CYCLIC VOLTAMMETRY

Center for Electrochemical Engineering Research
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Cyclic voltammetry
Cyclic potential sweep
Resulting cyclic voltammogram(initial potential and switching potential)
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Understanding Response
•AtapotentialwellpositiveofE0´,onlynonfaradaiccurrentsflowforawhile.
•WhenthepotentialreachesthevicinityofE0´,thereductionbeginsandcurrentstartstoflow.
•Asthepotentialcontinuestogrowmorenegative,thesurfaceconcentrationofthereactantmustdrop,hencethefluxtothesurfaceandthecurrentincrease.
•Asthepotentialmovespast,thesurfaceconcentrationdropstonearzeroandmasstransferofreactanttothesurfacereachesamaximumrate.
•Thenitdeclinesasthedepletioneffectsetsin.
Cyclic Voltammetry
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Cyclic Voltammetry
•E0= (Epa+ Epc) /2 .
•Separation of peaks for a reversible
couple is 0.059V/n volts.
•A one electron transfer fast reaction
thus gives 59mV separation.
•Half-peak potential Ep/2 = E1/2 + 0.028/n
•This potential is attained in the interval in which the rate of the charge-transfer process, and hence the current, increase monotonically with time.
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Randles-Sevcik equation
n = Number of electrons
F = Faraday’s Constant 96,485 C/mole
A = Electrode Area cm2
D = Analyte Diffusion Coefficient cm2 s-1
Ratio of ipa to ipc should be close to one, but vary with chemical
reactions coupled to electrode process.
  1 2
p i  0.4463nFAC nFvD RTCenter for Electrochemical Engineering Research
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•If Erepresents an electron transferat the electrode surface, and Crepresents a homogeneous chemical reaction.
•Classification of reactions: CEreaction, ECreaction, Catalytic (EC′) reaction, ECEreaction.
Electrode reactions with coupledhomogeneous chemical reactions
Reversible systems (Effect of scan rate on peak current)