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1、电动势与热动力学燃料电池你现在浏览的是第一页，共18页Reversibility1)Chemical ReversibilityPt is 0.222V more negative than Ag Shorted External batterychemically reversible:Reversing the cell current merely reverses the cell reaction.No new reactions appear,thus the cell is termed;chemically irreversible:different electrode re
2、actions as well as a different net process upon current reversal;你现在浏览的是第二页，共18页ReversibilityThermodynamically reversible:when an infinitesimal reversal in a driving force causes it to reverse directionIn electrochemistryIf a system follows the Nernst equation or an equation derived from it,the elec
3、trode reaction is often said to be thermodynamically or electrochemically reversible(or nernstian).你现在浏览的是第三页，共18页Free Energy and Cell emf你现在浏览的是第四页，共18页Reduction PotentialsThe primary reference,chosen by convention,is the normal hydrogen electrode(NHE),also called the standard hydrogen electrode(SH
4、E):你现在浏览的是第五页，共18页emf and Concentration你现在浏览的是第六页，共18页Reference Electrodes你现在浏览的是第七页，共18页你现在浏览的是第八页，共18页ImpedanceSpectroscopy(Or,howasinusoidallyvaryingvoltageisusedtoprobemultipleelectricalpropertiesofmaterials)你现在浏览的是第九页，共18页IntroductionIS measures the resistance of a circuit to an applied voltage
5、Z(t)=E(t)/I(t),Z()=E()/I()When E is applied as a sinusoidal function in a linear system,I response can be represented by a sum of sinusoidal fuctions with phase shifts.If an equivalent circuit for the system being probed can be constructed,then the resistance or capacitance values for each circuit e
6、lement can be backed out from Z.Especiallyinelectrochemicalimpendancespectroscopy(EIS),thethevoltageprobesignalissmall(1-10mV)sothecurrentresponseispseudolinear(sidebenefit:itdoesntperturbthesampleverymuch)ABardandLFaulkner,Electrochemical Methods:Fundamentals and Applications(2000)http:/ Impedance
7、and Circuit ElementsE(t)=E0cos(t),=2fI(t)=I0 cos(t-)Or,if one writes in complex notation:E(t)=E0 exp(it)I(t)=I0 exp(it-i)Z(t)=Z0 exp(i)=Z0(cos +isin)E/Iresponseforaresistor(=0)E/Iresponseforacapacitor(=-90)E/Iresponseforaninductor(=90)http:/ =-j Xc=j Xlhttp:/www.bath.ac.uk/chsacf/solartron/circp/htm
8、l/acrci.htmRFormorecomplexcircuits,useKirchoffsrules你现在浏览的是第十二页，共18页Plotting Impedance ACole-Cole(orNyquist)plotoftherealandimaginarycomponentsofZforacircuitcontainingacapacitorandresistorinparallel(realworldexample:achargedlayerataninterface).=1/=1/RCNamedafterKSColeandRHCole,J Chem Phys9,341(1941)
9、你现在浏览的是第十三页，共18页Plotting ImpedanceABodeplotofacircuitcontainingacapacitorandresistorinparallel.log|Z|andvs.logareplotted,showingexplicitlytheimpactofimpedance.http:/ Elements from Electrochemistry1.Electrolyte resistance2.Double layer capacitance(30F/cm2 for aqueous systems)3.Polarization resistance
10、4.Charge transfer resistance5.Coating capacitance 6.Constant phase element(a fudge factor)7.Virtual inductor(adsorption?)AndlAWE,RE,CER=l/Ahttp:/ Warburg Impedance)Warburg impedance=diffusion of chemical species to a large planar electrodeInfinitediffusionlayerthicknessDiffusionlayerthicknessAlso,in
11、theWarburgregion,=45http:/ Circuit Model for Electrochemical CellsMixedKinetic+DiffusionmodelCole-ColeplotBodeplothttp:/ Applications of ISDetermine corrosion rates of materials*Measure capacitance and resistance of SAMs to ascertain thickness and packing qualityProbe linearity of electrical/electro
12、chemical reactionsCharacterize electrical activity across interfaces to determine carrier concentration,etc.Determine diffusion rate of counter ions in conducting polymer/carbon nanotube compositesASLCastelaetal.,Prog Org Coat38,1-7(2000)SFlinketal.,Adv Mater12,1315-1327(2000)KKrischeretal.,Angew Chem Int Ed40,850-869(2001)GZ Chenetal.,Adv Mater 12,522(2000)你现在浏览的是第十八页，共18页