Ir纳米团簇负载于ZIF-8衍生的氮掺杂炭框架用于高效析氢反应.pdf

Cite this:NewCarbonMaterials,2024,39(1):164-172DOI:10.1016/S1872-5805(24)60832-2Ir nanoclusters on ZIF-8-derived nitrogen-doped carbon frameworksto give a highly efficient hydrogen evolution reactionWANGXi-ao1,GONGYan-shang1,LIUZhi-kun2,WUPei-shan3,*,ZHANGLi-xue1,SUNJian-kun1,*（1.College of Chemistry and Chemical Engineering,Collaborative Innovation Center for Hydrogen Energy Key Materials and Technologiesof Shandong Province,Qingdao University,Qingdao 266071,China;2.Wanhua Chemical Group Co.,Ltd.,Yantai 264000,China;3.Institute of Analysis,Guangdong Academy of Sciences,Guangdong Provincial Key Laboratory of Emergency Test forDangerous Chemicals,Guangzhou 510070,China）Abstract：Theprecisechangeoftheelectronicstructureofactivemetalsusinglow-activesupportsisaneffectivewayofdevel-opinghigh-performanceelectrocatalysts.Theelectronicinteractionofthemetalandsupportprovidesaflexiblewayofoptimizingthecatalyticperformance.Wehavefabricatedanefficienthydrogenevolutionreaction(HER)electrocatalyst,inwhichIrnanoclustersareuniformlyloadedonanitrogen-dopedcarbonframework(IrNC).Thesynthesisprocessentailsimmersinganannealedzeoliticimidazolateframework-8(ZIF-8),preparedat900Casacarbonsource,intoanIrCl3solution,followedbyacalcination-reductiontreatmentat400CunderaH2/Aratmosphere.Thethree-dimensionalporousstructureofthenitrogen-dopedcarbonframeworkex-posesmoreactivemetalsites,andthecombinedeffectoftheIrclustersandtheN-dopedcarbonsupportefficientlychangestheelec-tronicstructureofIr,optimizingtheHERprocess.Inacidicmedia,IrNChasaremarkableHERelectrocatalyticactivity,withanoverpotentialofonly23mVat10mAcm2,anultra-lowTafelslope(25.8mVdec1)andgoodstabilityforover24hat10mAcm2.Thehighactivityoftheelectrocatalystwithasimpleandscalablesynthesismethodmakesitahighlypromisingcandidateforthein-dustrialproductionofhydrogenbysplittingacidicwater.Key words:Irnanoclusters；Nitrogen-dopedcarbonsupport；Electronicinteraction；Electrocatalysis；Hydrogenevolutionreaction1IntroductionHydrogenenergywithhighenergydensityisacleanandsustainableenergyresourcewhichcanbeeasilytransportedandstored,allowingforflexibilityinenergydistribution13.Additionally,hydrogenfuelcellshavehighenergyconversionefficiencyandpro-duceonlywaterasabyproduct,minimizingenviron-mental impact45.However,obtaining green hydro-genviawaterelectrolysisislargelyhinderedbyitslowenergyefficiency.Recently,acidicelectrolyzers,generallyoperateatlowervoltagesandhavehigherenergyefficiencythanalkalinecounterparts,havebe-comeinterestingalternatives68.Furthermore,acidicelectrolyzersalsoexhibitfasterreactionkinetics,en-ablinghighercurrentdensitiesandoverallimprovedperformance9.However,onemajorchallengeinacid-ic catalytic systems is the stability of the catalysts.Mostofthecatalyststhatcanbeutilizedinalkalineconditions,especially the non-noble metal catalysts,areseverelydegradedinacidicelectrolytes1012.Thisinstabilitycanleadtodecreasedcatalyticactivityandshortened catalyst lifespan1314.Addressing catalyststabilityiscrucialforthedevelopmentandcommer-cializationofefficientanddurableelectrocatalytichy-drogenproductioninacidicconditions15.Despitethelowabundanceandhighcost,pre-ciousmetalslikePt,IrandRuarestillthemainelec-trocatalyststhatareextensivelyutilizedinacidicelec-trolytes1617.Forinstance,Youetal.reportedIrnano-particlesanchoredcucurbit6uril,whichexhibitedReceived date：2023-10-21；Revised date：2023-11-29Corresponding author：WUPei-shan,Researchassistant.E-mail:;SUNJian-kun,Professor.E-mail:Author introduction：WANGXi-ao,Masterstudent.E-mail:wangxiao_Supplementarydataassociatedwiththisarticlecanbefoundintheonlineversion.Homepage:http:/ superior HER catalytic activity,with a lowoverpotential of 49 mV to achieve 10 mA cm2 in0.5molL1H2SO4solution,byloweringtheenergybarrierofproton-coupledelectrontransfer19.Drouetet al.reported a porous Ru nanomaterial,whichneeded an overpotential of 83 mV to deliver10mAcm2in0.5molL1H2SO4solution,owingtotheporousstructureofthematerial20.Althoughgreatprogresshasbeenmadeinthisdirection,methodsforregulatingthe electronic structure while simultaen-ouslyincreasingtheutilizationefficiencyofpreciousmetalatomsisstillchallenging21.Nanoscalingofmaterialdimensionsplaysacrit-icalroleinenhancingthespecificsurfaceareaofcata-lyststoprovidemoreactivesites22.Thenano-cata-lystsoftenexhibitdistinctandimpressivepropertiescomparedtobulkmaterials.Inparticular,themetalnanoclusterswithextremelyhighspecificsurfaceareaandalowersurfacemetal-metalcoordinationnumber,improve the surface-to-volume ratio as well as theatomicefficiencyofcatalyst23.However,asthesizedecreases,thecatalystswithmuchhighersurfaceen-ergybecomefragileandunstable,inducingdegrada-tionandcollapseoftheactivecomponents.Themet-al-supportinteractionhasbeenconsideredasaprom-isingapproachtoregulatetheelectronicstructureoftheactivesitesandsimultaneouslypreventsidereac-tions that destroy their structures2426.For instance,Xiao and co-workers reported an IrMo nanocluster-embeddedN-richelectrocatalystunderalkalinecondi-tions,which possesses ultrasmall bimetal nano-clusters and distinctive porous structures,enhancingtheactivityandstabilityofmetalnanoclusters27.Inaddition,Zhang et al.reported a catalyst with IrclustersloadedonPdnanosheets,inwhichthechargeredistributionresultsinanoptimumhydrogenadsorp-tionattheinterface28.Apparently,loadingpreciousmetalnanoclustercatalystsonstablesupportswillen-ablethe combination of optimized electronic struc-tureandenhancedstabilityinacidicelectrolytes,butchallenging.Herein,weutilizedannealedZIF-8asacarbonsourcetoachieveuniformloadingofIrnanoclusterswithanaveragediameterof1.78nmontoathree-di-mensionalporousN-dopedcarbonscaffold.Thiswasaccomplishedbyasimpleimpregnationandcalcina-tion-reductionmethod.Theformationofstrongcova-lentIr-Nbondseffectivelysuppressedthecorrosionandagglomeration of Ir clusters in acidic environ-ments.Moreover,theiridiumelementinIrNCex-hibitedalowervalencestatecomparedtotheIrCsample,whichisconducivetotheHERprocess.ThisisattributedtotheabundantNdopedinthecarbonsupport,whichregulatestheelectronicstructureofIrthroughastrongelectroniceffect29.Asaresult,theelectrocatalyst exhibits superior HER performancethanPt/Cunderacidicconditions.Thisworkdemon-stratesthe importance of selecting appropriate cata-lystsupportstoimprovetheintrinsicactivityofmetalsandhighlightsthepotentialofN-dopedcarbonmateri-als in enhancing the HER performance of Ir-basedcatalystsunderacidicconditions.2Experimentalsection 2.1 Synthesis of NCTo prepare the ZIF-8 precursor,2-methylim-idazole(5.677g)andhexadecyltrimethylammoniumbromide(CTAB)(0.018g)weredissolvedin87mLofdeionizedwater.Thenthe13mLofdeionizedwa-tercontaining0.367gofZn(NO3)26H2Owasmixedwiththeabovesolution.Thesolutionwasstirredandagedfor6h.Thentheproductwascollectedanddriedat60C.ThedriedZIF-8wassubsequentlyannealedina10%H2/Aratmosphereat900Cfor2h.Thisprocessresultedintheformationofablacknitrogen-dopedcarbon(NC)powder.2.2 Synthesis of IrNCToprepareIrNC,NC(0.025g)andIrCl3nH2O(0.005g)weredispersedin1mLofdeionizedwater.Thenthesolutionwaskeptat60Cfor6h.Theres-ulting product was collected,washed and dried at60 C under vacuum conditions.Next,the driedproductwasannealedat400Cfor4hinaH2/Arat-第1期WANGXi-aoetal:IrnanoclustersonZIF-8-derivednitrogen-dopedcarbonframeworksto165mosphere.After cooling down,the black coloredIrNCpowderwasobtained.Forcomparison,IrCwaspreparedusingasim-ilar process,but instead of NC,Ketjenblack ECP-600JDwasusedasthecarbonsupport.3ResultsanddiscussionThe synthesis of IrNC sample involves asimple three-step method(Fig.1).First,ZIF-8 wasobtainedbysolvothermaltreatmentandthestructurewas confirmed by X-ray diffraction(XRD)patternswiththeobserveddiffractionpeaksconsistentwiththesimulatedones(Fig.S1).Then,aporousNCskeletonwasfabricatedbypyrolyzingZIF-8at900C.Thediffraction peaks of ZIF-8 disappeared and 2 broadpeaksatapproximately26and44thatbelongtothegraphitic carbon structure(Fig.2a)were observed,confirmingtheformationoftheNCskeleton30.Sub-sequently,the NC sample was immersed in an Ir3+solutiontoobtainIrprecursorNC.Finally,there-duction of Ir3+to Ir0 clusters was carried out underH2/Ar conditions,resulting in the formation ofIrNC.Notably,no diffraction peak of Ir was ob-servedprobablyduetothesmallsize.Scanningelectronmicroscopy(SEM)andtrans-mission electron microscopy(TEM)were used tocharacterizethemorphologyandstructureofthepre-paredsamples.SEMimageofZIF-8inFig.2bexhib-itsauniformcubicshapewithasizeof140nm.Afterthepyrolysistreatment,theNCsamplemaintainsitsinitialcubicmorphology,butareducedparticlesizeof75nmduetotheevaporationofIn3132(Fig.2c).Upon the incorporation of Ir clusters,the size ofIrNCisfurtherreduced,presentingashrunkencu-bicshapewithasmallersizeof60nm(Fig.2d).TEMimagesofIrNC(Fig.2e,f)revealthatultra-smallIrclusters are uniformly distributed on the cubic N-dopedcarbonframework.ThisuniformdispersioncanbeattributedtotheabundanceofNatomsontheNCsubstrate,which act as coordinating atoms andprovide nucleation sites for the formation of Irclusters33.TheaveragesizeoftheIrclustersisap-proximately1.78nm(Fig.2gandFig.S2),explain-ingtheabsenceoftheIrdiffractionpeaksintheXRDpattern.AsshowninFig.S3,aweakdiffuseringpat-tern for the IrNC sample is found from selected-area electron diffraction(SAED)images,consistentwiththeresultsofTEMandXRD.Moreover,high-angle annular dark-field scanning TEM(HAADF-STEM)imagesfurtherdemonstratetheuniformdistri-bution of Ir clusters supported on the NC substrate(Fig.2h),andX-rayenergydispersivespectroscopy(EDS)elementalmappingimagesconfirmthecoexist-enceofC,NandIrelementsintheIrNCsample(Fig.2i).TheIrcontentinIrNC,determinedbyin-ductivelycoupled plasma optical emission spectro-metry(ICP-OES),wasfoundtobe8.02%,whichisingoodagreementwiththeEDSresult(TableS1).Forcomparison,IrCsamplewaspreparedusingasimil-arprocess,butwithcarbonblackinsteadofZIF-8asthecarbonsource.FromtheXRDpatternshowninZIF-8NCPyrolysis900 oC,H2/ArReduction400 oC,H2/ArImmersionIr3+Ir precursorNCIrNCCNIrFig.1SchematicillustrationoftheformationofIrNCelectrocatalyst166新型炭材料（中英文）第39卷Fig.S4,nodiffractionpeakscorrespondingtoIrweredetectedintheIrCsample.Instead,onlytwobroadpeaksattributedtothegraphiticcarbonstructurewereobserved,whichissimilartotheIrNCsample.ThespecificsurfaceareaandporestructureofNCandIrNCweredeterminedbynitrogenadsorp-tion/desorptionanalysis.TheBrunauer-Emmett-Tell-er(BET)surfaceareaofNCandIrNCwascalcu-lated to be 1060 and 1163 m2 g1,respectively(Fig.3a and Table S2).The higher surface area ofIrNCcanbeduetotheincorporationofIrclusters.BoththeNCandIrNCsamplesexhibitahierarchic-alporestructurewithmicroporesandmesopores,asindicatedbythehysteresiscurvesandhysteresisloop,whichisverifiedbytheporesizedistributioncurves(Fig.3b).Thispresenceofmicroporesfacilitatestheiondiffusionintheelectrolyte,whilethemesoporousstructureenhancesthemasstransportofactivespe-cies and enables the exposure of more active sites.Therefore,thesynergisticeffectofporestructurepro-moteselectrochemicalreactionkinetics34.ThechemicalcompositionandvalencestatesofIrNC,NCandIrCsampleswereexaminedusingX-rayphotoelectron spectroscopy(XPS).The exist-enceofthecorrespondingelementsisconfirmedbytheXPSsurveyspectraofeachsample(Fig.4aandFig.S5).The weak peak of Zn 2p appears in bothIrNCandNCsamplesduetotheincompleteremov-alofZnfromZIF-8.TheresidualZndoesnotsigni-ficantlycontributetothecatalyticactivity26,aswillbefurtherverifiedbythefollowingelectrochemicalcharacterization.TheOelementdetectedinthespec-200 nm200 nm50 nm50 nm50 nm50 nm50 nm50 nm5 nmCNlrlr/NC200 nm1020304050607080902/(o)NCIntensity/(a.u.)IrNC(a)(d)(e)(f)(g)(h)(i)(b)(c)1.21.41.61.82.02.22.4051015202530Frequency/%Size/nmAverage size:1.78 nmFig.2(a)XRDpatternsofNCandIrNCsample.SEMimagesof(b)ZIF-8,(c)NCand(d)IrNC.(e-f)HRTEMimagesofIrNC.(g)SizedistributionofIrnanoclusters.(h)HAADF-STEMand(i)thecorrespondingEDSelementalmappingimagesofIrNC第1期WANGXi-aoetal:IrnanoclustersonZIF-8-derivednitrogen-dopedcarbonframeworksto167traoriginatesfrominevitablesurfaceoxidationwhenexposedtoair.IntheC1sspectra(Fig.4b),thefittedpeakslocatedat284.8and286.3eVbelongtoCCandCNcoordination,respectively.IntheN1sspectraofNCandIrNCsamples(Fig.4c),thesignalcanbewellfittedwith5peakscorrespondingtopyridinicnitrogen(398.4eV),met-alnitrogen bond(399.7 eV),pyrrolic nitrogen(400.8eV),graphiticnitrogen(401.9eV),andoxidicnitrogen(404.1 eV)species,respectively.The pres-ence of metalnitrogen bond in the NC samplemainlyoriginatesfromresidualZn,whileIrNCpos-sesses both ZnN and IrN bonds.Apart frompyridinicNandmetalN,theothernitrogenspeciesin both samples have nearly the same content.ThepyridinicNandmetalNaccountfor35%and9%ofthetotalNatomsintheNCsample,whileinIrNC,these 2 species account for 30%and 14%,respect-0.00.20.40.60.81.0020040060080010001200(a)(b)Volume adsorbed/(cm3 g1)Relative pressure/(p/p0)IrNC BET=1163 m2 g1NC BET=1060 m2 g1010203040500.000.050.100.150.200.25dV/dD/(cm3 g1 nm1)Pore diameter/nmIrNCNCFig.3(a)N2adsorption-desorptionisothermsandcorresponding(b)porediameterdistributioncurvesofNCandIrNC120010008006004002000IntensityBinding energy/eVO 1sIr 4fN 1sC 1sZn 2p(a)(b)(c)(d)IrNCNCO 1sN 1sC 1sZn 2pSurvey290288286284282C 1sC-CC-N/C=NIrNCNCIntensityBinding energy/eV408406404402400398396394N 1sIrNCPyridinic NMetal-NPyrrolic NGraphitic NOxidic NNCIntensityBinding energy/eV6866646260584f5/2IntensityIr 4fIrNC4f7/2Sat.Sat.IrCBinding energy/eVFig.4XPSspectraofNCandIrNC.(a)SurveyscanspectraofNCandIrNC.High-resolutionspectraof(b)C1sand(c)N1sforIrNCandNC.(d)High-resolutionspectraofIr4fforIrNCandIrC168新型炭材料（中英文）第39卷ively.This difference indicates that a portion ofpyridinicNwasconvertedintometal-nitrogenbondsowingtotheformationofIrNbondswiththeincor-porationofIrclusters.Theelectron-donatingproper-tiesofpyridinicNenableittoserveasmetal-coordin-ationsitestoimmobilizetheIratoms3334.Addition-ally,thepeakofmetalNinIrNCwasshiftedtoahigherbindingenergy,suggestingthesignificantelec-tronicinteractionbetweenpyridinicNandIratoms.IntheIr4fspectra(Fig.4d),doubletpeaksofIr4f7/2andIr4f5/2with2satellitepeaksat62.9and66.2eVwereobserved.ComparedtoIrC,thebindingenergiesofIr4f7/2andIr4f5/2inIrNCsamplearenegativelyshiftedfrom62.1and65.1eVto61.7and64.7eV,manifestingthesignificantinteractionbetweenIrandN,consistentwiththeresultsoftheN1s.Thecorres-pondingdataandvalencestatesofC1s,N1sandIr4finXPSspectrahavebeenlistedinTableS3-5.ThesynergisticeffectbetweenIrclustersandNCsupportallowstoeffectivelyregulateelectronicstructureofIrandoptimizeelectrocatalyticHERprocess3539.Thecatalyticpropertiesofdifferentsampleswereevaluatedin0.5molL1H2SO4andalllinearsweepvoltammetry(LSV)curveswerecorrectedwith85%IRtoeliminatetheeffectofinternalresistance.Not-ably,theimmersionconcentrationofIrsaltsolutionplaysacrucialroleindeterminingtheHERactivityduetothedifferentloadingamountsatdifferentcon-centrations,andtheoptimizedperformancewasob-tainedat5mmolL1(Fig.S6).Promisingly,IrNCexhibited remarkable HER catalytic activity withan ultra-low overpotential of 23 mV to deliver10mAcm2(10=23mV)inacidicsolution,betterthan the original NC with negligible activity