Synthetic Metals 160 (2010) 193199

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Synthetic Metals

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Alkali d ue

Jing Fua, hiroa Clean Energy , Chinb School of Env 99, Shc School of Reso , Melod National Insti , Ibara

a r t i c l

Article history:Received 11 SeReceived in reAccepted 6 NoAvailable onlin

Keywords:Alkaline solidPVAKOHChemical stabMicrostructureIonic-conductivityMethanol uptakeADMFC

alkaol) (PSEM

tobeg chaelevaen into hirane

to 4.73104 S cm1 at room temperature, which was greatly increased to 9.77104 S cm1 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 Naon115 after conditioned at 80 C. The membrane electrolyte assembly (MEA) fabricated with PVAKOH indirect methanol fuel cell (DMFC) mode showed an initial power density of 6.04mWcm2 at 60 C and

1. Introdu

Fuel cellthe past fe(PEM) fueltrolyte andPEM fuel celent chemicionic conduto fuel cellseveral signcarbon moncatalysts atfuel permea

To overccept fuel cehas been efuel cells isalkalinemecatalysts su

CorresponE-mail add

0379-6779/$ doi:10.1016/j.increased to 10.21mWcm2 at 90 C. 2009 Elsevier B.V. All rights reserved.

ction

technology has received an increasing interest overw decades, particular to proton-exchange membranecells. This fuel cell uses an acidic membrane as elec-gives excellent results. To date, the full potential of thells has not been realized although they show the excel-al, mechanical, and thermal stability as well as highctivity. The cost anddurability are twomajor challengescommercialization. Further, the PEM fuel cells exhibiticantdisadvantages includingslowelectrode-kinetics,oxide poisoning of expensive Pt and Pt-based electro-low temperatures, the high cost ofmembranes andhighbility (methano) [1].ome the drawbacks of the PEM fuel cells, a new con-ll using alkaline anion exchange membranes (AAEMs)voked great interest. One of the advantages of AAEMthe faster kinetics of oxygen reduction reactions in andia,which allows theuseof non-preciousmetal electro-ch as silver catalysts [2] and perovskite-type oxides [3].

ding author. Tel.: +86 21 6958 9480; fax: +86 21 6958 9355.ress: qiaojinli@hotmail.com (J. Qiao).

In addition, the water management is improved due to the electro-osmotic drag transporting water away from the cathode and theso-calledalcohol crossover problemalso ishighly reducedbecauseof 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 lm-forming capacities, hydrophilic properties and highdensity of reactive chemical functions favorable for cross-linkingby irradiation, chemical or thermal treatments [1214]. Due to itsperfect methanol tolerance effect, PVA also has been used to alka-line directmethanol fuel cell (ADMFC) studieswith inorganic llersincorporation [15,16]. However, little is reported on the chemicalstability of PVA-based alkaline solid polymer electrolyte, especiallyin alkalinemedium conditioned at high KOH concentration in solu-

see front matter 2009 Elsevier B.V. All rights reserved.synthmet.2009.11.013oped poly(vinyl alcohol) for potential fc, Jinli Qiaoa,b,, Xizhao Wanga, Jianxin Maa, TatsuAutomotive Engineering Center, Tongji University, Caoan Road 4800, Shanghai 201804ironmental Science and Engineering, Donghua Universtiy, Songjiang University City 29urce and Environmental Engineering, East China University of Science and Technologytute of Advanced Industrial Science and Technology, Higashi 1-1-1, Central 5, Tsukuba

e i n f o

ptember 2009vised form 18 October 2009vember 2009e 3 December 2009

polymer electrolyte

ility

a b s t r a c t

Optical transparent, chemically stableincorporation KOH in poly(vinyl alcohbrane were characterized by XRD andexist in thePVAmatrix,whichallow itbilities were investigated by measurinin various alkaline concentrations atmembranes were found very stable evintegrity and ionic conductivity duesured ionic conductivity of the memb/ locate /synmet

l cell applications

Okadad

aanghai 201260, Chinang Road 130, Shanghai 200237, Chinaki 305-8565, Japan

line solid polymer electrolyte membranes were prepared byVA). The distributions of oxygen and potassium in the mem-EDX. It is demonstrated that combined KOH molecules mayan ionic conductor. Inparticular, the chemical and thermal sta-nges of ionic conductivities after conditioned the membraneted temperatures for 24h for potential use in fuel cells. The10M KOH solution up to 80 Cwithout losing anymembranegh dense chemical cross-linking in PVA structure. The mea-by AC impedance technique ranged from 2.75104 S cm1

194 J. Fu et al. / Synthetic Metals 160 (2010) 193199

tion at temperatures above 60 C. One of themajor challenges withthe development of AAEMs is the availability of suitable ionic con-ductivity with high chemical stability under fuel cell operatingconditions.

In thisbrane basedproposed achemical stthe swellinformed melar interestmicrostructfurther impbrane fuel cKOHdopedby the lineadensity of t

2. Experim

2.1. Materi

Chemicasimple soluage Mw =86make a 10%solution wtransparentvacuum, ththe water wally dry, theand, samplwere soakehyde (GA) (at 30 C forthe OH ofan acid-catthe solutionthickness othickness othe volume

The prewere conduvarious consurface of thdeionized (stored in Dstructurem

2.2. Charac

The crysined withpowder difand operatiscanned inwith a scan

The com200 eld emat 5kV. Priotured in liqat 2000, 6bution in thX-rayMicrotime of 10m

nner scondin tim

ater

watemranee suimme

overess

WweW

Wwethe dred a

nic co

OH

by aanced froydraell etact w), was calculated according to the following equation:

l

W(2)

l is the length of themembrane between two potential sens-tinum wires, R is the membrane resistance, W and T are theand the thickness of the membrane, respectively.

embrane electrode assembly (MEA) fabrication andcell performance measurements

cell conguration: 2M MeOH+2M KOH|Pt/KOH|Pt/C|O2, was used in a single-cell of ADMFC. Thet for both anode and cathode was Pt/C on carbon paperatalyst loading of 1mg(Pt) cm2 (ElectroChem). The activede area for a single cell test was 4 cm2. The MEA wased by hot pressing the PVAKOHmembranewith anode ande at 90 C and 100kg cm2 for 5min. The MEA was insertedfuel cell hardware, which consisted of graphite block witharticle, the alkaline solid polymer electrolyte mem-on alkaline doped poly(vinyl alcohol) (PVAKOH) wasiming at a new cost-effective, easier preparing andable AAEM. Through chemical cross-linking procedure,g property of PVA was effectively controlled and thembranes were both exibility and toughness. Particu-was devoted to the chemical stability, on which theure of PVAKOH membranes were studied in detail forroved performance for potential use in alkali mem-ells. Additionally, the electrochemical characteristics ofPVAwere investigated in 2MKOH+2MCH3OHsolutionr polarization methods, especially, for the peak powerhe DMFC.

ental

als and membrane preparation

lly cross-linked PVA membranes were prepared by ation casting method where PVA (99% hydrolyzed, aver-,00089,000, Aldrich) was fully dissolved in water tosolution at 90 C. Appropriate amounts of the above

ere then mixed with water to get a homogeneous,and viscous appearance. After removing the air undere solutions were poured into plastic petri dishes and,as evaporated at ambient temperatures. When visu-membrane was peeled off from the plastic substrate

es of square pieces of membranes (ca. 1.5 cm2 cm)d in a reaction solution containing 10mass% glutaralde-25wt% solution in water, Shanghai Guoyao) in acetoneone hour [17]. The cross-linking proceeded betweenPVA and the CHO of GA in the membrane due to

alyzed reaction by addition of small amount of HCl in. Transparent, at membranes were obtained with af about several tens of micrometers (60100m). Thef the membranes can be easily controlled by adjustingof suspension.paration of the PVA alkaline membranes (PVAKOH)cted by immersion themembrane in KOH solutionwithcentrations at least for 24h. The absorbed KOH on theemembranewas removed by rinsing themembrane inD.I.) water numerous times, then the membranes were.I. water for measurements. Fig. 1 illustrates the innerodel of PVAKOHand some typicalmembrane pictures.

terization of PVAKOH membranes

tal structures of the compositemembraneswere exam-an X-ray diffractometer (XRD, PHILIPS PW 3040/60fractometer) using Cu K radiation (=0.15406nm)ng at 40kV and 100mA. The membrane samples werethe reectionmode with a 2 angle between 5 and 80

rate of 2 min1.posite morphology was evaluated using a FEI Sirionission scanning electron microscopy (SEM) operatingr to observations, the membrane samples were frac-uid nitrogen and sputtered with gold, then examined000 and 40,000 magnications. The element distri-e cross-section was determined by Oxford Instrumentanalysis INCA, operating at 20kVwith a data collectionin.

Fig. 1. I(b) PVAConditio

2.3. W

Thefrom thmembthen thitwasvacuumthe exp

WU =

whereand ofmeasu

2.4. Io

ThesuredimpedscanneFully htivity cin con(S/cm

=RT

whereing plawidth

2.5. Msingle-

TheC|PVAcatalyswith celectropreparcathodinto atructuremodel of PVAKOH andmembrane pictures for (a) pure PVA,tioned in 4M KOH at 25 C, (c) PVA conditioned in 4M KOH at 80 C.e: 24h, followed by complete removal of free KOH prior to testing.

and methanol uptake

er uptake (WU) of themembranes (g g1)was evaluatedass change before and after the complete dryness of the. A dry membrane was swelled in D.I. water for a day,rface water was wiped carefully with a lter paper, anddiatelyweighed. After drying the sample overnight in an at 60 C, thewater uptake (WU),was calculated usingion:

t Wdrydry

(1)

t and Wdry are the mass of fully hydrated membrane,ry membrane, respectively. The methanol uptake wast the same procedures.

nductivity measurements

ionic conductivity of the formedmembraneswasmea-n AC impedance technique using an electrochemicalanalyzer (VMP2/Z, PAR), where the AC frequency wasm 100kHz to 0.1Hz at a voltage amplitude of 100mV.ted membranes were sandwiched in a Teon conduc-quipped with Pt foil contacts [18]. The membrane wasith water over the measurements. Ionic conductivity,

MMFHighlight

J. Fu et al. / Synthetic Metals 160 (2010) 193199 195

Fig. 2. Ionic cotion in aqueouof KOH solutiotivity testing.

machined s2M MeOHanode chanrate 5mLmto enter ththrough a hcell was plaused to keewere obtaiSokken) ove

3. Results

3.1. Ionic co

The alkageneous wsolutions, thdecolored cshows thePVAKOH mthe PVAmetrations atmembranenumerous tfor ionic coAC impedanprocess in tthe semicirresistance,that the ionvalue of 4.724mol L1

ductivity obconcentrateThis resultthe polymedipoledipotion forces,KOHduringof PVA. HowdopingKOHcentration idoping KOH

ypicalne sucondu

ontrto betion.er ath asc con

emic

chefectsraturbilitranesres fe totempnducre. Shur conductivity values from the tested membranes ranged from104 S cm1 to 4.51104 S cm1 at 25 C. Generally speak-EMs are frequently less stable since the basic groups arenductivity of PVAmembranes as a function of dopingKOHconcentra-s solution. The membranes were immersed in various concentrationn for 24h followed by complete removal of free KOH prior to conduc-

erpentine ow channel and copper current collectors.+ 2M KOH aqueous solution was pumped into thenel of the cell under atmospheric pressure, with a owin1. Pure oxygen gas was supplied as the cathode fuele cathode channel with a gas ow rate 20mLmin1

umidier held at 25 C under ambient pressure. Theced in a temperature-controlled chamber, which wasp the cell at a constant temperature. Polarization curvesned using a fuel cell evaluation system (TFC-2100,r the temperature range of 6090 C.

and discussions

nductivity of alkaline PVA

line PVA membranes appeared transparent and homo-ith mechanical exibility. When immersed in KOHe PVAmembrane became orange in color but it almostompletely by rinsing the membrane in D.I. water. Fig. 2ionic conductivities of the PVAKOH membranes. Theembrane preparation was conducted by immersion

mbranes in KOH aqueous solutionwith various concen-least for 24h. The absorbed KOH on the surface of thewas removed by rinsing the membrane in D.I. waterimes, then the membranes were stored in D.I. waternductivity measurement. Fig. 3 illustrates the typical

Fig. 3. Tmembraprior to

tional cfoundin solupolymity (sucin ioni

3.2. Ch

Thethat aftempeical stamembperatutest thvatedthe coperatuwith foThe co1.36ing, AAce spectra, which are related to the ionic conductionhe bulk properties of the membrane. The intercept ofcular arc with the Z (ReZ) axis was taken as the bulkR, of the polymer electrolyte membrane. It can be seenic conductivity measured at 25 C reached a maximum3104 S cm1 for PVA in doping KOH concentration ofin solution. This is in the same order of the ionic con-tained by directly mixing a viscous PVA solution withd KOH aqueous solution as reported elsewhere [19].suggests that some of KOH molecules are taken intor by water molecules. The chemical interaction, such asle interaction including hydrogen bonding and induc-may take place betweenCOandOHgroups on PVA andalkali doping,which is helpful for the ionic conductivityever, the ionic conductivity decreased with additionalconcentration in solution, for example,whenKOHcon-n solution is larger than 4M. That is, additional higherconcentration in solution does not simply make addi-

inherentlyfact, the puor 1.0M KO[9] or evengreatly decour interesPVAKOH man increasesolution atand 10M Kand, exhibit9.77104tively. It seKOH after ttivity due tthe resultsbase treatmchemical crimpedance spectra of PVAdoped in 6MKOHat 25 C. The freeKOHonrface was completely removed by rinsed the membrane in D.I. waterctivity testing.

ibution to the conductivity. Themembrane samples aresupernatant at high doping KOH concentration (>8M)It seems that more OH could not be taken into thehigh KOH doping solution due to the weak ionic mobil-formed ion-pairs or increasedviscosity), thus adecreaseductivity.

al stability of alkaline PVA

mical stability of AAEMs is recognized as a key factorfuel cell performances, especially, in alkalinemediumates above 60 C and high KOH concentration. The chem-y of alkaline PVA was tracked by immersing the PVAin different concentrations of KOH at elevated tem-

or at least 24h. This was an experiment designed tolerance of the membrane to base treatments at ele-eratures [9]. After complete removal of the free KOH,tivity of the membrane was measured at room tem-own in Fig. 4 are the results of the typical candidatesncentrations (1, 4, 6, and 10M) of KOH for PVA applied.less stable than the acidic groups [11]. Because of therely quaternized polymers can be just subjected to 0.5H at 80 C but deteriorated only in 2.0M KOH at 60 Cin pure water at 80 C [8]. The ionic conductivity is

reased and even cannot be measured thereby [9]. Tot, however, no decrease in conductivity was found forembranes. Inversely, all tested membranes showed

d conductivity with increasing KOH concentration inelevated treating temperatures. The PVA soaked in 6OH showed the rapid increase in ionic conductivityed the highest conductivities of 8.74104 S cm1 andS cm1 after temperature conditioned at 80 C, respec-ems that PVA has a remarkable absorbent capacity toemperature treatment, thus an increased ionic conduc-o much increased charge carriers. On the other hand,suggest the tough tolerance of the PVA membranes toents even in 10M KOH at 80 C due to the high denseoss-linkage in PVA polymer matrix.

196 J. Fu et al. / Synthetic Metals 160 (2010) 193199

Fig. 4. Ionic conductivity of PVAmembranes after conditionedwithKOHat elevatedtemperatures. Themembraneswere conditioned in1, 4, 6 and10MKOHat 25, 40, 60and 80 C for 24h, followed by complete removal of free KOH prior to conductivitytesting. The conductivity was measured at 25 C.

Fig. 5 shows the temperature dependence of the ionic conduc-tivity of PVAKOH membranes. Here the PVA membranes dopingin 4M KOHdidates, resthe membrtemperaturno change wconditionedature afterwhich reachThis is in weis, the dynaditioned atcarriers.

It shouldple of addithigh ionic c101 S cm1

ionic condupreparationthus high Karation proconcentrati

Fig. 5. Ionic coconditioned intime: 24h, foll

Fig. 6. XRD pain 4M KOH atfollowed by co

tivity measHowever, iimmersion

wering tmbreas

ed inKOHork troug

cludigro

inkinctivit

D an

X-rae cryPVAedwrystamallKO, and then conditioned at r.t. and at 80 C as typical can-pectively. After complete removal of the free KOH onane surface, the conductivity was measured at elevatedes. It can be seen that the ionic conductivity was almostith the temperature up to 80 C after membrane beingin 4M KOH at r.t., but linearly increased with temper-

the membrane being conditioned in 4M KOH at 80 C,ed the highest ionic conductivity of 9.51104 S cm1.ll agreement with the results obtained from Fig. 4, thatmic properties seems to be greatly improved after con-high temperature of 80 C, due to an increased charge

bementioned that alkaline doped PVA, i.e., with a cou-ives such as PEO [20], SSA [21] and TiO2 ller [15] givesonductivities ranged from 103102 S cm1 and evenfor PVAHEMASiO2 so-gel membranes [22]. Lower

ctivity in this work stems from the differentmembraneprocedure. KOH was directly added into PVA solution,OH content in the polymer, but an obvious phase sep-duced [19,20,15] or immersed the membrane in KOHon in solution, then directly conduct the ionic conduc-

branesremovthe metivity mreportfreethis wKOH thtion inand OHcross-lcondu

3.3. XR

Theine thof wetremovsemi-cand a sof PVAnductivity of PVA/KOHmembranes as a function of temperature: (a)4M KOH at 25 C, (b) conditioned in 4M KOH at 80 C. Condition

owed by complete removal of free KOH prior to testing.

from KOH cseen clearlydecreasedwdomain of adue to dopmer electroanion in alocal structin amorphocan be concthus the PVamorphousionic condu

3.4. SEM an

SEM phand its corelements artterns for PVAKOH membranes: (a) pure PVA, (b) PVA conditioned25 C, (c) PVA conditioned in 4M KOH at 80 C. Condition time: 24h,mplete removal of free KOH prior to testing.

urement [21,22] without any treatment such as rinsing.n this work PVAKOH membranes were conducted bythe PVA membranes in KOH solution, then, the mem-e rinsed in D.I. water numerous times for completelyhe absorbed KOH on the surface of the membrane, thenanes were stored in D.I. water for nal ionic conduc-urements. Therefore, the high ionic conductivity valuesthe literature were mainly from the contribution ofabsorbed on membrane surface. Contrary to this, in

he ionic conductivity merely comes from the bondedh chemical interaction such as dipoledipole interac-nghydrogenbondingand induction forcesbetweenCOups on PVA and KOH as Fig. 1 shows. Additionally, highg in PVAnetworkmay also contribute to the lower ionicy of the resulting membrane.

alysis

y diffraction measurements were performed to exam-stallinity of the composite membranes. XRD patterndoping in 4M KOH concentration with surface KOH

as obtained as shown in Fig. 6. PVAmembrane exhibits alline structurewith a large peak at a 2 angle of 1920

peak of 3940 [23]. From the outline of XRD patternH, no abroad lump between 20 and 40 was observedrystal as reported elsewhere [24]. However, as can be

in Fig. 6, the peak intensity at 20 of PVAKOH washen in comparisonwith pure PVA. This implies that themorphous region into PVA polymer matrix augmenteded in KOH. Usually, the ionic conductivity of the poly-lyte could be attributed to the transport of cation andpolymer matrix by hopping between coordinate sites,ural relaxation and segmental motions of the polymerus domain, as well as ion transport in solvent. Thus, itlude that KOH simultaneously act as a plasticizer here,A polymer electrolyte becomes more exible and morephase (as XRD results indicated), which makes for thectivity of PVAKOH membranes.

d EDX characterization

otographs for the cross-sectional views of PVAKOHresponding EDX mappings for potassium and oxygene shown in Figs. 7 and8, respectively. Prior to the exper-

J. Fu et al. / Synthetic Metals 160 (2010) 193199 197

Fig. 7. SEM pi4M KOH at 80Condition time

iment, theits surface,SEM observ2,000magIt should btration in sotemperaturshows. But nsuch as holThe structu6000 magcentration (from PEOPwith differeIn this worevenly disption (Fig. 7eparticles anstability du

In the EDhigh elemeof potassiuimplied thactures of the cutview of the PVA/KOH membranes: (a) conditioned in 4M KOH at r.t (20C (6000), (d) conditioned in 10M KOH at 80 C (6000), (e) conditioned in 4M KOH: 24h, followed by complete removal of free KOH prior to testing.

sample was rinsed with D.I. water to remove KOH onand then it was freeze-fractured in the liquid nitrogen.ations of the sections of a membrane (Fig. 7a and b atnication) showed ahomogeneous anddensematerial.e mentioned that by increasing doping KOH concen-lution and/or conditioned at temperature above roome induced an orange color on the membranes as Fig. 1cot any surface degradation ormembranemodication,

es or phase separation phenomena, could be detected.re is very compact on the SEM pictures (Fig. 7c and d atnication) either being conditioned at high KOH con-10MKOH) or conditioned at 80 C. This is very differentVAKOH blend polymer, on which many small poresnt size are produced on the surface of the lm [20].k, the KOH particles are discernable as light dots andersed in the PVA polymermatrix at 40,000 magnica-and f). Therewere neither gaps nor cracks between thed polymermatrix, which proves the excellent chemicale to the cross-linkage in PVA matrix.Xmapping image, the highlighted bright dots revealednt concentration. It can be seen that distributionsm and oxygen elements were homogeneous, whicht KOH was well dispersed throughout PVA membrane.

An intriguinous changealkaline cohigher concat 80 C. Thiacetal grouthis reactiother that cmay exist iductivity ju

3.5. Water/

The impwell knownerty of the cwhich is hiof water inconductivitaffect othersional andthe water umembrane00), (b) conditioned in 10M KOH at r.t. (2000), (c) conditioned inat 80 C (40,000), (f) conditioned in 10M KOH at 80 C (40,000).

g result was revealed from EDXmapping that no obvi-in potassium element before and after conditioned inncentration (4M KOH) and temperature, but a muchentration in oxygen element particular to conditionedsmaybe due to the fact thatOH in KOHmay reactwithp in PVA matrix to generate OH and water, althoughnmay take place incompletely. This result suggests fur-ombined KOH molecules by long-distance interactionn the PVA matrix, which was helpful for the ionic con-st as described previously.

methanol uptake

ortanceof the ionic conductivity and fuel permeability is, particular to ADMFC. Furthermore, the swelling prop-onducting membranes is also an important parameter,ghly correlative to the cell performance. The presencethe membranes is a prerequisite for reaching high ionicy. On the other hand, excessively highwater uptakewillperformances of the membranes such as the dimen-thermal stability. Table 1 gives the changes in bothptake and the methanol uptake values of PVAKOHbefore and after conditioned in 4M KOH at r.t. and at

198 J. Fu et al. / Synthetic Metals 160 (2010) 193199

Fig. 8. EDX mconditioned at

Table 1Physico-chem

Membrane

PVANaon115

80 C, respeof Naon 1tions. As seedecreased fbeing condfrom 20.5%changes ocfor alkalinemental errouptake of Nshowed a m80 C, wherto 128.7%,measuremeability in copromising fcations.

3.6. Single-

Fig. 9 sdoped PVA2M KOH+apping of (a), (d) potassium element and (b), (c) oxygen element within PVA/KOH, rer.t., (c and d): conditioned at 80 C. Condition time: 24h, followed by complete removal

ical properties of alkaline PVA based on chemical cross-linking and Naon 115 membran

Membrane thickness(mm)

KOH dopingconcentration (M)

Liquid uptake (%)

4 r.t. Con

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

80100 39.4 20.5 36.135 34 41.8

ctively. For a comparison, water and methanol uptake15 was measured under the same experimental condi-n in Table 1, the water uptake of PVAKOHmembranerom 39.4%when being conditioned at r.t. to 36.1%whenitioned at 80 C, while the methanol uptake increasedto 21.4% correspondingly. In other words, no obviouscurred both in water uptake and in methanol uptakePVA even after conditioned at 80 C if the experi-rs are ignored. Conversely, although the lower wateraon 115 under the same measuring conditions, ituch higher methanol uptake especially conditioned ate the methanol uptake rapidly increased from 41.8%i.e., 6-fold of alkaline PVA membrane. Although thisnt is not a direct consequence of methanol perme-ntact with aqueous solution, these initial results areor future AAEMs fabrications in potential fuel cell appli-

cell performance test

hows IV characteristics of the DMFC using KOHas alkaline solid polymer electrolyte membrane in

2M CH3OH solution at the temperature between 60

and 90 C, rdensity ofwith a peaof 60 C. Amatic imprpotential o

Fig. 9. IV cuelectrolyte mespectively. Doping KOH concentration in solution: 4M; (a and b):of free KOH prior to testing.

es.

Ionic conductivity103 (S cm1)

ditioned at 80 C r.t. Conditioned at 80 C

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

1 21.4 0.47 0.75128.7

espectively. It can be seen that an initial peak power6.04mWcm2 was achieved at cell voltage =0.47Vk current density of 14.9mAcm2 at temperaturen increase in fuel cell temperature leads to a dra-ovement in the cell performance. The open circuitf the alkaline DMFC are about 0.870.91V. In spite

rves of the DMFC using KOH doped PVA as alkaline solid polymermbrane in 2M KOH+2M CH3OH solution at different temperatures.

J. Fu et al. / Synthetic Metals 160 (2010) 193199 199

of a low catalyst loading (1mgcm2 both on the anode andon the cathode), the MEA showed a good performance and,the power density increased from 6.04mWcm2 at 60 C to10.21mWcm2 at 90 C. However, we did not conclude thatthe PVAKOH is comparable to the PVATiO2KOH [15] or thePVAPSSAKOH [21] at this stage, since the air cathode is notconsidered and the Pt/C cathode electrode was used in thiswork.

4. Conclusions

In short, the chemically stable anion exchange membranesthat can conduct OH were prepared by incorporation KOH inPVA. The SEMEDX results demonstrated a dense structure ofPVAKOH membranes, where the bonded KOH contributes theionic conductivity through chemical interaction between COand OH groups on PVA and KOH. This is different from theusual doped one, where the ionic conductivities were mainlyfrom the free KOH absorbed on membrane surface. In par-ticular, the perfect tolerance of the PVAKOH membranes wasfound to base treatments even conditioned in 10M KOH at 80 Cwithout losing any membrane integrity and ionic conductiv-ity due to high dense chemical cross-linking in PVA structure.DMFC test using PVAKOH fabricated MEA showed an ini-tial power density of 6.04mWcm2 at 60 C and increased to10.21mWcm2 at 90 C. These initial results are very promis-ing for further improved AAEMs performance in potential fuelcell applications, considering the PVA superior methanol barrierproperties and its easy preparation and cost-effective mate-rial.

Acknowledgements

This work is nancially supported by Project Pujiang Founda-tion (grant no. 08PJ14096) andNatural 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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Alkali doped poly(vinyl alcohol) for potential fuel cell applicationsIntroductionExperimentalMaterials and membrane preparationCharacterization of PVA-KOH membranesWater and methanol uptakeIonic conductivity measurementsMembrane electrode assembly (MEA) fabrication and single-cell performance measurements

Results and discussionsIonic conductivity of alkaline PVAChemical stability of alkaline PVAXRD analysisSEM and EDX characterizationWater/methanol uptakeSingle-cell performance test

ConclusionsAcknowledgementsReferences