28

CHAPTER IV

Processing of Proton Exchange Membrane for Direct Methanol Fuel cell

Monchai Pianmanakij, Anuvat Sirivat*, Kitipat Siemanond The Petroleum and Petrochemical College, Chulalongkom University

AbstractProton exchange membrane (PEM) is a polymeric electrolyte for in direct methanol

fuel cells (DMFC). The membrane supports proton transport and separates the cathode from the anode. Nafion is widely used as the membrane in DMFC because of its high proton conductivity and mechanical strength. Nevertheless, it is of high methanol permeability and very expensive. The high methanol permeability leads to a decrease in DMFC performance. Therefore, alternate polymer membranes were developed. Polysulfone and polyvinylidene fluoride were fabricated as PEMs in this work. The polymer membranes were characterized for the degree of sulfonation, ion exchange capacity, proton conductivity, water uptake, and mechanical strength. The degree of sulfonation was improved with increasing ratio of acid per polymer and affected both proton conductivity and water uptake. The properties of membranes were directly compared with a commercial membrane Nafion.

Keywords: Fuel cell, Proton exchange membranes, Polysulfone, Polyvinylidene fluoride, Sulfonated polymer

4.1 IntroductionA direct methanol fuel cell (DMFC) is the one type of the alternative energy source

which utilizes methanol as a fuel to generate electricity (Carrette et al., 2001). Methanol is oxidized to generate proton, electron, and carbon dioxide at the anode position in DMFC system. The proton is transported through the polymeric electrolyte membrane from the anode to the cathode and then combined with oxygen and electron to generate electricity (พ ootthikanokkhan et al., 2006). Proton exchange membrane (PEM) is an important component of DMFC because it is responsible for proton transport from the anode to the cathode and the entire fuel cell performance (Higashihara et al., 2009; El-Araby et al., 2012). The requirements of PEM are reasonable proton conductivity, high stability and durability in

29

fuel cell environment, good mechanical toughness, high thermal stability, and impermeability to fuel gas or liquid (Higashihara et a i, 2009).

Presently, the most commonly-used perfluorinated polymer is known its trade name, Nafion developed by DuPont as PEM because of its high proton conductivity (~0.1 s/cm) at ambient temperature (Qiao et al., 2005), high chemical, electrochemical, and mechanical stability, a good thermal resistance (Wootthikanokkhan et al., 2006; Boroglu et al., 2011; Higashihara et al., 2009). However, these are many disadvantages as limited operation temperature (0-80 °C) (Higashihara et al., 2009), high cost, high methanol permeability (~10‘ 6cm2/s) (Boroglu et al., 2011), and difficulty in synthesis and processing (Chang et al., 2007; Rhim et al., 2004). Due to these shortcomings of Nafion, several researches have been reported sulfonated polymers used as a PEM. The sulfonation process enhances the hydrophilic pathway for proton transfer within a polymer matrix by attaching sulfonic groups (SO 3H ) on its polymer backbone. There are many sulfonated polymers such as poly(ether ether ketone) (Macksasitom et al., 2012; Zaidi et al., 2000; Liu et al., 2007), poly(phenylene) (Ghassemi et al., 2004; Kobayashi et al., 1998), poly(arylene ether) (Gao et al., 2005; Wang et al., 2001), polyimides (Chen et al., 2007; Miyatake et al., 2007), polysulfone (บทnikrishnan et al., 2012), and polyvinylidene (Macksasitom et al., 2012).

Kreuer et al. (2001) studied the sulfonated aromatic polymer as S-PEEK for PEM in DMFC application. The methanol permeability of S-PEEK was lower than that of Nafion membrane, which might help to reduce the high methanol crossover of Nafion in DMFC. Polysulfone (PSF) was modified by sulfonation process to prepare sulfonated polysulfone (SPSF) used as PEM in DMFC (Chen et al., 2005; Fu et al., 2006). The SPSF exhibited better performances comparable to those of Nafionll5 due to its lower methanol crossover and high current density. Wootthikanokkhan et al. (2006) fabricated sulfonated polyvinylidene (SPVDF) used as PEM. The methanol permeability of SPVDF was lower than that of Nafion because of the hydrophobic nature of PVDF.

In this work, polymers, PSF and PVDF, were fabricated membranes and sulfonated at various sulfuric acids to polymer mole ratio. The water uptake, ion exchange capacity, proton conductivity, methanol permeability, and mechanical properties were investigated under the effect of degree of sulfonation and compared with those of a commercial membrane Nafionl 17.

30

4.2 Experimental

4.2.1 MaterialsPolysulfone (PSF; Aldrich) and polyvinylidene fluoride (PVDF; Aldrich) were

used as polymer based membranes. Concentration sulfuric acid (H2SO4; Univar, Ar grade) was used as a sulfonating agent. Methanol (Univar, Ar grade) was used in the methanol permeation study. Dichloromethane (DCM; RCI Labscan, AR grade), N-methyl-2- pyrrolidinone (NMP; RCI Labscan, HPLC grade), dimethylacetamide (DMAc; RCI Labscan, AR grade), and deionized water were used as solvents. Sodium hydroxide (NaOFl; Ar Grade) was used in the titration processes find the degree of sulfonation and ion exchange capacities. Sodium chloride (NaCl; Analytical Grade) was used as an electrolyte for exchanging H+ in the sulfonic groups of the sulfonated polymers.

4.2.2 Preparation of sulfonated polysulfone (S-PSF)and sulfonated polvfvinylidene fluoride) (S-PVDF)

S-PSF was prepared by dissolving 2 g of polysulfone (PSF) in a 10 ml of DCM. S-PVDF was prepared by dissolving PVDF (2 g) in NMP (60 ml). The concentrate H2SO4 was added into the polymer solution (PSF or PVDF solution) at various acid per polymer ratios and at various reaction temperatures between 25 and 50 °c. The sulfonated solution was continuously stirred for 4 h, then the solution was precipitated by methanol in an ice bath. The precipitate was washed using DI water until pH of precipitate reached neutral. The sulfonated polymer as S-PSF and S-PVDF was dried at 100 °c for 24 h (Macksasitom et al, 2012; sâxena et al., 2009).

4.2.3 Fabricating polymer membrane (S-PSF and S-PVDF)Either S-PSF or S-PVDF (1.5g of S-PSF and 1.5 g of S-'PVDF was put in a

round bottom flask and dissolved in a DMAc solvent (20ml) to form a polymer solution. The polymer solution was continuously stirred 25 °c until homogenous. The film was formed by a casting method and heated in a vacuum oven at 80 °c for 24 h.

4.2.4 CharacterizationsThe sulfonated polymers functional groups were determined using a FT-IR

spectrometer (Nicolet, Nexus 670). The sulfonated polymers, used in a powder form, were

31

g r in d e d a n d m ix e d w i th p o ta s s iu m b r o m id e ( d r ie d a t 100 ๐c fo r 2 4 h ) a s b a c k g r o u n d , a n d c o m p re s s e d in to p e l le t s ( M a c k s a s i to m et al., 2 0 1 2 ) . T h e m e a s u r e m e n ts w e r e c a r r ie d o u t in th e in th e w a v e n u m b e r r a n g e o f 4 0 0 - 1 6 0 0 c m " 1 w i th 6 4 s c a n s .

T h e s t r u c tu r e s o f s u l fo n a te d P E E K a n d P P E E S w e re d e te r m in e d b y a N M R s p e c t r o m e te r ( B r u k e r B io s p in A v a n c e 5 0 0 M H z N M R s p e c t ro m e te r ) u s in g d e u te r a te d d im e th y l s u l fo x id e (D M S O -^ rt) a s th e s o lv e n t . F o r e a c h a n a ly s is , 3 w t% p o ly m e r s o lu t io n w a s p r e p a r e d in D M S O a n d th e e x p e r im e n t w a s c o n d u c te d a t r o o m te m p e ra tu re .

T h e th e rm a l p r o p e r ty o f s u l f o n a te d m e m b r a n e w a s in v e s t ig a te d u s in g a T h e r m o - G r a v im e tr ic /D if f e r e n t ia l T h e r m a l A n a ly z e r ( T G /D T A ; R e rk in E lm e r , P y r is D ia m o n d ) . T h e s a m p le s w e r e w e ig h e d in th e r a n g e o f 4 - 1 0 m g a n d in s e r te d in to a lu m in a

p a n s . T h e m e a s u r e m e n ts w e r e c a r r ie d o u t u n d e r n i t ro g e n f lo w b e tw e e n 2 5 ๐c to 7 0 0 °c a t a

h e a t in g r a te o f 10 °c. m in -1 ( Z h a n g et al., 2 0 1 1 ) .T h e c r y s ta l l in e s t r u c tu r e o f p o ly m e r a n d s u l f o n a te d p o ly m e r w a s e x a m in e d b y

a w id e a n g le X - r a y d i f f r a c t io n ( B r u k e r A X S , D 8 A d v a n c e ) . T h e C u K - a lp h a r a d ia t io n s o u r c e w a s o p e ra te d a t 4 0 k v /3 0 m A . T h e in te r f e r e n c e p e a k w a s e l im in a te d b y a K - b e ta f i l te r . D iv e r g e n c e s il t a n d s c a t te r in g s i l t o f 0 .5 ° to g e th e r w i th 0 .3 m m o f r e c e iv in g s i l t w e r e u s e d . T h e s a m p le s w e r e m o u n te d o n a s a m p le h o ld e r a n d a m e a s u r e m e n t w a s c o n t in u o u s ly ru n . T h e e x p e r im e n t w a s r e c o r d e d b y m o n i to r in g th e d i f f r a c t io n p a t te r n a p p e a r in g in th e 2 0 r a n g e f ro m 5 to 5 0 , w i th a s c a n s p e e d o f 1 7 m in , a n d a s c a n s te p o f 0 .0 2 ° .

4 .2 .5 D e g r e e o f S u l f o n a t io n ( P S )T h e d e g re e o f s u l f o n a t io n w a s d e te rm in e d a u s in g a t i t r a t io n m e th o d . T h e

p o ly m e r m e m b r a n e s w e r e a c id i f ie d b y 0.1 M o f h y d r o c h lo r ic s o lu t io n a t r o o m te m p e r a tu r e f o r 2 4 h . T h e n th e m e m b r a n e s w e r e w a s h e d w i th d e io n iz a t io n w a te r a n d d r ie d a t 80 °c f o r 2 4 h . A f t e r th a t th e m e m b r a n e s w e r e p l a c e d in a s o d iu m c h lo r id e s o lu t io n f o r 2 4 h . T h e d e g r e e o f s u l f o n a t io n o f p o ly m e r s o lu t io n w a s d e te r m in e d b y th e t i t r a t io n w ith 0 .0 1 M o f s o d iu m h y d r o x id e u s in g p h e n o lp h th a le in a s an in d ic a to r . T h e d e g re e o f s u l fo n a t io n w a s c a lc u la te d a s in th e f o l lo w in g E q . (1 ) :

DS( % ) = — ?1/w! 0" ! Cwa0" )/1000 - X 1 0 0 % (1 )M o le o f p o l y m e r m e m b r a n e

w h e re VNa0H r e f e r s to th e v o lu m e o f s o d iu m h y d r o x id e s o lu t io n , a n d CNa0H r e f e r s to th e c o n c e n t r a t io n o f s o d iu m h y d r o x id e s o lu t io n .

32

4 .2 .6 W a te r u p t a k eIn th e W a te r u p ta k e m e a s u r e m e n t , th e m e m b r a n e s w e re im m e rs e d in to D I

w a te r f o r 2 4 h a t r o o m te m p e ra tu re . E x c e s s w a t e r w a s r e m o v e d f ro m th e m e m b r a n e s u r f a c e w ith a p a p e r a n d th e m e m b ra n e w a s w e ig h e d ( n o te d a s พร). T h e m e m b r a n e s w e r e d r ie d a t

100 °c f o r 2 4 h in a v a c u u m o v e n a n d w e ig h e d (n o te d a s พd). T h e p e r c e n ta g e o f w a t e r u p ta k e w a s th e n c a lc u la te d a s in th e f o l lo w in g E q . (3 ) :

W a te r u p ta k e = ( พ ' - W h ) x 1 0 0 (2 )

Wd

w h e r e W d r e fe r s to th e w e ig h t o f d r ie d p o ly m e r , a n d พ ร is th e w e ig h t o f s w o l le n p o ly m e r

4 .2 .7 P ro to n C o n d u c t iv i tyP ro to n c o n d u c t iv i ty o f m e m b r a n e w a s m e a s u r e d b y a n im p e d a n c e p h a s e

a n a ly z e r (H P , 4 1 9 4 ) f o r m e a s u r in g u n d e r d r y s t a t e a n d u s in g a n im p e d a n c e p h a s e a n a ly s e r H P 4 1 9 4 f o r m e a s u r in g u n d e r w e t s ta te a t v a r io u s f r e q u e n c ie s f ro m 10 0 H z to 2 M H z a n d a t r o o m te m p e ra tu re . T h e m e m b ra n e s w e r e c u t in to a 5 X 5 c m 2 s p e c im e n f o r th e m e a s u r e m e n t w i th a n d w ith o u t im m e rs e d in d e io n iz e d w a te r a t ro o m te m p e r a tu r e f o r 2 4 h . P r o to n c o n d u c t iv i ty w a s c a lc u la te d a s in th e f o l lo w in g E q . (4 ) :

a (S o n - 1 ) = -^— (3 )

w h e r e <J is th e p r o to n c o n d u c t iv i ty (S c m " 1), d i s th e th ic k n e s s o f th e m e m b r a n e (c m ) , A is th e a re a o f th e in te r f a c e o f m e m b ra n e in c o n ta c t w i th th e e le c t ro d e s (c m 2), a n d R r e fe r s to th e m e a s u r e d r e s i s ta n c e o f th e m e m b r a n e d e r iv e d f r o m th e h ig h f r e q u e n c y s e m i- c i r c le o n th e c o m p le x im p e d a n c e p l a n e w ith th e z a x is (o h m ) .

4 .2 .8 Io n E x c h a n g e C a p a c i ty (IE C )Io n e x c h a n g e c a p a c i ty o f m e m b r a n e w a s d e te rm in e d b y a t i t r a t io n m e th o d . Io n

e x c h a n g e c a p a c ity is a m e th o d to d e te rm in e th e n u m b e r o f m i l l ie q u iv a le n t o f io n s in 1 g o f d ry p o ly m e r (m e q ./g ) . T h e m e m b r a n e s w e re s o a k e d in 0.1 M N a C l s o lu t io n fo r 2 4 h to

3 3

e x c h a n g e H + w ith N a +. H + w e r e t i t r a te d w i th 0 .01 M -N a O H s o lu t io n w i th u s in g p h e n o lp h th a le in a s a n in d ic a to r . I o n e x c h a n g e c a p a c i ty o f m e m b r a n e w a s c a lc u la te d u s in g f o l lo w in g E q . (2 ) ( M a c k s a s i to m et al. , 2 0 1 2 ) :

IEC (mmol g — 1 ) C o n s u m e d m l(N a O H )x m o la r ity N a O H w e ig h t d r i e d m e m b r a n e (4 )

w h e re c o n s u m e d m l ( N a O H ) i s th e c o n s u m e d v o lu m e o f N a O H s o lu t io n , m o la r i ty N a O H is th e m o la r o f N a O H s o lu t io n , a n d w e ig h t d r ie d m e m b r a n e is th e w e ig h t o f m e m b r a n e in a d r y s ta te .

4 .2 .9 M e th a n o l P e r m e a b i l i tyT h e m e th a n o l p e r m e a b i l i t y r e fe r s th e a m o u n t o f m e th a n o l th a t p e r m e a te s

th ro u g h t h e m e m b r a n e . T h e p e r m e a t io n c e ll f o r m e th a n o l p e r m e a b i l i ty m e a s u r e m e n t c o n s is te d o f c h a m b e r A a n d c h a m b e r B a s s e p a r a te d b y th e s u l fo n a te d p o ly m e r m e m b ra n e . C h a m b e r A w a s f d le d w i th 2 5 0 m l o f m e th a n o l s o lu t io n (2 .0 M ) . C h a m b e r B w a s f i l le d w i th 2 5 0 m l o f D I w a te r . T h e m e m b r a n e w a s p la c e d b e tw e e n c h a m b e r A a n d c h a m b e r B . T h e m e th a n o l p e r m e a b i l i t y w a s c a lc u la t e d a s in th e f o l lo w in g E q . (5 ) :

P ( c m 2/ s ) =kRx VR X L (5 )A X (CA- Cb)

w h e re p i s th e m e th a n o l p e r m e a b i l i t y , Ca a n d Cb a re th e m e th a n o l c o n c e n t r a t io n s in th e c o m p a r tm e n ts A a n d B r e s p e c t iv e ly , A a n d L a r e th e a re a a n d th e th ic k n e s s o f a m e m b r a n e r e s p e c t iv e ly , Vq is th e v o lu m e o f th e s o lu t io n in th e c o m p a r tm e n t B , kg is th e s lo p e o f th e m e th a n o l c o n c e n t r a t io n p r o f i l e in th e c o m p a r tm e n t B . T h e m e th a n o l c o n c e n t r a t io n s w e r e m e a s u r e d w i th a th e r m a l c o n d u c t iv i ty d e te c to r ( T C D ) in g a s c h r o m a to g r a p h y w h e r e e th a n o l w a s u s e d a s th e in te r n a l s ta n d a rd .

4 .2 .1 0 M e c h a n ic a l P r o p e r t ie sT h e m e c h a n ic a l p r o p e r t i e s n a m e ly th e te n s i le s tre n g th , y i e ld s tra in , a n d

Y o u n g ’s m o d u lu s w e r e m e a s u r e d u s i n g a u n iv e r s a l te s t in g m a c h in e (L lo y d , m o d e l S M T 2 - 5 0 0 N ) a t r o o m te m p e r a tu r e w i th a 2 5 m m .m in '1 s p e e d . T h e m e m b r a n e s w i th 2 0 0 p m th ic k

3 4

w e r e c u t in to 1 x 5 c m 2 s p e c im e n s . E a c h s a m p le w a s m e a s u r e d f ro m 5 s p e c im e n s a n d th e a v e r a g e v a lu e w a s ta k e n .

4.3 Results and Discussion

4 .3 .1 C h a r a c te r i z a t io n o f s u l f o n a te d p o ly m e r4 .3 .1 .1 F o u r ie r tr a n s fo r m in f r a r e d s p e c t r o s c o p y

F ig u r e 4 .1 s h o w s th e F T IR s p e c t r a o f P S F a n d S P S F . T h e p e a k s a t 1 4 8 5 c m '1-, 1 4 1 2 c m '1, 1 3 6 5 c m '1,a n d 1 2 4 4 c m '1 r e f e r to th e a r o m a tic 0 = c s t r e tc h in g , th e a s y m m e tr ic C -H b e n d in g d e f o r m a t io n o f m e th y l g r o u p , th e s y m m e tr ic C -H b e n d in g d e f o r m a t io n o f m e th y l g r o u p , a n d th e a s y m m e tr ic C - O - C s t r e tc h in g o f a ry l e th e r g ro u p , r e s p e c t iv e ly ( N a im e t al.', F ic a i e t a l . , 2 0 1 0 ) . T h e p e a k s a t 1 1 0 7 a n d 1 0 9 2 c m '1 c a n b e a s s ig n e d to th e a r o m a t ic r in g v ib r a t io n . T h e p e a k s a t l 3 2 5 a n d 12 9 8 c m 1, a n d 1 5 5 0 c m '1 c a n b e id e n t i f i e d w i th th e d o u b le t r e s u l t in g f ro m th e a s y m m e tr ic 0= s= 0 s t r e tc h in g o f s u l fo n e g r o u p a n d th e s y m m e tr ic 0 = s= 0 s t r e tc h in g o f s u l f o n e g ro u p , r e s p e c t iv e ly ( N a im e t a l; K a r ls s o n e t a l . , 2 0 0 4 ) . H o w e v e r , S P S F e x h ib i t s th e p e a k s a t 1 1 7 0 a n d 1 0 2 7 c m '1 c o r r e s p o n d in g to th e a s y m m e tr ic 0 = s= 0 s t r e tc h in g o f s u l fo n a te g r o u p a n d th e s y m m e tr ic 0= s= 0 s t r e tc h in g o f s u l f o n a te g r o u p , r e s p e c t iv e ly ( N a im e t a t) . T h e F T - I R p e a k s o f P V D F a n d S P V D F a p p e a r a t 1 4 0 3 a n d 1 1 8 5 c m '1 d u e to th e C H 2 w a g g in g v ib r a t io n a n d th e C -C b o n d , r e s p e c t iv e ly . T h e p e a k s a t 8 7 8 a n d 8 4 0 c m "1 r e f e r to th e C -C -C a s y m m e tr ic a l s t r e tc h in g v ib r a t io n a n d th e C F s t r e tc h in g v ib r a t io n (B a i e t a t , 2 0 1 2 ) . H o w e v e r , th e p e a k a t 1 4 0 0 c m '1 c a n b e r e f e r e d to th e s u l fo n a te g r o u p w h ic h o n ly a p p e a r s f ro m S P V D F ( C H 2 s c is s o r in g ) .

4 .3 .1 .2 N u c le a r M a g n e t ic " R esonance (N M R )F u r th e r m o r e , th e ~ s u lfo n a te d p o ly m e r s n a m e ly S P S F a n d S P V D F w e r e

id e n t i f i e d b y N M R s p e c tra . T h e N M R s p e c t r u m o f s u l fo n a te d P S F s h o w e d th e p r o to n r e s o n a n c e a t 7 .2 5 p p m w h ic h c a n b e a s s ig n e d to th e p r o to n a d ja c e n t to th e n e w p e n d e n t s u l f o n ic a c id o n th e P S F s t r u c tu r e ( D e u r im e t a t , 2 0 0 9 ) . W h ile s u l fo n a te d P V D F s p e c t ru m s h o w e d th e p r o to n r e s o n a n c e a t 2 .0 0 p p m id e n t i f y in g th e s u l fo n ic a c id o n th e P V D F b a c k b o n e . T h u s th e r e s u l t s o f F T IR a n d N M R s h o w e d th a t th e s u l f o n a te g r o u p w a s s u c c e s s f u l ly a t t a c h e d to th e p o ly m e r b a c k b o n e s .

3 5

4 .3 . น X - r a y D if f r a c t io n (X R D )T h e s u l f o n a te d p o ly m e r s n a m e ly b o th S P S F a n d S P V D F s h o w e d

b r o a d a m o r p h o u s s c a t te r in g X R D p a t te r n s f o r b o th p o ly m e r s a f te r s u l fo n a t io n . T h e in c r e a s e in D S p r o d u c e d m o r e a m o r p h o u s P S F a n d P V D F s t r u c tu r e s b e c a u s e m o r e s u l f o n ic a c id p e n d a n t g r o u p s p r e s e n t o n th e p o ly m e r b a c k b o n e s a f f e c t in g th e c h a in c o n f o r m a t io n a n d o r ie n ta t io n o f th e a m o r p h o u s s t r u c tu r e s ( R e y n a - V a le n c ia e t a h , 2 0 0 5 ; Z a id i , 2 0 0 3 ) . F ig u r e 4 .2 s h o w s th e X R D p a t te r n o f S P S F is b r o a d e r th a n S P V D F b e c a u s e th e S P S F h a s a b e n z e n e r in g in th e p o ly m e r b a c k b o n e r e s u l t in g in a lo w e r c h a in p a c k in g th a n S P V D F (R u i e t a l , 2 0 1 3 ) .

4 .3 .1 .3 T h e r m o g r a v im a tr ic A n a ly s is (T G A )T h e P S F th e rm o g ra m e x h ib i te d a s in g le - s te p d e g r a d a t io n te m p e r a tu r e

o f th e p o ly m e r b a c k b o n e a t h ig h e r th a n 4 5 0 °c. T h e S P S F th e r m o g r a m e x h ib i te d th r e e s te p s o f d e g ra d a t io n . T h e w e ig h t lo s s b e tw e e n 5 0 a n d 1 8 0 ๐c r e p r e s e n te d th e e v a p o r a t io n o f w a te r . T h e w e ig h t lo s s b e tw e e n 1 8 0 a n d 4 0 0 ๐c c a n b e a t t r ib u te d to th e d e c o m p o s i t io n o f th e s u l f o n ic a c id g r o u p o n th e p o ly m e r b a c k b o n e . F in a l ly , th e w e ig h t lo s s o f S P S F b a c k b o n e d e g r a d a t io n o c c u r r e d a t 4 5 0 °c. T h e P V D F th e r m o g r a m s h o w e d th e p o ly m e r b a c k b o n e d e g r a d a t io n a t a r o u n d 4 3 0 °c. T h e S P V D F th e r m o g r a m d is p la y e d th r e e s te p s d e g ra d a t io n . F ir s t , th e w e ig h t lo s s b e tw e e n 1 0 0 a n d 2 0 0 °c r e p r e s e n te d th e s p l i t o f w a te r . S e c o n d ly , th e d e c o m p o s i t io n o f th e s u l f o n ic a c id g r o u p o c c u r r e d b e tw e e n 2 0 0 a n d 4 0 0 °c. L a s t ly , th e w e ig h t lo s s o f S P V D F b a c k b o n e d e g r a d a t io n o c c u r r e d a t 4 4 0 ๐c ( D e v r im e t a l . , 2 0 0 9 ) .

4 .3 .2 D e g r e e o f S u l f o n a t io n (D S )T h e D S w a s in v e s t ig a te d b a s e d o n th e e f fe c t o f m o le r a t io s o f a c id p e r

p o ly m e r a n d te m p e r a tu r e o f s u l f o n a t io n p r o c e s s . T h e in c re m e n t o f m o le r a t io o f a c id p e r p o ly m e r in d u c e d in c r e a s in g o f D S ( F ig u r e 4 .3 ) b e c a u s e th e a c id p e r p o ly m e r r a t io e n h a n c e d th e o p p o r tu n i ty o f s u l f o n ic g r o u p a t t a c h m e n t o n th e p o ly m e r b a c k b o n e s (F u e t a l , 2 0 0 6 ) . T h e D S o f S P S F a t 2 5 ๐c w e r e 1 2 .7 % to 7 1 .5 5 % a t v a r io u s m o le r a t io s o f a c id p e r p o ly m e r o f 17 to 8 0 . F u r th e r m o r e , th e D S in c r e a s e d w i th in c r e a s in g s u l f o n a t io n te m p e r a tu r e f ro m 2 5 to 5 0 ๐c . T h e D S w a s p r o m o te d to 5 0 % D S a t 5 0 ๐c in th e s u l f o n a t io n p r o c e s s a t th e s a m e m o le r a t io s o f a c id p e r p o ly m e r . F ro m th is r e s u l t , i t a p p e a r s th a t th e s u l f o n ic g r o u p w a s a c c e le r a te d in a t t a c h in g o n to th e p o ly m e r b a c k b o n e s a t a h ig h e r t e m p e r a tu r e d u e to in c r e a s in g r e a c t io n r a te ( D u a r te e t a l , 2 0 1 1 ) .

12%VtoàOL

36

4 .3 .3 W a te r U p ta k eT h e w a te r u p ta k e in a m e m b r a n e g e n e ra l ly d ic ta te s th e h y d r o p h i l ic n a tu r e o f

p o ly m e r (บ ทท ik r i s h n a n et al., 2 0 1 2 ) . T h e w a t e r u p ta k e v a lu e s o f S P S F a n d S P V D F a re s h o w n in F ig u r e 4 .3 . T h e w a te r u p ta k e in c r e a s e s w i th in c r e a s in g D S b e c a u s e o f m o r e h y d r o p h i l ic o f p o ly m e r v ia s u l f o n ic g r o u p ( S e u n g et al., 2 0 0 6 ) . T h e w a te r u p ta k e o f S P S F m e m b r a n e s a r e b e tw e e n 2 .1 6 a n d 9 .0 1 % (D S 1 2 .7 5 - 7 1 .5 5 % ) . T h e w a te r u p ta k e o f S P V D F is 2 .7 8 a t D S a s 1 2 .3 4 % . F lo w e v e r , th e N a f io n 1 1 7 p r o v id e s th e h ig h e s t w a te r u p ta k e a s 1 6 .3 0 % b e c a u s e th e N a f io n m e m b r a n e h a s b e e n g r a f te d c h e m ic a l ly in to b a c k b o n e w i th h y d r o p h i l ic s u l f o n ic a c id g r o u p s ( H S O 3). T h e s e io n ic g r o u p s h a v e c a u s e d th e a b s o rp t io n o f th e la r g e a m o u n t o f w a te r b y p o ly m e r a n d th e r e f o r e , le d to h y d r a t io n o f p o ly m e r . F u r th e r m o r e , th e N a f io n h a s a h ig h e r f r e e v o lu m e b e tw e e n p o ly m e r ic c h a in s w h ic h in d u c e s m o r e w a te r a b s o rp t io n . ( P e ig h a m b a r d o u s t et al., 2 0 1 0 ) .

4 .3 .4 P r o to n C o n d u c t iv i tyT h e p r o to n c o n d u c t iv i ty o f S P S F a n d S P V D F w a s m e a s u r e d in a d r y s ta t e a n d

w e t s ta te a t 2 5 °c. T h e p r o to n c o n d u c t iv i ty in c r e a s e s w i th i n c r e a s i n g 't h e D S a s s h o w n in F ig u r e 4 .4 b e c a u s e th e s u l fo n ic g r o u p p r o to n a te d th e (SO 3H ) s i t e p r o v id e d m o r e h y d r o p h i l ic p a th w a y s fo r p r o to n t r a n s p o r t . T h e p r o to n s t r a n s p o r te d b y h o p p in g b e tw e e n o n e h y d r o ly z e d io n ic s i te ( ร 0 3' แ 3 0 +) to a n o th e r th o r o u g h ly th e m e m b ra n e ( M a c k s a s i to m et a l, 2 0 1 2 ) . M o r e o v e r , th e p r o to n c o n d u c t iv i ty o f S P S F a n d S P V D F u n d e r w e t s ta te is h ig h e r th a n th a t o f d r y s ta te b e c a u s e m o r e w a te r in s id e th e m e m b r a n e p r o m o te s th e p r o to n t r a n s f e r ( M a c k s a s i to m et a l, 2 0 1 2 ) . T h e S P S F m e m b r a n e s w e r e s h o w n to p o s s e s s th e p r o to n c o n d u c t iv i ty b e tw e e n 2 .4 3 x 1 0 "4 a n d 5 .4 2 x 1 0"4 s / c m u n d e r d r y s ta te a n d b e tw e e n 4 .6 0 x 1 O'4

a n d 9 .7 7 x 1 0 "4 s / c m u n d e r w e t s ta te a t 2 5 ° c . T h e p r o to n c o n d u c t iv i ty o f S P V D F w a s 2 .0 8 x 1 O'4 S /c m u n d e r d r y s ta te a n d 2 .0 9 x 1 O'4 s / c m u n d e r w e t s ta te . T h e p r o to n c o n d u c t iv i ty o f S P S F is h ig h e r th a n S P V D F a t 1 2 % o f D S b e c a u s e th e a r o m a t ic h y d r o c a r b o n p o ly m e r S P S F c o n s is ts o f p o la r g r o u p s u p p o r t in g p r o to n t r a n s p o r t ( R ik u k a w a et al, 2 0 0 0 ) . M o r e o v e r , a m o r e a m o r p h o u s s t r u c tu r e o f S P S F w i th h ig h e r f re e v o lu m e a l lo w s m o r e f o r w a te r a b s o r p t io n r e s u l t in g in e n h a n c e d p r o to n t r a n s p o r t ( R ik u k a w a et a l, 2 0 0 0 ) . T h e p r o to n c o n d u c t iv i ty o f N a f i o n l l 7 is 3 .1 7 X 1 0 -4 s / c m u n d e r d r y s ta te a n d 2 .8 8 X 1 0 '3 s / c m u n d e r w e t s ta te . T h e p r o to n c o n d u c t iv i ty o f N a f io n l 17 i s h ig h e r th a n th e s u l f o n a te d p o ly m e r s , S P S F a n d S P V D F , u n d e r b o th d r y a n d w e t s ta te s b e c a u s e N a f io n l 17 a l lo w m o r e w a te r a b s o r p t io n a s id e n t i f i e d b y th e h ig h e s t w a te r u p ta k e f o r p r o to n t r a n s p o r t ( B a s c h e k et a l, 1 9 9 9 ) . T h e p r o to n c o n d u c t iv i ty o f a l l S -P V D F a n d S -P S F m e m b r a n e s a r e r e la t iv e ly lo w e r th a n th e l i t e r a tu r e s a s

37

ta b u la te d in T a b le 4 .1 b e c a u s e o u r im p e d a n c e m e a s u r e m e n t c o n d i t io n w a s s e t a t 2 5 °c a n d w ith 5 0 % R H , th e m e m b r a n e s w e r e im m e rs e d in w a t e r fo r 2 4 h b e f o r e m e a s u r e m e n t . W h e r e a s in th e p r e v io u s w o rk r e p o r te d , S P S F a n d S P V D F p r o to n c o n d u c t iv i ty w a s m e a s u r e d u n d e r fu l ly h y d r a te d s ta te , so th e p r o to n c o n d u c t iv i t ie s o f c u r r e n t ly S -P V D F a n d S -P S F ( ~ 1 0 '4) w e r e o b v io u s ly lo w e r th a n th o s e o f th e p r e v io u s w o rk ( ~ 1 0 '3 - 1CT1) (Y u a n q in et al., 2 0 1 1 ; H o B u m et al., 2 0 0 4 ; N e d a l et al., 2 0 1 0 ; L u f fa n o et al., 2 0 0 9 ; S h e n g -L i et al., 2 0 0 5 ; Y i l s e r et al., 2 0 0 9 ; L u f fa n o et al., 2 0 1 1 ; Y o n g z h u et al., 2 0 0 7 ; C h a n g k h a m c h o m et al., 2 0 1 3 ) .

4 .3 J Io n E x c h a n g e C a p a c i ty ( IE C )T h e in c re a s e D S in d u c e s in c r e a s in g IE C a s s h o w n in F ig u re 4 .6 . T h e I E C is

r e la te d to th e c o n c e n t r a t io n o f s u l f o n ic a c id g r o u p w i th in p o ly m e r m e m b r a n e s b e c a u s e th e s u l f o n ic g ro u p s p r o v id e m o r e H + to e x c h a n g e w ith c a t io n (N a + f ro m N a O H s o lu t io n ) ( P e ig h a m b a r d o u s t et al., 2 0 1 0 ) . T h e IE C v a lu e s o f S P S F a re 0 .1 2 1 , 0 .1 6 6 , 0 .1 8 7 , 0 .5 2 2 , a n d 0 .5 3 0 m e q /g a t v a r io u s D S s . A t th e s a m e D S , th e IE C v a lu e o f S P V D F is c lo s e d to S P S F b e c a u s e o f n e a r ly th e s a m e a m o u n t o f s u l f o n ic g r o u p s p r e s e n t fo r p r o m o t in g H + to e x c h a n g e . H o w e v e r , th e IE C v a lu e o f N a f i o n l l 7 (0 .7 5 0 m e q /g ) is th e h ig h e s t b e c a u s e o f h ig h e r w a te r u p ta k e a n d p r o to n c o n d u c t iv i ty .

4 .3 .6 M e th a n o l P e r m e a b i l i tyT h e m e th a n o l , p e r m e a b i l i t y is th e c a u s e o f th e lo s s o f fu e l a n d d im in i s h e d

e f f ic i e n c y ( B a ld a u f et al. , 1 9 9 9 ) . A p r o to n c a n m o v e in to th e m e m b ra n e w i th a s s o c ia te d w a te r c o n te n t . T h e m e th a n o l m o le c u le c a n b e t r a n s p o r te d w i th th e e le c t r o - o s m o t ic d r a g a n d d u e to m e th a n o l p r o p e r t ie s ( C a r r e t t e et al., 2 0 0 1 ) . T h e in c r e m e n t o f D S in d u c e d a n in c r e a s e in m e th a n o l p e r m e a b i l i ty ( a s s h o w n in F ig u r e 4 .5 ) b e c a u s e th e h y d r o p h i l ic n a tu r e o f th e p o ly m e r s w a s im p ro v e d b y th e s u l fo n a t io n p r o c e s s . In F ig u r e 4 .5 , th e m e th a n o l p e r m e a b i l i t y o f S P S F v a r ie s f ro m 0 to 9 .5 9 x 1 0"°8 c m 2-/s a t v a r io u s D S s . T h e m e th a n o l p e r m e a b i l i t y o f S P V D F is 5 .2 3 x 1 0 " ’° c m 2/s w h ic h is lo w e r th a n th a t o f S P V D F a t th e s a m e D S . S P S F h a s a m o r e a m o r p h o u s s t r u c tu r e th a n S P V D F a s c o n f i r m e d b y th e X R D p a t te r n in F ig u r e 4 .2 w i th r e s u l t in g in p r o m o t in g m e th a n o l t r a n s fe r . W h e n c o m p a re d w i th N a f io n , th e p r o to n c o n d u c t iv i ty o f N a f io n i s th e h ig h e s t ( 3 .0 8 x 10"°5 c m 2/s ) b e c a u s e o f g r e a te r w a te r u p ta k e a n d p r o to n c o n d u c t iv i ty . T h e m e th a n o l p e r m e a b i l i t y o f a ll S -P V D F a n d S -P S F a re e x t r e m e ly lo w e r th a n N a f io n a n d o m p r e v io u s w o rk . T h e m e th a n o l p e r m e a b i l i t y v a lu e s o f S - P V D F a n d S -P S F a re in th e r a n g e o f ~ 1 0 " 10 - 1 0 '8 c m 2/s , w h e r e a s th e N a f io n a n d p r e v io u s m e m b r a n e s s h o w s th e m e th a n o l p e r m e a b i l i t ie s in th e r a n g e o f ~10~5 -10"7 c m 2/s c o r r e s p o n d in g to a h ig h e r

38

p r o to n c o n d u c t iv i ty ( Y u a n q in et al., 2 0 1 1 ; H o B u m et al., 2 0 0 4 ; N e d a l et al., 2 0 1 0 ; C h a n g k h a m c h o m et al., 2 0 1 3 ) .

4 .3 .6 M e c h a n ic a l P r o p e r t ie sT h e m e c h a n ic a l p r o p e r t ie s n a m e ly te n s i le s tre n g th , y ie ld s tr a in , a n d y o u n g ’s

m o d u lu s o f s u l fo n a te d p o ly m e r a r e ta b u la te d in T a b le 4 .2 . T h e te n s i l e s t r e n g th , y ie ld s t r a in , a n d y o u n g ’s m o d u lu s o f S P S F a re in th e r a n g e s 4 2 .0 - 2 8 .4 M P a , 6 .3 4 -6 .1 1 % , a n d 9 2 0 .6 - 8 4 3 .8 7 M P a , r e s p e c t iv e ly w h e n D S w a s v a r ie d f ro m 1 2 .7 4 % to 7 1 .5 5 % . T h e te n s i le s t r e n g th , y i e ld s tr a in , a n d y o u n g ’s m o d u lu s o f S P V D F a re 3 3 .5 M P a , 1 6 .5 3 % , a n d 8 8 4 .4 5 M P a , r e s p e c t iv e ly a t D S e q u a l to 1 2 .3 4 % . T h e te n s i l e s tr e n g th a n d y o u n g ’s m o d u lu s o f th e s u l f o n a te d S P S F d e c r e a s e d w i th in c re a s in g D S . O n th e o th e r h a n d , th e y ie ld s t r a in in c r e a s e d w i th in c r e a s in g D S . T h e s u l f o n ic g ro u p s o b s t r u c t th e p a c k in g a n d d e c r e a s e th e c r y s ta l l in i ty b e tw e e n th e n e a r b y c h a in s d u e to th e b u lk s u l f o n ic g r o u p s p r e s e n t ( C h a n g k h a m c h o m et al., 2 0 1 3 ) .

4.4 ConclusionsT h e S P S F a n d S P V D F w e re s u l f o n a te d w ith th e c o n c e n t r a te d s u l fu r ic a c id ( 9 8 % ) .

T h e D S o f s u l fo n a te d p o ly m e r s in c re a s e d w i th in c re a s in g th e ra t io o f m o l ( a c id /p o ly m e r ) a n d s u l f o n a t io n r e a c t io n te m p e r a tu r e . T h e in c r e a s e in D S in d u c e d in c r e a s in g w a te r u p ta k e , IE C , p r o to n c o n d u c t iv i ty , a n d m e th a n o l p e r m e a b i l i t y b e c a u s e , o f m o r e h y d r o p h i l ic p a th w a y s c r e a te d b y th e s u l fo n ic a c id g r o u p . A t th e h ig h e s t D S s o f S P S F a n d S P V D F , th e y p o s s e s s e d p r o to n c o n d u c t iv i ty v a lu e s o f 5 .4 2 x 1 0"4 a n d 2 .0 8 x 1 O'4 s/cm, r e s p e c t iv e ly . T h e p r o to n c o n d u c t iv i ty o f th e s u l f o n a te d p o ly m e rs is , h o w e v e r , s t i l l lo w e r th a n N a f io n ( 7 .4 9 x 1 0 ’°4 S /c m ) . H o w e v e r , th e m e th a n o l p e r m e a b i l i ty v a lu e s o f S P S F a t th e h ig h e s t D S a n d S P V D F w e r e lo w e r th a n N a f io n b y a b o u t 10 0 t im e s (S P S F D S = 7 1 % , 9 .5 9 x lO '08; S P V D F D S 1 2 .3 4 % , 5 .2 3 x lO " 10c m 2/s ; N a f io n l 17 D S = 1 0 0 % , 3 .0 8 x 1 0 '°5 c m 2/s ) . T h e te n s i le s t r e n g th o f th e s u l fo n a te d p o ly m e r s d e c r e a s e d w ith in c r e a s in g D S d u e th e r e d u c t io n in c r y s ta l l in i ty v ia th e s u l f o n a t io n p ro c e s s . T h u s , S P S F a n d S P V D F a re p o te n t ia l P E M c a n d id a te s in d i r e c t m e th a n o l fu e l c e l l a p p l ic a t io n b e c a u s e th e y p o s s e s s b e t te r o v e ra l l p r o p e r t ie s r e l a t i v e to N a f io n .

AcknowledgementsT h e a u th o r s w o u ld l i k e to a c k n o w le d g e th e f in a n c ia l s u p p o r t f ro m th e C o n d u c t iv e

a n d E le c t r o a c t iv e P o ly m e r s R e s e a r c h U n i t o f C h u la lo n g k o m U n iv e r s i ty , th e T h a i la n d

39

R e s e a r c h F u n d ( T R F ) , th e R o y a l T h a i G o v e r n m e n t b u d g e t , a n d A s s t . P r o f . D r. P o n g s a k o m J a n ta r a ta n a , D e p a r tm e n t o f P h y s ic s , F a c u l ty o f S c ie n c e , K a s e t s a r t U n iv e r s i ty , fo r p r o v id in g im p e d a n c e p h a s e a n a ly s e r F IP 4 1 9 4 .

ReferencesA b u - T h a b i t , N .Y ., A l i , S .A . a n d J a v a id , Z .S .M . N e w h ig h ly p h o s p h o n a te d

p o ly s u l f o n e m e m b r a n e s f o r P E M fu e l c e l l s . J o u rn a l o f M e m b ra n e S c ie n c e . 3 6 0 ( 1 - 2 ) , 2 6 - 3 3 .

B a i , F F , W a n g , X ., Z h o u , Y . a n d Z h a n g L . P r e p a r a t io n a n d c h a r a c te r iz a t io n o fp o ly ( v in y l id e n e f lu o r id e ) c o m p o s i t e m e m b r a n e s b le n d e d w i th n a n o - c r y s ta l l in e c e l lu lo s e . P r o g r e s s in N a tu r a l S c ie n c e : M a te r i a ls I n te r n a t io n a l , 2 0 1 2 , 2 2 (3 ) , 2 5 0 - 2 5 7 .

B a s c h e k , G ., H a r tw ig , G . a n d Z a h r a d n ik , F . E f f e c t o f w a te r a b s o r p t io n in p o ly m e r s a t lo w a n d h ig h te m p e ra tu re s . P o ly m e r , 1 9 9 9 , 4 0 , 3 4 3 3 -3 4 4 1 .

B o r o g l u l , M . ร ., C a v u s l , ร ., B o z l , I. a n d A ta , A . S y n th e s is a n d c h a r a c te r iz a t io n o f p o ly (v in y l a lc o h o l ) p ro to n e x c h a n g e m e m b r a n e s m o d if ie d w i th 4 ,4 - d i a m in o d ip h e n y le th e r - 2 ,2 - d i s u l f o n ic a c id . e X P R E S S P o ly m e r L e t te r s , 2 0 1 1 , 5 ( 5 ) , 4 7 0 - 4 7 8 .

C h a n g Y - W . , W a n g E . , S h in G -, H a n J -E . a n d M a th e r P .T . P o ly ( v in y l a lc o h o l)( P V A ) /s u l f o n a te d p o ly h e d r a l o l ig o s i l s e s q u io x a n e ( s P O S S ) h y b r id m e m b r a n e s f o r d i re c t m e th a n o l fu e l c e ll a p p l ic a t io n s . P o ly m e rs f o r A d v a n c e d T e c h n o lo g ie s , 2 0 0 7 , 18, 5 3 5 - 5 4 3 .

C h a n g k h a m c h o m , ร . a n d S ir iv a t A . P o ly m e r e le c t r o ly t e m e m b r a n e b a s e d o ns u l fo n a te d p o ly ( e th e r k e to n e e th e r s u l fo n e ) (S - P E K E S ) w i th lo w m e th a n o l p e r m e a b i l i t y f o r d i r e c t m e th a n o l fu e l c e ll a p p l ic a t io n . P o ly m e r - P la s t i c s T e c h n o lo g y a n d E n g in e e r in g , 2 0 1 3 , 5 2 (1 ) , 7 0 -7 9 .

C h e n , S -L ., B o c a r s ly , A .B . a n d B e n z ig e r , J . N a f io n - la y e r e d s u l f o n a te d p o ly s u l f o n e f u e l c e ll m e m b r a n e s . J o u rn a l o f P o w e r S o u r c e s , 2 0 0 5 , 1 5 2 (0 ) , 2 7 -3 3 .

C h e n , ร . , Y in , Y ., K i ta , H . a n d O k a m o to , K .- I . S y n th e s i s a n d p r o p e r t ie s o f s u l f o n a te d p o ly im id e s f r o m h o m o lo g o u s s u l f o n a te d d ia m in e s b e a r in g b i s ( a m in o p h e n o x y p h e n y l ) s u l f o n e . J o u rn a l o f P o ly m e r S c ie n c e P a r t A : P o ly m e r C h e m is t r y , 2 0 0 7 , 4 5 ( 1 3 ) , 2 7 9 7 -2 8 1 1 .

C h e n , D . , W a n g , ร . , X ia o , M . a n d M e n g , Y . P r e p a r a t io n a n d p r o p e r t i e s o f s u l f o n a te d

4 0

p o ly ( f lu o r e n y l e th e r k e to n e ) m e m b r a n e fo r v a n a d iu m r e d o x f lo w b a t te r y a p p l ic a t io n . J o u r n a l o f P o w e r S o u r c e s , 2 0 1 0 , 1 9 5 (7 ) , 2 0 8 9 - 2 0 9 5 .

F ic a i , M - D ., F ic a i , A . , V o ic u , G -, V a s i le , B .S ., G u ra n , c . a n d A n d r o n e s c u , E.P o ly s u l f o n e b a s e d M e m b ra n e s w i th D e s i r e d P o r e s C h a r a c te r i s t ic s . M a te r ia l P la s t i c e , 2 0 1 0 , 4 7 (1 ) .

D e v r im , Y . , E rk a n , ร . , B a ç , N . a n d E r o g lu , I. P r e p a r a t io n a n d c h a r a c te r iz a t io n o f s u l fo n a te d p o ly s u l f o n e / t i ta n iu m d io x id e c o m p o s i te m e m b r a n e s fo r p r o to n e x c h a n g e m e m b r a n e fu e l c e l ls . I n te r n a t io n a l J o u rn a l o f H y d r o g e n E n e r g y , 2 0 0 9 , 3 4 (8 ) , 3 4 6 7 - 3 4 7 5 .

D u a r te , G .W ., S i lv e ir a , F .Z . , B e c k e r , E .B . , S i lv a , L ., N a s p o l in i , A . M ., C o n s e n s o ,E .C . , P a u la M . M . ร . a n d F io r i M . A . E f f e c t o f t im e a n d te m p e r a tu r e ' e x p o s i t io n in th e c r y s ta l l in i ty d e g r e e o f s u l f o n a te d p o ly - { s ty r e n e a c r y l ic a c id } ( P S A A - S ) . E le c t r o c h im ic a A c t a . 2 0 1 1 . 5 7 (0 ) . 1 7 2 -1 7 5 .

E l- A r a b y . R ., A t t ia , N .K . , E ld iw a n i , G ., S o b h i , ร . a n d M o s ta f a , T . P r e p a r a t io n o f s u l fo n a te d m o n o m e r fo r p e rn fu e l c e ll a n d s o lv e n t o p t im iz a t io n fo r r e c r y s ta l l i z a t io n . W o r ld A p p l ie d S c ie n c e s J o u r n a l , 2 0 1 2 , 1 6 (8 ) , 1 0 8 2 -1 0 8 6 .

F u , Y ., L i, พ . a n d M a n th i r a m , A . S u l f o n a te d p o ly s u l f o n e w i th 1 ,3 -1 Hd ib e n z im id a z o le - b e n z e n e a d d i t iv e a s a m e m b r a n e f o r d i r e c t m e th a n o l fu e l c e l ls . J o u rn a l o f M e m b r a n e S c ie n c e . 2 0 0 8 . 3 1 0 ( 1 - 2 ) . 2 6 2 - 2 6 7 .

F u r ta d o , F . a n d G o m e s , A . s . S u l fo n a te d b i s p h e n o l - A - p o ly s u l f o n e b a s e d c o m p o s i t e P E M s c o n ta in in g tu n g s to p h o s p h o r i c a c id a n d m o d if ie d b y e le c t ro n b e a m ir r a d ia t io n . I n te r n a t io n a l J o u rn a l o f H y d r o g e n E n e r g y . 3 7 (7 ) , 6 2 2 8 -6 2 3 5 .

G a o , Y . , R o b e r ts o n , G . P . , G u iv e r , M . D . , J ia n , X ., M ik h a i le n k o , ร . D ., W a n g K . a n d K a l ia g u in e ร . S u l fo n a t io n o f p o ly ( p h th a la z in o n e s ) w i th f u m in g s u l f u r ic a c id m ix tu r e s fo r p r o to n e x c h a n g e m e m b r a n e m a te r ia ls . J o u r n a l o f M e m b r a n e S c ie n c e . 2 0 0 3 , 2 2 7 ( 1 - 2 ) , 3 9 -5 0 .

G h a s s e m i, H . a n d M c G r a th , J .E . S y n th e s i s a n d p r o p e r t i e s o f n e w s u l fo n a te d p o ly ( p - p h e n y le n e ) d e r iv a t iv e s fo r p r o to n e x c h a n g e m e m b r a n e s . I. P o ly m e r , 2 0 0 4 , 4 5 , 5 8 4 7 -5 4 .

H ig a s h ih a r a , T ., M a t s u m o to , K . a n d U e d a . M . S u l f o n a te d a r o m a t ic h y d r o c a r b o np o ly m e r s a s p r o to n e x c h a n g e m e m b r a n e s f o r fu e l c e l ls . P o ly m e r , 2 0 0 9 , 5 0 , 5 3 4 1 -5 3 5 7 .

K im , Y . ร . , E in s la , B ., S a n k ir , M ., H a r r i s o n , พ . a n d P iv o v a r , B . s . S t r u c tu r e -p r o p e r ty - p e r f o r m a n c e r e la t io n s h ip s o f s u l f o n a te d p o ly ( a r y ! e n e e th e r s u l f o n e ) s

a s a p o ly m e r e le c t ro ly te f o r fu e l c e ll a p p lic a tio n s '. P o ly m e r , 2 0 0 6 , 4 7 ( 1 1 ) , 4 0 2 6 - 4 0 3 5 .

41

K o b a y a s h i , T ., R ik u k a w a , M ., S a n u i , K . a n d O g a ta , N . P r o to n - c o n d u c t in g p o ly m e r s d e r iv e d f ro m p o ly ( e th e r - e th e r k e to n e ) a n d p o ly ( 4 - p h e n o x y b e n z o y l - l , 4 - p h e n y le n e ) . S o l id , 1 9 9 8 , 1 0 6 , 2 1 9 - 2 2 5 .

L iu , B . , R o b e r ts o n , G .P . , K im , D .S . , G u iv e r , M .D ., H u , พ . , J ia n g , z. A r o m a t icp o ly e th e r k e to n e s w i th p e n d a n t s u l fo n ic a c id p h e n y l g r o u p s p r e p a r e d b y a m i ld s u l f o n a t io n m e th o d fo r p r o to n e x c h a n g e m e m b r a n e s . M a c r o m o le c u le s , 2 0 0 7 , 4 0 , 1 9 3 4 -1 9 4 4 .

L u f r a n o , F ., B a g l io , V . , D i B la s i , O ., S ta i t i , P . , A n to n u c c i , V . a n d A r ic , A.s. S o l id p o ly m e r e le c t r o ly te b a s e d o n s u l f o n a te d p o ly s u l f o n e m e m b r a n e s a n d a c id ic s i l i c a f o r d i r e c t m e th a n o l fu e l c e l l s . S o l id S ta te Io n ic s , 2 1 6 ( 0 ) , 9 0 -9 4 .

L u f ra n o , F ., B a g l io , V . , S ta i t i , P . , S ta s s i , A . , A r ic , A.s. a n d A n to n u c c i , V .I n v e s t ig a t io n o f s u l fo n a te d p o ly s u l f o n e m e m b r a n e s a s e le c t r o ly te in a p a s s iv e ­m o d e d i r e c t m e th a n o l fu e l c e l l m in i - s ta c k . J o u rn a l o f P o w e r S o u r c e s , 1 9 5 (2 3 ) , 7 7 2 7 -7 7 3 3 .

M a y a h i , A ., I s m a i l , A .F . , I lb e y g i , H . , O th m a n , M .H .D .M ., G h a s e m i , N o r d d in ,M .N .A .M . a n d M a ts u u ra , T . E f f e c t o f o p e r a t in g te m p e r a tu r e o n th e b e h a v io r o f p r o m is in g S P E E K /c S M M e le c t r o ly te m e m b r a n e f o r D M F C s . S e p a r a t io n a n d P u r i f ic a t io n T e c h n o lo g y . 2 0 1 3 , 1 0 6 (0 ) , 7 2 -8 1 .

M iy a ta k e , K ., Y a s u d a , T ., H ira i , M . , N a n a s a w a , M . a n d W a ta n a b e , M . S y n th e s i s a n d p r o p e r t i e s o f a p o ly im id e c o n ta in in g p e n d a n t s u l f o p h e n o x y p r o p o x y g r o u p s . J o u r n a l o f P o ly m e r S c ie n c e P a r t A : P o ly m e r C h e m is t r y , 2 0 0 7 , 4 5 ( 1 ) , 1 5 7 -1 6 3 .

N a im , R . , I s m a i l , A .F . , S a id i, H . a n d S a io n , E . D e v e lo p m e n t o f s u l fo n a te dp o ly s u l f o n e m e m b r a n e s a s a m a te r ia l f o r P r o to n E x c h a n g e M e m b r a n e (P E M ). In : P r o c e e d in g s o f R e g io n a l S y m p o s iu m o n M e m b ra n e S c ie n c e a n d T e c h n o lo g y 2 0 0 4 , 2 1 -2 5 .

P a rk , H .B ., S h in , H - S ., L e e , Y .M . a n d R h im , J - W . A n n e a l in g e f f e c t o f s u l f o n a te d p o ly s u l f o n e io n o m e r m e m b r a n e s o n p r o to n c o n d u c t iv i ty a n d m e th a n o l t r a n s p o r t . J o u rn a l o f M e m b r a n e S c ie n c e , 2 0 0 5 , 2 4 7 ( 1 - 2 ) , 1 0 3 -1 1 0 .

Q ia o , J . , H a m a y a , T . a n d O k a d a , T . N e w h ig h ly p r o to n - c o n d u c t in g m e m b r a n ep o ly ( v in y lp y r r o l id o n e ) ( P V P ) m o d if ie d p o ly ( v in y l a lc o h o l ) /2 - a c r y la m id o - 2 - m e th y l - 1 - p r o p a n e s u l f o n ic a c id ( P V A - P A M P S ) f o r lo w te m p e r a tu r e d i r e c t m e th a n o l fu e l c e l l s ( D M F C s ) . P o ly m e r , 2 0 0 5 , 4 6 , 1 0 8 0 9 -1 0 8 1 6 .

4 2

R e y n a - V a le n c ia , A ., K a l ia g u in e , ร . a n d B o u s m in a , M . T e n s i le m e c h a n ic a l p r o p e r t i e s o f s u l fo n a te d p o ly ( e th e r e th e r k e to n e ) ( S P E E K ) a n d B P O 4/S P E E K m e m b r a n e . J o u r n a l o f A p p l ie d P o ly m e r S c ie n c e , 2 0 0 5 , 9 8 , 2 3 8 0 -2 3 9 3 .

R h im J - W ., P a rk H .B ., L e e C -S ., J u n J - H . , K im D.s. a n d L e e Y .M . C r o s s l in k e dp o ly (v in y l a lc o h o l ) m e m b r a n e s c o n ta in in g s u l fo n ic a c id g r o u p : P ro to n a n d m e th a n o l t r a n s p o r t th ro u g h m e m b r a n e s . J o u r n a l o f M e m b r a n e S c ie n c e , 2 0 0 4 , 2 3 8 ,1 4 3 - 1 5 1 . -

R ik u k a w a , M . a n d S a n u i , K . P r o to n - c o n d u c t in g p o ly m e r e le c t r o ly t e m e m b r a n e s b a s e d o n h y d r o c a r b o n p o ly m e r s . P r o g r e s s in P o ly m e r S c ie n c e , 2 0 0 0 , 2 5 (1 0 ) , 1 4 6 3 - 1 5 0 2 .

S o n g , R ., X ia , G ., X in g , X . , H e , L ., Z h a o Q . a n d M a , z. M o d i f ic a t io n o fp o ly m o r p h is m s in p o ly v in y l id e n e f lu o r id e th in f i lm s v ia w a te r a n d h y d r a te d s a l t . J o u rn a l o f C o l lo id a n d I n te r f a c e S c ie n c e , 2 0 1 3 , 4 0 1 ( 0 ) , 5 0 -5 7 .

W a n g , F . , H ic k n e r , M ., Q in g , J-, H a r r i s o n , พ . , M e c h a m f J . , Z a w o d z in s k i , T .A . a n d M c G ra th , J .E . S y n th e s is o f h i g h ly s u l f o n a te d p o ly ( a r y le n e e th e r s u l fo n e ) r a n d o m ( s t a t i s t ic a l ) c o p o ly m e rs v ia d i r e c t p o ly m e r iz a t io n , M a c r o m o le c u le . 2 0 0 1 , 1 7 5 ,3 8 7 - 3 9 5 .

W o o t th ik a n o k k h a n , J . a n d S e e p o n k a i , N . M e th a n o l p e r m e a b i l i ty a n d p r o p e r t ie s o f D M F C m e m b r a n e s b a s e d o n s u l f o n a te d P E E K /P V D F b le n d s . J o u rn a l o f A p p l ie d P o ly m e r S c ie n c e . 2 0 0 6 , 1 0 2 , 5 9 4 1 -5 9 4 7 .

Z a id i , S .M .J . , M ik h a i le n k o , S .D ., R o b e r t s o n , G .P . , G u iv e r , M .D . a n d K a l ia g u in e ร . P ro to n c o n d u c t in g c o m p o s i te m e m b r a n e s f ro m p o ly e th e r e th e r k e to n e a n d h e te r o p o ly a c id s f o r fu e l c e ll a p p l i c a t io n s . -J o u rn a l o f M e m b r a n e S c ie n c e .2 0 0 0 , 1 7 3 (1 ) , 1 7 -3 4 .

Z a id i , J . P o ly m e r s u l f o n a t io n - A v e r s a t i l e r o u te to p r e p a r e p r o to n - c o n d u c t in g m e m b r a n e m a te r ia l fo r a d v a n c e d te c h n o lo g ie s . T h e A r a b ia n J o u rn a l f o r S c ie n c e a n d E n g in e e r in g . 2 0 0 3 , 2 8 .

Z h u , Y . a n d M a n th i r a m , A . S y n th e s is a n d c h a r a c te r iz a t io n o f p o ly s u l f o n e - c o n ta in in gs u l f o n a te d s id e c h a in s fo r d i r e c t m e th a n o l fu e l c e lls . J o u r n a l o f P o w e r S o u rc e s . 2 0 1 1 ,1 9 6 ( 1 8 ) , 7 4 8 1 - 7 4 8 7 .

List of table and figure

Table 4.1 C o m p a r i s o n o f p r o to n e x c h a n g e m e m b r a n e s u s e d in D M F C

Polymerรmembrane

25 ° c RH 100% 8 0 ° cRH 100% 25 ° c 70 °c

ProtonConductivity

(S/cm)Proton

Conductivity(S/cm)

ProtonConductivity

(S/cm)Methanol

(cm2/ร)Methanol

(cm2/s)PSf-sph-63a - 8.00E-03 2.20E-02 2.92E-07 -

PSf-sph-82a - 1.90E-02 4.50E-02 7.41 E-07 .PSf-sph-100a - 4.40E-02 8.90E-02 1.15E-06 -

PSf-sph-1223 - 6.50E-02 1.43E-01 1.49E-06 -

PSf-sna-32a - 1.10E-02 2.50E-02 3.60E-08 -

PSf-sna-393 - 2.20E-02 5.10E-02 1.79E-07 -

PSf-sna-493 - 4.10E-02 7.50E-02 3.01E-07 -

PSf-sna-583 - 5.70E-02 E17E-01 5.23E-07 -

N ation3 - 9.00E-02 1.51E-01 1.68E-06 -

-SPSU-3b - 5.50E-03 - 1.50E-07 -SPSU-4 b - 1.50E-02 - 2.50E-07 -SPSU-5 b - 2.20E-02 - 3.30E-07 -SP S U -6b - 5.00E-02 - 6.00E-07 -

SPSU-7 b - 7.00E-02 - 7.50E-07 -

SPSU -3-tb - 1.30E-03 - 5.00E-08 -SPSU -4-tb - 5.50E-03 - 1.00E-07 -

SPSU -5-tb - 2.20E-02 - 1.25E-07 -

SPSU -6-tb - 5.00E+02 - 2.25E-07 -

SPSU -7-tb - 6.00E-02 - 4.55E-07 -

-

PPSU-A-0.75C - 2.00E-04 1.40E-03 3.98x10-08 -

P PSU -A -1.5c - 5.00E-05 6.00E-03 9 .12x10-08 -

N ation0 - 5.00E-02 8.00E-02 6.80x10-06 -

Polymer% % พ ไ:membrane

25 ° c RH 100% 8 0 ° cRH 100% 25 ๐C 70 ° c

ProtonConductivity

(S/cm)

ProtonConductivity

(S/cm)

ProtonConductivity

(S/cm)Methanol

(cm2/ร)Methanol

(cm2/ร)SPSf57d - 8.30E-03 - - -

SPSF66d - 2.80E-02 - - -

,SPSU 87e - - 9.00E-02 - -

SPSU 127 e - - 1.40E-01 - -

sPS-151 - 4.00E-03 2.10E-02 - -

sP S -251 - 7.00E-03 4.60E-02 - -

sP S -401 - 1.40E-02 1.20E-01 - -

" SPSf908 - 0.5 - - --

SPSfh - 2.4E-04 - - -

Nafion 115' - 0.144 - - -Nafion 117' - 0.143 - - -

Nafion 117J - 8.56E-07 - 1.41E-06 1.17E-0515s» i f z 5 . - 1.81E-08 - 4.57E-07 4.57E-07

150X F -0J8' - 8.45E-08 - 7.35E-07 7.35E-07

- 3.36E-07 - 1.06E-06 1.06E-06

* Remark"Yuanqin et al., 2011 bHo Bum et al., 2004 ‘Nedal et al., 2010 dLufrano et al., 2009 cSheng-Li et al., 2005 fYilser et al., 2009 sLufrano et al., 2011 bYongzhu et al., 2007 ‘Acâcio et al., 2012 jChangkhamchom et al., 2013

Table 4.2 M e c h a n ic a l p r o p e r t ie s o f p r i s t in e a n d s u l f o n a te d m e m b ra n e s a t 70 °c

S a m p le T e n s i l e s t r e n g th (M P a )

Y ie ld s t r a in

(% )

Y o u n g m o d u lu s ( M P a )

P S F 3 9 .9 ± 1.7 7 .7 ± 0 . 9 92 1 ± 85S P S F 1 2 .7 4 % 4 2 .0 ± 5 . 7 6 .3 ± 0 .7 1 1 6 2 ± 145S P S F 1 5 .6 5 % 3 0 .6 ± 3 .1 ,5 .2 ± 0 . 3 1 0 3 0 ± 171S P S F 1 9 .9 0 % 3 1 .6 db 1 .6 5 .3 ± 0 . 5 1 0 3 4 ± 8 3

S P S F 2 7 .9 9 % 2 9 .5 5 ± 0 . 9 - 5 .3 ± 0 . 5 9 9 2 ± 73

S P S F 4 4 .6 6 % 2 9 .3 2 ± 0 . 8 5 .3 ± 0 . 3 9 8 7 ± 6 4S P S F 6 1 .4 4 % ' 2 9 .0 ± 2 . 0 5 .3 ± 0 . 9 9 8 7 ± 171S P S F 7 1 .5 5 % 2 8 .4 ± 5 . 4 6.1 ± 0 . 6 8 4 4 ± 15 6

P V D F 2 5 .7 ± 2 . 9 3 0 .9 ± 1 .9 3 4 9 ± 1 1 4S P V D F 1 2 .3 4 % 3 3 .5 ± 1 .0 1 6 .5 ± 1 . 3 8 8 4 ± 2 8

46

Figure 4.1 T h e F T - I R s p e c t r a o f p o ly s u l f o n e ( P S F ) a n d s u l fo n a te d p o ly s u l f o n e ( S P S F ) a t v a r io u s d e g re e s o f s u l fo n a t io n .

Figure 4.2 X R D p a t te r n o f s u l f o n a te d S P S F a n d S P V D F .

Proto

n con

ducti

vity (

S/cm)

4 7

Figure 4 .3 W a te r u p ta k e o f S P S F , S P V D F , a n d N a t io n 11 7 .

.0012

.0010

.0008

.0006

.0004

.0002

0.000012.34 12.75 15.25 19.9 27.99 44.66 61.44 71.35 100

Degree o f sulfonation (%)

- o - Dry SPVDF 12.34%๐ Dry SPSF

—• — Dry Nation 117—0 — Wet SPVDF 12.34%

Wet SPSF—o— Wet Nation 117

o ..... o

■ๆ ----------- 1----------- r

.(ร-

-. o

Figure 4.4 Proton conductivity of SPSF, SPVDF, and Nation 117 under dry and wet state at25 ๐c .

Ion

exch

ange

cap

acity

(meq

/g)

In

Meth

anol

perm

eabilit

y (cm

2/S)

48

0 10 20 3 0 40 50 60 70 80Degree o f sulfonation (%)

M e th a n o l p e r m e a b i l i ty o f S P S F , S P V D F , a n d N a f io n 1 1 7 .

Figure 4 .6 Io n e x c h a n g e c a p a c ity o f S P S F , S P V D F , a n d N a f io n 1 1 7 .