【作者】 朱日龙；

【导师】 李国希；

【作者基本信息】 湖南大学 ， 应用化学， 2009， 博士

【摘要】 导电高分子具有特殊的结构和优异的物理化学性能,在金属防护、能源、光电子器件、分子器件、电磁屏蔽、隐身技术等方面具有广泛的诱人前景,是当前材料科学的研究热点。导电高分子对金属的保护作用及其机理很复杂,还不是很清楚。聚吡咯(PPy)是最有应用前景的导电高分子材料之一,具有优异的防蚀性能。本文研究了PPy的电化学合成方法,采用扫描电子显微镜、红外光谱、伏安曲线、动电位极化曲线、开路电位-时间曲线、电化学阻抗谱(EIS)等方法研究了PPy对不锈钢的保护机理,探讨了复合型导电高分子在防腐蚀和电化学电容器方面的应用,并对有关PPy电化学性能的基础问题进行了研究。一. PPy的电化学合成及其性质采用循环伏安法和恒电位法考察了PPy的电化学合成过程。结果表明已生成的PPy对吡咯在1 mol L-1十二烷基苯磺酸钠(SDBS)溶液中的氧化聚合具有催化作用,从而降低了吡咯的聚合电位。根据这个研究结果,提出了先在高电位下预合成一层薄PPy膜,再在较低电位下合成PPy膜的两步法。采用这种两步法在不锈钢表面合成PPy能够有效抑制不锈钢基体在合成过程中的阳极溶解和PPy膜的过氧化。研究了合成电位对PPy性质的影响。结果表明,采用低电位合成的PPy膜更均匀,膜过氧化程度低,与金属表面的附着力更好,电化学氧化还原活性更高,能更好地抑制不锈钢在3.5%NaCl溶液中的腐蚀。二. PPy对不锈钢的保护及腐蚀机理研究研究了PPy膜厚度对不锈钢/PPy在3.5%NaCl溶液中电化学行为的影响。结果表明,PPy膜越厚,不锈钢/PPy的EIS在高频段为容抗弧半圆越小;不锈钢/PPy的EIS在高频段的半圆主要反映PPy的氧化还原电荷转移电阻。有PPy膜保护的不锈钢阳极极化电流随PPy膜厚度增加而增大,在高于0.50 V(vs SCE)后阳极电流才迅速增加,表明PPy膜对不锈钢在NaCl溶液中的腐蚀具有抑制作用。低于0.50 V时的阳极极化电流主要反映PPy膜的氧化反应电流。测量了不锈钢/PPy和Pt/PPy在3.5%NaCl溶液中的EIS。不锈钢/PPy和Pt/PPy在高频端的半圆大小接近,这个半圆主要反映PPy的氧化还原电荷转移电阻,由此可认为PPy膜下不锈钢的腐蚀电阻非常大,不锈钢得到很好的保护。研究了浸泡时间对不锈钢/PPy在3.5%NaCl溶液中电化学行为的影响。结果表明刚浸入时不锈钢/PPy的阳极极化电流主要来自微孔处不锈钢的腐蚀电流,浸泡1 h后则主要来自PPy的氧化电流。比较了不锈钢/PPy和Pt/PPy在1 mol L-1SDBS溶液中的电化学行为。结果表明PPy与不锈钢发生电化学反应,使不锈钢钝化,自身发生还原;还原的PPy可以通过再氧化恢复到氧化态。建立了不锈钢/PPy在3.5%NaCl溶液中的EIS等效电路,分离出不锈钢的腐蚀电荷转移电阻与PPy的氧化还原电荷转移电阻。由不锈钢/PPy在3.5%NaCl溶液中的腐蚀电荷转移电阻、PPy的氧化还原电荷转移电阻随时间的变化曲线分析了不锈钢/PPy的腐蚀过程。结果表明,PPy膜通过与不锈钢发生电化学反应,使不锈钢钝化,释放出的十二烷基苯磺酸根离子也能抑制不锈钢的腐蚀。三. PPy独立膜的电化学性质测量了PPy独立膜在3.5%NaCl溶液中充氮气与不充氮气条件下的阴、阳极极化曲线。结果表明,在过电位很大的情况下PPy的氧化还原反应仍然处于电化学活化控制。在3.5%NaCl溶液中将PPy膜在-0.8V充分还原10min后,恒电位阳极极化的膜电阻随时间的变化呈指数衰减。从理论上建立了膜电阻与时间的关系方程。极化电位越正,半衰期越短。研究了在1 mol L-1NaCl溶液中pH值对PPy性质的影响。结果表明,当pH值小于11时,PPy独立膜的电位-pH直线斜率为-0.029 V/pH;当大于11时,直线斜率为-0.083 V/pH。在酸性溶液中,PPy发生质子酸掺杂,膜的导电性增强;在碱性溶液中发生去质子化脱掺杂,甚至发生过氧化,膜导电性变差。pH值愈大,过氧化峰的起始电位和峰电位越负,PPy越容易发生过氧化。四.导电高分子的应用以提高导电高分子的防蚀性能和电容性能为目的,用分层聚合或共聚合法制备了PPy-Pani(聚苯胺)复合型导电高分子材料并进行了表征。结果表明,双层膜或共聚合制备的膜均可以提高不锈钢在3.5%NaCl溶液中的点蚀电位。采用分层聚合制得的膜,以PPy为底层的膜的防蚀性能比以Pani为底层的好;对于采用共聚合制备的膜,聚合溶液中吡咯浓度越大膜的防蚀性能越好。以PPy为底层的复合型导电高分子电极电容器的电容性能比其它复合型电极或单层膜电极的好。SS/PPy/Pani和SS/PPy/Pani/PPy的阻抗近似为纯电容,其比电容高达206.11 F g-1和216.13 F g-1。更多还原

【Abstract】 Due to the special structure and the excellent physical chemical properties, conducting polymers have attracted great interest in many applied fields such as metal protection, energy, optoelectronic devices, molecular devices, electromagnetic shielding, stealth technology etc.. The anti-corrosion efficiency and mechanism of conducting polymers have not yet been fully understood, and thus are still open for further investigation. Polypyrroly (PPy) is one of the most promising conducting polymers for corrosion protection application. In this work, the electrosynthesis processes of PPy were firstly studied, then the protection mechanism of PPy was investigated by methods such as scanning electronic microscopy, infrared spectrum, cyclic voltammetry, potentiodynamic polarisation curve, open circuit potential-time curve and electrochemical impedance spectroscopy (EIS) etc.. The application researches for PPy in the field of corrosion protection and electrochemical super-capacitor were also carried out after the study of some fundamental problems related to its electrochemical properties were done.1. Electrosynthesis of PPy and its propertiesCyclic voltammetry and potentiostatic method were adopted to investigate the synthesis process of PPy. Results show that the pre-formed PPy films have a catalytic effect on oxidative polymerization of pyrrole in sodium dodecylbenzenesulfonate (SDBS) solution, thus lowering the polymerization potential. Therefore, a two-step process was proposed: the first step is the formation of a very thin PPy film at a higher potential, and the second step is the PPy film formation on the freshly produced thin film at a lower potential. PPy films prepared by this two-step method were found to be uniform and smooth in appearance, more flexible and adherent than those prepared using the conventional potentiostatic technique. Mostly, anodic metal substrate dissolution and over-oxidation of PPy can be avoided.The effects of applied potentials on the electrochemical, structural and protective properties of PPy films have been explored. Films electrodeposited at lower potentials have more homogeneous morphology, less overoxidation, better ahersion to metal surface and higher electroactivities. Applying lower potential for the synthesis improves the anti-corrosive efficiency of PPy film in 3.5% NaCl solution.2. Corrosion performance and mechanism research for PPy coated stainless steel The comparison of electrochemical properties of stainless steel/PPy in 3.5%NaCl solution for different thicknesses was performed. Interesting results were obtained that the thicker the PPy film was, the smaller the semicircle of EIS at high frequencies was, and thus the semicircle should correspond to the charge transfer impedance and the impedance diagram response is mainly ascribed to the polymer film rather than to the underlying stainless steel substrate. The anodic polarization current of stainless steel/PPy increased as film thickness increasing, and rose rapidly at about 0.50 V (vs SCE) indicating that the corrosion of stainless steel in 3.5%NaCl solution is inhibited. The polarization current mostly comes from redox current of PPy before the potential reaches 0.50 V.EIS of stainless steel/PPy and Pt/PPy in 3.5%NaCl solution were measured for the sake of comparision. Results show that the semicircle for stainless steel/PPy related to charge transfer impedance was found to be similar to that for Pt/PPy at high frequencies. The charge transfer impedance measured reflects the redox reaction of PPy, and the corrosion resistance of stainless steel substrate coated with PPy is very large indicating that the stainless steel is under protection of PPy film. The electrochemical behavior of stainless steel/PPy in 3.5%NaCl solution was investigated for different immersion time. The anodic polarization current is mainly ascribed to the dissolution of stainless steel at pinhole defects for initial immersion, and to PPy oxidation after 1 h immersion.The comparison of electrochemical properties for stainless steel/PPy and Pt/PPy in 1 mol L-1 SDBS solution was carried out. Results show that electrochemical reaction between PPy and stainless steel will take place when electrolyte reaches the surface of stainless steel causing passivation of stainless steel and dedoping of PPy. The dedoped PPy can be re-oxidized in doped form.An equivalent circuit of EIS for stainless steel/PPy in 3.5%NaCl solution was proposed, with which the charge transfer resistances for stainless steel corrosion and redox reaction of PPy were separated. Then the corrosion behavior of stainless steel/PPy was analyzed through the evolution of corrosion resistance and the redox reaction resistance with time in 3.5% NaCl solution for PPy coated stainless steel. Results show that PPy can inhibit corrosion of stainless steel by passivation and release of dodecylbenzenesulfonate anion.3. Electrochemical properties of free-standing PPy filmPotentiodynamic polarization curves of free-standing PPy film electrode in 3.5% NaCl with no-deaeration and deaeration were measured. Results show that the redox reaction of PPy is under electrochemical control even in large overpotential.Free-standing PPy films were firstly polarized at -0.8 V for 10 min to reach full reduce state, then potentiostatic anodic polarizations were performed. It is found that film resistance evolution as a function of time shows exponential decay. The relation equation between film resistance and time was analyzed in theory, the more higher the potential, the shorter the half-life.The influences of pH value on properties for free-standing PPy film in 1 mol L-1 NaCl were investigated. Results show that line slope of potential-pH curve is -0.029 V/pH for pH < 11, and is -0.083 V/pH for pH > 11. In acidic solution, proton-acid doping occurs and film conductivity increases. While in alkaline solution, PPy films are de-protonated and confronted over-oxidization thereby becoming less conductivity. The higher the value of pH is, the more negative the initial potential and peak potential are.4. Application of conducting polymerPPy-Pani (polyaniline) composite were prepaired through layer by layer deposition or copolymerization in order to improve the anti-corrosive efficiency and capacitance properties of conducting polymer, and subsequent material test or characterization were carried out. Results show that pitting potential of stainless steel in 3.5% NaCl solution can be raised by covering with bilayer PPy films or copolymerizated PPy films. The composite polymers with PPy as primer have better protection effect than that with Pani as primer. Copolymerizated PPy films synthesized with higher pyrrole concentration show better anti-corrosive performance. The capacitor properties quite depend on the deposit order: the composite polymers with PPy as primer have better capacity than that with Pani as primer. The specific capacitance of stainless steel/PPy/Pani and stainless steel/PPy/Pani/PPy electrodes is far higher (up to 206.11 F g-1 and 216.13 F g-1) than that of pure conducting polymers or other composite polymers.更多还原