Sulfonated bisphenol-A-polysulfone based composite PEMs containing tungstophosphoric acid and modified by electron beam irradiation

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

Available online at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/he

Sulfonated bisphenol-A-polysulfone based composite PEMs containing tungstophosphoric acid and modified by electron beam irradiation Aca´cio A.M. Furtado Filho a,*, Aı´lton S. Gomes b a b

Centro Tecnolo´gico do Exe´rcito (CTEx), Av. das Ame´ricas 28705, Guaratiba, Rio de Janeiro, Brazil Universidade Federal do Rio de Janeiro (UFRJ), Instituto de Macromole´culas Professora Eloı´sa Mano (IMA), Rio de Janeiro, Brazil

article info

abstract

Article history:

Composite sulfonated bisphenol-A-polysulfone (SPSF) based PEMs, containing tung-

Received 21 March 2011

stophosphoric acid (TPA) and modified by electron beam (EB) irradiation with doses of 50

Received in revised form

and 100 kGy, were prepared and characterized by a number of physico-chemical methods.

5 October 2011

The probability of the cross-linking was increased by post treatment of the irradiated

Accepted 12 October 2011

membranes at 180
C for 8 h into a vacuum oven. The cross-linking strongly affected

Available online 8 November 2011

membrane properties, reducing their swelling, but at the same time decreasing their proton conductivity. The proton conductivity of the membranes was measured by a two

Keywords:

electrode ac impedance technique using a frequency response analyzer. The PEMs

Cross-linking

performance was tested in H2/O2 fuel cell (FC) and found to approach that of Nafion
117

Electron beam

commercial PEM at the same conditions. The PEMs composite stability was adequate at

Polysulfone

least for 2 days, during which no degradation of the performance was observed.

Heteropolyacid

Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

Composite PEM

reserved.

1.

Introduction

Fuel cells have been given great attention as new energy conversion technologies for their promising applications in new clean power sources were applied. Fuel cell technology is also more efficient in its conversion of chemical energy to electrical energy than present technologies [1]. Among the technology types of fuel cells, proton exchange membrane fuel cell has been receiving great attention due to its highly attractive properties as power sources for both stationary and mobile applications [2e4]. Polymer electrolyte membranes play an important role in the development of the fuel cell technology. Perfluorinated polymer electrolytes such as Nafion
, Aciplex
, Flemion
and Dow membranes are the most widely used electrolyte in polymer electrolyte fuel cell

(PEFC) due to its high proton conductivity, mechanical, chemical and electrochemical stability. However, this type of membrane also exhibits some drawbacks, mainly the high cost and the operation temperature. Their performance is strongly dependent on their hydration degree and becomes very poor over 90
C and at a low relative humidity [5]. As a consequence, there are many efforts to find alternatives to these perfluorinated membranes [6e9]. Different ionomers have been explored such as: sulfonated aromatic polymers; composite membranes based on polybenzimidazole and strong acids; composite membranes based on fluorinated polymers and inorganic materials ranging from oxides to lamellar zirconium phosphates or phosphonates; perfluorinated membranes containing proton-conducting ionic liquids (PCILs) and inorganic/organic composite membranes

* Corresponding author. Present address: CTEx, Av. das Ame´ricas no. 28705, Guaratiba, 23020-470 Rio de Janeiro, Brazil. Tel.: þ55 21 24106288; fax: 55 21 24106268. E-mail addresses: [email protected], [email protected] (A.A.M. Furtado Filho), [email protected] (A.S. Gomes). 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.10.056

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

based on Nafion and inorganic micrometer to nanometer size fillers [5,10]. Aromatic hydrocarbon provides the opportunity to incorporate sulfonic acid groups by electrophilic substitution reaction. As the pKa of arylsulfonic acids is close to 6, a fairly good dissociation can therefore be expected [11]. Polysulfone bisphenol-A (PSF) is one of the engineering plastics having aromatic structure in the main chain with excellent mechanical properties and stability at high temperature [12]. To achieve FC conductivity, PSF must be highly sulfonated. As a result, these polymers swell substantially with water uptake and some are even soluble in water [13]. In the present study composite membranes were prepared by incorporation of inorganic filler (TPA) into a polymer matrix (SPSF). The TPA is one of the Keggin-type heteropolyacids with high proton conductivity (between 0.02 and 0.1 S cm1 at 25
C). In the hydrated phase, the proton in TPA molecules as a Bronsted acid is bridged with water by forming hydronium ions such as H3Oþ, or H5Oþ 2 [14]. So, the incorporation of TPA into SPSF membranes can facilitate the transport of protons into the membrane. However, it was found that embedding a fast proton conductor such as TPA ensures only temporary improvement of the PEM properties. When swollen in the FC hydrothermal environment the composite membranes lose the inorganic phase, gradually transforming into their initial form [14,15]. The EB irradiation cross-linking technique was employed to decrease the water swelling improving the mechanical strength and trap the TPA particles within a sulfonated polysulfone matrix. A significant improvement in PEM’s conductivity is attributed to the loading of extremely conductive hydrated TPA, which is found to be less often prone to leaching out of the composite due to restricted mobility of polymer cross-linking chains. The EB process utilizes ionizing radiation in the form of accelerated electrons which interact with matter by transferring energy to the electrons orbiting in the target materials’ atomic nuclei. These electrons may then be either released from atoms, yielding positively charged ions and free electrons, or moved to a higher-energy atomic orbital, yielding an excited atom or molecule to form free radical. These ions, electrons and excited species are the precursors of the chemical changes observed in irradiated material. Polymers generally respond to EB processing in one of three ways. The polymer may crosslink in which the molecular weight increases and improves the mechanical properties [16,17]. The polymer may degrade due to chain scission. Finally, the polymer may be radiation resistant where no significant degree of either cross-linking or chain scission occurs. This resistance is attributed to molecular protection typically afforded by means of an aromatic ring. EB cross-linking provides some material advantages, including tensile and impact strength, chemical resistance, and environmental stress crack resistance and barrier properties. The process neither does not require any additives, nor does it generate hazardous chemical by-products. The proton conductivity, water uptake, thermal properties and chemical structure examined by FTIR were monitored. The performances in the H2/O2 FC were tested for these composite membranes in order to reveal a consistent pattern for the SPSF cross-linking and its effect on the properties of the composite PEMs [15].

2.

Materials and methods

2.1.

Materials

6229

Bisphenol-A-polysulfone (PSF e Ultrason 56010, Mw ¼ 60.000) was kindly provided by BASF. SPSF was obtained by mild sulfonation of bisphenol-A-polysulfone with trimethylsilyl chlorosulfonate as sulfonation agent. Tungstophosphoric acid hydrate (H3PW12O40) of reagent grade was purchased commercially from Fluka and used as received.

2.2.

Membrane preparation

The membrane was prepared with 20 wt.% SPSF homogeneous solutions in N-N-dimethylacetamide (DMAc). The polymer was kept 8 h in contact with the solvent and dissolution was completed with mechanical stirring at 60
C. Composite membranes were prepared adding 8 wt.% of TPA to SPSF solutions before mechanical stirring. Afterward, the solution was cast onto a flat glass and the solvent was slowly evaporated at 60
C for 24 h. Subsequently, the membranes were peeled from the glass in deionized water. Then, to ensure complete solvent removal, the membranes were placed under vacuum at 80
C for 48 h. Thus, membranes of 100 mm thickness were obtained [13,18,19].

2.3.

Irradiation cross-linking

The EB irradiation was carried out at room temperature and atmospheric air under a Rodotron TT200 electron accelerator with an average dose rate of 630 kGy/min and energy of 10 MeV. The beam was applied in the form of scanning on the samples when they passed through the beam to be transported by the walkways system. EB irradiation was controlled by dosimeters located on the samples. After irradiation, the SPSF films were thermally treated in a vacuum oven at 120
C for 2 h for quenching any residual radicals [2]. Additional thermal cross-linking of the sulfonic acid groups in the irradiated SPSF membranes was carried out in vacuum oven at 180
C for 8 h. The degree of sulfonation of the membrane was determined before and after irradiation by acidebase titration [20].

2.4.

Membrane characterization

Fourier transform infrared (FTIR) spectra of the membranes were obtained in the range of wave number 4000e450 cm1 using a Perkin Elmer 1720-X FTIR spectrometer by attenuated total reflectance (ATR) techniques. Thermogravimetric analysis (TGA) was carried out using a TGA Q500 (TA Instruments) under nitrogen atmosphere. Samples (10e20 mg) were heated from room temperature up to 700
C at 10
C/min. The glass transition temperatures of the membranes were determined using a TA Instruments DSC Q1000 differential scanning calorimeter at a heating rate of 10
C/min from 40 to 300
C, in a nitrogen atmosphere. Before measurement, the sample was dried under vacuum at 120
C for 24 h.

6230

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

Ion exchange capacity of pristine and irradiated SPSF membranes was determined by a classical titration method. The membranes in Hþ form were immersed into 1 M NaCl solution for 48 h to liberate the Hþ ions (the Hþ ions in the membranes were replaced by Naþ ions). The Hþ ions in solution were then titrated with 0.01 M NaOH using phenolphthalein as indicator. The IEC was calculated from equation (1) [20,21] IEC ¼ ½consumed NaOHðmLÞ  molarity NaOH=
   weight of drymembrane meg g1

(1)

Water uptake (WU) was measured by weighing films (15 mm  15 mm) immersed in deionized water at 80
C for 48 h. Initially, protonate membranes were dried under vacuum at 120
C for 24 h to get dry weight (Wd). The liquid water on the surface of membrane was removed using tissue paper before weighing to get the wet weight (Ws). The WU was calculated by equation (2) [3,18,22] WUð%Þ ¼ ½ðWs  Wd Þ=Wd   100

components were dried under vacuum at 120
C for 24 h and determined by equation (3) Gel ¼ W=Wo

(3)

where Wo is the initial weight of the sample and W is the weight of the dry insoluble part. Membranes Chemical Stability (CS) was measured by Fenton’s test, using a H2O2 solution (3% v/v) containing Feþ2 (2 ppm) at 80
C. Membranes of 100 mm of thickness were cut into pieces (15 mm  15 mm) and immersed in Fenton’s reagent. The CS of the samples was characterized by the elapsed time that the membrane started to dissolve and dissolved completely in the solution [8,25,26]. The performance of the membranes was tested in H2/O2 FC at 80
C. The single cell with electrode area of 5.0 cm2 was fed with humidified H2 and O2 (RH ¼ 100%) at atmospheric pressure with flow rates of 100 and 200 STP cm3/min respectively. Membrane electrode assemblies (MEA) were made using Pt/C electrodes (E-TEK) with Pt loading of 0.4 mg/cm2 [15].

(2)

The proton conductivity (s) of the membranes was measured in the transversal direction in an electrochemical cell using a potenciostatic mode of two electrode. The cell is composed of two 1.0 cm2 effective area stainless steel electrodes. The membranes were sandwiched by flat gas diffusion electrode (E-TEK
Electrode) and tightly clamped by the stainless steel electrodes. Prior to the conductivity test, the membranes were equilibrated in 0.1 N HCl solutions at 80
C for 1.0 h and stored in deionized water. Impedance analysis was recorded in a thermostatic cell at 30 and 80
C, with an oscillation potential of 10 mV over the frequency range of 10.0 Hze1.0 MHz. The Autolab PGSTAT30 (Eco Chemie B. V., Netherlands) with frequency response analysis (FRA) software was used for data acquisition and treatment. Proton conductivity was determined using the relation s ¼ L/RS, where L and S are the thickness and area of the hydrated membrane, respectively, and R the membrane resistance obtained from impedance analysis [23,24]. Gel fraction measurement was performed using DMAc solvent, and the soluble fraction was extracted for 10 h at the boiling temperature of around 140
C. The residual gel

3.

Results and discussion

3.1. Radiation cross-linking of SPSF composite membranes As shown in Table 1, the degree of sulfonation and ion change capacity of the membranes tend to decrease with the EB irradiation. The irradiated membranes showed tendency to reduce the proton conductivity at 80
C in relation of SPSF pristine membranes. After irradiation, the composite membranes showed higher results of conductivity. This behavior can be explained by the intrinsic conductivity (101 S cm1) of the TPA. Many studies have investigated irradiation effects on SPSF. Thus, both cross-linking and main chain scission were reported for irradiation effects on SPSF membrane. Nevertheless, the EB irradiation effect on SPSF has not been well understood at room temperature [12]. The crosslinking mechanism that was proposed by Collette et al. [27] indicates the condensation of two sulfonic acid groups creating a cross-link SeOeS between two side groups which is accompanied by loss of one molecule of water (Fig. 1). The

Table1 e Degree of sulfonation (DS), ion exchange capacity (IEC), proton conductivity (s), gel fraction (gel), chemical stability (CS) of Nafion 117 and irradiated SPSF/TPA membranes. Sample

Dose (kGy)

DS (%)

IEC (meq g1)

s (mS cm1)


a

SPSF SPSFa SPSF/TPAa SPSF/TPAa SPSFb SPSF/TPAb SPSF/TPAb Nafion 117


a 120 C for 2 h. b 180
C for 8 h.

e

73.7 54.8 69.7 66.2 51.4 61.0 58.6

50 50 100 50 50 100 e

e

1.471 1.128 1.400 1.337 1.064 1.243 1.199 0.910

Gel (%)

CS (min)




30 C

80 C

34.0 13.2 39.5 39.3 22.4 44.6 41.4 68.0

72.0 29.5 40.7 58.9 26.3 55.5 59.7 112.0

e 37.2 8.7 9.4 45.6 29.1 33.9 e

98 162 77 57 140 105 93 230

6231

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

R R O

S

O O

OH

S

O

- H 2O O

OH O O

S

O

O

S

R R Fig. 1 e Reaction of sulfonic acids condensation [24].

3.2.

Water uptake and gel fraction

Fig. 3 presents the water absorption in function of time of SPSF membranes. The composite membranes present an unstable behavior with increasing absorption of water in function of time. When these membranes receive thermal additional treatment at 180
C they begin to present stability of water absorption in function of time. It was not possible to verify significative alteration in the absorption of water with the variation of the total dose of radiation of 50e100 kGy. The SPSF original membrane has a high degree of sulfonation (above 70%) and, as expected, it also didn’t present stability in the test of water absorption at 80
C [30,31]. When submitted at a radiation dose of 50 kGy, this membrane presented CH3 C

.

.

a significative reduction of the degree of sulfonation and consequently the IEC (Table 1), showing stability with little absorption of water. These results are enhanced with further heat treatment at 180
C. The formation of insoluble polymer network by means of cross-linking was confirmed with the increasing of the results of gel fraction of irradiated membranes (Table 1). The differential absorption of radiation in the composite membranes SPSF/TPA in comparison with the original SPSF membranes, can be justified due to the presence of TPA in the composites, which absorbs part of the ionization radiation dose thus limiting the formation of free radicals [3,27]. Polymeric materials when irradiated with ionizing radiation may undergo an increase in molecular weight due to cross-linking and/or a decrease in molecular weight due to chain scission. Considering higher radiation doses the scission reactions are supposed to compete with cross-linking, the increase in the extent of cross-linking can be accounted for by the fact that chain scissions lead to entanglement couplings which act as cross-linkings.

110 PSF SPSF Composite

100 90 80 70 60 50

CH3

40

Phenyl radical

Isopropylidene radical

Fig. 3 e Water uptake (%) versus time (h) for irradiated SPSF and composite membranes at 80
C.

Weight (%)

reaction of condensation is favored in hydrated membranes by increased mobility of the chains. The formation of cross-linking should influence the membrane properties with decrease of the membrane hydrophilicity due to the loss of the ionic groups. As the proton conductivity is strongly related to the membrane water content, an important property of PEM is affected by the loss of sulfonic groups [28]. Another way of cross-linking is the formation of T-type structure. Brown and O’Donnell [29] considered that aliphatic group in SPSF is involved in crosslinking. Reaction mechanism at room temperature occurs by scission between isopropylidene unit and phenyl ring that forms phenyl radical. Those radicals combine with methyl radicals in the aliphatic group (Fig. 2) [12]. This kind of crosslinking favors the evolution of mechanical properties without lost ionic groups, forming new arrangement in the internal morphology of the membrane.

30

.

CH2

CH2

C

C

CH3

CH3

Fig. 2 e Formation of cross-linking T-type structure [11].

20 0

100

200

300

400

500

600

700

Temperature ( C)

Fig. 4 e TGA signal: for PSF, original SPSF and composite membranes.

6232

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

Fig. 5 e Differential TGA signal: for PSF, original SPSF and composite membranes.

3.3.

Thermal properties

elated maximums to lower temperature (Figs. 4 and 5). TPA thermal degradation studied in Ref. [34] was found going through different stages of dehydration, accompanied by the formation of various protonic species and hydroxyl groups above 300
C. As a radical mechanism plays a significant role in the thermally driven SPSF decomposition, the increased easiness of main chain degradation of the composite membranes must be assigned to the presence of the radicals originated from the decomposition of the TPA. The DSC measurement was carried out to determine the glass transition temperature (Tg) of the SPSF and composite membranes. Fig. 6 shows DSC thermograms (50 to 300
C) of the tested membranes: SPSF irradiated with 50 kGy; composite irradiated with 50 and 100 kGy and treated with 180
C of temperature by 8 h. The results showed that addition of TPA and the increase of the dose from 50 to 100 kGy do not alter the Tg of the membranes. Usually, the Tg of sulfonated polymer depends on the degree of sulfonation, the existence of counterion and thermal history. The heat treatment of composite membranes at 180
C for 8 h increases the Tg of about 17
C as compared with that of SPSF irradiated membranes. It indicates that the microstructure of the SPSF membranes might be denser or more compact after heat treatment at high temperature due to additional cross-linking [30,35].

Thermal analysis of SPSF and their composite membranes in acid form were investigated by TGA and DSC. The results of TGA experiments are shown in Figs. 4 and 5. The thermal degradation of SPSF and composite membranes were more complex than PSF membrane. The weight loss at low temperature (around 100
C) was most probably due to evaporation of residual solvent and to the desorption of water bonded to the hydrophilic sulfonic groups, which was not totally removed by the drying process. This was confirmed by Lufrano et al. [32] analyzing the TGA spectrum of the sample of SPSF preheated at 160
C for 24 h. This thermal treatment does not produce significant modifications in the material except by the disappearance of the first peak. The differential thermogravimetric (DTG) spectrum includes two maximums: the first around 300
C is originating from the loss of sulfonic acid groups and the second over than 440
C is associated to main chain decomposition [30,33]. The main effect of introducing the inorganic acid (TPA) was a significant shift of the backbone

FTIR/ATR spectra for original SPSF and composite membranes are shown in Fig. 7. The composite membranes displayed several new absorptions, attributed to TPA vibrations, shown in Table 2 [15,36]. As reported in the literature, bulk TPA samples presents characteristics FTIR bands around 1082, 983, 886, 793, 595 (weak), and 521 (weak) cm1 assigned to the Keggin anion vibrations of yas(P-O), terminal, yas(W¼O), yas(W-Ob-W), yas(W-Oc-W), d(O-P-O), and ys(W-O-W), respectively [32,33]. The subscripts b and c indicate corner-sharing and edge-sharing oxygen, respectively, and the W-O-W bridges belong to the WO6 octahedral. The weak bands attributed to TPA at <600 cm1 fail to appear, because of low

Fig. 6 e DSC thermograms of SPSF and composite membranes (L50 to 300
C).

Fig. 7 e FTIR/ATR patterns of various samples: a) original SPSF; b) composite, 50 kGy; c) composite, 100 kGy; d) composite, 50 kGy, thermal treated at 180
C; e) composite, 100 kGy, thermal treated at 180
C.

3.4.

FTIR analysis

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

Table 2 e Correlation assignment of FTIR/ATR spectra of SPSF and composite membranes. Wavenumber (cm1) 820

Assignment Symmetric stretching of edge-shared octahedral W-O-W Symmetric stretching of corner-shared octahedral W-O-W Terminal W¼O vibrations Symmetric O¼S¼O stretching vibrations Central tetrahedral P-O band superposed with SO3 band

892 980 1014 1082

concentration of TPA due to its dilution by SPSF. A broad shoulder in the region of 886 cm1 that is observed for all composite is a characteristic vibration mode, yas(W-Ob-W), of TPA. The absence of prominent shift in the position of this peak, relative to the bulk TPA, suggests that TPA retains its Keggin structure after irradiation. A broad band centered at 1082 cm1 and assigned to the symmetric vibration of P-O indicates that TPA retains the Keggin structure on composite after irradiation, since the appearance of defect Keggin anions causes this band to split into two components at 1087 and 1055 cm1. However, the peak broadening and tailing suggest a degree of structural distortion of the Keggin molecule [37e41].

3.5.

Performance in H2/O2 fuel cell

The main objective of this study was to determine whether the composite TPA containing membranes, based on SPSF and cross-linked by EB irradiation, would yield improved performance in a FC. The tests typically involved recycling of the current, sweeping from 0 to the maximum possible value (corresponding to a voltage below 0.1 V) for at least 2 days in order to obtain a steady state response of the cell [42]. Original SPSF, composite and Nafion 117 membranes tested in single FC experiment had thickness of 100 mm. The polarization plots obtained for original, irradiated with 50 kGy and composite SPSF/TPA membranes are compared in Fig. 8 with Nafion 117

1000 900

Nafion 117 Composite, 100 kGy Original SPSF SPSF, 50 kGy

Cell potential, mV

800 700 600 500 400 300

6233

[15]. All SPSF membranes shown inferior performance to Nafion 117. The cell performance drastically decreased with operation time at 80
C due to excessive swelling of the SPSF original membrane. Although the cross-linked membrane structure increases dimensional stability at high temperature, the cross-linked process also causes reduction of water uptake and proton conductivity. The EB irradiation with 50 kGy of SPSF membrane provokes a significant decline of the performance as compared with original SPSF. However, composite membrane with 8 wt.% of TPA irradiated with 100 kGy show improvement of the performance [21]. The polarization responses of the MEAs (Fig. 8) were obtained after at least 2e4 h of intensive tests (cyclical electric loading up to a maximum possible current) when reached stability and did not show any deterioration for 2 days of experimental run. This may signify that the composite membranes and crosslinked by irradiation are stable enough under the working conditions of H2/O2 fuel cell. The particles of TPA embedded within the cross-linked membranes were found to be well retained, as their concentration seems not to be affected by experimental conditions of the H2/O2 fuel cell.

4.

Conclusions

The composite PEM of SPSF with 8 wt.% of TPA had been prepared by casting, successfully. The composite membranes were cross-linked by EB irradiation and thermal treatment. The chemical structures of SPSF and their composite membranes were characterized by TGA, DSC and FTIR. The TGA studies revealed that introduction to the sulfonic group by sulfonation reaction reduced the thermal stabilities of SPSF membranes. The introduction of TPA into SPSF matrix significantly reduced the main chain degradation to lower temperatures. The particles of TPA embedded within the cross-linked membranes were found to be well retained, as their FTIR results seems not to be affected by EB irradiation and thermal treatment at 180
C for 8 h. The formation of cross-linking by EB irradiation and thermal treatment provokes changes in morphology, in the hydrogen bond interactions and in the distribution of water domains in polar aggregates altering the interconnecting channels of the hydrated membrane. As a result, the conductivity of the composite membranes was higher than that of non-modified membranes. The chemical stability results showed that the thermal treatment at 180
C for 8 h increased the stabilities of the composite membranes. The performance of the PEMs based on SPSF composite membrane irradiated with 100 kGy was found to be very similar to Nafion 117 commercial PEM. Therefore, the composite SPSF/TPA membrane seems to be a promising candidate for PEMs applications in FC.

200 100 0 0.0

0.5

1.0

1.5

2.0

Current density, A/cm

2.5

3.0

Acknowledgments

2

Fig. 8 e Polarization curves corresponding to different PEMs: Nafion 117, composite irradiated with 100 kGy, original SPSF and SPSF irradiated with 50 kGy.

The authors would like to thank BASF for kindly supplying the PSF materials. The financial support of Brazilian agencies CAPES and CNPq. Dr. Ma´rcio Zamboti e Acele´tron, Rio de Janeiro, for EB irradiation.

6234

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

references [19] [1] Hotza D, Dinis da Costa JC. Fuel cells development and hydrogen production from renewable resources in Brazil. Int J Hydrogen Energy 2008;33:4915e35. [2] Chen J, Maekawa Y, Asano M, Yoshida M. Double crosslinked polyetheretherketone-based polymer electrolyte membranes prepared by radiation and thermal crosslinking techniques. Polymer 2007;48:6002e9. [3] Shahi VK. Highly charged proton-exchange membrane: sulfonated poly(ether sulfone)-silica polyelectrolyte composite membranes for fuel cells. Solid State Ion 2007;177:3395e404. [4] Furtado AAMF, Gomes AS. Crosslinked sulfonated polysulfone-based polymer electrolyte membranes induced by gamma ray irradiation. Int J Polym Mater 2010;59:424e37. [5] Di Noto V, Negro E, Sanchez J-Y, Iojoiu C. Structurerelaxation interplay of a new nanostructured membrane based on tetraethylammonium trifluoromethanesulfonate ionic liquid and neutralized Nafion 117 for high-temperature fuel cells. J Am Chem Soc 2010;132:2183e95. [6] Lufrano F, Baglio V, Staiti P, Arico AS, Antonucci V. Polymer electrolytes based on sulfonated polysulfone for direct methanol fuel cells. J Power Sourc 2008;179:34e41. [7] Heo K-B, Lee H-J, Kim H-J, Kim B-S, Lee S-Y, Cho E, et al. Synthesis and characterization of cross-linked poly (ether sulfone) for a fuel cell membrane. J Power Sourc 2008;172: 215e9. [8] Borup R, Meyers J, Pivovar B, Kim Y-S, Mukundan R, Garland N, et al. Scientific aspects of polymer electrolyte fuel cell durability and degradation. Chem Rev 2007;107:3904e51. [9] Peighambardoust SJ, Rowshanzamir S, Amjadi M. Review of the proton exchange membranes for fuel cell applications. Int J Hydrogen Energy 2010;35:9349e84. [10] Thayumanasundaram S, Piga M, Lavina S, Negro E, Jeyapandian M, Ghassemzadeh L, et al. Hybrid inorganiceorganic proton conducting membranes based on Nafion, SiO2 and triethylammonium trifluoromethanesulfonate ionic liquid. Electrochim Acta 2010;55:1355e65. [11] Sanchez J-Y, Chabert F, Iojoiu C, Salomon J, El Kissi N, Piffard Y, et al. Extrusion: an environmentally friendly process for PEMFC membrane elaboration. Electrochim Acta 2007;53:1584e95. [12] Murakami K, Kudo H. Gamma-rays irradiation effects on polysulfone at high temperature. Nucl Instrum Methods Phys Res B 2007;265:125e9. [13] Furtado AAMF, Gomes AS. Copolymerization of styrene onto polyethersulfone films induced by gamma ray irradiation. Polym Bull 2006;57:415e21. [14] Fu T, Wang J, Ni J, Cui Z, Zhong S, Zhao C, et al. Sulfonated poly(ether ether ketone)/aminopropyltriethoxysilane/ phosphotungstic acid hybrid membranes with non-covalent bond: characterization, thermal stability, and proton conductivity. Solid State Ion 2008;179:2265e73. [15] Celso F, Mikhailenko SD, Kaliaguine S, Duarte UL, Mauler RS, Gomes AS. SPEEK based composite PEMs containing tungstophosphoric acid and modified with benzimidazole derivatives. J Memb Sci 2009;336:118e27. [16] Mikhailenko SD, Wang K, Kaliaguine S, Xing P, Robertson GP, Guiver MD. Proton conducting membranes based on crosslinked sulfonated poly(ether ether ketone) (SPEEK). J Memb Sci 2004;233:93e9. [17] Yamaki T. Quantum-beam technology: a versatile tool for developing polymer electrolyte fuel-cell membranes. J Power Sourc 2010;195:5848e55. [18] Ekstro¨m H, Lafitte B, Ihonen J, Markusson H, Jacobsson P, Lundblad A, et al. Evaluation of a sulfophenylated

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27] [28]

[29] [30]

[31]

[32]

[33]

[34]

[35]

[36]

polysulfone membrane in a fuel cell at 60 to 110
C. Solid State Ion 2007;178:959e66. Silva VS, Ruffmann B, Silva H, Gallego YA, Mendes A, Madeira LM, et al. Proton electrolyte membrane properties and direct methanol fuel cell performance I. Characterization of hybrid sulfonated poly(ether ether ketone)/zirconium oxide membranes. J Power Sourc 2005; 140:34e40. Chennamsetty R, Escobar I, Xu X. Characterization of commercial water treatment membranes modified via ion beam irradiation. Desalination 2006;188:203e12. Park KT, Chun JH, Kim SG, Chun B-H, Kim SH. Synthesis and characterization of crosslinked sulfonated poly(arylene ether sulfone) membranes for high temperature PEMFC applications. Int J Hydrogen Energy 2011;36:1813e9. Bi H, Wang J, Chen S, Hu Z, Gao Z, Wang L, et al. Preparation and properties of cross-linked sulfonated poly(arylene ether sulfone)/sulfonated polyimide blend membranes for fuel cell application. J Memb Sci 2010;350:109e16. Park J-S, Choi J-H, Woo J-J, Moon S-H. An electrical impedance spectroscopic (EIS) study on transport characteristics of ion-exchange membrane systems. J Colloid Interface Sci 2006;300:655e62. Benavente J, Zhang X, Valls RG. Modification of polysulfone membranes with polyethylene glycol and lignosulfate: electrical characterization by impedance spectroscopy measurements. J Colloid Interface Sci 2005;285:273e80. Chen J, Asano M, Yamaki T, Yoshida M. Chemical and radiation crosslinked polymer electrolyte membranes prepared from radiation-grafted ETFE films for DMFC applications. J Power Sourc 2006;158:69e77. Zhang Q, Zhang S, Li S. Synthesis and characterization of novel cardo poly(aryl ether sulfone) bearing zwitterionic side groups for proton exchange membranes. Int J Hydrogen Energy 2011;36:5512e20. Collette FM, Lorentz C, Gebel G, Thominette F. Hygrothermal aging of Nafion. J Memb Sci 2009;330:21e9. Devrim Y, Erkan S, Bac¸ N, Eroglu I. Preparation and characterization of sulfonated polysulfone/titanium dioxide composite membranes for proton exchange membrane fuel cells. Int J Hydrogen Energy 2009;34:3467e75. Brown JR, O’Donnell JH. Effects of gamma radiation on two aromatic polysulfones. J Appl Polym Sci 1975;19:405e17. Park HB, Shin H-S, Lee YM, Rhim J-W. Annealing effect of sulfonated polysulfone ionomer membranes on proton conductivity and methanol transport. J Memb Sci 2005;247: 103e10. Zhou S, Kim J, Kim D. Cross-linked poly(ether ether ketone) membranes with pendant sulfonic acid groups for fuel cell applications. J Memb Sci 2010;348:319e25. Lufrano F, Gatto I, Staiti P, Antonucci V, Passalacqua E. Sulfonated polysulfone ionomer membranes for fuel cells. Solid State Ion 2001;145:47e51. Guan R, Zou H, Lu D, Gong C, Liu Y. Polyethersulfone sulfonated by chlorosulfonic acid and its membrane characteristics. Eur Polym J 2005;41:1554e60. Essayem N, Tong YY, Jobic H, Vedrine JC. Characterization of protonic sites in H3PW12O40 and Cs1.9H1.1PW12O40: a solidstate 1H; 2H; 31P MAS-NMR and inelastic neutron scattering study on samples prepared under standard reaction conditions. Appl Catal A Gen 2000;194e195:109e22. Kalapos TL, Decker B, Every HA, Ghassemi H, Zawodzinski TA. Thermal studies of the state of water in proton conducting fuel cell membranes. J Power Sourc 2007;172:14e9. Vinodh R, Purushothaman M, Sangeetha D. Novel quaternized polysulfone/ZrO2 composite membranes for solid alkaline fuel cell applications. Int J Hydrogen Energy 2011;36:7291e302.

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 e n e r g y 3 7 ( 2 0 1 2 ) 6 2 2 8 e6 2 3 5

[37] Rao PM, Wolfson A, Kababya S, Vega S, Landau MV. Immobilization of molecular H3PW12O40 heteropolyacid catalyst in alumina-grafted silica-gel and mesostructured SBA-15 silica matrices. J Catal 2005;232:210e25. [38] Kuang W, Rives A, Fournier M, Hubaut R. Structure and reactivity of silica-supported 12-tungstophosphoric acid. Appl Catal A Gen 2003;250:221e9. [39] Haber J, Pamin K, Matachowski L, Mucha D. Catalytic performance of the dodecatungstophosphoric acid on different supports. Appl Catal A Gen 2003;256:141e52.

6235

[40] Lo´pez-Salinas E, Hernandez-Cortez JG, Schifter I, TorresGarcia E, Navarrete J, Gutierrez-Carrillo A, et al. Thermal stability of 12-tungstophosphoric acid supported on zirconia. Appl Catal A Gen 2000;193:215e25. [41] Nowinska K, Fo´rmaniak R, Kaleta W, Waclaw A. Heteropoly compounds incorporated into mesoporous material structure. Appl Catal A Gen 2003;256:115e23. [42] Dai H, Zhang H, Zhong H, Li X, Xiao S, Mai Z. High performance composite membranes with enhanced dimensional stability for use in PEMFC. Int J Hydrogen Energy 2010;35:4209e14.