水脱盐用电容去离子化炭材料研究进展（英文）_稻垣道夫.pdf

Cite this:NewCarbonMaterials,2023,38(3):405-437DOI:10.1016/S1872-5805(23)60736-XCarbon materials for water desalination by capacitive deionizationMichioInagaki1,*,HUANGZheng-hong2,*（1.Hokkaido University,228-7399 Nakagawa,Hosoe-cho,Kita-ku,Hamamatsu 431-1304,Japan;2.Key Laboratory of Advanced Materials(MOE),School of Materials Science and Engineering,Tsinghua University,Beijing 100084,China)）Abstract：Recentdevelopmentsonthecapacitivedeionization(CDI)techniqueforwaterdesalinationarereviewedwithafocusoncarbonastheelectrodematerial.ThecapacityandrateofsaltadsorptionandchargeefficiencyofvarioustypesofCDIcells,i.e.flow-by,membrane,flow-through-electrode,andflowingelectrodecellsarecompared.Variouscarbonelectrodematerialsforcapa-citor-typeandbattery-typecellsarediscussed.Theflowingelectrodecellwiththeshort-circuitoperationmodeseemstobethemostpromisingoneforpracticalapplications.Key words:Carbonmaterials；Capacitivedeionization；Waterdesalination；Capacitor-type；Battery-type1IntroductionWaterpollutionandfreshwatersupplyaretwoofthemostseriousenvironmentalproblemsfacedbyhu-manaroundtheglobeinthe21stcentury.Here,waterdesalinationwasreviewedanddiscussedbyfocusingon the carbon materials for capacitive deionization(CDI).ThewaterdesalinationbythisCDIprocessaswellassolarsteam-generation1areconsideredtobethemost important technologies to address the in-creasinglynecessityforglobalwaterscarcity.CDIhasattractedmuchattentionoverthepastdecadeforthefacileremovalofionsfromwaterasamethod for removing dissolved salts from brackishwater by their adsorption onto electrode surfacesmainly to form electric double-layers(EDLs),andnowisoneofthepotentialmethodsfordesalinationofdrinkingwater.BasicconceptofCDIiselectrochem-icaladsorptionofionsinwater,thesameassuperca-pacitorswithaqueouselectrolytes2;thecationsofasalt,suchasNa+,areadsorbedontothesurfaceofthenegativeelectrodeandtheanions,suchasCl,ontothe positive electrode principally by forming EDLs.Therefore,porouscarbonshavebeenactivelystudiedastheelectrodematerialsandreviewed29,duetotheadvantagesuchastheenvironmentalfriendliness,costeffectiveness,lowenergyconsumptionandconveni-entelectroderegeneration.Itsadvantagesincomparis-onwithotherdesalinationtechniques,suchasdistilla-tion,arefollowings:(1)CDIcellscanbeassembledinmultiplepairstoconstructastack,whichcanbecon-nectedinparallelorinseriestoenhancetheionremo-valperformancesforpracticalapplications.(2)Waterdesalinationcanperformquicklyandthecarbonelec-trodescanberegeneratedeasilybyinversingtheap-pliedvoltage.(3)Theenergyusedfordesalinationcanbepartiallyrecoveredandutilizedtochargeanothercellfordesalinationorstoragemediumsuchassuper-capacitorsforlateruse.Enormousprogresshasbeenmadein the CDI research field and now it encom-passesvariouscellarchitecturesassembledwitheithercapacitiveelectrodesorbatteryelectrodes.Inthisreview,theelectrochemicalcellsforwa-terdesalinationaredividedinto2groups,eitherbasedonprincipallyEDLformationonthesurfaceofcar-bonelectrodes(i.e.,capacitor-typecells)orprincip-allyFaradaicreactionwiththecarbonelectrode(i.e.,battery-typecells),althoughapartialcontributionofFaradaicreactionintheformercellsandthatofEDLformation in the latter cells are observed in manycases.Thewaterdesalinationperformancesofthesecellsarecomparedanddiscussedonthebasesonsaltadsorptioncapacityandrateandchargeefficiency.VariousCDIcellshavebeenproposed,suchasReceived date：2023-01-27；Revised date：2023-04-04Corresponding author：MichioInagaki,Professor.E-mail:im-iiace.ocn.ne.jp;HUANGZheng-hong,Professor.E-mail:第38卷第3期新型炭材料（中英文）Vol.38No.32023年6月NEWCARBONMATERIALSJun.2023simple flow-by(FB)cell,flow-through-electrode(FTE)cell,membrane(M)cellandflowing-electrode(FE)cell,withsomemodifications,suchas,cellus-ingdifferentcarbonmaterialsattheelectrodes(asym-metriccell),chemicalmodificationofthesurfacesofthecarbonelectrodes(invertedcell),etc.InFig.1,4representativecellconstructions,i.e.,simpleFB-,M-(selectingcation-exchangemembrane),FTE-andFE-CDIcellsareschematicallyshown.Fig.1ashowsasimplecell(FB-cell),whichhasbeenmostfrequentlyemployedforthestudiesonCDIprocesses.Abrackishwaterisforcedtoflowthroughthegapbetween2electrodes,wherecationsareelec-trochemically adsorbed onto the negative electrodeandanionsontothepositiveelectrode.Thedesalin-atedwaterisobtainedattheoutletofthecellasanef-fluent.Thecapacitycalculatedfromthechangeinthesaltconcentrationoftheeffluentisasumof3deioniz-ationmechanisms:(1)theadsorptionduetotheform-ationof EDLs on the surfaces of the carbon elec-trodesunderelectricfield,(2)capturingofsaltionsdue to reversible Faradaic reaction with the surfacefunctionalgroupsofthecarbonelectrodes,(3)physic-al adsorption of salt ions onto the carbon surfacewithoutelectricfield.Thefirsttwooccurunderelec-tricfield,oftenbeingmeasuredasasumandsocalledelectrosorption,whichdependstronglyontheappliedvoltage.The third,however,occurs without electricfieldandismainlygovernedbythesaltionsandtheporestructureofcarbonelectrodes.By inserting a cation-exchange membrane(CEM)in front of the negative electrode,as illus-tratedinFig.1b,saltremovalefficiencyismarkedlyimproved(membraneCDI,M-CDIcell),becausethecationscanbeselectivelypassedthroughthemem-braneandaresubsequentlyadsorbedbythenegativeelectrodewithoutanyinterferenceofanions.Anion-exchangemembrane(AEM)inthefrontoftheposit-iveelectrodecanalsoimprovetheelectrosorptionofanions.Usingporouscarbonelectrodes,thebrackishwater was desalinated by passing through a pair ofelectrodes(flow-through-electrodes CDI,FTE-CDIcell,Fig.1c),evenastackofelectrodepairs,toob-tainhighefficiencyofdesalinationbecauseofahighopportunityofthecontactbetweensaltionsandelec-trode carbon surfaces.Flowing-electrode CDI cell(FE-CDI)isdeveloped(Fig.1d),wherethefixedcar-bon electrodes is replaced by the flowing carbonparticles by suspending the carbon particles in anaqueoussolution,whichflowsthroughthechannelscarvedonthecurrentcollectors.Thissystemhassomeadvantages,a continuous desalination process bycouplingwiththesamecellforthedesorptionofad-sorbatesintheelectrodecarbonparticlesandahighremovalefficiencyfromsaltedwaterwithhighcon-centration,becausetheflow-electrodecanhaveinfin-iteionadsorptioncapacity.Inthisreview,thebasiccellconfigurationsofde-ionizationdevicesareexplainedintheSection1.IntheSection2,variouscarbonmaterialsareintroduced(a)Simple(flow-by)CDI cell(FB-CDI-cell)(b)MembraneCDI cell(M-CDI cell)(c)Flow-through-electrodeCDI cell(FTE-CDI cell)(d)Flowing-electrodesCDI cell(FE-CDI cell)DeionizedwaterPositive electrodePositive electrodePositive electrodeNegative electrodeNegative electrodeNegative electrodeDeionizedwaterBrackish waterCationCation-exchange membraneAnion-exchange membraneCurrent collectorFlowing carbon electrodeAnionCarbon electrodeBrackish waterBrackish waterBrackish waterDeionizedwaterDeionizedwaterNegative electrodePositive electrodeFig.1SchematicillustrationsoffourrepresentativeCDIcells406新型炭材料（中英文）第38卷byusingNaClasanapplicablesaltbecausemostofinvestigationsareusingitandbyfocusingoncapacit-ivecontributionforthedesalination,followedbytheexplanationontheapplicationresultsonothercationsandthendiscussedonthecontributionofFaradaicre-actionforsaltionsadsorption,suggesting2adsorp-tion mechanisms for salt ions for CDI process,thecontributionsof capacitive and of Faradaic adsorp-tions.Subsequently a comparison between differentCDIcellsispresentedbydiscussingonthebasesofion-adsorptionmechanismswithparticularemphasisonthecontributionofFaradaicreaction,andthenin-troducedsomemodificationofCDIcells,particularlyon M-CDI cell and on operation modes of FE-CDIcell.Inaddition,abriefintroductionofnewproposalsonCDIcells,althoughcarbonmaterialsforelectrodeofthecellshavenotbeeninvestigatedindetail.IntheSection3,thebattery-typeCDIcellsareshortlyex-plained,becausenotmanycarbonmaterialshadbeenapplied.In the Section 4,co-generation of electricpowerinCDIprocesswasshortlyexplainedalthoughonlylimited number of the papers have been pub-lished.Fortheevaluationofperformancesofdeioniza-tion,saltadsorptioncapacity(SAC),saltadsorptionrate(SAR)and charge efficiency(CE)are mainlyusedinthisreview,eventhoughtherehavebeenusedmanyotherparameters,suchasenergyconsumption,removalefficiency,etc.2Carbonmaterialsforcapacitor-typecells 2.1 Performance for NaClCommercialgranularactivatedcarbons(AC)wasappliedaselectrodematerialforasymmetricFB-CDIcell10.WhengranularACwaspackedintoaCDIcellastheelectrodeswithoutpressure,ionremovalwasverysmallbecauseofhighelectricresistanceoftheACelectrodes.BycompressionoftheAContothecurrentcollectorsofacylindricalcell,theamountofion removal was significantly improved due to adrasticdecreaseintheelectricalresistance.TheSACincreased from 0.2 to 5.2 mg/g by compressing to677kPaattheappliedvoltageof1.2V,theACthick-nessof10mmandtheinitialNaClconcentrationof10mmol/L.Duringadsorptionanddesorptioncycles(desalinationandregenerationcycles)underpressure,the SAC was found to be stable between 9.6 and10.3mg/g.N-dopedhierarchicallyporouscarbonswerepre-paredfromthepowdermixtureofpotassiumcitrate(P)of3g,urea(U)of3gandammoniumcitrate(A)of0.6gbygrindingandfollowingcarbonizationat800Cfor1hinN2(codedasPCPUA)11.Forcompar-ison,thecarbonswerepreparedfromPwithoutmix-ingUandA,followedbyKOHactivationwithmassratioof51(codedasPCP),andthatfromPmixedwithUbyKOH-activationwithmassratioof11(PCPU).TheporestructureparametersoftheresultantcarbonsaresummarizedinTable1,andtheirSEMimagesinFig.2.TheseSEMimagesandporestruc-tureparametersdemonstratethattheresultantcarbonsarehighlyhierarchical.TheprecursorsUandAweresupposedtoworkasactivationagents,beingassistedbythe formation of decomposition gases.CDI per-formancesofthesehierarchicallyporouscarbonswereinvestigated using a symmetric FB CDI-cell withNaClsolution.InFig.3a-c,thechangesinSACwereshown as the functions of charging time,appliedvoltageandinitialNaClconcentrationfortheresult-ant four carbons.The carbon PCPUA delivered theTable 1 Pore structure parameters of the porous carbons prepared from the mixtures of potassium citrate(P),urea(U)andammonium citrate(A).Reprinted with permission from Ref.11.Copyright(2023)by ElsevierCodePrecursorsSBET/(m2/g)Vtotal/(cm3/g)Vmicro/(cm3/g)Vmeso/(cm3/g)Vmicro/Vtotal(%)Vmeso/Vtotal(%)PCPP11590.660.480.187327PCPAP+A(5/1)16680.900.520.385842PCPUP+U(1/1)27851.650.810.844951PCPUAP+U+A(5/5/1)32002.491.051.444258第3期MichioInagakietal:Carbonmaterialsforwaterdesalinationbycapacitivedeionization407highest performances:SAC of 25 mg/g,SAR of8.29mg/gminat1.2Vand500mg/LNaClconcen-tration.Italsoexhibitedastablelong-termcyclabilitywith88.7%SACretentionafter50adsorption-desorp-tioncycles.Cubicpieceswithasizeof50m50m5mcutfromanaturalbasswoodblock,whichwerecarbon-izedat1000Cfor6hinAr,followedbyactivationinCO2at750Cfor10h12.Carbonizedwoodpieceswithhoneycomb-liketexturewerepolishedbysand-paperstoobtainathinsheet(membraneof20mm35mmwithathicknessof1.2mm.Sandwichingaspacermembrane between two wood-derived mem-branes,asymmetricFB-CDIcellwith1.0mol/LNaClsolutionwasassembled.CDIperformancesmeasuredontheelectrodeofcarbonizedwood-membranewerecomparedwiththoseofacommercialAC.AsshowninFig.4a,themembranemakesaneffluentconductiv-itydecreaserapidlydownto40S/cmfrom200S/cmforthepristinesolution,whereastheACgivestheef-fluentconductivityof140S/cm,indicatingahigherSACofthecarbonizedmembraneelectrode.Tode-creasetheconductivitydownto60S/cm,itneedsonly32minwhiletheACspends180min.Forde-sorption(recoveryoftheconductivityupto200S/cm),in addition,the membrane completes after 30 min,whiletheACneeds68min.TheresultsdemonstratethatthemembraneelectrodenotonlydisplaysahighSACbutalsoafastSARtogetherwithahighdesorp-tionrate.ThemembraneexhibitedahigharealSACof0.3mg/cm2(ahighvolumetricSACof2.4mg/cm3,andagravimetricSACof5.7mg/g).Also,thegoodmechanicalstrengthandwatertoleranceofthemem-brane electrodes improve the cycling stability,asshownthechangesinconductivityandSACincom-parisonwithacommercialACinFig.4b-c,respect-ively.Cocoon wastewater(CW)obtained from a silkreeling factory,which contains silkworm cocoonwaste(protein-contentof45000-47000mg/L),wasremovedthesuspendedsolidimpuritiesbyfiltration,mixedwithZnCl2initsconcentrationof0.5,1.0,1.5and2.0mol/L,andthenheatedat300Cfor2htore-move the moisture and tar,and finally heated at(a)(b)(c)(d)(e)(f)(g)(h)5 m5 m5 m5 m1 m1 m1 m1 mFig.2SEMimagesofthecarbonspreparedfromthepowdermixtureofpotassiumcitrate(P),urea(U)andammoniumcitrate(A)bycarbonizationat800C.(a,e)PCP,(b,f)PCPA,(c,g)PCPU,and(d,h)PCPUA.ReprintedwithpermissionfromRef.11.Copyright(2023)byElsevier001224(a)60120PCPPCPAPCPUATime/sSAC/(mg/g)1800.80122436(b)(c)1.0PCPPCPUPCPAPCPUAPCPPCPUPCPAPCPUAVoltage/VInitial NaCl concentration/(mg/L)SAC/(mg/g)01002505001000102030SAC/(mg/g)1.2Fig.3CDIperformanceofthehierarchicallyporouscarbonspreparedfrompotassiumcitrate,ureaandammoniumcitratebycarbonizationat800C:thechangesofSACwith(a)time,(b)appliedvoltageand(c)initialNaClconcentration.ReprintedwithpermissionfromRef.11.Copyright(2023)byElsevier408新型炭材料（中英文）第38卷900Cfor1hinN2toobtainablacksolid(codedasCWC-0.5-2.0)13.The resultant black solid wasgroundinto powder,which was subsequently im-mersedintoa0.5mol/LHClsolutiontoremovethezincspecies.Forcomparison,purecocoonwaste(notwastewater)was also converted to carbon with thesamecondition(CWC-0.0).Thefinalproductswerehierarchicallyporous,asshownporestructurepara-metersinTable2.TheCDIperformancesofthesecar-bons were studied using a symmetric FB CDI cellwithNaClsolution.TheperformancesareshowninFig.5a-c.ThecarbonCWC-1.5exhibitsthehighestSACof30.3mg/gattheinitialNaClconcentrationof500mg/Land1.2 V,whereas it does not have thehighest SBET(Table 2),which may attribute to thehighest mesopore-content,Vmeso/Vtotal(more than70%).It exhibited high reusability and stability asonly3%reductioninSACevenafterthe50thcycle.Ahierarchicallyporoulscarbonfoamconsistingof entangled hollow filaments were prepared fromcultivatedmushroommycelium(MDC)14.Myceliumwaswashedwithde-ionizedwateranddriedat60Covernightandthencarbonizedat500Cfor2h,fol-lowedbymixingwithKOHincarbonizedmycelia/KOHmassratioof12andcarbonizedandactiv-atedat800Cfor3h.Forcomparison,sporophoreswas also carbonized and KOH-activated(SDC).InFig.6a,SEM images of the pristine mycelium is040120200(a)100WCFWCFWCFAC30 min68 minACAC180 min60 S/cm32 min200Time/minConductivity/(S/cm)040120200(b)8001600Time/minConductivity/(S/cm)002468(c)2040Time/minSAC/(mg/g)Fig.4CDIperformanceofthebasswood-derivedcarbonthinsectionincomparisonwithanAC:(a)conductivitychangeduringthefirstdesalination/regener-ationcycle,(b)conductivityand(c)SACchangewithcycle.ReprintedwithpermissionfromRef.12.Copyright(2018)byAmericanChemicalSocietyTable 2 Pore structure parameters of the carbons derived from cocoon wastewater.Reprinted with permission fromRef.13.Copyright(2023)by ElsevierCodeZnCl2concentration/(mol/L)SBET/(m2/g)Vtotal/(cm3/g)Vmicro/Vtotal(%)Vmeso/Vtotal(%)Vmacro/Vtotal(%)CWC-0.50.512950.6973.126.70.2CWC-1.01.013110.7469.530.30.2CWC-1.51.512821.1123.175.51.4CWC-2.02.09111.2116.169.114.8CWC-0.00.014091.1431.062.76.3001020(a)10AC0.51.02.01.5CWCTime/minSA