Anisotropic Janus SiP 2 Monolayer as a Photocatalyst for Water Splitting - Yu et al. - 2021 - Unknown

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pubs.acs.org/JPCLLetterAnisotropicJanusSiP2MonolayerasaPhotocatalystforWaterSplitting∥∥TongYu,CongWang,XuYan,GuochunYang,*andUdoSchwingenschlögl*CiteThis:J.Phys.Chem.Lett.2021,12,2464−2470ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Thedesignofmaterialsmeetingtherigorousrequirementsofphotocatalyticwatersplittingisstillachallenge.AnisotropicJanus2Dmaterialsexhibitgreatpotentialduetooutstandinglyhighphotocatalyticefficiency.Unfortunately,thesematerialsarescarce.Bymeansofabinitioswarm-intelligencesearchcalculations,weidentifyaSiP2monolayerwithJanusstructure(i.e.,out-of-planeasymmetry).Thematerialturnsouttobesemiconductingwithanindirectbandgapof2.39eVenclosingtheredoxpotentialsofwater.Notably,theoxygenandhydrogenevolutionhalfreactionscanhappensimultaneouslyattheSiandPatoms,respectively,drivenmerelybytheradiation-inducedelectronsandholes.Thecarriermobilityisfoundtobeanisotropicandhigh,upto10−4cm2V−1s−1,facilitatingfasttransportofthephotogeneratedcarriers.TheSiP2monolayershowsremarkablystrongopticalabsorptioninthevisible-to-ultravioletrangeofthesolarspectrum,ensuringefficientutilizationofthesolarenergy.hemoderneconomyandsocietydemandhugeamountsalsoisabletoimprovetheutilizationofphotogeneratedTofenergy,whilethereservesoftraditionalfossilenergy17carriers.TheprototypicalexampleisMoSSe(obtainedbyarelimited,andtheutilizationoffossilenergypollutesthereplacementoftheSatomsononesideof2DMoS2withSeenvironment.Environmentallyfriendly,low-cost,andsustain-atoms),whichexhibitslargepiezoelectricity.18SeveralJanusableenergysourcesthusareinurgentdemand.Photocatalyticmaterials,particularlyMX(M=Al,Ga,In;X=S,Se,Te)623decompositionofwaterintohydrogen(H2)andoxygen(O2)andBP,19achieveanoutstandingphotocatalyticefficiency,26isthebasisofoneofthemostpromisingenergysources,asiteveninexcessoftheconventionaltheoreticallimitof18%.directlyutilizesclean,renewable,andcost-freesolarenergy.TheyprovidearoutetorealizingtheoxygenevolutionreactionWhileseveralbreakthroughshaveemergedsincethepioneer-1(OER)andhydrogenevolutionreaction(HER)simulta-ingworkofFujishimaandHonda,theavailabilityofnontoxic20neouslyatdifferentatomicspecies.andhighlyefficientcatalystsremainsakeyissueforlarge-scale2,3Silicene,the2Dcounterpartofwidelyusedsilicon,hasaDownloadedvia222.254.62.142onMay14,2021at07:05:49(UTC).applications.buckledhoneycombstructure,realizesamixtureofsp2andsp32Dmaterialsdemonstrateuniqueadvantagesovertraditionalbulkmaterialsforachievinghighlyefficientphotocatalysis.4Inhybridization,andisnonmetallic,insharpcontractto21particular,largesurface-to-volumeratiosgiverisetoabundantgraphene.Phosphorenecombinesadirectbandgapwith5anisotropicmechanical,electronic(sp3hybridization),andactivesites.FastcarriertransportandshortdistancesSeehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.6opticalpropertiesoriginatingfromitsstructuralasymme-maximizetheutilizationofthephotogeneratedcarriers,and22,23dependenceoftheelectronpropertiesonquantitiessuchasthetry.Three-coordinationofSiorPatomsalsofacilitatesthethickness,surfacefunctionalization,andexternalstrainmakesitformationofa2Dstructure.Indeed,severalstable2DSixPy7possibletoenhancetheutilizationofthesunlight.materialshavebeenreportedwithnovelstructuresandAvarietyof2Dphotocatalyticmaterialsalreadyhavebeenextraordinaryproperties.24−26Whileg-CNshareswith348studiedexperimentallyand/ortheoretically,suchasg-C3N4,phosphorenetheexcellentcatalyticperformance,theweak91011BN,phosphorene,transition-metaldichalcogenides,absorptionofsunlightlimitsapplications.27However,though12,1314PdSeO3,andcovalentorganicframeworks,someCandSiaswellasNandPbelongtothesamegroupofthedemonstratingexcellentefficiency.Still,photocatalystsforperiodictable,theyaredistinguishedintermsoftheirwatersplittingarerare.Thus,besidesimprovingtheperform-15anceoftheknown2Dmaterials,itiscrucialtosearchfornewcandidates,notonlytoelevatethematerialpropertiesbutReceived:December30,2020alsotobroadentheknowledgeof2Dmaterialsingeneral.16Accepted:February26,2021Janusmaterials,aspecialkindof2Dmaterials,drawPublished:March4,2021attentionduetotheirout-of-planeasymmetry,inducinganisotropy,electricpolarization,piezoelectricity,andmagnet-ismsuitablefornovelelectronicdevices.TheJanusstructure©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.jpclett.0c038412464J.Phys.Chem.Lett.2021,12,2464−2470

1TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetter41electronegativityandwillhybridizedifferently;i.e.,anew2DalternatingSiandPatoms,likesilicene;andzigzagPchains,4243SixPymaterialstillcanrealizestrongopticalabsorption.like3Dboronmonophosphideand2DAsP.SincethePAscurrentlyabinitiostructuralpredictionplaysanatomsinthezigzagchainsareconnectedtoSiatoms,eachSi/28−30importantroleinthediscoveryofnewmaterials,wePatominthehoneycombstructureisthree-coordinatedwithconductinthepresentworkaglobalsearchforthelowest-P/Siatoms,andeachPatominthezigzagchainsconnectstoenergystructureof2DSiP(x=1−4andy=1−4).WeoneSiandtwoPatoms,givingrisetoansp3hybridizationandxyidentifystablesemiconductingSiP2andSiP3monolayers.satisfyingthechemicaloctetruleforboththeSiandPatoms.Interestingly,theSiP2monolayerrealizesananisotropicJanusNoticethatoneofthePhybridorbitalsholdsanelectronlonestructure.Itcombineshighcarriermobilitieswithstrongpair(Figure1c)andthattheuniquestructuralarrangementopticalabsorption.TheSiandPatomsgiverisetoactivesitesexposesthePatoms.Thebondingisstronglycovalent(FigurefortheOERandHER,respectively,anditturnsoutthatthe1c,d),andtheSi−P(2.28Å)andP−P(2.27Å)bondlengths44photogeneratedelectronsandholescantriggerthetwohalfarecomparabletothoseinSiP(2.33Å)andphosphorene45reactionstooccursimultaneously.Thisopensgreatpotential(2.24Å).oftheSiP2monolayerinphotocatalyticwatersplitting.Beingaprerequisiteforapplication,weexploretheWeapplythecrystalstructureanalysisbyparticleswarmdynamical,mechanical,thermal,andairstabilitiesoftheSiP231,32optimization(CALYPSO)code;seedetailsinthemonolayer.TheobtainedphononspectrumisindicativeofSupportingInformation.Structureoptimizationsandelec-dynamicalstability(absenceofimaginaryfrequenciesthrough-tronicpropertycalculationsareperformedintheframeworkofouttheBrillouinzone;Figure2a).Thehighestfrequency(529densityfunctionaltheory,usingtheViennaabinitiosimulation33,3435packageandprojectoraugmented-wavepseudopotentialswithSi3s23p2andP3s23p3valencestates.Theenergycutoffoftheplanewavesissetto400eV,theenergyconvergenceto10−6eV,andtheatomicforceconvergenceto10−3eVÅ−1.Tocreate2Dmodels,avacuumslabof∼20Åthicknessis36adopted.ThePerdew−Burke−Ernzerhoffunctionalisusedforthestructureoptimizations,andtodetermineaccuratebandgapsandopticalproperties,weadopttheHeyd−Scuseria−37Ernzerhof(HSE06)hybridfunctional.Deformationpotential38theoryisemployedtopredictthecarriermobilities;phonondispersionsarederivedbythesupercellapproachofthe39Phonopycode,andmoleculardynamics(MD)simulationsareexecutedtoevaluatethethermalstability.TheMDsimulationslast10pswithatimestepof1fsandarebasedon40anNVTensemblewithNose−́Hoovertemperaturecontrol.20O2moleculesareevenlydistributedonthetwosidesoftheSiP2monolayerwiththedistancetothemonolayerbetween2and3Å.Byextensivestructuralsearch,twohithertounknown2DmaterialswithstoichiometriesofSiP2andSiP3areidentified(structuralinformationinTablesS1andS2).OtherFigure2.(a)PhononspectrumoftheSiP2monolayer.PhonondensitiesofstatescanbefoundinFigureS1.(b)Totalenergyandstoichiometriesareincompatiblewithdynamicalstability.snapshotsoftheSiP2monolayerwith20O2moleculesbeforeandSiP2exhibitsout-of-planeasymmetry(Janusstructure;Figureaftera10psMDsimulationat300K.Polardiagramsof(c)E(θ)and1a,b),consistingofabuckledhoneycombstructurewith(d)v(θ).cm−1)iscomparabletoresultsforSiP(540cm−1)26and3phosphorene(470cm−1),46demonstratingtheformationofstrongcovalentbonds.MDsimulationscarriedoutfor10psat300and1000Kshowneitherbondbreakingnorsignificantstructuraldistortions,verifyingthermalstability(FigureS2).AsPcaneasilyreactwiththeoxygen(O2)moleculesintheair,47likephosphorene,andconsideringthatthePatomsoftheSiP2monolayerarestronglyexposedtotheenvironment,weemployMDsimulationsat300KtocheckthestabilityofaSiP2monolayerwith20O2moleculesina6×3×1supercell.After10ps,theSiP2monolayerremainsintact,andtheO2moleculestendtoseparatefromthemonolayerwithoutdissociatingintooxygenatoms(Figure2b).SimilarresultsareobtainedforCO2,H2,N2,andH2Omolecules(FigureS3).Basedonthecalculatedlinearelasticconstants,theSiP2monolayerisalsomechanicallystable(SupportingInforma-tion).Young’smodulusE(θ)characterizesamaterial’sFigure1.(a)Sideand(b)topviewsoftheSiP2monolayer.Electronflexibility/stiffness,andPoisson’sratiov(θ)describesitslocalizationfunctioninthe(c)topand(d)bottomsurfaces.mechanicalresponsetoanexternalload.WefindthatE(θ)2465https://dx.doi.org/10.1021/acs.jpclett.0c03841J.Phys.Chem.Lett.2021,12,2464−2470

2TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLettervariesfrom77to105Nm−1(Figure2c),thusbeingsmallershowsstrongSi−Phybridization(Figure3b),pointingtothanthatofgraphene(342Nm−1)48butcomparabletothatofcovalentbonds,whichisconsistentwithourabovestructuralphosphorene(24−102Nm−1).49Thein-planeflexibilityoftheanalysis.BoththeVBMandCBMmainlyoriginatefromtheSiSiP2monolayerconsequentlyismoderate.Wefurtherfindthat3pandP3porbitals.ThechargedensitiesattheVBM(Figurev(θ)variesfrom0.16to0.24(Figure2d).Thecohesiveenergy3c)andCBM(Figure3d)indicatethattheπelectroncloudis53isusefultoevaluatetheprospectsforexperimentalsynthesisofbrokenupbytheelectronlonepairs,asobservedinPC6.apredicted2Dmaterial.WefindfortheSiP2monolayeraWhile,ingeneral,everysemiconductorwithabandgapvalueof3.98eVatom−1.Whilethisvalueislowerthanthosebetween1.23and3eVisapotentialphotocatalystforwaterreportedforgraphene(7.91eVatom−1)50and2DMoS(5.15splitting,theenergeticpositionsoftheVBMandCBMmust2eVatom−1),51itsurpassesthecohesiveenergiesofalreadybesignificantlylowerandhigherthanthewateroxidationexistingsilicene(3.91eVatom−1),19germanene(3.24eVpotential(−5.67eV)andhydrogenreductionpotential(−4.44atom−1),19andphosphorene(3.30eVatom−1),52indicatingeV)atpH=0,respectively.Thelargertheenergydifferences,feasibilityofexperimentalsynthesisoftheSiPmonolayer.thebetteritisforthewatersplitting.TheVBM(−6.37eV)2WenextexploretheelectronicpropertiesoftheSiPandCBM(−3.98eV)oftheSiP2monolayersatisfythe2thermodynamicrequirements(Figure3e).Thisremainsvalidmonolayerbystudyingtheelectronbandstructureandpartialunderupto±5%strain.Whilestretchingsupportsthedensitiesofstates(PDOS).AttheHSE06leveloftheory,wehydrogenreduction,compressionsupportsthewateroxidation.findasemiconductingcharacterwithanindirectbandgapofAnexcellentphotocatalystmustbeabletoharvestsunlight2.39eV(Figure3a).Moreover,theconductionbandminimumefficiently,particularlyvisibleandultravioletlight.To(CBM)islocatedattheM(0.5,0.5,0.0)point,andthedeterminetheopticalabsorptioncoefficientoftheSiP2valencebandmaximum(VBM)islocatedbetweentheMandmonolayerinareliablemanner,theHSE06leveloftheoryisY(0.0,0.5,0.0)points.Notably,thedirectbandgapof2.51eVemployed.Between300and500nm,weobtainvaluesofuptoattheYpointcomesclosetotheindirectbandgap.ThePDOS5−110cm(Figure3f),whichismuchhigherthanthatreported54forg-C3N4.Theobtainedanisotropyoftheopticaladsorptionisnotverylarge.Moreinterestingly,wefindared-shiftofthespectrumunderstrain,supportingtheutilizationofvisiblelight,whileboththeanisotropyandhighopticalabsorptioncoefficientaremaintained.Hence,theSiP2monolayercaneffectivelyharvestsunlight,facilitatingutilizationasaphotocatalystforwatersplitting.Rapidtransportofthephotogeneratedelectronsandholestotheactivesitesiscrucialforahighlyefficientcatalysis.Highcarriermobilityisalsoaprerequisiteofmanyhigh-perform-20anceelectronicdevices.WeaimtoemploydeformationpotentialtheorytoestimatethecarriermobilityoftheSiP2monolayer.Toverifythatthisapproachissuitable,wepredicttheholemobilityofphosphoreneas2533cm2V−1s−1,whichisconsistentwiththereportedvalueof2200cm2V−1s−1.55ThemainparameterscalculatedfortheSiP2monolayeraregiveninTable1.Thehighcarriermobilitiesoutperform2DTable1.SiP2Monolayer:DeformationPotentialConstant(EDP),In-PlaneStiffness(C),EffectiveMass(m*),CarrierMobility(μ),andRelaxationTime(τ)alongtheaandbDirectionsat300KEDPm*carriertype(eV)C(Jm−2)(m)μ(cm2V−1s−1)τ(ps)0electron(a)12.51101.280.13212.360.02hole(a)0.31101.280.783.20×10415.60electron(b)0.2376.991.903.27×10438.80hole(b)0.5876.991.035.27×1033.39MoS(200cm2V−1s−1)56andg-CN(334cm2V−1s−1),57234showingstronganisotropywiththelowerelectronandholemobilityalongtheaandbdirection,respectively.ThisisFigure3.(a)ElectronicbandstructureoftheSiP2monolayer.Themainlyduetothedirection-dependences(Table1)ofthehorizontaldashedlineistheVBM.(b)PDOSofthePandSiatomsindeformationpotentialconstant(larger/smallerintheathantheSi3P3honeycombsandthePatomsinthezigzagPchains.Topthebdirectionforelectrons/holes)andtheeffectivemassandsideviewsofthechargedensitiesatthe(c)VBMand(d)CBM.(e)EnergeticpositionsoftheVBMandCBMunderbiaxialstrain.(smallerintheathanthebdirectionforbothelectronsandThedashedlinesmarktheredoxpotentialsofwateratpH=0.(f)holes)resultingfromthestructuralanisotropyinherenttotheOpticalabsorptioncoefficientoftheSiP2monolayercomparedtog-SiP2monolayer.Importantly,theSiP2monolayerisabletoC3N4.ensurefasttransportofthephotogeneratedelectronsandholes2466https://dx.doi.org/10.1021/acs.jpclett.0c03841J.Phys.Chem.Lett.2021,12,2464−2470

3TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLettertoeffectivelyparticipateintheredoxreaction.WhileitisaWefinallyturntothediscoveredSiP3monolayer,whichchallengetoachieve2DmaterialsthatcombinealargebandshowsamonoclinicstructurewithspacegroupC2/mandfour58−60gapwithhighcarriermobilityanddirectionalcontrol,theformulaunitsperunitcell(Figure5a−c).TheSiandPatomsSiP2monolayermeetstheserequirementsandthusisalsoapromisingcandidateforhigh-performanceelectronicdevices.TostudywhetherthephotogeneratedelectronsandholescanprovideenoughdrivingforcetotriggertheOERandHER,wefocusonneutralconditions(pH=7).TheenergeticpositionsoftheVBMandCBMstillenclosetheredoxpotentialsofwater.Thecalculatedpotentialsofthephoto-generatedelectronsandholesareUe=0.87VandUh=1.52V,respectively,andtheobtainedreactionpathways,structures,andGibbsfreeenergiesareillustratedinFigure4a,b.FortheFigure5.(a)Topand(b)sideviewsoftheSiP3monolayerand(c)Figure4.Proposedphotocatalyticpathwaysofthe(a)oxygenandbasicbuildingblock(Si6P20).(d)Electronicbandstructureand(b)hydrogenevolutionhalfreactionsontheSiP2monolayerforthePDOS.ThehorizontaldashedlineistheVBM.(e)Phononspectrum.(energeticallyfavorable)intermediatesOH*,O*,OOH*,andH*.PhonondensitiesofstatescanbefoundinFigureS1.(f)TotalenergyTheredandgreenballsareOandHatoms,respectively.GibbsfreeandsnapshotsoftheSiP3monolayerwith20O2moleculesbeforeandenergydiagramsofthe(c)OERand(d)HERontheSiP2monolayeraftera10psMDsimulationat300K.fordifferentconditions.showsp3hybridizationandcovalentbonds,satisfyingthechemicaloctetrule.Thecohesiveenergyturnsouttobe3.80OERandHER,absorptionisfavorableattheSiandPatoms,−1eVatom.ItisthusslightlylowerthanthatfoundfortheSiP2respectively,duetothehigherelectronegativityofPasmonolayer,butexceedstheliteraturevaluesreportedforthecomparedtoSi.Coexistenceofactivesitesforbothreactions−1−1SiP(3.64eVatom)andSi3P(3.78eVatom)booststhephotocatalyticefficiencybyavoidingrecombination2620monolayers.ofphotogeneratedcarriers.TheSiP3monolayerisanindirectbandgap(2.16eVattheInadarkenvironment(Uh=0V,blacklineinFigure4c),HSE06leveloftheory;Figure5d)semiconductorandtheGibbsfreeenergyincreasesineachofthefourstepsofthedynamically(Figure5e)andthermally(Figure5fandFigureOER,indicatingthatthereactiondoesnotproceedS2)stable.Theelectronandholemobilitiesareanisotropic,spontaneously.ΔGOOH*=1.50VisthelargestincreaseofwithaparticularlylargeelectronmobilityalongtheadirectiontheGibbsfreeenergyandthusthelimitingpotential,which(Table2).Generally,2Dmaterialscanenhancetheperform-consequentlyismuchsmallerthaninthecaseofg-C3N4(2.2861V).Inalightenvironment(Uh=1.52V,redlineinFigure4c),thephotogeneratedholesprovideadrivingforce,andtheTable2.SiP3Monolayer:DeformationPotentialConstantGibbsfreeenergythusdecreasesineachstep;i.e.,the(EDP),In-PlaneStiffness(C),EffectiveMass(m*),CarrierMobility(μ),andRelaxationTime(τ)alongtheaandbmoleculescanbeoxidizedintoO2inneutralconditions.LikeDirectionsat300KtheOER,theHER,whichcomprisestwosteps,doesnotproceedspontaneouslyinadarkenvironment(Figure4d),butcarriertypeE(eV)C(Jm−2)m*(m)μ(cm2V−1s−1)τ(ps)itcanoccurinalightenvironmentunder5%compression.DP0electron(a)1.1635.950.472.33×1030.68CompressionoftheSiP2monolayerthereforeenhancesnotonlytheopticalabsorption(Figure3e)butalsothedrivinghole(a)1.6835.955.7112.390.04forceofthephotogeneratedelectrons(Figure3f),enablingelectron(b)3.0173.710.58575.380.21efficientphotocatalysis.hole(b)2.6373.712.5822.940.042467https://dx.doi.org/10.1021/acs.jpclett.0c03841J.Phys.Chem.Lett.2021,12,2464−2470

4TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetteranceoffieldeffecttransistorsduetoconfinementofthechargeAuthors62,63carriersinatomicallythinchannels.ConsideringitsTongYu−StateKeyLaboratoryofMetastableMaterialsmoderatebandgapandhighelectronmobility,outperformingScience&TechnologyandKeyLaboratoryfor56MicrostructuralMaterialPhysicsofHebeiProvince,Schoolof2DMoS2,theSiP3monolayerhasgreatpotentialinthisfield.ThestructuralmotifsoftheSiP2monolayer(zigzagPScience,YanshanUniversity,Qinhuangdao066004,China;chains)andSiP3monolayer(Si6P20unitsconsistingofedge-CentreforAdvancedOptoelectronicFunctionalMaterialssharingSi2P2quadranglesandSiP4pentagons)complementResearchandKeyLaboratoryforUVLight-Emittingthefourmotifs(FigureS4)reportedintheliteraturefor2DMaterialsandTechnologyofMinistryofEducation,SiP,25,26,442DSiP,24and2DSiP.26Inthecaseof2DSiP,NortheastNormalUniversity,Changchun130024,China23buckledhexagonalSi3P3rings,consistingofalternatingSiandCongWang−StateKeyLaboratoryofMetastableMaterialsPatoms,26,44andinterconnectedchairlikeSiPandSiPScience&TechnologyandKeyLaboratoryfor3332rings,inwhichtheSiatomsarefour-coordinated,25havebeenMicrostructuralMaterialPhysicsofHebeiProvince,SchoolofScience,YanshanUniversity,Qinhuangdao066004,China;reported.Inthecaseof2DSiP2,achairlikeSi3P3ringandtwo24CentreforAdvancedOptoelectronicFunctionalMaterialsSi2P3ringsshareedges,leadingtodistortedPchains.TheResearchandKeyLaboratoryforUVLight-Emittingbasicstructuralunitof2DSi3PisSi6P6,whereeachSiatomof26MaterialsandTechnologyofMinistryofEducation,acentralhexagonalringbondstoaPatom.GreatvariabilityNortheastNormalUniversity,Changchun130024,ChinainthestructuralmotifsthereforeisfoundtobecharacteristicofXuYan−StateKeyLaboratoryofMetastableMaterials2DSixPy.Science&TechnologyandKeyLaboratoryforInconclusion,wediscovertwo2Dmaterials,theSiP2andMicrostructuralMaterialPhysicsofHebeiProvince,SchoolofSiP3monolayers,throughacombinationofevolutionarysearchScience,YanshanUniversity,Qinhuangdao066004,Chinaandabinitiocalculations.FortheSiP2monolayerweobtainaJanusstructurewithhighthermalanddynamicalstabilitiesCompletecontactinformationisavailableat:https://pubs.acs.org/10.1021/acs.jpclett.0c03841resultingfromstrongSi−PandP−Pcovalentbondsthatsatisfythechemicaloctetrule.TheSiP2monolayershows−42−1AuthorContributionsremarkablyhighcarriermobilitiesoftheorderof10cmV∥s−1withpreferentialelectrontransportalongthebdirectionT.Y.andC.W.contributedequally.andholetransportalongtheadirection.Also,theopticalNotesabsorptioncoefficientishigh.Interestingly,theSiandPatomsTheauthorsdeclarenocompetingfinancialinterest.giverisetoactivesitesfortheOERandHER,respectively,andwefindthatthematerialiscapableofsplittingwaterintoO2■ACKNOWLEDGMENTSandH2undersunlight.Overall,wedemonstratethattheSiP2TheauthorsacknowledgefundingfromtheNaturalSciencemonolayerisanexcellentcandidateforphotocatalyticwaterFoundationofChinaunder21873017and21573037,thesplitting.PostdoctoralScienceFoundationofChinaundergrant2013M541283,andtheNaturalScienceFoundationofJilin■ASSOCIATEDCONTENTProvince(20190201231JC).Theresearchreportedinthis*sıSupportingInformationpublicationwassupportedbyfundingfromKingAbdullahUniversityofScienceandTechnology(KAUST).TheworkTheSupportingInformationisavailablefreeofchargeatwascarriedoutattheNationalSupercomputerCenterinhttps://pubs.acs.org/doi/10.1021/acs.jpclett.0c03841.Tianjin,andthecalculationswereperformedonTianHe-1Descriptionofthecomputationalmethodsanddetailed(A).structuralinformationontheSiP2andSiP3monolayers(PDF)■REFERENCES(1)Fujishima,A.;Honda,K.ElectrochemicalPhotolysisofWaterataSemiconductorElectrode.Nature1972,238,37−38.■AUTHORINFORMATION(2)Wang,Z.;Li,C.;Domen,K.RecentDevelopmentsinCorrespondingAuthorsHeterogeneousPhotocatalystsforSolar-DrivenOverallWaterSplitting.Chem.Soc.Rev.2019,48,2109−2125.GuochunYang−StateKeyLaboratoryofMetastable(3)Lin,L.;Yu,Z.;Wang,X.CrystallineCarbonNitrideMaterialsScience&TechnologyandKeyLaboratoryforSemiconductorsforPhotocatalyticWaterSplitting.Angew.Chem.,MicrostructuralMaterialPhysicsofHebeiProvince,SchoolofInt.Ed.2019,58,6164−6175.Science,YanshanUniversity,Qinhuangdao066004,China;(4)Faraji,M.;Yousefi,M.;Yousefzadeh,S.;Zirak,M.;Naseri,N.;CentreforAdvancedOptoelectronicFunctionalMaterialsJeon,T.H.;Choi,W.;Moshfegh,A.Z.Two-DimensionalMaterialsinResearchandKeyLaboratoryforUVLight-EmittingSemiconductorPhotoelectrocatalyticSystemsforWaterSplitting.MaterialsandTechnologyofMinistryofEducation,EnergyEnviron.Sci.2019,12,59−95.NortheastNormalUniversity,Changchun130024,China;(5)Wang,L.;Zhang,Y.;Chen,L.;Xu,H.;Xiong,Y.2DPolymersAsorcid.org/0000-0003-3083-472X;Email:yanggc468@EmergingMaterialsforPhotocatalyticOverallWaterSplitting.Adv.Mater.2018,30,1801955.nenu.edu.cn(6)Fu,C.F.;Sun,J.;Luo,Q.;Li,X.;Hu,W.;Yang,J.IntrinsicUdoSchwingenschlögl−PhysicalScienceandEngineeringElectricFieldsinTwo-DimensionalMaterialsBoosttheSolar-To-Division(PSE),KingAbdullahUniversityofScienceandHydrogenEfficiencyforPhotocatalyticWaterSplitting.NanoLett.Technology(KAUST),Thuwal23955-69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