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
Received 5 June 2008
Received in revised form 26 September
Accepted 2 October 2008
Available online 22 October 2008
a b s t r a c t
Platinum nanoparticles have been supported on V2O5–C composite through the reduction of chloroplat-
inic acid with formaldehyde. The catalyst was characterized by X-ray diffraction and transmission elec-
tron 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 elec-
trode 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 elec-
trodes being poisoned.
Ó 2008 Elsevier B.V. All rights reserved.
Since the last decade, fuel cells have been receiving an increased
attention due to the depletion of fossil fuels and rising environmen-
tal 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 .
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 perﬂuorosulf-
onic acid membranes signiﬁcantly contribute to the cost of the de-
vices. 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 .
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] poly-
mers nanotubules,  polymer-oxide nanocomposites , three
dimensional organic matrices , and oxide matrices [12–22].
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 sup-
port, 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
Recently metal oxides like CeO2 , ZrO2 , MgO , TiO2
 and WO3  were used as electro-catalysts for direct oxida-
tion of alcohol which signiﬁcantly improve the electrode perfor-
mance for alcohols oxidation, in terms of the enhanced reaction
activity and the poisoning resistance.
V2O5 has been extensively used as cathode in lithium ion bat-
teries . Vanadium (IV)/vanadium (III) redox couple has been
used to construct a redox type of fuel cell . V2O5 has been
tested as anode for electro-oxidation of toluene . Furthermore,
V2O5 is a strong oxidant, V2O5 acts as a good oxidation catalyst for
The present report focuses on the efforts undertaken to develop
metal oxide supports based platinum catalysts for methanol oxida-
tion. In this communication the preparation of highly dispersed plat-
inum supported on V2O5–carbon composites, the evaluation of the
activity for the methanol oxidation of these electrodes and compar-
ison with the activity of conventional 20% Pt/C electrodes are re-
ported. These materials are characterized and studied, using XRD,
TEM and cyclic voltammetry. The electrochemical properties of the
1566-7367/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
* Corresponding author. Tel.: +91 0416 2202465; fax: +91 0416 2243092.
E-mail address: firstname.lastname@example.org (T. Maiyalagan).
Catalysis Communications 10 (2009) 433–436
Contents lists available at ScienceDirect
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electrode exhibited excellent catalytic activity and stability com-
pared to the 20 wt% Pt supported on the Vulcan XC-72R carbon.
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.
2.2. Preparation of electro-catalysts
The V2O5/C composite used in this study was prepared by a so-
lid-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 dis-
persion and aqueous formaldehyde (BDH, 37%) was added fol-
lowed 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 prepara-
tion 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 cata-
lysts 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 charac-
terized by X-ray diffraction (XRD) patterns employing Shimadzu
XD-D1 diffractometer using Cu Ka radiation (k = 1.5418 Å) operat-
ing at 40 kV and 48 mA. XRD samples were obtained by depositing
carbon-supported nanoparticles on a glass slide and drying the la-
ter 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-
sisting of the GC (0.07 cm2
) working electrode, Pt plate (5 cm2
counter electrode and Ag/AgCl reference electrode were used for
the cyclic voltammetry (CV) studies. The CV experiments were per-
formed 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 pre-
pared by using ultra pure water (Millipore, 18 MX). The electro-
lytes were degassed with nitrogen gas before the electrochemical
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 attrib-
uted to the hexagonal graphite structure (002) of Vulcan carbon.
The peaks can be indexed at 2h = 39.8° (111), 46.6° (200) and
67.9° (220) reﬂections of a Pt face-centered cubic (FCC) crystal
structure. The diffraction peak at 2h = 39.8° for Pt (111) corre-
sponds 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 stan-
dard powder diffraction ﬁle of Pt (JCPDS number 1-1311). From the
isolated Pt (220) peak, the mean particle size was about 3.1 nm
and 2.8 nm for the Pt/C and Pt/V2O5–C catalysts samples respec-
tively, calculated with the Scherrer formula . 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 indi-
cated the presence of smaller Pt nanoparticles. But the diffraction
peaks of Pt–V2O5/C are slightly shifted to lower values when com-
pared 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 asso-
ciated 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 cat-
alysts. 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 re-
sults from XRD.
The electro-catalytic activities for methanol oxidation of Pt/C
and Pt/V2O5–C electro-catalysts were analyzed by cyclic voltam-
20 30 40 50 60 70 80
(a) Vulcan XC-72
(b) 20% Pt/C
(c) 20% Pt/V2
Fig. 1. XRD spectra of (a) Vulcan XC-72 (b) Pt/Vulcan XC-72 and (c) Pt–V2O5/Vulcan
434 T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436
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 com-
pared 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 toler-
ance 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 short-
time 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 elec-
trodes 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 vana-
dium oxide (VO2+
) 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 subse-
quently 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 . 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
Fig. 2. TEM images of (a) Pt/C and (b) Pt/V2O5–C electro-catalysts.
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
Potential (V) vs Ag/AgCl
(b) 20% Pt/C
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.
Comparison of activity of methanol oxidation between Pt/V2O5–C and Pt/C electrodes.
S. No. Electrode Onset potential (V) Activitya
Forward sweep Reverse sweep
E (V) I (mA cmÀ2
) E (V) I (mA cmÀ2
1 Pt/C (J.M.) 0.31 0.76 12.25 0.62 13.49 0.9
2 Pt–V2O5/C 0.21 0.811 17.4 0.63 16.52 1.06
Activity evaluated from cyclic voltammogram run in 1 M H2SO4/1 M CH3OH.
T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436 435
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 neces-
sary 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,
CH3OHad ! COad þ 4Hþ
V2O5 þ 2Hþ
2 þ H2O
2 þ 4Hþ
þ O2 þ 2H2O
þ H2O ! VOOHþ
COad þ VOOHþ
! CO2 þ VO2þ
Highly dispersed nanosized Pt particles on V2O5–C composite
have been prepared by formaldehyde reduction.Pt/V2O5–C com-
posite catalyst exhibits higher catalytic activity for the methanol
oxidation reaction than Pt/C, which is attributed to the syner-
getic effects due to formation of an interface between the plati-
num and V2O5, and by spillover due to diffusion of the CO
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 electro-
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0 500 1000 1500
(a) 20% Pt/V2
(b) 20% Pt/C
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.
436 T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436