Influence of the incorporation of CeO2 nanoparticles on the ion exchange behavior of dodecylsulfate doped polypyrrole films: Ac-electrogravimetry investigations

Article abstract of DOI:10.1016/j.electacta.2014.07.151

Cerium oxide (CeO₂) nanoparticles (NPs) possessing defined size and crystallinity have been synthesised by a co-precipitation method. The effect of several parameters, such as the nature of the solvent and the calcination process, on the crystallite size was studied by XRD, TEM and BET methods. These CeO₂ nanoparticles were then incorporated in dodecylsulfate (DS) doped PPy films during their electrodeposition in potentiodynamic conditions in order to produce PPy-DS/CeO₂ NPs nanocomposite thin films on gold coated quartz crystals. Simultaneous EQCM experiments revealed successful incorporation of increasing amounts of cerium oxide nanoparticles in the polypyrrole matrix during each of the consecutive CV scans. This was confirmed using FEG-SEM and EDS microanalysis. The ion exchange phenomena occurring in the resulting nanocomposite materials were studied by ac-electrogravimetry in NaCl aqueous electrolyte. PPy-DS films appear to be mainly cation exchangers, independently from the incorporation of CeO₂ nanoparticles (NPs), even though chloride anions in smaller amounts, and free water molecules, are simultaneously transferred at the film/electrolytic solution interface. This study also reveals that the kinetics of Cl^- ion insertion occurring at the film/electrolyte interface upon oxidation is persistently slower in PPy-DS/CeO₂ NPs films than in PPy-DS films throughout the entire potential window of investigation. However, the relative concentration changes of Cl^- ions in PPy-DS/CeO₂ NPs films is about two times greater than that occurring in pristine PPy-DS films. Such conclusion tends to demonstrate that CeO₂ NPs have the ability to modify the morphology of electrodeposited PPy-DS thin films as well as their subsequent permeability towards ions contained in the electrolytic solution, possibly via the perturbation of polymer chain interactions and organisation.

Full text of DOI:10.1016/j.electacta.2014.07.151

Electrochimica Acta 145 (2014) 270–280
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Influence of the Incorporation of CeO2 Nanoparticles on the Ion
Exchange Behavior of Dodecylsulfate Doped Polypyrrole Films:
Ac-Electrogravimetry Investigations
C. Benmouhouba,c,d, J. Agrisuelasb, N. Benbrahima, F. Pillierc,d, C. Gabriellic,d
,
A. Kadria, A. Pailleretc,d,∗, H. Perrotc,d, O. Selc,d
a Laboratoire de Physique et Chimie des Matériaux (LPCM), Université Mouloud Mammeri, B.P. 17, 15000, Tizi-Ouzou, Algeria
b Univ Valencia, Dept Quim Fis, E-46100 Valencia, Spain
c Sorbonne Universités, UPMC Univ Paris VI, UMR 8235, Laboratoire Interfaces et Systèmes Electrochimiques (LISE), 4, place Jussieu, case courrier 133,
F-75005, Paris, France
d CNRS, UMR 8235, LISE, F-75005, Paris, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 June 2014
Received in revised form 25 July 2014
Accepted 27 July 2014
Available online 13 August 2014
Cerium oxide (CeO2) nanoparticles (NPs) possessing defined size and crystallinity have been synthe-
sised by a co-precipitation method. The effect of several parameters, such as the nature of the solvent
and the calcination process, on the crystallite size was studied by XRD, TEM and BET methods. These
CeO2 nanoparticles were then incorporated in dodecylsulfate (DS) doped PPy films during their elec-
trodeposition in potentiodynamic conditions in order to produce PPy-DS/CeO2 NPs nanocomposite thin
films on gold coated quartz crystals. Simultaneous EQCM experiments revealed successful incorpora-
tion of increasing amounts of cerium oxide nanoparticles in the polypyrrole matrix during each of the
consecutive CV scans. This was confirmed using FEG-SEM and EDS microanalysis.
The ion exchange phenomena occurring in the resulting nanocomposite materials were studied by
ac-electrogravimetry in NaCl aqueous electrolyte. PPy-DS films appear to be mainly cation exchang-
ers, independently from the incorporation of CeO2 nanoparticles (NPs), even though chloride anions in
smaller amounts, and free water molecules, are simultaneously transferred at the film/electrolytic solu-
tion interface. This study also reveals that the kinetics of Cl− ion insertion occurring at the film/electrolyte
interface upon oxidation is persistently slower in PPy-DS/CeO2 NPs films than in PPy-DS films through-
out the entire potential window of investigation. However, the relative concentration changes of Cl−
ions in PPy-DS/CeO2 NPs films is about two times greater than that occurring in pristine PPy-DS films.
Such conclusion tends to demonstrate that CeO2 NPs have the ability to modify the morphology of elec-
trodeposited PPy-DS thin films as well as their subsequent permeability towards ions contained in the
electrolytic solution, possibly via the perturbation of polymer chain interactions and organisation.
© 2014 Elsevier Ltd. All rights reserved.
Keywords:
polypyrrole
ac-electrogravimetry
ion-exchange behaviour
nanocomposite materials
cerium oxide nanoparticles
1. Introduction
Li-ion batteries [6]. Besides their applications, such composite
materials are also interesting from a fundamental point of view.
Composite materials based on an electronically conducting
polymer (ECP) matrix incorporating metal oxide nanoparticles con-
stitute a fascinating class of functional materials, as shown by
review articles [1]. They are potentially aimed at a vast range of
applications among which one can cite protection against cor-
rosion of iron [2], electrocatalysis [3], supercapacitors [4,5] or
Their complex chemical composition, the distribution of the dif-
ferent phases and their physico-chemical interactions inside the
bulk of the overall composite material make their main prop-
erties unpredictable. For example, in a recent contribution, our
group showed that the conductivity of electrodeposited polypyr-
role thin films undergoes opposite influences from dodecylsulfate
(DS) anions and incorporated iron oxide particles [2]. More specifi-
cally, PPy-DS films were shown to possess a rather good electronic
conductivity, compared to PPy films doped with other anions, as
a consequence of the beneficial effect of dodecylsulfate anions.
∗
Corresponding author.
E-mail address: alain.pailleret@upmc.fr (A. Pailleret).
http://dx.doi.org/10.1016/j.electacta.2014.07.151
0013-4686/© 2014 Elsevier Ltd. All rights reserved.

C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
271
However, PPy-DS films containing iron oxide particles were found
to have a lower conductivity that was moreover found to depend
on the identity and/or crystallographic variety of the incorporated
iron oxide (␣-Fe2O3, ␥-Fe2O3, Fe3O4) [2]. Literature also contains
many reports showing that incorporation of metal or metal oxide
nanomaterials in ECPs may substantially modify their well-known
physico-chemical properties, besides providing new ones, which is
beyond this discussion. In a non-exhaustive list, one can remind
that polypyrrole/WO3 nanomaterials based composite materials
possess a rare negative permittivity and their switching frequency
can be tuned with the help of particle loading. In particular, among
other parameters, increased nanoparticle loading was also shown
to improve the electrical conductivity, dielectric permittivity, and
thermal stability of the resulting nanocomposites [7]. One should
also notice that magnetite incorporation stabilizes the polaronic
form of polypyrrole matrices and also preserves it from further
oxidation [8] or allows production of unexpected 1 ␮m wide stripe-
like microstructures resulting from the self-assembly of magnetic
components [9].
In this contribution, one of our goals was to identify a likely influ-
ence of the incorporation of cerium oxide nanoparticles on the ion
transfer behaviour observed at the interface between PPy-DS/CeO2
NPs nanocomposite materials and an aqueous electrolytic solution.
During the last decades, cerium (IV) oxide (CeO2), also named ceria,
was widely applied in many fields and thus, established as one of
the most interesting rare earth oxides. Numerous CeO2 synthesis
procedures have been reported in literature [10–13] leading to var-
ious nanoparticle morphologies. These materials were extensively
studied owing to their many distinctive characteristics and appli-
cations such as catalysts in the fuel cell technology [14], gas sensor
[15], catalytic wet oxidation [16,17], oxygen storage and release
[18], wastewater treatment [19] or photo-catalytic oxidation of
water [20].
characterizing the ionic transfer at the film/electrolyte interface,
is the following:
ꢀC
Gi
i (ω) = −
(1)
ꢀE
jωdfilm + Ki
where ω = 2ꢂf is the pulsation, f is the potential perturbation fre-
quency, dfilm is the film thickness, Ci is the concentration of the
species i in the electroactive film and Ki and Gi are the partial
derivatives of flux with respect to the concentration and poten-
ꢀ
ꢁ
ꢀ
ꢁ
∂J
∂C
∂J
∂E
i
i
tial respectively, Ki =
and Gi =
, where Ji stands for
i
E
C
i
the flux of the species i crossing the film/electrolyte interface. From
ꢀm
Eq. (1),
(ω) is easily deduced in the case where three species are
ꢀE
involved:
ꢃ
ꢄ
ꢂ
ꢀm
Gi
ω = −d
)
m
(2)
(
film
ꢀE
i jωdfilm + Ki
i=a,c,s
where mi is the atomic mass of the species a, c, or s. Based on the
same model and according to Eq. (1),
taking into account only the charged species transferred through
the film/electrolyte interface. If one cation and one anion are
involved in the electrochemical process, the following equation can
ꢅ
ꢀE
ꢀI
ions(ω) is also obtained,
be used:
ꢁ
ꢀE
ꢀI
1
ꢆ
ω =
)
(3)
(
G
G
a
ions
c
jωdfilm
F
−
jωd
+K
jωd
+K
a
c
film
film
When the response of the electrochemical system is perturbed
at low frequencies with a parasitic electrochemical reaction, char-
acterized by a parasitic impedance (Zpar(␻)) described in equation
(4), in parallel with the ionic transfer, the global electrochemical
impedance (equation 5) becomes:
1
In our work, CeO2 oxide was selected as it is expected to
provide its strong oxidizing power to the resulting PPy-DS/CeO2
NPs nanocomposite materials.
The technique employed for the investigations of ion exchange
behaviour of nanocomposite PPy-DS/CeO2 NPs materials reported
hereafter is ac-electrogravimetry, according to recent contributions
showing it is an appropriate methodology for such investigations
Zpar(ω) = Rpar
+
(4)
(5)
jωCpar
ꢀE
1
ꢅ
(ω) = Rel
+
jωCdl
ꢀI
ꢀE
1
par
ꢀI
+
ω +
)
(
Z
(ω)
ions
In Eq. (5), Rel is the electrolyte resistance and Cdl is the interfacial
capacitance.
[21–28]. Specifically, ac-electrogravimetry, i.e. simultaneous mea-
Another pertinent transfer function can also be simulated here,
ꢀE
ꢀI
ꢀq
ꢀE
surements of the usual electrochemical impedance,
(ω), and of
the so-called charge/potential transfer function,
(ω). This trans-
ꢀm
the mass/potential transfer function,
(ω), provides a clear sepa-
fer function generally presents loops which correspond to the ionic
transfer occurring at low frequencies. By this way, it is easier to
determine the Ki and Gi parameters related to each species. The
equation used is given by:
ꢀE
ration and identification of all the species. These species involved in
the electrochemical reactions associated to the film can be charged
or non-charged and their contributions can be clearly determined
thanks to ac-electrogravimetry [21–28].
ꢇ
ꢈ
ꢀq
ꢀE
Gc
Ga
ω = dfilmF
−
(6)
(
)
jωdfilm + Kc
jωdfilm + Ka
These theoretical expressions were used to simulate the exper-
2. Theory
ꢀE
ꢀI
imental responses of the electrochemical impedances,
(ω), the
ꢀq
ꢀE
charge/potential transfer function,
(ω), and the electrogravimet-
Briefly, ac-electrogravimetry consists in coupling electrochem-
ical impedance measurements with a fast response quartz crystal
microbalance (QCM) used in ac-mode. It allows the response in
ꢀm
ꢀE
ric transfer function,
(ω). These results were compared with the
experimental data which provided the key parameters, mi, Ki and
Gi.
ꢀE
ꢀI
ꢀm
ꢀE
current,
(ω), electrical transfer function, and in mass,
(ω),
mass-potential transfer function to be simultaneously obtained
owing to a sinusoidal potential perturbation with a small amplitude
(ꢁE) [21–23]. The advantage of combining such transfer functions
is the possibility of a fair separation of the different electrochem-
ical processes, which involves concomitantly the mass and charge
changes. In fact, at the film/electrolyte interface, the ion-exchange
phenomenon is modified when a small sine wave potential pertur-
bation, (ꢁE), is applied.
3. Experimental
3.1. Synthesis of CeO2 nanoparticles
The schematic diagram of the experimental procedure described
hereafter is shown in Fig. 1. All the chemical reagents were
used without purification. The cerium (III) nitrate salt precur-
sor (Ce(NO3)3, 6 H2O) was initially dissolved in only H2O or in
a C2H5OH/H2O mixture (1/1 vol.). The solution was stirred at
The equation describing the insertion/expulsion of species
i (i = a, c, and s for anion, cation, and solvent, respectively),

272
C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
3.2. Morphological Characterisation of CeO2 nanoparticles using
XRD, TEM and BET
Water or (alcohol/water)
mixed solvent
Ce(NO3)3 . 6 H2O
The crystallite size (dXRD) was estimated using XRD (Bruker AXS,
D8 ADVANCE) by inserting Full Width Half Maximum (FWHM) of
characteristic peak (111) in the Scherrer equation [30] (see Table 1):
Stirring at temperature (T)
dXRD = 0.9ꢃ/FWHM cos Â
where ␭ was the incident wavelength (1.5406 A◦ in this study) of
X-ray and ␪ was the diffraction angle for the (111) plane.
(8)
NH4OH (pH=9.5)
The CeO2 nanoparticle diameter and morphology were deter-
mined by transmission electron microscopy (TEM, JEOL 2000Fx).
For that purpose, samples for TEM were prepared by ultrasoni-
cally dispersing the CeO2 NPs in ethanol, and then dropped onto
carbon-coated copper grids. Corresponding TEM images and elec-
tron diffraction patterns were recorded. The average particle size
(dTEM) was determined by TEM images with a 50 particles sample.
The specific surface area of CeO2 nanoparticles (A(m2.g−1)) was
measured by nitrogen adsorption at 77.3 K using a Quantachrome
instrument and calculated by Brunauer-Emmett-Teller equation,
assuming that the CeO2 nanoparticles are spherical and non-porous
[3]. The corresponding particle size (dBET) can be estimated as:
Precipitation of cerium hydroxide
Centrifugation
3 Times
Washing by water/ethanol
Drying (and calcination)
CeO2 nanoparticles
dBET = 6/ A
(9)
Fig. 1. Synoptic scheme of CeO2 nanoparticles synthesis.
where ␳ is the density of CeO2, ␳ =7.28 g.cm−3 [31].
30 ◦C and a solution of NH4OH was added. Immediately, a precipi-
tate of Ce(OH)3 was formed because of its low solubility product
(Ks(Ce(OH)3 = 7. 10−21) [29], leading in a further step to a light
brown coloration of the solution. Subsequently, as the pH was
maintained at 9-9.5, the coloration of the precipitate turned purple,
which is a characteristic of the oxidation of Ce(OH)3 into Ce(OH)4
by dissolved oxygen. At last, it became a light yellow suspension
of CeO2. The reaction is stopped after about 1.5 hour of vigorous
stirring. The obtained precipitate was centrifuged, washed with dis-
tilled H2O and ethanol alternatively three times, and then dried in
a drying oven at 60 ◦C for 24 hours (sometimes up to calcination at
600 ◦C in a furnace). In order to evaluate the influence of some of
the synthesis parameters, four different powders have been com-
pared in this work (see Table 1). Apart from CeO2 NPs of the a type
that were purchased from Aldrich, CeO2 NPs of the b and c types
were synthesized in aqueous medium and in a C2H5OH/H2O mix-
ture (1/1 by vol.) respectively. The latter one (c) was calcinated at
600 ◦C for 1 h and noted powder of the d type. The overall chemi-
cal reaction of formation of cerium oxide in alkaline solution is as
follows:
3.3. Electrosynthesis and characterization of PPy-DS/CeO2 NPs
nanocomposite thin films
PPy-DS and PPy-DS/CeO2 NPs nanocomposite films were elec-
trodeposited from an electrolytic and colloidal aqueous solution
containing freshly distilled pyrrole (Py, 0.1 mol.dm−3), sodium
dodecylsulfate (SDS, 0.025 mol.dm−3) and, when necessary, cerium
oxide nanoparticles (CeO2 NPs, 2 g.dm−3) ultrasonically dispersed
in the electrolytic solution prior to the proper electrosynthesis step.
This latter was carried out using a Bio-Logic SP300 potentiostat
connected to a frequencymeter (Keithley) and a lab-made oscilla-
tor by applying 10 consecutive cyclic voltammetric scans between
-1.5 and 0.4 V/SSE using a 50 mV.s−1 scan rate. The three-electrode
cell used for this purpose consists of a platinum grid as counter-
electrode, a reference electrode (saturated sulphate Hg2SO4/Hg
electrode, SSE) and a working electrode. This latter was either a
working electrode made from a modified gold-patterned quartz
crystal in view of simultaneous electrodeposition and EQCM exper-
iments, or a thin film of platinum deposited on mica with the help
of the sputtering technique for FEG-SEM experiments.
1
2
The morphology of the nanocomposite films was examined with
a scanning electron microscope (FEG-SEM, Ultra 55 from Zeiss)
coupled with EDS microanalysis.
2Ce(NO3)3
+
O2 + 6HO− → 2CeO2 + 6NO− + 3H2O
(7)
3
Let us emphasise that the liquid-phase precipitation process
includes three steps: chemical reaction, nucleation and crystal
growth. Generally, these three steps are fast, hence, the mixing step
has a large influence on the product particle size and its distribution
[29]. It is thus important to define the crystalline variety as well as
an accurate estimation of the size of the resulting nanoparticles.
3.4. ac-electrogravimetry
The electrochemical experiments were carried out in a classical
three-electrode cell adapted for ac-electrogravimetry experiments
in which the three electrodes were the same as those mentioned
above for EQCM experiments.
Table 1
The conditions for the electrochemical synthesis of PPy-DS and
PPy-DS/CeO2 NPs were identical to those reported above (see Part
3.3), except that, in the case of nanocomposite materials, the elec-
trosynthesis solution contained CeO2 nanoparticles at two different
concentrations, either 2 g.dm−3 or 5 g.dm−3) in order to evaluate
the influence of the amount of cerium oxide nanoparticles incor-
porated in the PPy-DS matrix on the ion exchange behaviour of the
resulting nanocomposite films.
Crystallite size values obtained by BET, XRD and TEM. (*size distribution for this
sample is very large, from 20 nm to 300 nm, as deduced from the exploitation of
Fig. 3a).
CeO2 samples
A (m2/g)
dBET (nm)
dXRD (nm)
dTEM (nm)
60 40*
a
b
c
-
-
43
13
9
62
84
70
13
10
12
15
10
12
2
1
1
As far as ac-electrogravimetry experiments are concerned, they
d
10
were carried out in a 0.5 mol.dm−3 NaCl aqueous electrolytic

C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
273
temperature and/or longer calcination duration both seem to tend
to increase the particle size (see Fig. 3d).
The CeO2 nanoparticle diameter was also determined from BET
technique by using specific area measurement (dBET) and from
direct measurement on TEM images (dTEM) and compared with that
measured by XRD (dXRD, see Table 1). One can observe from Table 1
that XRD, TEM and BET techniques give diameter values that are
fairly close for the three different synthesis methods. This demon-
strates that the CeO2 nanoparticles are primary and non-porous
and also monodisperse in terms of diameter.
(111)
(220)
(311)
(222)
(200)
(400)
a)
b)
c)
4.2. Electrosynthesis and composition of PPy-DS/CeO2 NPs
nanocomposite films.
d)
80
In the followinginvestigations, the CeO2 nanoparticlesthat were
used are those obtained from the synthesis method d for which
20
30
40
50
60
70
90
2 (°)
θ
dBET, dXRD and dTEM are 12 nm, 10 nm and 12 nm respectively (see
Table 1). Moreover, BET allowed the determination of a 70 m2/g
specific area for those ceria nanoparticles (see Table 1).
Fig. 2. XRD diffraction patterns of ceria nanoparticules (CeO2): a) commercial sam-
ple, b) prepared in water at 30 ◦C, c) prepared in water/ethanol (1/1 by vol.) at 30 ◦C,
d) as (c) then calcinated at 600 ◦C for 1 h.
In a first set of experiments, PPy-DS/CeO2 NPs nanocomposite
materials were electrodeposited on the gold electrode of an electro-
chemical quartz crystal microbalance (EQCM) used simultaneously
as a working electrode in a usual three electrode set-up (see section
3.3 and Fig. 4b). For the need of comparison, a similar experiment
was carried out in the absence of cerium oxide nanoparticles (see
Fig. 4a). Both voltammogramms are similar as they both show the
expected irreversible oxidation of the monomer known to consti-
tute the first step of the electropolymerisation of the monomer and
subsequent formation of the polymer film on the working electrode
surface. One can also observe an anodic and a cathodic peak corre-
sponding to the electroactivity of the polymer film. Intensity of both
peaks increases with the number of scans, which indicates that the
polymer film thickness increases as well. A similar conclusion can
be drawn for the mass of the film, as observed from the curve show-
ing the variation of the microbalance frequency. Let us remember
here that according to the well-known Sauerbrey’s law, a decrease
of the oscillation frequency of the quartz corresponds to an increase
of the mass of the deposit on the golden quartz electrode acting as a
working electrode. Such electrogravimetric curves show both mass
variations resulting from ions and solvent exchange occurring upon
oxidation/reduction (doping/undoping) of the conducting polymer
in the potential region situated between -0.5 and -1.5 V vs. SSE,
as well as global mass increase of the film in the potential region
allowing the monomer electrochemical oxidation and polymeri-
sation, i.e. between -0.25 and 0.4 V vs. SSE. The mass variation
deduced from the frequency variation measured at the end of each
cyclic scan, i.e. at -1.5 V vs. SSE on the backward scan, was extracted
and plotted as a function of each scan for both Fig. 4a and 4b (see
Fig. 4c). This potential value was chosen because it corresponds to
a situation where the electrodeposited film is in a reduced state.
By doing so, one can consider that the mass increase observed for
a given scan by comparison with the previous one actually cor-
responds to the global mass increase of the film. By considering
that the incorporation of CeO2 NPs do not alter the electrochemical
deposition of the polymer, one can consider that the difference in
the mass uptake for a given cyclic scan extracted from both figures
actually correspond to the mass uptake resulting exclusively from
the incorporation of NPs. This CeO2 mass uptake was plotted as a
function of the number of cycles (see blue curve on Fig. 4c) and
reaches 4 ␮g at the ninth scan. The insert in Fig. 4c shows a mag-
nification of this plot for the five initial cycles. It clearly indicates
that incorporation of CeO2 NPs in the PPy matrix starts right from
the first cycle. This possibly occurs thanks to electrostatic interac-
tions between the oxidised and thus cationic polypyrrole skeleton
and CeO2 NPs bearing negative surface charges as a consequence of
adsorption of dodecylsulfate anions on their surface, according to a
solution that was de-aerated prior to the measurements. They
were performed using a lab-made 9 MHz oscillator acting as a
microbalance as well as quartz resonators (AWS, Spain) with a
fundamental resonant frequency of 9 MHz. A four-channel fre-
quency response analyzer (FRA, Solartron 1254) and a potentiostat
(SOTELEM-PGSTAT) were used. The QCM was used under a dynamic
regime, the modified working electrode (0.2 cm2) was polarized
at a selected potential, and a sinusoidal small amplitude poten-
tial perturbation was superimposed. The microbalance frequency
change, ꢀfm, corresponding to the mass response, ꢀm, of the
modified working electrode was measured simultaneously with
the ac response, ꢀI, of the electrochemical system. The resulting
signals were sent to the four-channel FRA, which allowed the elec-
ꢀm
ꢀE
trogravimetric transfer function,
(ω), and the electrochemical
ꢀE
impedance,
(ω), to be simultaneously obtained at a given poten-
ꢀI
tial situated inside the potential range allowing the redox switching
ꢀq
ꢀE
of the polymer film [21–23]. The third transfer function,
(ω), can
be experimentally calculated by using the following equation:
ꢀq
ꢀE
1
ꢀE
ꢀI
ω =
)
(7)
(
jω
ω
( )
4. Results and Discussion
4.1. Characterization of CeO2 nanoparticles
The crystalline variety of the CeO2 nanoparticles prepared
according to different methods can be deduced from the X-ray
diffraction spectra shown on Fig. 2. Whatever the synthesis method,
these latter exhibit lines (111), (200), (220), (311), (222) and (400)
that are characteristics of CeO2, according to those of centered face
cubic (CFC) fluorite structured CeO2 crystal (see JCPDS N◦34-394).
Compared to the XRD patterns of a commercial sample, the rays
appeared broader for some of those spectra because of a smaller
crystallite size.
TEM was used to investigate the morphology of the synthesised
nanoparticles (see Fig. 3). The TEM images show a heterogeneous
size and non-uniform shape for the commercial powder (a). Conse-
quently, the size distribution is very large (from 20 to 300 nm). The
particles synthesised in a mixed solvent (water/ethanol: 1/1 in vol.)
are smaller, homogeneous in size and spherical in shape compared
to those prepared in pure water (see Figs. 3b-c). Moreover, one can
also observe the effect of calcination. Indeed, a higher calcination

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C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
Fig. 3. TEM images and corresponding electronic diffractions of a, b, c and d-type CeO2 nanoparticles.
situation already reported in literature and encountered in the case
of the incorporation of magnetite nanoparticles in polypyrrole films
[32]. Taking into account an average value of 5.7 nm for the radius
of spherical CeO2 NPs (see CeO2 NPs of the d type in Table 1) and
a density value of 7.28 g/cm−3 for CeO2 [31], one can estimate that
7.2 1011 CeO2 NPs were incorporated in the nanocomposite film
in the course of the electrodeposition process illustrated in Fig. 4b.
Due to the selected film thickness, our films can be considered as
acoustically thin enough and under these conditions, gravimetric
response are exclusively obtained here. In other words, viscoelastic
contributions can be neglected here.
[33]. On the surface of this complex morphology, CeO2 nanopar-
ticle aggregates were observed to be inhomogeneously dispersed.
All these observations remain true whatever the CeO2 NPs con-
centration in the electrosynthesis solution. The EDS microanalysis
confirms the presence of cerium, and thus of CeO2 nanoparticles
(see Fig. 5b), on and in the bulk of composite films (indeed EDS
revealed the presence of ceria even in places where CeO2 nanopar-
ticles could not be seen on the surface). Let us emphasise that the
other elements detected by this analysis came from the counter-
ions (S, O) and the polypyrrole skeleton (C, N).
4.4. Film electrogeneration
4.3. Composite morphology
DS doped PPy films were electrogenerated in the presence or
in the absence of ex-situ synthesized CeO2 nanoparticles accord-
ing to the electrochemical procedure reported above (see section
3.3, 3.4 and 4.2 and Fig. 4). It must be emphasized that consecu-
tive cyclic voltammograms corresponding to the electrodeposition
FEG-SEM observations and EDS analysis of the resulting
nanocomposite films show
a globular morphology bearing
randomly oriented platelets (see Fig. 5a), as already reported in lit-
erature for PPy films elaborated in similar experimental conditions

C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
275
a)
C
16
S
14
b)
12
10
8
O
6
4
N
S
2
Ce
Ce
Ce
0
0
2
4
6
8
Energy / keV
Fig. 5. a) SEM image and b) EDS spectrum of PPy-DS/CeO2 NPs nanocomposite films
electrodeposited from an electrolytic and colloidal aqueous solution containing SDS
(0.025 mol.dm−3), CeO2 NPs (1 g.dm−3) and pyrrole (0.1 mol.dm−3).
an electrolytic aqueous solution containing NaCl (0.5 mol.dm−3).
The consecutive voltammograms observed in Fig. 6 show the
expected pair of peaks corresponding to the above mentioned
doping/undoping process of polypyrrole. There is no significant
change of the shape and peak intensities of the voltammogram
upon potential cycling, indicating that PPy-DS and nanocomposite
0.10
0.05
0.00
-0.05
-0.10
Fig. 4. a,b) cyclic voltammetry (black curve) and EQCM response (blue curve)
obtained simultaneously in the course of the electrodeposition of PPy-DS films
on a gold coated quartz a) in the absence, b) in the presence of CeO2 nanopar-
ticles (2 g.dm−3), in an aqueous electrolytic solutions containing Py monomer
(0.1 mol.dm−3) and sodium dodecylsulfate (0.025 mol.dm−3) during 10 scans. Scan
rate: 50 mV.s−1. c) frequency variation (black and red dots) and mass variation dif-
ference (blue dots) all measured at the end of each cyclic voltammetry scan (−1.5 V
vs. SSE) and extracted from Figs. 4a,b. Mass variation difference is calculated from
the difference between the mass variation measured during the electrodeposition of
PPy-DS film in the presence of CeO2 NPs (red dots) and that measured in the absence
of CeO2 NPs (black dots) and is attributed in a first approximation to the uptake of
CeO2 NPs only.
of the films investigated in this work were very similar in every
aspects, whether the concentration of cerium oxide nanoparticles
-1.2
-1.1
-1.0
-0.9
-0.8
-0.7
E / V vs. SSE
in the electrodeposition solution was 0, 2, or 5 g.dm−3
.
Fig. 6. Consecutive cyclic voltammograms (solid line: 1st scan, dash line: 15th scan)
obtained for a working electrode modified with a PPy-DS/CeO2 NPs nanocomposite
thin film doped with DS anions in an aqueous electrolytic solution contain-
ing NaCl (0.5 mol.dm−3). Working electrode: gold coated quartz crystal adapted
for ac-electrogravimetry experiments, counter-electrode: platinum grid, reference
4.5. Classical electrochemical characterization
The electrochemical reactivity and stability of the resulting PPy-
DS and PPy-DS/CeO2 NPs films were then tested after transfer in
electrode: SSE and scan rate: 50 mV.s−1
.

276
C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
on the same graphs. A good agreement between the two sets of
data is obvious in terms of shape and frequency distribution.
1.0
0.8
0.6
0.4
0.2
0.0
5
4
3
2
1
0
a)
b)
d)
f)
Experimental
Theoretical
a
Experimental
Theoretical
b
ꢀE
The electrochemical impedance,
(ω), (see Figs. 7a, c and e)
and
: freq. decade
and
: freq. decade
ꢀI
has a usual shape, when dealing with a ion-blocking electrode,
from which it is difficult to easily extract information. The low fre-
quency trend was related to a parasitic response and was simulated
using equations 4 and 5. Nevertheless, considering the experimen-
tal responses given by these electrochemical impedances, it should
be noticed that the global response seems fairly constant indepen-
dent from the film composition. It should also be noted that there is
no obvious part with a slope equal to 45◦ or less in the electrochem-
ical impedance response. Therefore, the rate limiting step is not
mass transport in the film or in the solution but rather ionic transfer
0.1 Hz
10 Hz
1 Hz
0.1 Hz
4
1 Hz
0
1
2
3
5
0.0 0.2 0.4 0.6 0.8 1.0
Re( E/ I)/k cm2
Re( q/ E)/mC cm-2 V-1
5
4
3
2
1
0
1.0
c)
between the solution and the film [24]. The charge/potential trans-
Experimental
Theoretical
and
Experimental
Theoretical
d
c
ꢀq
ꢀE
fer function,
(ω), (see Figs. 7b, d and f) experimentally calculated
0.8
0.6
0.4
0.2
0.0
:
and
: freq. decade
freq. decade
through equation 7 permits to separate the ionic contribution with-
out any possibility to identify the ionic species involved. It should
be indicated here that the contribution of the parasitic reaction,
occurring at low frequencies, was removed for keeping only the
ionic transfer response. Two loops seem to appear in the three rep-
resentations even if a fair separation is not easy to obtain. Indeed,
the time constants corresponding to each ionic transfer appear to
be very close to each other. At this stage, it is impossible to distin-
guish between anion and cation contributions and to determine
which ionic species are involved. Nevertheless, the constants Ki
and Gi were determined for two ions (see Table 2 for the Ki val-
ues corresponding to the two ions) and were used in the following
simulations.
0.1 Hz
10 Hz
0.1 Hz
1 Hz
1 Hz
1
0
2
3
4
5
0.0 0.2 0.4 0.6 0.8 1.0
Re( E/ I)/k cm2
Re( q/ E)/mC cm-2 V-1
e)
1.0
5
4
3
2
1
0
Experimental
Theoretical
and
Experimental
Theoretical
e
f
0.8
0.6
0.4
0.2
0.0
:
and
: freq. decade
freq. decade
0.1 Hz
4.6.1.2. (ii) Electrogravimetric response. Then, to clarify the con-
tribution of the charged and also the uncharged species (i.e. free
ꢀm
ꢀE
10 Hz
solvent molecules), the mass/potential transfer functions,
(ω),
0.1 Hz
1 Hz
are scrutinized. To show the evolution of the ionic transfer behavior
1 Hz
ꢀm
ꢀE
as a function of the potential, the
(ω) responses at -1 V vs. SSE
0.0 0.2 0.4 0.6 0.8 1.0
Re( E/ I)/k cm2
0
1
2
3
4
5
Re( q/ E)/mC cm-2 V-1
of the PPy − DS (Fig. 8a), PPy-DS/CeO2 NPs (2 g.dm−3) (Fig. 8c) and
PPy-DS/CeO2 NPs (5 g.dm−3) (Fig. 8e) films are shown. For all the
responses, three species, sodium and chloride ions and free solvent
molecules, were used in their simulations.
ꢀq
ꢀE
Fig. 7. Measured and simulated transfer functions ꢀE (ω) and
(ω) of the PPy − DS
ꢀI
(a and b), PPy − DS/CeO2 NPs (2 g.dm−3) (c and d) and PPy−DS/CeO2 NPs (5 g.dm−3
)
(e and f) films at −1 V vs. SSE in 0.5 mol.dm−3 NaCl aqueous electrolyte. The film
The DS doped polypyrrole films have been studied earlier in our
group [24]. During oxidation, the anions were inserted in the film,
whereas cations and solvent were expelled during oxidation. The
kinetic constants of cations were the highest, followed by those of
free solvent molecules and the anions contributed at low frequen-
cies. As far as the PPy-DS films of the present study are concerned,
the time constants of cations, solvent and anions are very close to
each other and the different values obtained here do not correspond
exactly with those reported previously. This could be attributed to
the differences in the film preparation, specifically to the SDS con-
centration and potential range used during the potentiodynamic
electrogeneration of the present PPy-DS films.
thickness is 200 nm and the parameters used for the calculations are given in Table 1.
PPy-DS/CeO2 NPs films possess an electrochemical behaviour that
is sufficiently stable for ac-electrogravimetry investigations. It has
to be emphasized that such observations are also valid when the
CeO2 NPs are incorporated during the film electrodeposition. The
peak intensities are not significantly altered whatever the content
of CeO2 NPs in the electrodeposition solution and thus, in the result-
ing electrodeposited film.
4.6. ac-electrogravimetric measurements
It should be noted that the contributions of the cation, the anion
and the free solvent molecules are not perfectly separated as it
The ion exchange behaviour was studied by ac-
electrogravimetry in NaCl aqueous electrolyte (0.5 mol.dm−3) in
the active potential range between -0.6 to -1.1 V vs. SSE. In the fol-
lowing part, the interpretation procedure of ac-electrogravimetry
data is reported for a selected potential, at E = -1.0 V vs. SSE.
can be seen in Fig. 8. To solve this problem, partial transfer func-
ꢅ
ꢀm
ꢀE
tions,
as(ω) (corresponding to anion and solvent contribution)
ꢅ
ꢀm
ꢀE
and
cs(ω) (corresponding to cation and solvent contribution),
were calculated and simulated to separate these contributions as
it was already described elsewhere [24]. This method allows the
contribution of one charged species to be removed; for example
either a cation or an anion in case of cation, anion and free sol-
vent contributions. Moreover, the response of the cation or of the
anion is amplified in the resulting partial mass/potential transfer
functions. This permits to a better separation between the charged
4.6.1. ac-electrogravimetric measurements at E = -1.0 V vs. SSE:
4.6.1.1. (i) Electrochemical response. Fig. 7 exhibits the electro-
ꢀE
ꢀI
chemical impedance spectroscopy,
(ω), and the charge/potential
ꢀq
transfer function,
(ω), data for the three different PPy films mea-
ꢀE
sured at E = -1.0 V vs. SSE for PPy-DS (Figs. 7a-b), PPy-DS/CeO2 NPs
(2 g.dm−3) (Figs. 7c-d) and PPy-DS/CeO2 NPs (5 g.dm−3) (Figs. 7e-f)
films. The experimental transfer functions and the simulated data
from the model (see theoretical part, Eqs. (5) and (6)) are reported
species contribution and that of the free solvent. Here, only the
ꢅ
ꢀm
ꢀE
anion/solvent mass-potentiel transfer functions,
as(ω), were
shown in Figs. 8b, d and f for the three different films. The sodium

C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
277
Table 2
Estimated values for Ki, Rti and –Gi/Ki parameters from ac-electrogravimetry measurements/simulations in 0.5 mol.dm−3 NaCl at −1 V vs. SSE for the three tested films.
ꢅ
ꢀC
ꢀE
Ki × 105/cm.s−1
Rti
Na+
47.1
175.7
80.3
=
/ꢄ·cm2
= − GKi /mmol.cm−3.V−1
1
FG
i
−1 V vs. SSE
i
i
ω→0
Ions - solvent
Na+
Cl−
H2O
Cl−
H2O
Na+
Cl−
H2O
PPy-DS
15.7
6.4
11.3
2.5
1.4
1.5
116.0
27.0
11.6
1473.0
2585.0
2200.0
4.0
11.8
28.7
1.4
0.9
1.1
0.3
0.3
0.3
2.1
3.2
3.1
PPy-DS/CeO2 NPs (2 g.dm−3
PPy-DS/CeO2 NPs (5 g.dm−3
)
)
contribution was removed from the global mass-potential trans-
ms, the last two unknown parameters, Ks and Gs, associated to
the free solvent transfer, can be estimated. For the three differ-
ent films, at this potential, the ac-electrogravimetric response is
located in the third quadrant: H2O contribution appears at high
frequencies, Na+ for the intermediate frequencies and Cl− at low
frequencies. The values of the key parameters Ki and Gi, for the
three species, are listed in Table 2. The values of Ki are coher-
ent with the rate of transfer associated to the three species i.e.
Ks > Kc > Ka. In the case of the PPy-DS film, the three Ki values are
higher compared with those obtained with the two other films
containing CeO2 NPs. This result demonstrates qualitatively dif-
ferent ion-exchange behaviours between PPy-DS and PPy-DS/CeO2
NPs films. Another interesting parameter, the ionic transfer resis-
ꢅ
ꢀm
fer function,
(ω). For the three films, a high frequency loop
is observed inꢀthE e third quadrant indicating a motion in the same
direction as sodium ions and corresponding to the free solvent. At
low frequency appears a small loop, located in the fourth quadrant,
associated to chloride ions with an opposite flux compared with
cations and free solvent motion for a same potential change. This
approach is the only way to clearly demonstrate the anion contri-
ꢅ
ꢀm
bution since a minor loop is observed in the total
(ω) diagram.
For the water response, the semi-circle diameter ꢀisEsmaller for the
PPy-DS compared to the two composite films, which indicates a
greater contribution of water in this case.
At -1 V vs. SSE, using the parameters, Kc, Ka, Gc and Ga obtained
from the previous electrochemical simulations (Fig. 7 and Table 2),
the atomic weight of the three mentioned species, mc, ma and
tance, Rti, can also be estimated using the Gi values and the relation
1
Rti =
. For all the films, water transfer is easy as RtH show
O
2
FG
i
the smallest values. The chloride transfer, characterized by RtCl− ,
presents higher values, especially in the case of the composite
films. Thus, chloride transfer is more difficult and slower with the
composite layers. Another interesting variable named concentra-
ꢁ
ꢀC
ꢀE
i
tion/potential transfer function (
) can be described as the
concentration change related to the inωd→iv0idual species, following a
potential step. This quantity can be estimated through the following
ꢁ
ꢀC
ꢀE
G
i
relation
= − Ki . According to Table 2, in the case of PPy-
i
ω→0
DS, the water contribution is predominant which is followed by the
sodium contribution and finally, only a small part is due to chlo-
ride ions. In the case of the two PPy-DS/CeO2 NPs films, this ratio
remains constant for Cl−, it decreases slightly for Na+ and becomes
more important for H2O. A more porous structure can be pictured
in the case of composite films, which favors the water transfer after
a potential jump.
4.6.2. The changes of key parameters over the potential applied
For all the potential values selected in the active range, the two
key parameters Ki and Rti were determined according to the proce-
dure described above and shown for the measurements at -1 V vs.
SSE. These values are presented in Fig. 9.
For the sodium contribution (see Fig. 9a), two domains can be
distinguished in terms of transfer rate. In the cathodic region, i.e.
below -1 V vs. SSE, Na+ is faster for the PPy-DS films while it is faster
in the anodic region, i.e. above -0.9 V vs. SSE, for the composite films.
In the case of Cl− anions, the kinetics of transfer is independent of
the potential and remains faster in the case of the PPy-DS film (see
Fig. 9b). For the free solvent, the plot of the influence of potential
on Ks values shows bell-shaped curves for the composite materials
and decreasing trend for the PPy-DS film (Fig. 9c).
There are also two distinct domains in the charge transfer resis-
tance values for Na+ ions (see Fig. 9d). In the cathodic range situated
below -0.8 V vs. SSE, Na+ transfer is rather easier for the PPy-DS
films than in the anodic region situated above this same value.
When CeO2 particles are present in the films (Fig. 9d), the oppo-
site behaviour is observed with a threshold potential of -0.85 V vs.
SSE. The chloride ion transfer presents higher values in the case
of the composite films. This is more pronounced in the cathodic
region situated below -0.8 V vs. SSE. Thus, chloride transfer is more
difficult and slower in the composite layers (Fig. 9b and e).
Fig. 8. Measured and estimated mass transfer functions, ꢀm (ω), and partial anion-
ꢀE
solvent transfer functions of the PPy − DS (a and b), PPy − DS/CeO2 NPs (2 g.dm−3
)
(c and d) and PPy − DS/CeO2 NPs (5 g.dm−3) (e and f) films at −1 V vs. SSE in
0.5 mol.dm−3 NaCl aqueous electrolyte. The film thickness is 200 nm and the
molar mass of the species involved in the charge compensation as follows:
m(Na+) = 23 g.mol−1, m(Cl−) = 35.5 g.mol−1, m(H2O) = 18 g.mol−1). The parameters
used for the calculations are given in Table 1.

278
C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
a)
d)
b)
e)
c)
f)
1
FG
Fig. 9. Estimated values for the kinetic parameters a-c) Ki and d-f) Rti
NPs (5 g.dm−3) films.
=
/˝ cm2 as a function of potential for the PPy-DS, PPy-DS/CeO2 NPs (2 g.dm−3) and PPy-DS/CeO2
i
4.6.3. Evolution of the relative concentration, ꢀCi, of each species
materials. Total H2O amount involved indirectly in the charge com-
pensation process is magnified when the PPy-DS films contain CeO2
nanoparticles. The water content increases as a function of the
as a function of the applied potential.
ꢉ
ꢉ
ꢉ
ꢀC
ꢀE
i
To quantify the role of each species,
has been esti-
ω→0
CeO2 NPs content in the PPy-DS/CeO2 NPs films (Fig. 10b). This
is possibly due to the increased porous volume in the conducting
polymer as a result of the added CeO2 nanoparticles. Interestingly,
the ꢀCCl− values of PPy-DS/CeO2 NPs (2 g.dm−3) and PPy-DS/CeO2
(5 g.dm−3) films are about three times greater than that of PPy-
DS films (Fig. 10c). The kinetic study discussed above showed that
the Cl− ions in PPy-DS/CeO2 NPs films at the film/electrolyte inter-
face are slower compared with pristine PPy-DS films. Although the
kinetics is slower in the presence of CeO2 nanoparticles, the total
amount of the Cl− ions inserted during oxidation are substantially
higher than for pristine PPy-DS films.
Further experiments are currently underway to gain further
information about the reasons explaining why PPy-DS/CeO2 NPs
composite films possess a permeability to water and chloride
anions different from that observed for pristine PPy-DS films. One
possible explanation can be based on a predictable effect (although
mated as a function of the potential. It was shown that at low
ꢉ
ꢉ
ꢉ
ꢉ
ꢉ
ꢉ
ꢀC
ꢀE
ꢀC
ꢀE
G
i
i
i
frequencies,
becomes
= − K (Ki and Gi values
i
ω→0
are obtained from simulation of the ωd→at0a shown in Figs. 7 and 8)
ꢉ
ꢉ
ꢀC
ꢀE
i
[21–23]. The integration of the
against potential gives
ꢉ
ω→0
the insertion isotherm. Fig. 10 presents the rel−ative concentration
change, ꢀCNa+ , ꢀCCl− and ꢀCH O, for Na+, Cl and H2O, respec-
2
tively.
The ꢀCNa+ values of the PPy-DS films with and without incorpo-
ration of CeO2 nanoparticles do not show a remarkable difference.
CNa+ decreases, indicating the expulsion of the Na+ ions during oxi-
dation (Fig. 10a). Although slightly faster transfer of the cations
at the film/electrolyte interface was observed, when CeO2 NPs are
present in PPy-DS films, one can observe that at E = -0.8 V vs. SSE
for example, ꢀCNa+ becomes very close for the three investigated

C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
279
Fig. 10. Relative concentration change, ꢀCi, for a) Na+, b) H2O, and c) Cl− of the PPy-DS, PPy-DS/CeO2 NPs (2 g.dm−3) and PPy-DS/CeO2 NPs (5 g.dm−3) films as a function of
the applied potential in 0.5 mol.dm−3 NaCl aqueous electrolyte.
poorly characterised at the present stage of our investigations) of
cerium oxide nanoparticles incorporation on the porosity of such
films. Another interesting issue is the electrocatalytic behaviour of
cerium oxide nanoparticles towards water oxidation [20] resulting
in water consumption and protons production that may enhance
water and chloride exchanges observed at rather anodic potentials
for PPy-DS/CeO2 NPs composite films.
absence. All these observations tend to indicate that the incorpo-
ration of cerium oxide nanoparticles increases the permeability of
PPy-DS thin films towards chloride anions in terms of quantities
but not from a kinetic aspect.
Acknowledgements
C. Benmouhoub acknowledges sincerely the Algerian govern-
ment for having delivered to her a 18 month PNE-type scholarship.
5. Conclusion
References
In this contribution, PPy-DS/CeO2 NPs nanocomposite films
were electrogenerated successfully, as evidenced from cyclic elec-
trogravimetry, SEM-FEG and EDS experiments, from electrolytic
and colloidal aqueous solutions containing CeO2 nanoparticles syn-
thesised ex-situ. The incorporation of cerium oxide nanoparticles
was shown to affect substantially the ion exchange behaviour
of dodecylsulfate doped polypyrrole films upon electrochemical
doping/undoping, as revealed from ac-electrogravimetry experi-
ments, but not its electrochemical behavior as observed from cyclic
voltammetry technique used for the electrodeposition step or after
transfer in a blank electrolytic and aqueous solution. In this latter
case, whatever the CeO2 nanoparticles content is, upon electro-
chemical oxidation of the film, chloride anions and sodium cations
were actually found to be inserted in and expelled out of the film,
respectively. In addition, free water molecules were found to be
systematically expelled (as sodium cations) upon oxidation of the
film (except for rather anodic potentials in the absence of ceria
nanoparticles in the film). The main influence of the presence of
cerium oxide nanoparticles was observed on the transfer rates of
the exchanged species. As the cerium oxide nanoparticles con-
tent increases in the PPy-DS films, sodium cations and chloride
anions were found to be exchanged much faster and much slower
respectively. Finally, chloride anions were found to be exchanged in
higher amounts in the presence of CeO2 nanoparticles than in their
[1] D.W. Hatchett, M. Josowicz, Composites of Intrinsically Conducting Polymers
as Sensing Nanomaterials, Chem. Rev. 108 (2008) 746.
[2] A. Pailleret, N.T.L. Hien, D.T.M. Thanh, C. Deslouis, Surface reactivity of
polypyrrole/iron-oxide nanoparticles: electrochemical and CS-AFM investiga-
tions, J. Solid State Electrochem. 11 (2007) 1013.
[3] J.F. Rivera, C. Bucher, E. Saint-Aman, B.L. Rivas, M.C. Aguirre, J. Sanchez, I.
Pignot-Paintrand, J.C. Moutet, Removal of arsenite by coupled electrocatalytic
oxidation at polymer-ruthenium oxide nanocomposite and polymer-assisted
liquid phase retention, Appl. Catal. B 129 (2013) 130.
[4] R.K. Sharma, L. Zhai, Multiwall carbon nanotube supported poly(3,4-
ethylenedioxythiophene)/manganese oxide nano-composite electrode for
super-capacitors, Electrochim. Acta 54 (2009) 7148.
[5] M. Jin, G. Han, Y. Chang, H. Zhao, H. Zhang, Flexible electrodes based on
polypyrrole/manganese dioxide/polypropylene fibrous membrane composite
for supercapacitor, Electrochim. Acta 56 (2011) 9838.
[6] I. Boyano, J.A. Blazquez, I. De Meatza, M. Bengoechea, O. Miguel, H. Grande,
Y. Huang, J.B. Goodenough, Preparation of C-LiFePO4/Polypyrrole lithium
rechargeable cathode by consecutive potential steps electrodeposition, Journal
of Power Sources 195 (2010) 5351–5359.
[7] J. Zhu, S. Wei, L. Zhang, Y. Mao, J. Ryu, P. Mavinakuli, A.B. Karki, D.P. Young, Z.
Guo, Conductive Polypyrrole/Tungsten Oxide Metacomposites with Negative
Permittivity, J. Phys. Chem. C 114 (2010) 16335–16342.
[8] P. Montoya, F. Jaramilloa, J. Calderóna, S.I. Córdoba de Torresi, R.M. Tor-
resi, Evidence of redox interactions between polypyrrole and Fe3O4 in
polypyrrole–Fe3O4 composite films, Electrochimica Acta 55 (2010) 6116–6122.
[9] C. Janáky, C. Visy, O. Berkesi, E. Tombácz, Conducting Polymer-Based Electrode
with Magnetic Behavior: Electrochemical Synthesis of Poly(3-thiophene-
acetic-acid)/Magnetite Nanocomposite Thin Layers, J. Phys. Chem. C 113 (2009)
1352–1358.

280
C. Benmouhoub et al. / Electrochimica Acta 145 (2014) 270–280
[10] Q. Wu, F. Zhang, P. Xiao, H. Tao, X. Wang, Z. Hu, Y. Lü, Great Influence of
Anions for Controllable Synthesis of CeO2 Nanostructures: From Nanorods to
Nanocubes, J. Phys. Chem. C 112 (2008) 17076.
[11] N.J. Lawrence, J.R. Brewer, L. Wang, T.-S. Wu, J. Wells-Kingsbury, M.M. Ihrig,
G. Wang, Y.-L. Soo, W.-N. Mei, C.L. Cheung, Defect Engineering in Cubic
Cerium Oxide Nanostructures for Catalytic Oxidation, Nano Lett. 11 (2011)
2666.
[22] L.T.T. Kim, C. Gabrielli, A. Pailleret, H. Perrot, Ions/Solvent Exchanges and Elec-
tromechanical Processes in Hexasulfonated Calix[6]Arene Doped Polypyrrole
Films: Towards a Relaxation Mechanism, Electrochem. Solid-State Lett. 14
(2011) F9.
[23] C. Gabrielli, J.J. Garcia-Jareno, M. Keddam, H. Perrot, F. Vicente, Ac-
electrogravimetry study of electroactive thin films. I. Application to Prussian
Blue, J. Phys. Chem. B 106 (2002) 3182.
[12] X. Liang, J. Xiao, B. Chen, Y. Li, Catalytically Stable and Active CeO2 Mesoporous
Spheres, Inorg. Chem. 49 (2010) 8188.
[24] C. Gabrielli, J.J. Garcia-Jareno, M. Keddam, H. Perrot, F. Vicente, Ac-
electrogravimetry study of electroactive thin films. II. Application to
Polypyrrole, J. Phys. Chem. B 106 (2002) 3192.
[25] C. Gabrielli, H. Perrot, in: M. Schlesinger (Ed.), Modern Aspects of Electrochem-
istry No.44, Modeling and Numerical Simulations II, Springer, 2009, Chap. 5.
[26] O. Sel, L. To Thi Kim, C. Debiemme-Chouvy, C. Gabrielli, C. Laberty-Robert,
[13] C. Slostowski, S. Marre, O. Babot, T. Toupance, C. Aymonier, Near- and Super-
critical Alcohols as Solvents and Surface Modifiers for the Continuous Synthesis
of Cerium Oxide Nanoparticles, Langmuir 28 (2012) 16656.
[14] J. Kaspar, P. Fornasiero, N. Hickey, Automotive catalytic converters: current
status and some perspectives, Catal. Today 77 (2003) 419.
H. Perrot, C. Sanchez, Proton Insertion Properties in
a Hybrid Mem-
[15] N. Izu, W. Shin, N. Murayama, S. Kanzaki, Resistive oxygen gas sensors based
on CeO2 fine powder prepared using mist pyrolysis, Sens. Actuator B-Chem. 87
(2002) 95.
[16] A. Trovarrelli, C. De Leitenberg, M. Boaro, G. Dolcetti, The utilization of ceria in
industrial catalysis, Catal. Today 50 (1999) 353.
brane/Conducting Polymer Bilayer Investigated by AC Electrogravimetry, J.
Electrochem. Soc. 157 (2010) F69.
[27] L. To Thi Kim, C. Debiemme-Chouvy, C. Gabrielli, H. Perrot, Redox Switch-
ing of Heteropolyanions Entrapped in Polypyrrole Films Investigated by
ac-Electrogravimetry, Langmuir 28 (2012) 13746.
[17] F. Larachi, J. Pierre, A. Adnot, A. Bernis, Ce 3d XPS study of composite
CexMn1-xO2-y wet oxidation catalysts, Appl. Surf. Sci. 195 (2002) 236.
[18] H. Imagawa, A. Suda, K. Yamamura, S. Sun, Monodisperse CeO2 Nanoparticles
and Their Oxygen Storage and Release Properties, J. Phys. Chem. C 115 (2011)
1740.
[28] O. Sel, L. To Thi Kim, C. Debiemme-Chouvy, C. Gabrielli, C. Laberty-Robert, H.
Perrot, Determination of the Diffusion Coefficient of Protons in Nafion Thin
Films by ac-Electrogravimetry, Langmuir 29 (2013), 13665–13660.
[29] X.D. Zhou, W. Huebner, H.U. Anderson, Processing of nanometer-scale CeO2
particles, Chem. Mater. 15 (2) (2003) 378–382.
[19] H. Xiao, Z. Ai, L. Zhang, Nonaqueous Sol-Gel Synthesized Hierarchical CeO2
Nanocrystal Microspheres as Novel, Adsorbents for Wastewater Treatment, J.
Phys. Chem. C 113 (2009) 16625.
[20] G.R. Bamwenda, H. Arakawa, Cerium dioxide as a photocatalyst for water
decomposition to O(2) in the presence of Ce(aq)(4 + ) and Fe(aq)(3 + ) species,
J. Mol. Catal. A 161 (2000) 105.
[21] L.T.T. Kim, C. Gabrielli, A. Pailleret, H. Perrot, Correlation between ion-
exchange properties and swelling/shrinking processes in hexasulfonated
calix[6]arene doped polypyrrole films: ac-electrogravimetry and electrochem-
ical atomic force microscopy investigations, Electrochim. Acta 56 (2011)
3516.
[30] R. Jenkins, R.L. Snyder, X-Ray Powder Diffractometry, Ed., Wiley-Interscience,
1996, pp. 89–91.
[31] S. Tsunekawa, T. Fukuda, A. Kasuya, Blue shift in ultraviolet absorption
spectra of monodisperse CeO2-x nanoparticles, J. Appl. Phys. 87 (3) (2000)
1318–1321.
[32] C. Janáky, B. Endro˝ di, O. Berkesi, C. Visy, Visible-light-Enhanced electrocatalytic
activity of a polypyrrole/magnetite hybrid electrode toward the reduction of
dissolved dioxygen, J. Phys. CHem. C 114 (2010) 19338–19344.
[33] D. Kowalski, M. Ueda, T. Ohtsuka, Corrosion protection of steel by bi-layered
polypyrrole doped with molybdophosphate and naphthalenedisulfonate
anions, Corros. Sci. 49 (2007) 1635–1644.