Rotating disk slurry electrodeposition of platinum at Y-zeolite/carbon Vulcan XC-72R for methanol oxidation in alkaline media

Article abstract of DOI:10.1039/c4ra05877a

Platinum was electrodeposited onto Y-zeolite and Y-zeolite (Y)/Vulcan XC-72R (V) to produce Pt/Y/V and Pt/Y catalysts using a rotating disk slurry electrode technique. The activities of the two catalysts were measured towards methanol electro-oxidation in alkaline media by cyclic voltammetry and chronoamperometry. The materials were examined using electron microscopy. The results were compared to those obtained on commercial catalysts. Pt/Y/V (with 14 wt% Pt) catalyst was the most active, even more so than a commercial Pt/V catalyst with 20 wt% Pt. The Pt/Y/V catalysts contained Pt nanoparticles and tetrahedra, likely a consequence of the nucleation and growth within the zeolite framework.

Full text of DOI:10.1039/c4ra05877a

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Rotating disk slurry electrodeposition of platinum
at Y-zeolite/carbon Vulcan XC-72R for methanol
oxidation in alkaline media
Cite this: RSC Adv., 2015, 5, 7637
Amal Suleiman,a Christian L. Menendez,a Ramon Polanco,b Esteban Rosim Fachini,c
´
´
b
Yaritza Hernandez-Lebron,a Maxime J.-F. Guinel,ad Rolando Roque-Malherbe
*
´
´
a
*
and Carlos R. Cabrera
Platinum was electrodeposited onto Y-zeolite and Y-zeolite (Y)/Vulcan XC-72R (V) to produce Pt/Y/V and
Pt/Y catalysts using a rotating disk slurry electrode technique. The activities of the two catalysts were
measured towards methanol electro-oxidation in alkaline media by cyclic voltammetry and
chronoamperometry. The materials were examined using electron microscopy. The results were
compared to those obtained on commercial catalysts. Pt/Y/V (with 14 wt% Pt) catalyst was the most
active, even more so than a commercial Pt/V catalyst with 20 wt% Pt. The Pt/Y/V catalysts contained Pt
nanoparticles and tetrahedra, likely a consequence of the nucleation and growth within the zeolite
framework.
Received 17th June 2014
Accepted 16th December 2014
DOI: 10.1039/c4ra05877a
www.rsc.org/advances
Platinum, in general, is the most active catalysts.11 However,
in order to efficiently use platinum as catalyst the metal must be
1. Introduction
highly dispersed in the form of small nanoparticles, since, with
ultra-low loadings,4,7 therefore, reducing the total cost of the
catalyst.19
Efforts are made to develop the direct electrochemical oxidation
of alcohol and hydrocarbon fuels as an energy source.1–5 In
particular, methanol has been largely investigated, since it is
cheap, can be produced from fossil fuels or sustainable sources,
and can be delivered the same way used today for petroleum.6
However, the commercial expansion of this fuel cell type
depends largely on the catalysts since they are expensive and
show unstability during long operation periods.7
Direct methanol fuel cell (DMFC) is a variety of the polymer
electrolyte fuel cell, conformed by a polymeric membrane that
separates the anode and the cathode electrodes where methanol
is used as a liquid fuel.8–11 The operation of the cell can produce
catalyst loss by corrosion, catalyst particles sintering and cata-
lyst poisoning.12 Therefore, having highly dispersed nano-
particles on conductive high surface area supports may improve
the stability and robustness of the catalytic process. In this
direction, efforts are made preparing highly dispersed catalysts
on carbon based supports such as carbon black (carbon Vulcan
XC-72R)13,14 carbon nanotubes15,16 ordered porous carbon,17
carbon nano-onions,14 nanodiamond,18 among others.7
Aluminosilicate zeolites supports have been used in meth-
anol and CO oxidation as well as for the water–gas-shi reac-
tion.20–22 Their structure, composition and properties that offer
an elevated ionic strength environment. Rolison has shown the
use of these materials in electrochemistry.23–25 The properties of
aluminosilicate zeolites responsible for affecting charge trans-
fer reactions in electrochemical systems23 are, the zeolite size
and shape selectivity due to their rigid pores and channels, the
ion exchange properties, and their catalytic properties. In this
regard, hydrated zeolites conduct through intracrystalline and
intercrystalline cationic conduction, given that, the material
behave as an electrolyte, by the water adsorbed in the primary
and secondary porosity of the zeolite.26 On this ground, in the
formulation of the electro-catalyst included in the DMFC is
possible to incorporate an additional component, namely an
aluminosilicate zeolite,27 since this material in an aqueous
electrolyte solution may work as a solid ion conductor,28 provide
an adsorption space29 and supply ions by ionic exchange.30,31
The tested metallic catalysts were produced by electro-
chemical reduction of platinum from K2PtCl6on the plain
zeolite and a zeolite–carbon black composite, using the rotating
disk-slurry electrode (RoSDE) technique. The produced catalysts
were compared with three standard commercial catalysts,
specically, Pt-black, 20 wt% Pt/Vulcan XC-72R (ETEK) and
40 wt% Pt/Vulcan XC-72R (ETEK) catalysts. The materials
were examined using scanning and transmission electron
aDepartment of Chemistry and Molecular Sciences Research Building, University of
´
Puerto Rico, 1390 Ponce De Leon Ave. Suite 2, San Juan, Puerto Rico 00926. E-mail:
carlos.cabrera2@upr.edu
bInstitute for Physical Chemical Applied Research, School of Science, University of
Turabo, PO Box 3030, Gurabo, Puerto Rico, 00778-3030. E-mail: rroque@suagm.edu
cDepartment of Physical Sciences, General Studies College, University of Puerto Rico,
´
Rıo Piedras Campus, San Juan, Puerto Rico 00931
dDepartment of Physics, University of Puerto Rico, San Juan, Puerto Rico 00931
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 7637–7646 | 7637

View Article Online
RSC Advances
Paper
microscopy (SEM, TEM), thermo-gravimetric analysis (TGA), et al.13 Fig. 1 shows a scheme of RoDSE process where metal
powder X-ray diffraction (PXRD), inductive couple plasma- precursor is dissolved into dispersed in a slurry solution of a
optical emission spectrometry (ICP-OES), X-ray photoelectron colloidal support, and an electrodeposition potential is applied
spectrometry (XPS), diffuse reectance Fourier transform to the RDE while rotating at 900 rpm. Briey, a concentrated
infrared spectrometry (DRIFTS), and carbon dioxide adsorp- suspension was formed with 50 mg of zeolite in 20 mL of 0.1 M
tion. Finally, the electrochemical measurements were done for H2SO4, this slurry was placed in the center of the three-electrode
methanol oxidation in alkaline media.
cell assembly for the platinum electro-deposition. Then 5.00 mL
of the 3 mM K2PtCl6 (Aldrich) was added to the suspension in
the center compartment to make the slurry solution. The elec-
trochemical cell was sealed, and purged with nitrogen for 1 h,
while the RDE was rotated at 900 rpm in the slurry. The electro-
deposition took place at a constant potential, ꢀ0.200 V vs.
Ag/AgCl (Basic Electrochemical System of EG&G) for 2 h. The
electro-deposition was repeated six additional times (i.e. 6 ꢁ 2 h)
while adding the platinum complex solution (5.00 mL of 3 mM
K2PtCl6). Fig. 1 shows an illustration of the electrodeposition
technique describe above. Aerwards, the slurry was ltered
and rinsed with 600 mL of nanopure deionized water (18.2 MU
cm NANOpure Diamond of Barnstead) to remove the impuri-
ties. The ltered sample was air-dried. For the Pt/Y/V catalyst
preparation, slurry of 50 mg of Vulcan–zeolite (1 : 1) in 20 mL of
0.1 M H2SO4 was placed in the center of the three-electrode cell
assembly for the platinum electro-deposition. Aerwards, the
methodology was repeated for the preparation of the Pt/Y
sample.
2. Experimental method
2.1 Materials
All the chemicals were analytical grade without additional
purication. The water used in the synthesis process was bi-
distilled. Vulcan XC-72R (Cabot) and zeolite Na–Y (Si/Al ¼ 2.4)
(Sigma-Aldrich) were used as support materials. The Vulcan was
sonicated in 1.0 M H2SO4 for 8 h previous to be used to increase
the oxygen in the surface of the carbon black particles and
disperse it in the slurry. The zeolite was treated for the deal-
umination process and to exchange Na+ by H+ ions.30,33,34
The electro-deposition of the platinum nanoparticles was
performed using the rotating disk-slurry electrode (RoDSE)
methodology, following a procedure previously developed in a
three compartments, separated by fritted glass, electrochemical
cell. The cell was composed of a rotating disk electrode (RDE)
(PINE Instrument Company) in the central section, a graphite
rod, was used as counter electrode, and a Ag/AgCl (+0.197 V
versus NHE) (PINE Instrument Company) was the reference
electrode, both in aqueous sulfuric acid solution (0.1 M),
included in the right and le sectors of the cell respectively. The
disk electrode was a glassy carbon electrode (Bioanalytical
System) with an area of 0.20 cm2. The commercial catalysts used
to compare the activity of the Pt/Y/V catalysts were Pt black
(Johnson Matthey, high surface area), 20 wt% Pt/Vulcan XC-72R
(ETEK) and 40 wt% Pt/Vulcan XC-72R (ETEK).
2.3 Preparation of catalyst coated glassy carbon (GC)
electrodes
To produce the ink-paste-electrode (IPE), a suspension con-
taining 1.0 mg of the catalytic nanomaterial, 100 mL of nano-
pure water and 200 mL of isopropanol was placed under ultra-
sound for 30 minutes. Then, 8 mL of Fumion® (5% w/w poly-
arylene sulfonic acid polyelectrolyte dissolved in water/
isopropanol, FuMA-Tech GmbH, St. Ingbert, Germany) was
added and stirred for 30 minutes. The electrode was prepared
by adding 8 mL of the ink paste to the glassy carbon electrode
(3 mm diameter, Bioanalytical System) and then air dried for 30
minutes.
2.2 Catalyst preparation using the RoDSE electrodeposition
technique
The procedure used for the preparation of the Pt/Y/Vulcan
(Pt/Y/V) and Pt/Y catalysts was used as reported by Santiago
2.4 Characterization methods
The samples were examined using two scanning electron
microscopes (SEM, JEOL, JSM-7500F and JSM-6480LV). The
catalysts were also investigated using a high resolution trans-
mission electron microscope (HRTEM, JEOL, JEM-2200FS). The
elemental composition of the Pt/Y/Vulcan XC-72R catalyst was
measured using Perkin Elmer Inductively Coupled Plasma-
Optical Emission Spectrometer (ICP-OES) Optima 8000.
X-ray photoelectron spectroscopy (XPS) (PHI 5600ci) surface
analysis was done using an Al Ka monochromatic X-ray source
(350 W) and a hemispherical electron energy analyzer. The
analysis was made pressing the catalytic powder onto a Mo lm.
Powder X-ray diffraction (PXRD) (Bruker D8 Advance)
proles were collected using a Bragg–Brentano vertical goni-
ometer conguration. The thermal gravimetric analysis (TGA)
ꢂ
(TA, Q-500) measurements were done from 25 to 700 C, at a
Fig. 1 Schematic illustration of the RoDSE technique process.
7638 | RSC Adv., 2015, 5, 7637–7646
heating rate of 5 ꢂC minꢀ1, while owing 100 mL minꢀ1 of pure
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
N2. Diffuse reectance infrared Fourier transform spectroscopy compartment for 1200 seconds at a constant applied potential
(DRIFTS) was done by using a Thermo Scientic Nicolet iS10 of ꢀ0.7 V vs. Ag/AgCl. Aerward, N2 was bubbled for 300
FTIR spectrometer. The data were collected at a resolution of 4 seconds at the same potential to remove any remaining CO
cmꢀ1 employing 100 scans per sample. A background, with pure present in solution. The nal step was a linear sweep voltam-
KBr, provided by Nicolet, using the same conditions was always metry (LSV) from ꢀ0.7 V to 0.7 V vs. Ag/AgCl at a sweep rate of
made prior to sample analysis. The hydrated samples spectra 20 mV sꢀ1
were obtained at room temperature under N2 ow (Praxair,
99.99%), at 50 mL minꢀ1 rate. The spectra of the dehydrated
.
samples was done by heating at 473 K under a 50 mL minꢀ1 ow
of N2 (Praxair, 99.99%) for 2 hours. The spectra of the degassed
materials were subsequently obtained at room temperature,
under N2 ow. Additionally, DRIFTS spectra of carbon dioxide
(Praxair, 99.99%) adsorbed in the Pt/Y/V catalyst were obtained
utilizing as background the dehydrated sample at room
temperature. Aer that, CO2 (Praxair, 99.99%) ow at a 50 mL
minꢀ1 rate, for three minutes, was passed through the dehy-
drated samples, aerward, the sample was purged under N2
(Praxair, 99.99%) ow at a rate of 50 mL minꢀ1 for one minute,
next, a spectrum of the carbon dioxide molecule adsorbed on
the catalyst was obtained at room temperature under N2 ow.
Carbon dioxide (Praxair, 99.99%) adsorption19 at 273 K and
pressure up to ca. 1 atm. on samples degassed at 473 K for three
hours under high vacuum (10ꢀ6 Torr), was carried out using an
upgraded Quantachrome Autosorb-1 automatic volumetric
physisorption analyzer. The backlling process was carried out
using helium (Praxair, 99.99%).
3. Results and discussion
3.1 Morphology and structure of the catalysts
The structure and chemical identity of Pt/Y/V were veried by
the SEM, HRTEM and XRD studies. All the SEM images present
nearly cubic zeolite crystals.30 In Fig. 2, the platinum nano-
particles appear brighter. At the same time as the SEM study, an
EDAX elemental analysis of the as-synthesized catalysts was
done in ve different spots. The weight percent (wt%) average
values were 27% platinum, 12% oxygen, 7.6% silicon and 53%
carbon.
The structure and chemical identity of Pt/Y/V were veried by
HRTEM and XRD studies. The prepared sample by RoDSE
technique was characterized by high resolution transmission
electron microscope to detect if the platinum were deposited
onto the carbon/zeolite support. High resolution TEM images
showing platinum nanostructures are displayed in Fig. 3. The
nanoparticles measured in HRTEM had a particle size of 4 to 9
nm. Fig. 3A and B shows Pt nanoparticles. This is likely a result
of the nucleation of Pt on the carbon Vulcan XC-72R. Fig. 3C
and D show Pt tetrahedron nanostructures. This is likely a result
2.5 Cyclic voltammetry and constant potential experiments
The electrochemical activity of the catalysts were measured of the nucleation of Pt in the framework of the zeolite. XRD data
using a potentiostat/galvanostat system (EG&G) and a three suggested that there were 8 (1) nm nanoparticles of Pt. The XRD
electrode compartment electrochemical cell, separated by glass pattern (Fig. 4) shows the face-centered cubic crystal structure
frits.13,14 The potentials measured in this study were referenced of Pt with the presence of (111), (200), (220), (311) and (222)
to Ag/AgCl. The cyclic voltammetric (CV) experiments of the planes, demonstrating highly polycrystalline structure.
tested catalysts were done in 0.1 M KOH using a potential range
The contribution of an addition of Vulcan XC-72R to Pt/HY
of between ꢀ0.9 and 0.6 V vs. Ag/AgCl and a potential sweep rate was the ability to carry or conduct an electrical current and to
of 100 mV sꢀ1 at room temperature. The counter electrode was a avoid segregation or agglomeration of Pt. The presence and
Pt wire. All electrolyte solutions were bubbled with argon gas for
10 min before use. The Pt active surface areas were calculated
from the cyclic voltammograms in 0.1 M KOH solutions using
the hydrogen adsorption–desorption region. In addition, the
activity of the Pt/Y/V catalyst towards methanol oxidation in
basic media, 1.0 M methanol and 0.1 M KOH, was done and
compared against that of Pt black and 40% Pt/Vulcan XC-72R
(ETEK) catalysts.
The onset potential for each catalyst was determined at 5%
of the maximum anodic peak current density for the methanol
oxidation reaction. The chronoamperometry experiment was
done with an applied potential of ꢀ0.4 V vs. Ag/AgCl in 1.0 M
methanol and 0.1
temperature.
M KOH aqueous solution at room
2.6 CO stripping experiment
To perform CO oxidative stripping experiments in alkaline
medium, the ink paste electrodes were placed in a solution of
0.1 M KOH. Then, CO adsorption on the Pt surface was done by
Fig. 2 Scanning electron microscopy images of the Pt/Y/V catalysts
bubbling high purity CO through the working electrode cell prepared by RoDSE.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 7637–7646 | 7639

View Article Online
RSC Advances
Paper
Fig. 5 (a) Field emission electron microscopy images of the Pt/Y/V
catalyst on a carbon tape. EDX elemental mapping of (b) carbon (red),
(c) oxygen (green), (d) sodium (dark blue), (e) aluminum (yellow), (f)
silica (pink), (g) platinum (cyan) of the catalyst in (a). (h) Combined
mapping image of both C and Pt.
the curve-tting analysis for the Pt/Y/V sample, which appear to
have two different platinum species, Pt(0) and Pt(II). The rst set
of XPS doublets in the binding energy of 71.3 (55.46% area) and
74.6 (41.6% area) eV is the most intense and correspond to Pt(0)
followed by Pt(II) which is less intense and corresponds is found
at 74.5 (1.69% area) and 77.9 (1.27% area) eV. The appearances
of these two platinum species were as expected because of the
use of Pt complex as a precursor. On the other hand, the peak in
the C 1s binding energy region correspond to graphitic
carbon.37
Fig. 3 TEM images showing the Pt crystallites in the Y/V catalyst.
In Fig. 7 are exhibited the XRD proles of the Pt/Y/V and
commercial catalysts samples at room temperature. These XRD
proles were resolved into separate Bragg components using
the Pawley whole-powder pattern decomposition method while
the cell parameter was rened38 knowing that platinum crys-
tallizes in the cubic Pm3ꢀm space group. Besides, the Gaussian
crystallite size (4Pt) was calculated.39–41
The computer program used to perform these calculations
was the Bruker DIFFRACplus TOPAS™ soware. The calculated
Gaussian crystallite size is 5(1) nm 40 wt% Pt/Vulcan XC-72R,
4(1) nm 20 wt% Pt/Vulcan XC-72R, 7(1) nm platinum black
and 8(1) nm Pt/Y/V. Subsequently, to verify the loss of the guest
Fig. 4 X-ray diffraction of the Pt/Y/V sample prepared by RoDSE.
distribution of platinum, Vulcan and zeolite in this catalyst is
conrmed by EDX elemental mapping analysis shown in Fig. 5.
Fig. 6a presents X-ray photoelectron spectroscopy (XPS)
spectrum of the Pt 4f binding energy region corresponding to
the as-synthesized Pt/Y/V.35 Fig. 6b and d are exhibited the O 1s36
and C 1s37 binding energy regions of the XPS proles. Further,
in Fig. 6d is displayed the XPS peak corresponding to the Si 2p.
XPS showed a composition of 17.0% platinum, 9.11%
oxygen, 4.17% silicon, 69.25% carbon and 1.0% chlorine on the
surface of sample.
High resolution XPS spectra for the Pt 4f binding energy peak
were analyzed to identify the platinum oxidation states on the
prepared sample by the RoDSE technique. The XPS binding
energy data revealed that the majority of the platinum was in its
metallic form26,27 in the Pt/Y/V catalyst (Fig. 6a), i.e., the RoDSE
Fig. 6 X-ray photoelectron spectroscopy profiles corresponding to
Pt electrodeposition process was highly efficient. Fig. 6a shows the as-synthesized Pt/Y/V catalyst.
7640 | RSC Adv., 2015, 5, 7637–7646
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Vulcan was 1 : 1. On this ground, the amount of platinum in the
Pt/Y/V catalyst was, 0.19 ꢃ 0.06 g gꢀ1, while the amount of Pt in
the Pt/Y catalyst was, 0.1 ꢃ 0.02 g gꢀ1. The ICP data showed the
amount of Pt 14.7%, Si 32.2%, Na 0.59%, Al 0.61%, and the
remaining 51.9% was carbon, oxygen, and nitrogen. From the
ICP data we see a slightly lower value than the TGA data.
Nevertheless, the ICP data conrms the dealuminization
process when placing the NaY in 0.1 M H2SO4 and that the Pt
electrodeposition is possible at NaY/Vulcan using the RoDSE
technique. Finally, the small amount of Na is indicative that an
ion exchange with H+ and Pt complex during the sonication and
electrodeposition process. Consequently, the zeolite include in
the catalyst is in the acid form that is HY zeolite. In the presence
of Pt complex in the acid solution may have had an intercalation
process in the zeolite framework leading to the Pt tetrahedral
formation (see Fig. 3C and D).
An estimation of the chemical surface area (SCSA) of the plat-
inum phase included in the produced, Pt/Y/V, Pt black and the
commercial catalysts ETEK (40% Pt/Vulcan XC-72R) was made,
using the following relation, SCSA ¼ 6/Fr. In this regard knowing
that the measured crystallite size was, 4 to 9 nm for the Pt/Y/V
Fig. 7 X-ray diffraction profiles of the Pt/Y/V, Vulcan XC-72R, NAY
zeolite, Pt black, 20% Pt/Vulcan XC-72R and 40% Pt/Vulcan XC-72R.
molecules (fundamentally H2O) throughout heating and study
further structural features, the thermal gravimetric analysis
(TGA) method was used (Fig. 8).38
The TGA prole of the Pt/Y/V and Pt/Y catalysts and the Na–Y
zeolite are exhibited in Fig. 8a. Meanwhile, in Fig. 8b–d are
reported the TG prole derivatives of both catalysts and the
zeolite. These results indicated that adsorbed water was
released from ca. 50 to 200 ꢂC. Aerwards, zeolite dehydroxy-
lation from ca. 200 to 700 ꢂC was produced,42 next, was evi-
denced the characteristic slight decrease of weight from 200 to
700 C, normally observed in carbon black.43 Further, with the
ꢂ
TGA data were calculated the amount of platinum contained in
the Pt/Y/V and Pt/Y catalysts, by the comparison of the water
weight lost by the pure zeolite Y, the Y/Pt/V, and the Pt/Y cata-
lysts, namely, 0.24 g gꢀ1, 0.08 g gꢀ1 and 0.23 g gꢀ1. With this
information was estimated that, ca. 0.40 ꢃ 0.03 g gꢀ1 of zeolite Y
and 0.40 ꢃ 0.03 g gꢀ1 of Vulcan were contained in the Pt/Y/V
catalyst, since by design the proportion of zeolite Y and
Fig. 8 Thermal gravimetric analysis (TGA) profiles (a) and TGA deriv- Fig. 9 DRIFTS spectra of the hydrated and dehydrated Pt/Y/V catalyst
ative profiles of Pt/Y/V (b), Pt/Y (c) and Y zeolite (d).
(a), and spectrum in the OH region (b).
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 7637–7646 | 7641

View Article Online
RSC Advances
Paper
catalysts respectively and the platinum density, r ¼ 21.5 g cmꢀ3
,
As a nal point of the present section was performed the
then is possible the estimation of SCSA for the produced catalysts. tting of the Dubinin–Radushkevitch (DR) adsorption isotherm
The chemical surface area of Pt/Y/V is between 30 m2 gꢀ1 to equation,49 ln(na) ¼ ln(Na) ꢀ (RT/bE)2[ln(P0/P)]2, where, E, is a
70 m2 gꢀ1. Besides, using data previously published,44 namely, parameter known as the characteristic energy of adsorption, b,
SCSA for the 40% Pt/Vulcan XC-72R ETEK was 111 m2 gꢀ1
,
is the affinity coefficient, and, Na, is the maximum amount
adsorbed in the micropore volume, to the experimentally
whereas, the specic surface area of the Pt black was 28 m2 gꢀ1
.
45
Later, the DRIFTS spectra of the hydrated (as-synthesized) measured adsorption data, specically, the amount adsorbed,
and dehydrated Pt/Y/V in the range between: 600–3900 cmꢀ1 na, at 273 K, of CO2 on the Pt/V/Y catalyst and the inverse of the
were collected (Fig. 9a). The main IR active vibrations observed relative pressure, P0/P, in the range, 0.002 < P/P0 < 0.03.23 The
can be classied in two main regions. In the rst expanse, from process allowed the calculation of the best tting parameters,
600 to 2000 cmꢀ1, appear bands corresponding to the zeolite namely, Na and E. Aer that, the micropore volume was
structure, meanwhile the second section of the spectrum, computed using the Gurvich rule,19 i.e., WMP ¼ NaVL where VL ¼
CO2
namely, between 3200–3700 cmꢀ1, display the stretching, n(OH) 48.3 cm3 gꢀ1 is the carbon dioxide molar volume, yielding, W
MP
vibration produced by adsorbed water.31 Further, the DRIFTS ¼ 0.105 cm3 gꢀ1. Then, since the micropore volume of pure
spectrum of the Pt/Y/V catalyst, dehydrated at 200 ꢂC in N2 ow, zeolite Y is ca. 0.30 cm3 gꢀ1, subsequently, the amount of zeolite
is exhibited in Fig. 9b. This spectrum exhibit a peak at ca. 3605 Y in the Pt/V/Y catalyst is ca. 0.33 ꢃ 0.08 g gꢀ1
cmꢀ1 related with bridging acid hydroxyl (Si–OH–Al) groups, consistent with the TGA data.
and displays a very small band at ca. 3700 cmꢀ1, corresponding
,
a quantity
48
to the silanol (Si–OH) groups.44 The acid sites were produced by
3.2 KOH cyclic voltammetry and surface area determination
the electro-deposition, since this process was performed in acid
media, therefore, as was previously stated, the Na+ ions
included in the Na–Y zeolite were exchanged by H+, producing
the detected bridging acid hydroxyl (Si–OH–Al) groups.
Furthermore, the DRIFTS spectrum of carbon dioxide, adsorbed
at 760 Torr on the dehydrated Pt/Y/V can be examined in Fig. 10.
The free carbon dioxide molecule belongs to the DNh group
of symmetry, exhibiting four fundamental vibration modes,
namely, the symmetric stretching, n1 (1338 cmꢀ1), the doubly
degenerate bending vibration, n2a and n2b (667 cmꢀ1), and the
asymmetric stretching vibration n3 (2349 cmꢀ1).46 The, n2 and n3,
modes are infrared active, whereas n1 is only Raman active in
the free molecule.47 The asymmetric stretching vibration, n3, of
the adsorbed carbon dioxide molecule, at ca. 2332 cmꢀ1 corre-
sponds to carbon dioxide physically adsorbed inside the Y
zeolite framework.48 A red shi is observed the molecule is
adsorbed. Note that 2349 is larger than 2332, indicating that the
C]O bonding is weaker when the molecule is adsorbed.
To properly assess the activity of an electro-catalyst, the currents
produced as a result of the electrochemical reaction must be
normalized, namely, calculated with respect to the real surface
area in our case the electrochemical surface area (ECSA).50 In
this regard, in Fig. 11 are reported the normalized cyclic-
voltammetry curves corresponding to Pt/Y/V, NaY, Vulcan
XC-72R, 40% Pt-Vulcan XC-72R (ETEK) and Pt black catalysts in
0.1 M KOH.
The following reaction,51,52 Pt + H+ + eꢀ 4 Pt ꢀ Had
,
describes hydrogen adsorption–desorption, in basic media, in
the cathodic and anodic sections of the voltammograms. The
characteristic hydrogen adsorption–desorption phenomena are
manifested as peaks in the voltammograms, next, is found the
double-layer effect, and, aerwards, the oxide formation peak is
perceived. In the reported voltammograms evidence these
features. Particularly, the hydrogen adsorption–desorption
phenomena are notably informative, given that, platinum
nanoparticles exhibit certain crystallographic planes at the
Fig. 10 DRIFTS spectrum of adsorbed carbon dioxide on the dehy- Fig. 11 Cyclic voltammetry curves of Pt/Y/V, NaY, Vulcan XC-72R,
drated zeolite contained in the Pt/Y/V catalyst.
40% Pt-Vulcan XC-72R (ETEK) and Pt black catalysts in 0.1 M KOH.
7642 | RSC Adv., 2015, 5, 7637–7646
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
surface, known as facets, displaying the (111), (100), and (110)
The maximum current densities of the three catalysts are 2.5
indexes.53–55 The presence of these facets induces in the vol- (Pt/Y/V), 1.7 (40% Pt/Vulcan XC-72R), and 0.5 mA cmꢀ2 of Pt (Pt
tammograms peaks location at different potentials. The prin- black), respectively.
cipal shapes encountered for Pt nanoparticles are, tetrahedral–
Fig. 13 shows the chronoamperometric experiments which
octahedral exhibiting the (111) and (110) basal planes, cubic was carried out to observe the stability and possible poisoning
exhibiting the (100), hexagonal exhibiting the (100) and (111) between the ETEK and Pt/Y/V under short time continuous
and near spherical nanoparticles exhibiting the (111) and (100) operation toward methanol oxidation reaction. To measure the
facets.53,54 Hence, is possible to affirm that the peaks reported in tolerance of the Pt/Y/V nanocatalysts to methanol oxidation
Fig. 9 are related to polycrystalline nanoparticles,56 given that, reaction, it conducted chronoamperometry tests in 1.0 M
platinum nanoparticles normally tend to display a combination CH3OH/0.1 M KOH for 1800 s. As can been seen from Fig. 10,
of (111) and (100) facets to reduce the particle interfacial free the potentiostatic current decreases rapidly in the initial period
energy.
of time; and this can be due to the formation of COads and other
Meanwhile, the distinctive hydrogen adsorption–desorption intermediate species, such as CH3OHads, CHOads and OHads
,
phenomena in the Pt/Y catalyst were not clearly displayed as during methanol oxidation reaction. The Pt/Y/V seems to be
peaks in the voltammograms. This fact indicates that plain clearly more stable because exhibit a tolerance for intermediate
zeolite is an unsuitable support to produce an electro-catalyst. species formed during the methanol oxidation than the
In other words, the presence of a conducting support is, in commercial catalysts.
general, necessary in the catalyst formulation. Moreover, the
capacitance was higher in the all catalysts with zeolites.
3.4 CO stripping experiment
One of the principle facts to take in consideration at the time of
doing characterization of the nanocatalysts material for fuel
cells is the resistance of the CO poisoning. CO stripping vol-
tammetry is commonly used to test the activity of a catalyst for
electrochemically oxidizing adsorbed CO on the catalyst. In
Fig. 14 shows the CO stripping voltammograms of the Pt/Y/
Vulcan and 40% Pt/Vulcan XC-72R catalysts in 0.1 M KOH at
25 ꢂC aer full adsorption of CO and subsequent purging of the
solution with high-purity argon at a scan rate of 25 mV sꢀ1. CO
stripping voltammetry is a technique used to calculate the Pt–
CO saturated coverage at Pt. The charge required to oxidize the
saturated CO layer on a NaY/Vulcan/Pt was determined from the
electrochemical CO desorption method and assuming a full
CO–Pt coverage, which is used for Pt surface area determina-
tion. Basically, the CO adsorption method is the same as the
hydrogen adsorption method i.e. a probe molecule is adsorbed
3.3 Methanol electrooxidation
The activity of Pt/Y/V, ETEK and Pt-black towards methanol
oxidation in basic media: CH3OH + 6OHꢀ / CO2 + 5H2O + 6eꢀ,
was investigated by cyclic voltammetry in degassed CH3OH
(1 M)–KOH (0.1 M) aqueous solutions (Fig. 12 and Table 1).
The onset potential (Es) for methanol oxidation is at ꢀ0.35 V
vs. Ag/AgCl.
Fig. 12 Cyclic-voltammetry curves of Pt/Y/V, Pt black, and ETEK (40%
Pt-Vulcan XC-72R) catalysts in degassed CH3OH (1 M)–KOH (0.1 M)
aqueous solutions.
Table 1 Turnover number at maximum peak current in 1.0 M CH3OH/
0.1 M KOH for methanol oxidation
ꢀ
ꢁ
molecules
s ꢁ site
At maximum peak current
potential [V versus Ag/AgCl]
TONmax
Catalyst
Pt/Y/V
Pt-black
ETEK
1.72
1.10
0.34
0.00
Fig. 13 Chronoamperometry of Pt/Y/V, 40% Pt/Vulcan XC-72R, and Pt
black in 1.0 M CH3OH/0.1 M KOH at an applied potential of ꢀ0.4 V vs.
Ag/AgCl.
ꢀ0.04
ꢀ0.02
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 7637–7646 | 7643

View Article Online
RSC Advances
Paper
3.5 Role of the zeolite included in the catalyst in the reaction
mechanism
In the methanol oxidation electrochemical reaction many
electrons are released, therefore, this whole process requires a
complicated mechanism involving several steps, namely,
adsorbed intermediates and side-products to be produced,
then, if some of these intermediates are irreversibly adsorbed
(e.g. CO) on the platinum catalyst the course of the reaction is
hindered. In this regard, in both acid and basic media the
oxidation of adsorbed CO may occur via the Langmuir–Hin-
shelwood mechanism:60
COad + OHad / CO2 + H+ + eꢀ
(2)
Fig. 14 CO stripping voltammograms of the NaY/Vulcan/Pt and 40%
Pt/Vulcan XC-72R catalysts in 0.1 M KOH at 25 ꢂC after full adsorption
of CO and subsequent purging of the solution with high-purity argon
where, all the intermediate steps are fast, except CO removal,
accordingly, the rate of the overall methanol oxidation may be
controlled by this step. Therefore, the electro-catalytic activity is
determined by the accumulation rate of adsorbed CO formed
during methanol oxidation and their oxidation rate into CO2.
Within the frame of this mechanism was supposed that carbon
black act merely as a support.56 In contrast, it is accepted that
the physical properties of the support inuence the perfor-
mance of the catalyst, promoting dispersion of the platinum
nanoparticles and enabling the electron transfer.7
The main result evidenced by Fig. 12 and Table 1 is that the
Pt/Y/V catalyst presented a high activity towards methanol
oxidation when compared to Pt black and ETEK. This fact
should be related to this catalyst lower CO poisoning. To explain
this nding is necessary to take into account that Y zeolite is an
excellent adsorbent in gaseous and as well in liquid phase,61
therefore, is reasonable to suppose that the mechanism
producing the high activity of the Pt/V/Y catalyst is CO2
adsorption by the zeolite phase included in the catalyst
formulation, given that, the removal of this molecule promote
the oxidation of adsorbed CO (eqn (2)). However, carbon dioxide
interacts with water, according to the following equilibrium
reaction CO2 + H2O 4 HCO3ꢀ + H+, on this ground, the zeolite
should adsorb solvated molecular carbon dioxide and bicar-
bonate anions.
at a scan rate of 25 mV sꢀ1
.
at the Pt surface (at potential where CO oxidation does not
occur). Pt catalysts supported on zeolite have been reported for
the removal of CO, taking advantage of its “chemical and/or
physical molecular sieve effect” to make CO react with
oxygen.23 In Fig. 14 we see a lower CO stripping potential for
Pt/Y/V than for 40% Pt/Vulcan XC-72R.
Another way to evaluate the electro-catalytic activity for
methanol oxidation, the turnover number (TON) is normally
used (Table 1).57
The TON is just the number of revolutions of the catalytic
cycle per second, consequently is a parameter showing effects
close to the atomic-molecular nature of the catalytic process.
This parameter, in the concrete case of electro-catalytic meth-
anol oxidation, is dened as the number of reacted methanol
molecules per metallic catalytic site, in the catalyst surface
within one second. The turnover number is estimated, using the
maximum oxidation peak current in the cyclic voltammogram,
with the following relation:5,58
ꢀ
ꢁ
I ½mA cmꢀ2
ꢄ
molecules
TON ¼
(1)
n ꢁ e ½Cꢄ ꢁ NPt ½cmꢀ2
ꢄ
s ꢁ site
The framework of zeolite Y is composed of sodalite cages,
linked by 6-6 secondary building units, located in a face
centered cubic lattice, where half of the tetrahedral sites are
occupied by sodalite cages as is the case in the structure of
diamond.30,31 This framework, known as FAU type, contains 12-
member rings (MR) windows which lead to approximately
where, I, is the maximum steady-state current density, e ¼ 1.602
ꢁ 10ꢀ19 C, is the elementary charge of the electron, n ¼ 6, is the
number of electrons generated by the one mol of methanol in
the course of the electrochemical oxidation reaction, and NPt
[cmꢀ2] ¼ 1.51 ꢁ 1015 cmꢀ2, is the mean atomic density of
Pt(111) surface atoms.59 In Table 1 are reported the TON
calculated using eqn (1) for the tested catalysts.
In the complex process produced during methanol oxida-
tion, the extent of the anode peak current and the TON char-
acterize the electro-catalytic activity of the catalyst toward
methanol oxidation. In this regard, the Pt/Y/V catalyst exhibited
current density and TON values higher for methanol oxidation
than that of the Pt black and ETEK catalysts, although the
surface area of the platinum black and ETEK catalysts are
higher than that of the Pt/Y/V catalyst (Table 1).
˚
spherical cavities, with a radius of R ¼ 6.9 A, known as b cages,
that are connected in tetrahedral symmetry, and opened though
four 12-member rings (MR) windows each one with a diameter
62
˚
of d ¼ 7.4 A. When the solvated carbon dioxide and bicar-
bonate molecules are immersed in the Y zeolite adsorption
space31 they become subjected to diverse interaction elds, such
as, the dispersion, repulsion energies, the electrostatic inter-
actions, namely, polarization, eld dipole and eld gradient
quadrupole interactions48 and the adsorbate–adsorbate inter-
action.63 On this ground, the structure and surface chemistry of
the H–Y zeolite, included in the catalyst, allows carbon dioxide
7644 | RSC Adv., 2015, 5, 7637–7646
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
adsorption in liquid phase. This fact explains why the Pt/Y/V
catalyst is more active than both the Pt black and ETEK
catalysts.
Acknowledgements
This work was partially funded by NASA-URC Grant Number
NNX10AQ17A. The authors R.P. and R.R.M. (University of Tur-
abo) acknowledge the nancial support provided by the US
Department of Energy through the Massey Chair project and the
National Science Foundation (CHE-0959334). We thank Ms
In general, to reduce the CO poisoning problem the plat-
inum catalyst is alloyed with Ru, Sn, W, Mo, and other metals
oxides to produce bifunctional sites in the catalyst surface.32 On
the surface of this alloy, the Pt sites are centers for CO
adsorption and dehydrogenation, while on the other metallic
sites present in the alloy nanoparticles surface, the OHad
adsorbed species react with the adsorbed COad to produce, CO2,
in consequence, the CO poisoning species is detached from the
catalyst.64 Platinum–ruthenium alloys nanoparticles are
considered the most active electro-catalysts for methanol
oxidation.65 Conversely, ruthenium is expensive, hence the
tested catalyst may open an avenue for the formulation of effi-
cient and low-priced methanol oxidation Pt based catalysts.
˜
Frances Lugo, Mr Ian Gutierrez Molina, Mr Carlos Muniz and
the Puerto Rico Energy Center. NSF for its support (award
0701525) to the Nanoscopy Facility, an electron microscopy
facility at UPR.
References
1 P. Jena, J. Phys. Chem. Lett., 2011, 2, 206–211.
2 H. S. Wang and H. D. Abruna, in Fuel Cells and Hydrogen
Storage, ed. A. Bocarsly and D. M. P. Mingos, 2011, vol.
141, pp. 33–83.
3 D. Chu and R. Z. Jiang, Solid State Ionics, 2002, 148, 591–599.
4 C. Bianchini and P. K. Shen, Chem. Rev., 2009, 109, 4183–
4206.
5 E. H. Yu, U. Krewer and K. Scott, Energies, 2010, 3, 1499–
1528.
6 R. Z. Jiang and D. R. Chu, J. Electrochem. Soc., 2004, 151, A69–
A76.
7 E. Antolini, Appl. Catal., B, 2009, 88, 1–24.
8 A. D. Moore, S. M. Holmes and E. P. L. Roberts, RSC Adv.,
2012, 2, 1669–1674.
4. Conclusions
The electro-deposition of the platinum catalyst nanoparticles
was performed using the RoDSE technique on Y zeolite and Y
zeolite/Vulcan composite supports. The catalyst materials were
characterized with electron microscopy, X-ray photoelectron
spectrometry, powder X-ray diffraction, thermo-gravimetric
analysis, diffuse reectance Fourier transform infrared spec-
trometry and carbon dioxide adsorption.
TEM showed the presence of Pt nanoparticles and Pt tetra-
hedral, morphology due to the zeolite framework on nucleation.
The XPS data revealed that the majority of the platinum was in
9 S. C. Thomas, X. M. Ren, S. Gottesfeld and P. Zelenay,
Electrochim. Acta, 2002, 47, 3741–3748.
its metallic form indicating that the deposition process was very 10 E. Antolini, Mater. Chem. Phys., 2003, 78, 563–573.
efficient. The TGA, DRIFTS and adsorption data demonstrated 11 S. Wasmus and A. Kuver, J. Electroanal. Chem., 1999, 461, 14–
that the zeolite included in the Pt/Y/V catalyst conserved their
31.
structure aer all the treatments suffered by this materials, then 12 X. L. Sui, Z. B. Wang, M. Yang, L. Huo, D. M. Gu and
exhibiting a microporous channel system containing acid
bridging hydroxyls on their surface.
The voltammograms corresponding to Pt/Y/V, 40 wt% Pt/
Vulcan XC-72R, and Pt black catalysts exhibited a similar
G. P. Yin, J. Power Sources, 2014, 255, 43–51.
13 D. Santiago, G. G. Rodriguez-Calero, H. Rivera, D. A. Tryk,
M. A. Scibioh and C. R. Cabrera, J. Electrochem. Soc., 2010,
157, F189–F195.
behavior. In basic media, the Pt/Y/V catalyst exhibited current 14 D. Santiago, G. G. Rodriguez-Calero, A. Palkar, D. Barraza-
density values signicantly higher for methanol oxidation than
that of the 40 wt% Pt/Vulcan XC-72R, and Pt black catalysts.
Since, it is acknowledged that the electro-catalytic activity for
Jimenez, D. H. Galvan, G. Casillas, A. Mayoral, M. Jose-
Yacaman, L. Echegoyen and C. R. Cabrera, Langmuir, 2012,
28, 17202–17210.
the tested process is determined by the accumulation rate of 15 W. Z. Li, C. H. Liang, J. S. Qiu, W. J. Zhou, H. M. Han,
adsorbed CO, and the H–Y zeolite is an excellent adsorbent, Z. B. Wei, G. Q. Sun and Q. Xin, Carbon, 2002, 40, 791–794.
consequently, is rational to assume that the mechanism 16 C. M. Chang, H. Y. Li, J. Y. Lai and Y. L. Liu, RSC Adv., 2013,
producing the high activity of the Pt/V/Y catalyst is CO2 3, 12895–12904.
adsorption by the zeolite phase included in the catalyst 17 G. S. Chai, S. B. Yoon, J. S. Yu, J. H. Choi and Y. E. Sung, J.
formulation. Phys. Chem. B, 2004, 108, 7074–7079.
The platinum catalyst is normally alloyed with Ru, Sn, W, 18 L. La-Torre-Riveros, R. Guzman-Blas, A. E. Mendez-Torres,
´
Mo, and other metals to produce bifunctional sites in the
catalyst surface and reduce the CO poisoning. Platinum–
M. Prelas, D. A. Tryk and C. R. Cabrera, ACS Appl. Mater.
Interfaces, 2012, 4, 1134–1147.
ruthenium alloys nanoparticles are considered the most 19 K. V. Kordesch and G. R. Simader, Chem. Rev., 1995, 95, 191–
active electro-catalysts for methanol oxidation; however 207.
ruthenium is very expensive in comparison to a Na–Y zeolite. 20 T. M. Salama, I. O. Ali and H. A. Gumaa, Microporous
Consequently, the inclusion of a zeolite in the electro-catalyst Mesoporous Mater., 2008, 113, 90–98.
opens an avenue for the design of catalysts that may reduce 21 Z. Tang, J. Monroe, J. Dong, T. Nenoff and D. Weinkauf, Ind.
CO poisoning.
Eng. Chem. Res., 2009, 48, 2728–2733.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 7637–7646 | 7645

View Article Online
RSC Advances
Paper
22 P. Kaminski, I. Sobczak, P. Decyk, M. Ziolek, W. J. Roth, 44 H. Knozinger and S. Huber, J. Chem. Soc., Faraday Trans.,
B. Campo and M. Daturi, J. Phys. Chem. C, 2013, 117,
1998, 94, 2047–2059.
2147–2159.
45 J. Matthey, http://www.chemicals.matthey.com/userles/
23 D. R. Rolison and C. A. Bessel, Acc. Chem. Res., 2000, 33, 737–
744.
les/Pt(1).pdf, 2009.
46 A. Zecchina and C. O. Arean, Chem. Soc. Rev., 1996, 25, 187–
24 D. R. Rolison, Chem. Rev., 1990, 90, 867–878.
197.
25 D. R. Rolison, Advanced Zeolite Science and Applications, 47 J. A. Lercher, C. Grundling and G. EderMirth, Catal. Today,
1994, vol. 85, pp. 543–586. 1996, 27, 353–376.
26 M. Hernandez-Velez and R. Roque-Malherbe, J. Mater. Sci. 48 R. Roque-Malherbe, R. Polanco-Estrella and F. Marquez-
Lett., 1995, 14, 1112–1114. Linares, J. Phys. Chem. C, 2010, 114, 17773–17787.
27 T. M. Mudrinic, Z. D. Mojovic, A. Z. Ivanovic-Sasic, 49 B. P. Bering, M. M. Dubinin and V. V. Serpinsky, J. Colloid
´
ˇ
´
´
´
ˇ ´
ˇ
ˇ
´
´
´
N. S. Vukelic, Z. D. Cupic and D. M. Jovanovic, Russ. J.
Interface Sci., 1972, 38, 185–194.
Phys. Chem., 2013, 87, 2127–2133.
50 S. Trasatti and O. A. Petrii, Pure Appl. Chem., 1991, 63, 711–
28 O. Vigil, J. Fundora, H. Villavicencio, M. Hernandez-Velez
734.
and R. Roque-Malherbe, J. Mater. Sci. Lett., 1992, 11, 1725– 51 C. Korzeniewski, V. Climent and J. M. Feliu, Electroanalytical
1727. Chemistry: A Series of Advances, 2012, vol. 24, pp. 75–169.
29 R. Roque-Malherbe, Adsorption and Diffusion in Nanoporous 52 N. M. Markovic and P. N. Ross, Surf. Sci. Rep., 2002, 45, 121–
Materials, CRC Press, Boca Raton, FL, USA, 2007. 229.
30 D. W. Breck, Zeolite Molecular Sieves, Wiley-Interscience, J. 53 C. M. Sanchez-Sanchez, J. Solla-Gullon, F. J. Vidal-Iglesias,
Wiley & Sons, New York, 1974.
31 R. Roque-Malherbe, Physical Chemistry of Materials Energy
A. Aldaz, V. Montiel and E. Herrero, J. Am. Chem. Soc.,
2010, 132, 5622–5624.
and Environmental Applications, CRC Press, Boca Raton, FL, 54 R. Narayanan and M. A. El-Sayed, Nano Lett., 2004, 4, 1343–
USA, 2009. 1348.
32 G. R. Li, H. Xu, X. F. Lu, J. X. Feng, Y. X. Tong and C. Y. Su, 55 B. Lim, M. J. Jiang, P. H. C. Camargo, E. C. Cho, J. Tao,
Nanoscale, 2013, 5, 4056–4069.
33 M. C. Silaghi, C. Chizallet and P. Raybaud, Microporous
Mesoporous Mater., 2014, 191, 82–96.
34 T. C. Gruber, T. W. Zerda and M. Gerspacher, Carbon, 1993,
31, 1209–1210.
X. M. Lu, Y. M. Zhu and Y. N. Xia, Science, 2009, 324,
1302–1305.
56 J. Solla-Gullon, F. J. Vidal-Iglesias, A. Lopez-Cudero,
E. Garnier, J. M. Feliu and A. Aldaz, Phys. Chem. Chem.
Phys., 2008, 10, 3689–3698.
35 G. Selvarani, S. V. Selvaganesh, S. Krishnamurthy, 57 J. Kim, C. Jung, C. K. Rhee and T. H. Lim, Langmuir, 2007, 23,
G. V. M. Kiruthika, P. Sridhar, S. Pitchumani and
A. K. Shukla, J. Phys. Chem. C, 2009, 113, 7461–7468.
36 R. L. Barbosa, V. Papaehimiou, Y. T. Law, D. Teschner,
10831–10836.
58 E. Herrero, K. Franaszczuk and A. Wieckowski, J. Phys.
Chem., 1994, 98, 5074–5083.
M. Havecker, A. Knop-Gericke, R. Zapf, G. Kolb, R. Schlogl 59 L. Li and Y. C. Xing, Energies, 2009, 2, 789–804.
and S. Zafeiratos, J. Phys. Chem. C, 2013, 117, 6143–6150.
37 D. C. Higgins, D. Meza and Z. W. Chen, J. Phys. Chem. C,
2010, 114, 21982–21988.
60 N. M. Markovic, C. A. Lucas, B. N. Grgur and P. N. Ross, J.
Phys. Chem. B, 1999, 103, 9616–9623.
˜
´
61 C. Muniz-Lopez, J. Duconge and R. Roque-Malherbe, J.
Colloid Interface Sci., 2009, 329, 11–16.
38 R. Roque-Malherbe, O. N. C. Uwakweh, C. Lozano,
R. Polanco, A. Hernandez-Maldonado, P. Fierro, F. Lugo 62 R. F. Lobo, Handbook of Zeolite Science and Technology, ed. S.
and J. N. Primera-Pedrozo, J. Phys. Chem. C, 2011, 115,
15555–15569.
M. Auerbach, K. A. Carrado and P. K. Dutta, Marcell Dekker
Inc., New York, 2003, pp. 65–69.
39 J. W. Arblaster, Platinum Met. Rev., 1997, 41, 12–21.
40 X. W. Yu and S. Y. Ye, J. Power Sources, 2007, 172, 133–144.
63 R. Roque-Malherbe and F. Diaz-Castro, J. Mol. Catal. A:
Chem., 2008, 280, 194–202.
41 M. M. Treacy and J. B. Higgins, Collection of Simulated XRD 64 H. S. Wang, L. R. Alden, F. J. DiSalvo and H. D. Abruna,
Powder Patterns for Zeolites, Elsevier, Amsterdam, 2001.
42 A. Dyer, Thermochim. Acta, 1987, 110, 521–526.
43 W. Martinez, T. T. Thompson and M. A. Smit, Int. J.
Electrochem. Sci., 2010, 5, 931–943.
Langmuir, 2009, 25, 7725–7735.
65 S. L. Gojkovic, T. R. Vidakovic and D. R. Durovic, Electrochim.
Acta, 2003, 48, 3607–3614.
7646 | RSC Adv., 2015, 5, 7637–7646
This journal is © The Royal Society of Chemistry 2015