Anion-conductive membranes based on 2-mesityl-benzimidazolium functionalised poly(2,6-dimethyl-1,4-phenylene oxide) and their use in alkaline water electrolysis

Article abstract of DOI:10.1016/j.polymer.2018.05.008

For development of anion exchange membrane (AEM) water electrolysis systems, a series of polymers was synthesised by reacting 2-mesityl-benzimidazole (BIM) and brominated poly-(2,6-dimethyl-1,4-phenylene oxide) (Br-PPO) in a Menshutkin reaction, and perme

Full text of DOI:10.1016/j.polymer.2018.05.008

Accepted Manuscript
Anion-conductive membranes based on 2-mesityl-benzimidazolium functionalised
poly-(2,6-dimethyl-1,4-phenylene oxide) and their use in alkaline water electrolysis
Angela Marinkas, Izabela Struźyńska-Piron, Yona Lee, Ahyoun Lim, Hyun S. Park,
Jong Hyun Jang, Hyoung-Juhn Kim, Jihyun Kim, Artjom Maljusch, Oliver Conradi,
Dirk Henkensmeier
PII:
S0032-3861(18)30395-1
10.1016/j.polymer.2018.05.008
JPOL 20569
DOI:
Reference:
To appear in: Polymer
Received Date: 30 January 2018
Revised Date: 16 April 2018
Accepted Date: 3 May 2018
Please cite this article as: Marinkas A, Struźyńska-Piron I, Lee Y, Lim A, Park HS, Jang JH, Kim H-J,
Kim J, Maljusch A, Conradi O, Henkensmeier D, Anion-conductive membranes based on 2-mesityl-
benzimidazolium functionalised poly-(2,6-dimethyl-1,4-phenylene oxide) and their use in alkaline water
electrolysis, Polymer (2018), doi: 10.1016/j.polymer.2018.05.008.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Anion-conductive membranes based on 2-mesityl-benzimidazolium
functionalised poly-(2,6-dimethyl-1,4-phenylene oxide) and their use in
alkaline water electrolysis
a
a
a,b
a
a
Angela Marinkas , Izabela Struźyńska-Piron , Yona Lee , Ahyoun Lim , Hyun S. Park , Jong Hyun
a
a
c
d
d
a,b,e,
Jang , Hyoung-Juhn Kim , Jihyun Kim, Artjom Maljusch , Oliver Conradi , Dirk Henkensmeier
*
a
Korea Institute of Science and Technology, Fuel Cell Research Center, Hwarangno 14-gil 5, 02792
Seoul, Republic of Korea
b
Green school, Korea University, 145 Anamro, Seongbukgu, Seoul, 02841, Republic of Korea
c
Department of Chemical and Biological Engineering, Korea University, 145 Anamro, Seongbukgu,
Seoul, 02841, Republic of Korea
d
Evonik Creavis GmbH, Paul-Baumann-Straße 1, 45772 Marl, Germany
e
Division of Energy & Environment Technology, KIST School, Korea University of Science and
Technology, Seoul 02792, Republic of Korea
*
henkensmeier@kist.re.kr
Keywords: anion exchange membrane, 2-mesityl-benzimidazole, poly(2,6-dimethyl-1,4-phenylene oxide)
PPO), alkaline electrolysis, alkaline stability.
(
Abstract:
For development of anion exchange membrane (AEM) water electrolysis systems, a series of polymers
was synthesised by reacting 2-mesityl-benzimidazole (BIM) and brominated poly-(2,6-dimethyl-1,4-
phenylene oxide) (Br-PPO) in a Menshutkin reaction, and permethylating the attached BIM groups. The
degree of bromination of Br-PPO can be easily monitored by IR spectroscopy: A correlation with the shift
-1
of the band around 1190 cm was found. The IEC values of the prepared materials ranged between 1.6
-
-1
and 2.9 mmol OH g . Only materials with an IEC value of 1.9 (PPO24-BIM) reproducibly formed self-
supporting membranes. This may be related to the degree of crystallinity, which decreased from 14 to 3%
-
-1
when the IEC increased from 1.6 to 3 mmol OH g . Materials with IEC values of 1.6 and 2.2 can form
-1
self-supporting membranes, but not reproducibly. PPO24-BIM showed a conductivity of 8 mS cm at
room temperature, a thermal stability well above 200 °C, and mechanical properties similar to those of
-2
commercial FAA3-30 membranes. During water electrolysis, a current density of 300 mA cm at 1.8 V
was obtained. At 80 °C in 1 M KOH, degradation of BIM and the PPO backbone were observed by IR
spectroscopy and monitoring conductivity and weight loss.
1

ACCEPTED MANUSCRIPT
1
. Introduction
Alkaline water electrolysis is a well established technology, but is not well suited for dynamic operation,
which is required when electrolysis is combined with renewable energy sources. The reason is that
pressure differences between anode and cathode can lead to gas crossover through the porous diaphragms
used to separate anode and cathode in commercial systems. Another issue is the thickness of these
separators, which adds to the system resistance. For example, AGFA's Zirfon is 500 µm thick.[1] Ion
exchange membrane-based electrolysis is a specifically promising technology because it uses thin, non-
porous membranes, allowing for operation under more dynamic conditions. In addition, it can be operated
at neutral (PEM electrolysis)[2] or just slightly alkaline conditions (AEM electrolysis). While PEM
electrolysers are already quite advanced and in the focus of electrolysis industry, anion exchange
membrane (AEM)-based systems have the potential to combine the advantages of PEM electrolysis
(
dynamic operation, thin membrane, neutral feed water) and alkaline electrolysis (use of non-noble metal
catalysts) [3]. In addition, due to the thin dense membrane, AEM electrolysers are expected to show a
high voltage efficiency and can operate at high current densities, which improves the gas purity.
The electrode reactions for alkaline and AEM water electrolysis are shown in Equations 1-3:
-
-
Anode:
4 OH
‰
O + 2 H O + 4 e (0.401 V vs. SHE)
Eq. 1
Eq. 2
Eq. 3
2
2
-
-
Cathode:
4 H O + 4 e
‰ 2 H + 4 OH (-0.828 V vs. SHE)
2
2
Total reaction:
2 H O ‰ O + 2H (1.23 V)
2 2 2
The key towards commercialisation of AEM systems is the development of suitable AEMs. The research
on anion exchange membranes (AEM) and AEM based systems increased dramatically over the last 15
years, covering broad fields like actuators,[4] electrochemical pumping of CO ,[5] reverse
2
electrodialysis,[6] but especially fuel cells.[7] These days, the main challenge in AEM research is still to
improve the alkaline stability. Most of the cationic groups which have been attached to polymer chains
and evaluated for their hydroxide stability, i.e. trimethyl ammonium, guanidinium [8], imidazolium [9],
pyrrolidinium [10], sulfonium [11], phosphonium [12] or ruthenocene [13] cations, degrade relatively fast
when exposed to elevated temperatures in alkaline environments.[14] In addition, most employed
polymer backbones are derived from polyethersulfone- or ketone, and it was shown that these polymers
can degrade under alkaline conditions [15].
Another group of membrane polymers are alkylated polybenzimidazoles, where the stability of the
benzimidazolium group determines also the stability of the polymer backbone [16-21]. Degradation starts
with an attack of hydroxide ions on the C2 position of the imidazolium moieties.[17] It was shown that
alkaline stable systems can be obtained, when the phenyl group in position 2 bears bulky substituents,
which block the access of hydroxide ions to the reactive C2 position. Examples are methyl groups in
ortho position to the imidazolium, as shown in Figure 1 [22,23].
2

ACCEPTED MANUSCRIPT
I-
I-
N
N
*
+
+
n
*
N
N
methylated meta-PBI
I-
I-
N
N
*
+
+
*
n
N
N
methylated mes-PBI
I-
I-
N
N
+
N
*
+
*
n
N
HMT-PDMBI
O
*
*
n
syne-IM-functionalised PPO
O
N
+
N
O
I-
O
Figure 1: Chemical structure of imidazole containing polymer membranes
Recently, Yan et al. synthesised 2,4,6-trimethoxyphenyl substituted imidazoles and attached them as
functional group to poly-(2,6-dimethyl-1,4-phenylene oxide) (PPO).[24] The stability was much better
than that of a PPO to which less bulky imidazolium groups were attached. However, only one material
was reported, and since it had a relatively low IEC of 1.5 mmol/g, it is of interest to investigate materials
with higher IEC values. Furthermore, the synthesis of those materials involved several steps, and a more
straightforward way towards PPO substituted with sterically protected imidazoles seems to be
advantageous.
In this work, we report a series of polymers synthesised by attaching 2-mesityl-benzimidazole (BIM) to a
brominated poly-(2,6-dimethyl-1,4-phenylene oxide) (Br-PPO) backbone, followed by methylation of the
unsubstituted N atom of the BIM group. Br-PPOs with different degrees of bromination (DB) were used
for the synthesis, in order to adjust the ion exchange capacity (IEC) and the resulting water uptake and
-
-1
conductivity. The most stable membrane type, with an IEC of 1.9 mmol OH g , was also tested for its
performance in an electrolysis cell.
2
2
. Experimental
.1 Materials
3

ACCEPTED MANUSCRIPT
-1
Poly(2,6-dimethyl-1,4-phenylene oxide, PPO) (Sigma Aldrich, Mw
=
50,000
g
mol ),
azobisisobutyronitrile (AIBN, 98%, Sigma Aldrich), dimethylacetamide (DMAc, 99.8%, Sigma Aldrich),
dimethylsulfoxide (DMSO, 99.9 %, Sigma Aldrich), 2-propanol (IPA, Daejung), chlorobenzene (Sigma-
Aldrich, anhydrous, 99.8%,), N-methyl-2-pyrrolidone (NMP, Sigma Aldrich), Sodium Hydride (60 wt.-%,
Sigma), iodomethane (Sigma Aldrich, Daejung), bromine (Sigma Aldrich, reagent grade), trimethyl
benzoic acid (Alfa Aesar), ortho-phenylene diamine (Sigma-Aldrich), DMSO-d6 (Cambridge Isotope
Laboratories), chloroform CDCl (Cambridge Isotope Laboratories), and polyphosphoric acid (Sigma-
3
Aldrich) were all used as received. FAA-3-PK-75 and FAA3-30 membranes were obtained from
Fumatech.
2
.1.1 Synthesis of 2-(2,4,6-trimethylphenyl)-benzimidazole (BIM)
2
0.0258 g (122 mmol) 2,4,6-trimethyl-benzoic acid (purchased from Alfa Aesar), 13.1723 g (122 mmol)
ortho-phenylenediamine (Sigma-Aldrich) and 60 g (29.1 ml) PPA (Sigma-Aldrich) were placed into a
reaction flask and stirred at 200°C for 2 h. After this time, the reaction mixture was cooled down to
1
20 °C, and then the temperature was decreased to 60 °C and 3 ml of phosphoric acid were added in order
to make the solution less viscous. The solution was poured into water, and after short mixing, the product
was precipitated by addition of 815 ml of 7 wt.-% KOH solution, to reach a pH of ~8. The mixture was
magnetically stirred for 48 h to ensure the end of precipitation. The precipitate was filtered, rinsed with
water, and directly boiled in water for ~16 h. Subsequently, a vacuum filtering and washing with water
was performed. The filtered product was dried for 72 h at 60 °C under vacuum. 22.9276 g
1
(
80% yield) of the purified, off-white product was collected. H NMR (DMSO-d ,
δ
(ppm)): 12.45 (1 H,
6
NH), 7.66 (d, 1H, H4 or H7, J = 6.85), 7.49 (d, 1H, H4 or H7, J = 5.87), 7.20 (m, 2H, H5 and H6), 7.01 (s,
2
3 3
H, mesitylene CH), 2.32 (3 H, -CH ), 2.07 (6H, -CH ).
2
.1.2 Bromination of poly-(2,6-dimethyl-1,4-phenylene oxide) (Br-PPO)
Procedure described exemplary for Br-PPO33 (degree of bromination: 33%):
1
6.0320 g (133.433 mmol repeat units) PPO were added to a three necked round bottom flask equipped
with a dropping funnel, argon inlet and reflux condenser connected to a reaction vessel bubbler and two
washing flasks (empty and filled with 2 M NaOH solution and a drop of phenolphthalein solution). Then
1
60 mL chlorobenzene were added and the suspension was heated to 128°C and stirred until all the PPO
was dissolved. After complete dissolution the temperature of the oil bath was increased to 142 °C. A
mixture of 68.5 mg AIBN (0.4171 mmol), 35 mL chlorobenzene and 6.8 mL Br (21.209 g, 132.715
2
mmol) was prepared in a beaker and transferred into the dropping funnel. The solution was added drop-
wise over 30-45 minutes. After the addition was complete, the reaction solution was stirred for 4 h.
Finally the solution was cooled down and added drop-wise into 5 L isopropanol (acetone when the
expected degree of bromination is 50% or higher). The mixture was stirred over night, the precipitate was
removed by filtration and dried in the oven at 60 °C under vacuum for 48 h. The degree of bromination
was calculated from the nmr spectra by comparing the integral values of the aromatic signals and the
1
signals around 4.5 ppm (CH Br). H NMR (CDCl ,
δ
(ppm)), for Br-PPO33: 7.03-6.19 (m, 6.06H, CH,
2
3
4

ACCEPTED MANUSCRIPT
aromatic), 4.37 (bs, 2H, CH
2 3
-Br), 2.03-2.36 (several singulets, 11.97H, -CH ) (spectra are shown in the
supplementary material, Figures S1-S5).
To achieve other degrees of bromination, the molar ratios (bromine/PPO) were adjusted to 0.44, 0.6, 1, 2
and 4 for Br-PPO with a degree of bromination of 16, 24, 33, 50 and 87%, respectively.
2
.1.3 Reaction of Br-PPO with BIM
Procedure described exemplary for PPO24-BIM (based on Br-PPO24):
.1695 g (13.4 mmol) BIM were dissolved in 250 ml anhydrous DMAc at room temperature under an
3
argon atmosphere, followed by addition of 0.804 g (20.1 mmol) of NaH and stirring for 1 h. After this
time, 5 g (8.94 mmol) of Br-PPO24 dissolved in 250 ml DMAc (NMP for Br-PPO16) were added drop-
wise at 60 °C and the reaction temperature was increased to 80 °C, and the mixture was stirred for 48 h.
Subsequently, the reaction mixture was cooled down to 30 °C, and 2.92 ml (46.7 mmol) methyl iodide
were added drop-wise. The methylation was carried on for another 20 h at 80 °C. The solution was cooled
to 30 °C. The product was precipitated by pouring into isopropanol, filtrated and dried at 60 °C in the
1
vacuum (6.5 g dried product). H NMR (DMSO-d
6
,
δ
(ppm)): 8.4-6.0 (m, 10H, aromatic signals), 5.40 (bs,
2
H, NCH
2
), 3.79 (s, 3H, NCH
3
), 1.5-2.4 (18H, mesitylene -CH and PPO-CH ) (spectrum is shown in
3
2
Figure S6).
2
.1.4 Membrane preparation
BrPPO-BIM was dissolved in DMSO, DMAc or DMAc:DMSO 1:1 (vol.-%) at 60°C for 48 h under
vigorous stirring, to form about 5-15 wt% solutions. After stirring, the solution was filtrated using a 10
µm syringe filter. The filtrated solution was cast onto a glass plate with a doctor blade (air gap 400 µm).
The wet film was placed into an oven, and dried at 60 ±1 °C under atmospheric pressure for 4h and under
reduced pressure for 24 h. After solvent evaporation, the membrane was immersed in water at room
temperature for 24 h in order to remove solvent traces. Afterwards, the membrane was dried in a vacuum
oven at 60 °C for 48 h. The thickness of the membranes was between 25µm and 50µm.
2
2
.2. Analysis
.2.1 NMR analysis
The 1H NMR spectra were recorded on a 400 MHz spectrometer from Bruker at room temperature.
2
.2.3 ATR-FTIR analysis
An FTIR spectrometer (FTIR-7600 from, Lambda Scientific), equipped with an ATR system with a
-1
ZnSe-crystal was used at a resolution of 1 cm . The spectra were recorded by scanning 16 times the
-1
region between 4000 and 600 cm .
2
.2.4 Water uptake (WU)
5

ACCEPTED MANUSCRIPT
The water uptake of the membranes was determined at room temperature. After anion exchange from the
bromide to the chloride form, the membranes (10 x 40 mm) were immersed into water. After 24 h, the
membranes were wiped with a KIMTECH tissue and weighed (wet weight). Subsequently, the
o
membranes were dried under vacuum at 60 C for 24 h (dry weight). The water uptake was determined
based on Equation 4.
ꢅꢆꢇꢂꢈꢆꢈꢉꢊꢋꢌꢆꢂꢅꢆꢍꢎꢏꢇꢐꢑꢊꢒꢂꢈꢆꢈꢉꢊꢋꢌꢆꢂꢅꢆꢍꢎꢏꢇ
ꢀ
ꢁꢂꢃ%ꢄ =
· 100ꢂ%
(4)
ꢑꢊꢒꢂꢈꢆꢈꢉꢊꢋꢌꢆꢂꢅꢆꢍꢎꢏꢇ
2
.2.5 TGA analysis
The thermal stability of polymer powders and membranes was studied on a Q50 (TA instruments). The
thermal decomposition curves were recorded under an air atmosphere by heating from room temperature
-1
to 800 °C at a heating rate of 10 °C min .
2
.2.6 Mechanical properties
The mechanical properties of the prepared membranes, such as tensile strength and Young’s modulus,
were investigated on a testing machine Cometech (QC-508 E). A membrane sample of 40 x 10 mm was
-1
placed between two clamps; the upper clamp pulled upwards with a speed of 10 mm min , while the
o
lower clamp was fixed. The measurements were performed at the air temperature of 25.8 C and the
relative humidity of 26 % using a 50 N load cell.
2
.2.7 Conductivity measurements
In-plane conductivity was measured by contacting chloride exchanged membrane stripes with 4
electrodes and immersing the setup in DI water. The potential was varied between 0, 100, -100, 100, 0
-1
mV at a rate of 10 mV s . The slope of the voltage-current response curve gives access to the resistance R
(
I/U = 1/R). Ionic conductivity, (σ), was calculated according to Equation 5:
l
ꢓꢔꢐꢕ
(5)
σ ꢃ
Sꢂ
ꢄ
=
R·t·w
where l is the length of the membrane between the two potential sensing platinum wires (cm), R is the
membrane resistance ( ), T is the thickness of the membrane (cm) and W is the width of the membrane
Ω
(
cm).
2
.2.8 Wide-angle X-ray scattering (WAXS) analysis
The powder X-ray diffraction (XRD) patterns of membranes and polymer powder, as well as BIM were
measured on a Rigaku Mini Flex II X-ray diffractometer (Desktop X-ray diffractometer, Rigaku) using
o
Cu K
α
radiation in the 2
θ
range from 0 to 80 .
2
.2.9 Ex-situ chemical stability
6

ACCEPTED MANUSCRIPT
After ion exchange from the bromide to the chloride form, the membranes (10 x 40 mm) were placed in a
bottle containing 1 M KOH solution and kept at 80°C for up to 21 days. For each test time, several
samples were tested. After the test, the membranes were again ion exchanged into the chloride form.
Monitored parameters were weight loss, conductivity and the IR spectra.
2
.2.10 In-situ water electrolysis operation
The electrodes were prepared by CCG method spraying catalyst inks onto gas diffusion layers, titanium
-
2
paper (250 µm) for anode and carbon paper (TGP-H-120, Toray) for cathode, respectively (3 mg cm
-2
iridium oxide on anode and 1.5 mg cm Pt/C on cathode). The catalyst slurry was composed of IrO
Premion, Alfa Aesar, Anode), Pt/C (Pt 46.5 wt.-%, Tanaka K.K.), isopropyl alcohol, deionised water and
2
(
an aqueous solution of PTFE (60 wt.-% dispersion in H O, Aldrich). This slurry was homogenised in an
2
ultrasonic bath before spraying. The prepared GDE was heat treated at 350 °C for 5 minutes. The MEA
was fabricated by sandwiching the membrane between these electrodes. During the single cell test the
-1
anode side was fed with 0.5 M KOH solution at 1 ml min , while the cathode side was kept dry. The
temperature was 50 °C. Electrochemical performance was tested by voltage cycling from 1.5 V to 2.2 V
-1
at a scan rate of 20 mV s using a high-current potentiostat (HCP-803, Bio-Logic). Electrochemical
Impedance Spectroscopy (EIS) analysis was conducted at 1.8 V from 100 kHz to 30 mHz.
2
.2.11 Water permeability measurements
Water permeability tests were carried out in a climate chamber at 70°C and 50% RH. Small water flasks,
containing 15 mL DI water, were weighed before the test and the weights were checked every hour, in
2
total 6 times. The membranes were fixed in the bottle caps, in order to cover 0.567 cm holes, which were
through the bottle caps and the sealing.[25]
3
3
. Results And Discussion
.1 Synthesis and membrane formation
The synthesis of 2-mesityl-benzimidazole functionalised PPO (Br-PPO-BIM) is possible in 3 steps. In
the first step, ortho-diaminobenzene is reacted with 2,4,6-trimethylbenzoic acid to form BIM (Scheme
).[26] In another, parallel step, commercial PPO is brominated in a radical substitution reaction (Br-
1
PPO). There are several reports available in the literature for this reaction. As Xu et al. stressed, the
reaction temperature should be as high as possible (131 °C if chlorobenzene is used as solvent) to
suppress bromination of phenyl rings in an electrophilic aromatic substitution reaction.[27, 28] However,
there is no mentioning of the use of radical initiators. A bromine-containing chlorobenzene solution is
simply dropped to the hot polymer solution.[27, 28] We found that much more reproducible and selective
results are obtained when AIBN (a radical initiator) is added to the bromine solution, so that the
concentration of radicals is kept high throughout the reaction. When the amount of bromine was varied
between 0.6 and 4 equivalents per mole PPO repeat unit, the resulting degree of bromination (DOB) was
found to follow a highly linear trend (Figure 2), and can be described as
DOB = 12.7 + 18.9·(molar equivalents bromine).
Eq. 7
7

ACCEPTED MANUSCRIPT
Compared with the theoretically maximum possible DOB (assuming no losses or side reactions), all
obtained DOB values are smaller. However, when the molar ratio of bromine to PPO fell below 0.6, the
DOB fell below the observed linear trend line, and became more similar to the theoretically maximum
possible values. Probably, the concentration of bromine has to be kept low to avoid that bromine
evaporates from the reaction mixture. In the IR spectra, the development of a new band around 1210-1225
-
1
cm can be observed when PPO is brominated (Figure 3), while the methyl group signal around 2950
-
1
cm diminishes. Another observation is that the most intensive band of PPO (associated with asymmetric
C-O-C backbone stretching vibration[29] or plane CH bend [30]) shifts during bromination from 1186
-
1
-1
cm for pure PPO to 1213 cm for Br-PPO87. This seems to allow for a very convenient determination of
the DOB by IR spectroscopy. Keeping in mind that only 5 data points were considered, the relation
2
between the wavenumber x and the DOB could be fitted (R = 0.999) to the arbitrary equation
DOB [%] = -161.99 + 66.94·ln(x-1171.79)
Eq. 8
H
NH2
O
o
PPA, 200 C, 2h
N
+
HO
N
NH2
7 % KOH
BIM
Br and AIBN in chlorobenzene
2
O
*
*
*
O
R
n
n
*
chlorobenzene, 135 °C, 4h
PPO
Br-PPO
R = H, Br
H
N
N
BIM
1
) DMAc, 80 C, 48 h
o
+
O
O
*
*
m
o
o
2
) CH I, 80 C, 20 h
3
N
O
R
*
*
n
PPO-BIM
+
N
R = H, Br
Br-PPO
I
Scheme 1: Synthesis of BIM, Br-PPO and PPO-BIM.
8

ACCEPTED MANUSCRIPT
1
20
00
1
8
0
0
0
0
0
6
4
2
theoretical maximum
values
experiment
0
1
2
3
4
5
molar equivalents of bromine per
repeat unit of PPO
Figure 2. Dependence of the degree of bromination (obtained by NMR spectroscopy) on the amount of
bromine used during the bromination reaction.
In the third step, BIM and Br-PPO are reacted in a Menshutkin reaction. In order to obtain anion
conducting polymers, the BIM group needs to be transformed into an imidazolium group by methylation.
At first glance, it seems appropriate to use monomethylated BIM, to avoid crosslinking. Typically, a large
excess of 1-alkylimidazoles is used.[31] However, we found that it is more convenient to react BIM
directly with Br-PPO. This procedure eliminates the synthesis of Me-BIM, and the reaction can be
controlled in a way that practically no crosslinking occurs. The reason for this is the different reactivity of
the two imidazole nitrogen atoms. While alkylation of the first imidazole nitrogen atom is very fast (e.g.
room temperature, a few minutes), alkylation of the second nitrogen atom affords elevated temperatures
and elongated reaction times.[20] Therefore, it is possible to selectively react BIM molecules with only
one bromomethyl group of Br-PPO. In the next step, in a 1-pot-2-step process, iodomethane is added to
permethylate all BIM and Br-PPO-BIM molecules. In the IR spectra, three bands can be seen in the
-
1
-1
-1
region which is common for alkyl groups: 2960 cm , 2925 cm and 2855 cm , and a new band around
-1
1
1
510 cm can be found. Also several signals from BIM were found in PPO24-BIM, the bands around
450, 1410, 1265 and 755. The band around 1010 cm is also present but shifted to 1000 cm .
-
1
-1
9

ACCEPTED MANUSCRIPT
1
1
1
20
10
00
9
8
7
6
5
0
0
0
0
0
PPO
BIM
PPO24-BIM
1
600
1400
1200
1000
800
-
1
wavenumber[cm ]
1
00
8
6
4
2
0
0
0
0
PPO
Br-PPO16
Br-PPO24
Br-PPO33
Br-PPO50
Br-PPO87
0
2
000 1800 1600 1400 1200 1000 800
-
1
wavenumber [cm ]
1
00
8
6
4
2
0
0
0
0
PPO
Br-PPO16
Br-PPO24
Br-PPO33
Br-PPO50
Br-PPO87
0
1
300
1250
1200
1150
1100
-
1
wavenumber [cm ]
Figure 3: IR spectra of PPO, BIM and PPO24-BIM (top), normalised IR spectra of PPO and Br-PPO
middle) and same with an enlarged area (bottom).
(
For screening the casting conditions of PPO-BIM, membranes were first casted in petri dishes (Table 1).
It was found that most polymers are well soluble in DMAc or mixtures of DMSO and DMAc, with the
exception of PPO16-BIM, which showed a better solubility in NMP. However, only PPO24-BIM led
reproducibly to stable, self-supporting membranes. For PPO16-BIM and PPO33-BIM, stable membranes
were only obtained in a few casting trials, and these results could not be reproduced. Furthermore, it was
not possible to obtain membranes from PPO50-BIM and PPO87-BIM. PPO itself has a sufficient
-1
molecular weight of 50,000 g mol , as specified by Sigma. Also, Br-PPO with a DOB of 24%, 33% and
0% could be shaped into stable, flexible membranes by casting from chloroform solutions. Therefore,
5
10

ACCEPTED MANUSCRIPT
low molecular weight due to radical induced degradation during bromination is probably not the source of
the observed brittleness.
Table 1: Theoretical IEC values, membrane casting conditions and the appearance of the membranes.
IECtheoretical
Casting solvent
a) NMP
Membrane appearance
yellowish-brown, brittle
Material
-
-1
(
mmol OH g )
b) DMAc
1
.56
PPO16-BIM
c) DMSO
d) DMSO:DMAc 1:1 (V%)
1
2
2
.94
.23
.59
DMSO:DMAc 1:1 (V%)
DMSO:DMAc 1:1 (V%)
DMSO:DMAc 1:1 (V%)
DMSO:DMAc 1:1 (V%)
brown, flexible
PPO24-BIM
PPO33-BIM
PPO50-BIM
PPO87-BIM
dark brown, very brittle
dark brown, very brittle
dark brown, very brittle
2.98
To further investigate into the reason for the observed brittle nature of PPO-BIM membranes, the
membranes were analysed by X-ray diffraction. It is known that melt-processed PPO only crystallises
with difficulty,[32] and that a low degree of crystallisation can lead to materials of low mechanical
stability.[33] The X-ray diffraction curves (supplementary material, Figure S7) indicate that pure PPO (as
obtained) is highly crystalline (Figure 4), with an apparent degree of crystallinity (DOC) of about 30%.
Introduction of BIM strongly decreases the DOC, probably because the bulky BIM group hinders
alignment of the polymer chains. Between a DOB of 16 and 87% the DOC decreases practically linearly,
and PPO87-BIM is mainly amorphous. For comparison, recast Nafion was reported to have a DOC of
1
7.7%, while that of Nafion 212 was reported to be 13.6%.[34] However, if the casting temperature for
solution casted Nafion is too low (e.g. room temperature), no crystallinity can be detected, and the films
have inferior mechanical properties.[33] In a recent paper, He et al. describe a work which is very similar
to our present work, in which PPO of a DOB of 15% was reacted with various N-monoalkylated
imidazole groups.[35] The authors informed us, that it is possible to get stable materials up to a DOB of
5
0% when imidazole units are used. However, only brittle materials were obtained, when Br-PPO was
reacted with benzimidazole. These non-published results support our observations. In comparison, BIM is
even more bulky than benzimidazole, and acts like a cardo group, which sticks out from the main chain,
hindering chain interactions and chain rotation. This typically reduces the melting point and increases the
glass transition temperature. In summary, the observations suggest that the chain alignment is too much
11

ACCEPTED MANUSCRIPT
hindered at higher degrees of functionalisation. Possibly, stable membranes could be obtained if BIM is
tethered to PPO via a flexible alkyl chain.
3
2
2
1
1
0
5
0
5
0
5
PPO
0
10 20 30 40 50 60 70 80 90
Degree of Bromination [%]
Figure 4: Relation between degree of crystallinity (DOC) and degree of functionalisation for PPO-BIM.
3
.2
Mechanical strength
Because of the pronounced brittleness of PPO-BIM membranes, only the mechanical properties of
PPO24-BIM could be analysed (Table 2). In summary, the mechanical properties of the PPO24-BIM
membrane are comparable to commercial membranes. While its tensile strength is higher than that of
FAA3 membranes, its Young's modulus is slightly lower. Considering that FAA3-PK-75 is a reinforced
membrane, it could be expected that it is mechanically stronger than the non-reinforced FAA3 membrane.
But already in the early stages of the measurement, the reinforced membrane started to show cracks all
over the area. Apparently, the adhesion between the support and the matrix was not perfect for these
samples. The highest tensile strength, Young's modulus and elongation at break was measured for
Tokuyama's A201 membrane. The maximum proportional limit stress and strain values were reached by
FAA3-30, which can be expanded reversibly up to a stress of 28.3 MPa and a strain of 2.5%. PPO24-BIM
showed the lowest values, with a proportional limit stress and strain of 10.8 MPa and 1%, respectively.
Table 2: Mechanical properties of membranes.
Tensile
strength
Young's
Modulus
[MPa]
Temperature
[°C], relative
humidity [%]
Proportional
limit strain [%] at break [%]
Elongation
Proportional limit
stress [MPa]
Membrane
[
MPa]
45.9±6.5
6.4 ± 8.9
7.3 ± 4.7 1140 ± 30
26.9 ± 1.6 983 ± 71
PPO24-BIM
9
51 ± 26
10.8 ± 1.5
1.0 ± 0.1
6.0 ± 2.4
2
2
6, 55
6, 41
(
bromide form)
Tokuyama A201
chloride form)
9
20.7 ± 2.8
28.3 ± 3.2
13.0 ± 0.8
1.92 ± 0.4
2.5 ± 0.4
1.4 ± 0.3
61.7 ± 11.8
4.1 ± 0.8
1123 ± 77
(
FAA3-30
bromide form)
FAA3-PK-75
bromide form)
3
2
2
5, 50
6, 49
(
12.1 ± 1.3
(
12

ACCEPTED MANUSCRIPT
3
.2 Thermal stability
PPO16-BIM, PPO24BIM, PPO33-BIM and PPO50-BIM were tested for their thermal stability (Figure 5).
For all materials, degradation sets in above 200 °C. Since the thermal stability was previously shown to
increase with decreasing nucleophilicity of the anion,[18] the thermal stability of the hydroxide
exchanged materials is expected to be slightly higher than that of bromide exchanged materials, and
therefore well above the operating temperature of a water electrolysis system. For methylated
polybenzimidazole, it was shown that the thermal degradation arises from a nucleophilic substitution
reaction in which the anion reacts with an N-methyl group, with imidazole as leaving group. The step size
of the first degradative weight loss does not follow the expected trend (increasing with the IEC), and the
weight loss in the first degradation process is lowest for PPO33-BIM. The reason for this is not
understood, but it should be kept in mind that TGA data are not thermodynamic data but kinetic data, and
as thus depend on several factors. For example, the observed stability decreases with increasing chain
mobility, and increases with the heating rate, degree of crystallinity and permeability of oxygen and the
degradation products.[36]
PPO16-BIM
1
00
PPO24-BIM
PPO33-BIM
PPO50-BIM
8
6
4
2
0
0
0
0
0
bromide form
0
200
400
T / °C
600
800
Figure 5: TGA curves of PPO-BIM polymers.
3
.3 Water uptake and conductivity
Membrane conductivity usually correlates well with the ion exchange capacity and the resulting water
uptake. The water uptake of PPO16-BIM and PPO24-BIM followed the expected trend, and was 17.6 and
2
0.2 for the chloride exchanged form, and 23.5 and 27.0% for the hydroxide exchanged form,
respectively. For other materials, data was difficult to measure, because of their brittleness and small
available membrane area.
Also the conductivity of the chloride exchanged form followed the expected trend, and increased with the
IEC, and for one type of membranes with the temperature (Table 3). While the conductivity of PPO16-
BIM was too low to be useful, that of PPO24-BIM was in a useful range at room temperature, but did not
13

ACCEPTED MANUSCRIPT
increase much with the temperature. The conductivity of PPO33-BIM, finally, nearly doubled to 15.9 mS
-
1
cm when the temperature was increased from room temperature to 60 °C.
Table 3: Ionic conductivity of chloride exchanged membranes, when immersed in water.
PPO16-BIM
PPO24-BIM
PPO33-BIM
room temperature
begin of test)
0 °C
room temperature
end of test)
-
1
-1
-1
0
.8 mS cm
8 mS cm
9 mS cm
(
-1
-1
-1
6
1.2 mS cm
12 mS cm
16 mS cm
-1
-1
-1
0
.95 mS cm
8 mS cm
12 mS cm
(
3
.4 Water permeability test
In the electrolysis setup used in this work, the anode side is fed with KOH solution, while the cathode
side is left dry. Therefore, the water which is consumed at the cathode side needs to first permeate
through the membrane from the anode to the cathode side. This makes it important to determine the water
permeability of the used membranes. Following a previously reported protocol,[25] the vapour-vapour-
permeability was measured at 70 °C, for a humidity gradient between 50% and 100%. As shown in Table
-
2
-1
-2
4
, Nafion 212 showed the highest permeability of 29.2 mmol m s . This is higher than the 15 mmol m
-
1
-2
-
s reported by Holdcroft[37], but in the similar range as published before in a our setup (25.5 mmol m s
1
,
for a 58 µm thick sample[25]). The reason could be the ventilation of the climate chamber, which
transports water vapour away from the membrane surface and thus should have an effect on the data.
However, within one setup, the values are reproducible, and allow to compare different membranes.
The highest flux was observed for Nafion 212, followed closely by Tokuyama A201. PPO24-BIM (23 µm)
and FAA3-PK-75 (87 µm) were in a similar range, but showed about 40% lower fluxes than A201. A
similar trend was reported by Holdcroft et al. for experiments on liquid-vapour permeation. Nafion
membranes showed higher fluxes than FAA3 membranes of a comparable thickness.[38]
When the thickness of PPO24-BIM membranes was varied, a plot of the fluxes against the membrane
thickness showed a linear trend, as expected.[38]
Table 4: Water permeability results of the membranes at 70°C, 50% relative humidity (RH).
FAA3-
Nafion+
PPO24-
BIM (I )
PPO24-
BIM (I ) BIM (I )
PPO24- FAA3-30
Tokuyama
A201 (Cl )
Membrane
thickness
-
-
-
PK-75
-
-
2
12 (H )
(Br )
-
(
Br )
54 µm
23µm
36 µm 57 µm
38 µm
87 µm
35 µm
Water
vapour/vapour
permeation
2
9.2±1.0 12.3±0.16 10.1±0.9 6.3±0.8 15.1±1.4 12.7±0.1
21.3±2.0
-2
-1
[
mmol m s ]
14

ACCEPTED MANUSCRIPT
-
3
.5 Ex-situ stability to OH ions
The alkaline stability of PPO24-BIM was investigated by immersing samples in 1M KOH at 80 °C for
-
1
several days (Figure 6). When comparing the IR spectra, it was observed that the band around 1383 cm
-1
increased after 2 weeks in the hot alkaline solution, and the band at 1022 cm (which stems from PPO
and not from BIM, Figure 3) slightly decreased. Around 1020 cm , also bands from aromatic ether bond
-1
vibrations (although more commonly for mixed aliphatic-aromatic ethers) can be found.[39] The band at
-1
1
383 cm was assigned by Hamad et al.[30] to stem from symmetric bending of CH . However, it does
3
not seem to decrease during bromination, even Br-PPO87 shows this band (Figure 3). According to a
-1
classical textbook on preparative organic chemistry, strong bands around 1390-1370 cm may indeed
-1
stem from CH -bending vibrations, but weak-to-medium strong bands in the region of 1420-1340 cm
3
can also originate from -OH deformations of phenols.[40] In that case, an increase in the vibrational band
-1
-1
at 1383 cm and a decrease of the band at 1022 cm could indicate that the harsh, alkaline conditions led
to hydrolysis of ether bonds, and thus an increase in phenolic end groups and reduced molecular weight.
-1
This could explain the observed weight loss. The evolution of the new band at 1646 cm suggests the
formation of a carbonyl compound. Holdcroft et al. showed that hydrolysis of methylated BIM leads to a
-1
strong carbonyl band around 1680 cm .[21] This would explain the reduced conductivity (Figure 6 top).
The conductivity of Tokuyama's A201 was not much affected under the test conditions. The conductivity
of FAA3-30 was nearly stable for 2 weeks, but dropped after 3 weeks. PPO24-BIM, on the contrary,
showed clear signs of degradation from the first few days on. After 3 weeks, membrane samples were so
brittle that it was not possible anymore to measure their conductivity. This was also seen by the weight
loss after 3 weeks, which was in the range of 30%.
15

ACCEPTED MANUSCRIPT
2
1
1
0
5
0
5
0
FAA3-30
Tokuyama A201
PPO24-BIM
0
2
4
6
8
10
12
14
16
Time [days]
1
00
begin of test
after 2 weeks
80
60
40
20
PPO24-BIM
0
2
000 1800 1600 1400 1200 1000 800
-1
wavenumber [cm ]
4
2
0
0
0
PPO24-BIM
0
5
10
15
20
time [days]
Figure 6: Stability in 1M KOH solution at 80 °C: effect on conductivity (top), normalised IR spectra of
PPO24-BIM (middle) and PPO24-BIM sample weight (bottom). Data points were obtained for individual
samples.
NMR analysis of a PPO24-BIM membrane which was immersed for 21 days 1M KOH solution at 80 °C
(
Figure S11) revealed changes in the intensities. The intensities of the aromatic region (6-8 ppm) and the
region where the C-CH signals appear (1.5-2.4 ppm) more than doubled. This suggests loss of BIM or
3
16

ACCEPTED MANUSCRIPT
loss of polymer chains which bear BIM units. The latter would be supported by the IR analysis, which
also indicated degradation of ether bonds. Hydrolysis of BIM groups played a minor role. The typical
3
NCH signals for phenylmethylamine around 2.7-3.2 ppm[17] are seen, but in a very low intensity (3H
for BIM-NCH at 3.7 ppm, 0.2H at 3.0 ppm, 0.4H at 2.7 ppm), indicating that the BIM group itself is
3
quite stable in 1M KOH solution at 80 °C.
3
.6 Application in a water electrolysis system
6
5
4
3
2
1
00
00
00
00
00
00
(a)
PPO24-BIM
FAA3-PK-75
0
200
400
600
800
1000
Cycle number
1
1
1
400
200
000
th
(
b) 400 cycle
8
6
4
2
00
00
00
00
0
PPO24-BIM
FAA3-PK-75
1
.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2
Voltage / V
Figure 7: Development of the current density at 1.8 V when the cells were cycled between 1.5- 2.2 V for
th
9
00 cycles (a), and the i-V curves obtained at the 400 cycle (b).
The AEM water electrolysis performance at 50 °C was obtained by CV cycling from 1.5 V to 2.2 V. As
presented in Figure 7a, the current density increases rapidly during the initial 50 cycles due to the cell
17

ACCEPTED MANUSCRIPT
-
2
activation. For the cell with a 50 µm thick PPO24-BIM, the current density increased from 176 mA cm
st
-2
th
(
1 cycle) to 295 mA cm (50 cycle), while a benchmark membrane (FAA3-PK-75 from Fumatech,
-
2
st
nominally 70-80 µm thick) showed an activated current density from 99 mA cm (1 cycle) to 478 mA
-
2
th
th
th
cm (50 cycle). The average current densities at 1.8 V after the activation of the cell (51 cycle to 900
-2
-2
cycle) were 524 mA cm for the benchmark membrane and 318 mA cm for PPO24-BIM, which is about
0% lower. From the i-V curves (Figure 7B), the performance loss due to ohmic resistance of the
4
membranes can be estimated from the slope of the curves. Unlike the linearly increasing trend in the case
of the benchmark membrane, the slope is tilted from the point around 1.8 V in the case of PPO24-BIM.
This is due to mass transport limitation, which happens when the electrochemical reaction is faster than
the reactants can be replenished at the catalyst site. The observed mass transport limitation is not an
important factor in the low voltage region due to the low electrochemical reaction rate. Thus, the
performances of the two membranes are similar at low voltage. For example, the current densities are 85
-2
-2
mA cm and 86 mA cm at 1.55 V for PPO24-BIM and the benchmark membrane, respectively. Since
the anode side is filled with KOH solution, the oxygen evolution reaction should not be much affected by
the membrane, all reactants are supplied by the anolyte. Therefore, mass transport limitation by slow
release of gas bubbles should show a similar effect for both tested systems. However, to reduce the water
load of the produced hydrogen, and thus reduce the cost of the drying unit in a potential industrial system,
no feed water was supplied to the cathode. The water needed for the electrochemical reaction therefore
needs to diffuse through the membrane in the used cell setup. Therefore, not only the ion conductivity, but
also the water permeability of the membranes should be considered. Low water permeability limits the
reaction rate and thus reduces the performance, while high permeability increases the humidity of the
produced hydrogen, and thus the costs for the drying step in commercial systems. As shown in Table 4,
nominally 75 µm thick FAA3-PK-75 has a higher water permeability (measured for vapour-vapour
permeation) than 50 µm thick PPO24-BIM.
18

ACCEPTED MANUSCRIPT
Figure 8: Ohmic resistance, measured at 1.8 V by electrochemical impedance spectroscopy (EIS) in the
range of 100 kHz to 30 mHz (a), MEA after the test (b).
th
2
2
The ohmic resistances at the 400 cycle are 0.346 Ω cm (PPO24-BIM) and 0.245 Ω cm (benchmark
membrane) (Figure 8). Regarding the stability of the membranes, the increase rate of the ohmic
2
-1
2
-1
resistance is 0.11 mΩ cm cycle for PPO24-BIM, but only 0.03 mΩ cm cycle for the benchmark
membrane. This different increase rate can be explained by chemical degradation of the membrane,
caused by the attack of hydroxyl ions in the used KOH solution on the polymer backbone [41]. When the
cell was disassembled after the test, the membrane did not show any visible signs of degradation, and IR
showed the absence of carbonyl groups, indicating that the BIM groups were not hydrolysed. To a minor
-1
-1
degree, the band around 1383 cm increased, while that at 1022 cm decreased (supplementary material,
Figure S8), which could be related to starting backbone degradation, as discussed in part 3.5. NMR
analysis (Figure S9) showed no indication for BIM hydrolysis (no peaks for methyl-phenylamine around
3
.0 or 2.7 ppm). Since degradation of BIM was not observed in the IR and NMR spectra, a possible
reason for the observed increase in membrane resistance could be reduced membrane humidification,
because water needs to be transported from the anode to the cathode side, but hydroxide ions move in the
opposite direction, moving water with them (electro-osmotic drag).
1
9

ACCEPTED MANUSCRIPT
4
. Conclusions
A series of anion conducting polymers (PPO-BIM) based on a PPO backbone and methylated 2-mesityl-
benzimidazol (BIM) functional groups was synthesised. By controlling the degree of bromination (DOB)
of PPO, it is possible to tune the IEC of the PPO-BIM polymers. It was found that only polymers with an
-
-1
IEC of around 1.9 mmol OH g can be formed reproducibly into self-supporting membranes, probably
because the crystallinity decreases with increasing IEC. We believe that this is due to the bulky nature of
BIM, which is attached to PPO only by a methylene linker, so that a perpendicular arrangement of BIM to
the PPO chain can be assumed. For future work, ways should be found to attach BIM via longer, more
flexible linkers, or through a connection on the terminal ends (mesityl or the benzimidazole phenyl ring),
so that chain-chain interactions are less interrupted.
Typically, the DOB is determined by analysis of the NMR data. We found a correlation between the DOB
-1
-1
and the shift of the IR band around 1186 cm for pure PPO and 1213 cm for Br-PPO87, which allows to
calculate the DOB simply by inserting the wavenumber of that band into Equation 8. While more
validation is needed, the described relation potentially can be used for online monitoring the DOB during
bromination, for example with a flow cell in an industrial process, or by precipitating samples and
measuring their spectra immediately by ATR-FTIR.
PPO24-BIM was tested in an electrolysis system, which is fed with 0.5 M KOH solution on the anode
side, but has no feed on the cathode side, to lower the relative humidity of the produced hydrogen (and
thus to lower the costs for drying gases in commercial systems). We believe that water transport to the
cathode side was not fast enough to compensate for the water losses by a) production of hydrogen, b)
humidification of the produced hydrogen, and c) by electro-osmotic drag by hydroxide ions to the anode
side. Based on this, we postulate that future membrane development should focus especially on these
parameters: a) conductivity, b) water permeability and c) electro-osmotic drag.
IR analysis after the electrolysis test revealed that the 2-mesityl-benzimidazolium groups are alkaline
stable under the operating conditions (0.5 M KOH, 50 °C), but not in 1 M KOH at 80 °C, a condition at
which also severe weight loss was observed. This indicates that more work needs to be done on the
stability of the polymer backbone, e.g. towards backbones without ether groups.
Acknowledgements
Funding from Evonik Creavis and KIST is gratefully acknowledged. The authors also thank Prof.
Ronghuan He for helpful discussions, and Dr. Robert Jan Sedelmayer for help with the synthesis.
References
[
[
1]
2]
M. Schalenbach, W. Lueke, D. Stolten, J. Electrochem. Soc. 163 (2016) F1480-F1488.
M. Carmo, D.L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen Energy 38 (2013) 4901-4934.
20

ACCEPTED MANUSCRIPT
[
[
3]
4]
K.E. Ayers, E.B. Anderson, C.B. Capuano, M. Niedzwiecki, M.A. Hickner, C.-Y. Wang, Y. Leng,
W. Zhao, ECS Trans. 45 (2013) 121-130.
W.A. Rigdon, T.J. Omasta, C. Lewis, M.A. Hickner, J.R. Varcoe, J.N. Renner, K.E. Ayers, W.E.
Mustain, J. Electrochem. En. Conv. Stor. 14 (2017) 020701-020701-8.
[
[
[
5]
6]
7]
M. Nazemi, J. Zhang, M. C. Hatzell, J. Electrochem. En. Conv. Stor. 14 (2017) 020702-020702-6.
G. Merle, M. Wessling, K. Nijmeijer, J. Membr. Sci. 377 (2011) 1– 35.
T. Kwon, J.-W. Lee, H. Cho, D. Henkensmeier, Y. Kang, S.M. Hong, C.M. Koo, Sensors
Actuators B, 214 (2015) 43–49.
[
[
[
[
[
8]
9]
10]
11]
12]
Q. Zhang, S. Li and S. Zhang, Chem. Commun. 46 (2010) 7495–7497.
M. Guo, J. Fang, H. Xu, W. Li, X. Lu, C. Lan, K. Li, J. Membr. Sci. 362 (2010) 97–104.
F. Gu, H. Dong, Y. Li, Z. Sun, F. Yan, Macromolecules 47 (2014) 6740–6747.
B. Zhang, S. Gu, J. Wang, Y. Liu, A.M. Herring, Y. Yan, RSC Adv. 2 (2012) 12683–12685.
S. Gu, R. Cai, T. Luo, Z. Chen, M. Sun, Y. Liu, G. He, Y. Yan, Angew. Chem., Int. Ed. 48 (2009)
6
499–6502.
Y. Zha, M. L. Disabb-Miller, Z. D. Johnson, M.A. Hickner, G.N. Tew, J. Am. Chem. Soc. 134
2012) 4493–4496.
[
13]
(
[
[
[
14]
15]
16]
M.G. Marino, K.D. Kreuer, ChemSusChem 8 (2015) 513 – 523.
C.G. Arges, V. Ramani, PNAS 110 (2013) 2490-2495.
A.G. Wright, J. Fan, B. Britton, T. Weissbach, H.-F. Lee, E.A. Kitching, T.J. Peckham, S.
Holdcroft, Energy Environ. Sci. 9 (2016) 2130-2142.
[
[
[
[
[
[
17]
18]
19]
20]
21]
22]
D. Henkensmeier, H.-J. Kim, H.-J. Lee, D. H. Lee, I.-H. Oh, S.-A. Hong, S.-W. Nam, T.-H. Lim,
Macromol. Mater. Eng. 296 (2011) 899-908.
D. Henkensmeier, H. Cho, H.-J. Kim, C. Nunes Kirchner, J. Leppin, A. Dyck, J.H. Jang, E. Cho,
S.-W. Nam, T.-H. Lim, Polym. Degrad. Stability 97 (2012) 264-272.
H.-J. Lee, J. Choi, J.Y. Han, H.-J. Kim, Y.-E. Sung, H. Kim, D. Henkensmeier, E. Cho, J.H. Jang,
S.J. Yoo, Polym. Bull. 70 (2013) 2619-2631.
D. Henkensmeier, H. Cho, M. Brela, A. Michalak, A. Dyck, W. Germer, N.M.H. Duong, J.H.
Jang, H.-J. Kim, S.-W. Nam, T.-H. Lim, Int. J. Hydrogen Energy 39 (2014) 2842-2853.
O.D. Thomas, K.J.W.Y. Soo, T.J. Peckham, M.P. Kulkarni, S. Holdcroft, Polym. Chem. 2 (2011)
1
641-1643.
O.D. Thomas, K.J.W.Y. Soo, T.J. Peckham, M.P. Kulkarni, S. Holdcroft, J. Am. Chem. Soc. 134
2012) 10753 - 10756.
(
[
[
[
23]
24]
25]
A. Wright, S. Holdroft, ACS Macro Lett. 3 (2014) 444-447.
J. Wang, S. Gu, R. B. Kaspar, B. Zhang, Y. Yan, ChemSusChem 6 (2013) 2079 - 2082.
Q.K. Dang, D. Henkensmeier, N.N. Krishnan, J.H. Jang, H.-J. Kim, S.W. Nam, T.-H. Lim, J.
Membr. Sci. 460 (2014) 199-205.
[
26]
I. Strużyńska-Piron, M. Jung, A. Maljusch, O. Conradi, S. Kim, J.H. Jang, H.-J. Kim, Y. Kwon,
S.W. Nam, D. Henkensmeier, Europ. Polym. J. 96 (2017) 383-392.
[
[
[
[
[
27]
28]
29]
30]
31]
T. Xu, Y. Weihua, J. Membr. Sci. 190 (2001) 159–166.
Y. Wu, C. Wu, T. Xu, X. Lin, Y. Fu, J. Membr. Sci. 338 (2009) 51–60.
E. Benedetti, D. Moscatelli, P. Vergamini, Macromol. Chem. Phys. 203 (2002) 1497–1500.
F. Hamad, I.C. Khulbe, T. Matsuura, J. Membr. Sci. 186 (2001) 281-284.
J. Yang, Q. Li, J. O. Jensen, C. Pan, L.N. Cleemann, N.J. Bjerrum, R. He, J. Power Sources 250
(
2012) 114-121.
21

ACCEPTED MANUSCRIPT
[
[
[
[
[
[
32] A.S. Hay, Prog. Polym. Sci. 24 (1999) 45–80.
33]
34]
35]
R.B. Moore III, C.R. Martin, Macromolecules 21 (1988) 1334-1339.
J. Lin, P.-H. Wu, R. Wycisk, P.N. Pintauro, ECS Trans. 16 (2008) 1195-1204.
J. Yang, C. Liu, Y. Hao, X. He, R. He, Electrochim. Acta 207 (2016) 112–119.
36] M. Mucha and M. Kryszewski, Colloid & Polymer Sci. 258 (19080) 743-752.
37]
M. Adachi, T. Navessin, Z. Xie, F.H. Li, S. Tanaka, S. Holdcroft, J. Membr. Sci. 364 (2010) 183–
93.
1
[
[
38]
39]
X. Luo, A. Wright, T. Weissbach, S. Holdcroft, J. Power Sources, 375 (2018) 442-451.
B.C. Smith, Infrared Spectral Interpretation: A Systematic Approach, CRC press, Boca Raton,
London, New York, Washington, 1998, p. 78.
[
[
40]
41]
H. Becker, W. Berger, G. Domschke, E. Fanghänel, J. Faust, M. Fischer, F. Gentz, K. Gewald, G.
Gluch, R. Mayer, K. Müller, D. Pavel, H. Schmidt, K. Schollberg, K. Schwetlick, E. Seiler, G.
Zeppenfeld, Organikum, 15 ed., VEB Deutscher Verlag der Wissenschaften, Berlin, 1976, p.122.
th
A.D. Mohanty, S.E. Tignor, J.A. Krause, Y.-K. Choe, C. Bae, Macromolecules 49 (2016) 3361–
3
372.
22

ACCEPTED MANUSCRIPT
●
●
●
●
●
2-mesityl-1-methyl-benzimidazolium (BIM) functionalised PPO membranes were prepared
-1
shift of IR band at 1190 cm correlates with degree of bromination of PPO
due to BIM's bulkiness and PPO's brittleness, only some ratios give stable membranes
-2
alkaline water electrolysis at 1.8 V gave a current density of 300 mA cm
water vapour permeability of several membranes was measured