Electrochemical synthesis of flower-like Pd nanoparticles with high tolerance toward formic acid electrooxidation

Article abstract of DOI:10.1039/c3ra41681j

Flower-like nanoparticles exhibit unique properties due to the presence of edge and corner atoms, ad-atoms, pits and other collection of defects. In this work, flower-like Pd nanoparticles were obtained by surfactantless and additiveless square wave volta

Full text of DOI:10.1039/c3ra41681j

RSC Advances
View Article Online
View Journal
PAPER
Electrochemical synthesis of flower-like Pd
nanoparticles with high tolerance toward formic acid
Cite this: DOI: 10.1039/c3ra41681j
electrooxidation3
a
b
b
c
´
´
N. Arjona, M. Guerra-Balcazar, F. M. Cuevas-Mun˜iz, L. Alvarez-Contreras,
J. Ledesma-Garc´ıa*b and L. G. Arriaga*a
Flower-like nanoparticles exhibit unique properties due to the presence of edge and corner atoms, ad-
atoms, pits and other collection of defects. In this work, flower-like Pd nanoparticles were obtained by
surfactantless and additiveless square wave voltammetry as an electrochemical method of synthesis.
Furthermore, other well-defined Pd shapes with dendritic growth such as spinous flower-like, cone and
coral reef-like shapes were obtained by electrochemical methods using cyclic voltammetry, differential
pulse amperometry and second harmonic AC voltammetry. Crystal sizes were calculated through the X-ray
diffraction patterns for the spinous flower-like, cone, flower and coral reef-like palladium architectures
resulting in sizes of 33, 56, 44 and 47 nm, respectively. SEM and cross-section TEM images confirmed that
the architectures were composed of micro and nanostructures with dendritic growths. Cyclic voltammetry
in acidic medium confirmed the presence of certain facets and terraces in both, flower-like Pd and the
dendritic growths. The electrocatalytic properties of the palladium architectures were evaluated to the
formic acid electrooxidation at 0.1, 0.5 and 1 M. The flower-like Pd architectures exhibited the highest
tolerance to CO poisoning due to the process being carried out by a direct pathway and can be related to
the effect of the unique flower-like shape which due to its nature exhibits a high presence of terraces and
defects.
Received 8th April 2013,
Accepted 13th June 2013
DOI: 10.1039/c3ra41681j
www.rsc.org/advances
tuning its electrocatalytic properties. Particle shape with a
unique structural geometry (nanotubes, nanowires, nano-
Introduction
Low-temperature fuel cells are promising technologies to
provide energy to small portable devices. Their use is still
difficult due to the existence of several challenges to resolve,
principally the high cost of the components and the durability
of the fuel cell.1 Carbon supported catalysts have been used to
reduce the loading of the catalyst.2 However, corrosion of the
carbon support is an important cause of specific surface area
loss, which means a decrease in the cell performance.3,4 The
use of an unsupported nanostructured catalyst could provide
higher stability than a carbon-supported catalyst due to carbon
corrosion being eliminated.5
flowers, nanodendrites, etc.) usually presents a high SSA
compared with spherical metal nanoparticles. Elsewhere,
particle shape with certain face exposure (nanocubes, nano-
octahedrons, etc.) presents a high SA compared with spherical
metal nanoparticles.6,7 Materials with high SA and/or SSA have
started to develop as an alternative to classical nanoparticles
dispersed on a carbon support.1
Liquid fuels allows facility of storage, furthermore, small
organic molecules such as formic acid and methanol are
employed due to their low toxicity, handling and their high
energy density.8–10 Formic acid, compared with methanol, has
faster room temperature kinetics and fewer tendencies to
crossover.11 The mechanism of formic acid electrooxidation
on Pt occurs by two forms, direct and CO pathway. In the CO
pathway formic acid is oxidized to an intermediate like CO,
where a strong bond with Pt is formed, impeding the
adsorption of fuel species.12 Formic acid electrooxidation on
Pt and Pd surfaces occurs through both pathways.10 However,
palladium presents a higher activity for formic acid electro-
oxidation than the Pt catalyst.13–15
Mass activity (MA) of a catalyst is related to the specific
activity (SA) by the specific surface area (SSA). As well as size,
shape of unsupported material provides a powerful tool for
a
´
´
´
Centro de Investigacion y Desarrollo Tecnologico en Electroquımica, 76703
´
´
Queretaro, Mexico. E-mail: larriaga@cideteq.mx; Fax: +52 442 2116007;
Tel: +52 442 2116069
b
´
´
´
´
Division de Investigacion y Posgrado, Facultad de Ingenierıa, Universidad Autonoma
´
´
´
de Queretaro, 76010 Queretaro, Mexico. E-mail: janet.ledesma@uaq.mx;
Fax: +52 442 1921200 E. 6006; Tel: +52 442 1921200 E. 65411
c
´
´
Centro de Investigacion en Materiales Avanzados, 31109 Chihuahua, Mexico
On the other hand, the catalyst deposition on the
microfluidics fuel cells (MFCs) channels, where dimensions
Electronic supplementary information (ESI) available. See DOI: 10.1039/
3
c3ra41681j
This journal is ß The Royal Society of Chemistry 2013
RSC Adv.

View Article Online
Paper
RSC Advances
In general, the electrochemical syntheses were carried out
using 10 mM Na2PdCl4 (98%, Sigma-Aldrich) as source of Pd in
0.5 M H2SO4 (97.5%, J. T. Baker) as electrolyte, at 25 uC using
N2 (Infra, 99.999% pure) as inert atmosphere. Morphological
modification of palladium was carried out employing four
different electrochemical techniques: cyclic voltammetry
(namely system I) was used applying potentials between
are of hundredths of micrometres has been carried out
typically by ink painting.16–18 Nafion is used as a binder in
catalyst inks, providing good adhesion and good protonic
conductivity, but according to McGovern et al.19 Nafion also
decreases the surface area and in this way the oxidation
current density in Pt black nanoparticles-based inks.
Nevertheless, in channels where dimensions are of cents of
micrometres, the ink painting could not be the best option
due to several technical problems like controlling the flow of
the thrown material by the spray. Electrochemical deposition
technique presents the advantages that nanoparticles with
different shape and/or different face exposures can be directly
synthesized on the substrate,20–23 whereas that for colloidal
chemicals is still challenging. Moreover, the catalyst electro-
deposition technique is compatible with MEMS and post-
CMOS processing, allowing more straightforward integration
of MFCs in silicon-based microelectronic applications.24
The synthesis of materials with dendritic growth has several
advantages. The dendritic form can allow the presence of edge
and corner atoms, which could be more reactive than material
with low-index facets25 and semi-spherical nanoparticles.26 In
this sense, the electrochemical synthesis of nanoflowers has
been reported for Au27 and Pt28 as electrocatalysts founding
that this unique architecture exhibits high electrocatalytic
activity due to the existence of single ad-atoms, small islands,
pits, high presence of (100), (110) terraces and other collection
of defects. Also, nanoflower-like Au shapes, exhibited high
stability of its geometry after of been used in several
experiments, meanwhile other geometries did not.27
20.35 and 1.1 V vs. SCE, for 20 cycles at 0.1 V s21
.
Differential pulse amperometry (labelled as system II) was
utilized applying a lower pulse potential (EL) and an upper
pulse potential (EU) of 20.2 and 0.8 V vs. SCE, respectively; for
5000 cycles. Square wave voltammetry (labelled as system III)
was applying potentials between 20.3 and 0.8 V vs. SCE, at 20
Hz for 50 run times. Finally, second harmonic voltammetry
(labelled as system IV) was used with an initial deposition
potential of 20.2 V vs. SCE for 30 s. After, potentials between
20.2 and 0.8 V vs. SCE were applied at 1 Hz for 1 run time. The
amplitude, modulation and interval time were of 0.001 V rms,
2 and 4 s, respectively.
Physicochemical characterisation of palladium
The obtained architectures were characterized by X-ray
diffraction (XRD) using a Bruker D8 Advance diffractometer
operated at 30 KV and 30 mA. A JEOL JSM-7401F field emission
scanning electron microscope (FE-SEM) was used to investi-
gate the palladium morphology at different architectures.
Images of Pd films were obtained using a Philips Model
CM200 transmission electron microscope (TEM). TEM cross-
section samples were prepared using a focused ion beam (FIB)
JEOL JEM-9320 system operated at 30 kV.
In this paper, we report on the synthesis, physicochemical
characterization, and the electrochemical activity of palladium
with flower-like architecture and other architectures, some
with dendritic growth for comparison purposes, which as well
as flower architecture were obtained by electrochemical
methods. Dendritic shapes on glassy carbon could tune the
properties of the Pd-based materials, which is interesting to
the formic acid electrooxidation reaction. The aim of this
paper is the evaluation of different electrochemical alterna-
tives to the development of efficient electrocatalytic materials,
which could be easily deposited on microfluidic fuel cell
channels.
Electrochemical evaluation of palladium
Electrochemical experiments were carried out in a three
electrode glass cell, and consisted of cyclic voltammetry (CV),
linear sweep voltammetry (LSV) and chronoamperometric (CA)
experiments using a PGSTAT Auto Lab 302 Potentiostat/
Galvanostat (Metrohm1). Palladium architectures electrode-
posited on glassy carbon plates were employed as working
electrodes, Hg/Hg2SO4 saturated in K2SO4 (Radiometer, 0.65 V
vs. NHE) as a reference electrode and Pt wire as a counter
electrode. Electrocatalytic activities were evaluated to formic
acid electrooxidation reaction (88%, J. T. Baker) at 0.1, 0.5 and
1 M and 0.5 M H2SO4 as the electrolyte. The general procedure
was as follow: first, CV experiments (0.5 M H2SO4) were carried
out to obtain the electrochemical profiles of the electrocata-
lytic materials. After that, the working electrode was washed
with deionized water and a CV experiment was carried out to
formic acid electrooxidation. In this manner, LSV and stability
experiments by CA were obtained. Finally, the electroactive
area was calculated between each formic acid concentration,
in order to evaluate changes after CV and CA experiments.
Experimental section
Synthesis of different Pd architectures
Different architectures of palladium were synthesised by
electrochemical methods in a typical three electrode electro-
chemical cell employing glassy carbon plates (SPI1 instru-
ments, 1 cm2) as working electrodes, saturated calomel
electrode (BAS instruments) as reference electrode and Pt wire
as counter electrode. Glassy carbon plates were polished with
alumina 0.05 mm, until mirror finished and washed with
deionized water in an ultrasonic bath for 30 min. After, glassy
carbon plates were electrochemical cleaned in 0.5 M sulphuric
acid (J. T. Baker) by cyclic voltammetry (50 cycles).
Results and discussion
Physicochemical characterisation
X-ray diffraction patterns collected from palladium with
different architectures are shown in Fig. 1. Diffraction peaks
RSC Adv.
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
Fig. 1 XRD patterns of palladium synthesised by (I) cyclic voltammetry, (II)
differential pulse amperometry, (III) square wave voltammetry and (IV) second
harmonic AC voltammetry.
of a single face-centred cubic (fcc) structure were presented for
the different architectures (Fig. 1-I to 1-IV). Characteristic
palladium peaks were observed at 40.21, 46.80, 68.18 and
82.28 degrees for the crystallographic planes (111), (200), (220)
and (311), respectively. All systems exhibited the typical form
of the fcc structure of palladium. Nevertheless, system I
showed the closest proportionality between the (111) and (200)
planes and system IV showed the highest ration of peak
intensity between (111) and (200) planes. Peaks at 43, 53 and
78.3 degrees are characteristic of glassy carbon. Crystal size
approaches were estimated from the diffractograms (Fig. 1-I to
IV) using the Scherrer’s equation applied to the (111) plane for
the different systems, and are presented in Table 1. In this
manner, smaller crystal sizes were obtained as follows: system
I , III , IV , II.
Fig. 2 HR-SEM images of the different Pd architectures. Figures ‘‘a’’ illustrate the
architectures at a magnification of 10,0006, and figures ‘‘b’’ at 150,0006.
SEM images 2-Ia and 2-Ib showed spinous flower-like
architectures, which were obtained by the conditions of the
system I. In the image 2-Ia it was possible to see a uniform film
of palladium particles with a non-uniform distribution of
palladium architectures, which sizes were of few cents of
nanometres. In the image 2-Ib, particles with sizes of tens of
nanometres which integrates the spinous flower-like architec-
ture were observed. Approximations of the crystal size were
obtained by SEM images and also were listed in Table 1.
Values of crystal sizes using the Scherrer’s equation and SEM
images were similar, with the exception of system III; the
crystal size variation could be attributed to the influence of the
flower-like microstructure. In the image 2-IIa, rod and cone
shapes and dendritic growth were observed. The dendritic
growth was formed by cone-like shapes, as can be seen in
Fig. 2-IIb. Furthermore, a uniform film of palladium with well-
defined shapes was obtained. Fig. 2-IIIa and 2-IIIb showed the
presence of flower architectures.
Morphological modification of palladium by effect of the
electrochemical method of synthesis was investigated by SEM
and is shown in Fig. 2. In general, figures ‘‘a’’ showed the
microstructures and figures ‘‘b’’ showed the nanostructures.
Table 1 Determination of the crystal sizes by SEM images and XRD patterns
System
Crystal size (nm) SEM
Crystal size (nm) XRD
I
33
54
35
45
33
56
44
47
The flower architectures were homogenous, with sizes of
some hundredths of nanometres and formed by spherical
crystal between 10 and 50 nanometres of diameter. The film
II
III
IV
This journal is ß The Royal Society of Chemistry 2013
RSC Adv.

View Article Online
Paper
RSC Advances
hydrogen adsorption accompanied by (hydrogen-) sulphate
desorption.29 Processes 9 and 1 correspond to the hydrogen
evolution and desorption, processes 2 and 3 correspond to the
hydrogen desorption and (hydrogen-) sulphate adsorption.29
Processes 4 and 5 correspond to the formation of palladium
oxides, and process 6 corresponds to the reduction of
palladium oxides.30 High values of current density of processes
7 to 9 was observed when exist large, well-ordered (111)
terraces.29 In Fig. 4A can be observed the typical response of
Pd-based materials. Fig. 4B shows that process 3 has a higher
current density than process 2 and could be related to the
higher presence of (110) terraces, which has been previously
observed by Hoshi et al.31 The presence of terraces is a
consequence of the decrease of the atomic surface fraction of
the (111) and (100) facets.32,33
Electrochemical profiles in acid medium as well as the
formic acid electrooxidation were normalised by the electro-
active surface area (ECSA) which was calculated through the
reduction charge of palladium oxides using a theoretical value
Fig. 3 Cross-section TEM images of the different Pd architectures. Lower
of 424 mC cm22 34
. The obtained ECSA values were of 8.80,
12.38, 3.88 and 29.72 cm2 for the systems I to IV, respectively.
In terms of the different Pd architectures obtained, the system
IV exhibited the highest ECSA value which was expected due to
its dendritic growth. Notwithstanding the abundance of
magnifications of the Pd films were inset in the figure.
was almost uniform, due to the presence of non-deposited
zones, as can be seen in the image 2-IIIa. In Fig. 2-IVa and
2-IVb, coral reef-like dendritic growth was observed. The coral
reef-like architectures exhibited sizes of some micrometres.
Nevertheless, crystals that integrate the architecture were in
the order of some tens of nanometres. The film was uniform
as well as the architectures.
TEM images were acquired and presented in Fig. 3-I to
Fig. 3-IV. In agreement with the SEM images (Fig. 2-I to 2-IV
‘‘a’’ and ‘‘b’’), the different architectures along the transversal
section were observed in the TEM micrographs. Images of the
Pd films were inset in the TEM images showing the thickness
and the homogeneity/heterogeneity of the different films. The
film of the system I presented a thickness between 129 and 387
nm. This fluctuation is associated with the heterogeneity of
the film, as can be observed in Fig. 2-Ia. The thickness of the
film for system II was 180 nm, approximately for the non-
dendritic section of the Pd film and 923 nm for the dendritic
section (inset of Fig. 3-II). Due to the heterogeneity of the
system II, the dendritic growth section of the film was not
observed at Fig. 3-IIc due to the magnification. The thick-
nesses of the films for systems III and IV were 424 nm and 950
nm respectively. Also, systems III and IV exhibited high
homogeneity.
Electrochemical characterisation
The electrochemical responses of Pd with different architec-
tures in acidic medium (0.5 M H2SO4) are shown in Fig. 4A and
4B. In Fig. 4A are listed nine processes which were occurring in
the Pd electrode surface, which correspond to the three typical
regions of Pt and Pd materials: the hydrogen adsorption/
desorption (0–0.3 V vs. NHE) region, the capacitive region (0.3–
0.7 V vs. NHE) and the region which the formation of
palladium oxides and their respective reduction take place
(0.7–1.5 V vs. NHE). Processes 7 and 8 correspond to the
Fig. 4 Cyclic voltammograms of the different Pd architectures in acid medium.
Scan rate 50 mV s21 at 25 uC in presence of N2. Fig. 4B shows the hydrogen ad/
desorption region.
RSC Adv.
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
potential of the same monolayer observed in Fig. 4A. In the
negative sweeps, when broad peaks were observed, the rapid
decrease of the current densities at more negative potentials
y0.4 to 0.2 V, could be attributed to the contribution of the
deposition of some adsorbed hydrogen.37 When the current
densities associated to the FA oxidation in the negative sweeps
were higher than in the positive sweeps the formation of CO at
lower potentials in the positive sweeps was carried out, which
blocks the electrode surface for the direct reaction.38
The formic acid electrooxidation for system II was carried
out at 0.3, 0.37 and 0.57 V vs. NHE at 0.1, 0.5 and 1 M of FA,
respectively (Fig. 5-II). In the case of system III (Fig. 5-III), the
formic acid electrooxidation peak potential was located at
0.31, 0.34 and 0.23 V, indicating a faster electrode kinetic at
higher FA concentration (¢ 0.5 M) than the other shapes. The
thermodynamic potential for the formic acid electrooxidation
as a function of the concentration remained almost in the
same value of potential, and in our point of view this can be
attributed to the high stability due to the intrinsic properties
of the flower-like Pd architecture. The current densities
corresponding to FA oxidation were higher for the positive
sweep than the negative sweep for almost all FA concentra-
tions, which could mean that the CO formation was inhibited
or was neglected for system III. Even though the FA oxidation
potential was maintained for the three FA concentrations, the
current density decreased dramatically in the case of 1 M FA,
this could be attributed to the higher formation of CO2
bubbles which were blocking the surface area of Pd due to a
successive FA oxidation by a direct pathway.36 The principal
results of FA oxidation potential, current density and ECSA
were shown in Table 2. The electrocatalytic properties of the
system IV are shown in Fig. 5-IV. For this system, the FA
oxidation reaction was carried out at 0.31, 0.57 and 0.64 V for
the three FA concentrations, respectively. The maximum
current density associated to the FA oxidation corresponded
to the system IV (3.02 mA cm22) at 0.5 M FA as can be seen in
Table 2. The shift in the oxidation potential is related also to
the poisoning of the material by the CO formation.
Fig. 5 Cyclic voltammograms of the formic acid oxidation reaction as function of
the FA concentration for the systems I to IV. Scan rate 20 mV s21 at 25 uC.
flower-like Pd architectures, the system III exhibited the lowest
ECSA value, which indicates that the available sites of the
catalyst were lower than the other dendritic growths.
Electrocatalytic properties of formic acid (FA) electrooxida-
tion for Pd architectures were evaluated by cyclic voltammetry
at 0.1, 0.5 and 1 M (Fig. 5-I to 5-IV). The thermodynamic
standard potential of formic acid oxidation to carbon dioxide
is around 0.25 V vs. RHE.35 In Fig. 5-I, the FA oxidation for
system I was carried out at a peak potential of 0.26, 0.58 and
0.43 V vs. NHE at 0.1, 0.5 and 1 M respectively. Shifts in FA
oxidation peak potentials could be attributed to the poisoning
of the Pd surface by the effect of CO formation.36 Also in Fig. 5-
I, a second peak is observed at y0.8 V for the three formic acid
concentrations, which is related to the formation of a
palladium oxide monolayer, which was consistent with the
In the cases I, II and IV the FA oxidation potential increases
rapidly as increase the FA concentration, which could be
attributed to a different pathway of FA oxidation (not CO2
direct formation) and it is evidence in the negative sweep
curves, where in three cases (I, II and IV) the current densities
were higher than the positive sweep at high FA concentrations
(.0.1 M FA). In contrast, as commented before, the case III
Table 2 Determination of the potential and current densities associated to the formic acid electrooxidation as function of the formic acid concentrationa
0.1 M formic acid
Current
0.5 M formic acid
Current
1 M formic acid
Electroactive surface area (ECSA)
Current
Potential/
density/(jp)
Potential/
density/(jp)
Potential/
density/(jp)
System
(Ep) V
mA cm22
(Ep) V
mA cm22
(Ep) V
mA cm22
Initial/cm2
Final/cm2
I
0.26
0.30
0.31
0.31
0.10
1.68
2.28
0.70
0.58
0.37
0.34
0.57
1.90
1.89
1.92
3.02
0.43
0.57
0.23
0.64
1.34
1.98
0.32
2.46
8.80
12.38
3.88
7.995
12.39
3.90
II
III
IV
29.72
29.521
a
ECSA values were calculated before the 0.1 M FA electrooxidation (initial) and after the 1 M FA electrooxidation (final).
This journal is ß The Royal Society of Chemistry 2013
RSC Adv.

View Article Online
Paper
RSC Advances
exhibited the highest tolerance to the CO poisoning in terms
of the FA electrooxidation potential was maintained almost
constant and, with the current densities for negative sweep
curves always lowers than the positive potential for the FA
concentrations (Fig. 5-III). The dendritic growth of the systems
II and IV enhanced the FA electrooxidation reaction in terms
of the current density as comparison with the system I. The
pathway for the formic acid electrooxidation is very sensitive to
the structure; the reaction rate strongly depends of the surface
structure. In this sense, we found that the flower-like Pd
architecture exhibits high stability and high tolerance to the
CO poisoning as can be observed in Fig. 5-III, and as has been
previously reported for Au,27 this effect could be related to the
architecture.
Linear sweep voltammetry (LSV) technique at different scan
rate (20, 40, 60, 80 and 100 mV s21) was used to analyse the
behaviour of the systems. The corresponding current density vs.
square root of scan rate plots are shown in Fig. 6 for the three
working concentrations of formic acid (0.1, 0.5 and 1 M).
Meanwhile, the current density vs. potential plots at 0.1 M FA
are shown as an inset in Fig. 6. The results exhibited that the
current density increased linearly with the scan rate, which is
related to the diffusion-controlled processes. Nevertheless, for 1
M FA, non-linearly could be associated to the bubbles of CO2
formation. In the same way, the linear voltammogram of the
system IV for 0.1 M FA (inset in Fig. 6-IV), exhibited a non-linear
behaviour, which is expected due to the dendritic growth of the
coral reef-like architecture which can hold CO2 in its structure.
In order to evaluate the stability of the Pd flower
architectures (system III) chronoamperometric curves were
carried out for 1800 s at 0.31 V vs. NHE (Fig. 7). A decrease of
the current density with time was expected due to the
accumulation of intermediates in the active sites.39The current
density for 0.1 M FA decreased slower than 0.5 and 1 M, which
could be attributed to the higher CO2 formation due to the
higher concentration of formic acid.
Fig. 7 Chronoamperometric curves of system III to 1800 s at 0.31 V vs. NHE for
three FA concentrations (0.1, 0.5 and 1 M).
Conclusions
Spinous flower-like, cone-like, flower and coral reef-like
palladium dendritic growth architectures were successfully
synthesized employing different electrochemical methods
keeping the concentration and temperature as constants.
Spinous (system I), cone-like (system II) and coral reef-like
(system IV) architectures exhibited good electrocatalytic
properties and high stability at lower formic acid concentra-
tion (0.1 M); higher FA concentrations (0.5 and 1 M) showed
CO poisoning.
Nevertheless, the flower-like Pd architecture (system III)
exhibited the best electrocatalytic properties toward FA
oxidation in terms of potential, current densities and CO
poisoning. The FA oxidation potential remained almost
constant (y0.3 V vs. NHE), which means that the CO
poisoning could be neglected. The current densities were
2.28, 1.92 and 0.32 mA cm22 for 0.1, 0.5 and 1 M FA; the
decrease was caused by the higher formation of CO2 bubbles
by effect of the higher FA concentration. In summary, the
flower architectures offer feasibilities for their employment in
direct formic acid fuel cells even at high concentrations of
formic acid.
Acknowledgements
The authors gratefully acknowledge for financial support
through SEP-CONACYT (Grant 154263), REDES TEMATICAS-
CONACYT 2012 (Grant 193974) and CONACYT 2012 (Grant
188186).
Notes and references
1 E. Antolini and J. Perez, J. Mater. Sci., 2011, 46, 4435.
2 E. Antolini, Appl. Catal., B, 2009, 88, 1.
3 K. H. Kangasniemi, D. A. Condit and T. D. Jarvi, J. Electrochem.
Soc., 2004, 151, 125.
Fig. 6 Peak currents vs. scan rate plots for the systems I to IV at the different
concentrations of formic acid: 0.1 (%), 0.5 (#) and 1 M (n). Linear sweep
voltammetry for 0.1 M FA at different scan rates (up arrow indicates the increase
of the current by the effect of the increase of the scan rate in the order: 20, 40,
60, 80 and 100 mV s21, respectively) are shown as an inset in the images.
RSC Adv.
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
4 S. Maass, F. Finsterwalder, G. Frank, R. Hartmann and
C. Merten, J. Power Sources, 2008, 176, 444.
5 X. M. Ren, M. S. Wilson and S. Gottesfeld, J. Electrochem.
Soc., 1996, 143, 12.
22 J. Liu, J. Ye, C. Xu, S. P. Jiang and Y. Tong, Electrochem.
Commun., 2007, 9, 2334.
23 W. Pan, X. Zhang, H. Ma and J. Zhang, J. Phys. Chem. C,
2008, 112, 2456.
6 J. Y. Chen, B. Lim, E. P. Lee and Y. N. Xia, Nano Today,
2009, 4, 81.
7 Z. M. Peng and H. Yang, Nano Today, 2009, 4, 143.
8 S. Ha, R. Larsen, Y. Zhu and R. I. Masel, Fuel Cells, 2004, 4,
337.
9 B. D. McNicol, D. A. J. Rand and K. R. Williams, J. Power
Sources, 1999, 83, 15.
10 C. Rice, S. Ha, R. I. Masel, P. Waszczuk, A. Wieckowski and
T. Barnard, J. Power Sources, 2002, 111, 83.
11 Y. W. Rhee, S. Ha and R. I. Masel, J. Power Sources, 2003,
117, 35.
24 R. S. Jayashree, J. S. Spendelow, J. Yeom, C. Rastogi, M.
A. Shannon and P. J. A. Kenis, Electrochim. Acta, 2005, 50,
4674.
25 Y. Li, Y. Jiang, M. Chen, H. Liao, R. Huang, Z. Zhou, N. Tian,
S. Chen and S. Sun, Chem. Commun., 2012, 48, 9531.
26 C. Paoletti, A. Cemmi, L. Giorgi, R. Giorgi, L. Pilloni,
E. Serra and M. Pasquali, J. Power Sources, 2008, 183, 84.
´
´
27 N. Arjona, M. Guerra-Balcazar, G. Trejo, J. Ledesma-Garcıa
and L. G. Arriaga, New J. Chem., 2012, 36, 2555.
28 J. N. Tiwari, J. M. Pan and K. L. Lin, New J. Chem., 2009, 33,
1482.
12 J. Munk, P. A. Christensen, A. Hamnett and E. Skou, J.
Electroanal. Chem., 1996, 401, 215.
13 Z. Liu, L. Hong, M. P. Tham, T. H. Lim and H. Jiang, J.
Power Sources, 2006, 161, 831.
29 M. Hara, U. Linke and T. Wandlowski, Electrochim. Acta,
2007, 52, 5733.
30 L. H. Dall’Antonia, G. Tremiliosi-Filho and G. Jerkiewicz, J.
Electroanal. Chem., 2001, 502, 72.
31 N. Hoshi, M. Nakamura and K. Kida, Electrochem.
Commun., 2007, 9, 279.
32 G. Tamizhmani, J. P. Dodelet and D. Guay, J. Electrochem.
Soc., 1996, 143, 18.
14 D. Morales-Acosta, J. Ledesma-Garcia, L. A. Godinez, H.
´
´
G. Rodrıguez, L. Alvarez-Contreras and L. G. Arriaga, J.
Power Sources, 2010, 195, 461.
´
15 F. J. Vidal-Iglesias, J. Solla-Gullon, E. Herrero, A. Aldaz and
J. M. Feliu, J. Appl. Electrochem., 2006, 36, 1207.
33 K. Kinoshita, J. Electrochem. Soc., 1990, 137, 845.
34 D. A. J. Rand and R. Woods, J. Electroanal. Chem., 1971, 31,
29.
˜
´
16 F. M. Cuevas-Muniz, M. Guerra-Balcazar, F. Castaneda,
J. Ledesma-Garcia and L. G. Arriaga, J. Power Sources, 2011,
196, 5853.
35 X. Yu and P. G. Pickup, J. Power Sources, 2008, 182, 124.
´
17 M. Guerra-Balcazar, D. Morales-Acosta, F. Castaneda, J. Ledesma-
´
36 V. Grozovski, J. Solla-Gullon, V. Climent, E. Herrero and J.
Garcia and L. G. Arriaga, Electrochem. Commun., 2010, 12, 864.
M. Feliu, J. Phys. Chem. C, 2010, 114, 13802.
37 S. Garbarino and L. D. Burke, Int. J. Electrochem. Sci., 2010,
5, 828.
38 V. Grozovski, V. Climent, E. Herrero and J. M. Feliu,
ChemPhysChem, 2009, 10, 1922.
´
18 D. Morales-Acosta, H. G. Rodrıguez, L. A. Godinez and L.
G. Arriaga, J. Power Sources, 2010, 195, 1862.
19 M. S. McGovern, E. C. Garnett, C. Rice, R. I. Masel and
A. Wieckowski, J. Power Sources, 2003, 115, 35.
20 J. Chai, F. Li, Y. Bao, S. Liu, Q. Zhang and L. Niu, J. Solid
State Electrochem., 2012, 16, 1203.
39 N. V. Long, M. Ohtaki and M. Nogami, Int. J. Hydrogen
Energy, 2011, 36, 8478.
´
´
21 Y. Gimeno, A. Hernandez-Creus, P. Carro, S. Gonzalez, R.
C. Salvarezza and A. J. Arvia, J. Phys. Chem. B, 2002, 106,
4232.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv.