Improvement of proton transport via preparation composite membrane of SPSF/Nafion

Improvement of proton transport via preparation
composite membrane of SPSF/Nafion
B. Piluharto1, T. Haryati1, C.L. Radiman2
1

Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Jember, , Jawa Timur, Indonesia
Inorganic and Physical Chemistry Research Division, Faculty of Mathematics and Natural Sciences, Institut Teknologi
Bandung, Bandung, Jawa Barat, Indonesia

2

Abstract
SPSF/Nafion proton exchange composite membrane have been prepared by phase inversion technique. Here, the
matrix of SPSF was impregnated with a 5% Nafion solution in various time evaporation. The presence of Nafion in
the matrix is hypotheses to affect on structure formation of membrane, consequently affect on physicochemical and
proton transport properties. Characterisation of the composite membrane was performed include water uptake, ionic
exchange capacity, membrane morphology and proton conductivity. As the result, Water uptake and hydration
capacity decrease with increasing evaporation time up to 10 minutes, the further evaporation time increase
significantly. The proton conductivity of the composite membrane increase up to 10 minutes the further evaporation
times tend to decrease. Nevertheless, Compared with SPSF membrane, the composite membrane shows improvement
the proton conductivity.

Keywords: composite membrane; proton exchange membrane; phase inversion; proton transport

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1. Introduction
In fuel cell applications, Nafion is commonly used as the proton exchange membrane (PEM) due to
mechanical and thermal stability and high proton conductivity (0.08 S/cm). However, this material have
some drawbacks such as high cost (600-1000 $/m 2 ), high methanol crossover and undergo dehydration
when operated in high temperature [1,2]. Hence, exploring to alternative membrane materials which can
be overcome the major drawback of nafion is very necessary.
The sulfonated polysulfon-based electrolyte membrane is one of the PEM alternatives to replace Nafion
for fuel cell application. Polysulfone (PSF) is chosen because of their good mechanical and thermal
stability, toughness, and easy to be processed [3]. Introducing sulfonate groups in the polymer chains to
produce ionic polymer or polyelectrolyte. Increasing the sulfonation degree is one of the efforts to
achieve higher proton conductivity. However, an extensive sulfonation leads to swell the polymers and
some even change them to become soluble in water, thus they lose their mechanical stability. This is the
general problem of sulfonation process of polymers, includes polysulfon, therefore it has to be optimized
in order to reduce the loss in mechanical stability without decrease proton conductivity [4,5].
In several study, especially regarding synthesis and modification membranes of sulfonated polysulfonebase (SPSF)[6-8], in generally showed that the resulting membranes could improve some properties such
as thermal, mechanical stability and methanol permeability, however proton conductivity still lower if

compare with nafion membrane. Therefore, proton conductivity improvement of this membrane is still
necessary. In here, we have modified SPSF membrane by introducing Nafion in the SPSF membrane.
Incorporating Nafion into SPSF matrix provide a additional electrolyte component lead to improve the
proton conductivity.

2. Experimental
2.1 Materials
Udel PSF (polysulfone) (Mw=35,000 Da) was obtainedfrom Union Carbide. Chloroform, chlorosulfonic
acid,hydrochloric acid, sulfuric acid, sodium hydroxide, methanol, and N,N-dimetylacetamide (DMAc;
analytical grade reagent) were purchased from Merck and Aldrich except methanol. All chemicals were
used without any further purification.
2.2 Synthesis of SPSF
The PSF was sulfonated according to procedure previously described by B. Piluharto et.al (2011). Ten
grams PSF dissolved into 100 mL Chloroform. Each solution was kept in ice bath at 0 oC. Chlorosulfonic
acid in chloroform with concentration 8 % (v/v) is added drop wise to the PSF solution, with the
temperature kept constant in an ice batch at 0 oC. The resulting reaction mixture was stirred for 30
minutes. After the complete addition of the mixed solution, the polymer was precipitated in 500 mL
methanol, which then washed with methanol until it was free of acid and dried in a oven at 60 oC.
2.3 The Preparation of membrane

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The SPSF membrane was prepared by phase inversion technique from the polymer solution containing
20% (w/v) SPSF. The polymer solution was cast on glass plate and was allowed to evaporate at the
ambient temperature. To prepare composite membrane, 5% Nafion solution was poured on the cast film.
In here, Introducing Nafion solution on the cast film were controlled by different evaporation time (5, 10,
15, and 20 minute). Finally, membrane was allowed to evaporate for 24 hours.
2.4 Characterization of membranes
Water uptake
The membrane was measured the dry weight. Then, the membrane was soaking in pure water for 48
hours. After soaking period, the surface of membrane was quickly wiped with tissue paper and weighed.
Percent uptake was determined using the following relationship :
% Water Uptake =

Ww  Wd
100%
Wd

where Ww is weight wet and Wd is weight dry.
Ion-exchange capacity (IEC)

The IEC and DS were determined by titration. The procedure that previously described by Smitha et.al
(2003)4 was used to determine IEC of all membranes. Here, IEC value is calculated using the following
equation:

IEC 

( B  P ) x 0.01x5
m

where IEC is the ion-exchange capacity (meq/g), B is the required volume of sulfuric acid to neutralize
the blind sample soaked in NaOH (mL), P is the required volume of sulfuric acid to neutralize the
sulfonated membrane soaked in NaOH (mL), 0.01 is the normality of the sulfuric acid solution, 5 is the
factor that corresponds to the ratio between the amount of NaOH taken to dissolved the polymer and the
amount that used for titration and m is the mass of sample (g).
Proton conductivity measurements
Conductivity measurements are carried out in two-electrode AC impedance technique using frequency
response analyzer with frequencies 20 kHz – 2 MHz and 100 mV amplitude applied signal. Before
starting measurements, the membrane was immersed in distillated water overnight to get membrane in
swollen state. Thereafter, water in surface membrane was removed gently and was sandwiched between
two-wire platinum electrode in measurements cell quickly.

Hydration Capacity
The hidracy capacity () indicate amount of water per sulfonic group.  was obtained from relation
between ion-exchange capacity (IEC) and water uptake (WU) [10].

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3. Result and Discussion
As mentioned in method part, preparation membranes were carried out by introducing the electrolyte
component, namely, Nafion, into matrix of SPSF membrane. SPSF membran were prepared by phase
inversion technique with different evaporation time. The microstructure formation of membranes were
affected by some parameters such as polymer content, solvent, additive, and evaporation time. In this
work, the evaporation time is used as variable to study physiochemical and proton transport properties.
By introducing Nafion solution in the casting SPSF membrane lead to the system change. Consequently,
physicochemical and proton transport properties also change.
Physicochemical properties the composite membranes and unmodified membrane are summarized in
table 1. Nafion 117 membrane also include in the table 1 as the comparable membrane. Physicochemical
properties includes water uptake, ion-exchange capacity, hydration capacity, and proton conductivity
represent proton transport properties.
Membrane
SPSF

SPSF/NAF 0m
SPSF/NAF 5m
SPSF/NAF 10m
SPSF/NAF 15m
SPSF/NAF 20m
Nafion 117

WU (%)
192,6
103,7
71,1
67,7
115,3
181,8
20,0

IEC (meq/g)
2,4
2,7
2,3

2,7
2,0
2,1
0,7



 (S/cm) x10-2

44
21
17
14
33
47
17

0,54
1,74
2,2

2,34
1,72
1,09
48,7

From figure 1, increase evaporation time lead to decrease WU until evaporation time 10 minute, further
evaporation time increase WU. The other hand, increase evaporation time lead to IEC fluctuatively.
Nevertheless, evaporation time 10 minute showed highest IEC. This phenomenon can be explained by
process of membrane formation. In here membrane formation are obtained by phase inversion technique.
The membrane formation was affected by evaporation time lead to micro porous structure formation. The
difference of evaporation time affect on solidified stability of membrane.

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200

2,8

IEC
IECSPSF
WU

WUSPSF

160

2,7
2,6
2,5

WU (%)

140

2,4
2,3

120

IEC (mek/g)

180

2,2

100

2,1
80

2,0

60

1,9
0

5

10

15

20

evaporation time (minute)

Figure 1. The water uptake and ion-exchange capacity as function of evaporation time

2,8

2,50

2,7

2,25

2,6

2,00

2,5

1,75

2,4

1,50

2,3

 (S/cm)

IEC (meq/g)

Figure 2 show correlation between IEC and proton conductivity. Increase evaporation time lead to proton
conductivity until evaporation time 10 minute. This phenomena contra with WU and . This is indicated
that qualitatively amount of absorbed water in the membrane was not contribution in improvement proton
conductivity. However, main contribution of improvement proton conductivity is attributed by ionic
groups.

1,25

2,2

IEC
IECSPSF

2,1

1,00
0,75


SPSF

2,0

0,50

1,9
0,25
0

5

10

15

20

evaporation time (minute)

Figure 2. Ion-exchange capacity and proton conductivity as function of evaporation time
Figure 3 show correlation between hydration capacity and the proton conductivity. From this picture, the
curve pattern of hydration capacity have similar pattern with WU, where increase evaporation time up to
10 minute, decrease hydration capacity (), further the evaporation time tend to increase significantly.
The otherwise, it were occurred on proton conductivity where increase evaporation time 10 minute lead
to highest proton conductivity, further evaporation time tend to decrease. This phenomena can be
explained that the change of evaporation time affected on the microstructure of membrane formation.
Consequently, amount of Nafion that introduce to the matrix SPSF also change. Nevertheless, Nafion

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could be introduce to the matrix membrane optimally in evaporation time 10 minute. In here, the ionic
group of Nafion give contribution with ionic group from SPSF synergic ally that improvement the proton
conductivity. This condition was called “percolation threshold” where ionic clusters well connected [10].
50
2,4
45

2,2

Cond
CONspsf
KH
KHspsf

35



30

2,0
1,8
1,6

(S/cm)

40

1,4

25

1,2

20

1,0
15

0,8

10

0,6

5

0,4
0

5

10

15

20

evaporation time (minute)

Figure 3. Ion-exchange capacity and proton conductivity as function of evaporation time

4. Conclusion
Preparation the composit membrane have been prepared by introducing Nafion as electrolyte component
into matrix SPSF. The physicochemical and transport proton properties of membranes with different
evaporation time have studied. Water uptake and hydration capacity decrease with increasing evaporation
time up to 10 minutes, the further evaporation time increase significantly. The proton conductivity of the
composite membrane increase up to 10 minutes the further evaporation times tend to decrease.
Nevertheless, Compared with SPSF membrane, the composite membrane shows improvement the proton
conductivity.
Acknowledgement
The authors would like to thank to directorate of higher education, department of National eduction,
Republic of Indonesia for the financial support under Competitive Grant (Hibah Bersaing), contract No.
285/H25.3.1/PL.6/2011.
Refferences
[1] Dewi, E.L, (2005): Elektrokatalis Polinuclear Kompleks Dalam Teknologi Fuel Cell, Meeting of
Indonesian scientist in the 21st century, LIPI, 245-256
[2] Fu Y.Z, Manthiram A, (2006) Synthesis And Characterization Of Sulfonated Polysulfon Membrans
For Direct Methanol Fuel Cells, J. Power sources, 157, 222-225
[3] Manea C, Mulder M, (2002), Characterization of Polymer Blends of Polyethersulfone/Sulfonated
Polysulfone and Polyethersulfone/Sulfonated Polyetherketone For Direct Methanol Fuel Cells , J. of
Membr. Sci., 206, 443-453

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[4] Smitha, B, Sridhar, S, Khan, A.A, (2003), Synthesis And Characterization Proton Conducting
Polymer Membran For Fuel Cell, J. Membr. Sci., 259, 63-76
[5] Kerres, J.A, (2001), Development Of Ionomer Membran For Fuel Cells, J. Membr. Sci., 185, 3-27
[6] Benavente, J., Zhang, X., Garcia-Valls R., (2005) : Modification of Polysulfone Membrans with
Polyethylene Glycol and Lignosulfate: Electrical Characterization By Impedance Spectroscopy
Measurements, J. of Colloid and Interface science, 285, 273-280
[7] Nagarale, RK, Gohil, GS, Shahi, VK, Rangarajan, R (2005) : Preparation and Electrochemical
Characterization of Sulfonated Polysulfone Cation-Exchange Membrans: Effects of the Solvents on
the Degree of Sulfonation, J Appl Polym Sci., 96:2344–2351
[8] Shahi, V.K, (2007), Highly Charged Proton-Exchange Membrane: Sulfonated Poly(Ether Sulfone)Silica Polyelectrolyte Composite Membrane For Fuel Cells, Solid State Ionics, 177, 3395-3404
[9] Berezina, N. P.,and Komkova, E. N. (2003) : A Comparative Study of the Electric Transpor of Ions
and Water in Sulfonated Cation-Exchange Polymeric Membrans of the New Generation, Colloid
Journal, 65, 1, 2003, 1–10.
[10] Henderson, D. (eds.) (2005) : Ionic soft matter: modern trend in theory and application, 2005
Springer, Printed in the Netherland