优化炭表面氧官能团增强锌离子电容器的电容性能（英文）_袁平.pdf

Cite this:NewCarbonMaterials,2023,38(3):522-533DOI:10.1016/S1872-5805(23)60733-4Optimizing oxygen substituents of a carbon cathode for improvedcapacitive behavior in ethanol-based zinc-ion capacitorsYUANPing1,XIAOHao-ming2,LIJun-yi2,LUOJun-hui2,LUOXian-you1,CHENDa-ming1,*,LIDe1,*,CHENYong1,2,*（1.State Key Laboratory of Marine Resource Utilization in South China Sea,Hainan Provincial Key Laboratory of Research on Utilization ofSi-Zr-Ti Resources,Hainan University,Haikou 570228,China;2.Guangdong Key Laboratory for Hydrogen Energy Technologies,School of Materials Science and Hydrogen Energy,Foshan University,Foshan 528000,China）Abstract：Zincioncapacitors(ZICs)havebeenwidelystudiedinrecentyearsduetotheirhighenergydensity,excellentratecap-ability,longcyclinglifeandlowcost.Theincorporationofoxygenfunctionalgroups(OFGs)onthesurfaceofthecarbon-basedcathodesisaneffectivestrategyforimprovingthecapacitiveperformanceofaqueousZICs.However,whethertheirpresencehelpsimprovethecapacitanceofethanol(EtOH)-basedZICshasnotbeeninvestigated.Inthiswork,acombinationofnitricacidoxidationandthermaltreatmentwasusedtoregulatetheOFGsontheactivatedsurfaceofthecarboncathode.Theoptimizedsamplehadahighspecificcapacitanceof195Fg1at1Ag1usingZnCl2/EtOHastheelectrolyte,i.e.,a56%increasecomparedtoanunmodi-fiedcathode(125Fg1).ZICsalsoshownexcellentstabilityformorethan16000cyclesat3Ag1,whilemaintaining100%cou-lombicefficiency.ThissignificantlyimprovedperformanceisattributedtothepresenceofOFGs,especiallycarboxylandestergroups,whichprovideabundantelectrochemicalactivesitesforredoxreactionwiththezincions.Thisstudyreportsasignificantim-provementinthespecificcapacitanceofcarboncathodesforcommercialEtOH-basedZICsystems.Key words:Zinc-ioncapacitors；Oxygenfunctionalgroups；Ethanol；Activatedcarbon；Specificcapacitance1IntroductionElectrochemicalenergystorageinsupercapacit-ors,suchaselectricdouble-layercapacitors(EDLCs),can provide high power density with long cyclinglife12.Theenergystoragemechanismisbasedonionadsorption/desorption at the electric double layer ofelectrodematerials,suchasactivatedcarbon(AC)34.However,theirlowenergydensitylimitslarge-scalepracticalapplications5.Strategiestoimprovetheen-ergydensityofEDLCsincludeincreasingtheaccess-iblespecificsurfaceareabyoptimizingtheporestruc-tureandimprovingtheelectricalconductivityofACtoaccelerateion/electrontransport69.Thevolumet-ricandgravimetricenergydensitiesachievedthroughthese strategies have reached a plateau.Therefore,new types of capacitive energy storage systems areneededtopushtheenergydensityhigher.Zinc-ioncapacitors(ZICs),withmetalliczincastheanode,combinetheadvantagesofsupercapacitorsand batteries,i.e.,high power density and high en-ergy density,respectively,and are considered as apromisingnext-generationenergystoragedevice1012.Comparedwith lithium,sodium and potassium an-odes,zinchasabundantnaturalresources,highchem-ical stability,and offers high theoretical capacity(820mAhg1)13.Meanwhile,zinchasalowredoxpotential(0.76Vvs.SHE)andanoutstandingtwo-electronreactionsystem1416.Therefore,ZICsexhibitenormouspotentialashigh-performanceenergystor-age devices1718.Currently,reported ZIC cathodesmainlyincludevanadiumoxide,manganeseoxideandcarbonmaterials.Amongthem,porouscarbonshaveReceived date：2023-02-21；Revised date：2023-03-23Corresponding author：CHENDa-ming.E-mail:;LIDe.E-mail:;CHENYong,Professor.E-mail:Author introduction：YUANPingandXIAOHao-mingcontributedequallytothisworkSupplementarydataassociatedwiththisarticlecanbefoundintheonlineversion.第38卷第3期新型炭材料（中英文）Vol.38No.32023年6月NEWCARBONMATERIALSJun.2023theadvantages of high specific surface area,ad-justableporestructure,excellentphysicochemicalsta-bility,good electrical conductivity,abundant re-sources,andlowcost1922.Introducingoxygen-con-tainingfunctionalgroups(OFGs)hasbeenproventobeaneffectivestrategytoincreasethepseudocapacit-ance of porous carbons2325,which can further in-creasestheenergydensityofZICs.Forinstance,Shuoetal.26demonstratedthatOFGs,suchascarboxylandcarbonylgroupsongrapheneoxide(GO),playakeyroleinimprovingthechemisorptionofzincionsandelectrochemicalchargestorageinaqueousZICs.Linetal.27preparedGObysolvothermalmethod,andthespecificcapacitanceofGOwasashighas276Fg1at0.1Ag1in1molL1H2SO4electrolyte.Highcapa-citancecanbeattributedtotheOFGsonthecarbonsurface,mainlycarbonylandhydroxylgroups,lead-ingtoabundantpseudocapacitanceandgoodwettabil-ity.AlthoughaqueousZICshavereceivedsignific-antresearchattentionduetotheirlow-costandsafety,somelimitationsstillneedtobeovercome,suchasir-reversiblehydrogenevolutionreactionandpoorper-formance at low-temperature conditions.Comparedwithaqueoussystems,organicelectrolytesallowforawiderpotentialwindow,leadingtoimprovedenergydensity.Huetal.28proposedahigh-performanceZICusingZnCl2/EtOHaselectrolyte,whichcanworkatultra-lowtemperaturesof78Candexhibitexcel-lentcyclingperformanceofupto30000times.Com-paredwithotherorganicsolvents,EtOHisnon-toxic,cost-effective,and allows ZICs to be installed dir-ectlyunderair.Furthermore,thechemicalstabilityofEtOHinhibitssidereactionsandexpandsthevoltagewindow.Additionally,thesolvationstructureZnCl(EtOH)5+formed with ZnCl2 can inhibit thegrowthofzincdendritesandprovidegoodcyclingsta-bility.Therefore,ZICsbasedonEtOHshowhighen-ergy density,wide working temperature range andeasy fabrication,making this system promising forpracticalapplications.Sincenumerousstudiesreportthepositiveinflu-enceofOFGsinaqueousZICs,introducingOFGsinEtOH-basedZICsisapromisingstrategytoimproveperformance.However,this has not yet been ad-equatelyinvestigated.Therefore,inthisstudy,OFGswereintroducedtothesurfaceofACbynitricacidoxidation,andtheirevolutioninthesubsequentheattreatmentandtheirinfluenceontheperformanceofZICswithZnCl2/EtOHelectrolytewasstudied.Atop-timum conditions,a significant capacitance increaseby56%,i.e.,from125to195Fg1at1Ag1,wasob-served.This work provides new insights into con-structingOFGsonthesurfaceofcarbonmaterialsandhowtheyinfluencetheperformanceofEtOH-basedZICs.2ExperimentalACwaspreparedfromcoconutshellactivatedbywater steam,washed with 10%dilute nitric acid at120Cfor5handindeionizedwatertoobtainneut-ralpH(namedAC-O).Then,theobtainedAC-Oma-terialwasannealedat400,500and600Cfor2h,ataheatingrateof5Cmin1underAratmosphere,andthe samples were denoted as AC-O-400,AC-O-500andAC-O-600,respectively.ThespecificsurfaceareaoftheACswasmeas-uredbyArabsorptionat87K.Theporesizedistribu-tion was analyzed by the quenching solid densityfunctional theory(QSDFT)method based on a slitpore model.Scanning electron microscopy(SEM)was used to characterize the morphologies of thesamples.ThecrystallinestructureswereidentifiedbyX-raydiffraction(XRD)andRamanspectroscopy.X-ray photoelectron spectroscopy(XPS)and Fouriertransforminfrared spectroscopy(FTIR)were ex-ecutedto investigate the surface chemical composi-tionsandoxidationstatesoftheOFGsontheACma-terials.ThecathodeofZICwasmadeofactivatedcar-bon,conductive carbon black and polytetrafluoro-ethylene in the mass ratio of 85105 by rollingfilm method28.Then it was cut into carbon sheetswitha10mmdiameterandweighing1.5mgwhichwasthenpressedoncarbonpaperwithadiameterof12mmunder10MPapressure.TheanodeofZICwas第3期YUANPingetal:Optimizingoxygensubstituentsofacarboncathodeforimprovedcapacitive523zinc foil with thickness of 20 m and diameter of10mm.Theelectrolytewas2molL1ZnCl2/EtOHsolution.Cyclicvoltammogram(CV)andelectrochemicalimpedancespectroscopy(EIS)weremeasuredonanIVIUM electrochemical workstation to evaluate theelectrochemicalperformance.EISwasperformedatavoltageamplitudeof5mVinthefrequencyrangeof100kHz-0.01Hz.Thegalvanostaticcharging/dischar-ging(GCD)curvesweretestedonaNewarebatterycharging/dischargingsysteminavoltagewindowof1.8 V at 3 A g1.The energy density(E)and thepowerdensity(P)oftheZICswerecalculatedbasedontheEq.(1)andEq.(2):E=CV2/2(1)P=E/t(2)whereCand Vrepresentspecificgravimetriccapacit-anceandvoltagewindow,respectively.3ResultsanddiscussionFig.1a,1bandS1showthemorphologiesoftheAC,AC-O-500 and AC-O samples,respectively.They exhibited similar irregular particles with largepores,indicatingthatthemorphologyofcarbonwasnotsubjectedtosignificantchangeafternitricacidox-idation and thermal treatment.Some interconnectedporouschannelscaneasilybeobserved,whichcanactasreservoirsforelectrolyteionsandreducethedis-tancebetweentheelectrodesurfaceandions2930.TheEDSmappingsofAC-O-500(Fig.1candd)revealauniformdistributionofCandO,demonstratingthatOwas successfully retained in the sample after nitricacidandthermaltreatments.Tostudythechangeinthespecificsurfaceareasandporestructureofthesamples,Aradsorptionanddesorption isotherms were measured at 87 K,asshowninFig.2a.Allthesamplesexhibitedtype/isotherms,indicatingthattheACsweremainlycom-posedofmicro-andmesopores31.Suchporousfea-turesendowACswithagoodenergystoragecapacitybecausemicroporescanprovideabundantactivesitesandmesoporesarebeneficialforfastiontransport3233.ThespecificsurfaceareaoftheAC-Otreated with nitric acid decreased from 1751.16 to1240.78m2g1comparedwithAC(Table1).Afterannealing,the specific surface area of AC-O in-creased slightly to 1386.31 m2 g1 at 600 C.AsshowninFig.2b,theporesizedistributionsofAC,AC-O,AC-O-400,AC-O-500andAC-O-600indicatethepresenceofmainlymicroporeslessthan2nminsize.Thetotalporevolumeandmicroporesvolumedecreasedwhentreatedwithnitricacidandincreasedslightlyafterannealing,indicatingthatthenitricacidtreatment destroyed some micropores,reducing thespecificsurfaceareaandporevolume.Furthermore,theintroductionofexcessOFGscanalsoblockpartoftheporestructure,whichcanbeexplainedbythein-creaseinspecificsurfaceareaandporevolumeaftersubsequent thermal treatment reducing the oxygencontent34.ThecrystalstructureofAC,AC-O,AC-O-400,AC-O-500andAC-O-600wascharacterizedbyXRD(Fig.2c).Diffractionpeakscenteredat23and43correspond to the(002)and(100)crystal planes,whicharethecharacteristicsofdisorderedamorphouscarbon3536.AllthesamplesshowednearlyidenticalXRD patterns,indicating that the treatment processdidnotchangetheircrystalstructure.Furthermore,thedefectsandamorphousstructuresofthesampleswereanalyzed by Raman spectroscopy.As illustrated inFig.2d,theintensityratio(ID/IG)betweentheD-peak(a)(b)(c)(d)4 m4 m5 m5 mOCFig.1SEMimagesof(a)ACand(b)AC-O-500.(c,d)Elementalmap-pingimagesofAC-O-500524新型炭材料（中英文）第38卷0.00.20.40.60.81.00200400600800(a)(b)(c)(e)35.118.628.630.225.3ACAC-O-500AC-O-600AC-OAC-O-400(d)AC-O-600Volume/(cm3/g)Relative pressure/(p/p0)ACAC-OAC-O-400AC-O-500AC-O-600ACAC-OAC-O-400AC-O-500123450.00.20.40.60.8dV/(cm3 nm1 g1)Pore size/nm10203040506070802/()Intensity/(a.u.)AC-O-600AC-O-500AC-O-400AC-OAC5001000150020002500Raman shift/cm1AC-O-500AC-O-400AC-OACID/IG=1.18ID/IG=1.15ID/IG=1.12ID/IG=1.13ID/IG=1.12DGAC-O-600Intensity/(a.u.)Fig.2(a)Aradsorption/desorptionisotherms,(b)Poresizedistributions,(c)Ramanspectra,(d)XRDpatternsand(e)ContactanglesofAC,AC-O,AC-O-400,AC-O-500andAC-O-600Table 1 Structural parameters of AC,AC-O,AC-O-400,AC-O-500 and AC-O-600SamplesSBETa/(m2g1)SMicrob/(m2g1)VTotalc/(cm3g1)VMicrod/(cm3g1)AC1751.161500.970.9040.734AC-O1240.781093.440.7340.521AC-O-4001221.511001.250.6840.498AC-O-5001286.621020.910.6990.519AC-O-6001386.311086.030.7410.558Note:a-BET(Brunauer-Emmett-Teller)surfacearea.b-MicroporespecificsurfaceareaobtainedfromtheQSDFTmethod.c-Single-pointtotalporevolumeatp/p0=0.995.d-MicroporevolumeobtainedfromtheQSDFTmethod.第3期YUANPingetal:Optimizingoxygensubstituentsofacarboncathodeforimprovedcapacitive525at1350cm1andtheG-peakat1580cm1cande-scribethegraphitizationdegreeofthesamples.TheID/IGvalueoftheAC-Osampleafternitricacidtreat-mentwasslightlylowerthanAC,indicatingthatthegraphitizationdegreeofthecarbonmaterialwasim-provedbytheoxidationtreatment.TheID/IGvalueofthematerialremainedunchangedafterthermaltreat-ment.Contactanglemeasurementswereconductedtoinvestigatethesurfacechemistryofallsampleswith2molL1ZnCl2/EtOHelectrolyteasthetestdroplets(Fig.2e).ThecontactanglesfortheAC-O,AC-O-400,AC-O-500andAC-O-600samplesweresmallerthanthatobservedwithAC.AC-O-500hadthesmal-lest contact angle of 18.6,indicating its excellentwettability after the oxidization and heat treatment.Therefore,theintroductionofOFGselevatedthesur-facewettabilityofACmaterials.Theimprovedsur-facewettabilitycouldlowertheelectrode/electrolyteinterfaceresistance,inturn,facilitatingtheaccessibil-ityofzincions37.ToinvestigatetheinfluenceofOFGsontheca-pacitanceoftheACmaterialsaftertheoxidationandthermaltreatments,theelectrochemicalperformancesofAC,AC-O,AC-O-400,AC-O-500andAC-O-600weresystematicallystudiedbyCV,GCDandEIS.AsdepictedinFig.3a,underascanrateof10mVs1,acoupleofobviousredoxpeakscanbeobserved,indic-ating the reversible redox reaction during CV tests.Comparedtoothersamples,AC-O-500displayedthelargestintegralCVarea,indicatingitshighestspecif-iccapacitance and optimized surface functionaliza-tion.Besides,theCVcurvesdidnotexhibitsignific-antdeformationatascanraterangeof1-100mVs1(Fig.3b-d),implyingthatthesystemshowedfastelec-trochemicalreactionkinetics38.Tofurtherexplorethechargestoragecontributionandelectrochemicalkinet-ics behavior,the CV curves measured at differentscanningrateswereanalyzedtodistinguishthecapa-citivechargestoragecontributionanddiffusioncon-1510505101510 mV/s20 mV/s30 mV/s40 mV/s10 mV/s20 mV/s30 mV/s40 mV/s50 mV/s60 mV/s80 mV/s100 mV/s50 mV/s60 mV/s80 mV/s100 mV/sZnCl2/EtOH ACZnCl2/EtOH AC-O-5000.40.20.00.20.4AC-O-5001 mV/s Capacitance76.6%0.30.20.10.00.10.20.3 Capacitance1 mV/sAC71.9%0.40.20.00.20.4 AC AC-O-500ZnCl2/EtOH 1 mV/sPeak 1Peak 2Peak 3Peak 412345020406080100120Contribution/%Scan rate/(mV/s)AC AC-O-50071.976.676.179.983.185.482.479.685.188.10.00.20.40.60.80.60.30.00.30.6Log(current density)/(A g1)Log(scan rate,mV s1)Cathodic peak(AC-O-500),b=0.892Anodic peak(AC-O-500),b=0.806Cathodic peak(AC),b=0.781Anodic peak(AC),b=0.769010203040010203040Z/Z/ACAC-O-500FittingFitting0.00.40.81.21.63210123(a)(b)(c)(f)(e)(d)(g)(h)(i)AC-O-500 AC-O-600Current density/(A g1)Current density/(A g1)15105051015Current density/(A g1)Current density/(A g1)Current density/(A g1)Current density/(A g1)Potential/V0.00.40.81.21.6Potential/V0.00.40.81.21.6Potential/V0.00.40.81.21.6Potential/V0.00.40.81.21.6Potential/V0.00.40.81.21.6Potential/V ACAC-O AC-O-400ZnCl2/EtOH 10 mV/sR1W1R2R3CPE2CPE1Fig.3(a)CVcurvesatdifferentscanratesfor(b)ACand(c)AC-O-500,(d)CVcomparisonofACandAC-O-500at1mVs1,(e,f)contributionratioofthecapacitivecapacities,(g)contributionratios,(h)bvaluesinboththechargeanddischargeprocessesofACandAC-O-500,(i)nyquistplotsofACandAC-O-500526新型炭材料（中英文）第38卷trol charge contributions(Fig.3e-g)39.When thescanningratewas1mVs1,theobtainedresultre-vealedthatthecapacitivechargecontributionofACwas71.9%,whilethatofAC-O-500was76.6%.Thus,basedontheabovementionedresults,AC-O-500de-liveredthehighestspecificcapacitance.Thecorrelationbetweenthelogarithmofcurrentdensity(log i)and scan rate(log v)is shown inFig.3h,wherethebvalueofasample,indicativeofthereactionrate,canbecalculatedfromtheslopeofthetrend.Here,bvaluecloseto0.5indicatesslowre-actionkinetics,whilebvaluecloseto1corresp