Chemistry Reference
In-Depth Information
3
Carbon Paste as an
Electrode Material
In.the.previous.chapters,.carbon.paste.was.introduced.as.an.electrode.material.consisting.typically.
of.two.major.building.components.and.possessing.numerous.speciic.features..In.this.chapter,.the.
survey.of.mechanical.and.physicochemical.properties.is.carried.out,.which.includes.other.charac-
teristics.of.carbon.paste.that.have.a.direct.impact.on.the.resultant.behavior.of.carbon.paste.electrode.
(CPEs),.chemically.modiied.carbon.paste.electrodes.(CMCPES),.and.carbon.paste.(CP).biosensors,.
and.all.the.remaining.sensors,.including.their.electrochemical.characteristics.
3.1 PHYSICOCHEMICAL PROPERTIES OF CARBON PASTES
The. characteristics. in. which. carbon. pastes. differ. from. similar. electrode. materials,. that. is,. from.
solid.carbon.(graphite).and.some.noble.metals,.including.their.variants.with.additional.membranes,.
can.be.summarized.as.follows:
3.1.1 M
iCrosTruCTure
oF
C
arbon
p
asTes
Due.to.the.presence.of.liquid.binder,.carbon.paste.is.typically.a.
multicomponent material
,.exhib-
iting. a. rather. unique. microstructure.. In. order. to. deine. the. structural. character. of. carbon. pastes,.
basic. types. of. CPEs. made. of. mineral. and. silicone. oils. were. subjected. to. some. special. investi-
gations.. Surprisingly,. the. very. irst. attempts. had. not. been. microscopic. observations. but. indirect.
electrochemical.experiments.based.on.measurements.of.conductance.[2].or.electrolytic.and.polar-
ization.phenomena.[68]..Nevertheless,.the.most.comprehensive.insights.into.the.CP.microstructure.
were. obtained. later,. with. the. aid. of. modern. microscopic. techniques,. such. as. scanning. tunneling.
microscopy. (STM;. [172]),. optical. microscopy. (OM;. [617]),. scanning. electron. microscopy. (SEM;.
[96,618,619]),. and. atomic. force. microscopy. (AFM;. [620]).. SEM. can. also. be. advantageously.
combined. with. x-ray. microanalysis. [173]. or. proilometer. to. specify. the. surface. roughness. [327]..
Regarding.microscopic.imaging.of.carbon.pastes.and.their.surfaces,.further.details.are.available.in.
Section.6.5..Recently,.SEM.imaging.has.become.very.popular,.often.as.an.inevitable.instrumental.
tool.for.the.characterization.of.novel.types.of.electrodes.(see,.e.g.,.[96,173].and.references.therein).
and.completely.new.types.of.carbon.pastes,.such.as.those.made.of.carbon.nanotubes.[124].or.ionic.
liquids.[453]..And.it.should.also.be.mentioned.that.there.were.some.studies.on.the.effect.of.chemical.
modiiers.[243,618].or.structural.alterations.after.immobilization.of.biological.tissues.[619].
Of.considerable.interest.were.also.preplated.metallic.ilms.and.deposits.where.attention.was.focused.
on. diversities. in. the. structure. of. palladium. deposits. [621],. mercury. [189],. gold. [261],. and. bismuth.
ilms.[173,622],.and.related.structures.(like,.for.instance,.“solid”.dispersions.of.bismuth.and.antimony.
obtained.by.manual.homogenization.of.the.respective.ine.powders.in.the.native.carbon.paste.[188]).
Based.on.the.observations.from.OM,.STM,.and.mainly.SEM.studies,.the.irst.
theoretical models
on the carbon paste microstructure
.have.been.proposed.with.an.attempt.to.interpret.relations.between.
the.quality.and.mutual.ratio.of.both.main.carbon.paste.constituents.and.the.resultant.behavior.of.CPEs,.
thus.supporting.observations.from.electrochemical.measurements.
One.of.the.irst.models.of.this.kind.was.discussed.in.detail.in.the.fundamental.report.of.Adams's.
group.[68],.and.some.conclusions.can.be.summarized.as.follows..The.model.assumed.consequent.
49
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