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INTERFACIALCHEMISTRY SURFACESCIENCEANDELECTROCHEMISTRY Thispageintentionallyleftblank
ENCYCLOPEDIAOF INTERFACIALCHEMISTRY SURFACESCIENCEANDELECTROCHEMISTRY EDITORINCHIEF KlausWandelt
InstituteofPhysicalandTheoreticalChemistry,UniversityofBonn,Bonn,Germany; andInstituteofExperimentalPhysics,UniversityofWroclaw,Wroclaw,Poland
VOLUME1 1.1EXPERIMENTALMETHODS 1.2SURFACESCIENCEUNDERENVIRONMENTALCONDITIONS
Elsevier
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Copyright 2018ElsevierInc.Allrightsreserved
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ThisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythePublisher(otherthanasmaybenoted herein).
Notices
Knowledgeandbestpracticeinthis fieldareconstantlychanging.Asnewresearchandexperiencebroadenourunderstanding,changesin researchmethods,professionalpractices,ormedicaltreatmentmaybecomenecessary.
Practitionersandresearchersmayalwaysrelyontheirownexperienceandknowledgeinevaluatingandusinganyinformation,methods, compounds,orexperimentsdescribedherein.Inusingsuchinformationormethodstheyshouldbemindfuloftheirownsafetyandthe safetyofothers,includingpartiesforwhomtheyhaveaprofessionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assumeanyliabilityforanyinjuryand/or damagetopersonsorpropertyasamatterofproductsliability,negligenceorotherwise,orfromanyuseoroperationofanymethods, products,instructions,orideascontainedinthematerialherein.
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ISBN978-0-12-809739-7
Forinformationonallpublicationsvisitourwebsite at http://store.elsevier.com
Publisher:OliverWalter
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PrintedandboundintheUnitedStates
EDITORIALBOARD EDITORINCHIEF KlausWandelt
InstituteofPhysicalandTheoreticalChemistry,UniversityofBonn,Bonn,Germany; andInstituteofExperimentalPhysics,UniversityofWroclaw,Wroclaw,Poland
SUBJECTEDITORS ConradBecker
Aix-MarseilleUniversité,CNRS,CINaM,Marseille,France
PeterBroekmann
UniversityofBern,Bern,Switzerland
VictorCliment
InstituteofElectrochemistry,UniversityofAlicante,Alicante,Spain
FrancescoDiQuarto
DipartimentodiIngegneriaCivile,AerospazialeedeiMaterialiUniversitàdiPalermo,Palermo,Italy
JuanMFeliu
InstituteofElectrochemistry,UniversityofAlicante,Alicante,Spain
UeliHeiz
DepartmentofChemistry,TechnicalUniversityofMunich,Munich,Germany
KurtWKolasinski
WestChesterUniversity,WestChester,PA,USA
MarkusLackinger
TechnischeUniversitätMünchen&DeutschesMuseum,Munich,Germany
FalkoPNetzer
Karl-FranzensUniversityGrazInstituteofPhysics,SurfaceandInterfacePhysics,Graz,Austria
RobertoOtero
UniversidadAutónomadeMadridandIMDEANanoscience,Madrid,Spain
MiquelSalmeron
MaterialsScienceDivisionoftheLawrenceBerkeleyNationalLaboratory; andMaterialsScienceandEngineeringDepartmentoftheUniversityofCaliforniaatBerkeley,Berkeley,CA,USA
AndrewTeplyakov
DepartmentofChemistryandBiochemistry,UniversityofDelaware,Newark,DE,USA
PankajVadgama
SchoolofEngineeringandMaterialsScience,QueenMaryUniversityofLondon,London,UK
SomaVesztergom
EötvösLorándUniversity,Budapest,Hungary
KlausWandelt
InstituteofPhysicalandTheoreticalChemistry,UniversityofBonn,Bonn,Germany; andInstituteofExperimentalPhysics,UniversityofWroclaw,Wroclaw,Poland
PREFACE ThemotivationforcompilingandpublishingthisencyclopediaonInterfacialChemistrywastopromotethe communicationbetweenchemists,electrochemists,physicochemists,aswellassolid-stateandsurfacephysicists.Thegrowingdiversi ficationandspecializationofscienceandresearchmakesmutualunderstandingmore andmoredifficult,andthereforeinterdisciplinarycommunicationimperative.Chemiststakegreatadvantageof heterogeneouscatalystsoftenwithoutknowingtheirpropertiesandoperationontheatomicscale.This knowledge,however,isnecessaryforarationaldesignandoptimizationofthecatalysts’ activity,selectivity,and stability.Electrochemistsandsurfacephysicistsworkingonasimilarproblemsuchas filmdepositionand growth,justindifferentenvironment,maynotshareknowledgeduetodistinctlydifferent “languages,” suchas “underpotentialdeposition” and “Franck-van-der-Merwegrowth” forasimilarphenomenon.Andthereare knowndifferencesbetweenthemore “practical” approachofchemistsandthemore “formal” approachof physicists,includingtheresultantcommunication “barriers”.Ontheotherhand,allmodernexperimental analyticaltoolsarebasedonphysicalphenomena,suchasinteractionofradiationwithmatterandelectron tunneling,andareimplementedbyphysicists.Interfacialchemistry,asanexcellentexampleofinterdisciplinary research,canonlyprofitfromanunbiasedcommunicationandmutualunderstandingbetweenthedifferent involveddisciplines.
Interfacesarethedividesbetweenphases,e.g.,solid/gas,solid/liquid,solid/solid,liquid/gas,liquid/liquid, andthusaninherentpropertyofheterogeneoussystems. “Heterogeneous” sounds,andactuallyis,more complexthan “homogeneous” andthereforecallsforamultidisciplinaryapproach.Toinvestigateand understand “electrocatalysis,” itiscertainlyhelpfultotakeintoaccounttheexperienceandknowledgeof electrochemists and solid-stateandsurfacephysicists,twocommunitiesthatarenotknownforaclose connection.
Thedifferenceinpropertiesoneithersideofthedividehastwoimportantconsequences:(1)interfacesare thelocationsofgradientsthatareadrivingforceforprocessesand(2)interactionsacrosstheinterfacewill obviouslyalsoalterthepropertiesininterface-nearlayersoftheadjacentphases.Ifasolidironsurfaceis exposedtooxygengas,thesurfacewilloxidize;theresultantoxidelayerdiffersfromthepureironunderneath.If twodifferentsolids(orliquids)formacommonphaseboundary,interdiffusionwillchangethecompositionof theinterface-nearregionsonbothsides.Ifaplatinumelectrodeinsulfuricacidsolutionisnegativelypolarized, protons(hydroniumcations)areattractedwiththeconsequencethatthepHnearthePt/electrolyteinterfaceis lowerthaninthebulkofthesolution.Andifacopperelectrodeinhydrochloricacidsolutionispositively polarized,chlorideanionswillbeattracted,adsorb,andrestructurethesurface before surfaceatomsformsoluble copperchloridespecies.
Interestingly,notonlythepresenceofinteractionsacrossaninterfacecausesalterationsoneitherside,but alsothesudden absence ofinteractionsacrossaninterfacehasadecisiveinfluence:Whileanatominthebulkof asolidinequilibriumissurroundedbyandinteractswithatomsonallsides,anatomattheverysurfacein vacuumhasnoneighborstointeractwithonthevacuumside.Thisunbalancedrivesthesystemtowardanew equilibriumandcausesarepositioningofthesurfaceatoms;mostintuitivelythesurfaceatoms “relax” toward thebulkofthesolid.Butthereareevencaseswherethesurfaceatomlayerasawholeassumesatwodimensionallatticestructuredifferentfromthatofaparallelplaneinthebulk,thesurface “reconstructs.” Duetothemissingneighbors,the “unsaturatedbonds” of surface atoms(incontactwithvacuum)addtothe totalenergyofthesolid.Thesurface “relaxation” and “reconstruction” are aresponseofthesystemtolowerthis “excesssurfaceenergy.” Theverysameargumentexplainswhyinequilibriumalsothe surfacecomposition of multicomponentmaterials,e.g.,alloys,solutions,mustbeexpectedtobedifferentfromthebulkcomposition.
Inequilibriumthesurfacewillbeenrichedwiththoseatomswhoseunsaturatedbondsaddleasttotheexcess surfaceenergy.
Sinceitistheverysurfaceofasolid(orliquid),which firstinteractswiththeadjacentphase(gas,liquid,or solid),itschemicalcompositionandstructuremustbeknownindetail,i.e.,ontheatomicscale,tounderstand anddescribeitsinvolvementinchemicalprocesses.
Thisinformationisnowadaysavailablethankstothedevelopmentofabroadarsenalofincrediblysensitive high-resolutionmicroscopicandspectroscopictechniquesandtheso-called “surfacescienceapproach.” This approachstartswithstructurallyandchemicallywell-definedsurfaces,e.g.,single-crystalsurfaces,whichunder ultrahighvacuumconditionsareexposedtogasesorvaporsinaverycontrolledmanner.Inthiswayitis nowadayspossiblenotonlytocharacterizebareandadsorbatecoveredsurfacesandmonitorchangesatom-byatombutalsotomodifysurfacesbyarbitrarymanipulationofindividualatoms.Theseachievementsand abilitieshaveoccasionallymisled “insiders” tostatementssuchas “surfacesciencehasreachedcompletion.”
Apartfromthefactthatclaimslikethisinsciencehaveoftenbeenrash,thereareatleasttwoexpectationson “surfacescience” still.The firstis,duetotheubiquityanduniversalimportanceofinterfaces,todisseminatethe knowledgeabouttheirfundamentalpeculiaritiesmorewidelyto “outsiders” inotherdisciplines beyond materialssciences andinparticulartoincludeitmoreregularlyintocurricula.Thesecondistotransferand applytheconceptsandmethods,largelyresultingfromthe “surfacescienceapproach” underultrahighvacuum conditions,tomorecomplexsystemsinrealisticenvironmentsuchasambientgasesandliquids,astheyare dealtwithbyelectro-andbioelectrochemists,materialsscientists,andchemicalengineers.Thistransfer,of course,requirestoovercomethe “barriers” indicatedaboveand,sometimes,mayalsorequiretherevisionof “establishedviews.”
Thepresentencyclopediaisanattempttocontributetothistransferbyincludingpublicationsfromrather differentbutinherentlyinterface-relatedresearch fieldsunderthecommonheading “InterfacialChemistry.” WhenI firstproposedthisproject,Isuggested11subjects:(1)modelstudiesinheterogeneouscatalysis,(2) surfacescienceunderenvironmentalconditions,(3)ultrathin films,(4)clustersandnanoparticlesatsurfaces, (5)molecularself-assemblyatsurfaces,(6)surface-confinedpolymerization,(7)functionalizationandgrafting ofsurfacesandnanoparticles,(8)ultrafastsurfacedynamics,(9)generalinterfacialelectrochemistry,(10) interfacialelectrocatalysis,(11)modelstudiesoncorrosion,andlefta12thsubjectdeliberatelyopenforfurther suggestions.Thereportsof19(!)internationalreviewersofthisproposalwereunisonpositiveandledtothe suggestionofincluding(12)bioelectrochemistryasthe12thsubject.All12topicsarewellcoveredinthis encyclopediathankstotheteamofexcellentsubjecteditorswhomIaskedandwhoagreedtojointhisproject. Toaccentuate “InterfacialChemistry” asthecommonground,allcontributionsareexplicitlylinkedbycrossreferencesbetweenpapersinthevarioussections,and eventhoughpartlyverydifferentandsubject speci fic themostimportantexperimentalmethodsaregroupedinoneseparatesection “side-by-side.”
Inadditiontotheprintedversionofthisencyclopedia,allarticlesappearwithinthesection “Interfacial Chemistry” oftheoverarchingandwell-structuredelectronic-onlyReferenceModule “Chemistry,Molecular SciencesandChemicalEngineering”1,whichsupportsbothaneasyaccessibilityand,thereby,awidedisseminationamongitsreadership.
Thecomingtogetheroftherelevantdisciplinesisa “steady” process.In1995Ialreadyeditedjointlywith S.Trasatti,Milano,aspecialissue “SurfaceScienceandElectrochemistry” ofthejournal SurfaceScience2.Twenty yearslaterin2015IrepeatedthisinitiativetogetherwithA.Gross,Ulm,in SurfaceScience3,andwecametothe “disenchantinginsight” thattheprogressinbringingsolidstatesurfacephysicistsandelectrochemiststogether “wasonlymoderate” andthiseventhoughthe “interestinprocessesatelectrochemicalinterfacesinthecontext ofelectrochemicalenergyconversionandstorageplaysanenormouslyimportantroleforfutureenergy technology.”
Asstatedabove,thisencyclopediaisafurtherattempttopromotethemutualinsightintheimportanceof aclosecollaborationbetweentheinvolveddisciplines,andtheelectronicversionofthisencyclopedia embeddedinthesection “InterfacialChemistry” ofthegeneralReferenceModule “Chemistry,MolecularSciences andChemicalEngineering” evenoffersthepossibilityofacontinuousupdating.
Iamdeeplyindebtedtoallthosewhohavecontributedtothiswork,primarily,ofcourse,allauthorsofthe articles,myfellowcoeditorswhoidentifiedandmotivatedtheauthors,andlastbutnotleasttheElsevierstaffat theOxfordoffice,UK,whoorganizedandhandledthework flow.
KlausWandelt EditorinChief
References
1.ReferenceModuleinChemistry,MolecularSciencesandChemicalEngineering,EditorinChief,J.Reedijk.
2.Trasatti,S.;Wandelt,K.SurfaceScienceandElectrochemistry. Surf.Sci. 1995, 335, 1–447.
3.Gross,A.;Wandelt,K. SurfaceScienceandElectrochemistry-20YearsLater 2015, 631, 1–300.
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CONTRIBUTORSTOVOLUME1 CAAngelucci
FederalUniversityofABC(UFABC),SantoAndré,São Paulo,Brazil
RArrigo
DiamondLightSourceLtd.,Oxfordshire,United Kingdom
CAscoli
IstitutoNazionalediOttica(INO)delConsiglio NazionaledelleRicerche(CNR),Pisa,Italy
ABaber
JamesMadisonUniversity,Harrisonburg,VA,United States
SBarzilai
NRCN,Beer-Sheva,Israel
PBaschieri
IstitutoNazionalediOttica(INO)delConsiglio NazionaledelleRicerche(CNR),Pisa,Italy
CBecker
AixMarseilleUniversité,CNRS,Marseille,France
HBluhm
LawrenceBerkeleyNationalLaboratory,Berkeley,CA, UnitedStates
ABondarenko
ÉcolePolytechniqueFédéraledeLausanne(EPFLValais Wallis),Sion,Switzerland
JABoscoboinik
CenterforFunctionalNanomaterials,Brookhaven NationalLaboratory,Upton,NY,UnitedStates
ABraun
Empa.SwissFederalLaboratoriesforMaterialsScience andTechnology,Dübendorf,Switzerland
RKCampen
FritzHaberInstituteoftheMaxPlanckSociety,Berlin, Germany
MBCasu
UniversityofTuebingen,Tuebingen,Germany
Y-HChen
Max-Planck-InstitutfürEisenforschungGmbH, Düsseldorf,Germany
SCherevko
Helmholtz-InstituteErlangen-Nürnbergfor RenewableEnergy(IEK-11),Erlangen,Germany;and Max-Planck-InstitutfürEisenforschungGmbH, Düsseldorf,Germany
C-TChiang
Martin-Luther-UniversitätHalle-Wittenberg,Halle, Germany;andMax-Planck-Institutfür Mikrostrukturphysik,Halle,Germany
PMClawin
FreeUniversityofBerlin,Berlin,Germany
VCliment
InstitutodeElectroquímica,UniversidaddeAlicante, Alicante,Spain
ACzerwinski
UniversityofWarsaw,Warsaw,Poland;and IndustrialChemistryResearchInstitute,Warsaw, Poland
FDiFranco
UniversitàdegliStudidiPalermo,Palermo, Italy
FDinelli
IstitutoNazionalediOttica(INO)delConsiglio NazionaledelleRicerche(CNR),Pisa, Italy
FDiQuarto
UniversitàdegliStudidiPalermo,Palermo,Italy
ZDohnálek
PacificNorthwestNationalLaboratory,Richland,WA, UnitedStates;andWashingtonStateUniversity, Pullman,WA,UnitedStates
KFDomke
MaxPlanckInstituteforPolymerResearch,Mainz, Germany
J-CDong
XiamenUniversity,Xiamen,China
KDuanmu
ChemicalandBiomolecularEngineeringDepartment, UniversityofCalifornia,LosAngeles,CA,UnitedStates
AKEngstfeld
TechnicalUniversityofDenmark,Lyngby,Denmark
AErbe
NorwegianUniversityofScienceandTechnology, Trondheim,Norway
BEren
WeizmannInstituteofScience,Rehovot, Israel
SFearn
ImperialCollegeLondon,London,UnitedKingdom
JMFeliu InstitutodeElectroquímica,UniversidaddeAlicante, Alicante,Spain
SFerrer
AlbaSynchrotronLightSource,Barcelona,Spain
MFilez
UtrechtUniversity,Utrecht,TheNetherlands
AFoelske-Schmitz
ViennaUniversityofTechnology,Vienna, Austria
H-JFreund
FritzHaberInstituteoftheMaxPlanckSociety,Berlin, Germany
TFukuma
KanazawaUniversity,Kanazawa,Japan
KFushimi
HokkaidoUniversity,Sapporo,Japan
HHGirault
ÉcolePolytechniqueFédéraledeLausanne(EPFLValais Wallis),Sion,Switzerland
MJGladys UniversityofNewcastle,Callaghan,NSW,Australia
CGoletti
PhysicsDepartment,UniversityofRomeTorVergata, Roma,Italy
IMNGroot
LeidenUniversity,Leiden,TheNetherlands
H-LHan
LawrenceBerkeleyNationalLaboratory,Berkeley,CA, UnitedStates
ARHead
LawrenceBerkeleyNationalLaboratory,Berkeley,CA, UnitedStates
YHorowitz
LawrenceBerkeleyNationalLaboratory,Berkeley,CA, UnitedStates;andUniversityofCalifornia,Berkeley, CA,UnitedStates
KHubkowska
UniversityofWarsaw,Warsaw,Poland
TJones
Fritz-Haber-InstitutderMax-Planck-Gesellschaft, Berlin,Germany
MJurczyszyn UniversityofWrocł aw,Wrocł aw,Poland
MMKappes
KarlsruheInstituteofTechnology(KIT),Karlsruhe, Germany
MKeddam
SorbonneUniversités,Paris,France
AKlyushin
Fritz-Haber-InstitutderMax-Planck-Gesellschaft, Berlin,Germany;andHelmholtz-ZentrumBerlin fürMaterialienundEnergieGmbH,Berlin, Germany
AKnop-Gericke
Fritz-Haber-InstitutderMax-Planck-Gesellschaft, Berlin,Germany
JKnudsen
MAXIVLaboratory&LundUniversity,Lund,Sweden
FLaMantia
UniversitätBremen,Bremen,Germany
ALasia
UniversitédeSherbrooke,Sherbrooke,QC,Canada
ALesch
ÉcolePolytechniqueFédéraledeLausanne(EPFLValais Wallis),Sion,Switzerland
J-FLi
XiamenUniversity,Xiamen,China
T-ELin
ÉcolePolytechniqueFédéraledeLausanne(EPFLValais Wallis),Sion,Switzerland
M q ukaszewski UniversityofWarsaw,Warsaw,Poland
IMatsuda
TheInstituteforSolidStatePhysics,TheUniversityof Tokyo,Chiba,Japan
KJJMayrhofer
Helmholtz-InstituteErlangen-NürnbergforRenewable Energy(IEK-11),Erlangen,Germany;Max-PlanckInstitutfürEisenforschungGmbH,Düsseldorf, Germany;andFriedrich-Alexander-Universität Erlangen-Nürnberg,Erlangen,Germany
MHMintz
NRCN,Beer-Sheva,Israel;andBen-GurionUniversity oftheNegev,Beer-Sheva,Israel
AMiszczuk
UniversityofWrocł aw,Wrocł aw,Poland
IMorawski
UniversityofWrocł aw,Wrocł aw,Poland
KMudiyanselage
SABIC-CRDatKAUST,Thuwal,SaudiArabia
SNayak
UniversityofOxford,Oxford,UnitedKingdom
ANeff
LeibnizInstituteofSurfaceModi fication,Leipzig, Germany
FNiu
Max-Planck-InstitutfürEisenforschungGmbH, Düsseldorf,Germany
ZNovotny
UniversityofZürich,Zürich,Switzerland
MNowicki
UniversityofWroclaw,Wroclaw,Poland
TOhtsuka
HokkaidoUniversity,Sapporo,Japan
MEOrazem
UniversityofFlorida,Gainesville,FL,UnitedStates
DJO’Connor
UniversityofNewcastle,Callaghan,NSW,Australia
MPander
Max-Planck-InstitutfürEisenforschungGmbH, Düsseldorf,Germany
LSParreira
UniversityofSãoPaulo,SãoPaulo,Brazil
MPellegrino
IstitutoNazionalediOttica(INO)delConsiglio NazionaledelleRicerche(CNR),Pisa,Italy;and UniversitàdiPisa,Pisa,Italy
VPfeifer
Fritz-Haber-InstitutderMax-Planck-Gesellschaft, Berlin,Germany;andHelmholtz-ZentrumBerlin fürMaterialienundEnergieGmbH,Berlin, Germany
PPuschnig UniversityofGraz,Graz,Austria
JRadnik
FederalInstituteforMaterialTestingandResearch (BAM),Berlin,Germany
MGRamsey
UniversityofGraz,Graz,Austria
NFRichter
FreeUniversityofBerlin,Berlin,Germany
WRiedel
FreeUniversityofBerlin,Berlin,Germany
TRisse FreeUniversityofBerlin,Berlin,Germany
ZRistanovic
UtrechtUniversity,Utrecht,TheNetherlands
HRonneburg FreeUniversityofBerlin,Berlin,Germany
MJRost
LeidenUniversity,Leiden,TheNetherlands
AVRudnev UniversityofBern,Bern,Switzerland;andRussian AcademyofSciences,Moscow,Russia
ERuiz-Trejo
ImperialCollegeLondon,London,UnitedKingdom
GRupprechter
TechnischeUniversitätWien,Vienna,Austria
MSalmeron UniversityofCalifornia,Berkeley,CA,UnitedStates
CMSánchez-Sánchez
SorbonneUniversités,Paris,France
MSantamaria UniversitàdegliStudidiPalermo,Palermo,Italy
PVBarbosaSantiago
FederalUniversityofABC(UFABC),SantoAndré,São Paulo,Brazil
PSautet
ChemicalandBiomolecularEngineeringDepartment, UniversityofCalifornia,LosAngeles,CA, UnitedStates
JSchnadt
MAXIVLaboratory&LundUniversity,Lund, Sweden
DSchooss
KarlsruheInstituteofTechnology(KIT),Karlsruhe, Germany
AShavorskiy
MAXIVLaboratory&LundUniversity,Lund,Sweden
KRSiefermann
LeibnizInstituteofSurfaceModi fication,Leipzig, Germany
GASomorjai
LawrenceBerkeleyNationalLaboratory,Berkeley,CA, UnitedStates;andUniversityofCalifornia,Berkeley, CA,UnitedStates
JSouzaGarcia
FederalUniversityofABC(UFABC),SantoAndré,São Paulo,Brazil
DStacchiola
CenterforFunctionalNanomaterials,Brookhaven NationalLaboratory,Upton,NY,UnitedStates
MSterrer UniversityofGraz,Graz,Austria
YSuchorski
ViennaUniversityofTechnology,Vienna,Austria
GSun
ChemicalandBiomolecularEngineeringDepartment, UniversityofCalifornia,LosAngeles,CA,UnitedStates
KSundmacher
MaxPlanckInstituteforDynamicsofComplex TechnicalSystems,Magdeburg,GermanyandOtto-vonGuerickeUniversityMagdeburg,Magdeburg,Germany
YTakahashi
KanazawaUniversity,Kanazawa,Japan;andJapan ScienceandTechnologyAgency(JST),Saitama,Japan
STecklenburg
Max-Planck-InstitutfürEisenforschungGmbH, Düsseldorf,Germany
ETognoni
IstitutoNazionalediOttica(INO)delConsiglio NazionaledelleRicerche(CNR),Pisa,Italy
YTong
FritzHaberInstituteoftheMaxPlanckSociety,Berlin, Germany
CToparli
Max-Planck-InstitutfürEisenforschungGmbH, Düsseldorf,Germany
BTribollet
UniversitéPierreetMarieCurie,CNRS,Paris, France
J-JVelasco-Velez
Max-Planck-InstitutfürChemischeEnergiekonversion, Mülheim,Germany
SVesztergom
EötvösLorándUniversity,Budapest,Hungary
TVidakovic-Koch
MaxPlanckInstituteforDynamicsofComplex TechnicalSystems,Magdeburg,Germany
VVivier
SorbonneUniversités,Paris,France;andUniversité PierreetMarieCurie,CNRS,Paris, France
KWandelt
UniversityofBonn,Bonn,Germany;andUniversityof Wroclaw,Wroclaw,Poland
BMWeckhuysen
UtrechtUniversity,Utrecht,TheNetherlands
DPWoodruff
UniversityofWarwick,Coventry,UnitedKingdom AZaffora
UniversitàdegliStudidiPalermo,Palermo, Italy
ZZhang
BaylorUniversity,Waco,TX,UnitedStates
YZhou
KanazawaUniversity,Kanazawa,Japan
UEZhumaev
MaxPlanckInstituteforPolymerResearch,Mainz, Germany
CONTENTSOFVOLUME1 VOLUME1.1:EXPERIMENTALMETHODS AReviewonInSituSumFrequencyGenerationVibrationalSpectroscopyStudies ofLiquid SolidInterfacesinElectrochemicalSystems1 H-LHan,YHorowitz,andGASomorjai
AmbientPressureX-RayPhotoelectronSpectroscopy13 ARHeadandHBluhm
Angle-ResolvedPhotoelectronSpectroscopyatSurfacesWithHigh-OrderHarmonicGeneration28 C-TChiang
AtomicScaleSTMImagingofAlloySurfacesWithChemicalResolution39 AKEngstfeld
CyclicVoltammetry
48 VClimentandJMFeliu
DifferentialCapacitanceMeasurementsonPassiveFilms75 FDiQuarto,FDiFranco,MSantamaria,andFLaMantia
EISTechniqueinPassivityStudies:DeterminationoftheDielectricPropertiesofPassiveFilms93 BTribollet,VVivier,andMEOrazem
ElectrochemicalScanningTunnelingMicroscopy108 MNowickiandKWandelt
ElectronParamagneticResonanceSpectroscopyatSurfaces129 PMClawin,NFRichter,WRiedel,HRonneburg,andTRisse
EllipsometryinPassiveFilms 143 TOhtsukaandKFushimi
ExperimentalMethodsinInterfacialandSurfaceChemistry157 KWandelt
FieldIonandFieldDesorptionMicroscopy:SurfaceChemistryApplications162 YSuchorski
High-SpeedElectrochemicalSTM180 MJRost
HowtoProbeStructure,Kinetics,andDynamicsatComplexInterfacesInSituand OperandobyOpticalSpectroscopy199 AErbe,SNayak,Y-HChen,FNiu,MPander,STecklenburg,andCToparli
ImagingChemicalReactionsOneMoleculeataTime220 ZNovotny,ZZhang,andZDohnálek
ImpedanceSpectroscopyAppliedtotheStudyofElectrocatalyticProcesses241 ALasia
InSituPhotoelectronSpectroscopy264 ABraun
InSituProbingofAdsorbatesatElectrochemicalInterfacesWithVibrational SumFrequencySpectroscopy 280 YTongandRKCampen
InSituReal-TimeLow-EnergyElectronMicroscopy287 MBCasu
IonConductanceProbeMicroscopy MolecularResolution295 YZhou,TFukuma,andYTakahashi
Micro-SpectroscopytoInterrogateSolidCatalystsatWork304 MFilez,ZRistanovic,andBMWeckhuysen
OnlineChromatographicDetection321 AVRudnev
On-LineInductivelyCoupledPlasmaSpectrometryinElectrochemistry:BasicPrinciples andApplications 326 SCherevkoandKJJMayrhofer
OperandoScanningProbeMicroscopy,SurfaceX-RayDiffraction,andOptical MicroscopyforCatalysisStudies336 IMNGroot
PerspectivesofAdvancedIonBeamAnalysisofElectrochemicallyActiveSurfaces354 SFearnandERuiz-Trejo
PhotocurrentSpectroscopyinPassivityStudies361 FDiQuarto,FDiFranco,AZaffora,andMSantamaria
PhotoelectronDiffraction 372 DPWoodruff
PhotoemissionTomography:ValenceBandPhotoemissionasaQuantitativeMethod forInvestigatingMolecularFilms380 PPuschnigandMGRamsey
PorousElectrodesinBioelectrochemistry392 TVidakovic-KochandKSundmacher
QuartzCrystalNanobalanceMeasurementsinElectrocatalysis402 KHubkowska,M Łukaszewski,andACzerwinski
ReflectanceAnisotropySpectroscopy413 CGoletti
RotatingDiskandRing DiskElectrodes421 SVesztergom
ScanningElectrochemicalMicroscopyforBioimaging445 T-ELin,ABondarenko,ALesch,andHHGirault
ScanningElectrochemicalMicroscopyintheAC-Mode453 MKeddam,CMSánchez-Sánchez,andVVivier
ScanningIonConductanceMicroscopy MorphologyandMechanics465 ETognoni,PBaschieri,FDinelli,CAscoli,andMPellegrino
Shell-IsolatedNanoparticles-EnhancedRamanSpectroscopy475 J-FLiandJ-CDong
SpectroelectrochemistryAppliedtoElectrocatalyticProcesses486 JSouzaGarcia,CAAngelucci,LSParreira,andPVBarbosaSantiago
StructuralInvestigationsbyMeansofDirectionalElasticPeakElectronSpectroscopy496 MJurczyszyn,AMiszczuk,IMorawski,andMNowicki
SumFrequencyGenerationSpectroscopyandSecondHarmonicsGeneration509 GRupprechter
SurfaceCharacterizationbyIonScatteringSpectroscopy521 DJO’ConnorandMJGladys
SurfaceX-RayDiffractionUnderGases532 SFerrer
Surface-EnhancedInfraredAbsorptionSpectroscopy542 UEZhumaevandKFDomke
Time-ResolvedPhotoelectronSpectroscopy549 IMatsuda
Time-ResolvedPhotoemissionElectronMicroscopy557 KRSiefermannandANeff
TrappedIonElectronDiffractionofMetalClusterIons567 DSchoossandMMKappes
UHVSurfacePreparationMethods580 CBecker
X-RayPhotoelectronSpectroscopyinElectrochemistryResearch591 AFoelske-Schmitz
X-RayPhotoelectronSpectroscopyforInvestigationofHeterogeneousCatalyticProcess607 JRadnik
VOLUME1.2:SURFACESCIENCEUNDERENVIRONMENTALCONDITIONS CatalystElectronicSurfaceStructureUnderGasandLiquidEnvironments615 AKlyushin,RArrigo,VPfeifer,TJones,J-JVelasco-Velez,andAKnop-Gericke
SurfaceScienceApproachtoCatalystPreparationUsingThinOxideFilmsasSubstrates632 MSterrerandH-JFreund
SurfaceScienceattheDawnofthe21stCentury:FromUHVtoAmbientConditions inGasandLiquidEnvironments643 MSalmeron
SurfaceStructureandModificationsUnderAmbientPressure:ACaseStudyWithCopperSurfaces645 BEren
TheDynamicStructureofModelCatalystSurfacesUnderAmbientConditions658 ABaber,JABoscoboinik,KMudiyanselage,andDStacchiola
TheInitialStepsofHydrogen MetalReactions:TheGd H2 asaModelSystem676 MHMintzandSBarzilai
TheoreticalTreatmentofSurfacesinEquilibriumwithGases684 KDuanmu,GSun,andPSautet
Thin-FilmGrowthandOxidationofSurfacesUnderRelevantPressureConditions699 JSchnadt,JKnudsen,andAShavorskiy
PERMISSIONACKNOWLEDGMENTS ThefollowingmaterialisreproducedwithkindpermissionofAmericanAssociationfortheAdvancementof Science
Figure12CatalysisforEnergyConversion
Figure3(left)BiophotovoltaicSystems
Figure1bConductanceandLightEmissionFromOn-surfaceSynthesizedMolecularWires
Figure2bConductanceandLightEmissionFromOn-surfaceSynthesizedMolecularWires
Figure12Silicene
Figure7AtomicScaleSTMImagingofAlloySurfacesWithChemicalResolution http://www.aaas.org/
ThefollowingmaterialisreproducedwithkindpermissionofNaturePublishingGroup
Figure8SubstrateMediatedInteractions
Figure3(middle)BiophotovoltaicSystems
Figure4BiophotovoltaicSystems
Figure12A-CBiophotovoltaicSystems
Figure14G-HBiophotovoltaicSystems
Figure3Lanthanide-Based2DCoordinationNetworks
Figure2TemperatureControlofReactionPathways:Intramolecularvs.Intermolecular
Figure3TemperatureControlofReactionPathways:Intramolecularvs.Intermolecular
Figure5TemperatureControlofReactionPathways:Intramolecularvs.Intermolecular
Figure6TemperatureControlofReactionPathways:Intramolecularvs.Intermolecular
Figure1aConductanceandLightEmissionFromOn-surfaceSynthesizedMolecularWires
Figure1dConductanceandLightEmissionFromOn-surfaceSynthesizedMolecularWires
Figure2dConductanceandLightEmissionFromOn-surfaceSynthesizedMolecularWires
Figure1On-surfaceSynthesisofGrapheneNanoribbons
Figure2bOn-surfaceSynthesisofGrapheneNanoribbons
Figure2cOn-surfaceSynthesisofGrapheneNanoribbons
Figure2dOn-surfaceSynthesisofGrapheneNanoribbons
Figure3aOn-surfaceSynthesisofGrapheneNanoribbons
Figure3bOn-surfaceSynthesisofGrapheneNanoribbons
Figure3cOn-surfaceSynthesisofGrapheneNanoribbons
Figure3dOn-surfaceSynthesisofGrapheneNanoribbons
Figure6aOn-surfaceSynthesisofGrapheneNanoribbons
Figure8aOn-surfaceSynthesisofGrapheneNanoribbons
Figure8bOn-surfaceSynthesisofGrapheneNanoribbons
Figure8dOn-surfaceSynthesisofGrapheneNanoribbons
Figure8eOn-surfaceSynthesisofGrapheneNanoribbons
Figure9bOn-surfaceSynthesisofGrapheneNanoribbons
Figure9cOn-surfaceSynthesisofGrapheneNanoribbons
Figure9dOn-surfaceSynthesisofGrapheneNanoribbons
Figure11aOn-surfaceSynthesisofGrapheneNanoribbons
Figure11bOn-surfaceSynthesisofGrapheneNanoribbons
Figure11cOn-surfaceSynthesisofGrapheneNanoribbons
Figure11dOn-surfaceSynthesisofGrapheneNanoribbons
Figure11abSilicene
Figure14Silicene
Figure2OxideThinFilmsforMemristiveDevices
Figure2SteeringMolecularAssembliesandReactionsonSurface
Figure5SteeringMolecularAssembliesandReactionsonSurface
Figure10SteeringMolecularAssembliesandReactionsonSurface
Figure3UllmannCouplingofPorphyrins
Figure4UllmannCouplingofPorphyrins
http://www.nature.com
H-LHan, LawrenceBerkeleyNationalLaboratory,Berkeley,CA,UnitedStates
YHorowitzandGASomorjai, LawrenceBerkeleyNationalLaboratory,Berkeley,CA,UnitedStates;andUniversityofCalifornia, Berkeley,CA,UnitedStates
©2018ElsevierInc.Allrightsreserved.
Introduction:TheSignificanceofProbingElectrifiedInterfacesforRenewableEnergyProductionandStorage1 BasicConceptsofSFGVSforStudiesofElectri fiedSolid –LiquidInterfaces1 ProbingSolid –LiquidInterfacesUnderReactionCondition4 Li-IonBatteries
Introduction:TheSignificanceofProbingElectrifiedInterfacesforRenewableEnergyProductionandStorage
Asanenergy-drivensocietywearefacingsustainabilitychallenges1 andthereforeareconstantlylookingforbetterwaystodesign, manufacture,anduseenergystoragedevices,includingrechargeablebatteries,fuelcells,andlarge-scalegridenergystorage.Regardlessofthetechnology,thefundamentalelectrochemicalprocessismostlikelyoccurringonthenanoscale2 ataninterfaceoftwo phases(e.g.,solid–liquid)underappliedpotentials.Toimproveourenergyproductionandstoragedevices,wehavetogain insitu,real-timeinformationoftheelectri fiedinterfaceonthenanoscalelevel,suchasthesolidsurfacegeometricstructureand theelectronicpropertiesofthesolid –liquidinterface.Inaddition,weneedtoobtainaclearunderstandingoftheelectrochemical mechanismbyrevealingthemolecularstructuresofthereactants,intermediates,andproducts.3 Overtheyears,differentspectroscopytechniqueshavebeenadaptedtoprobeelectrochemicalinterfacessuchasinfraredreflectionadsorptionspectroscopy(IRRAS), Ramanspectroscopy,andX-rayspectroscopy.WhiletheIRRASandRamanspectroscopiesallowinsituprobing,noneofthemis highlysurface-speci fic.X-rayspectroscopyissurface-specificbutcannotyetbeappliedtosolid –liquidsystems,thoughsomeconsiderableadvanceswerereported.4 Hence,ourunderstandingofmanyaspectsofinterfacesinelectrochemicalsystemsisstilllacking, andtheneedforareal-timeanalyticaltoolthatcanaccesssolid –liquidinterfacesiscrucial.
Thedevelopmentofsumfrequencygenerationvibrationalspectroscopy(SFGVS)hasenabledsurface-speci ficstudiesofvarious surfacesandinterfaces.SFGVSisanondestructive,insitunonlinearopticalmethodthatdoesnotrequireanyphotoactivelabeling orhasanyrestrictionstothesample’spreparation.SFGVSisanonlinearopticalmethodthatyieldsvibrationalspectraofmolecules atburiedinterfaceswithhigh-interfaceselectivityandsensitivity.Vibrationalspectraareknowntobethe fingerprintsofmolecules. Consequently,SFGVScanbeusedtoidentifyinterfacial(adsorbed)speciesonasurface,probetheirdynamics,andsinceitisalaserbasedtechniquebypolarizingthelaserbeams,itcanprovidetheinterfacialspeciesorientationwithrespecttothesurfaceplane.
Inthisarticle,wepresentrecentapplicationsofSFGVSinstudiesofresearchgroupsthattookontheendeavortounderstand interfacialprocessesonthemolecularlevelofsystemsrelevanttoenergygenerationandstoragelikelithiumionbatteriesand fuelcells.
BasicConceptsofSFGVSforStudiesofElectrifiedSolid–LiquidInterfaces Vibrationalsum-frequencygeneration(VSFG)spectroscopyisasecond-ordernonlinearopticaltechniquethatisintrinsicallysensitivetoprobingvibrationalspectrumofmoleculeswithinafewmolecularlayers(Angstroms)ofaninterface.Thissectiondescribes thegeneralandbasictheoryofSFG,whichprovidesguidelinesforapplyingSFGforinterfacialcharacterization.
Briefly,theSFGprocessfromaninterfacialsystem(anytwomediumsincontact)comprisestwoincidentlaserbeamswith frequenciesof u1 and u2,overlappingontheinterfacebothspatiallyandtemporarytoinduceanonlinearpolarizationhaving thesumoftheincominglaserfrequencies us ¼ u1 þ u2.Theoutcomeofasumfrequencyradiation(beam)isinboththereflected andtransmitteddirections.Basedontheelectric-dipoleapproximation,SFGisforbiddeninthebulksinceithasaninversion symmetrybutisallowedattheinterfacewheretheinversionsymmetryisbroken.Ifthehigherorderelectricquadrupoleresponse fromabulkisnegligible,theSFGisdominatedbythesurfaceresponseandthereforeintrinsicallyinterfacesensitive. Fig.1A shows theSFGprocessinaninterfacialsystem.ThegeneratedSFGbeamisbothinthereflectedandthetransmitteddirections.In Fig.1A, thetwoincidentbeamscopropagatewithrespecttotheplanenormaltothesurfaceincidentontheinterfaceatangles q1 and q2, andtheresultedSFGreflectedandtransmittedbeamsexitatangles qSR and qST.Wecancalculate qSR and qST,basedonboundary
Fig.1 (A)AschematicofaSFGprocessataninterface.(B)EnergydiagramsanddescriptionofresonantSFGVSwith(1) u2 inresonancewith avibrationaltransition,(2) uS inresonancewithanelectronictransition,and(3)both u2 and uS areinresonances.
conditionsandphase-matchingrequirements, k1jj þ k2jj ¼ ksjj .Eq. (1) describestheemittedSFGdirectionbasedonthewavelength oftheinputbeamsandthegeometryofthesetup:
where n istherefractiveindexofthemediuminwhichtheSFGispresent.
Fig.1B showstheenergylevelsfortheexcitationsinaSFGprocess.IntheSFGVS, u1 istypicallyinthevisiblespectralregionand u2 isintheinfrared(IR)spectralregion.Whenevereither u1 or u2 or/and uS areinresonancewiththeelectronicorvibrational modeattheinterface,theSFGintensityincreasesseveralordersofmagnitudes.5 ByscanningtheIRfrequencyandmonitoring theSFGintensity,weobtainthevibrationalspectrumofsurfacemoleculesandthestructuralinformationfromthemolecules presentattheinterface.TheoutputintensityofthereflectedSFGisgivenbythesquareofthesumofthesecond-ordernonlinear susceptibilityandtheintensitiesoftheinputbeams,asshowninEq. (2)
denotetheFresnelfactorsfortheoutputandinputbeams.InSFGVS,inordertocharacterizethe vibrationalmodesofadsorbates,onewouldusetheexpressioninEq. (3) to fittheobservedspectrum.
where Aq ! , uq, Gq aretheamplitude,frequency,anddampingcoefficientofthe qthvibrationmode,respectively, cNR (2) isthesecondordernonlinearsusceptibilityfromthenonresonantbackground. Lu ! istheFresnelfactorat u,andtheselocal fieldfactorscanbe calculatedbasedonthephysicalandgeometricalpropertiesoftheSFGapparatusandexperiment:thebeamangles,therefractive indexofthemedium,etc.TheSFGdatahastobeprocessedsothatonecandeducethesurfacenonlinearsusceptibility, x ! 2 ðÞ s j from theSFGsignalamplitude.Usually,thisiscarriedoutbyremovingthegeometricfactorsandFresnelcoefficientsandsoweareleft withthesignal’samplitudethatinturngives x ! 2 ðÞ s j.Thenonlinearsusceptibilityholdstheinformationoftheadsorbate’ s molecularorientationandtheadsorbatelayerorderingdegree,6 ofwhichwegiveexampleslaterinthissection.
Whenstudyingelectrifiedinterfaces,theeffectfromanelectric fieldorso-calledelectricdoublelayer(EDL)ontheSFGsignal needstobeconsideredduetotheadditionalcontributionfromthesecond-orderbulknonlinearsusceptibilityinsidetheEDL. Thispotential-inducedcontributionoriginatesfromtheelectric-dipole-allowedthird-orderbulknonlinearsusceptibilityandthe fieldintheEDL.7–9 Theintensityofapotential-dependentreflectedSFGbeaminthepresenceofanEDLcanbeexpressedas7:
ISFG uVIS þ uIR ; f ðÞfI uIR ðÞI uVIS ðÞ c 2 ðÞ eff uIR ; f ðÞþ Z N 0 dzc 3 ðÞ uIR ; z; f ðÞEDC z ðÞ 2 (4)
where f ispotentialand EDC(z)isthestaticelectric fieldfromtheelectrodethatisadecayingfunctionof z.Thethird-order susceptibility, c(3)(uIR, z, f),varieswiththedistance z fromtheelectrodesurfacestartingat z ¼ 0.Ifweassumethatthe field EDC(z)isconstantinthedoublelayerandequalstozerointhebulkelectrolyte,theequationcanbeexpressedasfollows:
ISFG uVIS þ uIR ; f ðÞfI uIR ðÞI uVIS ðÞ c 2 ðÞ eff uIR ; f ðÞ 2 þ 2Re c 2 ðÞ eff uIR ; f ðÞc 3 ðÞ DL uIR ; f ðÞeid hi þ c 3 ðÞ DL uIR ; f ðÞ 2 ðÞ f2 (5) where cDL (3)(uIR, f)isthethird-orderpotential-dependentsusceptibilityofthedoublelayer.Thethird-ordersusceptibilityinthe doublelayeristhesumofthethird-orderhyperpolarizabilitiesofallthemoleculesinthedoublelayer.10 d isaphasefactorthatis
difficulttodetermineinthehomodyne(i.e., c ! 2 ðÞ eff 2 )detectionscheme.ThistermalsoimpliesthatSFGVSofmetalinterfacescan sufferfromaninterferenceduetoastrongbackgroundinthespectrumthatcomesfromthemetalor/andelectrolyteanddepends ontheelectrode’spotential.Inreality,thepresenceofastrongdispersivebackgroundthatdependsonthepotentialoftheelectrode needstobeconsideredintheSFGspectraanalysis,asitmayalsocausetheSFGspectratobeconvolutedandreducetheaccuracyof fitting.11 BycarefullyevaluatingtheSFGspectrumdependenceintheapplied field,onecanconstructthemolecularstructureofthe electrifiedinterface.
OneofSFGVSgreatestadvantagesistheabilitytocarryoutorientationanalysisoftheadsorbates.Wecandeducetheorientation ofmoleculesatinterfacesbyanalyzingsetsofSFGspectratakenunderdifferentpolarizationcombinationsoftheincidentincoming lightsandtheresultingSFGlight.Forexample,spectraacquiredatSSP(wheres-,s-,p-arethevisible,IR,andSFGpolarized fields, respectively)polarizationissensitivetodipolemomentsthatareorientedperpendiculartothesample’ssurfaceplaneforan isotropicsurface.Generally,themolecularorientationofanadsorbatecanbededucedfromtheratiobetweensymmetricandasymmetricstretchingvibrationsofaspecificgroup(e.g.,C]Oor –CH2–)byspeci ficpolarizationcombinations.Forexample,inthe caseofamonolayerofC]Ostretchingmodeonanazimuthallyisotropicsurfacehavinga CNv symmetry.Weconsiderthe Z axistobealongthesurfacenormalandthe X and Y axis,tolieinparalleltothesurface.ForaSFGmeasurementwiththeSSP andSPSpolarizationcombinations, xijk(2) canbereducedtononzerocomponent x 2 ðÞ yyz ¼ x 2 ðÞ xxz and x 2 ðÞ yzy ¼ x 2 ðÞ xzx respectively,where x 2 ðÞ ijk ¼ Ns P abc b i ∙ b a b j ∙ b b b k ∙ b c DEa 2 ðÞ abc a, b,and c representthemolecularcoordinatesasdescribedin Fig.2A, aabc(2) isthemolecular hyperpolarizabilityandisrelatedtotheIRdipoleandRamanpolarizabilityofavibrationalmode.ForthestretchingmodeofC]O:
with q denotingthetiltangleofC]Owithrespecttothe z-axis. R ishyperpolarizabilityratioof aacc and accc.Theanglebrackets representtheensembleaverageover f(q),withapolarorientationdistributionoftheC]Obondsinthetiltangle q,attherangeof 0 q p/2fromthesurfacenormal. Fig.2B showsasimulationfortheratioof xyzy (2) to xyyz (2) andtheorientationanglefordifferent angledistributionof0and10degrees.Wecancalculatetheaverage q fromthenormalizedintensityratiooftheSSPandSPSspectra. AnotherorientationanalysisexampleistheCH2 stretchingintensitiesofanazimuthallyisotropicsample.TheSSPmeasurementsof theCH2 stretchesyieldthat x 2 ðÞ xxz ¼ x 2 ðÞ yyz .TheexplicitexpressionforthesymmetricstretchingmodeofCH2 is:
andfortheasymmetricstretching:
with q denotingthepolarangleofthesymmetryaxis c withrespecttothe z-axis.Fromtheratiodeducedfromthes-CH2 andas-CH2 spectra,theaverage q canbedetermined.
Inpractice,whenappliedtometallicinterfaces,thedeterminationofthemolecularorientationischallengingasthes-polarized componentofthereflectedlightfrommetalsurfacesisusuallyweak.SFGwithallpolarizationcombinationscontainingan
Fig.2 (A)Themolecularcoordinatesofacarbonyl(C]O)groupandamethylene(CH2)group.(B)Theratioof xyzy (2) to xyyz (2) inregardtoaverage angle q ofacarbonylgroup. Black and red linesarefortheratioof xyzy (2) to xyyz (2) whichiscalculatedwiththeGaussiandistributionfunctionandangle distributionof0and10degrees,respectively.
s-component(exceptforPPP)hasshownlowsignal-to-noiseratio.Hence,mostSFGVSstudiesonmetalelectrochemicalinterfaces applythePPPpolarizationcombination.ThePPPcombinationinturnalsolimitstheaccuracyoforientationdeterminationsinceit hascontributionsfromallpossiblepolarizations.
ProbingSolid–LiquidInterfacesUnderReactionCondition Li-IonBatteries Sincethebirthofthecommerciallithiumionbatteryinthe1990swhenSonyInc.engineersclampedtogetheracarbonationsanode withadischargedoxidecathode,asenvisionedbyGoodenough,12,13 significanttechnologicaladvanceshadoccurredinthe fieldof energystorage,specificallyinthelithium(Li)ionbattery.Generally,theLi-ionbatteryiscomposedoftwoelectrodes,aseparator membranedesignedtoensureelectricalinsulationofthetwoelectrodesandamediumthatallowstheLi-ionstodiffusethroughit betweenthetwoelectrodes.ManyaspectsoftheLi-ionbatteryhavebeendesignedtoachievethemaximalefficiencywithout compromisingsafety,capacity,andpowerdemands.14,15 Thelithiumionbatteryisadynamicsystemevenatopencircuitpotential (OCP)whennoexternalpotentialisapplied.ThedifferenceoftheGibb’sfreeenergybetweentheorganicmoleculestotheelectrode energylevelsisenoughtoinitiateredoxreactionsuponmerecontactoftheelectrolyte/electrode16;thus,insitumethodologies shouldbeemployedfortheirstudy.Moreover,itwassuggestedthattheoverallbehavioroftheLi-ionbatteryisdefinedatthe electrode –electrolyteinterface.17 SFGVSisthebestoptionasitcanbeusedtoprobethelithiumionbatterycomponents(mainly electrodesurface,theeffectofsurfacetermination,andtheelectrode –electrolyteinterface)under “asprepared” andreactionconditions.Forexample,byapplyingSFGonecandeducethesurfaceconcentrationandorientationofthevariouselectrolytemolecules onacathodematerial.18 Yuetal.havedemonstratedthatatOCP,thereisapreferentialadsorptionofcycliccarbonates,mainly ethylenecarbonate(EC)overlinearcarbonatessuchasdiethylcarbonate(DEC)anddimethylcarbonate(DMC).19 ECwasfound tobethedominatingadsorbateontheLiCoO2 (cathodematerial)regardlessofitsmolecularproportioninthesolutionbulk.Refer to Fig.3
TheinterpretationofSFGspectraofsolid –liquidinterfacesischallengingandattimesambiguous;therefore,computational modelingcangreatlyimproveourunderstandinganddeciphertheresultingnonlinearvibrationalspectra.Asageneralcase,we canexaminethedifferencesbetweenprobingthe[c2]2 (absolutesquare)versusprobingtheimaginarypart Im[c2].Aswehave notedinourexplanationforEq. (3), c 2 holdsthechemicalandphysicalinformationoftheadsorbatesthatweprobebySFGVS. Eq. (3) canberearrangedsothat:
Fig.3 TheSPSpolarizedSFGspectraofLiCoO2 incontactwithEC:DMC(1:1involume)atopencircuitpotential.Toppanels:SFGspectrawhere thenonresonantbackgroundisremoved.Middlepanels:SFGspectra(circle)andtheir fittingresults(solidtraces).Bottompanels:deconvoluted bandsfortheSFGspectra.Theupwardanddownwardpeaksrepresentmodeswithreversedphases.Allthespectra(exceptforthemiddlepanels) areoffsetforclarity.AdaptedwithpermissionfromYu,L.;Liu,H.;Wang,Y.;etal.PreferentialAdsorptionofSolventsontheCathodeSurfaceof LithiumIonBatteries. Angew.Chem.Int.Ed.Engl. 2013, 52,5753–5756.
where fq isaphaseanglewithrespecttothenonresonantsignal cNR 2 .Whileobtaining[c2]2 iswellestablishedandisbasedon astraightforwarddesignoftheSFGapparatus,thereisafundamentalshortcomingofthistechnique,wherebyallinformationon thecomplexnatureof c 2 islost.Forexample,foragivenvibrationassociatedwithaspeci ficbond,wecandeducetheangle distributionofthedipolemomentbycalculatingtheintensityratiobetweenSSPandSPS.However,justfromthe c2 2 ssp c2 2 sps ratio,wecannotpredictifthedipolemomentispointingawayfromthesurfaceorpointingtothesurface.Probingthecomplex representationof c2,speci ficallyitsimaginarycomponent, Im[c2]readilyrevealsthedipoleorientation.Nevertheless,itrequires eitheraphase-modulationoraheterodyneSFGsetuptogetherwithsolidmathematicalmodeling.
Inordertosimplifytheinterpretationofphase-sensitiveSFGVS,thatis, Im[c2],MoritaandHynes,begunbymodelingtheSFG spectraaccordingtotheenergyrepresentationofthenonlinearsusceptibility, c2,inmoleculardynamics(MD)calculations.20 They havepioneeredthecomputationalanalysisofSFGspectroscopyingeneralandsuggestedanalternativeMDmodelbasedonthe timecorrelationfunction.21 Recently,Moritaetal.haveincorporatedthechargeresponsekernel(CRK)modelintheirworkbringing thecomputationalmodeltobetterinterprettheexperimentalSFGspectra.22,23 TheCRKwassuccessfullyimplementedininvestigatingthevapor –liquidinterfacestructureofDMCandpropylenecarbonate(PC),bothcommonsolventsinLi-ionelectrolytesolutions.22 ThestudyprobedtheC]Ostretchanditsorientationattheliquid –gasinterface.In Fig.4,wecanseethatthesimulatedMD SFG(A,C)andexperimentalSFG(B,D)spectraofPCandDMCatthesolid –gasinterfacecorrespondwell.However,theimportanceoftheMDsimulationwasdemonstratedbyrevealingthatthereasonfortheC]ObipolarbandslieswithDMChavingan almostisotropicorientationwhilePChasanorderedstructureduetoPCdimersasdiscussedinRef.[23].
TheadvantagesofSFGvibrationalspectroscopyasasurfacespeci ficspectroscopyaredemonstratedinthestudyofthesolid (electrode) –liquid(electrolyte)interfaceandevenmoresoinexaminingthesolidelectrolyteinterphase(SEI).24 TheSEI25,26 is atermandconceptthathasbeenwidelyacceptedforthereductionproductsformedonananodeoftheliquidhydrocarbonelectrolytemoleculesinteractingwithLi-ionsduringthechargingprocess.TheSEIservesasaphysicalbarrierandachemicallyinert coatingthathindersfurtherelectrolytereductiononthesurfaceoftheanode.Meanwhile,itallowslithiumionsdiffusion,at areasonablerate,throughittothelithiumionhost(anode)uponchargingandbacktotheelectrolytesolutiononcethedischarge oftheLi-ionbatterytakesplace.
OneofthekeystepsforamajorimprovementoftheLi-ionbatteryisunderstandingtheSEI’sstructure-relateddiffusioninenergy storagematerials.TheSEIformationisacrucialstepaschargeanddischargeratesofLi-ionbatteriesarediffusion-limited.The fundamentalunderstandingoftheiontransportanddiffusionmechanismwillultimatelyleadtofastercharging,longerlasting, andsaferLi-ionbatteries.Severalgroupshavesettoexplorethecomposition,structure,andformation/degradationmechanisms ofthesolidelectrolyteinterfaceonthesurfacesofelectrodesatOCPandduringcharge/dischargecyclesbyapplyingadvanced insituSFGvibrationalspectroscopy.
TheSEI’sbehaviorwasalsoinvestigatedunderappliedpotentials.Dlottetal.carefullychoseanelectrochemicalsystemto produceasingleSEIproduct.24 Theycycledlithiumperchlorate(LiClO4)saltdissolvedinanECdilutedwithtetrahydrofuran (THF)incontactwitheithergoldorcopperanodesbetween2.0and0.2V(vs.Li/Liþ).Thesinglereductionproductwaslithium ethylenedicarbonatewithatraceamountofethylenehavingtwoC]Odistinctvibrationalfrequenciesat1782and1800cm 1 , referto Fig.5.Theyhadreportedtwomain findings.The firstisthattheSEI “breaths” asafunctionofappliedpotentialonly whenreducedonacopperelectrode.ThisincreaseanddecreaseoftheSEIwidthisnotapparentwhenagoldelectrodeisused eventhoughthesameelectrolyteandthesameelectrochemicalconditionsasintheCucasearemaintained.Thesecond,presented in Fig.6,wasthattheappliedexternalpotentialaffectstheSFGprofile27 andsooneshouldcarefullyexaminetheSFGpro file obtainedunderpotentiodynamicconditions.
Fig.4 ThesimulatedMDSFG(A,C)andexperimentalSFG(B,D)spectraofpropylenecarbonate(PC)anddimethylcarbonate(DMC)solid–gas interface.Left TheSSP-polarizedSFGspectraareshownin red andSPSspectrain blue.Right TheSSPpolarizedimaginarycomponent,Im[c2], calculatedSFGspectraofPC(up)andDMC(bottom)solid–gasinterface.TheMDsimulationsshowthattheSFGbipolarbandoriginatesfrom differentmolecularinteractions,dimerizationforPC(up)andrandomforDMC(bottom).ReprintedwithpermissionfromWang,L.;Peng,Q.L.;Ye, S.;Morita,A.SurfaceStructureofOrganicCarbonateLiquidsInvestigatedbyMolecularDynamicsSimulationandSumFrequencyGenerationSpectroscopy. J.Phys.Chem.C 2016, 120,15185–15197;Ishiyama,T.;Morita,A.ComputationalAnalysisofVibrationalSumFrequencyGenerationSpectroscopy. Annu.Rev.Phys.Chem. 2017, 68,355–377.Copyright(2017)AmericanChemicalSociety.
