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Synthetic Metals 160 (2010) 193–199

Contents lists available at ScienceDirect

Synthetic Metals

journa l homepage: www.e lsev ier .com/ locate /synmet

lkali doped poly(vinyl alcohol) for potential fuel cell applications

ing Fua,c, Jinli Qiaoa,b,∗, Xizhao Wanga, Jianxin Maa, Tatsuhiro Okadad

Clean Energy Automotive Engineering Center, Tongji University, Caoan Road 4800, Shanghai 201804, ChinaSchool of Environmental Science and Engineering, Donghua Universtiy, Songjiang University City 2999, Shanghai 201260, ChinaSchool of Resource and Environmental Engineering, East China University of Science and Technology, Melong Road 130, Shanghai 200237, ChinaNational Institute of Advanced Industrial Science and Technology, Higashi 1-1-1, Central 5, Tsukuba, Ibaraki 305-8565, Japan

r t i c l e i n f o

rticle history:eceived 11 September 2009eceived in revised form 18 October 2009ccepted 6 November 2009vailable online 3 December 2009

eywords:lkaline solid polymer electrolyteVA–KOH

a b s t r a c t

Optical transparent, chemically stable alkaline solid polymer electrolyte membranes were prepared byincorporation KOH in poly(vinyl alcohol) (PVA). The distributions of oxygen and potassium in the mem-brane were characterized by XRD and SEM–EDX. It is demonstrated that combined KOH molecules mayexist in the PVA matrix, which allow it to be an ionic conductor. In particular, the chemical and thermal sta-bilities were investigated by measuring changes of ionic conductivities after conditioned the membranein various alkaline concentrations at elevated temperatures for 24 h for potential use in fuel cells. Themembranes were found very stable even in 10 M KOH solution up to 80 ◦C without losing any membraneintegrity and ionic conductivity due to high dense chemical cross-linking in PVA structure. The mea-

−4 −1

hemical stabilityicrostructure

onic-conductivityethanol uptake

DMFC

sured ionic conductivity of the membrane by AC impedance technique ranged from 2.75 × 10 S cmto 4.73 × 10−4 S cm−1 at room temperature, which was greatly increased to 9.77 × 10−4 S cm−1 after hightemperature conditioning at 80 ◦C. Although, a relatively higher water uptake, the methanol uptake ofthis membrane was one-half of Nafon 115 at room temperature and 6 times lower than that of Nafion115 after conditioned at 80 ◦C. The membrane electrolyte assembly (MEA) fabricated with PVA–KOH indirect methanol fuel cell (DMFC) mode showed an initial power density of 6.04 mW cm−2 at 60 ◦C and

−2 a

increased to 10.21 mW cm

. Introduction

Fuel cell technology has received an increasing interest overhe past few decades, particular to proton-exchange membranePEM) fuel cells. This fuel cell uses an acidic membrane as elec-rolyte and gives excellent results. To date, the full potential of theEM fuel cells has not been realized although they show the excel-ent chemical, mechanical, and thermal stability as well as highonic conductivity. The cost and durability are two major challengeso fuel cell commercialization. Further, the PEM fuel cells exhibiteveral significant disadvantages including slow electrode-kinetics,arbon monoxide poisoning of expensive Pt and Pt-based electro-atalysts at low temperatures, the high cost of membranes and highuel permeability (methano) [1].

To overcome the drawbacks of the PEM fuel cells, a new con-ept fuel cell using alkaline anion exchange membranes (AAEMs)

as been evoked great interest. One of the advantages of AAEM

uel cells is the faster kinetics of oxygen reduction reactions in anlkaline media, which allows the use of non-precious metal electro-atalysts such as silver catalysts [2] and perovskite-type oxides [3].

∗ Corresponding author. Tel.: +86 21 6958 9480; fax: +86 21 6958 9355.E-mail address: qiaojinli@hotmail.com (J. Qiao).

379-6779/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.synthmet.2009.11.013

t 90 ◦C.© 2009 Elsevier B.V. All rights reserved.

In addition, the water management is improved due to the electro-osmotic drag transporting water away from the cathode and theso-called alcohol ‘crossover’ problem also is highly reduced becauseof the opposite movement of the hydroxide ion to the movementof proton in acidic membrane.

The quaternized polymers based on AAEMs have been pro-posed as electrolytes in alkali fuel cells such as polysiloxane [4],poly(oxyethylene) methacrylates [5], polysulfone [6], polyether-sulfone cardo [7], poly(phthalazinon ether sulfone ketone) [8],poly(ether-imide) [9] and radiation-grafted PVDF and FEP [10].However, the quaternized polymers are unstable in alkalinemedium at temperatures above 60 ◦C. Therefore, the developmentof AAEMs for an improved performance is still urgent.

PVA is a polyhydroxy polymer, which is very commonin practical applications because of its easy preparation andbiodegradability [11]. It has been selected as epolymer matrix inview of its film-forming capacities, hydrophilic properties and highdensity of reactive chemical functions favorable for cross-linkingby irradiation, chemical or thermal treatments [12–14]. Due to its

perfect methanol tolerance effect, PVA also has been used to alka-line direct methanol fuel cell (ADMFC) studies with inorganic fillersincorporation [15,16]. However, little is reported on the chemicalstability of PVA-based alkaline solid polymer electrolyte, especiallyin alkaline medium conditioned at high KOH concentration in solu-

1 Metals 160 (2010) 193–199

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94 J. Fu et al. / Synthetic

ion at temperatures above 60 ◦C. One of the major challenges withhe development of AAEMs is the availability of suitable ionic con-uctivity with high chemical stability under fuel cell operatingonditions.

In this article, the alkaline solid polymer electrolyte mem-rane based on alkaline doped poly(vinyl alcohol) (PVA–KOH) wasroposed aiming at a new cost-effective, easier preparing andhemical stable AAEM. Through chemical cross-linking procedure,he swelling property of PVA was effectively controlled and theormed membranes were both flexibility and toughness. Particu-ar interest was devoted to the chemical stability, on which the

icrostructure of PVA–KOH membranes were studied in detail forurther improved performance for potential use in alkali mem-rane fuel cells. Additionally, the electrochemical characteristics ofOH doped PVA were investigated in 2MKOH + 2 M CH3OH solutiony the linear polarization methods, especially, for the peak powerensity of the DMFC.

. Experimental

.1. Materials and membrane preparation

Chemically cross-linked PVA membranes were prepared by aimple solution casting method where PVA (99% hydrolyzed, aver-ge Mw = 86,000–89,000, Aldrich) was fully dissolved in water toake a 10% solution at 90 ◦C. Appropriate amounts of the above

olution were then mixed with water to get a homogeneous,ransparent and viscous appearance. After removing the air underacuum, the solutions were poured into plastic petri dishes and,he water was evaporated at ambient temperatures. When visu-lly dry, the membrane was peeled off from the plastic substratend, samples of square pieces of membranes (ca. 1.5 cm × 2 cm)ere soaked in a reaction solution containing 10 mass% glutaralde-yde (GA) (25 wt% solution in water, Shanghai Guoyao) in acetonet 30 ◦C for one hour [17]. The cross-linking proceeded betweenhe –OH of PVA and the –CHO of GA in the membrane due ton acid-catalyzed reaction by addition of small amount of HCl inhe solution. Transparent, flat membranes were obtained with ahickness of about several tens of micrometers (60–100 �m). Thehickness of the membranes can be easily controlled by adjustinghe volume of suspension.

The preparation of the PVA alkaline membranes (PVA–KOH)ere conducted by immersion the membrane in KOH solution with

arious concentrations at least for 24 h. The absorbed KOH on theurface of the membrane was removed by rinsing the membrane ineionized (D.I.) water numerous times, then the membranes weretored in D.I. water for measurements. Fig. 1 illustrates the innertructure model of PVA–KOH and some typical membrane pictures.

.2. Characterization of PVA–KOH membranes

The crystal structures of the composite membranes were exam-ned with an X-ray diffractometer (XRD, PHILIPS PW 3040/60owder diffractometer) using Cu K� radiation (� = 0.15406 nm)nd operating at 40 kV and 100 mA. The membrane samples werecanned in the reflection mode with a 2� angle between 5◦ and 80◦

ith a scan rate of 2◦ min−1.The composite morphology was evaluated using a FEI Sirion

00 field emission scanning electron microscopy (SEM) operatingt 5 kV. Prior to observations, the membrane samples were frac-

ured in liquid nitrogen and sputtered with gold, then examinedt 2000×, 6000× and 40,000× magnifications. The element distri-ution in the cross-section was determined by Oxford Instrument-ray Microanalysis INCA, operating at 20 kV with a data collection

ime of 10 min.

Fig. 1. Inner structure model of PVA–KOH and membrane pictures for (a) pure PVA,(b) PVA conditioned in 4 M KOH at 25 ◦C, (c) PVA conditioned in 4 M KOH at 80 ◦C.Condition time: 24 h, followed by complete removal of free KOH prior to testing.

2.3. Water and methanol uptake

The water uptake (WU) of the membranes (g g−1) was evaluatedfrom the mass change before and after the complete dryness of themembrane. A dry membrane was swelled in D.I. water for a day,then the surface water was wiped carefully with a filter paper, andit was immediately weighed. After drying the sample overnight in avacuum oven at 60 ◦C, the water uptake (WU), was calculated usingthe expression:

WU = Wwet − Wdry

Wdry(1)

where Wwet and Wdry are the mass of fully hydrated membrane,and of the dry membrane, respectively. The methanol uptake wasmeasured at the same procedures.

2.4. Ionic conductivity measurements

The OH− ionic conductivity of the formed membranes was mea-sured by an AC impedance technique using an electrochemicalimpedance analyzer (VMP2/Z, PAR), where the AC frequency wasscanned from 100 kHz to 0.1 Hz at a voltage amplitude of 100 mV.Fully hydrated membranes were sandwiched in a Teflon conduc-tivity cell equipped with Pt foil contacts [18]. The membrane wasin contact with water over the measurements. Ionic conductivity,�(S/cm), was calculated according to the following equation:

� = l

RTW(2)

where l is the length of the membrane between two potential sens-ing platinum wires, R is the membrane resistance, W and T are thewidth and the thickness of the membrane, respectively.

2.5. Membrane electrode assembly (MEA) fabrication andsingle-cell performance measurements

The cell configuration: 2 M MeOH + 2 M KOH|Pt/C|PVA–KOH|Pt/C|O2, was used in a single-cell of ADMFC. Thecatalyst for both anode and cathode was Pt/C on carbon paper

with catalyst loading of 1 mg(Pt) cm−2 (ElectroChem). The activeelectrode area for a single cell test was 4 cm2. The MEA wasprepared by hot pressing the PVA–KOH membrane with anode andcathode at 90 ◦C and 100 kg cm−2 for 5 min. The MEA was insertedinto a fuel cell hardware, which consisted of graphite block with

J. Fu et al. / Synthetic Metals 160 (2010) 193–199 195

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ig. 2. Ionic conductivity of PVA membranes as a function of doping KOH concentra-ion in aqueous solution. The membranes were immersed in various concentrationf KOH solution for 24 h followed by complete removal of free KOH prior to conduc-ivity testing.

achined serpentine flow channel and copper current collectors.M MeOH + 2 M KOH aqueous solution was pumped into thenode channel of the cell under atmospheric pressure, with a flowate 5 mL min−1. Pure oxygen gas was supplied as the cathode fuelo enter the cathode channel with a gas flow rate 20 mL min−1

hrough a humidifier held at 25 ◦C under ambient pressure. Theell was placed in a temperature-controlled chamber, which wassed to keep the cell at a constant temperature. Polarization curvesere obtained using a fuel cell evaluation system (TFC-2100,

okken) over the temperature range of 60–90 ◦C.

. Results and discussions

.1. Ionic conductivity of alkaline PVA

The alkaline PVA membranes appeared transparent and homo-eneous with mechanical flexibility. When immersed in KOHolutions, the PVA membrane became orange in color but it almostecolored completely by rinsing the membrane in D.I. water. Fig. 2hows the ionic conductivities of the PVA–KOH membranes. TheVA–KOH membrane preparation was conducted by immersionhe PVA membranes in KOH aqueous solution with various concen-rations at least for 24 h. The absorbed KOH on the surface of the

embrane was removed by rinsing the membrane in D.I. waterumerous times, then the membranes were stored in D.I. water

or ionic conductivity measurement. Fig. 3 illustrates the typicalC impedance spectra, which are related to the ionic conductionrocess in the bulk properties of the membrane. The intercept ofhe semicircular arc with the Z′ (ReZ) axis was taken as the bulkesistance, R, of the polymer electrolyte membrane. It can be seenhat the ionic conductivity measured at 25 ◦C reached a maximumalue of 4.73 × 10−4 S cm−1 for PVA in doping KOH concentration of–4 mol L−1 in solution. This is in the same order of the ionic con-uctivity obtained by directly mixing a viscous PVA solution withoncentrated KOH aqueous solution as reported elsewhere [19].his result suggests that some of KOH molecules are taken intohe polymer by water molecules. The chemical interaction, such asipole–dipole interaction including hydrogen bonding and induc-ion forces, may take place between C–O and OH groups on PVA and

OH during alkali doping, which is helpful for the ionic conductivityf PVA. However, the ionic conductivity decreased with additionaloping KOH concentration in solution, for example, when KOH con-entration in solution is larger than 4 M. That is, additional higheroping KOH concentration in solution does not simply make addi-

Fig. 3. Typical impedance spectra of PVA doped in 6 M KOH at 25 ◦C. The free KOH onmembrane surface was completely removed by rinsed the membrane in D.I. waterprior to conductivity testing.

tional contribution to the conductivity. The membrane samples arefound to be supernatant at high doping KOH concentration (>8 M)in solution. It seems that more OH− could not be taken into thepolymer at high KOH doping solution due to the weak ionic mobil-ity (such as formed ion-pairs or increased viscosity), thus a decreasein ionic conductivity.

3.2. Chemical stability of alkaline PVA

The chemical stability of AAEMs is recognized as a key factorthat affects fuel cell performances, especially, in alkaline medium attemperatures above 60 ◦C and high KOH concentration. The chem-ical stability of alkaline PVA was tracked by immersing the PVAmembranes in different concentrations of KOH at elevated tem-peratures for at least 24 h. This was an experiment designed totest the tolerance of the membrane to base treatments at ele-vated temperatures [9]. After complete removal of the free KOH,the conductivity of the membrane was measured at room tem-perature. Shown in Fig. 4 are the results of the typical candidateswith four concentrations (1, 4, 6, and 10 M) of KOH for PVA applied.The conductivity values from the tested membranes ranged from1.36 × 10−4 S cm−1 to 4.51 × 10−4 S cm−1 at 25 ◦C. Generally speak-ing, AAEMs are frequently less stable since the basic groups areinherently less stable than the acidic groups [11]. Because of thefact, the purely quaternized polymers can be just subjected to 0.5or 1.0 M KOH at 80 ◦C but deteriorated only in 2.0 M KOH at 60 ◦C[9] or even in pure water at 80 ◦C [8]. The ionic conductivity isgreatly decreased and even cannot be measured thereby [9]. Toour interest, however, no decrease in conductivity was found forPVA–KOH membranes. Inversely, all tested membranes showedan increased conductivity with increasing KOH concentration insolution at elevated treating temperatures. The PVA soaked in 6and 10 M KOH showed the rapid increase in ionic conductivityand, exhibited the highest conductivities of 8.74 × 10−4 S cm−1 and9.77 × 10−4 S cm−1 after temperature conditioned at 80 ◦C, respec-tively. It seems that PVA has a remarkable absorbent capacity to

KOH after temperature treatment, thus an increased ionic conduc-tivity due to much increased charge carriers. On the other hand,the results suggest the tough tolerance of the PVA membranes tobase treatments even in 10 M KOH at 80 ◦C due to the high densechemical cross-linkage in PVA polymer matrix.

196 J. Fu et al. / Synthetic Metals 160 (2010) 193–199

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ig. 4. Ionic conductivity of PVA membranes after conditioned with KOH at elevatedemperatures. The membranes were conditioned in 1, 4, 6 and 10 M KOH at 25, 40, 60nd 80 ◦C for 24 h, followed by complete removal of free KOH prior to conductivityesting. The conductivity was measured at 25 ◦C.

Fig. 5 shows the temperature dependence of the ionic conduc-ivity of PVA–KOH membranes. Here the PVA membranes dopingn 4 M KOH, and then conditioned at r.t. and at 80 ◦C as typical can-idates, respectively. After complete removal of the free KOH onhe membrane surface, the conductivity was measured at elevatedemperatures. It can be seen that the ionic conductivity was almosto change with the temperature up to 80 ◦C after membrane beingonditioned in 4 M KOH at r.t., but linearly increased with temper-ture after the membrane being conditioned in 4 M KOH at 80 ◦C,hich reached the highest ionic conductivity of 9.51 × 10−4 S cm−1.

his is in well agreement with the results obtained from Fig. 4, thats, the dynamic properties seems to be greatly improved after con-itioned at high temperature of 80 ◦C, due to an increased chargearriers.

It should be mentioned that alkaline doped PVA, i.e., with a cou-le of additives such as PEO [20], SSA [21] and TiO2 filler [15] givesigh ionic conductivities ranged from 10−3–10−2 S cm−1 and even0−1 S cm−1 for PVAHEMA–SiO2 so-gel membranes [22]. Lower

onic conductivity in this work stems from the different membranereparation procedure. KOH was directly added into PVA solution,hus high KOH content in the polymer, but an obvious phase sep-ration produced [19,20,15] or immersed the membrane in KOHoncentration in solution, then directly conduct the ionic conduc-

ig. 5. Ionic conductivity of PVA/KOH membranes as a function of temperature: (a)onditioned in 4 M KOH at 25 ◦C, (b) conditioned in 4 M KOH at 80 ◦C. Conditionime: 24 h, followed by complete removal of free KOH prior to testing.

Fig. 6. XRD patterns for PVA–KOH membranes: (a) pure PVA, (b) PVA conditionedin 4 M KOH at 25 ◦C, (c) PVA conditioned in 4 M KOH at 80 ◦C. Condition time: 24 h,followed by complete removal of free KOH prior to testing.

tivity measurement [21,22] without any treatment such as rinsing.However, in this work PVA–KOH membranes were conducted byimmersion the PVA membranes in KOH solution, then, the mem-branes were rinsed in D.I. water numerous times for completelyremoving the absorbed KOH on the surface of the membrane, thenthe membranes were stored in D.I. water for final ionic conduc-tivity measurements. Therefore, the high ionic conductivity valuesreported in the literature were mainly from the contribution of“free” KOH absorbed on membrane surface. Contrary to this, inthis work the ionic conductivity merely comes from the “bonded”KOH through chemical interaction such as dipole–dipole interac-tion including hydrogen bonding and induction forces between C–Oand OH groups on PVA and KOH as Fig. 1 shows. Additionally, highcross-linking in PVA network may also contribute to the lower ionicconductivity of the resulting membrane.

3.3. XRD analysis

The X-ray diffraction measurements were performed to exam-ine the crystallinity of the composite membranes. XRD patternof wet PVA doping in 4 M KOH concentration with surface KOHremoved was obtained as shown in Fig. 6. PVA membrane exhibits asemi-crystalline structure with a large peak at a 2� angle of 19◦–20◦

and a small peak of 39◦–40◦ [23]. From the outline of XRD patternof PVA–KOH, no abroad lump between 20◦ and 40◦ was observedfrom KOH crystal as reported elsewhere [24]. However, as can beseen clearly in Fig. 6, the peak intensity at 20◦ of PVA–KOH wasdecreased when in comparison with pure PVA. This implies that thedomain of amorphous region into PVA polymer matrix augmenteddue to doped in KOH. Usually, the ionic conductivity of the poly-mer electrolyte could be attributed to the transport of cation andanion in a polymer matrix by hopping between coordinate sites,local structural relaxation and segmental motions of the polymerin amorphous domain, as well as ion transport in solvent. Thus, itcan be conclude that KOH simultaneously act as a plasticizer here,thus the PVA polymer electrolyte becomes more flexible and moreamorphous phase (as XRD results indicated), which makes for theionic conductivity of PVA–KOH membranes.

3.4. SEM and EDX characterization

SEM photographs for the cross-sectional views of PVA–KOHand its corresponding EDX mappings for potassium and oxygenelements are shown in Figs. 7 and 8, respectively. Prior to the exper-

J. Fu et al. / Synthetic Metals 160 (2010) 193–199 197

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ig. 7. SEM pictures of the cutview of the PVA/KOH membranes: (a) conditioned inM KOH at 80 ◦C (6000×), (d) conditioned in 10 M KOH at 80 ◦C (6000×), (e) condondition time: 24 h, followed by complete removal of free KOH prior to testing.

ment, the sample was rinsed with D.I. water to remove KOH onts surface, and then it was freeze-fractured in the liquid nitrogen.EM observations of the sections of a membrane (Fig. 7a and b at,000× magnification) showed a homogeneous and dense material.t should be mentioned that by increasing doping KOH concen-ration in solution and/or conditioned at temperature above roomemperature induced an orange color on the membranes as Fig. 1chows. But not any surface degradation or membrane modification,uch as holes or phase separation phenomena, could be detected.he structure is very compact on the SEM pictures (Fig. 7c and d at000× magnification) either being conditioned at high KOH con-entration (10 M KOH) or conditioned at 80 ◦C. This is very differentrom PEO–PVA–KOH blend polymer, on which many small poresith different size are produced on the surface of the film [20].

n this work, the KOH particles are discernable as light dots andvenly dispersed in the PVA polymer matrix at 40,000× magnifica-ion (Fig. 7e and f). There were neither gaps nor cracks between thearticles and polymer matrix, which proves the excellent chemical

tability due to the cross-linkage in PVA matrix.

In the EDX mapping image, the highlighted bright dots revealedigh element concentration. It can be seen that distributionsf potassium and oxygen elements were homogeneous, whichmplied that KOH was well dispersed throughout PVA membrane.

KOH at r.t (2000×), (b) conditioned in 10 M KOH at r.t. (2000×), (c) conditioned ind in 4 M KOH at 80 ◦C (40,000×), (f) conditioned in 10 M KOH at 80 ◦C (40,000×).

An intriguing result was revealed from EDX mapping that no obvi-ous change in potassium element before and after conditioned inalkaline concentration (4 M KOH) and temperature, but a muchhigher concentration in oxygen element particular to conditionedat 80 ◦C. This may be due to the fact that OH− in KOH may react withacetal group in PVA matrix to generate –OH and water, althoughthis reaction may take place incompletely. This result suggests fur-ther that combined KOH molecules by long-distance interactionmay exist in the PVA matrix, which was helpful for the ionic con-ductivity just as described previously.

3.5. Water/methanol uptake

The importance of the ionic conductivity and fuel permeability iswell known, particular to ADMFC. Furthermore, the swelling prop-erty of the conducting membranes is also an important parameter,which is highly correlative to the cell performance. The presenceof water in the membranes is a prerequisite for reaching high ionic

conductivity. On the other hand, excessively high water uptake willaffect other performances of the membranes such as the dimen-sional and thermal stability. Table 1 gives the changes in boththe water uptake and the methanol uptake values of PVA–KOHmembrane before and after conditioned in 4 M KOH at r.t. and at

198 J. Fu et al. / Synthetic Metals 160 (2010) 193–199

Fig. 8. EDX mapping of (a), (d) potassium element and (b), (c) oxygen element within PVA/KOH, respectively. Doping KOH concentration in solution: 4 M; (a and b):conditioned at r.t., (c and d): conditioned at 80 ◦C. Condition time: 24 h, followed by complete removal of free KOH prior to testing.

Table 1Physico-chemical properties of alkaline PVA based on chemical cross-linking and Nafion 115 membranes.

Membrane Membrane thickness(mm)

KOH dopingconcentration (M)

Liquid uptake (%) Ionic conductivity × 103 (S cm−1)

4 r.t. Conditioned at 80 ◦C r.t. Conditioned at 80 ◦C

9.8 wt

0.51.8

8otdbfcfmus8tmapc

3

d2

with a peak current density of 14.9 mA cm−2 at temperatureof 60 ◦C. An increase in fuel cell temperature leads to a dra-matic improvement in the cell performance. The open circuitpotential of the alkaline DMFC are about 0.87–0.91 V. In spite

D.I. water (%) 9

PVA 80–100 39.4 2Nafion115 135 34 4

0 ◦C, respectively. For a comparison, water and methanol uptakef Nafion 115 was measured under the same experimental condi-ions. As seen in Table 1, the water uptake of PVA–KOH membraneecreased from 39.4% when being conditioned at r.t. to 36.1% wheneing conditioned at 80 ◦C, while the methanol uptake increasedrom 20.5% to 21.4% correspondingly. In other words, no obvioushanges occurred both in water uptake and in methanol uptakeor alkaline PVA even after conditioned at 80 ◦C if the experi-

ental errors are ignored. Conversely, although the lower waterptake of Nafion 115 under the same measuring conditions, ithowed a much higher methanol uptake especially conditioned at0 ◦C, where the methanol uptake rapidly increased from 41.8%o 128.7%, i.e., 6-fold of alkaline PVA membrane. Although this

easurement is not a direct consequence of methanol perme-bility in contact with aqueous solution, these initial results areromising for future AAEMs fabrications in potential fuel cell appli-ations.

.6. Single-cell performance test

Fig. 9 shows I–V characteristics of the DMFC using KOHoped PVA as alkaline solid polymer electrolyte membrane inM KOH + 2 M CH3OH solution at the temperature between 60

% MeOH D.I. water (%) 99.8 wt% MeOH D.I. water (%)

36.1 21.4 0.47 0.75– 128.7

and 90 ◦C, respectively. It can be seen that an initial peak powerdensity of 6.04 mW cm−2 was achieved at cell voltage = 0.47 V

Fig. 9. I–V curves of the DMFC using KOH doped PVA as alkaline solid polymerelectrolyte membrane in 2 M KOH + 2 M CH3OH solution at different temperatures.

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f a low catalyst loading (1 mg cm−2 both on the anode andn the cathode), the MEA showed a good performance and,he power density increased from 6.04 mW cm−2 at 60 ◦C to0.21 mW cm−2 at 90 ◦C. However, we did not conclude thathe PVA–KOH is comparable to the PVA–TiO2–KOH [15] or theVA–PSSA–KOH [21] at this stage, since the air cathode is notonsidered and the Pt/C cathode electrode was used in thisork.

. Conclusions

In short, the chemically stable anion exchange membraneshat can conduct OH− were prepared by incorporation KOH inVA. The SEM–EDX results demonstrated a dense structure ofVA–KOH membranes, where the “bonded” KOH contributes theonic conductivity through chemical interaction between C–Ond OH groups on PVA and KOH. This is different from thesual doped one, where the ionic conductivities were mainlyrom the “free” KOH absorbed on membrane surface. In par-icular, the perfect tolerance of the PVA–KOH membranes wasound to base treatments even conditioned in 10 M KOH at 80 ◦Cithout losing any membrane integrity and ionic conductiv-

ty due to high dense chemical cross-linking in PVA structure.MFC test using PVA–KOH fabricated MEA showed an ini-

ial power density of 6.04 mW cm−2 at 60 ◦C and increased to

0.21 mW cm−2 at 90 ◦C. These initial results are very promis-

ng for further improved AAEMs performance in potential fuelell applications, considering the PVA superior methanol barrierroperties and its easy preparation and cost-effective mate-ial.

[[[[[

160 (2010) 193–199 199

Acknowledgements

This work is financially supported by Project Pujiang Founda-tion (grant no. 08PJ14096) and Natural Science Fundation (grant no.09ZR1433300) of Science and Technology Commission of ShanghaiMunicipality of China. Thanks also to Liuxue Guiguo Foundation ofChina Ministry of Education (grant no. 2009(1001)).

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