界面电化学改

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,界面电化学,邵 勇,1,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 useful 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,electrolyte,), and which involve electron transfer between the solid electrode and the electrolyte.,一、简介,2,（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: 1873,Helmholtz,:,双电层(1879),F. G. Cottrell,:,Cottrell 公式 1902,W. Nernst,:,Nernst 方程1904,Tafel,:,Tafel 公式1905,Gouy, Chapman: 1905,Stern,:,1924,Heyrovsky, Shikata,: Polarograph 1925 (1959 Nobel Prize,Winner).,3,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,.,Marcus,:,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: 1970s - 1980s,ultramicroelectrodes (UMEs),A.J.Bard,:,SECM, 1989,Sagiv et al: 1980s, self-assembled membranes,P.Hansma et al: STM - Electrochemistry, 1980s,Wang or Zhang or Li : ?,4,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, et al.,Electrochemistry in life science,Electrochromism, electrolysis, corrosion, electroplating, electrodeposition, et al.,Waste treatment in environments,Information storage and reading,5,电极表面状态,6,（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,r,O + ne,R,两个速率：,扩散(diffusion)速率,d,电极反应(electrode reaction)速率,r,1.电活性物质溶解于溶液中,7,x = 0,x,x + dx,c,c + dc,电极,溶液,线性扩散方向,x,O + 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d,t,内，扩散通过离电极表面,x,处截面的摩尔数d,N,x,t,与截面的面积,A,和当时当地的浓度梯度成正比:,d,N,x,t,= D,o,A(,C,o(,x,t,),/,x,),d,t,(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,f,x,t,:,f,x,t,= dN,x,t,/,(A d,t,)=D,o,(,C,o(,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的浓度是距离和时间的函数,8,考虑离电极表面距离为,x,和,x,+d,x,的两个截面，d,x,为无限小量。在时间dt内，两个截面间，O浓度的改变量d,c,o(,x,t,),等于在d,t,时间内，进入截面,x,+d,x,的总摩尔数（dN,x+,d,x,t,）减去在同一时间内由截面,x,出去的总摩尔数（dN,x,t,）除以两截面间所包含溶液的总体积A,d,x,:,d,C,o(,x,t,),= (dN,x+dx,t,- dN,x,t,),/ (,A,d,x,),(3),由式（2），,dN =,f, A d,t,(4),式（4）带入式（3），,d,C,o(,x,t,),= (,f,x+,d,x,t,-,f,x,t,)/ d,x,),dt (5),或，,C,o(,x,t,),/,t,= ,f,x,t,/,x,(6),由式（2），,f,x,t,/,x,= D,o,2,C,o(,x,t,),/,x,2,(7),式（7）带入式（6），,C,o(,x,t,),/,t,= D,o,2,C,o(,x,t,),/,x,2,(8),式（8）为Fick（菲克）第二定律,x = 0,x,x + dx,c,c + dc,电极,溶液,线性扩散方向,x,9,当外加电压加到产生极限电流处时，,初始条件：,t,= 0,x,= 0:,C,o(,x,t,),= C,o,*,C,R,= 0,边界条件：,t,0,x,= 0:,C,o(,x,t,),= 0,t, 0,x,=,:,C,o(,x,t,),= C,o,*,(,C,o(,x,t,),/,x,),x,= 0,= C,o,*,/ (,D,o,t,),1/2,极限扩散电流i,l,i,l,= nFA,f,x,=0,t,= nFAD,o,(,C,o(,x,t,),/,x,),x,= 0,= nFAC,o,*,(D,o,/,t,),1/2,Cottrell方程,离电极表面的距离,x,O,的浓度,t,x,C,O,*,扩散层厚度,扩散层的厚度：,(,D,o,t),1/2,E,1,E,2,10,B. 电极反应速率控制过程,O + ne,R,k,f,k,b,O和R均溶解于溶液中,-dN,o,/d,t,= dN,R,/d,t,=,k,f,C,O,0,-,k,b,C,R,0,k,f,=,k,0,exp-,nF,(E - E,0,)/RT,k,b,=,k,0,exp(1-,)nF(E - E,0,)/RT,为转移系数,E,0,为标准电位,i,c,= nFA,k,0,C,O,0,exp -,nF(E - E,0,)/RT,只存在O,i,a,= -nFA,k,0,C,R,0,exp (1-,),nF(E - E,0,)/RT,只存在R,i,=,i,c,+,i,a,O和R共存,根据绝对反应速率理论,则,离电极表面的距离,O,的浓度,t,2,C,O,*,t,1,11,经典极谱法,电极电位E,i,离电极表面的距离,O,的浓度,t,0,C,O,*,电极电位E,i,离电极表面的距离,O,的浓度,t,2,C,O,*,t,1,t,1,t,2,现代循环伏安法,(,C,o(,x,t,),/,x,),x,= 0,= (C,o,*,-C,s,) / (,D,o,t,),1/2,12,现代循环伏安法,13,2.电活性物质吸附于电极表面,14,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,15,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）,16,UV 5%,Visible 46%,Infrared 49%,Power reaching earth 1.37 KW/m,2,太阳辐射能,17,光电效应,A,photon induced 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 about 22% conversion efficiency.,p-n结,VB,CB,h,+,18,2. 光化学效应（,Dye-Sensitized Solar Cell,）,I,3,-,/I,-,由于TiO,2,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TiO,2,的导带，所以电子可以快速注入TiO,2,；,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(I,3,-,)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。,19,Reactions 1 and 2,: Excited State Decay and Electron Injection,Reaction 3,: Regeneration of the Oxidized Dyes,Reaction 4,: Electron Transport through the Mesoporous Oxide Film,Reactions 5 and 6,: Recombination of Electrons in the Semiconductor with Oxidized Dyes or Electrolyte Species,Reaction 7,: Reduction of Electron Acceptors in the Electrolyte at the Counter Electrode,涉及的反应：,20,Annu. Rev. Phys. Chem. 2007.58:143-184:Theoretical Studies of Photoinduced Electron Transfer in Dye-Sensitized TiO,2,Chem. Rev., 2010, Dye-sensitized solar cell,界面：,染料/TiO,2,TiO,2,/电解质,TiO,2,/TiO,2,TiO,2,/电极,电解质/对电极,21,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（SnO,2,）,制作Solar Cell,22,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。,23,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SnO,2,膜层组成的,用铅笔在导电面上均匀地涂上一层石墨。,24,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。,25,第五步：组装电池,26,光电化学其它应用,UV absorbing cosmetic sunscreens,Photocatalytic windshields,Operating rooms and public restrooms,(Japanese company TOTO),Self-cleaning coating,Water treatment by buoyant photocatalytic TiO,2,-coated hollow ceramic microbubbles,Anti-fogging coating for side-view mirror by sunlight induced superhydrophilic surface,27,3、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。,28,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,29,干电池发电时反应如下：,负极：Zn - 2e,-,= Zn,2+,正极：2NH,4,+,+ MnO,2,+2e,-,= 2NH,3,+ MnO + H,2,O,电池反应:Zn+2NH,4,Cl+MnO,2,=ZnCl,2,+2NH,3,+,MnO+H,2,O,使用过程中，负极锌筒逐渐消耗以致穿漏，正极处的MnO,2,的活性逐渐衰减，最后干电池不再供电而失效。,30,蓄电池,蓄电池又称二次电池，可以通过充电使活性物质再生。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,31,蓄电池,放电,时发生下列反应：,负极(Pb):Pb+SO,4,2-,-2e,-,= PbSO,4,正极(PbO,2,):PbO,2,+4H,+,+SO,4,2-,+2e,-,= PbSO,4,+2H,2,O,总反应:Pb+PbO,2,+2H,2,SO,4,= 2PbSO,4,+2H,2,O,电池,充电,时发生与上述反应相反的反应,电动自行车,32,目前，商业化锂离子二次电池的正极材料主要是LiCoO,2,，负极材料主要为C，,放电,时发生如下反应：,正极反应：,Li,1-x,CoO,2,+ xLi,+,+ xe,-, LiCoO,2,负极反应：,CLi,x, C + xLi,+,+ xe,-,电池总反应：,Li,1-x,CoO,2,+ CLi,x, LiCoO,2,+ C,充电,时发生上述反应的逆反应。,锂离子二次电池 （Lithium-ion batteries,）,33,正极材料,Material,Average Voltage,Gravimetric Capacity,LiCoO,2,3.7 V,140 mAh/g,LiMnO,2,4.0 V,100 mAh/g,LiFePO,4,3.3 V,170 mAh/g,Li,2,Fe(PO,4,F),2,3.6 V,115 mAh/g,Electrolytes,Liquid electrolytes,in Li-ion batteries consist of,solid lithium-salt electrolytes,such as,LiPF,6, LiBF,4, or LiClO,4,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,34,How to prolong Li-ion battery life and use in safety for mobile phone,Unlike,Ni-,Cd,batteries, lithium-ion batteries should be charged early and often. However, if they are,not used for a long time, they should 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). 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 batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.,When using a notebook computer running from fixed line power over extended periods, the battery should be,removed and stored in a cool place,so that it is not affected by the heat produced by the computer.,35,燃料电池（FC，Fuel Cell）,燃料电池优点：,能量密度是锂电池的10倍，使用时间是锂电池的5倍,36,FC工作原理（氢作为阳极燃料为例）,High pure H,2,High performance catalyst,Disadvantage:,Gas fuel, Explosive,金属铂作催化剂,37,直接醇类燃料电池,甲醇：,标准电势：1.18V,能量转换效率,：96.7%,3/2 O,2,+,6H,+,+ 6e,-,3H,2,O,CH,3,OH + H,2,O CO,2,+ 6H,+,+ 6e,-,_,CH,3,OH + 3/2 O,2,CO,2,+ 2H,2,O,CH,3,OH,H,2,O,Waste heat,Cathode Polymer Anode,membrane,Nafion,CO,2,H,2,O,H,2,O,CO,2,H,2,O,O,2,H,+,CH,3,OH,e,-,e,-,Loading,Cathode,catalyst,Anode,catalyst,CH,3,OH crossover,Why methanol?,难题：,38,4、 电光转换（LED，显示技术，激光器等）,5 、电解,电镀,6 、电化学原理研究,7 、,电催化,39,电极过程,Cottrell,方程以及实验伏安曲线的解释,电化学的应用,1.,光电转换（染料敏化太阳能电池界面电子转移）,2.,化学电源原理，界面反应（干电池，铅蓄电池，锂离子二次电池，燃料电池）,所讲内容重点,40,