Chemistry Reference
In-Depth Information
Current collector
Platinum grid
Metallic electrode
Polymer
Electroactive
solid
Carbon
particle
Electroactive solid
Carbon particle
Side view
Top view
(A)
(B)
FIGURE 7.3
(A).Two.less.common.conigurations.for.CPEE..(B).A.schematic.view..(For.details,.see.inscriptions.)
insoluble.polymer.in.an.appropriate.organic.solvent.(usually.tetrahydrofuran.or.dichloromethane).
and. the. deposition. of. a. drop. of. this. suspension. onto. a. solid. electrode. surface,. and. the. resulting.
evaporation.of.the.solvent.leads.to.the.formation.of.a.CPEE.as.illustrated.in.Figure.7.3A..Of.course,.
the.use.of.such.an.electrode.is.restricted.to.solvents.in.which.the.polymeric.binder.is.not.soluble.
The.second.coniguration.is.a.binder-free.CPEE.(see.Figure.7.3B).obtained.by.pressing.a.carbon.+.
solid.sample.mixture.onto.a.metallic.grid.(Pt.or.Au).under.2.or.3.tons.of.pressure.for.some.minutes.
to.form.a.composite.pellet.likely.to.be.used.in.any.solvent..This.coniguration.suffers.however.from.
some.lack.of.mechanical.stability.when.used.for.a.prolonged.time.in.solution.
Traditional.cyclic.voltammetry.(CV).with.linear-scan.potential.ramp.is.often.used.to.character-
ize.the.redox.properties.of.incorporated.solid.samples..By.adopting.careful.operational.conditions.
(low.amount.of.electroactive.material,.i.e.,.a.few.percent,.potential.scan.rates.typically.lower.than.
0.1.mV.s
−1
),.the.typical.shape.of.cyclic.voltammograms.obtained.with.CPEEs.in.the.simplest.cases.
(reversible. electron. transfer,. strictly. solid-state. transformations,. no. soluble. species). is. relevant. to.
thin-layer. voltammetry. (symmetric. anodic. and. cathodic. peaks. located. at. the. same. potential;. see.
peaks.
A
1
. and.
C
1
. in. Figure. 7.4. as. an. illustrative. example. for. chalcocite. (Cu
2
S). oxidation. [2025])..
Integration.of.these.peaks.enables.via.the.Faraday.law.to.determine.the.amount.of.electroactive.cen-
ters..In.most.cases,.however,.voltammograms.of.complex.shape.are.obtained.as.a.result.of.contribu-
tions.not.only.from.the.solid.but.also.from.soluble.electroactive.species.[2024];.dissolution.kinetics.
can.also.affect.the.cyclic.voltammograms,.making.the.interpretation.of.the.data.somewhat.complex.
Basically,.one.knows.the.amount.of.electroactive.material.present.in.the.paste.and,.in.the.pres-
ence.of.an.electrolytic.binder,.this.quantity.is.likely.to.be.transformed..This.is.not.always.true,.as.the.
charge.eficiency.of.CPEE.depends.on.various.parameters.such.as.the.paste.composition.(relative.
ratios.between.carbon,.solid,.and.binder),.the.nature,.the.structure.and.morphology.of.the.redox-
active.compound,.and.the.electrode.coniguration..It.has.been.reported,.for.instance,.that.some.iron.
oxides. can. be. totally. transformed. whereas. some. others. may. suffer. from. lack. of. charge. transfer.
eficiency.[2026,2027]..Too.large.loadings.of.CPEEs.with.electroactive.solids.(e.g.,.10%).also.cause.
decreases.in.reaction.yields,.as.reported.for.the.analysis.of.ferrocene.[38,2028].
The.quantitative.aspects.have.been.fully.studied.by.Lamache,.and.conditions.have.been.deined.
for.which.characteristic.voltammetric.and.chronoamperometric.curves.can.be.used.in.qualitative.
and.quantitative.analyses.of.solid.compounds.using.CPEEs.[2029]..Fundamentals.and.limitations.
for.the.application.of.CPEEs.in.the.electroanalysis.of.solids.are.also.discussed.using.Cu.and.TiC.as.
model.solids,.showing.the.critical.inluence.of.the.carbon.powder.type,.the.quality.and.content.of.
the.binder,.the.size.and.shape.of.carbon.and.solid.sample.particles,.as.well.as.the.paste.preparation.
with.respect.to.homogeneity.and.reproducibility.[2030].
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