Carbothermal shock synthesis of high-entropy-alloy nanoparticles

123 Pages·2017·11.8 MB·English

RESEARCH
NANOMATERIALS elementalcombinations(1,12,13).Intermsofbulk
materialsynthesis,meltprocessingisascalable
method that has led to the creation of high-
Carbothermal shock synthesis of
entropyalloys(HEAs)consistingoffiveormore
elementsinasolidsolution(uniformmixing),
high-entropy-alloy nanoparticles whichhaveshowngreatpotentialasstructural
materials(14–18).Todate,onlyalimitedfam-
ilyofHEAshavebeenachieved,duetothedif-
YonggangYao,1*ZhennanHuang,2*PengfeiXie,3*StevenD.Lacey,1*RohitJijiJacob,4 ficultyofmixingelementswithvastlydifferent
HuaXie,1FengjuanChen,1AnminNie,2TianchengPu,3MilesRehwoldt,4DaiweiYu,5 chemicalandphysicalproperties,aswellascool-
MichaelR.Zachariah,4ChaoWang,3†RezaShahbazian-Yassar,2† ingrateconstraints.Moreover,downsizingHEAs
JuLi,5†LiangbingHu1† tothenanoscaleisadauntingtask,especiallyby
conventional alloying methods. Therefore, the
Thecontrollableincorporationofmultipleimmiscibleelementsintoasinglenanoparticle development of a synthesis method where ele-
meritsuntoldscientificandtechnologicalpotential,yetremainsachallengeusing mentalcomposition,particlesize,andphasecan
conventionalsynthetictechniques.Wepresentageneralrouteforalloyinguptoeight bepreciselycontrolledcouldbringaboutanew
dissimilarelementsintosingle-phasesolid-solutionnanoparticles,referredtoas repertoireofalloysandnanostructureswithun-
high-entropy-alloynanoparticles(HEA-NPs),bythermallyshockingprecursormetalsalt precedentedfunctionalities.
mixturesloadedontocarbonsupports[temperature~2000kelvin(K),55-millisecond Wedevelopedafacile,two-stepcarbothermal
duration,rateof~105Kpersecond].Wesynthesizedawiderangeofmulticomponent shock(CTS)methodthatemploysflashheating
nanoparticleswithadesiredchemistry(composition),size,andphase(solidsolution, andcooling(temperatureof~2000K,shockdu-
phase-separated)bycontrollingthecarbothermalshock(CTS)parameters(substrate, rationof~55ms,andrampratesontheorderof Do
temperature,shockduration,andheating/coolingrate).Toproveutility,wesynthesized 105K/s)ofmetalprecursorsonoxygenatedcar- wn
quinaryHEA-NPsasammoniaoxidationcatalystswith~100%conversionand>99% bonsupporttoproducehigh-entropy-alloynano- lo
a
nitrogenoxideselectivityoverprolongedoperations. particles(HEA-NPs)withuptoeightdissimilar de
metallic elements (table S1). MMNPs synthe- d
M sizedbyCTShaveanarrowsizedistributionand fro
m
ultimetallicnanoparticles(MMNPs)are andphasescanbeattained(3,4,7,10).However, areuniformlydispersedacrossthecarbonsupport, h
ofinterestinawiderangeofapplications, moststudiesviawet-chemicalmethodsreport despitebeingexposedtohightemperaturesthat ttp
includingcatalysis(1–7),energystorage alloycompositionsnotexceedingthreeelements, conventionally cause particle coarsening. The ://s
(8),andbio/plasmonicimaging(8,9). whichlimitsthecompositionalspace.Addition- hightemperature,inconjunctionwiththecat- cie
Alloyingmultiplemetallicelementsinto ally,moresite-specificsynthesistechniques,in- alyticactivitiesoftheliquidmetals,drivesrapid nc
individualnanoscaleproductsoffersthepromise cludingprinting-andlithography-basedmethods particle“fission”and“fusion”eventsthatresult e.s
ofmaterialpropertiesthatcouldexceedsingle- (1,11,12),haveshiftedthecompositionalspace inuniformmixturesofmultipleelements.Sub- cie
element(orunary)nanoparticles(2,5,6).The towardquaternaryandevenquinarynanostruc- sequently,therapidcoolingratefacilitateski- nc
e
currentandprimaryapproachestowardtheprep- tures;however,thesubsequentreductionproce- neticcontroloverthethermodynamicmixing m
arationofMMNPsarisefromwet-chemistrysyn- durestendtolimitthestructuralcomplexityto regimesandenablestheformationofcrystal- ag
thesis,whereavarietyofparticlesizes,shapes, phase-separatedMMNPs,especiallyforimmiscible linesolid-solutionnanoparticles,analogousto .org
o /
n
Fig.1.CTSsynthesisofHEA-NPson M
a
carbonsupports.(A)Microscopyimagesof rc
h
microsizedprecursorsaltparticlesonthe 3
carbonnanofiber(CNF)supportbefore 1, 2
thermalshock,aswellasthesynthesized, 0
1
well-dispersed(PtNi)nanoparticlesafter 8
CTS.(B)Samplepreparationandthe
temporalevolutionoftemperature
duringthe55-msthermalshock.
(C)Low-magnificationandsingle-particle
elementalmaps,anHAADFimage,and
correspondingatomicmapsforabinary
PtNialloy.(D)Elementalmapsofan
HEA-NPcomposedofeightdissimilar
elements(Pt,Pd,Ni,Co,Fe,Au,Cu,andSn).
Scalebar,10nm.
Yaoetal.,Science359,1489–1494(2018) 30March2018 1of6
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Fig.2.ElementalcharacterizationofHEA-NPs.(A)Schematiccomparison PtPdCoNiFe),senary(PtCoNiFeCuAu),andseptenary(PtPdCoNiFeCuAu). rc
h
ofphase-separatedheterostructuressynthesizedbyaconventionalslow Scalebar,10nm.(D)Individualandlow-magnificationelementalmaps 3
reductionprocedure(slowkinetics)versussolid-solutionHEA-NPssynthesized (left)andahigh-resolutionHAADF-STEMimagewithfastFourier 1, 2
bytheCTSmethod(fastkinetics).(B)STEMelementalmapsofunary transformanalysis(right)ofoctonary(PtPdCoNiFeCuAuSn)HEA-NPs, 0
1
(Pt,Au,andFe),binary(PtNi,AuCu,andFeNi),andternary(PtPdNi, showingsolidsolutionswithanfccstructure.Thelow-magnification 8
AuCuSn,andFeCoNi)nanoalloys.Scalebar,5nm.(C)HAADFimages elementalmapsverifythestructuralandcompositionaluniformityofthe
andSTEMelementalmapsofHEA-NPs:quinary(PtFeCoNiCuand HEA-NPs.Scalebar,10nm.
martensiticsteelsandmetallicglassesthatare vast space for synthesizing alloys and nano- (e.g.,PtNi)thatformacrossthecarbonsurface
alsokineticallytrapped(19,20).Byadjustingthe crystals,whichhaspotentialforawiderangeof (Fig.1Aandfigs.S1toS4).Theelectricalpulse
inputelectricalpulseparameters,wecanalsopro- applications. thatweappliedcontrolsthethermalexposure
ducephase-separatednanoparticlesbydecreasing conditions(Fig.1B),withacommontempera-
the cooling rate. This CTS technique opens a Results tureof~2000Kandheating/coolingratesupto
TheCTSmethodweusedtosynthesizeuniformly ~105K/sasmeasuredwithapyrometer(figs.S5
1DepartmentofMaterialsScienceandEngineering,University dispersed,solid-solutionnanoparticles(uptoeight toS7).Wefoundnoapparentelementalsegrega-
ofMaryland,CollegePark,MD20742,USA.2Departmentof elements)requirestwosteps(21).First,wemixed tionorphaseseparationforthePtNinanoparticles
MechanicalandIndustrialEngineering,UniversityofIllinoisat
Chicago(UIC),Chicago,IL60607,USA.3Departmentof metalsaltprecursorsMClxHy(MisPt,Pd,Ni,Fe, (Fig.1Candfig.S4)usingscanningtransmission
ChemicalandBiomolecularEngineering,JohnsHopkins Co,Au,Cu,orSn,amongothers)intoasolution electronmicroscopy(STEM)elementalmaps.The
University,Baltimore,MD21218,USA.4DepartmentofChemical andloadedontoaconductivecarbonsupport, high-angleannulardark-field(HAADF)images
andBiomolecularEngineeringandChemistryandBiochemistry, suchascarbonnanofibers(CNFs).CNFscarbon- andatomicmapsalsodemonstratedbothuniform
UniversityofMaryland,CollegePark,MD20742,USA.
5DepartmentofNuclearScienceandEngineering,Department izedat1073K(CNF-1073K,denotedasCNFhere- atomicscalemixingandtheformationofaface-
ofMaterialsScienceandEngineering,andDepartmentof after)arethesubstratesusedinthisworkunless centeredcubic(fcc)crystallinestructure(Fig.1C).
ElectricalEngineeringandComputerScience,Massachusetts statedotherwise.Afterdrying,weexposedthe Ourgeneralmethodextendstomorecomplex
InstituteofTechnology,Cambridge,MA02139,USA. precursor-loaded sample to a rapid thermal HEA-NPs.Forexample,wereadilyfabricated
*Theseauthorscontributedequallytothiswork.
†Correspondingauthor.Email:[email protected](L.H.);rsyassar@ shock(55ms)inanAr-filledglovebox,which HEA-NPscomposedofeightdissimilarelements
uic.edu(R.S.-Y.);[email protected](J.L.);[email protected](C.W.) leadstoahighconcentrationofnanoparticles (Pt,Pd,Ni,Co,Fe,Au,Cu,andSn).Theseelements
Yaoetal.,Science359,1489–1494(2018) 30March2018 2of6
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carbonsupport(Fig.2,CandD,andfigs.S10to
S16).Moreover,theHEA-NPsareofnanoscale
dimensionsinfcccrystalstructures(Fig.2Dand
figs.S17andS18).
TheHEA-NPsexhibitedsolidsolutionmixing
viathesame55-msthermalshockprotocol(figs.
S19andS21).Weconfirmedthestructuraluni-
formity(nophaseseparation)andnegligiblechlo-
rinecontentwithSTEM(figs.S22toS26),x-ray
diffraction(XRD)(figs.S27toS29),andx-ray
photoelectronspectroscopy(XPS)(figs.S30to
S36).Astatisticalstudyconductedoverdifferent
sampleregionsconfirmsthecompositionaluni-
formityamongthesynthesizednanoparticles
(figs.S37toS43).Forexample,thecompositional
variationforeachelementinourquinaryHEA-
NPs(PtPdCoNiFe)is~10%,whichissmallerthan
the>50%variationreportedforlithography-
basedtechniques(fig.S42)(1).Additionally,the
macroscopiccompositionsthatwedetermined
byinductivelycoupledplasmamassspectros-
copy(ICP-MS)agreewellwiththeSTEM-derived D
o
statistics.TheHEA-NPcompositionhasasmall w
n
deviationfromtheidealcompositionbasedon lo
a
theinitialprecursorsaltmolarratios,dueto d
e
vaporlossathightemperature(figs.S44toS46 d
and table S3). To demonstrate compositional fro
m
control,weemployedthe(precursor)compen- h
sationapproach,whichisacommonstrategy ttp
inhigh-temperaturesynthesiswhenvolatileele- ://s
mentsareinvolved(figs.S47toS52). cie
TheHEA-NPsdeviatefromthephase-separated nc
e
thermodynamicequilibriumstructuresreported .s
inliterature(1,3,12)duetotherapidquench- cie
inducednucleation/growthprocessoftheCTS nc
method,which“freezes”theliquidalloystateto em
createsolid-solutionnanoparticles.Thesynthe- ag
Fig.3.ParticledispersionmechanismfortheCTSprocess.(A)SEMimagesofsynthesizedAuNi sizedHEA-NPsarestableatroomtemperature .org
nanoparticlesonCNFscarbonizedatdifferenttemperatures:873,1073,and1273K.Ahigher andremainedunchangedintermsofsize,struc- o /
carbonizationtemperatureleadstohighercrystallinityandlowerdefectconcentrationswithinthe ture,andcompositionafter11monthsofstorage n M
carbonsupport,whichaffectsparticlesizeanddispersion.(B)SEMimagesofCu,Au,andPtparticle understandardconditions. a
distributionssynthesizedonidenticalCNFsupportsviathesameCTSprocess.Thehighercatalytic Inadditiontotherichchemistries,themor- rch
activitiesofthemetalspecies(AuandPt)leadtosmallernanoparticlesandmoreuniformdistributions. phologiesofthesynthesizednanoparticlesindi- 31
(C)Anillustrationofthecatalysis-drivenparticlefission/fusionmechanismtosynthesizeuniformly cateaformationmechanismforCTSthatdiffers , 2
dispersedHEA-NPs.(D)HAADFimageandelementalmapsofultrafineandwell-dispersedquinary fromotheralloyingapproaches.Because~2000K 01
8
HEA-NPs(PtPdIrRhRu)onCO -activatedCNFs.Anarrowsizedistributionisachievedbyincreasing farexceedsthethermaldecompositiontempera-
2
thesupport’ssurfacedefectconcentrationthroughCO activation,aswellasemployingmetal tureofmetalprecursors(tableS1),thesaltseasily
2
specieswithhighcatalyticactivities. decompose:
MClxHy→M(liq)+gases↑ (1)
havearangeofatomicradii(1.24 to1.44Å), versatility by synthesizing a series of multi-
reductionpotentials(–0.25to1.5Vversusthe elementnanoparticlesandcharacterizedthem However,~2000Kisbelowtheboilingpoints
standardhydrogenelectrode),preferredcrystal bySTEM,transmissionEM(TEM),scanning ofthemetallicelements.Inthiscase,themetal-
structures(fcc,body-centeredcubic,hexagonal EM (SEM), and energy-dispersive x-ray spec- licelementsarelikelyintheliquidphaseand
close-packed,ortetragonal),andmeltingtem- troscopy(EDS).Wesynthesizedunary(Pt,Au, shouldbeonasimilarlengthscaleastheinitial
peratures(500to2000K)thattypicallyprevents and Fe), binary (PtNi, AuCu, and FeNi), and (microsized) salt precursors. Since metals are
solid-solutionformation(Fig.1DandtableS2). ternary(PtPdNi,AuCuSn,andFeCoNi)nano- nonwettingwithcarbon,theliquidmetalsshould
MMNPs have been previously synthesized particlesthatexhibitcompositionaluniformity coarsentominimizetheirsurfaceenergyathigh
usingconventionalreductionprocedures(1,3). (Fig.2B).Thenanoparticlesalsopossesssize temperature(22).Ourobservationdepartsfrom
However,thesesyntheticmethodstendtocreate uniformity,withdiametersof≥5nm(fig.S9), thisbehavior,requiringamechanismtoexplain
phase-separated heterostructures among im- regardlessoftheelementalcompositions.By howinitiallysingle-element,micron-sizedliquid
miscibleelements,whichgreatlyreducesthe addingadditionalmetalsaltstotheprecursor metaldropletsformuniformlydispersedalloy
configurational entropy of mixing (fig. S8). solutions,wesynthesizedquinary(PtCoNiFeCu nanoparticles.
TheCTSprocessleadstosolidsolutionMMNPs andPtPdCoNiFe),senary(PtCoNiFeCuAu), Weperformedtwocontrolexperimentstoex-
(i.e.,HEA-NPs),wherearbitrarymetallicelements septenary(PtPdCoNiFeCuAu)andoctonary ploreHEA-NPformation.Wefounddistinctpar-
are completely mixed to maximize the mixing (PtPdCoNiFeCuAuSn)HEA-NPs,whicharesol- ticlemorphologydifferencesusingthesameCTS
entropy(DS )(Fig.2A).Wedemonstratedthe idsolutionsandevenlydispersedacrossthe protocol(Fig.3Aandfigs.S53andS54),butwith
mix
Yaoetal.,Science359,1489–1494(2018) 30March2018 3of6
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supportsdifferingincarbonizationtemperature.
Specifically,electrospunpolyacrylonitrilefibers
carbonizedinargonatarangeoftemperatures
(873,1073,and1273K)generatedCNFsupports
withvariousdefectconcentrations.Lowercar-
bonizationtemperaturesresultedinsmaller,
moreuniformparticledispersions.Eachpyrol-
ysistemperaturewasinsufficienttodriveaway
allsurface-boundoxygen(O*)andthusresulted
inanincreasingamountofO*residualsremain-
ingonCNFscarbonizedatlowertemperatures
(fig.S2).Therefore,wesurmisedthatthesurface
defectconcentrationofthecarbonsupportisan
importantparameterforparticledispersion.Our
secondcontrolexperimentusedidenticalCNF
supports(CNF-1073K)andsynthesisconditions
(55ms,~2000K),butwithavarietyofsingle-
metalsaltprecursors(Fig.3Bandfigs.S55toS57).
Nanoparticlesizedistributionchangesinthis
casewithCuhavingamuchlargerparticlesize
(~56.8nm)thanAu(~13.5nm)andPt(~6.3nm).
Thistrendresemblesthecatalyticactivitiesofthe D
o
correspondingelements,withPtandCubeing w
n
themostandleastactive,respectively.Because lo
a
AuandCupossesssimilarphysicalproperties d
e
(tableS4),thediscrepancyrequiresadifferent d
particledispersionmechanismthanasimple, fro
m
physicalmelting-and-nucleationprocess. h
Sincedefectsandmetalcatalystsplayakey ttp
roleduringtheCTSprocess,weconsidereda ://s
catalyticallydrivenparticledispersionmecha- cie
nismforthedefectivecarbonsupports.Toverify nc
e
this,weusedinsitumassspectrometrytoanalyze .s
thegasescreatedduringCTSfordefectiveCNF cie
supportswithandwithoutprecursorsalts.Com- nc
e
paredwithbareCNF,theprecursor-loadedCNF m
exhibitedalargerandmuchsharperreleaseof ag
COgasduringtheCTSprocess(fig.S58).Thus, Fig.4.Kineticcontrolovernanoparticleformation.(A)TEMimagesdisplayingtheparticlesize .org
tfrhoemrealecaasetaolyftCicOalglyasduripvoenntchaerrbmoanlmsheotcakboarliissmes a(Bn)dPdaisrptiecrlesitsyizaetdviastrrioibuustitohneromfaPltNshioncaknodpuararttiicolness(o5nmCsN,F5s5.(mCsa,n1ds,Da)nCdo1o0linsg).rSactael–edbeapresn,d1e0n0tnm. on /
M
reaction: AuNinanostructuresdeterminedbyelementalmaps,HAADF,andABFimages.Ultrafastcooling a
rates(~105K/s)enabletheformationofsolid-solutionnanoparticles,whereasslowerrates(~10K/s) rc
h
C+O*→CO↑ (2) tendtoinducephaseseparation.Scalebar,10nm.(E)Time-temperature-transformation(TTT) 3
1
diagramshowingthekineticformationofmetallicglass,HEA,andphase-separatedstructures, , 2
whereO*denotessurface-boundresidualoxy- respectively,asafunctionofcoolingrate. 01
8
gen.ThecarbonmetabolismreactioninvolvesC
(fuel),O*(oxidizer),andmetal(catalyst),which depletedO*concentrationsshouldleadtode- ultrafineparticlesizesandnarrowdistributions
correlatesthesurfacedefectconcentration(e.g., creasedmobilityandthelocalizationofliquid whenmorecatalyticallyactivemetalcombina-
carbonizationtemperature)andthemetal’scat- droplets that coarsen slowly to reduce their tions(PtPdIrRhRuHEA-NPs,3.28±0.81nm)
alyticactivitytothefinalnanoparticlesizeand totalsurfaceenergy.Theliquidalloyshaveawide are employed on identical CO-activated CNF
2
levelofdispersity.Wehypothesizethatduring solubilityrangeat~2000K.Therefore,theliquid supports (Fig. 3D and figs. S61 and S62).
the55-mshigh-temperatureexposure,theliquid metal movement driven by O* harvesting al- Therefore,thecatalyticmetabolism-inducedpar-
metaldropletsactivelytravelaroundandsplit lowsdifferent dropletcompositionstocontinu- ticlefission/fusionmechanismformetalalloying
(“fission”)toharvestthedispersedO*onthecar- allymeetandfuseintosingle-phasealloysduring atthenanoscaleisdistinctcomparedwithpre-
bonsurfacebasedonthecatalyticallydrivenre- theCTSprocess.Numerousparticlefusionand viouslyreportedalloyingmethods(1,3,7,16).
action,C+O*=CO(gas)(DH=–110.5kJ/mol). fissionevents,whichwe estimatedtobe >106 Bytuning theshock duration andheating/
Previouslypublishedworks(23–26)andaninsitu times based on time-scale analysis (fig. S59) coolingrates,wecanadjusttheMMNPsize,dis-
TEMstudy(27)alsoshowedthatmetallicpar- (28–30),yieldadynamicsteadystateduringthe tribution,andstructure.WeloadedmultipleCNF
ticlescanmoveandsplitunderacatalyticdriv- 55-ms high-temperature shock. This enables samplesusinganidenticalPtNiprecursorsolu-
ingforce,whichissimilartoourproposedcarbon uniform nanoscale dispersions and homoge- tionandexposedthesupporttoatemperatureof
metabolismreaction. neoushigh-entropymixing.Toverifytheeffects ~2000Kfor5-ms,55-ms,1-s,and10-sdurations.
Mechanistically(Fig.3C),alargerO*concen- ofsupportswithmoresurface-bounddefects,we Thefasterexposuretimesyieldsmallerparticle
trationandtheuseofcatalyticallyactivemetals synthesizedquinaryHEA-NPs(PtFeCoNiCu)on sizes(3.51±0.62nmfor5msand5.01±1.69nm
candrivevigorousmetabolismwithmorefre- CNFswithandwithoutCO activation,resulting for55ms)comparedwithprolongedshockdura-
2
quent catalystmotionandfissionevents.This in 5.30 ± 1.31-nm particles on CO-activated tions(8.57±1.98nmfor1sand13.30±6.98nm
2
opposesequilibriumthermodynamicdirective CNFs and 11.3 ± 2.2-nm particles on CNFs for10s)(Fig.4,AandB).Weobservedsimilar
forthemetaldropletstocoarsen.Conversely, (fig.S60).Weachievedfurtherimprovementsin behaviorwithAuNi(fig.S63).Asthethermalshock
Yaoetal.,Science359,1489–1494(2018) 30March2018 4of6
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Fig.5.CatalyticperformanceofquinaryHEA-NPs(PtPdRhRuCe) (BandC)Temperature-dependentproductdistributionand c
ie
forammoniaoxidation.(A)Reactionschemefortheammonia conversionofNH3forPtPdRhRuCeHEA-NPsandPtPdRhRuCeMMNPs, nc
oxidationprocessaswellasthestructuralandperformance respectively.(D)STEMelementalmapsforPtPdRhRuCe e
.s
differencesbetweenthePtPdRhRuCeHEA-NPssynthesizedbyCTS HEA-NPs.(E)Thetime-dependentcatalyticperformanceof c
ie
andthecontrolsample(PtPdRhRuCeMMNPs)bywetimpregnation. PtPdRhRuCeHEA-NPsat700°C. n
c
e
m
durationincreasesto10s,thesizeoftheHEA-NPs aggregatesandanonuniformparticledispersion isthekeyprocessingstepintheindustrialsyn- ag
increasesandthesynthesizedparticlesbecome acrosstheCNFs(figs.S67andS68). thesisofnitricacid(Fig.5A)(32).Despiteexten- .org
less uniform; the high-temperature exposure Ourexperimentalresultsrevealvaluablein- siveeffortsontheexplorationofnewcatalysts, o /
depletesthenumberofO*presentontheCNF formationaboutthenucleationanddiffusion PtPdRh-basedmultimetalliccatalystsarestill n
M
support,whichinhibitsparticlefissionandcor- kineticsoftheCTSmethod.Thetransformation widelyemployedinindustrytothisday(33).Be- a
respondingdispersity(fig.S64). ofaliquidalloyintoasingle-phasesolidsolu- yondthehighcontentofpreciousmetals,these rc
h
Weinvestigatedtheeffectofcoolingrateby tionwithaspecificelementalcompositionre- catalystsalsorequireveryhightemperatures 3
1
tuningtheelectricalinputparameters(Fig.1B) quireslocalstructuralrearrangementsbutno (>800°C)toachievehighyieldsofNOx(NO+ , 2
withAu/NiandCu/Co,whichareimmisciblebi- long-rangesolutepartitioning.Thecoolingrate NO2)versusN2/N2Oandtendtodegradeunder 01
naryelementalcompositions(Fig.4,CandD, (~105K/s)thatweachievedbyCTSisstillslow continuousoperation(34).UsingtheCTSmethod, 8
andfigs.S65toS67).Duetodifferencesinlattice enoughtoformcrystallinestructures.Ifhigher quinaryPtPdRhRuCeHEA-NPs(figs.S69andS70
parametersandsurfaceenergies,thesemetallic coolingratesareattainedwiththeCTSmethod, andtableS5forthecompositions)wereprepared
combinationstendtophase-separateaccording itmaybepossibletousethisroutetosynthesize andemployedasammoniaoxidationcatalysts(21).
toequilibriumphasediagrams(3,20,31).How- metallicglasses.The~105K/scoolingrateisfast WeintroducedRuandCetoimprovetheoverall
ever,throughrapidquenching,thehigh-entropy enoughtopreventsolutepartitioningacrossa catalyticactivityandreducethePtcontent(35,36).
mixingstateoftheliquidmetalsisretainedand distanceof~10nm,enablingtheformationof Weachieved~100%conversionofammonia
yieldssingle-phasesolid-solutionnanoparticles high-entropy-alloystructures.Ontheotherhand, (NH3)and>99%selectivitytowardNOx(NO+
(i.e.,HEA-NPs)byavoidingthetime-temperature- slowercoolingrates(e.g.,~10K/s)enablesolute NO )atarelativelylowoperationtemperature
2
transformation(TTT)nose(Fig.4E).TheAuNibi- partitioningtooccurthrough(slow)kinetics, of700°CwiththePtPdRhRuCeHEA-NPcatalyst
naryalloyformedasolidsolutionwhenquenched whichcausedtheMMNPstophaseseparateinto (Fig.5B).Forcomparison,wepreparedsimilar
atboth~105and~103K/s(Fig.4Candfig.S66). aJanusparticle.Bothsingle-phaseandphase- catalysts(intermsofcomposition)bythewet
However,nanoscalephaseseparationoccurred separatednanoparticlesareusefulforapplica- impregnationmethod(denotedasPtPdRhRuCe
whencooledslowly(~10K/s),withaclearphase tionssuchascatalysisandplasmonicimaging MMNPs),whichproduceda18.7%yieldofNOxat
boundarybetweenAuandNishownintheannu- (2,3,9,10).TheCTSmethodhastheabilityto thesameoperationtemperature,whereasmost
larbright-field(ABF)image(Fig.4D)andHAADF controlphaseformationthroughrampratesand oftheoutputwasN (Fig.5C).Anelementalmap
2
image(fig.S66).FortheCuCobinarysystem,the maybeusefulfortargetednanoparticlesynthesis. comparisonbetweenthetwocatalystssuggests
105K/sproducedasolidsolution,butphasesep- TheCTSmethodenablesdiversecompositions that the enhanced catalytic selectivity of the
arationbeganatacoolingrateof~103K/s(fig. ofuniformlymixedHEA-NPsthathavepotential HEA-NPs is likely due to the highly homoge-
S65).Veryslowcoolingandheatingrates(~10K/s) forawiderangeofapplications.Asaproofof neousnatureofthesolid-solutionnanoparticles
alsoalterthedispersionandsizedistribution concept,wedemonstratedquinaryHEA-NPsas comparedwiththephase-separatedheterostruc-
ofthesynthesizednanoparticles,whichleadsto advancedcatalystsforammoniaoxidation,which turesderivedfromthewetimpregnationmethod
Yaoetal.,Science359,1489–1494(2018) 30March2018 5of6
RESEARCH | RESEARCHARTICLE
(Fig. 5D and fig. S70). Note that synthesizing ramprates)effectivelytunestheparticlesize, 26.F.Taoetal.,Science327,850–853(2010).
solid-solutionPtPdRhmultimetallicsystemsby dispersity,aswellasfinalstructure.Thesyn- 27.P.-H.Luetal.,arXiv:1802.00207[physics.app-ph]
conventionalsyntheticmethodsischallenging thesisofadiversearrayofnanoparticleswith (1Feb2018).
duetoimmiscibility(2,34).Wealsoperformed easilytunableprocessingparametersisidealfor 28.N.Combe,P.Jensen,A.Pimpinelli,Phys.Rev.Lett.85,110–113
(2000).
degradationtestingtostudycatalyticperformance large-scalenanomanufacturing,wherearapid 29.C.C.Wangetal.,NanoRes.8,2143–2151(2015).
under prolonged operation conditions, and we (synthesisinmilliseconds)andenergy-efficient 30.D.-G.Xieetal.,Nat.Mater.14,899–903(2015).
observenodegradationintermsofcatalyticac- (immediateheatingthroughanelectricalpulse) 31. D.Wang,Y.Li,J.Am.Chem.Soc.132,6280–6281(2010).
tivityorselectivityover~30hoursofcontinuous syntheticprocedurecouldenablehigh-rateand 32.D.M.Considine,ChemicalandProcessTechnology
Encyclopedia(CRCPress,1974).
operationat700°C(Fig.5Eandfig.S71).Weattri- high-volumeproductionofqualitynanoparti-
33.L.Xin,H.Yongqiang,J.Husheng,RareMet.Mater.Eng.46,
butedthisdurabilitytothehigh-entropynature cles.Moreover,ascalabilityevaluationexhibited 339–343(2017).
ofthecatalystspreparedbytheCTSmethod, a100-foldincreaseinHEA-NPproductionwith- 34.P.A.J.Bagotetal.,J.Phys.Chem.C118,26130–26138
whichhelpsstabilizetheMMNPsinsolidsolutions outsacrificingnanoparticlequalityordispersion (2014).
(i.e.,HEA-NPs)andpreventsphaseseparationor byemployingathree-dimensionalcarbonsupport 35.B.V.I.Chernyshov,I.M.Kisil,Platin.Met.Rev.37,136–143
(1993).
elementalsegregationunderthereactioncon- (figs.S73toS75).TheseCTScapabilitiesfacilitate
36.X.Hu,Y.Ning,L.Chen,Q.Shi,C.Jia,Platin.Met.Rev.56,
ditions (16, 18). Moreover, the precious metal anewresearchareaformaterialsdiscoveryand 40–46(2012).
contentoftheHEA-NPscanbereducedfurther optimization,wheretheelementalcomposition
withoutcompromisingcatalyticperformanceor andmixingentropyofnanoparticlescanbecare- ACKNOWLEDGMENTS
stabilitybyreplacing~37.5%ofPtwithCoand fullydesignedandcontrolled.Furthercomposi- TheauthorsthankK.GaskellandS.Xu,aswellasB.Liu,for
theirhelpwithXPSandXRDmeasurements/analysis,respectively.
eliminating Ru (e.g., PtPdRhCoCe HEA-NPs) tionalexplorationhasthepotentialtotranscend
TheauthorsacknowledgetheuseandsupportoftheMaryland
(fig.S72).Thus,HEA-NPsfabricatedbytheCTS researcheffortstobroadtechnologicalapplications. NanoCenteranditsAIMLab.ThisworkmadeuseoftheJEOL
method maybeageneralroutetowardhighly JEM-ARM200CFintheElectronMicroscopyService(Research
active, durable, and cost-effectivecatalysts (see REFERENCESANDNOTES ResourcesCenter,UIC).Funding:Thisworkhasnodirectfunding D
tableS6foradetailedliteraturecomparison). 1. P.-C.Chenetal.,Science352,1565–1569(2016). support.TheacquisitionoftheUICJEOLJEM-ARM200CF ow
Discussionandconclusion 23.. LS..BGu.Kewtoaln.,eStcaieln.,cNea3t5.4M,a1t4e1r.01–414,12415(–2022163).(2015). wFfionauasnnsdcuiaaptliposonurpt(epNdoSrbFty)fr(aoDmMMRNRI-S-0RF92D59Mgr4Ra7-n01t6).f2rR0o.m9S0.Y1th.aeanndNdaNtJSi.oLFn.aDalMcSkRcn-io1e4wn1cl0eed6g3e6, nload
4. M.Takahashietal.,Sci.Adv.3,e1700101(2017). e
TfohrenCanToSmmeteatlhluordgipcarlosvtiuddeisesa.nImexmceislcleibnltepelleamtfoenrmts 65.. GX..HCuhaenngeettaal.,l.,SSciceienncece334448,,419253–04–91923(420(1240)1.5). roefsDpeefcetnivseelyt.hSro.Dug.Lh.tahceknNoawtiloendagleDsesfuepnpseorStcbieyntcheeaDnedpEanrtgmineenetring d fro
acarerbaolnlosyuepdpionrttosswinitghleth-pehfaoslelonwainnogpfeaarttiucrleess:o(in) 78.. MN25..3RA2..–BF2ur5ec4yk,2,SJ(..2FP0.e0Bn9og)n,.dKi,.RC.hEe.nSgc,hSaa.kS,uNna,t.CChheemm..S4o,c3.7R–e4v4.3(280,11). GbRyerasadenuaraOctheffiIcFneeitlloioafwtiNvsehaivpga.rlaMRn.teR.s.PeZa..Xrac.nhadnMdRuC.lJt..iWJd.i.swaceciprkleninopawarylretdiUagnlleyivteshruespitCpyoartatelydst httpm
high-entropymixing,where multimetallicmix- 9. M.B.Cortie,A.M.McDonagh,Chem.Rev.111,3713–3735 andDiscoveryAwardsofJohnsHopkinsUniversity.Author ://s
ingleadstothecreationofsolid-solutionnano- (2011). cthoentprriebsuetniotnwso:rLk..HY..Yan.,dSY.D.Y.L..,coHn.Xce.,ivaenddtFh.eC.idceaarraienddoduetsitghneed cie
particleswithmaximizedconfigurationalmixing 10.K11.6D,.1G0il4ro14y–,1A0.47R2ud(i2ts0k1i6y,).H.-C.Peng,D.Qin,Y.Xia,Chem.Rev. experiments.Z.H.,A.N.,andR.S.Y.performeddetailed nce
entropy; (ii) nonequilibrium processing, where 11. E.Reddingtonetal.,Science280,1735–1737(1998). microscopiccharacterizations.P.X.,T.P.,andC.W.performed .s
the shock process takes milliseconds to create 12. P.C.Chenetal.,J.Am.Chem.Soc.137,9167–9173(2015). thecatalyticevaluation.R.J.J.,M.R.,andM.Z.conducted cie
HpbanyhEdaaAsv(-eoiNiiisdP)eisunpbngayirtfarohatreipmonindodqsaieusmpeoenofrnctshhgioienniTmg,TwamTnhidseccurtiehbrvluteesh(eepFlreicegmav.tee4annElytt)ss-; 11114563.... (BJSPB....--uWRSCta..t.enMCYrgewhuaherontnraeyt,tthehJ-taaH.l-an.eW,l,.iA,n.CedJYu.mver.Arha.Em,nSnnS.cg,.iC..2RMh80ae5a1nmt4,ge)1.ar.4.Sn06ao4t,ch–.2a119n439,09–H6,3i9g0(28h30-7E(062n–30t)r90o.8p48y)4.A(l2lo0y1s7). hmAmcaopilgealmphanali-spuuetuestedhrctmeiorfnmioprpgsrete.ritndnahCtittsrseouoc.rrmuueDesgsp.sthcYeseh.t.tdaiahPnrnetarghdocUetviJnenirs.rtiLeviieoz.seranudretasleitsilosvttnypesala:ooantTpfnedhendMecdtiaonaatrnhpuytseltpriahitlbnuimocudraemtste(cio6dodhl2neaet5csncol2iuash3tlrmaah6evre4enab6fnoiebnaaaealnmeyldsnis. ncemag.org
tpiecraaltlyurderievneanblceasrbuonnifomrmet,abwoellils-dmisaptehrsiegdh,taenmd- 1187.. 5YZ3..4FL.i,,Y2Ke2.,7G–Q.2.P3W0raad(n2eg0e,p1J6,.)YL..uD,Cen.gT,.DL.iuR,aYa.bYea,nCg.,CM.aTtaesr.aTno,dNaaytu1r9e, 6av2a5i9la1b6l3e8i)n.tDhaetamaannudsmcraiptterainadlsthaevasiulapbpilleitmye:nAtlalrdyatmaaatererials. on M /
cpoanrttircolellacbolayrsseizneidngn)a.noparticles(asopposedto 19. 3D4.9C–.3H6o2fm(2a0n1n6)e.tal.,Nature451,1085–1089(2008). SUPPLEMENTARYMATERIALS arch
Thissynthetictechniquealsoprovides(i)gen- 20.D.A.Porter,K.E.Easterling,M.Y.Sherif,Phase www.sciencemag.org/content/359/6383/1489/suppl/DC1 3
1
eitrya.lTithye,(miia)xtiumnuambiltietym,paenrdat(uiirie)opfottheenCtiaTlSsmcaeltahboild- 21. TMmraaattneesrrfiioaarllssm.aantidonmseinthModestaalsreanadvaAillalobylse(aCsRsCupPprelesms,eendta.r3y,2009). MSFiugapstep.rlSeia1mlsteoanntSad7r5yMTeethxotds , 2018
(2000to3000K)ishigherthanthedecomposition 22.N.Eustathopoulos,M.G.Nicholas,B.B.Drevet,Wettabilityat TablesS1toS6
temperatureofanymetalsalt,whichpromotes HighTemperatures(Elsevier,1999),vol.3. References(37–47)
uniformmixingofnearlyanymetalliccombi- 23.M.Lukasetal.,Nat.Commun.4,1379(2013).
24.F.Taoetal.,Science322,932–934(2008). 28April2017;resubmitted14December2017
nation(i.e.,generality).Precisecontroloverthe
25.M.A.Newton,C.Belver-Coldeira,A.Martínez-Arias, Accepted2February2018
shockparameters(temperature,duration,and M.Fernández-García,Nat.Mater.6,528–532(2007). 10.1126/science.aan5412
Yaoetal.,Science359,1489–1494(2018) 30March2018 6of6
Carbothermal shock synthesis of high-entropy-alloy nanoparticles
Yonggang Yao, Zhennan Huang, Pengfei Xie, Steven D. Lacey, Rohit Jiji Jacob, Hua Xie, Fengjuan Chen, Anmin Nie,
Tiancheng Pu, Miles Rehwoldt, Daiwei Yu, Michael R. Zachariah, Chao Wang, Reza Shahbazian-Yassar, Ju Li and Liangbing
Hu
Science 359 (6383), 1489-1494.
DOI: 10.1126/science.aan5412
Nanoparticle synthesis gets a shock
Nanoparticles are useful in a wide range of applications such as catalysis, imaging, and energy storage. Yao et al.
developed a method for making nanoparticles with up to eight different elements (see the Perspective by Skrabalak). The
method relies on shocking metal salt-covered carbon nanofibers, followed by rapid quenching. The ''carbothermal shock D
o
synthesis'' can be tuned to select for nanoparticle size as well. The authors successfully created PtPdRhRuCe w
nanoparticles to catalyze ammonia oxidation. nlo
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REFERENCES This article cites 41 articles, 9 of which you can access for free 31
http://science.sciencemag.org/content/359/6383/1489#BIBL , 2
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1
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Science is a registered trademark of AAAS.
NANOMATERIALS
Mashing up metals with carbothermal shock
Many elements can be combined in the formation of high-entropy-alloy nanoparticles
By Sara E. Skrabalak cally mixed phases before solidification (1, solutes. This observation gives insight into
3). By contrast, nanoscale alloys are often the formation mechanism of high-entropy
D ifferent materials and the capabili- made in solution by co-reducing metal salts alloyed NPs, in which a mixed phase must
ties they enabled have marked the along with capping agents that control crys- be achieved before solidification and then
ages of civilization. For example, tal growth and aggregation (6, 7). However, preserved through cooling at an optimal
the malleable copper alloys of the the compositional space of such alloys is of- rate so that neither phase separation nor
Bronze Age provided harder and ten limited because the precursors react at glass formation occurs (see the figure, left).
more durable tools. Most exploration different rates (8). The high surface energy This observation also suggests that this ap-
of new alloys has focused on random al- of NPs can be exploited to access new metal proach could yield new types of nanoscale
loys, in which the alloying metal sites have phases, but only simple compositions have heterostructures with further development.
no metal preference. In binary and ternary been reported (9). Even recent printing Distinctive properties can emerge when
metal systems, dissimilar elements do not methods for synthesizing multimetallic NPs new alloys undergo electron confinement
mix readily at high concentra- at the nanoscale materials. For D
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tions, which has limited alloy- example, Yao et al. showed that w
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ing studies to intermetallics Nanoscale high-entropy alloys their PtPdRhRuCe NPs were ef- lo
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(ordered multimetallic phases) fective catalysts for ammonia d
The synthesis route of Yao et al. makes mixtures of many elements. e
amnidn orr ancodmompo naellnotyss , airne wadhdicehd 1 Electric-shock heating Dilute and high-entropy alloys have oapxipdraotaiochn , haans dt heth ips otseynntitahle ttioc d from
to a principal element. In 2004, mixes all elements. diBerent elemental compositions. yield additional new catalysts. h
crystalline metal alloys consist- An exceptionally high number ttp
ing of five or more principal ele- Elemental Carbothermal of possible compositions and ://s
mixture shock c
ments in equal or nearly equal nanostructures can be envi- ie
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amounts (1, 2) were reported Dilute sioned, which introduces some ce
thhigaht wceornef igsutarabtiiloizneadl beyn trthopeiyr. ment C alloy fpuanrtdiacmuleanr,t iadle nchtiafilcleantigoens o(f4 h).i gIhn- .scien
Unlike most random alloys, the Conductive Ele entropy alloys with useful prop- ce
Cooling carbon m
“high-entropy” alloys (3, 4) re- erties by trial-and-error methods a
support g
side in the centers of their mul- is unsatisfactory given the large .o
t(sideiem tehnes ifoignuarle , prhigahset) . dOiang rpaamges Elem pchhaarsaec tesrpiazcaeti. onH oigf hc-othmrpoousgihtipount, on M rg/
1(54)8 9p roefs entht isa nis siunen,o vYaatoiv ee t anald. 2 A carbon support limits crystal growth Higha-ellonytropy ent B ntiaens oasrcea cleri tfiecaatlulyr ense, eadnedd (p1r2o, p1e3r)-. arc
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general route to high-entropy and coalescence during solidifcation. Element A These advances should be cou- 3
1
alloys that can mix up to eight pled with theory so that a deeper , 2
0
elements into single-phase, size-controlled yield phase-segregated multicomponent understanding of phase formation and the 1
8
nanoparticles (NPs). NPs when the input composition becomes emergence of new properties can be achieved
High-entropy alloys usually have a mini- too complex (10, 11). This observation is and enable materials by design. j
mum of five elements in nearly equal pro- consistent with varied precursor reactivity
portions. Synthesis of these compositions and slow cooling rates. REFERENCES
1. J.-W. Yeh et al., Adv. Eng. Mater. 6,299 (2004).
is challenging and not typically compat- By electrically shocking mixed-metal salt
2. B. Cantor, I. T. H. Change, P. Knight, A. J. B. Vincent, Mater.
ible with methods that yield well-defined precursors dispersed on conductive carbon Sci. Eng. A 375–377, 213 (2004).
nanoparticles. Such integration would supports, Yao et al. accessed high-entropy 3. D. B. Miracle, O. N. Senkov, Acta. Mater. 122,448 (2017).
4. Y. F. Ye, Q. Wang, J. Lu, C. T. Liu, Y. Yang, Mater. Today 19,349
enable the nanoscale properties of these alloys as size-controlled NPs. This method
(2016).
complex compositions to be studied and po- provided the high reaction temperatures 5. Y. Yao et al., Science 359,1489 (2018).
tentially leveraged in diverse applications. (~2000 K) and rapid heating and cooling 6. R. Ferrando, J. Jellinek, R. L. Johnston, Chem. Rev. 108,845
For example, high-entropy alloys are being rates (~105 K/s) necessary for high-entropy- (2008).
7. K. D. Gilroy, A. Ruditskiy, H.-C. Peng, D. Qin, Y. Xia, Chem.
studied as structural materials and for their alloy formation, while the underlying car- Rev.116,10414 (2016).
superparamagnetic and superconducting bon support inhibited coalescence of the 8. N. Ortiz, R. G. Weiner, S. E. Skrabalak, ACS Nano 8,12461
properties (4). NPs. Conveniently, the input ratio of metal (2014).
CE 9. V. F. Puntes, K. M. Krishnan, P. Alivisatos, Appl. Phys. Lett.
CIEN High-entropy alloys were initially synthe- was replicated in the final product, and the 78,2187 (2001).
N/S sized through high-temperature melting or method is scalable. 10. P.-C. Chen et al., Science 352,1565 (2016).
MA plasma routes that could produce atomi- The NP size could be tuned through 11. P.-C. Chen et al., J. Am. Chem. Soc. 137,9167 (2015).
KITTER the shock conditions. Interestingly, phase 12. M55. 9A .( P2a0y1n6e)., J. B. Miller, A. J. Gellman, ACS Comb. Sci.18,
A. segregated multicomponent NPs were 13. S. Ding, Y. Liu, Y. Li, Z. Liu, S. Sohn, F. J. Walker, J. Schroers,
PHIC: CEahsetm Kiisrtkrwy oDoedp Aavrtemnueen,t B, Ilnodoimaninag Utonniv,e INrs i4ty74–0B5lo, oUmSAin.g ton, 800 produced by slowing the cooling rate to Nat. Mater. 13,494 (2014).
GRA Email: [email protected] facilitate diffusion and partitioning of the 10.1126/science.aat1471
SCIENCE sciencemag.org 30 MARCH 2018 • VOL 359 ISSUE 6383 1467
Published by AAAS
DA_0330Perspectives.indd 1467 3/28/18 12:18 PM
Mashing up metals with carbothermal shock
Sara E. Skrabalak
Science 359 (6383), 1467.
DOI: 10.1126/science.aat1471
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ttp
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REFERENCES This article cites 13 articles, 2 of which you can access for free n
http://science.sciencemag.org/content/359/6383/1467#BIBL ce
.s
c
ie
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PERMISSIONS http://www.sciencemag.org/help/reprints-and-permissions ce
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Use of this article is subject to the Terms of Service
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licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. The title
Science is a registered trademark of AAAS.
www.sciencemag.org/content/359/6383/1489/suppl/DC1

Supplementary Materials for

Carbothermal shock synthesis of high-entropy-alloy nanoparticles
Yonggang Yao,* Zhennan Huang,* Pengfei Xie,* Steven D. Lacey,* Rohit Jiji Jacob,
Hua Xie, Fengjuan Chen, Anmin Nie, Tiancheng Pu, Miles Rehwoldt, Daiwei Yu,
Michael R. Zachariah, Chao Wang,† Reza Shahbazian-Yassar,† Ju Li,† Liangbing Hu†
*These authors contributed equally to this work.
†Corresponding author. Email: [email protected] (L.H.); [email protected] (R.S.-Y.);
[email protected] (J.L.); [email protected] (C.W.)
Published 30 March 2018, Science 359, 1489 (2018)
DOI: 10.1126/aan5412

This PDF file includes:

Materials and Methods
Supplementary Text
Figs. S1 to S75
Tables S1 to S6
References