江雷

High-PerformanceIonicDiodeMembraneforSalinityGradientPowerGeneration

JunGao,?WeiGuo,*,?,∥DanFeng,?HuantingWang,§DongyuanZhao,*,?andLeiJiang*,?

?BeijingNationalLaboratoryforMolecularSciences(BNLMS),KeyLaboratoryofOrganicSolids,InstituteofChemistry,ChineseAcademyofSciences,Beijing100190,P.R.China

?DepartmentofChemistryandShanghaiKeyLaboratoryofMolecularCatalysisandInnovativeMaterials,FudanUniversity,Shanghai200433,P.R.China

∥LaboratoryofBio-inspiredSmartInterfaceScience,TechnicalInstituteofPhysicsandChemistry,ChineseAcademyofSciences,Beijing100190,P.R.China

§DepartmentofChemicalEngineering,MonashUniversity,Clayton,Victoria3800,Australia

*SupportingInformation

Salinitydi?erencebetweenseawaterandriverwaterisabeexpectedfrombiomimeticsinglenanoporesduetohighsustainableenergyresourcethatcatcheseyesofthepublicandionic?uxandsurfacechargedensity.14?16

theinvestorsinthebackgroundofenergycrisis.1,2TocaptureTofullygoverntheiontransportinhigh-concentrationthisenergy,interdisciplinarye?ortsfromchemistry,materialselectrolytesforpracticalsalinitygradientpowergeneration(forscience,environmentalscience,andnanotechnologyhavebeenexample,?0.5Minseawater),thecharacteristiclengthscaleofmadetothe?uidicsystemshouldbefurtherreduceddowntosub-10

3?create6e?cientenergyconversionmethodsandmaterials.Throughmembrane-basedprocesses,suchasnmandthedeviceshouldbecapableofmassproduction.17?20reverseelectrodialysisandpressureretartedosmosis,electricHowever,thisrequirementcanhardlybemetwithexistingpowercanbeharnessedfromnaturalwaters.7?9However,single-channelnano?uidicdevices,becausetheirfabricationcurrentmembranematerialssu?erfromdeterioratedionprocesshighlyreliesonexpensivescienti?cequipmentandselectivity,inadequatemasstransportation,andsophisticatedmaterialprocessingsteps.21Amajorchallengeis

10,11hence,economicallyunviablepowerdensity.Technologicalbreak-

throughsareexpectedtoemergefromthenovel?uidicReceived:April14,2014

transportphenomenaonthenanoscale.12,13Anorders-of-Published:August19,2014

©http://wendang.chazidian.com/10.1021/ja503692z|J.Am.Chem.Soc.2014,136,12265?12272

Figuremesoporous1.Meso-/macroporouscarbon(MesoC)andheterostructuredpositivelychargedmembrane.macroporous(a)Schematicalumina(MacroA)illustration?lms.ofthe(b)porousThelateralheterojunctionsizeofthebetweenmembranenegativelyisaboutcharged1.5cm.(c)μXRDresultsshowacubicmesostructure(spacegroupFmmm)oftheMesoClayer.(d)SEMimageofthemembranecrosssectionrevealsa4.2-them-thicktestMesoCMesoC(SupportingandMacroAlayerisInformationlayers.ontheFigure

ThetopofporeaMacroAS3).

sizeofMacroAmembrane.is84(e±and16f)nm.MagniThe?peakedviewsdiameteroftheofmembraneMesoCisshow?6.7nmhighlydeterminedregularporebynitrogenstructuresorptioninbothFigurerecti?cation2.Highlyathighrecticoncentrations,?ediontransporteveninthroughsaturatedthesolution.ionicdiodeThehighestmembranerecti(IDM).?cationratio(a)Thefoundnanoin0.1?uidicMKClIDMisshows449.(b)distinctlyIncontrast,strongseparateionicmacroporoustransmembranealuminagovernediontransport.

ionicconductance(MacroA)?lm(circles)ormesoporousapparentlycarbondeviates(MesoC)frombulk?lledvalueMacroA(dashed?lmline)showfromnonrectibelow??ed1currentM,indicating?voltageafullyresponses.surface-charge-(c)Thetoextrapolatethesenanosized,single-channeldevicestoresultsinasubstantiallyhighpowerdensityofupto3.46W/m2macroscopicmaterials.22?26Inthiscontext,mesoporousofmembraneareabymixingarti?cialseawaterandriverwatermaterials,withhighlyuniformporesizeoftypicallyseveralthroughtheIDM,whichlargelyoutperformssomecommercialnanometers,27?29highspeci?csurfacearea,andsimplefabricationion-exchangemembranes.Themacroscopicandasymmetricmethods,becometheidealmaterialcomponenttonano?uidicstructureanticipateswidepotentialsforsustainableupgradecurrentsalinitygradientpowersystems.

powerHere,wereportamembrane-scalenano?uidicdevicewithasymmetricstructure,chemicalcomposition,andsurfacechargepolarity,termedionicdiodemembrane(IDM),forharvesting■

generation,waterpuri?cation,anddesalination.

RESULTSANDDISCUSSION

electricpowerfromsalinitygradient(SupportingInformationFigure1ashowstheschematicillustrationoftheIDMFigureS1).TheIDMcomprisesheterojunctionsbetweencomposedofathinlayerofMesoConthetopofMacroAmesoporouscarbon(MesoC,poresize?7nm,negativelysubstrate.Tofabricatetheheterostructuredmembrane,MesoCcharged)andmacroporousalumina(MacroA,poresize?80precursorwas?rstcoatedontotheMacroA(Supportingnm,positivelycharged).Themeso-/macroporousmembraneInformationandFigureS2).ThenorderedMesoCwasrecti?estheioniccurrentwithdistinctlyhighratioofca.450synthesizedviaevaporationinducedself-assembly.30Toandkeepsonrectifyinginhigh-concentrationelectrolytes.preventtheprecursorfrompenetratingintothealuminaExperimentalandcalculatedresultsprovethattheintroductionpores,asacri?ciallayerofpoly(methylmethacrylate)was?lledintotheMacroAbeforehandandwascompletelydecomposedofstructural,chemical,andelectrostaticasymmetriesintotheduringcarbonization(SupportingInformationandFigureS3).nano?uidicstructureselectivelyandpreferentiallyfacilitatestheThelateralsizeoftheIDMisabout1.5cm(Figure1b).cationtransportfromMesoCtoMacroA,andconsequently

Scanningelectronmicroscopy(SEM)observationof

the

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membranecrosssectionshowsthata4.2-μm-thickMesoCIDM(bluelineandlowerinsetinFigure3).Thecationlayerisattachedonthetopofa60-μm-thickMacroAsubstrateselectivitycanbealsoveri?edbythemuchhigherK+current(Figure1d).ThediameteroftheMacroAporesis84±16nm(atnegativepotential)thantheCl?current(atpositive(Figure1e).Highlyregularnanoporearrayisobservedinthepotential).NotethattheK+conductivityintheformercaseisMesoCarea(Figure1f),whichexhibitscubicmesostructure15.2%higherthanthatinthelattercase.Thisevidencesuggests(spacegroupFmmm)31characterizedbyX-raydi?ractionthattheiontransportthroughtheIDMisdirectionally(XRD,Figure1c).TheMesoChassmallpeakdiameterof?6.7asymmetric.Thereexistsapreferentialdirectionforcationnmandlargespeci?csurfaceareaof499m2g?1determinedbynitrogensorptionexperiment(SupportingInformationandtransportfromtheMesoCsidetowardtheMacroAside.FigureS3).TheMesoCpartisnegativelychargedandtheMacroAAtvariouselectrolyteconcentrations,theheterostructuredcarriespositivesurfacechargeinneutraloracidicsolutions.membraneexhibitsdiode-likecurrent?voltageresponseshow-Hence,intheIDM,theMacroAlayerdoesnotfunctionmerelyingstrongionicrecti?cation(Figure2a).Amaximumasasolidsupport,itformschargeheterojunctionwiththerecti?cationratio(f)ofupto449isfoundin0.1MKClMesoClayer(Figure4).Onthewhole,theionselectivityofthesolution,whichisthehighestvalueeverreportedinionicIDMisdominatedbytheMesoClayerduetothenarrowporerectifyingsystems.32Ofnote,theIDMkeepsonrectifyinginsize(SupportingInformationFigureS4).Theintroductionofhigh-concentrationelectrolytes.Eveninsaturatedsolution,fbothelectrostatic,chemical,andstructuralheterostructuresreaches8.Thisresultisdistinctfrompreviousreportsthatthemakesthetransmembraneioniccurrenthighlyrecti?ed.6ionicrecti?cationfailsinhigh-concentrationrange.33InThishypothesiscanbequantitativelysupportedbyacontrast,theunmodi?edMacroA?lmandtheMesoC?lledtheoreticalmodelbasedoncoupledPoissonandNernst?MacroA?lmshownoapparentrecti?catione?ect(Figure2b).Planck(PNP)equations(SupportingInformationandFigureTounderstandtheseresults,wetesttheionicconductanceofS5).TheseparateMesoC?lm(channelwidthis4nm)doesthemeso-/macroporousmembranewithrespecttotheionicnotrectifytheioniccurrent(Figure5aand5b).Afterawideconcentration(Figure2c).Thetransmembraneioniccon-segmentisintroducedononeend(channelwidthis60nm),ductanceremarkablydeviatesfrombulkvaluefrombelow1M,theioniccurrentthroughthehybridnano?uidicchannelsindicatingthattheionbecomesrecti?ed(f≈14).Ifthewidesegmenttakesopposite

34transportthroughtheIDMisfullysurface-charge-governed,eveninhigh-concentrationelectro-surface

lyte.≈charge,highlyrecti?edioniccurrentTotesttheionselectivityofthebipolarmembrane,the232)meso/macroduetotheremarkablecanbeobserved(finterfaceion-enrichmentundertheoppositeanddepletionelectricatelectrolytesolutionswithdi?erentconcentrationsareplacedpotentials.WhenthelengthpercentageoftheMesoCchannelonthetwosidesofthemembrane.Theconcentrationonreachesanoptimalvalueof20%?40%,thehighestrecti?cationMesoCside(cratioapproaches300(Figure5c).Inaddition,thechemicalMacroAside(cMesoC)was0.1Mandtheconcentrationoncompositionoftheheterojunctionstructureprovidesan

3).SinceMacroA)was1μM(redlineandupperinsertinFigurecextremelysharptransitionzonebetweenthenegativelyand

MesoCis105timeshigherthancMacroA,theionpositivelychargedpartsthatalsoaccountsfortheverylargerecti?cationratio.36Inshort,bysequentiallyintroducingstructural,electrostatic,andlengthasymmetries,therecti?ca-tionratioisenlargedstepwisely.Therecti?cationratiocanbefurtherincreasedwiththechannellengthinMesoC?lm(Figure5d).Therefore,theexperimentallyobservedstrongrecti?catione?ectcanberationallyexpected.Theselectiveandrecti?ediontransportshedsfurtherlightonsalinitygradientpowergeneration.WemounttheIDMintoatwo-compartmentelectrochemicalcell(Figure6a).Thetestingmembraneareais0.03mm2.Underasalinitygradient,forexample,cMesoC/candshort-circuitMacroA=0.1M/1μM,theopen-circuitvoltage(UOC)current(ISC)arereadfromtheinterceptsonthevoltageandcurrentaxes(Figure6b).Thecontributionfromtheredoxpotentialontheelectrodesisreadilysubtractedthroughsubsequentdataanalysis(Support-

FigureingInformationFigureS6andTableS1).Underreversedconductance3.IonsalinitygradientfromMesoCtoMacroA,theinternalresistanceWithmeasurementsselectivityunderoftheextremelyIDMishighveri?edbytheionic

ofthenano?uidicpowersourceisreducedby53%,owingto

+concentratedelectrolyteplacedonMesoCsideconcentration(redcurve),ratio.theKthepreferentialdirectionforcationtransport.37Hence,inthenegativecurrentsbias),(atpositiveshowingbias)strongaremuchcationlargerselectivity.thantheForCl?

thecurrentsreversed(at

concentrationgradient(bluecurve),similarconclusioncanbereached.

followingtests,theconcentrationontheMesoCsidewaskepthigh.ThegenerationofUvariousconditionsOCandI(SupportingSCisalsoveri?edbythePNPmodelinInformationFiguremigrationfromMacroAsidedoesnotcontributedecisivelytoS7).themeasuredioniccurrent.Toagoodapproximation,wecanWefurthertestthepowergenerationfromtheIDMunderacomparethe35ioniccurrentscarriedby?cationsorbyanions,http://wendang.chazidian.comparedwiththeCl+current(atnegative1μMto3M.MacroA=1μMandgraduallyelevatecpotential),thesubstantiallyenhancedKcurrent(atpositiveMesoCfromBothU6c).OCandIincreasewiththeconcentrationgradient(FigureTypically,SCpotential)suggestsstrongcationselectivity.Moreover,wetheUswitchedtheelectrolyteconcentrationsonthetwosidesofOCisseveraltenstomorethan100mV,andthemaximumcurrentdensityreaches98.8A/m2.The

energy

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Figurearrows).4.TheSchematicMacroAofcarriestheMesoC/MacroApositivechargeandheterojunctionitisanion-selectivestructure.(narrowTheMesoCgrayarrows).carriesnegativeOnthewhole,chargeowingandittoisthecation-selectivenarrowpore(widesizeofgraytheMesoC,theionselectivityoftheentiremembraneisdominatedbytheMesoC

layer.

Figurereveals5.Numericalsimulationofthe

negativethatvoltagetheultrahighbias.Amongionicfourrectitypes?cationhighly

of2Dresultsrecti?ed

con?guration,fromnanothe?uidic

symmetricremarkableIDM.(a

nanochannelsionandconcentrationb)Thecalculatedionconcentrationpro?leinsidethenanochannels

donotenrichmentrectifyionicatcurrentpositive(1).voltageBysequentiallybiasanddepletionintroducingat

structuralMacroAnanochannel(2),electrostaticissetto(3),beand4000lengthnm.Theasymmetriesmaximum(4),recti?thecationrectiratio?cationisfoundratiowhenisincreasedthepercentagestepwisely.ofMesoC(c)Theparttotalapproacheslengthof20%the?40%.MesoC/(d)Theparameterscalculatedarerectilisted?cationinSupportingratioincreasesInformationwiththeTableslengthS2ofandMesoC.S3.

ThelengthpercentageoftheMesoCissettobe50%.Allthecalculationconversione?ciencydeclineswiththeconcentrationgradientThisisbecause,forlargerporewidth,thesurface-governedfrom26.4%to5.7%(SupportingInformationFigureS8).Thepropertyislessdominant.

generatedpowercanbeoutputtoexternalcircuittosupplyanThegenerationofelectriccurrentundersalinitygradientlieselectronicload(Figure6d).Then,theelectricpower(Pintheionselectivityofthebipolarmembranechannels.consumedontheresistorload(RR)

L)intheexternalcircuitcanTheoreticalcalculationsareperformedbasedontheabove-

bedirectlyobtainedbyPR=I2mentionedPNPmodel.Detailedcalculationparameterscanbe

(0.01×RL.Whenarti?cialseawater

(0.5MNaCl)andriverwaterMNaCl)aremixed,withfoundinSupportingInformationTableS4.Thesymmetrictheincreaseofloadresistance,thedi?usioncurrentgraduallynano?uidicdiodeswithequalporesize,channellength,anddecreases,buttheoutputpowerreachesitspeakvaluewhenthesurfacecharge

loadresistanceis?10kΩ.Themaximumpowerdensity38densityofpositiveandnegativezonesarenotion-selective.Butstrongcationselectivityisachievedbythereaches3.46W/m2withane?ciencyof37.3%(Supportingnano?uidicIDMwithstructural,chemical,andelectrostaticInformation).Wealsotestthepowergenerationfromotherasymmetries(Figure7a).Quanti?ed

twotypesofIDMwithvariedporesizeofca.23and33nmon39viathecationtransferencenumbers(SupportingInformation),theionselectivityofthetheMesoCside(FDU-18,SupportingInformation).TheIDMisdominatedbythechargepropertiesontheMesoCpartmaximumoutputpowerdensitydecreaseswiththeporesizeofwithnarrowporesize.By?xingthechargedensityonMesoCMesoCfrom7to33nm(SupportingInformationFigureS9).(?0.06C/m2)andvaryingthechargedensityonMacroA,

the

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Figure6.Energyconversionfromsalinitydi?erence.(a)Schematicillustrationoftheenergyharvestingunderconcentrationgradient.(b)Forc=0.270.1

(c)TheμMA(red).andc

ITheenhanced=1μM,theionUMesoC

MacroAdiOC?usionandISCfromareMesoC108mVtowardand0.48MacroAμA(blue).reducesIfthetheinternalconcentrationresistancegradient(r)ofisthereversednano?(red),uidicsystemtheyareby129nearlymV53%.andSC(open)andUOC(solid)aremeasuredinaseriesofconcentrationgradient.TheconcentrationonMacroAsideis?xedat1μM.BothIandartiUwiththesalinitygradient.(d)ThegeneratedpowercanbeoutputtoSCOCincrease

?10?cialkΩ.

seawater(0.5MNaCl)andriverwater(0.01MNaCl),theoutputpowerdensityexternalreachescircuititspeakandvaluesupplyof3.46anelectronicW/m2attheload.resistanceBymixingofcalculatedcationtransferencenumberkeepsaround0.8,membrane2#,theconcentrationpolarizatione?ectislargelyshowingstrongcation-selectivity.Thisresultisalsocon?rmedsuppressed.Theionconcentrationisonlyslightlyhigherthanbytheselectivepermeationofcharged?uorescentdyesthebulkconcentration.Therefore,thepresenceofpositively(Supporting?xthechargeInformationdensityonFigureMacroAS10).chargedsegmentonthelow-concentrationsidee?ectivelypreventstheaccumulationofcations,whichisconductivetothecation(0.06OntransferenceC/mthe2contrary,ifwe)andvarythechargedensityonMesoC,numbercanthegenerationofnetdi?usioncurrentundersalinitygradient.40betunedinamuchwiderangefrom0.77(cation-selectivity)toThecalculationresultsonmembrane1#alsoshowsome0.18(anion-selectivity).Insomecases,forexample,iftheimplicationsinthecaseofion-exchangemembranes.41ThesurfacechargedensityofMacroAexceedsca.0.03C/m2,thesymmetricnarrownanochannelsprovidehigherselectivity,andpresenceofapositivelychargedMacroAsegmentontheendofconsequentlyhigherenergyconversione?ciency,buttheMesoCfacilitatesthegenerationofnetdi?usioncurrentandnarrowpromotestheselectivityofthedevice(Figure7b).Belowthisvalue,thecounterionicMacroAmayreducetheoverall?poresizerestrictsthethroughputofthetraversingionictheowinand?uenceinducesofconcentrationsevereconcentrationpolarizationpolarization.phenomenaTherefore,canbeselectivityoftheIDM.rationallyminimizedbyphysicalandchemicaldesignoftheFurthermore,theasymmetricporestructureandthebipolarchannelstructures.chargedistributionhelptosuppresstheconcentrationForcomparison,fourtypesofcommerciallyavailablecation-polarization,especiallyatthelow-concentrationside.40Weexchangemembranes,includingNa?on,Ionsep,CMI,andFKS,comparetheionconcentrationpro?leoftwotypesofweretestedunderidenticalexperimentalconditions(Support-membranechannelatthelow-concentrationside(Figure7c).ingInformation).Althoughtheenergyconversione?ciencyisThe?rstmembranetype(membrane1#)iscomposedof4nm-notashighasthatinthoseion-exchangemembranes,thewidenanochannelarrays.Thenanochannelsarenegativelynano?uidicIDMsubstantiallypromotesthepowerdensitychargedontheirinnerandouttersurface.Thelengthof(Table1).Inclassicion-exchangemembranes,thesizeoftheindividualnanochannelis4000nm.Thesecondmembraneionicspeciesiscomparabletothechannelwidth(typicallylesstype(membrane2#)isamodelIDMcontainingstructuralandthan1nm),sothattheiontransportthroughsuchmembraneelectrostaticheterojunctions.Thesmallchannelwidthisalso4channelsencountersnmandthelargechannelwidthis60nm.Fromthepro?lesof42greatsterichindrance,resultinginlowionicconductivity.Forananoporethatiswideenoughtocationconcentrationattheori?ceonthelow-concentrationoverlookthesenonelectrostaticinteractionsbetweentheside,onecannotethatstrongconcentrationpolarizationtakesmobileionsandtheporewall,suchasthenanochannelsinplaceinmembrane1#,fortheionconcentrationatthechanneltheIDM,thetransmembraneionicconductancecanbegreatlyori?cesigni?cantlydeviatesfromthebulkvalue.Whileforenhanced,leadingtohighionic?ux.Duetothelarge

channel

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