reports百度云100as

OxygenReductionattheRare-earthPhthalocyanine-modifiedGlassyCarbonElectrodeinAqueousMediaToshihiroIkai,TatsuyaYonekura,TakeoOhsakaandFusaoKitamuraDepartmentofElectronicChemistry,InterdisciplinaryGraduateSchoolofScienceandEngineering,TokyoInstituteofTechnology4259-G1-6Nagatsuta,Midori-ku,Yokohama226-8502JapanIntroductionTheoxygenreductionreaction(ORR)isthecathodereactionoffuelcellssuchastheprotonexchangemembranefuelcell(PEMFC).
Duetotheproblemsassociatedwithcostsandplatinumresources,itishighlydesiredtoutilizenon-noblemetalsastheelectrodecatalysts;organometallicmacrocyclessuchasporphrinesandphthalocyanineshavebeenconsideredasanalternativetoplatinum-basedcatalysts,becausetheyarehighlystableandhavereversibleredoxpropertiessuitablefortheelectrocatalystfortheORR[1].
Inaddition,thesemacrocycliccatalystsareexpectedtobemethanol-insensitiveduringoxygenelectroreductioninadirectmethanolfuelcell(DMFC).
Inthisrespect,transitionmetalphthalocyanineshavebeenthoroughlyexaminedfortheiractivitytowardtheORR.
However,therearescarcereportsonthecatalyticactivityoftherare-earthphthalocyaninestowardtheORR.
Wehavecontinuedinvestigationontheelectrochemicalandopticalpropertiesofrare-earthphthalocyanines.
ThepresentworkexploresthecatalyticactivitiesofthetitlecomplexfortheORRinaqueouselectrolytesolutions.
ExperimentalBis(phthalocyaninato)lanthanide(III)complexes,[LnPc2]z,(Ln=Nd,YborGdandz=-1)weresynthesizedastetrabutylammonium(TBA)saltsaccordingtotheproceduredescribedinref.
2.
WefabricatedLnPc2-modifiedGCelectrodesbythefollowingtwomethods:AnaliquotofacetonesolutionoftheTBA[LnPc2](1mM)wascastontheGCdiskelectrodesurfacewithamicrosyringeandthesolventwasdried(cast-coatedGC).
Anotherelectrodeisthedip-coatedGC,whichwaspreparedbysoakingbareGCelectrodeinthesolutionof1mMTBA[LnPc2]dissolvedinacetonefor30mininordertoestablishadsorptionequilibrium.
Afterwashedtheelectrodewithpureacetone,thesolventwasdriedandused.
Ag|AgCl|KCl(sat)wasusedasthereferenceelectrodeandallthepotentialswerequotedagainstthiselectrode.
ResultsanddiscussionThesolidcurveinFig.
1showsthecyclicvoltammogram(CV)oftheNdPc2modifiedGCelectrode(dip-coatedGC)measuredinO2saturated0.
5MH2SO4solution.
Comparedwiththeresponseobtainedatthebareelectrode(dottedcurve),itisobviousthattheO2reductionstartsatmorepositivepotentialsthanthebareelectrode.
Sincethepotentialcoincideswiththeredoxpotentialofthecomplex,wecanconsiderthatthecomplexcatalyzestheelectrochemicalO2reduction.
Accordingtotherotatingring-diskelectrode(RRDE)experiments,themainproductwasfoundasthehydrogenperoxide,butfour-electronreductionofO2wasalsosuggestedtotakeplaceaswellasthetwo-electronreductionprocessdependingonthepotential.
Thestabilityoftheelectrodeinstrongacidsolutionswas,unfortunately,notgoodanddegradedduringseveraltensofpotentialsweeps.
Ontheotherhand,fairlygoodstabilitywasattainedinneutralsolutions.
Inalkalinesolutions,theelectrodewasquitestable,butthecatalyticactivitytowardO2reductiongreatlydepressedsincethecomplexbecomeselectro-inactiveinsuchhighpHsolutions.
Wealsotriedsimilarexperimentsusingcast-coatedGCelectrodes.
Althoughtheamountofthecomplexdepositedontheelectrodesurfacewaslarger,thecatalyticcurrentwasfoundtobesmallerthanthoseobservedatthedip-coatedelectrode.
Thismightbeascribedtothecompactnessofthedeposits,suggestingtheimportanceofcontrollingthesurfacegeometryofthecomplextoattainmostefficientcatalyticactivity.
Dependenceonthecentralrare-earthmetalionswillalsobediscussed.
References[1]J.
H.
Zagal,Coord.
Chem.
Rev.
,119(1992)89.
[2]C.
Harnoode,K.
Takamura,H.
Kubota,K.
Sho,K.
Fujisawa,F.
Kitamura,T.
OhsakaK.
Tokuda,Electrochemistry61(1993)767.
AcknowledgmentsThisresearchwaspartlysupportedbyGrant-in-AidforScientificResearchonPriorityAreas(B)(no.
13134101)fromtheMinistryofEducation,Science,SportsandCulture,Japan.
Fig.
1Cyclicvoltammogramsobtainedatcast-coatedGCelectrodeintheO2saturated(solidcurve)andN2saturated(dottedcurve)0.
5MH2SO4solutions.
DashedcurvewasobtainedatbareGCelectrodeintheO2saturatedsolution.
Sweepratewas100mVs-1.
–5000500–200–1000E/mVvs.
Ag|AgClI/A