Impedance and ionic transport properties of proton-conducting electrolytes based on polyethylene oxide/methylcellulose blend polymers

Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

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Journal of Science: Advanced Materials and Devices
journal homepage: www.elsevier.com/locate/jsamd

Original Article

Impedance and ionic transport properties of proton-conducting
electrolytes based on polyethylene oxide/methylcellulose blend
polymers
Hawzhin T. Ahmed a, Omed Gh. Abdullah b, *
a
b

Charmo Center for Research, Training & Consultancy, Charmo University, 46023, Chamchamal e Sulaimani, Kurdistan Region, Iraq
Advanced Materials Research Lab., Department of Physics, College of Science, University of Sulaimani, 46001, Kurdistan Region, Iraq

a r t i c l e i n f o

a b s t r a c t

Article history:
Received 2 December 2019
Received in revised form
1 February 2020
Accepted 1 February 2020
Available online 8 February 2020

Proton-conducting polymer electrolyte films were prepared by dissolving NH4I salt in polyethylene

oxide/methylcellulose (PEO/MC) blend polymers using the solution cast technique. The semi-crystalline
nature of the sample was identified from the X-ray diffraction (XRD) pattern. The surface morphology on
the electrical conductivity was analyzed by scanning electron microscopy (SEM). The highest ionic
conductivity of 7:62 Â 10À5 S=cm was achieved at room temperature for the sample containing 30 wt. %
of NH4I. The temperature dependence of the Jonscher's exponent shows that the conduction mechanism
can be well represented by the overlapping large polaron tunneling (OLPT) model. The electrical conductivity enhancement was analyzed by the Rice and Roth model, which showed that the increase in the
salt concentration caused an increment in the mobility and the diffusion coefficient of the ions. For all
prepared samples, the highest value of conductivity was associated with the minimum value of activation energy. The dielectric data were analyzed for the highest ionic conducting sample at various temperatures to clarify an important factor of the ion conduction. The non-Debye behavior of the samples
can be expressed from the electric modulus formalism and the dielectric properties of the electrolytes
that have been proven by the incomplete semicircular arc of the Argand plots.
© 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
This is an open access article under the CC BY license ( />
Keywords:
Proton-conducting
Ionic conductivity
Diffusion coefficient
Electric modulus
Argand plot

1. Introduction
Nowadays, solid polymer electrolytes (SPEs) have great attraction through out the disciplines of electrochemistry, polymer science, organic chemistry, and inorganic chemistry. In its progress, in
turn, it revolutionizes in both academia and industry area the
development of science and technology [1]. The improvement of
the ionic conductivities at ambient temperature for SPEs has been
the main focus of most researchers [2]. Several strategies, such as
copolymerization, chemical modifications (grafting), physical
mixture (blending), plasticization, and the addition of micro/
nanofillers have been proposed to boost the electrical conductivity
of the polymer electrolytes [3,4]. Also, the ionic conductivity of
polymer-based electrolytes can be modulated by doping salts,

acids, metals, alkali, etc. to the polymer matrix [5]. In a few years

* Corresponding author.
E-mail address: (O.Gh. Abdullah).
Peer review under responsibility of Vietnam National University, Hanoi.

back, the attention of researchers deviated towards the blending of
polymers; this technique has opened a new wave of potential as an
effective method to enhance the electrical and mechanical properties of electrolyte systems [6,7]. The blending of polymers
together provides more complexation sites, which raise the ion
migration, resulting in an increase in the ionic conductivity [8,9].
According to Buraidah and Arof [8], the highest conductivity value
obtained at ambient temperature was 1.77 Â 10À6 S$cmÀ1 for the
chitosan-PVA-NH4I electrolyte system. As a comparison, the ionic
conductivity achieved for the unblended system of chitosan-NH4I
was 3.73 Â 10À7 S$cmÀ1. Very recently, among SPEs, most particular
attention has been paid to the development of the protonconducting polymer electrolytes due to their performance and
promising technological applications in advanced smart devices
[10], because they have attractive properties like shape versatility,
flexibility, lightweight, etc. [11]. Synthetic polar polymers utilized
in making proton-conducting films include polyethylene oxide
(PEO), polyvinyl alcohol (PVA), Poly (N-vinyl pyrrolidone) (PVP)
[12,13]. However, Cellulose, Chitosan (CA), Starch have been used as
a natural polar polymer for preparing proton-conducting

/>2468-2179/© 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license
( />

126

H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

electrolyte films [14e16]. When these polymers are complexed
with various host dopants, such as (inorganic-organic) acids or
salts, their structural and electrical properties have been
appreciably reformed [17]. Strong inorganic acids, such as phosphoric acid (H3PO4), hydrochloric acid (HCl) and sulfuric acid
(H2SO4) [18] have been used as proton donor for the SPE systems.
Nevertheless, these are not applicable for practical application due
to the fact that the polymereinorganic acid complex films suffer
more from chemical degradation and mechanical integrity [18,19].
Different ammonium salts have been reported as a good proton
donor in the polymer matrix [20]. It is believed that the ion
responsible for the ionic conductivity mechanism in such systems
is weakly bonded to Hþ of the NHþ4 cation [11].
A literature survey demonstrates that a good proton donor can
be obtained to the polymer matrix more easily from ammoniumbased salts [21]. The present research is an extension of our previously published papers where we discussed the structural and
electrical characterization of PEO/MC blend electrolyte system to
optimize the highest conductivity [22]. Thus, in this effort, PEO was
blended with MC at the ratio of 60:40 to form the blended polymer
solution, and then different concentrations of the NH4I were added.
The choice of NH4I among different types of ammonium salts as the
proton source is predicted to obtain a higher conductivity, because
it was well addressed in the previous investigation that NH4I exhibits a higher ionic conductivity due to the lower lattice energy
and relatively larger anion size compared to the other ammonium
salts [23]. The present work aims to develop a new type of protonconducting polymer electrolyte based on the PEO/MC blend polymer incorporated with different concentrations of NH4I. The
investigation focuses on the analysis of the ionic transport properties to understand and thus, improve the ionic conduction
mechanism of proton-conducting polymer electrolyte.
2. Experimental
2.1. Materials and methods
Poly(ethylene oxide) (PEO) (Alfa Aesar, 106 g/mol molecular

weight), and methylcellulose (MC) (Merck KGaA Germany, with
molecular weight 14,000 g/mol) are taken as primary and secondary polymer precursors for preparing the blend polymer electrolyte. To produce proton (Hþ ion)-conductivity in the polymer
matrix, ammonium iodide salt NH4I from Merck KGaA Germany,
with molecular weight of 144.94 g/mol was used. All the materials
were used for this preparation without any purification process.

our earlier investigations, the two solutions with 60:40 percent
weight ratio were intermixed with each other and made PEO/MC
blend polymer as a homogeneous mixture [22]. Next, the desired
amounts of NH4I were dissolved into 10 ml distilled water and
added to the polymer solution under stirring until complete
dissolution of the salt was obtained. The samples were coded based
on the concentrations of NH4I as PBE-10, PBE-20, PBE-30, PBE-40,
and PBE-50 for 10, 20, 30, 40, and 50 wt.% NH4I, respectively, as
shown in Table 1. Subsequently, all homogeneous mixtures were
cast into cleaned polypropylene dishes and left to dry at room
temperature for two weeks. For further drying, the harvested films
were stored in a desiccator. Finally, the obtained films were peeled
off gently from the polypropylene dishes for characterization and
further experiments.
2.3. Characterization techniques
The XRD spectra profiles of the PEO/MC-NH4I protonconducting polymer films were measured on the PANalytical
X'Pert PRO diffractometer system by using monochromatic X-rays
with l ¼ 1:5406 
A were generated by Cu À ka1 source. The X-ray
tube was operated at 45 kV voltage, and 40 mA anode current with
glancing angels ranged between 10 2q 80 at room temperature. Micromorphological characterization of the prepared polymer electrolyte samples, which dried naturally in room
temperature was examined using the MIRA3-TESCAN field emission scanning electron microscope (FE-SEM), where the dried
samples were gold-coated before scanned to prevent electrostatic
charging on the electrolytes. Ionic conductivity of the prepared

PEO/MC-NH4I films were investigated using precision LCR Meter
(KEYSIGHT E4980A) that was interfaced to a computer, in the frequency range 100 Hz to 2 MHz and in the temperature range between 303 À 373 K. When the required films were cut into suitable
size and sandwiched between two blocking aluminum electrodes.
The Nyquist plane plots were obtained from the recorded impedance data by applying a 100 mV perturbation to an open circuit
potential in the above-mentioned frequency range.
3. Results and discussion
3.1. XRD analysis
Fig. 1 represents the XRD pattern for the various PEO/MC-NH4I
electrolyte films. From Fig. 1 it can be observed that the two sharp

2.2. Proton-conducting polymer electrolyte preparation
For the preparation of the proton-conducting polymer electrolyte, 2 g of each PEO and MC powder were dissolved separately at
room temperature in the 120 ml and 240 ml distilled water,
respectively. These solutions were stirred at room temperature for
24 h to ensure a precise homogeneous composition. Then, based on
Table 1
Composition of the blend polymer electrolyte series containing different wt.% of
NH4I.
Designation PEO Solution

MC Solution

NH4I wt.% NH4I (g)

Powder (g) Solvent (ml) Powder Solvent
(g)
(ml)
PBE-10
PBE-20
PBE-30

PBE-40
PBE-50

2
2
2
2
2

120
120
120
120
120

2
2
2
2
2

240
240
240
240
240

10
20
30

40
50

0.222
0.500
0.857
1.333
2.000

Fig. 1. XRD patterns for PEO/MC-NH4I blend polymer electrolyte films incorporated
with different NH4I salt concentrations.


H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

127

Fig. 2. SEM micrograph of PEO/MC blend polymer films containing (a) 20 wt.% NH4I (b) 30 wt.% NH4I, (c) 40 wt.% NH4I and (d) 50 wt.% NH4I.

Bragg peaks at 19.2 and 23.0 for the PBE-10 sample described the
semi-crystalline nature of the sample [22]. According to Yahya et al.
[24], the strong intermolecular interaction between the polymer
chains due the intermolecular hydrogen bonding causes the formation of semi-crystalline peaks. These peaks become broader and
less intense, with the increasing NH4I concentration until overlapped in a single broad hump at 21.2 for sample PBE-30. Literally
this demonstrated that the reduction in the relative intensity and
broad nature of the characteristic peak clearly indicates that the
crystalline fraction in the electrolyte system was decreased [19,24].
This observation confirms that the blend polymer sample has a
semi-crystalline nature. The intensity of the semi-crystalline peaks
from the blend polymer sample was found to decrease progressively with the increase of NH4I contents until 30 wt.% which implies the decrease in the degree of crystallinity. This results from

the fact that the interaction between the PEO/MC and the NH4I
causes the decrease in the intermolecular interaction between PEO/
MC chains, thus, induces new coordination interactions between
the Hþ of NH4I and the (CeOeC) group of the PEO and/or the (OR)
group of MC of the blend polymer formed which helps for boost
ionic conductivity [25].
The XRD peak deconvolution method was utilized to estimate
the degree of crystallinity using the Fityk software [26]. The degree
of crystallinity was found to be 22.21, 18.74, 15.88, 18.92, and 19.98

for PBE-10, PBE-20, PBE-30, PBE-40, and PBE-50, respectively. It is
clear that the PBE-30 sample exhibits the highest amorphous nature. Many researchers have concluded that the ionic conductivity
is enhanced in the amorphous domain [27,28]. Thus, it can be
anticipated that the sample with the lowest crystalline region (PBE30) exhibits the highest electrical conductivity. For the highest salt
concentration sample (PBE-50) some multiple characteristic peaks
of NH4I were observed at 21.1, 24.5 , 34.9 , and 42.2 which is
revealing that the host polymers could no longer solvate the salt
[29]. The presence of undissolved salt in the system at higher salt
concentrations causes the salt deposition on the film surface due to
the recombination of ions. This eventually leads to a decrease in the
number of the mobile ions in the sample and the decrease in the
electrical conductivity.
3.2. Morphological analysis
Field emission scanning electron (FE-SEM) micrographs of the
PEO/MC-NH4I proton-conducting blend polymer electrolyte films
are presented in Fig. 2. A comparison of the surface morphology
shows a change in the surface properties and the texture structure
of the polymeric films upon the addition of NH4I salt with different
concentrations. In the present work, the FE-SEM study has been
studied to understand the variation of the electrical conductivity

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H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

with the salt concentration for the present membranes, then the
results are used to explain the decrease of DC conductivity at the
higher salt concentrations [30,31]. From Fig. 2 (a,b), it can be
observed that at low salt concentrations (PBE-20 and PBE-30), a
smooth surface without any phase separation is perceived while for
the PBE-40 sample, a rough surface appeared (Fig. 2c). Also, in the
PBE-50 sample, some crystalline aggregates of the NH4I salt have
formed and have protruded out of the surface (Fig. 2d). The micrographs of the PBE-20 and PBE-30 are a proof of the miscibility of
PEO and MC. Kadir et al. [9] reported that the smooth and homogeneous surface of the blend polymer samples indicates that both
polymers are miscible with each other. Also, it is well reported that
the smooth surface morphology of the polymer electrolyte samples
designates that the salt is completely dissolved in the host polymer
matrix. This behavior is utilized as an evidence describing the
amorphous nature of the system [32]. However, the surface of the
PBE-40 shows a rough and uneven, and that could be due to the
ions trapped in the host matrix [30]. Reddeppa et al. [33] reported
that the increase of the degree of roughness with the increasing salt
concentration indicates the segregation of the dopant in the host
polymer matrix.
For the highest salt concentration (PBE-50), the morphology
consists of solid structures that have protruded the surface of the
film. The X-ray diffractograms for the samples reveal that these
solid structures are due to the recrystallization of NH4I out of the
polymer film surface [24]. The inability of the salt to dissolve in the

host polymer matrix results in the recombination of the ions and
the recrystallization of the salt out of the film surface. This causes
the reduction of the density of ions, thus the decrease in the conductivity. This FE-SEM analysis, therefore, has been used to give
some answers describing the reduction of the conductivity in the
blend polymer electrolyte system at higher salt concentrations [9].
Kadir et al. [30] made a similar observation by incorporating
NH4NO3 in the chitosan - polyethylene oxide blend polymer matrix
at the high salt concentrations up to 40 wt.%. They attributed this
observation to the formation of crystalline aggregates of the
ammonium salt out of the polymer surface; they also reported that
these crystalline aggregates might be due to the excess salt that
could not be solvated by the polymer matrix and has recrystallized
upon drying.
3.3. Conductivity analysis
Fig. 3 illustrates the complex impedance plot of different wt.%
NH4I used as a dopant to form PEO/MC blend polymer electrolytes
at room temperature. The ColeeCole plots of PEO/MC-NH4I show
one spike with a semicircle. The semicircular arc can be utilized to
calculate the conductivity of the system by using this equation:

s ¼ t AÀ1 Rb À1

Fig. 3. ColeeCole plots for PEO/MC-NH4I blend polymer electrolyte films incorporated
with different NH4I salt concentrations.

all prepared samples, by expanding the temperature range, the bulk
resistance decreases inferring the improvement of the electrical
conductivity, as shown in Fig. 4. This feature explained by Sundaramahalingam et al. [34]. He reported that the increase in temperature causes the vibrational energy of the polymer segment to
rise, which is to compensate against the hydrostatic pressure forced
by its neighboring sites. The vibrational energy occurs in the

polymer segment free volume. As a result, the conductivity value
increased because the particles can move unconditionally in the
free volume around the polymer chain [34]. This result was
confirmed by the XRD and FE-SEM analysis that clearly showed the
recrystallization of the NH4I at high salt concentrations on the
surface of the polymer electrolyte samples.
The activation energy for the thermally activated hoping
mechanism in PEO/MC-NH4I can be evaluated from the slope of the
straight line of Fig. 5. The information was depicted in Fig. 5 and
Table 2 recommends that the electrolytes obey Arrhenius behavior
in the temperature range of 303e373 K and that the conductivity
occurs by a thermally activated transport process [35]. It is well
addressed in previous studies that the activation energy decreases
gradually with an increase in the conductivity of a polymer blend
electrolyte system, as it is shown in Fig. 6 [36], which means that

(1)

where t is the film thickness, A is the area of the film and Rb is the
bulk resistance determined from the intercept on the real axis at
the lower frequency end of the semicircle in the ColeeCole plot of
the complex impedance [34].
From Fig. 3 it can be obtained that the conductivity of the
complexes increases with the content of the doping salt and reaches a maximum value of 7:62 Â 10À5 S=cm for the PBE-30 sample
among all other compositions. However, upon further addition of
the NH4I salt, the conductivity decreases. It is well reported that the
increase in the conductivity is attributed to the enhancement of the
ionic mobility and the number of the free mobile ions [35].
Meanwhile, the decrease in the conductivity could be due to aggregates and the formation of the ion pairs, which produces neutral
species and thus reduces the number of free ions [36]. Moreover, for

Fig. 4. The temperature-dependent conductivity spectra for PEO/MC when mixed with
30 wt.% NH4I.


H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

Fig. 5. The PEO/MC-NH4I Arrhenius plot in the temperature range 303e373 K.

the ions necessitate a lower energy for migration in highly conducting samples. It was reported that the low activation energy for
the polymer blend system is due to the entirely amorphous nature
of the polymer electrolyte that assists the fast Hþ ions of NH4I to
move through the polymer network. Also, refer to Buraidah et al.
[8], the short distance between the transit sites of the polymer
blends has affected to lowering the activation energy. From Fig. 6, it
has been found that the highest conductivity sample (PBE-30)
possesses the lowest activation energy of 0.34 eV. Nowadays, the
low values of activation energies based on polymer electrolytes are
desirable for practical applications.
In order to identify the conduction mechanism in this electrolyte system, the exponent s is plotted as a function of the temperature, as depicted in Fig. 7. The behavior of the Jonscher exponent
(s) versus temperature can be used to derive the origin of the ionic
conduction mechanism. Several theoretical models have been
proposed to estimate the microscopic charge transport mechanism,
based on a variation of s with temperature [37,38]. Thus the temperature dependence of s plays a key role in the determination of
the conduction mechanism in the disordered materials.
In the present study, the values of s obtained at different temperatures are less than 0.8 and they are temperature dependent.
The conduction mechanism for the PEO/MC-NH4I system can be
most probable interpreted based on the overlapping large polaron
tunneling (OLPT) model. According to this model, the exponent s
decreases with the temperature, reaches a minimum value and

thereafter increases with temperature [39]. According to Majid and
Arof [40], this behavior implies that the addition of salt results in
the overlapping of the stress fields of the polarons and creates a
conducting path for the ions, thus the ions are able to tunnel
through the potential barrier that exists between the two possible
complexation sites [23,40].

129

Fig. 6. The ionic conductivity and activation energy of PEO/MC-NH4I blend polymer
electrolyte as a function of NH4I wt.%.

3.4. Ion transport study
The Rice and Roth model [41] hypothesized that there exists an
energy gap in the ionic conductor, and the ions as the conducting
species with the mass m can be thermally excited from the localized
ionic states to free-ion-like states in which an ion propagates
throughout the spaces with a velocity that is required for such
excitation given by [36]:

rffiffiffiffiffiffiffiffi
2Ea
y¼
m

(2)

where Ea is the activation energy. However, the Rice and Roth
equation was formulated for superionic conductors, but it has been
known to be intensively used to estimate the number of density

and the mobility of mobile ions, which are strongly related to the
ionic conductivity in the polymer electrolyte system, according to
the NernsteEinstein equation [29]:

s ¼ hem

(3)

where s is the ionic conductivity, h is the density of the mobile ions,
m is the mobility of the mobile ions, and e is the electron charge. The
conductivity can be calculated using the Rice and Roth equation as
follows:

Table 2
The ionic conductivity (s), activation energy (Ea ), and regression values (R2 ) for
various compounds of PEO/MC-NH4I blend polymer electrolyte films at ambient
temperature.
Samples

s ðS =cmÞ

E a ðeVÞ

R2

PBE-10

2:32 Â 10À6

0.536

0.98

PBE-20

9:60 Â 10À6

0.545

0.98

PBE-30

7:62 Â 10À5

0.344

0.94

PBE-40

4:76 Â 10À5

0.484

0.98

PBE-50

3:40 Â 10À6

0.627

0.98
Fig. 7. The temperature dependence values s for PEO/MC-NH4I electrolyte system.


130

H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

Table 3
Transport parameters for PEO/MC-NH4I electrolyte system.
Samples

t ðsÞ

m ðcm2 VÀ1 sÀ1 Þ

D ðcm2 sÀ1 Þ

PBE-10

1:03 Â 10À13

1:69 Â 10À09

4:42 Â 10À11

PBE-20

1:02 Â 10À13

1:21 Â 10À09

3:16 Â 10À11

PBE-30

1:28 Â

10À13

10À06

10À08

PBE-40

1:08 Â 10À13

1:16 Â 10À08

3:02 Â 10À10

PBE-50

9:49 Â 10À14

5:47 Â 10À11

1:43 Â 10À12

"
#


2 ðZeÞ2
E
s¼
hEa t exp À a
3 mKB T
KB T

2:07 Â

5:42 Â

(4)

Here Z is the vacancy of conducting species, m is the mass of the
ionic charge carrier, and t is the finite lifetime of the ions, which can
be calculated using t ¼ l=y, where, l is the mean free path between
two coordinating sites or two atoms with the lone pair electrons
across which the ions may hop and it was taken as 10.4 Å [36]. From
the equations (3) and (4), the density of the mobile ions, h, can be
found as an essential parameter to determine the mobility of the
mobile ions, m; and the diffusion coefficient, D, as follows:

h¼

3s mKB T
2

2ðZeÞ Ea t exp À





(5)

Ea
KB T

m¼

s
he

(6)

D¼

KB T s
he2

(7)

where D is the diffusion coefficient. The transport parameters as a

function of NH4I concentration that is related to the ionic conductivity are presented in Table 3, from the results obtained in this
table it can be perceived that the conductivity of NH4I is attributed
to the two important factors, directly derived from equations (6)
and (7), namely, m and D. The value of m lies between
5:47 Â 10À11 to 2:07 Â 10À6 cm2 V À1 sÀ1 , while the D value is in the
range of 1:43 Â 10À12 to 5:42 Â 10À8 cm2 sÀ1 . It is well reported that
the conductivity of the electrolyte is much affected by the ionic
diffusion, which can be a useful parameter to help increment the
conductivity value in a polymer matrix; therefore, the conductivity
is increased when the diffusion of ions increases [19]. From the data
results described in Table 3 the highest conducting sample (PBE-30)
possesses the highest mobility and the highest diffusion value. This
result is supported by the fact that the conductivity is governed by
the density of ions (h), and the mobility (m). In addition, it was
observable that for the higher salt concentrations the conductivity
decreases, and this phenomenon can be explained by the fact that
the aggregation of ions leads to the formation of ion clusters where
the dipole interaction between the protons in the medium increases, which causes the reduction of the ion mobility and diffusion [36]. These results reveal that the values of m and D influence
the ionic conductivity of the PEO/MC-NH4I proton-conducting
polymer electrolyte films.

3.5. Dielectric analysis
The dielectric properties of the PEO/MC-NH4I blended polymer
electrolytes are not much investigated earlier. Thus the dielectric
0
00
constant ðε Þ; dielectric loss ðε Þ, tangent loss and the electric
modulus for the PBE-30 films were studied as a function of the
frequency and the temperature. In order to understand the role of
the salt in enhancing the ionic conductivity the study of the

frequency-dependent dielectric parameters (dielectric constant
and dielectric loss) are required and calculated from the following
equations [24]:

Fig. 8. (a) Dielectric constant (b) Dielectric loss as a function of frequency for PBE-30 at
different temperatures between (303e373) K.

Fig. 9. Dielectric loss behavior for PBE-30 as a function of frequency from the temperature range between (303e373) K.


H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

Fig. 10. Frequency-depends of modulus formalism (a) real part of modulus, (b)
imaginary part of modulus at different temperatures.

ε0 ¼

Cd
ε0 A

;

ε00 ¼ ε0 tan d

(8)

where C is the sample capacitance measured from an LCR meter, ε0
is the permittivity of the free space (8.85 Â 10À12 F/m), A is the
cross-sectional area of the electrode and tan d is a tangent loss, both
of C and tan d were measured for all samples in the frequency range

100 Hze2 MHz. The frequency dependence of the dielectric con0
00
stant ðε Þ and dielectric loss ðε Þ are shown in Fig. 8 (a,b).
0
00
From Fig. 8 it can be noted that the values of ε and ε decrease
with the increasing frequency while these values rapidly increased
in the low-frequency region and at high temperatures. This attitude
has been observed in many polymer electrolytes [42,43]. The in0
crease in ε at lower frequencies is due to the electrode polarization
event, which associates with the accumulation of the ions and the
complete dissociation of the salt; this nature is known as a nonDebye type of behavior, as shown in Fig. 8a [44,45]. The blocking
electrodes prevent the ion migration to the external circuit, and this
results in the accumulation of ions on the opposite electrodes
termed as polarization [46]. The growth of the polarizing ionic
charges causes to increment the dielectric constant and dielectric
loss [34]. Moreover, the ion pairs stay in the immobilized state at
low-frequency regions and this hinders the long-range motion and
results in the high value of the dielectric constant due to sufficient
relaxation time [44].
Now, at higher frequencies, the decrease of the dielectric constant is attributed to the dominance of the relaxation process. Here,

131

the rapid change in the direction of the field makes ions incapable
of responding to the applied field, so that there is no excess ion
diffusion in the direction of the electric field, also due to the
inadequate time the ions could not sufficiently accumulate at the
electrodes, and thus, the dielectric permittivity decreases [44,45].
00

From Fig. 8b the large value of ε at low-frequencies is due to the
formation of free charges at the electrolyteeelectrode interface.
00
However, in the high-frequency region, the value of ε decreases
due to a reduction of the charge carriers at the interface between
0
electrode and electrolyte [45]. From Fig. 8 it is observed that both ε
00
and ε increase with an increase in the temperature. This behavior
generally differs for polar and non-polar polymers. In a non-polar
0
00
polymer the values of ε and ε are independent of the temperature, but in the case of strong polar polymers, the dielectric
permittivity increases with increases in temperature. Muthuvinayagam and Gopinathan [43] claimed that as the temperature
increases, the degree of salt dissociation and redissociation of the
ion aggregates increases, resulting in the increase in the numbers of
free ions and at low frequency the carriers have sufficient time to
0
remain at the interface causing an increase in ε .
Another important parameter providing insight into the number of charge carriers available for the conduction mechanism is the
loss tangent (tan d) [34]. The tan d is defined as the ratio of the
imaginary part of the permittivity to its real part or the ratio of the
energy loss to the energy stored [43]. The dynamics of the tan d
with the frequency for PBE-30 at different temperatures is presented in Fig. 9. From Fig. 9, it is observed that the dielectric loss
initially increases with an increase in the frequency and then reaches a maximum at the particular frequency (where ut ¼ 1), which
is followed by the decrease at high frequencies [43]. For the lower
frequency domain, the value of tand becomes high; this behavior
could be attributed to the space charge, which is built-up at the
interface between the polymer and the electrode. The existence of
the peak in the loss spectrum suggests the presence of relaxing

dipoles in the polymer films [42]. It is well known that the growth
of a movement of charge carriers can be noticed due to the height of
the tand peak at the time when the peak height increases by the
increment in temperature [34]. In addition, when the temperature
is increased the peak heights of tand are increased and sustain
almost the same at the relaxation frequency. This attitude indicates
the breaking of the bond formation from the dipoles [47]. The
electrical conductivity obtained due to the production of charge
carriers and their mobility of the charge carriers. The protonic
charges can be easily built by the collision of the ions in the dipoles
of the polymer chain molecules, which is identified from the
increment of the loss tangent peak height of blend polymer at the

0

00

Fig. 11. Argand plots (M vs. M ) for PBE-30 at different temperatures range between
(303e373) K.


132

H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133

increasing temperatures. With increasing temperature, the slight
increase of the relaxation frequency in the loss tangent spectra
designates the long-range mobility of charge carriers in polymer
chain molecules [47].
0

Fig. 10 (a,b) shows the frequency dependence of the real M and
00
imaginary M parts of the modulus formalism. The complex electric
modulus (M * ) is defined as the reciprocal of the complex permittivity (ε* ) as following [22]:

M* ¼

0
00
1
¼ M þ jM
ε*

(9)
0

Fig. 10 (a,b) shows the frequency dependence of the real (M )
00
and imaginary (M ) parts of the modulus formalism for PBE-30 at
different temperatures. In the higher frequency region the value of
0
00
M and M increases gradually as a function of temperature with a
tendency for saturation. When the temperature is increased the
0
00
peak shifts to the high frequencies and the M and M peaks
regularly decrease due to the plurality of relaxation mechanisms.
0
00

Shyly et al. [45] reported that the value of M and M is slowly
reduced at higher temperatures due to a decrease in the charge
carrier density at the space accumulation region. However, at lower
0
00
frequencies the M and M values become zero, which proposes that
the suppression of the electrode polarization at the interface is
negligible. The long straight line for the low-frequency region endorses a large equivalent capacitance associated with the electrode
interface in use and confirms the non-Debye behavior in the
samples.
The relaxation processes idea for the higher conducting polymer
electrolyte prepared sample (PBE-30) at various temperatures can
be exhibited by the investigation of the Argand plot, as shown in
Fig. 11. From this figure, the observed incomplete semicircle curves
exhibit non-Debye nature. The non-Debye behavior occurs due to
the contribution of more than one type of polarizations, the
relaxation mechanism, and many interactions between the ions
and the dipoles [48]. It is well reported that the radius of the arc is
highly connected to the conductivity of the polymer electrolyte
[44,49]. When the temperature is increased, the length of the arc is
decreased, which ensure increasing the conductivity [34]. Also, the
study of the Argand plots is crucial for determining the difference
between the conductivity relaxation and viscoelastic relaxations
0
processes, under the condition that the arc diameter of the M and
00
0
0
00
M matches with the M axis, it means that the M À M curve exhibits a complete semicircular arc, and thus a single relaxation time

can be estimated. This infers that the conductivity relaxation rec0
00
onciles the Debye model [49]. If the M À M curve appears as
incomplete semicircular arcs, then it means that there is a distribution of the relaxation times and subsequently, the ion transport
occurs through the viscoelastic relaxations [50]. In this study, the
Argand plots exhibit incomplete semicircular arcs, revealing the
distribution of relaxation times (non-Debye nature). Thus, the ion
transport occurs through the viscoelastic relaxation process.

4. Conclusion
Proton-conducting polymer electrolytes based on Polyethylene
oxide and Methylcellulose complexed with ammonium iodide have
been successfully prepared by the standard solution cast method.
The maximum ionic conductivity of 7:62 Â 10À5 S=cm was achieved at 273 K for the sample incorporated with 30% NH4I. The
increase in the sample conductivity is supported by XRD, FE-SEM,
and EIS characterization. The conduction mechanism for all electrolyte samples was explained by the overlapping large polaron
tunneling (OLPT) model. The long-range mobility of the charge
carriers in the polymer chain molecules can be understood as a

slight increase of the relaxation frequency in the loss tangent
spectra with the increasing temperature. The enhancement of the
ionic conductivity upon the addition of NH4I associates with an
increase in the mobility and the diffusion coefficient of the ions.
Employing the Rice and Roth model, the highest ionic conducting
sample (PBE-30) exhibites highest m and D values of
2:07 Â 10À06 cm2 V À1 sÀ1 and 5:42 Â 10À08 cm2 sÀ1 , respectively.
The dielectric behaviors of the sample PBE-30 show a strong
dependence on the frequency and the temperature and follow the
non-Debye type dielectric relaxation. Finally, the incomplete
semicircular arc in the Argand plots indicates the non-Debye type

of relaxation processes, and reveals that the ion transport occurs
through the viscoelastic relaxation process.

Declaration of Competing Interest
The authors declare no conflict of interest.

Acknowledgement
The authors gratefully acknowledge the support received for
carrying out this work from the University of Sulaimani, and
Charmo University at the Ministry of Higher Education and Scientific Research-KRG, Iraq.

References
[1] J.Y. Song, Y.Y. Wang, C.C. Wan, Review of gel-type polymer electrolytes for
lithium-ion batteries, J. Power Sources 77 (1999) 183e197, />10.1016/s0378-7753(98)00193-1.
[2] O.G. Abdullah, Y.A.K. Salman, S.A. Saleem, Electrical conductivity and dielectric
characteristics of in situ prepared PVA/HgS nanocomposite films, J. Mater. Sci.
Mater. Electron. 27 (2015) 3591e3598, />[3] V.B. Achari, T.J.R. Reddy, A.K. Sharma, V.V.R.N. Rao, Electrical, optical, and
structural characterization of polymer blend (PVC/PMMA) electrolyte films,
Ionics 13 (2007) 349e354, />[4] S.B. Aziz, S. Al-zangana, H.J. Woo, M.F.Z. Kadir, O.G. Abdullah, The compatibility of chitosan with divalent salts over monovalent salts for the preparation
of solid polymer electrolytes, Results Phys 11 (2018) 826e836, />10.1016/j.rinp.2018.10.040.
[5] S.K. Patla, M. Mukhopadhyay, R. Ray, Ion specificity towards structureproperty correlation of poly (ethylene oxide) [PEO]-NH4I and PEO-KBr composite solid polymer electrolyte, Ionics 25 (2019) 627e639, />10.1007/s11581-018-2711-3.
[6] M.S.A. Rani, N.S. Mohamed, M.I.N. Isa, Investigation of the ionic conduction
mechanism in carboxymethyl cellulose/chitosan biopolymer blend electrolyte
impregnated with ammonium nitrate, Int. J. Polym. Anal. Char. 20 (2015)
491e503, />[7] O.G. Abdullah, R.R. Hanna, Y.A.K. Salman, Structural and electrical conductivity
of CH:MC bio-poly-blend films: optimize the perfect composition of the blend
system, Bull. Mater. Sci. 42 (2019) 64, />[8] M.H. Buraidah, A.K. Arof, Characterization of chitosan/PVA blended electrolyte
doped with NH4I, J. Non-Cryst. Solids 357 (2011) 3261e3266, />10.1016/j.jnoncrysol.2011.05.021.
[9] M.F.Z. Kadir, S.R. Majid, A.K. Arof, Plasticized chitosan-PVA blend polymer
electrolyte based proton battery, Electrochim. Acta 55 (2010) 1475e1482,

/>[10] K. Gurunathan, A.V. Murugan, R. Marimuthu, U.P. Mulik, D.P. Amalnerkar,
Electrochemically synthesised conducting polymeric materials for applications towards technology in electronics, optoelectronics and energy storage
devices, Mater. Chem. Phys. 61 (1999) 173e191, />s0254-0584(99)00081-4.
[11] O.G. Abdullah, S.B. Aziz, M.A. Rasheed, Incorporation of NH4NO3 into MC-PVA
blend-based polymer to prepare proton-conducting polymer electrolyte films,
Ionics 24 (2017) 777e785, />[12] M. Kumar, S.S. Sekhon, Ionic conductance behaviour of plasticized polymer
electrolytes containing different plasticizers, Ionics 8 (2002) 223e233, https://
doi.org/10.1007/bf02376072.
[13] C.S. Ramya, S. Selvasekarapandian, T. Savitha, G. Hirankumar, P.C. Angelo,
Vibrational and impedance spectroscopic study on PVP-NH4SCN based polymer electrolytes, Phys. B Condens. Matter 393 (2007) 11e17, />10.1016/j.physb.2006.11.021.


H.T. Ahmed, O.Gh. Abdullah / Journal of Science: Advanced Materials and Devices 5 (2020) 125e133
[14] A. Pawlicka, D.C. Dragunski, K.V. Guimaraes, C.O. Avellaneda, Electrochromic
devices with solid electrolytes based on natural polymers, Mol. Cryst. Liq.
Cryst. 416 (2004) 105e112, />[15] M.H. Buraidah, L.P. Teo, S.R. Majid, A.K. Arof, Ionic conductivity by correlated
barrier hopping in NH4I doped chitosan solid electrolyte, Phys. B Condens.
Matter 404 (2009) 1373e1379, />[16] L.V.S. Lopes, D.C. Dragunski, A. Pawlicka, J.P. Donoso, Nuclear magnetic resonance and conductivity study of starch based polymer electrolytes, Electrochim. Acta 48 (2003) 2021e2027, />00181-6.
[17] G.K. Prajapati, R. Roshan, P.N. Gupta, Effect of plasticizer on ionic transport
and dielectric properties of PVAeH3PO4 proton conducting polymeric electrolytes, J. Phys. Chem. Solid. 71 (2010) 1717e1723, />j.jpcs.2010.08.023.
[18] M. Hema, S. Selvasekerapandian, A. Sakunthala, D. Arunkumar, H. Nithya,
Structural, vibrational and electrical characterization of PVAeNH4Br polymer
electrolyte system, Phys. B Condens. Matter 403 (2008) 2740e2747, https://
doi.org/10.1016/j.physb.2008.02.001.
[19] N.S. Salleh, S.B. Aziz, Z. Aspanut, M.F.Z. Kadir, Electrical impedance and conduction mechanism analysis of biopolymer electrolytes based on methyl
cellulose doped with ammonium iodide, Ionics 22 (2016) 2157e2167, https://
doi.org/10.1007/s11581-016-1731-0.
[20] M.F. Shukur, R. Ithnin, M.F.Z. Kadir, Electrical properties of proton conducting
solid biopolymer electrolytes based on starchechitosan blend, Ionics 20
(2014) 977e999, />[21] A.S. Samsudin, M.I.N. Isa, Structural and ionic transport study on CMC doped

NH4Br: a new types of biopolymer electrolytes, J. Appl. Sci. 12 (2012)
174e179, />[22] H.T. Ahmed, O.G. Abdullah, Preparation and composition optimization of PEO:
MC polymer blend films to enhance electrical conductivity, Polymers 11
(2019) 853, />[23] Y.M. Yusof, M.F. Shukur, H.A. Illias, M.F.Z. Kadir, Conductivity and electrical
properties of corn starchechitosan blend biopolymer electrolyte incorporated
with ammonium iodide, Phys. Scripta 89 (2014), 035701, />10.1088/0031-8949/89/03/035701.
[24] Y.A.K. Salman, O.G. Abdullah, R.R. Hanna, S.B. Aziz, Conductivity and electrical
properties of chitosan - methylcellulose blend biopolymer electrolyte incorporated with lithium tetrafluoroborate, Int. J. Electrochem. Sci. 13 (2018)
3185e3199, />[25] K.K. Kumar, M. Ravi, Y. Pavani, S. Bhavani, A.K. Sharma, V.V.R.N. Rao, Electrical
conduction mechanism in NaCl complexed PEO/PVP polymer blend electrolytes, J. Non-Cryst. Solids 358 (2012) 3205e3211, />j.jnoncrysol.2012.08.022.
[26] M. Wojdyr, Fityk: a general-purpose peak fitting program, J. Appl. Crystallogr.
43 (2010) 1126e1128, />[27] A.M. Sukeshini, A.R. Kulkarni, A. Sharma, PEO based solid polymer electrolyte
plasticized by dibutyl phthalate, Solid State Ionics 113e115 (1998) 179e186,
/>[28] O.G. Abdullah, R.R. Hanna, Y.A.K. Salman, S.B. Aziz, Characterization of lithium
ion-conducting blend biopolymer electrolyte based on CH-MC doped with
LiBF4, J. Inorg. Organomet. Polym. Mater. 28 (2018) 1432e1438, https://
doi.org/10.1007/s10904-018-0802-2.
[29] N.E.A. Shuhaimi, L.P. Teo, S.R. Majid, A.K. Arof, Transport studies of NH4NO3
doped methyl cellulose electrolyte, Synthetic Met 160 (2010) 1040e1044,
/>[30] M.F.Z. Kadir, Z. Aspanut, R. Yahya, A.K. Arof, ChitosanePEO proton conducting
polymer electrolyte membrane doped with NH4NO3, Mater. Res. Innovat. 15
(2011) s164es167, />[31] S.B. Aziz, M.G. Faraj, O.G. Abdullah, Impedance spectroscopy as a novel
approach to probe the phase transition and microstructures existing in CS:
PEO based blend electrolytes, Sci. Rep. 8 (2018) 14308, />10.1038/s41598-018-32662-1.
[32] R. Nadimicherla, R. Kalla, R. Muchakayala, X. Guo, Effects of potassium iodide
(KI) on crystallinity, thermal stability, and electrical properties of polymer

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

133

blend electrolytes (PVC/PEO:KI), Solid State Ionics 278 (2015) 260e267,
/>N. Reddeppa, A.K. Sharma, V.V.R.N. Rao, W. Chen, Preparation and characterization of pure and KBr doped polymer blend (PVC/PEO) electrolyte thin
films, Microelectron. Eng. 112 (2013) 57e62, />j.mee.2013.05.015.
K. Sundaramahalingam, D. Vanitha, N. Nallamuthu, A. Manikandan,
M. Muthuvinayagam, Electrical properties of lithium bromide poly ethylene
oxide/poly vinyl pyrrolidone polymer blend elctrolyte, Phys. B Condens.
Matter 553 (2019) 120e126, />A.M.M. Ali, N.S. Mohamed, A.K. Arof, Polyethylene oxide (PEO)eammonium
sulfate ((NH4)2SO4) complexes and electrochemical cell performance, J. Power
Sources 74 (1998) 135e141, />M.N. Chai, M.I.N. Isa, Electrical characterization and ionic transport properties
of carboxyl methylcellulose-oleic acid solid polymer electrolytes, Int. J. Polym.
Anal.
Char.
18
(2013)
280e286,
/>1023666x.2013.767033.
F. Dkhilalli, S. Megdiche, K. Guidara, M. Rasheed, R. Barille, M. Megdiche, AC
conductivity evolution in bulk and grain boundary response of sodium
tungstate Na2WO4, Ionics 24 (2017) 169e180, />s11581-017-2193-8.
O.G. Abdullah, S.A. Saleem, Effect of copper sulfide nanoparticles on the optical and electrical behavior of poly (vinyl alcohol) films, J. Electron. Mater. 45
(2016) 5910e5920, />T. Winie, A.K. Arof, Dielectric behaviour and AC conductivity of LiCF3SO3
doped H-chitosan polymer films, Ionics 10 (2004) 193e199, />10.1007/bf02382816.
S.R. Majid, A.K. Arof, Electrical behavior of proton-conducting chitosanphosphoric acid-based electrolytes, Phys. B Condens. Matter 390 (2007)
209e215, />M.J. Rice, W.L. Roth, Ionic transport in super ionic conductors: a theoretical
model, J. Solid State Chem. 4 (1972) 294e310, />K.N. Kumar, K. Saijyothi, M. Kang, Y.C. Ratnakaram, K.H. Krishna, D. Jin,

Y.M. Lee, Improved electrical properties of Fe nanofiller impregnated PEO þ
PVP:Liþ blended polymer electrolytes for lithium battery applications, Appl.
Phys. A 122 (2016) 698, />M. Muthuvinayagam, C. Gopinathan, Characterization of proton conducting
polymer blend electrolytes based on PVdF-PVA, Polymer 68 (2015) 122e130,
/>A. Arya, A.L. Sharma, Effect of salt concentration on dielectric properties of Liion conducting blend polymer electrolytes, J. Mater. Sci. Mater. Electron. 29
(2018) 17903e17920, />P.M. Shyly, K. Karuooasamy, T. Linda, P. Thiravetyan, S. Balakumar,
X.A. Shajan, Ionic conductivity and dielectric studies of chitin nanofiber (CNF)
incorporated PMMA based polymer electrolytes, IOSR J. Appl. Phys. 1 (2012)
47e51, />N. Tripathi, A.K. Thakur, A. Shukla, D.T. Marx, Dielectric, transport and thermal
properties of clay based polymer- nanocomposites, Polym. Eng. Sci. 58 (2017)
220e227, />N. Gondaliya, D.K. Kanchan, P. Sharma, P. Joge, Structural and conductivity
studies of poly(ethylene oxide) e silver triflate polymer electrolyte system,
Mater. Sci. Appl. 2 (2011) 1639e1643, />msa.2011.211218.
R.M. Hill, L.A. Dissado, Debye and non-Debye relaxation, J. Phys. C Solid
State Phys. 18 (1985) 3829e3836, />19/021.
S.B. Aziz, O.G. Abdullah, S.A. Hussein, H.M. Ahmed, Effect of PVA blending on
structural and ion transport properties of CS:AgNt-based polymer electrolyte
membrane, Polymers 9 (2017) 622, />O.G. Abdullah, R.R. Hanna, Y.A.K. Salman, Structural, optical, and electrical
characterization of chitosan: methylcellulose polymer blends based film,
J. Mater. Sci. Mater. Electron. 28 (2017) 10283e10294, />10.1007/s10854-017-6796-7.