电极过程动力学陈胜利.ppt

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1、化学学院物理化学专业研究生课程化学学院物理化学专业研究生课程“电极过程动力学电极过程动力学”授课教师授课教师：陈胜利陈胜利Tel:68754693Email:Office:化学楼化学楼 135授课教材授课教材查全性等著：电极过程动力学导论电极过程动力学导论 （第三版，科学出版社第三版，科学出版社，2002年）推荐参考书推荐参考书Written by Allen J.Bard and Larry F.Faulkner,Electrochemical Methods:Fundamentals and Applications （Second Edition,Wiley,2001）邵元华等译,电化学

2、方法：原理及应用电化学方法：原理及应用 （第二版，化学工业出版社第二版，化学工业出版社,2005 年）Chapter 1INTRODUTION AND OVERVIEW OF ELECTRODE PROCESSESElectrochemistry?n nThe laws(principles)and the technologies The laws(principles)and the technologies concerning the conversion between chemical concerning the conversion between chemical energ

3、y and electrical energyenergy and electrical energyn nInterrelation between chemical phenomena Interrelation between chemical phenomena(chemical reactions,chemical changes,etc.)(chemical reactions,chemical changes,etc.)and electric phenomena(charge,current,and electric phenomena(charge,current,poten

4、tial,electric field,etc.)potential,electric field,etc.)n nWith a With a history of more thanhistory of more than two centuriestwo centuries,electrochemistry has,electrochemistry has been a typical example of a been a typical example of a truly interdisciplinary(truly interdisciplinary(各学科间的各学科间的各学科间

5、的各学科间的)area of science and technology)area of science and technology.n nIts roots have been in Its roots have been in chemistry,physics,materials and biological chemistry,physics,materials and biological sciencescience and its applications spreading from and its applications spreading from electroch

6、emical electrochemical analysis and synthesis to environmental protection and energy analysis and synthesis to environmental protection and energy conversion and storageconversion and storage.n nEveryday life items such as Everyday life items such as batteriesbatteries,the glucose the glucose（葡萄糖）（葡

7、萄糖）（葡萄糖）（葡萄糖）sensor sensor and domestic or medical gas sensorsand domestic or medical gas sensors are now a commodity,while are now a commodity,while the prospect of mass production of the prospect of mass production of green electric green electric vehicles(Electric vehicles)vehicles(Electric vehic

8、les)is no more a challenge but a viable is no more a challenge but a viable option.option.n nOn an industrial scale,apart from the now mature On an industrial scale,apart from the now mature chlor-alkalichlor-alkali and and metal finishingmetal finishing and and extraction industriesextraction indus

9、tries,there is significant,there is significant activity in the areas of energy conversion and storage by means of activity in the areas of energy conversion and storage by means of fuel cells and solar cellsfuel cells and solar cells as well as in the use of electrochemical as well as in the use of

10、 electrochemical methods for methods for effluent treatmenteffluent treatment.“Electrochemistry provides Electrochemistry provides many opportunities for sustainable development.many opportunities for sustainable development.”Electrochemical Cells and Reactions PtPtPtPtH2SO4SolutionH2O2H2O2H+H+H2OH+

11、H2OH+eeeeCathode:1/2O2+2H+2e-=H2OAnode:H2=2H+2e-Overall cell reaction:H2+1/2O2=H2OPositive electrode:H2O=1/2O2+2H+2e-Negative electrode:2H+2e-=H2Overall cell reaction:H2O=H2+1/2O2 Galvanic Cell（原电池）Voltaic CellH+H+The features of electrochemical reactionsn nThe overall redox reaction is made up of t

12、wo The overall redox reaction is made up of two half-half-reactionsreactions taking place taking place independentlyindependently at two locations at two locations where electronic conductors(where electronic conductors(ElectrodesElectrodes)and ionic)and ionic conductors(conductors(electrolyteselect

13、rolytes)are made in contact;)are made in contact;n nCharge(electron or ions)transfer Charge(electron or ions)transfer between the between the electrodes and chemical species always occurs and a electrodes and chemical species always occurs and a currentcurrent flows in external circuit between two f

14、lows in external circuit between two electrodes;electrodes;n nThe extent and the direction of the reaction can be The extent and the direction of the reaction can be altered by the altered by the potentials potentials applied to the electrodes;applied to the electrodes;Electrode reaction at electrod

15、e/solution interfacesCharge transfer planeFeimi levelLUMOHOMOCharge transfer planeFeimi levelPotential shifts negativelyeOz +eRz-1Fe3+e Fe2+For Example:Possible processes involved in an electrode reactionOadORadRO*R*neObRb Mass transfer Mass transferPreceding Chemical reactionsFollowing Chemical rea

16、ctions ElectrodeCharge transferAdsorptionDesorptionWhat will we deal with in this course?n nThe kinetics of the electrode reactions of various The kinetics of the electrode reactions of various type and the factors that affect these kineticstype and the factors that affect these kineticsn nCurrent P

17、otentialCurrent Potential dependence dependenceThe philosophy in electrochemical studiesSchematic three-electrode cell used in electrochemical studiesStandard Hydrogen Electrode(SHE)Pt CH+=1mol.l-1 H2H2Saturated calomel electrode(SCE)Metal wireKCl solutionHg2Cl2 HgPt wireStrategies to study the elec

18、trode processesn nPotential-controlled techniquesn nCurrent-controlled techniquesCurrent-controlled techniquesPotentioPotentiostaticstatic（恒电势）（恒电势）methodsmethodsPotentioPotentiodynamicdynamic methods methodsA brief description of the electric double layer and its effects on the electrode reaction k

19、ineticsn nThe double layer is a result of re-The double layer is a result of re-arrangement and orientation of the charges arrangement and orientation of the charges and the dipoles at the electrode/electrolyte and the dipoles at the electrode/electrolyte interface.The electrode and the electrolyte

20、interface.The electrode and the electrolyte bear the same amount of charges with bear the same amount of charges with opposite nature:opposite nature:q qMM =-q-qS S;n nThe double layer consists of two regions:The double layer consists of two regions:Compact layer(also called“inner Compact layer(also

21、 called“inner Helmholtz layer”or “stern layer”)and Helmholtz layer”or “stern layer”)and diffuse layer(also called“outer Helmholtz diffuse layer(also called“outer Helmholtz layer”);layer”);n nThe effective potential to drive the The effective potential to drive the interfacial charge transfer may be

22、interfacial charge transfer may be significantly different from that applied the significantly different from that applied the the electrode/solution interface:the electrode/solution interface:E Eeffeff=E Eappapp (1)1)The capacitor（电容器）（电容器）-like nature of the electric double layern nRegardless of t

23、he nature of an Regardless of the nature of an electrode process,the double layer electrode process,the double layer itself would response to the itself would response to the electrochemical perturbations as a electrochemical perturbations as a series of capacitorsseries of capacitorsn nThe capacita

24、nce values of the double The capacitance values of the double layer are potential-dependentlayer are potential-dependentn nMost of the electrochemical Most of the electrochemical measurements are more or less measurements are more or less affected by the charging process of affected by the charging

25、process of the double layerthe double layerCcompactCdiffuseiRsolutionThe double layer charging effects in electrochemical measurementsEt=RsCdi=0.37 i01.Potential stepttThe double layer charging effects in electrochemical measurementsi2.Current stepttThe double layer charging effects in electrochemical measurementsEvCd1.Potential sweep（电势扫描）tEScan rate:vi