物理化學(xué)英文課件：Electrochemistry-4

1、Electrochemistry(4) Xuan ChengXiamen UniversityPhysical Chemistry1Given that rGo = -212.7 kJmol-1 for the cell reaction in the Daniel cell at 25 and that m(CuSO4) = 1.010-3 molkg-1 and m(ZnSO4) = 3.010-3 molkg-1, calculate (1) the ionic strength of the solutions(2) the mean ionic activity coefficien

2、ts in the respective compartments(3) the reaction quotient(4) the standard cell potential (5) the cell potentialPhysical ChemistryElectrochemistryQUIZ(15分)(3 points each)(take + = - = in the respective compartments)2Answers.(a)for CuSO4 solutionfor ZnSO4 solutionPhysical ChemistryElectrochemistryQUI

3、Z(1分)(1分)(1分)3Answers.Physical ChemistryElectrochemistryQUIZ(b) in very dilute aqueous solution at 25 (CuSO4) = 0.74 (ZnSO4) = 0.60(1分)(1分)(1分)4Answers.Physical ChemistryElectrochemistryQUIZ(c) The cell reaction: Cu2+ (m1) + SO42- (m1) + Zn Cu + Zn2+ (m2) + SO42- (m2)Since + (Cu2+)CuSO4 = - (SO42-)C

4、uSO4 = (CuSO4) = 0.74+ (Zn2+)ZnSO4 = - (SO42-)ZnSO4 = (ZnSO4) = 0.60Alsom1 = m (Cu2+)CuSO4 = m (SO42-)CuSO4 = 110-3 molkg-1m2 = m (Zn2+)ZnSO4 = m (SO42-)ZnSO4 = 310-3 molkg-1(1分)(1分)5Answers.Physical ChemistryElectrochemistryQUIZTherefore, (1分)(d) (1分) (2分)(e) (1分)(2分)6Electrode Processes 在電化學(xué)系統(tǒng)中有電流

5、通過(guò)時(shí)(電化學(xué)電源或電解池)在兩個(gè)電極的金屬和溶液界面間以一定速率進(jìn)行著電荷傳遞過(guò)程，即電極反應(yīng)過(guò)程。The electric charges are transferred at a certain rate within the metals (two electrodes) and solution interfaces when there is a current passing through the electrochemical system.Physical ChemistryElectrochemistry7 正反應(yīng)叫陰極過(guò)程或陰極反應(yīng)，設(shè)其反應(yīng)速率為c； 逆反應(yīng)叫陽(yáng)極過(guò)程

6、或陽(yáng)極反應(yīng)，設(shè)其反應(yīng)速率為a 。The electrode processesM+ + e- M ca電極上進(jìn)行的陰極與陽(yáng)極過(guò)程EcEaMa cM+eM電極金屬Physical ChemistryElectrochemistryCathodeAnodeEquilibrium8電化學(xué)反應(yīng)速率與電流密度電極反應(yīng)的反應(yīng)速率定義為式中，A電極的截面積，單位為m2； 反應(yīng)進(jìn)度，單位為mol。 電化學(xué)反應(yīng)速率，定義為單位時(shí)間內(nèi)，單位面積的電極上，反應(yīng)進(jìn)度的改變量。單位為molm-2s-1。Physical ChemistryElectrochemistryElectrochemical reaction

7、rate and current density9 在電化學(xué)中，易于由實(shí)驗(yàn)測(cè)定的量是電流，所以常用電流密度 j (單位電極截面上通過(guò)的電流，單位為Am-2)來(lái)表示電化學(xué)反應(yīng)速率的大小，j與的關(guān)系為j = Z F j0叫交換電流密度。Physical ChemistryElectrochemistry10Physical ChemistryThe rate of charge transferRate of reduction of Ox Ox = kcOxRate of oxidation of Red Red = kaRedCathodic current density jc = F kc

8、OxAnodic current density ja = F kaRedThe net current density at the electrode j = ja -jc = F kaRed F kcOx(8)Electrochemistry演示11Physical ChemistryThe activation Gibbs energyCathodic currentAnodic currentNet currentActivated complex theory(10)The net current density at the electrode j = ja -jc = F ka

9、Red F kcOx(8)G: the activation Gibbs energyB: a constantElectrochemistry(9)12The Butler-Volmer equationPhysical ChemistryConsider a reaction : Transfer coefficient (11)(12)(13)G: Activation Gibbs energy Consider a reaction Electrochemistry13The Butler-Volmer equationPhysical ChemistryConsider a reac

10、tion Ox + e- Red(12)(13)(10)(14)Electrochemistry14The Butler-Volmer equationPhysical Chemistry(13)(16)anodic cathodic (14)Electrochemistry15Physical Chemistry a c,e a ,e c e a cj(a) Electrolytic cells a a,e c,e c e j(b) Chemical power sources c a PolarizationPolarization indicates a departure of the

11、 electrode/electrolyte system from equilibrium due to passage of a current through electrodeElectrochemistry16Physical ChemistryMass-transfer, electron-transferFeH+diffusionmigrationHHH2Fe2+Fe in Oxygen-free, acid solution(4) mass-transfer of Fe2+(2) surface adsorption of H(3) electron-transfer(1) m

12、ass-transfer of H+H+ + e- HadsHads + Hads H2Fe Fe2+ + 2e-Fe + 2H+ Fe2+ + H2overalle-diffusionmigrationElectrochemistry17演示18Concentration polarizationPhysical ChemistryAg+c0c(c c0), Ag+ Ag(14.43)*(28)(30)(31)(32)Bulk solutionNernst diffusion layerelectrodeElectrochemistry19Concentration polarization

13、Physical ChemistryAg+c0c(c c0), Ag+ AgBulk solutionNernst diffusion layerelectrodeHow to minimize the concentration polarization?Agitation Rising temperatureElectrochemistry20The Butler-Volmer equationPhysical ChemistryOverpotential(18)(21)(19)Activation polarization(14)(20)Electrochemistry21The But

14、ler-Volmer equationPhysical Chemistry(21)(22)Activation polarizationLow overpotential limit Expand exponentials in (21) usingElectrochemistry22The Butler-Volmer equationPhysical Chemistry(23)Activation polarizationLow overpotential limit At low overpotential, the interface behaves as a conductor tha

15、t obeys Ohms law.(22)(13)(21)Electrochemistry23The Butler-Volmer equationPhysical Chemistry(25)(24)High overpotential limit High overpotential limit (27)(26)(21)Electrochemistry24The Butler-Volmer equationPhysical Chemistry(21)(25)(27)Electrochemistry25Tafel PlotPhysical Chemistrya, b: Tafel constan

16、tsElectrochemistry26Electrode ReactionsPhysical ChemistryCathode reactions(1) Metal ions(2) Hydrogen ionsThe species with the highest E values will be first reduced at the cathodeCathode reductionElectrochemistry27Electrode ReactionsPhysical ChemistryAnode reactions(1) Anions(2) Anode itselfThe spec

17、ies with the lowest E values will be first oxidized at the anodeAnode oxidationElectrochemistry28Potentiostat ControlPhysical ChemistryWorking electrodePotentiostat Control iVReference electrodeCounter electrodeAuxiliary electrodeControlling potential between reference electrode and working electrod

18、eMeasuring current flowing between counter electrode and working electrodeControlling current measuring potentialGalvanostat ControlElectrochemistry29Polarization CurvesPhysical Chemistry5% HF + C2H5OHj / (Acm-2)E / (V vs SCE)Tafel linesElectrochemistry30Physical ChemistryHydrogen OverpotentialHigh overpotentialLow overpotentialElectrochemistry31Cyclic VoltammetryPhysical ChemistryElectrochemistry20 mV/s0.5M H2