G

Galvaniccell(orgalvanicelement)289●GGGaiffecell(a)ThiswasavariationoftheLeclanchécell.(b)ThiswasavariantoftheDaniellcell.Seealsozinc,Zn+/Znelectrodes,Zn+/Zn(Hg)electrodes,zinc–airbatteries(cell).Ref.:[i]HauckWP()DieGalvanischenBatterien,AccumulatorenundThermosäulen,ndedn.Hartleben’sVerlagWienFSGalvani,Luigi(CourtesyofIEEEVirtualMuseum,RutgersUniversityHistoryCenter,USA)(Sep.,,Bologna,Papalstate,nowItaly–Dec.,,Bologna,CisalpinRepublic,nowItaly).Galvaniwasaphysicianandphysicistwhoinvestigatedthena-tureofelectricaleffectsinanimaltissue[i,ii].Inhisearlystudies,Galvaniworkedincomparativeanatomyandphysiology,includingastudyofthekidneysofbirdsandoftheirsenseofhearing.Hisinterestinelectri-calphenomenawasinitiatedwiththeaccidentalob-servation()ofthetwitchingofthelegsofadis-sectedfrogwhenabaredcruralnervewastouchedwiththesteelscalpel,whilesparkswerepassingfromanelectricmachinenearby.Thiswasthebeginningofhisextensivestudiesofelectricaleffectsproducedinani-maltissues[iii,iv].Electrochemistry,andparticularly,bioelectrochemistrywerestartedfromGalvani’sexper-iments.GalvaniprovidedthemajorstimulusforVoltatodiscoverasourceofconstantcurrentelectricity(Voltapile).Galvani’snamesurvivesintheGalvaniccell,thegalvanometer,galvanism,etc.Refs.:[i]GalvaniL,EncyclopædiaBritannica;[ii]KipnisN()AnnSci:;[iii]GalvaniL()DeViribusElectricitatisinMotuMus-culariCommentarius.(Commentaryontheeffectofelectricityonmus-cularmotion,essay)AccademiadelleScienze,Bologna;[iv]GalvaniL()Dell’Usoedell’Attivitàdell’ArcoConduttorenellaContrazionedeiMuscoli.(Ontheuseandactivityoftheconductivearchinthecontrac-tionofmuscles,essay)AccademiadelleScienze,BolognaEKGalvanic—FollowingtheepochalexperimentsofGalvani,inwhichelectricdischargeswereshowntoactivatethedissectedmusclesofafrog[i],theword“gal-vanic”wasadoptedbyasmallgroupofscientiststode-scribethisparticulareffect.However,shortlythereafter,Voltaannouncedtheinventionofhiseponymouspile(whichconsistedofalternatingdisksofzincandcop-perseparatedbybrine-soakedcloth),andwiththisnewsourceofelectricityitbecamepossibletocarryoutgal-vanicexperimentsforlongerperiods,andonamuchwiderrangeofmaterials,thanpreviously.Asaresult,theword“galvanic”rapidlyspreadintomuchwiderusage.Today,theword“galvanic”hasenteredmostlanguagesintheworld,andremainsinregularuseinthreeprin-cipalareasofscience:(a)todescribeelectricitygener-atedspontaneouslyfromavoltaicpile(galvaniccell),(b)todescribephenomenaoccurringatthejunctionoftwodissimilarmetals(galvaniccontact,galvaniccorro-sion),and(c)todescribephenomenaoccurringattheinterfacebetweenanelectrodeandlivingcells(galvanicskinresponse).Refs.:[i]GalvaniAL()Deviribuselectricitatisinmotumusculari,pub.AccademiadelleScienze,Bologna;[ii]VoltaA()PhilosTransRSocLondon:SFGalvaniccell(orgalvanicelement)—Agalvaniccellisanelectrochemicalcellinwhichreactionsoccurspon-taneouslyattheelectrodeswhentheyareconnectedexternallybyaconductor.Inthesecellschemicalenergycanbeconvertedintoelectricalenergy[i,ii].Thegal-vaniccellconsistsoftwoelectrodes,i.e.,electroncon-ductors(metal,carbon,semiconductoretc.)incontactwithoneormoreionicconductors(whichmaybeelectrolytesolutions,ionicliquids,electrolytemelts,orsolidelectrolytes).Theelectrodesmaybeseparatedbyasaltbridgeoraglassfrit,oranion-permeable(exchange)membraneoraporousinertdiaphragm,or–inthecaseofcon-centrationcellswithouttransferenceevenwithametalincontactwithitspoorlysolublesalts.Thegalvaniccellisrepresentedbyacelldiagram.Inthegalvaniccellanelectrochemicalcellreactionoccurs.TherelationshipbetweenthemolarGibbs(free)energychange(ΔG)ofthecellreactionandthepotentialofthecellreaction290Galvanicelement●G(Ecell)isasfollows:Ecell=−ΔGnF,()wherenisthechargenumberofthecellreactionandFistheFaradayconstant.Galvaniccellsaspower(current)sourcesincludeprimary(non-rechargeable)cells,secondary(recharge-able)cells(batteries),andfuelcells.Theconcentrationcellsareusedonlyfordetermi-nationoftransport(transference)numbers,activity,andactivitycoefficientsofelectrolytesandotherquan-tities.Theirpracticalapplicationislimitedbytheself-dischargeduetothespontaneousdiffusionprocess.Inconcentrationcellsnochemicalreactionsoccur,aphys-icalprocess(theequalizationofactivitiesbydiffusion)causesthepotentialdifferenceandsuppliestheenergy.Galvaniccellscanalsobeusedassensorssinceasup-plyofacompoundthatcanbeoxidizedorreduced,caninducecurrentflow.Thereareseveralgasanalyzersworkingbythisprinciple,atypicalexampleistheHer-schcellformonitoringoxygenconcentration.Refs.:[i]CohenER,CvitasT,FreyJGetal.(eds)()IUPACquan-tities,unitsandsymbolsinphysicalchemistry,p;[ii]BardAJ,FaulknerLR()Electrochemicalmethods,ndedn.Wiley,NewYork,pp–GIGalvanicelementgalvaniccellGalvanipotentialdifferencepotential,subentrygalvanicpotentialdifferenceGalvanicprocess—Electrochemicalprocessoccurringspontaneouslyinacellattwoelectrodesconnectedex-ternallybyaconductor.Theanodeduetotheoxida-tionofthesubstrateischargednegatively,thecathodeasadonorofelectron