Energy Tutorial: Electrocatalysis 101 - Jaramillo Group

Energy Tutorial: Electrocatalysis 101 Thomas Jaramillo Assistant Professor – Department of Chemical Engineering Stanford University GCEP Research Theme Leader – Electrochemical Energy Conversion and Storage


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Energy Tutorial:Electrocatalysis 101Thomas JaramilloAssistant Professor – Department of Chemical Engineering Stanford UniversityGCEP Research Theme Leader – Electrochemical Energy Conversion and StorageStanford University
GCEP RESEARCH SYMPOSIUM 2012 STANFORD, CAOCTOBER 11, 2012GLOBAL CHALLENGES — GLOBAL SOLUTIONS — GLOBAL OPPORTUNITIESGLOBAL CLIMATE AND ENERGY PROJECTSTANFORD UNIVERSITY
fortutorialIntroductionFundamentalselectrochemistryelectrocatalysisKineticsMethodselectrocatalysisresearchFiguresforelectrocatalystdevelopmentApplications–twoexampleshydrogenevolutionreactioncarbondioxidereductionreaction(CO
Whatcatalyst?: a substance that enables a chemical reaction to proceed at a usually faster rate or under different conditions (as at a lower temperature) than www.mw.comwww.newworldencyclopedia.orgElementarychemicalreaction:
Fivebroadcatalysisresearch
Biocatalystse.g.enzymesoxidationphotosynthesistransfersAmbientTempAmbientPressureHomogeneousCatalystse.g.transitionmetalcomplexeschemicalsOlefinmetathesisthermochemicalIntermediateT’srangeP’sElectrocatalystse.g.PtnanoparticlesWaterelectrolysisthermochemicalrangeTempsrangeP’sConventionalHeterogeneousCatalystse.g.nanoparticlesCatalyticconverterssynthesisThermochemicalrangeTempsrangeP’sUltraVacuumSurfacee.g.FundamentalstudiesAdsorption,desorption,reactionThermochemicalrangeTempsVery(vacuum)surface
Electrocatalysiscomesdifferentforms
ElectrocatalystsPhotocatalysts
MaterialsKarunadasaet.ScienceSurfaceElectrocatalystsK.P.Kuhlet.EnergyEnvironmentalScience
ThreekeyenergyconversionreactionsimprovedelectrocatalystsH+ mH
Consumption
Production
KeytermselectrochemistryWhatoxidation?Whatreduction?
lectronsxidation.lectronsJustremember:LEOgoes….”Whatcathode?What
RedCat
OxidationJustrememberRedCat
ChemistryElectrochemistry(oxidation)E(reduction)EG°=kJ/mol=Where:nelectronstransferred(overallFaraday’sconstantcanconfusing!nextslidestablesstandardelectrochemicalpotentialscalculateEquilibrium
EquilibriumPotentials
study
reactionsreactionsdefinedabsolutepotential(scale,
Potentialscalecanshiftedforconveniencee.g.–4.44voltages(
potentialaredifferencespotentialfromtwo
reactionsthatmakecompletereaction.
http://hsc.csu.edu.au
CalculatingPotentials:StatueImportant:arestandardreductiontablefromprecedingStepIdentifyrelevantredreactions.example,relevantreactionsareredreactionsinvolvingRxn1:Fe(s)ERxn2:Cu(s)EStepreactionoxidation,reductionarbitraryForexample,let’sRxn1oxidationStepcathode–E°becausearetabulateddatafromreductiontables.oxidationwhatoccursmustreversedreactionreversedirection.–(–0.02Stepoverallequation(cathoderxn+calculatetransferredG°=J/mol=Keyresult:G°isnegativeoverallrxnisspontaneouswritten
18862012
considerationsforelectrocatalyticconversionsrelatedenergy
0
VV+V+V+V+V+V+V
valuesareevolutionpotential2CO2CO3COVayenaset.(2008)
i(mA/cm
CO2/fuel
Reactioninvolving
M.T.M.Koper,H.A.Heering,Science”,Eds.Wieckowski,J.K.Nørskov,
Reactioninvolving
M.T.M.Koper,H.A.Heering,Science”,Eds.Wieckowski,J.K.Nørskov,
Electrochemicalelectrode
www.pineinst.comHydrodynamic(e.g.rotatingelectrode)areusefulforcaseswheretransferstudiedand/ormayproblematic(e.g.concentrationdissolvedgasesgasformationelectrocatalystsurface).WorkingElectrodeReferenceElectrodeAg/AgClSaturatedcalomelCounterElectrodePotentiostat
Threeprimaryfiguresforcatalysts
Stabilitymostcriticallycatalystdevelopment?three!everyreactiondifferentforcatalystdevelopment.
Electrochemicalreaction݅ൌ݅
െexp
question:currentachieveforamountoverpotentialthattwofactorsanychemicalreaction):(1)Theinherentkineticsreaction.(2)Effectstransfer.currentdensityexchangecurrentdensityelectronstransferredtransfercoefficientcathodic)Faraday’sconstant:overpotentialgasconstanttemperature
VolmerEquation
termcathodicterm
stepratedeterminingtermsareimportant.fartherfromtermdominates…canTafelEquation!
whereTafelslope݅ൌ݅ൌെ݅
Electrocatalystactivity:Figures
ThreewaysreportcurrentPergeometricareageoPersurfacearearealPerelectrochemicallyactivesurfaceareaECSAClosestTurnoverFrequency(TOF)
Volmer
Easy/PracticalDifficult/Useful
ൌെ݅
Fourprimaryfiguresforelectrocatalystactivity:Exchangecurrentdensity,(mA/cmTafelslope,(mV/decade)Currentgivenoverpotential:vs.(mA/cmOverpotentialneededreachgivencurrenti=10mA/cm^2
Tafel
RecappingfundamentalsKineticsMethodselectrocatalysisresearchFiguresforelectrocatalystdevelopmentThreewaysreportcurrentPergeometricareageoPersurfacearearealPerelectrochemicallyactivesurfaceareaECSAclosestprovidingTurnoverFrequency(TOF)Fourprimaryfiguresforelectrocatalystactivity:Exchangecurrentdensity,(mA/cmTafelslope,(mV/decade)Currentgivenoverpotential:vs.(mA/cmOverpotentialneededreachgivencurrenti=10mA/cm^2
mA/cm
Relevantmetricfor
thathavecoveredfundamentals,letexamineexampleselectrocatalystdevelopment.reductionchemicals
hydrogenevolutionreactionExperimental
RotatingElectrodeStandardelectrodeElectrochemicalelectrodeElectrochemical‘Compression
TafelPlotsforvariouscatalysts
mA/cmChen Z, Jaramillo T.F., et al. NanoLetters11, 10 (2011)
scaleview:evolutionVolmerTafelHinshelwood)
VolmerlmerTafelVolmerHeyrovskyEley
VolmerlmerHeyrovsky
+
+
+
+
+
+
Overall
Towardsquantitative‘descriptors’forcatalysisPaulSabatieroptimalcatalystreactionintermediatesmoderatelyonsurface;
toostronglytooweakly.RogerParsonsfirst‘qualitative’volcanoelectrocatalysis,indicatingthatbestcatalystsexhibiteV.
calculated
MeasuredcatalyticGreeley,T.F.Jaramillo,Chorkendorff,J.K.Nørskov,Materials
inspiredapproach
GH=GH=
T.F.Jaramillo,K.P.Jørgensen,J.H.Horch,Chorkendorff;ScienceHinnemannandJ.KNørskov,Adv.P.G.K.P.Jørgensen,Horch,Chorkendorff,J.K.Nørskov,Amer.
familynanostructuredcatalystsfor
Reinecke,Sunkara,T.F.Jaramillo,Letters,
Corenanowires
gyroidKibsgaard,Reinecke,T.F.Jaramillo,Materials[advancepublication10.1038/NMAT3439].
Currentcatalystdevelopmentforevolution
CatalystAdvantagesDisadvantagesPrecious metals (Pt, Pd)Best known catalysts.Expensive($65/gram for Pt).Common metals (Al, V)Inexpensive.Poor activity.Nickel alloys (NiMo, NiAl)Inexpensive, Lower activity than precious metals, Molybdenum sulfides (MoS)Inexpensive, stablein acid, very active.Lower activity than precious metals,
scalereduction
0
“Electrochemicalreductionmetalelectrodes”
valuesareevolutionpotential
2CO2CO3COPeterson,Pederson,Rossmeisl,J.K.Nørskov,Energy&Environmental1315.
K.P.Kuhl,Cave,D.N.Abram,T.F.Jaramillo,EnergyEnvironmentalScienceVol.electroreductioncopper
SummaryIntroductionroleelectrocatalysisandrelatesenergyconversionElectrochemistryfundamentalscathodes,redoxchemistryEquilibriumpotentialsreactionenergeticsKineticsKeyequations:VolmerandTafelfiguresdeterminingelectrocatalystactivityMethodselectrocatalysisresearchelectrodeelectrochemicalrotatingelectrodeFiguresforelectrocatalystevaluationdevelopmentApplicationsexamples:scaleviewelectrocatalysishydrogenevolutionreactioncarbondioxidereductionreaction(COReferencesA.J.BardFaulkner,FundamentalsApplicationsWiley,J.O’M.Bockris&S.U.M.SurfaceElectrochemistry:LevelSpringer,Alyea,SystemsWiley,

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