界面电化学改

1、界面电化学邵 勇电 化 学(Electrochemistry)（一）、什麽是电化学电化学是研究固态电极表（界）面电子转移规律的科学。 Electrochemistry is a branch of chemistry dealing with chemical reactions that involve electrical currents and potentials. Some chemical reactions that proceed spontaneously can generate electrical current, which can be used to do us

2、eful work; while other chemical reaction can be forced to proceed by using electrical current. Interface electrochemistry is a branch of chemistry that studies chemical reactions which take place at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the elect

3、rolyte), and which involve electron transfer between the solid electrode and the electrolyte. 一、简介（二）. 电化学发展简史Luigi Galvani (1737-1798): 发现生物电现象Alessandro Volta (1745-1827):发明电池Humphry Davy (1778-1829): 电解制碱金属Michael Faraday (1791-1867):电解定律Grove: 燃料电池(1839)Lippmann: 1873Helmholtz: 双电层(1879)F. G. Co

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

5、-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: 1970s - 1980s ultramicroelectrodes (UMEs)A.J.Bard: SE

6、CM, 1989Sagiv et al: 1980s, self-assembled membranesP.Hansma et al: STM - Electrochemistry, 1980sWang or Zhang or Li : ? 电化学是多学科交叉、具有重要应用背景和前景的科学，在支撑文明社会的自然科学以及能源、材料、生命、环境和信息等科学中都占有重要的地位。（三）、电化学的研究内容1、电极过程2、电解质溶液理论3、电化学平衡4、电极动力学5、应用电化学Throw-away battery, rechargeable battery, fuel cells, solar cell,

7、 et al. Electrochemistry in life science Electrochromism, electrolysis, corrosion, electroplating, electrodeposition, et al. Waste treatment in environments Information storage and reading 电极表面状态（五）、电极过程（一）扩散速率控制过程 r d（二）电极反应速率控制过程 d r（三）中间过程 d rO + ne R两个速率：扩散(diffusion)速率d电极反应(electrode reaction)速

8、率r1.电活性物质溶解于溶液中x = 0 xx + dxcc + dc电极溶液线性扩散方向xO + ne R在时间t时(即电解开始t秒钟的时候)，在一个无限短的时间间隔dt内，扩散通过离电极表面x处截面的摩尔数dNx,t与截面的面积A和当时当地的浓度梯度成正比:dNx,t = DoA(Co(x,t)/ x)dt (1)在单位时间内，通过截面上单位面积的摩尔数为单位流量; 在时间t时，离电极表面x处截面的单位流量fx,t :fx,t = dNx,t/(A dt)=Do (Co(x,t)/ x) (2)式(1),(2)为Fick(菲克)第一定律A. 扩散速率控制过程电极表面液层中O的浓度是距离和时

9、间的函数考虑离电极表面距离为x和x+dx的两个截面，dx为无限小量。在时间dt内，两个截面间，O浓度的改变量dco(x,t)等于在dt时间内，进入截面x+dx的总摩尔数（dNx+dx,t）减去在同一时间内由截面x出去的总摩尔数（dNx,t）除以两截面间所包含溶液的总体积Adx :dCo(x,t) = (dNx+dx,t- dNx,t )/ (Adx) (3)由式（2），dN = f A dt (4)式（4）带入式（3），dCo(x,t) = (fx+dx,t- fx,t )/ dx)dt (5)或，Co(x,t) /t = f x,t /x (6)由式（2），f x,t /x = Do 2Co

10、(x,t)/x2 (7)式（7）带入式（6），Co(x,t)/t = Do 2Co(x,t)/x2 (8)式（8）为Fick（菲克）第二定律x = 0 xx + dxcc + dc电极溶液线性扩散方向x当外加电压加到产生极限电流处时，初始条件： t = 0, x = 0: Co(x,t) = Co*, CR = 0边界条件： t 0, x = 0: Co(x,t) = 0 t 0, x = : Co(x,t) = Co*(Co(x,t) /x)x = 0 = Co* / (Dot)1/2极限扩散电流il,il = nFAfx=0,t = nFADo (Co(x,t) /x)x = 0 = nF

11、ACo*(Do/ t)1/2Cottrell方程离电极表面的距离xO的浓度txCO*扩散层厚度扩散层的厚度：(Dot)1/2E1E2B. 电极反应速率控制过程O + ne RkfkbO和R均溶解于溶液中-dNo/dt = dNR/dt = kf CO0 - kbCR0kf = k0 exp-nF(E - E0)/RTkb = k0 exp(1-)nF(E - E0)/RT为转移系数E0为标准电位ic = nFAk0CO0exp -nF(E - E0)/RT 只存在Oia = -nFAk0CR0exp (1-)nF(E - E0)/RT 只存在Ri = ic + ia O和R共存根据绝对反应速率

12、理论则离电极表面的距离O的浓度t2CO*t1经典极谱法电极电位Ei离电极表面的距离O的浓度t0CO*电极电位Ei离电极表面的距离O的浓度t2CO*t1t1t2现代循环伏安法(Co(x,t) /x)x = 0 = (Co*-Cs) / (Dot)1/2现代循环伏安法2.电活性物质吸附于电极表面A、太阳能电池, solar cell（光电转换）化石燃料有限太阳每秒钟照射到地球上的能量就相当于500万吨煤二、电化学的应用反应类型：阳极、阴极电势高低：正极、负极阳极(anode)阴极(cathode)电池(battery)负极(negative)正极(positive)电解池(electrolytic

13、 cell)正极(positive)负极(negative)太阳能电池简介按照所用材料的不同：硅太阳能电池(单晶硅、多晶硅、非晶硅） （光电转化效率高，成本高，制备工艺复杂！）以无机盐如砷化镓、硫化镉、铜铟硒等多元化合物为材料的电池 （镉：剧毒。铟、硒：稀有元素）功能高分子材料制备的大阳能电池 （处于研发初期、转化效率低、使用寿命短）染料敏化纳米晶体太阳能电池（Dye-Sensitized Solar Cell） （正在研发）UV 5%Visible 46%Infrared 49%Power reaching earth 1.37 KW/m2太阳辐射能光电效应A photon induced

14、hole-electron pair is separated by the local field of the junction.ShockleyQueisser limit：the maximum theoretical efficiency of a solar cell using a p-n junction around 30% assuming a p-n junction band gap of 1.1 eV (typical for silicon). Modern commercial single-crystalline solar cells produce abou

15、t 22% conversion efficiency.p-n结VBCBh+2. 光化学效应（Dye-Sensitized Solar Cell）I3-/I- 由于TiO2的禁带宽度较大(3.2eV，约387.5nm)，可见光不能将其直接激发；在其表面吸附一层染料敏化剂后，染料分子可以吸收太阳光而产生电子跃迁。由于染料的激发态能级高于TiO2的导带，所以电子可以快速注入TiO2；染料分子输出电子后成为氧化态，它们随后被电解质中的I-还原而得以再生，而氧化态的电解质(I3-)在Pt对电极上得到电子被还原，从而完成一个光电化学反应循环。Reactions 1 and 2: Excited Stat

16、e Decay and Electron Injection Reaction 3: Regeneration of the Oxidized DyesReaction 4: Electron Transport through the Mesoporous Oxide FilmReactions 5 and 6: Recombination of Electrons in the Semiconductor with Oxidized Dyes or Electrolyte SpeciesReaction 7: Reduction of Electron Acceptors in the E

17、lectrolyte at the Counter Electrode涉及的反应：Annu. Rev. Phys. Chem. 2007.58:143-184:Theoretical Studies of Photoinduced Electron Transfer in Dye-Sensitized TiO2 Chem. Rev., 2010, Dye-sensitized solar cell界面：染料/TiO2TiO2/电解质TiO2/TiO2TiO2/电极电解质/对电极第一步：二氧化钛膜的制备一、调制纳米二氧化钛浆料二、在导电玻璃片上涂膜三、用酒精灯烤干把二氧化钛胶体涂敷在透明导电玻璃

18、上。就象二氧化钛膜一样，透明导电玻璃上已经事先镀有一层透明导电膜（SnO2） 制作Solar Cell第二步：利用天然染料把二氧化钛膜着色把新鲜的或冰冻的黑莓、山莓石榴籽或红茶，用一大汤匙的水进行挤压，然后把二氧化钛膜放进去进行着色，大约需要5分钟，直到膜层变成深紫色，如果膜层两面着色的不均匀，可以再放进去浸泡5分钟，最后用乙醇冲洗，并用柔软的纸轻轻地擦干。第三步：制作反电极 电池既需要光阳极，又要一个对电极才能工作。对电极又叫反电极，是由涂有导电的SnO2膜层组成的,用铅笔在导电面上均匀地涂上一层石墨。第四步：注入电解质 注入含碘和碘离子的溶液作为太阳电池的电解质，它主要用于还原和再生染料。

19、第五步：组装电池光电化学其它应用UV absorbing cosmetic sunscreensPhotocatalytic windshieldsOperating rooms and public restrooms(Japanese company TOTO)Self-cleaning coatingWater treatment by buoyant photocatalytic TiO2-coated hollow ceramic microbubblesAnti-fogging coating for side-view mirror by sunlight induced sup

20、erhydrophilic surface3、化学电源电池的分类：电池按照其使用性质的不同可以分为干电池、蓄电池、储备电池和燃料电池等几大类。 干电池锌锰干电池：负极是锌做的圆筒，正极是一根碳棒，周围被二氧化锰、碳粉和氯化铵的混合剂包围。原电池干电池发电时反应如下：负极：Zn - 2e- = Zn2+正极：2NH4+ + MnO2+2e- = 2NH3 + MnO + H2O电池反应:Zn+2NH4Cl+MnO2=ZnCl2+2NH3+ MnO+H2O 使用过程中，负极锌筒逐渐消耗以致穿漏，正极处的MnO2的活性逐渐衰减，最后干电池不再供电而失效。蓄电池 蓄电池又称二次电池，可以通过充电使活性

21、物质再生。铅蓄电池的两极均以铅板为骨架，正极铅板上是二氧化铅，负极铅板上是海绵状铅。外部构造蓄电池放电时发生下列反应：负极(Pb):Pb+SO42-2e- = PbSO4正极(PbO2):PbO2+4H+SO42-+2e- = PbSO4+2H2O总反应:Pb+PbO2+2H2SO4 = 2PbSO4+2H2O电池充电时发生与上述反应相反的反应电动自行车目前，商业化锂离子二次电池的正极材料主要是LiCoO2，负极材料主要为C，放电时发生如下反应：正极反应：Li1-xCoO2 + xLi+ + xe- LiCoO2 负极反应：CLix C + xLi+ + xe- 电池总反应：Li1-xCoO2

22、 + CLix LiCoO2 + C 充电时发生上述反应的逆反应。锂离子二次电池 （Lithium-ion batteries ）正极材料MaterialAverage VoltageGravimetric CapacityLiCoO23.7 V140 mAh/gLiMnO24.0 V100 mAh/gLiFePO43.3 V170 mAh/gLi2Fe(PO4F)2 3.6 V115 mAh/gElectrolytes Liquid electrolytes in Li-ion batteries consist of solid lithium-salt electrolytes, suc

23、h as LiPF6, LiBF4, or LiClO4, and organic solvents, such as ether (乙烯碳酸酯、丙烯碳酸酯、二乙基碳酸酯). 铁酸锂How to prolong Li-ion battery life and use in safety for mobile phoneUnlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should

24、be brought to a charge level of around 40%60%. Lithium-ion batteries should not be frequently fully discharged and recharged (“deep-cycled”) like Ni-Cd batteries, but this is necessary after about every 30th recharge to recalibrate any external electronic “fuel gauge” (e. g. State Of Charge meter).

25、This prevents the fuel gauge from showing an incorrect battery charge.Li-ion batteries should never be depleted to below their minimum voltage, 2.4 V to 3.0 V per cell. Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly. Li-ion batteries should not be frozen (most lithium-ion battery electrolytes freeze at approximately 40 C; however, this is much colder than the lowest temperature reached by household freezers). Li-ion ba