Crosslinked styrene-maleic acid copolymer complexes of some transition metals and their adsorption behavior

POLYMERS FOR ADVANCED TECHNOLOGIES

Polym. Adv. Technol. 2007; 18: 419–426

nce.wiley.com) DOI: 10.1002/pat.830
Published online 23 April 2007 in Wiley InterScience (www.interscie
Modification of sulfonated poly(ether ether ketone)

with phenolic resin

P. C. Deb*, L. D. Rajputy, V. R. Hande, S. Sasane and A. KumarNaval Materials Research Laboratory, Shil-Badlapur Road, MIDC Area, Ambernath (E), Maharashtra-421506, India

Received 8 April 2006; Revised 18 July 2006; Accepted 25 July 2006

*Correspoof AdvanE-mail: pyPresentWest Ben

Soluble phenol formaldehyde resin containing hydroxymethyl groups has been used to modify

sulfonated poly(ether ether ketone) (SPEEK).Modification has been carried outwith films containing

both the polymers and using dimethyl formamide (DMF) as casting solvent at various temperatures

under reduced pressure. Associated solvent and the hydrogen-bonded by-product dimethyl amine

(DMA) were removed through mild alkali–acid–water treatment. Cured and treated films show good

and consistent mechanical properties, water uptake (22–25%), ion-exchange capacity (1.1–1.5meq/g)

and proton conductivity (125–150mS/cm) at 308C and hold promise for application in fuel cells, as

indicated by a polarization study in a fuel cell test station. Copyright# 2007 JohnWiley & Sons, Ltd.

KEYWORDS: sulfonated poly (ether ether ketone); phenol formaldehyde resin; crosslinking; proton conductivity

INTRODUCTION

Polymer electrolyte films representing proton exchange

membranes (PEMs) for fuel cell (FC) applications have

attracted attention due to lower operating temperature and

high efficiency. These membranes also hold promise for use

in direct methanol fuel cells (DMFCs). However, important

prerequisites, such as high proton conductivity, thermal

stability, optimum water uptake and retention, etc., are still

to be guaranteed by most candidate membranes for actual

application in fuel cell. DuPont NafionR, which is still now

considered superior to other membranes, has limitations

such as high cost, limited useful life under actual operation

and specifically undesirable methanol permeability when

used in DMFCs. Alternative membranes, such as those based

on polyphosphazenes,1 polyimides,2 polybenzimidazoles,3

polysulfones4–6 and poly(ether ether ketone)7–10 are being

extensively evaluated for possible use in PEMFCs and

DMFCs for both stationary and mobile applications.

Aromatic poly(ether ether ketone) (PEEK) is thermally

stable and gives good conductivity and hydrophilicity on

sulfonation.11 Direct synthesis of sulfonated PEEK (SPEEK)

from sulfonated monomer was found to give somewhat

better properties, due to meta-positional sulfonate groups

and possible avoidance of side-reactions during sulfona-

tion.12–14 However, the mechanical properties of SPEEK in

aqueous environments at relatively high temperatures may

not be sufficient for long-term application in fuel cells.

Attempts are therefore being made to improve the mech-

anical properties by crosslinking through a portion of the

sulfonic acid groups available in the polymer. Crosslinking/

ndence to: P. C. Deb, Present address: Defence Instituteced Technology, Grinagar, Pune-411025, [email protected]: Chemistry Department, IIT, Kharagpur,gal, India.

modification of SPEEK with low permeability polymers,

such as phenol formaldehyde, with optimum hydroxy-

methyl content is expected to lower the hydrophilicity, water

solubility and also the gas permeability, which are desirable

for better stability in fuel cell applications. At present, three

methods are reported for crosslinking, using aliphatic/

aromatic amines,15 imides containing amines,16 and di- and

trihydric alcohols such as glycol, glycerol and erythritol.17

Crosslinked SPEEKs using ethylene glycol and glycerol have

good proton conductivity, with considerable swelling in

water. These membranes have not, however, been subjected

to actual use in fuel cells for long-term applications.

The selection of a crosslinking agent and modification of

SPEEK are important aspects, as these should not adversely

affect the proton conductivity, hydrophilicity and thermal

stability appreciably, and should not contain chemical

components that may affect long-term performance, due

to lowering of conductivity and poisoning of the catalyst due

to leaching. The choice of casting solvent also plays a very

important role, as has been recently brought out by

Robertson et al. 18 These authors have demonstrated the

presence of bonded solvent and dimethyl amine (DMA)

when dimethyl formamide (DMF) in particular is used as the

casting solvent in otherwise stringently prepared films. The

application of possible chemical treatments to remove these

components has not, however, been attempted.

We considered that low molecular weight phenol formal-

dehyde resin (PFR) containing a hydroxymethyl group could

be a good choice as a possible crosslinking agent, and on

reaction this would have reasonably good mechanical

properties, water uptake and proton conductivity. This

Copyright # 2007 John Wiley & Sons, Ltd.

420 P. C. Deb et al.

modification would lower the inherent solubility of SPEEK

containing a higher percentage of sulfonic groups and is not

expected to drastically lower the useful thermal properties of

PEEK/SPEEK. The content of phenolic resin has been

controlled so that sufficient electrical conductivity is retained

for fuel cell application. Studies on preparation and

properties of modified SPEEK membranes using PFR as

crosslinker, DMF as casting solvent, and removal of bonded

solvent and DMA by chemical treatment are reported in this

communication.

EXPERIMENTAL

Sulfonation of PEEKCommercial PEEK (Vitrex, USA) was sulfonated as a 15%

solution in 98% sulfuric acid. The solution was kept at 308Cfor 1 h and then at 508C for 6 h with slow stirring. The

sulfonated polymer was precipitated into crushed ice with

vigorous agitation, when a fiber-like material separated out.

This was repeatedly washed with ice-cold water until the pH

of the filtrate was about 6.8–7.0. The sulfonated polymer was

dried at 1008C under reduced pressure for 24 h until further

removal of water was not observed. Residual water (1–2%)

was removed by azeotropic distillation with benzene, which

was added repeatedly until all the water was removed, as

indicated from the phase separation in the distillate. This

was thereafter dried at 608C under reduced pressure for 48 h

and the polymer was obtained as a dark-coloured light-

weight material. The sulfonic acid content of SPEEK was

determined by first suspending it in standardNaOH solution

(0.1N) followed by back-titration with standard acid

(0.05N).

Modification through crosslinking of SPEEKThe modifier used was a low molecular weight PFR (Romit

Resin, India) having a hydroxymethyl content of 6.5%,

corresponding to a hydroxyl value of 118.60 and containing

about 4% free phenol. The resin as 80% solution in methanol

was dried at 308C under reduced pressure for 120 h to ensure

constant weight and total removal of methanol. The final

resin was obtained as a highly viscous, brownish material.

Stock solutions of SPEEK and PFR were made in DMF to a

concentration of 15% and 30% by weight, respectively.

Requisite volumes of the solutions were mixed to achieve the

following compositions of mixtures of the two pure resins:

100:60, 100:40 and 100:20 by weight (films designated as 15R,

10R and 05R, respectively). Films were cast from the filtered

and degassed solutions, such that dry film thickness of about

100–150mmwas obtained. DMF was allowed to evaporate at

room temperature for 48 h. The films were then subjected to

508C, 808C, 1008C, 1208C and 1408C under reduced pressure

of 10�2 atm for 24 h at each temperature. Samples of

heat-treated films at each temperature were preserved for

analysis.

CharacterizationIR spectra of the films were recorded in an FTIR instrument

(Perkin-Elmer 1650). Element analysis of the films was

carried out in a CHNS analyser (Perkin-Elmer 2400).


Mechanical propertiesTensile properties were measured using a Hounsfield UTM

(Model No. 50K-S). The measurements were carried out with

water-equilibrated films at 308C with a crosshead speed of

10mm/min. The results were expressed in MPa and

percentage change for tensile strength and elongation,

respectively.

Thermal propertiesThe thermal stability and degradation pattern of modified

SPEEK were measured using a Hi-Res TGA 2950 thermo-

gravimetric analyser from TA instruments. Samples weigh-

ing about 10mg were heated from room temperature to

8008C at a heating rate of 208C/min.

Water absorption/uptake and dimensionalchangeEach film was cut to a size of about 10� 10 cm and was

equilibrated in distilled water at 308C for 24 h. The amount of

water absorbed into the samples was determined by

comparison of the weight of the original dried film and

the blotted soaked film after each exposure. Weighing of

blotted films was continued for about 60min to see the

desorption behavior. Water uptake studies were also carried

out at 508C, 608C, 708C and 808C and were determined from

the relationship (DW/W)� 100, where DW is the weight

increase of a dry film of weight W after water absorption.

Dimensional changes in water absorption were measured

in thickness and in plane directions and the results were

expressed as percentage change with respect to the

dimensions at 308C in water as standard.

Ion exchange capacity (IEC)The IEC of the membranes was determined by suspending

about 0.5 g of the membranes in 0.05M NaCl solution,

equilibrating for 24 h with slow stirring, and titrating the

liberated acid with 0.05M aqueous NaOH solution. The

exchanged film was brought to acid form in 24 h, washed

thoroughly, heated at 608C under reduced pressure for 12 h

and finally dried over P2O5 for 24 h to determine the dry

weight of the film.

Proton conductivity measurementProton conductivity of the membranes was measured using

the four-electrode DC conductivity method.19 The mem-

branes were conditioned in distilled water for 24 h, followed

by treatment with 0.1M sulfuric acid for 24 h at 308C.

Assessment of membrane electrode assemblyPt-impregnated carbon powder (Pt content of 0.18mg/cm2 of

crystallite size 60A) wasmade into a pourable slurry with 5%

Nafion solution and was spread over conducting carbon

paper. This was heated at 808C in air and at 1308C under

reduced pressure for 2 and 4h, respectively. The membrane

electrode assembly (MEA) was made by positioning the

cured and treated membrane in between two coated carbon

papers whose sides were covered with Teflon films. The

combination was then placed between two grooved graphite

plates to ensure uniform exposure of the electrode surfaces

(20 cm2 area) to hydrogen and oxygen on the two sides,


DOI: 10.1002/pat

-O- C-

O

CH

-CH -

-C- -O-

-[- O- -O-]--

CH OH OH OHCH -]-

SPEEK

+

SPEEK

OH

CH[--

OH

CH OHPF Resin

O

-O-]-

+

-[-O-

SO H

CROSS-LINKED SPEEK

SO H3

2

2

3

2

2

2

2

2

-2H O2CH

Figure 1. Possible crosslinking reaction of SPEEK with phenol–formaldehyde resin.

Modification of SPEEK with phenolic resin 421

respectively. The assembly was then put into a fuel cell test

station with a gas humidification and cell temperature

control facility. Polarization of the electrodes was carried out

at 458C, allowing 2–3h at each load and introducing

hydrogen and oxygen at 50 and 65ml/min, respectively,

under slightly above ambient pressure.

RESULTS AND DISCUSSION

Modification through crosslinkingCrosslinking of SPEEK has recently been a subject of interest,

due to the presence of a proton exchange sulfonic acid group

and good thermal andmechanical properties of the backbone

polymer. Crosslinking efforts have been restricted to sulfonic

acid groups, either for intra-/inter-chain self-condensation

or through crosslinker bridging sulfonic acid groups of

different molecules. The advantages and disadvantages of

such efforts have recently been elaborated.17 Extensive

crosslinking studies by the authors have identified thermal

conditions, choice of crosslinker and casting solvent. It has

emerged that the use of DMF and dimethyl acetamide

(DMAC) leads to the formation of a DMA–sulfonic acid

adduct which is stable even at high temperatures of curing.

The adduct affects the film properties and lowers the

conductivity of SPEEK film by consumption of sulfonic acid

groups. However, the effect of the casting solvent on

prolonged drying at ambient temperature and at reduced


pressure has not been fully demonstrated. Also, possible

chemical treatment to remove the amine and improve

theproperties has not been identified. DMF is a good solvent

for both SPEEK and PFR and offers optimum casting

properties. We have therefore used this solvent for casting

and tried to optimize the crosslinking procedure and

subsequent chemical treatment to eliminate the solvent

and its by-product from the films. The possible crosslinking

reaction, shown in Fig. 1, results in the formation of

–C–SO2–O–C– linkage.

The hydroxymethyl content of PFR was determined after

removal of methanol and hydroxyl value was confirmed to

remain almost unchanged at about 116, indicating negligible

crosslinking during removal of the solvent. The dried

product was also freely soluble in DMF and methanol. On

mixing with SPEEK, overall concentration of phenol reduces

to 0.7–1.5%. SPEEK has very good compatibility with PFR

and three-dimensional modeling of possible crosslinked

product indicates low steric energy for its formation. Due to

dilution of phenol in the cast films and possible interaction of

the hydroxymethyl group with sulfonic acid, it is expected

that the crosslinking reaction will take place preferentially

between SPEEK and PFR. An attempt has not, therefore, been

made to quantitatively estimate the phenol content of the

crosslinked product.

SPEEKused in our experiments has a degree of sulfonation

of 80� 2 and is soluble inwarmwater andDMF/DMAC. The


DOI: 10.1002/pat

Table 1. Properties of PFR-modified SPEEK

SampleComposition

(SPEEK:PFR, w/w)Thermal treatment(8C at 10�2 atm)

Water absorptionat 308C (wt%) Nitrogen IEC (%)

05R-80 100:20 80 21 2.85 Films disintegrated05R-100 100:20 100 23 2.70 Films disintigrated05R-120 100:20 120 13 3.10 0.70 (too soft)05R-140 100:20 140 10 3.10 0.70 (too soft)10R-80 100:40 80 21 3.01 0.65 (soft)10R-100 100:40 100 19 2.85 0.6310R-120 100:40 120 7 3.31 0.5610R-140 100:40 140 8 3.17 0.52I5R-120 100:60 120 8 2.90 0.40I5R-140 100:60 140 6 2.85 0.32


amounts of PFR used for crosslinking corresponded to about

14%, 28% and 42% consumption of sulfonic acid groups.

Temperature cycles, water uptake, IEC and nitrogen content

of the films are shown in Table 1. As is evident, prolonged

heating even under a reduced atmosphere, does not remove

the solvent/nitrogenous by-product, as has been shown by

Robertson et al.18 A 1:1 DMA:sulfonic acid complex for the

crosslinked films should contain about 3% nitrogen, which is

very close to the experimental values shown in Table 1. The

absence of nitrogen in either SPEEK or PFR used in the

present study was confirmed through microanalysis. Proton

conductivity measurements of a few cured films showed

0

50

100

150

200

250

90807060504030Temperature (ºC)

Wat

er u

pta

ke (

%)

Figure 2. Water absorption of modified and treated SPEEK

films as a function of temperature. *, 10R100; &, 10R120;

~, 10R140; &, 15R120; ^, 05R140.


values in the range 10�1–1mS/cm,whichwasmuch less than

expected for crosslinked SPEEK of 80% sulfonation,

confirming the contentions of Robertson et al.18

Water desorptionOne peculiar observation wasmade during water absorption

studies of the films at room temperature. Irrespective of the

temperature cycle and composition used, it was found that

the films lose the absorbed water quite fast and the final

weights of the water-depleted films were less than the dry

films noted before exposure to water, and the films became

tougher. The weight reduction between dry film and

water-desorbed film was found to vary by 1–10% relative

to dry weight of the films, being low for high temperature-

cured films. This showed that some component from the film

was evaporating along with water while water desorption

was being monitored. This is not possible solely for retained

DMF, and could be due to a very volatile component that also

forms hydrogen bonding with water. Dimethyl amine

(DMA) has a boiling point of 6.888C and has a strong

affinity for water. It thus appears that when the films are

immersed in water, DMF, and particularly DMA, separate

from the sulfonic acid group and bond with water to form

highly volatile adducts. This explains theweight reduction of

the water-desorbed films compared to the original dry

weight of the films. However, prolonged water treatment,

even at elevated temperatures, did not completely remove

the nitrogenous material from the films, as was observed

through nitrogen estimation at each water treatment (this

treatment could not reduce the nitrogen content to less than

1.5%).

Table 2. Tensile strength, elongation and dimension change

of crosslinked SPEEK membrane in water

MembraneTensile

strengtha

(Mpa)Elongation atbreaka (%)

Dimension changeb

~l% ~d%

458C 608C 458C 608C

10R-80 35–40 17–18 0 5.5 2.0 1710R-100 25–30 85–90 0 5.8 2.3 1810R-110 30–32 130–185 0 5.5 2.4 1410R-120 32–35 55–60 0 6.8 3.8 2110R-140 17–20 10–15 0 13.3 4.4 28

aWater-soaked film with soaking time of 12 h.b In water with soaking time of 6 h at each temperature.


DOI: 10.1002/pat


Treatment of modified SPEEKThe following two treatments were followed to remove

adhering DMF and DMA:

1. T

Co

he films were suspended in excess of 0.05N sulfuric acid

for 48 h at 308C with constant but slow stirring, followed

bywashingwithwater repeatedly until the filmswere free

from extraneous acid.

2. T
he films were suspended in excess of 0.05N aqueous
NaOH solution for 48 h at 308C with constant but slow

stirring, followed by repeated washing with water. The

%T

rans

mitt

ance

(ar

bitr

ary

units

)

2500 3000 3500 4000

Wave numb

Wave numb

(A)

(B)

%T

rans

mitt

ance

(ar

bitr

ary

units

)

2500 300035004000

Figure 3. IR spectra of SPEEK and modifie

temperatures for 10R films, (A) untreated, (B

808C; — — at 1008C; _��__��_, at 1108C. (B) ____

pyright # 2007 John Wiley & Sons, Ltd.

films were then suspended in 0.05N sulfuric acid for 48 h

and finally washed repeatedly with water.

All films were subsequently dried at 608C under reduced

pressure and kept over P2O5 to ensure complete removal

of water before taking IR spectra and estimating the nitrogen.

Properties of the treated filmsSulfuric acid-treated films did show an improvement in

elimination of nitrogenous adduct to about 0.5% nitrogen,

while alkali and acid treatment, as in method 2 above,

500 1000 1500 2000

ers (cm-1)

ers (cm-1)

500 10001500 2000

d SPEEK during crosslinking at various

) treated. (A) ��, SPEEK; - - - - -, at

, at 1008C; _____ at 1108C.


DOI: 10.1002/pat

0

20

40

60

80

100

120

9008007006005004003002001000Temperature (ºC)

Wei

gh

t lo

ss (

%)

Figure 4. TGA curves for phenolic resin modified

10R-SPEEK cured at 808C, 1008C, 1108C and 1208C.


removed it completely. Moreover, adhering phenol, which

was present to the extent of 0.7–1.5% in the cured films, could

be removed by alkali and acid treatment as was ascertained

from analysis of the yellowish alkali extract obtained in this

treatment.

The anomalous behavior of steady lowering of the wet film

weight in air to less than the original weight was also not

observed after the treatment. Apparently, the toughness of

the treated films is also better. Water uptake properties of a

few cured and treated films (method 2) as a function of

temperature are shown in Fig. 2. As is evident, water uptake

properties up to 608C (equilibrated for 24 h at each

temperature) are comparable to those of Nafion (30–35%

by weight). In contrast to treated films, untreated films

became soft and spongy at temperatures >508C, leading to

loss of mechanical properties. Those untreated films cured

at>1208C andwith>10% PFRwere mechanically somewhat

better, but showed poor water uptake. The mechanical

properties and dimensional changes in water uptake and

conductivities of treated films are shown in Table 2. It is seen

that while the tensile strengths remained almost unchanged,

there was wide variation in elongation of the treated films

cured at different temperatures. It appears that at about

1008C the films attained good elongation, which again fell at

1208C. In order to examine this further, a freshly cast film

with 10R composition but cured finally at 1108C was also

prepared and given chemical treatment as described in

method 2 above. The properties of this film are also shown in

Table 2, along with those of the other films. It is evident that

curing at 1108C improved the elongation behavior of the film,

while the tensile strength remained virtually unchanged,

showing optimal curing.

Dimensional changes with water uptake clearly show

anisotropic dimensional changes, with a much larger

swelling in thickness than in area, as has also been reported

by Yin et al.20 for sulfonated and branched/crosslinked

polyimide membranes.

Infrared spectraThe infrared spectra of crosslinked but untreated 10R-SPEEK

films cured at different temperatures are shown in

Fig. 3A along with that of SPEEK, while the spectra of two

cured and treated films are shown in Fig. 3B. Characteristic

peaks, as reported by Gil et al.13 and Muthu Lakshmi et al.,21

were present in all the films. Addition of PFR and subsequent

crosslinking resulted in shifting of the –OH absorption band

of SPEEK at 3400–3500 cm�1. This peak shifted in treated

films to 3370 cm�1 from 3440 cm�1 of untreated films. Bands

at 1080 cm�1, due to sulfur–oxygen symmetrical vibration,

and at about 1250 cm�1 for the sulfonic acid group, appeared

for all cured and treated samples. However, the asymme-

trical vibrations of the sulfonate group which appeared at

about 1250 cm�1 for SPEEK shifted to 1150–1300 cm�1 for the

cured films, indicating possible formation of sulfonate ester

groups. The band at 1650 cm�1 was assigned to the backbone

carbonyl group in all the samples. It was observed that

differences in the spectra started appearing only at 808C,indicating the onset of curing and removal of the adhering

DMF.


Thermal propertiesThermograms of modified 10R-SPEEK films cured at various

temperatures are shown in Fig. 4. These traces showed an

initial loss of about 8–10% until around 1008C, due to

removal of bound water. Since the membranes were heated

at 80–1208C for extended periods under reduced pressure to

constant weight, there was no possibility of degradation

until 1208C. The first weight loss due to degradation was in

the range 250–2808C, as reported by Xing et al.7 Further

weight loss at 450–6008C was due to decomposition of the

main chain. Char yield of about 42–45% at 8008C indicated

synergistic thermal stabilization. There was little variation in

the thermal degradation characteristics of films cured at

different temperatures. As is evident, the modified mem-

branes are expected to have good thermal stability in the

temperature range of interest for fuel cell application.

Ion exchange and proton conductivityThe ion-exchange capacity (IEC) properties of the untreated

membranes were not consistent and capacities varied over a

wide range (0.30–0.70meq/g). Reproducible IEC values

were obtained for the alkali–acid–water-treated membranes.

For example, IECs were 1.31,1.32 and 1.33meq/gm for

treated 10R100, 10R120 and 10R140 films, respectively, which

were comparable to directly synthesized but non-crosslinked

SPEEK membranes and were higher than those of Nafion

(0.91–0.95meq/gm),13 indicating the usefulness of the

treatment method followed. 05R- and 15R-crosslinked and

treated films showed consistent IECs of 1.72–1.78 and

0.22–0.30meq/g, which were considered either too high or

too low. Moreover, 05R films showed poor handling

characteristics, becoming too soft on water absorption. The

original SPEEK has an IEC of about 2.20, which on dilution

with PFR should give IECs in the range 1.40–1.80. IECs as

obtained for the treated films showed reduction due to

possible crosslinking.

Table 3 shows the properties of 10R100 films under various

treatments, alongwith the ex situ conductivity values in 0.1M


DOI: 10.1002/pat

Table 3. Tensile Properties of Injection-Molded Specimens of PEEK/TLCP/RCP Blends with different compatibilizer content

Composition (mass ratio)Abbreviation

PropertiesPEEK TLCP RCP E-modulus (MPa) Tensile Strength (Mpa) Strain (%)

100 0 0 PEEK 1712 (1580) 91 (87) 48.2 (76.9)98 2 0 PT1 1862 (1780) 101 (99) 35.5 (32.1)98 2 2 PTc1 1760 98 27.695 5 0 PT2 1824 (1797) 102 (97) 24.7 (37.6)95 5 2 PTc2 1930 103 19.590 10 0 PT3 1931 (1927) 109 (107) 18.6 (22.7)90 10 2 PTc31 2036 110 15.690 10 5 PTc32 2009 108 13.6

�The values in parentheses were determined from as-molded blends.The standard deviations of 5measurments in E-modulus and tensile Strengthwere less than 3%and the ones of elongation at breakwere less than 5%.


sulfuric acid. We have also included values for 10R110 for

comparison. As is evident, the alkali–acid–water-treated

films had appreciable conductivities of 115–150mS/cm for

both films and were comparable to that of Nafion.

0

200

400

600

800

1000

1200 (A)

(B)

150100500

Current den

Cel

l vo

ltag

e (m

V)

600

605

610

615

620

625

630

635

640

645

650

6040200

Time

Cel

l vo

ltag

e (m

V)

Figure 5. (A) Polarization curves of various

pressure with 99% humidification. ^, Nafio

(B) Voltage–time characteristic of 10R-110 fil

total gas pressure with 99% humidification.


Fuel cell performanceThe MEA performance data of 10R100, 10R110 and Nafion

under identical conditions are presented in Fig. 5A. As is

observed, the performance of 10R110 was comparable to that

350300250200

sity(mA/cm2)

12010080

(h)

films at 458C under ambient total gas

n; ~, 10R-100 film; &, 10R-110 film.

m at 50 mA/cm2 at 458C under ambient


DOI: 10.1002/pat


of Nafion, while 10R100 deteriorated at current densities

higher than 150mA/cm2 (lower performance relative to

reported values is attributable to lower Pt loading in the

catalyst and a lower operating temperature of 408C). Similar

evaluation of unmodified SPEEK showed deterioration of the

membrane in 2 h at a current density of 50mA/cm2. The

MEA experiment with 10R110 was continued for more than

100 h at 50mA/cm2without loss of performance, as shown in

Fig. 5B. In these experiments it was observed that proper

humidification of themembrane is essential, and depletion of

the moisture content in the gases in the fuel cell experiments

almost irreversibly lowered the performance of the mem-

branes. A polarization study with unmodified SPEEK

indicated loss of film integrity in about 3 h at 50mA/cm2.

Since the modified membranes have good conductivity and

IEC, further work is under way with thicker membranes and

with other modifiers, such as aromatic diols.

CONCLUSIONS

SPEEKwas crosslinked using a lowmolecular weight phenol

formaldehyde resin in various proportions, using DMF as a

casting solvent. Removal of solvent and curing were

accomplished through an elaborate heat-treatment schedule.

It was observed that the curing reaction starts at about 808Cunder reduced pressure. The associated by-product DMA

was removed through alkali–acid–water treatment. Films

obtained using 40 parts by weight of phenol formaldehyde

resin per 100 parts of SPEEK (10R-SPEEK) showed good

water absorption, ion-exchange capacity and proton con-

ductivity. The water absorption characteristics, proton

conductivity and integrity up to 608C showed their

suitability for application in PEM fuel cells. 10R film cured

at 1108C showed a performance comparable with Nafion in

the fuel cell test.

AcknowledgmentsThe authors thank Dr J. Narayanadas, Director, NMRL, for

his interest and for permission to publish this work. Thanks

are also due to Mrs L. Chandrasekhar and Mrs. S.

Roychoudhury for experimental assistance.

REFERENCES

1. Guo Q, Pintauro PN, Tang H, O’Connor S. Sulfonated andCrosslinked Polyphosphazene-Based Proton-ExchangeMembranes. J. Membr. Sci. 1999; 154: 175.

2. Kim H, Litt M. Synthesis and characterization of sulfonatedpolyamide for fuel cell application. Polym. Prepr. Am. Chem.Soc. Divn. Polym. Chem. 2002; 42: 486.


3. Wainright JS, Wang JT, Weng D, Savinell RF, Litt M. Acid-Doped Polybenzimidazoles: A New Polymer Electrolyte.J. Electrochem. Soc. 1995; 142: L121.

4. Nolte R, Ledjeff K, Bauer M, Mulhaupt R. Partially sulfo-nated poly(arylene ether sulfone)—A versatile proton con-ducting membrane material for modern energy conversiontechnologies. J. Membr. Sci. 1993; 83: 211.

5. Park HB, Shin HS, Lee YM, Rhim JW. Annealing effect ofsulfonated polysulfone ionomer membranes on proton con-ductivity and methanol transport. J. Membr. Sci. 2005; 247:103.

6. Wang F, Hickner M, Kim YS, Zawodzinski TA, McGrath JE.Direct polymerization of sulfonated poly(arylene ether sul-fone) random (statistical) copolymers: candidates for newproton exchange membranes. J. Membr. Sci. 2002; 197: 231.

7. Xing P, Robertson GP, Guiver MD, Mikhailenko SD, WangK, Kaliaguine S. Synthesis and characterization of sulfonatedpoly(ether ether ketone) for proton exchange membranes.J. Membr. Sci. 2004; 229: 95.

8. Kobayashi T, Rikukawa M, Sanui K, Ogata N. Proto-n-conducting polymers derived from poly (ether-etherketone)and poly (4- phenoxybenzoyl-1, 4-phenylene). Solid State Ionics1998; 106: 219.

9. Zaidi SMJ, Mikhailenko SD, Robertson GP, Guiver MD,Kaliaguine S. Proton conducting composite membranesfrom polyether ether ketone and heteropolyacids for fuelcell applications. J. Membr. Sci. 2000; 173: 17.

10. Ren S, Li C, Zhao X, Wu Z, Wang S, Sun G, Xin Q, Yang X.Surface modification of sulfonated poly (ether ether ketone)membranes using Nafion solution for direct methanol fuelcells. J. Membr. Sci. 2005; 247: 59.

11. Kreuer KD. On the Development of Proton ConductingPolymerMembranes for Hydrogen andMethanol Fuel Cells.J. Membr. Sci. 2001; 185: 29.

12. Harrison WL, Wang F, Mecham JB, Bhanu VA, Hill M, KimYS, McGrath JE. Influence of the bisphenol structure on thedirect synthesis of sulfonated poly (arylene ether) copoly-mers. J. Polym. Sci. Polym. Chem. 2003; 41: 2264.

13. Gil M, Ji X, Li X, NaH, Hampsey JE, Lu Y. Direct synthesis ofsulfonated aromatic poly (ether ether ketone) protonexchange membranes for fuel cell applications. J. Membr.Sci. 2004; 234: 75.

14. Trotta F, Drioli E, Morgalio G, Baima Poma E. Sulfonation ofpolyetheretherketone by chlorosulfuric acid. J. Appl. Polym.Sci. 1998; 70: 477.

15. Helmer-Metzmann F, Osan F, Schneller A, Ritter H, LedjeffK, Nolte R, Thorwirth R. US Patent No. 5438082, 1995.

16. Mao S, Hamrock SJ, Ylitalo DA. US Patent No. 6090895, 2000.17. Mikhailenko SD, Wang K, Kaliaguine S, Xing P, Robertson

GP, Guiver MD. Proton conducting membranes based oncross-linked sulfonated poly (ether ether ketone). J. Membr.Sci. 2004; 233: 93.

18. Robertson GP, Mikhailenko SD, Wang K, Xing P, GuiverMD, Kaliaguine S. Casting Solvent Interactions with Sulfo-nated Poly (Ether Ether Ketone) during Proton ExchangeMembrane Fabrication. J. Membr. Sci. 2004; 219: 93.

19. Slade S, Campbell SA, Ralph TR, Walsh FC. Ionic Conduc-tivity of an Extruded Nafion 1100 EW Series of Membranes.J. Electrochem. Soc. 2002; 149: A-1556.

20. Yin Y, Hayashi S, Yamada O, Kita H, Okamoto K. Pranched/Crosslinked Sulfonated Polylmide Membranes for PolymerElectrolyte Fuel Cells. Macromol. Rapid Commun. 2005; 26;696.

21. Muthu Lakshmi RTS, Choudhary V, Varma IK. Sulphonatedpoly (etheretherketone): Synthesis and characterization.J. Mater. Sci. 2005; 40: 629.


DOI: 10.1002/pat

Documents

Crosslinked styrene-maleic acid copolymer complexes of some transition metals and their adsorption behavior