This document summarizes research on developing Pt/V2O5-C composite catalysts for methanol oxidation in direct methanol fuel cells (DMFCs). Pt nanoparticles were dispersed on a V2O5-C composite support through chemical reduction. The catalyst was characterized using XRD and TEM, which showed the formation of small Pt nanoparticles (~3 nm) on the support. Electrochemical testing showed that the Pt/V2O5-C composite catalyst had higher catalytic activity for methanol oxidation compared to a commercial Pt/C catalyst, as indicated by a more positive onset potential and higher forward/reverse peak current ratios. The composite catalyst also demonstrated comparable stability during chronoamperometry testing. The improved performance is attributed to

1. Catalysis Communications 10 (2009) 433–436
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Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Electrochemical oxidation of methanol on Pt/V2O5–C composite catalysts
T. Maiyalagan *, F. Nawaz Khan
Department of Chemistry, School of Science and Humanities, VIT University, Vellore 632 014, India
a r t i c l e
i n f o
Article history:
Received 5 June 2008
Received in revised form 26 September
2008
Accepted 2 October 2008
Available online 22 October 2008
Keywords:
Pt nanoparticles
Methanol oxidation
DMFC
Electro-catalyst
a b s t r a c t
Platinum nanoparticles have been supported on V2O5–C composite through the reduction of chloroplatinic acid with formaldehyde. The catalyst was characterized by X-ray diffraction and transmission electron microscopy. Catalytic activity and stability for the oxidation of methanol were studied by using
cyclic voltammetry and chronoamperometry. Pt/V2O5–C composite anode catalyst on glassy carbon electrode show higher electro-catalytic activity for the oxidation of methanol. High electro-catalytic activities
and good stabilities could be attributed to the synergistic effect between Pt and V2O5, avoiding the electrodes being poisoned.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Since the last decade, fuel cells have been receiving an increased
attention due to the depletion of fossil fuels and rising environmental pollution. Fuel cells have been demonstrated as interesting and
very promising alternatives to solve the problem of clean electric
power generation with high efficiency. Among the different types
of fuel cells, direct methanol fuel cells (DMFCs) are excellent power
sources for portable applications owing to its high energy density,
ease of handling liquid fuel, low operating temperatures (60
À100 °C) and quick start up [1,2]. Furthermore, methanol fuel cell
seems to be highly promising for large-scale commercialization in
contrast to hydrogen-fed cells, especially in transportation [3].
The limitation of methanol fuel cell system is due to low catalytic
activity of the electrodes, especially the anodes and at present,
there is no practical alternative to Pt based catalysts. High noble
metal loadings on the electrode [4,5] and the use of perfluorosulfonic acid membranes significantly contribute to the cost of the devices. An efficient way to decrease the loadings of precious
platinum metal catalysts and higher utilization of Pt particles is
by better dispersion of the desired metal on the suitable support [6].
In order to reduce the amount of Pt loading on the electrodes,
there have been considerable efforts to increase the dispersion of
the metal on the support. Pt nanoparticles have been dispersed on
a wide variety of substrates such as carbon nanomaterials [7,8] polymers nanotubules, [9] polymer-oxide nanocomposites [10], three
dimensional organic matrices [11], and oxide matrices [12–22].
* Corresponding author. Tel.: +91 0416 2202465; fax: +91 0416 2243092.
E-mail address: maiyalagan@gmail.com (T. Maiyalagan).
1566-7367/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2008.10.011
Most often the catalyst is dispersed on a conventional carbon
support and the support material influences the catalytic activity
through metal support interaction. Dispersion of Pt particles on
an oxide matrix can lead, depending mainly on the nature of support, to Pt supported oxide system that shows better behaviour
than pure Pt. On the other hand, if the oxide is not involved in
the electrochemical reactions taking place on the Pt sites, it might
just provide a convenient matrix to produce a high surface area
catalyst [23,24].
Recently metal oxides like CeO2 [25], ZrO2 [26], MgO [17], TiO2
[18] and WO3 [27] were used as electro-catalysts for direct oxidation of alcohol which significantly improve the electrode performance for alcohols oxidation, in terms of the enhanced reaction
activity and the poisoning resistance.
V2O5 has been extensively used as cathode in lithium ion batteries [28]. Vanadium (IV)/vanadium (III) redox couple has been
used to construct a redox type of fuel cell [29]. V2O5 has been
tested as anode for electro-oxidation of toluene [30]. Furthermore,
V2O5 is a strong oxidant, V2O5 acts as a good oxidation catalyst for
methanol [31,32].
The present report focuses on the efforts undertaken to develop
metal oxide supports based platinum catalysts for methanol oxidation. In this communication the preparation of highly dispersed platinum supported on V2O5–carbon composites, the evaluation of the
activity for the methanol oxidation of these electrodes and comparison with the activity of conventional 20% Pt/C electrodes are reported. These materials are characterized and studied, using XRD,
TEM and cyclic voltammetry. The electrochemical properties of the
composite electrode were compared to those of the commercial electrode, using cyclic voltammetry. The Pt Supported V2O5–C composite

2. T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436
2.2. Preparation of electro-catalysts
The V2O5/C composite used in this study was prepared by a solid-state reaction under the microwave irradiation. The aqueous
solution of V2O5 was well dispersed with carbon black (Vulcan
XC-72R, Cabot Corp., USA) and precipitate was dried in oven at
100 °C. The mixture was then introduced into a microwave oven
and heated 10 s and paused 40 s for ten times alternately.
Pt nanoparticles supported on V2O5–C composite was prepared
through the reduction of chloroplatinic acid with formaldehyde.
The V2O5/C composite powder (ca. 100 mg) was ground gently
with a mortar and pestle then suspended in about 20 ml H2O.
H2PtCl6 solution was used (Aldrich) for deposition of Pt was then
added in an amount slightly greater than the desired loading.
The suspension was stirred at around 80 °C for 30 min to allow dispersion and aqueous formaldehyde (BDH, 37%) was added followed by heating at reflux for 1 h. The composite catalyst were
collected by filtration, washed thoroughly with water, and then
dried under vacuum (25–50 °C).
The same procedure as the above was repeated for the preparation of Pt/C catalyst. The same procedure and conditions were used
to make a comparison between the Pt/C and Pt/V2O5–C system.
2.3. Preparation of working electrode
Glassy carbon (GC) (Bas electrode, 0.07 cm2) was polished to a
mirror finish with 0.05 lm alumina suspensions before each
experiment and served as an underlying substrate of the working
electrode. In order to prepare the composite electrode, the catalysts were dispersed ultrasonically in water at a concentration of
1 mg mlÀ1 and 20 ll aliquot was transferred on to a polished glassy
carbon substrate. After the evaporation of water, the resulting thin
catalyst film was covered with 5 wt% Nafion solution. Then the
electrode was dried at 353 K and used as the working electrode.
2.4. Characterization methods
The phases and lattice parameters of the catalyst were characterized by X-ray diffraction (XRD) patterns employing Shimadzu
XD-D1 diffractometer using Cu Ka radiation (k = 1.5418 Å) operating at 40 kV and 48 mA. XRD samples were obtained by depositing
carbon-supported nanoparticles on a glass slide and drying the later in a vacuum overnight. For transmission electron microscopic
studies, the composite dispersed in ethanol were placed on the
copper grid and the images were obtained using JEOL JEM-3010
model, operating at 300 keV.
2.5. Electrochemical measurements
All electrochemical studies were carried out using a BAS 100
electrochemical analyzer. A conventional three-electrode cell con-
3. Results and discussion
The Pt/V2O5–C composite catalysts were characterized by XRD.
The XRD pattern of as-synthesized Pt/C and Pt/V2O5–C catalysts is
given in Fig. 1. The diffraction peak at 24–27° observed is attributed to the hexagonal graphite structure (002) of Vulcan carbon.
The peaks can be indexed at 2h = 39.8° (1 1 1), 46.6° (2 0 0) and
67.9° (2 2 0) reflections of a Pt face-centered cubic (FCC) crystal
structure. The diffraction peak at 2h = 39.8° for Pt (1 1 1) corresponds well to the inter-planer spacing of d111 = 0.226 nm and
the lattice constant of 3.924 Å. The facts agree well with the standard powder diffraction file of Pt (JCPDS number 1-1311). From the
isolated Pt (2 2 0) peak, the mean particle size was about 3.1 nm
and 2.8 nm for the Pt/C and Pt/V2O5–C catalysts samples respectively, calculated with the Scherrer formula [33]. This suggests that
very small Pt nanoparticles dispersed on the Pt/V2O5–C composite.
The formation of broad peaks in V2O5-modified Pt/C catalysts indicated the presence of smaller Pt nanoparticles. But the diffraction
peaks of Pt–V2O5/C are slightly shifted to lower values when compared to Pt/C. This is an indication that an alloy between Pt and
V2O5 is being formed on the Pt–V2O5/C catalysts. Moreover, in
the XRD patterns of the V2O5-modified Pt catalysts, the peaks associated with pure V2O5 did not appear prominently. This might be
due to the presence of very small amount of V2O5 in catalysts.
However, XRD measurements cannot supply exact information
of crystallite size when it is less than 3.0 nm, for this reason, the
figures obtained by the above equation will be slightly smaller
than true ones. Fig. 2 shows TEM images of Pt/C and Pt/V2O5–C catalysts. The mean size was estimated to be 2.9 nm for Pt/C and
3.4 nm for Pt/V2O5–C, which was in good agreement with the results from XRD.
The electro-catalytic activities for methanol oxidation of Pt/C
and Pt/V2O5–C electro-catalysts were analyzed by cyclic voltam-
(c)
(a) Vulcan XC-72
(b) 20% Pt/C
(c) 20% Pt/V2O5- C
Pt (220)
All the chemicals used were of analytical grade. V2O5 obtained
from Merck was used. Hexachloroplatinic acid was obtained from
Aldrich. Vulcan XC-72 carbon black was purchased from Cabot
Inc., Methanol and sulphuric acid were obtained from Fischer
chemicals. Nafion 5 wt% solution was obtained from Dupont and
was used as received.
Pt (200)
2.1. Materials
Pt (111)
2. Experimental
sisting of the GC (0.07 cm2) working electrode, Pt plate (5 cm2) as
counter electrode and Ag/AgCl reference electrode were used for
the cyclic voltammetry (CV) studies. The CV experiments were performed using 1 M H2SO4 solution in the absence and presence of
1 M CH3OH at a scan rate of 50 mV/s. All the solutions were prepared by using ultra pure water (Millipore, 18 MX). The electrolytes were degassed with nitrogen gas before the electrochemical
measurements.
C (002)
electrode exhibited excellent catalytic activity and stability compared to the 20 wt% Pt supported on the Vulcan XC-72R carbon.
Intensity (a.u)
434
(b)
(a)
20
30
40
50
60
70
80
2θ (degrees)
Fig. 1. XRD spectra of (a) Vulcan XC-72 (b) Pt/Vulcan XC-72 and (c) Pt–V2O5/Vulcan
XC-72.

3. 435
T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436
(a)
(a) 20%Pt/V O5- C
2
Current density (mA/cm2 )
15
(b) 20% Pt/C
(b)
10
5
0
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
Potential (V) vs Ag/AgCl
Fig. 3. Cyclic voltammograms of (a) Pt/V2O5–C and (b) Pt/C in 1 M H2SO4/1 M
CH3OH run at 50 mV/s.
Fig. 2. TEM images of (a) Pt/C and (b) Pt/V2O5–C electro-catalysts.
metry in an electrolyte of 1 M H2SO4 and 1 M CH3OH at 50 mV/s.
The cyclic voltammograms of Pt/C and Pt based V2O5 composite
electrodes are shown in Fig. 3, respectively. The data obtained from
the cyclic voltammograms of the composite electrodes were compared in Table 1.
The onset for methanol oxidation on Pt/C was found to be
0.31 V, which is 100 mV more positive than Pt/V2O5–C electrode
(0.21 V). This gives clear evidence for the superior electro-catalytic
activity of Pt/V2O5–C composite electrodes for methanol oxidation.
The ratio of the forward anodic peak current (If) to the reverse
anodic peak current (Ib) can be used to describe the catalyst tolerance to accumulation of carbonaceous species [34–38]. A higher
ratio indicates more effective removal of the poisoning species
on the catalyst surface. The If/Ib ratios of Pt/V2O5–C and Pt/C are
1.06 and 0.90, respectively, which are higher than that of Pt/C
(0.90), showing better catalyst tolerance of Pt/V2O5–C composites.
Chronoamperometric experiments were carried out to observe
the stability and possible poisoning of the catalysts under shorttime continuous operation. Fig. 4 shows the evaluation of activity
of Pt/C and Pt/V2O5–C composite electrodes with respect to time
at constant potential of +0.6 V. It is clear from Fig. 4 when the electrodes are compared under identical experimental conditions; the
Pt/V2O5–C composite electrodes show a comparable stability to the
20% Pt/C electrodes.
The higher activity of composite electrodes demonstrates the
better utilization of the catalyst. Also the redox potential of vanadium oxide (VO2+/V3+) is +337 mV (vs. SHE) which lying on the
electrode potential of methanol oxidation favours oxidation of
methanol. Enhancement in catalytic activity of Pt–Ru compared
to pure platinum can be attributed to a bifunctional mechanism:
platinum accomplishes the dissociative chemisorption of methanol
whereas ruthenium forms a surface oxy-hydroxide which subsequently oxidizes the carbonaceous adsorbate to CO2 [39,40]. Based
on most accepted bifunctional mechanism of Pt–Ru, similar type of
mechanism has been interpreted for enhancement in the catalytic
activity of Pt–V2O5 [41]. First, methanol is preferred to bind with Pt
surface atoms, and dehydrogenated to form CO adsorbed species.
The COad intermediates are thought as the main poisoning species
during electro-oxidation of methanol. Thus how to oxidize COad
intermediates as quickly as possible is very important to methanol
oxidation. Due to the higher affinity of vanadium oxides towards
Table 1
Comparison of activity of methanol oxidation between Pt/V2O5–C and Pt/C electrodes.
S. No.
Electrode
Onset potential (V)
Activitya
If/Ib
Forward sweep
Reverse sweep
E (V)
1
2
Pt/C (J.M.)
Pt–V2O5/C
a
0.31
0.21
I (mA cmÀ2)
E (V)
I (mA cmÀ2)
0.76
0.811
12.25
17.4
0.62
0.63
13.49
16.52
Activity evaluated from cyclic voltammogram run in 1 M H2SO4/1 M CH3OH.
0.9
1.06

4. 436
T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436
60
(a) 20% Pt/VO5- C
2
(b) 20% Pt/C
2
Current density (mA/cm )
50
intermediates. Easier formation of the oxygen-containing species
on the surface of V2O5 favours the oxidation of CO intermediates
to CO2 and releasing the active sites on Pt for further electrochemical reaction.
References
40
[1]
[2]
[3]
[4]
[5]
[6]
30
20
(a)
[7]
10
[8]
[9]
[10]
(b)
0
[11]
0
500
1000
1500
Time (Sec)
Fig. 4. Current density vs. time curves at (a) Pt/V2O5–C (b) Pt/C measured in 1 M
H2SO4 + 1 M CH3OH. The potential was stepped from the rest potential to 0.6 V vs.
Ag/AgCl.
[12]
[13]
[14]
[15]
[16]
oxygen-containing species, sufficient amounts of OHad to support
reasonable CO oxidation rates are formed at lower potential on
V2O5 composite sites than on Pt sites. The OHad species are necessary for the oxidative removal of COad intermediates. This effect
leads to the higher activity and longer lifetime for the overall
methanol oxidation process on Pt/V2O5–C composite. Based on
the experimental results, to illustrate the enhanced activity of
methanol electro-oxidation a similar promotional reaction model
is proposed as follows,
CH3 OHad ! COad þ 4Hþ þ 4eÀ
V2 O5 þ 2Hþ ! 2VOþ þ H2 O
2
4VOþ þ 4Hþ ! 4VO2þ þ O2 þ 2H2 O
2
VO2þ þ H2 O ! VOOHþ þ Hþ
COad þ VOOHþ ! CO2 þ VO2þ þ Hþ þ eÀ
4. Conclusion
Highly dispersed nanosized Pt particles on V2O5–C composite
have been prepared by formaldehyde reduction.Pt/V2O5–C composite catalyst exhibits higher catalytic activity for the methanol
oxidation reaction than Pt/C, which is attributed to the synergetic effects due to formation of an interface between the platinum and V2O5, and by spillover due to diffusion of the CO
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