Enhanced electrochemical performance of graphitized carbide-derived carbon in alkaline electrolyte - 图文

J.Xuetal./ElectrochimicaActa174(2015)411–416415Fig.7.(a)Highfrequencyseriesresistanceand(b)chargetransferresistancevs.workingelectrodepotentialdependenciesfortreatedTiC-CDCelectrodes(notedinFigure).(5and20mVsà1)haveslightbroadfaradaicpeaks,indicatingtheexistenceofpseudocapacitance.However,thepseudocapacitancepeakoftreatedTiC-CDCisnotobvious,andonlyoccursatlowerscanrateandathigherconcentrationofHNO3solution.Thisisbecausethatwell-orderedgraphitizedTiC-CDC-1000ishardtobetreatedbyHNO3,andnoabundantoxygen-containingfunctionalgroupscanbeintroducedontoTiC-CDC,leadingtolowerreversibleredoxpseudo-faradaiccapacitance.Galvanostaticcharge/dischargecurvesofTiC-CDCbeforeandafterHNO3treatmentat0.5Agà1withinapotentialwindow(0to1Vvs.Hg/HgO)areshowninFig4.ItisfoundthatelectrochemicalperformanceofTiC-CDCbeforeandaftertreatmentisstableandreversible,suggestingthesuperiorEDLCcharacteristic.Theareasurroundedbycharge/dischargecurvesandx-coordinateisobviouslyincreasedafterHNO3treatmentindicatinglargerspeci?ccapacitance.Theshapesofthecharge/dischargecurvesoftreatedTiC-CDC(>6M)slightlydeviatefromideallinearline,indicatingthatthecapacitanceconsistsofEDLCandpseudocapacitance.ItisinagreementwiththeCVcurves(Fig.3b).TheinsertinFig.4showsthepotentialdrop(IRdrop,atthebeginningofdischargeduringthechargingofpolarityfromthenegativetopositivecurrentandviceversa)relatedtocharge-transferresistance(i.e.internalresistance)ofiondiffusioninnanopores.ThedecreaseinIRdropoftreatedTiC-CDCindicatesthedecreaseofcharge-transferresis-tanceduetoimprovedwettability.ButhigherconcentrationofFig.8.SchematicmechanismofHNO3treatmentforTiC-CDC.HNO3solution(>6M)hasnofurthercontributiontothedecreaseinIRdrop.Fig.5showstheNyquistplotsforHNO3treatedTiC-CDCelectrodewithintherangeofacfrequency,from10mHzto100kHzat?xedworkingelectrodepotentialfromà1Vto0V.Theresultsobtaineddemonstratethattheshapeof–Z00,Z0plotsdependsnoticeablyonpotential.AndTiC-CDCswithdifferentdegreeofHNO3treatmentexhibitasimilarshape.TheNyquistplotsconsistmainlyofthreeparts:thesmallsemicircle,verywellexpressedso-called“porous”region[8]withaslopeofa%à45??inacfrequencyregion1