Anhydrous proton exchange membranes at elevated temperatures: Effect of protic ionic liquids and crosslinker on proton conductivity

Article abstract of DOI:10.1039/c4ra16106h

A series of novel anhydrous proton exchange membranes (poly(vinyl alcohol)-citric acid-ionic liquid (PVA-CA-IL)) were prepared using the low cost ionic liquids ethylammonium nitrate (EAN), diethylammonium nitrate (DEAN), and triethylammonium nitrate (TEAN) as conductive fillers in PVA support membrane. The properties of the PVA-CA-IL membranes can be controlled by changing the molar ratio of the PVA, ILs and CA. The thermal stability of PVA-CA-IL membrane was measured by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and the microstructure was investigated using scanning electron microscopy (SEM) and the Anton-paar SAX Sess mc2 system (SAXS). The effects of temperature, ILs and crosslinker dosage on proton conductivity were also systematically investigated. The results showed that the PVA-CA-IL membranes had excellent performance. The proton conductivity of PVA-CA-EAN (mole ratio = 1:0.05:0.4) could reach up to 7.8 mS cm^-1 at 140 °C. The introduction of ionic liquid into PVA membrane constituted a new and efficient kind of anhydrous proton exchange membrane. This journal is

Full text of DOI:10.1039/c4ra16106h

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Anhydrous proton exchange membranes at
elevated temperatures: effect of protic ionic liquids
Cite this: RSC Adv., 2015, 5, 17683
and crosslinker on proton conductivity
a
b
a
Yi Yang, Hejun Gao and Liqiang Zheng*
A series of novel anhydrous proton exchange membranes (poly(vinyl alcohol)–citric acid–ionic liquid (PVA–
CA–IL)) were prepared using the low cost ionic liquids ethylammonium nitrate (EAN), diethylammonium
nitrate (DEAN), and triethylammonium nitrate (TEAN) as conductive fillers in PVA support membrane. The
properties of the PVA–CA–IL membranes can be controlled by changing the molar ratio of the PVA, ILs
and CA. The thermal stability of PVA–CA–IL membrane was measured by thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC), and the microstructure was investigated using
scanning electron microscopy (SEM) and the Anton-paar SAX Sess mc2 system (SAXS). The effects of
temperature, ILs and crosslinker dosage on proton conductivity were also systematically investigated.
The results showed that the PVA–CA–IL membranes had excellent performance. The proton
Received 10th December 2014
Accepted 26th January 2015
ꢀ1
ꢁ
conductivity of PVA–CA–EAN (mole ratio ¼ 1 : 0.05 : 0.4) could reach up to 7.8 mS cm at 140 C. The
introduction of ionic liquid into PVA membrane constituted a new and efficient kind of anhydrous proton
exchange membrane.
DOI: 10.1039/c4ra16106h
www.rsc.org/advances
Admittedly, PVA has attracted a lot of attention as an excellent
membrane material because of its low cost, excellent fuel
1
. Introduction
With the development of industry and the inadequacy of energy barrier, controllable physical properties and microstruc-
21–23
24
resources, the sustainable energy generation by proton tures.
Won Rhim et al. reported a novel crosslinked PVA
exchange membrane fuel cells (PEMFCs) has received wide- membrane. The PEMs were prepared using poly(styrene
1,2
spread interest among the researchers. In the past years, sulfonic acid-co-maleic acid) (PSSA_MA) (PVA : PSSA_MA ¼
PEMFCs have been widely applied in a number of areas, such as 1 : 7) and clay 15A, which achieved an excellent inhibition
ꢀ
7
2
ꢀ1
3
–5
aerospace, transportation, and as mobile power stations. The methanol performance (2.19 ꢂ 10 cm s ) and outstanding
ꢀ1
25
proton exchange membrane (PEM) serves as the electrode proton conductivity (0.023 S cm ). Gomes and Filho
separator in addition to its primary role as a continuous successfully prepared a series of hybrid membranes using PVA,
6–10
medium for conducting protons from anode to cathode.
peruoride-based membrane of Naon® is the most common and found that the maximum conductivity could reach 8.59 ꢂ
The phosphotungstic acid and (diethylenetriamine)pentaacetic acid
3
ꢀ1
26
commercial PEM, which shows an outstanding chemical 10 S cm . Thanganathan and Nogami synthesized a new
11,12
stability and excellent proton conductivity.
However, the class of hybrid nanocomposite membranes by sol–gel method,
proton conductivity decreases signicantly at temperatures which contained PVA, phosphotungstic acid, 3-glycidylox-
ꢁ
above 80 C due to the evaporation of water from the ypropyltrimethoxysilane,
3-mercaptopropyltrimethoxysilane
13,14
membranes, thus limiting proton mobility.
In addition, the and glutaraldehyde, and the maximum conductivity was 2.5 ꢂ
ꢀ2
ꢀ1
15,16
membrane has very high cost and high fuel permeability.
10 S cm . All these membranes showed excellent proton
These drawbacks of Naon® hinder its future application. conductivities, which were measured under a certain relative
Therefore, the novel PEMFCs need to be developed in earnest. humidity. The proton transport in these PVA membranes is due
In order to develop excellent PEMs, polymers such as poly- to the mobility of water molecules in the water channel of these
17
imides, polybenzimidazole, poly(ether ether ketone) and membranes. The proton conductivity would decrease signi-
1
8–20
poly(vinyl alcohol) (PVA) have been investigated.
cantly at high temperatures, due to the evaporation of water
from the membranes, limiting proton mobility. The develop-
ment of membranes, which can be applied at high temperatures
a
Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of
Education, Jinan 250100, China. E-mail: lqzheng@sdu.edu.cn; Fax: +86 531
27
under anhydrous conditions, is the need of the hour.
Ionic liquids (ILs) can not only replace water to maintain a
channel for proton transfer, but can also donate protons. ILs are
receiving considerable attention due to their unique properties,
8
8564750; Tel: +86 531 88366062
b
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China
West Normal University, Nanchong 637000, China
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such as high thermal stability, high ionic conductivity and
28
environmental friendliness. These advantages of ILs can
overcome the restrictions imposed by temperatures. In other
words, the PEMs with ILs can be used at higher temperatures
and can also meet the demand of environmental protection.
29
Ven et al. prepared a high-temperature proton conductive
membrane based on the IL 1-H-3-methylimidazolium bis(tri-

uoromethanesulfonyl)imide with polybenzimidazole (PBI).
ꢀ1
The highest proton conductivity could reach to 1.86 mS cm at
ꢁ
30
1
90 C. Eguiz ´a bal et al. reported a new kind of high temper-
ature proton exchange membrane, which was composed of the
IL 1-H-3-methylimidazolium bis(triuoromethanesulfonyl)
4
imide, NH BEA, NaY and PBI. In this, a proton conductivity of
ꢀ1
ꢁ
Fig.
2
Possible reaction mechanism of cross-linked PVA–IL
54 mS cm was attained at 200 C. However, the costs of these
membrane. CA serves as a crosslinker; IL as proton conductor.
polymer matrices are high, so a membrane with low cost and
high operating temperature is needed.
In this work, anhydrous proton exchange membranes of PVA
have been prepared by the low cost protic ionic liquids (ethyl-
ammonium nitrate (EAN), diethylammonium nitrate (DEAN)
and triethylammonium nitrate (TEAN)). The controllable
structure of the membrane is provided by the PVA support and
the proton conductivity can be achieved by the protic ionic
liquids. The excellent properties of novel anhydrous proton
exchange membranes are based on the properties of the above
materials. The effects of temperature, ILs and crosslinker
dosage on proton conductivity have also been systematically
investigated.
solution with concentrations ranging from 20 to 55 wt%. Then,
an appropriate amount of CA was added into the mixture
solution. The composite membranes were prepared by solution
casting method at room temperature. The homogeneous hot
25
solutions were poured into a specic mold, and then dried at
room temperature. The composite membranes were peeled off
ꢁ
and cross-linked in a vacuum drying oven at 120 C for 2 h. The
crosslinking reaction is shown in Fig. 2. Aer cooling, the
crosslinked PVA–IL membranes (PVA–CA–IL) were cut into
pieces (ca. 1.5 ꢂ 2 cm).
2
.4. Structure and morphology characterization
2
. Experimental
Fourier transform infrared (FT-IR) spectra were recorded on
VERTEX-70 FT-IR spectrometer in the range of 4000 to 500
PVA (average MW 88 000–97 000 g mol ; 98–99% hydrolyzed), cm . H NMR spectroscopy was performed on a Bruker Avance
CA ($99.8%) were provided by Alfa Aesar. Nitric acid, ethyl- II 300 NMR spectrometer at a resonance frequency of 300 MHz,
2.1. Materials
ꢀ
1
ꢀ1
1
amine ($99%), diethylamine ($99%) and triethylamine using D
2
O as the solvent and tetramethylsilane (TMS) as an
(
$99%) were purchased from Beijing Chemical Reagent Co. All internal standard. The morphologies of composite membranes
chemicals were used without further purication.
were characterized using the scanning electron microscopy
SEM, JSM-7600F, EOL, Ltd., Japan). The structures of the
(
membranes were investigated using Anton-paar SAX Sess mc2
system (SAXS) with Ni-ltered Cu Ka radiation (0.154 nm)
operating at 50 kV and 40 mA. The DSC curves were measured
on a Perkin Elmer DSC-8500 instrument at a heating rate of 10
2
.2. Preparation of ILs
EAN, DEAN and TEAN (Fig. 1) were synthesized according to
literature. In a typical preparation, 50 ml nitric acid was added
to a round bottom ask and 83 ml ethylamine solution slowly
dropped into it with vigorous stirring at 0 C. Then, the mixture
31
ꢁ
ꢀ1
C min under dry nitrogen.
ꢁ
was puried with a rotary evaporator for removing the water and
excess ethylamine. DEAN and TEAN were produced in a similar
way.
2
.5. Thermal stability
Thermogravimetric analysis (TGA) was carried out using a
Rheometric Scientic TGA1500 (Piscataway, NJ) to investigate
the thermal properties of samples. Studies were conducted
under inert atmosphere of nitrogen using 8–10 mg samples
with a heating rate at 10 C min from ambient temperature to
6
2.3. Preparation of PVA–CA–IL membranes
ꢁ
PVA (5 g) was dissolved in distilled water (45 ml) at 85 C. Ionic
liquid (EAN, DEAN and TEAN) was added directly into the PVA
ꢁ
ꢀ1
ꢁ
00 C.
2.6. Proton conductivity
The proton conductivities of the membranes were measured
using the electrochemical workstation (660D, CH Instruments,
Co., China) using two copper electrodes, over the frequency
6
ꢀ4
Fig. 1 Chemical structures of ILs.
range 1 ꢂ 10 Hz to 1 ꢂ 10 Hz, aer placing in a nitrogen
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ꢁ
atmosphere under anhydrous conditions from 40 to 140 C for 2
h before each measurement. The bulk resistance (R ) was
b
determined from the equivalent circuit analysis by using a
frequency response analyzer. The proton conductivity was
calculated according to the following equation:
L
s ¼ R
(1)
b
A
where s is the proton conductivity, L is the distance between the
32
electrodes, A is the area of the sample.
2.7. Mechanical property
Mechanical tensile tests were performed using a Universal
Testing Machine (Yashima Works Co Ltd., model RTM-IT) at
room temperature. The crosshead displacement speed of
ꢀ
1
Fig. 4 TGA thermograms of PVA–CA and PVA–CA–IL membranes.
testing was set at the rate of 5 mm min . The membranes with
size of 6 mm ꢂ 25 mm were used for testing in 35% RH.
33
Tensile strength (T ) is the stress at the maximum in the
plastic portion of the stress–strain curve that may be sustained
by the membrane. Tensile strength was calculated as follows:
s
equipped with an ATR accessory, which measured both the
top and bottom surfaces. As shown in Fig. 3, all membranes that
we prepared exhibited strong absorbances at 1231 and 1718
ꢀ
1
cm , which are ascribed to the stretching vibrations of C–O–C
and of C]O, respectively. This indicates the occurrence of
T
s
¼ F/A
0
(2)
34,35
Moreover, ductility is another important mechanical prop- esterication.
erty. It is a measure of the degree of plastic deformation that has cm were also observed in all membranes, which indicate the
been sustained at fracture. Ductility (% EL) may be expressed as presence of ILs. Moreover, all membranes showed a very strong
The stretching vibrations of C–N around 1100
ꢀ
1
ꢀ
1
the percentage of elongation, which was the plastic strain broad peak around 3300 cm for the hydroxyl (O–H) stretching
percent at fracture and calculated as follows:
vibration. From these results, it could be demonstrated that the
PVA–CA–ILs membranes were prepared successfully.
Fig. 4 shows the TGA curves of PVA–CA (molar ratio 1 : 0.02),
PVA–CA–EAN, PVA–CA–DEAN, and PVA–CA–TEAN (molar ratio
%
EL ¼ (l
f
ꢀ l
)/l
0 0
(3)
where F is the maximum load, A
0
is the cross section area, l
f
and
1
: 0.02 : 0.2) composite membranes. It is obvious that all
l
0
are the fracture length and original gauge length, respectively.
membranes exhibit three main weight loss regions, which can
be attributed to the thermal salvation, thermal dehydroxylation
36
3. Results and discussion
and deamination, and thermo oxidation. Compared with PVA–
CA membrane, the other membranes (PVA–CA–EAN, PVA–CA–
DEAN and PVA–CA–TEAN) exhibit an initial weight loss (2–3%)
3.1. Composite membranes characterization
The Fourier transform infrared attenuated total reection (FT-
IR-ATR) spectra of the membranes were examined by FT-IR,
ꢁ
between 50 and 160 C, which is attributed to water desorption,
indicating the presence of free water loaded by ionic liquids and
3
7
the strong hydrogen-bond interactions between PVA and ILs.
ꢁ
The second weight loss occurs at 160–300 C, which can be
attributed to the decomposition of ester bond, N–H, and
38
39
ꢀ
40
NO
3
.
It is obvious that the weight loss of the PVA–CA–EAN
membrane is more than those of the PVA–CA, PVA–CA–DEAN,
and PVA–CA–TEAN membranes. It may be due to the molecular
structure of EAN, which possesses more N–H groups per
molecule than the others. Moreover, the starting decomposition
ꢁ
temperatures (160–300 C) of all the membranes we prepared
are higher than those of traditional PVA membranes, which are
ꢁ
41
ꢁ
usually below 80 C. Finally, the weight loss at 300–500 C is
42
attributed to the decomposition of the PVA backbone. This
TGA result illustrates that the composite membranes could be
ꢁ
used up to 160 C.
The morphologies of the PVA–CA–EAN membrane's surface
and cross-section are shown in Fig. 5. The surface morphology
of the composite membranes is smooth, homogeneous and
dense (Fig. 5a). The morphologies of membrane surfaces
Fig.
3 FT-IR spectra of PVA–CA–IL membranes (molar ratio
1
: 0.02 : 0.2).
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Fig. 5 SEM images of PVA–CA–EAN membrane: (a) surface; (b) cross-
section.
Fig. 7 DSC curves of pure TEAN and PVA–CA–TEAN membrane.
could be due to the intermolecular hydrogen bonds between OH
(
PVA) and N (ionic liquids), which shorten the average distance
48
between domains. This shortened distance is benecial for
proton conduction, which means that the ionic liquids play a
dominant role in the formation of the proton exchange
membrane. The incorporation of DEAN and TEAN cause the
single peaks to become much broader than that of PVA–CA–EAN
membrane, which indicates better homogeneity of EAN in the
PVA structure. The heterogeneous distributions of DEAN and
TEAN in the PVA matrix lead to a relatively poor conductivity
Fig. 6 SAXS spectra of PVA–CA and PVA–CA–IL membranes.
indicate the formation of continuous conducting channels
43
essential for enhancement of proton conductivity. Fig. 5b
shows the cross-section image. It is obvious that many little
holes are on the cross-section, which could have resulted from
the crosslinking reaction at high temperature. Due to the high
temperature, the free water could get out of the composite
membranes through these little holes. But the membrane was
48
compared to that of PVA–CA–EAN membrane.
DSC was used to elucidate the dispersed state of IL in the
crosslinked PVA–IL membranes. The PVA–CA–TEAN membrane
and pure TEAN were selected for investigation because of the
highest melting point of TEAN among the three ionic liquids,
which makes it easier to observe the changes between the PVA–
CA–TEAN membrane and pure TEAN. In the DSC curve of TEAN,
44
denser, indicating the importance of crosslinking reaction.
In order to further investigate the structure of the composite
membranes, SAXS was used as the appropriate tool for eluci-
dating the formation of the composite membrane. Fig. 6 shows
the SAXS curves of four different composite membranes (PVA–
CA, PVA–CA–EAN, PVA–CA–DEAN, and PVA–CA–TEAN). The
SAXS curve of the PVA–CA membrane displays a ‘knee’ type
shape. It is a single peak and the maximum value of scattering
ꢁ
the endothermic peak at ca. 117 C (Fig. 7) is the melting peak of
TEAN. However, it is obvious that the melting peak disappears
aer inserting TEAN into the crosslinked PVA structure. This
implies that the TEAN embedded inside the membrane is well-
dispersed with very small size. The highly dispersed state of
TEAN likely results from interactions between TEAN and the
polymer matrix. These interactions signicantly reduce the size
ꢀ
1
vector q is located at 0.18 nm , which indicates that PVA–CA
49
of the IL nanoaggregates.
45
membrane is a semi-crystalline structure. For the model of
isolated domains embedded in a continuous matrix, the
average distance between domains, d, can be estimated by the
equation below.
3.2. Proton conductivity of PVA–CA–IL membranes
The proton conductivity is one of the most crucial parameters
50
for characterizing a proton conducting membrane. Fig. 8a
D ¼ 2p/q
(4) shows the proton conductivity of the PVA–CA–IL (molar ratio
1
: 0.02 : 0.2) composite membranes. The proton conductivities
increase sharply with the increase of the tested temperature.
The membrane conductivities of PVA–CA–EAN, PVA–CA–DEAN,
and PVA–CA–TEAN membranes could reach values of 1.1, 1.5,
From this equation, the average distance of the PVA–CA
nano-crystallites is 34.9 nm, which is higher than that of pure
46
ꢀ1
ꢁ
PVA nano-crystallites (7–20 nm). This demonstrates that the
cross-linking reaction destroys the hydrogen bonds present in
the poly(vinyl alcohol) chain, which are important to stabilize
and 0.4 mS cm at 140 C, respectively. It is obvious that the
conductivity of PVA–CA–DEAN is higher than that of PVA–CA–
EAN though the distributions of the DEAN are poorer than that
of EAN. This may be attributed to higher ionicity of DEAN,
47
the polymer crystals. When ILs are added into the PVA–CA
membranes, the SAXS curves show shoulder peaks. The average
values of q increase and the peaks become wider. These results
51
which is benecial for the proton conductivity. The proton
conductivity of PVA–CA–TEAN is lowest among the three PVA–
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Fig. 8 (a) Proton conductivities of PVA–CA–IL membranes as a function of temperature (molar ratio PVA : CA : IL ¼ 1 : 0.02 : 0.2) and (b)
temperature dependence of proton conductivity.
Table 1
a
E values of PVA–CA–IL membranes and Nafion 117
ꢀ1
Composite membrane
Slope
Activation energy (kJ mol )
PVA–CA–TEAN
PVA–CA–DEAN
PVA–CA–EAN
Naon 117
ꢀ7.24
ꢀ9.17
ꢀ9.58
—
60
76
80
13
CA–IL composite membranes. This is attributed to the great
3
steric hindrance, which hinders the proton transfer.
The apparent activation energy (E
a
) for PVA–CA–IL
composite membranes was estimated using the following
52
equation:
Fig. 9 Effect of IL dosage on proton conductivity of PVA–CA–EAN
membrane measured at 100 C.
E
a
ln s ¼ ꢀ
(5)
ꢁ
RT
where s is the proton conductivity, R is the universal gas
constant, and T is the absolute temperature.
ꢀ1 57
ꢁ
at 100 C and
poly(ether ketone) membrane (1.3 mS cm
)
As shown in Fig. 8b, the ln s depends almost linearly on 1/T.
ꢀ1
ꢁ
58
H
3
PO doped PVA/PAM membrane (5.25 mS cm ) at 180 C.
4
The E
a
values of three PVA–CA–IL membranes are shown in
53
Table 1. All the E values are higher than that of Naon 117.
a
3.4. Effect of CA dose
This indicates that the proton mobility in PVA–CA–IL composite
The crosslinker (CA) plays an important role in the preparation
of PVA–IL composite membrane. First, the crosslinker can make
the membrane more compact and rigid, which is benecial to
the Young's modulus, tensile strength and oxidative stability of
membrane is limited, which can be attributed to the bulky size
of the IL.
54
59,60
membrane.
Second and notably, the degree of crosslinking
3.3. Effect of IL dose
of the polymer could affect the proton conductivity of the PVA–
In order to investigate the effect of IL dosage on the proton IL composite membrane. Therefore, it is important to investi-
conductivity, we measured the conductivities of PVA–CA–EAN gate CA dosage in PVA–IL (molar ratio PVA : EAN ¼ 1 : 0.4)
(
molar ratio PVA : CA ¼ 1 : 0.1) membranes with different composite membranes. When the mole ratio of CA–PVA is
ꢁ
dosage of IL at 100 C. As shown in Fig. 9, with the increase of IL 0.1 : 1, with increase of temperature, the increase in the proton
dosage, proton conductivity increases sharply when the mass conductivity becomes relatively slow (Fig. 9a). This indicates
percent of IL is higher than 42.4%. This may be due to the that the mobility of the proton is limited by the highly cross-
higher proton density (the proton number per unit volume), linked composite membrane. In other words, the high degree of
which can lead to an increase of proton conductivity of PVA–CA– crosslinking hinders the proton mobility. When the mole ratio
IL composite membrane. The maximum conductivity is 6.5 of CA–PVA was changed to 0.05 : 1, the curve shows a sharp
mS cm
ylethylammonium triuoromethanesulfonate (IL) doped hybrid conductivity reaches 7.8 mS cm at 140 C. This implies that
membrane (5.4 mS cm ) at 100 C, 1-butyl-3-methyl imida- the lower degree of crosslinking is benecial for the proton
zolium bis(triuoromethanesulfonyl)imide doped sulfonated conductivity. However, it is to be noted that the tensile strength
61
55
ꢀ
1
ꢁ
at 100 C, which is higher than those of dieth- increase (Fig. 10a) with increasing temperature. The maximum
ꢀ
1
ꢁ
ꢀ1
ꢁ
56
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Fig. 10 (a) Effect of CA dosage on proton conductivity of PVA–CA–EAN membrane measured at different temperatures and (b) temperature
dependence of proton conductivity (ln s–1000/T).
Table
2
E
a
values and mechanical stability of PVA–CA–EAN present alone in the composite structure. The IL and crosslinker
dosages had an important effect on proton conductivity. The
membranes with different molar ratios and Nafion 117
ꢀ1
ꢁ
maximum conductivity was 7.8 mS cm at 140 C, which was
higher than reported values. This work may provide a new
approach for the research and development of new anhydrous
proton exchange membranes.
Composite
membrane
Activation energy Tensile strength Elongation
ꢀ1
Slope (kJ mol
)
(MPa)
10.7
8.8
(%)
320.4
314.7
—
PVA–CA–EAN ꢀ8.97 75
1 : 0.1 : 0.4)
PVA–CA–EAN ꢀ3.73 31
1 : 0.05 : 0.4)
PVA–CA–EAN ꢀ9.58 80
1 : 0.05 : 0.2)
Naon 117
(
(
Acknowledgements
—
(
The authors are grateful to the National Basic Research Program
—
13
14.2
—
(2013CB834505), Specialized Research Fund for the Doctoral
Program of Higher Education of China (no. 20120131130003)
and the Shandong Provincial Natural Science Foundation,
decreases upon decreasing the mole ratio of CA–PVA (Table 2). China (ZR2012BZ001).
When the degree of crosslinking is low enough, the structures of
the membrane possibly cannot maintain a xed shape at high
temperature due to poor mechanical property. Thus, it is References
important to choose the optimal CA dosage for balancing the
proton conductivity and mechanical property of the
membranes.
Fig. 10b shows a linear relationship between ln s and 1/T.
The calculated values are shown in Table 2. Comparing the
1
2
E. A. Mistri and S. Banerjee, RSC Adv., 2014, 4, 22398–22410.
C. M. Chang, H. Y. Li, J. Y. Laia and Y. L. Liu, RSC Adv., 2013,
, 12895–12904.
H. Cheng, J. Xu, L. Ma, L. Xu, B. Liu, Z. Wang and H. Zhang, J.
Power Sources, 2014, 260, 307–316.
3
3
4
membrane with different CA dosages, the E
mole ratio ¼ 1 : 0.05 : 0.4) is lower. The lowest E
proton conductivity indicates the least energy needed for proton
a
of PVA–CA–EAN
Y. Zhang, X. Fei, G. Zhang, H. Li, K. Shao, J. Zhu, C. Zhao,
Z. Liu, M. Han and H. Na, Int. J. Hydrogen Energy, 2010, 35,
(
a
value of
6409–6417.
62
transfer in the membranes. Upon xing the CA dosage, the
5
6
S. Zhou and D. Kim, Electrochim. Acta, 2012, 63, 238–244.
M. A. Hickner, H. Ghassemi, Y. S. Kim, B. R. Einsla and
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dosage of EAN is reduced by half. The result shows that the E of
a
PVA–CA–EAN (mole ratio ¼ 1 : 0.05 : 0.2) reaches up to 80 kJ
ꢀ
1
mol (Table 2). All these results indicate the importance of CA
and EAN doses for elevating the proton conductivity.
7
8
2014, 4, 52001–52007.
9
B. Wang, Z. Cai, N. Zhang, B. Zhang, D. Qi, C. Zhao and
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4
. Conclusion
A series of novel anhydrous proton exchange membranes (PVA– 10 C. Ke, J. Li, X. Li, Z. Shao and B. Yi, RSC Adv., 2012, 2, 8953–
CA–IL) were prepared using the low cost ionic liquids EAN, 8956.
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17688 | RSC Adv., 2015, 5, 17683–17689
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