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Backgroundcurrent37●BBBacon,FrancisThomas(Dec.,,Billericay,Essex,UK–May,,Lit-tleShelford,nearCambridge,UK)BaconwaseducatedatEtonCollegespecializinginscienceandattheTrinityCollegeinCambridgeobtainingadegreeinmechanicalsciences.Hestartedtoworkonthehydrogen–oxygenfuelcellin.Heconstructedthefirstpracticalandefficientfuelcells.Heusedpotassiumhydroxidein-steadofacidswhichwaslesscorrosivetotheelectrodes;therefore,platinumcouldbereplacedbyinexpensivenickelelectrodes.Thedevelopmentoftheporousgas–diffusionelectrodesofhighsurfaceareawastheotherim-portantstep.Besideeverydayapplicationssuchastrans-port,themostnotablesuccesswasthatBaconcellspro-videdelectricalpowerforthefunctioningofsystemsandtheproductionofdrinkingwaterinthemannedmoonflightsoftheApollospaceprogram.FrancisThomasBaconwasadirectdescendantofSirFrancisBacon(–).AmongothershewaselectedafellowoftheRoyalSociety(),andawardedthefirstGroveMedal()[ii].Refs.:[i]eugenik/history/bacon.html;[ii]Ba-conFT()JElectrochemSoc:CGIBaconcell—Hydrogen–oxygenfuelcellinitiallydevel-opedbyBacon.gas–diffusionelectrodeswerepre-paredfromcarbonylnickelbypressingandsubsequentsintering.Thethree-phaseboundarywasfixedinsidetheporouselectrodebodybypreparingtheelectrodeasabi-layerstructure.The“workinglayer”withporesofabout–μmdiameteriscoveredontheelectrolytesolu-tionsidebyathinlayerwithanaverageporediameterof.μm.Pressureofthefeedgasneededforoperationisadjustedtoavalueatwhichthelargeporesarekeptfilledwithgaswhereasthesmallporesareleftfilledwithelectrolytesolutionbycapillaryaction,bubblingofreac-tantgasisthusavoided.Becauseofthepoorelectrocat-alyticactivityofnickelandthelimitedactual(true)sur-faceareatheoperationtemperaturehadtobeelevatedtoaboutC.Vaporpressureofthealkalineelectrolytesolution(–%KOH)requiredoperationpressuresof–atm.Corrosionoftheoxygen-consumingnickelelectrodeenhancedatthesetemperatureswaslimitedbypreoxidationoftheporouscathodebody.Byoxi-dizingtreatmentoftheelectrodeinlithium-containingcausticsolutionadopedsemi-conductingnickeloxideisformedshowingimprovedcorrosionresistance.Cellvoltagesof.VatcurrentdensitiesofmAcm−wereachieved.Ref.:[i]KordeschG,SimaderG()Fuelcellsandtheirapplications.VCH,WeinheimRHBackgroundcurrent—(i)Generally,inelectrochemicalsystems,anycurrentotherthanthewantedone(e.g.,seedarkcurrentinphotovoltaics).(ii)Involtammetryanycurrentthatisnotduetotheanalyte.Athighpotentialstheworkingwindowoftheindicatorelectrodeislimitedbytheoxida-tionofelectrodematerial,oranionsofthesup-portingelectrolyte,orthesolvent,andatlowpotentialsitislimitedbythereductionofhydrogenions,orcationsofthesupportingelectrolyte,orthesolvent,ortheelectrodematerial(e.g.,mercuryinthepresenceofammoniumsaltsinnon-aqueousmedia).Withinthewindow,aresidualcurrentconsistsofcapacitiveandfaradaiccomponents.Adoublelayerchargingcurrentcannotbeavoided,butitsinfluencecanbedi-minishedbythecurrentsamplingprocedureinpulsevoltammetrictechniques.Generally,thecapacitivecur-rentisproportionaltotherateofchangingtheelec-trodepotential(E),capacitance(C)andsurfacearea(S):I=CS+S(E−Eσ=)dCdEdEdt+C(E−Eσ=)dSdt.Thefirsttermlimitstherangeofscanratesthatcanbeappliedincyclicvoltammetryonstationaryelectrodes(dSdt=),whilethesecondtermisimportantonlyinDCpolarographywithdroppingmercuryelectrode.However,caremustbetakentoavoidaleakageofsolu-tionintoanygapbetweentheactiveelectrodediskandtheinsulatingsheath,aporosityofelectrodesurface,andtheformationofathinfilmofthesolutionsurroundingthelowerendofthemercurythreadwithinthetipofthecapillary.Inallthesecasesafluctuatingsurfaceareamaycausethefluctuationofcapacitivecurrent.Inpulsevoltammetry,thedecayofchargingcurrentassociated38Back-titration●Bwiththeseimperfectionsisslowerthanthedecayofca-pacitivecurrentoftheelectrodesurface[i,ii].Faradaiccomponentsofthebackgroundcurrentarecausedbythereductionofoxygenorotherimpuri-tiesinthesupportingelectrolyte,andbytheformationofoxidelayersonmetalelectrodes.Theconcentrationofoxygeninwell-aeratedelectrolyteisabout.mM.Oxy-genisreducedatnoncatalyticelectrodesintwosepa-ratetwo-electronstepsatpotentialsthatvarybetween.Vand−.Vvs.SCE,dependingonpHandonelectrodematerial.Forthemajorityofmeasurements,oxygenmustberemovedfromthesolution.Inthelab-oratory,solutionsaresaturatedwithnitrogenorargontoreducethepartialpressureofoxygentoaverylowvalue.Ultrapuregasesshouldalwaysbepreferred.How-ever,thereisachancetocontaminatesolutionswithoxy-genduetothepermeabilityofmostplastictubesusedtopropelnitrogenorargon.Inextremecasesfullglassapparatushastobeused.Oxygenadsorbedonparticlesofgraphitepowdermustberemovedbyheatingthepowderinnitrogenpriortothepreparationthecar-bonpasteelectrode.Otherwisetheresponsemayappearnoisy.Inanodicstrippingvoltammetrythepurityofmercuryisveryimportant.Itmustbeensuredthatnotracesofinvestigatedelementarepresentinmercurypriortotheaccumulation.Thesupportingelectrolyteshouldbepreparedbyusingextrapurechemicals.Fi-nally,thecellresponsemayappearnoi