DELIVERABLE REPORT 3-2... · 2018. 3. 27. · Critical Raw Material Elimination by a top-down Approach To hydrogen and Electricity generation Grant Agreement number 721065 CREATE

Critical Raw Material Elimination by a top-down Approach To hydrogen and Electricity generation Grant Agreement number 721065

CREATEDeliverableReportD.3.2

CRITICALRAWMATERIALSELIMINATIONBYATOP-DOWNAPPROACHTO

HYDROGENANDELECTRICITYGENERATIONGrantagreementno.:721065

Startdate:01.01.2017–Duration:42monthsProjectCoordinator:CNRS

DELIVERABLEREPORTDELIVERABLE3.2–SETOFCRM-FREEORRCATALYSTANDCRM-FREEORULTRALOW-PGMHORCATALYSTWITH

ACTIVITYVERIFIEDBYRDESENTTOWP5FORAEMFCTESTINGDueDate 30/12/2017(M12)

Author(s)FrédéricJaouen,DarioDekel,PietroGiovanniSantori,ElenaDavydova,TanjaKallio

WorkPackage WP3:Catalystsynthesisandcharacterization

WorkPackageLeader TanjaKallio(AALTO)

LeadBeneficiary CNRS

DatereleasedbyWPLeader 21/12/2017

DatereleasedbyCoordinator 22/12/2017

DISSEMINATIONLEVEL

PU Public X

PP Restrictedtootherprogrammeparticipants(includingtheCommissionServices)

RE Restrictedtoagroupspecifiedbytheconsortium(includingtheCommissionServices)

CO Confidential,onlyformembersoftheconsortium(includingtheCommissionServices)

NATUREOFTHEDELIVERABLE

R Report

P Prototype

D Demonstrator X

O Other



SUMMARY

Keywordsoxygen reduction reaction, hydrogen oxidation reaction, alkaline media,electrocatalyst,catalyst,criticalrawmaterial,platinumgroupmetal

FullAbstract(Confidential)

The report presents activity and stability data for selected electrocatalystsdeveloppedduringM1-M12inCREATEforhydrogenoxidationreaction(HOR)andoxygenreductionreaction(ORR)inalkalinemedium.ForORR,aFe-N-CcatalystpyrolyzedinArandthenNH3showshighactivity.Arestricted activity loss is observed after accelerated-stress-test ofelectrochemicalloadcyclinginrotatingdiskelectrode.TheORRcatalystreachesthe internal CREATE target of activity for Critical Raw Material (CRM)-freecatalystsandalsopassestheinternalstabilitycriterion.CompositesFe-N-C/Mn-oxideswerealsoexploredforimprovingperoxidescavengingproperties.ForHOR,twoCRM-freecatalystsweredevelopedandoneultralowcontentPt-catalyst.AsCRM-free,Nickelnanoparticlesonanitrogen-dopedcarbonsupport(Ni/N-CNT) andNickel-Iron nanoparticles on a carbon support (NiFe/C)weredevelopped. Their HOR activity was verified and, while comparable to thatreported for other CRM-free catalysts, is yet lower than the internal activitytarget of CREATE. The 8%Pt/SWNTHOR catalyst very closely approaches theinternalCREATEactivitytargetandpassesthestabilitycriterion.ApproachestoreducethecontentofPt(PGM)andto increasetheactivityofCRM-freecatalystswillbefurtherexploredwithhighthroughputmethodswhilethesynthesisparametersofCRM-freeORRcatalystswillbefurtherrefinedtoreachbeyondthestate-of-artactivities.

PublishableAbstract(Ifdifferentfromabove)

REVISIONSVersion Date Changedby Comments

1.0 20.11.2017 FrédéricJaouen(CNRS) Draftstructure

2.0 18.12.2017 ElenaDavydova(TECHNION) HORcatalysts

3.0 19.12Elena Davydova (TECHNION),FrédéricJaouen(CNRS),TaneliRajala(AALTO)

HORcatalysts

4.0 20.12 TanjaKallio(AALTO) HORcatalysts



SETOFCRM-FREEORRCATALYSTANDCRM-FREEORULTRALOW-PGMHORCATALYSTWITHACTIVITYVERIFIED

BYRDESENTTOWP5FORAEMFCTESTING

CONTENTSIntroduction.................................................................................................................................................4

1. ORRcatalyst.........................................................................................................................................5

1.1ExperimentalconditionsandprotocolforORRactivitymeasurement..............................................5

1.2ExperimentalconditionsandprotocolforORRstabilitymeasurement.............................................5

1.3SynthesisofORRCatalysts.................................................................................................................5

1.4ActivityandselectivityofORRCatalysts............................................................................................6

1.5ElectrochemicalstabilityofORRCatalysts.........................................................................................7

1.7ComparisontointernalCREATEtargets.............................................................................................8

2. HORcatalysts.....................................................................................................................................10

2.1ExperimentalconditionsandprotocolforHORactivitymeasurement...........................................10

2.2ExperimentalconditionsandprotocolforHORstabilitymeasurement..........................................11

2.3SynthesisofHORcatalysts...............................................................................................................11

2.3.1SynthesisofNi/N-CNT-hydrothermallytreated.......................................................................11

2.3.2SynthesisofNiFe/C–chemicallyreduced.................................................................................12

2.3.3SynthesisofPt/SWNTwithlowCRMcontent...........................................................................13

2.4ElectrochemicalActivityofHORCatalysts........................................................................................14

2.5ElectrochemicalstabilityofHORcatalysts.......................................................................................15

2.6ComparisontointernalCREATEtargets...........................................................................................16

References..................................................................................................................................................18



INTRODUCTIONThepurposeofD3.2istodemonstratethepreparationofafirstsetofCRM-freeandlow-CRMcatalystsdeveloppedinCREATEandwithsignificantactivityandstabilitytowardtheelectrodereactionsoccurringinanalkalinefuelcell,withactivityandstabilityverifiedinrotatingdiskelectrodes.

Inafuelcell,twoelectrochemicalreactionsoccur,namelythehydrogenoxidationreaction(HOR)ontheanodeandtheoxygenreductionreaction(ORR)onthecathode.Afirstsetofcatalystsforbothreactionsare demonstrated in the present deliverable, and those catalysts have been transferred to WP5 insufficientamountforsubsequenttestinginAEMFCdeviceswithreferencecommercialAEMmembranefromFUMATECH.

AlthoughtheultimatefocusoftheCREATEprojectisonthedevelopment,forAEMFCdevices,ofcriticalrawmaterial(CRM)freecatalysts(thelistofCRMsasdefinedbytheEUcanbeaccessedathttp://eur-lex.europa.eu/legal-content/EN/ALL/?uri=COM:2017:0490:FIN, both CRM-free and CRM-leanalternativesareconsideredinthisdeliverableforcatalyzingtheHORinalkalinemedium,asatrade-offbetweencostandperformance.This isnecessaryas thetargetedactivityperformancefor theHOR inalkalinemediumisnotyetachievedwithcatalyststhatareentirelyfreeofCRM.

Testprotocolsfortheelectrochemicalactivityanddurabilitymeasurementsaswellaspass/failcriteriaforcatalystintendedforeachreactionweredefinedinWP2(TechnicalSpecifications,CostAnalysis&LifeCycle)ofCREATE,andreportedinDeliverable2.1.Inthefollowing,thematerialperformanceisreflectedagainstthesecriteriaaswellasrelativetorecognizedstate-of-the-artelectrocatalystsfortheHORandORRinalkalineelectrolyte.



1. ORRCATALYST1.1EXPERIMENTALCONDITIONSANDPROTOCOLFORORRACTIVITYMEASUREMENT

TheelectrochemicalexperimentswereperformedwithaBiologicSP-300potentiostat.Athree-electrodecell configurationwas used for all experiments using 0.1M KOH as electrolyte solution, a reversiblehydrogenelectrodeasareferenceandagraphiteplateascounterelectrode.Asworkingelectrode,thecatalystinkwasdepositedinaglassycarbon.Thecatalyst-inkwaspreparedwith5mgofnon-PGMcatalystin54µLofionomer(Nafion,5%solutioninloweralcohols),744µLofethanoland92µLofultrapurewater.Theinkwasultrasonicatedonehourandtherequiredaliquotwasthendepositedwithapipetontheglassycarbon,sothatacatalystloadingof0.2mg·cm-2isreached.Oncetheelectrodewascompletelydry,adropofwaterwasdepositedonittominimisetheentrapmentofairbubblesduringtheimmersionoftheshaftandRDE-tipintheelectrolyte.N2wasbubbledintheelectrolytefor30minute,thenthecyclicvoltammograminN2-saturatedelectrolytewasrecordedbyscanningthepotentialat10mV·s-1between0.0and1.0Vvs.RHEforafewcycles,untilreproduciblescanswererecorded.TheelectrolytewasthensaturatedwithO2 for 30min, and thepolarizationmeasurements fromwhichORRactivity is directlyextractedwererecordedatalowscanrateof1mV·s-1inthepotentialrange0.0-1.1VvsRHE,andat1600rpmrotationrate.Itwasverifiedthatthescanrateof1mV·s-1islowenoughthatcapacitivecurrentcanbeneglectedfortheinvestigatedcatalysts.1.2EXPERIMENTALCONDITIONSANDPROTOCOLFORORRSTABILITYMEASUREMENT

Acceleratedstability tests (AST)wereperformedbycomparisonbetweenthe initialpolarizationcurve(followingtheproceduredescribedabove)andthepolarizationcurveobtainedwiththesameelectrodeafter5000potentialcyclesbetween0.6and1.0Vvs.RHE.The5000cycleswereappliedinN2-saturated0.1MKOHelectrolyte, ata scan rateof100mV·s-1 andwithoutany rotation (ASTprotocolNo.1, asdefinedinDeliverable2.1,"DefinitionofTestProtocols"oftheprojectCREATE).Forrecordingthefinalpolarisationcurve,afreshelectrolytewasused,andthesameconditionsasusedforrecordingtheinitialpolarisationcurvewereotherwiseapplied.1.3SYNTHESISOFORRCATALYSTS

CRM-freeFe-N-CcatalystTheFe-N-CcatalystwasobtainedstartingfromaZn-basedzeoliticimidazolateframework(ZIF-8,Basolite®Z1200,fromBASF),1,10-phenanthroline(phen)andironacetate.ThepowderprecursorsofZIF-8,phenand ferrous acetate were mixed with low energy ball milling, resulting in a homogeneous catalystprecursorcontaining0.5wt%Febeforepyrolysis.Thiscatalystprecursorwasthenpyrolyzedinargonat1050°Cfor1hour,thenpyrolyzedinNH3at950°Cfor5min.ItislabelledFe0.5-NC(Ar,NH3).CRM-freecompositeFe-N-C/Mn-oxideTofunctionalizeFe-N-Cwithaco-catalystthatcanscavengehydrogenperoxideduringAEMFCoperation,various Mn-oxides were screened for their ability to electro-reduce HO2

-. The Mn-oxide with bestcombinationofperoxidereductionactivityandstabilitywasselected,andthenphysicallymixedwithFe0.5-NC(Ar,NH3)inaratio20/80ratiotoprepareacompositeFe0.5-NC(Ar,NH3)/MnOx.



1.4ACTIVITYANDSELECTIVITYOFORRCATALYSTS

Thebeginning-of-lifeEvs.IpolarizationcurvesmeasuredinRRDEforthetwoabove-describedCRM-freeORRcatalystsareshowninFig.1,lowerpanel.Alsoshownisthepolarisationcurverecordedfora5%Pt/CcatalystfromJohnsonMatthey,comprisingPtnanoparticlessupportedoncarbonblack.TheactivityofbothCRM-freeORRcatalystsishigherthanthatof5%Pt/Candtheirselectivityiscomparablylow.Whilethevalueofthediffusion-limitedcurrentdensityatlowpotentialmaygiveafirstindicationastowhethertheORRmainlyproceedsviaa2or4electronpathway,all3catalystspresenthereavalueofdiffusion-limitedcurrentdensitythatisclosetothetheoreticalvalueexpectedfor4eORR.Togetamorepreciseinsightintoselectivity,RRDEmeasurementswerealsoperformed,andthe%peroxidemeasuredwiththistechniqueisreportedintheupperpanelofFig.1.Itconfirmsthehighselectivityofallthreecatalysts,andalsotheslightbeneficialroleplayedbyMnOxintheFe0.5-NC(Ar,NH3)/MnOxcomposite.Thelattershowslower%peroxide thanFe0.5-NC (Ar,NH3)atpotentialsbelow0.55Vvs.RHE,andalso lowerperoxidereleasethan5%Pt/C.

TheTafelrepresentationofthesamepolarizationcurvesbutaftercorrectionforO2diffusionimitationisshowninFig.2.TheTafelplotmorepreciselyshowtheloweractivityofthecompositerelativetothepureFe-N-Ccatalyst.WhiletheonsetforORRissimilar,theactivityorTafelslopeismodifiedforthecomposite,possiblyduetosomesurfacecoverageofFe-N-CbyMnOxparticles,decreasingtheaccessiblenumberofFe-basedactivesitesbyelectrolyteoraddingamass-transportbarriertothemostactiveORRsites.TheTafelslopesareca65mV/decadefor5%Pt/Cand57mV/decadeforFe0.5-NC(Ar,NH3)athighpotential.

0.0 0.2 0.4 0.6 0.8 1.0-6

-5

-4

-3

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-1

0

Cur

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den

sity

/ m

A cm

-2

5% Pt/C Fe0.5NC (Ar, NH3) Fe0.5NC (Ar, NH3)/MnOx

0

5

10

15

20

% H

O2-

Potential / V vs. RHE

Figure1:InitialORRpolarizationcurvesmeasuredwithRRDEat1600rpmforthetwoCRM-freeORRcatalystsandforareferencePt/Ccatalyst,measuredimmediatelyafterbreak-in.Scanrate1mV·s-1,0.1MKOH,room

temperature,catalystloading(massofallchemicalelements)200µgcm-2onglassycarbonRDEtip.IonomerbinderNafion.



0.01 0.1 1 100.80

0.85

0.90

0.95

Pote

ntia

l (V

vs R

HE)

Ikinetic (mA cm-2)

5wt % Pt/C Fe0.5NC (Ar, NH3)

Fe0.5NC (Ar, NH3)/MnOx

Figure2:TafelrepresentationoftheinitialORRpolarisationcurves,extractedfromthedatashowninFig.1.

1.5ELECTROCHEMICALSTABILITYOFORRCATALYSTS

TheresultsoftheelectrochemicalASTprotocolforORRthatwasdescribedin1.2areshowninFig.3.Thecurves showonlyminor changes,mostly related to changes in thediffusion-limited currentdensities,whichmayariseduetochangesinselectivityofthecatalysts.Thekineticcurrentdensityat0.9V(andabove)onlydecreasedslightly.TheinitialORRcurrentdensitiesachievedat0.9Vvs.RHEaresummarizedinTable1.

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0,01 0,1 10,90

0,95

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0,95

0,01 0,1 10,80

0,85

0,90

0,95

Before After

Fe0.5-NC (Ar, NH3) / MnOx

Potential (V vs RHE)

Cur

rent

Den

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/ m

A cm

-2

Before After

Cur

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/ m

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-2

Potential (V vs RHE)

Fe0.5-NC (Ar, NH3)

Pote

ntia

l / V

vs

RH

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Pote

ntia

l / V

vs

RH

E

Ik (mA cm-2)

0,0 0,2 0,4 0,6 0,8 1,0

-5

-4

-3

-2

-1

0

Ik (mA cm-2)

Figure3:StabilityofCRM-freeORRcatalysts.Lefthandside:Polarizationcurvesbefore(blackcurve)andafter(redcurve)5000cyclesintherange0.6-1.0VvsRHE.Righthandside:thecorrespondingTafelplotpresentations.



1.6COMPARISONTOINTERNALCREATETARGETSANDSTATE-OF-ARTCATALYSTS

Table1summarisestheinitialactivityat0.9Vvs.RHEofthetwoselectedCRM-freecatalystsdeveloppedinCREATEduringmonthsM1-M12andtheinternalpass/failactivitycriteriondefinedinD2.1fortransferintoAEMFC.BoththeseselectedCRM-freecatalystspasstheinitialactivitycriterion,howeveronlywithasmallmargin.Furtheroptimisationisongoingtoincreasetheactivity,whichcouldallowusdecreasingthecathodethicknessofAEMFCandtherebyimprovetheprospectsforhightransportofreactantsathighcurrentdensity.TheORRactivityofthesecatalystsiscomparableorhighertostateoftheartMetal-NCcatalysts.At0.9Von theTafelplots, thekinetic currentdensity is0.5-0.7mAcm-2, resulting inmassactivityof2.5-3.5A/g.ThismassactivityatpH13isveryclosetosomeofthebestreportedactivitiesofFeNCcatalystsat0.9V,e.g.7.5A/g[1],7.3A/g[2].Yamauchietal.reportedahighlyorderedmesoporousFe0.25-N-C catalyst, dodecahedral crystals englobed in particles. The systemwasobtainedby aqueoustreatmentfollowedbypyrolysisinN2andNH3showinghighactivityof1.42mAcm-2at0.9V(massactivityof7.1A/g).[3]Durabilitytestshowedalossof22.3mV,indicatingalowerstabilitythanforthepresentFeNCcatalyst.AtanassovetalreportedthreedifferentFe-N-Ccatalystsobtainedusingsacrificialsupportmethod.[4] Heat treatment at 975 °C for 45min in N2 first and then in NH3were applied. Differentprecursorswereused for the three catalysts,witha total amountof ̴1%wtof Fe. Thebest catalystshowedanactivityat0.9Vof1.41mAcm-2,whichmeansamassactivityof2.3A/g.Optimisation of CRM-free ORR catalysts is ongoing, focusing on pyrolysis duration, Fe content andbimetalliccatalyststofurtherimprovetheactivity.Table2summarisestheASTstabilityresult,reportedas"mVlostduring5000cycles",atafixedcurrentdensityonthepolarisationcurve.ForORR,thefixedcurrentdensitywaschosentobe-1mAcm-2(wherethecurve isalmostentirelycontrolledbyelectrokinetics).Table2showsthatbothCRM-freecatalystspassedthestabilitytest,althoughthecompositecatalystshowsmorelossthantheFe-basedonlycatalyst.This may be due to some Mn leaching from MnOx during the cycles. Longer stability tests will beperformed in the near future, as well as intermediate ORR-activity measurements. This will also becoupled to online detection ofmetal leaching (Fe orMn), and also post-AST determination ofmetalcontentleachedintheelectrolyte.Table1:CurrentdensityvaluesreportedatfixedpotentialforvariousFe-N-CcatalystsbeforeandafterASTNo.1.

CRM-freeORRCatalyst [email protected]/mA·cm-2

InternalpassactivitycriterionfortransfertoAEMFC(*)

Fe0.5-NC(Ar,NH3) 0.683 0.50

Fe0.5-NC(Ar,NH3)/MnOx 0.5105 0.50

(*)atacatalystloadingof200µg·cm-2orless,andwithaTafelslopeof60mV/decade.



Table2:Lossofcathodepotentialatfixedcurrentdensityof-1mAcm-2before/afterASTNo1(5000cyclesbetween0.6and1.0VvsRHE)

CRM-freeORRCatalyst Changeincathodepotentialbefore/afterASTNo1(readat1mA

cm-2ondiffusion-correctedpolarisationcurve

InternalpassstabilitycriterionfortransfertoAEMFC(*)

Fe0.5-NC(Ar,NH3) -4.5mV -40

Fe0.5-NC(Ar,NH3)/MnOx -17.1mV -40



2. HORCATALYSTS2.1EXPERIMENTALCONDITIONSANDPROTOCOLFORHORACTIVITYMEASUREMENT

Nickel-basedCRM-freecatalysts10mgoftheCRM-freeNickel-basedcatalystisultrasonicallysuspendedinamixtureof1.5mlisopropylalcohol,0.35mlmilli-Qwaterand0.15mlof1wt%Nafionsuspension(preparedbydilutinga10wt%commercial Nafion suspension in alcohol with the required aliquot of milli-Q water) for 1.5 h. Thecatalyst/Nafionweightratiois85/15.Analiquotof8µlofthesuspensionisappliedtoaglassy-carbonRDEtip(0.2cm2)anddriedinairatambienttemperature,resultinginacatalystloadingof200µg·cm-2.Beforeimmersingintotheelectrolyte(1MKOHat25°C),theworkingelectrodeisdippedintohotmilli-Qwater inordertohydrophylizethecatalytic layer.Theelectrochemicalmeasurementswerefulfilledaccordingtothefollowingprotocol.Hydrophylizedelectrodeisimmersedintotheelectrolytepre-purgedby H2 at the flow rate of 200-250mL/min. Open circuit potential is measured versus the referenceelectrode Hg/HgO/1 M KOH. The HOR polarization curves are registered by scanning the potentialbetween-0.925Vvs.Hg/HgOto-0.5Vvs.Hg/HgO(0to+0.4Vvs.RHE)atthescanrateof1mV·s-1androtationrateof1100rpm.ThemeasurementsarecompletedbyregisteringcyclicvoltammogramsintheelectrolytesaturatedwithN2,at thescanrateof20mV·s-1 inorder toestimatetheelectrochemicallyactivesurfaceareaofmetallicnickel.Low-PtcatalystRotatingdiskelectrode(RDE)experimentsforHORcatalystswereperformedin0.1MKOHat25°C,usingcarbonascounterelectrodeandRHEasthereference.Catalystwasdepositedonaglassycarbondiskof5mmdiameter, constituting theworking electrode. Ink for thedepositionwaspreparedby carefullydispersingcatalystpowderinsolventsothatpipettingtheinkontheworkingelectroderesultsinacatalystloadingof200μg·cm-2followedbyadditionof5μlofdilutedNafionionomersolution(50μlof5wt-%Nafionin2mlofethanol).Beforemeasuringtheactivity,abreak-inprocedurewas implemented.Thedriedcatalyst layerontheglassy carbonwas first contactedwith d-water, either by dropping hot deionized-water on topor byimmersingthecatalyzedRDEtipinavialwithhotmilli-Qwater(50-60°C).TheRDEwasthenscrewedontherotatingshaftandimmersedintheelectrolyte.Nitrogenwasbubbledintheelectrolytefor15-30min,afterwhichitwasdirectedabovetheelectrolyte,cyclingthepotentialbetween0.0and0.4Vvs.RHEat50-100mV·s-1untilCVswerereproducible.Fortheactivitymeasurement,theelectrolytewassaturatedwithH2forabout30minuntilOCPstabilized.Polarizationcurvesweremeasuredat1-2mV·s-1startingfromOCPto0.4Vvs.RHEandbackto0.0Vvs.RHE(onlyonecycleifpositiveandnegativegoingscanssuperimposed,twoormoreotherwise)at1600rpmrotation.



2.2EXPERIMENTALCONDITIONSANDPROTOCOLFORHORSTABILITYMEASUREMENT

Thestabilityofthecatalystmaterialwasevaluatedusinganacceleratedstresstests(AST)definedinWP2(TechnicalSpecifications,CostAnalysis&LifeCycle)ofCREATE,andreportedinDeliverable2.1.ForthepresentHORmaterialsforalkalinemedium,ASTNo.4wasapplied,andisdepictedbelow.TheelectrodewasnotrotatedduringtheAST,toavoidparticledetachmentafterprolongedrotation.Thecatalystpassesthestability test if thepotentialshiftduetothecyclingwasnomorethan+40mVatagivencurrentdensity.

Table3:DefinitionoftheASTforHORcatalysts(ASTNo.4).

Electrolyte Signalshape

Number ofcycles

lower / upperpotentiallimits

Scanrate(LSV)

AST4 N2-satd0.1MKOH LSV 5000 0.0/+0.4VvsRHE 100mVs-1

2.3SYNTHESISOFHORCATALYSTS

2.3.1SYNTHESISOFNI/N-CNT-HYDROTHERMALLYTREATED

AhydrothermalmethodwasusedtosynthesizeNi/N-CNTcatalyst.Oxidizedmultiwallcarbonnanotubes(MWCNT)areusedasthecarbonsupport.MWCNTarestirredinconcentratedH2SO4for24h.KMnO4isaddedslowlytothesuspensionofCNTwhilestirring,andthemixtureiskeptunder70°Cfor1h.Theoxidation iscompletedbyslowlyaddingofconcentratedH2O2.Theoxidizedcarbonmaterial,CNTox, isseparatedbyrepetitivecentrifuging,twice in5%HClsolutionandthen inmilli-Qwater,beforedryingovernight inavacuumovenat90−110°C.TheoxidizedCNT is suspended inof isopropylalcohol.ThechemicalreductionofNiCl2byNaBH4issimilartothechemicalreductionmethod,describedbelow.TheresultantsuspensionofNi/CNToxplacedintheTeflonreactorofautoclavewiththeadditionofN2H4×H2OsolutionandNH4OH25%solution.Themixtureisheatedupto150°Candkeptfor3hunderthepressureof8−10atm.Thecatalystisseparatedbyrepetitivecentrifugingisdriedovernightat80−90°Cinavacuumoven.Figure4presentstheSEMimageofthepristineMWCNT(A)andoxidizedMWCNT(B).ThefigureclearlyshowsthatthemorphologyoftheMWCNTismodifiedaftertheoxidationtreatment.Figure5showsSEMimagesofhydrothermallytreatedNi/N-CNTcatalyst,withNiparticlesdiameterof20−30nm.TheXRDshowsthemainpeaksofmetallicNickel,withcrystalsizeestimatedat4.4-6.3nmfromScherrerequation.TheelementalcompositionbyXPSis20.8at%Ni,44at%C,3.4at%Oand1.6at%N.



Figure4:SEMimagesof(A)pristineMWCNTand(B)oxidizedMWCNT.Magnification100K.200nmscalebar.

Figure5:SEMimagesofNi/N-CNTcatalyst.Magnification100Kand400K(insert).200nmscalebarand(insert)

100nmscalebar.

2.3.2SYNTHESISOFNIFE/C–CHEMICALLYREDUCED

A chemical reduction method was used to synthesize NiFe/C catalyst. Carbon black VXCMAX22 wasultrasonicallysuspendedinisopropylalcohol.ThesolutionsofNiCl2×6H2OandFeCl2×4H2Oinmilli-QH2Oeachareaddedtothecarbonsuspensionandultrasonicallydispersed.TheresultantsuspensionandthesolutionofNaBH4 in0.1MKOHarecooleddown inan icebath.Thereductionofmetalprecursors iscarriedoutinanair-freethree-neckflask,placedintheice-bath,addingcoldsolutionofNaBH4drop-wise.Themixtureiskeptfor2hbeforerepetitivecentrifuginginmilli-Qwater.Theprecipitateisdriedovernightat80−90°Cinavacuumoven.Figure6showsSEMimagesofNiFe/C.TheelementalcompositionbyXPSis2.8at%Ni,0.31at%Fe,82.5at%Cand11.8at%O.



Figure6:SEMimageof(A)NiFe/Ccatalystand(B)EsBdetectedimagefromthesamearea.Magnification100K.

200nmscalebar(5nmscalebarforinsert).LightpixelsinEsBimage(B)arerelatedtoametallicphase.

2.3.3SYNTHESISOFPT/SWNTWITHLOWCRMCONTENT

HORcatalystswithanultralowamountofPtonsingle-wallcarbonnanotubes(SWNTs)werepreparedbyatomic layerdeposition (ALD).Thepulse lengthsof thePtandoxidizerprecursorswerevaried,whichexpectedlyresultedinimprovedelectrochemicalactivityforlongerpulses.Figure7displaysthesizeanddistributionofPtparticlesontheSWNTsproducedbytheabove-mentionedmethods.TheweightcontentofPtinPt/SWNTwasdeterminedbyICP-MS(JULICHpartner)tobe8wt%.

Figure7:TEMimagesofthe8wt%Pt/SWNTcatalyst.ParticlesmarkedwitharedcrosshavebeenanalysedbyEDS.FeparticlesareremnantsofthecatalystusedfortheSWNTgrowth.



2.4ELECTROCHEMICALACTIVITYOFHORCATALYSTS

Nickel-basedCRM-freecatalystsFigure8AshowsthecyclicvoltammogramsrecordedinN2-saturated1MKOHforNi/N-CNTwhileFigure8BshowstheHORpolarisationcurverecordedinH2-saturated1MKOHatlowscanrate.Figure9Aand9BshowthesametypeofresultsbutfortheNiFe/Ccatalyst.Theelectrochemicallyestimatedsurfaceofmetallicnickelisaboutthreetimeshigherforthelattercatalyst.However,itsHORactivityisslightlylowerthanthatofNi/N-CNT.TheHORpolarizationcurvesshowan increase incurrentdensitywith increasepotential up to ca +0.15V vs. RHE, then a decreasing currentwith further increase potential. This isassignedtoincreasedsurfacecoveragebynickelhydroxide,decreasingtheelectrochemicalactivesurfacearea for HOR on theNi-based catalysts. The diffusion-limited current density for HOR thatwould beexpectedat1100rpm(ca2mAcm-2)isneverreached.

Figure8:Cyclicvoltammogram(A)andHORpolarizationcurve(B)forNi/N-CNTcatalyst.200µg·cm-2catalyst

loading,rotationrate1100rpm.Thenumbersindicatetheelectrochemicallyestimatedareaofmetallicnickelandthepotentialatwhichthepeakcurrentdensityisobserved.Nafionionomerusedasabinder.

Figure9:Cyclicvoltammogram(A)andHORpolarizationcurve(B)forNiFe/Ccatalyst.200µg·cm-2catalystloading,rotation rate 1100 rpm. The numbers indicate the electrochemically estimated area ofmetallic nickel and thepotential(inVvsHg/HgO)atwhichthepeakcurrentdensityisobserved.Nafionionomerusedasabinder.



Ultralow-PtcatalystFigure10showstheinitialHORpolarisationcurvefor8%Pt/SWNT.Thecurve(a)showsalinearbehaviournear the thermodynamic potential for H2O/H2 (kinetically controlled region), then increases withincreasingpotentialuptothediffusion-limitedcurrentexpected.Curve(b)isthediffusion-correctedcurveextracted from curve (a) with the Koutecky-Levich equation (assuming the HOR reaction rate isproportionaltotheH2concentration).WithrespecttothePtmassloading,exchangecurrentdensityof0.058A/mgPtwasobtainedafterKoutecký−LevichandTafelanalyses.Thedifferencewithliteraturevalueof0.35A/mgPtonPt/C[5]canbediminishedbyfurtherdevelopingthesynthesis.PtRubimetalliccatalystonSWNTwillalsobepreparedbyALD inthenear future,basedontheknownhigherHORactivity inalkalinemediumofPtRuvs.Pt.

0.0 0.1 0.2 0.3 0.40.0

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(c)

(b)

Cur

rent

den

sity

/ mA

cm-2

Potential / V vs. RHE

(a)

Figure10:HORpolarizationcurvefor8%Pt/SWNTcatalyst(a).200µg·cm-2catalystloading(16µgPtcm-2),

rotationrate1600rpm.Thecurve(b)representsthecurve(a)aftercorrectionforH2-diffusionlimitationwiththeKoutecky-Levichequationand(c)representsthetheoreticalcurveexpectedforinfinitelyfastreactionwith

concentrationoverpotentialonly.

2.5ELECTROCHEMICALSTABILITYOFHORCATALYSTS

ThestabilitytestresultforthePt/SWNTHORcatalystspreparedintheframeofCREATEisshowninFig.11.TheinitialactivityisclosetobutslightlylowerthanforthePt/SWNTelectrodeinsection2.4,howeverthe activity after ASTNo 4 is higher than before theAST, demonstrating the stability of 8%Pt/SWNTpreparedbyALDtotheASTNo4.ThestabilitywasexpectedunderthosecyclingconditionsforsuchacatalystbasedonPt.



Figure11:HORpolarizationcurvesbeforeandafterthestabilitytest(ASTNo.4)in0.1MKOH,scanrate2mV/s,

rotationrate1600rpm.

2.6COMPARISONTOINTERNALCREATETARGETS

Table4summarizestheHORkineticcurrentdensitiesat0.05Vvs.RHE.Kineticcurrentdensitiesatthatpotentialwere0.10,0.11and1.88mA·cm-2forNiFe/C,Ni/N-CNTandPt/SWNT.Inotherwords,atthismoment,onlyPt/SWNTapproachescloselytheHORactivitycriteriondefinedforHORcatalystsinCREATEDeliverable 2.1 (2.2mA·cm-2 at 0.05V for catalyst loadingof 200µg·cm-2 or less). As theperformanceachievedwiththeseCRMfreeNiFe/CandNi/N-CNTdonotmeettheCREATEtargets,innearfutureNibased bimetallic catalyst with different compositions will be screened. Furthermore, to achieve theCREATEtargetsforHORcatalysts,asaparallelapproachultra-low-CRMcatalystswithPdbasedbi-andtrimetallicaswellasPtbasedbimetalliccompoundsareinvestigated.Table4:SummaryofNickelsurfaceandelectrochemicalpropertiesofPt/SWNT,Ni/N-CNTandNiFe/Ccatalysts.

Catalyst Specificsurfaceareaofnickelorplatinum,

m2/gNickel

i(atη=0.05V)(*)/mAcm-2

NiFe/C 0.68m2/gNickel 0.10

Ni/CNT-N 2.18m2/gNickel 0.11

Pt/SWNT NM 1.88(*)

InternalCREATEpasscriterionofHORactivityfortransfertoAEMFC(atloadingof200

µg·cm-2orless)

-- 2.20(*)

(*)correctedforOhmicdropandH2diffusionlimitation



Table5summarisesthestabilityofPt/SWNTafterASTNo4(anactivityimprovementisinfactobserved),and thestatus relative to thepass/fail targetof stability for transfer toAEMFC.The table shows thatPt/SWNTpassestheHORstabilitycriteriondefinedinDeliverable2.1(maximumacceptablechangeinoverpotentialof+40mVafterASTNo.4).

Table5:SummaryofPt/SWNTstabilityafterASTNo4(5000cyclesbetween0and0.4VvsRHEat100mV/s)

Catalyst Max.shiftinpotentialat0.5mA/cm2afterASTNo4

Pass/failcriterion

8%Pt/SWNT −7.5mV ≤+40mV



REFERENCES

[1] Mengetal,pH-effectonoxygenreductionactivityofFe-basedelectro-catalysts,Electrochem.Commun.11(2009)1986-1989

[2] Kim et al, The role of pre-defined microporosity in catalytic site formation for the oxygen

reduction reaction in iron-andnitrogen-dopedcarbonmaterials, J.Mater.Chem.A,5 (2017)4199-4206

[3] Tan H. et al,Perfectly orderedmesoporous iron-nitrogen doped carbon as highly e ffi cient

catalystforoxygenreductionreactioninbothalkalineandacidicelectrolytes,NanoEnergy36(2017)286-294

[4] HossenM.etal,SynthesisandcharacterizationofhighperformingFe-N-Ccatalystforoxygen

reductionreaction(ORR)inAlkalineExchangeMembraneFuelCells,J.PowerSources375(2018)214-221

[5] Sheng,W. et al.,Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid Vs

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DELIVERABLE REPORT 3-2... · 2018. 3. 27. · Critical Raw Material Elimination by a top-down Approach To hydrogen and Electricity generation Grant Agreement number 721065 CREATE