Direct deposition of nanostructured Pt particles onto a Ni foam from lyotropic liquid crystalline phase by displacement plating

Article abstract of DOI:10.1016/j.electacta.2007.07.036

Nanostructured Pt particles are directly deposited onto a Ni foam by utilizing displacement plating after a lyotropic liquid crystalline phase including Pt species was prepared within macropores of the Ni foam. The EDS mapping of Pt after deposition corresponds to the macroscopic framework of the Ni foam, indicating the uniform displacement plating of Pt on the surface of the Ni foam. The Pt particles of 150-250 nm in size are formed over the entire area of the surface of the Ni foam. The TEM images prove that the nanoscale rods (width: about 3 nm) are aggregated with each other to form nanoscale porosity. The active area of Pt can be estimated to be ca. 12 m²/g by using the cyclic voltammogram in sulfuric acid. Our method realizes one-step production of hierarchical macro-meso type porous electrodes.

Full text of DOI:10.1016/j.electacta.2007.07.036

Electrochimica Acta 53 (2007) 604–609
Direct deposition of nanostructured Pt particles onto a Ni foam from
lyotropic liquid crystalline phase by displacement plating
a,b
c
c
c
c
Yusuke Yamauchi , Masaki Komatsu , Azusa Takai , Ryusuke Sebata , Makoto Sawada ,
c
b
b,c,∗,1
b,c,d,∗
Toshiyuki Momma , Minekazu Fuziwara , Tetsuya Osaka
, Kazuyuki Kuroda
a
International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan
Kagami Memorial Laboratory for Materials Science & Technology, Waseda University, Nishi-waseda 2-8-26, Shinjuku-ku, Tokyo 169-0051, Japan
Department of Applied Chemistry and Majors in Applied Chemistry and Nanoscience & Nanoengineering, Faculty of Science & Engineering,
b
c
Waseda University, Ohkubo 3-4-1, Shinjuku-ku, Tokyo 169-8555, Japan
CREST, Japan Science & Technology Agency (JST), Honcho 4-1-8, Kawaguchi-shi, Saitama 332-0012, Japan
d
Received 5 April 2007; received in revised form 3 July 2007; accepted 11 July 2007
Available online 25 July 2007
Abstract
Nanostructured Pt particles are directly deposited onto a Ni foam by utilizing displacement plating after a lyotropic liquid crystalline phase
including Pt species was prepared within macropores of the Ni foam. The EDS mapping of Pt after deposition corresponds to the macroscopic
framework of the Ni foam, indicating the uniform displacement plating of Pt on the surface of the Ni foam. The Pt particles of 150–250 nm in size
are formed over the entire area of the surface of the Ni foam. The TEM images prove that the nanoscale rods (width: about 3 nm) are aggregated
2
with each other to form nanoscale porosity. The active area of Pt can be estimated to be ca. 12 m /g by using the cyclic voltammogram in sulfuric
acid. Our method realizes one-step production of hierarchical macro–meso type porous electrodes.
©
2007 Elsevier Ltd. All rights reserved.
Keywords: Nanostructured metal; Electrocatalyst; Displacement plating; Ni foam; Platinum
1
. Introduction
because it allows to provide a high rate of mass transport and to
enhance reactive surface area.
The synthesis of metal-based nanoarchitectured materials
e.g. nanosheets, nanoparticles, nanorods, and nanowires) is
Attard et al. reported the preparation of mesoporous metals
from lyotropic liquid crystals (LLC) made of highly concen-
trated surfactants for the first time [29]. Since then, the LLC
templating has been recognized as one of the synthetic routes of
metal-based nanomaterials. To date, not only mesoporous metals
[29–46] but also several nanosheets and nanoparticles [19–23]
have been prepared by using this route. This LLC templating
method can be readily applied to a wide range of metals which
are generally known to be deposited by using electrochemical
processes.
In this study, we report one-pot synthesis of three-
dimensional (3D) electrode materials by the modified LLC
templating [47–50] through solvent evaporation. After the LLC
was formed within macropores of a Ni foam through the solvent
evaporation, nanostructured Pt particles were directly deposited
onto the Ni foam by utilizing displacement plating between the
foam and a Pt complex. The Ni foam is used as a scaffold on
which nanostructured Pt particles are grown. In a previous report
(
currently an active research field due to their potential appli-
cations in very wide areas such as electrochemistry, electronics,
magnetics, optics, photonics, and catalysis [1–23]. In particular,
nanostructured Pt-based materials have greatly attracted inter-
ests as catalysts in various chemical reactions (e.g. methanol
oxidation and oxygen reduction reactions in direct methanol fuel
cell and hydrogen fuel cell), because of their superior properties
in the adsorption and desorption of oxygen, hydrogen, and other
molecules [24–28]. For applications such as metal catalysts and
electrode materials, hierarchical open porosity is very desirable
∗
Corresponding authors. Tel.: +81 3 5286 3199; fax: +81 3 5286 3199.
E-mail addresses: osakatet@waseda.jp (T. Osaka), kuroda@waseda.jp
K. Kuroda).
ISE fellow.
(
1
0
013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2007.07.036

Y. Yamauchi et al. / Electrochimica Acta 53 (2007) 604–609
605
by Campbell and Bakker, a mesoporous Ni layer was deposited
onto a Ni foam electrode by using general liquid crystal tem-
plating [51]. However, the structural characterization of the
deposited mesoporous Ni was not satisfactorily described [51].
It is questionable whether the mesoporous Ni was uniformly
formed inside the Ni foam, because general LLC templating
mixtures are too difficult to be fully infiltrated into macropores
of the Ni foam due to their very high viscosities. Our process
utilizing solvent evaporation can allow the formation of LLC
templating mixtures from a diluted surfactant solution with very
low viscosity [47–50]. It becomes possible to uniformly form
the LLC templating mixtures even inside the Ni foam. Our novel
convenient pathway reported here should be very important for
the rapid production of a functional 3D electrode.
dent of the amount of ethanol [47–50]. Because the formation
of the LLC templating mixture is almost instantaneous, the Pt
deposition started from the Ni surface due to a galvanic reaction
between Ni and Pt complex (Scheme 1, stage d). The deposition
was carried out in a closed container at room temperature for
12 h, and then the resulting material was soaked in water and
subsequently in ethanol to remove the surfactants.
2.3. Characterization
Conventional θ-2θ scanning XRD profiles in the lower
diffraction angles were measured by a Mac Science M03XHF22
diffractometer with Mn-filtered Fe K␣ radiation (40 kV, 20 mA)
◦
at a scanning rate of 0.5 /min. The in-plane XRD profile was
measured by a Rigaku ATX-G diffractometer (50 kV, 300 mA)
◦
at a scanning rate of 0.5 /min. The cross-sectional FE-SEM and
2
. Experimental
EDS mapping images were obtained by a JEOL JSM-6500F
scanning electron microscope with an accelerating voltage
of 15 kV. HR-SEM images without any metal coating were
observed with a Hitachi S-5500 scanning electron microscope
using an accelerating voltage of 20 kV. TEM images were
obtained by a JEOL TEM JEM-2010 transmission electron
microscope with an accelerating voltage of 200 kV. For prepa-
ration of the TEM sample, the Ni foam was firstly dissolved
in dil. HCl (1 M). Then, nanostructured Pt particles were dis-
persed in ethanol by ultrasound and mounted on a carbon-coated
microgrid.
2
.1. Materials
Non-ionic surfactant (C H33(OCH2CH2)8OH, C EO8,
16
16
Fluka) was used to form lyotropic liquid crystals. Platinum (IV)
chloride hexahydrate (H2PtCl ·6H2O >98.5%, Kanto Kagaku
6
Co.) was used as a Pt source. Ethanol (H2O content <0.05%,
Wako Chemical Co.) was used for both dilution of precursors
and for removal of templates. Nickel foam used in this study is
8
0 ppi (pores per inch).
2
.2. Deposition of nanostructured Pt onto a Ni foam
3. Results and discussion
Our experimental procedure is illustrated in Scheme 1. Ini-
tially, a precursor solution was prepared by adding 0.059 g
Firstly, we made an LLC film containing Pt species on a
flat glass substrate through the same experimental procedure in
order to investigate which kind of LLC mesophases (e.g. L␣:
lamellar phase, HI: hexagonal phase, VI: cubic phase) is con-
structed within the Ni foam after the solvent evaporation. A
precursor solution was cast onto a flat substrate, and immedi-
ately dried by air spray. The transparent LLC film was obtained
(Fig. 1a, inset). The low angle XRD pattern (Fig. 1a) of the
LLC film on the glass substrate shows two intense diffraction
peaks (d10 = 4.6 nm, d20 = 2.3 nm) which can be assigned to be
(1 0) and (2 0) in a 2D-hexagonal (p6mm) symmetry (with a
lattice parameter a of 5.3 nm). The absence of the (1 1) peak
indicates that the formed LLC phase has some domains in which
the rod-like self-assemblies are parallel to the substrate surface
H2PtCl ·6H2O, 0.059 g deionized water, 0.12 g non-ionic sur-
6
factant C EO8, and 2.8 ml ethanol. The precursor solution was
16
dropped onto the Ni foam (1.5 cm × 7 cm × 0.5 cm) (Scheme 1,
stages a and b). An excess of precursor solution within the Ni
foam was removed by air spray (AD-152LN, Elecom Co.) and
ethanol was simultaneously evaporated to uniformly fill the LLC
templating mixture into the Ni foam. (Scheme 1, stage c). In the
present system, the progressive increase of surfactant concen-
tration through the preferential evaporation of ethanol drives the
self-organization of the Pt solution and surfactants. Such LLC
mesophases can be roughly predicted by a phase diagram [52]
of ternary compositions (surfactant/water/Pt species) indepen-
Scheme 1. Experimental procedure for direct deposition of nanostructured Pt particles onto a Ni foam by utilizing displacement plating.

6
06
Y. Yamauchi et al. / Electrochimica Acta 53 (2007) 604–609
Fig. 1. (a) Out-of-plane and in-plane XRD patterns for the as-prepared LLC film on the glass substrate. The inset image is the photograph of the as-prepared LLC
film. (b) Out-of-plane XRD patterns for both as-prepared LLC film and LLC film after 24 h.
and that the (1 0) face is aligned parallel to the substrate [53].
We investigated further the detailed microstructure of the
deposited Pt particles by TEM (Fig. 4). The highly magnified
image proves that the nanoscale rods (width: ca. 3 nm) are aggre-
gated with each other to form nanoscale porosity (Fig. 4a). The
selected-ED taken from the area in the 100 nm range shows the
ring patterns assigned to the fcc structure (Fig. 4a, inset), indicat-
ing the random orientation of fcc crystalline domains (Fig. 4b).
Though the deposited Pt has good crystallinity, the domain size
of the single atomic-crystallinity is measured to be 10–20 nm
from the dark field images (Fig. 5). The lattice fringes coherently
run across over the nanoporous structures to some extent.
In order to characterize the surface of obtained nanostruc-
tured Pt, the electrochemical method was applied for proving the
catalytically active surface area instead of the physical surface
area evaluated by the BET method of N2 adsorption (Fig. 6).
For the measurement of cyclic voltammogram in an aqueous
0.5 M H2SO4 solution, the Ni foam was completely dissolved
in HCl (1 M) solution (We confirm complete dissolution of the
Ni foam by EDS analysis. Also, the ED patterns (Fig. 4a, inset)
indicate the presence of platinum with the fcc structure only.).
The in-plane diffraction pattern (Fig. 1a) shows an intense peak
◦
(
2θχ = 1.6 , d = 5.5 nm). The in-plane peak can be assigned to be
(
0 1) or (1 1) on a 2D-hexagonal symmetry (Fig. 1a), which has
already been discussed in the in-plane X-ray diffraction studies
on mesoporous silica films [54–55]. From the above results, it
is proved that the 2D-hexagonal (p6mm) phase is mainly con-
structedontheglasssubstrate. Therefore, theLLCformedwithin
the Ni foam should also be the same 2D-hexagonal (p6mm)
structure.
Moreover, thestabilityoftheLLCphasecontainingPtspecies
was also investigated by the time-dependent XRD patterns
(Fig. 1b). The LLC film formed on the glass substrate was set
inside a closed container. Even after 24 h, the XRD pattern of the
LLC phase did not change at all, meaning that water molecules
tend not to evaporate once the LLC phase is formed. In other
words, water molecules could be stabilized in the hydrophilic
domains of the LLC phase. However, the LLC phase was com-
pletely collapsed when the glass substrate was put outside the
closed container. Water molecules play an important role for the
retention of the structure of the LLC phase [56–59]. Therefore,
the closed container was used in the experiment to prevent the
evaporation of water molecules during the Pt deposition.
After the Pt deposition (12 h), the color of the Ni foam
changed to black, indicating the progress of displacement plat-
ing (Fig. 2). The resultant material after the removal of templates
was observed by FE-SEM, EDS mapping and HR-SEM. Fig. 3a
shows the EDS mapping of the Ni foam after the Pt deposi-
tion. The EDS mapping of Pt after deposition corresponds to the
macroscopic framework of the Ni foam, indicating the uniform
displacement plating of Pt on the surface of the Ni foam. From
the low-magnified SEM image (Fig. 3b-1–b-3), deposition of Pt
particles of 150–250 nm in size can be confirmed over the entire
area. The thickness of the deposited Pt layer is measured to be
from 800 to 1500 nm (not shown). A highly magnified SEM
image proves that sponge-like structures ascribed to the LLC
phase can be observed on the outer surface of the Pt particles
Fig. 2. Photograph of Ni foams before (upper side) and after (bottom side) the
nanostructured Pt deposition.
(Fig. 3b-4).

Y. Yamauchi et al. / Electrochimica Acta 53 (2007) 604–609
607
Fig. 3. (a-1) Cross-sectional FE-SEM image and (a-2) EDS mapping of the Ni foam after Pt deposition. EDS mapping images are elemental distributions of both Ni
and Pt. Scale bar is 300 ␮m. (b-1–b-3) FE-SEM and (b-4) HR-SEM images of the surface of the Ni foam after Pt deposition. (b-2) and (b-3) are highly magnified
images of square areas in images (b-1) and (b-2), respectively.
Then, nanostructured Pt particles were precipitated. Note that
the macrostructure corresponding to the original Ni foam col-
lapsed. Coating of a thicker LLC film or repeated coatings may
prevent the collapse. The obtained nanostructured Pt particles
were dispersed in ethanol by ultrasound and mounted on a Au
substrate. The cyclic voltammogram of the nanostructured Pt
revealed a typical feature which is characteristic to a clean Pt
surface. The three anodic peaks at potentials of 0.06, −0.02, and
−
0.09 V(versusAg/AgCl)areconsistentwiththoseofpolycrys-
talline Pt. On the basis of the assumption that a monolayer of
2
hydrogen corresponds to an adsorption charge of 210 ␮C/cm ,
the active area of Pt can be estimated to be ca. 12 m /g from
2
the hydrogen adsorption/desorption charge. The literature val-
ues for the specific surface area of platinized Pt films and Pt
2
black powders are 2–30 and 20–26 m /g, respectively. In the
previous reports, the surface areas of 2D-hexagonally ordered
mesoporous Pt films and particles prepared from LLC phases
2
with the same surfactants (C EO8) range from 17 to 38 m /g
[
16
2
29–35]. Consequently, the surface areas of ca. 12 m /g obtained
in this studyis almostcomparable to the lower valuesin the range
and can be ascribed to the porous nanostructures formed in the
presence of LLC. It has been previously shown that the surface
areas change depending on the bath compositions and deposition
conditions [29–35]. Those of mesoporous Pt particles prepared
2
by a chemical reduction using Zn were 47 m /g by Kucernak
2
and Jiang [36] and 65 m /g by us [45], respectively, in which
the presence of necklace-like connected nanopartciles in frame-
works (i.e. bumpy morphology) may induce the enhancement of
the specific surface area.
Ordered nanostructure cannot be obtained in this study,
though LLC prepared from a diluted surfactant solution pos-
sesses a highly ordered 2D-hexagonal structure (Fig. 1). We
believe that Pt cannot be deposited along the rod-like self-
assemblies because the Pt deposition proceeded fast due to the
large difference between the standard electrode potentials of Pt
(E = 1.19 V) and Ni (E = −0.25 V). Further optimized control
Fig. 4. TEM images and selected ED patterns of Pt deposited onto the Ni foam.
a) Low-magnified TEM image (The inset image is the selected ED pattern of
the circle area.). (b) Highly magnified TEM image.
(
0
0

6
08
Y. Yamauchi et al. / Electrochimica Acta 53 (2007) 604–609
Fig. 5. Dark field (DF) images of the deposited nanoporous Pt. The dark field (DF) images (images b–d) were taken by reflections DF1, DF2 and DF3, respectively.
mesoporous metals with tunable functions and new solid-state
properties.
Acknowledgements
The authors acknowledge Prof. T. Ohsuna (Waseda Univer-
sity) for valuable discussion on TEM study. The authors also
acknowledge Mr. Y. Morioka (Waseda University) for illustra-
tion of Scheme 1. The present study was supported in part by the
21st Century COE Program “Practical Nano-Chemistry”, and
the Encouraging Development Strategic Research Centers Pro-
gram (Super COE) “Establishment of a Consolidated Research
Institute for Advanced Science and Medical Care” from the
Japanese Ministry of Education, Culture, Sports, Science and
Technology (MEXT). This work was also supported by the
A3 Foresight Program “Synthesis and Structural Resolution of
Novel Mesoporous Materials” from the Japan Society for the
Promotion of Science (JSPS).
Fig. 6. Cyclic voltammogram for nanostructured Pt particles in aqueous 0.5 M
H2SO4 solutionat100 mV/s. Ha:hydrogenadsorption, Hd:hydrogendesorption,
Oa: formation of Pt-O, Od: reduction of Pt oxide.
of Pt deposition rate by changing host materials as a scaffold may
lead to the enhancement of the ordering of the mesostructure.
4
. Conclusion
References
We have fabricated a 3D electrode with a hierarchical pore
[1] X. Teng, X. Liang, S. Maksimuk, H. Yang, Small 2 (2006) 249.
[
[
2] J. Chen, T. Herricks, Y. Xia, Angew. Chem. Int. Ed. 44 (2005) 2589.
3] R. Krishnaswamy, H. Remita, A. Imperor-Clerc, C. Evan, P. Davidson, B.
Pansu, Chem. Phys. Chem. 7 (2006) 1510.
system by combining the modified LLC templating with dis-
placement plating for the first time. This approach allows
the one-pot formation of nanostructured metals onto three-
dimensional and/or irregular scaffolds, which is considerably
important as a practical approach for one-step production of
hierarchical porous electrodes. Another advantageous point is
that the method will be applicable to the deposition of various
nanostructured metals and alloys from LLC templating mix-
tures (including several metal ions) [60]. In particular, alloying
has been focused as a key element to further develop novel
[
4] G. Surendran, G. Apostolescu, M. Tokumoto, E. Prouzet, L. Ramos, P.
Beaunier, P.J. Kooyman, A. Etcheberry, H. Remita, Small 1 (2005) 964.
[5] J.Y. Chen, Y.J. Xiong, Y.D. Yin, Y.N. Xia, Small 2 (2006) 1340.
[
[
[
6] X.G. Hu, T. Wang, S.J. Dong, J. Nanosci. Nanotechnol. 6 (2006) 2056.
7] X. Zhong, Y. Feng, I. Lieberwirth, W. Knoll, Chem. Mater. 18 (2006) 2468.
8] Y.J. Song, W.A. Steen, D. Pena, Y.B. Jiang, C.J. Medforth, Q.S. Huo, J.L.
Pincus, Y. Qiu, D.Y. Sasaki, J.E. Miller, J.A. Shelnuttt, Chem. Mater. 18
(
2006) 2335.
[9] M.H. Chen, L. Gao, Chem. Phys. Lett. 417 (2006) 132.

Y. Yamauchi et al. / Electrochimica Acta 53 (2007) 604–609
609
[
[
[
[
[
10] Y.Y. Mu, H.P. Liang, J.S. Hu, L.J. Wan, J. Nanosci. Nanotechnol. 5 (2005)
929.
11] W. Lee, R. Scholz, K. Niesch, U. Gosele, Angew. Chem. Int. Ed. 44 (2005)
050.
12] T. Sehayek, M. Lahav, R. Popovitz-Biro, A. Vaskevich, I. Rubinstein,
Chem. Mater. 17 (2005) 3743.
[34] H. Boo, S. Park, B. Ku, Y. Kim, J.H. Park, H.C. Kim, T.D. Chung, J. Am.
Chem. Soc. 126 (2004) 4524.
[35] B. Gollas, J.M. Elliott, P.N. Bartlett, Electrochim. Acta 45 (2000) 3711.
[36] A. Kucernak, J. Jiang, Chem. Eng. J. 93 (2003) 81.
[37] A.H. Whitehead, J.M. Elliott, J.R. Owen, G.S. Attard, Chem. Commun.
(1999) 331.
[38] P.N. Bartlett, P.N. Birkin, M.A. Ghanem, P. de Groot, M. Sawicki, J. Elec-
trochem. Soc. 148 (2001) C119.
[39] P.N. Bartlett, B. Gollas, S. Guerin, J. Marwan, Phys. Chem. Chem. Phys.
4 (2002) 3835.
1
6
13] Y. Ding, A. Mathur, M.W. Chen, J. Erlebacher, Angew. Chem. Int. Ed. 44
(
2005) 4002.
14] L.Z. Zhang, J.C. Yu, M.S. Mo, L. Wu, K.W. Kwong, Q. Li, Small 1 (2005)
49.
3
[
[
[
15] M. Asai, T. Onoe, H. Kanoh, K. Kaneko, Colloid Surf. A 253 (2005) 199.
16] J.H. He, T. Kunitake, T. Watanabe, Chem. Commun. (2005) 795.
17] J.Y. Chen, T. Herricks, M. Geissler, Y.N. Xia, J. Am. Chem. Soc. 126 (2004)
[40] P.N. Bartlett, J. Marwan, Chem. Mater. 15 (2003) 2962.
[41] T. Gabriel, I.S. Nandhakumar, G.S. Attard, Electrochem. Commun. 4
(2002) 610.
1
0854.
[42] P.A. Nelson, J.M. Elliott, G.S. Attard, J.R. Owen, Chem. Mater. 14 (2002)
524.
[
[
18] L.T. Qu, G.Q. Shi, X.F. Wu, B. Fan, Adv. Mater. 16 (2004) 1200.
19] T. Kijima, T. Yoshimura, M. Uota, T. Ikeda, D. Fujikawa, S. Mouri, S.
Uoyama, Angew. Chem. Int. Ed. 43 (2004) 228.
20] H. Kawasaki, M. Uota, T. Yoshimura, D. Fujikawa, G. Sakai, M. Annaka,
T. Kijima, Langmuir 21 (2005) 11468.
21] H. Kawasaki, M. Uota, T. Yoshimura, D. Fujikawa, G. Sakai, T. Kijima, J.
Colloid Interface Sci. 300 (2006) 149.
22] J.K. Zhao, X. Chen, L.Y. Jiao, Y.C. Chai, G.D. Zhang, J. Liu, Chem. Lett.
[43] P.N. Bartlett, J. Marwan, Microporous Mesoporous Mater. 62 (2003) 73.
[44] Y. Yamauchi, T. Yokoshima, H. Mukaibo, M. Tezuka, T. Shigeno, T.
Momma, T. Osaka, K. Kuroda, Chem. Lett. 33 (2004) 542.
[45] Y. Yamauchi, T. Momma, M. Fuziwara, S. Sadasivan Nair, T. Ohsuna, O.
Terasaki, T. Osaka, K. Kuroda, Chem. Mater. 17 (2005) 6342.
[46] Y. Yamauchi, S. Sadasivan Nair, T. Momma, T. Ohsuna, T. Osaka, K.
Kuroda, J. Mater. Chem. 16 (2006) 2229.
[
[
[
[
[
[
[
[
[
[
[
[
[
[
3
3 (2004) 842.
23] Q. Zhou, X.Y. Liu, L. Liu, Y.G. Li, Z.Y. Jiang, D.Y. Zhao, Chem. Lett. 34
2005) 1226.
[47] Y. Yamauchi, T. Momma, H. Kitoh, T. Osaka, K. Kuroda, Electrochem.
Commun. 7 (2005) 1364.
[48] Y. Yamauchi, H. Kitoh, T. Momma, T. Osaka, K. Kuroda, Sci. Technol.
Adv. Mater. 7 (2006) 438.
[49] Y. Yamauchi, K. Kuroda, Electrochem. Commun. 8 (2006) 1677.
[50] Y. Yamauchi, T. Momma, T. Osaka, K. Kuroda, Japanese Patent 233272
(2006).
[51] R. Campbell, M.G. Bakker, J. Porous Mater. 11 (2004) 63.
[52] G.S. Attard, P.N. Bartlett, N.R.B. Coleman, J.M. Elliott, J.R. Owen, Lang-
muir 14 (1998) 7340.
[53] H.W. Hillhouse, J.W. van Egmond, M. Tsapatsis, J.C. Hanson, J.Z. Larese,
Microporous Mesoporous Mater. 44 (2001) 639.
[54] Y. Yamauchi, M. Sawada, T. Noma, H. Ito, S. Furumi, Y. Sakka, K. Kuroda,
J. Mater. Chem. 15 (2005) 1137.
[55] Y. Yamauchi, M. Sawada, A. Sugiyama, T. Osaka, Y. Sakka, K. Kuroda, J.
Mater. Chem. 16 (2006) 3693.
(
24] K.W. Park, J.H. Choi, B.K. Kwon, S.A. Lee, Y.E. Sung, H.Y. Ha, S.A.
Hong, H. Kim, A. Wieckowski, J. Phys. Chem. B 106 (2002) 1869.
25] S. Motokawa, M. Mohamedi, T. Momma, S. Shoji, T. Osaka, Electrochem.
Commun. 6 (2004) 562.
26] U.A. Paulus, A. Wokaun, C.G. Scherer, T.J. Schmidt, V. Stamenkovic, V.
Radmilovic, N.M. Markovic, P.N. Ross, J. Phys. Chem. B 106 (2002) 4181.
27] N. Wakabayashi, M. Takeichi, H. Uchida, M. Watanabe, J. Phys. Chem. B
1
09 (2005) 5836.
28] H. Yang, C. Coutanceau, J.M. L e´ ger, N. Alonso-Vante, C. Lamy, J. Elec-
troanal. Chem. 576 (2005) 305.
29] G.S. Attard, C.G. G o¨ ltner, J.M. Corker, S. Henke, R.H. Templer, Angew.
Chem. Int. Ed. 36 (1997) 1315.
30] G.S. Attard, P.N. Bartlett, N.R.B. Coleman, J.M. Elliott, J.R. Owen, J.H.
Wang, Science 278 (1997) 838.
31] J.M. Elliott, P.R. Birkin, P.N. Bartlett, G.S. Attard, Langmuir 15 (1999)
¨
¨
¨
[56] O. C¸ elik, O. Dag, Angew. Chem. Int. Ed. 40 (2001) 3799.
¨
[57] O. Dag, O. Samarskaya, C. Tura, A. G u¨ nay, O. C¸ elik, Langmuir 19 (2003)
3671.
7
411.
¨
¨
32] S.A.G. Evan, J.M. Elliott, L.M. Andrews, P.N. Bartlett, P.J. Doyle, G.
Denuault, Anal. Chem. 74 (2002) 1322.
33] S. Park, T.D. Chung, H.C. Kim, Anal. Chem. 75 (2003) 3046.
[58] O. Dag, S. Alayo g˘ lu, C. Tura, O. C¸ elik, Chem. Mater. 15 (2003) 2711.
¨
˙
[59] O. Dag, S. Alayo g˘ lu, I. Uysal, J. Phys. Chem. B 108 (2004) 8439.
[60] Y. Yamauchi, T. Ohsuna, K. Kuroda, Chem. Mater. 19 (2007) 1335.