电极过程动力学(陈胜利).ppt

化学学院物理化学专业研究生课程,“电极过程动力学”,授课教师：陈胜利 Tel: 68754693 Email: Office: 化学楼 135,授课教材,查全性等著： 电极过程动力学导论 （第三版，科学出版社，2002年）,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, 电化学方法：原理及应用 （第二版，化学工业出版社, 2005 年）,Chapter 1,INTRODUTION AND OVERVIEW OF ELECTRODE PROCESSES,Electrochemistry ?,The laws (principles) and the technologies concerning the conversion between chemical energy and electrical energy Interrelation between chemical phenomena (chemical reactions, chemical changes, etc.) and electric phenomena (charge, current, potential, electric field, etc.),With a history of more than two centuries, electrochemistry has been a typical example of a truly interdisciplinary (各学科间的)area of science and technology. Its roots have been in chemistry, physics, materials and biological science and its applications spreading from electrochemical analysis and synthesis to environmental protection and energy conversion and storage. Everyday life items such as batteries, the glucose （葡萄糖）sensor and domestic or medical gas sensors are now a commodity, while the prospect of mass production of “green“ electric vehicles(Electric vehicles) is no more a challenge but a viable option. On an industrial scale, apart from the now mature chlor-alkali and metal finishing and extraction industries, there is significant activity in the areas of energy conversion and storage by means of fuel cells and solar cells as well as in the use of electrochemical methods for effluent treatment. “Electrochemistry provides many opportunities for sustainable development.”,Electrochemical Cells and Reactions,Pt,Pt,Pt,Pt,H2SO4 Solution,H2,O2,H2,O2,H+,H+,H2O,H+,H2O,H+,e,e,e,e,Cathode : 1/2O2 + 2H+ + 2e- = H2O Anode: H2 = 2H+ + 2e- Overall cell reaction: H2 + 1/2O2 = H2O,Positive electrode: H2O = 1/2O2 + 2H+ + 2e- Negative electrode: 2H+ + 2e- = H2 Overall cell reaction: H2O = H2 + 1/2O2,Galvanic Cell（原电池）,Voltaic Cell,H+,H+,The features of electrochemical reactions,The overall redox reaction is made up of two half-reactions taking place independently at two locations where electronic conductors(Electrodes) and ionic conductors(electrolytes) are made in contact; Charge (electron or ions) transfer between the electrodes and chemical species always occurs and a current flows in external circuit between two electrodes; The extent and the direction of the reaction can be altered by the potentials applied to the electrodes;,Electrode reaction at electrode/solution interfaces,Charge transfer plane,Feimi level,LUMO,HOMO,Charge transfer plane,Feimi level,Potential shifts negatively,e,For Example:,Possible processes involved in an electrode reaction,Oad,O,Rad,R,O*,R*,ne,Ob,Rb,Mass transfer,Mass transfer,Preceding Chemical reactions,Following Chemical reactions,Electrode,Charge transfer,Adsorption,Desorption,What will we deal with in this course ?,The kinetics of the electrode reactions of various type and the factors that affect these kinetics Current Potential dependence,The philosophy in electrochemical studies,Schematic three-electrode cell used in electrochemical studies,Standard Hydrogen Electrode (SHE),Pt,CH+=1mol.l-1,H2,H2,Saturated calomel electrode (SCE),Metal wire,KCl solution,Hg2Cl2,Hg,Pt wire,Strategies to study the electrode processes,Potential-controlled techniques,Current-controlled techniques,Potentiostatic（恒电势） methods,Potentiodynamic methods,A brief description of the electric double layer and its effects on the electrode reaction kinetics,The double layer is a result of re-arrangement and orientation of the charges and the dipoles at the electrode/electrolyte interface. The electrode and the electrolyte bear the same amount of charges with opposite nature: qM = - qS; The double layer consists of two regions: Compact layer (also called “inner Helmholtz layer” or “stern layer”) and diffuse layer (also called “outer Helmholtz layer”); The effective potential to drive the interfacial charge transfer may be significantly different from that applied the the electrode/solution interface: Eeff = Eapp ( 1 ),The capacitor（电容器）-like nature of the electric double layer,Regardless of the nature of an electrode process, the double layer itself would response to the electrochemical perturbations as a series of capacitors The capacitance values of the double layer are potential-dependent Most of the electrochemical measurements are more or less affected by the charging process of the double layer,The double layer charging effects in electrochemical measurements,E,= Rs