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.

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

2. 434 T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436
electrode exhibited excellent catalytic activity and stability com- sisting of the GC (0.07 cm2) working electrode, Pt plate (5 cm2) as
pared to the 20 wt% Pt supported on the Vulcan XC-72R carbon. 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
2. Experimental 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-
2.1. Materials lytes were degassed with nitrogen gas before the electrochemical
measurements.
All the chemicals used were of analytical grade. V2O5 obtained
from Merck was used. Hexachloroplatinic acid was obtained from
3. Results and discussion
Aldrich. Vulcan XC-72 carbon black was purchased from Cabot
Inc., Methanol and sulphuric acid were obtained from Fischer
The Pt/V2O5–C composite catalysts were characterized by XRD.
chemicals. Nafion 5 wt% solution was obtained from Dupont and
The XRD pattern of as-synthesized Pt/C and Pt/V2O5–C catalysts is
was used as received.
given in Fig. 1. The diffraction peak at 24–27° observed is attrib-
uted to the hexagonal graphite structure (002) of Vulcan carbon.
2.2. Preparation of electro-catalysts 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
The V2O5/C composite used in this study was prepared by a so- structure. The diffraction peak at 2h = 39.8° for Pt (1 1 1) corre-
lid-state reaction under the microwave irradiation. The aqueous sponds well to the inter-planer spacing of d111 = 0.226 nm and
solution of V2O5 was well dispersed with carbon black (Vulcan the lattice constant of 3.924 Å. The facts agree well with the stan-
XC-72R, Cabot Corp., USA) and precipitate was dried in oven at dard powder diffraction file of Pt (JCPDS number 1-1311). From the
100 °C. The mixture was then introduced into a microwave oven isolated Pt (2 2 0) peak, the mean particle size was about 3.1 nm
and heated 10 s and paused 40 s for ten times alternately. and 2.8 nm for the Pt/C and Pt/V2O5–C catalysts samples respec-
Pt nanoparticles supported on V2O5–C composite was prepared tively, calculated with the Scherrer formula [33]. This suggests that
through the reduction of chloroplatinic acid with formaldehyde. very small Pt nanoparticles dispersed on the Pt/V2O5–C composite.
The V2O5/C composite powder (ca. 100 mg) was ground gently The formation of broad peaks in V2O5-modified Pt/C catalysts indi-
with a mortar and pestle then suspended in about 20 ml H2O. cated the presence of smaller Pt nanoparticles. But the diffraction
H2PtCl6 solution was used (Aldrich) for deposition of Pt was then peaks of Pt–V2O5/C are slightly shifted to lower values when com-
added in an amount slightly greater than the desired loading. pared to Pt/C. This is an indication that an alloy between Pt and
The suspension was stirred at around 80 °C for 30 min to allow dis- V2O5 is being formed on the Pt–V2O5/C catalysts. Moreover, in
persion and aqueous formaldehyde (BDH, 37%) was added fol- the XRD patterns of the V2O5-modified Pt catalysts, the peaks asso-
lowed by heating at reflux for 1 h. The composite catalyst were ciated with pure V2O5 did not appear prominently. This might be
collected by filtration, washed thoroughly with water, and then due to the presence of very small amount of V2O5 in catalysts.
dried under vacuum (25–50 °C). However, XRD measurements cannot supply exact information
The same procedure as the above was repeated for the prepara- of crystallite size when it is less than 3.0 nm, for this reason, the
tion of Pt/C catalyst. The same procedure and conditions were used figures obtained by the above equation will be slightly smaller
to make a comparison between the Pt/C and Pt/V2O5–C system. 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
2.3. Preparation of working electrode 3.4 nm for Pt/V2O5–C, which was in good agreement with the re-
sults from XRD.
Glassy carbon (GC) (Bas electrode, 0.07 cm2) was polished to a The electro-catalytic activities for methanol oxidation of Pt/C
mirror finish with 0.05 lm alumina suspensions before each and Pt/V2O5–C electro-catalysts were analyzed by cyclic voltam-
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
Pt (111)
1 mg mlÀ1 and 20 ll aliquot was transferred on to a polished glassy (a) Vulcan XC-72
carbon substrate. After the evaporation of water, the resulting thin (b) 20% Pt/C
catalyst film was covered with 5 wt% Nafion solution. Then the
Pt (200)
(c) 20% Pt/V2O5- C
C (002)
electrode was dried at 353 K and used as the working electrode.
Pt (220)
(c)
Intensity (a.u)
2.4. Characterization methods
The phases and lattice parameters of the catalyst were charac-
terized by X-ray diffraction (XRD) patterns employing Shimadzu
(b)
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
(a)
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.
20 30 40 50 60 70 80
2.5. Electrochemical measurements
2θ (degrees)
All electrochemical studies were carried out using a BAS 100 Fig. 1. XRD spectra of (a) Vulcan XC-72 (b) Pt/Vulcan XC-72 and (c) Pt–V2O5/Vulcan
electrochemical analyzer. A conventional three-electrode cell con- XC-72.

3. T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436 435
(a)
(a) 20%Pt/V O5- C
2
15 (b) 20% Pt/C
Current density (mA/cm2 )
(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.
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+/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
Fig. 2. TEM images of (a) Pt/C and (b) Pt/V2O5–C electro-catalysts.
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-
metry in an electrolyte of 1 M H2SO4 and 1 M CH3OH at 50 mV/s. quently oxidizes the carbonaceous adsorbate to CO2 [39,40]. Based
The cyclic voltammograms of Pt/C and Pt based V2O5 composite on most accepted bifunctional mechanism of Pt–Ru, similar type of
electrodes are shown in Fig. 3, respectively. The data obtained from mechanism has been interpreted for enhancement in the catalytic
the cyclic voltammograms of the composite electrodes were com- activity of Pt–V2O5 [41]. First, methanol is preferred to bind with Pt
pared in Table 1. surface atoms, and dehydrogenated to form CO adsorbed species.
The onset for methanol oxidation on Pt/C was found to be The COad intermediates are thought as the main poisoning species
0.31 V, which is 100 mV more positive than Pt/V2O5–C electrode during electro-oxidation of methanol. Thus how to oxidize COad
(0.21 V). This gives clear evidence for the superior electro-catalytic intermediates as quickly as possible is very important to methanol
activity of Pt/V2O5–C composite electrodes for methanol oxidation. 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) 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
a
Activity evaluated from cyclic voltammogram run in 1 M H2SO4/1 M CH3OH.

4. 436 T. Maiyalagan, F.N. Khan / Catalysis Communications 10 (2009) 433–436
60 intermediates. Easier formation of the oxygen-containing species
on the surface of V2O5 favours the oxidation of CO intermediates
(a) 20% Pt/VO5- C
2 to CO2 and releasing the active sites on Pt for further electro-
50 (b) 20% Pt/C chemical reaction.
Current density (mA/cm )
2
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