Chemistry Reference
In-Depth Information
•.
Linear sweep (scan) voltammetry
.is,.in.fact,.DCV.at.higher.scan.rates,.which.can.go.up.to.
1000.mV.s
−1
.and.even.more..Sometimes.the.expressions.“linear.sweep.voltammetry”.and.
“direct.current.voltammetry”.are.used.or.referred.to.identically.in.the.literature.
•.
Cyclic voltammetry (CV)
.is.probably.the.most.important.technique.for.studying.electro-
chemical. reactions. proceeding. at. the. electrode. surface.. It. represents. an. extended. form.
of.LSV..With.CV.a.scan.in.one.potential.direction.(half-cycle).is.combined.with.a.scan.
in.the.counter-direction,.yielding.one.full.cycle..The.voltammograms.are.not.necessarily.
started.at.one.of.the.vertex.potentials.but.usually.at.a.potential.with.neglible.faradic.cur-
rent..Therefore,.it.is.a.powerful.tool.to.study.whether.reduction-oxidation.couples.appear.
in.the.voltammetric.scan.and.whether.they.are.reversible.or.not;.in.case.of.reversibility.
(quick.electron.transfer.for.both.components.of.the.redox.couple),.the.potential.difference.
between.corresponding.cathodic.and.anodic.peaks.should.be.59/n.mV.(see.Figure.6.7)..
In.fact,.CPEs.rarely.meet.the.criteria.of.ideal.reversibility.due.to.the.presence.of.pasting.
liquid.in.the.surface;.the.deviation.can.serve.as.a.characterization.criterion.for.the.paste.
(see.Sections.3.3.and.4.4.1)..Cycles.can.be.repeated.ad.libidum.and.may.yield.information.
on.adsorption-desorption.characteristics.or.chemical.changes.of.reactants.or.products.
•.
Square-wave voltammetry (SWV)
:.A.square.wave.is.superimposed.over.the.linear.potential.
ramp. yielding. a. peak-shaped. current. response.. The. current. is. measured. as. a. difference.
from.the.forward.and.the.backward.pulses;.SWV.often.yields.-higher.responses.than.DPV.
in.comparable.shorter.times;.the.rapidness.even.allows.its.use.with.electrochemical.detec-
tors..The.method.was.developed.by.Barker.based.on.older.works.from.Kalousek.[1925];.the.
method.was.popularized.by.J..Osteryoung.and.is.therefore.also.sometimes.referred.to.as.
“Osteryoung.SWV”.(similar.to.DC-polarography,.known.as.“Heyrovsky.polarography”).
•.
Alternating current voltammetry (ACV)
.superimposes.an.alternating.current.on.the.poten-
tial.ramp.and.measures.the.corresponding.harmonic.tone.or.overtones..Out-of-phase.mea-
surements.allow.detailed.studies.of.adsorption.processes.via.capacitive.currents.apart.from.
the.faradic.reactions.
For. investigating. electrochemical. reactions. with. heterogeneous. carbon. electrodes,. the. con-
siderations.shown.earlier.are.basically.applicable,.but.it.can.be.almost.always.noticed.that.devia-
tions.from.the.theoretical.behavior.occur..The.main.reason.is.the.presence.of.the.pasting.liquid.
Δ
E
p
Current
i
pa
Oxidation
Reduction
i
pc
Δ
E
p
=
E
pa
-
E
pc
≈
0.058
n
-—-—
FIGURE 6.7
A.typical.cyclic.voltammogram..
Note
:.For.a.reversible.redox.couple,.the.Δ
E
p
.value.should.be.
about.59/
n
.[mV].and.
i
pa
/
i
pc
.∼.−1.
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