-
crystals were determined by a Tecnai G2 F20 S-Twin high-
resolution transmission electron microscope (HRTEM) at
200 kV. The rhodium nanocrystal solution was deposited onto
the carbon supported copper grid with a pipettor, and the
solvent was allowed to evaporate for TEM detection. X-ray
diffraction (XRD) patterns of the samples were recorded on a
Rigaku D/max-2400 diffractometer operated at 40 kV and a
˚
200 mA current with Cu KR radiation (λ = 1.5418 A). The
rhodium nanocrystal solution was deposited onto the glass plate
with a pipettor, and the solvent was allowed to evaporate for
XRD detection. FTIR spectroscopy was performed on a Nicolet
560 spectrograph.
Test of Electrocatalytic Activity. Electrochemical experi-
ments were carried out in a standard three-electrode cell at
room temperature (about 25 °C) controlled by a PAR 263A
potentiostat/galvanostat (EG&G). A saturated calomel elec-
trode (SCE) and a platinum foil were used as the reference and
counter electrodes, respectively. All potentials reported in this
paper are referred to the SCE scale. The superpure water
(18 MΩ cm) purified through a Milli-Q Lab system (Nihon
Millipore Ltd.) was used as a solvent.
The original samples of PVP-capped Rh nanoparticles were
washed several times with superpure water. Finally, 10 μL of the
suspension of purified Rh nanoparticles was drop-cast onto a
well-polished glassy carbon (GC, φ = 5 mm; Takai Carbon Co.,
Ltd., Tokyo, Japan) electrode and dried under an infrared lamp,
to get the working electrode.
The cyclic voltammograms (CVs) were obtained in a nitrogen-
saturated 0.1 M HClO4 solution, and the potential was scanned
from -0.28 to 1.0 V (SCE) at a scan rate of 50 mV/s. Voltam-
metric measurment for ethanol oxidation was carried out in a
0.1 M ethanol þ 0.1 M HClO4 solution, and the potential was
scanned from -0.28 to 1.0 V (SCE) at a scan rate of 5.0 mV/s.
Figure 1. Summary of Rh nanostructures controlled by halogen anions.
synthesized the high-yield rhodium nanocubes and multipods
by reducing RhCl3 in the ethylene glycol-poly(vinylpyrroli-
done) (PVP) system using the seed growth method by mani-
pulating the temperature.17 Xia and co-workers also reported
rhodium tripods/tetrapods with anhydrous Na3RhCl6 as
a precursor in the ethylene glycol-PVP system.18 Son and
co-workers obtained high-yield rhodium tetrahedrons to
decompose the organometallic compound, [Rh2(CO)4Cl2], in
oleylamine.15 Somorjai and co-workers achieved rhodium
nanocubes with >85% selectivity in the ethylene glycol-
PVP-TTAB (trimethyl(tetradecyl)ammonium bromide) sys-
tem with RhCl3 hydrate as a precursor.19 However, the other
novel rhodium nanostructures such as dendrites and network-
shaped wires have not been reported thus far. In this paper,
rhodium nanostructures with highly selective morphologies
such as cubes, horned particles, dendrites, and network-
shaped wires have been synthesized (Figure 1). Moreover, the
electrocatalysis activity of Rh nanostructures toward ethanol
oxidation exhibits shape-dependent properties.
Results and discussion
Rhodium Nanodendrites. The typical rhodium nano-
dendrites were synthesized in an aqueous solution in the
presence of RhCl3, PVP, SLS, and NaF at 220 °C for 6 h.
Figure 2a and b show the representative TEM images of
as-synthesized Rh nanodendrites, indicating that the
products were made of uniform nanodendrites, and no
significant amounts of other morphologies were detected
by TEM. The sizes of the nanodendrites have a narrow
distribution from 18 to 25 nm. Meanwhile, the HAADF-
STEM image (Figure 2c) reveals that the nanodendrites
consist of many branches; each branch is along different a
direction, and the maximum number of branches can be
beyond 20. The HRTEM image (Figure 2d) shows each
branch of a single rhodium nanodendrite is of a rice shape
with a sharp tip and an edge-to-edge width W of about
4.8 nm, and an apex-to-apex length L around 7.3 nm. The
interval between two lattice fringes was examined to be
0.220 nm, closed to the (111) lattice spacing of the fcc
rhodium. Moreover, the lattice fringes of each branch are
along the same direction, which indicates that the branch
is single crystalline. The X-ray diffraction (XRD) pattern
(Figure 2a, inset) of as-synthesized products possessed
four peaks in the range of 30-90° corresponding to (111),
(200), (220), and (311) planes of fcc rhodium (JCPDS
88-2334).
Experimental Section
Chemicals. Poly(vinylpyrrolidone) (PVP; CP, MW = 30 000),
NaF(A.R.), NaCl(A.R.), NaBr(A.R.), NaI(A.R.), sodiumlauryl
sulfate (SLS; A.R.), and ethanol (99.99%) were purchased from
Beijing Chemical Reagent Company. RhCl3 nH2O (A.R., Rh
3
content: 40 wt %) was purchased from the Beijing Research
Institute for Nonferrous Metals. HClO4 were purchased from Alfa
Aesar. Chemicals were used as received without further purifica-
tion. Deionized water was used for the synthesis of nanocrystals.
Synthesis of Rh Nanodendrites and Other Morphology Crys-
tals. A total of 1.0 mL of RhCl3 (0.1 M) aqueous solution,
21.0 mg of NaF (0.5 mmol), 300 mg of PVP (MW = 30 000), and
289 mg of SLS were added to 7.0 mL of water and stirred for
5 min. The resulting homogeneous brown solution was trans-
ferred to a 12 mL Teflon-lined stainless-steel autoclave. The
sealed vessel was then heated at 220 °C for the desired time
(i.e., 1.5, 3.0, 6.0, 12, and 24 h) before it was cooled to room
temperature. The products were separated via centrifugation at
10 000 rpm for 20 min three times using deionized water. Then,
the products were dispersed with 5.0 mL of deionized water. The
other morphologies of rhodium were obtained using the same
process but, instead of NaF, with equal molar amounts of NaCl,
NaBr, and NaI for 6 h.
(17) Hoefelmeyer, J. D.; Niesz, K.; Somorjai, G. A.; Tilley, T. D.
Nano Lett. 2005, 5, 435.
(18) Zettsu, N.; McLellan, J. M.; Wiley, B.; Yin, Y.; Li, Z.; Xia, Y.
Angew. Chem., Int. Ed. 2006, 45, 1288.
(19) Zhang, Y.; Grass, M. E.; Kuhn, J. N.; Tao, F.; Habas, S. E.; Huang,
W.; Yang, P.; Somorjai, G. A. J. Am. Chem. Soc. 2008, 130, 5868.
To achieve insight into the formation mechanism of
rhodium nanodendrites, the effects of SLS and NaF were
also studied. The products in the absence of SLS and NaF
are displayed in Figure 3a. It shows that the products

Article
Inorganic Chemistry, Vol. 49, No. 12, 2010 5517
Figure 2. Representative TEM and HRTEM (a, b, and d) images of Rh nanodendrites synthesized at 220 °C for 6 h, the high-angle annular dark field
(HAADF)-STEM image (c), and XRD profile of as-synthesized products (a, inset).
Figure 3. TEM images of Rh particles synthesized without SLS and NaF (a), and without NaF (b).
consist of monodispersed mixtures of polyhedrons with
an average diameter of 8.5 ( 0.3 nm such as cubes,
tetrahedra, decanedra, and so on. It indicates that PVP
plays the role of a reducing and stabilizing agent, while
SLS and NaF may assist the formation of the nano-
dendrites.1 The FTIR spectra taken from representative
rhodium dendrites, PVP, and SLS showed the PVP was
on the surface of rhodium particles (Figure S1, Support-
ing Information) while SLS was almost negligible. When
SLS was added into the reaction solution, the products
consisted of ill-defined particles with uncontrollable size
(Figure 3b). It is interesting that no products can be
obtained in the absence of SLS while the solution con-
tained NaF, PVP, and RhCl3. These results clearly imply
that the SLS and NaF can tune the nuclei and growth rate
of Rh crystals with a synergetic effect.
The products obtained by varying the reaction time
often contribute to an understanding of shape evolution.
The TEM and HRTEM images of Rh nanodendrites
obtained at different reaction times (from 1.5 to 24 h)
are shown in Figure 4. It shows that the Rh nanodendrites
have formed at 1.5 h (Figure 4a). However, the number of
branches of particle is relatively less than that obtained at
6 h. The branches of the majority particles are not beyond
10. And the distribution of particle sizes is not uniform,
being below 15.0 nm. Moreover, there are a lot of fine
rhodium grains with a size below 2.0 nm (Figure 4a inset,
in the white dashed circle). With an increase in reaction
time, the fine rhodium grains disappeared and the size of
rhodium dendrites became bigger and more uniform
(Figure 4b). When the reaction time increased to 12 and
24 h, the size and uniformity of rhodium dendrites was

5518 Inorganic Chemistry, Vol. 49, No. 12, 2010
Yuan et al.
Figure 4. TEM images of Rh nanodendrites synthesized at different time. (a) 1.5 h; (b) 3 h; (c) 12 h and (d) 24 h. the insets are the corresponding HRTEM
images. (e) The TEM images of intermediates of Rh nanodendrites at primary growth stage.
almost unchanged (Figure 4c and d). But the shape of
branch in the dendrites evolved from a rice shape with
sharp tips to spheres, owing to the minimization of the
total surface energy (Figure 4c and d, inset).
to overgrow or were attached and aggregated to branched
structures (dendrites), with the reaction proceeding until
the complete consumption of all rice-shaped and horned
particles. A similar formation mechanism was also sug-
gested for other noble metal branched structures such as
Pt and Ag.21,22
Rhodium Horned Particles, Cubes, and Network-
Shaped Wires. The other morphologies of the Rh nano-
structure can be produced by replacement of F- with an
equal molar quantity of other halogen anions (Cl-, Br-,
and I-). Figure 5a shows that the products are made of
predominant particles with sharp horns when the F- is
replaced by Cl-. However, the size distribution is rela-
tively broad, in the range of 3.0 to 11.0 nm. High-yield
nanocubes (>90% selectivity) were achieved by usage of
Br- (Figure 5b and Figure S2, Supporting Information).
Furthermore, the size distribution of Rh nanocubes is
very narrow; the average diameter is about 4.8 ( 0.3 nm.
The clear lattice fringes of a single particle were observed
(Figure 5b, inset). The distance between two lattice
The overgrowth and self-catalysis process are often
used to deduce the formation mechanism of branched
nanostructures.18,20 In our synthetic system, for under-
standing the formation mechanism of rhodium nano-
dedrites, the TEM images of primary growth stages
of rhodium nanodedrites were captured, including the
monomer, dimer, trimer, and tetramer (Figure 4 e), which
indirectly indicated that the formation of dendritic struc-
tures of rhodium particles underwent different stages. On
the basis of the above-mentioned results, we deduced the
possible formation mechanism of rhodium dendrites as
follows: In the first stages, the Rh3þ ions were reduced by
PVP at elevated temperature and nucleated to sub-2-nm
seeds (Figure 4a inset, in the white dashed circles). The
seeds grew and sprouted in random directions to form
rice-shaped or horned particles with a size of ∼5 nm or
grew by Ostwald ripening and/or overgrowth. Then,
maybe the rice-shaped and horned particles continued
(21) Wang, L.; Yamauchi, Y. J. Am. Chem. Soc. 2009, 131, 9152.
(22) Wang, Y. L.; Camargo, P. H. C.; Skrabalak, S. E.; Gu, H. C.; Xia,
Y. N. Langmuir 2008, 24, 12042.
(20) Teng, X.; Liang, X.; Maksimuk, S.; Yang, H. Small 2006, 2, 249.

Article
Inorganic Chemistry, Vol. 49, No. 12, 2010 5519
Figure 5. TEM and HRTEM images of other rhodium nanostructures synthesized in the presence of NaCl, NaBr, and NaI. (a) Horned particles, NaCl;
(b) cubes, NaBr; (c) and (d) network-shaped wires, NaI.
fringes is approximately 0.191 nm, which is consistent
with the interplane distance of the (200) of fcc rhodium.
The nanocubes have a strong tendency to self-assemble
into a one-dimension linear array because of their small
size and uniform shape. Interestingly, when I- was added
into the solution, the high-yield network-shaped wires
were obtained (Figure 5c and Figure S3, Supporting
Information). The networks were made of different sized,
closed, pearl-necklace-shaped loops. The lattice fringes
can be observed by HRTEM clearly (Figure 5d). The
distance of two lattice fringes is 0.220 nm, which corre-
sponds to the (111) lattice spacing of fcc rhodium. It
indicates that the wires were surrounded by {111} planes.
Figure 6. Representative TEM image of network-shaped wires. Note:
The shapes in white dashed circles stand for rice-, sphere-, and triangle-
shaped particles.
The average diameter of the wires is about 5.1 ( 0.3 nm.
Furthermore, the pore diameter distribution of networks
is very broad, in the range of several nanometers to nearly
100 nanometers (Figure 5c). It implies that networks were
wire direction is not uniform and there are broad and
formed by random anisotropy growth.
narrow portions in single wires.
Theoriented attachmentisa classicalformationmechan-
Effects of SLS and Halogen Anions. It is well-known
that the size and shape of crystals are mainly controlled by
ism suggested to explain the wire-structured formation.23,24
In our system, the formation mechanism of network-
thermodynamic and kinetic factors. The dendritic struc-
shaped wires is suggested by interface-defect and tip-con-
ture is one of the most complex structures synthesized by
nection attachment. The existence of interface defects and
the colloidal chemistry process thus far and was produced
narrower portions in networks reasonably supported this
mainly via kinetic control, because their anisotropic shapes
assumption (Figure 5d). Furthermore, we deduce another
make them possess larger surface areas, which is meta-
factor for the formation of network instead of single wire
stable and energetically unfavorable for thermodynamic
structures is the presence of a variety of Rh intermediate
control. The sphere particles are often formed by thermo-
particles such as rice-, sphere- and triangle-shaped ones
dynamic control processes in colloidal chemistry. For
(Figure 6). This is the reason why the diameter along the
obtaining a variety of nonspherical crystal morphologies,
inorganic/organic additives were often introduced into
the synthesis process to tune the crystal growth through
kinetic control. Studies have shown that additives such
(23) Xu, X.; Zhuang, J.; Wang, X. J. Am. Chem. Soc. 2008, 130, 12527.
(24) Cho, K.; Talapin, D. V.; Gaschler, W.; Murray, C. B. J. Am. Chem.
Soc. 2005, 127, 7140.

5520 Inorganic Chemistry, Vol. 49, No. 12, 2010
Yuan et al.
Figure 7. TEM images of rhodium particles synthesized in the absence of SLS. (a) NaCl, (b) NaBr, and (c) NaI.
Figure 8. Representative TEM images of Rh nanoparticles synthesized at 220 °C for 6 h by varying the mole ratio of SLS and NaF. (a) SLS/NaF = 4:1
(i.e., SLS, 578 mg; NaF, 21 mg); (b) SLS/NaF = 1:1 (i.e., SLS, 289 mg; NaF, 42 mg).
as Fe3þ 25
,
Agþ,26 Cu2þ 27
,
Cl-,28 Br-,29 I-,30 CTAB,31
In order to further understand the effects of SLS and
halogen anions on the morphology of rhodium particles,
we took complex rhodium dendrites as an example by
varying the molar ratio of SLS and F-. Figure 8a showed
that the morphology of rhodium dendrites did not change
while increasing the quantity of SLS, but the size distribu-
tion was not uniform. However, when the quantity of NaF
was decreased, the rhodium dendrites sharply decreased
(Figure 8b). The products consisted of predominant irre-
gular particles and a small number of dendrites. And the
quantity of branches also sharply decreased. These indicate
that the SLS had a predominant effect on rhodium den-
drites and also showed that the uniform rhodium dendrites
were formed by the synergetic effect of an appropriate ratio
of SLS and NaF.
Electrochemical Test toward Ethanol Oxidation. In
order to investigate shape-dependent catalytic properties
of Rh particles, the typical horn-, cube-, and dendrite-
shaped particles were chosen to study their electrocata-
lytic performances on ethanol oxidation. The electrodes
were immersed in a nitrogen-saturated 0.1 M HClO4
solution, and the potential was scanned from -0.28 to
1.0 V (vs SCE) at a scan rate 50 mV/s to obtain the cyclic
voltammograms (CVs; Figure 9a). The hydrogen desorp-
tion/adsorption electric charges calculated from CVs
were used to estimate the electrochemically active surface
area (ECSA) of catalysts.35 The ECSAs of Rh cubes,
horned particles, and nanodendrites are 0.78, 0.95, and
1.44 cm2, respectively. The hydrogen desorption/adsorp-
tion peaks locate at different positions owing to the diff-
erences of surface atom arrangements originating from a
variety of morphologies (Figure 9a). The electrocatalytic
and ligands32-34 played very important roles in controlling
the particle morphology in different synthesis systems. In
our present system, it is proposed that the electronegativity
and ionic radii of different halogen anions (F-, Cl-, Br-,
and I-) should play the most important role in these
processes, which would affect the coordination strength/
number of rhodium and halogen. Maybe these factors
integrate to control the reduction, nuclei, and growth rate
of Rh crystals. Furthermore, the effect of SLS is also
important in obtaining rhodium crystals with highly selec-
tive morphologies. To verify the effect of SLS or halogen
anions, the control experiments were investigated in the
absence of SLS or halogen anions. As is mentioned above,
without halogens, the products consist of ill-defined par-
ticles with uncontrollable size (Figure 3b). And without
SLS, no Rh crystal products can be obtained in the
presence of RhCl3, PVP, and NaF. The size and shape
distributions of Rh particles were varied with only the
usage of NaCl, NaBr, and NaI (Figure 7). It indirectly
proved that SLS would also affect Rh crystal morphology.
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Article
Inorganic Chemistry, Vol. 49, No. 12, 2010 5521
Figure 9. Cyclic voltammetric curves (CVs) of Rh cubes (the black), horned particles (the red), and nanodendrites (the blue). (a) In a 0.1 M HClO4
solution. (b) In a 0.1 M ethanol þ 0.1 M HClO4 solution.
activities of catalysts were investigated in the 0.1 M
ethanol þ 0.1 M HClO4 solution at room temperature
(25 °C). The current densities (j) were 0.018, 0.022, and
0.035 mA cm-2, which correspond to the cube-, horn-,
and dendrite-shaped particles, respectively (Figure 9b). It
displayed a shape-dependent catalytic performance, and
the catalytic activity enhanced in the order of cube, horn,
and dendrite shapes. Among these particles, the Rh
nanodentrites have the maximum catalytic activity, which
is about 2 times that of nanocubes. It may be ascribed
to their maximum ECSA. The enhanced catalytic proper-
ties of dendrite-shaped particles were achieved by other
research groups.36,37
Br-, I-) in an environmentally benign solvent, water, using a
one-pot method. In particular, the rhodium nanodendrites
and networks were synthesized for the first time. The effects
of SLS and halogen anions on rhodium crystal morphology
were investigated, and the formation mechanism of rhodium
nanostructures is also suggested. This study has demon-
strated the successful tuning of the crystal morphology just
through utilizing different halogen anions while maintaining
other syntheticconditions. The results of electrocatalytic tests
toward ethanol oxidation have shown that the Rh nanopar-
ticles displayed shape-dependent properties, and the nano-
dendrites have the maximum catalytic activity.
Acknowledgment. This work was supported by NSFC
(20725102, 20933004 and 20921001), the Fok Ying Tung
Education Foundation (111012), Natural Science Foun-
dation of Guizhou Province (20072013), and the State
Key Project of Fundamental Research for Nanoscience
and Nanotechnology (2006CB932301).
Conclusions
In summary, the highly selective syntheses of Rh nano-
crystals with different morphologies such as horned particles,
cubes, dendrites, and networks have been achieved through
the synergetic effect of SLS and halogen anions (F-, Cl-,
Supporting Information Available: FTIR spectra and large-
area TEM images of Rh nanocubes and networks. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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