北京大学电分析课件电分析化学原理、方法和应用el.ppt

1、Fundamentals of Electroanalytical Chemistry 电分析化学原理、方法和应用 Yuanhua Shao（邵元华，教授 Ph.D.） College of Chemistry and Molecular Engineering Peking University,Outline: 1. Principles 2. Methods 3. Applications,Part 1 Principles 1.Introduction 2.Electrochemical Cell: Thermodynamic Properties and Electrode Pote

2、ntials 3.The Interfacial Region 4.Fundamentals of Kinetics and Mechanism of Electrode Reactions 5.Mass Transport 6.Kinetics and Transport in Electrode Reactions Part 2Methods 1Electrochemical Experiments 2Hydrodynamic Electrodes,主要内容,Part 2Methods 3Cyclic Voltammetry and Linear Sweep Techniques 4Ste

3、p and Pulse Techniques 5Impedance Methods 6Non-Electrochemical Probes of Electrodes and Electrode Processes Part 3Applications 1Potentiometric Sensors 2Amperometric and Voltammetric Sensors 3Electrochemistry in Industry 4Corrosion 5Bioelectrochemistry,主要内容,General Books: 1* A.J.Bard and L.R.Faulkner

4、, Electrochemical methods, fundamentals and applications, Wiley, New York, 1980(2nd Edition, 2001) 2 * C.M.A.Brett and A.M.O.Brett, Electrochemistry, Principles, Methods, and Applications, Oxford, 1993 3 * Southampton Electrochemistry Group, New Instrumental Methods in Electrochemistry, Ellis Horwoo

5、d, Chichester, 1985 4 A.M.Bond, Modern polarographic methods in Analytical Chemistry, Dekker, New York, 1980 5 J.Koryta, Principles of Electrochemistry, Wiley, 1987 6 P. Delahay, New Instrumental methods in Electrochemistry, 1954 7 R.N.Adams, Electrochemistry at solid electrodes, 1969 8 *J.OM.Bockri

6、s and A.N.Reddy, Modern Electrochemistry, Plenum, New York, 1970 9 电化学基础，张祖训，汪尔康， 2000 10生命科学中的电分析化学， 彭图治，杨丽菊 编著, 1999 11 *电极过程动力学导论， 查全性， 1976(1987 2nd Edition) 12电化学研究方法， 田昭武， 1984 13*电化学测定方法， 腾岛 昭 等著， 陈震等译， 1995 14电分析化学， 蒲国刚，袁倬斌，吴守国编著， 1993,Series 1. Electroanalytical Chemistry, ed. A.J.Bard 2. M

7、odern Aspects of Electrochemistry, eds. J.OM.Bockris, B.E.Conway, et al., Journals Nature, Science, JACS, Angew.Chem.Int Edit Anal.Chem.,(May 1, 2000) J.Phys.Chem.B., J.Electroanal.Chem., Electrochimica Acta, J.Electrochem.Society., Electroanalysis, Electrochemical and Solid State Letters, J.Applied

8、 Electrochemistry, Electrochemistry Communications, J.Solid State Electrochemistry,Reviews: Accounts of Chemical Research Analytical Chemistry Annual Reviews of Physical Chemistry Chemical Reviews Websites: /estir/,Chapter One ( 第一章) Introduction (导言) 1.1Introduction 1.2Sco

9、pe of Electroanalytical Chemistry 1.3Brief History 1.4Examples,1.1Introduction (导言) 电分析化学和电化学：两者没有区别！基本原理 相同，仅研究的侧重点可能不同。 电化学池： 原电池(Galvanic Cell)：化学能 电能 电解池(Electrolytic Cell)：电能 化学能 一个简单的电分析化学实验： 组成：工作(研究)电极(W), 参比电极(R)， 辅助(对)电极 (C), 电解质溶液，恒电位仪 (potentiostat), PC计算机(接口+软件)。,研究重点,Electroanalytical

10、Chemistry is the branch of chemistry concerned with the interrelation of electrical and chemical effects. A large part of this field deals with the study of chemical changes caused by the passage of an electric current and the production of electrical energy by chemical reactions. In fact, the field

11、 of electrochemistry encompasses a huge array of different phenomena (e.g., electrophoresis and corrosion), devices (electrochromic displays, electro- analytical sensors, batteries, and fuel cells), and technologies (the electroplating of metals and the large-scale production of aluminum and chlorin

12、e). While the basic principles of electro- chemistry discussed in this text apply to all of these, the main emphasis here is on the application of electrochemical methods to the study of chemical systems.,1.2 Scope of Electroanalytical Chemistry,Scientists make electrochemical measurements on chemic

13、al systems for a variety of reasons. They may be interested in obtaining thermodynamic data about a reaction. They may want to generate an unstable intermediate such as a radical ion and study its rate of decay or its spectroscopic properties. They may seek to analyze a solution for trace amounts of

14、 metal ions or organic species. In these examples, electro- chemical methods are employed as tools in the study of chemical systems in just the way that spectroscopic methods are frequently applied. There are also investigations in which the electrochemical properties of the systems themselves are o

15、f primary interest, for example, in the design of a new power source or for the electrosynthesis of some product. Many electrochemical methods have been devised. Their application requires an understanding of the fundamental principles of electrode reactions and the electrical properties of electrod

16、e- solution interfaces.,Variables affecting the rate of an electrode reaction,1.3 电化学的简史： Luigi Galvani (1737-1798): 从1786年开始，进行著名的animal electricity“ 实验解剖青蛙 Alessandro Volta (1745-1827): Humphry Davy (1778-1829): Michael Faraday (1791-1867): Grove: 燃料电池(1839) Lippmann: 1873 Helmholtz: 双电层(1879) F.G

17、.Cottrell: Cottrell 公式 1902 W.Nernst: Nernst 公式1904 Tafel: Tafel 公式1905 Gouy, Chapman: 1905 Stern: 1924 Heyrovsky, Shikata: Polarograph 1925(1959 Nobel Prize Winner)1.,J.Butler, M.Volmer: Butler-Volmer 公式1924-1930 P.Delahay, Gerischer, Frumkin, Levich, Baker et al: 1950s to 1960s 发展了各种理论，研究方法等 R.Mar

18、cus: 1950s-1960s, Electron Transfer Theory (Nobel Prize Winner, 1992) T.Kuwana: 1960s, 光谱电化学 Gavach, Koryta et al: 1970s 开始研究液/液界面电化学 Miller and Murray: 1975, 化学修饰电极 M.Fleischmann, A.Bewick et al: 1970s to 1980s, in situ 光谱、 波谱电化学 M.Fleischmann, W.Wightman et al: ultramicroelectrodes 1970s - 1980s A

19、.J.Bard: SECM, 1989 Sagiv et al: 1980s, self-assembled membranes P.Hansma et al: STM - Electrochemistry, 1980s Li or Zhang or Wang: ?,研究方法： 稳态和暂态技术： 光谱、波谱技术： 表面技术：SPM ( Scanning Probe Microscopy),(a)General principle of studying a system by application of an excitation(or perturbation)and observatio

20、n of response. (b)In a spectrophotometric experiment, the excitation is light of different wavelengths (), and the response is the absorbance (A)curve. (c)In an electrochemical(potential step)experiment, the excitation is the application of a potential step, and the response is the observed i-t curv

21、e.,应用领域： 1.化学电源(电池,燃料电池)： 2.电解电镀： 3.腐蚀： 4.电化学合成： 5.电催化： 6.生物电分析化学： 7.电化学传感器：Ion-Selective Electrodes 8. TAS 9. 单细胞和单分子测量,白鼠脑神经递质活体伏安分析示意图,Polarography (极谱) and Voltammetry (伏安法)的区别？,polarography A classical electroanalytical technique discovered in 1922 by J. Heyrovsky, for which he was awarded the

22、Nobel Prize for Chemistry in 1959. Essentially, it is linear-sweep voltammetry using a dropping-mercury electrode for working electrode and a large mercury pool as counter electrode.,voltammetry An electrochemical measuring technique used for electrochemical analysis or for the determination of the

23、kinetics and mechanism of electrode reactions. Voltammetry is a family of techniques with the common characteristics that the potential of the working electrode is controlled (typically with a potentiostat) and the current flowing through the electrode is measured. In one of the most common applicat

24、ions of the technique, the potential is scanned linearly in time; this is called the linear-sweep voltammetry, LSV, or LV. Cyclic voltammetry (CV) is a linear-sweep voltammetry with the scan continued in the reverse direction at the end of the first scan, this cycle can be repeated a number of times

25、.,Figure 1. Basic voltammetry. (a) Apparatus for voltammetry with a two-electrode cell, appropriate for use in solutions of low resistance and microelectrodes. (b) Apparatus for voltammetry with a three-electrode cell. In practice a potentiostat that automatically controls the potential of the worki

26、ng electrode with respect to a reference electrode is used.,Question: 两电极和三电极系统 有什么区别？为什么一般的电 化学研究需用三电极系统？,May 1, 2000; pp. 346 A-352 A (Analytical Chemistry) Voltammetry Retrospective Allen J. Bard, University of Texas-Austin and Cynthia G. Zoski, University of Rhode Island,Three-dimensional voltam

27、metry. Representation of the three-dimensional I - t - E surface for a Nernstian reaction. The typical steady-state voltammogram represents a cut parallel to the I-E plane. (b) A cut representing a linear potential sweep across this surface. (Adapted from Ref. 6.),电分析化学的特点： interdisciplinary nature

28、and versatility 异相反应，与表面、界面及相关的 区域有关， 可控催化。,电化学及电分析化学的发展趋势,1， 与纳米技术相结合 2， 与生物、生命科学相结合,信息科学 生命科学 能源科学 环境科学 材料科学,Chapter Two (第二章) Electrochemical Cells: Thermodynamic Properties and Electrode Potentials 2.1Introduction, Galvanic and electrolytic cells 2.2The cell potential of an electrochemical cell

29、2.3Calculation of cell potential: activities or concentrations?,2.4Electrode classification 2.5Reference electrodes 2.6The movement of ions in solution: diffusion and migration 2.7Conductivity and mobility 2.8Liquid junction potentials 2.9Ion-Selective Electrodes and Biomembranes,2.1导言，原电池和电解池 1.Why

30、 is it that half-reactions in electrochemical cells proceed spontaneously in one direction and furnish current? 2.What is the effect of the salt bridge? 3.What is the effect of ion migration? 4. What is absolute and relative potential differences? Zn/Zn2+(aq), Cu2+(aq)/Cu Hg/Hg2Cl2/Cl-(aq), Zn2+(aq)

31、/Zn Ag/AgCl/TBACl(aq)/TBATPB(o)/LiCl(aq)/AgCl/Ag 根据IUPAC的规定， 左边的半反应是氧化反应 (anode, 阳极)，右边的半反应是还原反应(cathode, 阴极),Ecell = Eright - Eleft,Potential: 电位， 电势 但物理学，“位”与“势”的概念是不同的。空间某点 的电位，是将单位正电荷从无穷远处(或以无任何 力作用的无穷远的真空为参考点)移到该点所做的 功，它具有绝对的意义。电势则是空间两点的电位差 (或电位降)，如金属和其离子溶液所形成的电极电势， 实际上是金属和溶液两相之间电位差的一种衡量，又是 该电极

32、电势与标准电极电势差的一种衡量。,电化学池： anode cathode 原电池(Galvanic Cell)：化学能 电能 - + 电解池(Electrolytic Cell)：电能 化学能 + - 一些电化学池既可以作为原电池，也可以作为电解池， 例如；汽车用的Lead-acid电池，在放电时是原电池， 反应为： anode(-ve): Pb+ SO42-PbSO4+2e cathode(+ev):PbO2+4H+SO42-+2e 2H2O+PbSO4 在充电时为电解池，上述半反应倒过来！ Question: 为什么Lead-acid电池或其它的电池 可以充电？,2.2电池的电动势和电极电

33、势 界面电势(绝对电势及绝对电势差) 内电势(Galvani, ), 外电势(Volta, )和表面电势() 外电势(Volta, ): 将单位正电荷从无穷远处的真空中移到物体 近旁距表面约10-4cm处作的功。(是可测的) 金属和电解质溶液界面外电势之差，叫做Volta电势： =电极 - 溶液 表面电势()：将单位正电荷从物体表面附近的一点移到物体 相内所做的电功称之为表面电势(涉及到化学作用，是不可测 的)。 = + “电位” 与 “电势”的区别！ = +,= ze,= ze,=ze +ze + =ze + (电化学势),Figure. A schematic diagram to ill

34、ustrate that, in the interphase region (indicated by shading), there generally is net dipole orientation and net, or excess, charge density,An electrode is like a giant central ion,Electrode/electrolyte,Double layer,Double layers are characteristic of all phase boundaries,1V, 1nm, the field strength

35、 (gradient of potential) is enormous - it is of the order 107 V/cm. The effect of this enormous field at the electrode- electrolyte interface is, in a sense, the essence of electrochemistry!,A,(a)物质相的内电势、外电势和表面电势 (b)电极与溶液间的内电位差和外电位差,To measure the potential difference across a metal- solution electr

36、ified interface (see exploded view), one terminal of the potential- measuring instrument is connected to the metal electrode. What is to be done with the second terminal?,All one can measure, in practice, is the potential difference across a system of interfaces, or cell, not the potential differenc

37、e across one electrode-electrolyte interface.,The absolute potential Difference across a single electrified interface cannot be measured!It is not necessary to know exact value of it but the difference of absolute potential difference is important for electrochemists!,J.OM.Bockris and A.N.Reddy, Mod

38、ern Electrochemistry, Plenum, New York, 1970, p623,电池电动势和电极电势 电池电动势：将电位差计接在电池的两个电极之间而直 接测得的电势值习惯上称之为电池的电动势 电极电势：当采用相对电势法时，系用一定的参比电极 与研究电极组成电池， 这一电池的电动势称为相对于给定参比 电极而确定的研究电极电势。(金属和溶液相接触的内电位差即 为金属电极和溶液间的电极电势),所谓“电极/溶液”之间的绝对电势不但无法直接 测量，在处理电极过程动力学问题时也不需要用 到它！ 在计算电池电动势时， 也完全可以采用相对电极 电势来代替绝对电极电势！,2.3计算电极电势

39、(E)： 活度 or 浓度？ eq =eqo + RT/(zF)lnaMz+ = E =Eo + RT/(zF) lnaMz+ Nernst 公式(方程) O + ze = R E =Eo + RT/(zF) lnaO/aR (A.J.Bard and L.R.Faulkner, Electrochemical methods, 1980,中译本， p61-71， 查全性， 电极过程动力学导论，第二版， 第二章) a = C,2.4电极的分类 一般来说，电极可以分为如下四类： (1). A. 一个金属电极与它的水溶液中的离子相接触, e.g. Cu/Cu2+ E =Eo + RT/(F) ln

40、aMz+ 半反应： Mz+ ze = M B. 一个非金属它的离子相接触， e.g. H2/H+ 或 Cl2/Cl-在一个惰性导电物质表面上 E =Eo + RT/(F) lnPH21/2/aH+ (2)一个金属电极与一个水溶液中的阴离子相接触， 此阴离子可与金属电极的离子形成难溶物。例如：Hg/Hg2Cl2/Cl-， the calomel electrode(甘汞电极) (3)惰性电极，Pt, Au, C, Hg etc (4)上述不能包括的电极，例如：化学修饰电极等,2.5参比电极 顾名思义，参比电极是给出一个固定的值，其它的电极电势的 测量以此为基础。一个好的参比电极应该不受温度、时间

41、和通 过小电流而变化, 应遵守Nernst 方程！ Type 1: the hydrogen electrode Type 2: the calomel electrode Type 3: glass electrode, ion-selective electrodes 各种参比电极的制备和盐桥的制备 (电化学测定方法， 腾岛 昭 等著， 陈震等译， 1995。 P87-99),The hydrogen electrode,The saturated calomel electrode,2.7电导和淌度(mobility) i =ziuiF (ui是离子淌度子)(i 是一种离子的摩尔导电率)

42、 = i i = zi2F2Di/RT Nernst-Einstein relation Di = kBT/(6r)Stokes-Einstein relation ti =i /transport number,2.8液接电势 Liquid junction potentials are the result of difference cation and anion mobilities under the influence of an electric field. Liquid junction potential can be classified into three types: (1)Two solutions of the same electrolyte but with different concentra