1、Cite this:NewCarbonMaterials,2024,39(1):17-41DOI:10.1016/S1872-5805(24)60833-4Defect engineering of carbon-based electrocatalysts for theCO2 reduction reaction:A reviewLUYan-kun,CHENGBai-xue,ZHANHao-yu,ZHOUPeng*（State Key Laboratory of Bio-fibers and Eco-textiles,College of Materials Science and Eng
2、ineering,Collaborative Innovation Center of Shandong MarineBiobased Fibers and Ecological Textiles,Institute of Marine Biobased Materials,Qingdao University,Qingdao 266071,China）Abstract：Electrocatalyticcarbondioxide(CO2)reductionisanimportantwaytoachievecarbonneutralitybyconvertingCO2in-tohigh-valu
3、e-addedchemicalsusingelectricenergy.Carbon-basedmaterialsarewidelyusedinvariouselectrochemicalreactions,includingelectrocatalyticCO2reduction,duetotheirlowcostandhighactivity.Inrecentyears,defectengineeringhasattractedwideattentionbyconstructingasymmetricdefectcentersinthematerials,whichcanoptimizet
4、hephysicochemicalpropertiesofthemater-ialandimproveitselectrocatalyticactivity.Thisreviewsummarizesthetypes,methodsofformationanddefectcharacterizationtech-niquesofdefectivecarbon-basedmaterials.Theadvantagesofdefectengineeringandtheadvantagesanddisadvantagesofvariousdefectformationmethodsandcharact
5、erizationtechniquesarealsoevaluated.Finally,thechallengesofusingdefectivecarbon-basedmaterialsinelectrocatalyticCO2reductionareinvestigatedandopportunitiesfortheirusearediscussed.Itisbelievedthatthisre-viewwillprovidesuggestionsandguidancefordevelopingdefectivecarbon-basedmaterialsforCO2reduction.Ke
6、y words:Defectengineering；Carbon-basedmaterials；Electrocatalysis；CO2reduction1IntroductionWiththerapiddevelopmentoftheeconomyandindustry,the excessive consumption of fossil fuelssuchascoalandpetroleumhascausedashortageofresourcesandalsoresultedintheemissionoflargeamounts of greenhouse gas carbon dio
7、xide(CO2),whichhasdestroyedthecarboncycleinnatureandin-ducedaseriesofenvironmentalproblems13.Inor-dertoreducetheconcentrationofCO2intheatmo-sphere,therearetwomainstrategies:(1)CO2collec-tionandstorage;(2)CO2conversionandutilization.However,CO2storagefacestheproblemofhighen-ergy consumption and easy
8、leakage,on the otherhand,theconversionofcapturedCO2intoenergy-richcarbonfuelsandchemicalsisaveryefficientway48.While the CO in linear CO2 molecules is verystable,andtheenergybarrierofitsconversionintothetargetproductishigh,itisdifficulttoachievethere-ductionandconversionofCO2molecule912.Atpresent,av
9、arietyoftechniqueshavebeende-velopedforthereductionandconversionofCO2,in-cluding biological catalysis,photocatalysis,thermalcatalysis,andelectrocatalysis1316.Amongthese,thetechniqueofelectrochemicalreductionofCO2playsakeyroleinthefuturesustainableenergyuseandde-velopment.Theelectrochemicalreductiono
10、fCO2hasthefollowingadvantages:(1)CO2canbedirectlycon-vertedintohigh-valuechemicalsandliquidfuels,suchascarbonmonoxide,formicacidandethanolunderrelatively mild reaction conditions.(2)This methodcanbecombinedwithrenewableenergy,suchasus-ingelectricenergygeneratedbyrenewablesourcesin-cludingsolar,winda
11、ndtidalasdrivingforce.(3)Thereactionprocesscanbecontrolledusingappliedpo-tentialandelectrocatalyst,sotheenergyconsumptioninthewholereactionprocesscanbeminimized,andno CO2 is produced during the reaction process.(4)Theelectrochemicalreactionsystemhasacom-pactstructure with modular device,this can be
12、ap-pliedtolarge-scaleindustrialapplications.Basedontheaboveanalysis,electrochemicalCO2reductionre-action(ECRR)isoneofthemostpromisingCO2con-versiontechnologiesandhasbecomeahotresearchtopicinthefieldofenergystorage1724.Among many other factors,the selection andReceived date：2023-10-13；Revised date：20
13、23-11-27Corresponding author：ZHOUPeng,Professor.E-mail:Author introduction：LUYan-kun,Mastercandidate.E-mail：LHomepage:http:/ materials have been widely used in energyconversion and storage as well as in catalysis2830.Compared to metal-based catalysts and molecularcatalysts,carbon-based catalysts(suc
14、h as MOFs-de-rived carbon,graphene,carbon nanotubes,carbonfibers,dopedcarbonmaterials,andporouscarbonma-terials,etc.)havegreatadvantages,mainlyreflectedinthefollowingpoints:(1)Lowprice;(2)Highstabilityunder strongly acidic or alkaline conditions;(3)Strongelectricalconductivity,whichcanrealizetherapi
15、dtransferofelectrons;(4)Economicalandenvir-onmentallyfriendly,conducivetolarge-scaleproduc-tion;(5)Strongoperability,activesubstancescanbeeasilyintroduced through certain strategies to regu-latethestructureofcarbonmaterials3135.Althoughcarbon-basedmaterialsexhibitmanyadvantages,theweak intrinsic cat
16、alysis properties still restrict theirfurtherdevelopment.Therefore,adoptingappropriatestrategiestooptimizethegeometric/electronicstruc-tureofthecatalystsandsupportsisessentialtoim-provetheperformanceofECRR.Defectengineeringcanpreciselyregulatethesur-face composition of the carbon materials from thea
17、tomicscaleandadjustthelocalmicroenvironmentofthecatalysts,which is an important strategy to im-provethecatalyticperformanceofthematerials3639.Crystalsare derived from the periodic repeated ar-rangement of atoms in three dimensions.The idealstate of this periodic arrangement can only exist atzerotemp
18、eratureinthermodynamics.Assoonasthistemperatureisexceeded,therearealwaysdefectsinthe crystal that deviate from the perfectly orderedidealstate.Therefore,defectsintheactualcrystalandvariousdefecttypes(Scheme1)anddifferentdefectconcentrationshaveaveryimportantimpactonthephysical and chemical propertie
19、s of the carbonitself4042.By deliberately introducing defects intospecificareasofthematerialinacertainway,theop-ticalandelectricalproperties,andbandstructureofthematerialcanbesignificantlyaffected,whichhasbeenconfirmedbynumerousreports4345.Therefore,becauseoftheproblemsfacedinelectrochemicalCO2reduc
20、tion,itisaneffectivestrategytoadoptdefecten-gineering for regulating the carbon-based materialsandchangingtheelectronicstructureofthecatalyststo improve the CO2 transformation performance,whichis a topic of concern for more and more re-searchers.Inthisreview,wefirstprovideasystematicsum-maryoftheadv
21、antagesofdefectengineeringandthevarious types of defective carbon-based materials.Then,themethodsofconstructingdefectivecarbon-basedmaterialsandthecharacterizationmethodsofdefectsaredescribedindetail.Finally,furtherdevel-opmentinthefieldofdefectengineeringhasalsopro-spected.Ingeneral,weanticipatetha
22、tsuchafunda-mentalandcomprehensiveoverviewwillprovidesci-entificguidancefortheapplicationsanddevelopmentofdefectivecarbon-basedmaterialsinECRR.2Effectofdefectengineeringofcar-bon-basedmaterialsforECRRECRRisacomplexprocessinvolvingmultipleVacancy defectTopological defectCarbon based materialsElectroc
23、atalysis CO2 reductionDefectengineeringEdge defectDoping defectScheme 1.Schematicillustrationforthetypesofthedefectiveincarbonmaterials18新型炭材料（中英文）第39卷reactionsteps and the transfer of protons and elec-trons.Therefore,thelocalenvironmentoftheactivesite,theadsorptionandactivationofthereactivespe-cies
24、,andthetransportofchargearethekeyfactorsaf-fecting the catalytic performance,which are closelyrelatedtotheelectronicstructureoftheelectrocata-lyst.DefectengineeringcanoptimizetheECRRper-formanceof carbon-based materials from these as-pects by regulating their intrinsic properties,whichwillbediscusse
25、dindetailinthissection.2.1 Optimize the adsorption behavior of reactivespeciesThefirststepinacatalyticreactionistheadsorp-tionprocess.Therefore,theadsorptionbehaviorofre-actantsandintermediateshasanimportanteffectonthecatalyticperformance.Theintroductionofdefectsincarbon-basedmaterialscaneffectively
26、improvethesurfacechemicalstateofthecatalysts,andthenregu-latetheadsorptionbehaviorofreactivespecies.Forexample,the introduction of intrinsic vacancy-typecarbondefectsinmetalorganicframework(MOF)-de-rived carbon materials(Fig.1a)can result in thebreakingofstructuralsymmetryofthecarbonmateri-als.There
27、sultsofelectrostaticpotentialandtheoretic-alcalculation(Fig.1b,c)showedthattheunsaturatedcoordinationstructurecaneffectivelypromotethead-sorption of electrophilic CO2.The high surface en-ergyofthedefectsitedistortsthelinearstructureoftheadsorbedreactivemolecule,thusacceleratingCO2activationandpromot
28、ingtheproductionoftheinter-(a)(d)(g)CPristine grapheneGraphitic NGraphitic PPyridinic N-Pbi-pyridinic N-Ptri-pyridinic N-PPyrrolic NPyridinic Nbi-pyridinic Ntri-pyridinic NNP(e)(f)(h)(b)(c)2.52.01.51.0GCOOH*/eV0.50.0V0V1V10V12V0V1V10V12V12Me2NH2+Ion exchangebio-MOF-1Top viewSide view123456987FFFFFK+
29、bio-MOF-1PyrolysisK-defect-C-11000.00.20.60.8UL(CO2)-UL(H2)/V1.01.210Free energy/eVFree energy/eVUL/(V vs.RHE)12*+CO2+2H+2eCOOH*+H+eC4C1C9C6C2Pristine CCO*+H2O*+CO+H2O2Reaction coordinateReaction coordinate3410.62Pyridinic Nbi-pyridinic Ntri-pyridinic Ntri-pyridinic N-Pbi-pyridinic N-PPyridinic N-P1
30、012UL(CO2)UL(H2)UL(CO2)-UL(H2)0.30.0H+eH+Pristine C1/2H2FC230.4Fig.1(a)ThesynthesisprocessoftheK-defect-carbon;(b,c)TheadsorptionfreeenergychangeandthevaluesofUL(CO2RR)UL(HER)onV0,V1,V10,andV12sites46.Copyright2022,Wiley-VCH.(d)ThetheoreticalcomputationalmodelmoleculeoftheF-dopeddefectcarbon;(e,f)Th
31、efreeenergychangeofdif-ferentcatalystsforECRRandtherelatedschematicofECRRpathway48.Copyright2018,Wiley-VCH.(g)TheN-doped,P-doped,andN,P-co-dopedcarbonconfigurations.(h)DifferenceinlimitingpotentialsforECRRandHERoverasimulatedN,P-co-dopedcarbonconfiguration49.Copyright2020,Wiley-VCH第1期LUYan-kunetal:D
32、efectengineeringofcarbon-basedelectrocatalystsfortheCO2reductionreaction:19mediateCOOHintherate-determiningstep46.Zhuetal.alsoshowedthattheelectroninteractionbetweenpyridineNandAuatomsinthedefectivecarbonop-timized the adsorption energy of the intermediateCOOH,thusimprovingtheECRRperformance47.Inadd
33、ition,hydrogenevolutionreaction(HER)willoccurintheprocessofCO2reduction,whichseri-ouslyaffectstheFaradayefficiency(FE)ofECRR.Therefore,improvingtheutilizationofelectronsandintermediateactivehydrogenbyinhibitingthecom-petitiveHERprocessisalsoanimportantwaytoim-provetheECRRperformanceofthematerials.Wa
34、ngetal.obtainedcarbonmaterialswithdefect-richstruc-turesthroughinterlayerFelementdoping.Comparedwiththeinitialporouscarbonmaterial,theintroduc-tionofFdopantscancausethepositivechargedens-ityandasymmetricspinofneighboringdefectivecar-bonatoms(Fig.1d,e),henceresultinginthelowesthydrogen adsorption fre
35、e energy at the local defectsite.TheenhancedH-bondingabilityleadstothedif-ficultyofdesorptionofactivehydrogenintermediateintheECRRprocess(Fig.1f),thusinhibitingtheoc-currence of competitive HER and improving theFaradayefficiencyofECRR48.Moreover,otherhet-eroatom-doped(N,P,etc.)defectivecarbonmateria
36、lsalsoshowedreducedHERpropertiescomparedwithunmodifiedones(Fig.1g,h),furtherconfirmingthatdefectivecarbon materials can improve ECRR per-formancebyinhibitingHERprocess49.Accordingtothepublishedresults,thecreationofdefectstructuresincarbon-basedmaterialscaneffectivelyoptimizetheadsorption behavior of
37、 reactants and intermediates,andthusimprovethecatalyticperformance.2.2 Provide anchor sitesBecauseofthebreakinthesymmetrystructure,the defect sites have an unsaturated coordinationstructureandhighsurfaceenergy.Therefore,thede-fectsitesofthematerialareparticularlysuitableforfurther loading and modifi
38、cation of foreign species,whichfillstheunsaturatedsitesandreducestheen-ergyofthesystem.Forexample,byusingdefectN-dopedgrapheneasacarboncarrier(Fig.2a),nitrogen-confinedatomicFemoieties(FeNCsites)canbeformedthroughthecoordinationofnitrogensitesandFe,whichcaneffectivelyanchorsingle-atomFespe-cies,prom
39、ote the highly dispersed distribution ofsingle atoms(Fig.2b-e),and greatly improve theECRR performance50.Wang et al.developed anECRRcatalystanchoredbysingleatomNiinanN-doped graphene shell with CO Faraday efficiency(FE)exceeding 90%at a current density of60mAmg1.Theoreticalcalculationsshowedthatthes
40、ingleatomicNisitehadauniqueelectronicstructurethankstotheanchoringeffectofdefectivegraphene,whichcanpromotetheconversionofCO2toCOmorethanthebulkNi(111)51.Thentheyfurtherinvestig-ated4differentconfigurationsofsingleNi-anchoredN-dopedgraphenenanosheets.Accordingtothedens-ityfunctionaltheory(DFT)calcul
41、ations,theCOde-sorption energy barrier of block Ni(111)was thehighest.In contrast,NiN coordination structurewithdoublevacancyexhibitedthelowestCOdesorp-tionenergyintheECRRprocess,whichwascondu-civetopromotingtheproductionofCO18.Inaddi-tion,reportsontheimprovementofECRRperform-ancebyothermetalsinglea
42、tom-defectivecarboncar-riers(CoNC,MnNC,CuNC,ZnNC,etc.)furtherconfirmedtheanchoringeffectofdefectivecarboncarriers(Fig.2f-j)5255.2.3 Improve electrical conductivityIndeed,CO2reductiononthesurfaceofcarbon-basedmaterialsinvolvesprotonandelectrontransfer,sothe conductivity of the material significantly
43、af-fectsthechargetransferduringthereaction.Defectregulationofcarbon-basedmaterialscandestroytheoriginalperiodicsymmetrystructureandimprovetheintrinsicphysicochemicalproperties.Theappropriatedefect structure can effectively regulate the bandstructureofthecarbon-basedmaterialsandimprovetheelectricalco
44、nductivity.Sharmaetal.synthesizedN-doped carbon nanotubes(NCNTs)with differentsurfacestructuresandNcontentbyregulatingdiffer-ent precursors and carbonization temperatures.Theresults showed that the catalytic activity of theNCNTsdependsonthetypeanddensityofNdefects.ThepresenceofgraphiteNdefectandpyri
45、dineNde-20新型炭材料（中英文）第39卷fectcansignificantlyenhancetheconductivityofthematerial,reduce the overpotential,and improve theCOselectivity56.Similarly,defect-richcarbon-basedmaterialssuchasF-dopedcarbonnanocagesandS-dopedcarbonnanosheetsalsoexhibitbetterelectricalconductivity57.Asformetal-carbonmaterials
46、,com-paredwithnon-defectivecarbon-metalmaterials,thepresenceofcarbondefects(suchasvacancycarbonordopedcarbon,etc.)inthecompositeismorecondu-civeforimprovingtheelectronicstructure,thuspro-motingthechargetransferinthereactionprocessandenchancing the catalytic performance(Fig.2k-m)5860.3Typesofcarbonde
47、fectsinECRRBecauseofthediversityofpreparationmethodsandmaterialstructures,therearedifferentdefecttypesincarbon-basedmaterialsincludingvacancy,edge,to-pological,dopingdefects,etc.Thediversityofdefectstructures have different effects on the electronicstructureofthematerials,andimprovethecatalyticperfo
48、rmanceinavarietyofaspects.Inthissection,wewillsummarizeindetailtheseveralcommondefecttypesofcarbon-basedmaterialsintheECRRprocess.3.1 Vacancy defectVacancydefectisakindofintrinsiccarbonde-fect,which usually refers to the defect formed bymissingoneorseveralcarbonatoms.TheresearchersdevelopedaK+-assis
49、tedsynthesisstrategytosynthes-izeavacancycarbonmaterialbasedonbio-MOF-1precursors.Duringthepyrolysis,K+inMOFacceler-atedtheremovalofN-dopantsandcarbonatomsfromthecarbonmatrix,whichpromotedtheetchingpro-cessandcreatedalargenumberofvacancydefectsinthecarbonmatrix.BenefitingfromtheenhancedCO2adsorption
50、 capacity and increased COOH formationrate,K-defect-C-1100withalargenumberofV12de-fectsshowedexcellentECRRactivitywithupto99%FECOat0.45V,whichwasfarsuperiortoothercom-paredsamples46.Zhangetal.foundthattheECRR(a)(f)(g)96500.00.5Normalized absorption1.01.5(i)(j)96609670Energy/eVRadial distance/9680SA-
