Assigment 02 Linear Sweep Voltametry (Qamir Ullah FA22-R06-050).pdf

Assignment on electrochemistry

1. DepartmentofChemistry
ElectrodeProcessesandKinetics(CHM-513)
AssignmentNo.02
LinearSweepVoltametry(LSV)
Submittedto: Dr.JaweriaAmbreen
Submittedby:
QamirUllah
CIIT/FA22-R06-050/ISB

2. LinearSweepVoltammetry
Linearsweepmethodsarethemostcommonelectrochemicalmethodsinusebychemists
today.Theyprovideanefficientandstraightforwardassessmentoftheredoxbehaviorof
molecularsystems.Inallpotentialsweepmethods,thepotential(V,volts)oftheworking
electrodeisvariedcontinuouslywithtimeaccordingtoapredeterminedpotentialwaveform
(akaexcitationfunction),whilethecurrent(I,amps)isconcurrentlymeasuredasafunctionof
thepotential.Theappliedpotentialattheworkingelectrodeismeasuredagainstareference
electrodeofchoice,whileacounter(akaauxiliary)electrodeisrequiredtobalancetheI-V
applied.
Thus,threeelectrodesarerequired:
► workingelectrode
► referenceelectrode
► counterelectrode
Anelectrolytesaltmustalsobedissolvedinsolutiontomaintainsufficientconductivityinthebulk
solutionandmaintaindiffusioncontrolledmasstransferattheelectrodeinterface.

3. Commonelectrodes
Workingelectrode
►Glassycarbon
►Platinum
►Silver
►Gold
Counterelectrode
►Ptwire
►Glassycarbonrod
Referenceelectrode
(physicallybutnotelectrochemically
isolatedwithaporousvycorfrit)
►Ag/AgCl3Maq.KCl
►NormalHydrogenElectrode(NHE)
►SaturatedCalomelElectrode
►Ag/AgNO
3(0.01Min0.1MBu
4NPF
6acetonitrile)

4. WorkingPrinciple
Linearsweepvoltammetryrepresentsthemostbasicpotentialsweepmethod.InLSVthepotentialofthe
workingelectrodeisvariedlinearlywithtimebetweentwovaluesi.e.,theinitial(E
i)andfinal(E
f)
potentials.Astheelectrodepotentialisconstantlyrising(ordecreasing)throughouttheexperiment,alevel
ofcapacitive(akaOhmic)currentflowscontinuously.Thesecurrentsareduetothecapacitivechargingof
theworkingelectrode'sdoublelayer.
Faradaiccurrentwillalsoflowwhenthepotentialreachesavalueatwhichthespeciesinsolution
canundergoelectrochemicalconversions.
Excitationfunction(potentialwaveform)foraLSVexperiment

5. PracticalApplications:
Herearesomepracticalapplicationsoflinearsweepvoltammetry:
i.DeterminationofRedoxPotentials:LSViswidelyemployedtomeasuretheredoxpotentialsof
electroactivespecies.Bysweepingthepotentiallinearlywhilemonitoringthecurrentresponse,the
redoxpotentialofaspeciescanbeidentifiedasthepotentialatwhichthecurrentexhibitsasignificant
change.Thisinformationiscrucialforunderstandingthethermodynamicsandkineticsofredox
reactions.
ii.ElectrochemicalKinetics:LSVallowsthedeterminationofreactionkineticsbyobservingthecurrent
responseasafunctionoftheappliedpotential.Byanalyzingtheshapeandmagnitudeofthecurrent-
timecurve,importantkineticparameterssuchastherateconstant,electrontransfercoefficient,and
reactionmechanismcanbeextracted.
iii.AnalyticalChemistry:LSVisemployedinvariousanalyticaltechniques,includingthedetectionand
quantificationofanalytesinsolution.Itcanbeusedforvoltammetricstrippinganalysis(VSA)and
anodicstrippingvoltammetry(ASV),whicharesensitivemethodsfortracemetalanalysis.LSVisalso
utilizedinthedeterminationoforganiccompounds,pharmaceuticals,andenvironmentalpollutants.
iv.SensorDevelopment:LSVisanessentialtoolforthedevelopmentofelectrochemicalsensors.By
immobilizingselectiverecognitionelementsontheelectrodesurface,LSVcanbeusedtoinvestigatethe
electrochemicalbehaviorofanalytesandtheirinteractionswiththerecognitionelements.
v.ElectrodeSurfaceCharacterization:LSVprovidesvaluableinformationaboutthebehaviorand
propertiesofelectrodesurfaces.Bystudyingthecurrentresponseduringpotentialscanning,insights
canbegainedintoelectrodeprocesses,surfacereactions,adsorptionphenomena,andthe
electrochemicalstabilityofmaterials.
vi.BatteryandEnergyStorageResearch:LSVisemployedinthecharacterizationandanalysisofbattery
materialsandenergystoragesystems.Itcanbeusedtoinvestigatetheelectrochemicalbehaviorof
electrodematerials,measurethecapacityandcyclingperformanceofbatteries,studythekineticsof
chargetransferprocesses,andoptimizethedesignofenergystoragedevices.

6. Linearsweepvoltammetryofferrocene
•TheFe
III/II
coupleofferrocene,(η
5
-C
5H
5)
2Fe,isanexampleofanelectrochemicallyreversible
systeminacetonitrilesolutionandisoftenusedasaninternalorpseudoreferencewhen
reportingformalpotentialsofinorganicandorganometalliccomplexes.
•Forexample,takinga1mMsolutionofferroceneunderthefollowingconditions:
►Workingelectrode=2mmdiameterplatinumdisc
►Counterelectrode=Ptwire
►Referenceelectrode=Ag/AgCl3Maq.KCl
►Electrolyte=0.1MBu
4NPF
6inacetonitrile
•Thevoltammetricscanisstartedatapotentialatwhichnoelectrochemicalreactionsmaytake
place,thatis,V<<E(atleast177mV).
•ScanningthepotentiallinearlyinthepositivedirectiongivesrisetoaFaradaiccurrentupon
oxidationoftheFe(II)centertoFe(III).
•Importantly,thesolutioniskeptquiescent,i.e.notstirred,sothatdiffusionistheonlymass
transportmechanismpossible.
•Iftheredoxcoupleiselectrochemicallyreversibleacharacteristicanodicwaveisobserved
withamaximumcurrentvaluegivenbytheRandles-Sevcikequation.

7. 0
b
a
-5 f
i
pa
e
c
-10 anodic
ExcitationfunctionforaLSVexperiment
d
E
pa
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
Potential(V)vs.Ag/AgCl
1mMferrocene(2mmPtdisc;0.1MBu4NPF6acetonitrile;Ptwire;Ag/AgCl3Maq.KCl)
Linearsweepvoltammetryofferrocene
Randles-Sevcikequation(at25C):
i
p=peakcurrent;n=#electrons;
A=electrodearea;C=concentration;v=scanrate
Current
(
A)

8. Linearsweepvoltammetryofferrocene
a.Theinitialpotentialat0.10Vshowsnocurrentandthereforenoelectrolysiswhentheelectrode
isswitchedon.
b.Theelectrodeisscannedtowardamorepositivepotential.
c.Asthepotentialismademorepositivetheelectrodeisnowasufficientlystrongoxidanttooxidize
theferrocenetoferrocenium.
d.Theconcentrationofferrocene
decreasesrapidlyattheelectrode
surfaceastheanodiccurrentincreases.
Atpointdtheconcentrationofferrocene
issubstantiallydiminishedcausingthe
currenttopeak.
e.Thecurrentnowdecaysastheferrocene
concentrationbecomesmoredepleted
andferroceniumsurroundstheelectrode.
f.Completeoxidationisensuredby
scanningto0.75V.
0
-5
-10
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
Potential(V)vs.Ag/AgCl
b
a
f
i
pa
e
c
anodic
d
E
pa
Current
(
A)

9. ImportantnotesonLSW
•Note:E
padoesnotequalthestandardreductionpotentialofthecorrespondingredoxcouple.
•Forreversibleone-electronredoxcouplestheanodicpeakE
paoccursatca.30mVmorepositive
thanEanditspositionisindependentofthescanrate,whereasthecathodicpeakE
pcoccursca.
30mVmorenegativeofE.
•Forarevesibleredoxcouple,thepositionofbothE
paandE
pcareindependentofthescanratebut
iv
1/2
.
•Ifthevoltammogramexhibitsanirreversiblepeak,thecorrespondingpeakpotentialwillshift
anodicallyforE
paasthescanrateincreases.
Refrences:
Bard,A.J.,&Faulkner,L.R.(2020).Electrochemicalmethods:Fundamentalsandapplications(2nded.).
Wiley.
Kissinger,P.T.,&Heineman,W.R.(2020).Laboratorytechniquesinelectroanalyticalchemistry(2nd
ed.).CRCPress.
Wang,J.(2016).Analyticalelectrochemistry(3rded.).Wiley-VCH.
Švorc,Ľ.,&Labuda,J.(Eds.).(2019).Linearsweepvoltammetry:Measuringandinterpretingresults.
Springer.
Compton,R.G.,&Banks,C.E.(Eds.).(2020).Understandingvoltammetry(2nded.).ImperialCollege
Press.
Ewing,A.G.,Bigelow,J.C.,Wightman,R.M.(2022).Electrochemicalmethodsforneuroscience.CRC
Press.