I

Ilkovičequation345●IIIcebergstructure—Watermoleculesadjacenttoanor-ganic(nonpolar)liquidorsolidphaseandalsoadjacenttosinglehydrophobicmoleculesorhydrophobicpartsofmoleculesareformingashell-likestructureviahydro-genbonding.FrankandEvans[i]havecalledthis‘ice-bergstructure’becauseofitssimilaritywiththestructureofice.Thisstructurebuildingisassociatedwithalossofentropy,andthereforethateffectispartiallyresponsi-bleforthelowsolubilityofnonpolarliquidsinwater,formicelleformation,proteinfolding,etc.[ii].Seealsohydrophobiceffect.Refs.:[i]FrankHS,EvansMW()JChemPhys:;[ii]TanfordC(,ndedn.)Thehydrophobiceffect:formationofmicellesandbiologicalmembranes.Wiley,NewYorkFSIdealnonpolarizableelectrode—Anelectrodewhosepotentialdoesnotchangeuponpassageofthecur-rent.Typicalsuchelectrodeswithfixedpotentialarethereferenceelectrodes.Seealsoelectrode.Ref.:[i]BardAJ,FaulknerLR()Electrochemicalmethods,nded.Wiley,NewYork,pJLIdealdepolarizedelectrode—Workingelectrodeinthesituation,whenelectrolysisstartstooccurandevenaverysmallchangeofpotentialresultsinalargechangeoffaradaiccurrent(inthepotentiostaticregime)orwhenthepassingcurrentdoesnotcausethechangeofthepotential(galvanostaticregime).Theidealnonpo-larizability(depolarization)ischaracterizedbythever-ticalpartofthepotentiostaticI–EcurveorhorizontalpartofthegalvanostaticE–tcurve.(Seealsoelec-trode.)JLIdealpolarizedelectrode—Workingelectrodeinthesituationwhenalargechangeofpotentialisaccompa-niedbyaninfinitesimalincreaseofthecurrent.TheidealpolarizabilityischaracterizedbyahorizontalregionofapotentiostaticI–Ecurve(so-called“potentialwindow”wheretheelectrodecanbeusedformeasurements).Seealsoelectrode.Ref.:[i]BardAJ,FaulknerLR()Electrochemicalmethods,ndedn.Wiley,NewYork,pJLIdentityreaction—Achemicalreactionwhoseprod-uctsarechemicallyidenticalwiththereactants,e.g.,thebimolecularself-exchangereactionofCHIwithI−.Ref.:[i]MullerP()PureApplChem:WKIIRfilterrecursivefilterIlkovič,Dionýz(CourtesyofDr.M.Heyrovský,Prague)(Jan.,,ŠarišskýŠtiavnik,Austro-HungarianEm-pire,nowSlovakia–Aug.,,Bratislava,Czecho-slovakia,nowSlovakia).IlkovičwasassistantofHey-rovský,Jaroslav,andfromProfessorofPhysicsattheTechnicalUniversityofBratislava,Slovakia.Ilkovičgreatlycontributedtothedevelopmentofpolarogra-phy.HeisparticularlyknownfortheIlkovičequa-tion(),whichdescribesthediffusioncurrentatadroppingmercuryelectrode[i,ii].TheHeyrovský–Ilkovičequation()describestheentirecurrent-potentialcurve(polarographicwave)[iii]ofareversibleredoxsysteminpolarography,fromwhichfollowsthedefinitionofthepolarographichalf-wavepotential.Ref.:[i]IlkovičD()CollCzechChemCommun:;[ii]IlkovičD()JChimPhys:;[iii]HeyrovskýJ,IlkovičD()CollCzechChemCommun:EKIlkovičequation—Therelationshipbetweenthecon-centrationofanelectrochemicallyactivespeciesattheelectrodesurface(c),insidetheelectrolytesolution(c),theflowofmercuryatthedroppingelectrode(m),thenumberofelectrons(z)transferredinthereductionstepofthespeciesunderinvestigationandthecurrentasafunctionofthetime(duringthelifeofadrop)underpurelydiffusionalcontrolID,tisID,t=.zFDmt(c−c).Thisformalreadytakesintoaccountthechangeofthediffusionlayerthicknessduringgrowthofthedrop.At346Imageplaneindoublelayertheory●Isufficientlylargeoverpotentialsthesurfaceconcentra-tionwilldroptozero,thustheequationwillbesimpli-fied:ID,lim=.zFDmtc.Mostlytheaveragecurrent(averagedoverdroptimettandthusdropsize)isused:¯ID,lim=.zFDmttc.Aslightlyvariedformcombinestheconstantsinto¯ID,lim=zDmttc(units:D/cms−;m/gs−;tt/s,c/molcm−,I/μA).SeealsoIlkovič.Refs.:[i]IlkovičD()CollCzechChemCommun:;[ii]IlkovičD()JChimPhys:RHImageplaneindoublelayertheory—Inclassicalelec-trostaticsachargeinfrontofametalsurfacegivesrisetoanimagechargeonthemetal,whosesurfaceformstheimageplane.Inarealmetaltheeffectiveimageplaneneednotbeidenticaltothemetalsurface,usuallyitliesadistanceoftheorderof.Åinfrontofit.Theimageplaneisalsotheeffectiveplatepositionofametalcapaci-tor.Theelectricdoublelayercanbeviewedasacapaci-torwithaneffectiveplateseparationofafewÅngstroms;henceasmallshiftoftheimageplanehasasizableef-fectonitscapacity.Theconceptoftheimageplanehasmostlybeenusedinmodelsinwhichthemetalisrepre-sentedasjelliummodel.Ref.:[i]SchmicklerW,HendersonD()ProgSurfSci:WSImaginarypartofimpedanceimpedanceImpedance—Symbol:Z,SIunit:Ohm(Ω)Impedance(or“compleximpedance”)ofanelectrochemicalsystemunderstudy,Z,isdefinedonthebasisofthepassingalternatingcurrent:I=Io+Icos(ωt+φ),atthesamefrequency,ω,astheimposedsinusoidalpertur-bationoftheelectrodepotential,E=Eo+Ecosωt,nearadirect(average)potentialbias,Eo.Usefulinformationonthesystemisgivenbytwomeasuredcharacteristics,theratiooftheamplitudesofthepotentialandcurrentoscillations,EI,andthephasedifference(phaseshift,orphaseangle),φ(sometimesdefinedwithanoppositesign).Bydefinition,theimpedancerepresentsacomplexquantitygivenbytheformula:Z=(EI)exp(−iφ),ibeingtheimaginaryunit:i=(