Synthesis of graphitic ordered macroporous carbon with a three-dimensional interconnected pore structure for electrochemical applications

Article abstract of DOI:10.1021/jp0541967

In this study, ordered macroporous carbon with a three-dimensional (3D) interconnected pore structure and a graphitic pore wall was prepared by chemical vapor deposition (CVD) of benzene using inverse silica opal as the template. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectrometry, nitrogen adsorption, and thermogravimetric analysis techniques were used to characterize the carbon samples. The electrochemical properties of the carbon materials as a carbon-based anode for lithium-ion batteries and as a Pt catalyst support for room-temperature methanol electrochemical oxidation were examined. It was observed that the CVD method is a simple route to fabrication of desired carbon nanostructures, affording a carbon with graphitic pore walls and uniform pores. The graphitic nature of the carbon enhances the rate performance and cyclability in lithium-ion batteries. The specific capacity was found to be further improved when SnO₂ nanoparticles were supported on the carbon. The specific activity of Pt catalyst supported on the carbon materials for room-temperature methanol electrochemical oxidation was observed to be higher than that of a commercial Pt catalyst (E-TEK). ? 2005 American Chemical Society.

Full text of DOI:10.1021/jp0541967

20200
J. Phys. Chem. B 2005, 109, 20200-20206
Synthesis of Graphitic Ordered Macroporous Carbon with a Three-Dimensional
Interconnected Pore Structure for Electrochemical Applications
Fabing Su,† X. S. Zhao,*,† Yong Wang,‡ Jianhuang Zeng,† Zuocheng Zhou,† and
Jim Yang Lee†,‡
Department of Chemical and Biomolecular Engineering, National UniVersity of Singapore,
10 Kent RidgeCrescent, Singapore 119260, and Singapore-MIT Alliance, National UniVersity of Singapore,
4 Engineering DriVe 3, Singapore 117576
ReceiVed: July 29, 2005; In Final Form: September 12, 2005
In this study, ordered macroporous carbon with a three-dimensional (3D) interconnected pore structure and
a graphitic pore wall was prepared by chemical vapor deposition (CVD) of benzene using inverse silica opal
as the template. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray
diffraction, Raman spectrometry, nitrogen adsorption, and thermogravimetric analysis techniques were used
to characterize the carbon samples. The electrochemical properties of the carbon materials as a carbon-based
anode for lithium-ion batteries and as a Pt catalyst support for room-temperature methanol electrochemical
oxidation were examined. It was observed that the CVD method is a simple route to fabrication of desired
carbon nanostructures, affording a carbon with graphitic pore walls and uniform pores. The graphitic nature
of the carbon enhances the rate performance and cyclability in lithium-ion batteries. The specific capacity
was found to be further improved when SnO2 nanoparticles were supported on the carbon. The specific activity
of Pt catalyst supported on the carbon materials for room-temperature methanol electrochemical oxidation
was observed to be higher than that of a commercial Pt catalyst (E-TEK).
1. Introduction
avoid the aggregation of SnO2 particles because of the confine-
ment of SnO2 nanoparticles in the pores,12 as well as the strong
interactions between the nanoparticles and the support.18
Moreover, the nanopores of the carbon provide a void space
when SnO2 nanoparticles experience a volume change.12 On
the other hand, a well-developed porous carbon structure with
a 3D connectivity enhances the ionic conductivity of electrolyte
and the movability of lithium ions, thus improving the rate
performance of lithium-ion secondary batteries.15 Therefore,
SnO2/carbon nanostructured anode composite is believed to
display a better cycle life than SnO2 alone and a higher capacity
than graphitic carbon itself.
For the direct-methanol fuel cell (DMFC) application, recent
studies have shown that the characteristics of a carbon support
for Pt catalyst have a significant impact on the electrochemical
properties. A highly accessible surface area enables a high
dispersion of Pt nanoparticles, thus enhancing the catalytic
activity of the Pt/carbon catalyst.19 A graphitic nature enables
rapid electron transfer.20 A 3D interconnected pore system
facilitates the transport of reactants and products during
electrochemical oxidation reactioin.7,21
In this paper, ordered graphitic macroporous carbons with a
3D interconnected pore structure were fabricated using the
chemical vapor deposition (CVD) method with inverse silica
opal as the template following a surface-templating route.22 The
fabrication involves the preparation of an inverse silica template,
carbon deposition on the template surface using the CVD
method with benzene vapor as the carbon source, and removal
of the template using HF solution. The electrochemical proper-
ties of the prepared carbon materials as carbon-based anode
materials in lithium-ion battery and as Pt catalyst supports
for methanol electrochemical oxidation in DMFCs were exam-
ined.
The demands for advanced energy conversion and storage
devices such as fuel cells, lithium-ion batteries, and superca-
pacitors have resulted in many recent studies on nanostructured
electrode materials.1 Carbon materials such as carbon black,
graphite, and highly ordered pyrolytic graphite have been used
as the working electrode materials.2 Recently, the preparation
of nanoporous carbons with different structural properties by
using a hard template has been described.3-6 Such carbon
materials are technologically significant in catalysis, adsorption,
and templating matrixes for fabricating nanomaterials. The
template approach allows one to obtain a desired carbon pore
structure, thus offering new opportunities to realize nanostruc-
tured carbon-based electrode materials for electrochemical
applications.7-14
As a promising anode in lithium-ion batteries, SnO2/carbon
nanostructured composite is attracting a great deal of interest.
It is well-known that SnO2 possesses a higher theoretical
capacity (800 (mA h)/g) than that of graphite (372 (mA h)/
g).15-18 However, its practical application is hampered by the
poor cyclability due to the large volume change (expansion and
contraction) during the lithium intercalation/deintercalation
process, which causes a fast capacity fading. Additionally, the
agglomeration of primitive SnO2 particles drastically reduces
the total entrance/exit sites available for lithium ions (i.e.,
reduction in surface-to-volume ratio).17 SnO2 nanoparticles
supported on a porous material may overcome these problems.
It has been observed that porous carbon can act as a barrier to
* To whom correspondence should be addressed. E-mail:
chezxs@nus.edu.sg.
† Department of Chemical and Biomolecular Engineering.
‡ Singapore-MIT Alliance.
10.1021/jp0541967 CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/12/2005

Graphitic Ordered Macroporous Carbon
J. Phys. Chem. B, Vol. 109, No. 43, 2005 20201
2. Experimental Section
at 130 °C overnight and heated in a tube furnace at 350 °C for
3 h. The exact amounts of SnO2 in the composites (74.5 and
18.6 wt %; designated as SnO2/GMC1000) were determined
by the inductively coupled plasma (ICP) spectroscopy. The
synthesized GMC1000 and SnO2/GMC1000 composites with
different loadings of SnO2 were used as the active anode
materials. The working electrode consisted of 90 wt % active
material, 5 wt % conductivity agent (Carbon Black, Super-P),
and 5 wt % binder (poly(vinylidene difluoride), PVDF, Aldrich).
A lithium foil was used as negative electrodes. The electrolyte
was 1 M LiPF6 in a 50:50 (w/w) mixture of ethylene carbonate
(EC) and diethyl carbonate (DEC). The room-temperature
electrode activities were measured by a Maccor Series 2000
battery tester (with anode Li+/Li). Cells were tested at the
constant currents 40, 200, 600, and 1000 mA/g and a fixed
voltage limit (5 mV to 2 V).
2.4. Preparation and Evaluation of Pt/Carbon Catalysts
for Methanol Electrochemical Oxidation. Pt catalysts sup-
ported on carbon samples GMC900 and GMC1000, designed
as Pt/GMC900 and Pt/GMC1000, respectively, were prepared
for room-temperature methanol oxidation using the established
borohydride reduction method.25 An appropriate amount of 0.05
M chloroplatinic acid (H2PtCl6‚6H2O, Aldrich) solution was
added in distilled water containing carbon powder under stirring.
Then, a stoichiometric excess of 0.5 M NaBH4 (Aldrich) solution
was used to initiate deposition of Pt nanoparticles. After stirring
for 12 h, the solid was recovered by centrifugation, extensively
washed with distilled water, and vacuum-dried at room tem-
perature overnight. The Pt loading in each catalyst was kept at
20 wt % to allow a comparison with a commercial E-TEK Pt/C
catalyst (Pt supported on carbon black Vulcan XC-72; Pt
loading, 20 wt %). A conventional three-compartment electro-
chemical cell was used to evaluate the electrochemical perfor-
mance by cyclic voltammetry. An Autolab PGSTAT12 was
employed as the potentiostat/galvansotat. The working electrode
with a Pt loading of 100 µg/cm2 was fabricated by casting
Nafion-impregnated catalyst ink onto a 5 mm diameter vitreous
glassy carbon disk electrode, which was cleaned with ethanol
and dried before use. The catalyst ink is prepared by ultrasoni-
cally dispersing 10 mg of Pt catalyst into a mixture of 0.1 mL
of Nafion (5 wt % solution from Aldrich) and 0.9 mL of ethanol.
A Pt gauze and a saturated calomel electrode (SCE) were used
as the counter and the reference electrodes, respectively, while
1 M CH3OH in 0.5 M H2SO4 was the electrolyte. All reported
potentials were referenced to the SCE. The catalysts were
electrochemically cleaned by continuous cycling until a stable
response was obtained before the cyclic voltammograms were
recorded.
2.1. Synthesis of Carbon Materials. The carbon preparation
procedure in this work is described as follows. First, monodis-
perse polystyrene (PS) spheres synthesized according to Shim
and co-workers23 were fabricated into colloidal crystals using
a flow-controlled vertical deposition method.24 Second, the
interstices between the PS spheres were infiltrated with a silica
sol, which was prepared by mixing tetraethyl orthosilicate (98%,
Acros Organics), ethanol, and 0.1 M HCl solution with a volume
ratio of 1:3:0.1. After hydrolysis and condensation of the silica
sol, the PS spheres were removed by calcination in air at 700
°C for 5 h, yielding a 3D macroporous inverse silica opal, which
was employed as the template. Third, deposition of carbon on
the surface of the inverse silica opal was carried out using a
CVD method with the benzene vapor as the carbon precursor.
In detail, a 0.5 g inverse silica template in quartz tube was placed
into a furnace and heated to 900 °C with a heating rate of 5
°C/min under highly pure N2 flow (30 cm3/min). Subsequently,
nitrogen gas containing 10 wt % benzene vapor at a flow rate
of 30 cm3/min was introduced into the quartz tube for 2 h. Then,
carbon/silica composite was cooled in pure nitrogen gas and
dissolved in 20% HF solution to remove the silica. The obtained
carbon was named as GMC900, where GMC means graphitic
macroporous carbon and 900 refers to the CVD temperature.
Another sample named GMC1000 was prepared at the CVD
temperature of 1000 °C for 2 h. The experimental results
demonstrated that when the CVD temperature is lower than 900
°C, there is no deposition of graphitic carbon on the surface of
the macroporous silica template. In contrast, at the temperature
higher than 1100 °C, the 3D structure of the silica template is
partially destroyed.
2.2. Characterization. The microscopic features of the
samples were observed with a field-emission scanning electron
microscope (FESEM; JSM-6700F, JEOL Japan) operated at 10
kV and transmission electron microscopy (TEM; JEM 2010F,
JEOL, Japan) operated at 200 kV. Thermogravimetric analysis
(TGA) was conducted on a thermogravimetric analyzer TGA
2050 (Thermal Analysis Instruments, USA) in air with a flow
rate of 100 cm3/min and a heating rate of 10 °C/min. X-ray
diffraction (XRD) patterns were collected on a Shimadzu XRD-
6000 (Japan) with Cu KR radiation (λ ) 0.15418 nm) operated
at 40 kV and 30 mA. The pore structural properties were
investigated by nitrogen adsorption at -196 °C on an automatic
volumetric sorption analyzer (Quantachrome, NOVA1200).
Prior to measurements, the samples were degassed at 200 °C
for 5 h. The specific surface area was determined according to
the Brunauer-Emmett-Teller (BET) method in the relative
pressure of 0.05-0.2. The micropore volume was calculated
from the Dubinin-Radushkevich (DR) equation.
3. Results and Discussion
2.3. Preparation and Electrochemical Measurements of
Carbon-Based Anode Materials for Lithium-Ion Batteries.
The SnO2/carbon composite was prepared by the microwave-
assisted hydrolysis method.18 Briefly, in a 100 mL glass vessel,
0.2 M urea (Aldrich, 98%) was dissolved in 0.1 M SnCl4
(Riedel-de Haen, 99%) aqueous solution to a mole ratio of urea
to SnCl4 of 4:1. A calculated amount of GMC1000 with two
different SnO2 loadings was added to the solution and sonicated
for 0.5 h. The glass vessel was then placed in the cavity of a
300 W CEM Discover microwave reactor. The temperature was
ramped from room temperature to 85 °C in 10 s and kept for 3
min under stirring. The resulting suspension, after cooling in
an ice bath, was centrifuged at 8000 rpm for 30 min to
precipitate the nanocomposites. After washing with a copious
amount of distilled water, the precipitate was dried in a vacuum
3.1. Pore Structures of GMCs. Figure 1a shows the cross-
section FESEM image of the inverse silica opal template. The
spherical voids with a diameter of about 220 nm packed in a
face-centered cubic (fcc) structure are seen. Each air void is
interconnected with spherical windows of about 50 nm in size.
Parts b and c of Figure 1 show the FESEM images of carbons
GMC900 and GMC1000 replicated from the macroporous silica
template. A 3D ordered structure with a fcc arrangement of
spherical voids is also seen, indicating that the long-range order
of the GMCs inherited from the inverse silica opal template. It
is also seen that the GMCs contain quasi-spherical cavities of
around 200 nm in diameter with smaller quasi-cylindrical pore
channels. Figure 1d is a higher magnification image of the
GMC1000 sample. The crack highlighted with a black circle
reveals the hollow carbon framework, demonstrating that the

20202 J. Phys. Chem. B, Vol. 109, No. 43, 2005
Su et al.
Figure 1. FESEM images: (a) inverse silica template; (b) GMC900; (c, d) GMC1000.
Figure 2. TEM image: (a, b) GMC900 with different magnifications; (c) GMC1000; (d) lattice-fringe image of GMC1000 framework.
macroporous carbon was replicated from the inverse silica
template via a surface-templating mechanism.22 From the broken
edge, it can be estimated that the carbon wall thickness is about
20-30 nm. It should be noted that the obtained macroporous
carbons are not highly perfect in pore structure due to some
fractures and defects, which may stem from structural collapses
of the inverse silica template during the calcination or template
removal process.
Shown in Figure 2 are the TEM images of the GMCs. It can
be seen that GMC900 substantially consists of hollow carbon
spheres with a diameter of around 200 nm, showing a highly
periodic carbon structure. Figure 2b further shows a homoge-
neous 3D interconnected pore structure with an average carbon
wall thickness of 20 nm. Similarly, carbon GMC1000 also
displays a 3D pore structure, but with a thicker carbon wall of
around 30 nm. The high-resolution TEM image of Figure 2d
taken from the carbon wall of Figure 2c reveals the presence
of imperfect graphene sheets, which are packed tightly. As a
result, significant lattice distortions and defects are observed.
These graphene layers are parallel to the surface of the carbon
wall. The microscopic features clearly indicate the low crystal-
linity of the carbon walls.
The nitrogen adsorption/desorption isotherms of GMC900 and
GMC1000 reveal a type-II isotherm with a type-H3 hysteresis

Graphitic Ordered Macroporous Carbon
J. Phys. Chem. B, Vol. 109, No. 43, 2005 20203
Figure 5. Thermogravimetric analysis of synthesized GMC1000,
GMC900, carbon black XC-72, and amorphous carbon C1000-2.
Figure 3. XRD patterns of synthesized GMC900, GMC1000, carbon
black XC-72, and amorphous carbon C1000-2.
TABLE 1: Specific Capacities of GMC1000 at Various
Specific Currents
specific current specific capacity specific current specific capacity
(mA/g)
((mA h)/g)
(mA/g)
((mA h)/g)
40
200
600
327
320
303
1000
15a
260
300a
150a
150a
a From ref 13.
(1580 cm-1), suggesting a structural imperfection of the
graphene sheets of the three samples.27 The relative intensities
of the two peaks (G and D bands) reflect the graphitization
degree. The observed low intensity of the broad D band peak
and the high intensity of the G band narrow peak indicate that
the carbons are composed of small graphene sheets with a low
graphitization degree.27 Additionally, the large Raman ∆νG value
(full width at the half-maximum (fwhm)) of the G band, which
is closely related to the structure regularity,28 also indicates a
low graphitization degree. The ∆νG values of GMC1000,
GMC900, and XC-72 are 72, 79, and 78 cm-1, respectively.
Therefore, the G-band peak position, the relative intensity of
the two peaks, and the Raman ∆νG values suggest the highest
graphitization degree of carbon GMC1000, in agreement with
the XRD data presented in Figure 3.
The thermogravimetric (TG) curves of the GMC carbons
prepared in this work are compared with that of carbon black
XC-72 and an amorphous carbon in Figure 5. The TG curves
of carbons GMC900 and GMC1000 clearly show that the silica
template had been completely removed by aqueous HF solution
because of the negligible residue at the temperature above 800
°C. The temperature range of weight loss was observed to be
between 500 and 600 °C for amorphous carbon C1000-2,
between 530 and 720 °C for carbon black XC-72 and carbon
GMC900 and between 580 and 800 °C for carbon GMC1000.
It has been reported that the oxidation reaction of carbon
materials first occurs on the graphene layer edge defects or
disordered graphene layers.29 In general, pure graphite with less
defects and a good organization of graphene layers has a much
higher oxidation temperature than amorphous carbon. In this
work, the sequence of oxidation temperature range of the
carbons in air follows the graphitization degree as characterized
by the XRD and the Raman spectrum data. It is also worthy to
note that in comparison with liquid carbon precursors, such as
divinylbenzene,7 resorcinol-formaldehyde,13 sucrose,30 phenol-
formaldehyde,31 and polyacrylonitrile,32 the aromatic hydrocar-
bon precursor, benzene, used in this study allows the formation
of graphitic nature except for the treatment of mesophase pitch
at a higher temperature (2500 °C).33
Figure 4. Raman spectra of the GMC1000, GMC900, and carbon black
XC-72.
(not shown here), characteristic of a macroporous material. The
Brunauer-Emmett-Teller (BET) surface areas of carbons
GMC900 and GMC1000 were measured to be 94 and 43 m2/g,
respectively. The micropore volumes of both carbon samples
estimated using the DR method are negligible, implying a dense
packing of graphene layers.
3.2. Graphitic Nature of GMCs. Compared in Figure 3 are
the XRD patterns of different carbons. It can be seen that
GMC1000, GMC900, and XC-72 possess a broad diffraction
peak at around 25°, which is assigned to the (002) diffraction
of graphitic carbon, showing the presence of graphitic carbon.
GMC1000 has the strongest intensity of this peak at 25.3°,
indicating the highest degree of graphitization among the carbon
samples. The peak at about 43° corresponds to (101) diffraction
of solid carbon materials. The intensity of the (002) peak of
carbon GMC900 is comparable to that of carbon black XC-72.
In contrast, carbon C1000-2 synthesized at 1000 °C using zeolite
Y as the template and furfuryl alcohol as the carbon precursor26
is amorphous in nature because no peak at around 25° is seen.
The interlayer distance values between graphene planes (d002
)
together with the crystalline size (Lc) can be determined from
the (002) peak using the Bragg’s law and Scherrer equation,
respectively. The broad width and lower position of the (002)
peak than the typical peak of graphite (d002 ) 0.335 nm) indicate
the low crystalline nature of GMC1000 (d002 ) 0.352 nm, Lc
) 3.8 nm), in agreement with the data revealed by the TEM
lattice-fringe images.
Figure 4 shows the Raman spectra of the carbon samples.
The strong peak at around 1590 cm-1 (G band) is attributed to
the vibration of sp2-bonded carbon atoms in a two-dimensional
hexagonal lattice, namely, the stretching modes of CdC bonds
of typical graphite, while the weak peak at about 1350 cm-1
(D band) is associated with the vibration of carbon atoms with
dangling bonds in plane terminations of the disordered graphite
and is also related to the defects and disorders of carbon
materials. It should be noted that the G band peaks of all three
3.3. Electrochemical Properties of Carbon-Based Anode
Materials for Lithium-Ion Batteries. Table 1 shows the
specific capacities of GMC1000 at various specific currents,
together with the results of an amorphous 3D macroporous
samples (for GMC1000 at 1585 cm-1, GMC900 at 1596 cm-1
,
and XC-72 at 1593 cm-1) are shifted to higher wavelength
numbers in comparison with that of graphite single crystals

20204 J. Phys. Chem. B, Vol. 109, No. 43, 2005
Su et al.
Figure 6. (a) FESEM image of SnO2/GMC1000 (74.5 wt %); (b) TEM image of SnO2/GMC1000 (74.5 wt %); (c) FESEM image of SnO2/
GMC1000 (18.6 wt %); (d) XRD patterns of SnO2/GMC1000 composite (18.6 wt %).
carbon for comparison purpose. It can be seen that the specific
capacity of GMC1000 was 326 (mA h)/g at a specific current
of 40 mA/g. When the current was increased from 40 to 600
mA/g, only a slight decrease in capacities from 326 to 303 (mA
h)/g was observed. Instead, the 3D amorphous carbon with a
similar macroporous structure to carbon GMC1000 prepared
in this study displayed a lower specific capacity at a similar
current,13 indicating a substantial improvement of rate perfor-
Figure 7. Cycling performances of GMC1000 and different SnO2/
GMC1000 composites (discharge potential limits, 5 mV to 2.0 V;
constant current, 0.1 C).
mance in the present work and a great application potential of
our carbon materials. In lithium-ion batteries, the electrochemical
behaviors largely depend on the chemical and physical properties
of the carbon material, such as crystallinity, surface chemistry,
pore structure, and micromorphology.15 Extremely high surface
area creates excessive side reactions with the electrolyte, forming
a solid-electrolyte interface (SEI) to inhibit reversible faradaic
reaction, giving rise to a poor cyclic stability. On the other hand,
a carbon with a very low surface area cannot provide sufficient
electrochemical active sites for the charge-discharge process.
The GMC1000 carbon with an appropriate surface area (around
42 m2/g) and an interconnected pore structure consists of
graphitic carbon walls with a thickness of around 30 nm, as
shown in Figure 2c. The stacked graphene layers as shown in
Figure 2d, together with the unique structure, not only improve
the electronic transport for electrochemical reaction but also
promote the lithium ion diffusion, leading to a good electro-
chemical performance as an anode material.
The FESEM image shown in Figure 6a and the TEM image
shown in Figure 6b of the SnO2/GMC1000 composite with a
SnO2 loading of 74.5 wt % all demonstrate the existence of a
large number of uniform SnO2 nanoparticles of around 5 nm in
diameter. The FESEM image of another SnO2/GMC1000
composite with a SnO2 loading of 18.6 wt % shown in Figure
6c indicates sparsely dispersed SnO2 nanoparticles of around 5
nm in size on the surface of GMC1000. The XRD pattern of
sample SnO2/GMC1000 with a SnO2 loading of 18.6 wt % in
Figure 6d exhibits four peaks of (110), (101), (200), and (211)
reflections of the rutile-like SnO2.34 The (002) reflection peak
of graphitic carbon of GMC1000, shown in Figure 3, overlaps
with the (110) reflection peak of SnO2. The particle size
calculated using the Scherrer equation is consistent with that
estimated from the TEM or FESEM data.
Figure 7 compares the cycling performance of pure carbon
GMC1000 with that of the SnO2/GMC1000 composite materials
of different loadings of SnO2. It can be seen that carbon
GMC1000 displays a very stable cyclability (specific capacity,
320 (mA h)/g after 60 cycles; 98% retention), which is better
than other template-synthesized carbon materials.10,13 After it
was coated with SnO2 nanoparticles, higher initial capacities
(415 (mA h)/g for 18.6 wt % SnO2 loading and 645 (mA h)/g
for 74.5 wt % loading) were observed in the first cycle.
However, after 12 cycles, the specific capacity of composite
SnO2/GMC1000 with a higher loading of SnO2 was found to
be lower than that of the composite with a lower loading of
SnO2. In addition, the lower loading composite retained about
90.5% of its initial specific capacity after 60 cycles, indicating
a better cycle performance than the higher loading composite
anode, which showed a dramatically faster capacity fading (25%
retention after 30 cycles). The average capacity fading of SnO2/
GMC1000 (18.6 wt % loading) is around 0.16%/cycle, which
is much better than that of previously reported 3D macroporous
carbon coated with SnO2 nanoparticles,13 hollow carbon spheres
encapsulated with Sn particles,35 and ordered mesoporous carbon
deposited with tin-based oxide nanoparticles.12 The enhancement

Graphitic Ordered Macroporous Carbon
J. Phys. Chem. B, Vol. 109, No. 43, 2005 20205
Figure 9. Cyclic voltammograms of Pt/GMC1000, Pt/GMC900, and
E-TEK Pt/C catalysts measured at a scan rate of 20 mV/s at room
temperature in the electrolyte of 1 M CH3OH + 0.5 M H2SO4. (Forward
scan, 0-1 V; reverse scan, 1-0 V).
Figure 9 compares the cyclic voltammograms of the three
catalysts measured in 0.5 M H2SO4 + 1 M CH3OH at room
temperature. The current density, which reflects the specific
activity and represents the intrinsic activity of the Pt active sites,
was normalized to the electrochemically active surface area of
the corresponding catalysts according to the standard tech-
nique.38 The peak at around 0.66 V is attributed to electrooxi-
dation of methanol in the forward scan, while the peak at around
0.53 V is due to the reactivation of Pt-oxides in the reverse
scan.39 The specific activities of catalyst Pt/GMC1000 (0.98 mA/
cm2) evaluated from the peak at 0.66 V in the forward scan are
significantly higher than that of Pt/GMC900 (0.66 mA/cm2) and
E-TEK Pt/C (0.57 mA/cm2). This is probably attributed to the
3D interconnected macroporous structure of the GMC supports,
which facilitates the transport of reactant methanol and product
CO2 as compared with carbon black XC-72.7,21 The highest
degree of the graphitic nature of GMC1000 also accounts for
the highest specific activity of catalyst Pt/GMC1000 because
of its high electrical conductivity.19,20
Figure 8. (a) FETEM images of Pt/GMC1000 catalyst; (b) FETEM
image Pt/C E-TEK catalyst; (c) XRD patterns of Pt/GMC900, Pt/
GMC1000, and Pt/C E-TEK.
4. Conclusions
In summary, the synthesis of ordered macroporous carbon
with three-dimensional periodicity was demonstrated by using
inverse silica opal as the template and benzene as the carbon
precursor. This simple CVD route based on a surface-templating
mechanism can be applied to fabricate 3D macroporous carbons
with a controllable thickness of pore walls and a tunable degree
of graphitic crystallinity. A high specific capacity (around 326
(mA h)/g), good rate performance, and good cyclability (98%
retention per cycle within 60 cycles) of the 3D graphitic
macroporous carbon prepared in this work as a carbon anode
material in lithium-ion batteries were noted. The SnO2/carbon
nanocomposite anode with a loading of 18.6 wt % also displays
a significant improvement in initial capacity (415 mAh/g) and
cyclic stability (90.5% retention over 60 cycles). The specific
activity of Pt catalyst supported on the synthesized carbon for
methanol electrochemical oxidation was found to be better than
that of a commercial catalyst E-TEK Pt/C with the same Pt
loading. The enhancement of these electrochemical character-
istics is presumably related to the graphitic nature and the 3D
interconnected open pore structures of the carbon materials. It
is anticipated that the nanostructured carbon can be used as the
novel anode material for electrochemical energy conversion and
storage devices.
of cycle performance is presumably related to the relatively good
graphitic crystallinity of carbon GMC1000 and the appropriate
particle size of SnO2, which was prepared by the microwave-
assisted hydrolysis method.18
3.4. Electrochemical Oxidation of Methanol on Pt/Carbon
Catalysts. The electrochemical properties of Pt catalyst sup-
ported on GMCs were experimentally compared with that of
commercial catalyst E-TEK Pt/C, which is a Pt catalyst
supported on Vulcan XC-72 carbon. The FETEM images of
catalysts Pt/GMC1000 and E-TEK Pt/C shown in Figure 8a,b
reveal the presence of a large number of Pt nanoparticles. The
Pt particle sizes are about 4 nm for catalyst E-TEK Pt/C and
around 6 nm for catalyst Pt/GMC1000. Figure 8c shows the
XRD patterns of the three Pt catalysts. The peak at 25.3° is
due to the (002) diffraction of the graphitic structure of the
carbon supports. The strong diffraction peaks at the Bragg angles
of 39.8, 46.3, 67.5, and 81.3° are assigned to the diffractions
of the (111), (200), (220), and (311) facets of Pt nanocrystals
with a fcc lattice structure. Using the Debye-Scherrer equation,
the average Pt nanoparticle sizes of catalysts Pt/C, Pt/GMC1000,
and Pt/GMC900 were estimated to be about 3.7, 5.3, and 5.9
nm, respectively, consistent with the observations from the
FETEM images shown in Figure 7. The difference of Pt particle
sizes may be due to the different surface areas accessible for Pt
nanoparticles or different surface chemistries of the carbon
supports.36-37
Acknowledgment. The authors gratefully thank NUS for
financial support (Grant No. R279000124112). We also thank
Prof. Shen Zexiang for the measurement of Raman spectra.

20206 J. Phys. Chem. B, Vol. 109, No. 43, 2005
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