【作者】 程岩；

【导师】 江志裕；

【作者基本信息】 复旦大学 ， 物理化学， 2006， 博士

【摘要】 表面电化学以两个凝聚相的荷电界面作为其主要研究对象，它广泛地应用于能源、材料、生命科学等重要的科学领域。为了从分子水平上深化对电化学界面的认识，自上世纪七十年代中期采用了红外、拉曼和紫外可见反射光谱技术对电化学体系进行现场研究，开创了新的光谱电化学研究领域。光谱电化学的迅速发展，推动电化学研究由宏观进入微观、由统计平均深入至分子水平。现场光谱电化学方法为界面提供了双电层中物种的化学本质、成键方式和它们随电极电位的变化等重要信息。另一方面，电池工业作为当今能源领域的重要组成部分受到了各国政府的高度重视，聚合物锂（离子）电池等新型高性能、长寿命、无污染的化学电源的研究与开发成为电池工业发展的主要趋势。 本论文主要围绕高能化学电源电极反应机理及现场红外光谱技术在电化学界面性质研究中的应用等方面进行了研究： 1．合成新型电极材料高价银氧化物Ag₃O₄，首次研究了其电化学制备条件及其在碱性溶液中的电化学性质，并提出了其电化学生长过程及反应机理。 对其电化学合成条件的研究发现，应用恒电位沉积方法，于电极电位＞1.15V（vs．SCE）时，可在Pt电极上得到黑色产物Ag₃O₄。在1.38V电极电位下可制备得到其单晶结构颗粒。在恒电位沉积过程中，Ag₃O₄晶体的形成经历了典型的晶种形成以及晶种继续生长的电结晶过程，其形成可能是经历了一价银向二价银以及三价银的逐步转化。 Ag₃O₄在碱性溶液中的循环伏安测试以及还原产物XRD分析结果表明：其电化学还原过程比较复杂，当电化学扫描速度较慢时，首圈循环伏安曲线上共有三个还原峰出现，Ag₃O₄中的三价银首先被还原为二价银，再进一步依次被还原为一价银和单质银；当电化学扫描速度较快时，首圈循环伏安曲线上共有四个还原峰出现，除了上述反应步骤以外，三价银可以直接被还原为一价银。Ag₃O₄在碱性溶液中的放电曲线测试结果验证了上述反应过程。 对Ag₃O₄在碱性溶液中测试的循环伏安曲线还原峰面积进行高斯（Gauss）拟合，分析其电化学还原过程中的电荷转移过程并探讨其还原反应机理，发现：Ag₃O₄分子中本就存在的二价银几乎全部在低电位下直接还原为单质银。对放电曲线各平台长度的数据分析可验证这一反应机理。另外，对不同还原阶段的电极进行交流阻抗研究，进一步深入了对Ag₃O₄在碱性溶液中还原过程的理解。 另外，值得一提的是，Ag₃O₄的理论容量为553.1mAh／g，比目前银锌电池中广泛使用的正极材料AgO（432.7mAh／g）高出27.8％。由放电测试可得，即使在119C放电倍率下，Ag₃O₄在碱性溶液中放电容量依然可达到理论容量的83％，显示了其作为一种新型化学电源正极材料的应用前景。2．应用现场红外光谱、拉曼光谱技术以及电化学方法，研究了凝胶型聚合物电解质体系中MCMB碳负极、金属锂电极以及二氧化锡负极材料与聚合物电解质的界面性质。 （1）以EC、DEC（体积比1∶1）为增塑剂，LiPF₆（1mol／L）为电解质锂盐，制备P（VdF-HFP）基凝胶型聚合物电解质，研究MCMB碳负极材料在该电解质中进行充放电时的界面性质变化。现场拉曼光谱技术及充放电曲线测试结果表明：在首次嵌锂过程中，MCMB颗粒首先由初始嵌锂结构转变为4阶结构，随后经过3阶结构、2阶结构，并于最终转变为1阶结构。现场红外反射光谱研究表明：在首次充电过程中，电解液（主要是碳酸乙烯酯）在0.8V左右分解，ROCO₂Li为其可能的分解产物。不同充电深度的交流阻抗结果分析，进一步深入了对于凝胶聚合物电解质中，MCMB电极在充电时的界面性质变化以及嵌锂过程的理解。 （2）以PC为增塑剂，LiClO₄（1mol／L）为电解质锂盐，制备PMMA基凝胶型聚合物电解质，研究MCMB碳负极材料在该电解质中电化学行为。循环伏安测试表明：首圈阴极充电过程中，电解质体系发生还原反应；而在阳极过程中，几乎没有锂离子可逆的脱出反应过程。现场红外反射光谱结果则表明电解质体系在1.3V左右即发生分解反应。 （3）利用现场红外反射光谱研究充放电过程中金属锂片电极与P（VdF-HFP）基凝胶型聚合物电解质的界面性质变化，测试结果表明，在充电和放电过程中，金属锂电极上生成的主要产物均为ROCO₂Li和Li₂CO₃。另外，由于金属锂非常活泼，在现场光谱电解池的组装过程中，金属锂片电极可能与所接触到的各种物质发生化学反应从而影响其表面性质。为了避免这种影响，我们尝试了组装现场光谱电解池以后，在光谱池的铜柱上现场沉积金属锂层并以其作为研究电极的实验方法。红外光谱与以金属锂片为工作电极测得的红外谱图完全一致，这一结果表明，光谱电解池中电沉积金属锂层作为研究电极是一种可靠的实验方法。 （4）研究了SnO＿2电极材料在液态电解液以及P（VdF-HFP）基凝胶型聚合物电解质中的充放电过程及其界面性质变化。现场红外光谱结果表明，在充电过程中电解液在较高电位下（＞1.5V）即在电极表面发生分解，主要产物为Li₂CO₃，而在较低电位下（＜0.7V），则生成ROCO₂Li。 （5）对于上述三种电极充电和放电过程的现场红外光谱研究发现，当电极在电解质中具有可逆循环充放电性质时，电极充、放电反应将引起电极表面附近电解质中锂离子溶剂化程度的可逆变化，现场反射红外光谱图则表现为谱峰方向发生倒反的独特现象。这一光谱现象的出现具有一定的普遍性，仅与涉及到Li⁺的电极反应是否可逆有关，而与电极材料（MCMB、Li、SnO2）和电解质体系的组成（P（VdF-HFP）一EC／DEC-LiPF₆、PMMA-PC-LiClO₄）无关。3．制备全固态聚合物电解质，并探讨其与金属锂电极的界面性质。 以LiN（CF₃SO₂）₂作为电解质锂盐，合成了以SBA-15为无机填料进行掺杂的PEO全固态聚合物电解质膜，该复合聚合物电解质膜的室温离子电导率可以达到10^-5数量级。红外光谱研究发现，锂盐LiN（CF₃SO₂）₂的加入可以降低PEO聚合物膜的结晶度，而10％重量比的SBA-15掺杂则使得聚合物PEO分子链段中反式构象成分增多，PEO分子部分结构由有序转变为无序，因此导致其室温离子电导率的提高。利用现场升温红外光谱对上述三种聚合物膜体系由晶态向非晶态转变过程进行了分析，结果表明纯相的PEO聚合物膜在60-70℃之间发生转变，对于PEO-Li盐聚合物电解质膜以及SBA-15掺杂的PEO-Li盐聚合物电解质膜，该温度分别降低至40-50℃和30-40℃范围内。 利用现场红外反射光谱技术对全固态梳状聚有机硅氧烷电解质膜（PMSMA-LiN（CF₃SO₂）₂）体系与金属锂电极的界面性质进行了初步探索。对于界面的稳定性研究发现：当金属锂电极与该聚合物体系接触后即发生化学反应，红外光谱图上表现为聚合物体系中分子的逐渐消耗；随着接触时间的增长，这种反应逐渐停止。因此，金属锂与所研究的全固态聚合物电解质体系之间有可能通过化学反应而在电极表面生成钝化膜，这层钝化膜可以阻止二者之间的进一步反应。对于金属锂电极在上述固态聚合物电解质体系中的充放电过程研究结果则表明：在金属锂电极发生溶解和沉积过程中，均伴随着聚合物体系分子的消耗反应，这一现象有可能是由于充放电过程中电极表面不断暴露出的“新鲜”金属锂与聚合物体系之间的反应造成的。 4．应用现场红外透射光谱技术研究乙醇分子在金电极以及铂电极上的电化学氧化过程，并探讨其电氧化机理。 分别研究了碱性、中性及酸性水溶液介质中，乙醇分子在Au电极上的电化学氧化过程，现场红外透射光谱信息表明：在碱性介质（1mol／L KOH水溶液）中，乙醇电氧化的主要产物为CH₃COO^-，在酸性介质（1mol／L HClO₄水溶液）及中性介质（1mol／L KClO₄水溶液）中的电化学氧化行为相似，电氧化产物均为CO₂，CH₃CHO和CH₃COOH。对于无水乙醇在金电极以及铂电极上的电化学氧化行为进行研究，结果表明：乙醇分子在两种电极上的电氧化产物基本相同，均为乙醛和乙缩醛，但在铂电极上的电化学氧化活性远高于金电极。 综合上述研究结果，我们认为乙醇在Au电极上的电催化氧化行为与溶液中OH^-的浓度有密切关系。其电化学氧化机理可能为：乙醇分子解离掉羟基（-OH）中的H原子，从而在Au电极表面形成吸附态乙醇分子CH₃CH₂O-Au。吸附态的乙醇分子在一定的电极电位下通过脱氢反应生成乙醛；同时，吸附态的乙醇分子也可能受到Au电极表面吸附态的活性羟基（Au-OH）的亲核进攻而在电极表面形成吸附态的含氧物种CH₃-CHOH-O-Au，在一定的电极电位下该吸附态的含氧物种氧化失去一个质子生成乙酸。另外，乙醛也有可能在更高的电极电位下进一步发生电氧化而形成乙酸。在碱性介质中，由于大量OH^-的存在，Au电极表面形成的吸附态羟基物种Au-OH远远高于中性或酸性介质，因此更加有利于其对吸附态乙醇分子（CH₃CH₂O-Au）亲核进攻，而生成乙酸（CH3COO^-）。而酸性及中性介质中，电极表面形成的Au-OH较少，吸附态的乙醇分子则更加倾向于在一定的电极电位下直接氧化脱氢生成乙醛，而当电极电位足够高使得Au电极被氧化而在电极表面形成Au的氧化物种后，加大了吸附态乙醇分子氧化生成乙酸的可能性，此时电极表面有乙酸生成。由于无水体系中，电极表面难以形成吸附态的活性羟基（Au-OH或Pt-OH），因此解离吸附在电极表面的乙醇分子主要是在一定的电极电位条件下通过一步脱氢反应生成乙醛分子，随后有可能进一步与乙醇相互作用形成乙缩醛。 5．首次应用现场红外透射光谱技术和电化学方法研究表面活性剂分子十二烷基硫酸钠在多晶金电极表面的吸脱附行为及其水解反应动力学。 分别研究了6mmol／L和16mmol／L十二烷基硫酸钠水溶液中，十二烷基硫酸根分子在多晶金电极上的吸脱附行为。研究发现：在6mmol／L浓度的水溶液中，随着电极电位的负移，吸附态的十二烷基硫酸根分子在-0.2V左右开始脱附，并在-0.8V左右完全脱附；而在16mmol／L浓度的水溶液中，这一过程显得较为复杂，随着电极电位的负移，吸附态的十二烷基硫酸根分子首先在-0.3V左右由不十分规律的半胶束聚集态转变为以碳氢链朝向电极表面的方式垂直排列的较为有序的吸附聚集体，随后在-0.8V左右完全脱附。 除了吸附态分子的变化以外，现场透射光谱同时检测到水溶液体相中由于十二烷基硫酸根的水解反应而引起的光谱信号变化。根据这一信号变化信息，可推算出十二烷基硫酸根分子的水解反应服从一级反应动力学，并可计算得到其在6mmol／L和16mmol／L水溶液中的水解反应常数分别为6.00×10^-4s^-1和4.99×10^-4s^-1。 另外，本部分工作证明了现场红外透射光谱方法是一种检测电化学过程的简单、方便而有效的实验技术，不但可以检测溶液体相发生的变化，也可以检测得到吸附态物种的变化信息。更多还原

【Abstract】 Surface electrochemistry, which has a wide application field including energy, material science and life science, focuses on the research of interfacial change between two agglomerate phases. The electrochemical spectroscopy has been established and developed since 1970s in order to get the interfacial information at a molecular or atomic level. Among them in situ Fourier transform infrared spectroscopy （FTIR）, in situ Raman spectroscopy and in situ UV-Vis spectroscopy have found many advantages. The development of spectro-electrochemistry prompts the research from macroscopic level to microscopic level and provides the useful information about the nature and chemical bond of the molecules at the interfaces. On the other hand, the battery industry, as an important section of energy, has been paid more attention world-widely. R&D of batteries, which have the advantages of high electrochemical energy, long life and environment friendly, etc., becomes one of the most attractive facets.In this work, the reaction mechanisms, especially the interfacial change on the electrode involving several kinds of high energy batteries, such as lithium or lithium ion battery, zinc-silver battery and direct alcohol fuel cells, were investigated by electrochemical techniques and in situ FTIR spectroscopy. In addition, the application of in situ FTIR spectroscopy on the electrochemical interfacial investigation has been discussed. The main results and conclusion are summarized as follows:1. A novel cathodic material, high-valence silver oxide （Ag₃O₄）, was prepared by electrochemical methods. The electrochemical condition for the preparation, the growth process and electrochemical behaviors in alkaline solution of this material has been investigated for the first time.High-valence silver oxide （Ag₃O₄） with black color could be anodically electrodeposited on platinum electrode at the constant potential higher than 1.15V （vs. SCE） in 0.1mol/L AgF solution. Especially, the single crystal structure can be obtained at 1.38 V （vs. SCE）. The growth process of Ag₃O₄ includes the typical the formation of crystal seed and the sequential development, which may undergo the following steps: Ag（ I ） →Ag（ II）→Ag（III）.The electrochemical behavior of Ag₃O₄ in 1mol/L KOH was investigated by voltammetry and chronopotentiometry measurements. XRD analysis was used for the confirmation of the products at different reduction extent. It was found that thereduction process of Ag₃O₄ was more complicated. Ag₃O₄ could be recognized as the combination of Ag₂O₃ and AgO^*. During cathodic process Ag₂O₃ could be reduced through the reactions Ag₂O₃→AgO→Ag2O→Ag or Ag₂O₃→Ag₂O→Ag. And AgO* could be reduced to Ag directly. This mechanism has been confirmed by the results of chronopotentiometry experiment. Electrochemical impedance spectroscopic results suggest a possible reason for the above electrochemical behavior of Ag₃O₄.In addition, it should be noted that the theoretical capacity for Ag₃O₄ is 553.0mAh/g, which is 27.8% higher than that of common used AgO （theoretical capacity of 432. 8 mAh/g） in zinc-silver oxide battery. It can be calculated that the discharge rate is as high as 119C, and discharge capacity of Ag₃O₄ still kept 83% of the theoretical value. This material presents not only high capacity but also prominent electrochemical performance at very high discharge rate. As a new material it will benefit to the practical application in high power zinc-silver oxide battery.2. The interfacial changes of anodic materials during charging and discharging process in lithium and lithium ion battery, including MCMB, lithium metal and tin dioxide, were investigated by in situ spectroscopy and electrochemical techniques.The P （VdF-HFP）-based gel electrolyte was prepared using the organic electrolyte EC/DEC （1:1） with 1 mol/LLiPF₆ as the plasticizer. Electrochemical techniques and in situ Raman and FTIR spectroscopic methods were used to investigate the interfacial reaction on MCMB electrode in the prepared P （VdF-HFP）-based gel electrolyte. In situ Raman spectroscopy and charge-discharge profile prove that the structure changes of MCMB during lithium ions intercalation are through several stage transitions from dilute stage 1 to stage 4, then stage 3, stage 2 and finally to stage 1. An initial irreversible capacity about 50mAhg^-1 was observed in the initial charge-discharge cycle of MCMB electrode. It can be ascribed to the consumption for the SEI formation on the MCMB surface, which was further confirmed by in situ reflectance FTIR spectroscopy and EIS measurements. In situ FTIR spectra for MCMB electrode during initial charging process mainly indicates the depletion of EC and may suggest the formation of ROCO₂Li.The PMMA-based gel electrolyte was prepared using PC with 1 mol/L UClO₄ as the plasticizer. Electrochemical behavior and in situ FTIR spectroscopic results of MCMB electrode in PMMA-based gel electrolyte indicate that the electrolyte decomposed at about 1.3 V in the first cathodic process and almost no reversible capacity was produced by lithium intercalation and deintercalation.For lithium metal electrode in P （VdF-HFP）-based gel electrolyte, SEI film was composes by ROCO₂Li and Li₂CO₃, which was detected by in situ reflectance FTIR spectroscopy during the charge-discharge process. In addition, in order to avoid the contamination of impurities for lithium metal electrode in the cell-assembling process, lithium electrode was directly prepared by electro-deposition method within a sealed spectro-electrochemical cell with gel electrolyte. In situ FTIR spectroscopic results recorded on the electro-deposited lithium electrode are almost accorded with those on lithium metal electrode, which suggests that the electro-deposited lithium metal can be used as a feasible method, especially for the experiments where the impurities on Li surface have to be avoided.The interfacial change between tin dioxide electrode and liquid organic electrolyte or P （VdF-HFP）-based gel electrolyte during charge-discharge process has been investigated by in situ FTIR reflectance spectroscopy and electrochemical methods. The results suggest that interfacial character of tin dioxide in liquid electrolyte and gel electrolyte are very similar. The electrolyte was decomposed in the first cathodic process at the potential higher than 1.5 V and Li₂CO₃ was the dominant product. At the potential lower than 0.7 V, the products involved ROCO₂LiIt is very interesting here to note that the spectra recorded by in situ FTIR reflectance spectroscopy present a strange "reversible" change during the cathodic and anodic process for almost all the above experiments, which displayed the reversible change of the peak direction. This phenomenon may be popular for the electrodes in lithium or lithium ion battery, which is just related to the reversible change of solvation extent between lithium ion and the organic molecules and irrespective of electrode materials and the electrolytes.3. Solid state polymer electrolyte including PEO-based and PMSMA electrolyte were prepared and the interfacial character was discussed according to in situ FTIR reflectance spectroscopic investigation.PEO-based electrolyte was prepared with SBA-15 as the filler and LiN（CF₃SO₂）₂ serves as the lithium source. The ion conductivity of the composite electrolyte at room temperature reached to the order of 10^-5 S·cm^-1. FTIR results indicate that the addition of lithium salt can reduced the crystalline of PEO polymer and SBA-15 can decrease the gauche/trans conformer ration along PEO chain because of the grain boundary effect. Along with the increase of trans conformer, PEO molecular chains undergo the transition from order to disorder, which leads to a higher ion conductivity at roomtemperature. In situ FTIR spectra at different temperature suggest that pure PEO polymer melts between 60-70℃ and the temperature can be decreased to 40-50℃ and 30-40℃ for PEO- LiN（CF₃SO₂）₂ and the composite PEO electrolyte with 10% SBA-15, respectively.The interfacial change between lithium electrode and PMSMA-LiN（CF₃SO₂）₂ solid state electrolyte was investigated by in situ FTIR spectroscopy. The primary results indicate that chemical reaction occurs as the lithium electrode touches the solid electrolyte because of the activity of lithium. A passivate film may be formed between them, which can prevent the further reaction between lithium and the electrolyte. However, in situ FTIR spectroscopic results recorded during charge-discharge process suggest the depletion of the solid electrolyte, which may be produced by the reaction of lithium with the electrolyte.4. The electro-oxidation of ethanol on Au and Pt were investigated by in situ transmission FTIR spectroscopy and the mechanism was proposed.The electro-oxidation of ethanol on Au electrode was investigated in the different aqueous media including 1mol/L KOH, 1mol/L KClO₄ and 1mol/L HClO₄. Acetate （CH₃COO^-） is the only detectable product in alkaline solution and at the same time the products involve acetaldehyde （CH₃CHO）, acetic acid （CH₃COOH） and carbon dioxide （CO₂） in both neutral and acidic solution. On the other hand, the electrochemical behaviors of non-aqueous ethanol on Au and Pt are very similar. The detectable products consist of acetaldehyde and acetal （CH₃CH（OC₂H₅）₂）. The electro-catalytic of Pt electrode for the non-aqueous ethanol solution is higher than that of Au.The above results are summarized and the possible mechanism for electro-oxidation of ethanol on Au electrode may be displayed as follows: ethanol can dissociate and adsorb on Au surface and the production of acetaldehyde is a simple dehydrogenation process of the adsorbed ethanol. At the same time, the adsorbed ethanol can react with the gold when hydroxyl species are formed on the electrode surface. The nucleophilic attack of the activated hydroxyl leads to the O-adsorbed species and at the proper potential the Au electrode promotes the loss of one proton with the formation of acetic acid. In alkaline solution, activate hydroxyl can be formed easily on the electrode surface, which will facilitate the formation of acetic acid. Otherwise, the adsorbed hydroxyl is less in neutral and acidic solution and the adsorbed ethanol tends to be dehydrogenated leading to acetaldehyde. As the potentialis higher than that Au was oxidized with the O-adsorbed species formation, the formation of acetic acid will be promoted. In non-aqueous ethanol solution, few adsorbed hydroxyl can be formed and acetaldehyde is the dominant product, which may further react with ethanol and lead to acetal.5. The adsorption of surfactant sodium dodecyl sulfate （SDS） at the Au electrode-solution interface was firstly investigated by in situ transmission FTIR spectroscopy. Moreover, the kinetics of hydrolysis reaction of SDS in aqueous solution was investigated by measuring the variation of in situ transmission difference FTIR spectra with time.It has been substantiated that the charging of the solid electrode surface has a significant impact on the surface assembly of ionic surfactant （sodium dodecyl sulfate）. Our results suggest that adsorption behavior on polycrystalline Au electrode may be different from that on single crystal electrode. With regard to 6mmol/L SDS solution, the adsorbed SDS molecules start to desorb at about -0.2 V and desorb entirely when the potential reaches to -0.8 V. However, more complicated phenomena have been inspected concerning 16mmol/L SDS solution. On the basis of the results, it may be inferred that the adsorbed SDS molecules initially transform from the hemimicells to an ordered adsorbed form （the condensed film with the CH terminal exposing to the surface） at the electrode surface at-0.3 V and then it will desorb from the surface with the potential further moving to -0.8 V. The reaction kinetics of SDS hydrolysis was also investigated and discussed in 6mmol/L and 16mmol/L SDS aqueous solutions. The rate constant of hydrolysis can be calculated based on the transmission FTIR spectroscopic results and the values are 6.00×10^-4 s^-1 and 4.99×10^-4 s^-1 for SDS solution with the concentration of 6mmol/L and 16mmol/L, respectively.Moreover, our results further illuminate that in situ transmission difference FTIR spectroscopy method is a very simple, convenient and efficient way to detect both the variations of adsorbed species at the interfaces and the species in the solution.更多还原