High CO tolerance of Pt/Fe/Fe2O3 nanohybrid thin film suitable for methanol oxidation in alkaline medium

Article abstract of DOI:10.1039/c4ra04138k

The toluene-water interface has traditionally been employed to prepare particle assemblies and films of metals and semiconductors. The interface between water and an organic liquid, however, has not been investigated sufficiently for possible use in preparing nanocrystals and thin films of magnetic alloys. In this article, we demonstrate the use of the liquid-liquid interface as a medium for preparing ultrathin films of magnetic Pt/Fe/Fe₂O₃ nanohybrid catalysts for methanol electrooxidation in NaOH medium. The resulting Pt/Fe/Fe₂O₃ hybrid catalyst shows the highest activity and CO tolerance (j_f/j_b = 8.09) among all other catalysts that were tested up to now toward methanol electrooxidation. The results reported in this article demonstrate the versatility and potential of the liquid-liquid interface for preparing nanomaterials and ultrathin films and encourage further research in this area. This journal is

Full text of DOI:10.1039/c4ra04138k

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High CO tolerance of Pt/Fe/Fe O nanohybrid thin
2
3
film suitable for methanol oxidation in alkaline
Cite this: RSC Adv., 2014, 4, 46992
medium
a
a
b
S. Jafar Hoseini,* Mehrangiz Bahrami and Mahmoud Roushani
The toluene–water interface has traditionally been employed to prepare particle assemblies and films of
metals and semiconductors. The interface between water and an organic liquid, however, has not been
investigated sufficiently for possible use in preparing nanocrystals and thin films of magnetic alloys. In
this article, we demonstrate the use of the liquid–liquid interface as a medium for preparing ultrathin
films of magnetic Pt/Fe/Fe
2
O
3
nanohybrid catalysts for methanol electrooxidation in NaOH medium. The
/j
¼ 8.09) among all
Received 5th May 2014
Accepted 10th September 2014
resulting Pt/Fe/Fe hybrid catalyst shows the highest activity and CO tolerance (j
2
O
3
f b
other catalysts that were tested up to now toward methanol electrooxidation. The results reported in this
article demonstrate the versatility and potential of the liquid–liquid interface for preparing nanomaterials
and ultrathin films and encourage further research in this area.
DOI: 10.1039/c4ra04138k
www.rsc.org/advances
alloys with low-cost metals. Among these alloy catalysts, Pt/Fe
alloy NPs have been demonstrated as an attractive candidate
Introduction
Direct alcohol fuel cells (DAFCs) are considered a promising for direct methanol fuel cells (DMFCs). Nanoscale magnetic
alternative power source, due to their unique advantages, such particles are of interest for developing a more complete meth-
21
as high energy conversion efficiency and being environmentally anol electrooxidation. However, in spite of the signicant
1–3
benign. However, large-scale applications of DAFCs are seri- enhancement in the methanol oxidation reaction (MOR)
ously hampered, due not only to high loading of expensive Pt activity, Pt/Fe nanostructured electrocatalysts can hardly be
ꢀ2
4,5
catalysts (i.e. >0.4 mgPt cmelectrode ), but also to poor catalyst used in electrode assembly due to difficulties in their synthesis.
6–8
CO tolerance. Bimetallic alloy catalysts were found to improve Previously, many researchers have attempted to chemically
9
–12
the CO tolerance of Pt catalysts.
(
Bimetallic nanoparticles synthesize monodisperse Pt/Fe NPs which occur at high
NPs) composed of a noble metal and a non-noble metal have temperature annealing, however this leads to particle aggrega-
22–24
attracted increasing interest among researchers because of the tion, and wider size distributions.
To prevent particle
high possibility of tailoring the electronic and geometric agglomeration, many methods have been developed such as
structures, which in turn can enhance the catalytic activity and doping with Ag, Au and Cu in the Pt/Fe phase to lower the onset
1
3–17
25–27
28,29
30
selectivity.
Besides, reducing the consumption of precious temperature,
coating Pt/Fe with iron oxide,
SiO
2
,
or
31
32
metals such as Pt by bimetallization with a low-cost metal is a MgO, and annealing with salt (i.e. NaCl). Nevertheless, a
popular approach to accelerate the practical application of denitive technique for magnetic recording fabrication has not
noble metal-based catalysts in new areas of energy technology, been achieved yet.
Toluene–water interface has been employed to prepare metal
combination of two metal elements into bimetallic particles can nanocrystals by the reduction of the metal salts. The liquid–
arise from an ensemble effect, a modied electronic structure, liquid interface itself has been exploited to form nanocrystals
18
such as fuel cells. The improvements derived from the
33
19,20
or the formation of new catalytic sites.
Although alloy particles such as Pt/Ru are very useful in the and Cu NPs, chalcogenides such as CdS, CdSe, ZnS, CoS, NiS,
anodic oxidation of methanol, high costs limit their practical CuS, PbS, oxides such as g-Fe , ZnO, CuO and nanostructured
and their assemblies to a limited extent, such as Au, Ag, Pt, Pd
2 3
O
3
4–43
application. Therefore, economical and effective alternative peptide brils.
The initial experiments carried out by Rao
yielded ultrathin nanocrystalline lms of
37–47
catalysts are required, and cost-effective routes are being sought and coworkers,
to make more efficient Pt catalysts. One approach is to use Pt metals, semiconducting chalcogenides, metal oxides, metal
suldes and other materials at the liquid–liquid interface and
indicated that the method may have greater potential than at
a
Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj 7591874831,
rst imagined. Thin lms are of great importance for many
Iran. E-mail: jhosseini@yu.ac.ir; sjhoseini54@yahoo.com; Fax: +98 741 3342172; Tel:
chemical and electrochemical applications such as electronic
devices, sensors, catalysts and electrodes. The method involves
+
98 7412223048
b
Department of Chemistry, Faculty of Sciences, Ilam University, Ilam 69315516, Iran
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dissolving an organic precursor of the relevant metal in the to prepare an orange color solution. This solution was stand in
organic layer and the appropriate reducing reagent in the contact with double distilled water (25 ml) in a beaker (100 ml).
aqueous layer. The product formed by the reaction at the inter- Once the two layers were stabilized, an appropriate volume of
face contains ultrathin nanocrystalline lms of the relevant aqueous NaBH (10 ml, 0.1 M) was injected into the aqueous
4
material formed by closely packed nanocrystals. Under layer using a syringe with minimal disturbance to the toluene
controlled conditions, ultrathin nanocrystalline lms of metals layer. The onset of reduction was marked by a coloration of the
48
with interesting properties have been obtained. It has been liquid–liquid interface. With the passage of time, the color
possible to prepare single crystalline 2D sheets of metal chal- became more vivid, nally resulting in a lm at the liquid–
cogenides and oxides. The liquid–liquid interface appears to liquid interface. The aqueous and organic layers below and
provide a general method of producing a variety of nano- above the lm were, however, transparent.
materials in the form of 2D lms, the important adjustable
parameters being the reactant concentrations, temperature, area
of the interface and viscosity of the aqueous medium. Previously,
Electrode preparation
To transfer thin lms from liquid–liquid interface to the surface
of glassy carbon electrode, the toluene phase (top phase) was
removed slowly by a syringe and then a solid substrate was
inserted into the liquid phase and pulled out.
we have investigated the effect of different stabilizers on the
structure and catalytic activity of Pt NPs thin lms at oil–water
39
interface. Also, we have reported the effect of different orga-
noplatinum(II) and organopalladium(II) complexes on the
morphology and size of Pt NPs and Pt–Pd NPs alloys at oil–water
interface in the absence of stabilizer and their electro-oxidation
Electrochemical measurements
47,49
activity was investigated in the MOR.
Recently, we fabricated
The catalyst was characterized using an Autolab Potentiostat/
Galvanostat PGSTAT12 (Eco Chemie, Switzerland). All charac-
terizations were conducted at room temperature in a standard
three-electrode system using an Ag/AgCl (sat. KCl) reference
electrode, a platinum wire counter electrode and glassy carbon
coated with prepared electrocatalysts as a working electrode.
However, all potentials in the manuscript were converted to
values with reference to a normal hydrogen electrode (NHE).
The glassy carbon electrode area diameter was 2 mm. All cyclic
voltammograms (CVs) were recorded under the same
conditions.
Pd NPs/reduced-graphene oxide thin lms as effective catalysts
50
for Suzuki–Miyaura reaction in water.
To the best of our knowledge, there is no report concerning
application of Pt/Fe/Fe alloy thin lm obtained from a
2 3
O
liquid–liquid interface in producing chemically modied elec-
trodes and using it as an electrocatalyst in the oxidation of small
organic molecules. To date, the effective method to control the
size, shape, and composition of Pt/Fe NPs alloy by using low
toxic precursors remains a challenge that must be overcome
before their potential applications will be fullled.
We describe herein, for the rst time, synthesis and char-
acterization of magnetic bimetallic Pt/Fe/Fe
lm via a simple reduction of [PtCl
(cod)], (cod ¼ cis,cis-1,5-
cyclooctadiene) and [Fe(acac)3], (acac
2 3
O NPs alloy thin

2
Results and discussion
¼
acetylacetonate)
complexes at toluene–water interface in the absence of stabi- In this study, Pt/Fe/Fe O alloy NPs thin lm was synthesized by
2
3
lizer. We also present the catalytic properties of the alloy thin the reduction of [PtCl (cod)] and [Fe(acac) ] complexes as plat-
2
3

lm in the MOR and investigate its tolerance toward CO inum and iron precursors at the toluene–water interface, shown
adsorption. This method provides a novel, simple and cheap in Scheme 1. [PtCl (cod)] and [Fe(acac) ] complexes were dis-
2
3
strategy to produce different bimetallic thin lms, suitable for solved in toluene at room temperature and then contacted with
application in DMFCs.
4
water. The aqua solution of NaBH was injected into the
aqueous layer with minimal disturbance to initiate the reduc-
tion and thin lm formation was indicated by the interface
color change from orange to black.
Experimental
The results of XRD spectrum indicate that the catalyst is well
synthesized. Fig. 1 shows the XRD pattern of the as-prepared
Pt/Fe/Fe O from the typical experiment. It can be observed
All of the chemical compounds were purchased from Merck
Company. The complexes [PtCl (cod)] and [Fe(acac) ], were
2 3
synthesized using reported procedures. X-ray diffraction (XRD)
patterns of the as-prepared electrocatalyst were recorded using
a Bruker AXS (D8, Avance) instrument equipped with Cu-Ka
51
52
2
3
ꢁ
ꢁ
ꢁ
from the XRD pattern that it has ve peaks at 2q ¼ 40 , 47 , 68 ,
ꢁ ꢁ
8
(
3 and 86 corresponded to planes (111), (200), (220), (311) and
53
222) of face-centered cubic (fcc) crystalline Pt, respectively.
˚
radiation (l ¼ 1.54184 A). Transmission electron microscopy
Besides, Fig. 1 exhibits other seven weak diffraction peaks at
(TEM) images of the electrocatalyst were recorded using a Phi-
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
2
(
q ¼ 36 , 51 , 53 , 57 , 61 , 67 and 78 corresponded to planes
lips CM-10 TEM microscope operated at 100 kV.
110), (113), (024), (116), (018), (214) and (300) which could be
assigned to a-Fe O with rhombohedral structure. Weak
54
2
3
Preparation of PtFe bimetallic thin lm at the toluene–water
interface
ꢁ
ꢁ
ꢁ
diffraction peaks at 2q ¼ 44 , 65 and 83 corresponded to
55
planes (110), (200) and (211) belongs to Fe(0). The XRD results
An equimolar solution of [PtCl
2
(cod)] (0.5 mM, 12.5 ml) and show that nanohybrid catalyst from the typical experiment
[
Fe(acac) ] (0.5 mM, 12.5 ml) in toluene was sonicated for 5 min consists of crystalline Pt, Fe, and Fe O .
3
2 3
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Scheme 1 Schematic illustration of the Pt/Fe/Fe
2
O
3
bimetallic NPs thin film formation at toluene–water interface, (a) addition of Pt and Fe
complexes solution into water, (b) stabilized mixture of [PtCl
the aqueous layer, (d) the thin film of Pt/Fe/Fe NPs appeared at the toluene–water interface after adding NaBH
top) phase by a syringe.
2
(cod)] and [Fe(acac)
3
] in toluene (orange colour) and water, (c) addition of NaBH
4
to
2
O
3
4
, and (e) remove the toluene
(
Fig. 4. Superparamagnetic behavior with coercivity (H ) of 0 Oe
c
ꢀ
1
r
and remanent magnetization (M ) of 0 emu g is observed.
Saturation of magnetization is not observed at this temperature.
At 298 K, typical behavior expected for a superparamagnet with
56
zero coercivity is observed. It is known that bulk a-Fe
behaves as an antiferromagnet with a Neel temperature (T
about 960 K. a-Fe O exhibits a rst-order magnetic transition
2 3
O
N
) of
2
3
called a Morin transition at about 263 K. The magnetic sub-
lattices are antiparallel below the Morin transition and the
material behaves like an antiferromagnet. Above the Morin
transition temperature, a-Fe
2 3
O exhibits a small net magnetic
moment due to spin canting, thereby resulting in weak ferro-
57
2 3
magnetism. The superparamagnetic property of Pt/Fe/Fe O
58
alloy thin lm decreased compared to Fe-free NPs.
It is reported that metal oxides had signicant promotion
59–62
Fig. 1 XRD pattern of Pt/Fe/Fe
O
2 3
NPs thin film on a glass.
effect on the alcohol electrooxidation for Pt-based catalysts.
The chemical composition of these NPs was determined by
energy dispersive X-ray analysis (EDX) (Fig. 2), conrming the
existence of Pt (52.89%), Fe (24.80%) and O (22.31%) elements.
TEM images (Fig. 3a–c) show that Pt/Fe/Fe O NPs have
2 3
spherical, connected chain-like structure with a mean diameter
of 20 nm (Fig. 3d).
Magnetic hysteresis loop (M/H plot) measured at 298 K for
the Pt/Fe/Fe O nanohybrid thin lm as a powder is shown in
2 3
2 3
Fig. 3 (a–c) TEM images of the spherical, chain-like Pt/Fe/Fe O
Fig. 2 EDX spectrum of the magnetic Pt/Fe/Fe
2
O
3
NPs thin film.
nanostructures and (d) histogram of particle size distribution.
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oxidized species accumulated on the surface of the elec-
63,64
trode.
A larger ratio of jf/jb represents more complete
methanol oxidation, less accumulation of CO or CO-like species
65
on the catalyst surface. The efficiencies of the Pt and Pt-alloys
nanostructures on methanol oxidation were compared with
regard to oxidation potential, forward oxidation peak current
density, and the ratio of the j
From Fig. 6, the j /j ratio for the Pt/Fe/Fe
thin lm is about 8.09 that is larger than 0.99 for ETEK Pt (ref.
f b
/j .
f
b
2 3
O synthesized
67
6
6) or 0.58 for other type of commercial Pt/C. Therefore, Pt/Fe/
Fe O thin lm electrode can lead to more complete methanol
2
3
oxidation and less accumulation of CO or CO-like species than
commercial Pt and Pt NPs thin lm. This may put down to
Fe
2 3
O that promotes the adsorbed intermediate species removal
2 3
Fig. 4 Magnetic hysteresis loop of Pt/Fe/Fe O thin film.
by supplying active oxygen species like other metal oxides
54
during the electrooxidation process. The results reveal that
Pt/Fe/Fe hybrid catalyst not only decreases the Pt dosage but
might be conducive to also enhances the performance of MOR in comparison with
improving the electrocatalytic performance of Pt/Fe/Fe
commercial Pt and Pt NPs thin lm. j /j data are summarized in
toward methanol oxidation, which was demonstrated by the Table 1.
2 3
O
2 3
Therefore, the introduction of Fe O
2 3
O
f
b
following electrochemical measurements.
The bifunctional mechanism suggested by Liu and Norskov
implies that the Ru sites provide the OH groups, which react
72
with CO adsorbed on Pt sites to form CO
2
.
Apart from Ru,
Electrocatalytic activity for methanol oxidation
several other elements including Sn, W and Mo showed
To investigate the catalytic activity of this electrocatalyst, we enhancement of methanol oxidation and specically CO
have studied hydrogen adsorption and methanol oxidation on oxidation due to co-catalytic effects when used as Pt based alloys
7
3,74
the Pt/Fe/Fe
strate that the Pt/Fe/Fe
methanol electrooxidation. As Fe
electrooxidation of methanol was investigated in alkaline
2
O
3
thin lm. The cyclic voltammograms demon- or layers adsorbed on Pt.
catalyst reveals high activity for oxidation catalyzed by Pt–Fe catalyst summarized as follows:
is acid soluble oxide, the
A similar mechanism for methanol
2 3
O
2 3
O
+
ꢀ
Pt + CH
3
OH(sol) / Pt–CH
3
OHad / Pt–COad + 4H + 4e (1)
54
medium. Cyclic voltammogram of Pt/Fe/Fe
0
2
O
3
NPs thin lm in
.5 M NaOH at a scan rate of 50 mV s is shown in Fig. 5. The
humps on Pt/Fe/Fe O diagram are associated with atomic
ꢀ
ꢀ
ꢀ1
Fe + OH / Fe–OHad + e
(2)
(3)
(4)
(5)
(6)
2
3
ꢀ
ꢀ
Pt + OH / Pt–OHad + e
hydrogen desorption and adsorption (I and III regions in Fig. 5).
Metal oxides formation was also observed (region II in Fig. 5).
If the maximum peak current density in the forward direc-
Pt–COad + Fe–OHad / Pt–COOHad + Fe
Pt–COad + Pt–OHad / Pt–COOHad + Pt
tion is designated as j
in the backward is designated as j
used to evaluate the tolerance of the catalysts to incompletely
f
and the maximum peak current density
b
, the ratio of j /j is generally
f b
Pt–COOHad + Pt–OHad / 2Pt + CO + H O
2
2
Fig. 5 Cyclic voltammogram of Pt/Fe/Fe
of NaOH (0.5 M) with a scan rate of 50 mV s
2
O
3
thin film in the presence Fig. 6 Cyclic voltammogram of Pt/Fe/Fe
2
O
3
thin film in 0.5 M NaOH
ꢀ1
ꢀ1
.
3
electrolyte containing 0.5 M CH OH with a scan rate of 50 mV s
.
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Table 1 Comparison of electrocatalytic activity of methanol oxidation
2 3
Typical cyclic voltammograms recorded for the Pt/Fe/Fe O
thin lm in 0.1 M NaOH and 0.1 M CH OH at different scan
rates ranging from 20 to 100 mV s are shown in Fig. 8a. The
3
Electrode
j
f
/j
b
ratio
Reference
ꢀ1
increase in the current density with the scan rate is observed
and the peak potentials almost show no change. Fig. 8b shows
that peak current densities are linearly proportional to the
square root of the scan rates. Following equations were used to
Comm-Pt/C
Pt/C
Pt–Ru/C
Pt–Ru–Co/C
Pt/C
0.57
68
69
69
69
54
49
70
71
47
70
49
54
54
68
0.605
0.629
0.868
1.18
1.19
1.20
1.23
1.28
1.32
1.50
1.73
1.98
2.13
8.09

nd out the number of exchanged electrons for an irreversible
Pt–Pd
75,76
electrochemical reaction during MOR:
Pt–CeO
Pt–Au
2
Pt thin lm
Pt–Fe –CeO
E ꢀ E ¼ 47.7 (mV)/ana
p
p/2
(7)
(8)
3
O
4
2
5
*
O
1/2
1/2 1/2
Pt–Pd/RGO
Pd/XC-72
I
¼ (2.99 ꢂ 10 )nAC
D
a
(an ) n
p
O
Pd–Fe
Hexa-Pt/C
Pt/Fe/Fe
2
O
3
Ep/2 is the potential where the current is half the peak value, Ep
is a function of scan rate, shiing (for oxidation) in a positive
direction by an amount in 1.15RT/(1 ꢀ a)F for each tenfold
2
O
3
This work
increase in n, a is an electron transfer coefficient and n is the
a
number of electrons involved in the rate-determining step (eqn
The strongly adsorbed CO intermediate (CO)ads is produced
during electrooxidation of methanol on the catalyst, which
could be a serious problem for both catalytic activity and
stability. Step (5) was proposed to be the rate-determining step,
in which the adsorbed hydroxyl ions removed the adsorbed CO
intermediate to form carboxylate and released free active cata-
lytic sites of Pt.
75,76
(7)).
p
In eqn (8), I is the peak current observed in amperes, n
is the number of electrons transfer during the electrochemical
2
process, A is the surface area of working electrode in cm , D is
O
2
ꢀ1
the diffusion coefficient for the oxidized species in cm s , n is
ꢀ1
*
O
the rate at which the potential is swept (V s ), C is the
concentration of the oxidized species before the electro-
ꢀ
3
chemical perturbation is applied in mol cm , a is an electron
transfer coefficient and n is the number of electrons involved
in the rate-determining step.
From Fig. 8a, E and Ep/2 are 2100 and 1925 (mV), respec-
tively and are taken for the scan rate of 100 mV s
The methanol electrooxidation was also investigated at lower
methanol concentration in order to see the oxidation peak more
obviously. Cyclic voltammogram of Pt/Fe/Fe O NPs thin lm in
a
75–77
2
3
ꢀ
1
p
0
3
.1 M NaOH and 0.1 M CH OH at a scan rate of 50 mV s is
ꢀ
1
:
shown in Fig. 7. The electrocatalytic activity of this thin lm for
the oxidation of methanol was investigated by the appearance of
an oxidation current in the positive potential region. The
E
p
ꢀ Ep/2 ¼ 47.7 (mV)/an
a
, 2100 ꢀ 1925 (mV) ¼ 47.7 (mV)/an
a
oxidation current for this electrocatalyst in 0.1 M CH
became lower than in 0.5 M CH OH. There is not distinguish-
able hump for determination of jb in Pt/Fe/Fe O cyclic vol-
3
OH
3
From eqn (7), an
scan rates and have obtained the same value for an . In eqn (8),
value is 0.27. Also, eqn (7) is used for all
a
2
3
a
2
*
tammogram in this methanol concentration (see Fig. 7). Not
A value is 0.0314 cm , an value is 0.27 (from eqn (7)), C value is
a
O
ꢀ
3
seeing the MOR peak clearly is due to the fact that Pt/Fe/Fe
2
O
3
0
.0001 mol cm , D is a diffusion coefficient of methanol and
O
ꢀ
5
2
ꢀ1
1/2
nanohybrid is a thin lm with a low metal loading.
its value is 1.3 ꢂ 10 cm s . I
p
/An can obtain from the slope
of Fig. 8b and its value is 0.27332. By these data deposition in
eqn (8) we have:
5
ꢀ5 1/2
1/2
n ¼ [(0.27332)]/[2.99 ꢂ 10 ꢂ 0.0001 ꢂ (1.3 ꢂ 10
)
ꢂ (0.27)
]
¼
5.97 z 6
From this equation the number of exchanged electrons is 6
76,78
and conrm that the MOR is an overall 6 electron process:
+
ꢀ
CH OH + H O / CO + 6H + 6e
(9)
3
2
2
2 3
Pt/Fe/Fe O electrocatalyst is a very thin layer that stick
strongly to the surface of the electrode. This nanohybrid has no
change during MOR due to its stability in alkaline media. The
electrocatalyst was analyzed by XRD aer catalytic cycle. It
can be observed from the XRD pattern that it has ve peaks at
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
2
(
q ¼ 40 , 47 , 68 , 83 and 86 corresponded to planes (111),
Fig. 7 Cyclic voltammogram of Pt/Fe/Fe
2
O
3
thin film in 0.1 M NaOH
53
200), (220), (311) and (222) of fcc crystalline Pt, respectively.
ꢀ1
electrolyte containing 0.1 M CH OH with a scan rate of 50 mV s
3
.
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Fig. 8 (a) Cyclic voltammograms of the Pt/Fe/Fe
2
O
3
thin film at different scan rates in 0.1 M NaOH + 0.1 M CH
3
OH. (b) Dependence of the peak
currents on the square root of the scan rates.
of methanol in alkaline medium via a simple toluene–water
interface strategy. Presence of iron oxides NPs resulted in a
signicant enhancement of methanol oxidation as evident from
the increase in the anodic peak current. The presence of iron
oxides is believed to provide oxygen to the adsorbed methanol
residues (e.g., CO) thus facilitating its oxidation to CO2 and
leads eventually to the retrieval of the Pt active surface site.
Therefore, iron oxide has a promoting effect on oxidizing and
removing the adsorbed CO-like intermediate species during
electrooxidation of methanol. These results indicate that due to
2 3
the low cost and enhanced performance, the Pt/Fe/Fe O hybrid
catalyst may be a superior candidate for DMFCs. Reducing the
consumption of precious metals such as Pt by bimetallization
with a low-cost metal or completely replacing Pt by other non-
noble metals is a popular approach. One of the most attrac-
tive advantages of alkaline fuel cells is the possibility of using
non-precious and low cost metal catalysts. Among different
metals, nickel is the most investigated Pt alternative anode
catalyst for methanol oxidation in alkaline media. Since nickel
placed in contact with a solution of aqueous alkali has been
shown to become covered with a layer of NiOOH, but it has
some disadvantages. The accumulation of NiOOH had an
inhibiting effect on activity and can be counteracted by a period
of re-activation. Also, activity of the Ni electrodes towards
methanol oxidation was found to vary with the amount of
Fig. 9 XRD pattern of Pt/Fe/Fe
catalytic cycle.
2
O
3
NPs thin film on a glass after
ꢁ
Besides, Fig. 9 exhibits other seven diffraction peaks at 2q ¼ 36 ,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
5
1 , 53 , 57 , 61 , 67 and 78 corresponded to planes (110),
(113), (024), (116), (018), (214) and (300) which could be
54
assigned to a-Fe
2
O
3
with rhombohedral structure. Diffraction
ꢁ
ꢁ
ꢁ
peaks at 2q ¼ 44 , 65 and 83 corresponded to planes (110),
5
5
(200) and (211) belongs to Fe(0). The XRD results show that
nanohybrid catalyst consists of crystalline Pt, Fe, and Fe
2 3
O .
47
In our previous study, platinum thin lm was formed using
[
PtCl (cod)] complex and its electrocatalytic activity was investi-
79
2
deposited Ni and high metal loading is needed. The MOR
2 4
gated in a 0.5 M H SO solution containing 0.5 M methanol. But
activity of Ni can be enhanced by alloying with Ru and Cu in
in this paper, we used previous strategy to synthesize Pt/Fe/Fe
O
2 3
80
alkaline solutions and is higher than that of Ni and Ru alone.
metal alloy for the electro-catalytic oxidation of methanol in
alkaline medium. On the other hand, using of metal binary alloy
strategy can lead to a lower amount of Pt catalysts and in turn,
can decrease the price of the electrocatalysts for MOR. Also, the
j /j ratio for Pt/Fe/Fe O thin lm was about 8.09, that was larger
In some cases, MOR activity of non-noble metals can be
enhanced by using stabilizers. For example gold lms deposited
81
on the surface of ultrane PAni bers, Ni dispersed on
82
83
graphite, a Ni zeolite, or by using polymer templates like
polymer template coordination with metal-ions loaded with a
carbon-reduction method (P–M–C complexes), P stands for
f
b
2 3
than 1.28 for Pt thin lm. Therefore, Pt/Fe/Fe O3 thin lm
electrode can lead to more complete methanol oxidation and
less accumulation of CO or CO-like species than Pt NPs thin lm.
2
84
polymer, M ¼ Fe, Co and Ni and C is carbon. Some of the non-
noble electrocatalysts need heat treatment. Heat treatment was
85
shown to improve oxidation performance for Co–W alloy. Pd,
Au, Ni, . are active for methanol oxidation in alkaline media,
Conclusions
86–89
but their activity is remarkably lower than that of platinum.
The current study introduces a novel preparation method for In this study, using liquid–liquid self-assembly (a facile strategy
metal oxide modied Pt NPs for the electro-catalytic oxidation to prepare metal alloys), can decrease the cost of the Pt-based
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alloy electrocatalysts with a low metal loading. Here, the Pt 16 H. Abe, F. Matsumoto, L. R. Alden, S. C. Warren,
amount is too low and all the metal atoms of the alloy are on the
surface of the electrocatalyst. Synthesizing Pt-based alloys thin
H. D. Abru n˜ a and F. J. DiSalvo, J. Am. Chem. Soc., 2008,
130, 5452.

lms via the liquid–liquid interface have lower cost even 17 P. Rodriguez, F. D. Tichelaar, M. T. M. Koper and
compare to non-noble metal catalysts with high metal loading.
A. I. Yanson, J. Am. Chem. Soc., 2011, 133, 17626.
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Acknowledgements
17479.
We thank the Iran National Science Foundation (Grant no. 20 X. Wang, J. Stover, V. Zielasek, L. Altmann, K. Thiel, K. Al-
90004019) for nancial support. We would also like to thank the
Shamery, M. Baumer, H. Borchert, J. Parisi and J. Kolny-
Yasouj University Research Council, Renewable Energy Orga-
Olesiak, Langmuir, 2011, 27, 11052.
nization of Iran and the Iranian Nanotechnology Initiative 21 H. Zeng, J. Li, J. P. Liu, Z. L. Wang and S. Sun, Nature, 2002,
Council for their partial support.
420, 395.
22 T. Shima, K. Takanashi, Y. K. Takahashi and K. Hono, Appl.
Phys. Lett., 2002, 81, 1050.
23 Y. K. Takahashi, K. Hono, T. Shima and K. Takanashi, J.
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