Rational synthesis of Pt spheres with hollow interior and nanosponge shell using silica particles as template

Article abstract of DOI:10.1039/c0cc05233g

Here we report a facile and efficient method to prepare Pt spheres with hollow interior and nanosponge shell with high surface area. Such a unique Pt nanostructure can effectively improve the electrocatalytic performance of Pt catalysts by facilitating the access of electroactive species to the full-extent Pt surface. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0cc05233g

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COMMUNICATION
Rational synthesis of Pt spheres with hollow interior and nanosponge
shell using silica particles as templatew
Hamed Ataee-Esfahani,ab Yoshihiro Nemoto,a Liang Wang*a and Yusuke Yamauchi*abc
Received 28th November 2010, Accepted 3rd February 2011
DOI: 10.1039/c0cc05233g
Here we report a facile and efficient method to prepare Pt spheres
with hollow interior and nanosponge shell with high surface area.
Such a unique Pt nanostructure can effectively improve the electro-
catalytic performance of Pt catalysts by facilitating the access of
electroactive species to the full-extent Pt surface.
which is noneconomic for practical scale up. Furthermore, in the
previous works, the Pt shell thicknesses were not precisely
controlled.13–22 The most disadvantageous point in the previous
works is that the Pt shell of the hollow structures has no well-
developed nanoporosity. Therefore, guest species from outside
are not allowed to get access to inner parts of the hollow
structures, resulting decreasing the effective Pt surfaces. Hence,
the development of a facile and economic method for synthesis of
Pt spheres with hollow interior and nanosponge shell with very
high surface area is a practical and challenging issue to be solved
urgently.
In the last decades, a great deal of attention has been paid to
nano- and/or meso-structured materials with highly porous
networks and high surface area due to their impressive industrial
applications involving electrochemical catalysts, inclusion vessels,
and adsorbents. Up to now, a wide range of compositions such
as silica, carbon, inorganic–organic hybrids, polymers, and
metals, have been successfully prepared by various methods.1,2
Recently, a great deal of effort has been devoted to the synthesis
of metal-based nanostructures with high surface areas, because of
their unique electrocatalytic properties.3 In particular, Pt-based
nanostructured materials have currently attracted widespread
interest, because of their potential application as a catalyst in
PEM fuel cells. Both soft- and hard-templates have been
commonly employed for the synthesis of nanostructured Pt
materials. In hard-templating method, well ordered mesoporous
silica has been generally used as rigid templates.4–8 Alternatively,
soft-templates, such as surfactants, also can be used for the
forming nanopores structures.9,10 For instance, well-ordered
mesoporous Pt can be easily prepared by chemical or electro-
chemical reduction of dissolved Pt salts in lyotropic liquid
crystals made of highly concentrated surfactants.9–12
In this communication, we newly propose a facile and efficient
method to prepare Pt spheres with hollow interior and nano-
sponge shell with high surface. Silica particles functionalized with
amino group (with around 100 nm in diameter) are used as
template to form the hollow interior, while nonionic surfactant
assist to create the Pt nanosponge shell.23,24
To prepare the Pt spheres with hollow interior and nanosponge
shell, silica nanoparticles modified with amino group were
ultrasonically dispersed in K2PtCl4 solution containing Pluronic
F127. The used amounts of 20 mM K2PtCl4 solution were varied
from 0.0 ml to 10 ml, while the amounts of the added silica
particles were fixed to 6.0 mg. Then, 0.1 M ascorbic acid (AA)
was added, and the mixture was sonicated for 15 min. After
washing three times with water, the product was added to 10 wt%
hydrofluoric acid solution and placed for 3 days at room
temperature in order to completely remove silica template. The
final product was washed five times with water and dried at 45 1C.
Fig. 1 shows transmission electron microscopy (TEM) images
of the hollow Pt spheres prepared under a typical solution with
7.5 ml Pt solution. The lower magnification image (Fig. 1a)
revealed that the resulting Pt dendritic structure was assembled
with plentiful interconnected nanowires with 2 nm in diameter.
The Pt hollow particles were uniform in morphology without
formation of by-products, demonstrating the high yield synthesis
(Fig. S1a, bw). As shown in Fig. 1b, lattice fringes with a
d spacing of 0.23 nm were clearly observed, which corresponded
to a h111i plane of Pt face-centered cubic (fcc) structure.
In the present synthetic process, NH2-modified silica particles
were well dispersed in Pt precursor solution containing
surfactants. Then, by addition of AA to the solution, the Pt
deposition was occurred. At the early stages of the reaction, the
Pt seeds were formed on the silica particle surface, because of
the high surface affinity for the Pt seeds which is derived from the
To realize high Pt surface areas, there have been some reports
on Pt hollow nanostructures, which have superior electro-
chemical properties.13–16 So far, the Pt hollow nanostructures
have been successfully synthesized by coating Pt on various
spherical templates such as silica,13,17 Co,16,18 Ag19–21 and other
materials.14,22 However, in all of these cases, complex procedures
and the use of expensive materials as templates are employed,
a World Premier International (WPI) Research Center for Materials
Nanoarchitectonics (MANA), National Institute for Materials
Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
E-mail: Wang.Liang@nims.go.jp, Yamauchi.Yusuke@nims.go.jp
b Faculty of Science and Engineering, Waseda University,
3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
c Precursory Research for Embryonic Science and Technology
(PRESTO), Japan Science and Technology Agency (JST),
4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c0cc05233g
c
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It is noteworthy that in a small amount of Pt solution (2.5 ml),
the hollow structures were mechanically unstable (Fig. 2a),
because the spherical hollow nanostructures collapsed after the
silica removal by HF treatment. When the amount of Pt solution
was not enough, individual entities could not be joined well
(Fig. S3bw) and the hollow structures were destroyed easily. As
shown in TEM images (Fig. 2a and b), the hollow structures
prepared from 5.0 ml Pt solution collapsed partially. In contrast,
when the amounts of Pt solution were increased up to 10 ml,
irregular Pt dendrites without inner hollows were formed as a
by-product (Fig. 2d). The isolated Pt seeds nucleated, resulting in
Pt dendrites independently grew. The optimum amount of Pt
solution was found to be 7.5 ml. Under the optimized condition,
after immobilization of Pt seeds on silica particles, Pt nanowires
grew and branched out in various directions. Also, with
the assistance of surfactants,23,24 nanosponge shells consisting
of interconnected highly branched nanowires were uniformly
coated on the silica particle surface without by-products. Even
after removing silica and applying the centrifugation and
sonication processes, the hollow structures did not collapse,
showing very manically stable robust hollows (not shown).
As preliminary investigation on electrocatalytic activity
of the obtained hollow Pt spheres with different shell
thicknesses, methanol oxidation was measured by using cyclic
voltammograms (CVs) method (The details of electrochemical
measurements were given in ESI.w). Fig. 4 shows mass-
normalized activities. The Pt hollow particles with the lowest
shell thicknesses (prepared with 2.5 ml Pt solution) exhibited the
lowest catalytic activity. It can be supposed that access of
methanol molecules to inner parts of electrode was restricted,
because the inner void spaces of the original hollow structures
Fig.
1 (a) Low-magnification and (b) high-magnification TEM
images of hollow Pt spheres under a typical solution with 7.5 ml Pt
solution.
strong interaction between the amino group and the metal
particles.25 During the progress of the Pt deposition, the primary
Pt seeds covering on the silica particles served as the nucleation
sites for the further growth of Pt. At this stage, Pluronic F127
chains as a structure directing agent were absorbed on the surface
of deposited Pt to facilitate the growth of the dendritic Pt
shells.23,24 To elucidate the effect of amino modification on the
silica surface, further investigation was performed in which silica
particles without amino group were used as template (Fig. S1c).
It was clearly revealed that the amino groups on the silica surface
played an important key role for making attachment sites for
initial Pt seeds and then acted as nucleation sites for the
subsequent Pt growth, whereas non-functioned silica template
could not act as template for the formation of hollow Pt spheres
and led to the separation of silica particles and Pt dendrites
(Fig. S1cw).
The SEM images clearly confirmed the three-dimensional (3D)
globular shape and also clearly verified the empty spaces of
highly branched nanowires (Fig. S1a, bw). In the dendritic Pt
shells, lots of Pt nanowires were highly branched and extended
in various directions, to form an interconnected nanosponge
structure. In such a nanoporous structure, accessibility to inner
parts of Pt hollows will be improved by the diffusion of guest
species through empty spaces among interconnected nanowires.
N2 adsorption-desorption isotherm of the obtained Pt spheres
gave a BET surface area of 36.3 m2 gꢀ1 (Fig. S2w), which is
higher than the reported value (29.0 m2 ꢀ1) for hollow Pt
g
spheres prepared by photocatalytic reduction of Pt complex
under light illumination.13 For comparison, surface areas of
commercial platinum catalysts (Pt black) ranges from 20 to
25 m2 gꢀ1. The improved surface area was most likely derived
from the presence of nanoporous dendritic shells.
Furthermore, in our method, the Pt shell thicknesses could
be precisely tuned simply by varying the amounts of Pt
precursor. To investigate the effect of Pt amounts on the shell
thicknesses, several hollow Pt spheres were synthesized with
various amounts of Pt precursor solution in the range between
0.0 ml to 10 ml (The amounts of the added silica particles were
fixed to 6.0 mg. See the details in ESI.w). TEM images of
hollow Pt spheres before and after the silica removal were
shown in Fig. 2 and S3,w respectively. The average shell
thicknesses were measured by TEM images (Fig. 3). The
average shell thicknesses were proportionally increased with
increasing the Pt amounts.
Fig. 2 TEM images of hollow Pt spheres after silica removal. Various
hollow Pt spheres were prepared from precursor solutions containing
different Pt amounts. The amounts of added Pt solution are (a) 2.5 ml,
(b) 5.0 ml, (c) 7.5 ml, and (d) 10 ml, respectively. The collapse of the
hollow structures is indicated by while arrows, while the isolated Pt
dendrite (as by-product) is indicated by white arrows.
c
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inorganic core-shell26,27 and hollow materials28–34 in material
research fields. However, their compositions have been very
limited to polymers, silica, carbon, and metal oxides.26–34
This synthetic concept can open a new avenue to create
nanostructured metals.
Notes and references
1 Y. Wan and D. Zhao, Chem. Rev., 2007, 107, 2821.
2 A. H. Lu and F. Schuth, Adv. Mater., 2006, 18, 1793.
¨
3 Y. Yamauchi and K. Kuroda, Chem.–Asian J., 2008, 3, 664.
4 Z. Liu, Y. Sakamoto, T. Ohsuna, K. Hiraga, O. Terasaki, C. H. Ko,
H. J. Shin and R. Ryoo, Angew. Chem. Int. Ed., 2000, 39,
3107.
5 A. Takai, Y. Doi, Y. Yamauchi and K. Kuroda, J. Phys. Chem. C,
2010, 114, 7586.
6 H. J. Shin, C. H. Ko and R. Ryoo, J. Mater. Chem., 2001, 11, 260.
7 H. J. Shin, R. Ryoo, Z. Liu and O. Terasaki, J. Am. Chem. Soc.,
2001, 123, 1246.
Fig. 3 Relationship between the average Pt shell thicknesses and the
added amounts of Pt solutions. The amounts of added Pt solution in
the starting solutions are noted in parentheses.
8 Y. Doi, A. Takai, Y. Sakamoto, O. Terasaki, Y. Yamauchi and
K. Kuroda, Chem. Commun., 2010, 46, 6365.
9 G. S. Attard, C. G. Goltner, J. M. Corker, S. Henke and
R. H. Templer, Angew. Chem., 1997, 109, 1372.
collapsed and the Pt particles were highly aggregated (Fig. 2a).
With increasing the amounts of the Pt solution to 7.5 ml,
electrocatalytic activity for methanol oxidation reaction was
dramatically increased. The maximum electrocatalytic activity
(80 mA mgꢀ1) was around 1.7 times larger than that of
commercially available Pt black. By improvement of mechanical
stability of hollow structures, electroactive species could easily
gain access to the whole surface of Pt through the hollow spaces.
However, with the further increase of Pt amounts to 10 ml, the
catalytic activity was decreased. As shown in TEM results
(Fig. 2d), the formation of the undesired by-products and thicker
shells prevented accessibility of methanol molecules to all the
exposed Pt surfaces. In other words, all of the exposed Pt surface
could not effectively act as reaction media.
10 G. S. Attard, P. N. Bartlett, N. R. B. Coleman, J. M. Elliott,
J. R. Owen and J. H. Wang, Science, 1997, 278, 838.
11 Y. Yamauchi, A. Sugiyama, R. Morimoto, A. Takai and
K. Kuroda, Angew. Chem., Int. Ed., 2008, 47, 5371.
12 Y. Yamauchi, T. Yokoshima, H. Mukaibo, M. Tezuka,
T. Shigeno, T. Momma, T. Osaka and K. Kuroda, Chem. Lett.,
2004, 33, 542.
13 H. Wang, Y. Song, Z. Wang, C. J. Medforth, J. E. Miller,
L. Evans, P. Li and J. A. Shelnutt, Chem. Mater., 2008, 20, 7434.
14 Y. Song, R. M. Garcia, R. M. Dorin, H. Wang, Y. Qiu and
J. A. Shelnutt, Angew. Chem., Int. Ed., 2006, 45, 8126.
15 G. Lee, S. I. Choi, Y. H. Lee and J. T. Park, Bull. Korean Chem.
Soc., 2009, 30, 1135.
16 H. P. Liang, H. M. Zhang, J. S. Hu, Y. G. Guo, L. J. Wan and
C. L. Bai, Angew. Chem., Int. Ed., 2004, 43, 1540.
17 L. Lu, R. Capek, A. Kornowski, N. Gaponik and A. Eychmuller,
Angew. Chem., Int. Ed., 2005, 44, 5997.
18 J. Zhao, W. Chen, Y. Zheng and X. Li, J. Power Sources, 2006,
162, 168.
In conclusion, we developed a facile method to synthesize
hollow Pt spheres with tunable nanosponge shell thicknesses
by using silica particles as templates. The obtained hollows
possessed highly nanoporous structure, providing high surface
area. Such a unique Pt nanostructure effectively improved the
electrocatalytic performance as Pt catalysts by facilitating the
access of electroactive species to the whole Pt surface.
Currently, a great deal of attention has been attracted to the
19 S. Guo, S. Dong and E. Wang, Chem.–Eur. J., 2008, 14, 4689.
20 J. Yang, J. Y. Lee, H. P. Too and S. Valiyaveettil, J. Phys. Chem. B,
2006, 110, 125.
21 H. M. Chen, R. S. Liu, M. Y. Lo, S. C. Chang, L. D. Tsai,
Y. M. Peng and J. F. Lee, J. Phys. Chem. C, 2008, 112, 7522.
22 H. Wang, Y. Song, C. J. Medforth and J. A. Shelnutt, J. Am.
Chem. Soc., 2006, 128, 9284.
23 L. Wang and Y. Yamauchi, J. Am. Chem. Soc., 2009, 131, 9152.
24 (a) H. Ataee-Esfahani, L. Wang and Y. Yamauch, Chem.
Commun., 2010, 46, 3684; (b) H. Ataee-Esfahani, L. Wang,
Y. Nemoto and Y. Yamauchi, Chem. Mater., 2010, 22, 6310.
25 T. Pham, J. B. Jackson, N. J. Halas and T. R. Lee, Langmuir, 2002,
18, 4915.
26 Y. Deng, Y. Cai, Z. Sun, J. Liu, C. Liu, J. Wei, W. Li, C. Liu,
Y. Wang and D. Zhao, J. Am. Chem. Soc., 2010, 132, 8466.
27 Y. Deng, D. Qi, C. Deng, X. Zhang and D. Zhao, J. Am. Chem.
Soc., 2008, 130, 28.
28 J. Fu, Q. Xu, J. Chen, Z. Chen, X. Huang and X. Tang, Chem.
Commun., 2010, 46, 6563.
29 S. A. Dergunov, K. Kesterson, W. Li, Z. Wang and E. Pinkhassik,
Macromolecules, 2010, 43, 7785.
30 Y. Wang, C. Tang, Q. Deng, C. Liang, D. H. L. Ng, F. L. Kwong,
H. Wang, W. Cai, L. Zhang and G. Wang, Langmuir, 2010, 26, 14830.
31 M. Feyen, C. Weidenthaler, A. H. Lu and F. Schuth, J. Am. Chem.
¨
Soc., 2010, 132, 6791.
32 A. H. Lu, W. C. Li, G. P. Hao, B. Spliethoff, H. J. Bongard,
B. B. Schaack and F. Schuth, Angew. Chem. Int. Ed., 2010, 49,
¨
Fig.
4 Cyclic voltammograms displaying oxidation reaction of
1615.
33 P. M. Arnal, M. Comotti and F. Schuth, Angew. Chem., Int. Ed.,
methanol, catalyzed by hollow Pt particles prepared from (a) 2.5 ml,
(b) 5.0 ml, (c) 7.5 ml, (d) 10 ml Pt solution, respectively. For
comparison, (e) commercially available Pt black powders are also
measured.
¨
2006, 45, 8224.
34 F. Zhang, G. B. Braun, Y. Shi, Y. Zhang, X. Sun, N. O. Reich,
D. Zhao and G. Stucky, J. Am. Chem. Soc., 2010, 132, 2850.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 3885–3887 3887