ChitosanPolyvinylAlcoholSulfonatedPolyethersulfone

Chitosan-PolyvinylAlcohol-SulfonatedPolyethersulfoneMixed-MatrixMembranesasMethanol-BarrierElectrolytesforDMFCsS.Meenakshi,1S.D.Bhat,1A.K.Sahu,1P.Sridhar,1S.Pitchumani,1A.K.Shukla21CSIR—CentralElectrochemicalResearchInstitute—MadrasUnit,CSIRMadrasComplex,Chennai600113,India2SolidStateandStructuralChemistryUnit,IndianInstituteofScience,Bangalore560012,IndiaReceived13April2011;accepted22August2011DOI10.1002/app.35522Publishedonline6December2011inWileyOnlineLibrary(wileyonlinelibrary.com).ABSTRACT:Chitosan(CS)-polyvinylalcohol(PVA)cross-linkedwithsulfosuccinicacid(SSA)andmodifiedwithsulfonatedpolyethersulfone(SPES)mixed-matrixmembranesarereportedfortheirapplicationindirectmethanolfuelcells(DMFCs).Polyethersulfone(PES)issulfonatedbychlorosulfonicacidandfactorsaffectingthesulfonationreaction,suchastimeandtemperature,arestudied.Theion-exchangecapacity,degreeofsulfonation,sorption,andprotonconductivityforthemixed-matrixmembranesareinvestigated.Themixed-matrixmem-branesarealsocharacterisedfortheirmechanicalandthermalproperties.Themethanol-crossoverfluxacrossthemixed-matrixmembranesisstudiedbymeasuringthemassbalanceofmethanolusingthedensitymeter.Themethanolcross-overforthesemembranesisfoundtobeabout33%lowerinrelationtoNafion-117membrane.TheDMFCemployingCS-PVA-SPESmixed-matrixmem-branewithanoptimumcontentof25wt%SPESdeliversapeakpower-densityof5.5mWcm
2ataloadcurrent-densityof25mAcm
2whileoperatingat70C.VC2011WileyPeriodicals,Inc.JApplPolymSci124:E73–E82,2012Keywords:mixed-matrixmembrane;SPES;degreeofsulfonation;methanolcross-over;DMFCsINTRODUCTIONDirectmethanolfuelcells(DMFCs)havebeenfoundtobeattractiveoptionforvariousportablepowerapplica-tions.1DMFCsemployperfluorinatedmembranes,suchasNafionorFlemion,aselectrolyte.Althoughthesemembraneshavegoodphysicalandchemicalstabilityalongwiththeirhighproton-conductivity,thesearepronetomethanolcrossoverfromanodetothecathodethatpoisonsthecathodeand,consequently,affectstheperformanceoftheDMFCs.2,3SuchasituationdemandsthedevelopmentofmembraneelectrolytesforDMFCsthatareimpervioustomethanol.Intheliterature,4,5effortshavebeenexpendedtode-velopmethanolimperviousmembraneelectrolytesforDMFCs.Inrecentyears,naturalandsynthetic–polymercompositemembraneshavemadesignificantimpactaspolymerelectrolytesforDMFCs.6,7Amongthese,natu-ralpolymerchitosan(CS)andsyntheticpolymerpoly(vinylalcohol)(PVA)havedrawnconsiderableatten-tioninthepastdecade.8,9CSisthesecondmostabun-dantnaturalbiopolymerobtainedbyalkalinedeacety-lationofchitin,amajorcomponentinexo-skeletonofcrustaceans.10Becauseofitslowcostofproduction,naturalabundanceandecocompatibility,CSisapre-ferredmembranematerialforultrafiltration,reverseosmosis,andpervaportion.11–13ItisalsoreflectedthatCS-basednaturalpolymericcompositemembranescanhelpreducingmethanolcrossoverinDMFCs.14–16PVAcanalsobeusedasanattractivematerialformem-braneelectrolyteinDMFCsowingtoitsgoodmechani-calandchemicalstability.17PVA-basedblendsorcom-positemembranescanalsoofferhighelectrochemicalselectivityinDMFCs.18,19Ironically,however,CSandPVAsufferfromhighmodulusofelasticitywithlowstrain-to-breakandhighcrystallinity,andhenceneedtobeblendedwitheachothertoimprovehydrophilic-ityandmechanicalproperties.20–23Intheliterature,20CS-PVAblendmembraneshavebeenpreparedandusedforpervaporativedehydrationofisopropanolandethyleneglycol.CarboxyethylCS-PVAnanofi-brousmembraneshavealsobeenusedaswound-dressingmaterialsforskinregeneration.21Theeffectofchemicalcrosslinkingandformationofsingleanddual-networkstructuresinCS-PVAfilmshavealsobeenstudied.22Wuetal.23havereportedthatCS-PVAblendhashigherselectivity,mechanicalstrengthandstabilitythanthepristinePVAmembranes.OurrecentfindingssuggestthatPVA-PSSA,24mod-ernite(MOR)-incorporatedPVA-PSSAwithvaryingCorrespondenceto:A.K.Shukla([e-mail]).Contractgrantsponsor:CSIR,NewDelhi;contractgrantnumber:DU-OLP-0058.JournalofAppliedPolymerScience,Vol.124,E73–E82(2012)VC2011WileyPeriodicals,Inc.degreeofsulfonationandPVA-sulfosuccinicacid(SSA)-heteropolyacid(HPA)compositemembranesexhibitattractivemechanicalstabilityandprovidepromisingDMFCperformance.25,26Itisalsofoundthatchitosan(CS)-hydroxyethylcellulose(HEC),CS-gelatin(GL),andsodiumalginate(NaAlg)-PVAblendswiththeirmodifi-cationbyincorporatingHPAscanbesuccessfullyemployedaselectrolytemembranesforDMFCsowingtotheirlowcostandexcellentmethanol-barrierpropertiesinrelationtocommerciallyavailablemembranes.27–29Recently,avarietyofhydrocarbon-basedsulfonatedpolymershavebeensynthesizedandusedasmem-braneelectrolytesinfuelcellstomitigatetheproblemsassociatedwithperfluorinatedpolymersorlessstableself-supportedmembranes.30–35Inparticular,sulfo-natedpoly(ethersulfone)(SPES),30sulfonatedpolyetheretherketone(SPEEK),31sulfonatedpolyimides,32sulfonatedpolysulfones,33sulfonatedpolyphthalazi-nones,34andsulfonatedpolybenzimidazoles35havebeenwidelyusedtopreparepolymerelectrolytemem-branesforfuelcellapplications.Amongthesepoly-mers,polyethersulfone(PES)exhibitshighmechanical,chemical,andbiologicalstabilities.30SulfonationofPESca