potential membranes derived from poly (aryl hexafluoro ......high-temperature pem fuel cells p....

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Potential membranes derived from poly(aryl hexafluoro sulfone benzimidazole) and poly(aryl hexafluoro ethoxy benzimidazole) forhigh-temperature PEM fuel cells

P. Muthuraja a,1, S. Prakash a,1, A. Susaimanickam b, P. Manisankar a,*

a Department of Industrial Chemistry, Alagappa University, Karaikudi 630006, Indiab Department of Chemistry, Arumugam Pillai Seethai Ammal College, Tirupattur 630211, India

a r t i c l e i n f o

Article history:

Received 13 December 2017

Received in revised form

6 March 2018

Accepted 10 March 2018

Available online xxx

Keywords:

Poly (aryl hexafluoro sulfone

benzimidazole)

Poly (aryl hexafluoro ethoxy

benzimidazole)

Fuel cells

Proton conductivity

Stability

* Corresponding author.E-mail address: manisankarp@alagappau

1 These authors contributed equally to thihttps://doi.org/10.1016/j.ijhydene.2018.03.0580360-3199/© 2018 Hydrogen Energy Publicati

Please cite this article in press as: Muthurajand poly (aryl hexafluoro ethoxy benzimidahttps://doi.org/10.1016/j.ijhydene.2018.03.05

a b s t r a c t

Poly (aryl hexafluoro sulfone benzimidazole) and poly (aryl hexafluoro ethoxy benzimid-

azole), termed as PArF6SO2BI and PArF6OBI, are synthesized and characterized systemati-

cally. PArF6SO2BI membranes illustrate good chemical stability in terms of oxidative weight

loss due to the electron-withdrawing sulfone functional group. PArF6OPBI membranes

exhibit weak chemical stability after immersion in Fenton's solution. Many of the mem-

branes show good conductivities. Higher conductivities of 3.26 � 10�2 S cm�1 at 160 �C with

286.8 wt% acid doped level for 3:1 (2.335 mmol of 4,40-sulfonyldibenzoic acid and

7.005 mmol of 2, 2-bis(4-carboxyphenyl) hexafluoropropane) ratio of PArF6SO2BI and

7.31 � 10�2 S cm�1 with 356.9 wt% for 3:1 ratio of PArF6OBI are observed. PArF6SO2BI and

PArF6OPBI membranes exhibit good conductivity, thermal and mechanical stabilities

which are crucial requirements for high temperature fuel cells.

© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Introduction

Need for novel high temperature polymer electrolyte mem-

brane fuel cell (HTPEMFC) assumes significance today to meet

the challenges for renewable energy and climate change

problems [1]. Even though Nafion membranes, perfluorinated

sulfonic acid membranes and composite membranes are

used, the Department of Energy, US targeted only acid doped

polybenzimidazole (PBI) membranes for HTPEMFC. But the

niversity.ac.in (P. Manisas work.

ons LLC. Published by Els

a P, et al., Potential membzole) for high-temperatur8

main drawback of PBI membranes is its increased degrada-

tion. Since the membrane is the main component, it neces-

sitates synthesizing novel PBI based membranes [2e6].

In the last decade, various methods have been tried to

improve the conductivity, stability and solubility of PBI. Phos-

phoric acid doped PBI (PA-PBI) was studied extensively for

HTPEMFC due to their proton conductivity mechanism and

stability [2,7] But leaching of phosphoric acid poses main

problem and it leads to corrosion also. Tang group developed

nkar).

evier Ltd. All rights reserved.

ranes derived from poly (aryl hexafluoro sulfone benzimidazole)e PEM fuel cells, International Journal of Hydrogen Energy (2018),

mailto:[email protected]

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https://doi.org/10.1016/j.ijhydene.2018.03.058



i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 8 ) 1e1 02

the 3D gel type framework as matrix and the resultant proton

conductivity at high temperature was decreased in compari-

son with PA doped PBI membrane [8e11]. Cross-linked porous

PBI membranes were suggested to improve the mechanical

strength and oxidative stability [11e13]. Flexible spacer groups

such as ether linkages [14], fluorines [15,16], azoles [17], pyri-

dine [18], asymmetric bulky pendants (phenyl and methyl-

phenyl) [19], 4,40,5,50-tetraaminodiphenyldiphenyl ether [20]

and4,40-bibromomethenyldiphenyl ether [21]were introduced

in the PBI backbones, to make novel PBI based polymers with

improved physicochemical properties. Yang et al. developed

the sulfone linked PBI and its copolymer with good solubility

[22]. However, these approaches have some problem with the

tedious synthetic procedures, poor solubility, cross-linking

during polymerization and poor mechanical integrity.

Recently, several PBI composite membranes have been devel-

oped, i.e. PBI with SPEEK [23], 1-(3-trimethoxysilylpropyl)-3-

methylimidazolium chloride [24], dispersion of graphene

oxide [25,26], and inorganic fillers such as SiO2 [27], ZrP [28],

Fe2TiO5 nanoparticles [29], mesoporous silica [30,31], and

cerium sulfophenyl phosphate [32] composite membranes

have been demonstrated to for improved conductivity, and

stabilities properties. Moreover, perovskite-type SrCeO3 [33],

CaTiO3 [34] and BaZrO3 [35] based PBI composite membranes

exploited for enhanced electrochemical properties of high

temperature proton exchange membranes. While this earlier

works have indeed yielded improvements in conductivity and

acid doping levels of membrane, some persistent challenges

remain as lowmembrane dimensional-mechanical stability.

Theoretically, fluorinated polymers are likely to have

higher stability and increased acid strength compared with

their non-fluorinated polymers [36]. Hence in the search of a

new membrane with higher physicochemical characteristics,

we focus in this work, the synthesis and characterization of

new partially-fluorinated polymers with sulfone or ether

linkage in the PBI backbone. Thiswork reports the synthesis of

two poly (aryl hexafluoro sulfone benzimidazole) (PArF6SO2BI)

and poly (aryl hexafluoro ethoxy benzimidazole) (PArF6OBI) by

polycondensation reaction between bis(4-carboxyphenyl)

hexafluoro propane, 3,30-diamino benzidine, sulfonyl diben-

zoic acid or oxybisbenzoic acid and characterizations.

Experimental

Instrumentation

The 13C and 15N NMR spectra were taken at 300 and 75 MHz

respectively using Bruker NMR spectrometer. The membrane

morphology was examined by a high resolution scanning

electron microscopy (FESEM) (FEI Quanta 250 Microscope,

Netherland). Fourier transform infrared (FTIR) spectra were

recorded using KBr pellet using Nicolet 5700 spectrophotom-

eter (Thermo Electron Co., USA). Dynamic mechanical anal-

ysis (DMA) was used to determine glass transition

temperature for the prepared membrane using Thermal

Analysis 2980DMA in a temperature range 100e400 �C. Tensiletests of the membranes were carried out on a CMT-8500

electro-mechanical universal tester (SANS), and the samples

were directly mounted to the sample clamps and stretched at

Please cite this article in press as: Muthuraja P, et al., Potential memband poly (aryl hexafluoro ethoxy benzimidazole) for high-temperaturhttps://doi.org/10.1016/j.ijhydene.2018.03.058

a speed of 10 mmmin�1. TGA experiments were carried out in

the TA instruments Inc., onmodel SDT Q600 by heating under

nitrogen condition using at 10 �C min�1. The inherent vis-

cosity of the obtained polymers was measured using an

Ubbelohde viscometer with a concentration of 5 g L�1 in 96 wt

% sulfuric acid at 30 �C. Poly[2,20-(m-phenylene)-5,50-benz-imidazole] (mPBI) was synthesized in the laboratory using the

method described earlier [37,38] and the dried polymer has an

inherent viscosity value of 1.10 dL g�1.

Synthesis of polymers and membrane fabrications

PArF6SO2BI and PArF6OBI were prepared by condensation

polymerization of 3,30-diaminobenzidine (DAB) (97% Tokyo

Kasei, TCI), 2,2-bis(4-carboxyphenyl) hexafluoropropane (95%

Alfa Aesar), and 4,40-sulfonyldibenzoic acid (97%Alfa Aesar) or

oxybisbenzoic acid (98% Alfa Aesar) in a presence of poly-

phosphoric acid (PPA, Aldrich). The synthetic reaction is

shown in Scheme 1.

A 500 mL, three-necked, round-bottom flask was set with

an overhead mechanical stirrer. A thermal couple was con-

nected with thermosensor and two glass tubes for the nitro-

gen inlet and outlet were inserted. A 9.3mmol of DABwas first

dissolved in 60 g PPA at 120 �C. Then, three quantities of BCHFP

(4.67 mmol, 2.335 mmol, 7.005 mmol) and SDBA (4.67 mmol,

7.005 mmol, 2.335 mmol) or OBBA (4.67 mmol, 7.005 mmol,

2.335 mmol) were added independently. The mixture was

stirred at 220 �C in the nitrogen atmosphere for 24 h to follow

polymerization. After the reaction, the product was poured

into water and the polymer was separated and washed with

dilute sodium bicarbonate solution to neutralize excess acid

in the polymer. The polymer was washed thoroughly with

water and methanol, successively, followed by drying under

vacuum to obtain the polymer powder. The fabrication of

membranes was done by solution casting method by pouring

2 wt% polymer solutions in DMSO onto glass plate andmaking

film using a Gardner film applicator. The film was dried at

80 �C for 24 h. The resultant membranes were then peeled off

and soaked in distilled water at 80 �C for 2 h and further dried

at 200 �C for 1 h. The thickness of the membranes was

measured and maintained in the range 80e100 mm.

Physico-electrochemical characterizations

Synthesizedmembraneswere immersed in 14.0M phosphoric

acid (PA) at 90 �C for 12 h. After that, the membranes were

cleaned with a tissue paper to eliminate the extra acid on the

membrane surface and dried at 110 �C for 4 h. The PA doping

of the membrane (%) was determined by weight gain from the

doping and calculated according to the following Eq. (1):

PA doping levelð%Þ ¼�WPA �W

W

��100 (1)

whereWPA andW are the weight of driedmembrane after and

before doping, respectively.

Water uptake of the membranes was studied to ascertain

the stability of the membranes at RT with water. Membrane

samples were immersed in water for 24 h, subsequent to the

water absorption, the residual water from the samples surface

was removed by the absorption using paper [39]. The water




Scheme 1 e A synthetic method for PArF6SO2BI and PArF6OBI.

i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 8 ) 1e1 0 3

uptake of the membranes were then recorded and calculated

using the following Eq. (2):

Water uptakeð%Þ ¼�Ww �Wd

Wd

��100 (2)

where Ww and Wd are the weights of the membrane at the

swelling and dehydrated state, respectively.

The oxidative ability of the membrane was examined by

Fenton's test. The membrane was immersed in a 3.0 wt%

hydrogen peroxide aqueous solution containing 4 ppm Fe2þ at

80 �C. Every 20e24 h, the membranes were taken out, washed

completely with distilled water and dried at 110 �C for 10 h.

Then, the membrane samples were transferred to fresh Fen-

ton solutions again for continued testing.

The proton conductivity measurement was carried out

using a CHI760 electrochemical workstation (CH Instruments,

USA). The measurement of conductivity completely followed

that has been described in previous study [40,41]. The mem-

brane was kept between two in-house made stainless steel

circular electrodes (1.0 cm2) and connected with Pt wire as

current collector. Direct current (dc) and sinusoidal alter-

nating currents were applied to the above electrodes for


monitoring the frequency at 1 mA s�1 scan rate within 105 to

1 Hz. The membrane resistance was measured using Fit and

Simulation method from Nyquist plots. The measurements

were taken at different temperatures from 90 to 160 �C. Theconductivity was calculated using the following equation.

k ¼ LA

� 1R

(3)

Where k is a proton conductivity of themembrane (S cm�1)

and R, L, and A are the measured resistance (U), thickness

(cm), and cross-sectional area of the membrane (cm2),

respectively.

Conductivity follows Arrhenius equation for hopping-like

conduction mechanism which depends on temperature:

In k ¼ In ko � Ea

RT(4)

where k is the proton conductivity of the membrane (S cm�1),

ko is the pre-exponential factor (S K�1 cm�1), Ea is the proton

conducting activation energy (kJ mol�1), R is the ideal gas

constant (J mol�1 K�1) and T is the temperature (Kelvin). The

minimum energy (Ea) required for proton conduction is ob-

tained from the slope of linear fit of Eq. (4).




Fig. 1 e FTIR spectra of PArF6SO2BI and PArF6OBI

membranes.


Results and discussion

Solubility study

For the monomer concentration of 2,2-bis(4-carboxyphenyl)

hexafluoropropane, and 4,40-sulfonyldibenzoic acid or oxy-

bisbenzoic acid was varied from 2.335 mmol to 7.005 mmol in

PPA. Three different polymers from the monomers of 4,40-sulfonyldibenzoic acid and 2,2-bis(4-carboxyphenyl) hexa-

fluoropropane in the molar ratio of 1:1, 1:3 and 3:1 were syn-

thesized (Scheme 1) and designated as 1:1 PArF6SO2BI, 1:3

PArF6SO2BI and 3:1 PArF6SO2BI. In a similar manner, three

more polymerswere synthesized fromoxybisbenzoic acid and

2,2-bis(4-carboxyphenyl) hexafluoropropane in the ratio 1:1,

1:3 and 3:1 and designated as 1:1 PArF6OBI, 1:3 PArF6OBI and

3:1 PArF6OBI respectively. The inherent viscosities were in

between 1.45 and 1.75 dL g�1. The solubility of PArF6SO2BI and

PArF6OBI was tested with solvents such as DMAc, DMSO, and

NMP at 130 �C (Table 1). All the polymers showed good solu-

bility in DMSO and poor solubility in NMP. PArF6SO2BI showed

good solubility in DMAc while PArF6OBI were moderately

soluble [40]. The presence of sulfone linkage in the molecular

chain resulted in increased solubility in DMAc and DMSO.

Spectral investigations

FTIR spectra of the membranes were presented in Fig. 1. FTIR

spectrum of PArF6SO2BI shows a broad peak at 3362 cm�1

which is due to formation imidazole rings (N-H stretching

vibration). The peaks at 1596 cm�1 and 1462 cm�1 correspond

to the formation of C]N and C]C stretch, revealed the

presence of conjugation between benzene and the imidazole

ring. The strong peak observed at 2922 cm�1 is attributed to

the C-H stretching vibration. The characteristic band at

1249 cm�1 is assigned to the O-S-O stretching vibration. The

peak observed at 1172 cm�1 is due to the C-F asymmetric

stretching vibration. The peaks at 937 cm�1, 803 cm�1 and

731 cm�1 are due to C-C bending vibration, C-F bending vi-

bration and C- S stretching vibration, respectively. Further,

FTIR spectrum of PArF6OBI shows a broad peak at 3349 cm�1

due to N-H stretching vibration. The band at 1630 cm�1 and

1485 cm�1 correspond to the formed C]N and C]C stretching

confirming the presence of conjugation between benzene and

Table 1 e Acid doping percent, water uptake, conductivity andmembranes doped in 14.0 M H3PO4 at 90 �C.

Membranes Water uptake (wt%) Acid doping (wt%) k at 160 �

1:1 PArF6SO2BI 13.3 230.9

1:3 PArF6SO2BI 9.5 171.4

3:1 PArF6SO2BI 11.3 286.8

1:1 PArF6OBI 17.9 111.0

1:3 PArF6OBI 22.1 312.0

3:1 PArF6OBI 12.2 356.9

þþ Good solubility, þ Moderate solubility, and - Insolubility.a PArF6SO2BI and PArF6OBI without doping of acid.


the imidazole ring. The peaks at 2958, 1230, 1152, 979, 876 and

740 cm�1 are assigned to C-H stretching, C-O-C stretching, C-F

asymmetric stretching, C-C bending, C-F bending and C- S

stretching vibrations respectively.

The solid state 15N and 13C NMR spectra are presented in

Fig. 2A and B for PArF6SO2BI and PArF6OBI (Table S1,

supplementary information). 15N NMR spectrum shows a

single strong signal at 195 ppm which is mainly attributed to

the nitrogen atom of imidazole ring (Fig. 2B). The signal at

146 ppm (denoted as c) in the 13C NMR spectrum represents

the attachment of sulfone substituted carbon to phenylene

ring and signal at 148 ppm (denoted as a) corresponds to the

mechanical strength of PArF6SO2BI and PArF6OBI

C (�10�2 S cm�1) aSolubility test at130 �C

Maximum load/MPa

DMAc DMSO NMP

2.70 þþ þþ - 32.0

2.92 þþ þþ - 51.0

3.26 þþ þþ - 18.0

3.19 þ þþ - 22.6

5.67 þ þþ - 12.5

7.31 þ þþ - 8.2




Fig. 2 e (A) Solid state 13C NMR, and (B) solid state 15N NMR of synthesized polymers (Inset Fig. 2, chemical structure of

polymers and notation of m and n are 1 and 1 equivalent ratio of the reactants).


imidazole carbon connecting benzene rings in the benzimid-

azole system (Fig. 2A). The signal at 147 ppm represents the

hexafluoro propane substituted carbon attached to phenylene

ring (denoted as b). The signals at 141.9, 132 and 127 ppm are

due to the sulfone substituted carbons (denoted as e, k andm).

Hexafluoro substituted carbons are observed at 135, 128 and

120 ppm (denoted as h, l and o). The signals at 134, 119 and

117 ppm (denoted as i, q and p) are assigned to aromatic car-

bons bound to the nitrogen atoms and other peaks at 136, 133

and 125 ppm (denoted as g, j and n) are due to the other


aromatic sulfone substituted carbons. This result suggests

that amine and carboxyl groups are involved in the conden-

sation reaction, followed by the polymerization of sulfonyl

benzene and hexafluoro propane takes place to give

PArF6SO2BI.

Fig. 2B shows a single strong signal at 188 ppm which is

mainly attributed to the nitrogen atom of imidazole group.

The signal at 156 and 152 ppm (denoted as a, b) in the 13C NMR

spectrum represents the attachment of oxy substituted car-

bon to phenylene ring and signal at 147 ppm (denoted as c)




Fig. 4 e DMA curves of PArF6SO2BI and PArF6OBI

membranes at different temperatures.


corresponds to the imidazole carbon connecting benzene

rings in the benzimidazole system (Fig. 2A). The signal at 145,

120 and 119 represents the hexafluoro propane substituted

carbons attached to phenylene ring (denoted as d, k and l). The

signals at 127 and 113 ppm are due to the oxy substituted

carbons of aromatic ring (denoted as h and o). Other oxy

substituted carbons directly attached to imidazole ring are

observed at 121, 114 and 111 ppm (denoted as j, n and p). The

signals at 142 and 135 ppm (denoted as e and f) are assigned to

aromatic carbons bound to the nitrogen atoms and other

peaks at 123, 116 and 113 ppm (denoted as l, m and o) are due

to the other aromatic carbons in benzimidazole system. From

this study, the amine and carboxyl groups involved in the

condensation reaction, followed by the polymerization of oxy

benzene and hexafluoropropane to give PArF6OBI is

ascertained.

Fig. 3 shows SEM images of the surface section of all

membranes. Typically all membranes showed uniform and

dense surface. From the SEM images, it is observed that all the

membranes have homogeneous surface.

Mechanical, thermal and chemical stabilities

Dynamical mechanical analysis (DMA) is a complementary

and widely used characterization technique for polymers.

Commonly, membranemechanical properties are specified by

elastic modulus, tensile strength, and ductility. Table 1 shows

the mechanical strength of PArF6SO2BI and PArF6OBI mem-

branes measured at room temperature. All the three

Fig. 3 e SEM images of PA-doped different membranes variant: (

(d) 1:1 PArF6OBI, (e) 3:1 PArF6OBI, and (f) 1:3 PArF6OBI.


PArF6SO2BI membranes and 1:3 PArF6OBI showed good me-

chanical strength. Increase in the concentration of hexafluo-

ride group in PArF6OBI increases the mechanical strength

substantially. The samples were also tested to a periodic

mechanical strain at constant rate and different tempera-

tures. The storage modulus E0 (elastic response) and loss

modulus E00 (viscous response) are measured as a function of

temperature for all membranes (Fig. 4). The storage modulus

values are 3800 MPa (1:3 PArF6SO2BI at 200 �C), and 3780 MPa

a) 1:1 PArF6SO2BI, (b) 3:1 PArF6SO2BI, and (c) 1:3 PArF6SO2BI,




100

)%(

a b c d e f g


(1:1 PArF6SO2BI at 200 �C) and 2 MPa (3:1 PArF6SO2BI at 200 �C)for PArF6SO2BI membranes, whereas ether linkedmembranes

storage modulus are 250 MPa (3:1 PArF6OBI at 200 �C), and247 MPa (1:3 PArF6OBI at 200 �C) and 3000 MPa (1:1 PArF6OBI at

200 �C). The resulted 3:1 PArF6 SO2BI, 1:1 PArF6 SO2BI, and 1:1

PArF6OBI membranes showed substantial mechanical rein-

forcement and retains the elastic nature even at increased

temperatures. Other membranes are not having mechanical

stability i.e., poor elastic nature with raised temperature.

Further, the glass transition temperature (Tg) was found from

the peak of tan (d), for all membranes and they exhibited a

well-defined relaxation peak in between 275 �C and 315 �C,which are is assigned to the glass transition temperature (Tg)

of the polymer chains. Generally, high mobility of the back-

bone, cluster networkwas showed by high value loss of tan (d).

The tan (d) value for 3:1 PArF6 SO2BI and 1:1 PArF6 SO2BI

membranes showed 0.065 and 0.045 at 275 �C, respectively,which are better than that for othermembranes [42]. Thus, the

1:3 PArF6 SO2BI and 1:1 PArF6 SO2BI membranes had more

elastic nature and can withstand higher temperatures

compared to other membranes. From these studies it is

concluded that the 1:3 PArF6 SO2BI, 1:1 PArF6 SO2BI, and 1:1

PArF6OBI membranes can very well be used in fabrication of

HTPEMFC.

TGA curves of different PArF6SO2BI, PArF6OBI membranes

andm-PBI are presented in Fig. 5. The evaporation of absorbed

water was observed at temperature around 100 �C for all

membranes. The percentage loss was found to be 10 wt% and

13 wt% for 3:1 PArF6OBI and 1:3 PArF6OBI membranes

respectively. Other polymer membranes attained 3e6%

weight loss. It suggests that the 3:1 PArF6OBI and 1:3 PArF6OBI

membranes have higher capacity for water uptake compared

to other membranes studied. In the temperature range of

150e250 �C, there is weight loss around 10.1 wt% for 1:3 PArF6SO2BI and 1:1 PArF6OBI membranes which indicates the

beginning of decomposition. Thus the thermal stability of

these membranes is up to 250 �C which is higher than that of

many membranes used in HTPEMFC. But, m-PBI were also

showed good thermal stability than the 1:3 PArF6OBI, 3:1

PArF6OBI, and 1:3 PArF6 SO2BI, and 1:3 PArF6 SO2BI mem-

branes. Overall ~23% weight loss at 250e450 �C can be

observed indicated that the membrane integrity remains un-

broken for 1:1 PArF6 SO2BI and 1:1 PArF6 OBI membranes [43].

0

20

40

60

80

100

120

50 150 250 350 450 550 650 750 850 950

m-PBI

Temperature (oC)

Wei

ght l

oss

(%)

1:1 PArF6OBI

1:3PArF6OBI

ab

cdef

g

Fig. 5 e TGA curves of PArF6SO2BI and PArF6OBI

membranes.


The oxidative stability of the membranes affects the long-

termoperation of fuel cells and it is of great importance for the

life time and the performance. Well known that the peroxy

radicals can attack themembranes and cause the degradation

of membranes. The tolerance nature against the peroxy

radical induced degradation is called oxidative stability and

tested by Fentons reagent. One of the major drawbacks of the

m-PBI membranes used in fuel cells is its poor oxidative

chemical stability compared to other [44,45]. PArF6SO2BI and

PArF6OBI membranes have better radical resistance because

they have aromatic rings and chemically strong bonding be-

tween carbon, sulfur and oxygen [46]. Fig. 6 shows the test

results of different membranes and m-PBI in Fenton reagent

(3%H2O2 containing 4.0 ppm FeSO4) at 80 �C for comparison. It

is seen that the all PArF6SO2BI membranes displayed signifi-

cant mass retention than the m-PBI and other membranes.

Thismay be attributed to the electron-withdrawing properties

of the sulfone group, since radicals predominantly attract

electron-rich compounds [39]. 1:1 PArF6OBI membrane also

showed good mass retention. However, 3:1 and 1:3 PArF6OBI

membranes have showed poor oxidative stability in compared

to the m-PBI after about 120 h Fenton test. The presence of

sulfone/oxygen and fluorine in the membranes leads to sig-

nificant oxidative stability [36,47].

Proton conductivity and Arrhenius equation

The acid doping level acts a main role in proton conductivity

for PBI membranes, thus all membranes were immersed in

14.0 M PA and kept at different temperatures for 12 h. The

proton conductivity of membranes at different temperature

and doping level are presented in Fig. 7A. For the PArF6SO2BI

and PArF6OBI membranes, the temperature, and PA doping

level influenced the proton conductivity significantly. At 90 �C,the conductivities of membranes are 1.52 � 10�2 S cm�1 (1:1

PArF6SO2BI with 230.9 wt%), 2.14� 10�2 S cm�1 (3:1 PArF6SO2BI

with 286.8 wt%), and 1.91 � 10�2 S cm�1 (1:3 PArF6SO2BI with

171.4 wt%), and 1.78 � 10�2 S cm�1 (1:1 PArF6OBI with 111.0 wt

%), 1.94 � 10�2 S cm�1 (1:3 PArF6OBI with 312.0 wt%), and

0 20 40 60 80 100 120 1400

20

40

60

80noitneterssa

M

Time (hour)

Fig. 6 e Fenton test results of PA-doped different

membranes at in 3 wt% H2O2 solution containing 4 ppm

Fe2þ at 80 �C: (a) 1:1 PArF6 SO2BI, (b) 3:1 PArF6 SO2BI, and (c)

1:3 PArF6 SO2BI, (d) 1:1 PArF6OBI, (e) 3:1 PArF6OBI, and (f) 1:3

PArF6OBI.




Fig. 7 e The proton conductivities for the PA-doped

different membranes (A) at temperatures variant, and (B)

Arrhenius plot.


2.19 � 10�2 S cm�1 (3:1 PArF6OBI with 356.9 wt%). It is found

that the 3:1 PArF6OBI membrane exhibits highest conductivity

at 90 �C. The conductivity increases with increasing in the

temperature due to speed up of protonmobility. At 160 �C, theproton conductivities of membranes are 2.70 � 10�2 S cm�1

(1:1 PArF6SO2BI with 286.8 wt%), 3.26 � 10�2 S cm�1 (3:1

PArF6SO2BI with 286.8 wt%), and 2.92 � 10�2 S cm�1 (1:3

PArF6SO2BI with 171.4 wt%), 3.19 � 10�2 S cm�1 (1:1 PArF6OBI

with 111.0 wt%), 5.67� 10�2 S cm�1 (1:3 PArF6OBI with 312.0 wt

%), and 7.31 � 10�2 S cm�1 (3:1 PArF6OBI with 356.9 wt%). This

study reveals that PArF6SO2BI membranes showed lower

proton conductivity compared to the PArF6OBI membranes.

The conductivity values from this work are higher than that of

other PBI membranes reported [48e55]. The high conductivity

of 3:1 PArF6OBI and 1:3 PArF6SO2BI was aroused by the more

fluorine structure in the matrix. In conclusion, prepared

membranes could efficiently enhance the proton conductiv-

ity; displayed excellent combined properties and may become

a candidate PEM for HT-PEMFC applications.

For hopping-like conduction mechanism dependent on

temperature, conductivity follows Arrhenius equation [56].

The Arrhenius plot represented through temperature depen-

dence of proton conductivity of the all membranes in Fig. 7B.

The minimum energy (Ea) required for proton conduction is


obtained from the slope of linear fit of Eq. (3). Fig. 7B shows

Arrhenius plots of ionic conductivity for different membranes

and the activation energies calculated in the temperature

range 90e160 �C. The data fit fairly well the Arrhenius equa-

tion which implies that the proton transport is mainly regu-

lated by Grotthus mechanism occurring as a result of proton

hopping between protonated part of polymer chains and non-

protonated part of the modifier chains or vice versa. The

activation energies, calculated from the slope of the curves,

are 10.8 kJ mol�1 (1:1 PArF6SO2BI), 7.40 kJ mol�1 (3:1 PArF6-SO2BI), 7.69 kJ mol�1 (1:3 PArF6SO2BI), and10.97 kJ mol�1 (1:1

PArF6OBI), 20.28 kJ mol�1 (1:3 PArF6OBI), 22.8 kJ mol�1 (3:1

PArF6OBI). It indicates that the activation energy of conduc-

tion is dependent on the membrane properties, such as hy-

drophilicity, which was slightly higher than the previous

reports [57e59].

Conclusions

We presented the synthesis of PArF6SO2BI and PArF6OBI

membranes via condensation reaction. Most of the mem-

branes exhibited good thermal, chemical and mechanical

stabilities. Synthesized membranes showed good conductiv-

ity. Higher conductivity of 3.26 � 10�2 S cm�1 at 160 �C with

acid doped level of 286.8 wt% for 3:1 PArF6SO2BI and

7.31 � 10�2 S cm�1 at 160 �C with 356.9 wt% for 3:1 PArF6OBI is

observed. The as-synthesized PArF6SO2BI and PArF6OBI

membranes exhibit improved proton conductivity. Thus it is

concluded that the PArF6SO2BI and PArF6OBI membranes

posses better characteristics to be used as polymer electrolyte

membrane in the fabrication of HTPEMFC.

Acknowledgements

One of the authors, Dr. S. Prakash (File no: 201516-PDFSS-2015-

17-TAM-10968) is thankful to University Grants Commission

(UGC), New Delhi, for providing Post Doctoral Research

Fellowship. Authors acknowledge to University Grants Com-

mission (UGC), New Delhi, for providing the BSR Faculty

Fellowship (No. F. 18-1/2011(BSR)). Authors also thank to Dr. K.

Krishnamoorthy (Scientist, CSIR-NCL, Pune) and Dr. Tushar

Jana (Associate Professor, University of Hyderabad) for sup-

porting the analysis.

Appendix A. Supplementary data

Supplementary data related to this article can be found at

https://doi.org/10.1016/j.ijhydene.2018.03.058.

r e f e r e n c e s

[1] Chuang SW, Hsu SLC. Synthesis and properties of a newfluorine-containing polybenzimidazole for high-temperature fuel-cell applications. J Polym Sci A2006;44:4508e13.



http://refhub.elsevier.com/S0360-3199(18)30819-X/sref1








[2] Couto RN, Linares JJ. KOH-doped polybenzimidazole foralkaline direct glycerol fuel cells. J Membr Sci2015;486:239e47.

[3] Li L-Y, Yu B-C, Shih C-M, Lue SJ. Polybenzimidazolemembranes for direct methanol fuel cell: acid-doped oralkali-doped? J Power Sources 2015;287:386e95.

[4] Hou H, Sun G, He R, Sun B, Jin W, Liu H, et al. Alkali dopedpolybenzimidazole membrane for alkaline direct methanolfuel cell. Int J Hydrogen Energy 2008;33:7172e6.

[5] Sana B, Jana T. Polymer electrolyte membrane frompolybenzimidazoles: influence of tetraamine monomerstructure. Polymer 2018;137:312e23.

[6] Li S, Zhu X, Liu D, Sun F. A highly durable long side-chainpolybenzimidazole anion exchange membrane for AEMFC. JMembr Sci 2018;546:15e21.

[7] XiaoL,ZhangH,ScanlonE,RamanathanLS,ChoeEW,RogersD,etal.Hightemperaturepolybenzimidazole fuelcellmembranesvia a sol-gel process. ChemMater 2005;17:5328e33.

[8] Tang Q, Huang K, Qian G, Benicewicz BC. Phosphoric acid-imbibed three-dimensional polyacrylamide/poly(vinylalcohol) hydrogel as a new class of high-temperature protonexchange membrane. J Power Sources 2013;229:36e41.

[9] Tang Q, Cai H, Yuan S, Wang X, Yuan W. Enhanced protonconductivity from phosphoric acid-imbibed crosslinked 3Dpolyacrylamide frameworks for high-temperature protonexchange membranes. Int J Hydrogen Energy2013;38:1016e26.

[10] Tang Q, Yuan S, Cai H. High-temperature proton exchangemembranes from microporous polyacrylamide cagedphosphoric acid. J Mater Chem A 2013;1:630e6.

[11] Tang Q, Wu J, Tang Z, Li Y, Lin J. High-temperature protonexchange membranes from ionic liquid absorbed/dopedsuperabsorbents. J Mater Chem 2012;22:15836e44.

[12] Shen CH, Jheng LC, Hsu SLC, Wang JTW. Phosphoric acid-doped cross-linked porous polybenzimidazole membranesfor proton exchange membrane fuel cells. J Mater Chem2011;21:15660e5.

[13] Jingshuai Y, Haoxing J, Liping G, Jin W, Yixin X, Ronghuan H.Fabrication of crosslinked polybenzimidazole membranes bytrifunctional crosslinkers for high temperature protonexchange membrane fuel cells. Int J Hydrogen Energy2018;43:3299e307.

[14] Wang S, Zhao C, Ma W, Zhang G, Liu Z, Ni J, et al. Preparationand properties of epoxy-cross-linked porouspolybenzimidazole for high temperature proton exchangemembrane fuel cells. J Membr Sci 2012;411:54e63.

[15] Kim TH, Kim SK, Lim TW, Lee JC. Synthesis and properties ofpoly(aryl ether benzimidazole) copolymers for high-temperature fuel cell membranes. J Membr Sci2008;323:362e70.

[16] Li Q, Rudbeck HC, Chromik A, Jensen JO, Pan C, Steenberg T,et al. Properties, degradation and high temperature fuel celltest of different types of PBI and PBI blend membranes. JMembr Sci 2010;347:260e70.

[17] Kumbharkar SC, Islam MN, Potrekar RA, Kharul UK.Variation in acid moiety of polybenzimidazoles:investigation of physico-chemical properties towards theirapplicability as proton exchange and gas separationmembrane materials. Polymer 2009;50:1403e13.

[18] Kim SK, Kim TH, Jung JW, Lee JC. Polybenzimidazolecontaining benzimidazole side groups for high-temperaturefuel cell applications. Polymer 2009;50:3495e502.

[19] Fang J, Lin X, Cai D, He N, Zhao J. Preparation andcharacterization of novel pyridine-containingpolybenzimidazole membrane for high temperature protonexchange membrane fuel cell. J Membr Sci 2016;502:29e36.

[20] Lia X, Maa H, Shena Y, Hub W, Jianga Z, Liua B, et al.Dimensionally-stable phosphoric acid-doped


polybenzimidazoles for high-temperature proton exchangemembrane fuel cells. J Power Sources 2016;336:391e400.

[21] Chena J-C, Chen P-Y, Liu YC, Chen K-H. Polybenzimidazolescontaining bulky substituents and ether linkages for high-temperature proton exchange membrane fuel cellapplications. J Membr Sci 2016;513:270e9.

[22] Yue Z, Cai Y-B, Xu S. Phosphoric acid-doped cross-linkedsulfonated poly(imide-benzimidazole) for proton exchangemembrane fuel cell applications. J Membr Sci 2016;501:220e7.

[23] Song M, Lu X, Li Z, Liu G, Yin X, Wang Y. Compatible ioniccrosslinking composite membranes based on SPEEK and PBIfor high temperature proton exchange membranes. Int JHydrogen Energy 2016;41:12069e81.

[24] Tian X, Wang S, Li J, Liu F, Wang X, Chen H, et al. Compositemembranes based on polybenzimidazole and ionic liquidfunctional SieOeSi network for HT-PEMFC applications. Int JHydrogen Energy 2017;42:21913e21.

[25] Uregen N, Pehlivanoglu K, Ozdemir Y, Devrim Y.Development of polybenzimidazole/graphene oxidecomposite membranes for high temperature PEM fuel cells.Int J Hydrogen Energy 2017;42:2636e47.

[26] Cai Y, Yue Z, Teng X, Xu S. Radiation grafting graphene oxidereinforced polybenzimidazole membrane with a sandwichstructure for high temperature proton exchange membranefuel cells in anhydrous atmosphere. Euro Polym J 2018.https://doi.org/10.1016/j.eurpolymj.2018.02.020.

[27] Devrim Y, Devrim H, Erogluc I. Polybenzimidazole/SiO2

hybrid membranes for high temperature proton exchangemembrane fuel cells. Int J Hydrogen Energy2016;41:10044e52.

[28] Ozdemir Y, Uregen N, Devrim Y. Polybenzimidazole basednanocomposite membranes with enhanced protonconductivity for high temperature PEM fuel cells. Int JHydrogen Energy 2017;42:2648e57.

[29] Moradi M, Mohe A, Javanbakht M, Hooshyari K. Experimentalstudy and modeling of proton conductivity of phosphoricacid doped PBI-Fe2TiO5 nanocomposite membranes for usingin high temperature proton exchange membrane fuel cell.Int J Hydrogen Energy 2016;41:2896e910.

[30] Lia SW, Lin HL, Yu TL, Lee LP, Weng BJ. Hydrogen releasefrom ammonia borane embedded in mesoporous silicascaffolds: SBA-15 and MCM-41. Int J Hydrogen Energy2012;37:14393e404.

[31] Kuo Y-J, Lin H-L. Effects of mesoporous fillers on propertiesof polybenzimidazole composite membranes for high-temperature polymer fuel cells. Int J Hydrogen Energy2018;43:4448e57.

[32] Peng S, Zhongfang L, Feilong D, Suwen W, Xiaoyan Y,Yuxin W. High temperature proton exchange membranesbased on cerium sulfophenyl phosphate dopedpolybenzimidazole by end-group protection and hot-pressing method. Int J Hydrogen Energy 2017;42:486e95.

[33] Shabanikia A, Javanbakht M, Amoli HS, Hooshyari K,Enhessari M. Polybenzimidazole/strontium ceratenanocomposites with enhanced proton conductivity forproton exchange membrane fuel cells operating at hightemperature. Electrochim Acta 2015;154:370e8.

[34] Hooshyari K, Javanbakht M, Shabanikia A, Enhessari M.Fabrication BaZrO3/PBI-based nanocomposite as a newproton conducting membrane for high temperature protonexchange membrane fuel cells. J Power Sources2015;276:62e72.

[35] Muthuraja P, Prakash S, Shanmugam VM, Radhakrishnan S,Manisankar P. Novel perovskite structured calcium titanate-PBI composite membranes for high-temperature PEM fuelcells: synthesis and characterizations. Int J Hydrogen Energy2018;43:4763e72.





















































































































https://doi.org/10.1016/j.eurpolymj.2018.02.020

























































[36] Yang J, Li Q, Cleemann LN, Xu C, Jensen JO, Pan C, et al.Synthesis and properties of poly(aryl sulfonebenzimidazole) and its copolymers for high temperaturemembrane electrolytes for fuel cells. J Mater Chem2012;22:11185e95.

[37] Dhara MG, Banerjee S. Fluorinated high-performancepolymers: poly(arylene ether) and aromatic polyimidescontaining trifluoromethyl groups. Prog Polym Sci2010;35:1022e77.

[38] Sannigrahi A, Arunbabu D, Jana T. Thermoreversible gelationof polybenzimidazole in phosphoric acid. Macromol RapidCommun 2006;27:1962e7.

[39] Sannigrahi A, Arunbabu D, Sankar RM, Jana T. Aggregationbehavior of polybenzimidazole in aprotic polar solvent.Macromolecules 2007;40:2844e51.

[40] Prakash S, Charan C, Singh AK, Shahi VK. Mixed metalnanoparticles loaded catalytic polymer membrane forsolvent free selective oxidation of benzyl alcohol tobenzaldehyde in a reactor. Appl Catal B 2013;132:62e9.

[41] Chuang SW, Hsu SLC, Liu YH. Synthesis and properties offluorine-containing polybenzimidazole/silicananocomposite membranes for proton exchange membranefuel cells. J Membr Sci 2007;305:353e63.

[42] Sannigrahi A, Arunbabu D, Sankar RM, Jana T. Tuning themolecular properties of polybenzimidazole bycopolymerization. J Phys Chem 2007;111:12124e32.

[43] Jalani NH, Dunn K, Datta R. Synthesis and characterization ofNafion®-MO2 (M¼Zr, Si, Ti) nanocomposite membranes forhigher temperature PEM fuel cells. Electrochim Acta2005;51:553e60.

[44] Kannan R, Kagalwala HN, Chaudhari HD, Kharul UK,Kurungota S, Pillai VK. Improved performance ofphosphonated carbon nanotubeepolybenzimidazolecomposite membranes in proton exchange membrane fuelcells. J Mater Chem 2011;21:7223e31.

[45] Wang S, Zhao C, Ma W, Zhang N, Zhang Y, Zhang G, et al.Silane-cross-linked polybenzimidazole with improvedconductivity for high temperature proton exchangemembrane fuel cells. J Mater Chem A 2013;1:621e9.

[46] Han M, Zhang G, Liu Z, Wang S, Li M, Zhu J, et al. Cross-linkedpolybenzimidazole with enhanced stability for hightemperature proton exchange membrane fuel cells. J MaterChem 2011;21:2187e93.

[47] Kim S, Tighe TB, Schwenzer B, Yan J, Zhang J, Liu J, et al.Chemical and mechanical degradation of sulfonatedpoly(sulfone) membranes in vanadium redox flow batteries. JAppl Electrochem 2011;41:1201e13.


[48] Hajdok I, Atanasov V, Kerres J. Perfluoro-p-xylene as a NewUnique monomer for highly stable arylene main-chainionomers applicable to low-T and high-T fuel cellmembranes. Polymers 2015;7:1066e87.

[49] Rewar AS, Chaudhari HD, Illathvalappil R, Sreekumar K,Kharul UK. New approach of blending polymeric ionic liquidwith polybenzimidazole (PBI) for enhancing physical andelectrochemical properties. J Mater Chem A 2014;2:14449e58.

[50] Xu C, Wu X, Wang X, Mamlouk M, Scott K. Compositemembranes of polybenzimidazole and caesium-salts-of-heteropolyacids for intermediate temperature fuel cells. JMater Chem 2011;21:6014e9.

[51] Mamlouk M, Scott KJ. A boron phosphate-phosphoric acidcomposite membrane for medium temperature protonexchange membrane fuel cells. J Power Sources2015;286:290e8.

[52] Mait S, Jana T. Polybenzimidazole block copolymers for fuelcell: synthesis and studies of block length effects onnanophase separation, mechanical properties, and protonconductivity of PEM. Appl Mater Interfaces 2014;6:6851e64.

[53] Guo Z, Xu X, Xiang Y, Lu S, Jiang SP. New anhydrous protonexchange membranes for high-temperature fuel cells basedon PVDF-PVP blended polymers. J Mater Chem A2015;3:148e55.

[54] Mustarelli P, Quartarone E, Grandi S, Angioni S, Magistris A.Increasing the permanent conductivity of PBI membranes forHT-PEMs. Solid State Ionics 2012;225:228e31.

[55] Namazi H, Ahmadi H. Improving the proton conductivity andwater uptake of polybenzimidazole-based proton exchangenanocomposite membranes with TiO2 and SiO2

nanoparticles chemically modified surfaces. J Power Sources2011;196:2573e83.

[56] Hazarika M, Jana T. Proton exchange membrane developedfrom novel blends of polybenzimidazole and poly(vinyl-1,2,4-triazole). Appl Mater Interfaces 2012;4:5256e65.

[57] Singha S, Jana T. Structure and properties ofpolybenzimidazole/silica nanocomposite electrolytemembrane: influence of organic/inorganic interface. ApplMater Interfaces 2014;6:21286e96.

[58] He RH, Li QL, Xiao G, Bjerrum NJ. Proton conductivity ofphosphoric acid doped polybenzimidazole and itscomposites with inorganic proton conductors. J Membr Sci2003;226:169e84.

[59] Yang J, Li QF, Jensen JO, Pan C, Cleemann LN, Bjerrum NJ,et al. Phosphoric acid doped imidazolium polysulfonemembranes for high temperature proton exchangemembrane fuel cells. J Power Sources 2012;205:114e21.






























































































































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