Pt-supported carbon nanotubes/reduced graphene oxide composite electrodes for a methanol oxidation

Article abstract of DOI:10.1166/jnn.2016.12501

Electrochemical analysis of platinum (Pt) supported on single-walled carbon nanotube (SWCNT) and reduced graphene oxide (RGO) composites were investigated. The Pt/SWCNT/RGO composite simultaneously synthesized by chemical reduction method in ethylene glycol (EG) solution. The catalytic activity of Pt/SWCNT/RGO composite compared with that of Pt/RGO composite. The SWCNT in graphene oxide sheets can serve as functioned spacers which impede aggregation of GO. The prepared Pt/SWCNT/RGO composite presented improved performance in terms of electrocatalytic activity. Electrochemical properties of the composite were characterized by cyclic voltammetry (CV). The morphology and structure of the composites indicated that the Pt nanoparticles were deposited on the RGO or SWCNT and the SWCNTs were located between RGO sheets by field emission scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM).

Full text of DOI:10.1166/jnn.2016.12501

Article
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Nanoscience and Nanotechnology
Vol. 16, 8598–8601, 2016
Copyright © 2016 American Scientific Publishers
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Pt-Supported Carbon Nanotubes/Reduced Graphene
Oxide Composite Electrodes for a Methanol Oxidation
Sung Sang Kwon1, Yongju Jung2, and Seok Kim1ꢀ∗
1School of Chemical and Biochemical Engineering, Pusan National University San 30, Jangjeon-dong,
Geumjeong-gu, Busan 609-735, South Korea
2Department of Chemical Engineering, Korea University of Technology and Education,
Cheonam-si, Chungnam-do, 330-708, South Korea
Electrochemical analysis of platinum (Pt) supported on single-walled carbon nanotube (SWCNT)
and reduced graphene oxide (RGO) composites were investigated. The Pt/SWCNT/RGO composite
simultaneously synthesized by chemical reduction method in ethylene glycol (EG) solution. The cat-
alytic activity of Pt/SWCNT/RGO composite compared with that of Pt/RGO composite. The SWCNT
in graphene oxide sheets can serve as functioned spacers which impede aggregation of GO. The
prepared Pt/SWCNT/RGO composite presented improved performance in terms of electrocatalytic
activity. Electrochemical properties of the composite were characterized by cyclic voltammetry (CV).
The morphology and structure of the composites indicated that the Pt nanoparticles were deposited
on the RGO or SWCNT and the SWCNTs were located between RGO sheets by field emission
Delivered by Ingenta to: State University of New York at Binghamton
scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM).
IP: 37.230.212.109 On: Sat, 08 Apr 2017 16:55:40
Copyright: American Scientific Publishers
Keywords: Reduced Graphene Oxide, Platinum, Fuel Cell, SWCNT, Catalyst.
1. INTRODUCTION
enhanced support can maximize electrocatalytic activity by
immobilizing Pt catalyst and dispersing Pt particles well.
Also, the modified supports reduce usage of Pt which is
expensive noble transition metal.
Recently, owing to depletion of fossil fuel and environ-
mental problem, the much effort has been attempted to
solve the problems. As some alternatives, the different type
of fuel cells such as Proton Exchange Membrane Fuel
Cells (PEMFCs), Solid Oxide Fuel Cells (SOFCs) and
Direct Methanol Fuel Cells (DMFCs) have been presented
as renewable and eco-friendly energy conversion devices.
Among them, DMFCs have received a great attention as
promising energy converters for the portable application
due to much advantage such as low operating temperature,
low pollutant emission, high energy conversion efficiency
and ease of handling liquid fuel.1ꢀ2 However, successful
commercialization of DMFCs has some problems about
low activity and durability of electrocatalyst. To overcome
these problems, the developments of new electrocatalyst
have been attempted. One of the methods is to synthe-
size bimetal such as Pt/Co, Pt/Ru, Pt/Pd, Pt/Sn so that CO
poison of Pt catalyst is mitigated.3
Carbon materials such as carbon blacks, single walled
carbon nanotube and graphene are attracted as a great
support for electrocatalyst of DMFCs.2ꢀ5 Among them,
graphene, honeycomb structure consist of two dimensional
SP2 carbon atoms has remarked in recent years due to
its great characters which are planer structure, large sur-
face area, strong mechanical strength, high conductivity
and thermal properties.4–6 However, the production of per-
fect graphene is very difficult because they have a high
tendency to aggregate themselves through the van der
walls interaction during production process. Because of
this reason, many scientists have studied the prevention
of aggregation between graphenes.7 It is expected that an
introduction of conductive spacer would be an effective
method. The method could provide not only prevention of
their aggregation but also conductive path for charge trans-
fer. In this work, the SWCNT is introduced as a spacer
for prevention of graphenes aggregation. It is expected to
bring the higher effective surface area for Pt deposition
resulting the better electrocatalytic activity.
Another method is to develop the renovated support
such as functionalized various carbon materials.1ꢀ4 The
∗Author to whom correspondence should be addressed.
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doi:10.1166/jnn.2016.12501

Kwon and Kim
Pt-Supported Carbon Nanotubes/Reduced Graphene Oxide Composite Electrodes for a Methanol Oxidation
2. EXPERIMENTAL DETAILS
2.1. Materials
that, 3 ꢁl of suspension was pitted onto grassy carbon
electrode (GCE, 3 mm in diameter). And then, the elec-
ꢀ
trode was coated by dry at 60 C for 30 min. Completed
Graphite powder (99.9%) was purchased from Bay Car-
bon Co. Ltd. Single walled carbon nanotubes and H2PtCl6 ·
6H2O was purchased from Sigma-Aldrich. Ethanol
(99.8%), methanol (99.8%), ethylene glycol (99.0%) were
purchased from DAE JUNG Company, Korea. Distilled
water was used throughout the experiment.
electrode was used as working electrode. Platinum wire
as counter electrode and Ag/AgCl as reference electrode
were used in three-electrode cell system.
2.5. Characterization
The morphology and structure of the composites were
investigated by Field Emission Scanning Electron Micro-
scope (FE-SEM, SUPRA25 and Raith Quantum Elphy)
and Transmission Electron Microscope (TEM, JEOL JSM-
6700F). Cyclic voltammetry (CV) of the composites was
carried out using a potentiostat/galvanostat (Ivium Stat,
Netherlands) in a three-electrode system.
2.2. Synthesis of the Graphite Oxide
Graphite oxide was synthesized using natural graphite by
a modified Hummers’ method.8 First, 1 g of graphite and
1 g of NaNO3 were added in 46 ml H2SO4 (98%). And
then the mixture was stirred in the ice bath for 15 min.
5 g of KMnO4 was slowly added in the mixture and the
temperature of mixture was maintained below 20 ꢀC. After
that, the ice bath was removed and the mixture was stirred
under water bath for 2 h at 35 ꢀC. Then, 80 ml of deionized
(DI) water was added to mixture. 140 ml of hot deion-
ized (DI) water and 6 ml of H2O2 Sequentially was added.
The oxidized solution was filtered and washed with water
through a centrifugation (3600 rpm, 5 min). The graphite
oxide (GO) of bright yellow powder was obtained after
freeze drying.
3. RESULTS AND DISCUSSION
We have introduced simple a manufacture procedure by
the scheme in Figure 1. The process is preceded by chem-
ical method in ethylene glycol. The GO and SWCNT
are dispersed well by sonication. The dispersed RGO and
SWCNT have been stacked again during the reduction
reaction. In the process, the SWCNT could be sandwiched
between graphene layers.
Figure 2 shows the CVs of the Pt/SWCNT/RGO com-
pared to Pt/RGO in 1.0 M H2SO at a potential range
from −0.2 to 1.0 V versus Ag/AgCl at a scan rate of
50 mV·s−1. The adsorption/desorption region of hydro-
gen from −0.2 V to 0.1 V appear according to clear
peaks which are related to surface area of platinum for H2
adsorption.9 When SWCNT was added, the performance
presented considerable increase in adsorption/desorption
area of hydrogen as well as overall CV area. This means
the increased effective surface area of Pt catalyst via
spacer which was produced by inserting SWCNT between
graphenes. The adsorption/desorption region of hydro-
gen are used to calculate electrochemical surface area
(ECSA) that is dependent on the electrocatalytic activ-
ity. The ECSA was calculated according to the following
equation.10
2.3. Synthesis of the Pt/SWCNT/RGO Composites
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The Pt/SWCNT/RGO composite was simultaneously syn-
IP: 37.230.212.109 On: Sat, 08 Apr 2017 16:55:40
thesized with GO, SWCNT and Pt by chemical reduction
Copyright: American Scientific Publishers
method. H2PtCl6 · H2O was introduced in Ethylene gly-
col and it was adjusted to PH about 10∼11 using NaOH
(1.0 M). The SWCNT and GO was added to the solution.
The mixture was then sonicated for 20 min and N2 bub-
bling to remove side reaction products, resulting a good
dispersion ofꢀGO and SWNCT. This was followed by stir-
ring at 120 C for 4 h. After the mixture was filtered,
it was collected by centrifugation and washed repeatedly
with distilled water. And then the product was obtained
through freeze-drying for 24 h.
2.4. Electrochemical Activity Measurement
Electrochemical activity was measured in a three-electrode
cell system using potentiostat/galvanostat. Each sample
was prepared; first, 5 mg of sample was dispersed in a
mixed solution (0.5 ml of distilled water and 0.1 ml of 5%
Nafion D521 solution) with ultrasonication for 1 hr. After
ECSA = QH/ꢂꢃPtꢄ ×0ꢅ21ꢆ
QH means integral charge for absorption/desorption region
of hydrogen (mC/cm2ꢆ and [Pt] means loading of platinum
on electrode (g/cm2ꢆ. 0.21 expresses the charge required
Figure 1. Schematic diagram for a preparation procedure of the Pt/SWCNT/RGO composites.
J. Nanosci. Nanotechnol. 16, 8598–8601, 2016
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Pt-Supported Carbon Nanotubes/Reduced Graphene Oxide Composite Electrodes for a Methanol Oxidation
Kwon and Kim
Figure 3. Cyclic voltammograms of (a) Pt/SWCNT/RGO and (b)
Pt/RGO in methanol solution (1.0 M H2SO4 +2ꢅ0 M methanol).
Figure 2. Cyclic voltammograms of (a) Pt/SWCNT/RGO and
(b) Pt/RGO in 1.0 M H2SO4 solution.
It indicates that the Pt/SWCNT/RGO exhibited the bet-
ter dispersion of deposited Pt and conductive supports
through spacer formed by SWCNT. The result, the
Pt/SWCNT/RGO has high electrocatalytic activity and
stability for a methanol oxidation in comparison to
Pt/RGO.
to oxidize a monolayer of H2 on pure Pt (mC/cm2ꢆ. The
calculated ECSA shows Pt/SWCNT/RGO (70.6 m2/g) is
higher than Pt/RGO (39.1 m2/g) from Table I.
CV graphs for a methanol oxidation reaction (MOR)
are shown in Figure 3 at a potential range from −0.2
to 1.0 V versus Ag/AgCl at a scan rate of 50 mV · s−1
.
To analyze morphological structure, carbon supports or
Pt particle dispersion, the FE-SEM and TEM are shown
Two peaks are observed around 0.7 V and 0.4 V corre-
sponding to methanol oxidation and its intermediate such
as CO adsorbed on Pt surface, respectively. The higher
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in Figure 5. Figure 5(b) shows typically GO sheets which
IP: 37.230.212.109 On: Sat, 08 Apr 2017 16:55:40
have a planar form. When the SWCNTs were added
current density of Pt/SWCNT/RGO explains the enhanced
catalytic activity. The other factor of catalyst performance
is the ratio of the forward anodic peak current (IFꢆ to the
reverse anodic peak current (IRꢆ. Generally, the IF/IR ratio
has been known that CO poisoning increases IR. A higher
IF/IR value indicates that CO poisoning is effectively
removed.5 In other words, it means that methanol is rela-
tively further oxidized to carbon dioxide. Table I present
a value of IF, IR, IF/IR. The IF/IR value of Pt/RGO and
Pt/SWCNT/RGO shows approximately equal value. How-
ever, IF of Pt/SWCNT/RGO showed the higher methanol
oxidation current than that of Pt/RGO. It means that the
addition of SWCNT could improve the catalytic activity
by role of increase of conductivity and the better exfolia-
tion of RGO.11ꢀ12
Copyright: American Scientific Publishers
into GO solution, we identified that the SWCNTs were
located between RGO sheets through Figures 5(a, c). TEM
images represented dispersion of Pt nanoparticles. The Pt
nanoparticles were homogeneously dispersed on Pt/RGO,
Pt/SWCNT/RGO. In case of Pt/SWCNT/RGO, the TEM
images showed that SWCNTs were located between RGO
sheets and Pt deposition on the SWCNT or RGO in
Figure 5(c).
The stabilities of catalytic activity for Pt/RGO and
Pt/SWCNT/RGO were evaluated by chronoamperometry
in Figure 4. The current density decline behavior of
Pt/SWCNT/RGO is slower than the Pt/RGO in the ini-
tial period and the current density of the Pt/SWCNT/RGO
maintained higher than Pt/RGO during the whole time.
Table I. The ECSA, IF, IR, IF/IR value of Pt/SWCNT/RGO, Pt/RGO.
Samples
ECSA (m2/g) IF (mA/cm2ꢆ IR (mA/cm2ꢆ IF/IR
Pt/SWCNT/RGO
Pt/RGO
70.6
39.1
13.7
11.2
8.33
6.66
1.64
1.68
Figure 4. I–t curves of the (a) Pt/SWCNT/RGO and (b) Pt/RGO at
0.7 V for 1200 s in 1.0 M H2SO4 +2ꢅ0 M CH3OH solution.
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J. Nanosci. Nanotechnol. 16, 8598–8601, 2016

Kwon and Kim
Pt-Supported Carbon Nanotubes/Reduced Graphene Oxide Composite Electrodes for a Methanol Oxidation
Figure 5. FE-SEM image of (a) Pt/SWCNT/RGO, (b) Pt/RGO. TEM image of (c) Pt/SWCNT/RGO, (d) Pt/RGO.
4. CONCLUSION
Science, ICT and Future Planning, Korea (Grant No.:
NRF-2011-0009007).
The Pt/SWCNT/RGO composites were successfully pre-
pared and exhibited the better performance than Pt/RGO.
When SWCNT was added, the SWCNT showed a
role of spacer additive between graphenes, which pre-
vent the aggregation. From the electrochemical result,
References and Notes
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Pt/SWCNT/RGO composite has high electrochemical sur-
Delivered by Ingenta to: State University of New York at Binghamton
130, 397 (2014).
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3. S. H. Park, S. J. Joo, and H. S. Kim, J. Electrochem. Soc. 161, F405
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