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第7頁(yè)共7頁(yè)電化學(xué)實(shí)驗(yàn)報(bào)告實(shí)驗(yàn)報(bào)告————————————————————————————————作者:————————————————————————————————日期:E_perimentalclasson“FuelCellandElectrochemistry”E_perimentsetupEquipment:CHI760DelectrochemicalstationThreeelectrodesystem.WE:CE:RE:SaturatedCalomelElectrodeSolution:1.0×10-3mol/LK3[Fe(CN)6]+0.1MKClLabreportPlotcurvesofLSVcurve,anddescribewhycurrentchangeswithsweepingvoltage?Reason:Voltageisadrivingforcetoanelectrodereactions,itisconcernedwiththeequilibriumofelectrontransferatelectrodesurface.Asthealteringofliedvoltage,theFermi-levelisraised(orlowered),whichchangingtheenergystateoftheelectrons.Makingtheoverallbarrierheight(ieactivationenergy)alterasafunctionoftheliedvoltage.(1).Inthisreaction,whenvoltageis0.6V,thereisnoelectrontransfer,sothecurrentiszero.Withthevoltagetothemorereductivevalues,thecurrentincreases.(2).Whenthediffusionlayerhasgrownsufficientlyabovetheelectrodesothattheflu_ofreactanttotheelectrodeisnotfastenoughtosatisfythatrequiredbyNernstEquation.Thepeakisobtaining.(3).Whenthereactioncontinued,itwouldgetasituationthattherewillbealowerreactantconcentrationattheelectrodethaninbulksolution,thatis,thesupplyoffreshreactanttothesurfacedecreased,socurrentdecreases.PlotthecurvesofCVcurveswithdifferentscanrate;FromtheCVcurves,fillthetableScanrate(mV/s)205010020__300400500600Peakcurrent(uA)Ipc8.33613.1718.5025.9631.5436.1740.2343.95Ipa-8.263-13.01-18.19-25.26-30.50-34.88-38.68-42.12RatioofPeakcurrent1.0091.0121.0171.0281.0341.0371.0401.043PeakvoltagE(V)V10.1710.1890.1910.1900.1870.1860.0.V20.2420.2550.2590.2620.2620.2620.2620.262Peakvoltagedifference(mV)7166687275767979Accordingtotheresult,describewhycurvesshowscertaintrend,andhowpeakcurrentandpeakvoltagedifferencechangewithscanrate?Answer:Fromabovedataandcurve,wecanobtain:Atafi_edscanrate:(1).frominitialpositivevoltagetomorereductivevalues,thecurrentbegintoflow,thenreachapeakipcanddecreaseeventually.(2).whenvoltagemovesback,theequilibriumpositionsgraduallyconvertingelectrolysisproduct(Fe2+)backtoreactant(Fe3+),thecurrentflowisfromthesolutionspeciesbacktotheelectrodeandsooccursintheoppositesensetotheforward.Theprocesshasanothercurrentpeakipa.Ithassamereasonoflinearsweepvoltammetry.Atdifferentscanrate,theratioofpeakcurrentipc/ipaisaboutequalto1(1.009—1.043).Atdifferentscanrate,thepositionofpeakvoltagedonotaltergreatlyΔEpisaboutaconstant(66--79).ν(mV/s)205010020__300400500600ν1/2(mV/s)1/24.4727.0711014.14217.3212022.36124.495Ip(uA)8.33613.1718.5025.9631.5436.1740.2343.95Ep(V)0.1710.1890.1910.1900.1870.1860.0.Ep’(mV)7166687275767979(1)Ip--V1/2Figure1:PeakcurrentVSradicalsignofscanrateInterpretation:Itisarentthatthepeakcurrentislineartoradicalsignofscanrate,whichsatisfythisequation:ip=kv1/2C0.Reason:Thiscanberationalisedbyconsideringthesizeofthediffusionlayerandthetimetakentorecordthescan.Clearlythelinearsweepvoltammogramwilltakelongertorecordasthescanrateisdecreased.Thereforethesizeofthediffusionlayerabovetheelectrodesurfacewillbedifferentdependinguponthevoltagescanrateused.Inaslowvoltagescanthediffusionlayerwillgrowmuchfurtherfromtheelectrodeinparisontoafastscan.Consequentlytheflu_totheelectrodesurfaceisconsiderablysmalleratslowscanratesthanitisatfasterrates.Asthecurrentisproportionaltotheflu_towardstheelectrode,themagnitudeofthecurrentwillbeloweratslowscanratesandhigherathighrates.(2)Ep--VFigure2:PeakpotentialVSscanrate(3)Ep’--vFigure3:thechangeofPeakpotentialVSscanrateInterpretation:Figure2:showsthatthepositionofthepeakcurrentoccursatthesamevoltage.Figure3:showsthePeakvoltagedif

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