A PEGylated deep eutectic solvent for controllable solvothermal synthesis of porous NiCo2S4 for efficient oxygen evolution reaction

Article abstract of DOI:10.1039/c7gc01012e

As ionic liquid analogues or quasi-ionic liquids, deep eutectic solvents (DESs) have been applied in many fields in the past few years. Herein, a novel PEGylated DES composed of PEG 200 and thiourea was formed for the first time and used for solvothermal synthesis of nickel cobalt sulfides. The structure and composition of the as-synthesized sulfides can be tuned by adjustment of the ratio of the reactants. The PEGylated DES plays multiple roles as a solvent, a shape-control agent, and a sulfur source in the synthesis of sulfides. Compared with traditional sulfuration routes, this proposed route is cost-effective and energy-efficient by combining solvothermal synthesis and the sulfuration process. The prepared sulfides were used as catalysts for electrochemical water oxidation and they exhibited excellent oxygen evolution reaction (OER) performance, especially for NiCo₂S₄ with hierarchical pores. The overpotential (η) demand was 337 mV for the current density reaching 10 mA cm^-2 and the Tafel slope was 64 mV dec^-1 in an alkaline medium (1 M KOH) for NiCo₂S₄. In addition, NiCo₂S₄ demonstrated long-term stability with little deactivation after either thirty hours of continuous operation or two thousand cycles and a high faradaic efficiency of 95.8%. Synergistic effects including a relatively high Brunauer-Emmett-Teller area, abundant active sites, easy diffusion of electrolytes and oxygen gas, and strong structural integrity contribute to the high activity and long-term stability of the catalyst for OER. This study provides a new method for the synthesis of hierarchically structured metal sulfides for energy conversion and storage applications.

Full text of DOI:10.1039/c7gc01012e

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Green
Chemistry
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7
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April 2016 Pages 1821–2242
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CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Page 1 of 9
Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
View Article Online
DOI: 10.1039/C7GC01012E
JournalꢀNameꢀ
ꢀ
ARTICLEꢀ
PEGylatedꢀdeepꢀeutecticꢀsolventꢀforꢀcontrollableꢀsolvothermalꢀ
synthesisꢀofꢀporousꢀNiCo S ꢀforꢀefficientꢀoxygenꢀevolutionꢀreactionꢀꢀ
2
4
Receivedꢀ00thꢀJanuaryꢀ20xx,ꢀ
Acceptedꢀ00thꢀJanuaryꢀ20xxꢀ
a
a
a
a
b
aꢀ
JingyunꢀJiang, ꢀChuanyuꢀYan, ꢀXinhuiꢀZhao, ꢀHongxiaꢀLuo, ꢀZhiminꢀXue, ꢀꢀandꢀTianchengꢀMu*
DOI:ꢀ10.1039/x0xx00000xꢀ
Asꢀionicꢀliquidsꢀanaloguesꢀorꢀquasi-ionicꢀliquids,ꢀdeepꢀeutecticꢀsolventsꢀ(DESs)ꢀhaveꢀbeenꢀappliedꢀinꢀmanyꢀfieldsꢀinꢀtheꢀpastꢀ
fewꢀyears.ꢀHerein,ꢀaꢀnovalꢀPEGylatedꢀDESꢀcomposedꢀofꢀPEGꢀ200ꢀandꢀthioureaꢀwasꢀformedꢀforꢀtheꢀfirstꢀtimeꢀandꢀwasꢀusedꢀ
forꢀsolvothermalꢀsynthesisꢀofꢀnickelꢀcobaltꢀsulfides.ꢀTheꢀstructureꢀandꢀcompositionꢀofꢀtheꢀas-synthesizedꢀsulfidesꢀcanꢀbeꢀ
tunedꢀbyꢀadjustmentꢀofꢀtheꢀratioꢀofꢀtheꢀreactants.ꢀTheꢀPEGylatedꢀDESꢀplaysꢀmultipleꢀrolesꢀasꢀsolvent,ꢀshape-controlꢀagent,ꢀ
andꢀsulfurꢀsourceꢀinꢀtheꢀsynthesisꢀofꢀtheꢀsulfides.ꢀComparedꢀwithꢀtraditionalꢀsulfurationꢀroutes,ꢀthisꢀproposedꢀrouteꢀisꢀcost-
effectiveꢀandꢀenergy-efficientꢀbyꢀcombiningꢀsolvothermalꢀsynthesisꢀandꢀsulfurationꢀprocess.ꢀTheꢀpreparedꢀsulfidesꢀwereꢀ
usedꢀ asꢀ catalystsꢀ forꢀ electrochemicalꢀ waterꢀ oxidationꢀ andꢀ theyꢀ exhibitedꢀ excellentꢀ oxygenꢀ evolutionꢀ reactionꢀ (OER)ꢀ
www.rsc.org/ꢀ
performance,ꢀespeciallyꢀforꢀNiCo
2
S
4
ꢀwithꢀhierarchicalꢀpores.ꢀTheꢀdemandingꢀoverpotentialꢀ(ɳ)ꢀwasꢀ337ꢀmVꢀforꢀtheꢀcurrentꢀ
-
2
-1
densityꢀreachingꢀ10ꢀmA·cm ꢀandꢀtheꢀTafelꢀslopeꢀwasꢀ64ꢀmV·dec ꢀinꢀanꢀalkalineꢀmediumꢀ(1ꢀMꢀKOH)ꢀforꢀNiCo
2
S
4
.ꢀInꢀaddition,ꢀ
2 4
NiCo S ꢀdemonstratedꢀaꢀlong-termꢀstabilityꢀwithꢀlittleꢀdeactivationꢀafterꢀeitherꢀthirtyꢀhoursꢀcontinuousꢀoperationꢀorꢀtwoꢀ
thousandꢀcyclesꢀandꢀhighꢀFaradicꢀefficiencyꢀofꢀ95.8ꢀ%.ꢀSynergisticꢀeffectsꢀincludingꢀrelativelyꢀhighꢀBrunauer-Emmett-Tellerꢀ
area,ꢀabundantꢀactiveꢀsites,ꢀeasyꢀdiffusionꢀofꢀelectrolytesꢀandꢀoxygenꢀgas,ꢀandꢀstrongꢀstructureꢀintegrityꢀcontributeꢀtoꢀtheꢀ
highꢀ activityꢀ andꢀ long-termꢀ stabilityꢀ ofꢀ theꢀ catalystꢀ forꢀ OER.ꢀ Thisꢀ studyꢀ providesꢀ aꢀ newꢀ wayꢀ forꢀ theꢀ synthesisꢀ ofꢀ
hierarchicallyꢀstructuredꢀmetalꢀsulfidesꢀforꢀenergyꢀconversionꢀandꢀstorageꢀapplications.ꢀꢀꢀ
throughꢀphotosynthesisꢀinꢀnaturalꢀsystem,ꢀwaterꢀsplittingꢀhasꢀ
attractedꢀ numerousꢀ attentions.
13-17
Introductionꢀꢀ
ꢀ Aꢀ typicalꢀ waterꢀ splittingꢀ
reactionꢀcanꢀbeꢀdividedꢀintoꢀtwoꢀhalfꢀreactions:ꢀtheꢀhydrogenꢀ
evolutionꢀ reactionꢀ (HER)ꢀ atꢀ cathodeꢀ andꢀ oxygenꢀ evolutionꢀ
reactionꢀ (OER)ꢀ atꢀ anode;ꢀ andꢀ theꢀ multi-electronꢀ transferꢀ
processꢀassociatedꢀwithꢀtheꢀbreakdownꢀofꢀO-Hꢀbondꢀandꢀtheꢀ
formationꢀofꢀO-OꢀbondꢀinꢀtheꢀOERꢀlimitsꢀtheꢀoverallꢀefficiencyꢀ
Ionicꢀliquidsꢀhaveꢀbeenꢀwidelyꢀusedꢀinꢀnanomaterialsꢀsynthesisꢀ
becauseꢀofꢀtheirꢀuniqueꢀphysicalꢀandꢀchemicalꢀproperties,ꢀsuchꢀ
asꢀ lowꢀ volatility,ꢀ lowꢀ flammability,ꢀ wideꢀ electrochemicalꢀ
window,ꢀ highꢀ thermalꢀ stability,ꢀ andꢀ extendedꢀ hydrogenꢀ
1-5
network. ꢀ Asꢀ ionicꢀ liquidsꢀ analoguesꢀ orꢀ quasi-ionicꢀ liquids,ꢀ
deepꢀeutecticꢀsolventsꢀ(DESs)ꢀcanꢀbeꢀpreparedꢀbyꢀmixingꢀtwoꢀ
componentsꢀ(usuallyꢀtheꢀhydrogenꢀbondꢀdonorsꢀandꢀhydrogenꢀ
bondꢀ acceptors)ꢀ throughꢀ theꢀ self-associationꢀ effects.ꢀ Theꢀ
meltingꢀpointsꢀofꢀtheꢀformedꢀDESsꢀareꢀusuallyꢀfarꢀbelowꢀthoseꢀ
18-20
ofꢀwaterꢀsplitting.
ꢀBecauseꢀofꢀlargeꢀoverpotentialsꢀderivedꢀ
fromꢀ theꢀ twoꢀ halfꢀ reactions,ꢀ theꢀ electrochemicallyꢀ waterꢀ
splittingꢀ processꢀ isꢀ rarelyꢀ usedꢀ inꢀ industrialꢀ applicationsꢀ untilꢀ
21
now. ꢀ Thus,ꢀ developingꢀ earth-abundantꢀ waterꢀ oxidationꢀ
catalystꢀ forꢀ theꢀ OERꢀ withꢀ lowꢀ overpotential,ꢀ highꢀ energyꢀ
efficiency,ꢀ durability,ꢀ andꢀ costꢀ effectivenessꢀ isꢀ ofꢀ greatꢀ
importanceꢀ andꢀ hasꢀ attractedꢀ tremendousꢀ researchꢀ
6
ofꢀtheꢀindividualꢀcomponents. ꢀPriorꢀtoꢀionicꢀliquids,ꢀDESsꢀareꢀ
particularlyꢀ tractable,ꢀ cheap,ꢀ biodegradableꢀ andꢀ non-
7
cytotoxic. ꢀMaterialsꢀsynthesisꢀinꢀDESsꢀsometimesꢀcanꢀresultꢀinꢀ
20,ꢀ22-25
attention.
ꢀTraditionally,ꢀcommerciallyꢀavailableꢀRu-ꢀandꢀ
interestingꢀstructuresꢀwhichꢀareꢀnotꢀeasyꢀtoꢀbeꢀobtainedꢀfromꢀ
8,ꢀ9
Ir-basedꢀ oxidesꢀ areꢀ consideredꢀ asꢀ theꢀ state-of-the-artꢀ OERꢀ
catalystꢀ whichꢀ canꢀ efficientlyꢀ lowerꢀ theꢀ overpotentialꢀ andꢀ
otherꢀconventionalꢀfabricationꢀroutes. ꢀThroughꢀtheꢀsynthesisꢀ
ꢀ However,ꢀ theꢀ
10-12
process,ꢀ DESsꢀ couldꢀ playꢀ multipleꢀ roles.
14
increaseꢀtheꢀreactionꢀrate. ꢀHowever,ꢀtheꢀhighꢀpriceꢀandꢀlowꢀ
naturalꢀabundanceꢀpreventꢀtheirꢀlargeꢀscaleꢀproductionꢀforꢀtheꢀ
industrialꢀ scaleꢀ electrolysisꢀ system.ꢀ Toꢀ reduceꢀ orꢀ evenꢀ
eliminateꢀ theꢀ useꢀ ofꢀ theꢀ preciousꢀ metal-basedꢀ catalysts,ꢀ
considerableꢀ effortsꢀ haveꢀ beenꢀ madeꢀ toꢀ synthesizingꢀ non-
synthesisꢀofꢀnanomaterialsꢀinꢀDESsꢀisꢀlessꢀstudied.ꢀꢀ
Asꢀ aꢀ mimicꢀ ofꢀ solar-to-chemicalꢀ energyꢀ conservationꢀ
26
preciousꢀ metalꢀ catalystsꢀ withꢀ highꢀ efficiencyꢀ forꢀ OER. ꢀ Theꢀ
promisingꢀ alternativesꢀ forꢀ OERꢀ includingꢀ oxides,ꢀ hydroxides,ꢀ
sulfides,ꢀ carbides,ꢀ nitrides,ꢀ andꢀ phosphidesꢀ ofꢀ first-rowꢀ
2
2
20,ꢀ23,ꢀ27
23,ꢀ28
29
30,ꢀ
transitionꢀmetalꢀ(suchꢀasꢀFe, ꢀCo,
26,ꢀ32
ꢀNi,
ꢀMn, ꢀandꢀCu
ꢀareꢀusuallyꢀprioritizedꢀbecauseꢀofꢀtheirꢀ
31
)ꢀandꢀtheirꢀalloys
highꢀ activities.ꢀ Inꢀ particular,ꢀ theꢀ multi-metalꢀ catalystsꢀ areꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ1ꢀꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
Page 2 of 9
ARTICLEꢀ
JournalꢀNameꢀ
believedꢀ toꢀ beꢀ moreꢀ activeꢀ andꢀ stableꢀ dueꢀ toꢀ theꢀ tailoredꢀ
electronicꢀ andꢀ surfaceꢀ propertiesꢀ ofꢀ theꢀ hostꢀ structureꢀ byꢀ
View Article Online
DOI: 10.1039/C7GC01012E
27
introducingꢀ secondaryꢀ metalꢀ ion. ꢀ Amongꢀ theꢀ multi-metalꢀ
basedꢀ OERꢀ catalysts,ꢀ Niꢀ andꢀ Co-basedꢀ samplesꢀ haveꢀ alreadyꢀ
beenꢀappliedꢀasꢀOERꢀcatalystsꢀbecauseꢀtheyꢀareꢀhighlyꢀresistantꢀ
toꢀ corrosionꢀ inꢀ alkalineꢀ aqueousꢀ solutionꢀ andꢀ theyꢀ haveꢀ
24,ꢀ33
sufficientꢀvariableꢀvalenceꢀstates.
ꢀꢀ
Recently,ꢀnanostructuredꢀmetalꢀsulfidesꢀhaveꢀbeenꢀwidelyꢀ
usedꢀ inꢀ energyꢀ conversion,ꢀ supercapacitors,ꢀ andꢀ lithiumꢀ
34
storageꢀdevicesꢀforꢀtheirꢀexcellentꢀelectrochemicalꢀactivities. ꢀ
Moreover,ꢀ nickelꢀ cobaltꢀ sulfidesꢀ areꢀ believedꢀ toꢀ haveꢀ muchꢀ
higherꢀ conductivityꢀ thanꢀ theꢀ relatedꢀ ternaryꢀ nickelꢀ cobaltꢀ
ꢀ
2 4
Fig.ꢀ 1ꢀ Schematicꢀ representationꢀ ofꢀ theꢀ formationꢀ ofꢀ NiCo S ꢀ inꢀ theꢀ
35,ꢀ 36
multifunctionalꢀDESꢀcomposedꢀofꢀPEGꢀ200ꢀandꢀthioureaꢀinꢀtheꢀmolarꢀ
ratioꢀofꢀ2:1.ꢀꢀ
oxidesꢀ becauseꢀ ofꢀ theirꢀ smallerꢀ bandꢀ gap.
ꢀ Althoughꢀ theꢀ
reportedꢀ nickelꢀ cobaltꢀ sulfidesꢀ exhibitꢀ promisingꢀ
electrochemicalꢀ activities,ꢀ theꢀ synthesisꢀ ofꢀ thoseꢀ sulfidesꢀ
usuallyꢀneedsꢀaꢀcomplicatedꢀprocess,ꢀandꢀtheꢀcomponentsꢀofꢀ
theꢀfabricatedꢀsulfidesꢀareꢀoftenꢀcomplex,ꢀwhichꢀleadsꢀtoꢀextraꢀ
Resultsꢀandꢀdiscussionꢀꢀ
riskꢀ ofꢀ uncertainty.ꢀ Usually,ꢀ nickelꢀ cobaltꢀ sulfidesꢀ wereꢀ Theꢀ PEGylatedꢀ DESꢀ wasꢀ obtainedꢀ byꢀ simpleꢀ mixingꢀ PEGꢀ 200ꢀ
synthesizedꢀbyꢀaꢀtwo-stepꢀhydrothermalꢀmethodꢀincludingꢀtheꢀ andꢀthioureaꢀinꢀtheꢀmolarꢀratioꢀofꢀ2:1ꢀatꢀroomꢀtemperature.ꢀ
formationꢀofꢀnickelꢀcobaltꢀoxidesꢀorꢀcarbonateꢀhydroxidesꢀandꢀ Theꢀ formationꢀ ofꢀ theꢀ PEGylatedꢀ DESꢀ wasꢀ confirmedꢀ byꢀ theꢀ
furtherꢀsulfurizationꢀbyꢀreactingꢀwithꢀadditionalꢀsulfideꢀsourcesꢀ Fourierꢀ Transformꢀ Infraredꢀ Spectroscopyꢀ (FTIR)ꢀ analysisꢀ (Fig.ꢀ
3
6-38
39
40
1
(
sodiumꢀ sulphide,
desirableꢀ toꢀ combineꢀ theꢀ twoꢀ stepsꢀ (solvothermalꢀ synthesisꢀ scanningꢀ calorimetryꢀ (DSC)ꢀ experimentꢀ (Fig.ꢀ S1c).ꢀ Theꢀ
andꢀsulfurationꢀprocess)ꢀtoꢀreduceꢀcost.ꢀꢀ
characteristicꢀ absorptionꢀ peaksꢀ ofꢀ C-O-C,ꢀ -OH,ꢀ andꢀ –CH2ꢀ
Liquidꢀ poly(ethyleneꢀ glycol)sꢀ (PEGs,ꢀ molecularꢀ weightꢀ ˂ꢀ stretchingꢀ vibrationꢀ derivedꢀ fromꢀ PEGꢀ 200, ꢀ andꢀ –NH2,ꢀ C-Nꢀ
ꢀ thiourea, ꢀ thioacetamide, ꢀ etc.).ꢀ Itꢀ isꢀ S1a),ꢀ HꢀNMRꢀspectroscopyꢀanalysisꢀ(Fig.ꢀS1b)ꢀandꢀdifferentialꢀ
45
-1
46
8
fields.
00ꢀ g·mol )ꢀ haveꢀ beenꢀ usedꢀ asꢀ greenꢀ solventsꢀ inꢀ variousꢀ stretchingꢀvibrationꢀderivedꢀfromꢀthiourea ꢀwereꢀobservedꢀinꢀ
41,ꢀ 42
ꢀ ꢀ Weꢀ haveꢀ developedꢀ PEGylatedꢀ quasi-ionicꢀ liquidꢀ theꢀPEGylatedꢀDESꢀ(Fig.ꢀS1a).ꢀTheꢀslightꢀshiftsꢀofꢀ–OHꢀandꢀ–NH2ꢀ
electrolytesꢀandꢀusedꢀasꢀmediaꢀforꢀefficientꢀelectrodepositionꢀ stretchingꢀ vibrationꢀ peaksꢀ furtherꢀ proveꢀ theꢀ existenceꢀ ofꢀ
43
ofꢀaluminum. ꢀPEGꢀ200ꢀisꢀanꢀefficientꢀshape-controlꢀagentꢀforꢀ interactionꢀ betweenꢀ PEGꢀ 200ꢀ andꢀ thiourea.ꢀ Inꢀ addition,ꢀ asꢀ
nanoparticlesꢀ formationꢀ becauseꢀ itsꢀ twoꢀ –OHꢀ groupsꢀ whichꢀ depictedꢀinꢀFig.ꢀS1b,ꢀtheꢀchemicalꢀshiftꢀofꢀhydroxylꢀhydrogenꢀ
canꢀ beꢀ selectivelyꢀ adsorbedꢀ onꢀ certainꢀ facesꢀ toꢀ increaseꢀ theꢀ atomsꢀ onꢀ PEGꢀ movedꢀ downfield,ꢀ whichꢀ isꢀ attributedꢀ toꢀ theꢀ
growthꢀrateꢀofꢀtheseꢀfaces,ꢀandꢀtheꢀstericꢀhindranceꢀeffectꢀtoꢀ hydrogenꢀ bondingꢀ betweenꢀ theꢀ thioureaꢀ andꢀ theꢀ terminalꢀ
4
3,ꢀ47
obtainꢀtheꢀwellꢀassembledꢀsecondaryꢀandꢀtertiaryꢀbranchesꢀonꢀ alcoholicꢀgroupsꢀfromꢀPEG.
ꢀDSCꢀanalysisꢀ(Fig.ꢀS1c)ꢀwasꢀusedꢀ
33,ꢀ44
theꢀlongerꢀtrunk.
ꢀInꢀaddition,ꢀthioureaꢀworksꢀasꢀnotꢀonlyꢀ toꢀ assessꢀ theꢀ effectꢀ ofꢀ addingꢀ thioureaꢀ toꢀ theꢀ PEGꢀ 200.ꢀ Theꢀ
theꢀsulfurꢀsourceꢀbutꢀalsoꢀaꢀbidentateꢀligandꢀtoꢀformꢀrelativelyꢀ endothermsꢀ atꢀ 178ꢀ Cꢀ forꢀ thioureaꢀ andꢀ -58ꢀ Cꢀ forꢀ PEGꢀ 200ꢀ
o
o
39,ꢀ44
stableꢀmetal-thioureaꢀthroughꢀtheꢀM-Sꢀbonds.
ꢀꢀ
showedꢀ theꢀ onsetꢀ meltingꢀ pointꢀ ofꢀ thioureaꢀ andꢀ PEGꢀ 200,ꢀ
Herein,ꢀaꢀnovelꢀPEGylatedꢀDESꢀwasꢀdevelopedꢀandꢀusedꢀ respectively.ꢀ Theꢀ onsetꢀ meltingꢀ pointꢀ ofꢀ theꢀ synthesizedꢀ DESꢀ
o
forꢀ cost-effectiveꢀ one-stepꢀ solvothermalꢀ synthesisꢀ ofꢀ nickelꢀ (PEGꢀ200ꢀ:ꢀthioureaꢀ=ꢀ2ꢀ:ꢀ1)ꢀisꢀ-87ꢀ Cꢀ,ꢀlowerꢀthanꢀbothꢀPEGꢀ200ꢀ
11,ꢀ48
cobaltꢀsulfidesꢀ(Fig.ꢀ1).ꢀTheꢀuniqueꢀadaptabilityꢀandꢀflexibilityꢀofꢀ andꢀthiourea,ꢀwhichꢀfurtherꢀprovedꢀtheꢀformationꢀofꢀDES.
ꢀ
PEGylatedꢀDESꢀmakeꢀitꢀpossibleꢀforꢀprovidingꢀaꢀpowerfulꢀrouteꢀ Forꢀ betterꢀ understandingꢀ theꢀ PEGylatedꢀ DES,ꢀ theꢀ viscosityꢀ
-1
-2
forꢀ synthesizingꢀ metalꢀ sulfidesꢀ andꢀ theꢀ compositionꢀ andꢀ (170.2ꢀ mPa·s )ꢀ andꢀ conductivityꢀ (6.8ꢀ μS·cm )ꢀ wereꢀ
structureꢀ ofꢀ theꢀ as-synthesizedꢀ sulfideꢀ canꢀ beꢀ tuned.ꢀ Theꢀ determinedꢀ atꢀ 298.15ꢀ K.ꢀ Nickelꢀ cobaltꢀ sulfidesꢀ wereꢀ
synthesizedꢀnickelꢀcobaltꢀsulfides,ꢀespeciallyꢀNiCo2S4,ꢀexhibitedꢀ synthesizedꢀthroughꢀaꢀone-stepꢀsolvothermalꢀsynthesisꢀinꢀtheꢀ
excellentꢀ OERꢀ performance,ꢀ long-termꢀ stabilityꢀ andꢀ aꢀ highꢀ synthesizedꢀ DESꢀ composedꢀ ofꢀ PEGꢀ 200ꢀ andꢀ thioureaꢀ inꢀ theꢀ
Faradicꢀ efficiency.ꢀ Deepꢀ eutecticꢀ solvothermalꢀ synthesisꢀ ofꢀ molarꢀ ratioꢀ ofꢀ 2:1.ꢀ Theꢀ detailedꢀ synthesisꢀ procedureꢀ canꢀ beꢀ
hierarchicallyꢀ structuredꢀ metalꢀ sulfidesꢀ withꢀ theꢀ cheapꢀ andꢀ foundꢀinꢀtheꢀexperimentalꢀsection.ꢀSpecially,ꢀtheꢀcompositionꢀ
environmentꢀ benignꢀ PEGylatedꢀ DESꢀ actsꢀ asꢀ simultaneouslyꢀ ofꢀ sulfidesꢀ canꢀ beꢀ tunedꢀ simplyꢀ adjustingꢀ theꢀ ratioꢀ ofꢀ theꢀ
solvent,ꢀ shape-controlꢀ agent,ꢀ asꢀ wellꢀ asꢀ sulfurꢀ sourceꢀ mayꢀ reactantsꢀ(TableꢀS1).ꢀInꢀtheꢀsynthesisꢀprocessꢀofꢀtheꢀsulfides,ꢀ
supportꢀaꢀnewꢀpossibilityꢀinꢀtheꢀdevelopmentꢀofꢀhighlyꢀefficientꢀ PEGꢀ 200ꢀ isꢀ anꢀ efficientꢀ surfactantꢀ toꢀ controlꢀ theꢀ shapeꢀ ofꢀ
sulfidesꢀusedꢀforꢀOER.ꢀꢀ
sulfidesꢀandꢀthioureaꢀisꢀaꢀsulfurꢀsourceꢀforꢀinꢀsituꢀsulfuration.ꢀ
2+
2+
Theꢀ metalꢀ chelateꢀ ionsꢀ ofꢀ thioureaꢀ withꢀ Ni ꢀ andꢀ Co ꢀ
contributeꢀ toꢀ aꢀ highꢀ monomerꢀ concentrationꢀ afterꢀ theꢀ
nucleationꢀstageꢀforꢀfurtherꢀgrowth.ꢀTheꢀsynergisticꢀeffectsꢀofꢀ
PEGꢀ200ꢀandꢀthioureaꢀpromoteꢀtheꢀspecialꢀstructureꢀofꢀsulfides.ꢀ
Forꢀcomparison,ꢀternaryꢀnickelꢀcobaltꢀoxideꢀwasꢀsynthesizedꢀinꢀ
PEGꢀ200ꢀbutꢀwithoutꢀthiourea.ꢀꢀ
2
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
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Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
JournalꢀNameꢀ
ꢀARTICLEꢀ
Toꢀ evaluateꢀ theꢀ crystallographicꢀ structureꢀ andꢀ phaseꢀ Co,ꢀNi,ꢀandꢀSꢀelementsꢀinꢀtheꢀsampleꢀwasꢀverifiedꢀbyꢀfulellꢀXPneSꢀ
View Artic Onli
purityꢀofꢀtheꢀpreparedꢀsulfides,ꢀX-rayꢀdiffractionꢀ(XRD)ꢀanalysisꢀ spectrumꢀinꢀtheꢀ0–1000ꢀeVꢀrange.ꢀTheꢀCDo Oꢀ 2I : p1 0, ꢀ. N1 0i 3ꢀ 29 /pC , 7ꢀ aG nC d0 ꢀ1 S0 ꢀ1 22 Ep ꢀ
wasꢀcarriedꢀoutꢀandꢀtheꢀresultsꢀwereꢀshownꢀinꢀFig.ꢀ2aꢀandꢀFig.ꢀ spectraꢀ areꢀ presentedꢀ inꢀ Fig.ꢀ 2b,ꢀ 2c,ꢀ andꢀ 2d,ꢀ respectively.ꢀ
S2.ꢀ Theꢀ productsꢀ areꢀ differentꢀ withꢀ theꢀ variationꢀ ofꢀ theꢀ Accordingꢀ toꢀ theꢀ Gaussianꢀ fittingꢀ method,ꢀ twoꢀ spin-orbitꢀ
precursorꢀratio,ꢀwhichꢀcouldꢀbeꢀverifiedꢀbyꢀtheꢀXRDꢀpattern.ꢀAsꢀ doubletsꢀ (whichꢀ canꢀ beꢀ contributedꢀ toꢀ theꢀ characteristicꢀ ofꢀ
2+
3+
depictedꢀinꢀFig.ꢀ2a,ꢀatꢀtheꢀmolarꢀratioꢀofꢀNi(NO3)2ꢀandꢀCo(NO3)2ꢀ Co ꢀandꢀCo )ꢀandꢀtwoꢀshake-upꢀsatellitesꢀ(Sat.)ꢀareꢀobservedꢀ
ofꢀ 1:2,ꢀ theꢀ diffractionꢀ peaksꢀ ofꢀ theꢀ productꢀ locateꢀ atꢀ 2θꢀ ofꢀ inꢀFig.ꢀ2b.ꢀTheꢀpeakꢀlocatedꢀatꢀ795.6ꢀeVꢀcanꢀbeꢀascribedꢀtoꢀCoꢀ
o
6.9 ,ꢀ 31.6 ,ꢀ 38.4 ,ꢀ 50.6 ,ꢀ andꢀ 55.3 ꢀ whichꢀ couldꢀ beꢀ wellꢀ 2p1/2ꢀwithꢀaꢀsatelliteꢀatꢀ800.9ꢀeV,ꢀwhileꢀtheꢀpeakꢀatꢀ784.2ꢀeVꢀisꢀ
o
o
o
o
2
indexedꢀtoꢀtheꢀ(220),ꢀ(311),ꢀ(400),ꢀ(511),ꢀandꢀ(440)ꢀplanesꢀofꢀ relatedꢀtoꢀCoꢀ2p3/2ꢀwithꢀaꢀsatelliteꢀatꢀ779.3ꢀeV.
4
9,ꢀ53
ꢀTheꢀspin-
theꢀcubicꢀNiCo2S4ꢀphase,ꢀrespectively,ꢀwhichꢀareꢀinꢀagreementꢀ energyꢀseparationꢀofꢀCoꢀ2p1/2ꢀandꢀCoꢀ2p3/2ꢀisꢀhigherꢀthanꢀ15ꢀeVꢀ
2+
3+ 54
withꢀ theꢀ standardꢀ XRDꢀ patternꢀ ofꢀ theꢀ cubicꢀ NiCo2S4ꢀ phaseꢀ whichꢀalsoꢀprovedꢀtheꢀexistenceꢀofꢀCo ꢀandꢀCo . ꢀSimilarly,ꢀ
4
9
(
JCPDSꢀ cardꢀ No.ꢀ 43-1477). ꢀ Theꢀ absenceꢀ ofꢀ otherꢀ impurityꢀ twoꢀ spin-orbitꢀ doubletsꢀ includingꢀ peaksꢀ locatedꢀ atꢀ 855.6ꢀ eVꢀ
peaksꢀcouldꢀbeꢀascribedꢀtoꢀtheꢀhighꢀpurityꢀofꢀtheꢀsample.ꢀWhileꢀ andꢀ873.1ꢀeVꢀareꢀfittedꢀtoꢀtheꢀNiꢀ2p3/2ꢀandꢀNiꢀ2p1/2ꢀwhichꢀcanꢀ
2+
3+
atꢀ equimolarꢀ quantitiesꢀ ofꢀ Ni(NO3)2ꢀ andꢀ Co(NO3)2,ꢀ theꢀ beꢀownedꢀtoꢀtheꢀcharacteristicꢀofꢀNi ꢀandꢀNi ,ꢀandꢀtwoꢀshake-
55
diffractionꢀpeaksꢀcouldꢀbeꢀindexedꢀtoꢀtheꢀmixtureꢀofꢀNi2CoS4ꢀ upꢀ satellitesꢀ areꢀ obtainedꢀ fromꢀ theꢀ Niꢀ 2pꢀ spectraꢀ (Fig.ꢀ 2c). ꢀ
(
50
JCPDSꢀ cardꢀ No.ꢀ 24-0334) ꢀ andꢀ CoS2ꢀ (JCPDSꢀ cardꢀ No.ꢀ 65- Additionally,ꢀtheꢀSꢀ2pꢀspectraꢀcanꢀbeꢀfittedꢀtoꢀtwoꢀmainꢀpeaksꢀ
51
3
322) .ꢀ Inꢀ thisꢀ regard,ꢀ binaryꢀ cobaltꢀ sulfideꢀ CoS2ꢀ appearsꢀ andꢀoneꢀshake-upꢀsatelliteꢀ(Fig.ꢀ2d).ꢀTheꢀpeakꢀlocatedꢀatꢀ163.6ꢀ
easierꢀ formationꢀ comparedꢀ withꢀ nickelꢀ sulfideꢀ NiS2.ꢀ Furtherꢀ eVꢀisꢀcharacteristicꢀpeakꢀofꢀmetal-sulfideꢀbonds,ꢀandꢀtheꢀpeakꢀ
2-
increasingꢀtheꢀmolarꢀratioꢀofꢀNi(NO3)2ꢀandꢀCo(NO3)2ꢀtoꢀ2:1,ꢀtheꢀ locatedꢀ atꢀ 161.2ꢀ eVꢀ isꢀ ownedꢀ toꢀ theꢀ S ꢀ inꢀ theꢀ lowꢀ
diffractionꢀpeaksꢀcouldꢀbeꢀindexedꢀtoꢀNi2CoS4ꢀ(JCPDSꢀcardꢀNo.ꢀ coordination.
3
5,ꢀ55,ꢀ56
2+ 3+
ꢀAccordingꢀtoꢀtheꢀXPSꢀanalysis,ꢀCo ,ꢀCo ,ꢀ
36,ꢀ40
2+
3+
2-
ꢀLikewise,ꢀsingleꢀcomponentꢀNi(NO3)2ꢀorꢀCo(NO3)2ꢀ Ni ,ꢀ Ni ꢀ andꢀ S ꢀ wereꢀ observedꢀ inꢀ theꢀ near-surfaceꢀ ofꢀ theꢀ
2
4-0334).
inꢀ theꢀ DESꢀ couldꢀ beꢀ indexedꢀ toꢀ theꢀ formationꢀ ofꢀ theꢀ synthesizedꢀNiCo2S4ꢀsample,ꢀwhichꢀwasꢀconsistꢀwithꢀNiCo2S4.ꢀꢀ
correspondingꢀbinaryꢀmetalꢀsulfidesꢀNiS2ꢀ(JCPDSꢀcardꢀNo.ꢀ03- Theꢀmorphologiesꢀandꢀstructuresꢀofꢀsynthesizedꢀsamplesꢀ
734) ꢀorꢀCoS2ꢀ(JCPDSꢀcardꢀNo.ꢀ65-3322),ꢀrespectivelyꢀ(Fig.ꢀS2).ꢀ wereꢀinvestigatedꢀbyꢀscanningꢀelectronꢀmicroscopyꢀ(SEM).ꢀAsꢀ
52
0
Therefore,ꢀtheꢀformationꢀofꢀcrystallineꢀandꢀhighlyꢀpurityꢀnickelꢀ depictedꢀ inꢀ Fig.ꢀ 3a,ꢀ theꢀ as-preparedꢀ NiCo2S4ꢀ isꢀ consistedꢀ ofꢀ
cobaltꢀsulfidesꢀwasꢀprovedꢀbyꢀtheꢀXRDꢀresults.ꢀInꢀaddition,ꢀwithꢀ sphericalꢀseaꢀurchin-likeꢀnanostructureꢀwithꢀdiametersꢀaroundꢀ
theꢀmolarꢀratioꢀofꢀNi(NO3)2ꢀandꢀCo(NO3)2ꢀinꢀPEGꢀ200ꢀofꢀ1:2,ꢀtheꢀ 1.9ꢀ μm.ꢀ Theꢀ seaꢀ urchin-likeꢀ morphologyꢀ isꢀ composedꢀ ofꢀ
diffractionꢀ peaksꢀ wereꢀ wellꢀ inꢀ agreementꢀ withꢀ ternaryꢀ metalꢀ uniformlyꢀinterconnectedꢀnanorodsꢀ(uniformꢀdiameterꢀaroundꢀ
33
oxideꢀ NiCo2O4ꢀ (JCPDSꢀ cardꢀ No.ꢀ 02-1074). ꢀ Therefore,ꢀ theꢀ 70ꢀnmꢀandꢀlengthꢀofꢀ300ꢀnm)ꢀradiallyꢀgrownꢀfromꢀtheꢀcenterꢀ
preparedꢀcatalystsꢀwereꢀnamedꢀasꢀNiCo2O4,ꢀNiS2,ꢀCoS2,ꢀNiCo2S4,ꢀ (Fig.ꢀ3b).ꢀItꢀcouldꢀbeꢀspeculatedꢀthatꢀtheꢀuniqueꢀmorphologyꢀ
Ni2CoS4ꢀ +ꢀ CoS2,ꢀ andꢀ Ni2CoS4ꢀ accordingꢀ toꢀ theirꢀ composition,ꢀ mightꢀ haveꢀ aꢀ highꢀ surfaceꢀ areaꢀ owingꢀ toꢀ theꢀ hierarchicalꢀ
respectively.ꢀꢀ
structures.ꢀToꢀrecognizeꢀtheꢀcomponentsꢀofꢀNiCo2S4,ꢀelementalꢀ
mappingꢀ wasꢀ performedꢀ withꢀ energy-dispersiveꢀ X-rayꢀ
spectrometerꢀ(EDX)ꢀattachedꢀtoꢀtheꢀSEMꢀinstrumentꢀandꢀtheꢀ
correspondingꢀEDXꢀelementalꢀmappingꢀ(Fig.ꢀ3c)ꢀconfirmedꢀtheꢀ
presenceꢀofꢀevenlyꢀdispersedꢀNi,ꢀCo,ꢀandꢀSꢀelements.ꢀꢀ
ꢀ
Fig.ꢀ2ꢀa)ꢀXRDꢀpatternꢀofꢀtheꢀhierarchicallyꢀstructuredꢀNiCo
2
S
4
,ꢀandꢀXRDꢀ
dataꢀ wasꢀ indexedꢀ toꢀ JCPDSꢀ (43-1477);ꢀ XPSꢀ spectraꢀ ofꢀ theꢀ preparedꢀ
NiCo ꢀsample:ꢀb)ꢀCoꢀ2p,ꢀc)ꢀNiꢀ2pꢀandꢀd)ꢀSꢀ2p.ꢀTheꢀXPSꢀspectraꢀwereꢀ
2 4
S
fittedꢀaccordingꢀtoꢀtheꢀGaussianꢀfittingꢀmethod.ꢀꢀ
Toꢀfurtherꢀstudyꢀtheꢀnearꢀsurfaceꢀchemicalꢀcompositionsꢀ
andꢀ oxidationꢀ statesꢀ ofꢀ NiCo2S4,ꢀ X-rayꢀ photoelectronꢀ
ꢀ
2 4
spectroscopyꢀ(XPS)ꢀanalysesꢀwereꢀperformed.ꢀTheꢀexistenceꢀofꢀ Fig.ꢀ3ꢀSEMꢀimagesꢀofꢀtheꢀseaꢀurchin-likeꢀNiCo S ꢀatꢀlowꢀmagnificationꢀa)ꢀ
andꢀhighꢀmagnificationꢀb);ꢀc).ꢀEDXꢀelementalꢀmappingꢀofꢀNi,ꢀCo,ꢀandꢀSꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ3ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
Page 4 of 9
ARTICLEꢀ
JournalꢀNameꢀ
V w Article Onli
;ꢀe).ꢀHRTEMꢀimageꢀofꢀ precursorꢀofꢀmetalꢀion.ꢀForꢀsulfideꢀbasedꢀsamples,ꢀtieheꢀBETꢀareneaꢀ
elements;ꢀd).ꢀTEMꢀimageꢀofꢀanꢀindividualꢀNiCo
2
S
4
2 4
S
ꢀcollectedꢀfromꢀtheꢀmarkedꢀareaꢀinꢀd);ꢀ decreasesꢀ inꢀ theꢀ followingꢀ order:ꢀ NiCo2 DS O4 ꢀI ˃: 1ꢀ 0N . 1i 0S 32 ꢀ9 ˃/ Cꢀ 7N Gi 2C C0 o1 0S 14 2ꢀ E˃ ꢀ
hierarchicallyꢀstructuredꢀNiCo
andꢀf).ꢀHRTEMꢀimageꢀandꢀtheꢀcorrespondingꢀlatticeꢀfringesꢀofꢀNiCo
2
S
4
.ꢀꢀ CoS2ꢀ˃ꢀNi2CoS4ꢀ+ꢀCoS2.ꢀInꢀaddition,ꢀtheꢀporeꢀdistributionꢀofꢀallꢀ
theꢀsamplesꢀisꢀwellꢀconsistentꢀwithꢀtheꢀsizesꢀofꢀporesꢀshownꢀinꢀ
Theꢀ detailedꢀ morphologyꢀ andꢀ hierarchicallyꢀ structuredꢀ HRTEMꢀresults.ꢀꢀ
NiCo2S4ꢀcanꢀbeꢀconfirmedꢀbyꢀtransmissionꢀelectronꢀmicroscopyꢀ
(
(
TEM)ꢀ andꢀ high-resolutionꢀ transmissionꢀ electronꢀ microscopyꢀ
HRTEM),ꢀasꢀshownꢀinꢀFig.ꢀ3d-3f.ꢀAnꢀindividualꢀseaꢀurchinꢀlike-
NiCo2S4ꢀwithꢀaꢀdiameterꢀofꢀaboutꢀ1.9ꢀμmꢀisꢀdepictedꢀinꢀFigꢀ3d,ꢀ
whichꢀisꢀinꢀaccordanceꢀwithꢀtheꢀSEMꢀresult.ꢀAfterwards,ꢀfromꢀ
theꢀ HRTEMꢀ imageꢀ inꢀ Fig.ꢀ 3e,ꢀ theꢀ seaꢀ urchin-likeꢀ NiCo2S4ꢀ hasꢀ
hierarchicallyꢀporousꢀstructureꢀrangingꢀfromꢀ1ꢀnmꢀtoꢀ20ꢀnm.ꢀInꢀ
addition,ꢀ anꢀ HRTEMꢀ imageꢀ takenꢀ fromꢀ Fig.ꢀ 3eꢀ (shownꢀ inꢀ theꢀ
insetꢀofꢀFig.ꢀ3f)ꢀconfirmedꢀtheꢀcrystallineꢀnatureꢀofꢀNiCo2S4.ꢀTheꢀ
latticeꢀfringesꢀdisplayedꢀinꢀFig.ꢀ3fꢀincludingꢀ0.241ꢀnmꢀandꢀ0.235ꢀ
nmꢀ couldꢀ be,ꢀ respectively,ꢀ indexedꢀ toꢀ theꢀ (311)ꢀ andꢀ (400)ꢀ
crystalꢀplanes,ꢀsuggestingꢀtheꢀformationꢀofꢀNiCo2S4.ꢀTheꢀspecialꢀ
interconnectedꢀ nanorodꢀ structureꢀ andꢀ theꢀ resultingꢀ
mesoporousꢀandꢀmicroporousꢀstructuresꢀmayꢀcreateꢀplentifulꢀ
ꢀ
57
catalyticꢀsitesꢀandꢀpromoteꢀtheꢀmassꢀtransportationꢀinꢀOER. ꢀꢀꢀ
Theꢀ morphologyꢀ ofꢀ otherꢀ samplesꢀ wasꢀ alsoꢀ studiedꢀ byꢀ
SEMꢀandꢀHRTEM,ꢀandꢀtheꢀrelatedꢀresultsꢀareꢀgivenꢀinꢀFig.ꢀS3-S7.ꢀ
Flower-likeꢀternaryꢀmetalꢀoxideꢀNiCo2O4ꢀwithꢀaꢀmeanꢀdiameterꢀ
ofꢀaboutꢀ3ꢀμmꢀwasꢀobservedꢀ(Fig.ꢀS3a).ꢀAndꢀtheꢀpetalsꢀofꢀtheꢀ
flowersꢀareꢀmadeꢀupꢀofꢀporousꢀ2Dꢀnanosheetsꢀ(Fig.ꢀS3b).ꢀTheꢀ
hierarchicallyꢀ structuredꢀ NiCo2O4ꢀ couldꢀ beꢀ furtherꢀ confirmedꢀ
byꢀHRTEMꢀimagesꢀ(Fig.ꢀS3c-3d).ꢀTheꢀas-synthesizedꢀNi2CoS4ꢀisꢀ
composedꢀofꢀnanorodsꢀwithꢀ100-150ꢀnmꢀwideꢀandꢀupꢀtoꢀaboutꢀ
Fig.ꢀ4ꢀNitrogenꢀadsorptionꢀandꢀdesorptionꢀisothermsꢀandꢀtheꢀinsertedꢀ
2 4
correspondingꢀporeꢀsizeꢀdistributionꢀofꢀtheꢀNiCo S .ꢀꢀ
TheꢀelectrocatalyticꢀOERꢀperformanceꢀofꢀtheꢀsamplesꢀwasꢀ
-1
determinedꢀ inꢀ 1ꢀ Mꢀ KOHꢀ solutionꢀ atꢀ 5ꢀ mV·s ꢀ usingꢀ aꢀ threeꢀ
electrodeꢀelectrochemicalꢀconfigurationꢀwithꢀAg/AgClꢀ(3MꢀKCl)ꢀ
asꢀtheꢀreferenceꢀelectrodeꢀandꢀplatinumꢀwireꢀasꢀtheꢀcounterꢀ
electrode.ꢀItꢀshouldꢀbeꢀnotedꢀthatꢀtheꢀworkingꢀelectrodesꢀwereꢀ
obtainedꢀ byꢀ theꢀ modificationꢀ ofꢀ theꢀ as-preparedꢀ samplesꢀ
(
50ꢀ nmꢀ inꢀ lengthꢀ (Fig.ꢀ S4).ꢀ Inꢀ addition,ꢀ nanorodsꢀ andꢀ
catalysts)ꢀonꢀtheꢀsimpleꢀglassyꢀcarbonꢀ(GC)ꢀelectrodeꢀ(notꢀonꢀ
4
metalꢀ foam,ꢀ carbonꢀ cloth,ꢀ orꢀ carbonꢀ paperꢀ electrodesꢀ withꢀ
largeꢀ supportiveꢀ surfaceꢀ areasꢀ highꢀ non-Faradaicꢀ backgroundꢀ
current)ꢀ utilizingꢀ theꢀ drop-castingꢀ method,ꢀ respectively.ꢀ Forꢀ
comparison,ꢀtheꢀOERꢀperformanceꢀofꢀotherꢀfourꢀsamplesꢀwasꢀ
alsoꢀtestedꢀunderꢀtheꢀsameꢀconditions.ꢀBecauseꢀofꢀtheꢀeffectꢀofꢀ
ohmicꢀ resistance,ꢀ theꢀ as-measuredꢀ reactionꢀ currentsꢀ didꢀ notꢀ
nanoparticlesꢀ wereꢀ shownꢀ inꢀ theꢀ synthesizedꢀ mixtureꢀ ofꢀ
Ni2CoS4ꢀ andꢀ CoS2ꢀ (Fig.ꢀ S5).ꢀ Unlikeꢀ ternaryꢀ metalꢀ sulfides,ꢀ theꢀ
hierarchicallyꢀ structuredꢀ binaryꢀ metalꢀ sulfideꢀ (NiS2ꢀ andꢀ CoS2)ꢀ
areꢀ composedꢀ ofꢀ rough-surfacedꢀ sphericalꢀ particlesꢀ withꢀ
similarꢀsizesꢀ(Fig.ꢀS6-S7).ꢀTheꢀmeanꢀdiameterꢀofꢀNiS2ꢀandꢀCoS2ꢀ
wasꢀ 150ꢀ nmꢀ andꢀ 240ꢀ nm,ꢀ respectively.ꢀ Theꢀ latticeꢀ fringesꢀ
depictedꢀinꢀtheꢀHRTEMꢀimagesꢀwereꢀwellꢀconsistentꢀwithꢀtheꢀ
formerꢀXRDꢀpattern.ꢀꢀ
19
directlyꢀ reflectꢀ theꢀ intrinsicꢀ performanceꢀ ofꢀ catalysts. ꢀ Weꢀ
appliedꢀ anꢀ iRꢀ correctionꢀ toꢀ allꢀ theꢀ originalꢀ dataꢀ forꢀ furtherꢀ
analysisꢀ(Fig.ꢀ5).ꢀꢀ
absorption-desorptionꢀ isothermsꢀ andꢀ theꢀ
N2ꢀ
correspondingꢀ poreꢀ sizeꢀ distributionꢀ plotsꢀ ofꢀ theꢀ synthesizedꢀ
samplesꢀareꢀdisplayedꢀinꢀFig.ꢀ4ꢀandꢀFig.ꢀS8-12.ꢀAsꢀshownꢀinꢀFig.ꢀ
4
,ꢀNiCo2S4ꢀpresentsꢀaꢀtypeꢀIVꢀisothermꢀaccordingꢀtoꢀtheꢀrulesꢀ
58
setꢀ byꢀ Unionꢀ ofꢀ Pureꢀ andꢀ Appliedꢀ Chemistryꢀ (IUPAC), ꢀ
suggestingꢀtheꢀnatureꢀofꢀmesoporousꢀmaterial.ꢀAndꢀtheꢀsampleꢀ
hasꢀ aꢀ relativelyꢀ highꢀ Brunauer-Emmett-Tellerꢀ (BET)ꢀ surfaceꢀ
2
-1
areaꢀ ofꢀ 33.1ꢀ m ·g ꢀ withꢀ meanꢀ poreꢀ diameterꢀ ofꢀ 8.93ꢀ nm.ꢀ
Besides,ꢀ theꢀ absorption-desorptionꢀ curveꢀ wasꢀ usedꢀ toꢀ
introduceꢀtheꢀporeꢀsizeꢀdistributionꢀbyꢀtheꢀBJHꢀmethodꢀandꢀtheꢀ
resultꢀshowsꢀthatꢀtheꢀsizeꢀofꢀtheꢀporesꢀrangesꢀfromꢀ1ꢀnmꢀtoꢀ20ꢀ
nm,ꢀwhichꢀisꢀinꢀaccordanceꢀwithꢀHRTEMꢀimageꢀ(Fig.ꢀ3e).ꢀTheꢀ
hierarchicalꢀporousꢀNiCo2S4ꢀincludingꢀmesoporeꢀandꢀmicroporeꢀ
mayꢀ beꢀ inꢀ favorꢀ ofꢀ theꢀ diffusionꢀ ofꢀ theꢀ activeꢀ speciesꢀ andꢀ
39,ꢀ59
releaseꢀofꢀgas.
ꢀTheꢀN2ꢀabsorption-desorptionꢀisothermsꢀofꢀ
otherꢀ fiveꢀ samplesꢀ areꢀ depictedꢀ inꢀ Fig.ꢀ S8-12ꢀ andꢀ theꢀ
correspondingꢀparametersꢀincludingꢀBETꢀareaꢀandꢀmeanꢀporeꢀ
diameterꢀareꢀshownꢀinꢀTableꢀS1.ꢀInterestingly,ꢀitꢀwasꢀobservedꢀ
ꢀ
thatꢀtheꢀBETꢀarea,ꢀtheꢀmeanꢀporeꢀsizeꢀandꢀdistributionꢀofꢀtheꢀ Fig.ꢀ 5ꢀ a)ꢀ Polarizationꢀ curvesꢀ andꢀ b)ꢀ Overpotentialsꢀ ofꢀ NiCo
2 4 2
O ,ꢀ NiS ,ꢀ
hierarchicalꢀ porousꢀ sulfidesꢀ wereꢀ associatedꢀ withꢀ theꢀ CoS ,ꢀNiCo ,ꢀNi CoS ꢀ+ꢀCoS ,ꢀandꢀNi CoS ꢀmodifiedꢀGCꢀelectrodesꢀinꢀ1ꢀ
2
2
S
4
2
4
2
2
4
4
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Page 5 of 9
Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
JournalꢀNameꢀ
ꢀARTICLEꢀ
-
1
61
MꢀKOHꢀatꢀ5ꢀmV·s ꢀutilizingꢀAg/AgClꢀ(3MꢀKCl)ꢀelectrodeꢀandꢀPtꢀwireꢀasꢀ NiCo
theꢀ referenceꢀ andꢀ counterꢀ electrode,ꢀ respectively;ꢀ c)ꢀ Tafelꢀ plotsꢀ
doped-rGO
obtainedꢀfromꢀpolarizationꢀcurvesꢀinꢀa);ꢀandꢀd)ꢀNyquistꢀplotꢀofꢀNiCo ,ꢀ
Ni Co
NiS ,ꢀCoS ,ꢀNiCo ,ꢀNi CoS ꢀ+ꢀCoS ,ꢀandꢀNi CoS ꢀelectrocatalystsꢀforꢀtheꢀ
2
S
4
@N/Sꢀ
0.1ꢀMꢀ
KOH
0.1ꢀMꢀ
KOH
1ꢀMꢀ
GC
GC
GC
ꢀ
ꢀ
ꢀ
-
-
ꢀ
ꢀ
470
ꢀ
View-ꢀArticle Onli[n1e] ꢀ
DOI: 10.1039/C7GC01012E
ꢀ
ꢀ
6
2
2
O
4
1
1
ꢀ
399
339
ꢀ
ꢀ
87.3
64.0
60.0
ꢀ
ꢀ
ꢀ
[2] ꢀ
2
2
2
S
4
2
4
2
2
4
ꢀ
6
3
OERꢀ carriedꢀ outꢀ underꢀ potentialꢀ ofꢀ 1.51ꢀ Vꢀ (vs.ꢀ RHE)ꢀ andꢀ theꢀ fittingꢀ
resultꢀwasꢀshownꢀasꢀsolidꢀtraces.ꢀꢀ
Co
9
S
8
/S-C-
1
280
330
230
ꢀ
ꢀ
ꢀ
[3] ꢀ
800 ꢀ
KOH
ꢀ
5
4
NiCo
2
O
4
ꢀ
1ꢀMꢀ
Tiꢀfoil
ꢀ
-
-
ꢀ
ꢀ
[4] ꢀ
Theꢀ linearꢀ sweepꢀ voltammetryꢀ (LSV)ꢀ curvesꢀ onꢀ aꢀ
reversibleꢀ hydrogenꢀ electrodeꢀ (RHE,ꢀ allꢀ potentialsꢀ relatedꢀ inꢀ
thisꢀ workꢀ wereꢀ vs.ꢀ RHEꢀ unlessꢀ statedꢀ otherwise)ꢀ scaleꢀ areꢀ
KOH
ꢀ
2
3
β-Ni(OH)
2
ꢀ
1ꢀMꢀ
GC
GC
ꢀ
ꢀ
132
71.0
67.5
84.0
71.0
ꢀ
[5] ꢀ
KOH
ꢀ
2
60
[6] ꢀ
presentedꢀ inꢀ Fig.ꢀ 5a.ꢀ Inꢀ eachꢀ LSVꢀ measurement,ꢀ theꢀ voltageꢀ NꢀdopedꢀCG -
1ꢀMꢀ
-
ꢀ
340
350
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
appliedꢀtoꢀtheꢀworkingꢀelectrodeꢀwasꢀlinearlyꢀsweptꢀfromꢀ1.00ꢀ
toꢀ1.65ꢀV.ꢀFig.ꢀ5aꢀindicatesꢀthatꢀallꢀtheꢀmodifiedꢀGCꢀelectrodesꢀ
showedꢀhighꢀperformanceꢀtowardꢀOER,ꢀwhereasꢀtheꢀbareꢀGCꢀ
electrodeꢀ showedꢀ negligibleꢀ OERꢀ performanceꢀ (Fig.ꢀ S13,ꢀ theꢀ Co
CoOꢀ
KOH
ꢀ
3
1
2
Cu O-Cuꢀ
1ꢀMꢀ
Cuꢀ
foam
Niꢀ
250
290
240
ꢀ
ꢀ
ꢀ
[7] ꢀ
KOH
ꢀ
ꢀ
3
20
[8] ꢀ
3
O
4
ꢀMTA ꢀ
1ꢀMꢀ
-
ꢀ
-
2
currentꢀdensityꢀreachedꢀ0.3ꢀmA·cm ꢀbyꢀapplyingꢀ1.65ꢀV).ꢀTheꢀ
substrateꢀ ofꢀ theꢀ GCꢀ contributesꢀ littleꢀ toꢀ theꢀ OERꢀ activity,ꢀ
implyingꢀthatꢀtheꢀcatalystsꢀareꢀmainlyꢀresponsibleꢀforꢀtheꢀOERꢀ
activity.ꢀ Theꢀ onsetꢀ potentialꢀ (theꢀ currentꢀ densityꢀ reachedꢀ 1ꢀ
KOH
ꢀ
foam
Niꢀ
ꢀ
ꢀ
6
4
IrO
2
ꢀ
1ꢀMꢀ
290
ꢀ
[9] ꢀ
KOH
ꢀ
foam
1
o
S-C-800,ꢀSꢀdopedꢀCꢀobtainedꢀatꢀcalcinationꢀtemperatureꢀofꢀ800ꢀ C;ꢀ N-
2
-
2
mA·cm )ꢀofꢀNiCo2S4ꢀmodifiedꢀGCꢀelectrodeꢀwasꢀ1.45ꢀVꢀversusꢀ
RHE,ꢀwhichꢀwasꢀmuchꢀsmallerꢀthanꢀNiCo2O4ꢀ(1.54ꢀV),ꢀNiS2ꢀ(1.54ꢀ
V),ꢀCoS2ꢀ(1.53ꢀV),ꢀNi2CoS4ꢀ+ꢀCoS2ꢀ(1.52ꢀV),ꢀandꢀNi2CoS4ꢀ(1.55ꢀV).ꢀ
Inꢀ otherꢀ words,ꢀ theꢀ NiCo2S4ꢀ exhibitedꢀ theꢀ lowestꢀ onsetꢀ
potentialꢀcomparedꢀwithꢀotherꢀcatalysts,ꢀsuggestingꢀitsꢀhigherꢀ
OERꢀ performanceꢀ comparedꢀ withꢀ otherꢀ sulfides.ꢀ Thoughꢀ
hierarchicalꢀ porousꢀ NiCo2O4ꢀ hasꢀ largerꢀ BETꢀ areas,ꢀ itsꢀ OERꢀ
performanceꢀwasꢀlowerꢀthanꢀNiCo2S4,ꢀwhichꢀmightꢀbeꢀdueꢀtoꢀ
3
dopedꢀCG,ꢀN-dopedꢀ3Dꢀcrumpledꢀgraphene;ꢀ MTA,ꢀmicrotubeꢀarrays;ꢀ
4
ɳ
onset,ꢀ onsetꢀ overpotential,ꢀ wasꢀ donatedꢀ asꢀ theꢀ overpotentialꢀ atꢀ theꢀ
-
currentꢀdensityꢀofꢀ1ꢀmA·cm ;ꢀ ɳ,ꢀoverpotentialꢀatꢀtheꢀcurrentꢀdensityꢀofꢀ
2 5
-
0ꢀmA·cm .ꢀꢀ
2
1
Theꢀ superiorꢀ OERꢀ performanceꢀ ofꢀ NiCo2S4ꢀ couldꢀ beꢀ
attributedꢀtoꢀseveralꢀfactors.ꢀFirstly,ꢀtheꢀcloselyꢀpackedꢀarraysꢀ
2-
2-
ofꢀ largeꢀ S ꢀ anionsꢀ (largerꢀ thanꢀ O ꢀ anions)ꢀ withꢀ Niꢀ andꢀ Coꢀ
26
theꢀbiggerꢀbandꢀgapꢀexistingꢀinꢀoxides. ꢀMoreover,ꢀtheꢀhigherꢀ
activityꢀ ofꢀ as-preparedꢀ NiCo2S4ꢀ isꢀ alsoꢀ evidentꢀ fromꢀ theꢀ
smallestꢀoverpotentialꢀcomparedꢀwithꢀrecentlyꢀreportedꢀmetalꢀ
oxidesꢀandꢀsulfidesꢀatꢀfixedꢀcurrentꢀdensity.ꢀNiCo2S4ꢀexhibitedꢀ
anꢀoverpotentialꢀofꢀ337ꢀmVꢀ(Fig.ꢀ5b)ꢀatꢀaꢀfixedꢀcurrentꢀdensityꢀ
2+
3+
2+
3+
cationsꢀ inꢀ variousꢀ valenceꢀ statesꢀ (Ni ,ꢀ Ni ,ꢀ Co ,ꢀ andꢀ Co )ꢀ
presentꢀinꢀNiCo2S4ꢀ(asꢀshownꢀinꢀFig.ꢀ2b-2d),ꢀresultingꢀinꢀmoreꢀ
activeꢀ siteꢀ forꢀ efficientꢀ OERꢀ performanceꢀ atꢀ aꢀ lowꢀ activationꢀ
55
potential. ꢀ Secondly,ꢀ goodꢀ electronicꢀ conductivityꢀ ofꢀ Niꢀ andꢀ
Coꢀ facilitatesꢀ electronꢀ transferꢀ toꢀ theꢀ substrate.ꢀ Thirdly,ꢀ theꢀ
hierarchicallyꢀ structureꢀ isꢀ beneficialꢀ forꢀ enhancingꢀ theꢀ OERꢀ
performanceꢀbecauseꢀofꢀtheꢀincreasingꢀactiveꢀsitesꢀexposedꢀinꢀ
electrolyteꢀandꢀtheꢀeasyꢀreleaseꢀofꢀO2ꢀgas.ꢀInꢀaddition,ꢀtheꢀBETꢀ
areaꢀ ofꢀ NiCo2S4ꢀ wasꢀ higherꢀ thanꢀ thatꢀ ofꢀ otherꢀ catalysts.ꢀ
Therefore,ꢀrelativelyꢀhighꢀBrunauer-Emmett-Tellerꢀ(BET)ꢀarea,ꢀ
abundantꢀactiveꢀsites,ꢀeasyꢀdiffusionꢀofꢀelectrolytesꢀandꢀoxygenꢀ
-2
ofꢀ 10ꢀ mA·cm ꢀ whichꢀ wasꢀ lowerꢀ thanꢀ NiCoꢀ layeredꢀ doubleꢀ
25
hydroxideꢀ (367ꢀ mV), ꢀ N-dopedꢀ 3Dꢀ crumpledꢀ graphene-CoOꢀ
54
6
0
(
340ꢀmV), ꢀandꢀNiCo2O4ꢀ(360ꢀmV). ꢀTheꢀsynthesizedꢀNiCo2O4ꢀ
requiredꢀ anꢀ overpotentialꢀ ofꢀ 377ꢀ mVꢀ toꢀ affordꢀ aꢀ currentꢀ
-2
densityꢀofꢀ10ꢀmA·cm ,ꢀwhichꢀwasꢀ38ꢀmVꢀhigherꢀthanꢀthatꢀofꢀ
NiCo2S4.ꢀAꢀmoreꢀdetailedꢀcomparisonꢀwasꢀgivenꢀinꢀTableꢀ1.ꢀꢀ
Tableꢀ1ꢀOERꢀbehaviorsꢀcomparisonꢀbetweenꢀtheꢀsynthesizedꢀcatalystsꢀ gas,ꢀandꢀstrongꢀstructureꢀintegrityꢀcontributeꢀtoꢀtheꢀfullꢀuseꢀofꢀ
andꢀ representativeꢀ metalꢀ oxidesꢀ andꢀ sulfidesꢀ catalystsꢀ publishedꢀ inꢀ theꢀ wholeꢀ catalystꢀ whenꢀ performingꢀ theꢀ electrochemicalꢀ
literature.ꢀꢀ
reactions.ꢀꢀ
Forꢀ betterꢀ understandingꢀ theꢀ kineticsꢀ process,ꢀ theꢀ
4
5
ɳ
onset
ꢀ
ɳꢀ
Catalysts
ꢀ
Electro
Subs-
trate
Tafelꢀslopeꢀ
Ref.ꢀ correspondingꢀTafelꢀplotsꢀofꢀtheꢀcatalystsꢀwereꢀobtainedꢀfromꢀ
theꢀ polarizationꢀ curves.ꢀ Thoseꢀ Tafelꢀ plotsꢀ wereꢀ fittedꢀ toꢀ theꢀ
Oursꢀ equation:ꢀ ɳꢀ =ꢀ bꢀ logꢀ jꢀ +ꢀ a,ꢀ whereꢀ ɳꢀ isꢀ overpotential,ꢀ jꢀ isꢀ theꢀ
currentꢀ density,ꢀ andꢀ bꢀ isꢀ theꢀ Tafelꢀ slope.ꢀ Seaꢀ urchin-likeꢀ
-
1
(
mV)
ꢀ
(mV)
ꢀ
-
lytes
1ꢀMꢀ
ꢀ
ꢀ
(mV·dec )ꢀ
NiCo
2
S
4
ꢀ
GC
GC
GC
GC
GC
GC
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
220
ꢀ
337
377
413
428
399
386
ꢀ
64.0
91.0
94.0
ꢀ
ꢀ
ꢀ
KOH
ꢀ
-1
NiCo
2
O
4
ꢀ
1ꢀMꢀ
333
296
308
318
296
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Oursꢀ NiCo2S4ꢀ possessedꢀ theꢀ lowestꢀ Tafelꢀ slopeꢀ (64ꢀ mV·dec )ꢀ
-1
-1
comparedꢀwithꢀNiCo2O4ꢀ(91ꢀmV·dec ),ꢀNiS2ꢀ(94ꢀmV·dec ),ꢀCoS2ꢀ
KOH
ꢀ
-
1
-1
NiS
2
ꢀ
1ꢀMꢀ
Oursꢀ (103ꢀmV·dec ),ꢀNi2CoS4ꢀ+ꢀCoS2ꢀ(94ꢀmV·dec ),ꢀandꢀNi2CoS4ꢀ(91ꢀ
-1
KOH
ꢀ
mV·dec ),ꢀandꢀwasꢀevenꢀsmallerꢀthanꢀthatꢀofꢀtheꢀreportedꢀIrO2ꢀ
-
1 64
CoS
2
ꢀ
1ꢀMꢀ
103
94.0
91.0
ꢀ
Oursꢀ (71ꢀ mV·dec ), ꢀ implyingꢀ itsꢀ moreꢀ favorableꢀ reactionꢀ kineticsꢀ
forꢀOERꢀ(Fig.ꢀ5c).ꢀTheꢀimprovedꢀOERꢀperformanceꢀofꢀNiCo2S4ꢀ
Oursꢀ wasꢀ originatedꢀ fromꢀ itsꢀ shortꢀ diffusionꢀ routeꢀ andꢀ fastꢀ
transportationꢀforꢀactiveꢀspecies,ꢀandꢀtheꢀeasyꢀreleaseꢀofꢀtheꢀ
Oursꢀ formedꢀO2ꢀgasꢀbubbles.ꢀꢀ
KOH
ꢀ
Ni
2
CoS
4
ꢀ+ꢀ
1ꢀMꢀ
ꢀ
ꢀ
CoS
2
ꢀ
KOH
ꢀ
Ni
2
4
CoS ꢀ
1ꢀMꢀ
KOH
ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ5ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
Page 6 of 9
ARTICLEꢀ
JournalꢀNameꢀ
Moreover,ꢀ theꢀ reactionꢀ kineticsꢀ ofꢀ theseꢀ samplesꢀ wasꢀ AsꢀshownꢀinꢀFigureꢀ5f,ꢀtheꢀmeasuredꢀamountꢀofꢀoxygenꢀwasꢀininꢀ
View Article Onl e
investigatedꢀbyꢀelectrochemicalꢀimpedanceꢀspectroscopyꢀ(EIS)ꢀ goodꢀ agreementꢀ withꢀ theꢀ theoretica Dl ꢀO aI : m1 0 o. 1 u0 n3 9t ꢀ/ C c7 aG l Cc u0 1l a0 t1 e2 Ed ꢀ
analysesꢀandꢀtheꢀcorrespondingꢀresultsꢀwereꢀdisplayedꢀinꢀFig.ꢀ accordingꢀ toꢀ theꢀ transferredꢀ charge.ꢀ Theꢀ FEꢀ ofꢀ 95.8%ꢀ wasꢀ
5
d.ꢀTheꢀNyquistꢀplotsꢀwereꢀfittedꢀwithꢀtheꢀsimplifiedꢀRandlesꢀ obtainedꢀbasedꢀonꢀtheꢀexperimentalꢀandꢀtheoreticalꢀamountsꢀ
equivalentꢀ circuitꢀ andꢀ presentedꢀ inꢀ Fig.ꢀ S14.ꢀ Theꢀ fittingꢀ ofꢀ theꢀ evolvedꢀ O2ꢀ gas,ꢀ implyingꢀ thatꢀ theꢀ producedꢀ chargesꢀ
impedanceꢀ parametersꢀ includingꢀ theꢀ uncompensatedꢀ seriesꢀ wereꢀ nearlyꢀ consumedꢀ forꢀ OERꢀ (Fig.ꢀ S17).ꢀ ꢀ CPꢀ andꢀ CAꢀ
resistanceꢀRs,ꢀtheꢀchargeꢀtransferꢀresistanceꢀ(Rct)ꢀwhichꢀcanꢀbeꢀ experimentsꢀ ofꢀ theꢀ otherꢀ synthesizedꢀ samplesꢀ includingꢀ
assignedꢀtoꢀcharge-transferꢀprocessꢀofꢀoxygenꢀevolutionꢀatꢀtheꢀ NiCo2O4,ꢀ NiS2,ꢀ CoS2,ꢀ Ni2CoS4ꢀ +ꢀ CoS2,ꢀ andꢀ Ni2CoS4ꢀ wereꢀ
catalystꢀ interface,ꢀ andꢀ theꢀ accompanyingꢀ double-layerꢀ performedꢀandꢀtheꢀresultsꢀwereꢀdisplayedꢀinꢀFig.ꢀS18.ꢀAllꢀtheꢀ
capacitanceꢀ Cdlꢀ wereꢀ listedꢀ inꢀ Tableꢀ S1.ꢀ Theꢀ Rsꢀ valuesꢀ ofꢀ theꢀ samplesꢀexhibitedꢀlong-termꢀstability.ꢀꢀ
NiCo2O4,ꢀNiS2,ꢀCoS2,ꢀNiCo2S4,ꢀCoS2ꢀ+ꢀNi2CoS4,ꢀandꢀNi2CoS4ꢀwereꢀ
similarꢀ indictingꢀ thatꢀ theꢀ experimentalꢀ configurationꢀ wasꢀ
consistent.ꢀ Theꢀ Rctꢀ valuesꢀ increasedꢀ inꢀ theꢀ followingꢀ order:ꢀ
-2
-2
NiCo2S4ꢀ(7.046ꢀΩ·cm )ꢀ˂ꢀNiCo2O4ꢀ(10.37ꢀΩ·cm )ꢀ˂ꢀNiS2ꢀ(17.70ꢀ
-
2
-2
Ω·cm )ꢀ˂ꢀCoS2ꢀ(32.68ꢀΩ·cm )ꢀ˂ꢀCoS2ꢀ+ꢀNi2CoS4ꢀ(65.98ꢀΩ·cm )ꢀ˂ꢀ
-2
-2
Ni2CoS4ꢀ (63.06ꢀ Ω·cm ).ꢀ Aꢀ fastꢀ chargeꢀ transferꢀ rateꢀ (whichꢀ isꢀ
characterizedꢀ byꢀ theꢀ smallestꢀ Rctꢀ value)ꢀ occurringꢀ atꢀ theꢀ
NiCo2S4ꢀ couldꢀ beꢀ attributedꢀ toꢀ itsꢀ abundantꢀ activeꢀ sitesꢀ andꢀ
excellentꢀ electronicꢀ conductivity.ꢀ Thisꢀ furtherꢀ ledꢀ toꢀ theꢀ
improvementꢀ ofꢀ accessꢀ ofꢀ currentꢀ onꢀ theꢀ electrodeꢀ andꢀ theꢀ
ꢀ
24
enhancementꢀ ofꢀ theꢀ capabilityꢀ ofꢀ chargeꢀ transport. ꢀ Theꢀ
NiCo2S4ꢀ hadꢀ abundantꢀ electrocatalyticꢀ sitesꢀ andꢀ largeꢀ activeꢀ
surfaceꢀarea,ꢀwhichꢀcanꢀbeꢀprovedꢀbyꢀtheꢀrelatedꢀdouble-layerꢀ
capacitanceꢀ(Cdl).ꢀTheꢀdataꢀofꢀCdlꢀderivedꢀfromꢀtheꢀEISꢀanalysisꢀ
Fig.ꢀ6ꢀa)ꢀChronopotentiometryꢀtestꢀofꢀOERꢀbyꢀNiCo
2
S
4
ꢀmodifiedꢀGCꢀelectrodeꢀ
-2
inꢀ1ꢀMꢀKOHꢀatꢀaꢀcurrentꢀdensityꢀofꢀ10ꢀmA·cm ;ꢀandꢀb)ꢀPolarizationꢀcurveꢀofꢀ
NiCo
2 4
S ꢀmodifiedꢀGCꢀelectrodeꢀbeforeꢀ(blackꢀline)ꢀandꢀafterꢀ2000ꢀcyclesꢀ(redꢀ
dashedꢀline).ꢀꢀ
-2
wereꢀlistedꢀinꢀTableꢀS1.ꢀTheꢀCdlꢀofꢀNiCo2S4ꢀreachesꢀ9.95ꢀμF·cm ,ꢀ
-2
whichꢀ isꢀ higherꢀ thanꢀ thoseꢀ ofꢀ NiCo2O4ꢀ (8.699ꢀ μF·cm ),ꢀ NiS2ꢀ
-2
-
2
(
9,637ꢀ μF·cm ),ꢀ CoS2ꢀ (9.090ꢀ μF·cm ),ꢀ Ni2CoS4ꢀ +ꢀ CoS2ꢀ (9.264ꢀ Experimentalꢀꢀ
-
2
-
2
μF·cm ),ꢀ andꢀ Ni2CoS4ꢀ (9.008ꢀ μF·cm )ꢀ (shownꢀ inꢀ Tableꢀ S1).ꢀ
Therefore,ꢀ theꢀ NiCo2S4ꢀ hasꢀ moreꢀ effectiveꢀ activeꢀ sitesꢀ forꢀ
waterꢀ oxidationꢀ comparedꢀ withꢀ otherꢀ mentionedꢀ
ChemicalsꢀandꢀMaterialsꢀꢀ
PEGꢀ 200,ꢀ thiourea,ꢀ nickel(II)ꢀ nitrateꢀ hexahydrate,ꢀ andꢀ
cobaltous(II)ꢀ nitrateꢀ hexahydrateꢀ wereꢀ purchasedꢀ fromꢀ
Sinopharmꢀ Chemicalꢀ Reagentꢀ Co.,ꢀ Ltd..ꢀ Allꢀ chemicalsꢀ wereꢀ
28,ꢀ65,ꢀ66
electrocatalysts. ꢀꢀꢀ
Inꢀtheꢀviewꢀofꢀpracticalꢀapplication,ꢀlong-termꢀstabilityꢀofꢀ
theꢀ electrocatalystsꢀ isꢀ anotherꢀ importantꢀ parameter.ꢀ Theꢀ analyticalꢀ gradeꢀ andꢀ usedꢀ asꢀ receivedꢀ withoutꢀ furtherꢀ
-1
chronopotentiometryꢀ (CP)ꢀ experimentꢀ wasꢀ usedꢀ toꢀ evaluateꢀ purification.ꢀ Milli-Qꢀ waterꢀ ofꢀ 18.2ꢀ MΩ·cm ꢀ wasꢀ usedꢀ inꢀ allꢀ
theꢀelectrocatalyticꢀdurabilityꢀofꢀNiCo2S4ꢀforꢀOERꢀinꢀ1ꢀMꢀKOHꢀ experiments.ꢀ
withoutꢀ iRꢀ compensation.ꢀ Asꢀ depictedꢀ inꢀ Fig.ꢀ 6a,ꢀ theꢀ
overpotentialꢀofꢀNiCo2S4ꢀwasꢀalmostꢀunchangedꢀatꢀtheꢀcurrentꢀ
ꢀ
Syntheticꢀproceduresꢀꢀꢀ
-2
Synthesisꢀ ofꢀ NiCo S .ꢀ Inꢀ aꢀ typicalꢀ synthesisꢀ process,ꢀ theꢀ
2
4
densityꢀ ofꢀ 10ꢀ mA·cm ꢀ forꢀ thirtyꢀ hours,ꢀ suggestingꢀ thatꢀ theꢀ
deepꢀ eutecticꢀ solvothermalꢀ synthesizedꢀ NiCo2S4ꢀ ownedꢀ
excellentꢀ stabilityꢀ forꢀ OERꢀ inꢀ alkalineꢀ media.ꢀ Theꢀ uniqueꢀ
structureꢀ ofꢀ hierarchicalꢀ porousꢀ NiCo2S4ꢀ ensuredꢀ theꢀ easyꢀ
PEGylatedꢀ DESꢀ wasꢀ obtainedꢀ byꢀ simplyꢀ mixingꢀ polyethyleneꢀ
glycolꢀ 200ꢀ (PEGꢀ 200)ꢀ andꢀ thioureaꢀ inꢀ theꢀ molarꢀ ratioꢀ ofꢀ 2:1.ꢀ
Then,ꢀ 10ꢀ mmolꢀ Ni(NO3)2·6H2Oꢀ (2.91ꢀ g)ꢀ andꢀ 20ꢀ mmolꢀ
releaseꢀ ofꢀ theꢀ O2ꢀ gas.ꢀ Asꢀ aꢀ result,ꢀ theꢀ NiCo2S4ꢀ behavedꢀ theꢀ Co(NO3)2·6H2Oꢀ(5.82ꢀg)ꢀwereꢀdissolvedꢀinꢀ40ꢀmlꢀPEGylatedꢀDESꢀ
necessaryꢀenhancedꢀstabilityꢀandꢀdurabilityꢀforꢀprolongedꢀOERꢀ toꢀformꢀaꢀhomogeneousꢀsolution.ꢀFollowing,ꢀtheꢀmixtureꢀwasꢀ
operation.ꢀAfterꢀtheꢀCPꢀtestꢀforꢀthirtyꢀhours,ꢀtheꢀmorphologyꢀofꢀ putꢀ intoꢀ aꢀ 50ꢀ mlꢀ Teflon-linedꢀ stainlessꢀ steelꢀ autoclave.ꢀ Theꢀ
NiCo2S4ꢀwasꢀexaminedꢀbyꢀSEMꢀ(FigꢀS15)ꢀandꢀtheꢀresultꢀshowedꢀ autoclaveꢀ wasꢀ treatedꢀ atꢀ 433.15ꢀ Kꢀ andꢀ maintainedꢀ forꢀ 16ꢀ hꢀ
thatꢀ itsꢀ morphologyꢀ wasꢀ almostꢀ unchanged,ꢀ indictingꢀ itsꢀ
structureꢀ stability.ꢀ Theꢀ long-termꢀ stabilityꢀ wasꢀ furtherꢀ
confirmedꢀbyꢀtheꢀcontinuousꢀcyclicꢀvotammogramꢀscanningꢀforꢀ
beforeꢀ coolingꢀ inꢀ air.ꢀ Theꢀ resultingꢀ precipitatesꢀ wereꢀ filteredꢀ
andꢀwashedꢀthoroughlyꢀwithꢀdeionizedꢀ(DI)ꢀwaterꢀandꢀethanolꢀ
forꢀthreeꢀtimesꢀandꢀthenꢀdriedꢀinꢀairꢀatꢀ353.15ꢀKꢀforꢀ12ꢀh.ꢀꢀ
Characterizationsꢀꢀ
-1
twoꢀthousandꢀcyclesꢀinꢀ1ꢀMꢀKOHꢀatꢀaꢀscanꢀrateꢀofꢀ100ꢀmV·s ꢀ
Fig.ꢀ 6b).ꢀ Asꢀ shownꢀ inꢀ Fig.ꢀ 6b,ꢀ thereꢀ wasꢀ onlyꢀ 4ꢀ %ꢀ cathodicꢀ
(
TheꢀIRꢀspectraꢀwereꢀobtainedꢀbyꢀtheꢀcoupleꢀofꢀtheꢀattenuatedꢀ
totalꢀreflectionꢀ(ATR-IR)ꢀequipmentꢀwithꢀtheꢀFTIRꢀspectrometerꢀ
currentꢀ loss,ꢀ indictingꢀ theꢀ outstandingꢀ abilityꢀ ofꢀ NiCo2S4ꢀ toꢀ
endureꢀ acceleratedꢀ electrochemicalꢀ process.ꢀ Inꢀ addition,ꢀ
chronoamperometryꢀ(CA)ꢀtestꢀwasꢀperformedꢀatꢀ1.6ꢀVꢀ(vs.ꢀRHE)ꢀ
forꢀfiveꢀhoursꢀtoꢀobtainꢀFaradicꢀefficiencyꢀ(FE)ꢀandꢀtheꢀresultꢀ
indicatedꢀthatꢀNiCo2S4ꢀmodifiedꢀGCꢀelectrodeꢀdeliveredꢀstableꢀ
(
Prestigeꢀ21,ꢀShimadzu,ꢀJapan,ꢀDTGSꢀdetector)ꢀinꢀtheꢀrangeꢀofꢀ
-1
6
00ꢀ toꢀ 1500ꢀ cm .ꢀ Solutionꢀ 1Hꢀ NMRꢀ experimentsꢀ wereꢀ
performedꢀonꢀaꢀBrukerꢀDMXꢀ300ꢀNMRꢀspectrometerꢀ(300ꢀMHz)ꢀ
6
-2
OERꢀ currentꢀ densityꢀ ofꢀ aroundꢀ 23ꢀ mA·cm ꢀ (Fig.ꢀ S16).ꢀ Theꢀ withꢀ d -dimethylꢀ sulfoxideꢀ asꢀ theꢀ standard. Theꢀ dataꢀ ofꢀ
detailedꢀcalculationꢀofꢀFEꢀisꢀshownꢀinꢀtheꢀexperimentalꢀsection.ꢀ chemicalꢀ shiftsꢀ wereꢀ laterꢀ processedꢀ byꢀ theꢀ MestReNovaꢀ
6
ꢀ|ꢀJ.ꢀName.,ꢀ2012,ꢀ00,ꢀ1-3ꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Page 7 of 9
Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
JournalꢀNameꢀ
ꢀARTICLEꢀ
Program.ꢀ Differentialꢀ scanningꢀ calorimetryꢀ (DSC)ꢀ wasꢀ transportꢀandꢀremoveꢀgeneratedꢀgasꢀbubblesꢀonꢀsVuierwfaAcrteicꢀleoOfꢀntlhinee ꢀ
DOI: 10.1039/C7GC01012E
performedꢀ usingꢀ aꢀ Q2000ꢀ DSCꢀ (TAꢀ Instruments-Watersꢀ LLC,ꢀ electrode,ꢀtheꢀelectrolyteꢀwasꢀstirredꢀatꢀaꢀconstantꢀrateꢀofꢀ300ꢀ
o
-1
USA)ꢀsystemꢀatꢀaꢀheatingꢀrateꢀofꢀ10ꢀ C·min .ꢀThioureaꢀwasꢀrunꢀ rpm.ꢀ Theꢀ potentialꢀ wasꢀ calibratedꢀ againstꢀ theꢀ reversibleꢀ
inꢀ anꢀ aluminiumꢀ panꢀ inꢀ aꢀ sealedꢀ furnaceꢀ fromꢀ roomꢀ hydrogenꢀelectrodeꢀ(RHE)ꢀinꢀoxygenꢀsaturatedꢀelectrolyteꢀwithꢀ
temperatureꢀtoꢀ200ꢀ°C.ꢀPEGꢀ200ꢀwasꢀcooledꢀtoꢀ-70ꢀ°Cꢀbeforeꢀ aꢀ platinumꢀ wireꢀ asꢀ theꢀ workingꢀ electrode.ꢀ Theꢀ relatedꢀ
heatingꢀupꢀtoꢀ20ꢀ°C,ꢀwhile,ꢀtheꢀpreparedꢀDESꢀwasꢀcooledꢀtoꢀ- polarizationꢀcurvesꢀshownꢀinꢀtheꢀarticleꢀwereꢀcalibratedꢀafterꢀ
1
20ꢀ °Cꢀ beforeꢀ heatingꢀ upꢀ toꢀ 20ꢀ °Cꢀ .ꢀ Theꢀ viscosityꢀ (η)ꢀ ofꢀ theꢀ iRꢀcorrection.ꢀTheꢀonsetꢀpotentialꢀisꢀdefinedꢀasꢀtheꢀpotentialꢀatꢀ
-2
PEGylatedꢀDESꢀwasꢀmeasuredꢀatꢀ298.15ꢀKꢀusingꢀanꢀAntonꢀPaarꢀ theꢀcurrentꢀdensityꢀofꢀ1.0ꢀmA·cm ꢀforꢀOER.ꢀꢀ
DMAꢀ5000Mꢀforꢀfiveꢀtimesꢀandꢀtheꢀaverageꢀvalueꢀwasꢀreported.ꢀ Theꢀlinearꢀsweepꢀvoltammogramsꢀ(LSV)ꢀcurvesꢀofꢀNiCo2S4ꢀ
-1
TheꢀconductivityꢀofꢀtheꢀPEGylatedꢀDESꢀwasꢀmeasuredꢀbyꢀusingꢀ wereꢀperformedꢀwithꢀaꢀscanꢀrateꢀofꢀ5ꢀmV·s ꢀforꢀOERꢀinꢀ1ꢀMꢀ
aꢀ conductivityꢀ meterꢀ (DDS-307A,ꢀ Shanghaiꢀ INESAꢀ Scientificꢀ KOH.ꢀ Electrochemicalꢀ impedanceꢀ spectroscopyꢀ (EIS)ꢀ wasꢀ
Instrumentꢀ Co.,ꢀ Ltd.,ꢀ China)ꢀ forꢀ fiveꢀ timesꢀ atꢀ 298.15ꢀ K.ꢀ Theꢀ performedꢀinꢀpotentiostaticꢀmodeꢀfromꢀ0.1ꢀkHzꢀtoꢀ1000ꢀkHz.ꢀ
deviationꢀofꢀtheꢀequipmentꢀwasꢀlessꢀthanꢀ±ꢀ0.5ꢀ%.ꢀꢀ
Theꢀ Faradicꢀ efficiencyꢀ wasꢀ obtainedꢀ duringꢀ theꢀ
X-rayꢀ powderꢀ diffractionꢀ (XRD)ꢀ measurementsꢀ ofꢀ theꢀ chronoamperometryꢀ test.ꢀ Theꢀ experimentalꢀ evolvedꢀ O2ꢀ gasꢀ
samplesꢀ wereꢀ performedꢀ withꢀ Shimadzuꢀ XRD-7000ꢀ X-rayꢀ amountꢀ wasꢀ measuredꢀ byꢀ gasꢀ chromatographyꢀ analysisꢀ (Arꢀ
diffractometerꢀ (Shimadzu,ꢀ Japan)ꢀ usingꢀ Cuꢀ Kꢀ radiationꢀ atꢀ aꢀ carrier,ꢀmoleculeꢀsieveꢀ5Aꢀcolumn,ꢀTCDꢀdetector).ꢀ
ꢀ
o
-1
scanningꢀrateꢀofꢀ1ꢀ ·s .ꢀTheꢀsurfaceꢀmorphologyꢀandꢀelementalꢀ
compositionꢀ ofꢀ samplesꢀ wereꢀ analyzedꢀ byꢀ aꢀ fieldꢀ emissionꢀ
scanningꢀ electronꢀ microscopyꢀ (FESEM)ꢀ (Hitachiꢀ SU8010,ꢀ
Hitachiꢀ High-technologiesꢀ Corporation,ꢀ Japan)ꢀ equippedꢀ withꢀ
Conclusionsꢀꢀ
Inꢀsummary,ꢀaꢀnovelꢀPEGylatedꢀDESꢀcomposedꢀofꢀPEGꢀ200ꢀandꢀ
anꢀOxford-HoribaꢀIncaꢀXMax50ꢀenergyꢀdispersiveꢀX-rayꢀ(EDX)ꢀatꢀ thioureaꢀinꢀmoleꢀratioꢀofꢀ2:1ꢀwasꢀdevelopedꢀandꢀitꢀwasꢀusedꢀ
anꢀ acceleratingꢀ voltageꢀ ofꢀ 5ꢀ keVꢀ andꢀ 15ꢀ keV,ꢀ respectively.ꢀ forꢀsolvothermalꢀsynthesisꢀofꢀmetalꢀsulfidesꢀwithꢀuniformꢀandꢀ
Transmissionꢀ electronꢀ microscopyꢀ (TEM)ꢀ andꢀ high-resolutionꢀ hierarchicalꢀstructureꢀandꢀtunableꢀcomposition.ꢀTheꢀPEGylatedꢀ
transmissionꢀ electronꢀ microscopyꢀ (HRTEM)ꢀ wereꢀ conductedꢀ DESꢀplaysꢀmultipleꢀrolesꢀasꢀsolvent,ꢀshape-controlꢀagent,ꢀandꢀ
usingꢀ aꢀ JEM-2100Fꢀ field-emissionꢀ TEM.ꢀ Forꢀ TEMꢀ andꢀ HRTEMꢀ reactantꢀ(sulfurꢀsource)ꢀinꢀtheꢀsynthesisꢀofꢀtheꢀmetalꢀsulfides.ꢀ
TheꢀXRDꢀpatternꢀofꢀtheꢀsampleꢀconfirmedꢀtheꢀcrystalꢀstructureꢀ
andꢀ highꢀ purityꢀ ofꢀ theꢀ as-synthesizedꢀ metalꢀ sulfides.ꢀ Thisꢀ
proposedꢀone-stepꢀrouteꢀforꢀtheꢀsynthesisꢀofꢀmetalꢀsulfidesꢀisꢀ
cost-effectiveꢀ andꢀ energy-efficientꢀ byꢀ combingꢀ solvothermalꢀ
synthesisꢀ andꢀ sulfurationꢀ processꢀ togetherꢀ comparedꢀ withꢀ
traditionalꢀ two-stepꢀ (solvothermalꢀ synthesisꢀ andꢀ sulfuration)ꢀ
routes.ꢀFurthermore,ꢀtheꢀpreparedꢀnickelꢀcobaltꢀsulfidesꢀwereꢀ
experiments,ꢀ theꢀ samplesꢀ wereꢀ preparedꢀ byꢀ dispersingꢀ theꢀ
productsꢀ inꢀ ethanolꢀ andꢀ droppingꢀ theꢀ suspensionꢀ onꢀ aꢀ Cuꢀ
microgrid.ꢀN2ꢀadsorption-desorptionꢀisothermsꢀwereꢀobtainedꢀ
atꢀ 77ꢀ Kꢀ onꢀ Belsorp-Miniꢀ IIꢀ (BELꢀ Japanꢀ Inc.,ꢀ Japan)ꢀ afterꢀ theꢀ
sampleꢀwasꢀdegassedꢀinꢀvacuumꢀatꢀ573ꢀKꢀforꢀ4ꢀh.ꢀꢀ
Modificationꢀofꢀelectrodeꢀꢀ
Theꢀ NiCo2S4ꢀ modifiedꢀ glassyꢀ carbonꢀ (GC)ꢀ electrodesꢀ wereꢀ usedꢀasꢀcatalystsꢀforꢀelectrochemicalꢀwaterꢀsplittingꢀandꢀtheyꢀ
exhibitedꢀ excellentꢀ oxygenꢀ evolutionꢀ reactionꢀ (OER)ꢀ
performance.ꢀ Theꢀ relativelyꢀ highꢀ BETꢀ areaꢀ andꢀ multiꢀ porousꢀ
structureꢀ ofꢀ sulfidesꢀ increasedꢀ theꢀ catalyticꢀ surfaceꢀ areaꢀ andꢀ
improvedꢀtheꢀtransportꢀpropertyꢀofꢀelectronsꢀthroughoutꢀtheꢀ
entireꢀelectrode.ꢀWeꢀalsoꢀfoundꢀthatꢀsulfidesꢀhaveꢀanꢀimprovedꢀ
OERꢀ performanceꢀ comparedꢀ withꢀ theꢀ correspondingꢀ oxides.ꢀ
Amongꢀ them,ꢀ hierarchicallyꢀ structuredꢀ ternaryꢀ metalꢀ sulfideꢀ
NiCo2S4ꢀ exhibitedꢀ bestꢀ OERꢀ performance.ꢀ Notably,ꢀ theꢀ as-
preparedꢀ NiCo2S4ꢀ catalystꢀ exhibitedꢀ lowꢀ overpotentialꢀ ofꢀ 337ꢀ
preparedꢀbyꢀdispersingꢀ1mgꢀNiCo2S4ꢀinꢀ0.5ꢀmLꢀwaterꢀandꢀ0.5ꢀ
mLꢀ ethanolꢀ withꢀ 10ꢀ μLꢀ Nafionꢀ solutionsꢀ (5ꢀ %)ꢀ toꢀ formꢀ
homogeneousꢀ inks.ꢀ Then,ꢀ asꢀ preparedꢀ inksꢀ (5ꢀ μL)ꢀ wasꢀ dropꢀ
2
coatingꢀonꢀGCꢀelectrodeꢀ(3ꢀmm)ꢀwithꢀaꢀ0.07069ꢀcm ꢀareaꢀandꢀ
thenꢀ driedꢀ underꢀ theꢀ infraredꢀ lamp.ꢀ Thisꢀ yieldedꢀ aꢀ NiCo2S4ꢀ
-2
powderꢀ loadingꢀ weightꢀ ofꢀ aboutꢀ 0.07ꢀ mg·cm .ꢀ Theꢀ bareꢀ GCꢀ
electrodeꢀ wasꢀ polishedꢀ withꢀ 10ꢀ µmꢀ Al2O3ꢀ powder,ꢀ
subsequentlyꢀrinsedꢀbyꢀwaterꢀandꢀsonicatedꢀinꢀdistilledꢀwaterꢀ
andꢀethylꢀalcohol.ꢀTheꢀNiCo2S4ꢀNiCo2O4,ꢀNiS2,ꢀCoS2,ꢀNi2CoS4ꢀ+ꢀ
CoS2,ꢀandꢀNi2CoS4ꢀmodifiedꢀGCꢀelectrodesꢀwereꢀobtainedꢀinꢀtheꢀ
sameꢀprocedure.ꢀꢀ
-2
mVꢀwithꢀtheꢀcurrentꢀdensityꢀreachingꢀ10ꢀmA·cm ꢀandꢀlowꢀTafelꢀ
-1
slopeꢀ ofꢀ 64ꢀ mV·dec ꢀ performingꢀ onꢀ theꢀ GCꢀ electrode.ꢀ
Moreover,ꢀ theꢀ NiCo2S4ꢀ catalystꢀ alsoꢀ hasꢀ excellentꢀ durabilityꢀ
andꢀhighꢀFEꢀofꢀ95.8%.ꢀTheꢀproposedꢀPEGylatedꢀDESꢀcouldꢀbeꢀanꢀ
excellentꢀmediaꢀtoꢀsynthesisꢀefficientꢀelectrocatalystsꢀforꢀOERꢀ
andꢀ opensꢀ aꢀ newꢀ areaꢀ inꢀ theꢀ synthesisꢀ ofꢀ metalꢀ sulfidesꢀ notꢀ
onlyꢀforꢀwaterꢀoxidationꢀbutꢀalsoꢀforꢀotherꢀenergyꢀconversionꢀ
andꢀstorageꢀapplications.ꢀꢀ
Electrochemicalꢀmeasurementsꢀꢀꢀ
TheꢀelectrocatalyticꢀactivityꢀofꢀsamplesꢀforꢀOERꢀwasꢀstudiedꢀinꢀ
1
ꢀMꢀKOHꢀsolutionꢀandꢀrecordedꢀonꢀaꢀCHIꢀ660Eꢀelectrochemicalꢀ
stationꢀatꢀambientꢀtemperature.ꢀAllꢀtestsꢀwereꢀperformedꢀinꢀaꢀ
three-electrodeꢀelectrochemicalꢀcellꢀwithꢀanꢀAg/AgClꢀelectrodeꢀ
(
3MꢀKCl)ꢀandꢀaꢀPtꢀwireꢀasꢀtheꢀreferenceꢀelectrodeꢀandꢀcounterꢀ
electrode,ꢀ respectively.ꢀ Theꢀ preparedꢀ NiCo2S4,ꢀ NiCo2O4,ꢀ NiS2,ꢀ
CoS2,ꢀNi2CoS4ꢀ+ꢀCoS2,ꢀandꢀNi2CoS4ꢀmodifiedꢀGCꢀelectrodesꢀwereꢀ
usedꢀ asꢀ theꢀ workingꢀ electrodesꢀ toꢀ investigateꢀ theirꢀ
electrocatalyticꢀ activitiesꢀ towardꢀ OER.ꢀ Toꢀ enhanceꢀ massꢀ
Acknowledgementsꢀ
Theꢀ authorsꢀ thankꢀ Nationalꢀ Naturalꢀ Scienceꢀ Foundationꢀ ofꢀ
Chinaꢀ(21473252ꢀandꢀ21575160)ꢀforꢀfinancialꢀsupport.ꢀꢀ
Thisꢀjournalꢀisꢀ©ꢀTheꢀRoyalꢀSocietyꢀofꢀChemistryꢀ20xxꢀ
J.ꢀName.,ꢀ2013,ꢀ00,ꢀ1-3ꢀ|ꢀ7ꢀ
Pleaseꢀdoꢀnotꢀadjustꢀmarginsꢀ

Pleas Ge ꢀ rd eo eꢀ nn o Ct ꢀha ed mj u is st ꢀt mr yarginsꢀ
Page 8 of 9
ARTICLEꢀ
JournalꢀNameꢀ
3
4.ꢀM.-R.ꢀGao,ꢀY.-F.ꢀXu,ꢀJ.ꢀJiangꢀandꢀS.-H.ꢀYu,ꢀChem.ꢀSoVice.wꢀRAertvic.l,eꢀ2O0n1lin3e,ꢀ
Notesꢀandꢀreferencesꢀ
4
2,ꢀ2986-3017.ꢀ
DOI: 10.1039/C7GC01012E
1
2
3
.ꢀ M.ꢀWatanabe,ꢀM.ꢀL.ꢀThomas,ꢀS.ꢀZhang,ꢀK.ꢀUeno,ꢀT.ꢀYasudaꢀandꢀK.ꢀ 35.ꢀJ.ꢀ Pu,ꢀ F.ꢀ Cui,ꢀ S.ꢀ Chu,ꢀ T.ꢀ Wang,ꢀ E.ꢀ Shengꢀ andꢀ Z.ꢀ Wang,ꢀ ACSꢀ
Dokko,ꢀChem.ꢀRev.,ꢀ2017,ꢀDOI:ꢀ10.1021/acs.chemrev.6b00504.ꢀ
SustainableꢀChem.ꢀEng.,ꢀ2013,ꢀ2,ꢀ809-815.ꢀ
.ꢀ S.ꢀZhang,ꢀJ.ꢀZhang,ꢀY.ꢀZhangꢀandꢀY.ꢀDeng,ꢀChem.ꢀRev.,ꢀ2016,ꢀDOI:ꢀ 36.ꢀH.ꢀChen,ꢀJ.ꢀJiang,ꢀL.ꢀZhang,ꢀH.ꢀWan,ꢀT.ꢀQiꢀandꢀD.ꢀXia,ꢀNanoscale,ꢀ
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Green Chemistry
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DOI: 10.1039/C7GC01012E
Table of contents
PEGylated deep eutectic solvent was developed and used for one step
solvothermal synthesis NiCo for efficient oxygen evolution reaction.
S
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