Available online at www.sciencedirect.com

Journal of Membrane Science 311 (2008) 98103

Modification of Nafion membrane using ittea, P

a Labo l Phynces,mberr 200

Abstract

In order t embr(VRB) base o formembrane. uredNafion mem eductand a little h cienmembrane(V incubsignificantly. The value is 96.297.3%, which is higher than that obtained with the VRB single cell based on unmodified Nafion membrane(VRB-Nafion) (around 93.8%). Due to the little higher area resistance caused by the modification, the voltage efficiency of VRB-modified Nafion is lowerthan that of VRB-Nafion. Furthermore, the water transfer across the modified membrane was also reduced. The ion exchange capacity (IEC) ofthe modified Nafion membrane was also evaluated. The formation of the thin cationic charged layer on the membrane surface was confirmed byIR spectra a 2007 Else

Keywords: V

1. Introdu

The vaSkyllas-Kations worldresponse tistorage. Itin the negawhich aretion of theand negativions, suchthe circuitshould posconductivit

CorresponE-mail ad

0376-7388/$doi:10.1016/jnalysis.vier B.V. All rights reserved.

anadium redox flow battery; Interfacial polymerization; Membrane modification; Self-discharge phenomena

ction

nadium redox flow battery (VRB) proposed byzacos and co-workers [1] has attracted many atten-wide due to its long cycle life, flexible design, fast

me, deep-discharge capability, and low cost in energyemploys V2+/V3+ and VO2+/VO2+ redox couplestive and positive half-cell electrolytes, respectively,separated by an ion exchange membrane. The func-membrane is to prevent cross mixing of the positivee electrolytes, while still allowing the transport ofas proton in the case of VRB-Nafion, to completeduring the passage of current. The ideal membranesess low permeability of vanadium ions, high protony, good chemical stability, and low cost [2,3].

ding author. Tel.: +86 411 84379072; fax: +86 411 84665057.dress: zhanghm@dicp.ac.cn (H. Zhang).

Nafion membrane is generally served as VRB membranes dueto its high proton conductivity and excellent chemical stabilityin VO2+ solution [2,4]. However, the selectivity of Nafion mem-brane between proton and vanadium ions is not high enough. Sothat it will lead to the undesired transport of vanadium ions acrossthe membrane during the chargedischarge processes of VRB.If vanadium ions with different oxidation states transport to theopposite half cell and react with each other, electrochemicalenergy loss and energy efficiency reduction of the battery cannotbe prevented [5]. Moreover, a significant amount of water trans-fers across Nafion membrane during chargedischarge processesof VRB, causing the undesired preferential volumetric change asone half cell is flooded and diluted while the other becomes moreconcentrated, adversely affecting the overall operation of theVRB. Although the detail mechanism of water transfer across themembrane is not understood comprehensively, some researchesindicated that the transfer of hydrate vanadium ions between thetwo half-cell solutions is the main reason of water transfer [6,7].

In order to reduce the permeation of multivalent vanadiumions through the membrane and maintain the conductivity of

see front matter 2007 Elsevier B.V. All rights reserved..memsci.2007.11.055for vanadium redox flow baQingtao Luo a,b, Huaming Zhang a,, Jian Chen

ratory of PEMFC Key Materials and Technologies, Dalian Institute of Chemicab Graduate School of the Chinese Academy of Scie

Received 1 September 2007; received in revised form 26 NoveAvailable online 8 Decembe

o reduce the permeation of vanadium ions across the ion exchange md on Nafion membrane, the interfacial polymerization was applied tThe area resistance and the permeability of vanadium ions were measbrane, the modification of Nafion membrane results in a dramatic righer area resistance of the membrane. As a result, the columbic effiRB-modified Nafion), which is related to the concentration of thenterfacial polymerizationry applicationseng Qian a,b, Yunfeng Zhai a,bsics, Chinese Academy of Sciences, Dalian 116023, ChinaBeijing 100039, China2007; accepted 27 November 20077

ane during the operation of vanadium redox flow batterym a cationic charged layer on the surface of Nafion 117. The results indicate that comparing with the unmodifiedion in crossover of vanadium ions across the membranecy for the VRB single cell based on the modified Nafionation solution of polyethylenimine (PEI), was increased

Q. Luo et al. / Journal of Membrane Science 311 (2008) 98103 99

proton simultaneously, the ion exchange membrane with mono-valent cation permselectivity is required. In general, multivalentcations arecompared teffect. Acclayer is fomeation ofbe decreasbranes witmade [810

In thisfor the forthe surfacePolyethyleselected asFor gettinggroups werNafion memarea resistapermeabilicomparisonmances ofNafion memconfirm thmembrane

2. Experim

2.1. Mater

Nafionpany. Phosfrom Beijinand usedchased fromIsophthaloyChemical CHexane anpurchasedcal Reagenpurification

2.2. Memb

Mechanis shown ithis work.to introducface of Nafimembranemembranetions wereisophthaloylayer on th

The Naride form117 memb

ig. 1.

ide/bottoactioile hefluxarbollingCl) grane.resu

aqueas t

d off, the membrane was submerged in isophthaloylride hexane solution. Thus the reaction occurs at thece between the two solutions to form a very thin denseer layer on the surface of membrane. After the reaction,

posite membrane was taken out and air-dried at 100 C.

embrane characterization

IEC and the area resistance of the membrane were mea-y using the methods described in literature [12]. For the

easurements, the membrane sample was immersed for 1a large volume of 1 M HCl aqueous solution to give the

rane in the H-form. The membrane was then washed freeess HCl with distilled water and for a further 4 h equili-with distilled water, with frequent changes of the distilledto remove the last traces of acid.

membrane was then equilibrated with exact 50 mL ofNaOH aqueous solution for 24 h and the cation exchange

ty was determined from the reduction in alkalinity deter-by back titration. The ion exchange capacity of the cationdifficult to be adsorbed on the cationic charged layero monovalent cations because of Donnan exclusionordingly, it is expected that when cationic chargedrmed on the cation exchange membrane, the per-multivalent cations through the membrane should

ed. Many efforts to prepare cation exchange mem-h permselectivity for monovalent cation have been].

study, the interfacial polymerization was appliedmation of an ultra-thin cationic charged layer onof Nafion membrane for the application in VRB.

nimine (PEI) with a great deal of amino groups waspolyelectrolyte to form the cationic charged layer.a better adsorption of PEI, chlorosulfonyl (SO2Cl)e introduced as reactive groups onto the surface ofbrane in advance. The ion exchange capacity (IEC),

nce, water transfer properties and vanadium ionsty of the modified Nafion membrane was tested in

with unmodified Nafion membrane. The perfor-VRB single cells using modified and unmodifiedbrane were tested. IR spectra analysis was used to

e formation of a cationic charged layer on Nafionsurface after modification.

ental

ials

membranes were purchased from DuPont Com-phorus pentachloride and phosphorus oxychlorideg Chemical Reagent Company were reagent grade

for the chlorosulfonation reaction. PEI was pur-Shanghai ShengYu Chemical Reagent Company.

l dichloride was purchased from Jiangxi LianKeo. Ltd. Other reagents used in the study such as

d carbon tetrachloride were all reagent grades andfrom Tianjin JinDong TianZheng Precision Chemi-t Factory. All chemicals were used without further.

rane preparation

ism of the modification of Nafion 117 membranen Fig. 1. Nafion 117 membrane was employed inFirstly, chlorosulfonation reaction was carried outed the chlorosulfonyl (SO2Cl) groups onto the sur-on 117 membrane (a). Then PEI was adsorbed on thesurface through acidamide bonds between Nafionand PEI (b). Finally, interfacial polymerization reac-carried out by submerging the above membrane inl dichloride hexane solution to form cationic charged

e surface of Nafion 117 membrane (c).fion membrane was converted into sulfonyl chlo-as described in literature [11]. A piece of Nafionrane was immersed in a mixture of phosphorus pen-

F

tachlorround-tion reoff whbrief rfresh ccontro(SO2memb

Thein PEIbrane wdrainedichlointerfapolymthe comfor 1 h

2.3. M

Thesured bIEC mday inmembof excbratedwater

The0.01 McapaciminedMechanism of the modification of Nafion 117 membrane.

phosphorus oxychloride (1:2, w/w) in a three-neckmed flask with a cooler to carry out chlorosulfona-n for about 4 h at 90 C. Then, the liquid was pouredot and carbon tetrachloride was added. Following a, the carbon tetrachloride was decanted. Twice moren tetrachloride was added, refluxed and decanted. Bythe reaction temperature and time, the chlorosulfonylroups were partially introduced onto the surface of

lting Nafion sulfonyl chloride membrane was soakedous solutions for about 2 h. Then, the treated mem-aken out of the solution. After the excessive solution

100 Q. Luo et al. / Journal of Membrane Science 311 (2008) 98103

Fig. 2. Devicmembrane.

exchange m

IEC = M0

where M0,NME,NaOH isweight of t

For theexposed tosides in aref. [12]). Tmembraneelectrochemrange of 10of the cell( cm2) isr = (r1 r

The devvanadium iThe left res3 M H2SO41.5 M MgSionic strengpressure efcompartmeBefore useeffective arume of thesolution fr

interval and analyzed for vanadium ions concentration by usingan UVvis spectrometer. The experiments were conducted atroom temperature.

The static water transfer across the membranes was evaluatedby the methods described in literature [6]. Negative and positiveelectrolytes at 50% state of charge (SOC) [0.75 M V2+ + 0.75 MV3+ on one side and 0.75 M VO2+ + 0.75 M VO2+ on the otherside] were used to evaluate the water transport behavior of themembranes. The membrane area exposed to the electrolytes was15 cm2. The tube connected to each compartment had an internal

ter on is eotherthe V

he soVO2e electrodors.e ofcell w

of 5de a75 V

IRtotalr.370o coface

ults

C, a

promem

-PEId toI aq

Table 1Comparison o

Membrane

Nafion 117Nafion-PEI-2Nafion-PEI-5e for the measurements of VO2+ ions permeability across the

embrane is calculated from Eq. (1).,NaOH ME,NaOH

W(1)

aOH is the moles of NaOH in the flask at the start,the moles of NaOH after equilibration, and W is the

he dry membrane(g).area resistance a measurement, the membrane wasa solution of 1.5 M VOSO4 in 3 M H2SO4 on bothconductivity cell (scheme is same with Fig. 1 inhe electric resistances of the conductivity cell with(r1) and without membrane (r2) were measured byical impedance spectroscopy (EIS) over a frequency0 mHz to 100 kHz. The effective membrane area Swas 1 cm2. The area resistivity of the membrane rcalculated by Eq. (2).2)S (2)ice used for the measurement of the permeability ofons through the membrane was illustrated in Fig. 2.

diamesolutioto the

Fortests, tVO2+/positivthe elecollectvolumsingledensityelectrowas 1.

Theuated(Avataorder tthe sur

3. Res

3.1. IE

TheNafionNafionsponde5% PEervoir was filled with the solution of 1.5 M VOSO4 in, and the right reservoir was filled with the solution ofO4 in 3 M H2SO4. MgSO4 was used to equalize theths of the two solutions and to minimize the osmotic

fects. Both solutions were circulated through the cellnts which were separated by the membrane samples., the membrane was immersed in distilled water. Theea of the exposed membrane is 5 cm2 while the vol-solutions for each reservoir was 50 mL. Samples of

om the right reservoir were taken at a regular time

It can bebrane presemembrane,decreased.modified NPEI aqueouthe IEC va2.5 membrfrom the vmembrane.

f the properties between Nafion 117 membrane and the modified Nafion membrane

PEI concentration (% (w/w)) Thickness (m) IEC (mmol g1) A0 175 0.91 1

.5 2.5 196 0.89 15 208 0.87 1f 3.76 mm. The change of 9 cm in the height of thequivalent to 1 mL solution transferring from one side.

RB single cell (Fig. 2) used in the chargedischargelutions of 1.5 M V2+/V3+ in 3.0 M H2SO4 and 1.5 M+ in 3.0 M H2SO4 were employed as negative andctrolytes, respectively. The carbon felt was served ases and the graphite plates were served as the current-The active area of the electrode was 5 cm2 while theelectrolyte was 30 mL in each half cell. The VRBas charged and discharged with the constant current-0 mA/cm2. To avoid the corrosion of the carbon felt

nd graphite plates, the upper limit of charge voltage, and the lower limit of discharge voltage was 0.8 V.spectra were recorded by using the ATR (atten-reflection) technique with a FT-IR spectrometerE.S.P., Nicolet Continuum Infrared Microscope) in

nfirm the formation of the cationic charged layer onof Nafion membrane.

and discussion

rea resistance and other properties of membrane

perties of Nafion 117 membrane and the modifiedbranes were tested and summarized in Table 1. The

-2.5 membrane and Nafion-PEI-5 membrane corre-the Nafion membrane treated by soaking in 2.5% andueous solutions, respectively.seen from Table 1 that the unmodified Nafion mem-nted the highest IEC value. Comparing with Nafionthe IEC values of the modified Nafion membraneIt can also be seen clearly from Table 1 that theafion membrane treated with higher concentrations solutions presented lower IEC value. For example,lue decreased to 0.89 mmol g1 for Nafion-PEC-

ane and 0.87 mmol g1 for Nafion-PEC-5 membranealue of 0.91 mmol g1 for the unmodified NafionThe reduction of the IEC value can be attributed to

rea resistance ( cm2) Permeability of VO2+(107 cm/min).06 36.55.24 5.23.34 1.70

Q. Luo et al. / Journal of Membrane Science 311 (2008) 98103 101

the formation of acidamide bonds between Nafion membraneand PEI achieved by forming chlorosulfate groups in advance.

From Table 1, it can also be seen that the modification ofNafion membrane increased the area resistance of the modi-fied membrane. The unmodified Nafion membrane presented thesmallest area resistance of 1.06 cm2. This value correspond-ing to Nafion-PEI-2.5 membrane and Nafion-PEI-5 membraneis 1.24 and 1.34 cm2, respectively. The increase of the arearesistance was caused by the formation of an ultra-thin cationiccharged layer that was obtained with the adsorption of PEI andfollowing interfacial polymerization. The cationic charged layeracts as an electrical repulsion barrier for not only vanadium ionsbut also protons to permeate the membrane, leading to a higher,but still acceptable area resistance.

3.2. Permeability of vanadium ions

Another important characteristic for the ion exchange mem-brane for VRB application is that the membrane should providean effectiveDiffusion ostates acrosand other umembraneions of the

In this smembranecondition. TThe amounmonitoredtion. The cthe time isions diffusconsiderabNafion memsurface ofwith highevanadium i

Fig. 3. The inFig. 1. The m

The permeability of vanadium ion through the membranewas calculated by using the pseudo-steady-state conditionand listed in Table 1. From Table 1, it can be seen thatthe permeability of vanadium ion decreased significantly to5.23 107 cm/min and 1.70 107 cm/min corresponding toNafion-PEI-2.5 membrane and Nafion-PEI-5 membrane fromthe value of 36.55 107 cm/min for the unmodified Nafionmembrane. It can be concluded that the modification of Nafionmembrane by PEI provides a barrier to vanadium ions perme-ation. These phenomena can be mainly attributed to the Donnanexclusion effect of the cationic charged layer on the surface ofNafion membrane [9].

3.3. Water transport measurements

The transfer of water across the membrane during the processof chargedischarge, which is caused by several processes, canseverely affect the performance of VRB. When selecting the suit-able membranes for VRB, therefore, one of the most importantrequirements is that the membrane should be able to prevent

ive transfer of water from one half cell to the other. Inrk,

ranesultsn thmem

e hawor

iteraon thon tt ofas a

transultsn of Nr acr

easuodifieseparation of the positive and negative electrolytes.r leakage of vanadium ions with different oxidations the membrane lead to self-discharge of the batteryndesirable consequences. From the point of view ofapplying in the VRB, low permeability of vanadiumion exchange membrane is required.tudy, the vanadium ions permeability of the Nafionbefore and after modification is compared at the samehe device applied in this work is presented in Fig. 2.

t of vanadium transferring across the membrane wasby detecting vanadium concentration in MgSO4 solu-oncentration of VO2+ in the solution of MgSO4 withillustrated in Fig. 3. It was clear that the vanadiumion through the unmodified Nafion membrane wasly faster than those diffusion through the modified

brane. Due to the increase of PEI adsorbed on theNafion membrane when the membrane was treatedr concentration of PEI solution, the permeability ofons across the modified Nafion membrane decreased.

crease of VO2+ concentration in the right reservoir as shown inembrane used in the device as shown in Fig. 1.

excess

this womembThe rebe seeNafionpositivof thisvious lbasedbasedamoun

brane wwaterthe resficatiotransfe

Fig. 4. Mand unmthe water transporting across the unmodified Nafionand the modified Nafion membrane were measured.obtained at 50% SOC are presented in Fig. 4. It can

at a significant amount of water transferred acrossbrane from the negative half-cell electrolyte to the

lf-cell electrolyte under the experimental conditionk. This is in agreement with that reported in the pre-ture [6]. The direction of water transfer in the devicee modified Nafion membrane was the same as that

he unmodified Nafion membrane. Furthermore, thewater transferred across the modified Nafion mem-pproximately 1 mL, which is just half of the value offer across the unmodified Nafion membrane. Fromabove-mentioned it can be concluded that the modi-

afion membrane can effectively minimize the wateross the membrane in a VRB single cell.

rements of water transfer across the modified Nafion membraned Nafion membrane using electrolytes at an initial SOC of 50%.

102 Q. Luo et al. / Journal of Membrane Science 311 (2008) 98103

Some studies [6,7] indicated that the transfer of water acrossthe membranes during the chargedischarge cycling of VRB isdetermined by the hydration shells of the different vanadium ionsand the osmosis pressure difference between the two half-cellsolutions. Under the certain condition, for a VRB using cationexchange membrane the net water transfer is toward the positivehalf cell, whereas for a VRB using anion exchange membranesthe net water transfer is toward the negative half cell. As shownin Fig. 4, under the work condition in this work the net trans-fer of water across Nafion membrane is from the negative halfcell to the positive half cell. This is in accord with the resultsobtained under the same work conditions by [6]. The authorsindicated the transfer of water from the negative half cell to thepositive half cell was caused by the hydration shells of V2+ andV3+ ions which carry a large amount of water and can easily per-meate through the cation exchange membrane [6]. In the caseof the modified Nafion membrane, the amount of water trans-ferred across the membrane was reduced obviously. This maydue to the fact that the transfer of V2+ and V3+ ions across themembrane is significantly reduced by employing the modifiedNafion membrane.

3.4. Perfor

The traresult in theopen circuiused to indwork, the mthe electroVRB singlOCV valueobtained wbrane weregradually dexperimentmodified N1.0 V exten

Fig. 5. CompNafion 117 an

Fig. 6. ChargNafion-PEI-2

only 96 h. Ithe crossov

he mcha

ed Ne ofed Nhers, this aby t

ployperfrren

be sfionandafio

y emncyd Natively. The lower voltage efficiency obtained with VRB-ed Nafion is resulted from the higher area resistance ofdified membrane, Although Nafion-PEI-5 membrane pre-the best capability for reducing the crossover of vanadiumnd the proton conductivity of it is also reduced obviously.rder to meet the requirements for VRB application, the

ed Nafion membrane with low permeability of vanadiumd high conductivity of proton should be developed.

le cell performance efficiency of VRB based on Nafion 117 membraneified Nafion membrane

ne Nafion 117 Nafion-PEI-2.5 Nafion-PEI-5

bic efficiency (%) 93.8 96.2 97.3efficiency (%) 90.7 88.4 83.3efficiency (%) 85.0 85.1 81.1mance of VRB single cell

nsfer of vanadium ions across the membrane willself-discharge of VRB, representing the decrease of

t voltage (OCV) [13]. Thus the value of OCV can beicate the degree of self-discharge of a VRB. In thiseasurements of OCV were performed by pumping

lyte solutions through the cell unceasingly after thee cells were charged to a SOC value of 50%. Thes were recorded unceasingly too. The OCV valueith VRB single cell based on different Nafion mem-illustrated in Fig. 5. As can be seen, the OCV valueecreased from the initial value of 1.43 V with theal time at first and then decreased sharply. For VRB-afion, the time for OCV value remaining larger thanded to 265 h. But for VRB-Nafion, this value was

arison of the decrease of OCV between VRB single cell based ond Nafion-PEI-2.5 membrane.

using tThe

modifivoltagmodifithe higBesideNafioncausedby em

Theat a cuAs canand Na96.2%VRB-NVRB befficie2.5 anrespecmodifithe mosentedions, aSo in omodifiions an

Table 2The singand mod

Membra

CoulomVoltageEnergyedischarge curves of VRB single cell based on Nafion117 and.5 at a current density of 50 mA/cm2.

t indicated that the self-discharge of VRB caused byer of vanadium ions can be reduced significantly byodified Nafion membrane.rgedischarge curves of VRB-Nafion and VRB-afion were presented in Fig. 6. The average chargeVRB-Nafion is a little bit lower than that of VRB-afion. This is due to the larger IR drop caused byarea resistance of the modified Nafion membrane.e chargedischarge capacity (Ah) of VRB-modifiedlittle larger than that of VRB-Nafion. This may be

he reduction of self-discharge of the VRB single celling the modified Nafion membrane.ormances of VRB-Nafion and VRB-modified Nafiont density of 50 mA/cm2 were presented in Table 2.een, the VRB single cell employing Nafion-PEI-2.5-PEI-5 membrane presented a columbic efficiency of97.3%, which are larger than the value of 93.8% forn. This is due to the reduction of self-discharge ofploying the modified Nafion membrane. The voltage

for VRB single cell based on Nafion, Nafion-PEI-fion-PEI-5 membrane is 90.7%, 88.4% and 83.3%,

Q. Luo et al. / Journal of Membrane Science 311 (2008) 98103 103

Fig. 7. FT-IRmembrane, an

3.5. FT-IR

To furt(SO2Cl) gon the surftra of Nafiand the moated total respectra forNafion memNafion areat 978 andteristic peathe symmevibration osulfonationis assignedface, as shomembrane,1659 and 1presence ovibration ocharged laymembrane.

4. Conclu

Surfacecial polymvanadiumhigher areacell significmembrane

the columbic efficiency for the chargedischarge cycle per-formed with VRB-modified Nafion is obviously higher thanthat obtained with VRB-Nafion. However, due to the higherarea resistance of the modified Nafion membrane, the voltageefficiency obtained with VRB-modified Nafion is lower thanthat obtained with VRB-Nafion. The overall energy efficiency

bictly. Fdifiehat tlysin ththat

o mo

nce

Sum,tem f(1985

ohambran

(199. Hwated eltery, JSkyllcs andurcesWiedem wi98) 2

Mohaoss co

tery, JSukkactrolytery, JSata,perm02) 3Vallospectra of (a) Nafion membrane, (b) Nafion sulfonyl chlorided (c) the modified Nafion membrane.

spectroscopy analysis

her confirm the introduction of chlorosulfonylroups and then the presence of cationic charged layerace of the modified Nafion membrane, FT-IR spec-on membrane, Nafion sulfonyl chloride membrane,dified Nafion membrane were determined by attenu-flectance (ATR) analysis. In Fig. 7, the typical FT-IR

the membranes above-mentioned were presented. Forbrane, the antisymmetric vibration of CF bonds in

presented at 1148 and 1204 cm1. The doublet peaks983 cm1, and the peak at 1058 cm1 are charac-

ks of the side chain in Nafion, and are assigned totric vibrations of COC bonds and SO stretchingf SO3 groups, respectively [14]. After the chloro-reaction, new peaks appeared at 1427 cm1 whichto SO2Cl groups introduced on the membrane sur-wn in Fig. 7(b). In the case of the modified Nafionas shown in Fig. 7(c), two new absorption bands at

(columnificanthe movalue ttra analayer oshownfully tVRB.

Refere

[1] E.sys16

[2] T. Mme

107[3] G.J

era

bat[4] M.

istiSo

[5] E.diu(19

[6] T.acr

bat[7] T.

elebat

[8] T.ing(20

[9] C.

454 cm1 appeared. The former is attributed to thef C O bonds and the latter is due to the stretchingf CN bonds. These results all confirm that a cationicer was successfully formed on the surface of Nafion

sions

modification of Nafion membrane using interfa-erization has drastically reduced the permeation ofions across the membrane accompanied by a little

resistance. The self-discharge of the VRB singleantly decreased by employing the modified Nafionas an alternative of Nafion membrane. As a result,

cations bJ. Memb

[10] R. Zengmembran102.

[11] T. HayasthroughMembr.

[12] G.J. Hwaarator fo5567.

[13] X.L. Luthroughflow batt

[14] A. GrugemembranSpectrosefficiency voltage efficiency) did not change sig-urthermore, the amount of water transferred across

d Nafion membrane was minimized to just half of theransferred across the unmodified membrane. IR spec-s also confirmed the formation of cationic chargede surface of membrane after modification. It hasthe interfacial polymerization can be used success-dify Nafion membrane to improve the operation of

s

M. Rychcik, M. Skyllas-Kazacos, Investigation of the V(V)/V(IV)or use in the positive half-cell of a redox battery, J. Power Sources) 8595.mmadi, M. Skyllas-Kazacos, Preparation of sulfonated compositee for vanadium redox flow battery applications, J. Membr. Sci.5) 3545.ng, H. Ohya, Crosslinking of anion exchange membrane by accel-ectron radiation as a separator for the all-vanadium redox flow. Membr. Sci. 132 (1997) 5561.as-Kazacos, D. Kasherman, D.R. Hong, M. Kazacos, Character-

performance of 1 kW UNSW vanadium redox battery, J. Power35 (1991) 399404.mann, A. Heintz, R.N. Lichtenthaler, Sorption isotherms of vana-

th H3O+ ions in cation exchange membranes, J. Membr. Sci. 14107213.mmadi, S.C. Chieng, M. Skyllas-Kazacos, Water transport studymmercial ion exchange membranes in the vanadium redox flow. Membr. Sci. 133 (1997) 151159.r, M. Skyllas-Kazacos, Modification of membranes using poly-tes to improve water transfer properties in the vanadium redox. Membr. Sci. 222 (2003) 249264.

T. Sata, W.K. Yang, Studies on cation-exchange membranes hav-selectivity between cations in electrodialysis, J. Membr. Sci. 206160.is, P. Sistat, S. Roualdes, G. Pourcelly, Separation of H+/Cu2+y electrodialysis using modified proton conducting membranes,r. Sci. 216 (2003) 1325., Z.C. Pang, H.S. Zhu, Modification of a Nafion ion exchangee by a plasma polymerization process, J. Electr. Chem. 490 (2000)

hita, J.C. Lee, R.A. Bartsch, Transport of alkali metal cationsmonoazacrown ether-modified NafionTM 117 membrane, J.

Sci. 116 (1996) 243251.ng, H. Ohya, Preparation of cation exchange membrane as a sep-

r the all-vanadium redox flow battery, J. Membr. Sci. 120 (1996)

o, Z.Z. Lu, J.Y. Xi, Influences of permeation of vanadium ionsPVDF-g-PSSA membranes on performances of vanadium redoxeries, J. Phys. Chem. B 109 (2005) 2031020314.r, A. Regis, T. Schmatko, P. Colomban, Nanostructure of Nafiones at different states of hydration an IR and Raman study, Vib.

c. 26 (2001) 215225.

Modification of Nafion membrane using interfacial polymerization for vanadium redox flow battery applicationsIntroductionExperimentalMaterialsMembrane preparationMembrane characterization

Results and discussionIEC, area resistance and other properties of membranePermeability of vanadium ionsWater transport measurementsPerformance of VRB single cellFT-IR spectroscopy analysis

ConclusionsReferences