Seediscussions,stats,andauthorprofilesforthispublicationat:https://www.researchgate.net/publication/229005509

PreparationofthePVA/HAPcompositepolymermembraneforalkalineDMFCapplication

ARTICLEinDESALINATION·AUGUST2007

ImpactFactor:3.76·DOI:10.1016/j.desal.2007.09.036

CITATIONS

43

READS

115

3AUTHORS,INCLUDING:

Chun-ChenYang

MingchiUniversityofTechnology

85PUBLICATIONS1,831CITATIONS

SEEPROFILE

Availablefrom:Chun-ChenYang

Retrievedon:09February2016

Preparation of the PVA/HAP composite polymer

membrane for alkaline DMFC application

Chun-Chen Yang*, Che-Tseng Lin, Shwu-Jer Chiu

Department of Chemical Engineering, Mingchi University of Technology,

Taipei Hsien 243, Taiwan, ROC

Tel. þ886-290 89899; Fax þ886-290 41914; email: ccyang@ccsun.mit.edu.tw

Received 10 July 2007; accepted revised 29 September 2007

Abstract

A novel polyvinyl alcohol/hydroxyapatite (PVA/HAP) composite polymer membrane was prepared by thedirect blend process and solution casting method. Glutaraldehyde (GA) was used as a crosslinker for the com-posite polymer membrane in order to enhance the chemical, thermal and mechanical stabilities and to reducethe swelling ratio. The characteristic properties of the PVA/HAP composite polymer membranes were exam-ined by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM),micro-Raman spectroscopy and AC impedance method. Alkaline DMFC, consisting of an air cathode electrodewith MnO2 carbon inks, an anode electrode with PtRu black inks on Ti-mesh matrix and the PVA/HAP com-posite polymer membrane, was assembled and investigated. It was found that the alkaline DMFC using a novelcheap PVA/HAP composite polymer membrane showed good electrochemical performance at ambienttemperature and pressure.

Keywords: PVA/HAP; Composite polymer membrane; Direct methanol fuel cell (DMFC); Alkaline; MnO2

1. Introduction

Direct methanol fuel cells (DMFCs) [1–13]

have recently received a lot of attentions due

to these power sources presenting a high-energy

efficiency and low emission of pollutants. The

DMFC has attracted much attention because

of using liquid methanol fuel, which is easy to

deliver and store. More importantly, liquid fuel

can use at ambient temperature and pressure,

which makes the DMFC easily be applied on

the portable 3C electronic devices. However, the

development of acidic DMFC has faced several

serious problems: (i) slow methanol oxidation

kinetics, (ii) the poisoning of CO intermediate on

the Pt surface, (iii) the high methanol crossover*Corresponding author.

Presented at the Fourth Conference of Aseanian Membrane Society (AMS 4), 16–18 August 2007, Taipei,

Taiwan.

0011-9164/08/$– See front matter # 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.desal.0000.00.000

Desalination 233 (2008) 137–146

through the polymer membrane, (iv) the high costs

of the Nafion membrane and Pt catalyst. Presently,

the perfluorosulfonate ionomer membranes,

such as Nafion membrane (Dupont), are the pri-

mary polymer membranes used on the DMFC.

However, the commercial Nafion polymer

membranes showed serious methanol crossover

problem [2,4], which methanol permeates from

the anode to the cathode. The methanol permea-

tion not only causes a loss of fuel but also forms

a mixed potential at the cathode and leading to a

lower electrochemical performance of the

DMFC. Thus, for the liquid methanol fuel cell,

it is imperative that the most important charac-

teristic properties of a solid polymer membrane

on the DMFC must have a lower methanol

permeation of liquid fuel.

Alkaline polymer electrolytes based on PVA

have been studied for application on Ni–MH

[14], Zn–air [15], and DMFC cells [16,17]. They

reported the alkaline PVA–KOH polymer elec-

trolyte exhibiting the ionic conductivity around

10�2–10�1 S cm�1 at room temperature. Recently,

Yang [17] synthesized the alkaline crosslinked

PVA/TiO2 composite polymer membranes applied

on the DMFC.

Hydroxyapatite (Ca10(PO4)6(OH)2, HAP) has

long been used as an implant material due to

excellent biocompatibility, bioactivity and che-

mical stability. The addition of hydroxyapatite

(HAP) ceramic filler into polymer matrix is allow

to reduce the glass transition temperature (Tg)

and the crystallinity of the PVA polymer, and

also allow the increase the amorphous phases

of polymer matrix, then increase the ionic con-

ductivity. There are various ceramic fillers, such

as Al2O3, TiO2 [2], SiO2 [3], have been exten-

sively studied. As we know, when the HAP filler

used as a stiffer material added into the PVA

matrix, the swelling ratio of PVA/HAP composite

polymer membrane is effectively reduced. The

thermal property, dimension stability and swelling

ratio are at the same time improved.

Experimental results indicated improvements

in the ionic conductivity, thermal property, and

dimension stability as different amounts of the

ceramic fillers were added into the solid

polymer electrolyte (SPE). The reason for the

increase in the ionic conductivity of composite

polymer electrolyte was explained that the cera-

mic particle fillers in the polymer matrix created

some defects at interface of the ceramic particles

and the polymer chain. In this work, we

attempted to disperse these HAP ceramic fillers

into the PVA matrix act as a solid plasticizer

capable of enhancing chemical, thermal and

mechanical stabilities for the PVA composite

polymer membrane.

TGA was used to analyze the thermal stab-

ility properties of the PVA/HAP composite

polymer membrane. XRD was used to examine

the crystallinity of the PVA/HAP polymer mem-

brane. SEM was used to examine the surface

morphology of the composite polymer film.

Micro-Raman spectroscopy was applied to

examine the composition of the PVA/HAP poly-

mer membrane. The ionic conductivity of alka-

line PVA/HAP composite polymer electrolytes

was measured by AC impedance spectroscopy.

The characteristic properties of the crosslinked

PVA/HAP polymer membranes with different

weight percents of HAP fillers (2.5–10 wt.%)

were examined and discussed in detail.

In this work, the alkaline DMFC, composed

of the air cathode electrode loaded with MnO2/

BP2000 carbon inks, the PtRu black anode elec-

trode (4.00 mg cm�2) and the PVA/HAP com-

posite polymer membrane, was assembled and

investigated. The PVA/HAP composite polymer

membrane was first prepared through directing

blend PVA with HAP fillers under ultrasonic

condition. The composite polymer membrane

was then further immersed in 5 wt.% glutaralde-

hyde (GA) solution for a crosslinking treatment.

For anodic methanol electro-oxidation reaction,

cathodic oxygen reduction reaction (ORR) and

138 C.-C. Yang et al. / Desalination 233 (2008) 137–146

the overall reaction of the DMFC in alkaline

media can be described as follows:

Anodic reaction:

CH3OHþ 6OH� ! CO2 þ 5H2Oþ 6e�;

E�a ¼ �0:810 V ðvs: SHEÞ

Cathodic reaction:

1:5O2 þ 3H2Oþ 6e� ! 6OH�;

E�c ¼ 0:402 V ðvs: SHEÞ

Overall reaction:

CH3OHþ 1:5O2 ! CO2 þ 2H2O;

E�cell ¼ 1:21 V

The electrochemical characteristics of the

DMFCs employing alkaline PVA/HAP compo-

site polymer membranes were investigated by

the linear polarization and the potentiostatic

method; especially, for the peak power density

of the DMFC.

2. Experimental

2.1. Preparation of the PVA/HAP composite

polymer membranes

PVA (Aldrich), HAP ceramic fillers (Aldrich),

and KOH (Merck) were used as received with-

out further purification. Degree of polymeriza-

tion and saponification of PVA were 1700 and

98–99%, respectively. The PVA/HAP compo-

site polymer membranes were prepared by a

solution casting method. The appropriate weight

ratios of PVA:HAP ¼ 1:2.5–10 wt.% were dis-

solved in distilled water under stirring, respec-

tively. The above resulting solution was stirred

continuously until the solution mixture became

a homogeneous viscous appearance at 90�C for

2 h. The addition sequence of powders and the

time of blending in the beaker were well controlled.

The resulting mixture solution was poured out

into a Petri dish. The thickness of wet composite

polymer membrane is between 0.20 and 0.40

mm. The Petri dish with viscous PVA/HAP

composite polymer sample was weighed again

and then the excess water was allowed to evapo-

rate slowly at 25�C with a relative humidity of

30%. After water solvent evaporation, the Petri

dish with the composite polymer membrane was

weighed again. The composition of the PVA/HAP

composite polymer membrane was determined

from the mass balance. The thickness of the

composite polymer membrane was controlled

at between 0.15 and 0.30 mm.

2.2. Crystal structure, morphology, and

thermal analyses

TGA thermal analysis was carried out using a

METTLER TOLEDO TGA/ SDTA 815e sys-

tem. Measurements were carried out by heating

from 25 to 600�C, under N2 atmosphere at a

heating rate of 10�C min�1 with about 10 mg

sample. The crystal structures of all PVA/HAP

composite polymer membranes were examined

using a Philips X’Pert X-ray diffractometer

(XRD) with Cu Ka radiation of wavelength

� ¼ 1.54056 A for 2� angles between 10 and

90�. The surface morphology and microstructure

of all PVA/HAP composite polymer membranes

were investigated by a Hitachi S-2600H scan-

ning electron microscope (SEM).

2.3. Ionic conductivity measurements

Conductivity measurements were made for

alkaline PVA/HAP composite polymer mem-

brane by an AC impedance method. The PVA/

HAP composite samples were immersed in

8 M KOH solutions for at least 24 h before test-

ing. The alkaline PVA/HAP composite polymer

membranes were sandwiched between SS304

stainless steel, ion-blocking electrodes, each of

surface area 1.32 cm2, in a spring-loaded glass

holder. A thermocouple was kept in close to the

composite polymer membrane for temperature

C.-C. Yang et al. / Desalination 233 (2008) 137–146 139

measurement. Each sample was equilibrated at

the experimental temperature for at least 60 min

before measurement. AC impedance measurements

were carried out using an Autolab PGSTAT-30

equipment (Eco Chemie B.V., Netherlands). The

AC frequency range from 10 kHz to 10 Hz at

an excitation signal of 5 mV was recorded. The

impedance of the composite polymer membrane

was recorded at a temperature range between

30 and 70�C. Experimental temperatures were

maintained within +0.5�C by a convection oven.

All alkaline PVA/HAP composite polymer

membranes were examined at least three times.

2.4. Micro-Raman spectroscopy analyses

Raman spectrum is a unique tool to charac-

terize the PVA/HAP blend polymer membrane.

The Raman spectroscopy analysis was carried

out by a Renishaw confocal microscopy Raman

spectroscopy system with a microscope equipped

with 5�, 20�, and 50� objectives, and a charge

coupled device (CCD) detector. Raman excita-

tion source was provided by 633 nm laser beam,

which had the beam power 25 mW and was

focused on the sample with a spot size of about

1 mm in diameter.

2.5. Preparation of the anode and

cathode electrodes

The preparation of the catalyst slurry ink for

the anode electrode was prepared by mixing

90 wt.% PtRu black inks (Alfa, HiSPEC 6000,

PtRu black with Pt:Ru ¼ 1:1 molar ratio),

10 wt.% PTFE binder solution (Dupont, 60 wt.%

base solution), and a suitable amount of distilled

water and alcohol. The resulting PtRu black

mixtures were ultrasonicated for 2 h. The PtRu

black inks were loaded onto the Ti-mesh (Delker,

USA) by a paintbrush method to achieve a

loading of PtRu black of 4.0 mg cm�2. The

as-prepared PtRu anode electrode was dried in

a vacuum oven at 365�C for 1 h.

The carbon slurry for the gas diffusion layer

of the air cathode was prepared with a mixture of

70 wt.% Shawinigan acetylene black (AB50)

with specific surface area of 80 m2 g�1 and

40 wt.% PTFE (Teflon-30J suspension) as a

wet-proofing agent and binder. The carbon slurry

was coated on the Ni-foam as a current collector

and then pressed at a pressure of 120 kgf cm�2.

The gas diffusion layer was then sintered at

temperature of 370�C, 60 min. The catalyst

layer of the air electrode was then prepared

by spraying a mixture of a 36 wt.% of PTFE

solution binder and 64 wt.% of mixed powders

consisting of �-MnO2 (electrolytic manganese

oxide, EMD) catalyst supported on BP2000

carbon black. The Ni-foam current collector

was cut from 1 � 1 cm2. The preparation meth-

ods of the air cathode electrodes have been

reported in detail [18].

2.6. Electrochemical measurements

The PVA/HAP composite polymer membrane

was sandwiched between the sheets of the anode

electrode and the cathode electrode, and then

hot-pressed at 60�C for 120 kgf cm�2 for 5 min

to obtain a membrane electrode assembly (MEA).

The electrode area of the MEA was about 1 cm2.

The electrochemical measurements were car-

ried out in a two-electrode system. The i–t and

the power density curves of the DMFC using alka-

line PVA/HAP composite polymer membrane

were recorded at the potentials of 0.2–0.40 V,

respectively. All electrochemical measurements

were performed on an Autolab PGSTAT-30

electrochemical system with GPES 4.8 package

software (Eco Chemie, The Netherland). The

electrochemical performances of the DMFC

with the alkaline PVA/HAP composite polymer

membrane and the cathode electrode open to the

atmospheric air were studied in 8 M KOHþ 2 M

CH3OH solutions at ambient temperatures and

air. The construction of test cell for alkaline

DMFC was also described in detail [17].

140 C.-C. Yang et al. / Desalination 233 (2008) 137–146

3. Results and discussion

3.1. TGA thermal analysis

Fig. 1 shows TGA and differential gravimetric

analysis (DTG) thermographs of the PVA/HAP

composite polymer membrane with various

HAP compositions. For comparison, TGA and

DTG curves for the PVA þ GA polymer mem-

brane also present in Fig. 1. TGA and DTG

curves of the PVA/HAP polymer film reveal

three main weight loss regions, which appear

as three peaks in the DTG curves. The first region

at a temperature of 80–100�C (Tmax,1¼ 100�C) is

due to the evaporation of physical weakly and

chemically strongly bound H2O; the weight

loss of the membrane is about 2–3 wt.%. The

second transition region at around 350–380�C(Tmax,2 ¼ 363�C) is due to the degradation of

PVA polymer membrane; the total weight loss

corresponds to this stage about 38–46 wt.%. The

peak of third stage at 439�C (Tmax,3 ¼ 439�C) is

due to the cleavage backbone of PVA polymer

membrane (or so-called carbonation); the total

weight loss is about 90 wt.% at 600�C, as listed

in Table 1.

Overall, the degradation peaks of the cross-

linked PVA/HAP composite polymer samples

are less intense and shift towards higher tempera-

tures in the temperature range of 100–380�C (PVA

film shows larger weight loss in this temperature

range). It can be seen that the improved thermal

stability is probably due to the additive effect of

the HAP filler and the chemical crosslink reac-

tion of between PVA and GA.

3.2. Surface morphology, X-ray diffraction,

and Raman analyses

SEM photographs of the surface morphology

of the PVA/5 wt.%HAP and PVA/10 wt.%HAP

composite polymer membranes are shown in

Fig. 2(a) and (b), respectively. As seen in

Fig. 2(b), the surface morphology of the PVA/

10 wt.%HAP composite polymer sample shows

a lot of large irregular HAP aggregates or

chunks that are randomly distributed on the top

surface. It was found that the dimension of

those HAP particles embedded in PVA matrix

was about 5–200 mm. This indicated that the

HAP particle fillers were not completely dis-

persed-well within the PVA polymer matrix

due to the HAP filler having flake-like irregular

structure.

As a whole, the hydrophilic PVA polymer

and the HAP ceramic fillers are compatible

Temperature/ °C0 100 200 300 400 500 600

Wei

ght l

oss/

wt.%

0

20

40

60

80

100

120

dw/ d

t /m

g S

–1

–0.012

–0.008

–0.004

0.000

0.004

0.008

0.0122.5 wt.%HAP5 wt.%HAP10 wt.%HAPPVA

PVA

Fig. 1. TGA thermographs of the PVA/HAP composite

polymer membranes with different compositions of

HAP fillers.

Table 1

The results of weight loss (%) of the PVA/HAP compo-

site polymer membranes at various temperatures

Types Temperature

100�C 250�C 350�C 600�C

HAP powders 0.68 6.81 2.79 3.49

PVA þ GA 3.81 38.00 42.10 90.70

PVA/2.5 wt.%HAP 3.75 12.13 35.98 90.67

PVA/5 wt.%HAP 2.93 7.26 27.96 91.90

PVA/10 wt.%HAP 2.58 6.81 27.39 87.06

C.-C. Yang et al. / Desalination 233 (2008) 137–146 141

when the content of HAP ceramic fillers is less

than 10 wt.%.

The X-ray diffraction measurement was per-

formed to examine the crystallinity of the PVA/

HAP composite polymer membrane. Fig. 3

shows the diffraction pattern of the PVA/HAP

composite polymer membranes that were pre-

pared by a blending process with different HAP

compositions. It is well known that the PVA

polymer exhibits a semi-crystalline structure

with a large peak at a 2� angle of 19–20� and

a small peak of 39–40� [14–17]. As can be seen

clearly in Fig. 3, a large peak at 2� of 20� for

the PVA/2.5–10 wt.%HAP composite polymer

membranes was seen. But, it was clearly seen

that the peak intensity of XRD for the PVA/HAP

composite polymer films greatly reduced when

the amount of added HAP fillers increased.

It was indicated that the amorphous domain in

the PVA/HAP composite polymer membrane

markedly augmented (i.e. the degree of crystal-

linity decreased). Experimental result indicates

that the PVA/HAP composite polymer mem-

brane with the HAP filler becomes more

amorphous.

Fig. 4(a) shows the micro-Raman spectra for

the PVA powders and PVA polymer membranes,

respectively. Fig. 4(b) shows the micro-Raman

spectra for the PVA/HAP composite polymer

membranes at different compositions of HAP

fillers. It can be seen clearly from micro-Raman

spectra that the strong characteristic scattering

peak of HAP fillers at 958 cm�1 is for –PO3�4 ;

it was due to the P–O stretching. By contrast, the

strong peak for the PVA polymer at 1438 cm�1

is due to the C–H bending and O–H bending.

Moreover, the two weak vibrational peaks for

the PVA polymer at 912 and 851 cm�1 are due

(a)

(b)

Fig. 2. SEM photographs for (a) PVA/5wt.%HAP

composite polymer membrane at 4.5 kx; (b) PVA/

10wt.%HAP composite polymer membrane at 1 kx.

2θ/ deg.10 20 30 40 50 60 70 80 90

Inte

nsity

/ a.u

.

(1) PVA film(2) PVA/2.5%HAP(3) PVA/5%HAP(4) PVA/10%HAP

10%HAP

5%HAP

2.5%HAP

PVA

Fig. 3. XRD spectra for the PVA/HAP composite

polymer membranes at different HAP compositions.

142 C.-C. Yang et al. / Desalination 233 (2008) 137–146

to the C–C stretching. Additionally, there are

several weak scattering peaks at 1145, 1088 cm�1;

they may be due to the C–C stretching and C–O

stretching, as displayed in Fig. 4(a). Most

importantly, it can be seen that the intensities

of those characteristic vibrational peaks for those

PVA/HAP composite polymer membranes are

decreased; it indicates that the amorphous

regions in the PVA/HAP composite polymer

membranes are augmented.

3.3. Ionic conductivity measurements

The typical AC impedance spectra of alka-

line PVA/HAP composite polymer membrane

by a direct blending PVA polymer with HAP

fillers (5 wt.%) at different temperatures are

shown in Fig. 5. The AC spectra are typically

non-vertical spikes for stainless steel (SS) block-

ing electrodes, i.e., SSjPVA/HAP SPEjSS cell.

Analysis of the spectra yields information about

the properties of the PVA/HAP polymer electro-

lyte, such as bulk resistance, Rb. Taking into

account the thickness of the composite electro-

lyte films, the Rb value was converted into the

ionic conductivity value, �, according to the

equation: � ¼ L/Rb � A, where L is the thickness

(cm) of the PVA/HAP polymer membrane, A is

the area of the blocking electrode (cm2), and Rb

is the bulk resistance (ohm) for alkaline compo-

site polymer membrane.

Typically, the Rb values of the PVA/HAP

composite polymer membranes are of the order

1–2 ohm and are dependent on the contents of

HAP fillers and KOH in the film. Note that the

composite polymer membrane was immersed in

800 900 1000 1100 1200 1300 1400 1500 1600

Cou

nts

0

5000

10,000

15,000

20,000

25,000

30,000

35,000

40,000(1) PVA powders(2) PVA membrane

(1)

(2)14

40

1145

926

852

(a)

Raman shift/cm–1

Raman shift/cm–1

800 1000 1200 1400 1600

Inte

nsity

/a.u

.

0

(1) HAP powders(2) PVA/2.5%HAP(3) PVA/5%HAP(4) PVA/10%HAP

(1)

(4)

(2)

(3)

958 (*HAP)

*

*

*

1438

(P

VA

)

912

(PV

A)

851

(PV

A)

(b)

Fig. 4. Micro-Raman spectra for the PVA/HAP

composite polymer membranes with different composi-

tions of HAP fillers.

Z' /ohm

0 2 4 6 8 10 12 14

–Z" /

ohm

0

5

10

15

20

25

30

35

40

30°C40°C50°C60°C70°C

Fig. 5. AC spectra for the PVA/10wt.%HAP com-

posite polymer membrane (in 8 M KOH) at different

temperatures.

C.-C. Yang et al. / Desalination 233 (2008) 137–146 143

8 M KOH solutions for at least 24 h before mea-

surement. Table 2 shows the ionic conductivity

values of the alkaline PVA/2.5–10 wt.%HAP

composite polymer membranes at different

temperatures. As a result, the ionic conductiv-

ity value for the alkaline PVA/2.5 wt.%HAP

composite polymer membranes is about

0.0182 S cm�1 at 30�C.

Comparatively, the ionic conductivity values

for the alkaline PVA/HAP composite polymer

membrane with 5 and 10 wt.% HAP fillers are

about 0.0251 and 0.0442 S cm�1 at 30�C,

respectively. It was found that the highest ionic

conductivity value of the alkaline PVA/HAP

composite polymer membrane is 10 wt.% HAP

fillers (about 0.0442 S cm�1 at ambient tem-

perature). According to the above results, it can

be concluded that the ionic conductivity of the

PVA/HAP composite polymer membranes

increases when the content of added HAP cera-

mic fillers increases.

Generally, the HAP fillers are added into the

PVA polymer membrane, it shows more accessi-

ble free volumes (or more defect sites and voids)

to retain the KOH electrolyte; therefore, the

ionic conductivity is in the order of 10�2 S cm�1

at ambient temperature. The temperature depen-

dence of the ionic conductivity is of the Arrhe-

nius type: � ¼ �0 exp � Ea

RT

� �, where �0 is a

pre-exponential factor, Ea is the activation

energy, and T is the temperature in Kelvin. The

log10(�) vs. 1/T plots, as shown in Fig. 6, obtains

the activation energy (Ea) of the PVA/

10 wt.%HAP composite SPE, which is depen-

dent on the content of HAP fillers. The Ea value

of alkaline PVA/10 wt.%HAP composite polymer

membrane is about 9.71 kJ mol�1, normally the

crosslinked SPE shows Ea value over 15 kJ mol�1.

As we know, when the HAP ceramic filler used

as a stiffer material is added into the PVA

matrix, the swelling ratio of PVA polymer mem-

branes can be effectively reduced from 90.7 to

54.7% as the content of HAP fillers is increased

from 2.5 to 10 wt.%. Experimental results found

that the film dimension stability and ionic

conductivity are at the same time improved.

3.4. Electrochemical measurements

Fig. 7 shows the i–t curves of alkaline DMFC

consisting of the PtRu black anode Ti-electrode

with a loading of PtRu black of 4.0 mg cm�2,

the cathode electrode with MnO2/BP2000

carbon inks of 3.63 mg cm�2 and the PVA/

10 wt.%HAP composite polymer membrane in

Table 2

The ionic conductivities of the PVA/HAP composite

polymer membranes with different compositions HAP

fillers at different temperatures

T (�C) � (S cm�1)

2.5 wt.%HAP 5 wt.%HAP 10 wt.%HAP

30 0.0182 0.0251 0.0442

40 0.0212 0.0272 0.0465

50 0.0263 0.0295 0.0483

60 0.0314 0.0315 0.0514

70 0.0378 0.0335 0.0542

1/T *1000

2.8 2.9 3.0 3.1 3.2 3.3 3.4

log(

σ)/ S

cm

–1

–1.46

–1.44

–1.42

–1.40

–1.38

–1.36

–1.34

–1.32

–1.30

–1.28

–1.26

–1.24

Intercept = 0.0588244251Slope = –0.4551877425r = 0.9983741117Ea = 9.71 kJ/mol

Fig. 6. Arrhenius plot of alkaline PVA/10 wt.%HAP

composite polymer membrane in 8 M KOH.

144 C.-C. Yang et al. / Desalination 233 (2008) 137–146

8 M KOHþ 2 M CH3OH solutions at 0.40, 0.30,

and 0.20 V, respectively. The average current

densities of the DMFC utilizing the PtRu anode

based on Ti-mesh are 18.59, 33.84, and 52.96

mA cm�2, respectively. In spite of a tendency

to drop at the beginning of the test, the discharge

current densities are also stabilized and remain

constant during the 600 min test; it shows good

electrochemical stability of the DMFC. In fact,

the results indicate that the peak power density

of the DMFC in 8 M KOH þ 2 M CH3OH

solutions at 0.40 V was about 10.59 mW cm�2

(0.20 V� 52.96 ¼ 10.59 mW cm�2) at 25�C.

Fig. 8 shows the potential-current density

and the power density–current density curves

for the air-breathing DMFC in 8 M KOH þ 2 M

CH3OH solution at 25�C. Clearly, the maximum

power density of 11.48 mW cm�2 for the alka-

line DMFC using Ti-based anode with 4 mg cm�2

PtRu black was achieved at Ep,max¼ 0.22 V with

a peak current density (ip,max) of 52.20 mA cm�2.

On the other hand, the maximum power den-

sity of the DMFC using a ELAT anode with

4 mg cm�2 PtRu/C was only 5.81 mW cm�2

at Ep,max ¼ 0.190 V with a peak current density

of 30.58 mA cm�2 at 25�C. It was demonstrated

that alkaline DMFC system exhibits some

advantages over than that of the acidic DMFC

system. In particular, alkaline DMFC consists

of the air electrode using non-precious metal

catalyst (i.e., use MnO2/BP2000 catalyst inks

instead of with Pt/C inks) and the low-cost

PVA/HAP composite polymer membrane (i.e.,

a cheap non-perfluorosulfonated polymer mem-

brane instead of expensive Nafion membrane).

4. Conclusions

The composite polymer membrane based on

PVA/HAP was obtained by a solution casting

method. Alkaline air-breathing direct methanol

fuel cell (DMFC) utilizing the PVA/HAP com-

posite polymer membrane was assembled and

systematically examined. The DMFC is com-

prised of the air cathode electrode with MnO2/

BP2000 catalyst inks, the PtRu black Ti-anode

Time/ min

0 100 200 300 400 500 600

i/ m

A c

m–2

0

10

20

30

40

50

60

70

80

90

(1) 0.2 V(2) 0.3 V(3) 0.4 V

(1)

(2)

(3)

Fig. 7. The i–t curves for the DMFC employing the

PVA/10 wt.%HAP composite polymer membrane in

8 M KOH þ 2 M CH3OH at 25�C and ambient air.

i/ mA cm–2

0 10 20 30 40 50 60 70 80 90 100 110

Cel

l pot

entia

l/ V

0.0

0.2

0.4

0.6

0.8

1.0

P.D

./ m

W c

m–2

0

2

4

6

8

10

12

14

(1)

(2)

(3)

(4)

Fig. 8. The IV and P.D. curves for the DMFC using the

PVA/10 wt.%HAP composite polymer membrane in

8 M KOH þ 2 CH3OH at 25�C; (1) IV curve for ELAT

E-TEK anode; (2) IV curve for Ti-based anode;

(3) P.D. curve for ELAT anode; (4) P.D. curve for

Ti-based anode.

C.-C. Yang et al. / Desalination 233 (2008) 137–146 145

electrode and the PVA/HAP composite polymer

membrane. It was demonstrated that the alkaline

DMFC with the PVA/HAP composite polymer

membrane shows good electrochemical perfor-

mances at ambient temperatures and pressure.

The maximum peak power density of the

alkaline DMFC is 11.48 mW cm�2 at 25�C.

From the application point of view, the PVA/

HAP composite polymer membranes can easily

be prepared and controlled. These composite

polymer membranes show a high potential for

future alkaline DMFC applications.

Acknowledgement

Financial support from the National Science

Council, Taiwan (Project No. NSC-95-2221-

E131-032) is gratefully acknowledged.

References

[1] N. Nakagawa and Y. Xiu, Performance of a direct

methanol fuel cell operated at atmospheric

pressure, J. Power Sources, 118 (2003) 248.

[2] V. Baglio, A.S. Arico, A.D. Blasi, V. Antonucci,

P.L. Antonucci, S. Licoccia, E. Traversa and

F.S. Fiory, Nifion–TiO2 composite DMFC mem-

branes: physico-chemical properties of the filler

versus electrochemical performance, Electrochim.

Acta, 50 (2005) 1241.

[3] S. Panero, P. Fiorenza, M.A. Navarra,

J. Romanowska and B. Scrosati, Silica-added,

composite poly(vinyl alcohol) membranes for fuel

cell application, J. Electrochem. Soc., 152 (12)

(2005) A2400.

[4] J.H. Choi, Y.M. Kim, J.S. Lee, K.Y. Cho,

H.Y. Jung, J.K. Park, I.S. Park and Y.E. Sung,

A polyaniline supported PtRu nanocomposite

anode and a Pd-impregnated nanocomposite

Nafion membrane for DMFCs, Solid State Ionics,

176 (2005) 3031.

[5] V.S. Silva, S. Weisshaar, R. Reissner, B. Ruffmann,

S. Vetter, A. Mendes, L.M. Madeirs and S. Nunes,

Performance and efficiency of a DMFC using

non-flourinated composite membranes operating

at low/medium temperatures, J. Power Sources,

145 (2005) 485.

[6] E. Antolini, Formation of carbon-supported PtM

alloys for low temperature fuel cells: a review,

Mater. Chem. Phys., 78 (2003) 563.

[7] G.Q. Lu and C.Y. Wang, Development of micro

direct methanol fuel cells for high power applica-

tions, J. Power Sources, 144 (2005) 141.

[8] C.Y. Chen and P. Yang, Performance of an air-

breathing direct methanol fuel cell, J. Power

Sources, 123 (2003) 37.

[9] T. Shimizu, T. Momma, M. Mohamedi, T. Osaka

and S. Sarangapani, Design and fabrication of pump-

less small direct methanol fuel cells for portable

applications, J. Power Sources, 137 (2004) 277.

[10] K. Kordesch, V. Hacker and U. Bachhiesl, Direct

methanol-air fuel cells with membranes plus

circulating electrolyte, J. Power Sources, 96

(2001) 200.

[11] J.G. Liu, T.S. Zhao, R. Chen and C.W. Wong, The

effect of methanol concentration on the perfor-

mance of a passive DMFC, Electrochem. Com-

mun., 7 (2005) 288.

[12] B.K. Kho, I.H. Oh, S.A. Hong and H.Y. Ha,

The effect of pretreatment methods on the perfor-

mance of passive DMFCs, Electrochim. Acta, 50

(2004) 781.

[13] H. Chang, J.R. Kim, J.H. Cho, H.K. Kim and

K.H. Choi, Materials and processes for small fuel

cells, Solid State Ionics, 148 (2002) 601.

[14] C.C. Yang, Polymer Ni–MH battery based on

PEO–PVA–KOH polymer electrolyte, J. Power

Sources, 109 (2002) 22.

[15] C.C. Yang and S.J. Lin, Alkaline composite

PEO–PVA-glass-fiber-mat polymer electrolyte for

Zn-air battery, J. Power Sources, 112 (2002) 497.

[16] C.C. Yang, Synthesis and characterization of

the crosslinked PVA/TiO2 composite polymer

membrane for alkaline DMFC, J. Membr. Sci.,

288 (2006).

[17] C.C. Yang, S.J. Chiu and W.C. Chien, Develop-

ment of alkaline direct methanol fuel cells based

on crosslinked PVA polymer membranes, J. Power

Sources, 162 (2002) 21.

[18] C.C. Yang, S.T. Hsu, W.C. Chien, M.C. Shih,

S.J. Chiu, K.T. Lee and C.L. Wang, Electrochemi-

cal properties of air electrodes based on MnO2

catalysts supported on binary carbons, Int.

J. Hydrogen Energy, 31 (2006) 2076.

146 C.-C. Yang et al. / Desalination 233 (2008) 137–146