C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7

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Graphene-supported platinum and platinum–rutheniumnanoparticles with high electrocatalytic activity for methanoland ethanol oxidation

Lifeng Dong a,*, Raghavendar Reddy Sanganna Gari a, Zhou Li b,Michael M. Craig c, Shifeng Hou d

a Department of Physics, Astronomy, and Materials Science, Missouri State University, Springfield, MO 65897, USAb Greenwood Laboratory School, Missouri State University, Springfield, MO 65897, USAc Department of Biomedical Sciences, Missouri State University, Springfield, MO 65897, USAd Department of Chemistry and Biochemistry, Montclair State University, Montclair, NJ 07043, USA

A R T I C L E I N F O

Article history:

Received 26 August 2009

Accepted 20 October 2009

Available online 23 October 2009

0008-6223/$ - see front matter � 2009 Elsevidoi:10.1016/j.carbon.2009.10.027

* Corresponding author: Fax: +1 417 8366226.E-mail address: LifengDong@MissouriStat

A B S T R A C T

In this study, Pt and Pt–Ru nanoparticles were synthesized on graphene sheets and their

electrocatalytic activity for methanol and ethanol oxidation was investigated. Experimen-

tal results demonstrate that, in comparison to the widely-used Vulcan XC-72R carbon black

catalyst supports, graphene-supported Pt and Pt–Ru nanoparticles demonstrate enhanced

efficiency for both methanol and ethanol electro-oxidations with regard to diffusion effi-

ciency, oxidation potential, forward oxidation peak current density, and the ratio of the for-

ward peak current density to the reverse peak current density. For instance, the forward

peak current density of methanol oxidation for graphene- and carbon black-supported Pt

nanoparticles is 19.1 and 9.76 mA/cm2, respectively; and the ratios are 6.52 and 1.39,

respectively; the forward peak current density of ethanol oxidation for graphene- and car-

bon black-supported Pt nanoparticles is 16.2 and 13.8 mA/cm2, respectively; and the ratios

are 3.66 and 0.90, respectively. These findings favor the use of graphene sheets as catalyst

supports for both direct methanol and ethanol fuel cells.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Fuel cells have been receiving increased attention recently

due to the depletion of fossil fuels and the increase in envi-

ronmental pollution. Among different types of fuel cells, di-

rect methanol and ethanol fuel cells are excellent power

sources due to their high energy density, low pollutant emis-

sion, low operating temperature (60–100 �C), and ease of han-

dling liquid fuel. However, there are still some critical

obstacles inhibiting broad applications of direct methanol

and ethanol fuel cells, including low electrocatalytic activity

of anodes for methanol and ethanol oxidation reactions and

er Ltd. All rights reservede.edu (L. Dong).

the high cost of noble metal platinum (Pt)-based catalysts.

In order to enhance the catalytic activity and reduce the

usage of Pt-based catalysts, one strategy is to explore novel

carbon materials to effectively disperse catalyst particles.

Vulcan XC-72R carbon black has been the most widely-used

carbon support for the preparation of fuel cell catalysts be-

cause of its exceptional electronic conductivity and surface

area [1–3]. During the past several years, a number of research

groups have investigated carbon nanotubes as catalyst sup-

ports and have demonstrated that carbon nanotubes can

more effectively improve electrocatalytic activity of Pt nano-

particles for methanol and ethanol oxidation compared to

.

782 C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7

Vulcan XC-72R carbon black [4–12]. In 2005, graphene, a

mono-atomic sheet of hexagonally arranged carbon atoms,

was successfully synthesized [13–15]. Graphene has exhibited

excellent electrical conductivity and extremely high specific

surface area (2600 m2/g), and therefore, graphene should be

explored as a support material to improve electrocatalytic

activity of catalyst particles for methanol and ethanol oxida-

tions [16,17]. In this study, for the first time to our knowledge,

we have systematically investigated the effects of graphene

as a catalyst support on the electrocatalytic activity of Pt

and Pt–Ru nanoparticles for both methanol and ethanol oxi-

dation used in fuel cell applications.

2. Experimental

2.1. Synthesis of graphene-supported Pt and Pt–Runanoparticles

Because graphene has a structure similar to that of carbon

nanotubes, we adapted a method used to prepare carbon

nanotube-supported Pt and platinum–ruthenium (Pt–Ru) cat-

alysts to generate graphene-supported Pt and Pt–Ru catalysts

[18]. For the synthesis of graphene-supported Pt catalysts,

100 mg of graphene oxide powder was dispersed in 10 ml of

ethylene glycol (EG) solution and sonicated for 30 min. Graph-

ene oxide was prepared from graphite powder according to a

method reported by Hummers and Offeman [19]. An aliquot

(1.5 ml) of hexachloroplatinic acid (H2PtCl6, Sigma–Aldrich)

EG solution (7.4 mg H2PtCl6/ml EG) was added into the graph-

ene oxide solution and mechanically stirred for 2 h. Sodium

hydroxide (2.5 M in EG solution) was added to adjust the pH

of the solution to 13.0 (Accumet Model 15 pH meter), and then

the solution was fluxed under flowing argon at 130 �C for 3 h.

The solid was filtered, washed with DI water, and dried in an

oven at 80 �C for 12 h. For the synthesis of graphene-sup-

ported Pt–Ru catalysts, the only difference was to add 1.5 ml

of EG solution, including both H2PtCl6 and ruthenium chloride

(RuCl3, Sigma–Aldrich) (7.4 mg H2PtCl6 and 7.4 mg RuCl3 per

ml of EG), into the graphene oxide solution. Similar proce-

dures were used to prepare graphite (99%, 300 mesh, Fisher

Scientific) and carbon black (Vulcan XC-72R, Fuel Cell Store)

supported Pt and Pt–Ru catalysts.

2.2. Electron microscopy characterization

The morphology of catalyst supports, Pt and Pt–Ru nanoparti-

cles, and the distribution of the nanoparticles on different

supports were explored using a JEOL JSM-840A scanning elec-

tron microscope (SEM) and an FEI Quanta 200 field emission

scanning electron microscope (FESEM) equipped with an Ox-

ford INCA 250 silicon drift X-ray energy dispersive spectrom-

eter (EDS).

2.3. Electrocatalytic activity measurements

Electrocatalytic activities of Pt and Pt–Ru nanoparticles on dif-

ferent supports were measured in a conventional three elec-

trode cell using a CHI 600C electrochemical work station. Pt

wire served as a counter electrode, Ag/AgCl as a reference

electrode, and glassy carbon (3 mm diameter), coated with

nanoparticles, as a working electrode. To fabricate a working

electrode, 7.6 mg of catalyst powder was dispersed in 2 ml of

ethanol solution and sonicated for 30 min; 30 ll of the sus-

pension was placed onto the surface of a glassy carbon elec-

trode and dried for 15 min; and 10 ll of 5% Nafion 117 solution

(Sigma–Aldrich) was sequentially applied and dried for

15 min. The Nafion acted as an adhesive to affix the catalyst

membrane to the electrode surface. Prior to electrochemical

characterizations, all electrolyte solutions were de-aerated

under flowing nitrogen gas for 20 min. Electrocatalytic oxida-

tion of methanol on graphene-, graphite-, and carbon black-

supported Pt and Pt–Ru nanoparticles was measured in 1 M

CH3OH + 0.5 M H2SO4 electrolyte by cyclic voltammetry be-

tween �0.3 and 1.0 V. The potentials were measured and re-

ported with respect to the Ag/AgCl electrode. After

methanol oxidation measurements, the electrodes were

stored in distilled water for 30 min prior to ethanol oxidation

measurements. Electrocatalytic oxidation of ethanol on

graphene-, graphite-, and carbon black-supported Pt and Pt–

Ru nanoparticles was measured in 1 M CH3CH2OH + 0.5 M

H2SO4 electrolyte by cyclic voltammetry between �0.3 and

1.0 V.

Electrical current density was calculated by normalizing

electrical current on the area of 3 mm diameter glassy carbon

electrodes. In order to ensure the reproducibility of experi-

mental results, all electrocatalyst powders, including graph-

ene-, graphite-, and carbon black-supported Pt and Pt–Ru

nanoparticles, were synthesized for three times; the same

amount of catalytic powder was cautiously loaded onto the

electrodes.

3. Results and discussion

3.1. Structural characterization

Graphene, graphite, and Vulcan XC-72R carbon black have dif-

ferent morphologies and dimensions (Fig. 1). Graphene sheets

(Fig. 1a) are rippled and crumpled, with a dimension of sev-

eral hundred nm to several lm; graphite supports (Fig. 1b)

are platelets with a dimension ranging from 5 to 60 lm; and

carbon black (Fig. 1c) has a much smaller dimension that var-

ies from 30 to 100 nm. The morphological variety of graphene

and graphite supports will assist in the correlations between

support morphology and its effects on electrocatalytic activity

of methanol and ethanol oxidations in comparison to the

widely-used Vulcan XC-72R carbon black.

Several groups have reported that metallic nanoparticles

not only play an essential role in catalytic reduction of graph-

ene oxide with ethylene glycol, but also prevent the aggrega-

tion and restacking of the reduced graphene oxide by the

formation of graphene particle composites [20,21]. Since Pt

has a much higher atomic number (Z = 78) than C (Z = 6), we

employed a backscattered electron (BSE) detector to investi-

gate the configuration of Pt nanoparticles formed on graph-

ene sheets. Backscattered electron imaging is a Z-contrast

technique that yields compositional contrast information in

the acquired images. The signal from the BSE detector is

proportional to the backscatter coefficient, which nearly

Fig. 1 – SEM images of three types of catalyst supports

demonstrating different morphologies and dimensions: (a)

graphene, (b) graphite, and (c) Vulcan XC-72R carbon black.

Images are presented at magnifications appropriate for

demonstration of support features.

C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7 783

monotonically increases with increasing Z. A typical second-

ary electron (SE) image of graphene-supported Pt nanoparti-

cles is demonstrated in Fig. 2a, and a corresponding BSE

image of the same region is shown in Fig. 2b. In Fig. 2b, the

higher Z particles appear brighter than the lower Z back-

ground structures. The bright particles are Pt nanoparticles,

with a size of less than 10 nm, that are difficult to detect in

the SE image (Fig. 2a). EDS spectra in Fig. 2c and d further con-

firm that Pt and Pt–Ru nanoparticles, respectively, were

formed on graphene sheets. The oxygen signal indicates that

the conversion of graphene oxide into graphene with ethyl-

ene glycol is incomplete, and the sodium signal results from

sodium nitrate and sodium hydroxide, which were used dur-

ing the preparation of graphene oxide and the synthesis of

nanoparticles, respectively. Similar results were observed for

graphite- and carbon black-supported Pt and Pt–Ru

nanoparticles.

3.2. Electrocatalytic activity for methanol oxidationreaction

The electrocatalytic activity of methanol oxidation on graph-

ene-supported Pt and Pt–Ru nanoparticles was characterized

by cyclic voltammetry in an electrolyte of 1 M CH3OH and

0.5 M H2SO4 at 50 mV/s. The voltammograms of each sample

became similar and stable after the fifth cycle. The resulting

voltammograms from the fifth cycle are shown in Fig. 3.

The efficiencies of the Pt and Pt–Ru nanoparticles on metha-

nol oxidation were compared with regard to oxidation poten-

tial, forward oxidation peak current density, and the ratio of

the forward peak current density to the reverse peak current

density; these data are summarized in Table 1.

Graphene-supported Pt nanoparticles have a higher activ-

ity for methanol oxidation and a better tolerance to CO in

comparison to carbon black- and graphite-supported Pt nano-

particles (Fig. 3a). On the forward potential sweep, the current

increases slowly at lower potentials and then quickly in-

creases at potentials higher than 0.5 V, with oxidation occur-

ring at approximately 0.65 V. The magnitude of the peak

current density is directly proportional to the amount of

methanol oxidized at the electrode. The peak current density

observed with graphene is approximately 19 mA/cm2, nearly

two times to three times the peak current density for carbon

black and graphite, respectively; this result suggests that

graphene plays a critical role in promoting the methanol oxi-

dation of Pt nanoparticles. In the reverse potential sweep, an

oxidation peak is observed around 0.46 V, putatively associ-

ated with the removal of CO and other residual carbon species

formed on the electrode in the forward sweep. The reverse

anodic peak current density (2.93 mA/cm2) is much lower

than those measurements for carbon back (7.01 mA/cm2)

and graphite (6.17 mA/cm2). The ratio of the forward anodic

peak current density (IF) to the reverse anodic peak current

density (IR) can be used to describe the catalyst tolerance to

CO and other carbonaceous species. Graphene-supported Pt

nanoparticles have a ratio of 6.52, much higher than carbon

black (1.39) and graphite (1.03) supported Pt nanoparticles, a

result which suggests that graphene-supported Pt nanoparti-

cles generate a more complete oxidation of methanol to car-

bon dioxide.

As shown in Fig. 3b, the addition of Ru results in a negative

shift of oxidation potential of methanol at all three electrodes

with the decreasing of IR and the increasing of the IF to IR ratio.

The oxidation peak potential of methanol was 0.50 V com-

pared with an oxidation potential of 0.65 V for graphene-Pt

nanoparticles. This observation suggests that the presence

of Ru can significantly decrease the barrier to methanol oxi-

dation, and that Pt–Ru nanoparticles perform in a better fash-

ion than Pt nanoparticles. Conversely, the oxidation potential

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((c) (d)

Fig. 2 – (a) SE image of graphene-supported Pt nanoparticles and its corresponding Z-contrast BSE image (b) shows that Pt

nanoparticles with a dimension less than 10 nm were synthesized on graphene sheets. EDS spectra (c and d) were obtained

from graphene-supported Pt and Pt–Ru nanoparticles, respectively.

784 C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7

of methanol at both carbon black- and graphite-supported Pt–

Ru nanoparticles minimally shifts 0.02 V (0.58–0.56 V) and

0.01 V (0.59–0.58 V), respectively. These data indicate that

graphene-supported Pt–Ru nanoparticles may be an ideal

candidate for direct methanol fuel cell electrodes. The above

data also clearly support the proposition that Ru–Pt nanopar-

ticles can effectively advance the oxidation of methanol to

CO2 and inhibit the accumulation of CO and other carbona-

ceous species formed on the graphene, carbon black, and

graphite electrodes. For graphene electrodes especially, there

is no obvious reverse peak in Fig. 3b. Similar effects of Ru on

other catalysts for methanol oxidation have been reported by

a number of research groups [22,23].

As given in Fig. 3c and d, for all graphene-, carbon black-,

and graphite-supported Pt and Pt–Ru nanoparticles, the for-

ward oxidation current density (IF) is proportional to the

square root of the scan rate, suggesting that the oxidation

behavior of methanol at all electrodes is controlled by diffu-

sion processes. The slopes for graphene supports are larger

than those for carbon black and graphite, indicative of a faster

diffusion process of methanol on the surfaces of graphene

sheets than that for methanol on the carbon black and graph-

ite substrata.

3.3. Electrocatalytic activity for ethanol oxidation reaction

In comparison to direct methanol fuel cells, fuel cells based

on direct ethanol oxidation possess several advantages, such

as demonstrating enhanced safety, having a higher energy

density (8.01 vs. 6.09 kW/kg), and being more easily produced

in large quantities from agricultural products and from the

fermentation of biomass [24]. A complete ethanol electro-oxi-

dation involves the release of 12 electrons per molecule and

the cleavage of the C–C bond. Experimental studies have re-

vealed that ethanol is largely and partially oxidized to acetal-

dehyde and acetic acid (two- and four-electron oxidation,

respectively) instead of being fully oxidized (12-electron oxi-

dation) [25]. The ethanol electro-oxidation was considered

more complicated than that of methanol, and consequently,

needs more active and selective catalysts. In this study, we

investigated effects of graphene as a catalyst support for eth-

anol electro-oxidation of Pt and Pt–Ru nanoparticles in com-

parison to the extensively-used Vulcan XC-72R carbon black.

Compared with carbon black and graphite, graphene en-

hances considerably the electrocatalytic activity of Pt nano-

particles for ethanol oxidation by increasing the forward

oxidation current density and decreasing the reverse peak

(a) (b)

(c) (d)

Fig. 3 – Electrocatalytic activity of graphene-, Vulcan XC-72R carbon black-, and graphite-supported Pt and Pt–Ru

nanoparticles for methanol oxidation: cyclic voltammograms of (a) Pt nanoparticles and (b) Pt–Ru nanoparticles in 1 M

CH3OH/0.5 M H2SO4 at 50 mV/s between �0.3 and +1.0 V vs. Ag/AgCl; and the relationship of peak current density vs. scan

rate for (c) Pt nanoparticles and (d) Pt–Ru nanoparticles.

Table 1 – Comparison of electrocatalytic activity of methanol oxidation on graphene-, carbon black-, and graphite-supportedPt and Pt–Ru nanoparticles.

Electrode Forward sweep Reverse sweep IF/IR Ratio

IF (mA/cm2) E (V) IR (mA/cm2) E (V)

Pt–graphene 19.1 0.65 2.93 0.46 6.52Pt–CB 9.76 0.59 7.01 0.43 1.39Pt–graphite 6.33 0.58 6.17 0.41 1.03Pt–Ru–graphene 16.5 0.50 – – –Pt–Ru–CB 5.23 0.58 1.51 0.36 3.46Pt–Ru–graphite 2.32 0.56 1.53 0.37 1.52

C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7 785

current density (Fig. 4a and Table 2). Both IF to IR ratios for car-

bon black and graphite were less than 1.0. As discussed above,

the ratio describes the catalyst tolerance to CO-like interme-

diates formed on electrodes during the forward potential

sweep. The high forward peak current density and the high

IF to IR ratio for graphene-supported Pt nanoparticles indicate

that graphene effectively enhances the complete oxidation of

ethanol to CO2, and fewer CO-like carbonaceous species accu-

mulate on the electrode surface.

As given in Fig. 4b, the addition of Ru effectively lowers the

potentials for ethanol oxidations and increases the IF to IR ra-

tios. The oxidation peak potential of ethanol was 0.66 V for

graphene-supported Pt–Ru nanoparticles in comparison to

an oxidation potential of 0.72 V for graphene-supported Pt

nanoparticles. The potential shift of ethanol oxidation is

0.06 V, a value that is less than the potential shift of methanol

oxidation (0.15 V, from 0.65 to 0.50 V), thus suggesting that the

graphene-supported Pt–Ru nanoparticles are more suitable

(a) (b)

(c) (d)

Fig. 4 – Electrocatalytic activity of graphene-, Vulcan XC-72R carbon black-, and graphite-supported Pt and Pt–Ru

nanoparticles for ethanol oxidation: cyclic voltammograms of (a) Pt nanoparticles and (b) Pt–Ru nanoparticles in 1 M

CH3CH2OH/0.5 M H2SO4 at 50 mV/s between �0.3 and + 1.0 V vs. Ag/AgCl; and the relationship of peak current density vs.

scan rate for (c) Pt nanoparticles and (d) Pt–Ru nanoparticles.

Table 2 – Comparison of electrocatalytic activity of ethanol oxidation on graphene-, carbon black-, and graphite-supported Ptand Pt–Ru nanoparticles.

Electrode Forward sweep Reverse sweep IF/IR Ratio

IF (mA/cm2) E (V) IR (mA/cm2) E (V)

Pt–graphene 16.2 0.72 4.43 0.48 3.66Pt–CB 13.8 0.65 15.3 0.46 0.90Pt–graphite 7.42 0.63 8.97 0.46 0.83Pt–Ru–graphene 18.1 0.66 5.23 0.46 3.46Pt–Ru–CB 7.50 0.64 4.93 0.36 1.52Pt–Ru–graphite 2.43 0.61 1.22 0.31 1.99

786 C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7

for methanol oxidation than for ethanol oxidation. In addi-

tion, no significant shifts of oxidation potential for ethanol

were observed for carbon black (from 0.65 to 0.64 V) and

graphite (0.63 to 0.61 V) supported Pt nanoparticles.

For all graphene-, carbon black-, and graphite-supported Pt

and Pt–Ru nanoparticles, the forward oxidation peak current

density (IF) is proportional to the square root of the scan rate,

suggesting that the oxidation of ethanol at all electrodes is a

diffusion-controlled phenomenon (Fig. 4c and d). Graphene

has a larger slope than the carbon black and graphite, suggest-

ing that the diffusion efficiency of ethanol inside graphene

sheets is higher than that inside carbon black and graphite

and therefore, can enhance the efficiency and capacity of fuel

cells.

Experimental results on electrocatalytic activity of both

methanol and ethanol oxidations clearly demonstrate that

graphene-supported Pt and Pt–Ru nanoparticles possess

superior electrocatalytic activity compared to Vulcan XC-72R

C A R B O N 4 8 ( 2 0 1 0 ) 7 8 1 – 7 8 7 787

carbon black and graphite supports. Exceptional electrical

conductivity and large surface area are two critical parame-

ters for the development of novel catalyst supports for direct

methanol and ethanol fuel cells. Graphene sheets possess

both advantages when compared to Vulcan XC-72R carbon

black and graphite.

4. Conclusions

Pt and Pt–Ru nanoparticles were successfully synthesized on

graphene sheets. In comparison to Vulcan XC-72R carbon

black as a catalyst support, graphene can more effectively en-

hance electrocatalytic activity of Pt and Pt–Ru nanoparticles

for the oxidation of methanol and ethanol into CO2. With

the introduction of Ru, the reverse peak current density for

graphene is difficult to observe, a result which indicates that

the addition of Ru can efficiently release CO-like carbona-

ceous species adsorbed on the Pt surface. Similar enhance-

ment effects occur regarding the electrocatalytic activity of

Pt and Pt–Ru nanoparticles for ethanol oxidation. These find-

ings suggest promising applications for graphene as catalyst

supports, contingent upon the development of large scale

graphene sheet production.

Acknowledgements

This research was financially supported by a Faculty Research

Grant from Missouri State University and the National Sci-

ence Foundation under Award No. DMR-0821159. Acknowl-

edgment is also made to the Donors of the American

Chemical Society Petroleum Research Fund (47532-GB10) for

partial support of this research.

R E F E R E N C E S

[1] Lin YH, Cui XL, Yen CH, Wai CM. PtRu/carbon nanotubenanocomposites synthesized in supercritical fluid: a novelelectrocatalyst for direct methanol fuel cells. Langmuir2005;21:11474–9.

[2] Maiyalagan T, Viswanathan B, Varadaraju UV. Nitrogencontaining carbon nanotubes as supports for Pt-alternateanodes for fuel cell applications. Electrochem Commun2005;7(9):905–12.

[3] Guo YL, Zheng YZ, Huang MH. Enhanced activity of PtSn/Canodic electrocatalyst prepared by formic acid reduction fordirect ethanol fuel cells. Electrochim Acta 2008;53:3102–8.

[4] Tsai MC, Yeh TK, Tsai CH. An improved electrodepositiontechnique for preparing platinum and platinum–rutheniumnanoparticles on carbon nanotubes directly grown on carboncloth for methanol oxidation. Electrochem Commun2006;8:1445–52.

[5] Chen CC, Chen CF, Chen CM, Chuang FT. Modification ofmulti-walled carbon nanotubes by microwave digestionmethod as electrocatalyst supports for direct methanol fuelcell applications. Electrochem Commun 2007;9:159–63.

[6] Selvaraj V, Alagar M. Pt and Pt–Ru nanoparticles decoratedpolypyrrole/multi-walled carbon nanotubes and their

catalytic activity towards methanol oxidation. ElectrochemCommun 2007;9:1145–53.

[7] Maiyalagan T. Synthesis and electro-catalytic activity ofmethanol oxidation on nitrogen containing carbonnanotubes supported Pt electrodes. Appl Catal B: Environ2008;80:286–95.

[8] Rajesh B, Thampi KR, Bonard JM, Xanthopoulos N, MathieuHJ, Viswanathan B. Carbon nanotubes generated fromtemplate carbonization of polyphenyl acetylene as thesupport for electrooxidation of methanol. J Phys Chem B2003;107:2701–8.

[9] Tang H, Chen JH, Huang ZP, Wang DZ, Ren ZF, Nie LH, et al.High dispersion and electrocatalytic properties of platinumon well-aligned carbon nanotube arrays. Carbon2004;42:191–7.

[10] Zhao XS, Li WZ, Jiang LH, Zhou WJ, Xin Q, Yi BL, et al. Multi-wall carbon nanotube supported Pt–Sn nanoparticles as ananode catalyst for the direct ethanol fuel cell. Carbon2004;42:3263–5.

[11] Girishkumar G, Hall TD, Vinodgopal K, Kamat PV. Single wallcarbon nanotube supports for portable direct methanol fuelcells. J Phys Chem B 2006;110:107–14.

[12] Halder A, Sharma S, Hegde MS, Ravishankar N. Controlledattachment of ultrafine platinum nanoparticles onfunctionalized carbon nanotubes with high electrocatalyticactivity for methanol oxidation. J Phys Chem C2009;113:1466–73.

[13] Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y,Dubonos SV, et al. Electric field effect in atomically thincarbon films. Science 2004;306:666–9.

[14] Novoselov KS, Geim AK, Morozov SV, Jiang D, Katsnelson MI,Grigorieva IV, et al. Two-dimensional gas of massless Diracfermions in graphene. Nature 2005;438:197–200.

[15] Zhang YB, Tan YW, Stormer HL, Kim P. Experimentalobservation of the quantum Hall effect and Berry’s phase ingraphene. Nature 2005;438:201–4.

[16] Seger B, Kamat PV. Electrocatalytically active graphene-platinum nanocomposites: role of 2-D carbon support in PEMfuel cells. J Phys Chem C 2009;113:7990–5.

[17] Yoo EJ, Okata T, Akita T, Kohyama M, Nakamura J, Honma I.Enhanced electrocatalytic activity of Pt subnanoclusters ongraphene nanosheet surface. Nano Lett 2009;9:2255–9.

[18] Li WZ, Liang CH, Zhou WJ, Qiu JS, Zhou ZH, Sun GQ, et al.Preparation and characterization of multiwalled carbonnanotube-supported platinum for cathode catalysts of directmethanol fuel cells. J Phys Chem B 2003;107:6292–9.

[19] Hummers WS, Offeman RE. Preparation of graphitic oxide. JAm Chem Soc 1958;80:1339.

[20] Xu C, Wang X, Zhu JW. Graphene-metal particlenanocomposites. J Phys Chem C 2008;112:19841–5.

[21] Si YC, Samulski ET. Exfoliated graphene separated byplatinum nanoparticles. Chem Mater 2008;20:6792–7.

[22] Long JW, Stroud RM, Swider-Lyons KE, Rolison DR. How tomake electrocatalysts more active for direct methanoloxidation avoid PtRu bimetallic alloys! J Phys Chem B2000;104:9772–6.

[23] Maillard F, Gloaguen F, Leger JM. Preparation of methanoloxidation electrocatalysts: ruthenium deposition on carbon-supported platinum nanoparticles. J Appl Electrochem2003;33:1–8.

[24] Lamy C, Lima A, LeRhun V, Delime F, Cutanceau C, Leger JM.Recent advances in the development of direct alcohol fuelcells. J Power Sources 2002;105:283–96.

[25] Wang HF, Liu ZP. Selectivity of direct ethanol fuel cell dictatedby a unique partial oxidation channel. J Phys Chem C2007;111:12157–60.