电化学实验报告实验报告

Experimentalclasson“FuelCellandElectrochemistry”ExperimentsetupEquipment:CHI760DelectrochemicalstationThreeelectrodesystem.WE:CE:RE:SaturatedCalomelElectrodeSolution:1.0×10-3mol/LK3[Fe(CN)6]+0.1MKClLabreportPlotcurvesofLSVcurve,anddescribewhycurrentchangeswithsweepingvoltage?Reason:Voltageisadrivingforcetoanelectrodereactions,itisconcernedwiththeequilibriumofelectrontransferatelectrodesurface.Asthealteringofappliedvoltage,theFermi-levelisraised(orlowered),whichchangingtheenergystateoftheelectrons.Makingtheoverallbarrierheight(ieactivationenergy)alterasafunctionoftheappliedvoltage.(1).Inthisreaction,whenvoltageis0.6V,thereisnoelectrontransfer,sothecurrentiszero.Withthevoltagetothemorereductivevalues,thecurrentincreases.(2).WhenthediffusionlayerhasgrownsufficientlyabovetheelectrodesothatthefluxofreactanttotheelectrodeisnotfastenoughtosatisfythatrequiredbyNernstEquation.Thepeakisobtaining.(3).Whenthereactioncontinued,itwouldgetasituationthattherewillbealowerreactantconcentrationattheelectrodethaninbulksolution,thatis,thesupplyoffreshreactanttothesurfacedecreased,socurrentdecreases.PlotthecurvesofCVcurveswithdifferentscanrate;FromtheCVcurves,fillthetableScanrate(mV/s)2050100200300400500600Peakcurrent(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)V10.1710.1890.1910.1900.1870.1860.1830.183V20.2420.2550.2590.2620.2620.2620.2620.262Peakvoltagedifference(mV)7166687275767979Accordingtotheresult,describewhycurvesshowscertaintrend,andhowpeakcurrentandpeakvoltagedifferencechangewithscanrate?Answer:Fromabovedataandcurve,wecanobtain:Atafixedscanrate:(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)2050100200300400500600ν1/2(mV/s)1/24.4727.0711014.14217.3212022.36124.495Ip(uA)8.33613.1718.5025.9631.5436.1740.2343.95Ep(V)0.1710.1890.1910.1900.1870.1860.1830.183Ep’(mV)7166687275767979(1)Ip--V1/2Figure1:PeakcurrentVSradicalsignofscanrateInterpretation:Itisapparentthatthepeakcurrentislineartoradicalsignofscanrate,whichsatisfythisequation:ip=kv1/2C0.Reason:Thiscanberationalisedbyconsideringthesizeofthediffusionlayerandthetimetakentorecordthescan.Clearlythelinearsweepvoltammogramwilltakelongertorecordasthescanrateisdecreased.Thereforethesizeofthediffusionlayerabovetheelectrodesurfacewillbedifferentdependinguponthevoltagescanrateused.Inaslowvoltagescanthediffusionlayerwillgrowmuchfurtherfromtheelectrodeincomparisontoafastscan.Consequentlythefluxtotheelectrodesurfaceisconsiderablysmalleratslowscanratesthanitisatfasterrates.Asthecurrentisproportionaltothefluxtowardstheelectrode,themagnitudeofthecurrentwillbeloweratslowscanratesandhigherathighrates.(2)Ep--VFigure2:PeakpotentialVSscanrate(3)Ep’--vFigure3:thechangeofPeakpotentialVSscanrateInterpretation:Figure2:showsthatthepositionofthepeakcurrentoccursatthesamevoltage.Figure3:showsthePeakvoltagedifferenceisconstantindifferentscanrate.Reason:Thecharacteristicofthiselectrodereactionhasrapidelectrontransferkineticsandthereisnochargetransferindoublelayer,sothisreactionisreversible.