Incorporation of benzimidazolium ionic liquid in proton exchange membranes ABPBI-H3PO4

Article abstract of DOI:10.1016/j.molliq.2013.02.014

This paper presents the development of proton exchange membranes (PEM) from the incorporation of poly (2,5-benzimidazole) (ABPBI) in phosphoric acid (H₃PO₄) and ionic liquid (IL) 1-butyl-3- ethylbenzimidazolium dihydrogen phosphate (BEBzIm-H₂PO₄). We show structural, physicochemical and electrochemical characterization of synthesized IL and prepared membranes. The addition of IL in composite membranes of ABPBI-H₃PO₄ increases thermal stability. Also, the conductivity of membranes increases with temperature and the amount of absorbed mixture. Conductivity at a range of 10^{- 4} S/cm was achieved at 150 C by 50% IL and 50% phosphoric acid impregnation. This conducting composite membrane shows promise for operation in temperature proton exchange membrane fuel cells at working temperatures up to 100 C.

Full text of DOI:10.1016/j.molliq.2013.02.014

Journal of Molecular Liquids 181 (2013) 115–120
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Incorporation of benzimidazolium ionic liquid in proton exchange
membranes ABPBI-H3PO4
Rubí Hernández Carrillo a, Jullieth Suarez-Guevara b, Luis Carlos Torres-González a,
Pedro Gómez-Romero b, Eduardo M. Sánchez a,
⁎
a
LabMat2: Almacenamiento y Conversión de Energía, Facultad de Ciencias Químicas, Universidad Autónoma de Nuevo León, Guerrero y Progreso s/n Col. Treviño, Monterrey NL 64570, México
Centro de Investigación en Nanociencia y Nanotecnología, CIN2 (CSIC-ICN), Campus UAB, E-08193 Bellaterra, Barcelona, Spain
b
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper presents the development of proton exchange membranes (PEM) from the incorporation of poly
(2,5-benzimidazole) (ABPBI) in phosphoric acid (H3PO4) and ionic liquid (IL) 1-butyl-3-ethylbenzimidazolium
dihydrogen phosphate (BEBzIm-H2PO4). We show structural, physicochemical and electrochemical characteri-
zation of synthesized IL and prepared membranes. The addition of IL in composite membranes of ABPBI-H3PO4
increases thermal stability. Also, the conductivity of membranes increases with temperature and the amount
of absorbed mixture. Conductivity at a range of 10−4 S/cm was achieved at 150 °C by 50% IL and 50% phosphoric
acid impregnation. This conducting composite membrane shows promise for operation in temperature proton
exchange membrane fuel cells at working temperatures up to 100 °C.
Received 21 December 2012
Received in revised form 15 February 2013
Accepted 18 February 2013
Available online 7 March 2013
Keywords:
Ionic liquids
Proton exchange membrane
ABPBI
© 2013 Elsevier B.V. All rights reserved.
Ionic conductivity
High temperature PEMFC
1. Introduction
[8], polymer blends [9,10], zirconium oxide [11] and pyrophosphate
[12], BPO4 nanoparticles [13] and cerium sulfophenyl phosphate [14]
Polymer electrolyte membrane fuel cell (PEMFC) offers good pros-
pects in the field of automotive and portable power [1]. High proton
conductivity, adequate gas impermeability, good electrical insulation,
high chemical and thermomechanical stability are desirable features
[2] for polymeric membranes. Nafion® is the most used PEM material
and is based on perfluorinated polymer [3] but inevitably lose proton
conductivity when exposed to harsh operating conditions [4] (near
100 °C).
It is well known that the high-temperature PEMFCs provide several
potential benefits such as improved electrode kinetics, high tolerance to
fuel impurities and simplified thermal and water management systems.
Polybenzimidazole (PBI) is a basic polymer with excellent thermal and
chemical stability and has been realized that this system is a promising
candidate for high-temperature PEM applications [5]. When it is
dipped in aqueous phosphoric acid to form an acid−base complex,
the PBI/H3PO4 complex shows high proton conductivity at high tempera-
tures even in the anhydrous state. Particularly, poly(2,5-benzimidazole)
(ABPBI) offers [6] high imidazolium density per monomer unit resulting
in higher capacity to incorporate inorganic additives as H3PO4 enhancing
ionic conductivity and thermal stability.
to ABPBI membranes have been accomplished with moderated im-
provement of proton conductivity. Also, copolymer membranes based
on poly(2,5-benzimidazole) had been attained [15,16] where mem-
brane processability has been improved.
Ionic liquids (ILs) incorporation into nafion membranes was pro-
posed by Proulx [17] seeking plasticizer and thermal stability effect.
ILs are molten salts at room temperature and have a variety of useful
properties like low vapor pressure, high thermal and electrochemical
stability, non-flammability, good solvent miscibility and high conductiv-
ity [18]. These qualities make them useful in a diversity of applications
such as catalysis, electrochemistry, photochemistry, organic synthesis,
solar cells, batteries and fuel cells.
There is a wide variety of PEM materials being doped by ILs [19,20].
In particular, J.Y. Sanchez [21] modified Nafion 117 by incorporating
different degrees of ILs in the membrane. Sekhon [22] prepared mem-
branes of polyvinylidene fluoride-co-hexafluoro propylene blended
with 2,3-dimethyl-1-octylimidazolium hexafluorophosphate where con-
ductivity depended upon IL concentration. Greenbaum [23] proposed the
incorporation of 1-methyl-3-propyl-methyl-imidazolium dihydrogen
phosphate in a PBI/H3PO4 system and obtained homogeneous, flexible
and thermally stable membranes presenting ionic conductivity up to
2 × 10−3 S/cm at 150 °C. Furthermore, porous PBI was recently doped
[24] with IL 1-H-3-methylimidazolium bis(trifluoromethanesulfonyl)
imide where the pores were filled with IL by direct immersion of
PBI. After impregnation the proton conductivity reached a value of
1.86 × 10−3 S/cm at 190 °C.
In order to overcome acid leaching, several approaches including sul-
fonation of main polymer backbone [7] and addition of heteropolyacids
⁎
Corresponding author. Tel.: +52 8183294000.
E-mail address: eduardo.sanchezcv@uanl.edu.mx (E.M. Sánchez).
0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molliq.2013.02.014

116
R. Hernández Carrillo et al. / Journal of Molecular Liquids 181 (2013) 115–120
Table 1
Surprisingly, there is no literature available on IL incorporation in
Doping bath composition of [BEBzIm][H2PO4]:H3PO4 mixtures used in the impregna-
tion of ABPBI.
ABPBI matrix for FC applications. ABPBI material has great potential as
PEM material due to facile preparation and high proton conductivity.
Stability issues are yet to be improved in order to accomplish this pro-
spective. Therefore, this work proposes the development of ABPBI
proton exchange membranes impregnated with mixtures of H3PO4
and 1-butyl-3-ethylbenzimidazolium dihydrogen phosphate (BEBzIm]
[H2PO4]) in order to obtain a material with good thermal and conductiv-
ity properties to be applied as electrolyte in high temperature PEMFCs.
Sample
Bath composition
IL:H3PO4
Membrane
weight before
doping/g
Membrane
weight after
doping/g
% absorption
M1
M2
M3
M4
M5
0:100
25:75
50:50
75:25
100:0
0.2430
0.2750
0.3493
0.2174
0.1195
0.2824
0.6172
0.6540
0.3066
0.1218
16.21
124.43
87.23
41.03
1.92
2. Experimental
The chemicals were ethyl acetate 98% (Control Técnico
y
(Cambridge Viscosity, Medford, MA) at 10 °C intervals with 30 min
equilibration at each temperature. Accordingly, 1 mL samples were
transferred inside a stainless steel cylinder sample holder and then
hermetically closed in the upper end. Electrical conductivities were
determined from complex impedance technique using a frequency
response analyzer (PCI4-750, Gamry Instruments) where an AC voltage
signal of 10 mV was applied at a frequency range of 1 Hz–100 kHz. Gold
was deposited on polymer membranes (10 mm diameter, thickness
~0.2 mm) on both sides using a cathode sputter coater (Pelco SC-7).
The samples were sandwiched between two nickel electrodes in a
closed stainless steel-bodied cell and measurements were carried out
under a slow dry nitrogen flow (30 mL/min). IL electrochemical stability
was measured employing a potentiostat/galvanostat Biologic Science In-
strument model VMP3. A conventional three-electrode electrochemical
cell was used. Glassy carbon electrode was used as working electrode, Pt
wire as counter electrode and a silver wire was used as pseudo-reference
(Ag-QR) electrode. The experiments were performed at different scan
rates from 50 to 500 mV/s.
Representaciones, CTR), phosphoric acid 85% (CTR), and the rest
from Aldrich: benzimidazole 98%, bromobutane 99%, bromoethane
99%, tetramethyl ammonium bromide 98%, 3,4-diaminobenzoic acid
97% and polyphosphoric acid 85%. All were used as received. For
1-ethylbenzimidazole (EBzIm) preparation, we dissolved in a flask
12.06 g (100 mmol) of benzimidazole and 0.70 g (4.5 mmol) of
tetramethyl ammonium bromide as catalyst in 100 ml of 40% KOH
aqueous solution. Then, 11.00 g (100 mmol) of bromoethane was
added dropwise. After, the mixture was heated at 45 °C for 12 h.
The resulting product was washed with ethyl acetate, and then re-
moved by distillation. For 1-butyl-3-ethylbenzimidazolium bromide
([BEBzIm][Br]) preparation, we placed 2.3 g (50 mmol) of EBzIm in a
three-necked flask with reflux condenser followed by addition of
50 ml toluene. Then 6.92 g (50 mmol) of 1-bromobutane was
added dropwise and solution was stirred at 70 °C for 24 h. Finally,
for [BEBzIm][H2PO4] preparation, 11.32 g (40 mmol) of [BEBzIm]
[Br] was dissolved in 100 mL of anhydrous dicloromethane and
2.5 mL (40 mmol) of phosphoric acid was added dropwise. The mix-
ture was stirred for 48 h, after the remaining solvent was removed in
a vacuum oven at 70 °C overnight. An amber liquid was obtained.
The 1-butyl-3-ethylbenzimidazolium dihydrogen phosphate, FTIR
(ATR, ν/cm-1): 3147, 2964, 2880, 2753, 2300, 2127, 1621, 1565,
1485, 1462, 1124, 960, 890, 741. 1H NMR (500 MHz, DMSO-d6): 0.90
(t,3H, CH2CH2CH3), 1.13 (m,2H, CH2CH2CH3), 1.52 (t, 2H, CH2CH3),
1.87 (m, 2H, CH2CH2CH3), 3.81 (m, 2H, NCH2CH2), 4.48 (m, 2H,
NCH2CH3), 7.66 (m, 2H, Ph), 8.03 (m, 2H, Ph), 9.77 (s, 1H, NCHN) y
10.04 (s, 1H, OH).
The ABPBI was obtained by heating a solution of 3.14 g (20 mmol)
of 3,4-diaminobenzoic acid in 50 g of polyphosphoric acid at 200 °C
for 5 h under N2 atmosphere. The product was isolated by water
precipitation, filtered and washed repeatedly with water. After, the dark
powder was washed with 10% NaOH for 12 h to remove polyphosphoric
acid residuals. For ABPBI membrane preparation, 400 mg of ABPBI pow-
der was dissolved in 6 ml of methanesulfonic acid, the solution was
poured into a petri dish and evaporated over a hot plate at 150 °C for
about 8 h to obtain a dark film (200-micrometer thick in average). For
H3PO4 and IL impregnation, 2 × 2 cm samples were cut and immersed
in different phosphoric acid–ionic liquid baths. Table 1 shows bath
composition in which ABPBI membranes were impregnated for 24 h.
Then, sample squares were dried in a vacuum oven at 80 °C over-
night. The polymer was dried under vacuum at 100 °C overnight.
FTIR (ATR, ν/cm-1): 3349, 3121, 2987, 2325, 1622, 1550, 1426, 1271,
1131, 1064, 976, 858, 801, 723. Elemental analysis: C7H4N2•2H2O: C,
55.26; H, 18.42; N, 5.26.
3. Results and discussion
Results from temperature stability testing of [BEBzIm][H2PO4]
using DTA/TGA show expected thermal behavior (see Fig. 1). On
Table 2, we tabulated thermal decomposition temperatures at 90%
weight on TGA experiment along similar compounds from literature.
We notice that thermal stability strongly depends on the nature of the
anion. Thus, weight losses of our IL will be associated to dihydrogen anion
decomposition where DTA peaks are linked to the following discussion.
Weight loss up to510 K is associated to adsorbed moisture. Within
510–610 K we relate weight losses to the first dehydration of the anion
according to Prinsloo [25] where pyrophosphoric unit (H2PO7)−2 is
formed. A second dehydration occurs immediately at 630–700 K
range where metaphosphoric unit (PO3)− is produced. Subsequent
weight losses are associated to thermal decomposition of aliphatic
chains attached to benzimidazolium ring at 760–860 K range and
FTIR spectra were recorded on a Perkin-Elmer Spectrum One spec-
trophotometer with universal attenuated total reflectance accessory.
Nuclear magnetic resonance spectra was obtained using a Bruker
Avance II 300 with QNP-z sensor using DMSO-d6 as solvent. For ele-
mental analysis we used a Eurovector 3011 elemental analyzer with
a Mettler Toledo MX5 microbalance connected to a gas chromatogra-
pher. The thermal stability was determined using a TA Instruments
SDT 2960 thermogravimetric analyzer between with heating rate of
10 °C/min. Viscosity was measured using a Viscolab 3000 viscometer
Fig. 1. Thermal behavior of [BEBzIm][H2PO4] in air atmosphere at 10 °C/min.

R. Hernández Carrillo et al. / Journal of Molecular Liquids 181 (2013) 115–120
117
Table 2
On the insert of Fig. 2, we display an Arrhenius type plot of the vis-
cosity data. Fitting lines were calculated using the Vogel–Tammann–
Fulcher (VTF) equation [18]:
Thermal properties of several 1-R1-3-R2-benzimidazoliums with different anions (X).
R1
R2
X
T/K at 90%
weight
Reference
ꢀ
ꢁ
B
T−T
Butyl
Pentafluoro-benzyl
Butyl
Butyl
Butyl
Ethyl
H2PO4
Br
Br
BF4
PF6
510.0
458.1
529.1
603.1
640.1
This work
[34]
[35]
[35]
[35]
0
η ¼ η0e
ð1Þ
2,4,6-trimethylbenzyl
Ethyl
Ethyl
Ethyl
where η represents the viscosity of the ionic liquid at temperature T,
0 is a pre-exponential constant, B is a factor related to the activation
η
energy and T0 is the ideal glass transition temperature (see Table 3 for
calculated values). From this data, the strength parameter, D, was calcu-
lated as D = B/To and could be used as a measure of fragility [28]. In the
strength–fragility scheme, originally proposed by Angell [29], a D
value lower than 10 represents fragile behavior, and higher values
(around 100) are typical for strong liquids, similar to SiO2. The calculat-
ed D value decreases in the order MMOIm+ > BEBzIm+ > MMBIm+
suggesting a relationship among fragility and viscosity with VdW
interactions.
after we interpreted it as heterocycle decomposition [26]. DTA/TGA
data is accurate for the chosen IL only, in which the molecules are
highly mobile; the incorporation into a polymer membrane changed
the thermal stabilities of the mixtures. This situation will be discussed
later on.
Generally, ILs have higher viscosity than regular solvents (For
example, water viscosity at room temperature is 0.9 cP). Indeed, their
viscosities typically range from 30 cP–100 cP at room temperature;
however, values as high as 500–800 cP are typically reported. The chem-
ical nature of anions and cations has a huge effect on viscosity. With re-
spect to anion moiety, higher basicity, size, and relative capacity to form
hydrogen bonds result in more viscous ILs. Polymer electrolytes
containing ionic liquid 2,3-dimethyl-1-alkyl-imidazolium dihydrogen
phosphate ([MMRIm][H2PO4] R = Octyl, and Butyl) where previously
reported [27] showed possibility of use as high temperature membranes
for fuel cell applications. Fig. 2 shows [BEBzIm][H2PO4] viscosity behav-
ior along [MMOIm][H2PO4] and [MMBIm][H2PO4] ILs for comparison.
The different behavior observed for viscosity results is probably due to
the difference in bulk viscosity – which is measured experimentally
and local viscosity – which is related to mobility of the ionic species.
The imidazolium-based IL with octyl group ([MMOIm][H2PO4]) has
higher viscosity whereas the imidazolium-based IL with butyl group
([MMBIm][H2PO4]) has lower value. Our benzimidazolium-based IL
[BEBzIm][H2PO4] has an intermediate viscosity value. The length of
alkyl group affects the viscosity of the resulting IL. The exact contribu-
tion of alkyl group on the modification of viscosity cannot be estimated,
as some other parameters such as ion size, degree of dissociation also
affect the properties of IL. Moreover, the viscosities of ionic liquids
appear to be ruled by Van der Waals (VdW) interactions, where long
octyl chain group provides higher Van der Waals interactions increasing
IL viscosity. On the other hand, benzimidazolium cation has larger size
than imidazolium and consequently increases the internal resistance
to flow as well as the viscosity of [BEBzIm][H2PO4] in comparison to
([MMBIm][H2PO4]).
Ionic conductivity is one of the most important properties of ILs
considered as electrolytes. Generally, ILs have better ionic conductivi-
ties compared with organic solvents/electrolyte systems. However,
at room temperature, their conductivities are usually lower than
those of concentrated aqueous electrolytes, based on the fact that
ionic liquids are composed exclusively of ions. There is a difference on
thermal dependence of conductivity when compared to similar ILs as
2,3-dimethyl-1-alkyl-imidazolium dihydrogen phosphate ([MMRIm]
[H2PO4] R = Octyl and Butyl and) [27]. At room temperature, conduc-
tivity values of BEBzIm+ are lower compared to MMRIm+. However,
as temperature rises there is marked increase and this behavior should
be associated to the benzilimidazolium ion contribution. Since BEBzIm+
cation is rather bulky compared to MMBIm+ cation and the former has
higher viscosity we could think at this point that this increase on
ionic conductivity is due to higher decoupling of the H2PO4− anion
with benzimidazolium ion compared to the imidazolium ion. In a recent
study, Goward [30] demonstrated that benzimidazolium ring is somehow
sluggish compared to imidazolium rings in analogous salts. This situation
favors the mobility of added phosphonate groups thus increasing proton
dynamics and conductivity as well. Another plausible explanation to this
conductivity increase relies on the fact that liquids benzimidazoliums are
prone to water adsorption. According to Alselmi [31] (BzImH)+ in molten
state, after short exposure to (humid) ambient air, absorbed water mole-
cules may remove protons from (BImH)+ groups, thereby enabling a
chain mechanism of proton-hopping through non-protonated BIm sites,
enhancing conduction properties remarkably.
On the other hand, the curved behavior of the Arrhenius type plot
(see insert, Fig. 3) suggests the highly viscous nature of those ILs and
this variation can be explained by VTF behavior. The VTF equation for
conductivity is
ꢀ
ꢁ
B
T−T
−
0
σ ¼ σ0e
ð2Þ
where σ represents the viscosity of the ionic liquid at temperature T,
σ0 is a pre-exponential constant, B is a factor related to the activation
energy and T0 is the ideal glass transition temperature (see Table 3 for
calculated values).
Electrolytes for electrochemical devices should have large stability
against oxidation-reduction processes. The electrochemical window
(EW) is a term commonly used to indicate both the potential range
and the potential difference in which the ionic liquid is stable. Fig. 4
Table 3
VTF parameters for the viscosity and conductivity of the prepared IL [BEBzIm][H2PO4].
Ao
B
To/K
D
Fig. 2. Viscosity behavior of several dihydrogen phosphate ionic liquids. (⊙) [BEBzIm]+
from this work, (▲) MMOIm+ and (■) MMBIm+ both from reference no. 27. Insert displays
Arrhenius plot. In all cases, dotted line represents VTF fitted line.
Viscosity
Conductivity
0.09
3.50
1273.4
563.4
173
260
7.6
–

118
R. Hernández Carrillo et al. / Journal of Molecular Liquids 181 (2013) 115–120
at 2977. The aromatic C\H stretching at about 2600 is hidden behind
the N\H stretchings. The spectra for the impregnated membranes are
quite similar. There are only small differences in the intensity of bands
due to the polymer impregnation grade. A very broad band appears
between 2500 and 3000 cm−1 due to the protonation of the imine to
the polymer by the interaction of this with the other system compo-
nents. N\H stretching; the O\H stretching leads to a broad band at
2500–2250 cm−1. Bands at 1550 and 1620 can be assigned to the
C_N and C_C stretchings for the doped ABPBI samples. The phosphoric
acid and dihydrogen phosphate anion (H2PO4−) bands appear at around
1200–650 cm−1
.
The thermal stability of impregnated membranes was determined
by thermogravimetric analysis in air atmosphere from room temper-
ature to 400 °C with a heating rate of 10 °C/min. In Fig. 6, the thermo-
gram of ABPBI before impregnation (undoped) shows weight loss on
the 25–150 °C range and is due to absorbed water, after which the
weight is almost constant. Membrane M5 displays weight loss pattern
similar to undoped ABPBI and IL itself suggesting a little amount of
impregnation. The rest of the doped membranes showed better ther-
mal stability. The first weight loss is due to the elimination of mois-
ture absorbed by the membrane and is equivalent to 5% by weight.
This suggests a strong interaction between the IL and ABPBI causing
an increase in the thermal stability of material itself.
Conductivity was measured in the range of 25–150 °C. Only we
tested membranes M3 to M5 because they could be properly handled.
M1 and M2 membranes were soft to measure under the present ex-
perimental conditions. Fig. 7 displays membrane conductivity as a
function of temperature. In the impregnated membranes, the conduc-
tivity increases as a function of the temperature and the amount of
mixture (H3PO4/BEBIm-HP) absorbed by the membrane. The values
obtained are on the 10−4 S/cm range for the tested materials. We also
observe that above 100 °C there is a conductivity increase. We believe
that conductivity behavior below 100 °C is performed through a hopping
mechanism and as temperature increases, the diffusion of charges occurs
more easily due to vehicular mechanism. Membranes containing IL with
conductivity higher than 10−3 S/cm above 100 °C can find potential use
in various electrochemical devices. However, for their use in PEM fuel
cells, the conductivity has to be improved by more than one order of
magnitude and secondly protons should be the mobile species. Although
cations and anions are the main mobile species in ILs yet the presence of
Fig. 3. Conductivity behavior of several dihydrogen phosphate ionic liquids. (⊙) [BEBzIm]+
from this work, (▲) MMOIm+ and (■) MMBIm+ both from reference no. 27. Insert displays
Arrhenius plot. In all cases dotted, line represents VTF fitted line.
displays the EW for [BEBzIm][H2PO4]. The resulting EW was 1.2 V vs.
Ag-QR electrode and is limited by the reduction reaction of the cation
(BEBzIm)+ and H2PO4− oxidation. This value is comparable to 1.3 V
reported [32] for benzimidazole-bis(trifluoromethanesulfonyl)imide
1:1 melt and is suitable for PEM applications [33].
Comparing the amount of absorbed IL:H3PO4 mixture in the ABPBI
polymer (see Table 1) we observe a marked increase of doping mix-
ture absorption at 25% of IL compared to sole H3PO4 impregnation.
Then, a gradual diminution of doping mixture incorporation is ob-
served as IL amount is increased. This is attributed to the increase
of the bath viscosity so that there is greater difficulty for mixture
integration into the ABPBI polymer. It should be mentioned that
the difference in weight in sample M1 is mainly attributed to the
dissolution of the membrane in the H3PO4 thus no acid uptake by the
ABPBI. To account for IL-H3PO4-ABPBI interactions, Fig. 5 displays several
FTIR spectra obtained for ABPBI membranes impregnated with H3PO4
and IL according to Table 1. First, in the undoped ABPBI membrane, the
remaining MSA absorbs at 1200 and 1100 (sulfonated group); the bands
assigned to O\H stretching at 3300 cm−1, the free N\H stretching
band is situated at 3121 and that for hydrogen bonded N\H stretching
Fig. 4. Cyclic voltammetry of [BEBzIm][H2PO4].

R. Hernández Carrillo et al. / Journal of Molecular Liquids 181 (2013) 115–120
119
Fig. 7. Ionic conductivity of doped membranes.
Fig. 5. FTIR characterization of doped membranes.
acidic dihydrogenphosphate anion (H2PO4)− and phosphoric acid
(H3PO4) suggests that protons also contribute to the conductivity
of these membranes. It is important for their future use as proton
conducting membranes. However, more experimental studies are re-
quired to establish the nature of mobile species in these membranes
containing ionic liquids.
matrix increases the thermal stability of the membrane. The conductivity
of the membranes impregnated is directly proportional to temperature
and the amount absorbed by ABPBI polymer. The membranes have an
acceptable ionic conductivity up to 9.02 × 10−4 S/cm at 150 °C. The
graphs of conductivity obtained suggest that the proton conduction is
performed by two mechanisms, the first occurs below 100 °C through
the hydrogen bond network by a hopping mechanism above this tem-
perature the predominant mechanism is a transport vehicle.
4. Conclusions
Ionic liquid with acidic (H2PO4)− counteranion and having composi-
tion: 1-butyl-3-ethylbenzimidazolium dihydrogen phosphate ([BEBzIm]
[H2PO4]) has been prepared and characterized and its conductivity and
viscosity behavior has been studied. ABPBI/H3PO4/[BEBzIm][H2PO4]
membranes were prepared. The incorporation of the IL into polymer
Acknowledgment
The authors express their gratitude to CONACyT (Project # 151587)
and the Universidad Autónoma de Nuevo León (PAICyT) for the eco-
nomic support for this project.
Fig. 6. TGA characterization of doped membranes.

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R. Hernández Carrillo et al. / Journal of Molecular Liquids 181 (2013) 115–120
[18] A. García, L.C. Torres-González, K.P. Padmasree, M.G. Benavides-Garcia, E.M.
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