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Contents lists available at ScienceDirect

Chemical Engineering Research and Design

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h e r d

Nafion/Analcime and Nafion/Faujasite composite

membranes for polymer electrolyte membrane fuel cells

Paisan Kongkachuichay, Siraprapa Pimprom

Department of Chemical Engineering, Faculty of Engineering, Kasetsart University, Bangkok, 10900, Thailand

a b s t r a c t

The Nafion/zeolite composite membranes were synthesized for polymer electrolyte fuel cells (PEMFCs) by adding

zeolite in the matrix of Nafionpolymer. Two kindsof zeolites, Analcime and Faujasite, having differentSi/Al ratio were

used. The physico-chemical properties of the composite membranes such as water uptake, ion-exchange capacity,

hydrogen permeability, and proton conductivity were determined. The fabricated composite membranes showed the

significant improvement of all tested properties compared to that of pure Nafion membrane. The maximum proton

conductivity of 0.4373S cm1 was obtained from Nafion/Analcime (15%) at 80 C which was 6.8 times of pure Nafion

(0.0642Scm1 at 80 C). Conclusively, Analcime exhibited higher improvement than Faujasite.

2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords: Composite membrane; Fuel cell; Nafion; Zeolites

1. Introduction

Polymer electrolyte membrane fuel cell (PEMFC) is one of the

most attractive power sources for a variety of applications. It

has high efficiency and is environment-friendly (Alberti et al.,

2001; Adjemian et al., 2002; Costamagna et al., 2002; Havenga

et al., 2003; Hogarth et al., 2005). PEMFC operation requires

an electrolyte membrane to separate the chemical reaction

at anode from cathode both chemically and electrically. The

effective membrane must have good chemical, physical and

thermal stabilities as well as high proton conductivity (Smitha

et al., 2005). The most widely used electrolyte membrane is

Nafion, a perfluorinated sulfonated polymer. However, one

limitation of the current PEMFC is thetrace of CO in thehydro-gen supply, which can poison the Pt anode. The CO poisoning

effect can be retarded by operating at an alleviated tempera-

ture (Alberti et al., 2001; Adjemian et al., 2002; Costamagna et

al., 2002; Sacc et al., 2005). The reaction rates at the anode

and cathode are increased at higher temperature. However,

the proton conductivityof Nafion membrane strongly depends

on water content in the membrane. Hence, Nafion membrane

cannot operate at too high temperature because it will loss too

much water, resulting in the decrease in proton conductivity.

Thus, the concept of operating a cell at higher temperature is

keeping the membrane hydrated to maintain its proton con-

Corresponding author. Tel.: +66 25792083; fax: +66 25614621.E-mail address: fengpsk@ku.ac.th (P. Kongkachuichay).Received27 March 2009; Receivedin revisedform 12 August 2009; Accepted 28 August 2009

ductivity (Yang et al., 2001; Sasikumar et al., 2004; Shao etal., 2004; Hogarth et al., 2005; Sacc et al., 2005; Smitha et al.,

2005).

Several researchers have tried to prevent the loss of water

from the ionic pores of the Nafion by modifying the mem-

brane. One of the approaches is incorporating hydrophilic

metal oxide particles (e.g., SiO2, ZrO2, TiO2) to enhance the

water retention property (Yang et al., 2001; Shao et al., 2004;

Jalani and Datta, 2005; Kim et al., 2004; Antonucci et al., 2008).

Other hybrid membranes have been also fabricated by adding

phosphotungstic acid (Shao et al., 2004), cesium sulfate and

zirconium phosphate (Yang et al., 2001 and Costamagna et al.,

2002), and mordenite (Kwak et al., 2003).

Zeolites are microporous aluminosilicate minerals. Theyhave three-dimensional structures arising from the coordina-

tion of silicate ([SiO4]4) and aluminate ([AlO4]5) tetrahedral

linked by all corners (Dyer, 1988). Because of the difference

charge between [SiO4]4 and [AlO4]5, when both tetrahe-

dral link together it will create a negative charge inside the

secondary building unit. Subsequently, this charge will be neu-

tralized by attracting metal ion (e.g., Na+, K+). Accordingly,

zeolites are widely used as ion-exchangers and can hydrate

with high amount of water (Breck, 1974). In addition, their

properties are mostly depended on the Si/Al ratio of their

structures.

0263-8762/$ see front matter 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.doi:10.1016/j.cherd.2009.08.017

http://www.sciencedirect.com/science/journal/02638762mailto:fengpsk@ku.ac.thhttp://dx.doi.org/10.1016/j.cherd.2009.08.017http://dx.doi.org/10.1016/j.cherd.2009.08.017mailto:fengpsk@ku.ac.thhttp://www.sciencedirect.com/science/journal/02638762

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Nomenclature

Wwet weight of wetted membrane (g)

Wdry weight of dried membrane (g)

N1 concentration of NaOH (M)

N2 concentration of HCl (M)

V1 total volume of NaOH (ml)V2 volume of HCl (ml)

V3 titrated volume of NaOH (ml)

m mass of membrane (g)

Q hydrogen flow rate through the membrane

(cm3/s)

h thickness of membrane (cm)

P pressure drop across the membrane (cm Hg)

A area of membrane (cm2)

L distance between the Pt electrodes (cm)

R resistance (ohm)

a cross section area of the membrane (cm2)

In this work, two kinds of zeolites, Analcime (Si/Al=2)

and Faujasite (Si/Al = 2.43), were incorporated into the Nafion

matrix forming composite membranes. Analcime possesses

higher polarity than Faujasite. They were expected to retain

water and enhance proton conductivity of the composite

membranes. The effect of different structures of selected

zeolites on the key properties of fabricated membranes was

investigated and also compared with those of Nafion mem-

brane.

2. Materials and methods

2.1. Preparation of composite membranes

Analcime (Na16Si32Al16O9616H2O, Zeolyst) and Faujasite

(Na56Si136Al56O384250H2O, Zeolyst) were converted into H-

form by exchanging Na ion with 1 M NH4NO3 for 72 h followed

by rinsing with deionized water and calcined at 400 C for 8h.

Nafion solution (5% (w/w), ion power) was dried at 50 C for

30 min. and diluted with dimethyl-acetamide (DMAc) (10%

(w/w) solution). An appropriate amount of zeolite powder

(5, 10, 15, 25, and 35wt.%) was added and dispersed in

Nafion solution by a sonicator (Starsonic 35, LIARRE) and a

microscan ultrasonic probe. The membranes were casted onglass plates and dried at 50 C for 2 h. Then they were com-

pressed between a pair of Teflon plates and dried at 160 C for

30min.

2.2. Morphology analysis

The surface of the Nafion/zeolite composite membrane was

inspected by a scanning electron microscope (SEM, Phillips

XL30). The distribution of added zeolite particles in the Nafion

matrix was assessed by an energy dispersive X-ray spec-

trophotometer (EDS, Phillips XL30).

2.3. Water uptake measurement

The membrane was dried at 100C for 24h, weighed,soakedin

deionized water overnight at 25 C, blotted with an absorbent

paper to remove excess surfacemoisture, and reweighed. Sub-

sequently, water uptake was calculated from Eq. (1):

%wateruptake =Wwet Wdry

Wwet 100 (1)

2.4. Ion-exchange capacity measurement

The ion-exchange capacity (IEC) of the membrane was deter-mined by an acidbase titration. The dried membrane was

immersed in 0.01M NaOH solution for 24h and then, the solu-

tion was sampled and titrated with 0.005 M HCl. Afterwards,

the IEC was obtained using the following equation:

IEC =N1V1 (N2V1V2/V3)

m(2)

2.5. Hydrogen permeability measurement

Practically, a good membrane must allow less hydrogen gas

diffusing through its matrix. Otherwise, the PEMFC will loss

the hydrogen before it is dissociated to protons. The hydro-

gen permeability (P) through the fabricated membrane wasmeasured under constant input pressure. The flow rate of

hydrogen passing through the membrane was detected and

the permeability was determined according to the following

equation:

P =Qh

ADP(3)

2.6. Proton conductivity measurement

The proton conductivity of the membrane was determined by

a four-probemethod. Themembrane(1 cm4 cm) was assem-

bled in the cell contacting with two platinum electrodes. Thehydrogen having different relative humidity was filled into

the cell and the temperature was controlled isothermally. The

resistance between two probes was measured by a milliohm

meter (Hewlett Packard 4338A). The conductivity () was then

determined by the following equation:

=L

Ra(4)

3. Results and discussion

3.1. Morphology of composite membrane

The dimension of the prepared membrane was

5 cm 5 cm3070m. The typical surface morphology

of the composite membrane is presented in Fig. 1. Fig. 1(a)

and (c) were taken by the SEM showing the quite smooth

surface of the membranes. Using the EDS mode of the SEM,

the well distribution of Si atoms that represent the added

zeolite particles can be seen from Fig. 1(b) and (d).

3.2. Water uptake

The variations of the water uptake of the Nafion/zeolite mem-

branes are shown in Fig. 2. It is clearly seen that thecomposite

membrane can adsorb water much more than that of pure

Nafion membrane (shown in Table 1), especially with high

amounts of zeolites.

The water uptake of the composite membranes increases

with increasing amount of added zeolites. Because zeo-

lite structure consists of 3D connected pores having strong

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Fig. 1 SEM/EDS pictures of Nafion/zeolite (35%) membranes (a) surface of Nafion/Analcime membrane, (b) Si-mapping (as

white dots) of Nafion/Analcime, (c) surface of Nafion/Faujasite membrane and (d) Si-mapping (as white dots) of

Nafion/Faujasite.

Fig. 2 Water uptake of Nafion/zeolite membranes at 25 C.

polarity, it can adsorb water well. Comparing between

Nafion/Analcime and Nafion/Faujasite, it is found that

Nafion/Analcime membrane can adsorb higher water content

than Nafion/Faujasite membrane. This difference may come

from the stronger polarity of Analcime that has lower Si/Al

than Faujasite (more [AlO4]5 in the structure leads to more

negative charges in the secondary building units of zeolite).

Table 1 Properties of Nafion membranea.

Water uptake (%) 6IEC (mequiv. g1) 2.50

H2 permeability at 25 C (Barrel) 590

Proton conductivity at 25 C (Scm1) 0.031

a Tested by this work.

3.3. Ion-exchange capacity (IEC)

The ion-exchange capacities (IEC) of the fabricated mem-

branes are presented in Fig. 3. Similar to water uptake,

the addition of zeolite into the Nafion increases the IEC of

the composite membrane to be much higher than that of

pure Nafion membrane. The maximum IEC 8.07mequiv. g1

that is 3.2 times of pure Nafion was obtained from the

Nafion/Analcime (35%). Comparing between Analcime and

Faujasite, the former has higher IEC than the latter (4.45

and 3.39 mequiv. g1, respectively (GSA Resources, 2000)).

Accordingly, Nafion/Analcime possesses higher IEC than

Nafion/Faujasite.

Fig. 3 Ion-exchange capacity of Nafion/zeolite

membranes.

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Fig. 4 H2 permeability of Nafion/zeolite membranes (a)

Nafion/Analcime and (b) Nafion/Faujasite.

3.4. Hydrogen permeability

The result of hydrogen permeability tested at varied tempera-

tures (2880

C) is shown in Fig. 4. It shows that hydrogen gascan diffuse through the Nafion matrix easier than through

zeolite particles because the solid particle has much higher

density than the polymer matrix. Thus, the larger amount of

zeolite added, the higher resistance to the hydrogen diffusion

achieved. On the other hand, when temperature is increased,

the hydrogen molecules move faster due to the higher kinetic

energy causing an increase in diffusion. In this work, the

used Analcime had average particle size larger than Faujasite

(4m compared to 0.5m); therefore, it could obstruct hydro-

gen movement more than the smaller one. Consequently, the

Nafion/Analcime membranes exhibit lower hydrogen perme-

ability.

Fig. 5 Proton conductivity of Nafion/zeolite membranes at

25 C.

Fig. 6 Proton conductivity of Nafion/zeolite membranes

compared with Nafion membrane at varied temperatures.

3.5. Proton conductivity

Fig. 5 shows the proton conductivity of the Nafion/zeolite

membrane under controlled relative humidity (99.9%), 25 C.

The addition of zeolite enhances the proton conductivity

compared to pure Nafion membrane.However,above 15% zeo-

lite the conductivity declines with the incorporated amount.

When large amount of zeolite was dispersed inside the

polymer matrix, it might reach the limitation of uniform

dispersion and started to agglomerate creating some voids

among the clusters. These voids caused the increase of resis-

tance to proton transfer. The maximum obtained conductivity

at 25C is 0.3531S cm1 from Nafion/Analcime (15%) that is 11

times of pure Nafion (0.0316 S cm1). This improvement may

come from thehydration insidethe 3D channels of zeolite. Thehydrated water enhances the motion of proton or hydronium

ion via the exchange of proton between hydronium ion and

water molecule (Kwak et al., 2003; Hogarth et al., 2005). Sim-

ilar to previous properties, Nafion/Analcime exhibited better

proton conductivity than Nafion/Faujasite.

When the temperature was raised from room temperature,

the proton conductivity increases for all tested membranes

as shown in Fig. 6 and reaches the maximum point at

80 C, before decreasing drastically. The maximum value of

0.4373Scm1 was obtained from Nafion/Analcime (15%) at

80 C which is 6.8 and 1.6 times of pure Nafion (0.0642 S cm1

at 80 C) and Nafion/Faujasite (15%) (0.2803S cm1 at 90 C),

respectively. At high temperature the dissociation of hydro-gen is promoted causing an increase of proton conductivity.

However, at temperatures above 80 C, which are close to the

boiling point of water, the adsorbed water inside the mem-

brane vaporized rapidly. Moreover, under this severe condition

zeolites could be leached out from the Nafion matrix via

hydrothermal degradation (Gmez et al., 2000) and hydro-

gen permeation could be enhanced resulting in the drastic

decrease in proton conductivity.

4. Conclusions

The zeolites, Analcime and Faujasite, were added into Nafion

to form composite membranes. The prepared Nafion/zeolite

membranes yielded better tested properties than that

of Nafion membrane. The proton conductivity of the

Nafion/Analcime membrane can be improved 11 times at

room temperature and 6.8 times at 80 C, compared to Nafion

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membrane.However,there is a limitation of zeolitedispersion

causing a reduction of conductivity.

Acknowledgements

This work was supported in part by the Kasetsart Univer-

sity Research and Development Institute (KURDI) and the

National Center of Excellence for Petroleum, Petrochemicals,and Advanced Materials.

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